({alpha},{eta}) phase diagrams in tilted chiral smectics

Energy Technology Data Exchange (ETDEWEB)

Rjili, M., E-mail: medrjili@yahoo.fr [Laboratoire de Physique de la Matiere Molle et de la Modelisation Electromagnetique, Faculte des Sciences de Tunis, Universite Tunis El Manar, 2092 El Manar Tunis (Tunisia); Marcerou, J.P., E-mail: marcerou@crpp-bordeaux.cnrs.fr [Centre de Recherches Paul Pascal, 115, Av. Albert-Schweitzer, 33600 Pessac (France); Gharbi, A.; Othman, T. [Laboratoire de Physique de la Matiere Molle et de la Modelisation Electromagnetique, Faculte des Sciences de Tunis, Universite Tunis El Manar, 2092 El Manar Tunis (Tunisia)

2013-02-01

The polymorphism of tilted chiral smectics liquid crystals is incredibly rich and encompasses many subphases such as SmC{sub A}{sup Low-Asterisk }; SmC{sub Fi1}{sup Low-Asterisk }; SmC{sub Fi2}{sup Low-Asterisk }; SmC{sup Low-Asterisk }; SmC{sub {alpha}}{sup Low-Asterisk }. The continuum theory established by Marcerou (2010) is used to derive an expression for the free energy density of those subphases. The minimization of this free energy is obtained through a combination of analytical and numerical methods. It leads to a phase diagram built in the ({alpha},{eta}) plane where {alpha} is local angular parameter and {eta} describes the variation of the temperature. From this graphical representation, many experimentally observed phase sequences of ferroelectric liquid crystals can be explained, even them including subphases which were recently observed like the SmC{sub 5}{sup Low-Asterisk} and the SmC{sub 6}{sup Low-Asterisk} ones. However, it should be emphasized that the details of predicted phase diagram are strongly dependent on the compound studied.

Spontaneous formation of stringlike clusters and smectic sheets for colloidal rods confined in thin wedgelike gaps.

Science.gov (United States)

Maeda, Hideatsu; Maeda, Yoshiko

2013-08-20

Monodispersed colloidal rods of β-FeOOH with sizes ranging from 270 to 580 nm in length and 50 to 80 nm in width were synthesized. Narrow wedgelike gaps (0 to 700 nm in height) were formed around the inner bottom edge of the suspension glass cells. Optical microscopic observations revealed the formation of stringlike clusters of the rods and smectic sheets (by spontaneous side-by-side clustering of the strings) in the isotropic phase of the rod suspensions confined in narrow gaps; the electrolyte (HCl) concentrations of the suspensions are 5-40 mM, at which inter-rod interactions are attractive. The strings exhibit different colors that were used to investigate the structures of the strings with the help of interference color theory for thin films. The results are as follows. (1) The rods, lying flat on the gap bottom, are connected side-by-side and stacked upward to form stringlike clusters with different thicknesses depending on the gap height. (2) The stacking numbers (N(sr)) of the rods are estimated to be 1-5. With N(sr) increasing from 2 to 5, the volume fractions (ϕ) of the rods in the strings increased typically from 0.25-0.3 to 0.35-0.42 to reach limiting values (close to the ϕ values of the rods in the bulk smectic phase). (3) Unexpected low-ϕ strings are found in regions with an intermediate height in the gaps. These behaviors of ϕ may be caused by thermal fluctuations of the strings.

Induced Smectic X Phase Through Intermolecular Hydrogen-Bonded Liquid Crystals Formed Between Citric Acid and p- n-(Octyloxy)Benzoic Acid

Science.gov (United States)

Sundaram, S.; Subhasri, P.; Rajasekaran, T. R.; Jayaprakasam, R.; Senthil, T. S.; Vijayakumar, V. N.

2017-08-01

Hydrogen-bonded liquid crystal (HBLC) is synthesized from citric acid (CA) and 4-(octyloxy)benzoic acid (8OBA) with different mole ratios. Fourier transform infrared spectroscopy (FT-IR) confirms the presence of hydrogen bond between CA and 8OBA. Nuclear magnetic resonance (NMR) spectroscopic studies validate the intermolecular complementary, cyclic type of hydrogen bond, and molecular environment in the designed HBLC complex. Powder X-ray diffraction analysis reveals the monoclinic nature of liquid crystal complex in solid phase. Liquid crystal parameters such as phase transition temperature and enthalpy values for the corresponding mesogenic phases are investigated using a polarizing optical microscope (POM) and differential scanning calorimetry (DSC). It is observed that the change in chain length and steric hindrance while increasing the mole ratio in HBLC complex induces a new smectic X (Sm X) along with higher-order smectic G (Sm G) phases by quenching of smectic C (Sm C). From the experimental observations, induced Sm X phase has been identified as a finger print texture. Also, Sm G is a multi-colored mosaic texture in 1:1, 1:2, and 1:3 mol ratios. The optical tilt angle, thermal stability factor, and enhanced thermal span width of CA + 8OBA complex are discussed.

Smectic-like phase for modulated XY spins in two dimensions

International Nuclear Information System (INIS)

Benakli, M.; Gabay, M.; Saslow, W.M.

1997-09-01

The row model for frustrated XY spins on a triangular lattice in 2D is used to study incommensurate (IC) and commensurate (C) phases, in the regime where a (C)-(IC) transition may be observed. Thermodynamic quantities for the (IC) state are computed analytically by means of the NSCHA, a new variational method appropriate for frustrated systems. On the commensurate side of the (C)-(IC) boundary, NSCHA predicts an instability of the (C) phase suggesting that this state is in fact spatially inhomogeneous. Detailed Monte-Carlo (MC) simulations using fluctuating boundary conditions and specific histogram techniques show that in this regime the configuration consists of stripes of (C) and (IC) phases alternating in space. This state, which resembles the smectic-A phase of liquid crystals, exists because of the strong coupling between chiral and phase (spin angle) variables. As a result, the transition between the (IC) and the (C) states can only occur at zero temperature T so that the Lifshitz point is at T = 0 for modulated XY spins in 2D. (author)

A novel model for smectic liquid crystals: Elastic anisotropy and response to a steady-state flow.

Science.gov (United States)

Püschel-Schlotthauer, Sergej; Meiwes Turrión, Victor; Stieger, Tillmann; Grotjahn, Robin; Hall, Carol K; Mazza, Marco G; Schoen, Martin

2016-10-28

By means of a combination of equilibrium Monte Carlo and molecular dynamics simulations and nonequilibrium molecular dynamics we investigate the ordered, uniaxial phases (i.e., nematic and smectic A) of a model liquid crystal. We characterize equilibrium behavior through their diffusive behavior and elastic properties. As one approaches the equilibrium isotropic-nematic phase transition, diffusion becomes anisotropic in that self-diffusion D ⊥ in the direction orthogonal to a molecule's long axis is more hindered than self-diffusion D ∥ in the direction parallel to that axis. Close to nematic-smectic A phase transition the opposite is true, D ∥ flow depending on whether the convective velocity is parallel or orthogonal to the plane of smectic layers. We find that in Poiseuille-like flow the viscosity of the smectic A phase is higher than in plug flow. This can be rationalized via the velocity-field component in the direction of the flow. In a sufficiently strong flow these smectic layers are not destroyed but significantly bent.

Molecular tilt near nanoparticles in the smectic A phase of de Vries liquid-crystalline compound

Czech Academy of Sciences Publication Activity Database

Lejček, Lubor; Novotná, Vladimíra; Glogarová, Milada

2014-01-01

Roč. 89, č. 1 (2014), "012505-1"-"012505-6" ISSN 1539-3755 R&D Projects: GA ČR(CZ) GAP204/11/0723 Institutional support: RVO:68378271 Keywords : liquid crystals * smectic phases * nanoparticles * deVries behaviour Subject RIV: JJ - Other Materials Impact factor: 2.288, year: 2014 http://pre. aps .org/abstract/PRE/v89/i1/e012505

Smectic order and backbone anisotropy of a side-chain liquid crystalline polymer by Small-Angle Neutron Scattering

Science.gov (United States)

Noirez, L.; Pépy, G.; Keller, P.; Benguigui, L.

1991-07-01

We have simultaneously measured, for the first time, the extension of the polymer backbone of a side-chain liquid crystalline polymer and the intensity of the 001 Bragg reflection, which gives the smectic order parameter Psi as a function of temperature in the smectic phase. We have qualitatively demonstrated that the more the smectic phase is ordered, the more the polymer backbone is localized between the mesogenic layers. It is shown that the Landau theory allows us to relate the radius of gyration parallel to the magnetic field of the polymer backbone to the smectic order parameter. We also show that the Renz-Warner theory is suitable at low temperatures.

Landau-de Gennes theory of surface-enhanced ordering in smectic films.

Science.gov (United States)

Shalaginov, A N; Sullivan, D E

2001-03-01

A Landau theory for surface-enhanced ordering in smectic-A free-standing films is described, based on a generalization of de Gennes' model for a "presmectic" fluid confined between two walls. According to the theory, smectic ordering in free-standing films heated above the bulk smectic melting temperature is due to an intrinsic surface contribution rather than an external field. The theory yields a persistent finite-size effect, in that the film melting temperatures do not tend to the bulk transition temperature in the limit of infinite film thickness. It also predicts that a continuous transition from (N+1)- to N-layer films is impossible without an external field. The theory closely fits existing experimental data on layer-thinning transitions in compounds which exhibit a bulk smectic-A to nematic phase transition. Possible origins of the intrinsic surface contribution are discussed.

Biaxiality in Nematic and Smectic Liquid Crystals. Final Report

Energy Technology Data Exchange (ETDEWEB)

Kumar, Satyendra [Kent State Univ., Kent, OH (United States); Li, Quan [Kent State Univ., Kent, OH (United States); Srinivasarao, Mohan [Georgia Inst. of Technology, Atlanta, GA (United States); Agra-Kooijman, Dena M. [Kent State Univ., Kent, OH (United States); Rey, Alejandro [McGill Univ., Montreal, QC (Canada)

2017-01-24

During the award period, the project team explored several phenomena in a diverse group of soft condensed matter systems. These include understanding of the structure of the newly discovered twist-bend nematic phase, solving the mystery of de Vries smectic phases, probing of interesting associations and defect structures in chromonic liquid crystalline systems, dispersions of ferroelectric nanoparticles in smectic liquid crystals, investigations of newly synthesized light sensitive and energy harvesting materials with highly desirable transport properties. Our findings are summarized in the following report followed by a list of 36 publications and 37 conference presentations. We achieved this with the support of Basic Sciences Division of the US DOE for which we are thankful.

Smectic liquid crystals in anisotropic colloidal silica gels

Energy Technology Data Exchange (ETDEWEB)

Liang, Dennis [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Borthwick, Matthew A [Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Leheny, Robert L [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)

2004-05-19

We report x-ray scattering studies of the smectic liquid crystal octylcyano-biphenol (8CB) confined by strained colloidal silica gels. The gels, comprised of aerosil particles, possess an anisotropic structure that stabilizes long-range nematic order in the liquid crystal while introducing random field effects that disrupt the smectic transition. The short-range smectic correlations that form within this environment are inconsistent with the presence of a topologically ordered state predicted for 3D random field XY systems and are quantitatively like the correlations of smectics confined by isotropic gels. Detailed analysis reveals that the quenched disorder suppresses the anisotropic scaling of the smectic correlation lengths observed in the pure liquid crystal. These results and additional measurements of the smectic-A to smectic-C transition in 4-n-pentylphenylthiol-4'-n-octyloxybenzoate (8barS5) indicate that the observed smectic behaviour is dictated by random fields coupling directly to the smectic order while fields coupling to the nematic director play a subordinate role.

Calamitic Smectic A-Polar Smectic APA Transition Observed in Bent Molecules with Large Bent-Angle Central Core of 4,6-Dichlorobenzene and Alkylthio Terminal Tail

Science.gov (United States)

Nguyen, Ha; Kang, Sungmin; Tokita, Masatoshi; Watanabe, Junji

2011-07-01

New homologs of bent molecules with a large bent-angle central core of 4,6-dichloro benzene and an alkylthio terminal tail have been synthesized. Although the corresponding alkoxy-tail homologs show only the calamitic phases because of its large bent angles around 160°, the new homologs with an alkylthio tail exhibit the antiferroelectric smectic APA (SmAPA) banana phase that is transformed on cooling from the calamitic smectic A (SmA) phase. The biaxial polar packing of bent molecules in the SmAPA phase is considered to arise from the hindered rotation around the molecular long axis due to the expansion of the mesophase temperatures to a lower temperature region. This study indicates that the bent molecules, even with a large bent angle, have the potential to form a switchable banana phase with a remarkable decrease in its phase temperature range to around 60 °C.

From antiferroelectricity to ferroelectricity in smectic mesophases ...

Indian Academy of Sciences (India)

are not ferroelectric in the ground state, but upon alignment within an electric field .... Figure 3. Molecular organisation within polar smectic phases and possible ways to escape from a macroscopic polarisation in mesophases built up by polar layers. .... in which the molecules adapt a twisted orientation from the top to bottom.

Flexoelectricity and piezoelectricity: the reason for the rich variety of phases in antiferroelectric smectic liquid crystals.

Science.gov (United States)

Cepic, M; Zeks, B

2001-08-20

The free energy of antiferroelectric smectic liquid crystals which takes into account polar order explicitly is presented. Steric, van der Waals, piezoelectric, and flexoelectric interactions to the nearest layers, and dipolar electrostatic interactions to the nearest and to the next-nearest layers, induce indirect tilt interactions with chiral and achiral properties, which extend to the third- and to the fourth-nearest layers. Although the strength of microscopic interactions changes monotonically with decreasing temperature, the effective interlayer interactions change nonmonotonically and give rise to a nonmonotonic change of the modulation period through various phases. Increased chirality changes the phase sequence.

Neutron quasi-elastic scattering study of translational motions in the smectic H, C and A phases of TBBA

International Nuclear Information System (INIS)

Dianoux, A.J.; Volino, F.; Heidemann, A.; Hervet, H.

1975-01-01

Neutron quasi-elastic scattering experiments in the smectic H, C and A phases of TBBA are presented, using the high resolution backscattering technique. The data are analyzed in terms of translational motion and are characterized by an apparent self diffusion coefficient Dsub(ap). The physical meaning of Dsub(ap) is discussed in terms of the true bulk self diffusion tensor and other kinds of translational motions [fr

Shear flow in smectic A liquid crystals

International Nuclear Information System (INIS)

Stewart, I W; Stewart, F

2009-01-01

This paper considers the onset of a shear-induced instability in a sample of smectic A liquid crystal. Unlike many previous models, the usual director n need not necessarily coincide with the local smectic layer normal a; the traditional Oseen constraint (∇xa=0) is not imposed when flow is present. A recent dynamic theory for smectic A (Stewart 2007 Contin. Mech. Thermodyn. 18 343-60) will be used to examine a stationary instability in a simple model when the director reorientation and smectic layer distortions are, firstly, assumed not to be coupled to the velocity and, secondly, are supposed coupled to the velocity. A critical shear rate at which the onset of the instability occurs will be identified, together with an accompanying critical director tilt angle and critical wavenumber for the associated smectic layer undulations. Despite some critical phenomena being largely unaffected by any coupling to the flow, it will be shown that the influence of some material parameters, especially the smectic layer compression constant B 0 and the coupling constant B 1 , upon the critical shear rate and critical tilt angle can be greatly affected by flow.

Instability of a Lamellar Phase under Shear Flow: Formation of Multilamellar Vesicles

Science.gov (United States)

Courbin, L.; Delville, J. P.; Rouch, J.; Panizza, P.

2002-09-01

The formation of closed-compact multilamellar vesicles (referred to in the literature as the ``onion texture'') obtained upon shearing lamellar phases is studied using small-angle light scattering and cross-polarized microscopy. By varying the shear rate γ ˙, the gap cell D, and the smectic distance d, we show that: (i)the formation of this structure occurs homogeneously in the cell at a well-defined wave vector qi, via a strain-controlled process, and (ii)the value of qi varies as (dγ ˙/D)1/3. These results strongly suggest that formation of multilamellar vesicles may be monitored by an undulation (buckling) instability of the membranes, as expected from theory.

Determination and theoretical analysis of supercritical fluid chromatographic retention of polycyclic aromatic hydrocarbons in a polymeric smectic phase

International Nuclear Information System (INIS)

Chao Yan; Martire, D.E.

1992-01-01

A mean-field lattice model is used to describe the partitioning of blocklike molecules between an isotropic mobile phase and an anisotropic stationary phase in chromatography by applying it to supercritical fluid retention of polycyclic aromatic hydrocarbons in a polymeric smectic phase. This concludes that the logarithm of the capacity factor (1) increases linearly with increasing reciprocal temperature, (2) decreases with increasing mobile phase density more rapidly for solute molecules with a relatively larger contact area with the mobile phase, and (3) is a linear function of the minimum area. The van't Hoff plot slope is also determined to be more negative for solute molecules with a relatively larger ratio of contact area with the stationary phase versus the mobile phase. 18 refs., 9 figs., 5 tabs

Persistence of Smectic-A Oily Streaks into the Nematic Phase by UV Irradiation of Reactive Mesogens

Directory of Open Access Journals (Sweden)

Ines Gharbi

2017-12-01

Full Text Available Thin smectic liquid crystal films with competing boundary conditions (planar and homeotropic at opposing surfaces form well-known striated structures known as “oily streaks”, which are a series of hemicylindrical caps that run perpendicular to the easy axis of the planar substrate. The streaks vanish on heating into the nematic phase, where the film becomes uniform and exhibits hybrid alignment. On adding sufficient reactive mesogen and polymerizing, the oily streak texture is maintained on heating through the entire nematic phase until reaching the bulk isotropic phase, above which the texture vanishes. Depending on the liquid crystal thickness, the oily streak structure may be retrieved after cooling, which demonstrates the strong impact of the polymer backbone on the liquid crystal texture. Polarizing optical, atomic force, and scanning electron microscopy data are presented.

Flexible Bistable Smectic-A Liquid Crystal Device Using Photolithography and Photoinduced Phase Separation

Directory of Open Access Journals (Sweden)

Yang Lu

2012-01-01

Full Text Available A flexible bistable smectic-A liquid crystal (SmA LC device using pixel-isolated mode was demonstrated, in which SmA LC molecules were isolated in pixels by vertical polymer wall and horizontal polymer layer. The above microstructure was achieved by using ultraviolet (UV photolithography and photoinduced phase separation. The polymer wall was fabricated by photolithography, and then the SmA LC was encapsulated in pixels between polymer wall through UV-induced phase separation, in which the polymer wall acts as supporting structure from mechanical pressure and maintains the cell gap from bending, and the polymer layer acts as adhesive for tight attachment of two substrates. The results demonstrated that all the intrinsic bistable properties of the SmA LC are preserved, and good electrooptical characteristics such as high contrast ratio and excellent stability of the bistable states were characterized. This kind of SmA bistable flexible display has high potential to be used as electronic paper, smart switchable reflective windows, and so forth.

Group theoretical arguments on the Landau theory of second-order phase transitions applied to the phase transitions in some liquid crystals

International Nuclear Information System (INIS)

Rosciszewski, K.

1979-01-01

The phase transitions between liquids and several of the simplest liquid crystalline phases (nematic, cholesteric, and the simplest types of smectic A and smectic C) were studied from the point of view of the group-theoretical arguments of Landau theory. It was shown that the only possible candidates for second-order phase transitions are those between nematic and smectic A, between centrosymmetric nematic and smectic C and between centrosymmetric smectic A and smectic C. Simple types of density functions for liquid crystalline phases are proposed. (author)

Defect dynamics and coarsening dynamics in smectic-C films

Science.gov (United States)

Pargellis, A. N.; Finn, P.; Goodby, J. W.; Panizza, P.; Yurke, B.; Cladis, P. E.

1992-12-01

We study the dynamics of defects generated in free-standing films of liquid crystals following a thermal quench from the smectic-A phase to the smectic-C phase. The defects are type-1 disclinations, and the strain field between defect pairs is confined to 2π walls. We compare our observations with a phenomenological model that includes dipole coupling of the director field to an external ordering field. This model is able to account for both the observed coalescence dynamics and the observed ordering dynamics. In the absence of an ordering field, our model predicts the defect density ρ to scale with time t as ρ lnρ~t-1. When the dipole coupling of the director field to an external ordering field is included, both the model and experiments show the defect coarsening proceeds as ρ~e-αt with the strain field confined to 2π walls. The external ordering field most likely arises from the director's tendency to align with edge dislocations within the liquid-crystal film.

The alignment of smectic A liquid crystals with director tilt on the boundaries

International Nuclear Information System (INIS)

Stewart, I W

2007-01-01

Equilibrium solutions are presented for smectic A liquid crystals in which the usual director n and unit layer normal a do not necessarily coincide. Previous applications often equate n with a; the model in this paper allows n and a to differ and has been motivated by the recent investigations of Auernhammer et al (2000 Rheol. Acta 39 215-22, 2002 Phys. Rev. E 66 061707), Soddemann et al (2004 Eur. Phys. J. E 13 141-51) and Stewart (2007 Contin. Mech. Thermodyn. 18 343-60). The two experimental geometries studied consist of planar homeotropically aligned smectic layers and 'bookshelf' aligned layers. In both cases a director tilt at the boundaries will be imposed. Solutions to the fully nonlinear bookshelf problem where both the director and the layer normal can vary with an element of decoupling are presented and are particularly relevant to the experimental observations of Elston (1994 Liq. Cryst. 16 151-7); there are two boundary layer effects, as will be discussed, that are related to the biasing of the director towards the smectic A phase and the reorientation of the smectic layers themselves

The alignment of smectic A liquid crystals with director tilt on the boundaries

Energy Technology Data Exchange (ETDEWEB)

Stewart, I W [Department of Mathematics, University of Strathclyde, Livingstone Tower, 26 Richmond Street, Glasgow, G1 1XH (United Kingdom)

2007-05-18

Equilibrium solutions are presented for smectic A liquid crystals in which the usual director n and unit layer normal a do not necessarily coincide. Previous applications often equate n with a; the model in this paper allows n and a to differ and has been motivated by the recent investigations of Auernhammer et al (2000 Rheol. Acta 39 215-22, 2002 Phys. Rev. E 66 061707), Soddemann et al (2004 Eur. Phys. J. E 13 141-51) and Stewart (2007 Contin. Mech. Thermodyn. 18 343-60). The two experimental geometries studied consist of planar homeotropically aligned smectic layers and 'bookshelf' aligned layers. In both cases a director tilt at the boundaries will be imposed. Solutions to the fully nonlinear bookshelf problem where both the director and the layer normal can vary with an element of decoupling are presented and are particularly relevant to the experimental observations of Elston (1994 Liq. Cryst. 16 151-7); there are two boundary layer effects, as will be discussed, that are related to the biasing of the director towards the smectic A phase and the reorientation of the smectic layers themselves.

Nanoparticles inclusions in self assembly thin smectic films

International Nuclear Information System (INIS)

Hamdoun, B.; Charara, J.; Zaiour, A.

2004-01-01

Full text. Processing of nanocomposites based on nanoparticles inclusion in thin smectic-A liquid crystal was reviewed. Thin smectic-A liquid crystal consists of a stack of regularly spaced membranes that are frequently formed in thin diblock copolymers. Particular attention was given to the scientific concepts that underpin the fabrication of special composite derived copolymer components. The complex interplay between suspension stability and its structural evolution during nanomaterials processing was highlighted. Inclusions, such as nanoparticles, coupled locally to the smectic may deform the membranes over a large length scale. We determined the distortion field due to one inclusion using the Landau-de Gennes description of smectic liquid crystals and by neglecting the interactions between nanoparticles. The equilibrium position of the particle was shown to depend on both the surface tension at the film boundary and the volume fraction of the nanoparticles

Ferroelectric Nematic and Ferrielectric Smectic Mesophases in an Achiral Bent-Core Azo Compound.

Science.gov (United States)

Kumar, Jitendra; Prasad, Veena

2018-03-22

Here, we report the observation of ferroelectric nematic and ferrielectric smectic mesophases in an achiral bent-core azo compound consisting of nonsymmetrical molecules with a lateral fluoro substitution on one of the wings. These mesophases are enantiotropic in nature with fairly low transition temperatures and wide mesophase ranges. The liquid crystalline properties of this compound are investigated using polarizing optical microscope, differential scanning calorimeter, X-ray diffraction, and electro-optical studies. As revealed by X-ray diffraction measurements, the nematic mesophase is composed of skewed cybotactic clusters and, in the smectic mesophase, the molecules are tilted with respect to the layer normal. The polar order in these mesophases was confirmed by the electro-optical switching and dielectric spectroscopy measurements. The dielectric study in the nematic mesophase shows a single relaxation process at low frequency ( f interest is the fact that the smectic phase exhibits a field induced ferrielectric state, which can be exploited for designing of the potential optical devices due to multistate switching.

One- and two-dimensional fluids properties of smectic, lamellar and columnar liquid crystals

CERN Document Server

Jakli, Antal

2006-01-01

Smectic and lamellar liquid crystals are three-dimensional layered structures in which each layer behaves as a two-dimensional fluid. Because of their reduced dimensionality they have unique physical properties and challenging theoretical descriptions, and are the subject of much current research. One- and Two-Dimensional Fluids: Properties of Smectic, Lamellar and Columnar Liquid Crystals offers a comprehensive review of these phases and their applications. The book details the basic structures and properties of one- and two-dimensional fluids and the nature of phase transitions. The later chapters consider the optical, magnetic, and electrical properties of special structures, including uniformly and non-uniformly aligned anisotropic films, lyotropic lamellar systems, helical and chiral structures, and organic anisotropic materials. Topics also include typical and defective features, magnetic susceptibility, and electrical conductivity. The book concludes with a review of current and potential applications ...

Optical modulation in nematic phase of halogen substituted hydrogen bonded liquid crystals

Science.gov (United States)

Vijayakumar, V. N.; Madhu Mohan, M. L. N.

2012-01-01

A series of halogen-substituted hydrogen-bonded liquid crystalline complexes have been designed and synthesised. A successful attempt has been made to form complementary hydrogen bonding between the dodecyloxy benzoic acid (12BAO) and halogen-substituted benzoic acids and the physical properties exhibited by the individual complexes are studied. The complexes obtained are analysed by polarising optical microscope (POM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and dielectric studies. The formation of complementary hydrogen bond is confirmed through FTIR spectra. An interesting feature of this series is the observation of a field-induced transition (FiT) in nematic phase. Another interesting phenomenon is the observation of a new smectic X phase (worm-like texture) in all the synthesised complexes. Dielectric relaxation studies in the smectic C phase of these hydrogen bonded complexes along with the Arrhenius and the Cole-Cole plots are discussed. Optical tilt angle in smectic C phase and the corresponding fitted data analysis concur with the Mean field theory prediction.

Study of variation in thermal width of nematic and induced smectic ordering phase of citric acid (CA) and 4-heptyloxybenzoic acid (7OBA) hydrogen bonded liquid crystal complexes

Science.gov (United States)

Sundaram, S.; Jayaprakasam, R.; Praveena, R.; Rajasekaran, T. R.; Senthil, T. S.; Vijayakumar, V. N.

2018-01-01

Hydrogen-bonded liquid crystals (HBLCs) have been derived from nonmesogenic citric acid (CA) and mesogenic 4-heptyloxybenzoic acid (7OBA) yielding a highly ordered smectic C (Sm C) phase along with the new smectic X (Sm X) phase which has been identified as fingerprint-type texture. Optical (polarizing optical microscopy), thermal (differential scanning calorimetry) and structural (Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy) properties are studied. A noteworthy observation is that the intermolecular H-bond (between CA and 7OBA) influences on its melting point and clearing temperature of the HBLCs which exhibits lower value than those of the individual compounds. A typical extended mesophase region has been observed in the present complex while varying the mixture ratio (1:1 to 1:3) than those of individual compounds. The change in the ratio of the mesogenic compound in the mixture alters thermal properties such as enthalpy value and thermal span width in nematic (N) region of HBLC complex. Optical tilt angle measurement of CA+7OBA in Sm C phase has been discussed to identify the molecular position in the mesophase.

Squeezing-out dynamics in free-standing smectic films

Energy Technology Data Exchange (ETDEWEB)

S̀liwa, Izabela, E-mail: izasliwa@ifmpan.poznan.pl [Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznaǹ (Poland); Vakulenko, A.A. [Saint Petersburg Institute for Machine Sciences, The Russian Academy of Sciences, Saint Petersburg 199178 (Russian Federation); Zakharov, A.V., E-mail: alexandre.zakharov@yahoo.ca [Saint Petersburg Institute for Machine Sciences, The Russian Academy of Sciences, Saint Petersburg 199178 (Russian Federation)

2016-05-06

Highlights: • We model the dynamics of layer transitions. • We model the thermally activated nucleation of a small hole. • We model the dynamics of squeezing-out one layer. - Abstract: We have carried out a theoretical study of the dynamics of the squeezing-out of one layer from the N-layer free-standing smectic film (FSSF) coupled with a meniscus, during the layer-thinning process. Squeezing-out is initiated by a thermally activated nucleation process in which a density fluctuation forms a small void in the center of the circular FSSF. The pressure gradient develops between the squeezed-out and nonsqueezed-out areas and is responsible for the driving out of one or several layer(s) from the N-layer smectic film. The dynamics of the boundary between these areas in the FSSF is studied by the use of the conservation laws for mass and linear momentum with accounting for the coupling between the meniscus and the smectic film. This coupling has a strong effect on the dynamics of the squeezing-out process and may significantly change the time which is needed to completely squeezed-out one or several layer(s) from the N-layer smectic film.

Reversibility of temperature driven discrete layer-by-layer formation of dioctyl-benzothieno-benzothiophene films.

Science.gov (United States)

Dohr, M; Ehmann, H M A; Jones, A O F; Salzmann, I; Shen, Q; Teichert, C; Ruzié, C; Schweicher, G; Geerts, Y H; Resel, R; Sferrazza, M; Werzer, O

2017-03-22

Film forming properties of semiconducting organic molecules comprising alkyl-chains combined with an aromatic unit have a decisive impact on possible applications in organic electronics. In particular, knowledge on the film formation process in terms of wetting or dewetting, and the precise control of these processes, is of high importance. In the present work, the subtle effect of temperature on the morphology and structure of dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) films deposited on silica surfaces by spin coating is investigated in situ via X-ray diffraction techniques and atomic force microscopy. Depending on temperature, bulk C8-BTBT exhibits a crystalline, a smectic A and an isotropic phase. Heating of thin C8-BTBT layers at temperatures below the smectic phase transition temperature leads to a strong dewetting of the films. Upon approaching the smectic phase transition, the molecules start to rewet the surface in the form of discrete monolayers with a defined number of monolayers being present at a given temperature. The wetting process and layer formation is well defined and thermally stable at a given temperature. On cooling the reverse effect is observed and dewetting occurs. This demonstrates the full reversibility of the film formation behavior and reveals that the layering process is defined by an equilibrium thermodynamic state, rather than by kinetic effects.

The mathematics of instabilities in smectic C liquid crystals

Energy Technology Data Exchange (ETDEWEB)

Anderson, D.A

2001-07-01

The theoretical effects of applying a magnetic or electric field to samples of smectic A and smectic C{sup *} liquid crystals are studied in this thesis. In Chapter 2 general background material on liquid crystals is introduced as well as the continuum theory which we shall use in subsequent chapters. We consider a planar sample of ferroelectric smectic C{sup *} liquid crystal in Chapter 3, where an electric field is applied perpendicular to the smectic layers. In particular, we obtain an exact solution to a dynamic equation which governs director reorientation (within a sample which is bounded in the z direction) which appears in the literature. We then consider the linear stability of this solution by applying a perturbation, in both space and time, and examine its growth. In Chapter 4 we again consider the stability of a planar sample of ferroelectric smectic C{sup *} when an electric field is applied perpendicular to the smectic planes. However, unlike in Chapter 3, we derive the relevant governing equation. After having introduced the relevant theory, the linear and nonlinear stability of a constant equilibrium state in both finite and infinite domains is examined. We then obtain information upon the relaxation times for each of these cases. The relaxation time gives an indication of how quickly the director relaxes back to equilibrium. The dynamic equation which is derived in Chapter 4 is extended in Chapter 5 to include the effects of lilting the applied electric field. The equilibrium equation which we then obtain is not tractable explicitly due to the form of the sinusoidal nonlinearity which appears in it. We therefore solve a simplified approximating dynamic equation as well as the full sinusoidal nonlinearity case numerically. In both cases the linear stability of the equilibrium solution is examined. Finally, in Chapter 6 we consider the layer deformations in a cylindrical sample of smectic A liquid crystal when a magnetic field is applied across the

The mathematics of instabilities in smectic C liquid crystals

International Nuclear Information System (INIS)

Anderson, D.A.

2001-01-01

The theoretical effects of applying a magnetic or electric field to samples of smectic A and smectic C * liquid crystals are studied in this thesis. In Chapter 2 general background material on liquid crystals is introduced as well as the continuum theory which we shall use in subsequent chapters. We consider a planar sample of ferroelectric smectic C * liquid crystal in Chapter 3, where an electric field is applied perpendicular to the smectic layers. In particular, we obtain an exact solution to a dynamic equation which governs director reorientation (within a sample which is bounded in the z direction) which appears in the literature. We then consider the linear stability of this solution by applying a perturbation, in both space and time, and examine its growth. In Chapter 4 we again consider the stability of a planar sample of ferroelectric smectic C * when an electric field is applied perpendicular to the smectic planes. However, unlike in Chapter 3, we derive the relevant governing equation. After having introduced the relevant theory, the linear and nonlinear stability of a constant equilibrium state in both finite and infinite domains is examined. We then obtain information upon the relaxation times for each of these cases. The relaxation time gives an indication of how quickly the director relaxes back to equilibrium. The dynamic equation which is derived in Chapter 4 is extended in Chapter 5 to include the effects of lilting the applied electric field. The equilibrium equation which we then obtain is not tractable explicitly due to the form of the sinusoidal nonlinearity which appears in it. We therefore solve a simplified approximating dynamic equation as well as the full sinusoidal nonlinearity case numerically. In both cases the linear stability of the equilibrium solution is examined. Finally, in Chapter 6 we consider the layer deformations in a cylindrical sample of smectic A liquid crystal when a magnetic field is applied across the circular cross

Polymer stabilization of the smectic C-alpha* liquid crystal phase—Over tenfold thermal stabilization by confining networks of photo-polymerized reactive mesogens

International Nuclear Information System (INIS)

Labeeb, A.; Gleeson, H. F.; Hegmann, T.

2015-01-01

The smectic C*-alpha (SmC α *) phase is one of the sub-phases of ferroelectric liquid crystals that has drawn much interest due to its electro-optical properties and ultrafast switching. Generally observed above the ferroelectric SmC* phase in temperature, the SmC α * commonly shows only very narrow phase temperature range of a few degree Celsius. To broaden the SmC α * phase, polymer stabilization was investigated for thermal phase stabilization. Two different reactive monomers were tested in three mixtures, and all three broadened the temperature range of the SmC α * phase from 3 °C to 39 °C. The current reversal method was used to determine the phase existence versus temperature. Moreover, the texture and network structure was studied by polarized optical microscopy and scanning electron microscopy, with the latter revealing the confinement of the smectic layer structure within the porous polymer network

Single molecule translocation in smectics illustrates the challenge for time-mapping in simulations on multiple scales.

Science.gov (United States)

Mukherjee, Biswaroop; Peter, Christine; Kremer, Kurt

2017-09-21

Understanding the connections between the characteristic dynamical time scales associated with a coarse-grained (CG) and a detailed representation is central to the applicability of the coarse-graining methods to understand molecular processes. The process of coarse graining leads to an accelerated dynamics, owing to the smoothening of the underlying free-energy landscapes. Often a single time-mapping factor is used to relate the time scales associated with the two representations. We critically examine this idea using a model system ideally suited for this purpose. Single molecular transport properties are studied via molecular dynamics simulations of the CG and atomistic representations of a liquid crystalline, azobenzene containing mesogen, simulated in the smectic and the isotropic phases. The out-of-plane dynamics in the smectic phase occurs via molecular hops from one smectic layer to the next. Hopping can occur via two mechanisms, with and without significant reorientation. The out-of-plane transport can be understood as a superposition of two (one associated with each mode of transport) independent continuous time random walks for which a single time-mapping factor would be rather inadequate. A comparison of the free-energy surfaces, relevant to the out-of-plane transport, qualitatively supports the above observations. Thus, this work underlines the need for building CG models that exhibit both structural and dynamical consistency to the underlying atomistic model.

Single molecule translocation in smectics illustrates the challenge for time-mapping in simulations on multiple scales

Science.gov (United States)

Mukherjee, Biswaroop; Peter, Christine; Kremer, Kurt

2017-09-01

Understanding the connections between the characteristic dynamical time scales associated with a coarse-grained (CG) and a detailed representation is central to the applicability of the coarse-graining methods to understand molecular processes. The process of coarse graining leads to an accelerated dynamics, owing to the smoothening of the underlying free-energy landscapes. Often a single time-mapping factor is used to relate the time scales associated with the two representations. We critically examine this idea using a model system ideally suited for this purpose. Single molecular transport properties are studied via molecular dynamics simulations of the CG and atomistic representations of a liquid crystalline, azobenzene containing mesogen, simulated in the smectic and the isotropic phases. The out-of-plane dynamics in the smectic phase occurs via molecular hops from one smectic layer to the next. Hopping can occur via two mechanisms, with and without significant reorientation. The out-of-plane transport can be understood as a superposition of two (one associated with each mode of transport) independent continuous time random walks for which a single time-mapping factor would be rather inadequate. A comparison of the free-energy surfaces, relevant to the out-of-plane transport, qualitatively supports the above observations. Thus, this work underlines the need for building CG models that exhibit both structural and dynamical consistency to the underlying atomistic model.

Examination of new chiral smectics with four aromatic rings

Science.gov (United States)

Żurowska, Magdalena; Czerwiński, Michał; Dziaduszek, Jerzy; Filipowicz, Marek

2018-05-01

This paper presents the results of the study of four chiral mesogens with the acronym (4X1X2). The investigated compounds might be of interest for use as components of multicomponent mixtures useful in technical devices. The compounds have high chemical stability. Their mesomorphic properties were tested by means of polarizing optical microscopy and differential scanning calorimetry. The helical pitch of the prepared compounds and mixtures was estimated using the selective reflection method. Their phase smectic layer structure and usefulness for formulation of multicomponent antiferroelectric mixtures were then reported.

Polymer stabilization of the smectic C-alpha* liquid crystal phase—Over tenfold thermal stabilization by confining networks of photo-polymerized reactive mesogens

Energy Technology Data Exchange (ETDEWEB)

Labeeb, A. [Liquid Crystal Institute, Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio 44242 (United States); Microwave Physics and Dielectrics, National Research Center, Dokki 12622 (Egypt); Gleeson, H. F. [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom); Hegmann, T., E-mail: thegmann@kent.edu [Liquid Crystal Institute, Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio 44242 (United States)

2015-12-07

The smectic C*-alpha (SmC{sub α}*) phase is one of the sub-phases of ferroelectric liquid crystals that has drawn much interest due to its electro-optical properties and ultrafast switching. Generally observed above the ferroelectric SmC* phase in temperature, the SmC{sub α}* commonly shows only very narrow phase temperature range of a few degree Celsius. To broaden the SmC{sub α}* phase, polymer stabilization was investigated for thermal phase stabilization. Two different reactive monomers were tested in three mixtures, and all three broadened the temperature range of the SmC{sub α}* phase from 3 °C to 39 °C. The current reversal method was used to determine the phase existence versus temperature. Moreover, the texture and network structure was studied by polarized optical microscopy and scanning electron microscopy, with the latter revealing the confinement of the smectic layer structure within the porous polymer network.

Smectic Layer Origami via Preprogrammed Photoalignment.

Science.gov (United States)

Ma, Ling-Ling; Tang, Ming-Jie; Hu, Wei; Cui, Ze-Qun; Ge, Shi-Jun; Chen, Peng; Chen, Lu-Jian; Qian, Hao; Chi, Li-Feng; Lu, Yan-Qing

2017-04-01

Hierarchical architecture is of vital importance in soft materials. Focal conic domains (FCDs) of smectic liquid crystals, characterized by an ordered lamellar structure, attract intensive attention. Simultaneously tailoring the geometry and clustering characteristics of FCDs remains a challenge. Here, the 3D smectic layer origami via a 2D preprogrammed photoalignment film is accomplished. Full control of hierarchical superstructures is demonstrated, including the domain size, shape, and orientation, and the lattice symmetry of fragmented toric FCDs. The unique symmetry breaking of resultant superstructures combined with the optical anisotropy of the liquid crystals induces an intriguing polarization-dependent diffraction. This work broadens the scientific understanding of self-assembled soft materials and may inspire new opportunities for advanced functional materials and devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

On a Minimum Problem in Smectic Elastomers

International Nuclear Information System (INIS)

Buonsanti, Michele; Giovine, Pasquale

2008-01-01

Smectic elastomers are layered materials exhibiting a solid-like elastic response along the layer normal and a rubbery one in the plane. Balance equations for smectic elastomers are derived from the general theory of continua with constrained microstructure. In this work we investigate a very simple minimum problem based on multi-well potentials where the microstructure is taken into account. The set of polymeric strains minimizing the elastic energy contains a one-parameter family of simple strain associated with a micro-variation of the degree of freedom. We develop the energy functional through two terms, the first one nematic and the second one considering the tilting phenomenon; after, by developing in the rubber elasticity framework, we minimize over the tilt rotation angle and extract the engineering stress

Rim instability of bursting thin smectic films

Science.gov (United States)

Trittel, Torsten; John, Thomas; Tsuji, Kinko; Stannarius, Ralf

2013-05-01

The rupture of thin smectic bubbles is studied by means of high speed video imaging. Bubbles of centimeter diameter and film thicknesses in the nanometer range are pierced, and the instabilities of the moving rim around the opening hole are described. Scaling laws describe the relation between film thickness and features of the filamentation process of the rim. A flapping motion of the retracting smectic film is assumed as the origin of the observed filamentation instability. A comparison with similar phenomena in soap bubbles is made. The present experiments extend studies on soap films [H. Lhuissier and E. Villermaux, Phys. Rev. Lett. 103, 054501 (2009), 10.1103/PhysRevLett.103.054501] to much thinner, uniform films of thermotropic liquid crystals.

New theories for smectic and nematic liquid crystalline polymers

International Nuclear Information System (INIS)

Dowell, F.

1987-01-01

A summary of results from new statistical-physics theories for both backbone and side-chain liquid crystalline polymers (LCPs) and for mixtures with LCPs is presented. Thermodynamic and molecular ordering properties (including odd-even effects) have been calculated as a function of pressure, density, temperature, and molecule chemical structures (including degree of polymerization and the following properties of the chemical structures of the repeat units: lengths and shapes, intra-chain rotation energies, dipole moments, site-site polarizabilities and Lennard-Jones potentials, etc.) in nematic and multiple smectic-A LC phases and in the isotropic liquid phase. These theories can also be applied to combined LCPs. Since these theories have no ad hoc or arbitrarily adjustable parameters, these theories have been used to design new LCPs and new solvents and to predict and explain properties

Inclusions with finite surface anchoring energies in smectic C and chiral smectic C* free-standing films

Czech Academy of Sciences Publication Activity Database

Lejček, Lubor

2016-01-01

Roč. 49, č. 1 (2016), 116-128 ISSN 0015-0193 R&D Projects: GA ČR GA13-14133S; GA ČR GA15-02843S Institutional support: RVO:68378271 Keywords : smectic C and C* * free standing films * inclusions, disclinations Subject RIV: BE - Theoretical Physics Impact factor: 0.551, year: 2016

Effect of smectic A temperature width on the soft mode in ferroelectric liquid crystals

Science.gov (United States)

Choudhary, A.; Kaur, S.; Prakash, J.; Sreenivas, K.; Bawa, S. S.; Biradar, A. M.

2008-08-01

The behavior of soft mode range with respect to the temperature width of smectic A (Sm A) phase has been studied in four different ferroelectric liquid crystal (FLC) materials in the frequency range 10Hz-10MHz. The studies have been carried out in a planarly well aligned cells at different temperatures and different bias fields in Sm C* and Sm A phases. Dielectric studies of these FLCs near Sm C*-Sm A phase transition show that the temperature range of soft mode relaxation frequency phenomenon varies with the temperature width of Sm A phase. The dependence of tilt angle on temperature shows the nature of the order of transition at Sm C*-Sm A phase. The coupling between order parameters of Sm C* and Sm A phase influences the soft mode and phase transition in Sm C* and Sm A phases.

New theory for competing interactions and microstructures in partially-ordered (liquid-crystalline) phases

International Nuclear Information System (INIS)

Dowell, F.

1987-01-01

A summary of results from a unique statistical-physics theory to predict and explain competing interactions and resulting microstructures in some partially-ordered [in this case, liquid-crystalline (LC)] phases is presented. The static aspects of both partial orientational and partial positional ordering of the molecules into various microstructures in these phases (including the incommensurate smectic-Ad phase) can be understood in terms of various competing interactions (both entropic and energetic) involved in the packing together of the different molecular sub-units at given pressures and temperatures. These microstructures are predicted and explained (using no ad hoc or arbitrarily adjustable parameter) as a function of molecule chemical structure [including lengths and shapes (from bond lengths and angles), intramolecular rotations, site-site polarizabilities and pair potentials, dipole moments, etc]. Theoretical results are presented for the nematic, re-entrant nematic, smectic-Ad, and smectic-Al LC phases and the isotropic phase

Stability of equilibrium states in finite samples of smectic C* liquid crystals

International Nuclear Information System (INIS)

Stewart, I W

2005-01-01

Equilibrium solutions for a sample of ferroelectric smectic C (SmC*) liquid crystal in the 'bookshelf' geometry under the influence of a tilted electric field will be presented. A linear stability criterion is identified and used to confirm stability for typical materials possessing either positive or negative dielectric anisotropy. The theoretical response times for perturbations to the equilibrium solutions are calculated numerically and found to be consistent with estimates for response times in ferroelectric smectic C liquid crystals reported elsewhere in the literature for non-tilted fields

Stability of equilibrium states in finite samples of smectic C* liquid crystals

Energy Technology Data Exchange (ETDEWEB)

Stewart, I W [Department of Mathematics, University of Strathclyde, Livingstone Tower, 26 Richmond Street, Glasgow G1 1XH (United Kingdom)

2005-03-04

Equilibrium solutions for a sample of ferroelectric smectic C (SmC*) liquid crystal in the 'bookshelf' geometry under the influence of a tilted electric field will be presented. A linear stability criterion is identified and used to confirm stability for typical materials possessing either positive or negative dielectric anisotropy. The theoretical response times for perturbations to the equilibrium solutions are calculated numerically and found to be consistent with estimates for response times in ferroelectric smectic C liquid crystals reported elsewhere in the literature for non-tilted fields.

Observation of Algebraic Decay of Positional Order in a Smectic Liquid Crystal

DEFF Research Database (Denmark)

Als-Nielsen, Jens Aage; Litster, J. D.; Birgeneau, R. J.

1980-01-01

A smectic-A liquid crystal in three dimensions has been predicted to exhibit algebraic decay of the layer correlations rather than true long-range order. As a consequence, the smectic Bragg peaks are expected to be power-law singularities of the form q∥-2+η and q⊥-4+2η, where ∥(⊥) is along (perpe......, the explicit values of η required to describe the measured profiles are in accordance with calculations of η using the harmonic approximation with empirically determined splay and layer compressibility elastic constants. ©1980 The American Physical Society...

Biaxial and antiferroelectric structure of the orthogonal smectic phase of a bent-shaped molecule and helical structure in a chiral mixture system

Science.gov (United States)

Kang, Sungmin; Nguyen, Ha; Nakajima, Shunpei; Tokita, Masatoshi; Watanabe, Junji

2013-05-01

We examined the biaxial and antiferroelectric properties in the Smectic-APA (Sm-APA) phase of bent-shaped DC-S-8. The biaxiality, which results from the existence of a secondary director, was well established from birefringence observations in the homeotropically aligned Sm-APA. By entering into Sm-APA phase, the birefringence (Δn, difference between two refractive indices of short axes) continuously increased from 0 to 0.02 with decreasing temperature. The antiferroelectric switching and second harmonic generation (SHG) activity on the field-on state were also observed in the Sm-APA phase, and the evaluated spontaneous polarization (PS) value strongly depended on temperature. The temperature dependence of Δn and PS resembles each other and follows Haller's approximation, showing that the biaxiality is due to polar packing in which the molecules are preferentially packed with their bent direction arranged in the same direction, and that the phase transition of Sm-APA to Sm-A is second order. The biaxiality was further examined in chiral Sm-APA*. Doping with chiral components induced the helical twisting of the secondary director in the Sm-APA* phase, which was confirmed by observing the reflection of the circular dichroism (CD) bands in the homeotropically aligned cell. The helical pitch of Sm-APA* is tunable in the range of 300-700 nm wavelength with a variation in the chiral content of 5 to 10 weight (wt)%.

Preparation and thermo-optical characteristics of a smart polymer-stabilized liquid crystal thin film based on smectic A–chiral nematic phase transition

International Nuclear Information System (INIS)

Sun, Jian; Wang, Huihui; Cao, Hui; Ding, Hangjun; Yang, Zhou; Yang, Huai; Wang, Ling; Xie, Hui; Luo, Xueyao; Xiao, Jiumei

2014-01-01

A smart polymer stabilized liquid crystal (PSLC) thin film with temperature-controllable light transmittance was prepared based on a smectic-A (SmA)–chiral nematic (N*) phase transition, and then the effect of the composition and the preparation condition of the PSLC film on its thermo-optical (T-O) characteristics has been investigated in detail. Within the temperature range of the SmA phase, the PSLC shows a strong opaque state due to the focal conic alignment of liquid crystal (LC) molecules, while the film exhibits a transparent state result from the parallel alignment of N* phase LC molecules at a higher temperature. Importantly, the PSLC films with different temperature of phase transition and contrast ratio can be prepared by changing the composition of photo-polymerizable monomer/LC/chiral dopant. According to the competition between the polymerization of the curable monomers and the diffusion of LC molecules, the ultraviolet (UV) curing surrounding temperature and the intensity of UV irradiation play a critical role in tuning the size of the polymer network meshes, which in turn influence the contrast ratio and the switching speed of the film. Our observations are expected to pave the way for preparing smart PSLC thin films for applications in areas of smart windows, thermo-detectors and other information recording devices. (paper)

Calculation of the Dielectric Constant as a Function of Temperature Close to the Smectic A-Smectic B Transition in B5 Using the Mean Field Model

Directory of Open Access Journals (Sweden)

Hamit Yurtseven

2012-01-01

Full Text Available The temperature dependence of the static dielectric constant ( is calculated close to the smectic A-smectic B ( transition ( = 71.3°C for the liquid crystal compound B5. By expanding the free energy in terms of the order parameter in the mean field theory, the expression for the dielectric susceptibility (dielectric constant is derived and is fitted to the experimental data for which was obtained at the field strengths of 0 and 67 kV/cm from literature. Coefficients in the free energy expansion are determined from our fit for the transition of B5. Our results show that the observed behaviour of the dielectric constant close to the transition in B5 can be described satisfactorily by our mean field model.

Mechanism of smectic arrangement of montmorillonite and bentonite clay platelets incorporated in gels of poly(acrylamide) induced by the interaction with cationic surfactants.

Science.gov (United States)

Starodoubtsev, S G; Lavrentyeva, E K; Khokhlov, A R; Allegra, G; Famulari, A; Meille, S V

2006-01-03

Structure transitions, induced by the interaction with the cationic surfactant cetylpyridinium chloride in nanocomposite gels of poly(acrylamide) with incorporated suspensions of the two closely related layered clays bentonite and montmorillonite, were studied. Unexpectedly, different behaviors were revealed. X-ray diffraction measurements confirm that, due to the interaction with the surfactant, initially disordered bentonite platelets arrange into highly ordered structures incorporating alternating clay platelets and surfactant bilayers. The formation of these smectic structures also in the cross-linked polymer gels, upon addition of the surfactant, is explained by the existence of preformed, poorly ordered aggregates of the clay platelets in the suspensions before the gel formation. In the case of montmorillonite, smectic ordering of the disordered platelets in the presence of the surfactant is observed only after drying the suspensions and the clay-gel composites. Rheology studies of aqueous suspensions of the two clays, in the absence of both surfactant and gel, evidence a much higher viscosity for bentonite than for montmorillonite, suggesting smaller clay-aggregate size in the latter case. Qualitatively consistent results are obtained from optical micrographs.

Molecular dynamics studies and quantification of the effect of chirality on the formation of liquid crystal mesophases

International Nuclear Information System (INIS)

Solymosi, Miklos

2002-01-01

Results are presented from theoretical studies and from a series of molecular dynamics simulations undertaken to quantify the effect of chirality on the formation of liquid crystal mesophases. In the theoretical studies we have proposed a scaled chiral index with a formulation which allows comparison to be made between molecules comprising different numbers of atoms. We have undertaken chirality calculations utilizing the proposed scaled chiral index, G 0S , for one optimized static molecular geometry for a range of liquid crystal chiral dopants and ferroelectric liquid crystal molecules. The scaled chiral index, G 0S , allows a rapid calculation to be made of a pseudoscalar quantity which shows a good correlation with the helical twisting power of liquid crystal chiral dopants in a nematic liquid crystal solvent. This could prove a powerful aid in the design of novel dopant molecules where the dopant is rigid and the helical twisting is predominantly a steric effect. The same scaled chirality index, G 0S , calculation for ferroelectric liquid crystal molecules hints at an inverse correlation with spontaneous polarization agreeing with some experimental results. The scaled chiral index is a chemically useful index that can also be decomposed into atomic or functional group contributions, thereby creating a new measure of the asymmetric potential of functional groups and their different possible substitution positions. In the molecular dynamics simulation studies we have investigated two three-site Gay-Berne models, one chiral and the other achiral, each with a rotated central site forming a zigzag shape. In the chiral model one of the end site was additionally rotated out of the plane of the other two sites by a chiral angle θ c . Results from the achiral phase simulations support the theory that steric molecular shape can be associated with a driving force that leads to the smectic A - smectic C phase transition since such a transition was observed in the achiral

Dynamics of cylindrical domain walls in smectic C liquid crystals

International Nuclear Information System (INIS)

Stewart, I W; Wigham, E J

2009-01-01

An analysis of the dynamics of cylindrical domain walls in planar aligned samples of smectic C liquid crystals is presented. A circular magnetic field, induced by an electric current, drives a time-dependent reorientation of the corresponding radially dependent director field. Nonlinear approximations to the relevant nonlinear dynamic equation, derived from smectic continuum theory, are solved in a comoving coordinated frame: exact solutions are found for a π-wall and numerical solutions are calculated for π/2-walls. Each calculation begins with an assumed initial state for the director that is a prescribed cylindrical domain wall. Such an initial wall will proceed to expand or contract as its central core propagates radially inwards or outwards, depending on the boundary conditions for the director, the elastic constants, the magnitude of the field and the sign of the magnetic anisotropy of the liquid crystal

Physical properties of smectic C liquid crystal cells

International Nuclear Information System (INIS)

Dunn, P.E.

1998-01-01

The aim of this work was to investigate some of the fundamental physical properties of surface stabilised ferroelectric liquid crystal devices (SSFLCDs) using optical, electrical and x-ray diffraction techniques. The measured physical parameters are then related to the performance of display devices. Refractometry measurements on homeotropically aligned FLC samples are used to accurately determine the smectic cone angle and information is also gained on FLC biaxial order. Propagation of optically excited guided modes along liquid crystalline layers is then used to obtain detailed director configuration information. Wavelength dependent extinction angle spectroscopy is also used to extract smectic C director profiles, albeit with a slightly lower accuracy than the guided mode method. A triangular director profile model is found to describe the wavelength dependent extinction angle properties of achiral samples, and examination of the cell spacing dependence of the director profile enables a ratio of bulk elasticity to surface anchoring energy to be determined. Information is obtained on the behaviour of smectic C materials under high frequency electric fields using a continuum director profile model, providing a novel measurement of bend and splay elastic constants. Additionally an extension of the wavelength dependent extinction angle technique allows half splayed states to be characterised. A variety of simple electro-optic techniques are used to characterise several key material parameters. Polarisation reversal current is used to measure both the spontaneous polarisation and an effective FLC switching viscosity. Monochromatic extinction angle measurements under applied d.c. fields are used to determine the cone and layer tilt angles, whilst a comparison of d.c. and a.c. extinction angle characteristics provides an estimate of the dielectric biaxiality. An automated measurement technique is used to determine FLC response time characteristics, which are described

Physical properties of smectic C liquid crystal cells

Energy Technology Data Exchange (ETDEWEB)

Dunn, P E

1998-07-01

The aim of this work was to investigate some of the fundamental physical properties of surface stabilised ferroelectric liquid crystal devices (SSFLCDs) using optical, electrical and x-ray diffraction techniques. The measured physical parameters are then related to the performance of display devices. Refractometry measurements on homeotropically aligned FLC samples are used to accurately determine the smectic cone angle and information is also gained on FLC biaxial order. Propagation of optically excited guided modes along liquid crystalline layers is then used to obtain detailed director configuration information. Wavelength dependent extinction angle spectroscopy is also used to extract smectic C director profiles, albeit with a slightly lower accuracy than the guided mode method. A triangular director profile model is found to describe the wavelength dependent extinction angle properties of achiral samples, and examination of the cell spacing dependence of the director profile enables a ratio of bulk elasticity to surface anchoring energy to be determined. Information is obtained on the behaviour of smectic C materials under high frequency electric fields using a continuum director profile model, providing a novel measurement of bend and splay elastic constants. Additionally an extension of the wavelength dependent extinction angle technique allows half splayed states to be characterised. A variety of simple electro-optic techniques are used to characterise several key material parameters. Polarisation reversal current is used to measure both the spontaneous polarisation and an effective FLC switching viscosity. Monochromatic extinction angle measurements under applied d.c. fields are used to determine the cone and layer tilt angles, whilst a comparison of d.c. and a.c. extinction angle characteristics provides an estimate of the dielectric biaxiality. An automated measurement technique is used to determine FLC response time characteristics, which are described

Possible Moessbauer or neutron experiments on fluid interfaces and on smectics

International Nuclear Information System (INIS)

Gennes, P.G. de

1975-01-01

The spectrum of γ rays emitted from an atom bound to the free surface of a fluid is expected to show a low frequency anomaly associated with the two dimensional character of the capillary waves. This is discussed here a) for liquid metals, where initial effects should be dominant, b) for viscous fluids, c) for thin films (100A) of a liquid above a solid surface. If the anomaly turns out to be visible, it could give some informations on dissipative effects in monomolecular layers at frequencies of the order 10 8 -10 9 cycles. The theoretical emission spectrum from a smectic A liquid crystal is also considered. Finally, some remarks are presented concerning the incoherent, quasi elastic scattering of neutrons by smectics with a scattering vector normal to the layers: the same anomalies are expected and could possibly be seen with present high resolution spectrometers [fr

Double smectic self-assembly in block copolypeptide complexes

KAUST Repository

Haataja, Johannes S.

2012-11-12

We show double smectic-like self-assemblies in the solid state involving alternating layers of different polypeptide α-helices. We employed rod-coil poly(γ-benzyl l-glutamate)-block-poly(l-lysine) (PBLG-b-PLL) as the polymeric scaffold, where the PLL amino residues were ionically complexed to di-n-butyl phosphate (diC4P), di(2-ethylhexyl) phosphate (diC2/6P), di(2-octyldodecyl) phosphate (diC8/12P), or di-n-dodecyl phosphate (diC12P), forming PBLG-b-PLL(diC4P), PBLG-b-PLL(diC2/6P), PBLG-b-PLL(diC8/12P), and PBLG-b-PLL(diC12P) complexes, respectively. The complexes contain PBLG α-helices of fixed diameter and PLL-surfactant complexes adopting either α-helices of tunable diameters or β-sheets. For PBLG-b-PLL(diC4P), that is, using a surfactant with short n-butyl tails, both blocks were α-helical, of roughly equal diameter and thus with minor packing frustrations, leading to alternating PBLG and PLL(diC4P) smectic layers of approximately perpendicular alignment of both types of α-helices. Surfactants with longer and branched alkyl tails lead to an increased diameter of the PLL-surfactant α-helices. Smectic alternating PBLG and PLL(diC2/6P) layers involve larger packing frustration, which leads to poor overall order and suggests an arrangement of tilted PBLG α-helices. In PBLG-b-PLL(diC8/12P), the PLL(diC8/12P) α-helices are even larger and the overall structure is poor. Using a surfactant with two linear n-dodecyl tails leads to well-ordered β-sheet domains of PLL(diC12P), consisting of alternating PLL and alkyl chain layers. This dominates the whole assembly, and at the block copolypeptide length scale, the PBLG α-helices do not show internal order and have poor organization. Packing frustration becomes an important aspect to design block copolypeptide assemblies, even if frustration could be relieved by conformational imperfections. The results suggest pathways to control hierarchical liquid-crystalline assemblies by competing interactions and by

Double smectic self-assembly in block copolypeptide complexes

KAUST Repository

Haataja, Johannes S.; Houbenov, Nikolay; Iatrou, Hermis; Hadjichristidis, Nikolaos; Karatzas, A.; Faul, Charl F. J.; Rannou, Patrice; Ikkala, Olli T.

2012-01-01

We show double smectic-like self-assemblies in the solid state involving alternating layers of different polypeptide α-helices. We employed rod-coil poly(γ-benzyl l-glutamate)-block-poly(l-lysine) (PBLG-b-PLL) as the polymeric scaffold, where the PLL amino residues were ionically complexed to di-n-butyl phosphate (diC4P), di(2-ethylhexyl) phosphate (diC2/6P), di(2-octyldodecyl) phosphate (diC8/12P), or di-n-dodecyl phosphate (diC12P), forming PBLG-b-PLL(diC4P), PBLG-b-PLL(diC2/6P), PBLG-b-PLL(diC8/12P), and PBLG-b-PLL(diC12P) complexes, respectively. The complexes contain PBLG α-helices of fixed diameter and PLL-surfactant complexes adopting either α-helices of tunable diameters or β-sheets. For PBLG-b-PLL(diC4P), that is, using a surfactant with short n-butyl tails, both blocks were α-helical, of roughly equal diameter and thus with minor packing frustrations, leading to alternating PBLG and PLL(diC4P) smectic layers of approximately perpendicular alignment of both types of α-helices. Surfactants with longer and branched alkyl tails lead to an increased diameter of the PLL-surfactant α-helices. Smectic alternating PBLG and PLL(diC2/6P) layers involve larger packing frustration, which leads to poor overall order and suggests an arrangement of tilted PBLG α-helices. In PBLG-b-PLL(diC8/12P), the PLL(diC8/12P) α-helices are even larger and the overall structure is poor. Using a surfactant with two linear n-dodecyl tails leads to well-ordered β-sheet domains of PLL(diC12P), consisting of alternating PLL and alkyl chain layers. This dominates the whole assembly, and at the block copolypeptide length scale, the PBLG α-helices do not show internal order and have poor organization. Packing frustration becomes an important aspect to design block copolypeptide assemblies, even if frustration could be relieved by conformational imperfections. The results suggest pathways to control hierarchical liquid-crystalline assemblies by competing interactions and by

Smectic liquid crystal cell with heat pulse and laser

International Nuclear Information System (INIS)

Mash, D.H.

1984-01-01

A method of operating a homeotropically aligned smectic liquid crystal cell in which the cell is turned from a clear to a scattering state by illumination with an intense flash of light after which a focused laser beam is scanned across the layer to leave clear tracks where homeotropic alignment has been restored thereby producing a display providing, in projection, bright lines on a dark background

Alloy hardening of a smectic A liquid crystal doped with gold nanoparticles

Czech Academy of Sciences Publication Activity Database

Oswald, P.; Milette, J.; Relaix, S.; Reven, L.; Dequidt, A.; Lejček, Lubor

2013-01-01

Roč. 103, AUG (2013), "46004-p1"-"46004-p6" ISSN 0295-5075 Institutional support: RVO:68378271 Keywords : smectic A liquid crystals * gold nanoparticles * edge dislocation * precipitation hardening Subject RIV: BK - Fluid Dynamics Impact factor: 2.269, year: 2013

Higher-order-structure formation in liquid crystal epoxy thermosets investigated by synchrotron radiation-wide-angle X-ray diffraction

International Nuclear Information System (INIS)

Maeda, Rina; Okuhara, Kenta; Nakamura, Akihiro; Hayakawa, Teruaki; Uehara, Yasushi; Motoya, Tsukasa; Nobutoki, Hideharu

2016-01-01

We report the investigation of the mesophase transformations of a liquid crystalline molecule with terminal epoxy groups from the initial stages of curing with a diamine compound. The ordered arrangement of molecules within the smectic layers in the thermoset formed at the end of the curing process was characterized by synchrotron radiation-wide-angle X-ray diffraction (SR-WAXD). Data from this experiment helps us understand the phase transitions from the nematic to smectic phases of curing liquid crystalline epoxies. (author)

Phase Diagram of Binary Mixture E7:TM74A Liquid Crystals

Directory of Open Access Journals (Sweden)

Serafin Delica

1999-12-01

Full Text Available Although there are many liquid crystalline materials, difficulty is often experienced in obtaining LCs that are stable and has a wide mesophase range. In this study, mixtures of two different LCs were used to formulate a technologically viable LC operating at room temperature. Nematic E7(BDH and cholesteric TM74A were mixed at different weight ratios at 10% increments. Transition temperatures were determined via Differential Scanning Calorimetry and phase identification was done using Optical Polarizing Microscopy. The phase diagram showed the existence of three different phases for the temperature range of 10-80°C. Mixtures with 0-20% E7 exhibit only the cholesteric-nematic mesophase, which could be due to the mixture's being largely TM74A and its behavior in the temperature range considered is similar to the behavior of pure TM74A. With an increase in the concentration of E7, the smectic phase of the pure cholesteric was enhanced, as seen from the increased transition to the cholesteric-nematic phase and a broader smectic range. The cholesteric-nematic to isotropic transition increased as the nematic concentration increases, following the behavior expected from LC mixtures. For mixtures that are largely nematic (more than 50% E7, the smectic phase has vanished and the cholesteric-nematic phase dominated from 30-60°C.

Liquid Crystals - The 'Fourth' Phase of Matter

Indian Academy of Sciences (India)

possibilities of novel technological applications. Liquid crystalline materials ... advanced instrumentation, including laptops and futuristic flat panel displays. .... The twist grain-boundary phase is formed when the layers of a smectic A phase are .... the optic axis) is uniformly oriented parallel to the glass plate. (see Figure IIa).

Dicyanamide Salts that Adopt Smectic, Columnar, or Bicontinuous Cubic Liquid-Crystalline Mesophases.

Science.gov (United States)

Park, Geonhui; Goossens, Karel; Shin, Tae Joo; Bielawski, Christopher W

2018-04-25

Although dicyanamide (i.e., [N(CN) 2 ] - ) has been commonly used to obtain low-viscosity, halogen-free, room-temperature ionic liquids, liquid-crystalline salts containing such anions have remained virtually unexplored. Here we report a series of amphiphilic dicyanamide salts that, depending on their structures and compositions, adopt smectic, columnar, or bicontinuous cubic thermotropic liquid-crystalline mesophases, even at room temperature in some cases. Their thermal properties were explored by polarized light optical microscopy, differential scanning calorimetry, thermogravimetric analysis (including evolved gas analysis), and variable-temperature synchrotron X-ray diffraction. Comparison of the thermal phase characteristics of these new liquid-crystalline salts featuring "V-shaped" [N(CN) 2 ] - anions with those of structural analogues containing [SCN] - , [BF 4 ] - , [PF 6 ] - , or [CF 3 SO 3 ] - anions indicated that not only the size of the counterion but also its shape should be considered in the development of mesomorphic salts. Collectively, these discoveries may be expected to facilitate the design of thermotropic ionic liquid crystals that form inverted-type bicontinuous cubic and other sophisticated liquid-crystalline phases. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermotropic phase transition in an adsorbed melissic acid film at the n-hexane-water interface

Science.gov (United States)

Tikhonov, A. M.

2017-06-01

A reversible thermotropic phase transition in an adsorption melissic acid film at the interface between n-hexane and an aqueous solution of potassium hydroxide (pH ≈ 10) is investigated by X-ray reflectometry and diffuse scattering using synchrotron radiation. The experimental data indicate that the interface "freezing" transition is accompanied not only by the crystallization of the Gibbs monolayer but also by the formation of a planar smectic structure in the 300-Å-thick adsorption film; this structure is formed by 50-Å-thick layers.

Influence of weak anchoring upon the alignment of smectic A liquid crystals with surface pretilt

International Nuclear Information System (INIS)

De Vita, R; Stewart, I W

2008-01-01

Equilibrium configurations for smectic A liquid crystals in a 'bookshelf' geometry are determined from a nonlinear continuum model under strong and weak anchoring conditions at the boundary for the usual director n. Natural boundary conditions are derived for n and the smectic layer normal a when a preferred director orientation n p , which generally induces a director pretilt, is prescribed on the boundaries. Two key aspects are examined via the nonlinear equilibrium equations: the separation of n from a and the influence of weak anchoring. The orientations of n and a relative to n p may differ significantly and depend very much upon the magnitude of the anchoring strength. These results from a nonlinear theory are natural and novel developments of previous classical linearized models for which n ≡ a. Comparisons are also drawn between solutions for strong and weak anchoring conditions

Influence of weak anchoring upon the alignment of smectic A liquid crystals with surface pretilt

Energy Technology Data Exchange (ETDEWEB)

De Vita, R [Department of Engineering Science and Mechanics, Virginia Tech, 230 Norris Hall, Blacksburg, VA 24061 (United States); Stewart, I W [Department of Mathematics, University of Strathclyde, Livingstone Tower, 26 Richmond Street, Glasgow G1 1XH (United Kingdom)], E-mail: devita@vt.edu, E-mail: i.w.stewart@strath.ac.uk

2008-08-20

Equilibrium configurations for smectic A liquid crystals in a 'bookshelf' geometry are determined from a nonlinear continuum model under strong and weak anchoring conditions at the boundary for the usual director n. Natural boundary conditions are derived for n and the smectic layer normal a when a preferred director orientation n{sub p}, which generally induces a director pretilt, is prescribed on the boundaries. Two key aspects are examined via the nonlinear equilibrium equations: the separation of n from a and the influence of weak anchoring. The orientations of n and a relative to n{sub p} may differ significantly and depend very much upon the magnitude of the anchoring strength. These results from a nonlinear theory are natural and novel developments of previous classical linearized models for which n {identical_to} a. Comparisons are also drawn between solutions for strong and weak anchoring conditions.

Electro-Optical Characterization of Bistable Smectic A Liquid Crystal Displays

Science.gov (United States)

Buyuktanir, Ebru Aylin

My dissertation focuses the characterization and optimization of the electro-optical properties of smectic A (SmA) based liquid crystal (LC) displays. I present the development of robust and flexible bistable SmA LC displays utilizing polymer dispersed liquid crystal (PDLC) technology. The SmA PDLC displays produced on plastic substrates present electrically reversible memory, high contrast ratio, paper-like sunlight readability, and wide viewing angle characteristics. In order to optimize the SmA PDLC display, I investigated polymerization conditions, such as polymer concentration effect, polymerization temperature, and UV-light intensity variations. I characterized the electro-optical responses-such as static-response, time-response, threshold characteristics, and contrast ratio values' of the optimized SmA PDLC display and compared them to those of the pure SmA LC. The best electro-optical performance of SmA PDLC formulation was obtained using the combination of low mW/cm 2 and high mW/cm2 UV-light curing intensity. The contrast ratio of the optimum SmA PDLC at a 5o collection angle was 83% of that of the pure SmA material on plastic substrates. I fabricated 2.5 x 2.5 in., 4 x 4 in., and 6 x 6 in. sized monochrome flexible SmA PDLC displays, as well as red, yellow, and fluorescent dyes colored SmA PDLC displays on plastic substrates. The electro-optic performance of the bistable SmA LC display consisting of a patterned field-induced polymer wall infrastructure was also studied and compared to those of pure SmA material. I found that the contrast ratio of the SmA LC encapsulated between polymer walls was much greater than that of the SmA PDLC system, approaching the contrast ratio value of the pure SmA material. I also improved the electro-optical characteristics of bistable SmA LC displays by adding ferroparticles into the system. Finally, I illustrated the unique capabilities of polarized confocal Raman microscopy (CRM) to resolve the orientational order of Sm

Electroclinic effect in a chiral carbosilane-terminated 5-phenylpyrimidine liquid crystal with 'de Vries-like' properties.

Science.gov (United States)

Schubert, Christopher P J; Müller, Carsten; Wand, Michael D; Giesselmann, Frank; Lemieux, Robert P

2015-08-14

The chiral carbosilane-terminated liquid crystal 2-[(2S,3S)-2,3-difluorohexyloxy]-5-[4-(12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecyloxy)phenyl]pyrimidine () undergoes a smectic A*-smectic C* phase transition with a maximum layer contraction of only 0.2%. It exhibits an electroclinic effect (ECE) comparable to that reported for the 'de Vries-like' liquid crystal and shows no appreciable optical stripe defects due to horizontal chevron formation.

Understanding crumpling lipid vesicles at the gel phase transition

Science.gov (United States)

Hirst, Linda; Ossowski, Adam; Fraser, Matthew

2011-03-01

Wrinkling and crumpling transitions in different membrane types have been studied extensively in recent years both theoretically and computationally. There has also been very interesting recent work on defects in liquid crystalline shells. Lipid bilayer vesicles, widely used in biophysical research can be considered as a single layer smectic shell in the liquid crystalline phase. On cooling the lipid vesicle a transition to the gel phase may take place in which the lipid chains tilt and assume a more ordered packing arrangement. We observe large scale morphological changes in vesicles close to this transition point using fluorescence microscopy and investigate the possible mechanisms for this transition. Confocal microscopy is used to map 3D vesicle shape and crumpling length-scales. We also employ the molecular tilt sensitive dye, Laurdan to investigate the role of tilt domain formation on macroscopic structure. Funded by NSF CAREER award (DMR - BMAT #0852791).

Guided mode studies of smectic liquid crystals

International Nuclear Information System (INIS)

Hodder, B.

2000-03-01

Recently there has been considerable interest in the use of ferroelectric liquid crystals in low power, fast switching display devices. At present the voltage switching process in surface stabilised ferroelectric liquid crystal (SSFLC) devices is not fully understood and a convenient theory for such cells has yet to be found. It is the primary aim of this work to characterise the optic tensor configuration (director profile) in thin cells (∼ 3.5 μm) containing ferroelectric liquid crystal (FLC) material. These results form a benchmark by which continuum theories may be tested. Polarised microscopy is, perhaps, the most common optical probe of liquid crystal cells. It should be appreciated that this technique is fundamentally limited, as the results are deduced from an integrated optical response of any given cell, and cannot be used to spatially resolve details of the director profile through the cell. The guided mode techniques used in this study are the primary non-integral probe and enable detailed spatial resolution of the director profile within liquid crystal cells. Analysis of guided mode data from cells containing homeotropically aligned FLC reveals the temperature dependence of the optical biaxiality and cone angle for a 40% chiral mixture of the commercially available FLC SCE8*. From these optical biaxiality measurements the temperature dependence of the biaxial order parameter C is determined. Guided mode studies of cells containing homogeneously aligned SCE8* (the conventional alignment for SSFLC devices) reveal the 0V equilibrium director profile from which a cone and chevron model is constructed. Subsequent studies of voltage induced elastic deformations of the director profile are presented and compared with a single elastic constant continuum theory which is shown to be inadequate. Optical guided mode techniques are not directly sensitive to the smectic layer configuration but X-ray scattering is. Here, for the first time, results are presented

Self-organisation of semi-flexible rod-like particles

Science.gov (United States)

de Braaf, Bart; Oshima Menegon, Mariana; Paquay, Stefan; van der Schoot, Paul

2017-12-01

We report on a comprehensive computer simulation study of the liquid-crystal phase behaviour of purely repulsive, semi-flexible rod-like particles. For the four aspect ratios we consider, the particles form five distinct phases depending on their packing fraction and bending flexibility: the isotropic, nematic, smectic A, smectic B, and crystal phase. Upon increasing the particle bending flexibility, the various phase transitions shift to larger packing fractions. Increasing the aspect ratio achieves the opposite effect. We find two different ways in which the layer thickness of the particles in the smectic A phase may respond to an increase in concentration. The layer thickness may either decrease or increase depending on the aspect ratio and flexibility. For the smectic B and the crystalline phases, increasing the concentration always decreases the layer thickness. Finally, we find that the layer spacing jumps to a larger value on transitioning from the smectic A phase to the smectic B phase.

High-Resolution X-Ray Study of a Smectic-A-Smectic-C Phase Transition

DEFF Research Database (Denmark)

Safinya, C. R.; Kaplan, M.; Als-Nielsen, Jens Aage

1980-01-01

We report measurements of the tilt angle Φ and the planar spacing dC near the second-order SmC-SmA transition in 4-n-pentyl-phenylthiol-4′-n-octyloxybenzoate (8S̅ 5). We find that the ratio Φ/invcos(dC/dA) is constant (1.2 ± 0.1) through the C phase, supporting a simple molecular-tilt model...... for the transition. For 5×10-3>1-T/Tc>3×10-5, Φ exhibits mean-field behavior. A simple Ginzburg-criterion argument indicates that the true critical region should be unobservably small for most A-C transitions....

Fixation of chiral smectic liquid crystal (S)-(+)-4-(2-methyl-1-butyloyloxy)phenyl 4-[1-(propenoyloxy) butiloxy] benzoate using UV curing techniques

Energy Technology Data Exchange (ETDEWEB)

Afrizal,, E-mail: rizalunj04@yahoo.com; Nurdelima,; Umeir [Faculty of Mathemathics and Natural Science, University of State Jakarta, Jakarta (Indonesia); Hikam, Muhammad; Soegiyono, Bambang [Department of Materials Science, University of Indonesia, Depok (Indonesia); Riswoko, Asep [Center for Material Technology, BPPT, Jl. MH.Thamrin 8 Jakarta (Indonesia)

2014-03-24

Chiral Smectic Liquid Crystal (S)-(+)-4-(2-methyl-1-butyloyloxy)phenyl 4-[1-(propenoyloxy) butiloxy] benzoate has been synthesized using method of steglich esterification at room temperature. The mesomorphic behavior of chiral smectic at 55°C that showed schlieren texture in POM analysis. Fixation of structure chiral smectic liquid crystal by means of photopolymerization of monomer (S)-(+)-4-(2-methyl-1-butyloyloxy)phenyl 4-[1-(propenoyloxy) butiloxy] benzoate under UV irradiation which called UV curing techniques. The curing process using UV 3 lamps 100 volt at 60°C for an hour. The product of photopolymerization could be seen by analysis of FTIR spectra both monomer and polymer. FTIR spectra of monomer, two peaks for ester carbonyl and C-C double bond groups appeared at 1729.09 cm-1and 3123.46 cm{sup −1}. After UV curing process, peak for the carbonyl group at 1729.09 cm{sup −1} decreased and a new peak at 1160.21 cm{sup −1} appeared due to the carbonyl group attached to a C-C bond group and then peak at 3123.46 cm{sup −1} for C-C double bond group was disappeared.

The cone phase of liquid crystals: Triangular lattice of double-tilt ...

Indian Academy of Sciences (India)

(figure 3) and analyse the mechanism which stabilizes it. Liquid crystals are soft ... There is no change in the smectic layer spacing along .... with the case of blue phases of cubic symmetry where the pitch of the helix provides a natural length ...

The Gas-Phase Formation of Methyl Formate in Hot Molecular Cores

Science.gov (United States)

Horn, Anne; Møllendal, Harald; Sekiguchi, Osamu; Uggerud, Einar; Roberts, Helen; Herbst, Eric; Viggiano, A. A.; Fridgen, Travis D.

2004-08-01

Methyl formate, HCOOCH3, is a well-known interstellar molecule prominent in the spectra of hot molecular cores. The current view of its formation is that it occurs in the gas phase from precursor methanol, which is synthesized on the surfaces of grain mantles during a previous colder era and evaporates while temperatures increase during the process of high-mass star formation. The specific reaction sequence thought to form methyl formate, the ion-molecule reaction between protonated methanol and formaldehyde followed by dissociative recombination of the protonated ion [HCO(H)OCH3]+, has not been studied in detail in the laboratory. We present here the results of both a quantum chemical study of the ion-molecule reaction between [CH3OH2]+ and H2CO as well as new experimental work on the system. In addition, we report theoretical and experimental studies for a variety of other possible gas-phase reactions leading to ion precursors of methyl formate. The studied chemical processes leading to methyl formate are included in a chemical model of hot cores. Our results show that none of these gas-phase processes produces enough methyl formate to explain its observed abundance.

New theories for smectic and nematic liquid-crystal polymers: Backbone LCPs [liquid crystalline polymers] and their mixtures and side-chain LCPs

International Nuclear Information System (INIS)

Dowell, F.

1987-01-01

A summary of predictions and explanations from statistical-physics theories for both backbone and side-chain liquid crystalline polymers (LCPs) and for mixtures with backbone LCPs are presented. Trends in the thermodynamic and molecular ordering properties have been calculated as a function of pressure, density, temperature, and molecule chemical structures (including degree of polymerization and the following properties of the chemical structures of the repeat units: lengths and shapes, intra-chain rotation energies, dipole moments, site-site polarizabilities and Lennard-Jones potentials, etc.) in nematic and multiple smectic-A LC phases and in the isotropic liquid phase. The theoretical results are found to be in good agreement with existing experimental data. These theories can also be applied to combined LCPs. Since these theories have no ad hoc or arbitrarily adjustable parameters, these theories can be used to design new LCPs and new solvents as well as to predict and explain properties. 27 refs., 4 tabs

Phase formation in contact of dissimilar metals

Energy Technology Data Exchange (ETDEWEB)

Savvin, V S; Kazachkova, Yu A; Povzner, A A [Ural State Technical University-UPI, Mira st., 19, A-203, Yekaterinburg 620002 (Russian Federation)], E-mail: savvin-vs@yandex.ru

2008-02-15

Formation and growth of intermediate phases in contact of the crystalline samples forming a two-component eutectic system is considered. It is shown that during the competition to a growing liquid phase the intermediate solid phases cannot grow by diffusion. The alternative is formation of metastable areas of a liquid phase. Measurements of liquid layers extent in Pb-Bi and In-Bi systems have allowed to define the composition of liquid on interface where formation of metastable liquid is possible. The results show that the concentration interval of a liquid layer corresponds to a stable constitution diagram. In order to explain the experimental results the hypothesis according to which the intermediate solid phases are formed as a result of precipitation from metastable melt is considered. The experimental confirmation of formation and crystallization of a metastable liquid is the fact that intergrowth of the samples forming system with an intermetallic phase at temperatures below the temperature of fusion of the most low-melting eutectic is observed. The possibility of the processes concerned with the occurrence of metastable areas of a liquid is showed by means of computer imitation.

Phase formation of physically associating polymer blends

International Nuclear Information System (INIS)

Tanaka, Fumihiko

1993-01-01

Polymers exhibit a variety of condensed phases when some of their segments are capable of forming weak bonds which can be created and destroyed by thermal motion. Transition from one phase to another caused by such 'segment association' is reversible by the change of the temperature and the concentration, so that it is called 'reversible phase transition'. What types of reversible phase formation are possible for a given associative interaction? What is the most fundamental laws which govern the competition between molecular association and phase separation? This paper surveys, as typical examples of reversible phases, macroscopic phase separation, microphase formation, solvation, gelation, etc. from the unified point of view, and explores the possibility of new condensed phases caused by their mutual interference. (author)

A structural study of lamellar phases formed by nucleoside-functionalized lipids

CERN Document Server

Berti, D; Baglioni, P; Dante, S; Hauss, T

2002-01-01

We report a neutron-scattering investigation of lamellar phases formed by novel phospholipids bearing nucleosides at the polar-head-group region. These nucleolipids can interact through stacking and H-bond interactions, following a pattern that resembles base-base coupling in natural nucleic acids (DNA, RNA), i.e. they have similar recognition properties. Bilayer stacks formed of DPP-adenosine, DPP-uridine and their 1:1 mixture were investigated after equilibration in a 98% relative humidity atmosphere. The DPP-adenosine spectrum can be accounted for (in analogy to DPPC) by a lamellar phase with a smectic period of about 60 A. DPP-uridine displays a not so straightforward behavior that we have tentatively ascribed to the coexistence of lamellae with different smectic periods. In the 1:1 mixture the lamellar mesophase of DPP-uridine is retained, suggesting a specific interaction of the uridine polar-head group with the adenosine moiety of DPP-adenosine. It should be stressed that this behavior can be considere...

The three phases of galaxy formation

Science.gov (United States)

Clauwens, Bart; Schaye, Joop; Franx, Marijn; Bower, Richard G.

2018-05-01

We investigate the origin of the Hubble sequence by analysing the evolution of the kinematic morphologies of central galaxies in the EAGLE cosmological simulation. By separating each galaxy into disc and spheroidal stellar components and tracing their evolution along the merger tree, we find that the morphology of galaxies follows a common evolutionary trend. We distinguish three phases of galaxy formation. These phases are determined primarily by mass, rather than redshift. For M* ≲ 109.5M⊙ galaxies grow in a disorganised way, resulting in a morphology that is dominated by random stellar motions. This phase is dominated by in-situ star formation, partly triggered by mergers. In the mass range 109.5M⊙ ≲ M* ≲ 1010.5M⊙ galaxies evolve towards a disc-dominated morphology, driven by in-situ star formation. The central spheroid (i.e. the bulge) at z = 0 consists mostly of stars that formed in-situ, yet the formation of the bulge is to a large degree associated with mergers. Finally, at M* ≳ 1010.5M⊙ growth through in-situ star formation slows down considerably and galaxies transform towards a more spheroidal morphology. This transformation is driven more by the buildup of spheroids than by the destruction of discs. Spheroid formation in these galaxies happens mostly by accretion at large radii of stars formed ex-situ (i.e. the halo rather than the bulge).

Synthesis and Characterization of Ferroelectric Liquid Crystalline Organosiloxanes Containing 4-(4-undecanyloxy bi-phenyl-1-carboxyloxyphenyl (2S,3S-2-chloro-3-methylvalerate and 4-(4-undecanyloxybenzoyloxybiphenyl (2S,3S-2-chloro-3-methylvalerate

Directory of Open Access Journals (Sweden)

Chih-Hung Lin

2013-10-01

Full Text Available A series of new organosiloxane ferroelectric liquid crystalline (FLC materials have been synthesized, and their mesomorphic and physical properties have been characterized. Four new disiloxanes and trisiloxanes, containing biphenyl 4-hydroxybenzoate and phenyl 4-hydroxybiphenylcarboxylate as mesogenic units and eleven methylene unit as spacers and (2S,3S-2-chloro-3-methylvalerate unit as chiral end groups. The molecule, using three phenyl ring as a mesogenic unit, formulates much wider liquid crystalline phase temperature ranges than that of a two phenyl ring unit. The phenyl arrangement differences of mesogenic unit result in the greater differences of the liquid crystal phase formation. The siloxane molecule induction is helpful to the more regular smectic phase formation and smectic phase stabilization, such as chiral SC (SC* and SB phases. The siloxane molecule is helpful to reduce the phase transition temperature and broaden the liquid crystal temperature range of the SC* phase and, simultaneously, it will not induce chain crystallization phenomenon and dilute the Ps value. The synthesis and characterization of the new FLCs materials, which exhibit a room temperature SC* phase and higher spontaneous polarization are presented.

Twist deformation in anticlinic antiferroelectric structure in smectic B.sub.2./sub. imposed by the surface anchoring

Czech Academy of Sciences Publication Activity Database

Lejček, Lubor; Novotná, Vladimíra; Glogarová, Milada

2008-01-01

Roč. 35, č. 1 (2008), s. 11-19 ISSN 0267-8292 R&D Projects: GA ČR GA202/05/0431 Institutional research plan: CEZ:AV0Z10100520 Keywords : smectic liquid crystals * bent-shaped molecules * anticlinic antiferroelectric structure * ferroelectric structure * twist deformation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.132, year: 2008

Formation of ω-phase in Zr-4 at.% Cr alloy

International Nuclear Information System (INIS)

Dobromyslov, A.V.; Kazantseva, N.V.

1996-01-01

The ω-phase has been discovered in zirconium-base alloys with the transition metals of Period 4 of the Periodic Table only in Zr-V, Zr-Cr, and Zr-Cu alloys. The first mention about the ω-phase formation in Zr-Cr alloys was given for Zr-4.5 at.%. However, there were no experimental data that confirmed this fact. W.M. Rumball and F.G. Elder presented the X-ray results on the ω-phase formation in Zr-3.9 at.%Cr, but at the present time there are no electron microscope studies of the structure of the ω-phase in this system. Investigations of the features of the ω-phase formation, morphology of the ω-phase and the mechanism of its formation in the different zirconium-base alloys are necessary to establish the common features of the formation of structures with the metastable phases. The task of the present work is to study the conditions and features of the ω-phase formation in the Zr-Cr alloys and the effect of the eutectoid decomposition on the formation of ω-phase. This article is part of the detailed investigations of the feature and condition of the ω-phase formation in zirconium-base alloys with the transition metals of the groups I and V to VIII of the Periodic Table

NMR studies of liquid crystals and molecules dissolved in liquid crystal solvents

Energy Technology Data Exchange (ETDEWEB)

Drobny, Gary Peter [Univ. of California, Berkeley, CA (United States)

1982-11-01

This thesis describes several studies in which nuclear magnetic resonance (nmr) spectroscopy has been used to probe the structure, orientation and dynamics of liquid crystal mesogens and molecules dissolved in liquid crystalline phases. In addition, a modern high field nmr spectrometer is described which has been used to perform such nmr studies. Chapter 1 introduces the quantum mechanical formalisms used throughout this thesis and briefly reviews the fundamentals of nuclear spin physics and pulsed nmr spectroscopy. First the density operator is described and a specific form for the canonical ensemble is derived. Then Clebsch-Gordon coefficients, Wigner rotation matrices, and irreducible tensor operators are reviewed. An expression for the equilibrium (Curie) magnetization is obtained and the linear response of a spin system to a strong pulsed r.f. irradiation is described. Finally, the spin interaction Hamiltonians relevant to this work are reviewed together with their truncated forms. Chapter 2 is a deuterium magnetic resonance study of two 'nom' liquid crystals which possess several low temperature mesomorphic phases. Specifically, deuterium quadrupolar echo spectroscopy is used to determine the orientation of the liquid crystal molecules in smectic phases, the changes in molecular orientation and motion that occur at smectic-smectic phase transitions, and the order of the phase transitions. For both compounds, the phase sequence is determined to be isotropic, nematic, smectic A, smectic C, smectic B_A, smectic B_C, and crystalline. The structure of the smectic A phase is found to be consistent with the well-known model of a two dimensional liquid in which molecules are rapidly rotating about their long axes and oriented at right angles to the plane of the layers. Molecules in the smectic C phase are found to have their long axes tilted with respect to the layer normal, and the tilt angle is temperature dependent, increasing from

Unconventional phase transitions in liquid crystals

Science.gov (United States)

Kats, E. I.

2017-12-01

According to classical textbooks on thermodynamics or statistical physics, there are only two types of phase transitions: continuous, or second-order, in which the latent heat L is zero, and first-order, in which L ≠ 0. Present-day textbooks and monographs also mention another, stand-alone type—the Berezinskii-Kosterlitz-Thouless transition, which exists only in two dimensions and shares some features with first- and second-order phase transitions. We discuss examples of non-conventional thermodynamic behavior (i.e., which is inconsistent with the theoretical phase transition paradigm now universally accepted). For phase transitions in smectic liquid crystals, mechanisms for nonconventional behavior are proposed and the predictions they imply are examined.

Optic and electro-optic investigations on SmQ, SmCA* and L phases in highly chiral compounds

International Nuclear Information System (INIS)

Manai, M.; Gharbi, A.; Marcerou, J.P.; Nguyen, H.T.; Rouillon, J.C.

2005-01-01

Chiral molecules give rise to a large variety of mesophases. Well-known examples are cholesteric or ferroelectric smectic phases where the chirality tends to favor a macroscopic twist. Furthermore, the molecular core length (l) plays an important role on the range of the mesophases and on the temperature (T NI ) for the onset of orientational order. The tendency for T NI is to increase (going over 200 - bar C for some compounds) with increasing l. We report in this paper on a selection of compounds which have been designed in order to favor an anticlinic smectic ordering together with high chirality. As a common feature, they have a long rigid core with four benzene rings and a chiral chain (usually the same) at each end. They display a locally anisotropic liquid phase referred to as ''L phase'' in a large temperature range between T NI and the low temperature SmQ or SmC A * phase. Optical rotatory power (ORP), birefringence and electro-optic studies have been performed with these compounds

DSC and X-ray diffraction investigations of phase transitions in HxBABA and NBABA

International Nuclear Information System (INIS)

Usha Deniz, K.; Paranjpe, A.S.; Mirza, E.B.; Parvathanathan, P.S.; Patel, K.S.

1979-01-01

The phase transitions and the heats of transformation, of the hexyl (HxBABA) and nonyl (NBABA) members of the series of compounds, p-n-Alkoxybenzylidene-p-Aminobenzoic Acids, have been studied by DSC in the temperature range, - 100 0 C to 300 0 C. A scheme of transitions has been proposed for each of the compounds. X-ray diffraction measurements have been done in the smectic C(Ssub(c)) and nematic (N) phases of these materials. The results reveal that (1) the Ssub(c) phase in both compounds is of the C 1 -type, (2) Ssub(c)-type order is seen throughout the nematic phase in HxBABA, whereas in NBABA, it is seen only in the neighbourhood of the Ssub(c)-N transition, (3) the temperature dependence of the smectic layer thickness, d, and of the directly measured tilt angle, theta sub(t,d), reflect faithfully the strength of the first order transition, Ssub(c)-N, and (4) there is a marked difference between the values and the temperature variations of theta sub(t,d) and theta sub(t,c) (tilt angle calculated from d) which is not completely understood, at present

Effects of monoclinic symmetry on the properties of biaxial liquid crystals

Science.gov (United States)

Solodkov, Nikita V.; Nagaraj, Mamatha; Jones, J. Cliff

2018-04-01

Tilted smectic liquid crystal phases such as the smectic-C phase seen in calamitic liquid crystals are usually treated using the assumption of biaxial orthorhombic symmetry. However, the smectic-C phase has monoclinic symmetry, thereby allowing disassociation of the principal optic and dielectric axes based on symmetry and invariance principles. This is demonstrated here by comparing optical and dielectric measurements for two materials with highly first-order direct transitions from nematic to smectic-C phases. The results show a high difference between the orientations of the principal axes sets, which is interpreted as the existence of two distinct cone angles for optical and dielectric frequencies. Both materials exhibit an increasing degree of monoclinic behavior with decreasing temperature. Due to fast switching speeds, ferroelectric smectic-C* materials are important for fast modulators and LCoS devices, where the dielectric biaxiality influences device operation.

Small Angle Neutron Scattering (sans) Studies on "SIDE-END FIXED" and "SIDE-ON FIXED" Liquid Crystal Polymers

Science.gov (United States)

Hardouin, F.; Noirez, L.; Keller, P.; Leroux, N.; Cotton, J. P.

The following sections are included: * Introduction * Experimental * Results and discussion * Determination of the backbone conformation in the nematic and smectic A phases of "side-end fixed" L.C. polymethacrylates (PMA) or polyacrylates (PA) * Determination of the global and backbone conformation in the nematic and smectic A phases of "side-end fixed" L.C. polysiloxanes (PMS) * Determination of the backbone conformation in the unique nematic phase (without smectic A phase) or in the reentrant nematic phase (below smectic A phase) of "side-end fixed" L.C. polyacrylates (PA) * Determination of the global conformation in the nematic phase of "side-on fixed" L.C. polysiloxanes (PMS) * Determination of the global conformation in the nematic phase of "diluted side-on fixed" L.C. copolysiloxanes * Determination of the backbone conformation in the nematic phase of "side-on fixed" L.C. polyacrylates * Conclusions * References

A structural study of lamellar phases formed by nucleoside-functionalized lipids

Energy Technology Data Exchange (ETDEWEB)

Berti, D.; Fratini, E.; Baglioni, P. [Department of Chemistry and CSGI, University of Florence, Via G. Capponi 9, 50121 Florence (Italy); Dante, S.; Hauss, T. [Berlin Neutron Scattering Center, Hahn Meitner Institut, Glienicker Strasse 100, Wannsee, 14109 Berlin (Germany)

2002-07-01

We report a neutron-scattering investigation of lamellar phases formed by novel phospholipids bearing nucleosides at the polar-head-group region. These nucleolipids can interact through stacking and H-bond interactions, following a pattern that resembles base-base coupling in natural nucleic acids (DNA, RNA), i.e. they have similar recognition properties. Bilayer stacks formed of DPP-adenosine, DPP-uridine and their 1:1 mixture were investigated after equilibration in a 98% relative humidity atmosphere. The DPP-adenosine spectrum can be accounted for (in analogy to DPPC) by a lamellar phase with a smectic period of about 60 A. DPP-uridine displays a not so straightforward behavior that we have tentatively ascribed to the coexistence of lamellae with different smectic periods. In the 1:1 mixture the lamellar mesophase of DPP-uridine is retained, suggesting a specific interaction of the uridine polar-head group with the adenosine moiety of DPP-adenosine. It should be stressed that this behavior can be considered as an indication of the recognition process occurring at the polar-head-group region of the mixed phospholiponucleoside membrane. (orig.)

Modeling of metastable phase formation diagrams for sputtered thin films.

Science.gov (United States)

Chang, Keke; Music, Denis; To Baben, Moritz; Lange, Dennis; Bolvardi, Hamid; Schneider, Jochen M

2016-01-01

A method to model the metastable phase formation in the Cu-W system based on the critical surface diffusion distance has been developed. The driver for the formation of a second phase is the critical diffusion distance which is dependent on the solubility of W in Cu and on the solubility of Cu in W. Based on comparative theoretical and experimental data, we can describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation. Metastable phase formation diagrams for Cu-W and Cu-V thin films are predicted and validated by combinatorial magnetron sputtering experiments. The correlative experimental and theoretical research strategy adopted here enables us to efficiently describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation during magnetron sputtering.

Surface induced smectic order in ionic liquids - an X-ray reflectivity study of [C22C1im]+[NTf2].

Science.gov (United States)

Mars, Julian; Hou, Binyang; Weiss, Henning; Li, Hailong; Konovalov, Oleg; Festersen, Sven; Murphy, Bridget M; Rütt, Uta; Bier, Markus; Mezger, Markus

2017-10-11

Surface induced smectic order was found for the ionic liquid 1-methyl-3-docosylimidazolium bis(trifluoromethlysulfonyl)imide by X-ray reflectivity and grazing incidence scattering experiments. Near the free liquid surface, an ordered structure of alternating layers composed of polar and non-polar moieties is observed. This leads to an oscillatory interfacial profile perpendicular to the liquid surface with a periodicity of 3.7 nm. Small angle X-ray scattering and polarized light microscopy measurements suggest that the observed surface structure is related to fluctuations into a metastable liquid crystalline SmA 2 phase that was found by supercooling the bulk liquid. The observed surface ordering persists up to 157 °C, i.e. more than 88 K above the bulk melting temperature of 68.1 °C. Close to the bulk melting point, we find a thickness of the ordered layer of L = 30 nm. The dependency of L(τ) = Λ ln(τ/τ 1 ) vs. reduced temperature τ follows a logarithmic growth law. In agreement with theory, the pre-factor Λ is governed by the correlation length of the isotropic bulk phase.

Electroclinic effect in the chiral lamellar α phase of a lyotropic liquid crystal

Science.gov (United States)

Harjung, Marc D.; Giesselmann, Frank

2018-03-01

In thermotropic chiral Sm -A* phases, an electric field along the smectic layers breaks the D∞ symmetry of the Sm -A* phase and induces a tilt of the liquid crystal director. This so-called electroclinic effect (ECE) was first reported by Garoff and Meyer in 1977 and attracted substantial scientific and technological interest due to its linear and submicrosecond electro-optic response [S. Garoff and R. B. Meyer, Phys. Rev. A 19, 338 (1979), 10.1103/PhysRevA.19.338]. We now report the observation of an ECE in the pretransitional regime from a lyotropic chiral lamellar Lα* phase into a lyo-Sm -C* phase, the lyotropic analog to the thermotropic Sm -C* phase which was recently discovered by Bruckner et al. [Angew. Chem. Int. Ed. 52, 8934 (2013), 10.1002/anie.201303344]. We further show that the observed ECE has all signatures of its thermotropic counterpart, namely (i) the effect is chiral in nature and vanishes in the racemic Lα phase, (ii) the effect is essentially linear in the sign and magnitude of the electric field, and (iii) the magnitude of the effect diverges hyperbolically as the temperature approaches the critical temperature of the second order tilting transition. Specific deviations between the ECEs in chiral lamellar and chiral smectic phases are related to the internal field screening effect of electric double layers formed by inevitable ionic impurities in lyotropic phases.

Chromonic liquid crystalline nematic phase exhibited in binary mixture of two liquid crystals

Energy Technology Data Exchange (ETDEWEB)

Govindaiah, T. N., E-mail: tngovi.phy@gmail.com; Sreepad, H. R. [Post-Graduate Department of Physics, Government College (Autonomous), Mandya-571401 (India); Sridhar, K. N.; Sridhara, G. R.; Nagaraja, N. [Government College for Boys, Kolar-563101 (India)

2015-06-24

A binary mixture of abietic acid and orthophosphoric acid (H{sub 3}PO{sub 4}) exhibits co-existence of biphasic region of Nematic+Isotropic (N+I), lyotropic Nematic (ND) and Smectic-G (SmG) phases. The mixture exhibits N+I, N and SmG phases at different concentrations and at different temperatures. Mixtures with all concentrations of abietic acid exhibit I→N+I→N→SmG phases sequentially when the specimen is cooled from its isotropic melt. These phases have been characterized by using differential scanning calorimetric, X-ray diffraction, and optical texture studies.

Tuning the phase diagrams: the miscibility studies of multilactate liquid crystalline compounds

Czech Academy of Sciences Publication Activity Database

Bubnov, Alexej; Tykarska, M.; Hamplová, Věra; Kurp, K.

2016-01-01

Roč. 89, č. 9 (2016), s. 885-893 ISSN 0141-1594 R&D Projects: GA ČR GA13-14133S; GA MŠk(CZ) LD14007; GA ČR GA15-02843S Grant - others:EU - ICT(XE) COST Action IC1208 Institutional support: RVO:68378271 Keywords : miscibility study * binary mixture * polar smectic phase * lactic acid derivative * miscibility study * phase diagram * self-assembling behaviour Subject RIV: JJ - Other Materials Impact factor: 1.060, year: 2016

Frustrated smectic liquid crystalline phases in lactic acid derivatives

Czech Academy of Sciences Publication Activity Database

Glogarová, Milada; Novotná, Vladimíra

2016-01-01

Roč. 89, č. 7-8 (2016), s. 829-839 ISSN 0141-1594 R&D Projects: GA ČR GA15-02843S Institutional support: RVO:68378271 Keywords : field * liquid crystals * TGB phases Subject RIV: JJ - Other Materials Impact factor: 1.060, year: 2016

Can a droplet break up under flow without elongating? Fragmentation of smectic monodisperse droplets

Science.gov (United States)

Courbin, L.; Engl, W.; Panizza, P.

2004-06-01

We study the fragmentation under shear flow of smectic monodisperse droplets at high volume fraction. Using small angle light scattering and optical microscopy, we reveal the existence of a break-up mechanism for which the droplets burst into daughter droplets of the same size. Surprisingly, this fragmentation process, which is strain controlled and occurs homogeneously in the cell, does not require any transient elongation of the droplets. Systematic experiments as a function of the initial droplet size and the applied shear rate show that the rupture is triggered by an instability of the inner droplet structure.

Effect of alteration phase formation on the glass dissolution rate

International Nuclear Information System (INIS)

Ebert, W.L.

1997-01-01

The dissolution rates of many glasses have been observed to increase upon the formation of certain alteration phases. While simulations have predicted the accelerating effect of formation of certain phases, the phases predicted to form in computer simulations are usually different than those observed to form in experiments. This is because kinetically favored phases form first in experiments, while simulations predict the thermodynamically favored phases. Static dissolution tests with crushed glass have been used to measure the glass dissolution rate after alteration phases form. Because glass dissolution rates are calculated on a per area basis, an important effect in tests conducted with crushed glass is the decrease in the surface area of glass that is available for reaction as the glass dissolves. This loss of surface area must be taken into account when calculating the dissolution rate. The phases that form and their effect on the dissolution rate are probably related to the glass composition. The impact of phase formation on the glass dissolution rate also varies according to the solubility products of the alteration phases and how the orthocilicic acid activity is affected. Insight into the relationship between the glass dissolution rate, solution chemistry and alteration phase formation is provided by the results of accelerated dissolution tests

Effect of alteration phase formation on the glass dissolution rate

Energy Technology Data Exchange (ETDEWEB)

Ebert, W L [Argonne National Laboratory, Chemical Technology Div. (United States)

1997-07-01

The dissolution rates of many glasses have been observed to increase upon the formation of certain alteration phases. While simulations have predicted the accelerating effect of formation of certain phases, the phases predicted to form in computer simulations are usually different than those observed to form in experiments. This is because kinetically favored phases form first in experiments, while simulations predict the thermodynamically favored phases. Static dissolution tests with crushed glass have been used to measure the glass dissolution rate after alteration phases form. Because glass dissolution rates are calculated on a per area basis, an important effect in tests conducted with crushed glass is the decrease in the surface area of glass that is available for reaction as the glass dissolves. This loss of surface area must be taken into account when calculating the dissolution rate. The phases that form and their effect on the dissolution rate are probably related to the glass composition. The impact of phase formation on the glass dissolution rate also varies according to the solubility products of the alteration phases and how the orthocilicic acid activity is affected. Insight into the relationship between the glass dissolution rate, solution chemistry and alteration phase formation is provided by the results of accelerated dissolution tests.

Kinetics of sigma phase formation in a Duplex Stainless Steel

Directory of Open Access Journals (Sweden)

Rodrigo Magnabosco

2009-09-01

Full Text Available This work determines the kinetics of sigma phase formation in UNS S31803 Duplex Stainless Steel (DSS, describing the phase transformations that occur in isothermal aging between 700 and 900 ºC for time periods up to 1032 hours, allowing the determination of the Time-Temperature-Precipitation (TTP diagram for sigma phase and proposing a model to predict the kinetics of sigma phase formation using a Johnson-Mehl-Avrami (JMA type expression. The higher kinetics of sigma phase formation occurs at 850 ºC. However, isothermal aging between 700 and 900 ºC for time periods up to 1032 hours are not sufficient to the establishment of thermodynamic equilibrium. Activation energy for both nucleation and growth of sigma phase is determined (185 kJ.mol-1 and its value is equivalent to the activation energy for Cr diffusion in ferrite, indicating that diffusion of Cr is probably the major thermally activated process involved in sigma phase formation. The determined JMA type expression presents good fit with experimental data between 700 and 850 ºC.

Gel phase formation in dilute triblock copolyelectrolyte complexes

Science.gov (United States)

Srivastava, Samanvaya; Andreev, Marat; Levi, Adam E.; Goldfeld, David J.; Mao, Jun; Heller, William T.; Prabhu, Vivek M.; de Pablo, Juan J.; Tirrell, Matthew V.

2017-02-01

Assembly of oppositely charged triblock copolyelectrolytes into phase-separated gels at low polymer concentrations (simulations. Here we show that in contrast to uncharged, amphiphilic block copolymers that form discrete micelles at low concentrations and enter a phase of strongly interacting micelles in a gradual manner with increasing concentration, the formation of a dilute phase of individual micelles is prevented in polyelectrolyte complexation-driven assembly of triblock copolyelectrolytes. Gel phases form and phase separate almost instantaneously on solvation of the copolymers. Furthermore, molecular models of self-assembly demonstrate the presence of oligo-chain aggregates in early stages of copolyelectrolyte assembly, at experimentally unobservable polymer concentrations. Our discoveries contribute to the fundamental understanding of the structure and pathways of complexation-driven assemblies, and raise intriguing prospects for gel formation at extraordinarily low concentrations, with applications in tissue engineering, agriculture, water purification and theranostics.

Highly tilted liquid crystalline materials possessing a direct phase transition from antiferroelectric to isotropic phase

Energy Technology Data Exchange (ETDEWEB)

Milewska, K.; Drzewiński, W. [Institute of Chemistry, Military University of Technology, 00-908 Warsaw (Poland); Czerwiński, M., E-mail: mczerwinski@wat.edu.pl [Institute of Chemistry, Military University of Technology, 00-908 Warsaw (Poland); Dąbrowski, R. [Institute of Chemistry, Military University of Technology, 00-908 Warsaw (Poland); Piecek, W. [Institute of Applied Physics, Military University of Technology, 00-908 Warsaw (Poland)

2016-03-01

Pure compounds and multicomponent mixtures with a broad temperature range of high tilted liquid crystalline antiferroelectric phase and a direct phase transition from antiferroelectric to isotropic phase, were obtained. X-ray diffraction analysis confirms these kinds of materials form a high tilted anticlinic phase, with a fixed layer spacing and very weak dependency upon temperature, after the transition from the isotropic phase. Due to this, not only pure orthoconic antiferroelectric liquid crystals but also those with a moderate tilt should generate a good dark state. Furthermore, due to the increased potential for forming anticlinic forces, such materials could minimize a commonly observed asymmetry of a rise and fall switching times at a surface stabilized geometry. - Highlights: • The new class of liquid crystalline materials with the direct SmC{sub A}*. • Iso phase transition were obtained. • Materials possess the layer spacing fixed and very weak dependent upon temperature. • Smectic layers without shrinkage are observed. • A good dark state can be generate in SSAFLC.

Structures and Correlations in Ideally Aligned Polar Gay-Berne Systems

International Nuclear Information System (INIS)

Longa, L.; Cholewiak, G.; Stelzer, J.

2000-01-01

We study an ideally oriented system of Gay-Berne particles with embedded longitudinal dipole moments. While keeping the translational degrees of freedom of the molecules unrestricted we assume that their dipoles can be oriented either parallel or antiparallel to the positive z axis of the laboratory frame. At high temperatures, this frustrated Gay-Berne mesogen exhibits an ideally oriented nematic phase, which is the reference state of the system. In the limit of vanishing dipole moment nematic, smectic-A and smectic B phases are stable. Interestingly, by changing the magnitude and location of the molecular dipole in the nematic reference state we found dipole-induced smectic A, smectic B and tetragonal crystal phases, in addition to crystalline structures with smectic A d and A 2 -like dipolar organization. Various singlet, pair and triplet distribution functions were evaluated to elucidate short and long range organization in these phases. In particular, the importance of triplet correlations for a proper understanding of the structures and their local, dipolar organization is demonstrated. (author)

Dielectric spectroscopy of the SmQ* phase

Science.gov (United States)

Perkowski, P.; Bubnov, A.; Piecek, W.; Ogrodnik, K.; Hamplová, V.; Kašpar, M.

2011-11-01

Liquid crystal possessing two biphenyl moieties in the molecular core and lateral chlorine substitution far from the chiral chain has been studied by dielectric spectroscopy. On cooling from the isotropic phase, the material possesses the frustrated smectic Q* (SmQ*) and SmCA* phases. It has been confirmed by dielectric spectroscopy that the SmQ* phase can be related to the SmCA* anti-ferroelectric phase. However, only one relaxation process has been observed in the SmQ* phase, while in the SmCA*, two relaxations are clearly detectable. It seems that the mode found in the SmQ* can be connected with high-frequency anti-phase mode observed in the SmCA* phase. Its relaxation frequency is similar to PH relaxation frequency, but is weaker. The same relaxation has been observed even a few degrees above the SmQ*-Iso phase transition. Another explanation for the mode detected in SmQ* and isotropic phases can be molecular motions around short molecular axis.

Structure in a confined smectic liquid crystal with competing surface and sample elasticities

International Nuclear Information System (INIS)

Idziak, S.H.; Koltover, I.; Israelachvili, J.N.; Safinya, C.R.

1996-01-01

We report on studies using the x-ray surface forces apparatus (XSFA) to compare the structure of a liquid crystal confined between hard surfaces and, for the first time, between soft surfaces that can deform due to the stresses imposed by the confined fluid. We find that the alignment of smectic domains in confined films depends critically on both the shape and compliance of the confining walls or surfaces: open-quote open-quote Soft surfaces close-quote close-quote exhibit a critical gap thickness of 3.4 μm for the liquid crystal studied at which maximum alignment occurs, while open-quote open-quote hard surfaces close-quote close-quote do not exhibit gap-dependent alignment. copyright 1996 The American Physical Society

Effect of metallic silver nanoparticles on the alignment and relaxation behaviour of liquid crystalline material in smectic C* phase

Science.gov (United States)

Vimal, Tripti; Kumar Gupta, Swadesh; Katiyar, Rohit; Srivastava, Atul; Czerwinski, Michal; Krup, Katarzyna; Kumar, Sandeep; Manohar, Rajiv

2017-09-01

The influence of silver nanoparticles dispersed in a Ferroelectric Liquid Crystal (FLC) on the properties of the resultant composite system has been investigated by thermal, electro-optical, and dielectric methods. We show that the concentration of thiol capped silver nanoparticles is a critical factor in governing the alignment of nanoparticles (NPs) in the host FLC. The orientation of NPs in composite samples affects the ordering of the LC (Liquid Crystal) phase and consequently changes the various phase transition temperatures of the host LC. Formation of self-assembled 2D (two dimensional) arrays of nanoparticles is observed for high concentration of dopant in the LC, oriented perpendicular to the direction of rubbing. We propose that the molecular interaction between the thiol capped NPs and LC molecules is the key factor behind such an arrangement of NPs. Orientation of NPs has affected the relaxation behaviour and various other material parameters, significantly. A noteworthy change in DC conductivity articulates our proposed idea of the formation of 2D array of NPs perpendicular to the direction of rubbing. This comprehensive study endorses the importance of dopant concentration in modifying the properties of the host LC material.

Conversion of Phase II Unsteady Aerodynamics Experiment Data to Common Format; TOPICAL

International Nuclear Information System (INIS)

Hand, M. M.

1999-01-01

A vast amount of aerodynamic, structural, and turbine performance data were collected during three phases of the National Renewable Energy Laboratory's Unsteady Aerodynamics Experiment (UAE). To compare data from the three phases, a similar format of engineering unit data is required. The process of converting Phase II data from a previous engineering unit format to raw integer counts is discussed. The integer count files can then be input to the new post-processing software, MUNCH. The resulting Phase II engineering unit files are in a common format with current and future UAE engineering unit files. An additional objective for changing the file format was to convert the Phase II data from English units to SI units of measurement

Soft Elasticity in Main Chain Liquid Crystal Elastomers

Directory of Open Access Journals (Sweden)

Anselm C. Griffin

2013-06-01

Full Text Available Main chain liquid crystal elastomers exhibit several interesting phenomena, such as three different regimes of elastic response, unconventional stress-strain relationship in one of these regimes, and the shape memory effect. Investigations are beginning to reveal relationships between their macroscopic behavior and the nature of domain structure, microscopic smectic phase structure, relaxation mechanism, and sample history. These aspects of liquid crystal elastomers are briefly reviewed followed by a summary of the results of recent elastic and high-resolution X-ray diffraction studies of the shape memory effect and the dynamics of the formation of the smectic-C chevron-like layer structure. A possible route to realizing auxetic effect at molecular level is also discussed.

Mechanical model for filament buckling and growth by phase ordering.

Science.gov (United States)

Rey, Alejandro D; Abukhdeir, Nasser M

2008-02-05

A mechanical model of open filament shape and growth driven by phase ordering is formulated. For a given phase-ordering driving force, the model output is the filament shape evolution and the filament end-point kinematics. The linearized model for the slope of the filament is the Cahn-Hilliard model of spinodal decomposition, where the buckling corresponds to concentration fluctuations. Two modes are predicted: (i) sequential growth and buckling and (ii) simultaneous buckling and growth. The relation among the maximum buckling rate, filament tension, and matrix viscosity is given. These results contribute to ongoing work in smectic A filament buckling.

Experimental formation enthalpies for intermetallic phases and other inorganic compounds

Science.gov (United States)

Kim, George; Meschel, S. V.; Nash, Philip; Chen, Wei

2017-01-01

The standard enthalpy of formation of a compound is the energy associated with the reaction to form the compound from its component elements. The standard enthalpy of formation is a fundamental thermodynamic property that determines its phase stability, which can be coupled with other thermodynamic data to calculate phase diagrams. Calorimetry provides the only direct method by which the standard enthalpy of formation is experimentally measured. However, the measurement is often a time and energy intensive process. We present a dataset of enthalpies of formation measured by high-temperature calorimetry. The phases measured in this dataset include intermetallic compounds with transition metal and rare-earth elements, metal borides, metal carbides, and metallic silicides. These measurements were collected from over 50 years of calorimetric experiments. The dataset contains 1,276 entries on experimental enthalpy of formation values and structural information. Most of the entries are for binary compounds but ternary and quaternary compounds are being added as they become available. The dataset also contains predictions of enthalpy of formation from first-principles calculations for comparison. PMID:29064466

Local layer structure of smectic liquid crystals by X-ray micro-diffraction

CERN Document Server

Takanishi, Y

2003-01-01

The local layer structure of smectic liquid crystal has been measured using time-resolved synchrotron X-ray micro-diffraction. Typical layer disorders observed in surface stabilized (anti-) ferroelectric liquid crystals, i.e. a stripe texture, a needed-like defect and a zigzag defect, are directly analyzed. The detailed analysis slows that the surface anchoring force due to the interaction between the liquid crystal molecule and the alignment thin film plays an important role to realize both the static and dynamic local layer structures. The layer structure of the circular domain observed in the liquid crystal of bent-shaped molecules found to depend on the applied electric field though the optical micrograph shows little difference. The frustrated, double and single layer structures of the bent-shaped molecule liquid crystal are determined depending on the terminal alkyl chain length. (author)

Simulation of bulk phases formed by polyphilic liquid crystal dendrimers

Directory of Open Access Journals (Sweden)

J.M. Ilnytskyi

2010-01-01

Full Text Available A coarse-grained simulation model for a third generation liquid crystalline dendrimer (LCDr is presented. It allows, for the first time, for a successful molecular simulation study of a relation between the shape of a polyphilic macromolecular mesogen and the symmetry of a macroscopic phase. The model dendrimer consists of a soft central sphere and 32 grafted chains each terminated by a mesogen group. The mesogenic pair interactions are modelled by the recently proposed soft core spherocylinder model of Lintuvuori and Wilson [J. Chem. Phys, 128, 044906, (2008]. Coarse-grained (CG molecular dynamics (MD simulations are performed on a melt of 100 molecules in the anisotropic-isobaric ensemble. The model LCDr shows conformational bistability, with both rod-like and disc-like conformations stable at lower temperatures. Each conformation can be induced by an external aligning field of appropriate symmetry that acts on the mesogens (uniaxial for rod-like and planar for disc-like, leading to formation of a monodomain smectic A (SmA or a columnar (Col phase, respectively. Both phases are stable for approximately the same temperature range and both exhibit a sharp transition to an isotropic cubic-like phase upon heating. We observe a very strong coupling between the conformation of the LCDr and the symmetry of a bulk phase, as suggested previously by theory. The study reveals rich potential in terms of the application of this form of CG modelling to the study of molecular self-assembly of liquid crystalline macromolecules.

Formation of Ion Phase-Space Vortexes

DEFF Research Database (Denmark)

Pécseli, Hans; Trulsen, J.; Armstrong, R. J.

1984-01-01

The formation of ion phase space vortexes in the ion two stream region behind electrostatic ion acoustic shocks are observed in a laboratory experiment. A detailed analysis demonstrates that the evolution of such vortexes is associated with ion-ion beam instabilities and a nonlinear equation for ...

Electro–optic response in thin smectic C* film with chevron structures

International Nuclear Information System (INIS)

Kudreyko, Aleksey A; Migranov, Nail G; Migranova, Dana N

2016-01-01

The effects in electrostatic models of chevron surface-stabilized ferroelectric liquid crystals are investigated through numerical modeling. To study smectic C* director distribution within the cell, we consider two nonlinear approaches: the chevron interface does not interplay with the electric field; the electric field interplays with the chevron interface. The obtained results of the director field distribution are compared with the earlier linearized studies. We find that whether or not the electric field interplays with the chevron interface, the electro–optic response requires a generalized approach for its description. The threshold electric field, which is necessary for switching between two stable director states in the chevron cell is evaluated. This study suggests that, in many cases of practical interest, electro–optic response to the electric field and the threshold electric field can be precisely estimated. We argue that, beside being numerically efficient, our approach provides a convenient and a novel standpoint for looking at the electro–optic response problem. (paper)

The Power of Poincar\\'e: Elucidating the Hidden Symmetries in Focal Conic Domains

OpenAIRE

Alexander, Gareth P.; Chen, Bryan Gin-ge; Matsumoto, Elisabetta A.; Kamien, Randall D.

2010-01-01

Focal conic domains are typically the "smoking gun" by which smectic liquid crystalline phases are identified. The geometry of the equally-spaced smectic layers is highly generic but, at the same time, difficult to work with. In this Letter we develop an approach to the study of focal sets in smectics which exploits a hidden Poincar\\'e symmetry revealed only by viewing the smectic layers as projections from one-higher dimension. We use this perspective to shed light upon several classic focal...

Experimental Observation of Anomalous Ordering in a Landau-Peierls System

DEFF Research Database (Denmark)

Als-Nielsen, Jens Aage; Birgenau, R. J.; Kaplan, M.

1977-01-01

The smectic-A phase of a liquid crystal is characterized by a one-dimensional mass density wave in a three-dimensional liquid. High-resolution x ray measurements in the smectic-A phase of octyloxycyanobenzylidene (8OCB) show that the order-parameter scattering does not exhibit normal Bragg line...

Fluorinated tolane and dioxane liquid crystals for ferroelectric display applications

International Nuclear Information System (INIS)

Chu Chuan Dong

1994-05-01

The aim of this thesis was to make low viscosity, low birefringence, large negative dielectric anisotropy liquid-crystalline materials for use in ferroelectric liquid crystal mixtures to be used in high speed display devices. Saturated heterocyclic rings, dioxane and dioxaborinane, were chosen separately to be linked with a difluorophenyl system as the main component of the mesogenic core. In order to optimise the physical properties and to reduce the cost of the chiral materials, the strategy of making dopant-host mixtures was used. In addition to the difluorobiphenyl dioxaborinanes, three types of compounds were prepared possessing difluorophenyl rings and a dioxane ring: (i) difluorophenyl dioxanes and difluorobiphenyl dioxanes with the fluorinated ring in the middle of or at the end of the core; (ii) a number of compounds with linking groups, dimethylene (CH 2 CH 2 ), ester (COO), ethenylene (CH=CH) and ethynylene (C≡C) between adjacent benzene rings or between a dioxane ring and a benzene ring; (iii) difluorobiphenyl dioxanes possessing a chiral aliphatic chain were chosen as chiral dopants whose structure matched those of the host materials. Other compounds which have been synthesised are the difluorotolanes and difluorophenyl-ethynyl compounds, which were targeted because of the low viscosity of the tolane compounds and the negative dielectric anisotropy of the difluorophenyl ring. Fifty-six 2-(2,3-difluorobiphenyl-4'-yl)-1,3-dioxanes (n = 5-9, m = 5-10 or O5-O9; or n = 9, R' = OCH 2 CH(CH 3 )C 4 H 9 ) were prepared. Smectic C and nematic phases were observed for most of the alkyl-alkoxy homologues. Conversely, most of the dialkyl compounds exhibited smectic C, smectic A and nematic phases. The birefringences (Δn) and the dielectric anisotropies (Δε) of a number of materials have been determined. Three 2-(2,3-difluorobiphenyl-4-yl)-5-alkyl-1,3-dioxanes (n = 7, m = O7-O9) were prepared and only exhibit nematic phases. Two difluorophenyl dioxanes were

Formation of nano quasicrystalline and crystalline phases by mechanical alloying

International Nuclear Information System (INIS)

Shamah, A.M.; Ibrahim, S.; Hanna, F.F.

2011-01-01

Research highlights: → Mechanical alloying (MA) is an important method to investigate the formation of nano sized quasicrystalline phases in Al 86 Cr 14 , Al 84 Fe 16 and Al 62.5 Cu 25 Fe 12.5 compounds. The second part of the present work is an attempt to examine the possibility of formation of the i-phase of the Al 62.5 Cu 25 Fe 12.5 , which lies in the region of the perfect i-phase in the ternary phase diagram, by rapid solidification method. To perform the obtained quasi phase mechanical alloying and heat treatment at the rapid solidified sample were done. - Abstract: In the present work, the formation of nano quasicrystalline icosahedral phase in Al 86 Cr 14 , Al 84 Fe 16 and Al 62.5 Cu 25 Fe 12.5 alloys has been investigated by mechanical alloying. Mixtures of quasicrystalline and related crystalline phases have been observed under various milling conditions. The X-ray diffraction, differential thermal analysis and electrical resistivity techniques have been used for characterization and physical property measurements. The particle size was calculated by X-ray profile using Williamson-Hall plot method and it was found to be 25-50 nm size.

Phase formation in multicomponent monotectic aluminium alloys

Energy Technology Data Exchange (ETDEWEB)

Mirkovic, Djordje; Groebner, Joachim; Schmid-Fetzer, Rainer [Institute of Metallurgy, Clausthal University of Technology (Germany)

2008-07-01

Alloys with a miscibility gap in the liquid state are potential materials for advanced bearings in automotive and other applications. While binary alloys, such as Al-Pb or Al-Bi, are well known, the information available for ternary monotectic Al-alloys is scarce. However, the phase formation in multicomponent alloys is not only more challenging from a scientific aspect, it is also a prerequisite for a focused development of advanced alloys. This motivated our detailed study of monotectic Al-Bi-Cu-Sn alloys including both experimental and computational thermodynamic methods. Based on the initially established systematic classification of monotectic ternary Al-alloys, the first promising monotectic reaction was observed in the ternary Al-Bi-Zn system. Further ternary systems Al-Cu-Sn, Al-Bi-Sn, Al-Bi-Cu and Bi-Cu-Sn were investigated as basis for quaternary Al-Bi-Cu-Sn alloys. Experimental investigations of phase equilibria, enthalpies and solidification microstructures were combined with thermodynamic modeling. The results demonstrate that the developed precise thermodynamic description is vital to reveal the distinct multicomponent monotectic features of pertinent phase diagrams. The solidification paths of ternary monotectic alloy systems, Al-Bi-Zn, Al-Sn-Cu and Al-Bi-Cu, were also studied using thermodynamic calculations, revealing specific details of phase formation during solidification of selected alloys.

Phase coexistence in ferroelectric solid solutions: Formation of monoclinic phase with enhanced piezoelectricity

Directory of Open Access Journals (Sweden)

Xiaoyan Lu

2016-10-01

Full Text Available Phase morphology and corresponding piezoelectricity in ferroelectric solid solutions were studied by using a phenomenological theory with the consideration of phase coexistence. Results have shown that phases with similar energy potentials can coexist, thus induce interfacial stresses which lead to the formation of adaptive monoclinic phases. A new tetragonal-like monoclinic to rhombohedral-like monoclinic phase transition was predicted in a shear stress state. Enhanced piezoelectricity can be achieved by manipulating the stress state close to a critical stress field. Phase coexistence is universal in ferroelectric solid solutions and may provide a way to optimize ultra-fine structures and proper stress states to achieve ultrahigh piezoelectricity.

Effect of aluminium on formation of metastable phases in titanium-niobium alloys

International Nuclear Information System (INIS)

Trenogina, T.L.; Derevyanko, V.N.; Vozilkin, V.A.

2001-01-01

Specific features of phase transformations in the alloy of Ti-20Nb-29Al (at.%) are investigated in comparison with those in the aluminium-free Ti-21Nb alloy. It is states that in the alloy Ti-20Nb-29Al on quenching the ordering of β-solid solution takes place with B2-structure formation. The B2-matrix experiences decomposition with the formation of ordered Ω 0 -phase which field ranges up to 700 deg C. The investigation results show that the sequence of phase formation in Ti-Nb-Al and aluminium-free alloys is much the same. The only difference between them is the formation of ordered phases in the alloy Ti-20Nb-29Al [ru

Transient phases during fast crystallization of organic thin films from solution

Science.gov (United States)

Wan, Jing; Li, Yang; Ulbrandt, Jeffrey G.; Smilgies, Detlef-M.; Hollin, Jonathan; Whalley, Adam C.; Headrick, Randall L.

2016-01-01

We report an in situ microbeam grazing incidence X-ray scattering study of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) organic semiconductor thin film deposition by hollow pen writing. Multiple transient phases are observed during the crystallization for substrate temperatures up to ≈93 °C. The layered smectic liquid-crystalline phase of C8-BTBT initially forms and preceedes inter-layer ordering, followed by a transient crystalline phase for temperature >60 °C, and ultimately the stable phase. Based on these results, we demonstrate a method to produce extremely large grain size and high carrier mobility during high-speed processing. For high writing speed (25 mm/s), mobility up to 3.0 cm2/V-s has been observed.

Probing the Texture of the Calamitic Liquid Crystalline Dimer of 4-(4-Pentenyloxybenzoic Acid

Directory of Open Access Journals (Sweden)

Maher A. Qaddoura

2010-01-01

Full Text Available The liquid crystalline dimer of 4-(4-pentenyloxybenzoic acid, a member of the n-alkoxybenzoic acid homologous series, was synthesized using potassium carbonate supported on alumina as catalyst. The acid dimer complex exhibited three mesophases; identified as nematic, smectic X1 and smectic X2. Phase transition temperatures and the corresponding enthalpies were recorded using differential scanning calorimetry upon both heating and cooling. The mesophases were identified by detailed texture observations by variable temperature polarized light microscopy. The nematic phase was distinguished by a fluid Schlieren texture and defect points (four and two brushes while the smectic phases were distinguished by rigid marble and mosaic textures, respectively.

Modeling of formation of binary-phase hollow nanospheres from metallic solid nanospheres

International Nuclear Information System (INIS)

Svoboda, J.; Fischer, F.D.; Vollath, D.

2009-01-01

Spontaneous formation of binary-phase hollow nanospheres by reaction of a metallic nanosphere with a non-metallic component in the surrounding atmosphere is observed for many systems. The kinetic model describing this phenomenon is derived by application of the thermodynamic extremal principle. The necessary condition of formation of the binary-phase hollow nanospheres is that the diffusion coefficient of the metallic component in the binary phase is higher than that of the non-metallic component (Kirkendall effect occurs in the correct direction). The model predictions of the time to formation of the binary-phase hollow nanospheres agree with the experimental observations

Structural formation of aluminide phases on titanium alloy during annealing

International Nuclear Information System (INIS)

Mamaeva, A.A.; Romankov, S.E.; Sagdoldina, Zh.

2006-01-01

Full text: The aluminum layer on the surface of titanium alloy has been formed by thermal deposition. The structural formation of aluminide phases on the surface has been studied. The sequence of structural transformations at the Ti/Al interface is limited by the reaction temperature and time. The sequence of aluminide phase formation is occurred in compliance with Ti-Al equilibrium phase diagram. At the initial stages at the Ti/Al interface the Al3Ti alloy starts forming as a result of interdiffusion, and gradually the whole aluminum films is spent on the formation of this layer. The Al3Ti layer decomposes with the increase of temperature (>600C). At 800C the two-phase (Ti3Al+TiAl) layer is formed on the titanium surface. The TiAl compound is unstable and later on with the increase of the exposure time at 800C gradually transforms into the Ti3Al. The chain of these successive transformations leads to the formation of the continuous homogeneous layer consisting of the Ti3Al compound on the surface. At temperatures exceeding the allotropic transformation temperature (>900C) the Ti3Al compound starts decomposing. All structural changes taking place at the Ti/Al interface are accompanied by considerable changes in micro hardness. The structure of initial substrate influences on kinetics of phase transformation and microstructure development. (author)

Formation of nano quasicrystalline and crystalline phases by mechanical alloying

Energy Technology Data Exchange (ETDEWEB)

Shamah, A.M.; Ibrahim, S. [Faculty of Petroleum and Mining Engineering, Suez Canal University, Suez (Egypt); Hanna, F.F., E-mail: fariedhanna@yahoo.com [Faculty of Petroleum and Mining Engineering, Suez Canal University, Suez (Egypt)

2011-02-03

Research highlights: > Mechanical alloying (MA) is an important method to investigate the formation of nano sized quasicrystalline phases in Al{sub 86}Cr{sub 14}, Al{sub 84}Fe{sub 16} and Al{sub 62.5}Cu{sub 25}Fe{sub 12.5} compounds. The second part of the present work is an attempt to examine the possibility of formation of the i-phase of the Al{sub 62.5}Cu{sub 25}Fe{sub 12.5}, which lies in the region of the perfect i-phase in the ternary phase diagram, by rapid solidification method. To perform the obtained quasi phase mechanical alloying and heat treatment at the rapid solidified sample were done. - Abstract: In the present work, the formation of nano quasicrystalline icosahedral phase in Al{sub 86}Cr{sub 14}, Al{sub 84}Fe{sub 16} and Al{sub 62.5}Cu{sub 25}Fe{sub 12.5} alloys has been investigated by mechanical alloying. Mixtures of quasicrystalline and related crystalline phases have been observed under various milling conditions. The X-ray diffraction, differential thermal analysis and electrical resistivity techniques have been used for characterization and physical property measurements. The particle size was calculated by X-ray profile using Williamson-Hall plot method and it was found to be 25-50 nm size.

Power of the Poincare Group: Elucidating the Hidden Symmetries in Focal Conic Domains

International Nuclear Information System (INIS)

Alexander, Gareth P.; Chen, Bryan Gin-ge; Matsumoto, Elisabetta A.; Kamien, Randall D.

2010-01-01

Focal conic domains are typically the 'smoking gun' by which smectic liquid crystalline phases are identified. The geometry of the equally spaced smectic layers is highly generic but, at the same time, difficult to work with. In this Letter we develop an approach to the study of focal sets in smectics which exploits a hidden Poincare symmetry revealed only by viewing the smectic layers as projections from one-higher dimension. We use this perspective to shed light upon several classic focal conic textures, including the concentric cyclides of Dupin, polygonal textures, and tilt-grain boundaries.

Laws of phase formation in ion-implanted metals

International Nuclear Information System (INIS)

Kazdaev, H.R.; Abylkhalykova, R.B.; Skakov, M.K.

2004-01-01

Full text: Main laws of ordered structures formation at molybdenum implantation by elements forming phases of introduction (B, C, N, 0, Si, P, S) are discovered in this work. According to them the character of structural and phase transformations in molybdenum at ion implantation is determined not by kinetic parameters of bombarding particles and their chemical activity but by size factor η x/Me (ratio of nuclear radii of introduced elements and atoms of a matrix). At change of its meaning in the certain limits the following can be observed: superstructures formation (η x/Mo x/Mo x/Mo >0.69). In the latter case at the further implantation doze increasing recrystallization of molybdenum monocrystalline layers amorphized during previous bombarding with chemical connection formation takes place, characterized by us as ion-inducted synthesis. The phenomenon discovered on the samples implanted by phosphorus ions. As the result, the high-temperature phase of molybdenum monophosphide MoP having densely situated lattice was synthesized. The complete confirmation of the main laws of structural and phased transformations at ion implantation established by results on molybdenum monocrystals with OCC lattice was achieved at realization of similar researches on the other transitive metal - zirconium which differs from molybdenum according to a number of attributes: a type of an initial lattice structural condition (large scaled polycrystal), presence of interparticle borders and high solubility of atmospheric impurities (nitrogen, carbon, oxygen). The discovered laws have proved to be true also according to ion implanted samples of monocrystal tungsten and polycrystal tantalum

Phase separation and nanocrystal formation in Al-based metallic glasses

International Nuclear Information System (INIS)

Antonowicz, Jerzy

2007-01-01

Nanocrystallization in a group of Al-RE and Al-RE-TM (RE = rare earth, TM = transition metal) melt-spun amorphous alloys was studied using in situ small- and wide-angle X-ray scattering techniques (SAXS/WAXS) and transmission electron microscopy (TEM). The SAXS/WAXS measurements were carried out during isothermal annealing at temperatures close to crystallization point. A continuously growing interference maximum shifting progressively toward lower angles was found to develop in SAXS regime. Simultaneously taken WAXS spectra reveal formation of the primary fcc-Al nanocrystalline phase. The presence of the SAXS signal maximum indicates the spatial correlation between the compositional fluctuations. The peak position decay is an evidence of an increase of the fluctuation spacing characteristic for the coarsening stage of phase separation. The SAXS/WAXS data analysis indicates that amorphous phase decomposition triggers and controls the fcc-Al nanocrystalline phase formation. The glassy phase initially decomposes into Al-rich and RE-rich regions with typical lengths scale of about 10 nm. The nanocrystals nucleate preferentially inside the Al-rich amorphous regions and their growth is constrained by the region size because of the sluggish atomic diffusion in the RE-rich zones. A different crystallization mechanism is demonstrated in Al-Y-Ni-Co glass where WAXS spectra show formation of the fcc-Al primary phase but no interference peak in SAXS regime was found

Transient phases during fast crystallization of organic thin films from solution

Directory of Open Access Journals (Sweden)

Jing Wan

2016-01-01

Full Text Available We report an in situ microbeam grazing incidence X-ray scattering study of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT organic semiconductor thin film deposition by hollow pen writing. Multiple transient phases are observed during the crystallization for substrate temperatures up to ≈93 °C. The layered smectic liquid-crystalline phase of C8-BTBT initially forms and preceedes inter-layer ordering, followed by a transient crystalline phase for temperature >60 °C, and ultimately the stable phase. Based on these results, we demonstrate a method to produce extremely large grain size and high carrier mobility during high-speed processing. For high writing speed (25 mm/s, mobility up to 3.0 cm2/V-s has been observed.

Phase separation and formation of omega phase in the beta matrix of a Ti-V-Cu alloy

Energy Technology Data Exchange (ETDEWEB)

Ng, H.P. [ARC Centre of Excellence for Design in Light Metals, Department of Materials Engineering, Monash University, Victoria 3800 (Australia); Devaraj, A.; Nag, S. [Center for Advanced Research and Technology, Department of Materials Science and Engineering, University of North Texas, Denton, TX (United States); Bettles, C.J. [ARC Centre of Excellence for Design in Light Metals, Department of Materials Engineering, Monash University, Victoria 3800 (Australia); Gibson, M. [CSIRO Process Science and Engineering, Locked Bag 10, Clayton South, Victoria 3169 (Australia); Fraser, H.L. [Center for the Accelerated Maturation of Materials, Department of Materials Science and Engineering, The Ohio State University, Columbus, OH (United States); Muddle, B.C. [ARC Centre of Excellence for Design in Light Metals, Department of Materials Engineering, Monash University, Victoria 3800 (Australia); Banerjee, R., E-mail: rajarshi.banerjee@unt.edu [Center for Advanced Research and Technology, Department of Materials Science and Engineering, University of North Texas, Denton, TX (United States)

2011-05-15

The formation of the {omega} phase in the presence of simultaneous development of compositional modulations (or phase separation) within the body-centered cubic {beta} matrix phase of a Ti-10V-6Cu (wt.%) alloy during continuous cooling has been investigated using a combination of transmission electron microscopy and atom probe tomography. While a water quench from the high-temperature {beta} phase field allows apparently athermal formation of {omega} domains without any significant partitioning of solute or modulation in matrix composition, subsequent annealing at 500 {sup o}C for just 60 s leads to unusually rapid growth of the {omega} domains concurrent with, but apparently independent of, a slower development of finer-scale modulations in solute composition occurring apparently uniformly across both {omega} and {beta} phases. In contrast, on slower air cooling from the solution treatment temperature, there are pronounced compositional fluctuations within the {beta} phase, presumably as a product of spinodal decomposition, that are detectable prior to the formation of {omega} phase. The {omega} phase subsequently forms preferentially in solute-depleted regions of the matrix {beta}, with a composition reflecting the local matrix composition and a solute content significantly lower than the average matrix composition. As a result, it has a cuboidal morphology, distinguishably different from the elliposoidal form that is observed in samples water-quenched and annealed at 500 deg. C.

Formation of aqueous-phase α-hydroxyhydroperoxides (α-HHP: potential atmospheric impacts

Directory of Open Access Journals (Sweden)

R. Zhao

2013-06-01

Full Text Available The focus of this work is on quantifying the degree of the aqueous-phase formation of α-hydroxyhydroperoxides (α-HHPs via reversible nucleophilic addition of H2O2 to aldehydes. Formation of this class of highly oxygenated organic hydroperoxides represents a poorly characterized aqueous-phase processing pathway that may lead to enhanced SOA formation and aerosol toxicity. Specifically, the equilibrium constants of α-HHP formation have been determined using proton nuclear-magnetic-resonance (1H NMR spectroscopy and proton-transfer-reaction mass spectrometry (PTR-MS. Significant α-HHP formation was observed from formaldehyde, acetaldehyde, propionaldehyde, glycolaldehyde, glyoxylic acid, and methylglyoxal, but not from methacrolein and ketones. Low temperatures enhanced the formation of α-HHPs but slowed their formation rates. High inorganic salt concentrations shifted the equilibria toward the hydrated form of the aldehydes and slightly suppressed α-HHP formation. Using the experimental equilibrium constants, we predict the equilibrium concentration of α-HHPs to be in the μM level in cloud water, but it may also be present in the mM level in aerosol liquid water (ALW, where the concentrations of H2O2 and aldehydes can be high. Formation of α-HHPs in ALW may significantly affect the effective Henry's law constants of H2O2 and aldehydes but may not affect their gas-phase levels. The photochemistry and reactivity of this class of atmospheric species have not been studied.

Formation of InN phase by sequential ion implantation

International Nuclear Information System (INIS)

Santhana Raman, P.; Ravichandran, V.; Nair, K.G.M.; Kesavamoorthy, R.; Kalavathi, S.; Panigrahi, B.K.; Dhara, S.

2006-01-01

Formation of InN phase by sequentially implanting nitrogen on indium implanted silica was demonstrated. The growth of embedded InN phase on as-implanted and post-implantation annealed sample was studied using Glancing Incidence X-Ray Diffraction (GIXRD) and Raman spectroscopy. Existence of both cubic and hexagonal phases of InN was observed. Results of irradiation induced ripening of In nanoclusters due to N + ion implantation was also studied. (author)

Maps of Fe-Al phases formation kinetics parameters during isothermal sintering

Energy Technology Data Exchange (ETDEWEB)

Pochec, Ewelina, E-mail: epochec@wat.edu.pl [Department of Advanced Materials and Technology, Military University of Technology (Poland); Jozwiak, Stanislaw; Karczewski, Krzysztof; Bojar, Zbigniew [Department of Advanced Materials and Technology, Military University of Technology (Poland)

2012-10-10

Highlights: Black-Right-Pointing-Pointer The sintering temperature and compaction pressure have a strong influence on the sinters structure. Black-Right-Pointing-Pointer The measurements confirmed the presence of the high-aluminium phases from Fe-Al equilibrium system in tested sinters. Black-Right-Pointing-Pointer The kinetics of Fe-Al phase formation can be described by Johnson-Mehl-Avrami modelling. - Abstract: The influence of technological parameters (compaction pressure and sintering temperature) on Fe-Al phase formation was investigated. The kinetics of phase transformation preceding and during an SHS reaction was studied in isothermal conditions by DSC using the JMA (Johnson-Mehl-Avrami) model. This model allowed us to determine basic kinetic parameters, including the Avrami exponent, which characterises the rate and manner of particular phase nucleation. The activation energy (E{sub a}) of particular phase formation was determined by the Kissinger method. XRD analysis and SEM observations of sintered material showed that not only Fe{sub 2}Al{sub 5} phase and low-aluminium solid solution in iron but also aluminium-rich FeAl{sub 2} and FeAl{sub 3} phases are formed during the sintering of an FeAl50 elementary powder mixture in isothermal conditions with an SHS reaction. The above conclusions were confirmed by iron-based solid solution lattice parameter studies and microhardness measurements.

Influence of the strength of the smectic order on the backbone anisotropy of side-chain liquid crystal polymers as revealed by SANS

Science.gov (United States)

Noirez, L.; Keller, P.; Cotton, J. P.

1992-06-01

It is proposed that the strength of the smectic order determines the backbone anisotropy of side-chain liquid crystal polymers. Here this strength increases with the length of the alkyl terminal group of the mesogens. Two liquid crystal polymethacrylates differing only by the mesogenic tails —OCH3 and —OC4H9 are considered. The backbone anisotropy of these polymers is measured by small angle neutron scattering (SANS) whereas the smectic order is evaluated from the intensity of the 001 Bragg peak. Il est proposé que la qualité de l'ordre smectique détermine l'anisotropie du squelette de polymères mésomorphes en peigne confinés dans les lamelles. Ici l'ordre smectique est augmenté en allongeant le groupe alkyl terminal des mésogènes. Nous étudions deux polyméthacrylates cristal liquide qui ne différent que par leurs groupes terminaux : —OCH3 et —OC4H9. L'anisotropie du squellete est mesurée par diffusion de neutrons aux petits angles tandis que l'ordre smectique est évalué à l'aide de l'intensité du pic de Bragg 001.

Evidence of hexatic phase formation in two-dimensional Lennard-Jones binary arrays

International Nuclear Information System (INIS)

Li, M.; Johnson, W.L.; Goddard, W.A. III

1996-01-01

We report evidence of the hexatic phase formation in Lennard-Jones binary substitutional random arrays from isothermal-isobaric molecular-dynamics simulations. The hexatic phase is analogous to those predicted in Kosterlitz-Thouless theory of melting that is characterized by short-range translational order and quasi-long-range orientational order. At the crystal to hexatic phase transition, dislocation pairs are observed to unbind into isolated dislocations. Further disordering of the hexatic phase, however, does not lead to dissociation of dislocations into disclinations. Instead, the dislocations become clustered and form dislocation networks which results in formation of amorphous phases. copyright 1996 The American Physical Society

BCT phase formation in synthesis via microwave assisted hydrothermal method

International Nuclear Information System (INIS)

Barra, B.C.; Souza, A.E.; Teixeira, S.R.; Santos, G.T.A.; Lanzi, C.A.C.

2012-01-01

In previous work, samples of barium and calcium titanate (Ba1-xCaxTiO3 (BCT x = 0- 1) were prepared using the microwave assisted hydrothermal method in conditions of relatively short time and temperature. To the sample with 75wt% of Ca no BCT phase was formed but the photoluminescent emission was improved. In the present study, these titanates were synthesized by the same method with other concentrations of Ca, Ba1-xCaxTiO3 (x = 0, 0.20, 0.40, 0. 60, 0.80 and 1) to evaluate the limit of BCT phase formation. Results of X-ray diffraction showed that the phase BCT is formed between zero and 50wt%-Ca, in Ba substitution. Above this concentration, was observed only the formation of carbonates, and to x = 1 there was carbonate formation together with CaTiO3. These results were confirmed by micro Raman spectroscopy. (author)

Power of the Poincaré group: elucidating the hidden symmetries in focal conic domains.

Science.gov (United States)

Alexander, Gareth P; Chen, Bryan Gin-Ge; Matsumoto, Elisabetta A; Kamien, Randall D

2010-06-25

Focal conic domains are typically the "smoking gun" by which smectic liquid crystalline phases are identified. The geometry of the equally spaced smectic layers is highly generic but, at the same time, difficult to work with. In this Letter we develop an approach to the study of focal sets in smectics which exploits a hidden Poincaré symmetry revealed only by viewing the smectic layers as projections from one-higher dimension. We use this perspective to shed light upon several classic focal conic textures, including the concentric cyclides of Dupin, polygonal textures, and tilt-grain boundaries.

E-T phase diagram of an antiferroelectric liquid crystal with re-entrand smectic C* phase

Czech Academy of Sciences Publication Activity Database

Na, Y.-H.; Naruse, Y.; Fukuda, N.; Orihara, H.; Fajar, A.; Hamplová, Věra; Kašpar, Miroslav; Glogarová, Milada

2008-01-01

Roč. 364, č. 1 (2008), s. 13-19 ISSN 0015-0193 Institutional research plan: CEZ:AV0Z10100520 Keywords : phase diagram * liquid crystals * dielectric measurements * electric field Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.562, year: 2008

Banana-shaped molecules derived from substituted isophthalic acids

Indian Academy of Sciences (India)

Different precursors inducing the bending angle of the banana-shaped molecules. Figure 2. ... Pramana – J. Phys., Vol. 61, No. 2, August ... isotropic liquid; N: nematic; SmA: smectic A; SmC: smectic C. For other phase assign- ments, see text.

Phase formation in Zr/Fe multilayers during Kr ion irradiation

International Nuclear Information System (INIS)

Motta, A. T.

1998-01-01

A detailed study has been conducted of the effect of Kr ion irradiation on phase formation in Zr-Fe metallic multilayers, using the Intermediate Voltage Electron Microscopy (IVEM) at Argonne National Laboratory. Metallic multilayers were prepared with different overall compositions (near 50-50 and Fe-rich), and with different wavelengths (repetition thicknesses). These samples were irradiated with 300 keV Kr ions at various temperatures to investigate the final products, as well as the kinetics of phase formation. For the shorter wavelength samples, the final product was in all cases an amorphous Zr-Fe phase, in combination with Fe, while specially for the larger wavelength samples, in the Fe-rich samples the intermetallic compounds ZrFe 2 and Zr 3 Fe were formed in addition to the amorphous phase. The dose to full reaction decreases with temperature, and with wavelength in a manner consistent with a diffusion-controlled reaction

Effect of alloying elements on σ phase formation in Fe-Cr-Mn alloys

International Nuclear Information System (INIS)

Okazaki, Yoshimitsu; Miyahara, Kazuya; Hosoi, Yuzo; Tanino, Mitsuru; Komatsu, Hazime.

1989-01-01

Alloys of Fe-(8∼12%) Cr-(5∼30%) Mn were solution-treated at 1373 K for 3.6 ks, followed by cold-working of 50% reduction. Both solution-treated and 50% cold-worked materials were aged in the temperature range from 773 to 973 K for 3.6 x 10 3 ks. The identification of σ phase formation was made by using X-ray diffraction from the electrolytically extracted residues of the aged specimens. The region of σ phase formation determined by the present work is wider than that on the phase diagram already reported. It is to be noted that Mn promotes markedly the σ phase formation, and that three different types of σ phase formation are observed depending on Mn content: α→γ + α→γ + α + σ in 10% Mn, α→γ + σ in 15 to 20% Mn alloys, α→χ(Chi) →χ + σ + γ in 25 to 30% Mn alloys. An average electron concentration (e/a) in the σ phase was estimated by quantitative analysis of alloying elements using EPMA. The e/a value in the σ phase formed in Fe-(12∼16%) Cr-Mn alloys aged at 873 K for 3.6 x 10 3 ks is about 7.3, which is independent of Mn content. In order to prevent σ phase formation in Fe-12% Cr-15% Mn alloy, the value of Ni * eq of 11 (Ni * eq = Ni + 30(C) + 25(N)) is required. (author)

Size distribution dynamics reveal particle-phase chemistry in organic aerosol formation

Science.gov (United States)

Shiraiwa, Manabu; Yee, Lindsay D.; Schilling, Katherine A.; Loza, Christine L.; Craven, Jill S.; Zuend, Andreas; Ziemann, Paul J.; Seinfeld, John H.

2013-01-01

Organic aerosols are ubiquitous in the atmosphere and play a central role in climate, air quality, and public health. The aerosol size distribution is key in determining its optical properties and cloud condensation nucleus activity. The dominant portion of organic aerosol is formed through gas-phase oxidation of volatile organic compounds, so-called secondary organic aerosols (SOAs). Typical experimental measurements of SOA formation include total SOA mass and atomic oxygen-to-carbon ratio. These measurements, alone, are generally insufficient to reveal the extent to which condensed-phase reactions occur in conjunction with the multigeneration gas-phase photooxidation. Combining laboratory chamber experiments and kinetic gas-particle modeling for the dodecane SOA system, here we show that the presence of particle-phase chemistry is reflected in the evolution of the SOA size distribution as well as its mass concentration. Particle-phase reactions are predicted to occur mainly at the particle surface, and the reaction products contribute more than half of the SOA mass. Chamber photooxidation with a midexperiment aldehyde injection confirms that heterogeneous reaction of aldehydes with organic hydroperoxides forming peroxyhemiacetals can lead to a large increase in SOA mass. Although experiments need to be conducted with other SOA precursor hydrocarbons, current results demonstrate coupling between particle-phase chemistry and size distribution dynamics in the formation of SOAs, thereby opening up an avenue for analysis of the SOA formation process. PMID:23818634

Size distribution dynamics reveal particle-phase chemistry in organic aerosol formation.

Science.gov (United States)

Shiraiwa, Manabu; Yee, Lindsay D; Schilling, Katherine A; Loza, Christine L; Craven, Jill S; Zuend, Andreas; Ziemann, Paul J; Seinfeld, John H

2013-07-16

Organic aerosols are ubiquitous in the atmosphere and play a central role in climate, air quality, and public health. The aerosol size distribution is key in determining its optical properties and cloud condensation nucleus activity. The dominant portion of organic aerosol is formed through gas-phase oxidation of volatile organic compounds, so-called secondary organic aerosols (SOAs). Typical experimental measurements of SOA formation include total SOA mass and atomic oxygen-to-carbon ratio. These measurements, alone, are generally insufficient to reveal the extent to which condensed-phase reactions occur in conjunction with the multigeneration gas-phase photooxidation. Combining laboratory chamber experiments and kinetic gas-particle modeling for the dodecane SOA system, here we show that the presence of particle-phase chemistry is reflected in the evolution of the SOA size distribution as well as its mass concentration. Particle-phase reactions are predicted to occur mainly at the particle surface, and the reaction products contribute more than half of the SOA mass. Chamber photooxidation with a midexperiment aldehyde injection confirms that heterogeneous reaction of aldehydes with organic hydroperoxides forming peroxyhemiacetals can lead to a large increase in SOA mass. Although experiments need to be conducted with other SOA precursor hydrocarbons, current results demonstrate coupling between particle-phase chemistry and size distribution dynamics in the formation of SOAs, thereby opening up an avenue for analysis of the SOA formation process.

Charge Transport and Phase Behavior of Imidazolium-Based Ionic Liquid Crystals from Fully Atomistic Simulations.

Science.gov (United States)

Quevillon, Michael J; Whitmer, Jonathan K

2018-01-02

Ionic liquid crystals occupy an intriguing middle ground between room-temperature ionic liquids and mesostructured liquid crystals. Here, we examine a non-polarizable, fully atomistic model of the 1-alkyl-3-methylimidazolium nitrate family using molecular dynamics in the constant pressure-constant temperature ensemble. These materials exhibit a distinct "smectic" liquid phase, characterized by layers formed by the molecules, which separate the ionic and aliphatic moieties. In particular, we discuss the implications this layering may have for electrolyte applications.

Numerical modeling of experimental observations on gas formation and multi-phase flow of carbon dioxide in subsurface formations

Science.gov (United States)

Pawar, R.; Dash, Z.; Sakaki, T.; Plampin, M. R.; Lassen, R. N.; Illangasekare, T. H.; Zyvoloski, G.

2011-12-01

One of the concerns related to geologic CO2 sequestration is potential leakage of CO2 and its subsequent migration to shallow groundwater resources leading to geochemical impacts. Developing approaches to monitor CO2 migration in shallow aquifer and mitigate leakage impacts will require improving our understanding of gas phase formation and multi-phase flow subsequent to CO2 leakage in shallow aquifers. We are utilizing an integrated approach combining laboratory experiments and numerical simulations to characterize the multi-phase flow of CO2 in shallow aquifers. The laboratory experiments involve a series of highly controlled experiments in which CO2 dissolved water is injected in homogeneous and heterogeneous soil columns and tanks. The experimental results are used to study the effects of soil properties, temperature, pressure gradients and heterogeneities on gas formation and migration. We utilize the Finite Element Heat and Mass (FEHM) simulator (Zyvoloski et al, 2010) to numerically model the experimental results. The numerical models capture the physics of CO2 exsolution, multi-phase fluid flow as well as sand heterogeneity. Experimental observations of pressure, temperature and gas saturations are used to develop and constrain conceptual models for CO2 gas-phase formation and multi-phase CO2 flow in porous media. This talk will provide details of development of conceptual models based on experimental observation, development of numerical models for laboratory experiments and modelling results.

Phase formation and crystallization behavior of melt spun Sm-Fe-based alloys

International Nuclear Information System (INIS)

Shield, J.E.

1999-01-01

The phase formation and microstructures of Sm-Fe alloys have been investigated at Sm levels of 11 and 17 atomic percent and with alloying additions of Ti and C. At lower Sm content, virtually phase pure SmFe 7 formed, while higher Sm content resulted in the formation of SmFe 7 , SmFe 2 and amorphous phases. The addition of Ti and C resulted in greater stability and a larger volume fraction of the amorphous phase. The binary Sm-Fe alloys at both Sm levels had tremendously variable microstructures, with large discrepancies in grain size and phase distribution from region to region. The addition of Ti and C tended to result in a more homogeneous microstructure, as well as a refinement in the microstructural scale. (orig.)

Formation and Disruption of W-Phase in High-Entropy Alloys

Directory of Open Access Journals (Sweden)

Sephira Riva

2016-05-01

Full Text Available High-entropy alloys (HEAs are single-phase systems prepared from equimolar or near-equimolar concentrations of at least five principal elements. The combination of high mixing entropy, severe lattice distortion, sluggish diffusion and cocktail effect favours the formation of simple phases—usually a bcc or fcc matrix with minor inclusions of ordered binary intermetallics. HEAs have been proposed for applications in which high temperature stability (including mechanical and chemical stability under high temperature and high mechanical impact is required. On the other hand, the major challenge to overcome for HEAs to become commercially attractive is the achievement of lightweight alloys of extreme hardness and low brittleness. The multicomponent AlCrCuScTi alloy was prepared and characterized using powder X-ray diffraction (PXRD, scanning-electron microscope (SEM and atomic-force microscope equipped with scanning Kelvin probe (AFM/SKP techniques. Results show that the formation of complex multicomponent ternary intermetallic compounds upon heating plays a key role in phase evolution. The formation and degradation of W-phase, Al2Cu3Sc, in the AlCrCuScTi alloy plays a crucial role in its properties and stability. Analysis of as-melted and annealed alloy suggests that the W-phase is favoured kinetically, but thermodynamically unstable. The disruption of the W-phase in the alloy matrix has a positive effect on hardness (890 HV, density (4.83 g·cm−3 and crack propagation. The hardness/density ratio obtained for this alloy shows a record value in comparison with ordinary heavy refractory HEAs.

In-situ investigation of the icosahedral Al-Cu-Fe phase formation in thin films

Energy Technology Data Exchange (ETDEWEB)

Haidara, F., E-mail: fanta.haidara@im2np.fr [IM2NP, UMR 6242 CNRS - Universite Aix-Marseille, Av. Escadrille Normandie-Niemen, Case 142, 13397 Marseille Cedex 20 (France); Duployer, B. [Universite Paul Sabatier CIRIMAT-LCMIE 2R1, 118, Route de Narbonne, 31062 Toulouse Cedex 09 (France); Mangelinck, D.; Record, M.-C. [IM2NP, UMR 6242 CNRS - Universite Aix-Marseille, Av. Escadrille Normandie-Niemen, Case 142, 13397 Marseille Cedex 20 (France)

2012-09-05

Highlights: Black-Right-Pointing-Pointer We investigated the phase formation of i-Al{sub 62.5}Cu{sub 25}Fe{sub 12.5} in thin films. Black-Right-Pointing-Pointer We characterized the samples by DSC and in-situ XRD and resistance measurements. Black-Right-Pointing-Pointer The resistivity value for i-Al{sub 62.5}Cu{sub 25}Fe{sub 12.5} was determined. - Abstract: This work is an investigation of the formation by reactive diffusion at high temperatures of the icosahedral phase, i-Al{sub 62.5}Cu{sub 25}Fe{sub 12.5}, in thin films. The samples were prepared by sputtering at room temperature. The elements Al, Cu and Fe were sequentially deposited onto oxidized silicon substrates. The two following stacking sequences, Al/Cu/Fe and Al/Fe/Cu, were investigated. The phase formation was studied using in situ resistivity, in situ X-ray Diffraction and Differential Scanning Calorimetry measurements. Whatever the stacking sequence, the sequences of phase formation evidenced during the heating treatment are similar. However the temperatures of formation for the first phases that are formed are different; they are higher in the case of the Al/Fe/Cu stacking sequence.

Elimination of impurity phase formation in FePt magnetic thin films prepared by pulsed laser deposition

International Nuclear Information System (INIS)

Wang, Ying; Medwal, Rohit; Sehdev, Neeru; Yadian, Boluo; Tan, T.L.; Lee, P.; Talebitaher, A.; Ilyas, Usman; Ramanujan, R.V.; Huang, Yizhong; Rawat, R.S.

2014-01-01

The formation of impurity phases in FePt thin films severely degrades its magnetic properties. The X-ray diffraction patterns of FePt thin films, synthesized using pulsed laser deposition (PLD), showed peaks corresponding to impurity phases, resulting in softer magnetic properties. A systematic investigation was carried to determine the factors that might have led to impurity phase formation. The factors include (i) PLD target composition, (ii) substrate material, (iii) annealing parameters such as temperature, duration and ambience and (iv) PLD deposition parameters such as chamber ambience, laser energy fluence and target–substrate distance. Depositions on the different substrates revealed impurity phase formation only on Si substrates. It was found that the target composition, PLD chamber ambience, and annealing ambience were not the factors that caused the impurity phase formation. The annealing temperature and duration influenced the impurity phases, but are not the cause of their formation. A decrease in the laser energy fluence and increase of the target–substrate distance resulted in elimination of the impurity phases and enhancement in the magnetic and structural properties of FePt thin films. The energy of the ablated plasma species, controlled by the laser energy fluence and the target–substrate distance, is found to be the main factor responsible for the formation of the impurity phases.

A new method in prediction of TCP phases formation in superalloys

International Nuclear Information System (INIS)

Mousavi Anijdan, S.H.; Bahrami, A.

2005-01-01

The purpose of this investigation is to develop a model for prediction of topologically closed-packed (TCP) phases formation in superalloys. In this study, artificial neural networks (ANN), using several different network architectures, were used to investigate the complex relationships between TCP phases and chemical composition of superalloys. In order to develop an optimum ANN structure, more than 200 experimental data were used to train and test the neural network. The results of this investigation shows that a multilayer perceptron (MLP) form of the neural networks with one hidden layer and 10 nodes in the hidden layer has the lowest mean absolute error (MAE) and can be accurately used to predict the electron-hole number (N v ) and TCP phases formation in superalloys

Third phase formation revisited: the U(VI), HNO3 - TBP, n-dodecane system

International Nuclear Information System (INIS)

Chiarizia, R.; Jensen, M.P.; Borkowski, M.; Ferraro, J.R.; Thiyagarajan, P.; Littrell, K.C.

2003-01-01

In this work, the system U(VI), HNO 3 -tri-n-butylphosphate (TBP), n-dodecane has been revisited with the objective of gaining information on the coordination chemistry and structural evolution of the species formed in the organic phase before and after third phase formation. Chemical analyses, spectroscopic and EXAFS data indicate that U(VI) is extracted as the UO 2 (NO 3 ) 2 ·2TBP adduct, while the third phase species have the average composition UO 2 (NO 3 ) 2 ·2TBP·HNO 3 . Small-angle neutron scattering (SANS) measurements on TBP solutions loaded with only HNO 3 or with increasing amounts of U(VI) have revealed the presence, before phase splitting, of ellipsoidal aggregates with the major and minor axes up to about 64 and 15 A, respectively. The formation of these aggregates, very likely of the reverse micelle-type, is observed in all cases, that is, when only HNO 3 , only UO 2 (NO 3 ) 2 , or both HNO 3 and UO 2 (NO 3 ) 2 are extracted by the TBP solution. Upon third phase formation, the SANS data reveal the presence of smaller aggregates in the light organic phase, while the heavy organic phase contains pockets of diluent, each with an average of about two molecules of n-dodecane.

Growth Law For Peritectic Phases Formation In The Zinc Coating

Directory of Open Access Journals (Sweden)

Guzik E.

2015-09-01

Full Text Available Some experiments dealing with the isothermal hot dip galvanizing were carried out. The (Zn – coating settled on the Armco-iron substrate were examined after arresting the solidification for different periods of time. The measurement of the thickness of each sub-layer in the coating were performed due to the SEM – analysis. The zinc segregation on the cross-section of the studied sub-layers were also determined by the EDS technique. The growth laws are formulated mathematically for each of the observed sub-layer. The mechanism of the sub-layer formation is also analysed due to the observation of the birth/nucleation of the phases in the sub-layers and the effect of flux onto the sub-layers morphology formation. The appearance of each phase is referred to the Fe-Zn diagram for stable equilibrium according to which these phases are the products of the adequate peritectic transformation.

Lattice dynamical study of omega phase formation in Zr-Al system

International Nuclear Information System (INIS)

Ghosh, P.S.; Arya, A.; Kulkarni, U.D.; Dey, G.K.

2011-01-01

The hexagonal ω phase occurs in the alloys in which the high temperature β phase (bcc) is stabilized with respect to the martensitic β -> ω transformation. The compositional ranges over which the ω phase can be stabilized is the characteristic of the alloy system under consideration. The formation of ordered ω (B8 2 -Zr 2 Al) phase, having space group P6 3 /mmc has been viewed in terms of a superimposition of displacive and replacive components of phase transformation. While the lattice collapse mechanism of β -> ω transformation is displacive in nature; a replacive transformation involving diffusion is required for decorating different sublattice sites by different atomic species. Although, the extent of overlap of these transformations in the formation of ordered ω phase has not been established so far; attempts have been made to explore this aspect by examining the sequential formation of several intermediate stable/metastable phases. The partial collapse of 2nd - 3rd and 5th - 6th planes along (111) direction leads to intermediate trigonal ω ' phase upto which the transformation is purely displacive in nature. A chemical ordering sets in after this step leading to B82 structure via ω'' structure. Density functional plane wave based calculations using the projector augmented wave (PAW) potentials are employed under the generalized gradient approximation to exchange and correlation to study (a) relative ground state stabilities of these phases, (b) variation of total energy as a function of displacement (z, z = 0 to 1/12) and (c) Frozen-phonon calculations for 2/3 longitudinal phonon along (111) direction. The energy-displacement curve for the B2 structure shows nearly harmonic behavior for small displacements but shows strong anharmonic behavior for large displacements making trigonal ω ' structure metastable with respect to this kind of transformations. The phonon dispersion of B2 structure exhibits imaginary frequencies along (111) making it a

Effect of hardness of martensite and ferrite on void formation in dual phase steel

DEFF Research Database (Denmark)

Azuma, M.; Goutianos, Stergios; Hansen, Niels

2012-01-01

The influence of the hardness of martensite and ferrite phases in dual phase steel on void formation has been investigated by in situ tensile loading in a scanning electron microscope. Microstructural observations have shown that most voids form in martensite by evolving four steps: plastic...... deformation of martensite, crack initiation at the martensite/ferrite interface, crack propagation leading to fracture of martensite particles and void formation by separation of particle fragments. It has been identified that the hardness effect is associated with the following aspects: strain partitioning...... between martensite and ferrite, strain localisation and critical strain required for void formation. Reducing the hardness difference between martensite and ferrite phases by tempering has been shown to be an effective approach to retard the void formation in martensite and thereby is expected to improve...

Enhancement of polar crystalline phase formation in transparent PVDF-CaF{sub 2} composite films

Energy Technology Data Exchange (ETDEWEB)

Lee, Sang Goo; Ha, Jong-Wook, E-mail: jongwook@krict.re.kr; Sohn, Eun-Ho; Park, In Jun; Lee, Soo-Bok

2016-12-30

Highlights: • The crystalline phase in transparent PVDF-CaF{sub 2} composite films was investigated. • CaF{sub 2} promoted the formation of polar crystalline phases in PVDF matrix. • Ordered γ-phase was obtained by thermal treatment of as-cast films at the vicinity of its melting temperature. - Abstract: We consider the influence of calcium fluoride (CaF{sub 2}) nanoparticles on the crystalline phase formation of poly(vinylidene fluoride) (PVDF) for the first time. The transparent PVDF-CaF{sub 2} composite films were prepared by casting on PET substrates using N,N-dimethylacetamide (DMAc) as a solvent. It was found that CaF{sub 2} promoted the formation of polar crystalline phase of PVDF in composites, whereas nonpolar α-phase was dominant in the neat PVDF film prepared at the same condition. The portion of polar crystalline phase increased in proportional to the weight fraction of CaF{sub 2} in the composite films up to 10 wt%. Further addition of CaF{sub 2} suppressed completely the α-phase formation. Polar crystalline phase observed in as-cast composite films was a mixture of β- and γ-polymorph structures. It was also shown that much ordered γ-phase could be obtained through thermal treatment of as-cast PVDF-CaF{sub 2} composite film at the temperatures above the melting temperature of the composite films, but below that of γ-phase.

Experimental redetermination of the gas-phase enthalpy of formation of ethyl 2-thiophenecarboxylate

International Nuclear Information System (INIS)

Santos, Ana Filipa L.O.M.; Ribeiro da Silva, Manuel A.V.

2013-01-01

The condensed phase standard (p° = 0.1 MPa) molar enthalpy of formation of ethyl-2-thiophenecarboxylate was derived from the remeasured standard molar energy of combustion, in oxygen, at T = 298.15 K, by rotating bomb combustion calorimetry and the standard molar enthalpy of vaporization, at T = 298.15 K, remeasured by Calvet microcalorimetry. Combining these two values, the following enthalpy of formation in the gas phase, at T = 298.15 K, was then derived for ethyl-2-thiophenecarboxylate: −(277.7 ± 2.9) kJ · mol −1 . The calculated gas-phase enthalpy of formation of the title compound, through the G3(MP2)//B3LYP approach was found to be 278.9 kJ · mol −1 , in excellent agreement with the experimental measured value

Structural control of void formation in dual phase steels

DEFF Research Database (Denmark)

Azuma, Masafumi

The objective of this study is to explore the void formation mechanisms and to clarify the influence of the hardness and structural parameters (volume fraction, size and morphology) of martensite particles on the void formation and mechanical properties in dual phase steels composed of ferrite...... and (iii) strain localization. The critical strain for void formation depends on hardness of the martensite, but is independent of the volume fraction, shape, size and distribution of the martensite. The strain partitioning between the martensite and ferrite depends on the volume fraction and hardness...... of the martensite accelerates the void formation in the martensite by enlarging the size of voids both in the martensite and ferrite. It is suggested that controlling the hardness and structural parameters associated with the martensite particles such as morphology, size and volume fraction are the essential...

Statistics of errors in fibre communication lines with a phase-modulation format and optical phase conjugation

International Nuclear Information System (INIS)

Shapiro, Elena G; Fedoruk, Mikhail P

2011-01-01

Analytical formulas are derived to approximate the probability density functions of 'zero' and 'one' bits in a linear communication channel with a binary format of optical signal phase modulation. Direct numerical simulation of the propagation of optical pulses in a communication line with optical phase conjugation is performed. The results of the numerical simulation are in good agreement with the analytical approximation. (fibreoptic communication lines)

Asymmetric flavone-based liquid crystals: synthesis and properties

Energy Technology Data Exchange (ETDEWEB)

Timmons, Daren J. [Department of Chemistry, Virginia Military Institute, Lexington, VA, USA; Jordan, Abraham J. [Department of Chemistry, Virginia Military Institute, Lexington, VA, USA; Kirchon, Angelo A. [Department of Chemistry, Virginia Military Institute, Lexington, VA, USA; Murthy, N. Sanjeeva [New Jersey Center for Biomaterials, Rutgers, The State University of New Jersey, Piscataway, NJ, USA; Siemers, Troy J. [Department of Applied Mathematics, Virginia Military Institute, Lexington, VA, USA; Harrison, Daniel P. [Department of Chemistry, Virginia Military Institute, Lexington, VA, USA; Slebodnick, Carla [Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA

2017-02-01

A series of flavones (n-F) substituted at the 4', and 6 positions was prepared, characterised by NMR (1H,13C), HRMS, and studied for liquid crystal properties. The 4'-alkoxy,6-methoxyflavones (4-F–16-F) exhibit varying ranges of nematic and smectic A phases as evidenced by polarised optical microscopy and differential scanning calorimetry (DSC). As the tail length is increased, the smectic phase becomes more prevalent. Smectic phases for (8-F–16-F) were further analysed by powder X-ray diffraction (XRD), and the rate of structural transformations was explored by combined DSC/XRD studies. Flavonol 6-F–OH was also prepared but no mesogenic behaviour was observed. The molecular structures of 6-F and 6-F–OH were determined by single-crystal XRD and help to explain the differences in material properties. Additionally, fluorescence and electrochemical studies were conducted on solutions of n-F.

Nonionic diethanolamide amphiphiles with isoprenoid-type hydrocarbon chains: thermotropic and lyotropic liquid crystalline phase behaviour

Energy Technology Data Exchange (ETDEWEB)

Sagnella, Sharon M.; Conn, Charlotte E.; Krodkiewska, Irena; Drummond, Calum J. (CSIRO/MSE)

2014-09-24

The thermotropic and lyotropic liquid crystalline phase behaviour of a series of diethanolamide amphiphiles with isoprenoid-type hydrocarbon chains (geranoyl, H-farnesoyl, and phytanoyl) has been investigated. When neat, both H-farnesoyl and phytanoyl diethanolamide form a smectic liquid crystalline structure at sub-zero temperatures. In addition, all three diethanolamides exhibit a glass transition temperature at around -73 C. Geranoyl diethanolamide forms a lamellar crystalline phase with a lattice parameter of 17.4 {angstrom} following long term storage accompanied by the loss of the glass transition. In the presence of water, H-farnesoyl and phytanoyl diethanolamide form lyotropic liquid crystalline phases, whilst geranoyl diethanolamide forms an L{sub 2} phase. H-farnesoyl diethanolamide forms a fluid lamellar phase (L{sub {alpha}}) at room temperature and up to {approx} 40 C. Phytanoyl diethanolamide displays a rich mesomorphism forming the inverse diamond (Q{sub II}{sup D}) and gyroid (Q{sub II}{sup G}) bicontinuous cubic phases in addition to an L{sub {alpha}} phase.

Droplets formation and merging in two-phase flow microfluidics.

Science.gov (United States)

Gu, Hao; Duits, Michel H G; Mugele, Frieder

2011-01-01

Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i) the emulsification step should lead to a very well controlled drop size (distribution); and (ii) the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed.

Influence of second phase dispersion on void formation during irradiation

International Nuclear Information System (INIS)

Sundararaman, M.; Banerjee, S.; Krishnan, R.

Irradiation-induced void formation in alloys has been found to be strongly influenced by the microstructure, the important microstructural parameters being the dislocation density and the nature, density and distribution of second-phase precipitates. The effects of various types of precipitates on void swelling have been examined using the generally-accepted model of void formation : void embryos are assumed to grow in a situation where equal numbers of vacancies and interstitials are continuously generated by the incident irradiation, the interstitials being somewhat perferentially absorbed in some sinks present in the material. The mechanism of the trapping of defects by a distribution of precipitates has been discussed and the available experimental results on the suppression of void formation in materials containing coherent precipitates have been reviewed. Experimental results on the microstructure developed in a nickel-base alloys, Inconel-718 (considered to be a candidate material for structural applications in fast reactors), have been presented. The method of determination of the coherency strain associated with the precipitates has been illustrated with the help of certain observations made on this alloy. The major difficulty in using a two-phase alloy in an irradiation environment is associated with the irradiation-induced instability of the precipitates. Several processes such as precipitate dislocation (in which the incident radiation removes the outer layer of precipitates by recoil), enhanced diffusion disordering, fragmentation of precipitates, etc. are responsible for bringinq about a significant change in the structure of a two-phase material during irradiation. The effect of these processes on the continued performance of a two-phase alloy subjected to irradiation at an elevated temperature has been discussed. (auth.)

Structure and phase transitions of monolayers of intermediate-length n-alkanes on graphite studied by neutron diffraction and molecular dynamics simulation

Science.gov (United States)

Diama, A.; Matthies, B.; Herwig, K. W.; Hansen, F. Y.; Criswell, L.; Mo, H.; Bai, M.; Taub, H.

2009-08-01

We present evidence from neutron diffraction measurements and molecular dynamics (MD) simulations of three different monolayer phases of the intermediate-length alkanes tetracosane (n-C24H50 denoted as C24) and dotriacontane (n-C32H66 denoted as C32) adsorbed on a graphite basal-plane surface. Our measurements indicate that the two monolayer films differ principally in the transition temperatures between phases. At the lowest temperatures, both C24 and C32 form a crystalline monolayer phase with a rectangular-centered (RC) structure. The two sublattices of the RC structure each consists of parallel rows of molecules in their all-trans conformation aligned with their long axis parallel to the surface and forming so-called lamellas of width approximately equal to the all-trans length of the molecule. The RC structure is uniaxially commensurate with the graphite surface in its [110] direction such that the distance between molecular rows in a lamella is 4.26 Å=√3 ag, where ag=2.46 Å is the lattice constant of the graphite basal plane. Molecules in adjacent rows of a lamella alternate in orientation between the carbon skeletal plane being parallel and perpendicular to the graphite surface. Upon heating, the crystalline monolayers transform to a "smectic" phase in which the inter-row spacing within a lamella expands by ˜10% and the molecules are predominantly oriented with the carbon skeletal plane parallel to the graphite surface. In the smectic phase, the MD simulations show evidence of broadening of the lamella boundaries as a result of molecules diffusing parallel to their long axis. At still higher temperatures, they indicate that the introduction of gauche defects into the alkane chains drives a melting transition to a monolayer fluid phase as reported previously.

Investigation of the phase formation from nickel coated nanostructured silicon

Science.gov (United States)

Shilyaeva, Yulia I.; Pyatilova, Olga V.; Berezkina, Alexandra Yu.; Sysa, Artem V.; Dudin, Alexander A.; Smirnov, Dmitry I.; Gavrilov, Sergey A.

2016-12-01

In this paper, the influence of the conditions of chemical and electrochemical nickel plating of nanostructured silicon and subsequent heat treatment on the phase composition of Si/Ni structures with advanced interface is studied. Nanostructured silicon formed by chemical and electrochemical etching was used for the formation of a developed interphase surface. The resulting Si/Ni samples were analyzed using scanning electron microscopy, energy dispersive X-ray analysis, and X-ray phase analysis. The experiments have revealed the differences in phase composition of the Si/Ni structures obtained by different methods, both before and after heat treatment.

Characteristics of the stress-induced formation of R-phase in ultrafine-grained NiTi shape memory wire

International Nuclear Information System (INIS)

Olbricht, J.; Yawny, A.; Pelegrina, J.L.; Eggeler, G.; Yardley, V.A.

2013-01-01

Highlights: •We investigated the stress-induced formation of R-phase in NiTi shape memory wires. •The R-phase related strains were isolated from the overall stress-strain-behavior. •The stress–strain characteristics of R-phase suggest a homogeneous transformation. •Thermography confirms the homogeneous R-phase formation in ultrafine-grained NiTi. -- Abstract: The transformation between the cubic B2 and monoclinic B19′ phases in ultrafine-grained pseudoelastic NiTi can occur as a two-step process involving the intermediate rhombohedral R-phase. Experimental work using differential scanning calorimetry, electrical resistance measurements and transmission electron microscopy has demonstrated the formation of this intermediate phase during thermal cycling and during mechanical loading. In the present paper, complementary mechanical and thermographic results are presented which allow to further assess the character of the stress-induced R-phase formation. The transformation from B2 to R-phase is demonstrated to occur homogeneously within the gauge length rather than via advancing Lüders-type transition regions as it is the case in the localized transformation from B2 or R-phase to B19′

On mechanism of substructure formation in SmS during isomorphic phase transformations

International Nuclear Information System (INIS)

Aptekar', I.L.; Ivanov, V.I.; Tonkov, E.Yu.; Shmyt'ko, I.M.

1986-01-01

X-ray diffraction study of substructure characteristics of SmS samples subjected to treatment at different temrerature and pressure in media with different viscosity ( graphite, silicon oil) for realization of P-M-P transformations ( p-semiconductor phase, M - high pressure phase) is performed. It is assumed that with M - phase formation P - matrix volume relaxation delays, therefore the new phase particles occupy smaller volume than the initial matrix which causes the M - phase disorientation. The difference between the phase transformation rate and deformation rate under the pressure in media with various viscosity results in arising different substructural characteristics

Phase formation and texture of thin nickel germanides on Ge(001) and Ge(111)

Energy Technology Data Exchange (ETDEWEB)

De Schutter, B., E-mail: deschutter.bob@ugent.be; Detavernier, C. [Department of Solid-State Sciences, Ghent University, Krijgslaan 281/S1, 9000 Ghent (Belgium); Van Stiphout, K.; Santos, N. M.; Vantomme, A. [Instituut voor Kern- en Stralingsfysica, KU Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium); Bladt, E.; Bals, S. [Electron Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp (Belgium); Jordan-Sweet, J.; Lavoie, C. [IBM T.J. Watson Research Center, Yorktown Heights, New York 10598 (United States); Comrie, C. M. [Department of Physics, University of Cape Town, Rondebosch 7700 (South Africa)

2016-04-07

We studied the solid-phase reaction between a thin Ni film and a single crystal Ge(001) or Ge(111) substrate during a ramp anneal. The phase formation sequence was determined using in situ X-ray diffraction and in situ Rutherford backscattering spectrometry (RBS), while the nature and the texture of the phases were studied using X-ray pole figures and transmission electron microscopy. The phase sequence is characterized by the formation of a single transient phase before NiGe forms as the final and stable phase. X-ray pole figures were used to unambiguously identify the transient phase as the ϵ-phase, a non-stoichiometric Ni-rich germanide with a hexagonal crystal structure that can exist for Ge concentrations between 34% and 48% and which forms with a different epitaxial texture on both substrate orientations. The complementary information gained from both RBS and X-ray pole figure measurements revealed a simultaneous growth of both the ϵ-phase and NiGe over a small temperature window on both substrate orientations.

Droplets Formation and Merging in Two-Phase Flow Microfluidics

Directory of Open Access Journals (Sweden)

Hao Gu

2011-04-01

Full Text Available Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i the emulsification step should lead to a very well controlled drop size (distribution; and (ii the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed.

Chiral domain formation from the mixture of achiral rod-like liquid crystal and tri boomerang-shaped molecule

Science.gov (United States)

Lee, Ji-Hoon; Yoon, Tae-Hoon

2013-08-01

Spontaneous formation of chiral domains such as a helical filament and a bent-broom texture was observed from the mixture of a rod-like liquid crystal octylcyano-biphenyl (8CB) and a tri boomerang-shaped 2,4,6-triphenoxy-1,3,5-triazine (triphenoxy) molecule. Although the constituent molecules were achiral, their mixture showed the chiral domains with the equal fraction of the opposite handedness. No tilt of 8CB molecules in the smectic layer was observed, implying the chirality is not due to the polar packing and tilt of the molecules. In addition, the splay and bend elastic constant of 8CB was decreased after doping triphenoxy. A structural conformation of triphenoxy and an orientational coupling between 8CB and triphenoxy are considered to be related to the chiral domain formation.

Formation of the minor phase shell on the surface of hypermonotectic alloy powders

International Nuclear Information System (INIS)

Zhao, J.Z.

2006-01-01

The microstructure evolution in an atomized hypermonotectic alloy drop is calculated. The results indicate that the formation of the minor phase shell on the surface of the powder is due to the heterogeneous nucleation of the minor phase droplets on the atomized drop surface and the resultant diffusional transfer of solute during the liquid-liquid phase transformation

Mesophase and size manipulation of itraconazole liquid crystalline nanoparticles produced via quasi nanoemulsion precipitation.

Science.gov (United States)

Mugheirbi, Naila A; Tajber, Lidia

2015-10-01

The fabrication of drug nanoparticles (NPs) with process-mediated tunable properties and performances continues to grow rapidly during the last decades. This study investigates the synthesis and phase tuning of nanoparticulate itraconazole (ITR) mesophases using quasi nanoemulsion precipitation from acetone/water systems to seek out an alternative pathway to the nucleation-based NP formation. ITR liquid crystalline (LC) phases were formed and nematic-smectic mesomorphism was achieved via controlling solvent:antisolvent temperature difference (ΔTS:AS). The use of ΔTS:AS=49.5°C was associated with a nematic assembly, while intercalated smectic A layering was observed at ΔTS:AS=0°C, with both phases confined in the nanospheres at room temperature. The quasi emulsion system has not been investigated at the nanoscale to date and in contrary to the microscale, quasi nanoemulsion was observed over the solvent:antisolvent viscosity ratios of 1:7-1:1.4. Poly(acrylic acid) in the solvent phase exhibited a concentration dependent interaction when ITR formed NPs. This nanodroplet-based approach enabled the preparation of a stable ITR nanodispersion using Poloxamer 407 at 80°C, which was unachievable before using precipitation via nucleation. Findings of this work lay groundwork in terms of rationalised molecular assembly as a tool in designing pharmaceutical LC NPs with tailored properties. Copyright © 2015 Elsevier B.V. All rights reserved.

Nonequilibrium phase formation in oxides prepared at low temperature: Fergusonite-related phases

International Nuclear Information System (INIS)

Mather, S.A.; Davies, P.K.

1995-01-01

Sol-gel methods have been developed to prepare YNbO 4 , YTaO 4 , and other rare-earth niobates and tantalates with fergusonite-related crystal structures. At low temperatures, all of the fergusonites, with the exception of SmTaO 4 , crystallize in a metastable tetragonal (T') structure similar to that of tetragonal zirconia. Although all of the equilibrium forms of these oxides adopt a crystal structure containing an ordered distribution of the trivalent and pentavalent cations, a random cation distribution is obtained in the metastable T' phase. Metastable phase formation is often ascribed solely to kinetically limited topotactic crystallization. However, the changes in the grain size and unit-cell volumes that accompany the metastable-to-equilibrium fergusonite conversions imply that other physical phenomena induced by small-particle synthesis, namely the Gibbs-Thompson pressure effect and the increased contribution of surface energy, cannot be ignored

Formation, stability and crystal structure of the {sigma} phase in Mo-Re-Si alloys

Energy Technology Data Exchange (ETDEWEB)

Bei, H., E-mail: beih@ornl.gov [Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge, TN 37831 (United States); Yang, Y., E-mail: ying.yang@computherm.com [CompuTherm LLC, Madison, WI 53719 (United States); Viswanathan, G.B. [Air Force Research Laboratory, Wright-Patterson AFB, OH 45433 (United States); Rawn, C.J.; George, E.P. [Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge, TN 37831 (United States)] [University of Tennessee, Department of Materials Science and Engineering, Knoxville, TN 37996 (United States); Tiley, J. [Air Force Research Laboratory, Wright-Patterson AFB, OH 45433 (United States); Chang, Y.A. [CompuTherm LLC, Madison, WI 53719 (United States)] [University of Wisconsin-Madison, Madison, WI 53705 (United States)

2010-10-15

The formation, stability and crystal structure of the {sigma} phase in Mo-Re-Si alloys were investigated. Guided by thermodynamic calculations, six critically selected alloys were arc melted and annealed at 1600 deg. C for 150 h. Their as-cast and annealed microstructures, including phase fractions and distributions, the compositions of the constituent phases and the crystal structure of the {sigma} phase were analyzed by thermodynamic modeling coupled with experimental characterization by scanning electron microscopy, electron probe microanalysis, X-ray diffraction and transmission electron microscopy. Two key findings resulted from this work. One is the large homogeneity range of the {sigma} phase region, extending from binary Mo-Re to ternary Mo-Re-Si. The other is the formation of a {sigma} phase in Mo-rich alloys either through the peritectic reaction of liquid + Mo{sub ss} {yields} {sigma} or primary solidification. These findings are important in understanding the effects of Re on the microstructure and providing guidance on the design of Mo-Re-Si alloys.

A new method for determining gas phase heat of formation of aromatic energetic compounds

Energy Technology Data Exchange (ETDEWEB)

Keshavarz, Mohammad H. [Department of Chemistry, Malek-ashtar University of Technology, Shahin-shahr P. O. Box 83145/115 (Iran); Tehrani, Masoud K. [Department of Physics, Malek-ashtar University of Technology, Shahin-shahr P. O. Box 83145/115 (Iran)

2007-04-15

A new correlation is introduced for desk calculation of gas phase heat of formation of aromatic energetic compounds that contain the elements of carbon, hydrogen, nitrogen and oxygen. Predicted gas phase heats of formation for 26 energetic compounds have a root mean square of deviation from experiment of 20.67 kJ/mol, which is in good agreement with respect to measured values of oxygen-lean and oxygen-rich aromatic energetic compounds. (Abstract Copyright [2007], Wiley Periodicals, Inc.)

New insights in third phase formation in the U(VI)-HNO3, TBP-alkane system

International Nuclear Information System (INIS)

Jensen, M. P.; Chiarizia, R.; Ferraro, J. R.; Borkowski, M.; Nash, K. L.; Thiyagarajan, P.; Littrell, K. C.

2001-01-01

In this work, the system U(VI)-HNO 3 -tributylphosphate (TBP)-n-dodecane has been revisited with the objective of gaining coordination chemistry and structural information on the species that are formed in the organic phase before and after third phase formation. Chemical analyses, spectroscopic and EXAFS data indicate that U(VI) is extracted as the UO 2 (NO 3 ) 2 · 2TBP adduct, while the third phase species has the composition UO 2 (NO 3 ) 2 · 2TBP · HNO 3 . Small-angle neutron scattering (SANS) data reveal the presence in the organic phase, both before and after phase splitting, of ellipsoidal aggregates whose formation seems to depend more on the extraction of HNO 3 than that of U(VI)

Kinetics and mechanism of solid-phase reactions of formation of yttrium ferrite with garnet structure

Energy Technology Data Exchange (ETDEWEB)

Pashchenko, V P; Yakushevskaya, F T; Chalyi, V P

1977-04-01

The perovskite phase is formed in the process of ferrogarnet formation both from the mixture of Y and Fe oxides and from mutually precipitated carbonates. The amount of the perovskite phase decreases with increasing duration of annealing. The process of the ferritoformation in the investigated systems can be presented as isovalent cationic substitution on the basis of the crystalline structure of Y/sub 2/O/sub 3/ with the formation of the perovskite structure. When the Fe concentration in orthoferrite increases, the phase with a garnet structure is formed.

Polymorphism and mesomorphism of oligomeric surfactants: effect of the degree of oligomerization.

Science.gov (United States)

Jurašin, D; Pustak, A; Habuš, I; Šmit, I; Filipović-Vinceković, N

2011-12-06

A series of cationic oligomeric surfactants (quaternary dodecyldimethylammonium ions with two, three, or four chains connected by an ethylene spacer at the headgroup level, abbreviated as dimer, trimer, and tetramer) were synthesized and characterized. The influence of the degree of oligomerization on their polymorphic and mesomorphic properties was investigated by means of X-ray diffraction, polarizing optical microscopy, thermogravimetry, and differential scanning calorimetry. All compounds display layered arrangements with interdigitated dodecyl chains. The increase in the degree of oligomerization increases the interlayer distance and decreases the ordering in the solid phase; whereas the dimer sample is fully crystalline with well-developed 3D ordering and the trimer and tetramer crystallize as highly ordered crystal smectic phases. The number of thermal phase transitions and sequence of phases are markedly affected by the number of dodecyl chains. Anhydrous samples exhibit polymorphism and thermotropic mesomorphism of the smectic type, with the exception of the tetramer that displays only transitions at higher temperature associated with decomposition and melting. All hydrated compounds form lyotropic mesophases showing reversible phase transitions upon heating and cooling. The sequence of liquid-crystalline phases for the dimer, typical of concentrated ionic surfactant systems, comprises a hexagonal phase at lower temperatures and a smectic phase at higher temperatures. In contrast, the trimer and tetramer reveal textures of the hexagonal phase. © 2011 American Chemical Society

Simulating the formation and evolution of galaxies: multi-phase description of the interstellar medium, star formation, and energy feedback

Science.gov (United States)

Merlin, E.; Chiosi, C.

2007-10-01

Context: Modelling the gaseous component of the interstellar medium (ISM) by Smoothed Particles Hydrodynamics in N-Body simulations (NB-TSPH) is still very crude when compared to the complex real situation. In the real ISM, many different and almost physically decoupled components (phases) coexist for long periods of time, and since they spread over wide ranges of density and temperature, they cannot be correctly represented by a unique continuous fluid. This would influence star formation which is thought to take place in clumps of cold, dense, molecular clouds, embedded in a warmer, neutral medium, that are almost freely moving throughout the tenuous hot ISM. Therefore, assuming that star formation is simply related to the gas content without specifying the component in which this is both observed and expected to occur may not be physically sound. Aims: We consider a multi-phase representation of the ISM in NB-TSPH simulations of galaxy formation and evolution with particular attention to the case of early-type galaxies. Methods: Cold gas clouds are described by the so-called sticky particles algorithm. They can freely move throughout the hot ISM medium; stars form within these clouds and the mass exchange among the three baryonic phases (hot gas, cold clouds, stars) is governed by radiative and Compton cooling and energy feedback by supernova (SN) explosions, stellar winds, and UV radiation. We also consider thermal conduction, cloud-cloud collisions, and chemical enrichment. Results: Our model agrees with and improves upon previous studies on the same subject. The results for the star formation rate agree with recent observational data on early-type galaxies. Conclusions: These models lend further support to the revised monolithic scheme of galaxy formation, which has recently been strengthened by high redshift data leading to the so-called downsizing and top-down scenarios.

Magnesium nitride phase formation by means of ion beam implantation technique

International Nuclear Information System (INIS)

Hoeche, Daniel; Blawert, Carsten; Cavellier, Matthieu; Busardo, Denis; Gloriant, Thierry

2011-01-01

Nitrogen implantation technique (Hardion + ) has been applied in order to modify the surface properties of magnesium and Mg-based alloys (AM50, AZ31). Nitrogen ions with an energy of approximately 100 keV were used to form the Mg 3 N 2 phase leading to improved surface properties. The samples were investigated using various characterization methods. Mechanical properties have been tested by means of nanoindention, the electrochemical behavior was measured by potentiodynamic polarization and impedance spectroscopy, phase formation by using grazing incidence Xray diffraction, the chemical state was determined by means of Xray induced photoelectron spectroscopy (XPS) and depth profiling by using secondary ions mass spectroscopy (SIMS). Additionally, the results were compared to calculated depth profiles using SRIM2008. The correlation of the results shows the nitride formation behavior to a depth of about 600 nm.

640 Gbit/s RZ-to-NRZ format conversion based on optical phase filtering

DEFF Research Database (Denmark)

Maram, Reza; Kong, Deming; Galili, Michael

2014-01-01

We propose a novel approach for all optical RZ-to-NRZ conversion based on optical phase filtering. The proposed concept is experimentally validated through format conversion of a 640 Gbit/s coherent RZ signal to NRZ signal using a simple phase filter implemented by a commercial optical waveshaper....

Fundamental thermochemical properties of amino acids: gas-phase and aqueous acidities and gas-phase heats of formation.

Science.gov (United States)

Stover, Michele L; Jackson, Virgil E; Matus, Myrna H; Adams, Margaret A; Cassady, Carolyn J; Dixon, David A

2012-03-08

The gas-phase acidities of the 20 L-amino acids have been predicted at the composite G3(MP2) level. A broad range of structures of the neutral and anion were studied to determine the lowest energy conformer. Excellent agreement is found with the available experimental gas-phase deprotonation enthalpies, and the calculated values are within experimental error. We predict that tyrosine is deprotonated at the CO(2)H site. Cysteine is predicted to be deprotonated at the SH but the proton on the CO(2)H is shared with the S(-) site. Self-consistent reaction field (SCRF) calculations with the COSMO parametrization were used to predict the pK(a)'s of the non-zwitterion form in aqueous solution. The differences in the non-zwitterion pK(a) values were used to estimate the free energy difference between the zwitterion and nonzwitterion forms in solution. The heats of formation of the neutral compounds were calculated from atomization energies and isodesmic reactions to provide the first reliable set of these values in the gas phase. Further calculations were performed on five rare amino acids to predict their heats of formation, acidities, and pK(a) values.

Coarsening and pattern formation during true morphological phase separation in unstable thin films under gravity

Science.gov (United States)

Kumar, Avanish; Narayanam, Chaitanya; Khanna, Rajesh; Puri, Sanjay

2017-12-01

We address in detail the problem of true morphological phase separation (MPS) in three-dimensional or (2 +1 )-dimensional unstable thin liquid films (>100 nm) under the influence of gravity. The free-energy functionals of these films are asymmetric and show two points of common tangency, which facilitates the formation of two equilibrium phases. Three distinct patterns formed by relative preponderance of these phases are clearly identified in "true MPS". Asymmetricity induces two different pathways of pattern formation, viz., defect and direct pathway for true MPS. The pattern formation and phase-ordering dynamics have been studied using statistical measures such as structure factor, correlation function, and growth laws. In the late stage of coarsening, the system reaches into a scaling regime for both pathways, and the characteristic domain size follows the Lifshitz-Slyozov growth law [L (t ) ˜t1 /3] . However, for the defect pathway, there is a crossover of domain growth behavior from L (t ) ˜t1 /4→t1 /3 in the dynamical scaling regime. We also underline the analogies and differences behind the mechanisms of MPS and true MPS in thin liquid films and generic spinodal phase separation in binary mixtures.

Keeping a Step Ahead: formative phase of a workplace intervention trial to prevent obesity.

Science.gov (United States)

Zapka, Jane; Lemon, Stephenie C; Estabrook, Barbara B; Jolicoeur, Denise G

2007-11-01

Ecological interventions hold promise for promoting overweight and obesity prevention in worksites. Given the paucity of evaluative research in the hospital worksite setting, considerable formative work is required for successful implementation and evaluation. This paper describes the formative phases of Step Ahead, a site-randomized controlled trial of a multilevel intervention that promotes physical activity and healthy eating in six hospitals in central Massachusetts. The purpose of the formative research phase was to increase the feasibility, effectiveness, and likelihood of sustainability of the intervention. The Step Ahead ecological intervention approach targets change at the organization, interpersonal work environment, and individual levels. The intervention was developed using fundamental steps of intervention mapping and important tenets of participatory research. Formative research methods were used to engage leadership support and assistance and to develop an intervention plan that is both theoretically and practically grounded. This report uses observational data, program minutes and reports, and process tracking data. Leadership involvement (key informant interviews and advisory boards), employee focus groups and advisory boards, and quantitative environmental assessments cultivated participation and support. Determining multiple foci of change and designing measurable objectives and generic assessment tools to document progress are complex challenges encountered in planning phases. Multilevel trials in diverse organizations require flexibility and balance of theory application and practice-based perspectives to affect impact and outcome objectives. Formative research is an essential component.

Effect of lead addition on the formation of superconducting phases in Bi-Sr-Ca-Cu-O ceramics

International Nuclear Information System (INIS)

Martinelli, A.E.

1991-01-01

Superconducting ceramics with starting composition Bi 2 - x Pb x Sr 2 Ca 2 Cu 3 O y (0,0 ≤ X ≤ 0,6) were prepared in order to investigate the effects of partial substitution of Pb for Bi and sintering time and atmosphere in the formation of superconducting phases. For all samples X-ray diffraction analyses were performed to estimate the amount of superconducting phases; superconductivity was analysed by dc electrical resistance and ac magnetic susceptibility measurements. The main results show that: a) the longer the sintering time (up to 168 h), the larger the volume fraction of superconducting phases with critical temperature (T c ) greater than the temperature of nitrogen liquefaction; b) by partially substituting Pb for Bi it is possible to restrain the formation of 2212 phase (T c = 80 K) and to enhance the amount of 2223 phase (T c = 105 K); C) a heat treatment under oxygen atmosphere before sintering enhances the formation of 2223 phase. (author)

The sensitivities of in cloud and cloud top phase distributions to primary ice formation in ICON-LEM

Science.gov (United States)

Beydoun, H.; Karrer, M.; Tonttila, J.; Hoose, C.

2017-12-01

Mixed phase clouds remain a leading source of uncertainty in our attempt to quantify cloud-climate and aerosol-cloud climate interactions. Nevertheless, recent advances in parametrizing the primary ice formation process, high resolution cloud modelling, and retrievals of cloud phase distributions from satellite data offer an excellent opportunity to conduct closure studies on the sensitivity of the cloud phase to microphysical and dynamical processes. Particularly, the reliability of satellite data to resolve the phase at the top of the cloud provides a promising benchmark to compare model output to. We run large eddy simulations with the new ICOsahedral Non-hydrostatic atmosphere model (ICON) to place bounds on the sensitivity of in cloud and cloud top phase to the primary ice formation process. State of the art primary ice formation parametrizations in the form of the cumulative ice active site density ns are implemented in idealized deep convective cloud simulations. We exploit the ability of ICON-LEM to switch between a two moment microphysics scheme and the newly developed Predicted Particle Properties (P3) scheme by running our simulations in both configurations for comparison. To quantify the sensitivity of cloud phase to primary ice formation, cloud ice content is evaluated against order of magnitude changes in ns at variable convective strengths. Furthermore, we assess differences between in cloud and cloud top phase distributions as well as the potential impact of updraft velocity on the suppression of the Wegener-Bergeron-Findeisen process. The study aims to evaluate our practical understanding of primary ice formation in the context of predicting the structure and evolution of mixed phase clouds.

Effect of Fe and Zr additions on ω phase formation in β-type Ti-Mo alloys

International Nuclear Information System (INIS)

Min, X.H.; Emura, S.; Zhang, L.; Tsuzaki, K.

2008-01-01

The effect of 1% Fe and/or 5% Zr (mass%) additions on ω phase formation was investigated for the Ti-15Mo alloy by means of X-ray diffraction analysis and hardness testing. Upon water quenching following solution treatment in the β phase region, the athermal ω phase formation could not be observed in all the alloys, regardless of Fe and Zr additions. The lattice parameter of the β phase decreases with Fe addition, while it increases with Zr addition. Solid solution strengthening by Fe and Zr is not recognized for the β phase. The isothermal ω phase formed after aging at 723 K and 773 K for 3.6 ks, which results in a decrease in the lattice parameter of the β phase and an increase in the hardness. The isothermal ω phase formation is suppressed with Fe and/or Zr additions. This is interpreted as the consequence of the increase in the average value of the bond order (Bo) for the Ti-15Mo-5Zr and Ti-15Mo-5Zr-1Fe alloys, and of the decrease in the average value of the metal d-orbital energy level (Md) for the Ti-15Mo-1Fe alloy. In addition, the degree of the suppression of isothermal ω phase can be predicted by the average values of Bo and Md

Synthesis, characterization and formation mechanism of metastable phase VO2(A) nanorods

International Nuclear Information System (INIS)

Cheng, X.H.; Xu, H.F.; Wang, Z.Z.; Zhu, K.R.; Li, G.; Jin, Shaowei

2013-01-01

Graphical abstract: - Highlights: • Pure phases of VO 2 (B) and VO 2 (A) were prepared by a facile hydrothermal method. • Belt-like particles prepared at 180 °C was indexed as monoclinic VO 2 (B) phase. • Rod-like particles prepared at 230 °C was indexed as tetragonal VO 2 (A) phase. • VO 2 (A) nanorods resulted from VO 2 (B) nanobelts by assembly and crystal adjustment. - Abstract: Pure phase VO 2 (A) nanorods were synthesized via the reduction of V 2 O 5 by oxalic acid during the hydrothermal treatment. Two sets of samples were prepared by varying both system temperature and reaction time under a filling ratio of 0.40 for observing the formation and evolution of VO 2 (A) nanorods. Structures were characterized by X-ray diffraction, scanning and transmission electron microscopies, respectively. It was found that VO 2 (B) was firstly formed and then transformed into VO 2 (A) as the increasing system temperature or extending reaction time. An assembling and following crystal adjustment was proposed for explanation the formation process of VO 2 (A) from VO 2 (B). For VO 2 (A) nanorods, the phase transition temperature of 169.7 °C was higher than that of the VO 2 (A) bulk, it might be ascribed to the lower crystallinity or nonstoichiometry in VO 2 (A) nanorods. VO 2 nanostructures with controllable phases and properties should find their promising applications in a single VO 2 nanodevice

Formation of tungsten blue oxide and its phase constitution

International Nuclear Information System (INIS)

Zou, Z.; Wu, E.; Tan, A.; Qian, C.

1984-01-01

By means of X-ray diffraction structure analysis, SEM observation, chemical analysis and particle specific surface analysis etc., an investigation was made in order to determine the regularity of tungsten blue oxide formation during reductional calcine process of APT. It was found that the oxygen index (OI) decreased continuously with increasing calcine temperature. The decrease rate of OI variated as the calcine atmosphere being changed, the stronger the reductivity of the atmosphere is, the more OI decreases. The deammonia-dewater process and the phase constitution variation during calcine was studied, some idea for description of phase transformation path was suggested. It was found that the most important parameter affecting phase constitution and transformation is calcine temperature. At the temperature lower than 450 0 C, the main formed phase was ATB, while at higher temperature, the different phase like W/sub 20/O/sub 58/, WO/sub 3/ etc., could be formed by different ways depending on the atmosphere reductivity. The composition and the OI of ATB are changeable. An experiment for some blue oxides reduction at low temperature was carried out. It was found that OI and the constitution of blue oxide strongly affected the particle size of the formed W-powder

From phase to microphase separation in flocking models: the essential role of nonequilibrium fluctuations.

Science.gov (United States)

Solon, Alexandre P; Chaté, Hugues; Tailleur, Julien

2015-02-13

We show that the flocking transition in the Vicsek model is best understood as a liquid-gas transition, rather than an order-disorder one. The full phase separation observed in flocking models with Z(2) rotational symmetry is, however, replaced by a microphase separation leading to a smectic arrangement of traveling ordered bands. Remarkably, continuous deterministic descriptions do not account for this difference, which is only recovered at the fluctuating hydrodynamics level. Scalar and vectorial order parameters indeed produce different types of number fluctuations, which we show to be essential in selecting the inhomogeneous patterns. This highlights an unexpected role of fluctuations in the selection of flock shapes.

Phase separation like dynamics during Myxococcus xanthus fruiting body formation

Science.gov (United States)

Liu, Guannan; Thutupalli, Shashi; Wigbers, Manon; Shaevitz, Joshua

2015-03-01

Collective motion exists in many living organisms as an advantageous strategy to help the entire group with predation, forage, and survival. However, the principles of self-organization underlying such collective motions remain unclear. During various developmental stages of the soil-dwelling bacterium, Myxococcus xanthus, different types of collective motions are observed. In particular, when starved, M. xanthus cells eventually aggregate together to form 3-dimensional structures (fruiting bodies), inside which cells sporulate in response to the stress. We study the fruiting body formation process as an out of equilibrium phase separation process. As local cell density increases, the dynamics of the aggregation M. xanthus cells switch from a spatio-temporally random process, resembling nucleation and growth, to an emergent pattern formation process similar to a spinodal decomposition. By employing high-resolution microscopy and a video analysis system, we are able to track the motion of single cells within motile collective groups, while separately tuning local cell density, cell velocity and reversal frequency, probing the multi-dimensional phase space of M. xanthus development.

σ and η Phase formation in advanced polycrystalline Ni-base superalloys

Energy Technology Data Exchange (ETDEWEB)

Antonov, Stoichko, E-mail: santonov@hawk.iit.edu [Illinois Institute of Technology, 10 W. 32nd Street, Chicago, IL 60616 (United States); Huo, Jiajie; Feng, Qiang [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Isheim, Dieter; Seidman, David N. [Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, IL 60208 (United States); Northwestern University Center for Atom Probe Tomography (NUCAPT), 2220 Campus Drive, Evanston, IL 60208 (United States); Helmink, Randolph C.; Sun, Eugene [Rolls-Royce Corporation, 450 S. Meridian Street, Indianapolis, IN 46225 (United States); Tin, Sammy [Illinois Institute of Technology, 10 W. 32nd Street, Chicago, IL 60616 (United States)

2017-02-27

In polycrystalline Ni-base superalloys, grain boundary precipitation of secondary phases can be significant due to the effects they pose on the mechanical properties. As new alloying concepts for polycrystalline Ni-base superalloys are being developed to extend their temperature capability, the effect of increasing levels of Nb alloying additions on long term phase stability and the formation of topologically close packed (TCP) phases needs to be studied. Elevated levels of Nb can result in increased matrix supersaturation and promote the precipitation of secondary phases. Long term thermal exposures on two experimental powder processed Ni-base superalloys containing various levels of Nb were completed to assess the stability and precipitation of TCP phases. It was found that additions of Nb promoted the precipitation of η-Ni{sub 6}AlNb along the grain boundaries in powder processed, polycrystalline Ni-base superalloys, while reduced Nb levels favored the precipitation of blocky Cr and Mo – rich σ phase precipitates along the grain boundary. Evaluation of the thermodynamic stability of these two phases in both alloys using Thermo-calc showed that while σ phase predictions are fairly accurate, predictions of the η phase are limited.

Liquid phase stabilization versus bubble formation at a nanoscale curved interface

Science.gov (United States)

Schiffbauer, Jarrod; Luo, Tengfei

2018-03-01

We investigate the nature of vapor bubble formation near a nanoscale-curved convex liquid-solid interface using two models: an equilibrium Gibbs model for homogenous nucleation, and a nonequilibrium dynamic van der Waals-diffuse-interface model for phase change in an initially cool liquid. Vapor bubble formation is shown to occur for sufficiently large radius of curvature and is suppressed for smaller radii. Solid-fluid interactions are accounted for and it is shown that liquid-vapor interfacial energy, and hence Laplace pressure, has limited influence over bubble formation. The dominant factor is the energetic cost of creating the solid-vapor interface from the existing solid-liquid interface, as demonstrated via both equilibrium and nonequilibrium arguments.

Novel criterion for formation of metastable phase from undercooled melt

International Nuclear Information System (INIS)

Kuribayashi, Kazuhiko; Nagashio, Kosuke; Niwata, Kenji; Kumar, M.S. Vijaya; Hibiya, Taketoshi

2007-01-01

Undercooling a melt facilitates the preferential nucleation of a metastable phase. In the present study, the formation of metastable phases from undercooled melts was considered from the viewpoint of the competitive nucleation criterion. The classical nucleation theory shows us that the most critical factor for forming a critical nucleus is the interface free energy σ. Furthermore, Spaepen's negentropic model on σ generated the role of the scaling factor α that depends on the polyhedral order in the liquid and solid phases prominent in simple liquids such as the melt of monoatomic metals. In ionic materials such as oxides, however, in which oxygen polyhedrons including a cation at their center are the structural units both in the solid and liquid phases, the entropy of fusion, rather than α, can be expected to become dominant in the determination of σ. In accordance with this idea, using REFeO 3 as the model material (where RE denotes rare-earth elements) the entropy-undercooling regime criterion was proposed and verified

Phase transitions during formation of Ag nanoparticles on In{sub 2}S{sub 3} precursor layers

Energy Technology Data Exchange (ETDEWEB)

Liu, Yang, E-mail: yang.liu@helmholtz-berlin.de; Fu, Yanpeng; Dittrich, Thomas; Sáez-Araoz, Rodrigo; Schmid, Martina; Hinrichs, Volker; Lux-Steiner, Martha Ch.; Fischer, Christian-Herbert

2015-09-01

Phase transitions have been investigated for silver deposition onto In{sub 2}S{sub 3} precursor layers by spray chemical vapor deposition from a trimethylphosphine (hexafluoroacetylacetonato) silver (Ag(hfacac)(PMe{sub 3})) solution. The formation of Ag nanoparticles (Ag NPs) on top of the semiconductor layer set on concomitant with the formation of AgIn{sub 5}S{sub 8}. The increase of the diameter of Ag NPs was accompanied by the evolution of orthorhombic AgInS{sub 2}. The formation of Ag{sub 2}S at the interface between Ag NPs and the semiconductor layer was observed. Surface photovoltage spectroscopy indicated charge separation and electronic transitions in the ranges of corresponding band gaps. The phase transition approach is aimed to be applied for the formation of plasmonic nanostructures on top of extremely thin semiconducting layers. - Highlights: • Silver nanoparticles were deposited onto In{sub 2}S{sub 3} precursor layer by spray pyrolysis. • The silver nanoparticle size and density could be controlled by deposition time. • Phase transitions during deposition and material properties were investigated. • The layers still show semiconducting properties after phase transitions. • Plasmonic absorption enhancement has been demonstrated.

Acid-base equilibrium. A thermodynamic study of formation and stability of the Bi-2223 phase

International Nuclear Information System (INIS)

Xi, Z.; Zhou, L.

1993-01-01

A general acid-base equilibrium theory was proposed to explain the formation and stability of the Bi-2223 phase based on the Lewis acid base theory and principle of metallurgical physical chemistry. The acid-base nature of oxide was defined according to the electrostatic force between cation and oxygen anion. A series of experimental facts were systematically explained based on the theory: substitution of Bi for Ca in the Pb-free 2223 phase, and the effect of substitution of the high-valent cation for Bi 3+ ; oxygen-pressure atmosphere, and the heat-schocking technique on the formation and stability of the 2223 phase. 14 refs., 2 tabs

Complex 3D Vortex Lattice Formation by Phase-Engineered Multiple Beam Interference

Directory of Open Access Journals (Sweden)

Jolly Xavier

2012-01-01

Full Text Available We present the computational results on the formation of diverse complex 3D vortex lattices by a designed superposition of multiple plane waves. Special combinations of multiples of three noncoplanar plane waves with a designed relative phase shift between one another are perturbed by a nonsingular beam to generate various complex 3D vortex lattice structures. The formation of complex gyrating lattice structures carrying designed vortices by means of relatively phase-engineered plane waves is also computationally investigated. The generated structures are configured with both periodic as well as transversely quasicrystallographic basis, while these whirling complex lattices possess a long-range order of designed symmetry in a given plane. Various computational analytical tools are used to verify the presence of engineered geometry of vortices in these complex 3D vortex lattices.

Gas phase enthalpies of formation of nitrobenzamides using combustion calorimetry and thermal analysis

International Nuclear Information System (INIS)

Ximello, Arturo; Flores, Henoc; Rojas, Aarón; Adriana Camarillo, E.; Patricia Amador, M.

2014-01-01

Graphical abstract: - Highlights: • Formation enthalpies of the nitrobenzamides were derived from combustion calorimetry. • Enthalpies of vaporisation and sublimation were calculated by thermogravimetry. • From gas phase enthalpies of formation the stability of the isomers is studied. • Stability of isomers is not driven by a steric hindrance between functional groups. - Abstract: The standard molar energies of combustion of 2-nitrobenzamide, 3-nitrobenzamide and 4-nitrobenzamide were determined with an isoperibolic, static-bomb, combustion calorimeter. From the combustion results, the standard molar enthalpies of combustion and formation for these compounds in the condensed phase at T = 298.15 K were derived. Subsequently, to determine the enthalpies of sublimation, the vapour pressure data as a function of the temperature for the compounds under investigation were estimated using thermogravimetry by applying Langmuir’s equation, and the enthalpies of vaporisation were derived. Standard enthalpies of fusion were measured by differential scanning calorimetry then added to those of vaporisation to obtain reliable results for the enthalpy of sublimation. From the combustion and sublimation data, the gas phase enthalpies of formation were determined to be (−138.9 ± 3.5) kJ · mol −1 , (−122.9 ± 2.9) kJ · mol −1 and (−108.5 ± 3.7) kJ · mol −1 for the ortho, meta and para isomers of nitrobenzamide, respectively. The meaning of these results with regard to the enthalpic stability of these molecular structures is discussed herein

Intradomain phase transitions in flexible block copolymers with self-aligning segments

Science.gov (United States)

Burke, Christopher J.; Grason, Gregory M.

2018-05-01

We study a model of flexible block copolymers (BCPs) in which there is an enlthalpic preference for orientational order, or local alignment, among like-block segments. We describe a generalization of the self-consistent field theory of flexible BCPs to include inter-segment orientational interactions via a Landau-de Gennes free energy associated with a polar or nematic order parameter for segments of one component of a diblock copolymer. We study the equilibrium states of this model numerically, using a pseudo-spectral approach to solve for chain conformation statistics in the presence of a self-consistent torque generated by inter-segment alignment forces. Applying this theory to the structure of lamellar domains composed of symmetric diblocks possessing a single block of "self-aligning" polar segments, we show the emergence of spatially complex segment order parameters (segment director fields) within a given lamellar domain. Because BCP phase separation gives rise to spatially inhomogeneous orientation order of segments even in the absence of explicit intra-segment aligning forces, the director fields of BCPs, as well as thermodynamics of lamellar domain formation, exhibit a highly non-linear dependence on both the inter-block segregation (χN) and the enthalpy of alignment (ɛ). Specifically, we predict the stability of new phases of lamellar order in which distinct regions of alignment coexist within the single mesodomain and spontaneously break the symmetries of the lamella (or smectic) pattern of composition in the melt via in-plane tilt of the director in the centers of the like-composition domains. We further show that, in analogy to Freedericksz transition confined nematics, the elastic costs to reorient segments within the domain, as described by the Frank elasticity of the director, increase the threshold value ɛ needed to induce this intra-domain phase transition.

The kinetics of the β→α transformation in unalloyed plutonium after partial formation of the β phase

International Nuclear Information System (INIS)

Robinson, A.C.; Stacey, R.J.

1976-01-01

The kinetics of the isothermal β→α transformation after complete and only partial formation of the β phase in unalloyed plutonium containing about 900 ppm of impurity are reported and compared with previously published and conventionally accepted β→α transformation kinetics after complete formation of the β phase in this material. In these experiments the heating was provided by constant temperature oil baths and the transformations were monitored by electrical resistance measurements on 0.63 mm diameter wire samples at temperatures ranging from -65 0 C to +75 0 C. After complete formation of the β phase in the plutonium used in these experiments the kinetics of the β→α transformation were in general agreement with previously published data, although the present transformations were slower than reported by previous workers. After only partial formation of the β phase the subsequent β→α transformations were found to be very fast and to be characterised by zero or very short incubation periods, rapid rates of transformation and a final equilibrium consisting of more than 90% β phase. (Auth.)

Systematic Search for Chemical Reactions in Gas Phase Contributing to Methanol Formation in Interstellar Space.

Science.gov (United States)

Gamez-Garcia, Victoria G; Galano, Annia

2017-10-05

A massive search for chemical routes leading to methanol formation in gas phase has been conducted using computational chemistry, at the CBS-QB3 level of theory. The calculations were performed at five different temperatures (100, 80, 50, 20, and 10 K) and at three pressures (0.1, 0.01, and 0.001 atm) for each temperature. The search was focused on identifying reactions with the necessary features to be viable in the interstellar medium (ISM). A searching strategy was applied to that purpose, which allowed to reduce an initial set of 678 possible reactions to a subset of 11 chemical routes that are recommended, for the first time, as potential candidates for contributing to methanol formation in the gas phase of the ISM. They are all barrier-less, and thus they are expected to take place at collision rates. Hopefully, including these reactions in the currently available models, for the gas-phase methanol formation in the ISM, would help improving the predicted fractional abundance of this molecule in dark clouds. Further investigations, especially those dealing with grain chemistry and electronic excited states, would be crucial to get a complete picture of the methanol formation in the ISM.

Regularities of texture formation in alloys undergoing phase transformations during heat treatment and plastic working

International Nuclear Information System (INIS)

Ageev, N.V.; Babarehko, A.A.

1983-01-01

Peculiarities of texture formation in metals undergoing phase transformations in the temperature range of heat treatment and hot working are investigated theoretically and experimentally. A low-temperature phase after hot working is shown to inherite a high-temperature phase texture due to definite orientation conformity during phase transformation. Strengthened heat and thermomechanical treatments, as a rule, do not destroy material texture but change it

Formation of omega phase under shock pressure, hydrostatic pressure and irradiation

International Nuclear Information System (INIS)

Dey, G.K.

2016-01-01

The omega transformation is one of the most intriguing phase transformations. The aspects which make it unique and interesting are the facts that this phase can form from two different parent phases viz. the alpha phase and the beta phase. The alpha to omega transformation has been observed under shock and static pressure and the mechanism involved has been studied in detail. Starting from the nucleation stage to the completion of the transformation, various interesting aspects of the mechanism of transformation has emerged in these studies. Although the parent and product phases are same under these conditions of transformation, a variation in the morphology and the kinetics of the product phase indicate different pathways for alpha to omega transformations. Similarly, the beta to omega transformation is also replete with several interesting features. This transformation can occur under application of pressure, thermal activation and also under irradiation. Here again the morphology of the product phase, the nucleation mechanisms and the kinetics of the phase transformation depend on the path of transformation, though the parent and product phases are same in each path. This presentation highlights the formation of the omega phase under different activations including the ones in extreme conditions in pure Zr and Zr based alloys. Theoretical aspects of the feasibility, pathways and kinetics of the transformations are also emphasized. (author)

Bit-rate-transparent optical RZ-to-NRZ format conversion based on linear spectral phase filtering

DEFF Research Database (Denmark)

Maram, Reza; Da Ros, Francesco; Guan, Pengyu

2017-01-01

We propose a novel and strikingly simple design for all-optical bit-rate-transparent RZ-to-NRZ conversion based on optical phase filtering. The proposed concept is experimentally validated through format conversion of a 640 Gbit/s coherent RZ signal to NRZ signal.......We propose a novel and strikingly simple design for all-optical bit-rate-transparent RZ-to-NRZ conversion based on optical phase filtering. The proposed concept is experimentally validated through format conversion of a 640 Gbit/s coherent RZ signal to NRZ signal....

Formation of U(IV) Nanoparticles and Their Growth Mechanism in Mildly Acidic Aqueous Phases

Energy Technology Data Exchange (ETDEWEB)

Cha, Wan Sik; Kim, Sun Tae; Cho, Hye Ryun; Jung, Euo Chang [KAERI, Daejeon (Korea, Republic of)

2016-05-15

Previous studies suggest that U(IV) nanoparticle (NP) formation is one of key steps in mineralization or immobilization of uranium which can be mediated either by microbes or by abiotic geochemical reactions. Colloidal NPs in a groundwater system are potential carrier phases influencing RN migration in subsurface environment. However, the mechanism of U(IV) NP formation and the potential reaction intermediates during this solid phase formation process have not been elucidated in detail so far. In this study we attempted to examine the U(IV) nanoparticle formation reactions preceded by the hydrolysis of U{sup 4+} at different pHs, concentrations and temperatures. The kinetics of U(IV) NP formation from dissolved U(IV) species was monitored under mildly acidic conditions (pH 2 ∼ 3) mainly by using UV-Vis absorption spectrophotometry. Dynamic light scattering (DLS) analysis, nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM) were used to characterize the NPs produced during the reactions. The results demonstrate that the U(IV) NP formation process is very sensitive toward temperature variation. The main outcome of this study is the discovery of the autocatalytic nature of U(IV) NP formation from the supersaturated U(OH){sup 3+} solution in a mildly acidic aqueous solution. The structure of reaction intermediates is proposed to contain oxide linkage. In the presentation the proposed mechanism of the U(IV) NP formation reaction and the properties of primary NPs and their clusters will be discussed in detail.

Liquid phase diffusion bonding of A1070 by using metal formate coated Zn sheet

Science.gov (United States)

Ozawa, K.; Koyama, S.; shohji, I.

2017-05-01

Aluminium alloy have high strength and easily recycle due to its low melting point. Therefore, aluminium is widely used in the manufacturing of cars and electronic devices. In recent years, the most common way for bonding aluminium alloy is brazing and friction stir welding. However, brazing requires positional accuracy and results in the formation of voids by the flax residue. Moreover, aluminium is an excellent heat radiating and electricity conducting material; therefore, it is difficult to bond together using other bonding methods. Because of these limitations, liquid phase diffusion bonding is considered to the suitable method for bonding aluminium at low temperature and low bonding pressure. In this study, the effect of metal formate coating processing of zinc surface on the bond strength of the liquid phase diffusion bonded interface of A1070 has been investigated by SEM observation of the interfacial microstructures and fractured surfaces after tensile test. Liquid phase diffusion bonding was carried out under a nitrogen gas atmosphere at a bonding temperature of 673 K and 713 K and a bonding load of 6 MPa (bonding time: 15 min). As a result of the metal formate coating processing, a joint having the ultimate tensile strength of the base aluminium was provided. It is hypothesized that this is because metallic zinc is generated as a result of thermal decomposition of formate in the bonded interface at lower bonding temperatures.

Correlative theoretical and experimental investigation of the formation of AlYB_1_4 and competing phases

International Nuclear Information System (INIS)

Hunold, Oliver; Chen, Yen-Ting; Music, Denis; Baben, Moritz to; Achenbach, Jan-Ole; Keuter, Philipp; Schneider, Jochen M.; Persson, Per O. Å.; Primetzhofer, Daniel

2016-01-01

The phase formation in the boron-rich section of the Al-Y-B system has been explored by a correlative theoretical and experimental research approach. The structure of coatings deposited via high power pulsed magnetron sputtering from a compound target was studied using elastic recoil detection analysis, electron energy loss spectroscopy spectrum imaging, as well as X-ray and electron diffraction data. The formation of AlYB_1_4 together with the (Y,Al)B_6 impurity phase, containing 1.8 at. % less B than AlYB_1_4, was observed at a growth temperature of 800 °C and hence 600 °C below the bulk synthesis temperature. Based on quantum mechanical calculations, we infer that minute compositional variations within the film may be responsible for the formation of both icosahedrally bonded AlYB_1_4 and cubic (Y,Al)B_6 phases. These findings are relevant for synthesis attempts of all boron rich icosahedrally bonded compounds with the space group: Imma that form ternary phases at similar compositions.

Correlative theoretical and experimental investigation of the formation of AlYB{sub 14} and competing phases

Energy Technology Data Exchange (ETDEWEB)

Hunold, Oliver, E-mail: hunold@mch.rwth-aachen.de; Chen, Yen-Ting; Music, Denis; Baben, Moritz to; Achenbach, Jan-Ole; Keuter, Philipp; Schneider, Jochen M. [Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, D-52074 Aachen (Germany); Persson, Per O. Å. [Department of Physics, Chemistry and Biology (IFM), Linköping University, S-58183 Linköping (Sweden); Primetzhofer, Daniel [Department of Physics and Astronomy, Uppsala University, Lägerhyddsvägen 1, S-75120 Uppsala (Sweden)

2016-02-28

The phase formation in the boron-rich section of the Al-Y-B system has been explored by a correlative theoretical and experimental research approach. The structure of coatings deposited via high power pulsed magnetron sputtering from a compound target was studied using elastic recoil detection analysis, electron energy loss spectroscopy spectrum imaging, as well as X-ray and electron diffraction data. The formation of AlYB{sub 14} together with the (Y,Al)B{sub 6} impurity phase, containing 1.8 at. % less B than AlYB{sub 14}, was observed at a growth temperature of 800 °C and hence 600 °C below the bulk synthesis temperature. Based on quantum mechanical calculations, we infer that minute compositional variations within the film may be responsible for the formation of both icosahedrally bonded AlYB{sub 14} and cubic (Y,Al)B{sub 6} phases. These findings are relevant for synthesis attempts of all boron rich icosahedrally bonded compounds with the space group: Imma that form ternary phases at similar compositions.

Magnetic field effect on Gd2(MoO4)3 domain structure formation in the phase transformation range

International Nuclear Information System (INIS)

Flerova, S.A.; Tsinman, I.L.

1987-01-01

The behaviour of ferroelastic-ferroelectric domain structure of gadolinium molybdate crystal (GMO)during its formation in the magnetic field in the vicinity of phase transformation is studied.It is shown that the formation of domain structure in the presence of a temperature gradient occurs in the field of mechanical stresses whose mainly stretching effect is concentrated near phase boundaries.The magnetic field intensifies summary mechanical stresses where a domain structure in a ferroelectric phase is formed due to interaction with the elements of inhomogeneous and differently oriented currents near phase boundaries

NEPHELINE FORMATION STUDY FOR SLUDGE BATCH 4: PHASE 3 EXPERIMENTAL RESULTS

International Nuclear Information System (INIS)

Fox, K

2006-01-01

This Phase 3 study was undertaken to complement the previous phases of the nepheline formation studies1, 2 by continuing the investigation into the ability of the nepheline discriminator to predict the occurrence of nepheline crystallization in Sludge Batch 4 (SB4) glasses and into the impact of such phases on the durability of the SB4 glasses. The Phase 3 study had two primary objectives. The first was to continue to demonstrate the ability of the discriminator value to adequately predict the nepheline formation potential for specific glass systems of interest. The second was to generate additional data that have a high probability of supporting the SB4 variability study. To support these two objectives, sixteen glasses were selected based on the most recent SB4 compositional projection, Case 15C Blend 1.3 Four different frits were included, based on previous assessments of projected operating windows and melt rate,4, 5 with four WLs selected for each frit. Eight of these frit-sludge combinations covered WLs which tightly bound the nepheline discriminator value of 0.62, with the intent of refining this value to a level of confidence where it can be incorporated into offline administrative controls and/or the Process Composition Control System (PCCS) to support Slurry Mix Evaporator (SME) acceptability decisions. The remaining eight frit-sludge combinations targeted lower WLs (35 and 40%) and were prepared and analyzed to contribute needed data to the ComPro database6 to support a potential variability study for SB4

Propagation dynamics and X-pulse formation in phase-mismatched second-harmonic generation

International Nuclear Information System (INIS)

Valiulis, G.; Jukna, V.; Jedrkiewicz, O.; Clerici, M.; Rubino, E.; DiTrapani, P.

2011-01-01

This paper concerns the theoretical, numerical, and experimental study of the second-harmonic-generation (SHG) process under conditions of phase and group-velocity mismatch and aims to demonstrate the dimensionality transition of the SHG process caused by the change of the fundamental wave diameter. We show that SHG from a narrow fundamental beam leads to the spontaneous self-phase-matching process with, in addition, the appearance of angular dispersion for the off-axis frequency components generated. The angular dispersion sustains the formation of the short X pulse in the second harmonic (SH) and is recognized as three-dimensional (3D) dynamics. On the contrary, the large-diameter fundamental beam reduces the number of the degrees of freedom, does not allow the generation of the angular dispersion, and maintains the so-called one-dimensional (1D) SHG dynamics, where the self-phase-matching appears just for axial components and is accompanied by the shrinking of the SH temporal bandwidth, and sustains a long SH pulse formation. The transition from long SH pulse generation typical of the 1D dynamics to the short 3D X pulse is illustrated numerically and experimentally by changing the conditions from the self-defocusing to the self-focusing regime by simply tuning the phase mismatch. The numerical and experimental verification of the analytical results are also presented.

The study of membrane formation via phase inversion method by cloud point and light scattering experiment

Science.gov (United States)

Arahman, Nasrul; Maimun, Teuku; Mukramah, Syawaliah

2017-01-01

The composition of polymer solution and the methods of membrane preparation determine the solidification process of membrane. The formation of membrane structure prepared via non-solvent induced phase separation (NIPS) method is mostly determined by phase separation process between polymer, solvent, and non-solvent. This paper discusses the phase separation process of polymer solution containing Polyethersulfone (PES), N-methylpirrolidone (NMP), and surfactant Tetronic 1307 (Tet). Cloud point experiment is conducted to determine the amount of non-solvent needed on induced phase separation. Amount of water required as a non-solvent decreases by the addition of surfactant Tet. Kinetics of phase separation for such system is studied by the light scattering measurement. With the addition of Tet., the delayed phase separation is observed and the structure growth rate decreases. Moreover, the morphology of fabricated membrane from those polymer systems is analyzed by scanning electron microscopy (SEM). The images of both systems show the formation of finger-like macrovoids through the cross-section.

Double hydrogen bonded ferroelectric liquid crystals: A study of field induced transition (FiT)

Science.gov (United States)

Vijayakumar, V. N.; Madhu Mohan, M. L. N.

2009-12-01

A novel series of chiral hydrogen bonded liquid crystals have been isolated. Hydrogen bond was formed between chiral nonmesogen ingredient levo tartaric acid and mesogenic p-n-alkoxybenzoic acids. Phase diagram was constructed from the transition temperatures obtained by DSC and polarizing optical microscopic (POM) studies. Thermal and electrical properties exhibited by three complexes namely LTA+8BA, LTA+7BA and LTA+5BA were discussed. Salient feature of the present work was the observation of a reentrant smectic ordering in LTA+8BA complex designated as C r∗ phase. This reentrant phenomenon was confirmed by DSC thermograms, optical textures of POM and temperature variation of capacitance and dielectric loss studies. Tilt angle was measured in smectic C ∗ and reentrant smectic C r∗ phases. Another interesting feature of the present investigation was the observation of a field induced transition (FiT) in the LTA+ nBA homologous series. Three threshold field values were noticed which give rise to two new phases (E 1 and E 2) induced by electric field and on further enhancement of the applied field the mesogen behaves like an optical shutter. FiT is reversible in the sense that when applied field is removed the original texture was restored.

On the role of Nb in Z-phase formation in a 12% Cr steel

DEFF Research Database (Denmark)

Cipolla, L.; Danielsen, Hilmar Kjartansson; Di Nunzio, P.E.

2010-01-01

Z-phase precipitation in two model alloys, 12CrVNbN and 12CrVN, has been investigated. The alloys were aged up to 104 h and their precipitate evolution was followed by X-ray diffraction and transmission electron microscopy. The formation rate of Z-phase from vanadium-based nitrides, (V,Nb)N, in t...

Simulating the Phases of the Moon Shortly after Its Formation

Science.gov (United States)

Noordeh, Emil; Hall, Patrick; Cuk, Matija

2014-01-01

The leading theory for the origin of the Moon is the giant impact hypothesis, in which the Moon was formed out of the debris left over from the collision of a Mars sized body with the Earth. Soon after its formation, the orbit of the Moon may have been very different than it is today. We have simulated the phases of the Moon in a model for its…

Formation of residual NAPL in three-phase systems: Experiments and numerical simulations

NARCIS (Netherlands)

Hofstee, C.; Oostrom, M.

2002-01-01

The formation of residual, discontinuous nonaqueous phase liquids (NAPLs) in the vadose zone is a process that is not well understood. The simulators have conveniently implemented the Leverett concept (Leverett and Lewis, 1941) which states that in a water-wet porous media, when fluid wettabilities

Effect of phase formation on valence band photoemission and photoresonance study of Ti/Ni multilayers using synchrotron radiation

International Nuclear Information System (INIS)

Bhatt, Pramod; Chaudhari, S.M.

2006-01-01

This paper presents investigation of Ti-Ni alloy phase formation and its effect on valence band (VB) photoemission and photoresonance study of as-deposited as well as annealed Ti/Ni multilayers (MLs) up to 600 deg. C using synchrotron radiation. For this purpose [Ti (50 A)/Ni (50 A)]X 10 ML structures were deposited by using electron-beam evaporation technique under ultra-high vacuum (UHV) conditions. Formation of different phases of Ti-Ni alloy due to annealing treatment has been confirmed by the X-ray diffraction (XRD) technique. The XRD pattern corresponding as-deposited ML sample shows crystalline nature of both Ti and Ni deposited layers, whereas 300 deg. C annealed ML sample show solid-state reaction (SSR) leading to amorphization and subsequent recrystallisation at higher temperatures of annealing (≥400 deg. C) with the formation of TiNi, TiNi 3 and Ti 2 Ni alloy phases. The survey scans corresponding to 400, 500 and 600 deg. C annealed ML sample shows interdiffusion and intermixing of Ni atoms into Ti layers leading to chemical Ti-Ni alloys phase formation at interface. The corresponding recorded VB spectra using synchrotron radiation at 134 eV on as-deposited ML sample with successive sputtering shows alternately photoemission bands due to Ti 3d and Ni 3d, respectively, indicating there is no mixing of the consequent layers and any phase formation at the interface during deposition. However, ML samples annealed at higher temperatures of annealing, particularly at 400, 500 and 600 deg. C show a clear shift in Ni 3d band and its satellite peak position to higher BE side indicates Ti-Ni alloy phase formation. In addition to this, reduction of satellite peak intensity and Ni 3d density of states (DOS) near Fermi level is also observed due to Ti-Ni phase formation with higher annealing temperatures. The variable photon energy VB measurements on as-deposited and ML samples annealed at 400 deg. C confirms existence and BE position of observed Ni 3d satellite

Local structural ordering in surface-confined liquid crystals

Science.gov (United States)

Śliwa, I.; Jeżewski, W.; Zakharov, A. V.

2017-06-01

The effect of the interplay between attractive nonlocal surface interactions and attractive pair long-range intermolecular couplings on molecular structures of liquid crystals confined in thin cells with flat solid surfaces has been studied. Extending the McMillan mean field theory to include finite systems, it has been shown that confining surfaces can induce complex orientational and translational ordering of molecules. Typically, local smectic A, nematic, and isotropic phases have been shown to coexist in certain temperature ranges, provided that confining cells are sufficiently thick, albeit finite. Due to the nonlocality of surface interactions, the spatial arrangement of these local phases can display, in general, an unexpected complexity along the surface normal direction. In particular, molecules located in the vicinity of surfaces can still be organized in smectic layers, even though nematic and/or isotropic order can simultaneously appear in the interior of cells. The resulting surface freezing of smectic layers has been confirmed to occur even for rather weak surface interactions. The surface interactions cannot, however, prevent smectic layers from melting relatively close to system boundaries, even when molecules are still arranged in layers within the central region of the system. The internal interfaces, separating individual liquid-crystal phases, are demonstrated here to form fronts of local finite-size transitions that move across cells under temperature changes. Although the complex molecular ordering in surface confined liquid-crystal systems can essentially be controlled by temperature variations, specific thermal properties of these systems, especially the nature of the local transitions, are argued to be strongly conditioned to the degree of molecular packing.

Two-Phase Flow Effect on the Ex-Vessel Corium Debris Bed Formation in Severe Accident

International Nuclear Information System (INIS)

Kim, Eunho; Park, Jin Ho; Kim, Moo Hwan; Park, Hyun Sun; Ma, Weimin; Bechta, Sevostian V.

2014-01-01

In Korean IVR-ERVC(In-Vessel Retention of molten corium through External Reactor Vessel Cooling) strategy, if the situation degenerates into insufficient external vessel cooling, the molten core mixture can directly erupt into the flooded cavity pool from the weakest point of the vessel. Then, FCI (molten Fuel Coolant Interaction) will fragment the corium jet into small particulates settling down to make porous debris bed on the cavity basemat. To secure the containment integrity against the MCCI (Molten Core - Concrete Interaction), cooling of the heat generating porous corium debris bed is essential and it depends on the characteristics of the bed itself. For the characteristics of corium debris bed, many previous experimental studies with simulant melts reported the heap-like shape mostly. There were also following experiments to develop the correlation for the heap-like shaped debris bed. However, recent studies started to consider the effect of the decay heat and reported some noticeable results with the two-phase flow effect on the debris bed formation. The Kyushu University and JAEA group reported the experimental studies on the 'self-leveling' effect which is the flattening effect of the particulate bed by the inside gas generation. The DECOSIM simulation study of RIT (Royal Institute of Technology, Sweden) with Russian researchers showed the 'large cavity pool convection' effect, which is driven by the up-rising gas bubble flow from the pre-settled debris bed, on the particle settling trajectories and ultimately final bed shape. The objective of this study is verification of the two-phase flow effect on the ex-vessel corium debris bed formation in the severe accident. From the analysis on the test movie and resultant particle beds, the two-phase flow effect on the debris bed formation, which has been reported in the previous studies, was verified and the additional findings were also suggested. For the first, in quiescent pool the

Parasitic phase formation in the La Ba2 Cu3 O7-x superconductor

International Nuclear Information System (INIS)

Baltra, T.; Fuenzalida, V.M.; Grahmann, C.R.

1996-01-01

The parasitic phase formation during the thermal processing of the H Tc La Ba 2 Cu 3 O 7-x superconductor, particularly the Ba Cu O 2 , is studied. The formation of the stable parasitic phase depends on the temperature of the initial treatments and on the heating rate during the sintering process. The superconducting highest purity material is obtained with treatment at 900 deg C and lowest heating rate. The temperature during the final annealing in oxygen of the sample did also affect the transport properties. Samples with the lowest resistivity in the normal state were produced by annealing in oxygen at 300 deg C. The largest orthorhombic distortion was obtained at 325 deg C. (author)

Effects of Phytoplankton Growth Phase on the Formation and Properties of Marine Snow

Science.gov (United States)

Montgomery, Q. W.; Proctor, K. W.; Prairie, J. C.

2016-02-01

Marine snow aggregates often dominate carbon export from the upper mixed layer to the deep ocean. Thus, understanding the formation and the properties of these aggregates is essential to the study of the biological pump. Aggregate formation is determined by both the encounter rate and the stickiness of the particles that they are composed of. Stickiness of phytoplankton has been linked to production of transparent exopolymer particles (TEP), which has been previously shown to vary in concentration throughout different parts of the phytoplankton growth cycle. The objective of this study is to determine the effects of the growth phase of the diatom Thalassiosira weissflogii to both TEP production and the properties of the resulting aggregates produced. Cultures of T. weissflogii were stopped at separate phases of the phytoplankton growth curve and incubated in rotating cylindrical tanks to form aggregates. Aggregate properties such as size, density, and porosity were measured at the end of each period of roller incubation. Preliminary results describe little variation in the size of the aggregates formed from different parts of the growth phase, but show a significant effect of growth phase on aggregate density. Density is an important factor in the settling of marine aggregates. Therefore, variations in aggregate density during different growth phases may have large implications for the efficiency of the biological pump during different stages of a phytoplankton bloom. Further examination will be performed on the potential effects of TEP abundance on the properties of the aggregates formed at separate growth phases and the resulting implications for carbon flux.

The formation of quasicrystal phase in Al-Cu-Fe system by mechanical alloying

Directory of Open Access Journals (Sweden)

Dilermando Nagle Travessa

2012-10-01

Full Text Available In order to obtain quasicrystalline (QC phase by mechanical alloying (MA in the Al-Cu-Fe system, mixtures of elementary Al, Cu and Fe in the proportion of 65-20-15 (at. % were produced by high energy ball milling (HEBM. A very high energy type mill (spex and short milling times (up to 5 hours were employed. The resulting powders were characterized by X-ray diffraction (XRD, differential scanning calorimetry (DSC and scanning electron microscopy (SEM. QC phase was not directly formed by milling under the conditions employed in this work. However, phase transformations identified by DSC analysis reveals that annealing after HEBM possibly results in the formation of the ψ QC phase.

Condensed-phase biogenic-anthropogenic interactions with implications for cold cloud formation.

Science.gov (United States)

Charnawskas, Joseph C; Alpert, Peter A; Lambe, Andrew T; Berkemeier, Thomas; O'Brien, Rachel E; Massoli, Paola; Onasch, Timothy B; Shiraiwa, Manabu; Moffet, Ryan C; Gilles, Mary K; Davidovits, Paul; Worsnop, Douglas R; Knopf, Daniel A

2017-08-24

Anthropogenic and biogenic gas emissions contribute to the formation of secondary organic aerosol (SOA). When present, soot particles from fossil fuel combustion can acquire a coating of SOA. We investigate SOA-soot biogenic-anthropogenic interactions and their impact on ice nucleation in relation to the particles' organic phase state. SOA particles were generated from the OH oxidation of naphthalene, α-pinene, longifolene, or isoprene, with or without the presence of sulfate or soot particles. Corresponding particle glass transition (T g ) and full deliquescence relative humidity (FDRH) were estimated using a numerical diffusion model. Longifolene SOA particles are solid-like and all biogenic SOA sulfate mixtures exhibit a core-shell configuration (i.e. a sulfate-rich core coated with SOA). Biogenic SOA with or without sulfate formed ice at conditions expected for homogeneous ice nucleation, in agreement with respective T g and FDRH. α-pinene SOA coated soot particles nucleated ice above the homogeneous freezing temperature with soot acting as ice nuclei (IN). At lower temperatures the α-pinene SOA coating can be semisolid, inducing ice nucleation. Naphthalene SOA coated soot particles acted as ice nuclei above and below the homogeneous freezing limit, which can be explained by the presence of a highly viscous SOA phase. Our results suggest that biogenic SOA does not play a significant role in mixed-phase cloud formation and the presence of sulfate renders this even less likely. However, anthropogenic SOA may have an enhancing effect on cloud glaciation under mixed-phase and cirrus cloud conditions compared to biogenic SOA that dominate during pre-industrial times or in pristine areas.

Chemical-Reaction-Controlled Phase Separated Drops: Formation, Size Selection, and Coarsening

Science.gov (United States)

Wurtz, Jean David; Lee, Chiu Fan

2018-02-01

Phase separation under nonequilibrium conditions is exploited by biological cells to organize their cytoplasm but remains poorly understood as a physical phenomenon. Here, we study a ternary fluid model in which phase-separating molecules can be converted into soluble molecules, and vice versa, via chemical reactions. We elucidate using analytical and simulation methods how drop size, formation, and coarsening can be controlled by the chemical reaction rates, and categorize the qualitative behavior of the system into distinct regimes. Ostwald ripening arrest occurs above critical reaction rates, demonstrating that this transition belongs entirely to the nonequilibrium regime. Our model is a minimal representation of the cell cytoplasm.

Nematic phase formation in suspensions of graphene oxide

Science.gov (United States)

Fresneau, Nathalie; Campidelli, Stéphane

The last decade has seen the rise of graphene. Graphene is a single layer of graphite; it can be obtained by direct liquid phase exfoliation of the latter through harsh sonication. This technique presents the disadvantage to produce small graphene flakes (typically in the 0.05 to 0.4 μm2 range for the monolayers) and multilayer graphene with uncontrolled thickness distributions. In order to improve the exfoliation process, one has to counter the strong van der Waals interactions between the carbon planes of graphite. This implies to increase the distance between two planes and it can be done, for example, by oxidizing graphite to introduce oxygen species in the graphenic planes. The fabrication of graphite oxide is known for almost 150 years, and it became popular again these last ten years. Generally, the oxidation of graphite is performed following a method described by Hummers in the 1950's and the material produced by this technique exfoliates quasi-spontaneously into monolayer species called graphene oxide (GO). The highly anisotropic shape of GO (several μm in length and width for a thickness of ca. 1 nm) combined with the presence of oxygenated functions on the sp2 carbon structure of graphene lead to the formation of a lyotropic liquid crystalline phase in water. Above a certain concentration of graphene flakes the gain in translational entropy for a long-range ordered phase outweighs the loss in rotational entropy, and the liquid crystal phase then forms. The value of the threshold is affected by the aspect ratio of the graphene flakes but other factors such as the interactions also play a strong role.

Starless Clumps and the Earliest Phases of High-mass Star Formation in the Milky Way

Science.gov (United States)

Svoboda, Brian

2018-01-01

High-mass stars are key to regulating the interstellar medium, star formation activity, and overall evolution of galaxies, but their formation remains an open problem in astrophysics. In order to understand the physical conditions during the earliest phases of high-mass star formation, I report on observational studies of dense starless clump candidates (SCCs) that show no signatures of star formation activity. I identify 2223 SCCs from the 1.1 mm Bolocam Galactic Plane Survey, systematically analyze their physical properties, and show that the starless phase is not represented by a single timescale, but evolves more rapidly with increasing clump mass. To investigate the sub-structure in SCCs at high spatial resolution, I study the 12 most high-mass SCCs within 5 kpc using ALMA. I report previously undetected low-luminosity protostars in 11 out of 12 SCCs, fragmentation equal to the thermal Jeans length of the clump, and no starless cores exceeding 30 solar masses. While uncertainties remain concerning the star formation effeciency in this sample, these observational facts are consistent with models where high-mass stars form from intially low- to intermediate-mass protostars that accrete most of their mass from the surrounding clump.

The quasicrystalline phase formation in Al-Cu-Cr alloys produced by mechanical alloying

Energy Technology Data Exchange (ETDEWEB)

Sviridova, T.A.; Shevchukov, A.P.; Shelekhov, E.V. [National University of Science and Technology ' MISIS' , Moscow 119049 (Russian Federation); Diakonov, D.L. [Bardin Central Research Institute for the Iron and Steel Industry, Moscow 105005 (Russian Federation); Tcherdyntsev, V.V.; Kaloshkin, S.D. [National University of Science and Technology ' MISIS' , Moscow 119049 (Russian Federation)

2011-06-15

Research highlights: > Formation of decagonal quasicrystalline phase in Al-Cu-Cr alloys. > Obtained decagonal phase belongs to D{sub 3} family of decagonal quasicrystals. > Decagonal phase has 1.26 nm periodicity along 10-fold axis. > Alloys were produced by combination of mechanical alloying and subsequent annealing. > Phase composition of as-milled powders depending on annealing temperature. - Abstract: Almost single-phase decagonal quasicrystal with periodicity of 1.26 nm along 10-fold axis was produced in Al{sub 69}Cu{sub 21}Cr{sub 10} and Al{sub 72.5}Cu{sub 16.5}Cr{sub 11} alloys using combination of mechanical alloying (MA) and subsequent annealing. Phase transformations of as-milled powders depending on annealing temperature in the range of 200-800 deg. C are examined. Since the transformations can be explained based on kinetic and thermodynamic reasons it seems that applied technique (short preliminary MA followed by the annealing) permits to produce the equilibrium phases rather than metastable ones.

Superconductivity optimization and phase formation kinetics study of internal-Sn Nb3Sn superconducting wires

International Nuclear Information System (INIS)

Zhang, Chaowu

2007-07-01

Superconductors Nb 3 Sn wires are one of the most applicable cryogenic superconducting materials and the best choice for high-field magnets exceeding 10 T. One of the most significant utilization is the ITER project which is regarded as the hope of future energy source. The high-Cu composite designs with smaller number of sub-element and non-reactive diffusion barrier, and the RRP (Restacked Rod Process) internal-Sn technology are usually applied for the wire manufacturing. Such designed and processed wires were supplied by MSA/Alstom and WST/NIN in this research. The systematic investigation on internal-Sn superconducting wires includes the optimization of heat treatment (HT) conditions, phase formation and its relation with superconductivity, microstructure analysis, and the phase formation kinetics. Because of the anfractuosity of the configuration design and metallurgical processing, the MF wires are not sufficient for studying a sole factor effect on superconductivity. Therefore, four sets of mono-element (ME) wires with different Sn ratios and different third-element addition were designed and fabricated in order to explore the relationship between phase formation and superconducting performances, particularly the A15 layer growth kinetics. Different characterization technic have been used (magnetization measurements, neutron diffraction and SEM/TEM/EDX analysis). The A15 layer thicknesses of various ME samples were measured and carried out linear and non-linear fits by means of two model equations. The results have clearly demonstrated that the phase formation kinetics of Nb 3 Sn solid-state reaction is in accordance with an n power relation and the n value is increased with the increase of HT temperature and the Sn ratio in the wire composite. (author)

Effect of Al doping on phase formation and thermal stability of iron nitride thin films

Energy Technology Data Exchange (ETDEWEB)

Tayal, Akhil [Amity Center for Spintronic Materials, Amity University, Sector 125, Noida 201 303 (India); Gupta, Mukul, E-mail: mgupta@csr.res.in [Amity Center for Spintronic Materials, Amity University, Sector 125, Noida 201 303 (India); Pandey, Nidhi [Amity Center for Spintronic Materials, Amity University, Sector 125, Noida 201 303 (India); Gupta, Ajay [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452 001 (India); Horisberger, Michael [Laboratory for Developments and Methods, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Stahn, Jochen [Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland)

2015-11-25

In the present work, we systematically studied the effect of Al doping on the phase formation of iron nitride (Fe–N) thin films. Fe–N thin films with different concentration of Al (Al = 0, 2, 3, 6, and 12 at.%) were deposited using dc magnetron sputtering by varying the nitrogen partial pressure between 0 and 100%. The structural and magnetic properties of the films were studied using x-ray diffraction and polarized neutron reflectivity. It was observed that at the lowest doping level (2 at.% of Al), nitrogen rich non-magnetic Fe–N phase gets formed at a lower nitrogen partial pressure as compared to the un-doped sample. Interestingly, we observed that as Al doping is increased beyond 3 at.%, nitrogen rich non-magnetic Fe–N phase appears at higher nitrogen partial pressure as compared to un-doped sample. The thermal stability of films were also investigated. Un-doped Fe–N films deposited at 10% nitrogen partial pressure possess poor thermal stability. Doping of Al at 2 at.% improves it marginally, whereas, for 3, 6 and 12 at.% Al doping, it shows significant improvement. The obtained results have been explained in terms of thermodynamics of Fe–N and Al–N. - Highlights: • Doping effects of Al on Fe–N phase formation is studied. • Phase formation shows a non-monotonic behavior with Al doping. • Low doping levels of Al enhance and high levels retard the nitridation process. • Al doping beyond 3 at.% improve thermal stability of Fe–N films.

Thermotropic phase transitions of catanionic dodecylsulfates with multi-charged and multi-tailed quaternary ammonium centers

Energy Technology Data Exchange (ETDEWEB)

Mihelj, Tea, E-mail: tmihelj@irb.hr [Ruđer Bošković Institute, Department of Physical Chemistry, Laboratory for Synthesis and Processes of Self-assembling of Organic Molecules, Bijenička c. 54, P.O. Box 180, HR-10002 Zagreb (Croatia); Popović, Jasminka [Division for Materials Physics, Ruđer Bošković Institute, POB 180, HR-10002 Zagreb (Croatia); Skoko, Željko [Department of Physics, Faculty of Science, University of Zagreb, Bijenička cesta 32, HR-10000 Zagreb (Croatia); Tomašić, Vlasta, E-mail: vlastom@irb.hr [Ruđer Bošković Institute, Department of Physical Chemistry, Laboratory for Synthesis and Processes of Self-assembling of Organic Molecules, Bijenička c. 54, P.O. Box 180, HR-10002 Zagreb (Croatia)

2014-09-10

Highlights: • Thermal behavior of quaternary ammonium n-dodecylsulfates is characterized. • Typical layered structure dominates in all examined compounds at room temperature. • The dimeric didodecylsulfate crystallizes in monoclinic space group P21/m. • Thermotropic phases formation characteristic for multi-tailed n-dodecylsulfates. • Multi-charged n-dodecylsulfates are soft crystals at higher temperatures. - Abstract: Five novel anhydrous catanionic dodecylsulfates containing multi-charged and multi-tailed quaternary ammonium centers were synthesized and examined with light microscopy, differential scanning calorimetry and X-ray powder diffraction. This study is an attempt to explain the relationship between chemical structure, molecular architecture, phase transition characteristics and thermodynamics and the nature of intermolecular interactions of the individual amphiphiles that ultimately lead to different mesomorphic product. All examined compounds are of typical layered structure at room temperature. The long spacing decreases linearly with the increase of either ionic head or n-dodecyl chain number. The thermal analysis of the examined multi-charged catanionics indicates thermotropic mesomorphism, whereas multi-tailed dodecylsulfates show only properties of soft crystals. Maltese crosses, oily streaks textures, stepped drops and fan-shaped textures affirmed the existence of various smectic mesophases at room and higher temperatures. Thermodynamically the most ordered compound is dimeric didodecylsulfate, and the most disordered is three-tailed dodecylsulfate. The addition of the new quaternary ammonium center or alkyl chain causes the increment of the lattice energy first, and it decreases by further changes in the structure. The temperatures of crystallization decrease by any mentioned addition.

SURVIVAL OF INTERSTELLAR MOLECULES TO PRESTELLAR DENSE CORE COLLAPSE AND EARLY PHASES OF DISK FORMATION

International Nuclear Information System (INIS)

Hincelin, U.; Wakelam, V.; Hersant, F.; Guilloteau, S.; Commerçon, B.

2013-01-01

An outstanding question of astrobiology is the link between the chemical composition of planets, comets, and other solar system bodies and the molecules formed in the interstellar medium. Understanding the chemical and physical evolution of the matter leading to the formation of protoplanetary disks is an important step for this. We provide some new clues to this long-standing problem using three-dimensional chemical simulations of the early phases of disk formation: we interfaced the full gas-grain chemical model Nautilus with the radiation-magnetohydrodynamic model RAMSES, for different configurations and intensities of the magnetic field. Our results show that the chemical content (gas and ices) is globally conserved during the collapsing process, from the parent molecular cloud to the young disk surrounding the first Larson core. A qualitative comparison with cometary composition suggests that comets are constituted of different phases, some molecules being direct tracers of interstellar chemistry, while others, including complex molecules, seem to have been formed in disks, where higher densities and temperatures allow for an active grain surface chemistry. The latter phase, and its connection with the formation of the first Larson core, remains to be modeled

Araçatuba Formation: palustrine deposits from the initial sedimentation phase of the Bauru Basin

Directory of Open Access Journals (Sweden)

Fernandes Luiz A.

2003-01-01

Full Text Available The Bauru Basin (Upper Cretaceous accumulated an essentially sandy continental sedimentary sequence. In a first desertic phase the basaltic substratum was covered by a widespread and homogeneous aeolian sand unit with minor loess intercalations. The substratum relief favored the formation of an endorheic drainage system under semi-arid climate, a process that started the development of the Araçatuba Paleoswamp. The palustrine deposits (Araçatuba Formation comprise siltstone and tipically greenish gray narrow tabular strata of sandstone cemented by carbonate. Moulds and gypsite and dolomite pseudomorphs were identified. The moulds seem to be genetically associated with desiccation cracks, root marks and climbing ripple lamination levels, that, on the whole, indicate calm shallow saline waters undergoing phases of subaerial exposition. At the boundaries of the study area, sand units may exhibit sigmoidal features and convolute bedding structure, which is characteristic of marginal deltaic deposits. The Araçatuba Formation is enclosed in and later overlaid by the aeolian deposits of the Vale do Rio do Peixe Formation.

Neutron scattering studies of molecular conformations in liquid crystal polymers

Science.gov (United States)

Noirez, L.; Moussa, F.; Cotton, J. P.; Keller, P.; Pépy, G.

1991-03-01

A comblike liquid crystal polymer (LPC) is a polymer on which mesogenic molecules have been grafted. It exhibits a succession of liquid crystal phases. Usually the equilibrium conformation of an ordinary polymeric chain corresponds to a maximum entropy, i.e., to an isotropic spherical coil. How does the backbone of a LCP behave in the nematic and smectic field? Small-angle neutron scattering may answer this question. Such measurements are presented here on four different polymers as a function of temperature. An anisotropy of the backbone conformation is found in all these studied compounds, much more pronounced in the smectic phase than in the nematic phase: the backbone spreads more or less perpendicularly to its hanging cores. A comparison with existing theories and a discussion of these results is outlined.

Formation of primary pit connection during conchocelis phase of Porphyra yezoensis (Bangiophyceae, Rhodophyta)

Science.gov (United States)

Shual, Li; Jiang, Ming; Duan, Delin

2006-09-01

The formation of pit connection during conchocelis phase of Porphyra yezoensis Ueda was observed and examined with transmission electron microscope (TEM) and epifluorence microscope. It is indicated that the pit connection was formed in late stage of conchocelis phase and the early stages of conchosporangial cell development, and disappeared in bispore stage. The pit connection contained a thin membrane layer at outer pit plug. Stained with 4', 6'-diamidino-2-phenylidole dihydrochloride hydrate (DAPI), transferring of DNA or RNA between adjacent cells were observed in late stage of conchocelis development, it was deduced that pit connection might serve as a channel for signal transduction and genetic substance transportation in conchocelis phase.

Influence of phase transition on pattern formation during catalytic reactions

OpenAIRE

Andrade, Roberto Fernandes Silva; Lima, D.; Cunha, F. B.

2000-01-01

p.434–445 We investigate the influence of the order of surface phase transitions on pattern formation during chemical reaction on mono-crystal catalysts. We use a model consisting of two partial differential equations, one of which describes the dynamics of the surface state with the help of a Ginzburg–Landau potential. Second- or first-order transitions are described by decreasing or increasing the relative value of the third-order coefficient of the potential. We concentrate on the stabi...

Modeling of Eutectic Formation in Al-Si Alloy Using A Phase-Field Method

Directory of Open Access Journals (Sweden)

Ebrahimi Z.

2017-12-01

Full Text Available We have utilized a phase-field model to investigate the evolution of eutectic silicon in Al-Si alloy. The interfacial fluctuations are included into a phase-field model of two-phase solidification, as stochastic noise terms and their dominant role in eutectic silicon formation is discussed. We have observed that silicon spherical particles nucleate on the foundation of primary aluminum phase and their nucleation continues on concentric rings, through the Al matrix. The nucleation of silicon particles is attributed to the inclusion of fluctuations into the phase-field equations. The simulation results have shown needle-like, fish-bone like and flakes of silicon phase by adjusting the noise coefficients to larger values. Moreover, the role of primary Al phase on nucleation of silicon particles in Al-Si alloy is elaborated. We have found that the addition of fluctuations plays the role of modifiers in our simulations and is essential for phase-field modeling of eutectic growth in Al-Si system. The simulated finger-like Al phases and spherical Si particles are very similar to those of experimental eutectic growth in modified Al-Si alloy.

Dislocations and other topological oddities

Science.gov (United States)

Pieranski, Pawel

2016-03-01

We will show that the book Dislocations by Jacques Friedel, published half a century ago, can still be recommended, in agreement with the author's intention, as a textbook ;for research students at University and for students at engineering schools as well as for research engineers;. Indeed, today dislocations are known to occur not only in solid crystals but also in many other systems discovered more recently such as colloidal crystals or liquid crystals having periodic structures. Moreover, the concept of dislocations is an excellent starting point for lectures on topological defects occurring in systems equipped with order parameters resulting from broken symmetries: disclinations in nematic or hexatic liquid crystals, dispirations in chiral smectics or disorientations in lyotropic liquid crystals. The discussion of dislocations in Blue Phases will give us an opportunity to call on mind Sir Charles Frank, friend of Jacques Friedel since his Bristol years, who called these ephemeral mesophases ;topological oddities;. Being made of networks of disclinations, Blue Phases are similar to Twist Grain Boundary (TGB) smectic phases, which are made of networks of screw dislocations and whose existence was predicted by de Gennes in 1972 on the basis of the analogy between smectics and superconductors. We will stress that the book by Jacques Friedel contains seeds of this analogy.

New structural studies of liquid crystal by reflectivity and resonant X-ray diffraction

International Nuclear Information System (INIS)

Fernandes, P.

2007-04-01

This memory presents three structural studies of smectic Liquid Crystals by reflectivity and resonant diffraction of X-rays. It is divided in five chapters. In the first a short introduction to Liquid Crystals is given. In particular, the smectic phases that are the object of this study are presented. The second chapter is consecrated to the X-ray experimental techniques that were used in this work. The three last chapters present the works on which this thesis can be divided. Chapter three demonstrates on free-standing films of MHPOBC (historic liquid crystal that possesses the antiferroelectric sub-phases) the possibility to extend the technique of resonant X-ray diffraction to liquid crystals without resonant element. In the fourth chapter the structure of the B 2 liquid crystal phase of bent-core molecules (or banana molecules) is elucidated by using resonant X-ray diffraction combined with polarization analysis of the diffracted beam. A model of the polarization of the resonant beam diffracted by four different structures proposed for the B 2 phase is developed in this chapter. In the fifth chapter a smectic binary mixture presenting a very original critical point of phase separation is studied by X-ray reflectivity and optical microscopy. A concentration gradient in the direction perpendicular to the plane of the film seems to be induced by the free-standing film geometry. The results of a simplified model of the system are compatible with this interpretation

New structural studies of liquid crystal by reflectivity and resonant X-ray diffraction; Nouvelles etudes structurales de cristaux liquides par reflectivite et diffraction resonante des rayons X

Energy Technology Data Exchange (ETDEWEB)

Fernandes, P

2007-04-15

This memory presents three structural studies of smectic Liquid Crystals by reflectivity and resonant diffraction of X-rays. It is divided in five chapters. In the first a short introduction to Liquid Crystals is given. In particular, the smectic phases that are the object of this study are presented. The second chapter is consecrated to the X-ray experimental techniques that were used in this work. The three last chapters present the works on which this thesis can be divided. Chapter three demonstrates on free-standing films of MHPOBC (historic liquid crystal that possesses the antiferroelectric sub-phases) the possibility to extend the technique of resonant X-ray diffraction to liquid crystals without resonant element. In the fourth chapter the structure of the B{sub 2} liquid crystal phase of bent-core molecules (or banana molecules) is elucidated by using resonant X-ray diffraction combined with polarization analysis of the diffracted beam. A model of the polarization of the resonant beam diffracted by four different structures proposed for the B{sub 2} phase is developed in this chapter. In the fifth chapter a smectic binary mixture presenting a very original critical point of phase separation is studied by X-ray reflectivity and optical microscopy. A concentration gradient in the direction perpendicular to the plane of the film seems to be induced by the free-standing film geometry. The results of a simplified model of the system are compatible with this interpretation.

Metallurgical features of the formation of a solid-phase metal joint upon electric-circuit heating

Science.gov (United States)

Latypov, R. A.; Bulychev, V. V.; Zybin, I. N.

2017-06-01

The thermodynamic conditions of formation of a joint between metals using the solid-phase methods of powder metallurgy, welding, and deposition of functional coatings upon electric-current heating of the surfaces to be joined are studied. Relations are obtained to quantitatively estimate the critical sizes of the circular and linear active centers that result in the formation of stable bonding zones.

Spontaneous and Flow-Driven Interfacial Phase Change: Dynamics of Microemulsion Formation at the Pore Scale.

Science.gov (United States)

Tagavifar, Mohsen; Xu, Ke; Jang, Sung Hyun; Balhoff, Matthew T; Pope, Gary A

2017-11-14

The dynamic behavior of microemulsion-forming water-oil-amphiphiles mixtures is investigated in a 2.5D micromodel. The equilibrium phase behavior of such mixtures is well-understood in terms of macroscopic phase transitions. However, what is less understood and where experimental data are lacking is the coupling between the phase change and the bulk flow. Herein, we study the flow of an aqueous surfactant solution-oil mixture in porous media and analyze the dependence of phase formation and spatial phase configurations on the bulk flow rate. We find that a microemulsion forms instantaneously as a boundary layer at the initial surface of contact between the surfactant solution and oil. The boundary layer is temporally continuous because of the imposed convection. In addition to the imposed flow, we observe spontaneous pulsed Marangoni flows that drag the microemulsion and surfactant solution into the oil stream, forming large (macro)emulsion droplets. The formation of the microemulsion phase at the interface distinguishes the situation from that of the more common Marangoni flow with only two phases present. Additionally, an emulsion forms via liquid-liquid nucleation or the Ouzo effect (i.e., spontaneous emulsification) at low flow rates and via mechanical mixing at high flow rates. With regard to multiphase flow, contrary to the common belief that the microemulsion is the wetting liquid, we observe that the minor oil phase wets the solid surface. We show that a layered flow pattern is formed because of the out-of-equilibrium phase behavior at high volumetric flow rates (order of 2 m/day) where advection is much faster than the diffusive interfacial mass transfer and transverse mixing, which promote equilibrium behavior. At lower flow rates (order of 30 cm/day), however, the dynamic and equilibrium phase behaviors are well-correlated. These results clearly show that the phase change influences the macroscale flow behavior.

Circular Formation Control of Multiagent Systems with Any Preset Phase Arrangement

Directory of Open Access Journals (Sweden)

Lina Jin

2018-01-01

Full Text Available This paper deals with the circular formation control problem of multiagent systems for achieving any preset phase distribution. The control problem is decomposed into two parts: the first is to drive all the agents to a circle which either needs a target or not and the other is to arrange them in positions distributed on the circle according to the preset relative phases. The first part is solved by designing a circular motion control law to push the agents to approach a rotating transformed trajectory, and the other is settled using a phase-distributed protocol to decide the agents’ positioning on the circle, where the ring topology is adopted such that each agent can only sense the relative positions of its neighboring two agents that are immediately in front of or behind it. The stability of the closed-loop system is analyzed, and the performance of the proposed controller is verified through simulations.

Phase formation and stability of quasicrystal/α-Mg interfaces in the Mg–Cd–Yb system

International Nuclear Information System (INIS)

Ohhashi, S.; Suzuki, K.; Kato, A.; Tsai, A.P.

2014-01-01

Phase formation involving icosahedral quasicrystals (iQc) in the Mg–Cd–Yb system was investigated. The phase diagrams obtained revealed that the iQc is in equilibrium with either (Mg, Cd) 2 Yb or an α-Mg phase over a wide composition range at 673 K. A eutectic reaction, where the melt decomposed to a rod-like lamella structure consisting of iQc and α-Mg phases was observed for Mg 68 Cd 24 Yb 8 at 735 K. High-angle annular dark-field scanning transmission microscopy observation of the iQc in Mg 96 Cd 3 Yb 1 verified the atomic positions of the Yb icosahedra and confirmed that the i-MgCdYb is isostructural to the i-CdYb. The formation of the eutectic structure is responsible for the high stability of the iQc/α-Mg interfaces because of good lattice matching; which is coincident interplanar spacing over several planes for the two phases. This coincidence in interplanar spacing was further confirmed in the real atomic structure, for which the twofold planes of the iQc, and the [0 0 0 2] and [2 −1 −1 0] planes of α-Mg are dominant factors in determining the stability of the interfaces

Determination of complex formation constants by phase sensitive alternating current polarography: Cadmium-polymethacrylic acid and cadmium-polygalacturonic acid.

Science.gov (United States)

Garrigosa, Anna Maria; Gusmão, Rui; Ariño, Cristina; Díaz-Cruz, José Manuel; Esteban, Miquel

2007-10-15

The use of phase sensitive alternating current polarography (ACP) for the evaluation of complex formation constants of systems where electrodic adsorption is present has been proposed. The applicability of the technique implies the previous selection of the phase angle where contribution of capacitive current is minimized. This is made using Multivariate Curve Resolution by Alternating Least Squares (MCR-ALS) in the analysis of ACP measurements at different phase angles. The method is checked by the study of the complexation of Cd by polymethacrylic (PMA) and polygalacturonic (PGA) acids, and the optimal phase angles have been ca. -10 degrees for Cd-PMA and ca. -15 degrees for Cd-PGA systems. The goodness of phase sensitive ACP has been demonstrated comparing the determined complex formation constants with those obtained by reverse pulse polarography, a technique that minimizes the electrode adsorption effects on the measured currents.

Photopyroelectric Calorimetry Investigations of 8CB Liquid Crystal-Microemulsion System

Science.gov (United States)

Paoloni, S.; Zammit, U.; Mercuri, F.

2018-02-01

In this work, the photopyroelectric technique has been used to investigate the phase transitions in a liquid crystal microemulsion by combining the simultaneous high temperature resolution thermal diffusivity measurements and optical polarization microscopy observations. It has been found that, during the conversion from the isotropic phase into the nematic one, the micelles are expelled from the nematic domains and remain confined in islands of isotropic material which survive down to the smectic temperature range. A hysteresis in the thermal diffusivity profiles between heating and cooling run over the isotropic-nematic transition temperature range has been observed which has been ascribed to the different micelles distribution into the sample volume during cooling and heating runs. Finally, the almost bulk-like behavior of the thermal diffusivity over the nematic-smectic phase transition confirms that a significant fraction of the micelles are expelled during the nucleation of the nematic phase.

Phase-field modeling of microstructural pattern formation during directional solidification of peritectic alloys without morphological instability

International Nuclear Information System (INIS)

Shing Lo, Tak; Karma, Alain; Plapp, Mathis

2001-01-01

During the directional solidification of peritectic alloys, two stable solid phases (parent and peritectic) grow competitively into a metastable liquid phase of larger impurity content than either solid phase. When the parent or both solid phases are morphologically unstable, i.e., for a small temperature gradient/growth rate ratio (G/v p ), one solid phase usually outgrows and covers the other phase, leading to a cellular-dendritic array structure closely analogous to the one formed during monophase solidification of a dilute binary alloy. In contrast, when G/v p is large enough for both phases to be morphologically stable, the formation of the microstructure becomes controlled by a subtle interplay between the nucleation and growth of the two solid phases. The structures that have been observed in this regime (in small samples where convection effects are suppressed) include alternate layers (bands) of the parent and peritectic phases perpendicular to the growth direction, which are formed by alternate nucleation and lateral spreading of one phase onto the other as proposed in a recent model [R. Trivedi, Metall. Mater. Trans. A 26, 1 (1995)], as well as partially filled bands (islands), where the peritectic phase does not fully cover the parent phase which grows continuously. We develop a phase-field model of peritectic solidification that incorporates nucleation processes in order to explore the formation of these structures. Simulations of this model shed light on the morphology transition from islands to bands, the dynamics of spreading of the peritectic phase on the parent phase following nucleation, which turns out to be characterized by a remarkably constant acceleration, and the types of growth morphology that one might expect to observe in large samples under purely diffusive growth conditions

Phase formation in titanium alloys during their quenching from liquid state

International Nuclear Information System (INIS)

Golub, S.Ya.; Kotko, A.V.; Kuz'menko, N.N.; Kulak, L.D.; Firstov, S.A.; Khaenko, B.V.

1992-01-01

Methods of X-ray diffractin analysis, light and electron microscopy were applied to study structural state of titanium base alloys quenched from liquid state by spinning with cooling in inert gas or at the surface of solid heat exchanger. Phase formation under rapid cooling conditions was considered. The morphology of phases and mutual orientation of their crystal lattices were investigated along with the character of crystallization texture. It was revealed that on melt quenching with 10 5 -10 6 K/s cooling rates the growth of columnar branches of degenerated dendrites was accopanied by Si atoms movement of the order of 0.1 μm. Structure and crack resistance of compacted articles produced from rapidly solidified powders were under study

Halo formation in three-dimensional bunches with various phase space distributions

Directory of Open Access Journals (Sweden)

A. V. Fedotov

1999-01-01

Full Text Available A realistic treatment of halo formation must take into account 3D beam bunches and 6D phase space distributions. We recently constructed, analytically and numerically, a new class of self-consistent 6D phase space stationary distributions, which allowed us to study the halo development mechanism without being obscured by the effect of beam redistribution. In this paper we consider nonstationary distributions and study how the halo characteristics compare with those obtained using the stationary distribution. We then discuss the effect of redistribution on the halo development mechanism. In contrast to bunches with a large aspect ratio, we find that the effect of coupling between the r and z planes is especially important as the bunch shape becomes more spherical.

Superconductivity optimization and phase formation kinetics study of internal-Sn Nb{sub 3}Sn superconducting wires

Energy Technology Data Exchange (ETDEWEB)

Zhang, Chaowu

2007-07-15

Superconductors Nb{sub 3}Sn wires are one of the most applicable cryogenic superconducting materials and the best choice for high-field magnets exceeding 10 T. One of the most significant utilization is the ITER project which is regarded as the hope of future energy source. The high-Cu composite designs with smaller number of sub-element and non-reactive diffusion barrier, and the RRP (Restacked Rod Process) internal-Sn technology are usually applied for the wire manufacturing. Such designed and processed wires were supplied by MSA/Alstom and WST/NIN in this research. The systematic investigation on internal-Sn superconducting wires includes the optimization of heat treatment (HT) conditions, phase formation and its relation with superconductivity, microstructure analysis, and the phase formation kinetics. Because of the anfractuosity of the configuration design and metallurgical processing, the MF wires are not sufficient for studying a sole factor effect on superconductivity. Therefore, four sets of mono-element (ME) wires with different Sn ratios and different third-element addition were designed and fabricated in order to explore the relationship between phase formation and superconducting performances, particularly the A15 layer growth kinetics. Different characterization technic have been used (magnetization measurements, neutron diffraction and SEM/TEM/EDX analysis). The A15 layer thicknesses of various ME samples were measured and carried out linear and non-linear fits by means of two model equations. The results have clearly demonstrated that the phase formation kinetics of Nb{sub 3}Sn solid-state reaction is in accordance with an n power relation and the n value is increased with the increase of HT temperature and the Sn ratio in the wire composite. (author)

Analytical model of chemical phase and formation of DSB in chromosomes by ionizing radiation

Czech Academy of Sciences Publication Activity Database

Barilla, J.; Lokajíček, Miloš; Pisaková, Hana; Šimr, P.

2013-01-01

Roč. 36, č. 1 (2013), s. 11-17 ISSN 0158-9938 Institutional support: RVO:68378271 Keywords : radiobiological mechanism * chemical phase * DSB formation * oxygen effect Subject RIV: BF - Elementary Particles and High Energy Physics Impact factor: 0.848, year: 2013

Photo-orientation at liquid crystal–polymer interfaces

Indian Academy of Sciences (India)

affected by the phase of the liquid crystal covering the polymer. Photo-orientation is significantly more efficient when the liquid crystal is in the isotropic phase than when it exhibits orientational order. The observations are interpreted by assuming that in the smectic and nematic phases the liquid crystal stabilises to a large ...

Spontaneous membrane formation and self-encapsulation of active rods in an inhomogeneous motility field

NARCIS (Netherlands)

Grauer, J.; Löwen, H.; Janssen, L.M.C.

2018-01-01

We study the collective dynamics of self-propelled rods in an inhomogeneous motility field. At the interface between two regions of constant but different motility, a smectic rod layer is spontaneously created through aligning interactions between the active rods, reminiscent of an artificial,

Effects of S/V on secondary phase formation on waste glasses

International Nuclear Information System (INIS)

Feng, X.; Buck, E.C.; Bates, J.K.; Gong, M.; Dietz, N.L.; Pegg, I.L.

1994-01-01

Simulated West Valley high-level nuclear waste glass, WV205, was leached with and without buffered media in both deuterated and ordinary water at glass surface area to solution volumes (S/N) of 200--6000 m -1 . Examination of the glass surface after testing for 14 days indicated that the S/V-induced pH change plays a dominant role in the development of the altered surface layer and the secondary phases formed. The changes due to SN-induced pH determine the rate of surface layer formation, the element distribution in the surface layer, and possibly, the identities of the secondary phases. Changes due to SN-induced elemental concentration also influence glass reaction rate in terms of the layer thickness and the elemental distribution in the surface layers

Third phase formation in the extraction of Th(NO_3)_4 by Tri-sec-butyl phosphate. A comparison with Tri-n-butyl phosphate

International Nuclear Information System (INIS)

Chandrasekar, Aditi; Suresh, A.; Sivaraman, N.

2017-01-01

Earlier studies carried out in our laboratory indicated that Tri-sec-butyl phosphate (TsBP) is a potential extractant for U/Th separation. Also, the third phase formation tendency of TsBP is lower compared to its isomers, Tri-n-butyl-phosphate (TBP) and Tri-iso-butyl phosphate (TiBP). In this context, the extraction and third phase formation behaviour of 1.1 M solutions of TiBP and TsBP in n-dodecane in the extraction of Th(IV) from 1 M HNO_3 at 303 K over a wide range of Th concentrations were investigated in the present study and the results are compared with the literature data on TBP system. Concentrations of Th(IV) and HNO_3 loaded in the organic phase before third phase formation (biphasic region) as well as in third phase and diluent-rich phase after third phase formation (triphasic region) were measured as a function of equilibrium aqueous phase Th(IV) concentration. The density of loaded organic phase was also measured at various Th(IV) concentrations. The extraction profiles in the biphasic region indicated that extraction of Th(IV) by TBP is higher than that of TiBP which in turn is higher than that of TsBP. Extractant concentration in the diluent-rich phase and third phase was measured for the triphasic region.

Methodology for determination of trace elements in mineral phases of iron banded formation by LA-ICP-MS

International Nuclear Information System (INIS)

Sousa, Denise V.M. de; Nalini Junior, Herminio A.; Sampaio, Geraldo M.S.; Abreu, Adriana T. de; Lana, Cristiano de C.

2015-01-01

The study of the chemical composition of mineral phases of iron formation (FF), especially of trace elements, is an important tool in the understanding of the genesis of these rocks and the contribution of the phases in the composition of whole rock. Low mass fraction of such elements in the mineral phases present in this rock type requires a suitable analytical procedure. The laser ablation technique coupled with ICP-MS (LA-ICP-MS) has been widely used for determination of trace elements in geological samples. Thus, the aim of this study is to develop calibration curves for determination of trace elements (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) in mineral phases of banded iron formations by LA-ICP-MS. Several certified reference materials (CRM) were used for calibrate the equipment. The analytical conditions were checked by CRM NIST SRM 614. The results were satisfactory, since the curves showed good linearity coefficients, good accuracy and precision of results. (author)

Electric properties of a liquid crystalline methacrylic polymer

International Nuclear Information System (INIS)

Gonzalez Henriquez, C.M.; Soto Bustamante, E.A.; Haase, W.

2009-01-01

The formation of a liquid crystalline polymer called PM6R8 is reported. The polymers were obtained with different concentration of AIBN as initiator (0.25, 0.50, 1 and 2mg in 5ml solution) and time of reaction (24, 36 and 48 hours). The compounds were characterized by 1 H-NMR, differential thermal analysis (DTA), X-ray diffractometer and pyroelectric measurements. For the polymer a smectic C 2 phase occurs over broad temperature range, which is a possible explanation for the electric signal. The arrangement of the molecules within of the crystalline lattice is related with the kinetic of precipitation. (author)

Influence of powder pre-annealing on the phase formation and critical current of Bi-2223/Ag tapes

DEFF Research Database (Denmark)

Chen, X.P.; Grivel, Jean-Claude; Li, M.Y.

2004-01-01

. The effects of different precursors were investigated by XRD, SEM/EDS and critical current measurements. It has been found that both the microstructure and phase formation depended strongly on the different lead-rich phases, which determined the reactivity of the precursor. Tapes fabricated using...... the precursor with Ca2PbO4 phase (tape T1) had lower transformation rate of 2223 phase than tapes fabricated using the precursor with 3321 phase (tape T2). SEM results show that a large fraction of secondary phases with big particle size was formed in the tape T1 during the subsequent sintering, which might...

Effect of elemental composition of ion beam on the phase formation and surface strengthening of structural materials

International Nuclear Information System (INIS)

Avdienko, K.I.; Avdienko, A.A.; Kovalenko, I.A.

2001-01-01

The investigation results are reported on the influence of ion beam element composition on phase formation, wear resistance and microhardness of surface layers of titanium alloys VT-4 and VT-16 as well as stainless steel 12Kh18N10T implanted with nitrogen, oxygen and boron. It is stated that ion implantation into structural materials results in surface hardening and is directly dependent on element composition of implanted ion beam. The presence of oxygen in boron or nitrogen ion beams prevents the formation of boride and nitride phases thus decreasing a hardening effect [ru

The U phase formation in cement-based systems containing high amounts of Na2SO4

International Nuclear Information System (INIS)

Li, G.; Moranville, M.; Le Bescop, P.

1996-01-01

Simulated cemented low level wastes containing high amounts of Na 2 SO 4 (10--15%) were examined with respect to the mineralogy of the solid phases, chemical composition of the interstitial aqueous phase and immersion behavior in water. All results reveal the formation of a mineral called U phase, first observed by Dosch and zur Strassen in 1967, and its deleterious effects on the samples immersed in water. It appears that this phase can form only at very high alkaline concentration, not compatible with traditional cement paste. Two possible degradation mechanisms associated with the U phase are proposed which are to be elucidated in further works

FORMATION REGULARITIES OF PHASE COMPOSITION, STRUCTURE AND PROPERTIES DURING MECHANICAL ALLOYING OF BINARY ALUMINUM COMPOSITES

Directory of Open Access Journals (Sweden)

F. G. Lovshenko

2015-01-01

Full Text Available The paper presents investigation results pertaining to  ascertainment of formation regularities of phase composition and structure during mechanical alloying of binary aluminium composites/substances. The invetigations have been executed while applying a wide range of methods, devices and equipment used in modern material science. The obtained data complement each other. It has been established that presence of oxide and hydro-oxide films on aluminium powder  and introduction of surface-active substance in the composite have significant effect on mechanically and thermally activated phase transformations and properties of semi-finished products.  Higher fatty acids have been used as a surface active substance.The mechanism of mechanically activated solid solution formation has been identified. Its essence is  a formation of  specific quasi-solutions at the initial stage of processing. Mechanical and chemical interaction between components during formation of other phases has taken place along with dissolution  in aluminium while processing powder composites. Granule basis is formed according to the dynamic recrystallization mechanism and possess submicrocrystal structural type with the granule dimension basis less than 100 nm and the grains are divided in block size of not more than 20 nm with oxide inclusions of 10–20 nm size.All the compounds  with the addition of  surface-active substances including aluminium powder without alloying elements obtained by processing in mechanic reactor are disperse hardened. In some cases disperse hardening is accompanied by dispersive and solid solution hardnening process. Complex hardening predetermines a high temperature of recrystallization in mechanically alloyed compounds,  its value exceeds 400 °C.

Effect of Preparation Method on Phase Formation Process and Structural and Magnetic Properties of Mn2.5Ge Samples

Directory of Open Access Journals (Sweden)

R. Sobhani

2016-12-01

Full Text Available In this paper, the phase formation process of Mn2.5Ge samples, prepared by mechanical alloying of Mn and Ge metal powders and annealing, has been studied. Results showed that in the milled samples the stable phase is Mn11Ge8 compound with orthorhombic structure and Pnam space group. The value of saturation magnetization increases by increasing milling time from 0.2 up to 1.95 (Am2Kg-1. The remanece of the samples increases by increasing the milling time while the coercivity decreases. Annealing of 15-hour milled sample results in disappearance of Mn and Ge and the formation of new phases of Mn3Ge, Mn5Ge2, Mn5Ge3 and Mn2.3Ge. Mn3Ge is the main phase with Do22 tetragonal structure and I4/mmm space group which is stable and dominant. The enhancement of saturation magnetization in the annealed sample is related to the formation of three new magnetic phases and the increase of coercivity is due to the presence of Mn3Ge compound with tetragonal structure. Studies were replicated on samples made by arc melting method to compare the results and to investigate the effect of the preparation method on phase formation and structural and magnetic properties of the materials. In these samples the saturation value was in range of 0.2 up to 1.95 (Am2Kg-1 depending on preparation methods. Rietveld refinement shows that Mn2.3Ge sample prepared from arc melted under 620oC anealing is single phase. Magnetic analysis of this sample show a saturation magnetization of 5.252(Am2Kg-1 and 0.005 T coercive field.

Microstructure Formations in the Two-Phase Region of the Binary Peritectic Organic System TRIS-NPG

Science.gov (United States)

Mogeritsch, Johann; Ludwig, Andreas

2012-01-01

In order to prepare for an onboard experiment on the International Space Station (ISS), systematic directional solidification experiments with transparent hypoperitectic alloys were carried out at different solidification rates around the critical velocity for morphological stability of both solid phases. The investigations were done in the peritectic region of the binary transparent organic TRIS-NPG system where the formation of layered structures is expected to occur. The transparent appearance of the liquid and solid phase enables real time observations of the dynamic of pattern formation during solidification. The investigations show that frequently occurring nucleation events govern the peritectic solidification morphology which occurs at the limit of morphological stability. As a consequence, banded structures lead to coupled growth even if the lateral growth is much faster compared to the growth in pulling direction.

Vacancy enhanced formation and phase transition of Cu-rich precipitates in α - iron under neutron irradiation

Energy Technology Data Exchange (ETDEWEB)

Lv, G. C. [Basic Experimental Center of Natural Science, University of Science and Technology Beijing, Beijing, 100083 (China); Corrosion and Protection Center, Key Laboratory of Environmental Fracture (MOE), University of Science and Technology Beijing, Beijing, 100083 (China); Zhang, H. [Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Canada, T6G2V4 (Canada); He, X. F.; Yang, W. [China Institute of Atomic Energy, Beijing, 102413 (China); Su, Y. J., E-mail: yjsu@ustb.edu.cn [Corrosion and Protection Center, Key Laboratory of Environmental Fracture (MOE), University of Science and Technology Beijing, Beijing, 100083 (China)

2016-04-15

In this paper, we employed both molecular statics and molecular dynamics simulation methods to investigate the role of vacancies in the formation and phase transition of Cu-rich precipitates in α-iron. The results indicated that vacancies promoted the diffusion of Cu atoms to form Cu-rich precipitates. After Cu-rich precipitates formed, they further trapped vacancies. The supersaturated vacancy concentration in the Cu-rich precipitate induced a shear strain, which triggered the phase transition from bcc to fcc structure by transforming the initial bcc (110) plane into fcc (111) plane. In addition, the formation of the fcc-twin structure and the stacking fault structure in the Cu-rich precipitates was observed in dynamics simulations.

Formation and structural phase transition in Co atomic chains on a Cu(775) surface

International Nuclear Information System (INIS)

Syromyatnikov, A. G.; Kabanov, N. S.; Saletsky, A. M.; Klavsyuk, A. L.

2017-01-01

The formation of Co atomic chains on a Cu(775) surface is investigated by the kinetic Monte Carlo method. It is found that the length of Co atomic chains formed as a result of self-organization during epitaxial growth is a random quantity and its mean value depends on the parameters of the experiment. The existence of two structural phases in atomic chains is detected using the density functional theory. In the first phase, the separations between an atom and its two nearest neighbors in a chain are 0.230 and 0.280 nm. In the second phase, an atomic chain has identical atomic spacings of 0.255 nm. It is shown that the temperature of the structural phase transition depends on the length of the atomic chain.

Formation and structural phase transition in Co atomic chains on a Cu(775) surface

Energy Technology Data Exchange (ETDEWEB)

Syromyatnikov, A. G.; Kabanov, N. S.; Saletsky, A. M.; Klavsyuk, A. L., E-mail: klavsyuk@physics.msu.ru [Moscow State University (Russian Federation)

2017-01-15

The formation of Co atomic chains on a Cu(775) surface is investigated by the kinetic Monte Carlo method. It is found that the length of Co atomic chains formed as a result of self-organization during epitaxial growth is a random quantity and its mean value depends on the parameters of the experiment. The existence of two structural phases in atomic chains is detected using the density functional theory. In the first phase, the separations between an atom and its two nearest neighbors in a chain are 0.230 and 0.280 nm. In the second phase, an atomic chain has identical atomic spacings of 0.255 nm. It is shown that the temperature of the structural phase transition depends on the length of the atomic chain.

Effects of degradation on third phase formation in the extraction of Th(NO3)4 by trialkyl phosphates

International Nuclear Information System (INIS)

Benadict Rakesh, K.; Suresh, A.; Vasudeva Rao, P.R.

2014-01-01

It is well known that solvents undergo chemical and radiolytic degradation during processing and in general the degradation products affect organic-aqueous phase separation, extraction and stripping behaviour, density, viscosity etc. In the present study, an attempt has been made to understand the effects of irradiation (100 MRad with 60 Co- γ-source) on third phase formation in the extraction of Th(IV) from nitric acid media by 1.1 M solutions of tri-n-butyl phosphate (TBP) and tri-iso-amyl phosphate (TiAP) in n-dodecane (n-DD). Two types of irradiated solvents, namely Type 1 solvents containing only primary degradation products (formed by the degradation of TBP molecules) and Type 2 solvents containing primary as well as secondary degradation products (surfactant type molecules formed by the reaction between the degradation products of extractant and diluent) were prepared by dissolving required amount of irradiated extractant in unirradiated n-DD and irradiating 1.1 M solutions of extractant in n-DD, respectively. These solvents with and without washing with 5 M NaOH solution have been investigated for third phase formation. The variations of limiting organic concentration (LOC) for third phase formation as a function of equilibrium aqueous phase acidity are shown. LOC values for third phase formation by unirradiated solvents reported in our earlier work are also shown. These figures depict that LOC values for Type 1 solvents are lower than the corresponding unirradiated solvents and can be attributed to the decrease in the extractant concentration by degradation. Estimation of extractant in Type 1 solvents by nitric acid equilibration method after the removal of primary degradation products by washing with 5 M NaOH solution revealed that extractant concentrations have been reduced to 1.03 M and 1.05 M for TBP and TiAP, respectively. Estimation of extractant in Type 2 solvents revealed 1.07 M extractant concentration in TBP and TiAP solvents. However, data

SANS study of Th (IV) third phase formation in HNO3 / DHDECMP-n-dodecane system

International Nuclear Information System (INIS)

Lohithakshan, K.V.; Aggarwal, S.K.; Aswal, V.K.

2009-01-01

Third phase formation taking place during the extraction of Th (IV) from nitric acid medium by DHDECMP in dodecane has been investigated by small angle neutron scattering (SANS) and explained the process with Baxter model. (author)

Influence of the selected alloy additions on limiting the phase formation in Cu-Zn alloys

OpenAIRE

J. Kozana; St. Rzadkosz; M. Piękoś

2010-01-01

Influence of the selected alloy additions into copper and zinc alloys was investigated in order to find out the possibility of limiting the precipitation of unfavourable phase . The observation of microstructures and strength tests were performed. The results of metallographic and strength investigations indicate positive influence of small amounts of nickel, cobalt or tellurium. The precise determination of the influence of the selected alloy additions on limiting the gamma phase formation ...

Pattern Formation During Phase Separation of Polymer-Ionic Liquid Co-Solutions

Science.gov (United States)

Meng, Zhiyong; Osuji, Chinedum

2010-03-01

Co-solutions of polystyrene (PS) with a 1-butyl-3-methylimidazolium based ionic liquid (IL) in DMF phase separated into IL-rich and PS-rich domains on solvent evaporation. Over a limited range of polymer molecular weights and substrate temperatures, a variety of striped and cellular or polygonal structures were found on the resulting film surface, as visualized using bright-field and phase-contrast optical microscopy. This effect appears to be due to a Benard-Marangoni instability at the free surface of the liquid film as it undergoes evaporation, setting up convection rolls inside the fluid which become locked in place as the system vitrifies on solvent removal. Differential scanning calorimetry shows that the IL does not significantly plasticize the polymer, suggesting that the viscosity of the polystyrene solution itself controls the formation of this instability.

On the competition in phase formation during the crystallisation of Al-Ni-Y metallic glasses

International Nuclear Information System (INIS)

Styles, M.J.; Sun, W.W.; East, D.R.; Kimpton, J.A.; Gibson, M.A.; Hutchinson, C.R.

2016-01-01

Glassy metals exhibit a range of interesting properties including high strength and corrosion resistance, but often have poor toughness and tensile ductility in the fully amorphous state. It has been shown that combinations of desirable properties can be achieved by the partial crystallisation of glass-forming alloys, either during controlled solidification or by annealing a fully amorphous glass. The aim of this investigation is to understand the competition in phase formation during the crystallisation of metallic glasses in the Al-Ni-Y system. High-resolution, in situ synchrotron powder diffraction has been used to quantitatively follow the evolution of phases in 5 different alloys between Al 87 Ni 9 Y 4 and Al 75 Ni 15 Y 10 , as they were continuously heated to melting and subsequently cooled back to ambient temperature. Upon heating, the first crystallisation product was found to vary from FCC Al to the intermetallic Al 9 Ni 2 phase with increasing Ni concentration. In addition, the crystallisation sequence also changed from a two-stage to a three-stage process. High number densities of crystallites (∼10 23  m −3 ) were observed initially for both FCC Al and Al 9 Ni 2 . Upon cooling, the partially disordered Al 9 Ni 3 Y phase was found to form preferentially over the intermetallic phases observed during heating. The difference in competition in phase formation during heating and cooling are discussed in terms of nucleation barriers calculated using a recent thermodynamic assessment of the Al-Ni-Y system. The role of compositional heterogeneities in the as-quenched glasses and long-range diffusion on the nucleation process is discussed. - Graphical abstract: High-resolution, in situ synchrotron powder diffraction has been used to quantitatively follow the evolution of phases in 5 different alloys between Al 87 Ni 9 Y 4 and Al 75 Ni 15 Y 10 , as they were continuously heated to melting and subsequently cooled back to ambient temperature. Upon heating, the

Rapid formation of the 110 K phase in Bi-Pb-Sr-Ca-Cu-O through freeze-drying powder processing

International Nuclear Information System (INIS)

Song, K.H.; Liu, H.K.; Dou, S.X.; Sorrell, C.C.

1990-01-01

This paper reports three techniques for processing Bi-Pb-Sr-Ca-Cu-O (BPSCCO) powders investigated: dry-mixing, sol-gel formation, and freeze-drying. It was found that sintering for 120 h at 850 degrees C is required to form nearly single-phase (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10-y by dry-mixing, whereas sintering for 30 h at 840 degrees C was sufficient to form the 110 K (2223) phase when freeze-drying was used. The sol-gel route was found to be intermediate in efficiency between these two techniques. Freeze-drying provided highly reactive, intimately mixed, and carbon-free precursors. The presence of carbonates in the uncalcined powders was the major cause of phase segregation and sluggishness of the 110 K phase formation

Brownian dynamics and dynamic Monte Carlo simulations of isotropic and liquid crystal phases of anisotropic colloidal particles: a comparative study.

Science.gov (United States)

Patti, Alessandro; Cuetos, Alejandro

2012-07-01

We report on the diffusion of purely repulsive and freely rotating colloidal rods in the isotropic, nematic, and smectic liquid crystal phases to probe the agreement between Brownian and Monte Carlo dynamics under the most general conditions. By properly rescaling the Monte Carlo time step, being related to any elementary move via the corresponding self-diffusion coefficient, with the acceptance rate of simultaneous trial displacements and rotations, we demonstrate the existence of a unique Monte Carlo time scale that allows for a direct comparison between Monte Carlo and Brownian dynamics simulations. To estimate the validity of our theoretical approach, we compare the mean square displacement of rods, their orientational autocorrelation function, and the self-intermediate scattering function, as obtained from Brownian dynamics and Monte Carlo simulations. The agreement between the results of these two approaches, even under the condition of heterogeneous dynamics generally observed in liquid crystalline phases, is excellent.

Formation of secondary phases during the corrosion of vitrified nuclear waste

International Nuclear Information System (INIS)

Zimmer, P.

2003-11-01

The first aim of this work was the examination of the formation and long-term stability of secondary phases that form during an aquatic attack on simulated, vitrified nuclear waste. In the glasses used for the investigations actinides had been replaced by rare earth elements (chemical analogues), other radionuclides by inactive isotopes. For predictions about the long-term safety of nuclear waste disposals it is important to identify secondary phases that have formed during the glass corrosion process and to determine their stability. Two different saline solutions (rich in MgCl 2 and in NaCl, respectively) are relevant as a corrosion medium for waste disposals. It showed that in such an environment sulfates, silicates and molybdates represent the main new formations of minerals after 7.5 years of corrosion. However, the formation, long-term stability and sorption characteristics of those minerals regarding rare earth elements depend to a high degree on the corrosion medium as well as on changes in the geochemical environment in the course of the experiment. By means of SEM/EDX barytes of different morphology with up to 15% w/w Sr ((Ba,Sr)SO 4 ) were identified in both corrosion media; they were capable of binding long-term stable radionuclides like Sr. Furthermore, pure rare earth (RE) sulfates were observed in the saline solution rich in MgCl 2 . This formation of RE-sulfates has not been described in the literature so far. Depending on the saline solution, the secondary silicate and molybdate minerals that formed on the glass surfaces differed noticeably in their sorption characteristics and their stability. Another focus of the work was a more profound understanding of the glass corrosion mechanism in the presence of metallic iron since steel jackets are used as technical barriers for the vitrified nuclear waste in nuclear waste disposals. Another important point in connection with the mobilization and immobilization of radionuclides released during glass

p-type doping efficiency in CdTe: Influence of second phase formation

Science.gov (United States)

McCoy, Jedidiah J.; Swain, Santosh K.; Sieber, John R.; Diercks, David R.; Gorman, Brian P.; Lynn, Kelvin G.

2018-04-01

Cadmium telluride (CdTe) high purity, bulk, crystal ingots doped with phosphorus were grown by the vertical Bridgman melt growth technique to understand and improve dopant solubility and activation. Large net carrier densities have been reproducibly obtained from as-grown ingots, indicating successful incorporation of dopants into the lattice. However, net carrier density values are orders of magnitude lower than the solubility of P in CdTe as reported in literature, 1018/cm3 to 1019/cm3 [J. H. Greenberg, J. Cryst. Growth 161, 1-11 (1996) and R. B. Hall and H. H. Woodbury, J. Appl. Phys. 39(12), 5361-5365 (1968)], despite comparable starting charge dopant densities. Growth conditions, such as melt stoichiometry and post growth cooling, are shown to have significant impacts on dopant solubility. This study demonstrates that a significant portion of the dopant becomes incorporated into second phase defects as compounds of cadmium and phosphorous, such as cadmium phosphide, which inhibits dopant incorporation into the lattice and limits maximum attainable net carrier density in bulk crystals. Here, we present an extensive study on the characteristics of these second phase defects in relation to their composition and formation kinetics while providing a pathway to minimize their formation and enhance solubility.

Energy of formation for AgIn liquid binary alloys along the line of phase separation

CERN Document Server

Bhuiyan, G M; Ziauddin-Ahmed, A Z

2003-01-01

We have investigated the energy of formation for AgIn liquid binary alloys along the solid-liquid phase separation line. A microscopic theory based on the first order perturbation has been applied. The interionic interaction and a reference liquid are the fundamental components of the theory. These are described by a local pseudopotential and the hard sphere liquids, respectively. The results of calculations reveal a characteristic feature that the energy of formation becomes minimum at the equiatomic composition, and thus indicates maximal mix-ability at this concentration. The energy of formation at a particular thermodynamic state that is at T 1173 K predicts the experimental trends fairly well.

Formation of metastable and equilibrium phases in the decomposition of the β solid solution in Zr alloys

International Nuclear Information System (INIS)

Zakharova, M.I.; Kirov, S.A.; Khundzhua, A.G.

1978-01-01

The decomposition of the β solid solution is studied in Zr-Nb alloys with adding Mo, Al, V, Fe by the methods of electron microscopy and X-ray diffraction on single crystals. The intermetallic compounds forming during crystallization of the alloys do not influence the precipitation of the ω- and α-phases during ageing. In the local regions of foils prepared by electropolishing after ageing the formation of the metastable f.c.c. phase and in some cases the inverse transformation of two phase state to the parent phase is observed. (author)

A study of the formation processes of the 2212 phase in the Bi-based superconductor systems. [BiSrCaCuO

Energy Technology Data Exchange (ETDEWEB)

Wai, Lo; Glowacki, B A [Interdisciplinary Research Centre in Superconductivity, Univ. of Cambridge (United Kingdom)

1992-04-15

A study towards the identification of the reactions contributing to and accompanying the formation of the 2212 phase from oxides and carbonates by solid state reaction processes was conducted. The formation processes were investigated by thermal analysis, powder X-ray diffractometry and AC magnetic susceptometry. The 2212 phase was found to form from reactions between the 2201 phases (the non-superconducting pseudo-tetragonal and the superconducting monoclinic phases), Bi{sub 6}Ca{sub 7}O{sub 16}, CuO and SrCO{sub 3}. The 2201 phases were produced by the reactions of Bi-Sr-Cu-O or Bi-Sr-O compounds with SrCO{sub 3} or CuO. The 2201 phases could also be formed through the direct reaction between Bi{sub 2}CuO{sub 4} and SrCO{sub 3}. (orig.).

Quasicrystalline phase formation in the mechanically alloyed Al{sub 70}Cu{sub 20}Fe{sub 10}

Energy Technology Data Exchange (ETDEWEB)

Medeiros, S. N. de, E-mail: snm@dfi.uem.br; Cadore, S.; Pereira, H. A.; Santos, I. A.; Colucci, C. C.; Paesano, A. [Universidade Estadual de Maringa, Departamento de Fisica (Brazil)

2010-01-15

In the present work, the formation of the Al{sub 70}Cu{sub 20}Fe{sub 10} icosahedral phase by mechanical alloying the elemental powders in a high-energy planetary mill was investigated by X-ray diffraction and Moessbauer spectroscopy. It was verified that the sample milled for 80 h produces an icosahedral phase besides Al(Cu, Fe) solid solution ({beta}-phase) and Al{sub 2}Cu intermetallic phase. The Moessbauer spectrum for this sample was fitted with a distribution of quadrupole splitting, a doublet and a sextet, revealing the presence of the icosahedral phase, {beta}-phase and {alpha}-Fe, respectively. This compound is not a good hydrogen storage. The results of the X-ray diffraction and Moessbauer spectroscopy of the sample milled for 40 h and annealed at 623 deg. C for 16 h shows essentially single i-phase and tetragonal Al{sub 7}Cu{sub 2} Fe phase.

Mechanism of formation of perovskite phase and dielectric properties of Pb(Zn,Mg)1/3Nb2/3O3 ceramics prepared by columbite precursor routes

International Nuclear Information System (INIS)

Jang, H.M.; Cho, S.R.; Lee, K.M.

1995-01-01

The mechanism of formation of the perovskite phase and the dielectric properties of Pb(Zn,Mg) 1/3 Nb 2/3 O 3 (PZMN) ceramics were examined using two different types of columbite precursors, (Mg,Zn)Nb 2 O 6 (MZN) and MgNb 2 O 6 + ZnNb 2 O 6 (MN + ZN). The formation of perovskite phase in the PbO + MN + ZN system is characterized by an initial rapid formation of Mg-rich perovskite phase, followed by a sluggish formation of Zn-rich perovskite phase. On the other hand, due to the formation of pyrochlore phase of mixed divalent cations Pb 2-x (Zn,Mg) y Nb 2-y O 7-x-3y/2 , the pyrochlore/perovskite transformation in the PbO + MZN system proceeded uniformly with a spatial homogeneity. Further analysis suggested that the formation of perovskite phase is a diffusion-controlled process. The degree of diffuseness of the rhombohedral/cubic phase transition (DPT) is higher in the PbO + MN + ZN system than in the PbO + MZN specimen for T > T max (temperature of the dielectric permittivity maximum), indicating a broadened compositional distribution of the B-site cations in the PbO + MN + ZN system

Up-scaling, formative phases, and learning in the historical diffusion of energy technologies

International Nuclear Information System (INIS)

Wilson, Charlie

2012-01-01

The 20th century has witnessed wholesale transformation in the energy system marked by the pervasive diffusion of both energy supply and end-use technologies. Just as whole industries have grown, so too have unit sizes or capacities. Analysed in combination, these unit level and industry level growth patterns reveal some consistencies across very different energy technologies. First, the up-scaling or increase in unit size of an energy technology comes after an often prolonged period of experimentation with many smaller-scale units. Second, the peak growth phase of an industry can lag these increases in unit size by up to 20 years. Third, the rate and timing of up-scaling at the unit level is subject to countervailing influences of scale economies and heterogeneous market demand. These observed patterns have important implications for experience curve analyses based on time series data covering the up-scaling phases of energy technologies, as these are likely to conflate industry level learning effects with unit level scale effects. The historical diffusion of energy technologies also suggests that low carbon technology policies pushing for significant jumps in unit size before a ‘formative phase’ of experimentation with smaller-scale units are risky. - Highlights: ► Comparative analysis of energy technology diffusion. ► Consistent pattern of sequential formative, up-scaling, and growth phases. ► Evidence for conflation of industry level learning effects with unit level up-scaling. ► Implications for experience curve analyses and technology policy.

Effect of calcination routes on phase formation of BaTiO3 and their electronic and magnetic properties

Science.gov (United States)

Majumder, Supriyo; Choudhary, R. J.; Tripathi, M.; Phase, D. M.

2018-05-01

We have investigated the phase formation and correlation between electronic and magnetic properties of oxygen deficient BaTiO3 ceramics, synthesized by solid state reaction method, following different calcination paths. The phase analysis divulge that a higher calcination temperature above 1000° C is favored for tetragonal phase formation than the cubic phase. The core level X-ray photo electron spectroscopy measurements confirm the presence of oxygen vacancies and oxygen vacancy mediated Ti3+ states. As the calcination temperature and calcination time increases these oxygen vacancies and hence Ti3+ concentrations reduce in the sample. The temperature dependent magnetization curves suggest unexpected magnetic ordering, which may be due to the presence of unpaired electron at the t2g state (d1) of nearest-neighbor Ti atoms. In magnetization vs magnetic field isotherms, the regular decrease of saturation moment value with increasing calcination temperature and calcination time, can be discussed considering the amount of oxygen deficiency induced Ti3+ concentrations, present in the sample.

Phase formation in Mg-Sn-Si and Mg-Sn-Si-Ca alloys

Energy Technology Data Exchange (ETDEWEB)

Kozlov, A.; Groebner, J. [Institute of Metallurgy, Clausthal University of Technology, Robert-Koch-Str. 42, D-38678 Clausthal-Zellerfeld (Germany); Schmid-Fetzer, R., E-mail: schmid-fetzer@tu-clausthal.de [Institute of Metallurgy, Clausthal University of Technology, Robert-Koch-Str. 42, D-38678 Clausthal-Zellerfeld (Germany)

2011-02-17

Research highlights: > The solidification paths of ternary and quaternary alloys are analyzed in detail, using the tool of thermodynamic calculations. > The precipitation sequence of phases and their amounts compare well with the microstructure of alloys. > The most efficient comparison to the experimental thermal analysis data is done by calculation of the enthalpy variation with temperature. > The viability of a procedure for the selection of multicomponent key samples is demonstrated for the development of the Mg-Ca-Si-Sn phase diagram. - Abstract: Experimental work is done and combined with the Calphad method to generate a consistent thermodynamic description of the Mg-Ca-Si-Sn quaternary system, validated for Mg-rich alloys. The viability of a procedure for the selection of multicomponent key samples is demonstrated for this multicomponent system. Dedicated thermal analysis with DTA/DSC on sealed samples is performed and the microstructure of slowly solidified alloys is analyzed using SEM/EDX. The thermodynamic description and phase diagram of the ternary Mg-Si-Sn system, developed in detail also in this work, deviates significantly from a previous literature proposal. The phase formation in ternary and quaternary alloys is analyzed using the tool of thermodynamic equilibrium and Scheil calculations for the solidification paths and compared with present experimental data. The significant ternary/quaternary solid solubilities of pertinent intermetallic phases are quantitatively introduced in the quaternary Mg-Ca-Si-Sn phase diagram and validated by experimental data.

Heterogeneity-enhanced gas phase formation in shallow aquifers during leakage of CO2-saturated water from geologic sequestration sites

DEFF Research Database (Denmark)

Plampin, Michael R.; Lassen, Rune Nørbæk; Sakaki, Toshihiro

2014-01-01

sands. Soil moisture sensors were utilized to observe the formation of gas phase near the porous media interfaces. Results indicate that the conditions under which heterogeneity controls gas phase evolution can be successfully predicted through analysis of simple parameters, including the dissolved CO2......, it is important to understand the physical processes that CO2 will undergo as it moves through naturally heterogeneous porous media formations. Previous studies have shown that heterogeneity can enhance the evolution of gas phase CO2 in some cases, but the conditions under which this occurs have not yet been...... quantitatively defined, nor tested through laboratory experiments. This study quantitatively investigates the effects of geologic heterogeneity on the process of gas phase CO2 evolution in shallow aquifers through an extensive set of experiments conducted in a column that was packed with layers of various test...

Influence of the selected alloy additions on limiting the phase formation in Cu-Zn alloys

Directory of Open Access Journals (Sweden)

J. Kozana

2010-01-01

Full Text Available Influence of the selected alloy additions into copper and zinc alloys was investigated in order to find out the possibility of limiting the precipitation of unfavourable phase . The observation of microstructures and strength tests were performed. The results of metallographic and strength investigations indicate positive influence of small amounts of nickel, cobalt or tellurium. The precise determination of the influence of the selected alloy additions on limiting the gamma phase formation will be the subject of further examinations.

The Genealogical Tree of Ethanol: Gas-phase Formation of Glycolaldehyde, Acetic Acid, and Formic Acid

Science.gov (United States)

Skouteris, Dimitrios; Balucani, Nadia; Ceccarelli, Cecilia; Vazart, Fanny; Puzzarini, Cristina; Barone, Vincenzo; Codella, Claudio; Lefloch, Bertrand

2018-02-01

Despite the harsh conditions of the interstellar medium, chemistry thrives in it, especially in star-forming regions where several interstellar complex organic molecules (iCOMs) have been detected. Yet, how these species are synthesized is a mystery. The majority of current models claim that this happens on interstellar grain surfaces. Nevertheless, evidence is mounting that neutral gas-phase chemistry plays an important role. In this paper, we propose a new scheme for the gas-phase synthesis of glycolaldehyde, a species with a prebiotic potential and for which no gas-phase formation route was previously known. In the proposed scheme, the ancestor is ethanol and the glycolaldehyde sister species are acetic acid (another iCOM with unknown gas-phase formation routes) and formic acid. For the reactions of the new scheme with no available data, we have performed electronic structure and kinetics calculations deriving rate coefficients and branching ratios. Furthermore, after a careful review of the chemistry literature, we revised the available chemical networks, adding and correcting several reactions related to glycolaldehyde, acetic acid, and formic acid. The new chemical network has been used in an astrochemical model to predict the abundance of glycolaldehyde, acetic acid, and formic acid. The predicted abundance of glycolaldehyde depends on the ethanol abundance in the gas phase and is in excellent agreement with the measured one in hot corinos and shock sites. Our new model overpredicts the abundance of acetic acid and formic acid by about a factor of 10, which might imply a yet incomplete reaction network.

Local Cloudiness Development Forecast Based on Simulation of Solid Phase Formation Processes in the Atmosphere

Science.gov (United States)

Barodka, Siarhei; Kliutko, Yauhenia; Krasouski, Alexander; Papko, Iryna; Svetashev, Alexander; Turishev, Leonid

2013-04-01

Nowadays numerical simulation of thundercloud formation processes is of great interest as an actual problem from the practical point of view. Thunderclouds significantly affect airplane flights, and mesoscale weather forecast has much to contribute to facilitate the aviation forecast procedures. An accurate forecast can certainly help to avoid aviation accidents due to weather conditions. The present study focuses on modelling of the convective clouds development and thunder clouds detection on the basis of mesoscale atmospheric processes simulation, aiming at significantly improving the aeronautical forecast. In the analysis, the primary weather radar information has been used to be further adapted for mesoscale forecast systems. Two types of domains have been selected for modelling: an internal one (with radius of 8 km), and an external one (with radius of 300 km). The internal domain has been directly applied to study the local clouds development, and the external domain data has been treated as initial and final conditions for cloud cover formation. The domain height has been chosen according to the civil aviation forecast data (i.e. not exceeding 14 km). Simulations of weather conditions and local clouds development have been made within selected domains with the WRF modelling system. In several cases, thunderclouds are detected within the convective clouds. To specify the given category of clouds, we employ a simulation technique of solid phase formation processes in the atmosphere. Based on modelling results, we construct vertical profiles indicating the amount of solid phase in the atmosphere. Furthermore, we obtain profiles demonstrating the amount of ice particles and large particles (hailstones). While simulating the processes of solid phase formation, we investigate vertical and horizontal air flows. Consequently, we attempt to separate the total amount of solid phase into categories of small ice particles, large ice particles and hailstones. Also, we

Controlling phase formation during aluminium/steel Nd:YAG laser brazing

Directory of Open Access Journals (Sweden)

Rodriguez, L.

2006-12-01

Full Text Available The reduction of fuel consumption of internal combustion motors, imposed by the new anti-pollution and energy saving laws may be attained by reducing the weight of vehicles, introducing, for example, aluminium sections into the main steel car-body. Laser brazing is a process which can be used to perform such a junction. The main problem of welding this kind of materials combination with conventional processes is the potential formation of inter-metallic phases, which reduces the good performance of the joint. Laser brazing allows a very good control of the thermal development of the joint, with a limited precipitation of these brittle phases. This paper presents the results of a feasibility study made with ZnAl-30 as filler metal. The study shows that the type of configuration used for the assembly has a particular influence on the formation of brittle phases and consequently on the mechanical performance of the joint.

La reducción en el consumo de combustibles fósiles y las emergentes leyes mundiales anti-contaminación, obligan a prever una reducción en el peso de los vehículos de transporte. Esta condición se puede cumplir por ejemplo, introduciendo componentes de Aluminio en el cuerpo de la carrocería principal de acero de los mencionados vehículos. El principal problema que se presenta al realizar este tipo de ensamblaje es la formación de fases íntermetálicas frágiles que pueden comprometer el buen desenvolvimiento de la unión. La soldadura con rayo láser permite un buen control de calor aportado y una formación muy limitada de este tipo de fases. Este trabajo presenta los resultados preliminares de los estudios realizados en uniones soldadas con ZnAl-30 como material de aportación. El estudio muestra que el tipo de configuración utilizada para realizar la soldadura tiene una influencia importante sobre la posibilidad de formación de estas fases ínter-metálicas.

Third phase formation in the extraction of Th(NO{sub 3}){sub 4} by Tri-sec-butyl phosphate. A comparison with Tri-n-butyl phosphate

Energy Technology Data Exchange (ETDEWEB)

Chandrasekar, Aditi; Suresh, A.; Sivaraman, N. [Indira Gandhi Centre for Atomic Research, Kalpakkam (India). Chemistry Group

2017-06-01

Earlier studies carried out in our laboratory indicated that Tri-sec-butyl phosphate (TsBP) is a potential extractant for U/Th separation. Also, the third phase formation tendency of TsBP is lower compared to its isomers, Tri-n-butyl-phosphate (TBP) and Tri-iso-butyl phosphate (TiBP). In this context, the extraction and third phase formation behaviour of 1.1 M solutions of TiBP and TsBP in n-dodecane in the extraction of Th(IV) from 1 M HNO{sub 3} at 303 K over a wide range of Th concentrations were investigated in the present study and the results are compared with the literature data on TBP system. Concentrations of Th(IV) and HNO{sub 3} loaded in the organic phase before third phase formation (biphasic region) as well as in third phase and diluent-rich phase after third phase formation (triphasic region) were measured as a function of equilibrium aqueous phase Th(IV) concentration. The density of loaded organic phase was also measured at various Th(IV) concentrations. The extraction profiles in the biphasic region indicated that extraction of Th(IV) by TBP is higher than that of TiBP which in turn is higher than that of TsBP. Extractant concentration in the diluent-rich phase and third phase was measured for the triphasic region.

Phase recording for formation of holographic optical elements on silver-halide photographic emulsions

Science.gov (United States)

Ganzherli, Nina M.; Gulyaev, Sergey N.; Maurer, Irina A.; Chernykh, Dmitrii F.

2009-05-01

Holographic fabrication methods of regular and nonregular relief-phase structures on silver-halide photographic emulsions are considered. Methods of gelatin photodestruction under short-wave ultra-violet radiation and chemical hardening with the help of dichromated solutions were used as a technique for surface relief formation. The developed techniques permitted us to study specimens of holographic diffusers and microlens rasters with small absorption and high light efficiency.

Resonant x-ray scattering study of the antiferroelectric and ferrielectric phases in liquid crystal devices

International Nuclear Information System (INIS)

Matkin, L. S.; Watson, S. J.; Gleeson, H. F.; Pindak, R.; Pitney, J.; Johnson, P. M.; Huang, C. C.; Barois, P.; Levelut, A.-M.; Srajer, G.

2001-01-01

Resonant x-ray scattering has been used to investigate the interlayer ordering of the antiferroelectric and ferrielectric smectic C * subphases in a device geometry. The liquid crystalline materials studied contain a selenium atom and the experiments were carried out at the selenium K edge allowing x-ray transmission through glass. The resonant scattering peaks associated with the antiferroelectric phase were observed in two devices containing different materials. It was observed that the electric-field-induced antiferroelectric to ferroelectric transition coincides with the chevron to bookshelf transition in one of the devices. Observation of the splitting of the antiferroelectric resonant peaks as a function of applied field also confirmed that no helical unwinding occurs at fields lower than the chevron to bookshelf threshold. Resonant features associated with the four-layer ferrielectric liquid crystal phase were observed in a device geometry. Monitoring the electric field dependence of these ferrielectric resonant peaks showed that the chevron to bookshelf transition occurs at a lower applied field than the ferrielectric to ferroelectric switching transition

Observation of paramorphic phenomenon and non-tilted orthogonal smectic phases in hydrogen bonded ferroelectric liquid crystals for photonic applications

Science.gov (United States)

Subhasri, P.; Venugopal, D.; Jayaprakasam, R.; Chitravel, T.; Vijayakumar, V. N.

2018-06-01

A new class of hydrogen bonded ferroelectric liquid crystals (HBFLC) have been designed and synthesized by intermolecular hydrogen bonds between mesogenic 4-decyloxybenzoic acid (10OBA) and non-mesogenic (R)-(+)-Methylsuccinic acid (MSA) which have been confirmed through experimental and theoretical studies. Further, Mulliken population analysis clearly reveals that the existence of hydrogen bonds, strength and dynamic properties. Textural observation and its corresponding enthalpy values are analyzed by polarizing optical microscope (POM) and differential scanning calorimetry (DSC) respectively. Paramorphic changes in Sm C* phase due to the change of refractive index, which clearly reveal that the complex could be used for filtering action in photonic devices. The transition from lone pair to π* with large stabilization energy evidently exposes the chiral phases in the present HBFLC complex. Intermolecular interaction is analyzed by using natural bond orbital (NBO) studies. The highest energy in the HOMO-LUMO shows the stable phase in the HBFLC complex. Molecular structure of the HBFLC complex possesses the monoclinic which has been evinced through x-ray analysis. The randomly oriented bunch of homogeneous molecules in Sm A* phase of the HBFLC complex is reported.

Calorimetric Study of Phase Transitions Involving Twist-Grain-Boundary TGB{A} and TGB{C} Phases

Science.gov (United States)

Navailles, L.; Garland, C. W.; Nguyen, H. T.

1996-09-01

High-resolution calorimetry has been used to determine the heat capacity and latent heat associated with phase transitions in the homologous series of chiral liquid crystals nF_2BTFO_1M_7 [ 3-fluoro-4(1-methylheptyloxy)4'-(4''-alkoxy-2'', 3''-difluorobenzoyloxy)tolane] . These compounds exhibit smectic-C^* (SmC^*), twist-grain-boundary (TGBA for n=10, TGBC for n=11, 12) and cholesteric (N^*) phases. All the phase transitions are first order with small to moderate latent heats. There is a large rounded excess heat capacity peak in the N^* phase that is consistent with the predicted appearance of short-range TGB order (chiral line liquid character). This is analogous to the development of an Abrikosov flux vortex liquid in type-II superconductors. Both the n=11 and 12 homologs exhibit two closely spaced transitions in the region where a single TGBC - N^* transition was expected. This suggests the existence of two thermodynamically distinct TGBC phases. Des exprériences de calorimétrie haute résolution ont été réalisées pour déterminer les chaleurs spécifiques et les chaleurs latentes associées aux transitions de phase des homologues de la série crystal liquide nF_2BTFO_1M_7: 3-fluoro-4[1-methyl-heptyloxy]4'-(4''-alcoxy-2'', 3''-difluorobenzoyloxy)tolanes. Ces produits présentent la phase smectique C^* (SmC^*), les phases à torsion par joint de grain (TGBA pour n=10 et TGBC pour n=11, 12) et la phase cholestérique (N^*). Toutes les transitions de phase sont du premier ordre. La chaleur latente associée à ces transitions est faibles ou modérée. Nous observons, dans la phase N^*, un grand pic arrondi qui est en accord avec les prédictions de l'apparition d'un ordre TGB à courte distance (liquide de ligne de dislocation). Ce phénomène est l'analogue du liquide de vortex dans les supraconducteurs de type II. Les composés n=11 et 12 présentent, dans la région où nous attendions une transition TGBC - N^* unique, deux transitions sur un très faible

Asymmetric Conjugated Molecules Based on [1]Benzothieno[3,2-b][1]benzothiophene for High-Mobility Organic Thin-Film Transistors: Influence of Alkyl Chain Length.

Science.gov (United States)

He, Keqiang; Li, Weili; Tian, Hongkun; Zhang, Jidong; Yan, Donghang; Geng, Yanhou; Wang, Fosong

2017-10-11

Herein, we report the synthesis and characterization of a series of [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based asymmetric conjugated molecules, that is, 2-(5-alkylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene (BTBT-Tn, in which T and n represent thiophene and the number of carbons in the alkyl group, respectively). All of the molecules with n ≥ 4 show mesomorphism and display smectic A, smectic B (n = 4), or smectic E (n > 4) phases and then crystalline phases in succession upon cooling from the isotropic state. Alkyl chain length has a noticeable influence on the microstructures of vacuum-deposited films and therefore on the performance of the organic thin-film transistors (OTFTs). All molecules except for 2-(thiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene and 2-(5-ethylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene showed OTFT mobilities above 5 cm 2 V -1 s -1 . 2-(5-Hexylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene and 2-(5-heptylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene showed the greatest OTFT performance with reliable hole mobilities (μ) up to 10.5 cm 2 V -1 s -1 because they formed highly ordered and homogeneous films with diminished grain boundaries.

Altering the cooling rate dependence of phase formation during rapid solidification in the Nd{sub 2}Fe{sub 14}B system

Energy Technology Data Exchange (ETDEWEB)

Branagan, D.J. [USDOE, Ames, IA (United States). Ames Lab.]|[Iowa State Univ. of Science and Technology, Ames, IA (United States). Dept. of Materials Science and Engineering; McCallum, R.W. [USDOE, Ames, IA (United States). Ames Lab.]|[Iowa State Univ. of Science and Technology, Ames, IA (United States). Dept. of Materials Science and Engineering

1995-04-26

In order to evaluate the effects of additions on the solidification behavior of Nd{sub 2}Fe{sub 14}B, a stoichiometric alloy was modified with elemental additions of Ti or C and a compound addition of Ti with C. For each alloy, a series of wheel speed runs was undertaken, from which the optimum wheel speeds and optimum energy products were determined. On the BH{sub max} versus wheel speed plots, regions were identified in order to analyze the changes with cooling rates leading to phase formation brought about by the alloy modifications. The compilation of the regional data of the modified alloys showed their effects on altering the cooling rate dependence of phase formation. It was found that the regions of properitectic iron formation, glass formation, and the optimum cooling rate can be changed by more than a factor of two through appropriate alloying additions. The effects of the alloy modifications can be visualized in a convenient fashion through the use of a model continuous cooling transformation (CCT) diagram which represents phase formation during the solidification process under continuous cooling conditions for a wide range of cooling rates from rapid solidification to equilibrium cooling. ((orig.)).

Investigation on the formation of a third phase in the extraction of Pu(IV) nitrate with tributyl phosphate

International Nuclear Information System (INIS)

Yu Enjiang; Liu Liming; Huang Huaian

1986-01-01

The formation of a third phase is studied in the system Pu(IV) nitratenitric acid-TBP-alkane diluent (or kerosine). The maximum concentration (solubility, S Pu ) of Pu(IV) in the equilibrium organic phase at which still no third phase is formed is measured as a function of the nitric acid concentration in the equilibrium aqueous phase C H , the temperature, and the molecular size of n-alkane duluent. Results show that maxima of S Pu at 6 to 7 M nitric acid are observed at 17 deg C, 26 deg C and 35 deg C while not at 40 deg C. Minima on the S Pu vs. C H curves at 0.5 to 2 M mitric acid have been observed at 17 deg C and 26 deg C. It is found that the molecular size of n-alkane diluents has a very pronounced effect on S Pu . The effect of aqueous equilibrium Pu(IV) concentration on the formation of a third phase is investigated, when the equilibrium HNO 3 concentration is 3.5 M. It is shown that the plutonium concentration of the third phase is increased with increasing aqueous equilibrium Pu(IV) concentration. The effect of the addition of lauryl alcohol on the S Pu is preliminarily studied

Characterisation of iron inclusion during the formation of calcium sulfoaluminate phase

International Nuclear Information System (INIS)

Idrissi, M.; Diouri, A.; Damidot, D.; Greneche, J.M.; Talbi, M. Alami; Taibi, M.

2010-01-01

The iron distribution among the sulfoaluminate clinker phases and its ability to enter the calcium sulfoaluminate lattice in solid solution can have a significant influence on manufacturing process and reactivity of calcium sulfoaluminate (CSA) cements. X-ray diffraction (XRD) analysis, Moessbauer spectroscopy, scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analysis system (EDAX) and infrared spectroscopy were used to identify the mineralogical conditions of iron inclusion during the formation of calcium sulfoaluminate (C 4 A 3 S) phase from different mixtures in the CaO-Al 2 O 3 -Fe 2 O 3 -SO 3 system. The mixtures, heated in a laboratory electric oven, contained stoichiometric amounts of reagent grade CaCO 3 , Al 2 O 3 , Fe 2 O 3 and CaSO 4 .2H 2 O for the synthesis of Ca 4 Al (6- 2x) Fe 2x SO 16 , where x, comprised between 0 and 3, is the mole number of Al 2 O 3 substituted by Fe 2 O 3 . With x increasing from 0 to 1.5, both the iron content of C 4 A 3 S phase and the amounts of side components such as C 2 F and CS increased. For x values included in the range of 1.5-3.0, at temperatures higher than 1200 o C, melting phenomena were observed and, instead of the C 4 A 3 S solid solution, ferritic phases and anhydrite were formed.

Synthesis and Properties of Nanoparticle Forms Saponite Clay, Cancrinite Zeolite and Phase Mixtures Thereof.

Science.gov (United States)

Shao, Hua; Pinnavaia, Thomas J

2010-09-01

The low-temperature synthesis (90°C) of nanoparticle forms of a pure phase smectic clay (saponite) and zeolite (cancrinite) is reported, along with phase mixtures thereof. A synthesis gel corresponding to the Si:Al:Mg unit cell composition of saponite (3.6:0.40:3.0) and a NaOH/Si ratio of 1.39 affords the pure phase clay with disordered nanolayer stacking. Progressive increases in the NaOH/Si ratio up to a value of 8.33 results in the co-crystallization of first garronite and then cancrinite zeolites with nanolath morphology. The resulting phase mixtures exhibit a compound particulate structure of intertwined saponite nanolayers and cancrinite nanolaths that cannot be formed through physical mixing of the pure phase end members. Under magnesium-free conditions, pure phase cancrinite nanocrystals are formed. The Si/Al ratio of the reaction mixture affects the particle morphology as well as the chemical composition of the cancrinite zeolite. Ordinarily, cancrinite crystallizes with a Si/Al ratio of 1.0, but a silicon-rich form of the zeolite (Si/Al=1.25) is crystallized at low temperature from a silica rich synthesis gel, as evidenced by (29)Si NMR spectroscopy and XEDS-TEM. Owing to the exceptionally high external surface areas of the pure phase clay (875 m(2)/g) and zeolite end members (8.9 - 40 m(2)/g), as well as their unique mixed phase composites (124 - 329 m(2)/g), these synthetic derivatives are promising model nanoparticles for studies of the bioavailability of poly-aromatic hydrocarbons immobilized in silicate bearing sediments and soils.

Influence of Homogenization and Micro/Nano Source of Starting Powders on Format Ion of the Single YAP Phase

Directory of Open Access Journals (Sweden)

Michalik D.

2016-12-01

Full Text Available Manufacturing high purity polycrystalline YAlO3 (YAP ceramics could replace monocrystalline YAP thus recently it is an interesting task for low cost producers of scintillators. The paper presents influence of different source of initial oxide powders (micro/nano powders of Y2O3 and Al2O3 and the method of their homogenization on the formation of a YAP phase. The solid state reaction method was used to prepare YAP powder or ceramic pellets. After preheating, all samples in the form of powders and pellets were heat-treated in the temperature range of 1050-1650 °C. DTA method was applied for examination of the phase crystallization in the tested system. X-ray diffraction method (XRD was used for characterization of the phase composition. X-ray microanalysis (EDS was used to control homogeneity in the small areas. Morphology of the resultant samples are presented on SEM pictures. The results show a significant influence of the starting powders on the homogeneity, purity and temperature of formation of the main phase.

Formation of Microcracks During Micro-Arc Oxidation in a Phytic Acid-Containing Solution on Two-Phase AZ91HP

Science.gov (United States)

Zhang, R. F.; Chang, W. H.; Jiang, L. F.; Qu, B.; Zhang, S. F.; Qiao, L. P.; Xiang, J. H.

2016-04-01

Micro-arc oxidation (MAO) is an effective method to produce ceramic coatings on magnesium alloys and can considerably improve their corrosion resistance. The coating properties are closely related with microcracks, which are always inevitably developed on the coating surface. In order to find out the formation and development regularity of microcracks, anodic coatings developed on two-phase AZ91HP after different anodizing times were fabricated in a solution containing environmentally friendly organic electrolyte phytic acid. The results show that anodic film is initially developed on the α phase. At 50 s, anodic coatings begin to develop on the β phase, evidencing the formation of a rough area. Due to the coating successive development, the microcracks initially appear at the boundary between the initially formed coating on the α phase and the subsequently developed coating on the β phase. With the prolonging treatment time, the microcracks near the β phase become evident. After treating for 3 min, the originally rough area on the β phase disappears and the coatings become almost uniform with microcracks randomly distributed on the sample surface. Inorganic phosphates are found in MAO coatings, suggesting that phytate salts are decomposed due to the high instantaneous temperature on the sample surface resulted from spark discharge.

Predictive calculation of phase formation in Al-rich Al-Zn-Mg-Cu-Sc-Zr alloys using a thermodynamic Mg-alloy database

International Nuclear Information System (INIS)

Groebner, J.; Rokhlin, L.L.; Dobatkina, T.V.; Schmid-Fetzer, R.

2007-01-01

Three series of Al-rich alloys in the system Al-Zn-Mg-Cu-Sc-Zr and the subsystems Al-Zn-Mg-Cu-Sc and Al-Zn-Mg-Sc were studied by thermodynamic calculations. Phase formation was compared with experimental data obtained by DTA and microstructural analysis. Calculated phase diagrams, phase amount charts and enthalpy charts together with non-equilibrium calculations under Scheil conditions reveal significant details of the complex phase formation. This enables consistent and correct interpretation of thermal analysis data. Especially the interpretation of liquidus temperature and primary phase is prone to be wrong without using this tool of computational thermodynamics. All data are predictions from a thermodynamic database developed for Mg-alloys and not a specialized Al-alloy database. That provides support for a reasonable application of this database for advanced Mg-alloys beyond the conventional composition ranges

Predictive calculation of phase formation in Al-rich Al-Zn-Mg-Cu-Sc-Zr alloys using a thermodynamic Mg-alloy database

Energy Technology Data Exchange (ETDEWEB)

Groebner, J. [Institute of Metallurgy, Clausthal University of Technology, Robert-Koch Strasse 42, D-38678 Clausthal-Zellerfeld (Germany); Rokhlin, L.L. [Baikov Institute of Metallurgy and Materials Science, Leninsky prosp. 49, 119991 GSP-1, Moscow (Russian Federation); Dobatkina, T.V. [Baikov Institute of Metallurgy and Materials Science, Leninsky prosp. 49, 119991 GSP-1, Moscow (Russian Federation); Schmid-Fetzer, R. [Institute of Metallurgy, Clausthal University of Technology, Robert-Koch Strasse 42, D-38678 Clausthal-Zellerfeld (Germany)]. E-mail: schmid-fetzer@tu-clausthal.de

2007-05-16

Three series of Al-rich alloys in the system Al-Zn-Mg-Cu-Sc-Zr and the subsystems Al-Zn-Mg-Cu-Sc and Al-Zn-Mg-Sc were studied by thermodynamic calculations. Phase formation was compared with experimental data obtained by DTA and microstructural analysis. Calculated phase diagrams, phase amount charts and enthalpy charts together with non-equilibrium calculations under Scheil conditions reveal significant details of the complex phase formation. This enables consistent and correct interpretation of thermal analysis data. Especially the interpretation of liquidus temperature and primary phase is prone to be wrong without using this tool of computational thermodynamics. All data are predictions from a thermodynamic database developed for Mg-alloys and not a specialized Al-alloy database. That provides support for a reasonable application of this database for advanced Mg-alloys beyond the conventional composition ranges.

The gas chimney formation during the steam explosion premixing phase

International Nuclear Information System (INIS)

Leskovar, M.

2001-01-01

The crucial part in isothermal premixing experiment simulation is the correct prediction of the gas chimney, which forms when the spheres penetrate into water. The first simulation results with the developed original combined multiphase model showed that the gas chimney starts to close at the wrong place at the top of the chimney and not in the middle, like it was observed in the experiments. To find the physical explanation for this identified weakness of our numerical model a comprehensive parametric analysis (mesh size, initial water-air surface thickness, water density, momentum coupling starting position) has been performed. It was established that the reason for the unphysical gas chimney closing at the top could be the gradual air-water density transition in the experiment model, since there is due to the finite differences description always a transition layer with intermediate phases density over the pure water phase. It was shown that this difference between our numerical model and the experiment can be somewhat compensated if the spheres interfacial drag coefficient at the upmost mesh plane of the unphysical air-water transition layer is artificially risen. On this way a more correct gas chimney formation can be obtained.(author)

Kaempferol Inhibits the Primary Attachment Phase of Biofilm Formation in Staphylococcus aureus.

Science.gov (United States)

Ming, Di; Wang, Dacheng; Cao, Fengjiao; Xiang, Hua; Mu, Dan; Cao, Junjie; Li, Bangbang; Zhong, Ling; Dong, Xiaoyun; Zhong, Xiaobo; Wang, Lin; Wang, Tiedong

2017-01-01

The ability to form biofilms on surfaces makes Staphylococcus aureus the main pathogenic factor in implanted medical device infections. The aim of this study was to discover a biofilm inhibitor distinct from the antibiotics used to prevent infections resulting from S. aureus biofilms. Here, we describe kaempferol, a small molecule with anti-biofilm activity that specifically inhibited the formation of S. aureus biofilms. Crystal violet (CV) staining and fluorescence microscopy clearly showed that 64 μg/ml kaempferol inhibited biofilm formation by 80%. Meanwhile, the minimum inhibitory concentration (MIC) and growth curve results indicated that kaempferol had no antibacterial activity against the tested bacterial strain. Kaempferol inhibited the primary attachment phase of biofilm formation, as determined by a fibrinogen-binding assay. Moreover, a fluorescence resonance energy transfer (FRET) assay and quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) analyses revealed that kaempferol reduced the activity of S. aureus sortaseA (SrtA) and the expression of adhesion-related genes. Based on these results, kaempferol provides a starting point for the development of novel anti-biofilm drugs, which may decrease the risk of bacterial drug resistance, to prevent S. aureus biofilm-related infections.

Formation of {1 0 0} textured columnar grain structure in a non-oriented electrical steel by phase transformation

Energy Technology Data Exchange (ETDEWEB)

Xie, Li; Yang, Ping, E-mail: yangp@mater.ustb.edu.cn; Zhang, Ning; Zong, Cui; Xia, Dongsheng; Mao, Weimin

2014-04-01

This study confirms the effect of anisotropic strain energy on the formation of {1 0 0} textured columnar grain structure induced by temperature gradient during γ to α phase transformation in pure hydrogen atmosphere. Results indicate that high temperature gradient in pure hydrogen atmosphere induces a significant strain energy difference across grain boundaries during γ to α phase transformation, leading to the formation of {1 0 0} texture with columnar grains. Given its simplicity in processing and its ability to obtain good texture-related magnetic properties, the proposed approach is helpful to the development of new types of non-oriented electrical steel. - Highlights: • A strong {1 0 0} texture with columnar grains was obtained. • Good texture and magnetic properties are attributed to the anisotropic strain energy. • The anisotropy in elastic strain energy was induced by the temperature gradient. • The phase transformation rate affects columnar grain morphology.

L1{sub 0} phase formation in ternary FePdNi alloys

Energy Technology Data Exchange (ETDEWEB)

Montes-Arango, A.M. [Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA 02115 (United States); Bordeaux, N.C. [Department of Chemical Engineering, Northeastern University, Boston, MA 02115 (United States); Liu, J.; Barmak, K. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027 (United States); Lewis, L.H., E-mail: lhlewis@neu.edu [Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA 02115 (United States); Department of Chemical Engineering, Northeastern University, Boston, MA 02115 (United States)

2015-11-05

Metallurgical routes to highly metastable phases are required to access new materials with new functionalities. To this end, the stability of the tetragonal chemically ordered L1{sub 0} phase in the ternary Fe–Pd–Ni system is quantified to provide enabling information concerning synthesis of L1{sub 0}-type FeNi, a highly attractive yet highly elusive advanced permanent magnet candidate. Fe{sub 50}Pd{sub 50−x}Ni{sub x} (x = 0–7 at%) samples were arc-melted and annealed at 773 K (500 °C) for 100 h to induce formation of the chemically ordered L1{sub 0} phase. Coupled calorimetry, structural and magnetic investigations allow determination of an isothermal section of the ternary Fe–Pd–Ni phase diagram featuring a single phase L1{sub 0} region near the FePd boundary for x < 6 at%. It is demonstrated that increased Ni content in Fe{sub 50}Pd{sub 50−x}Ni{sub x} alloys systematically decreases the order-disorder transition temperature, resulting in a lower thermodynamic driving force for the ordering phase transformation. The Fe{sub 50}Pd{sub 50−x}Ni{sub x} L1{sub 0} → fcc disordering transformation is determined to occur via a two-step process, with compositionally-dependent enthalpies and transition temperatures. These results highlight the need to investigate ternary alloys with higher Ni content to determine the stability range of the L1{sub 0} phase near the FeNi boundary, thereby facilitating kinetic access to the important L1{sub 0} FeNi ferromagnetic phase. - Highlights: • Chemical ordering in FePdNi enhances intrinsic and extrinsic magnetic properties. • 773 K annealed FePdNi alloys studied show a stable L1{sub 0} phase for Ni ≤ 5.2 at%. • Chemical disordering in FePdNi occurs by a previously unreported two-step process. • Ni additions to FePd dramatically decrease the chemical order-disorder temperature. • The chemical-ordering transformation kinetics are greatly affected by Ni content.

Synthesis and characterization of wide range mesogenic esters based on asymmetrical 2,5-disubstituted 1,3,4-thiadiazole

Science.gov (United States)

Tomi, Ivan H. R.; Jaffer, Hamed J.; Aldhaif, Yasmeen A.

2018-04-01

A homologous series of new 13 esters, 4-(5-(p-tolyl)-1,3,4-thiadiazol-2-yl)-phenyl-4-alkoxybenzoate, (IVn), based on 1,3,4-thiadiazole core has been synthesized. The structures of these esters were confirmed by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance and mass techniques. Their mesophases behavior was investigated with hot-stage polarizing optical microscope and differential scanning calorimetry. The thermal stability for most of these derivatives was measured by thermal gravimetric analysis. All the target esters showed enantiotropic mesomorphic behaviors with nematic and nematic/smectic C phases. The phase transition temperatures and liquid crystalline properties were affected by the nature of heterocyclic ring and the length of the alkoxy chain. Only the nematic phase was observed in the first 10 derivatives, (n = 1-10), while the last 3, (n = 12, 16 and 18) showed nematic and smectic C phases. These compounds demonstrated high liquid crystalline ranges, both in heating and cooling cycles. The mesomorphic results obtained were compared with the reported analogs of similar constituents.

Synthesis, characterization and electro-optic properties of novel siloxane liquid crystalline with a large tilt angle

International Nuclear Information System (INIS)

Liao, Chien-Tung; Lee, Jiunn-Yih; Lai, Chiu-Chun

2011-01-01

Research highlights: → In this study we report the synthesis and characterization of new ferroelectric liquid crystal material. → We examined the influence of the addition of a trisiloxane end-group on one side-chain of an achiral alkyl chain on the phase transition. → Finally, the properties of the chiral smectic C (SmC*) phase were measured for target compounds. - Abstract: This paper presents a study of the ferroelectric behavior in low molar mass organosiloxane liquid crystal materials. A few novel series of compounds with a large tilt angle were synthesized, and the mesophases exhibited were compared. The mesophases under discussion were investigated by means of polarizing microscopy (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and electro-optical experiments. The influence of the molecular structure on the occurrence of the chiral smectic C (SmC*) phase was investigated. Finally, the electro-optical properties of the SmC* phase, such as tilt angle, dielectric permittivity and switching behavior were also measured. As a consequence, the correlation between the electro-optical properties and chemical structures of these compounds was investigated.

Organic charge transfer phase formation in thin films of the BEDT-TTF/TCNQ donor-acceptor system

DEFF Research Database (Denmark)

Solovyeva, Vita; Keller, K.; Huth, M.

2009-01-01

We have performed charge transfer phase formation studies on the donor/acceptor system bis-(ethylendithio)tetrathiafulvalene (BEDT-TTF)/tetracyanoquinodimethane,(TCNQ) by means of physical vapor deposition. We prepared donor/acceptor bilayer structures on glass and Si(100)/SiO substrates held...

Cement Formation

DEFF Research Database (Denmark)

Telschow, Samira; Jappe Frandsen, Flemming; Theisen, Kirsten

2012-01-01

Cement production has been subject to several technological changes, each of which requires detailed knowledge about the high multiplicity of processes, especially the high temperature process involved in the rotary kiln. This article gives an introduction to the topic of cement, including...... an overview of cement production, selected cement properties, and clinker phase relations. An extended summary of laboratory-scale investigations on clinkerization reactions, the most important reactions in cement production, is provided. Clinker formations by solid state reactions, solid−liquid and liquid......−liquid reactions are discussed, as are the influences of particles sizes on clinker phase formation. Furthermore, a mechanism for clinker phase formation in an industrial rotary kiln reactor is outlined....

Effect of the Heusler phase formation on the magnetic behavior of the Cu–10 wt.%Mn alloy with Al and Ag additions

Energy Technology Data Exchange (ETDEWEB)

Carvalho, T.M., E-mail: thaisa.mary@gmail.com [Instituto de Química – UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil); Adorno, A.T.; Santos, C.M.A. [Instituto de Química – UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil); Silva, R.A.G. [Departamento de Ciências Exatas e da Terra – UNIFESP, 09972-270 Diadema, SP (Brazil); Magnani, M. [Instituto de Química – UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil)

2015-09-15

Highlights: • The presence of the Cu{sub 2}MnAl phase was observed in annealed alloys. • Al and Ag additions shift the equilibrium concentration to higher Al values. • There is a correlation between the Ag-rich phase and the Cu{sub 2}MnAl phase. - Abstract: In this work, the formation of the Cu{sub 2}AlMn Heusler phase and its influence on the magnetic behavior of the Cu–Mn–Al–Ag alloys in the range of 8–10 wt.% of aluminum and 2–4 wt.% of silver were studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and saturation magnetization measurements at 4 K. The results showed that there is a correlation between the presence of the Ag-rich phase and the formation of the Cu{sub 2}MnAl phase.

Effect of temperature on the reaction pathway of calcium carbonate formation via precursor phases

Science.gov (United States)

Purgstaller, Bettina; Mavromatis, Vasileios; Konrad, Florian; Dietzel, Martin

2016-04-01

It has been earlier postulated that some biogenic and sedimentary calcium carbonate (CaCO3) minerals (e.g. calcite and aragonite) are secondary in origin and have originally formed via a metastable calcium carbonate precursor phase (e.g. amorphous CaCO3, [1-2]). Such formation pathways are likely affected by various physicochemical parameters including aqueous Mg and temperature. In an effort to improve our understanding on the formation mechanism of CaCO3 minerals, precipitation experiments were carried out by the addition of a 0.6 M (Ca,Mg)Cl2 solution at distinct Mg/Ca ratios (1/4 and 1/8) into a 1 M NaHCO3 solution under constant pH conditions(8.3 ±0.1). The formation of CaCO3 was systematically examined as a function of temperature (6, 12, 18 and 25 ±0.3° C). During the experimental runs mineral precipitation was monitored by in situ Raman spectroscopy as well as by continuous sampling and analyzing of precipitates and reactive solutions. The results revealed two pathways of CaCO3 formation depending on the initial Mg/Ca ratio and temperature: (i) In experiments with a Mg/Ca ratio of 1/4 at ≤ 12° C as well as in experiments with a Mg/Ca ratio of 1/8 at ≤ 18° C, ikaite (CaCO3 6H2O) acts as a precursor phase for aragonite formation. (ii) In contrast higher temperatures induced the formation of Mg-rich amorphous CaCO3 (Mg-ACC) which was subsequently transformed to Mg-rich calcite. In situ Raman spectra showed that the transformation of Mg-ACC to Mg-calcite occurs at a higher rate (˜ 8 min) compared to that of ikaite to aragonite (> 2 h). Thus, the formation of aragonite rather than of Mg-calcite occurs due to the slower release of Ca2+and CO32- ions into the Mg-rich reactive solution during retarded ikaite dissolution. This behavior is generally consistent with the observation that calcite precipitation is inhibited at elevated aqueous Mg/Ca ratios. [1] Addadi L., Raz S. and Weiner S. (2003) Advanced Materials 15, 959-970. [2] Rodriguez-Blanco J. D

Formation of random and regular relief-phase structures on silver halide photographic emulsions by holographic methods

Science.gov (United States)

Ganzherli, N. M.; Gulyaev, S. N.; Gurin, A. S.; Kramushchenko, D. D.; Maurer, I. A.; Chernykh, D. F.

2009-07-01

The formation of diffusers and microlens rasters on silver halide emulsions by holographic methods is considered. Two techniques for converting amplitude holographic recording to relief-phase recording, selective curing and irradiation of the emulsion gelatin by short-wavelength UV radiation, are compared.

Equilibrium aluminium hydroxo-oxalate phases during initial clay formation; H +-Al 3+-oxalic acid-Na + system

Science.gov (United States)

Bilinski, Halka; Horvath, Laszlo; Ingri, Nils; Sjöberg, Staffan

1986-09-01

The conditions necessary for initial clay formation have been studied in different model systems comprising different organic acids besides Si and Al. In the present paper the solid phases and the precipitation boundary characterizing the subsystem H +-Al 3+-oxalic acid (H 2L) are discussed. pH and tyndallometric measurements were performed in an ionic medium of 0.6 M Na(Cl) at 25 °C. The two phases Al 3(OH) 7(C 2O 4) · 3H 2O (phase I) and NaAl(OH) 2(C 2O 4) · 3H 2O (phase II) determine the precipitation boundary. The following formation constants for the two phases were deduced: lgβ1 = lg([ Al3+] -3[ H2C2O4] -1[ H+] 9 = -21.87 ± 0.08 and lgβ11 = lg([ Al3+] -1[ H2C2O4] -1[ H+] 4 = -5.61 ± 0.06. Phase I exists in the range [ Al] tot≥ 10 -4.4moldm-3,[ H2C2O4] tot ≥ 10 -4.9moldm-3 and at pH oxalic-rich natural waters. The more soluble sodium phase is unlikely to exist in natural waters. The two phases are metastable relative to crystalline gibbsite and may be considered as the first precipitation step in the transition from aqueous Al oxalates down to stable Al hydroxide. Model calculations illustrating these competing hydrolysis-complexation reactions are discussed in terms of predominance and speciation diagrams. The solid phases have been characterized by X-ray analysis of powders, TGA and IR spectra, and tentative structures are proposed. Phase I seems to be an octahedral layer structure, in which 3/5 of the octahedral sites between two close packed oxygen sheets are occupied by Al 3+ and the oxalate ion acts as a bridge ligand between two aluminium atoms. Phase II forms a more open sheet structure and has ion exchange properties. Powder data for a phase crystallized from the studied solution after a year are also presented. This phase, Na 4Al 2(OH) 2(C 2O 4) 4 · 10H 2O, supports the results from the equilibrium analysis of recent solution data by SJöBERG and ÖHMAN (1985), who have found the dinuclear complex Al 2(OH) 2(C 2O 4) 44- to exist in a

The formation of α-phase SnS nanorods by PVP assisted polyol synthesis: Phase stability, micro structure, thermal stability and defects induced energy band transitions

Energy Technology Data Exchange (ETDEWEB)

Baby, Benjamin Hudson; Mohan, D. Bharathi, E-mail: d.bharathimohan@gmail.com

2017-05-01

We report the formation of single phase of SnS nanostructure through PVP assisted polyol synthesis by varying the source concentration ratio (Sn:S) from 1:1M to 1:12M. The effect of PVP concentration and reaction medium towards the preparation of SnS nanostructure is systematically studied through confocal Raman spectrometer, X-ray diffraction, thermogravimetry analysis, scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectroscopy, UV–Vis–NIR absorption and fluorescence spectrophotometers. The surface morphology of SnS nanostructure changes from nanorods to spherical shape with increasing PVP concentration from 0.15M to 0.5M. Raman analysis corroborates that Raman active modes of different phases of Sn-S are highly active when Raman excitation energy is slightly greater than the energy band gap of the material. The presence of intrinsic defects and large number of grain boundaries resulted in an improved thermal stability of 20 °C during the phase transition of α-SnS. Band gap calculation from tauc plot showed the direct band gap of 1.5 eV which is attributed to the single phase of SnS, could directly meet the requirement of an absorber layer in thin film solar cells. Finally, we proposed an energy band diagram for as synthesized single phase SnS nanostructure based on the experimental results obtained from optical studies showing the energy transitions attributed to band edge transition and also due to the presence of intrinsic defects. - Highlights: • PVP stabilizes the orthorhombic (α) phase of SnS. • Optical band gap of P type SnS tuned by PVP for photovoltaic applications. • The formation of Sn rich SnS phase is investigated through XPS analysis. • Intrinsic defects enhance the thermal stability of α-SnS. • The feasibility of energy transition liable to point defects is discussed.

Multilevel modeling of micromechanics and phase formation for microstructural evolution of magnetic zones

International Nuclear Information System (INIS)

Suwa, Yoshihiro; Aizawa, Tatsuhiko; Takaya, Shigeru; Nagae, Yuji; Aoto, Kazumi

2005-03-01

The present research aims at a proposal of theoretical treatise to describe the local phase transformation from austenite to ferrite in the stainless steels under hot cyclic fatigue conditions. In experiments, this local phase transformation is detected as a magnetized region in the non-magnetic matrix after low-cycle fatigue test at the elevated temperature. The theoretical frame proposed here is composed of two methodologies. In the first approach, microstructure evolution with γ → α transformation is described by the phase field method. In the second approach, micromechanical method on the basis of the unit cell modeling is proposed to develop a new micromechanical analysis. The details of two approached are summarized in the following. (1) Phase formation simulation by the phase field method. Most of reports have started that γ-α phase transformation as a creep damage is induced by dechromization, which comes from carbide precipitation around grain boundaries. A new theoretical treatise is proposed for simulating this γ → α transformation in Fe-Cr-Ni system. Stabilities of both phases are investigated for various chemical compositions. Furthermore, in order to investigate dechromization phenomena in Fe-Cr-Ni-C system, a new theoretical frame is also proposed to handle an interstitial element in phase field method. (2) Low cycle fatigue elasto-plastic analysis by the unit-cell modeling. In experiments, the magnetized zones are generated to distribute at the vicinity of the hard, delta-phase inclusion in the austenitic matrix. The cumulative plastic region advances in the surroundings of this hard inclusion with increasing the number of cycles in the controlled strain range. This predicted profile of cumulative plastic regions corresponds to the experimentally measured, magnetized zones. In addition, the effect of geometric configuration of this inclusion on the plastic region evolution has close relationship of creep damage advancement in experiments

Mechanism of Formation of Li ₇ P ₃ S ₁₁ Solid Electrolytes through Liquid Phase Synthesis

Energy Technology Data Exchange (ETDEWEB)

Wang, Yuxing [Energy; Lu, Dongping [Energy; Bowden, Mark [Environmental; El Khoury, Patrick Z. [Environmental; Han, Kee Sung [Environmental; Deng, Zhiqun Daniel [Energy; Xiao, Jie [Energy; Zhang, Ji-Guang [Energy; Liu, Jun [Energy

2018-01-22

Crystalline Li7P3S11 is a promising solid electrolyte for all solid state lithium/lithium ion batteries. A controllable liquid phase synthesis of Li7P3S11 is more desirable compared to conventional mechanochemical synthesis, but recent attempts suffer from reduced ionic conductivities. Here we elucidate the formation mechanism of crystalline Li7P3S11 synthesized in the liquid phase (acetonitrile, or ACN). We conclude that the crystalline Li7P3S11 forms through a two-step reaction: 1) formation of solid Li3PS4∙ACN and amorphous Li2S∙P2S5 phases in the liquid phase; 2) solid-state conversion of the two phases. The implication of this two-step reaction mechanism to the morphology control and the transport properties of liquid phase synthesized Li7P3S11 is identified and discussed.

Can macular xanthophylls replace cholesterol in formation of the liquid-ordered phase in lipid-bilayer membranes?

Science.gov (United States)

Subczynski, Witold K; Wisniewska-Becker, Anna; Widomska, Justyna

2012-01-01

Lateral organization of membranes made from binary mixtures of dimyristoylphosphatidylcholine (DMPC) or dipalmitoylphosphatidylcholine (DPPC) and macular xanthophylls (lutein or zeaxanthin) was investigated using the saturation-recovery (SR) EPR spin-labeling discrimination by oxygen transport (DOT) method in which the bimolecular collision rate of molecular oxygen with the nitroxide spin label is measured. This work was undertaken to examine whether or not lutein and zeaxanthin, macular xanthophylls that parallel cholesterol in its function as a regulator of both membrane fluidity and hydrophobicity, can parallel other structural functions of cholesterol, including formation of the liquid-ordered phase in membranes. The DOT method permits discrimination of different membrane phases when the collision rates (oxygen transport parameter) differ in these phases. Additionally, membrane phases can be characterized by the oxygen transport parameter in situ without the need for separation, which provides information about the dynamics of each phase. In gel-phase membranes, two coexisting phases were discriminated in the presence of macular xanthophylls - namely, the liquid-ordered-like and solid-ordered-like phases. However, in fluid-phase membranes, xanthophylls only induce the solitary liquid-ordered-like phase, while at similar concentrations, cholesterol induces coexisting liquid-ordered and liquid-disordered phases. No significant differences between the effects of lutein and zeaxanthin were found.

Formation of secondary phases during deep geological final disposal of research reactor fuel elements. Structure and phase analysis

International Nuclear Information System (INIS)

Neumann, Andreas

2012-01-01

For the assessment of a confident und sustainable final disposal of high level radioactive waste - fuel elements of german research reactors also account for such waste - in suitable, deep geological facilities, processes of the alteration of the disposed of waste and therefore the formation of the corrosion products, i. e. secondary phases must be well understood considering an accident scenario of a potential water inflow. In order to obtain secondary phases non-irradiated research reactor fuel elements (FR-BE) consisting of UAl x -Al were subjected to magnesium chloride rich brine (brine 2, salt repository) and to clay pore solution, respectively and furthermore of the type U 3 Si 2 -Al were solely subjected to magnesium chloride rich brine. Considering environmental aspects of final repositories the test conditions of the corrosion experiments were adjusted in a way that the temperature was kept constant at 90 C and a reducing anaerobic environment was ensured. As major objective of this research secondary phases, obtained from the autoclave experiments after appropriate processing and grain size separation have been identified and quantified. Powder X-ray diffraction (PXRD) and the application of Rietveld refinement methods allowed the identification of the corrosion products and a quantitative assessment of crystalline and amorphous contents. Scanning and transmission electron microscopy were additionally applied as a complementary method for the characterisation of the secondary phases. The qualitative phase analysis of the preprocessed secondary phases of the systems UAl x -Al and U 3 Si 2 -Al in brine 2 shows many similarities. Lesukite - an aluminium chloro hydrate - was observed for the first time considering the given experimental conditions. Further on different layered structures of the LDH type, iron oxyhydroxide and possibly iron chlorides, uncorroded residues of nuclear fuel and elementary iron were identified as well. Depending on preceding

Effect of finite chemical potential on QGP-hadron phase transition in a statistical model of fireball formation

International Nuclear Information System (INIS)

Ramanathan, R.; Singh, S.S.; Jha, A.K.; Gupta, K.K.

2011-01-01

We study the effect of finite chemical potential for the QGP constituents in the Ramanathan et al. statistical model. While the earlier computations using this model with vanishing chemical potentials indicated a weakly first order phase transition for the system in the vicinity of 170 MeV, the introduction of finite values for the chemical potentials of the constituents makes the transition a smooth roll over of the phases, while allowing fireball formation with radius of a few 'fermi' to take place. This seems to be in conformity with the latest consensus on the nature of the QGP-Hadron phase transition. (author)

Phase formation in systems Re-Se-Br-MBr (M=Li, Na, K, Rb, Cs

International Nuclear Information System (INIS)

Yarovoj, S.S.; Mironov, Yu.V.; Tkachev, S.V.; Fedorov, V.E.

2009-01-01

Phase formation in the systems Re-Se-Br-MBr (M=K, Rb, Cs) has been studied by NMR-spectroscopy and X-ray phase analysis. Polymer complexes Re 6 Se 8 Br 2 and M 2 Re 6 Se 8 Br 4 (M=Cs, Rb), and salts containing cluster anions [Re 6 Se 6 Br 8 ] 2- and [Re 6 Se 7 Br 7 ] 3- are the main products of reactions occurring in molten alkali metal halides in the number of cluster anions [{Re 6 Se 8-n Br n }Br 6 ] (4-n)- (0≤n≤4). Effect of alkali metal cation on the composition and ratios of formed products is established

Supra-molecular structure of TGBC* phases studied by means of Deuterium NMR line-shape analysis

Czech Academy of Sciences Publication Activity Database

Domenici, V.; Veracini, C.A.; Hamplová, Věra; Kašpar, Miroslav

2008-01-01

Roč. 495, č. 11 (2008), s. 133-144 ISSN 1542-1406 Institutional research plan: CEZ:AV0Z10100520 Keywords : banana -shaped * deuterium NMR * magnetic field * rod-like * smectic * twist grain boundary Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.537, year: 2008

Alignment structures in ferroelectric liquid crystals

Energy Technology Data Exchange (ETDEWEB)

Islam, N.U

1998-07-01

Although for many years liquid crystals were of purely scientific interest, they have now become ubiquitous in everyday life. The use of the nematic liquid crystal phase in flat panel display applications has been the main factor in this popularity. However, with the advent of the SuperTwist Nematic (STN) device, the limits to which this phase could be exploited for display applications was perhaps reached. With the discovery by Clark et al. of the Surface Stabilised Ferroelectric Liquid Crystal (SSFLC) configuration, the possibility arose of using chiral smectic liquid crystals to create large area, passively addressed, fast switching, flat panel displays. Unfortunately, the structures that form within smectic liquid crystals, and the dynamics of the switching within these, are still not fully understood. In this thesis we address the former of these, making a detailed the study of the structures that form within tilted smectic liquid crystal devices. We present here the first complete theoretical and experimental study of various different ferroelectric liquid crystal materials, where we employed theoretical models based on a simple set of assumptions to understand the behaviour of a set of increasingly complex experimental systems. We started with the simplest of these, Freely Suspended Smectic Films (FSSFs) and then worked with progressively more realistic systems in the form of homeotropically, and later, homogeneously aligned liquid crystal cells. The equilibrium structures that form get particularly complex in the last case, taking the form of tilted and chevron layering structures. In each of these cases, the predictions of the modelling are compared with our experimental results. Further, we present here the first model of the chevron cusp that seeks to include the effects of biaxiality in the S{sub C} phase. We also present a model that seeks to analyse the stability of the chevron layering structure and its relationship with tilted layers. This includes

Alignment structures in ferroelectric liquid crystals

International Nuclear Information System (INIS)

Islam, N.U.

1998-01-01

Although for many years liquid crystals were of purely scientific interest, they have now become ubiquitous in everyday life. The use of the nematic liquid crystal phase in flat panel display applications has been the main factor in this popularity. However, with the advent of the SuperTwist Nematic (STN) device, the limits to which this phase could be exploited for display applications was perhaps reached. With the discovery by Clark et al. of the Surface Stabilised Ferroelectric Liquid Crystal (SSFLC) configuration, the possibility arose of using chiral smectic liquid crystals to create large area, passively addressed, fast switching, flat panel displays. Unfortunately, the structures that form within smectic liquid crystals, and the dynamics of the switching within these, are still not fully understood. In this thesis we address the former of these, making a detailed the study of the structures that form within tilted smectic liquid crystal devices. We present here the first complete theoretical and experimental study of various different ferroelectric liquid crystal materials, where we employed theoretical models based on a simple set of assumptions to understand the behaviour of a set of increasingly complex experimental systems. We started with the simplest of these, Freely Suspended Smectic Films (FSSFs) and then worked with progressively more realistic systems in the form of homeotropically, and later, homogeneously aligned liquid crystal cells. The equilibrium structures that form get particularly complex in the last case, taking the form of tilted and chevron layering structures. In each of these cases, the predictions of the modelling are compared with our experimental results. Further, we present here the first model of the chevron cusp that seeks to include the effects of biaxiality in the S C phase. We also present a model that seeks to analyse the stability of the chevron layering structure and its relationship with tilted layers. This includes an

Mechanism of Phase Formation in the Batch Mixtures for Slag-Bearing Glass Ceramics - 12207

Energy Technology Data Exchange (ETDEWEB)

Stefanovsky, Sergey V.; Stefanovsky, Olga I.; Malinina, Galina A. [SIA Radon, 7th Rostovskii lane 2/14, Moscow 119121 (Russian Federation)

2012-07-01

Slag surrogate was produced from chemicals by heating to 900 deg. C and keeping at this temperature for 1 hr. The product obtained was intermixed with either sodium di-silicate (75 wt.% waste loading) or borax (85 wt.% slag loading). The mixtures were heat-treated within a temperature range of 25 to 1300 deg. C. The products were examined by X-ray diffraction and infrared spectroscopy. The products prepared at temperatures of up to 1000 deg. C contained both phase typical of the source slag and intermediate phases as well as phases typical of the materials melted at 1350 deg. C such as nepheline, britholite, magnetite and matrix vitreous phase. Vitrification process in batch mixtures consisting of slag surrogate and either sodium di-silicate or sodium tetraborate runs through formation of intermediate phases mainly silico-phosphates capable to incorporate Sm as trivalent actinides surrogate. Reactions in the batch mixtures are in the whole completed by ∼1000 deg. C but higher temperatures are required to homogenize the products. If in the borate-based system the mechanism is close to simple dissolution of slag constituents in the low viscous borate melt, then in the silicate-based system the mechanism was found to be much complicated and includes re-crystallization during melting with segregation of newly-formed nepheline type phase. (authors)

Formation, Phase, and Elemental Composition of Micro- and Nano-Dimensional Particles of the Fe-Ti System

Science.gov (United States)

Dresvyannikov, A. F.; Kolpakov, M. E.

2018-05-01

X-ray fluorescence, X-ray phase analysis, and transmission Mössbauer and NGR spectrometry are used to study the formation, phase, and elemental composition of Fe-Ti particles. The interaction between Fe(III) ions and dispersed titanium in an aqueous solution containing chloride ions and HF is studied. It is shown that the resulting Fe-Ti samples are a set of core-shell microparticles with titanium cores coated with micro- and nanosized α-Fe nucleation centers with the thinness outer layer of iron(III) oxide characterized by a developed surface.

Liquid phase formation due to solid/solid chemical interaction and its modelling: applications to zircaloy/stainless steel system

International Nuclear Information System (INIS)

Garcia, E.A.; Piotrkowski, R.; Denis, A.; Kovacs, J.

1992-01-01

The chemical interaction at high temperatures between Zircaloy (Zry) and stainless steel (SS) and the liquid phase formation due to eutectic reactions were studied. In a previous work the Zry/Inconel system was modelled assuming that the kinetics of phase growth is controlled by diffusion. The same model and the obtained Zr diffusion coefficient in the liquid phase were applied in the present work. In order to obtain an adequate description of the Zry/SS the major component of both alloys and also Cr and Ni had to be considered. (author)

Phase Transitions in a Social Impact Model for Opinion Formation

Science.gov (United States)

Bordogna, Clelia M.; Albano, Ezequiel V.

A model for opinion formation in a social group, based on the Theory of Social Impact developed by Latané, is studied by means of numerical simulations. Interactions among the members of the group, as well as with a strong leader competing with the mass media, are considered. The model exhibits first-order transitions between two different states of opinion, which are supported by the leader and the mass media, respectively. The social inertia of the group becomes evident when the opinion of the leader changes periodically. In this case two dynamic states are identified: for long periods of time, the group follows the changes of the leader but, decreasing the period, the opinion of the group remains unchanged. This scenery is suitable for the ocurrence of dynamic phase transitions.

Thermodynamic behavior of poly(3-alkyl thiophene) blends: Equilibrium cocrystal formation and phase segregation.

Science.gov (United States)

Pal, Susmita; Nandi, Arun K

2005-02-24

The equilibrium cocrystal formation of poly(3-alkyl thiophene) (P3AT) blends has been studied by isothermal cocrystallization in a differential scanning calorimeter (DSC-7). The equilibrium melting points (T(m)0) of the cocrystals are measured using the Hoffman-Weeks extrapolation procedure. The equilibrium phase diagrams are of three different types: (a) concave upward, (b) linear, and (c) linear with phase separation at higher content of lower melting component. The phase diagram nature depends on the regioregularity difference and also on the difference in the number of carbon atoms in the pendent alkyl group of the components. The origin of biphasic nature of type "c" phase diagram has been explored from the glass transition temperature (Tg) measurement using a dynamic mechanical analyzer. The biphasic compositions show two glass transition temperatures (Tg) as well as two beta transition temperatures (T beta). The T(g)s of phase-separated regions correspond to almost the component values but the T(beta)s correspond to that of a lower (T beta) component value, and the other is higher than that of the higher (T beta) component value. Possible reasons are discussed from the interchain lamella thickness in the P3AT blends and molecular modeling using molecular mechanics program.

Synchrotron X-ray diffraction using triple-axis spectrometry

International Nuclear Information System (INIS)

Als-Nielsen, J.

1980-12-01

High resolution X-ray diffraction studies of (i) monolayers of the noble gases Kr and Ar physiosorbed on graphite (ii) smectic A fluctuations in the nematic and the smectic A phases of liquid crystals are described. The apparatus used is a triple axis spectrometer situated at the storage ring DORIS at Hasylab, DESY, Hamburg. A monochromatic, well collimated beam is extracted from the synchrotron radiation spectrum by Bragg reflection from perfect Si or Ge crystals. The direction of the beam scattered from the sample is determined by Bragg reflection from a perfect Si or Ge crystal. High intensities even with resolution extending beyond the wavelength of visible light can be obtained. (Auth.)

Gas-phase hydrolysis of triplet SO2: A possible direct route to atmospheric acid formation

Science.gov (United States)

Donaldson, D. James; Kroll, Jay A.; Vaida, Veronica

2016-07-01

Sulfur chemistry is of great interest to the atmospheric chemistry of several planets. In the presence of water, oxidized sulfur can lead to new particle formation, influencing climate in significant ways. Observations of sulfur compounds in planetary atmospheres when compared with model results suggest that there are missing chemical mechanisms. Here we propose a novel mechanism for the formation of sulfurous acid, which may act as a seed for new particle formation. In this proposed mechanism, the lowest triplet state of SO2 (3B1), which may be accessed by near-UV solar excitation of SO2 to its excited 1B1 state followed by rapid intersystem crossing, reacts directly with water to form H2SO3 in the gas phase. For ground state SO2, this reaction is endothermic and has a very high activation barrier; our quantum chemical calculations point to a facile reaction being possible in the triplet state of SO2. This hygroscopic H2SO3 molecule may act as a condensation nucleus for water, giving rise to facile new particle formation (NPF).

The formation of urea in space. I. Ion-molecule, neutral-neutral, and radical gas-phase reactions

Science.gov (United States)

Brigiano, Flavio Siro; Jeanvoine, Yannick; Largo, Antonio; Spezia, Riccardo

2018-02-01

Context. Many organic molecules have been observed in the interstellar medium thanks to advances in radioastronomy, and very recently the presence of urea was also suggested. While those molecules were observed, it is not clear what the mechanisms responsible to their formation are. In fact, if gas-phase reactions are responsible, they should occur through barrierless mechanisms (or with very low barriers). In the past, mechanisms for the formation of different organic molecules were studied, providing only in a few cases energetic conditions favorable to a synthesis at very low temperature. A particularly intriguing class of such molecules are those containing one N-C-O peptide bond, which could be a building block for the formation of biological molecules. Urea is a particular case because two nitrogen atoms are linked to the C-O moiety. Thus, motivated also by the recent tentative observation of urea, we have considered the synthetic pathways responsible to its formation. Aims: We have studied the possibility of forming urea in the gas phase via different kinds of bi-molecular reactions: ion-molecule, neutral, and radical. In particular we have focused on the activation energy of these reactions in order to find possible reactants that could be responsible for to barrierless (or very low energy) pathways. Methods: We have used very accurate, highly correlated quantum chemistry calculations to locate and characterize the reaction pathways in terms of minima and transition states connecting reactants to products. Results: Most of the reactions considered have an activation energy that is too high; but the ion-molecule reaction between NH2OHNH2OH2+ and formamide is not too high. These reactants could be responsible not only for the formation of urea but also of isocyanic acid, which is an organic molecule also observed in the interstellar medium.

Study on the Formation and Precipitation Mechanism of Mn5Si3 Phase in the MBA-2 Brass Alloy

Science.gov (United States)

Li, Hang; Jie, Jinchuan; Zhang, Pengchao; Jia, Chunxu; Wang, Tongmin; Li, Tingju

2016-06-01

Mn5Si3 is an attractive dispersion in the special brass, owing to its high hardness and high wear resistance. In the present study, synchrotron X-ray radiography and rapid cooling were applied to investigate the formation mechanism of Mn5Si3 phase in the MBA-2 brass alloy. The primary Mn5Si3 phase is proved to exist stably in the alloy melt and nucleate from the melt at temperatures above 1373 K (1100 °C). In addition, the precipitation mechanism of Mn5Si3 phase is addressed systematically by the isothermal heat treatment. The Mn5Si3 particles are observed to precipitate from the matrix at temperatures above 1023 K (750 °C), and a crystallographic orientation relationship is found between the precipitated Mn5Si3 particle and β phase: (110)_{β } //(1overline{1} 00)_{{{{Mn}}5 {{Si}}3 }} and [overline{1} 11]_{β } //[11overline{2} overline{2} ]_{{{{Mn}}5 {{Si}}3 }} . However, the precipitation of Mn5Si3 phase is thermodynamically inhibited at lower temperatures, which can be ascribed to the increase in the Gibbs free energy of formation of Mn5Si3 with decreasing the temperature.

Quantitative phase imaging characterization of tumor-associated blood vessel formation on a chip

Science.gov (United States)

Guo, Peng; Huang, Jing; Moses, Marsha A.

2018-02-01

Angiogenesis, the formation of new blood vessels from existing ones, is a biological process that has an essential role in solid tumor growth, development, and progression. Recent advances in Lab-on-a-Chip technology has created an opportunity for scientists to observe endothelial cell (EC) behaviors during the dynamic process of angiogenesis using a simple and economical in vitro platform that recapitulates in vivo blood vessel formation. Here, we use quantitative phase imaging (QPI) microscopy to continuously and non-invasively characterize the dynamic process of tumor cell-induced angiogenic sprout formation on a microfluidic chip. The live tumor cell-induced angiogenic sprouts are generated by multicellular endothelial sprouting into 3 dimensional (3D) Matrigel using human umbilical vein endothelial cells (HUVECs). By using QPI, we quantitatively measure a panel of cellular morphological and behavioral parameters of each individual EC participating in this sprouting. In this proof-of-principle study, we demonstrate that QPI is a powerful tool that can provide real-time quantitative analysis of biological processes in in vitro 3D biomimetic devices, which, in turn, can improve our understanding of the biology underlying functional tissue engineering.

Kinetic modeling of sporulation and product formation in stationary phase by Bacillus coagulans RK-02 vis-à-vis other Bacilli.

Science.gov (United States)

Das, Subhasish; Sen, Ramkrishna

2011-10-01

A logistic kinetic model was derived and validated to characterize the dynamics of a sporogenous bacterium in stationary phase with respect to sporulation and product formation. The kinetic constants as determined using this model are particularly important for describing intrinsic properties of a sporogenous bacterial culture in stationary phase. Non-linear curve fitting of the experimental data into the mathematical model showed very good correlation with the predicted values for sporulation and lipase production by Bacillus coagulans RK-02 culture in minimal media. Model fitting of literature data of sporulation and product (protease and amylase) formation in the stationary phase by some other Bacilli and comparison of the results of model fitting with those of Bacillus coagulans helped validate the significance and robustness of the developed kinetic model. Copyright © 2011 Elsevier Ltd. All rights reserved.

Formation of organic solid phases in hydrocarbon reservoir fluids. Final report

Energy Technology Data Exchange (ETDEWEB)

Andersen, S.I.; Lindeloff, N.; Stenby, E.H.

1998-12-31

The occurrence of solid phases during oil recovery is a potential problem. The present work has mainly been concerned with wax formation due to cooling of oils with a large paraffin content. 8 oils have been included in this project, although only a few of these have till now been subject to all the experimental techniques applied. The oils and wax fractions from these have been characterized using techniques such as GC-MS and Ftir. The goal has in part been to get a detailed description of the oil composition for use in model evaluation and development and in part to get a fundamental understanding of waxy oil properties and behaviour. A high pressure (200 bar) equipment has been developed for automatic detection of wax appearance using a filtration technique and laser light turbidimetry. The latter was found to be far superior to the filtration. The filtration was used to sample the incipient solid phase for characterization. However entrapment of liquid in the filters currently used have hampered this part. A number of model systems and one gas condensate have been investigated. The GC-MS procedure was found only to been able to detect molecules up to n-C45 and the group type analysis was not accurate enough for modelling purposes. Using Ftir it was obvious that incipient phases may contain very complex molecules (asphaltenes) which are not captured by GC-MS especially when fractionation is done using the acetone precipitation at elevated temperature. The latter fractionation procedure has been investigated thoroughly as a tool for understanding wax distribution etc. Within thermodynamic modelling a delta lattice parameter model has been developed which incorporates the non-ideality of the solid phases into the calculation of SLE. The non-ideality is estimated from pure component properties. A new algorithm for phase equilibria involving gas-liquid-solid has been developed. Currently both the model work and the experimental works are continued. (au)

Locally formation of Ag nanoparticles in chalcogenide phase change thin films induced by nanosecond laser pulses

International Nuclear Information System (INIS)

Huang, Huan; Zhang, Lei; Wang, Yang; Han, Xiaodong; Wu, Yiqun; Zhang, Ze; Gan, Fuxi

2012-01-01

A simple method to optically synthesize Ag nanoparticles in Ge 2 Sb 2 Te 5 phase change matrix is described. The fine structures of the locally formed phase change chalcogenide nanocomposite are characterized by high-resolution transmission electron microscopy. The formation mechanism of the nanocomposite is discussed with temperature evolution and distribution simulations. This easy-prepared metal nano-particle-embedded phase change microstructure will have great potential in nanophotonics applications, such as for plasmonic functional structures. This also provides a generalized approach to the preparation of well-dispersed nanoparticle-embedded composite thin films in principle. -- Highlights: ► We describe a method to prepare chalcogenide microstructures with Ag nanoparticles. ► We give the fine structural images of phase change nanocomposites. ► We discuss the laser-induced fusion mechanism by temperature simulation. ► This microstructure will have great potential in nanophotonics applications.

Polymer and Polymer Gel of Liquid Crystalline Semiconductors

Institute of Scientific and Technical Information of China (English)

Teppei Shimakawa; Naoki Yoshimoto; Jun-ichi Hanna

2004-01-01

It prepared a polymer and polymer gel of a liquid crystalline (LC) semiconductor having a 2-phenylnaphthalene moiety and studied their charge carrier transport properties by the time-of-flight technique. It is found that polyacrylate having the mesogenic core moiety of 2-phenylnaphtalene (PNP-acrylate) exhibited a comparable mobility of 10-4cm2/Vs in smectic A phase to those in smectic A (SmA) phase of small molecular liquid crystals with the same core moiety, e.g., 6-(4'-octylphenyl)- 2-dodecyloxynaphthalene (8-PNP-O12), and an enhanced mobility up to 10-3cm2/Vs in the LC-glassy phase at room temperature, when mixed with a small amount of 8-PNP-O12. On the other hand, the polymer gel consisting of 20 wt %-hexamethylenediacrylate (HDA)-based cross-linked polymer and 8-PNP-O12 exhibited no degraded mobility when cross-linked at the mesophase. These results indicate that the polymer and polymer composite of liquid crystalline semiconductors provide us with an easy way to realize a quality organic semiconductor thin film for the immediate device applications.

Formation of the Ni3Nb δ-Phase in Stress-Relieved Inconel 625 Produced via Laser Powder-Bed Fusion Additive Manufacturing

Science.gov (United States)

Lass, Eric A.; Stoudt, Mark R.; Williams, Maureen E.; Katz, Michael B.; Levine, Lyle E.; Phan, Thien Q.; Gnaeupel-Herold, Thomas H.; Ng, Daniel S.

2017-11-01

The microstructural evolution of laser powder-bed additively manufactured Inconel 625 during a post-build stress-relief anneal of 1 hour at 1143 K (870 °C) is investigated. It is found that this industry-recommended heat treatment promotes the formation of a significant fraction of the orthorhombic D0a Ni3Nb δ-phase. This phase is known to have a deleterious influence on fracture toughness, ductility, and other mechanical properties in conventional, wrought Inconel 625; and is generally considered detrimental to materials' performance in service. The δ-phase platelets are found to precipitate within the inter-dendritic regions of the as-built solidification microstructure. These regions are enriched in solute elements, particularly Nb and Mo, due to the micro-segregation that occurs during solidification. The precipitation of δ-phase at 1073 K (800 °C) is found to require up to 4 hours. This indicates a potential alternative stress-relief processing window that mitigates δ-phase formation in this alloy. Ultimately, a homogenization heat treatment is recommended for additively manufactured Inconel 625 because the increased susceptibility to δ-phase precipitation increases the possibility for significant degradation of materials' properties in service.

Thermodynamics of phase formation and heavy quasiparticles in Sr{sub 3}Ru{sub 2}O{sub 7}

Energy Technology Data Exchange (ETDEWEB)

Rost, Andreas W.; Bruin, Jan A.N.; Tian, Demian; Mackenzie, Andrew P. [SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews KY169SS (United Kingdom); Grigera, Santiago A. [SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews KY169SS (United Kingdom); Instituto de Fisica de Liquidos y Sistemas Biologicos, UNLP-CONICET, La Plata 1900 (Argentina); Perry, Robin S. [SUPA, School of Physics, University of Edinburgh, Mayfield Road, Edinburgh EH93JZ (United Kingdom); Raghu, Sri [Department of Physics and Astronomy, Rice University, Houston, Texas, 77005 (United States); Kivelson, Steve A. [Department of Physics, Stanford University, Stanford, California, 94305 (United States)

2012-07-01

The itinerant metamagnet Sr{sub 3}Ru{sub 2}O{sub 7} has motivated a wide range of experimental and theoretical work in recent years because of the discovery of an unusual low temperature phase which is forming in the vicinity of a proposed quantum critical point. A major challenge is the investigation of the thermodynamic properties of both this unusual phase and the fluctuations associated with the quantum critical point. Here we report on new specific heat measurements extending previous work to the wider phase diagram. Our results shed light on two important aspects of the system. First we discuss the entropic details of the formation of heavy quasiparticles as a function of temperature in this compound relevant for a wide class of materials. Secondly we present thermodynamic evidence for the anomalous low temperature phase forming directly out of the critical high temperature phase.

Effects of KOH:ZnCl2 mole ratio on the phase formation, morphological and inhibitive properties of potassium zinc phosphate (PZP) pigments

International Nuclear Information System (INIS)

Askari, F.; Ghasemi, E.; Ramezanzadeh, B.; Mahdavian, M.

2015-01-01

Graphical abstract: This figure illustrates the inhibition mechanism. The film precipitation on the anodic and cathodic regions of the metal surface causes a drop in dissolution rate of steel. - Highlights: • We synthesized the ZP pigments via coprecipitation method. • Effect of KOH:ZnCl 2 on phase formation, morphology and inhibitive performance of pigment. • KOH:ZnCl 2 ratio is effective on phase formation and morphology of ZP pigments. • KZn 2 H(PO 4 ) 2 phase showed superior corrosion inhibition behavior than KZnPO 4 . - Abstract: Different types of potassium zinc phosphate (PZP) pigments were synthesized by a co-precipitation method. The PZPs were obtained through changing KOH:ZnCl 2 mole ratio. The chemical composition of the pigments was studied by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy (SEM). Then, the extracts of the PZPs were prepared in 3.5% (w/w) NaCl solution. The inhibitive performance of the pigments was investigated by polarization technique and SEM surface analysis through dipping mild steel panels in the pigment extracts for different immersion times. Results showed that changing ZnCl 2 /KOH mole ratio could influence formation of KZn 2 H(PO 4 ) 2 and KZnPO 4 phases. It was known that the KZn 2 H(PO 4 ) 2 phase has a superior corrosion inhibition behavior in 3.5% NaCl solution than KZnPO 4 phase

Interfacial phase formation of Al-Cu bimetal by solid-liquid casting method

Directory of Open Access Journals (Sweden)

Ying Fu

2017-05-01

Full Text Available The solid-liquid method was used to prepare the continuous casting of copper cladding aluminium by liquid aluminum alloy and solid copper, and the interfacial phase formation of Al-Cu bimetal at different pouring temperatures (700, 750, 800 oC was investigated by means of metallograph, scanning electron microscopy (SEM and energy dispersive spectrometry (EDS methods. The results showed that the pouring temperature of aluminum melt had an important influence on the element diffusion of Cu from the solid Cu to Al alloy melt and the reactions between Al and Cu, as well as the morphology of the Al-Cu interface. When the pouring temperature was 800 oC, there were abundant Al-Cu intermetallic compounds (IMCs near the interface. However, a lower pouring temperature (700 oC resulted in the formation of cavities which was detrimental to the bonding and mechanical properties. Under the conditions in this study, the good metallurgical bonding of Al-Cu was achieved at a pouring temperature of 750 oC.

The phase equilibria of multicomponent gas hydrate in methanol/ethylene glycol solution based formation water

International Nuclear Information System (INIS)

Xu, Shurui; Fan, Shuanshi; Yao, Haiyuan; Wang, Yanhong; Lang, Xuemei; Lv, Pingping; Fang, Songtian

2017-01-01

Highlights: • The equilibrium data in THI solution based formation water is first investigated. • The 0.55 mass fraction concentration of EG 0.55 mass fraction fills the vacancy of this area. • The testing pressure range from 4.22 MPa to 34.72 MPa was rare in published data. - Abstract: In this paper, the three-phase coexistence points are generated for multicomponent gas hydrate in methanol (MeOH) solution for (0.05, 0.10, 0.15, and 0.35) mass fraction and ethylene glycol (EG) solution for (0.05, 0.10, 0.15, 0.35, 0.40 and 0.55) mass fraction. The phase equilibrium curves of different system were obtained by an isochoric pressure-search method on high pressure apparatus. The phase equilibrium regions of multicomponent gas hydrate were measured using the same composition of natural gas distributed in the South China Sea. And the different concentration solutions were prepared based formation water. The experimental data were measured in a wide range temperature from 267.74 to 298.53 K and a wide range pressure from 4.22 MPa to 34.72 MPa. The results showed that the hydrate phase equilibrium curves shifted to the inhibition region in accordance with the increased inhibitor concentration. In addition, the equilibrium temperature would decrease about 2.7 K when the concentration of MeOH increased 0.05 mass fraction. Besides, the suppression temperature was 1.25 K with the 0.05 mass fraction increase of EG concentration in the range of 0.05 mass fraction to 0.15 mass fraction. While in high EG concentration region, the suppression temperature was 3.3 K with the same increase of EG concentration (0.05 mass fraction).

Using three-phase theory-based formative research to explore healthy eating in Australian truck drivers.

Science.gov (United States)

Vayro, Caitlin; Hamilton, Kyra

2016-03-01

In Australia, fruit and vegetable consumption is lower than recommended while discretionary foods (i.e., foods high in fat, sugar, and salt) are eaten in excess. Long-haul truck drivers are a group at risk of unhealthy eating but have received limited attention in the health literature. We aimed to examine long-haul truck drivers eating decisions in order to develop theory-based and empirically-driven health messages to improve their healthy food choices. Drawing on the Theory of Planned Behavior, three-phased formative research was conducted using self-report surveys. Phase 1 (N = 30, Mage = 39.53, SDage = 10.72) identified modal salient beliefs about fruit and vegetable (FV) intake and limiting discretionary choices (DC). There were nine behavioral and seven normative beliefs elicited for both FV and DC; while nine and five control beliefs were elicited for FV and DC, respectively. Phase 2 (N = 148, Mage = 44.23, SDage = 12.08) adopted a prospective design with one week follow-up to examine the predictors of FV and DC intention and behavior. A variety of behavioral and control beliefs were predictive of FV and DC intention and behavior. Normative beliefs were predictive of FV intention and behavior and DC intention only. Phase 3 (N = 20, Mage = 46.9, SDage = 12.85) elicited the reasons why each belief is held/solutions to negative beliefs, that could be used as health messages. In total, 40 reasons/solutions were identified: 26 for FV and 14 for DC. In summary, we found that specific behavioral, normative and control beliefs influenced FV and DC eating decisions. These results have implications for truck driver's health and provide formative research to inform future interventions to improve the food choices of a unique group who are at risk of unhealthy eating behaviors. Copyright © 2015 Elsevier Ltd. All rights reserved.

Effect of Ag additions on the β phase formation reaction in the Cu–9 wt.%Al–6 wt.%Mn alloy

Energy Technology Data Exchange (ETDEWEB)

Adorno, A.T., E-mail: atadorno@iq.unesp.br [Departamento de Físico-Química, Instituto de Química, UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil); Carvalho, T.M. [Departamento de Físico-Química, Instituto de Química, UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil); Silva, R.A.G. [Departamento de Ciências Exatas e da Terra, UNIFESP, 09972-270 Diadema, SP (Brazil); Santos, C.M.A.; Magdalena, A.G. [Departamento de Físico-Química, Instituto de Química, UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil)

2015-09-15

Highlights: • The results suggest a multi-step process involving reversible reactions. • Ag solubilizes preferably at the Cu matrix. • Ag additions decrease the activation energy for the process. - Abstract: The influence of 4 and 5 wt.%Ag additions on the kinetics of β [T{sub 7}-(CuMn){sub 3}Al] phase formation reaction in the Cu–9 wt.%Al–6 wt.%Mn alloy was studied using differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results indicate that the conversion dependence of the activation energy has a descending shape, suggesting a multi-step process involving reversible reactions. The presence of Ag facilitates the formation of the β phase. The results also showed that the Ag precipitates formation includes the dissolution of Mn and Al atoms, thus decreasing the partial fraction of these elements available to react.

The influence of temperature on σ-phase formation and the resulting hardening of Fe-Cr-Mo-alloys

International Nuclear Information System (INIS)

Waanders, F.B.; Vorster, S.W.; Pollak, H.

1999-01-01

Hardening in Fe-Cr-Mo-alloys due to the formation of σ-phase, has been the subject of theoretical and experimental interest. In the present investigation Fe-Cr-alloys containing 0, 2, 4 and 6% Mo were prepared and were fully transformed to the σ-phase by isothermally annealing the samples for various periods at temperatures of 600-800 deg. C. After each annealing cycle room temperature CEMS-spectra were recorded and micro-hardness tests were performed. The micro-hardness increases with annealing time and temperature, in accordance with the fraction of σ-phase present, and ranged from about 140 HV to 200 HV. From the measurements, activation energies were also deduced

Influence of the ion implantation on the nanoscale intermetallic phases formation in Ni-Ti system

International Nuclear Information System (INIS)

Kalashnikov, M.P.; Kurzina, I.A.; Bozhko, I.A.; Kozlov, E.V.; Fortuna, S.V.; Sivin, D.O.; Stepanov, I.B.; Sharkeev, Yu.P.

2005-01-01

Full text: The ion implantation at a high intensity mode is an effective method for modification of the surface properties of metals and alloys. Improvement of mechanical and tribological properties of irradiated materials using the high intensity implantation is connected with an element composition and microstructure modification of the surface and subsurface layers. One shows a great interest in intermetallic phase's synthesis by ion implantation, because of unique physical-mechanical properties of the intermetallic compounds. The influence of the irradiation conditions on the structural state and surface properties of implanted materials is not clear enough. The study of the factors influencing on the formation of the surface ion - alloyed layers of metal targets having the high tribological and mechanical properties by high intensity ion implantation is actual. The aim of the present work is a study of the microstructure, phase composition, physical and mechanical properties of the ion-alloyed Ni surfaces formed at high intensity implantation of Ti ions. The implantation Ti ions into Ni samples at high intensity mode was realized using ion source 'Raduga - 5'. The implantation Ti ions into Ni was carried out at accelerating voltage 20 kV for 2 h. The regimes were differed in the samples temperature (580 - 700 K), the distance from the ion implanted samples to the ion source (0.43-0.93 m) and the dose of irradiated ions (0.3·10 18 -2.9·10 18 ion/cm -2 ). The element composition of the implanted samples was analyzed by the electron spectroscopy. The structural-phase state of the Ni ion-modified layers was investigated by the transmission electron microscopy and X-ray diffraction methods. Additionally, the investigation of mechanical and tribological properties of the implanted Ni samples was carried out. It was established that the maximum thickness of the ion-alloyed nickel layers at high intensity mode allows forming the nanoscale intermetallic phases (Ni

Immiscibility of Fluid Phases at Magmatic-hydrothermal Transition: Formation of Various PGE-sulfide Mineralization for Layered Basic Intrusions

Science.gov (United States)

Zhitova, L.; Borisenko, A.; Morgunov, K.; Zhukova, I.

2007-12-01

Fluid inclusions in quartz of the Merensky Reef (Bushveld Complex, South Africa) and the Chineisky Pluton (Transbaikal Region, Russia) were studied using cryometry, microthermometry, Raman-spectroscopy, LA ICP- MS, scanning electronic microscopy, gas-chromatography and isotopic methods. This allowed us to document some examples of fluid phase separation resulting in formation of different types of PGE-sulfide mineralization for layered basic intrusions. The results obtained show at least three generations of fluid separated from boiling residual alumosilicate intercumulus liquid of the Merensky Reef. The earliest fluid phase composed of homogenous high-dense methane and nitrogen gas mixture was identified in primary gas and co-existing anomalous fluid inclusions from symplectitic quartz. The next generation, heterophase fluid, composed of brines containing a free low-dense (mostly of carbon dioxide) gas phase, was observed in primary multiphase and coexisting gas-rich inclusions of miarolitic quartz crystals. The latest generation was also a heterophase fluid (low salinity water-salt solution and free low-dense methane gas phase) found in primary water-salt and syngenetic gas inclusions from peripheral zones of miarolitic quartz crystals. For the Chineisky Pluton reduced endocontact magmatogene fluids changed to oxidized low salinity hydrothermal fluids in exocontact zone. This resulted in formation of sulfide-PGE enrichment marginal zones of intrusion. The results obtained give us a possibility to suggest that: 1) Fluid phase separation is a typical feature of magmatogene fluids for layered basic intrusions. 2) Reduced fluids can extract and transport substantial PGE and sulfide concentrations. 3) Oxidation of reduced fluids is one of the most important geochemical barriers causing abundant PGE minerals and sulfides precipitation. This in turn results in both formation of PGE reefs or enriched contact zones of layered basic intrusions. This work was supported by

Formation of the second organic phase during uranyl nitrate extraction from aqueous solution by 30% tributylphosphate solution in paraffin

International Nuclear Information System (INIS)

Yhrkin, V.G.

1996-01-01

For extraction systems aqueous solution of uranyl nitrate-30% solution of tributylphosphate in individual paraffins from C 13 to C 17 the influence of the second organic phase of uranyl nitrate concentration in aqueous and organic phases, the length of hydrocarbon chain of paraffin hydrocarbon and temperature from 25 to 50 deg C on formation conditions has been defected. A special method of achieving the conditions of organic phase stratification from three-phase region, involving definition of equilibrium phases composition by density and refractive index, has been elaborated for more precise definition of organic phase homogeneity region. It has been revealed that without addition of nitric acid to uranyl nitrate solution the organic phase homogeneity limits can be achieved solely on paraffins C 15 , C 16 and C 17 and only under conditions similar to equeous phase saturation in terms of uranyl nitrate. 16 refs., 2 figs

8OCB and 8CB Liquid Crystals Confined in Nanoporous Alumina: Effect of Confinement on the Structure and Dynamics.

Science.gov (United States)

Selevou, Aristoula; Papamokos, George; Steinhart, Martin; Floudas, George

2017-08-03

The effect of oxygen substitution is studied in two homologous compounds of n-cyanobiphenyls with n = 8 in the bulk and under confinement within self-ordered nanoporous alumina (AAO). Oxygen substitution in 8OCB increases the dipole moment and stabilizes the crystalline, smectic, and nematic phases to higher temperatures relative to 8CB. Within their smectic- A (SmA) phase both 8CB and 8OCB behave as weak viscoelastic solids with low shear moduli reflecting the underlying supramolecular defect structure. Dielectric spectroscopy assisted by DFT calculations identified strong dipolar associations within the isotropic phases characterized by a Kirkwood-Fröhlich interaction parameter, g ∼ 0.36. Dielectric spectroscopy further identified a slow process (∼ kHz) of low dielectric strength. The proximity of this process to the rheology time scale suggests as common origin a cooperative relaxation of the defect structure. Confinement alters the phase diagram by stabilizing certain crystalline phases and by reducing the N-I transition temperature in agreement with surface tension effects. However, the N-I transition seems to retain its first order character. Surface treatment with n-decyltrichlorosilane results in destabilization of the SmA phase at the expense of the N phase. This is consistent with a picture of surface anchored LC molecules at the pore walls that stabilize the nematic phase.

Phase formation in K2O(K2CO3)-CdO-MoO3 system

International Nuclear Information System (INIS)

Tsirenova, G.D.; Tsybikova, B.A.; Bazarova, Zh.G.; Solodovnikov, S.F.; Zolotova, E.S.

2000-01-01

Phase formation in K 2 O(K 2 CO 3 )-CdO-MoO 3 system are studied by the methods of x-ray diffraction, thermal and crystal optical analyses. Three potassium-cadmium molybdates are detected: K 4 Cd(MoO 4 ) 3 with a new structure, alluodite-like K 4-2x Cd 1+x (MoO 4 ) 3 (0.26≤x≤0.38 at 470 Deg C) and K 4 CdMo 4 O 15 of K 4 MnMo 4 O 15 type. First of them decomposes in solid phase at 580 Deg C, and others melt incongruently at 720 and 515 Deg C correspondingly. It is established that K 4-2x Cd 1+x (MoO 4 ) 3 compound undergoes phase transition of the second type in the temperature interval of 500-550 Deg C. Phase diagram of quasibinary cross section K 2 MoO 4 -CdMoO 4 is plotted [ru

RPPAML/RIMS: a metadata format and an information management system for reverse phase protein arrays.

Science.gov (United States)

Stanislaus, Romesh; Carey, Mark; Deus, Helena F; Coombes, Kevin; Hennessy, Bryan T; Mills, Gordon B; Almeida, Jonas S

2008-12-22

Reverse Phase Protein Arrays (RPPA) are convenient assay platforms to investigate the presence of biomarkers in tissue lysates. As with other high-throughput technologies, substantial amounts of analytical data are generated. Over 1,000 samples may be printed on a single nitrocellulose slide. Up to 100 different proteins may be assessed using immunoperoxidase or immunoflorescence techniques in order to determine relative amounts of protein expression in the samples of interest. In this report an RPPA Information Management System (RIMS) is described and made available with open source software. In order to implement the proposed system, we propose a metadata format known as reverse phase protein array markup language (RPPAML). RPPAML would enable researchers to describe, document and disseminate RPPA data. The complexity of the data structure needed to describe the results and the graphic tools necessary to visualize them require a software deployment distributed between a client and a server application. This was achieved without sacrificing interoperability between individual deployments through the use of an open source semantic database, S3DB. This data service backbone is available to multiple client side applications that can also access other server side deployments. The RIMS platform was designed to interoperate with other data analysis and data visualization tools such as Cytoscape. The proposed RPPAML data format hopes to standardize RPPA data. Standardization of data would result in diverse client applications being able to operate on the same set of data. Additionally, having data in a standard format would enable data dissemination and data analysis.

RPPAML/RIMS: A metadata format and an information management system for reverse phase protein arrays

Directory of Open Access Journals (Sweden)

Hennessy Bryan T

2008-12-01

Full Text Available Abstract Background Reverse Phase Protein Arrays (RPPA are convenient assay platforms to investigate the presence of biomarkers in tissue lysates. As with other high-throughput technologies, substantial amounts of analytical data are generated. Over 1000 samples may be printed on a single nitrocellulose slide. Up to 100 different proteins may be assessed using immunoperoxidase or immunoflorescence techniques in order to determine relative amounts of protein expression in the samples of interest. Results In this report an RPPA Information Management System (RIMS is described and made available with open source software. In order to implement the proposed system, we propose a metadata format known as reverse phase protein array markup language (RPPAML. RPPAML would enable researchers to describe, document and disseminate RPPA data. The complexity of the data structure needed to describe the results and the graphic tools necessary to visualize them require a software deployment distributed between a client and a server application. This was achieved without sacrificing interoperability between individual deployments through the use of an open source semantic database, S3DB. This data service backbone is available to multiple client side applications that can also access other server side deployments. The RIMS platform was designed to interoperate with other data analysis and data visualization tools such as Cytoscape. Conclusion The proposed RPPAML data format hopes to standardize RPPA data. Standardization of data would result in diverse client applications being able to operate on the same set of data. Additionally, having data in a standard format would enable data dissemination and data analysis.

Kinetic study of the formation of the superconducting A15 phase in the Nb-Al-Si system

International Nuclear Information System (INIS)

Binh-Phung.

1978-12-01

So far, aluminum-containing superconductors showed excellent critical fields and temperatures. Powder Metallurgy shows the most promise in producing these particular kinds of superconductors in the near future. The scope of this research is to apply a kinetic study to observe the behavior of the Nb(Al,Si) system at elevated temperatures. From such observations, an optimized method of obtaining the A15 superconducting phase can be achieved. This study has resulted in a two step heat treatment to obtain the A15 phase. For the primary heat treatment of infiltrated rods, 600 0 C for 11 hours or 650 0 C for 1 hour was found suitable to form a barrier of intermetallic compound around the pores. For the secondary heat treatment, 1700 0 C for 15 seconds resulted in the formation of the A15 superconducting phase with a critical temperature of 18.25 0 K. A15 formation for wires is similar to infiltrated rods. The only difference is the diffusion path which is now much shorter. 600 0 C for 1 hour was found suitable for the primary heat treatment and 1700 0 C for 15 seconds was the most suitable for the secondary heat treatment. The highest critical temperature found thus far was 18.78 0 K

The N-salicylidene aniline mesogen: Microscopic and macroscopic properties

International Nuclear Information System (INIS)

Nesrullazade, A.

2004-01-01

The vast majority of compounds exhibiting Iiquid crystalline phases may be regarded as having a rigid molecular central group with one or two flexible terminal alkyl or alkyloxy chains. The N-saIicyIidene anilines are very interesting and important materials both from fundamental and application points of view. These materials are on the one hand the ligands used to obtain metal containing complexes and on the other hand they are materials having the thermotropic mesomorphism. In this work we present investigations of microscopic and macroscopic properties of the 4-(Octyloxy)-N-(4-hexylphenyl)-2-hydrobenzaIimine (8SA) compound which was synthesized by our group. The 8SA compound shows the smectic C and nematic mesophases. These mesophases are enantiotropic and display specific confocal and schlieren textures, respectively. Thermotropic and thermodynamical properties of the straight and reverse phase transitions between smectic C and nematic mesophases and between nematic mesophase and isotropic liquid have been investigated

REE interactions with hydroxyapatite. Formation of secondary solid phases

International Nuclear Information System (INIS)

Seco, F.; Pablo, J. de; Bruno, J.

2005-01-01

Full text of publication follows: Lighter rare earth elements (REE) commonly occur in nature as the phosphate mineral monazite, while the heavier REE and Yttrium occur as the phosphate mineral xenotime, which has a similar composition, but different coordination environment of the cation. The geochemical behaviour of REE is mainly controlled by their interactions with phosphate minerals such as hydroxyapatite, Ca 5 (PO 4 ) 3 OH, which is a very common phosphate phase in subsurface environments. Furthermore, is a material considered to be used in a High Level Nuclear Waste repository due to its high capacity in the retention of radionuclides. The objective of this work has been to study the reaction mechanisms and thermodynamics of the interaction of La(III) and Yb(III) with hydroxyapatite as a model for general Ln(III) and Ac(III) behaviour. The surface interaction of La(III) and Yb(III) with synthetic hydroxyapatite has been investigated in batch experiments with low REE 3+ initial concentrations in constant 0.1 M NaClO 4 , at room temperature and in N 2 (g) atmosphere to avoid carbonate complex formation. The initial kinetic experiments indicated that a short contact time is needed to reach equilibrium ( 4 .nH 2 O, where a 0.83 4 .nH 2 O with 1.78 4 medium and under N 2 (g) atmosphere. The experimental data indicate that the solubility equilibria is mainly controlled by the aqueous species REE 3+ until approximately pH=5 where the formation of aqueous complexes of the form REEHPO 4 + , REEPO 4 and REE(PO 4 ) 2 3- must be considered. (authors)

Phase sensitive molecular dynamics of self-assembly glycolipid thin films: A dielectric spectroscopy investigation

Science.gov (United States)

Velayutham, T. S.; Ng, B. K.; Gan, W. C.; Majid, W. H. Abd.; Hashim, R.; Zahid, N. I.; Chaiprapa, Jitrin

2014-08-01

Glycolipid, found commonly in membranes, is also a liquid crystal material which can self-assemble without the presence of a solvent. Here, the dielectric and conductivity properties of three synthetic glycolipid thin films in different thermotropic liquid crystal phases were investigated over a frequency and temperature range of (10-2-106 Hz) and (303-463 K), respectively. The observed relaxation processes distinguish between the different phases (smectic A, columnar/hexagonal, and bicontinuous cubic Q) and the glycolipid molecular structures. Large dielectric responses were observed in the columnar and bicontinuous cubic phases of the longer branched alkyl chain glycolipids. Glycolipids with the shortest branched alkyl chain experience the most restricted self-assembly dynamic process over the broad temperature range studied compared to the longer ones. A high frequency dielectric absorption (Process I) was observed in all samples. This is related to the dynamics of the hydrogen bond network from the sugar group. An additional low-frequency mechanism (Process II) with a large dielectric strength was observed due to the internal dynamics of the self-assembly organization. Phase sensitive domain heterogeneity in the bicontinuous cubic phase was related to the diffusion of charge carriers. The microscopic features of charge hopping were modelled using the random walk scheme, and two charge carrier hopping lengths were estimated for two glycolipid systems. For Process I, the hopping length is comparable to the hydrogen bond and is related to the dynamics of the hydrogen bond network. Additionally, that for Process II is comparable to the bilayer spacing, hence confirming that this low-frequency mechanism is associated with the internal dynamics within the phase.

Phase-field simulation of microstructure formation in technical castings - A self-consistent homoenthalpic approach to the micro-macro problem

Science.gov (United States)

Böttger, B.; Eiken, J.; Apel, M.

2009-10-01

Performing microstructure simulation of technical casting processes suffers from the strong interdependency between latent heat release due to local microstructure formation and heat diffusion on the macroscopic scale: local microstructure formation depends on the macroscopic heat fluxes and, in turn, the macroscopic temperature solution depends on the latent heat release, and therefore on the microstructure formation, in all parts of the casting. A self-consistent homoenthalpic approximation to this micro-macro problem is proposed, based on the assumption of a common enthalpy-temperature relation for the whole casting which is used for the description of latent heat production on the macroscale. This enthalpy-temperature relation is iteratively obtained by phase-field simulations on the microscale, thus taking into account the specific morphological impact on the latent heat production. This new approach is discussed and compared to other approximations for the coupling of the macroscopic heat flux to complex microstructure models. Simulations are performed for the binary alloy Al-3at%Cu, using a multiphase-field solidification model which is coupled to a thermodynamic database. Microstructure formation is simulated for several positions in a simple model plate casting, using a one-dimensional macroscopic temperature solver which can be directly coupled to the microscopic phase-field simulation tool.

Phase-field simulation of microstructure formation in technical castings - A self-consistent homoenthalpic approach to the micro-macro problem

International Nuclear Information System (INIS)

Boettger, B.; Eiken, J.; Apel, M.

2009-01-01

Performing microstructure simulation of technical casting processes suffers from the strong interdependency between latent heat release due to local microstructure formation and heat diffusion on the macroscopic scale: local microstructure formation depends on the macroscopic heat fluxes and, in turn, the macroscopic temperature solution depends on the latent heat release, and therefore on the microstructure formation, in all parts of the casting. A self-consistent homoenthalpic approximation to this micro-macro problem is proposed, based on the assumption of a common enthalpy-temperature relation for the whole casting which is used for the description of latent heat production on the macroscale. This enthalpy-temperature relation is iteratively obtained by phase-field simulations on the microscale, thus taking into account the specific morphological impact on the latent heat production. This new approach is discussed and compared to other approximations for the coupling of the macroscopic heat flux to complex microstructure models. Simulations are performed for the binary alloy Al-3at%Cu, using a multiphase-field solidification model which is coupled to a thermodynamic database. Microstructure formation is simulated for several positions in a simple model plate casting, using a one-dimensional macroscopic temperature solver which can be directly coupled to the microscopic phase-field simulation tool.

Influence of sigma-phase formation on the localized corrosion behavior of a duplex stainless steel

International Nuclear Information System (INIS)

Adhe, K.N.; Kain, V.; Madangopal, K.; Gadiyar, H.S.

1996-01-01

Because of their austenitic-ferritic microstructures, duplex stainless steels offer a good combination of mechanical and corrosion resistance properties. However, heat treatments can lower the mechanical strength of these stainless steels as well as render them susceptible to intergranular corrosion (IGC) and pitting corrosion. In this study, a low-carbon (0.02%) duplex stainless steel is subjected to various heat treatments at 450 to 950 C for 30 min to 10 h. The heat-treated samples than undergo ASTM IGC and pitting corrosion tests, and the results are correlated with the microstructures obtained after each heat treatment. In the absence of Cr 23 C 6 precipitation, σ-phase precipitates render this duplex stainless steel susceptible to IGC and pitting corrosion. Even submicroscopic σ-phase precipitates are deleterious for IGC resistance. Longer-duration heat treatments (at 750 to 850 C) induce chromium diffusion to replenish the chromium-depleted regions around the σ-phase precipitates and improve IGC resistance; pitting resistance, however, is not fully restored. Various mechanisms of σ-phase formation are discussed to show that regions adjacent to σ-phase are depleted of chromium and molybdenum. The effect of chemical composition (pitting resistance equivalent) on the pitting resistance of various stainless steels is also noted

Omega phase in materials

International Nuclear Information System (INIS)

Sikka, S.K.; Vohra, Y.K.; Chidambaram, R.

1982-01-01

The subject is reviewed under the headings: introduction; occurrence and some systematics of omega phase; crystallography; physical properties; kinetics of formation, synthesis and metastability of omega phase; electronic structure of omega phase; electronic basis for omega phase stability; omega phase formation under combined thermal and pressure treatment in alloys; transformation mechanisms and models for diffuse omega phase; conclusion. The following elements of nuclear interest (or their alloys) are included: Zr, Hf, Nb, V, Mo. (U.K.)

Formation of multiple focal spots using a high NA lens with a complex spiral phase mask

Science.gov (United States)

Lalithambigai, K.; Anbarasan, P. M.; Rajesh, K. B.

2014-07-01

The formation of a transversally polarized beam by transmitting a tightly focused double-ring-shaped azimuthally polarized beam through a complex spiral phase mask and high numerical aperture lens is presented based on vector diffraction theory. The generation of transversally polarized focal spot segment splitting and multiple focal spots is illustrated numerically. Moreover, we found that a properly designed complex spiral phase mask can move the focal spots along the optical axis in the z direction. Therefore, one can achieve a focal segment of two, three or multiple completely transversely polarized focal spots, which finds applications in optical trapping and in material processing technologies.

Key Role of Nitrate in Phase Transitions of Urban Particles: Implications of Important Reactive Surfaces for Secondary Aerosol Formation

Science.gov (United States)

Sun, Jiaxing; Liu, Lei; Xu, Liang; Wang, Yuanyuan; Wu, Zhijun; Hu, Min; Shi, Zongbo; Li, Yongjie; Zhang, Xiaoye; Chen, Jianmin; Li, Weijun

2018-01-01

Ammonium sulfate (AS) and ammonium nitrate (AN) are key components of urban fine particles. Both field and model studies showed that heterogeneous reactions of SO2, NO2, and NH3 on wet aerosols accelerated the haze formation in northern China. However, little is known on phase transitions of AS-AN containing haze particles. Here hygroscopic properties of laboratory-generated AS-AN particles and individual particles collected during haze events in an urban site were investigated using an individual particle hygroscopicity system. AS-AN particles showed a two-stage deliquescence at mutual deliquescence relative humidity (MDRH) and full deliquescence relative humidity (DRH) and three physical states: solid before MDRH, solid-aqueous between MDRH and DRH, and aqueous after DRH. During hydration, urban haze particles displayed a solid core and aqueous shell at RH = 60-80% and aqueous phase at RH > 80%. Most particles were in aqueous phase at RH > 50% during dehydration. Our results show that AS content in individual particles determines their DRH and AN content determines their MDRH. AN content increase can reduce MDRH, which indicates occurrence of aqueous shell at lower RH. The humidity-dependent phase transitions of nitrate-abundant urban particles are important to provide reactive surfaces of secondary aerosol formation in the polluted air.

The diversity in thermal behavior of novel catanionic cholates: The dominant effect of quaternary ammonium centers

International Nuclear Information System (INIS)

Mihelj, Tea; Vojta, Danijela; Tomašić, Vlasta

2014-01-01

Graphical abstract: - Highlights: • Quaternary ammonium cholates characterized as crystal smectics at room temperature. • The domination of quaternary ammonium center seen through diverse thermal behavior. • Thermal changes of cholates keto–enol balance results with prevalence of one form. • Polynomial regression of isotropisation temperatures vs. dodecyl chain number. • Linear descending trend of isotropisation temperatures with higher headgroup number. - Abstract: The thermal behavior of novel catanionic compounds based on cholate anion was examined. The study explains the effect of the raising dodecyl chain number, as well as of the raising headgroup number in quaternary ammonium salts on their physico-chemical properties. The examined samples are crystal smectic phases at room temperature. Their rich and diverse thermal behavior is seen through polymorphic phase transitions, thermotropic mesomorphism of smectic nature and in some cases, kinetically managed crystallization that lasts in days. The changes of the cholates keto–enol isomer balance during thermal treatment are obtained. For both groups of samples temperatures of isotropisation and the thermodynamic parameters follow polynomial regression. Introduction of the new dodecyl chain leads to more ordered structure, while implementation the new headgroup leads to advanced polymer-like structure. The obtained results demonstrate an effort for getting and controlling the regularity of the physico-chemical and thermotropic properties for new compounds by systematic changing of cationic part of the molecule. These informations could provide in the future the easiest way for selection of potentially new and targeted applicable materials

The diversity in thermal behavior of novel catanionic cholates: The dominant effect of quaternary ammonium centers

Energy Technology Data Exchange (ETDEWEB)

Mihelj, Tea, E-mail: tmihelj@irb.hr [Department of Physical Chemistry, Ruđer Bošković Institute, POB 180, HR-10002 Zagreb (Croatia); Vojta, Danijela [Department of Organic Chemistry and Biochemistry, Ruđer Bošković Institute, POB 180, HR-10002 Zagreb (Croatia); Tomašić, Vlasta [Department of Physical Chemistry, Ruđer Bošković Institute, POB 180, HR-10002 Zagreb (Croatia)

2014-05-01

Graphical abstract: - Highlights: • Quaternary ammonium cholates characterized as crystal smectics at room temperature. • The domination of quaternary ammonium center seen through diverse thermal behavior. • Thermal changes of cholates keto–enol balance results with prevalence of one form. • Polynomial regression of isotropisation temperatures vs. dodecyl chain number. • Linear descending trend of isotropisation temperatures with higher headgroup number. - Abstract: The thermal behavior of novel catanionic compounds based on cholate anion was examined. The study explains the effect of the raising dodecyl chain number, as well as of the raising headgroup number in quaternary ammonium salts on their physico-chemical properties. The examined samples are crystal smectic phases at room temperature. Their rich and diverse thermal behavior is seen through polymorphic phase transitions, thermotropic mesomorphism of smectic nature and in some cases, kinetically managed crystallization that lasts in days. The changes of the cholates keto–enol isomer balance during thermal treatment are obtained. For both groups of samples temperatures of isotropisation and the thermodynamic parameters follow polynomial regression. Introduction of the new dodecyl chain leads to more ordered structure, while implementation the new headgroup leads to advanced polymer-like structure. The obtained results demonstrate an effort for getting and controlling the regularity of the physico-chemical and thermotropic properties for new compounds by systematic changing of cationic part of the molecule. These informations could provide in the future the easiest way for selection of potentially new and targeted applicable materials.

Heterogeneity-enhanced gas phase formation in shallow aquifers during leakage of CO2-saturated water from geologic sequestration sites

Science.gov (United States)

Plampin, Michael R.; Lassen, Rune N.; Sakaki, Toshihiro; Porter, Mark L.; Pawar, Rajesh J.; Jensen, Karsten H.; Illangasekare, Tissa H.

2014-12-01

A primary concern for geologic carbon storage is the potential for leakage of stored carbon dioxide (CO2) into the shallow subsurface where it could degrade the quality of groundwater and surface water. In order to predict and mitigate the potentially negative impacts of CO2 leakage, it is important to understand the physical processes that CO2 will undergo as it moves through naturally heterogeneous porous media formations. Previous studies have shown that heterogeneity can enhance the evolution of gas phase CO2 in some cases, but the conditions under which this occurs have not yet been quantitatively defined, nor tested through laboratory experiments. This study quantitatively investigates the effects of geologic heterogeneity on the process of gas phase CO2 evolution in shallow aquifers through an extensive set of experiments conducted in a column that was packed with layers of various test sands. Soil moisture sensors were utilized to observe the formation of gas phase near the porous media interfaces. Results indicate that the conditions under which heterogeneity controls gas phase evolution can be successfully predicted through analysis of simple parameters, including the dissolved CO2 concentration in the flowing water, the distance between the heterogeneity and the leakage location, and some fundamental properties of the porous media. Results also show that interfaces where a less permeable material overlies a more permeable material affect gas phase evolution more significantly than interfaces with the opposite layering.

Effect of Ag additions on the lengthening rate of Ω plates and formation of σ phase in Al-Cu-Mg alloys during thermal exposure

Energy Technology Data Exchange (ETDEWEB)

Zhou, Yaru; Liu, Zhiyi, E-mail: liuzhiyi@csu.edu.cn; Bai, Song; Ying, Puyou; Lin, Lianghua

2017-01-15

Effect of Ag additions on the mechanical properties and microstructures of the peak-aged Al-Cu-Mg alloys during prolonged thermal exposure at 150 °C, was investigated by tensile testing, conventional transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The results showed that after exposure for 500 h, > 85% of the peak strength remained. Microstructure observations indicated that increasing the Ag content from 0.14 to 0.57% promoted the precipitation of a fine and uniform Ω phase and suppressed the formation of the θ′ phase, leading to a notable improvement of the strength properties and thermal stability of the studied alloys. Quantitative TEM analysis showed that the coarsening of Ω phase was predominated by plate lengthening rather than thickening, while its lengthening rate was independent of various Ag additions during exposure at 150 °C. In addition, an increase of Ag also facilitated the formation of a cubic σ phase, which was further supported by STEM results. - Highlights: •Increasing Ag improved strength properties and thermal stability of the alloys. •After exposure for 500 h, > 85% of the peak strength remained. •The lengthening rate of Ω plates remained constant as Ag increased at 150 °C. •Increasing Ag content facilitated the formation of σ phase.

Effects of calcination temperature on phase formation and particle size of Zn{sub 2}Nb{sub 34}O{sub 87} powder synthesized by solid-state reaction

Energy Technology Data Exchange (ETDEWEB)

Amonpattaratkit, Penphitcha, E-mail: p.amonpattaratkit@gmail.com [Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand); Ananta, Supon, E-mail: suponananta@yahoo.com [Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand)

2013-05-15

The solid-state mixed oxide method via a rapid vibro-milling technique was explored for the preparation of single-phase Zn{sub 2}Nb{sub 34}O{sub 87} nanopowders. Phase formation of zinc niobate was investigated as a function of calcination temperature by using a combination of thermogravimetric/differential thermal analyzer (TG/DTA) and X-ray diffraction (XRD) techniques. Morphology, particle size and chemical composition of the powders were determined by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) technique. The obtained results clearly revealed the influences of calcination temperature on phase formation and particle size of Zn{sub 2}Nb{sub 34}O{sub 87} nanopowder. - Highlights: ► Single phase Zn{sub 2}Nb{sub 34}O{sub 87} was firstly prepared by solid-state mixed oxide method via a rapid vibro-milling technique. ► The influences of calcination temperature on phase formation and particle size were investigated. ► Zn{sub 2}Nb{sub 34}O{sub 87} powders were characterized by TG–DTA, XRD, SEM and EDX.

Formation of clusters and the percolation threshold in a two-phase system with a random distribution of ZnSe quantum points

Science.gov (United States)

Bondar', N. V.

2009-03-01

A characteristic feature due to the formation of a percolation phase transition of carriers has been observed in a two-phase system consisting of borosilicate glass with ZnSe quantum dots. For near-threshold quantum-dot concentrations, changes due to microscopic fluctuations of the quantum-dot density have been observed in the intensities of radiation emission bands. This phenomenon is reminiscent of critical opalescence, where similar fluctuations of the density of a pure substance arise near a phase transition. It is proposed that the dielectric mismatch between the matrix and ZnSe plays a large role in the carrier (exciton) delocalization, resulting in the appearance of a "dielectric trap" on the interface and the formation there of surface states of excitons. The spatial overlapping of states which occurs at the critical concentration of quantum dots results in carrier tunneling and the appearance of a percolation transition in such a system.

Shear-induced formation of vesicles in membrane phases: Kinetics and size selection mechanisms, elasticity versus surface tension

Science.gov (United States)

Courbin, L.; Panizza, P.

2004-02-01

Multilamellar vesicles can be formed upon shearing lamellar phases (Lα) and phase-separated lamellar-sponge (Lα/L3) mixtures. In the first case, the vesicle volume fraction is always 100% and the vesicle size is monitored by elasticity (“onion textures”). In the second system the vesicle volume fraction can be tuned from 0 to 100% and the mean size results from a balance between capillary and viscous forces (“Taylor droplets”). However, despite these differences, in both systems we show that the formation of vesicles is a strain-controlled process monitored by a universal primary buckling instability of the lamellae.

Phase separation and structure formation in gadolinium based liquid and glassy metallic alloys

International Nuclear Information System (INIS)

Han, Junhee

2014-01-01

In this PhD research the liquid-liquid phase separation phenomena in Gd-based alloys was investigated in terms of phase equilibria, microstructure formation upon quenching the melt and corresponding magnetic properties of phase-separated metallic glasses. The phase diagrams of the binary subsystems Gd-Zr and Gd-Ti were experimentally reassessed. Especially the phase equilibria with the liquid phase could be determined directly by combining in situ high energy synchrotron X-ray diffraction with electrostatic levitation of the melt. The Gd-Zr system is of eutectic type with a metastable miscibility gap. The eutectic composition at 18 ± 2 at.% Zr, the liquidus line and the coexistence of bcc-Zr and bcc-Gd at elevated temperature could be determined. The Gd-Ti system is a monotectic system. The experimental observations in this work led to improved new Gd-Zr and Gd-Ti phase diagrams. The phase equilibria of the ternary Gd-Ti-Co system were analyzed for two alloy compositions. The XRD patterns for molten Gd 35 Ti 35 Co 30 gave direct evidence for the coexistence of two liquid phases formed by liquid-liquid phase separation. The first experimental and thermodynamic assessment of the ternary Gd-Ti-Co system revealed that the stable miscibility gap of binary Gd-Ti extends into the ternary Gd-Ti-Co system (up to about 30 at.% Co). New phase-separated metallic glasses were synthesized in Gd-TM-Co-Al (TM = Hf, Ti or Zr) alloys. The microstructure was characterized in terms of composition and cooling rate dependence of phase separation. Due to large positive enthalpy of mixing between Gd on the one side and Hf, Ti or Zr on the other side, the alloys undergo liquid-liquid phase separation during rapid quenching the melt. The parameters determining the microstructure development during phase separation are the thermodynamic properties of the liquid phase, kinetic parameters and quenching conditions. By controlling these parameters and conditions the microstructure can be

Phase separation of a Lennard-Jones fluid interacting with a long, condensed polymer chain: implications for the nuclear body formation near chromosomes.

Science.gov (United States)

Oh, Inrok; Choi, Saehyun; Jung, YounJoon; Kim, Jun Soo

2015-08-28

Phase separation in a biological cell nucleus occurs in a heterogeneous environment filled with a high density of chromatins and thus it is inevitably influenced by interactions with chromatins. As a model system of nuclear body formation in a cell nucleus filled with chromatins, we simulate the phase separation of a low-density Lennard-Jones (LJ) fluid interacting with a long, condensed polymer chain. The influence of the density variation of LJ particles above and below the phase boundary and the role of attractive interactions between LJ particles and polymer segments are investigated at a fixed value of strong self-interaction between LJ particles. For a density of LJ particles above the phase boundary, phase separation occurs and a dense domain of LJ particles forms irrespective of interactions with the condensed polymer chain whereas its localization relative to the polymer chain is determined by the LJ-polymer attraction strength. Especially, in the case of moderately weak attractions, the domain forms separately from the polymer chain and subsequently associates with the polymer chain. When the density is below the phase boundary, however, the formation of a dense domain is possible only when the LJ-polymer attraction is strong enough, for which the domain grows in direct contact with the interacting polymer chain. In this work, different growth behaviors of LJ particles result from the differences in the density of LJ particles and in the LJ-polymer interaction, and this work suggests that the distinct formation of activity-dependent and activity-independent nuclear bodies (NBs) in a cell nucleus may originate from the differences in the concentrations of body-specific NB components and in their interaction with chromatins.

Microstructural characterization, formation mechanism and fracture behavior of the needle δ phase in Fe–Ni–Cr type superalloys with high Nb content

Energy Technology Data Exchange (ETDEWEB)

Ning, Yongquan, E-mail: luckyning@nwpu.edu.cn [School of Materials Science & Engineering, Northwestern Polytechnical University, Xi' an 710072 (China); Huang, Shibo [Anshan Iron & Steel Group Corporation Bayuquan Subsidiary Company, Bayuquan 115007 (China); Fu, M.W. [Department of Mechanical Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong (China); Dong, Jie [Inspection & Research Institute of Boiler & Pressure Vessel of Jiangxi Province, Nanchang 330029 (China)

2015-11-15

Microstructural characterization, formation mechanism and fracture behavior of the needle δ phase in Fe–Ni–Cr type superalloys with high Nb content (GH4169, equivalent to Inconel 718) have been quantitatively investigated in this research. The typical microstructures of δ phases with the stick, mixed and needle shapes obviously present in Inconel 718 after the isothermal upsetting at the temperature of 980–1060 °C with the initial strain rate of 10{sup −3}–10{sup −1} s{sup −1}. It is found that the shape of the δ phase has a great effect on the mechanical properties of the alloy, viz., the stick δ phase behaves good plasticity and the needle δ phase has good strength. In addition, the needle δ phase can be used to control the grain size as it can prevent grain growth. The combined effect of the localized necking and microvoid coalescence leads to the final ductile fracture of the GH4169 components with the needle δ phase. Both dislocation motion and atom diffusion are the root-cause for the needle δ phase to be firstly separated at grain boundary and then at sub-boundary. The formation mechanism of the needle δ phase is the new finding in this research. Furthermore, it is the primary mechanism for controlling the needle δ phase in Fe–Ni–Cr type superalloys with high Nb content. - Highlights: • Shape of the δ phase takes great effect on mechanical property. • Needle δ phase plays a great role to prevent grain growth. • Needle δ phase can enhance the fracture strength. • Microstructure mechanism of the needle δ phase has been investigated. • Fracture behavior of the needle δ phase has been studied.

A Massive Galaxy in Its Core Formation Phase Three Billion Years After the Big Bang

Science.gov (United States)

Nelson, Erica; van Dokkum, Pieter; Franx, Marijn; Brammer, Gabriel; Momcheva, Ivelina; Schreiber, Natascha M. Forster; da Cunha, Elisabete; Tacconi, Linda; Bezanson, Rachel; Kirkpatrick, Allison;

On the formation of molecules and solid-state compounds from the AGB to the PN phases

Science.gov (United States)

García-Hernández, D. A.; Manchado, A.

2016-07-01

During the asymptoyic giant branch (AGB) phase, different elements are dredge- up to the stellar surface depending on progenitor mass and metallicity. When the mass loss increases at the end of the AGB, a circumstellar dust shell is formed, where different (C-rich or O-rich) molecules and solid-state compounds are formed. These are further processed in the transition phase between AGB stars and planetary nebulae (PNe) to create more complex organic molecules and inorganic solid-state compounds (e.g., polycyclic aromatic hydrocarbons, fullerenes, and graphene precursors in C-rich environments and oxides and crystalline silicates in O-rich ones). We present an observational review of the different molecules and solid-state materials that are formed from the AGB to the PN phases. We focus on the formation routes of complex fullerene (and fullerene-based) molecules as well as on the level of dust processing depending on metallicity.

Evidence of liquid phase during laser-induced periodic surface structures formation induced by accumulative ultraviolet picosecond laser beam

Energy Technology Data Exchange (ETDEWEB)

Huynh, T. T. D.; Petit, A.; Semmar, N., E-mail: nadjib.semmar@univ-orleans.fr [GREMI, UMR7344, CNRS/University of Orleans, 14 rue d' Issoudun, BP6744, 45067 Orleans Cedex 2 (France); Vayer, M. [ICMN, UMR 7374, CNRS/University of Orleans, 1b rue de la Ferollerie, CS 40059, 45071 Orleans Cedex (France); Sauldubois, A. [CME, UFR Sciences, University of Orleans, 1 Rue de Chartres, BP 6759, 45067 Orleans Cedex 2 (France)

2015-11-09

Laser-induced periodic surface structures (LIPSS) were formed on Cu/Si or Cu/glass thin films using Nd:YAG laser beam (40 ps, 10 Hz, and 30 mJ/cm{sup 2}). The study of ablation threshold is always achieved over melting when the variation of the number of pulses increases from 1 to 1000. But the incubation effect is leading to reduce the threshold of melting as increasing the number of laser pulse. Also, real time reflectivity signals exhibit typical behavior to stress the formation of a liquid phase during the laser-processing regime and helps to determine the threshold of soft ablation. Atomic Force Microscopy (AFM) analyses have shown the topology of the micro-crater containing regular spikes with different height. Transmission Electron Microscopy (TEM) allows finally to show three distinguished zones in the close region of isolated protrusions. The central zone is a typical crystallized area of few nanometers surrounded by a mixed poly-crystalline and amorphous area. Finally, in the region far from the protrusion zone, Cu film shows an amorphous structure. The real time reflectivity, AFM, and HR-TEM analyses evidence the formation of a liquid phase during the LIPSS formation in the picosecond regime.

Lactic acid derivatives with three-phenyl ring molecular core: design and mesomorphic properties

Czech Academy of Sciences Publication Activity Database

Hamplová, Věra; Novotná, Vladimíra; Kašpar, Miroslav

2014-01-01

Roč. 468, č. 1 (2014), s. 18-27 ISSN 0015-0193 R&D Projects: GA ČR GA13-14133S; GA MŠk 7AMB13PL038 Institutional support: RVO:68378271 Keywords : liquid crystals * smectic phases * ferroelectricity Subject RIV: JJ - Other Materials Impact factor: 0.469, year: 2014

Effect of Magnesium Content and Processing Conditions on Phase Formation and Stability in Mg2+ δ Si0.3Sn0.7

Science.gov (United States)

Goyal, Gagan K.; Dasgupta, T.

2018-03-01

Mg2+ δ Si0.3Sn0.7 compositions with nominal Mg content of δ = 0, 0.2 are synthesized using a single-step quartz tube reaction method with different heating rates and holding times. The resulting powders are sintered using a uniaxial induction hot press under similar conditions to produce near-dense compacts. The effect of Mg content and processing conditions on the phase formation and its stability are studied using x-ray diffraction measurements, scanning electron microscopy (SEM) with elemental mapping and compositional analysis using energy dispersive spectroscopy (EDS). Results indicate that with sufficient Mg content and shorter synthesis time, the powder remains single phasic; however, prolonged heat treatment during synthesis results in Mg loss and causes the system to become biphasic. Compaction results in single-phase formation in all the specimens. This is attributed to the removal of the low-melting secondary Sn-rich phases present in the system. The decomposition of the specimens depends on the Mg content after the compaction step with a δ around - 0.15 necessary to preserve the single phase. The decomposition also results in Mg enrichment of the matrix (due to formation of elemental Sn), thereby acting as a self-healing mechanism. Annealing the dense products at 773 K for 24 h in static vacuum is carried out. Progressive Mg loss is observed resulting in degradation of the specimen.

Phase formation and magnetic properties of YFe12-xNbx (x=0.70-0.90) compounds

International Nuclear Information System (INIS)

Fuquan, B.; Wang, J.L.; Tegus, O.; Dagula, W.; Tang, N.; Yang, F.M.; Wu, G.H.; Brueck, E.; Boer, F.R. de; Buschow, K.H.J.

2005-01-01

The phase formation and the magnetic properties of YFe 12-x Nb x (x=0.70-0.90) compounds have been investigated by means of X-ray diffraction and magnetization measurements. The powder X-ray diffraction patterns show that all compounds investigated crystallize single phase in the tetragonal ThMn 12 -type of structure. The lattice parameters and the unit-cell volume increase slightly with increasing Nb content, but the Curie temperature does not change. The X-ray-diffraction patterns of aligned powders of the samples show that all the compounds investigated have uniaxial anisotropy at room temperature. At 1.5K, the spontaneous magnetization, the anisotropy field and the anisotropy constant K 1 decrease with increasing Nb content

Effects of KOH:ZnCl{sub 2} mole ratio on the phase formation, morphological and inhibitive properties of potassium zinc phosphate (PZP) pigments

Energy Technology Data Exchange (ETDEWEB)

Askari, F. [Inorganic Pigment and Glazes Department, Institute for Color Science and Technology, Tehran 1668814811 (Iran, Islamic Republic of); Surface Coatings and Corrosion Department, Institute for Color Science and Technology, Tehran 1668814811 (Iran, Islamic Republic of); Ghasemi, E., E-mail: eghasemi@iust.ac.ir [Inorganic Pigment and Glazes Department, Institute for Color Science and Technology, Tehran 1668814811 (Iran, Islamic Republic of); Ramezanzadeh, B.; Mahdavian, M. [Surface Coatings and Corrosion Department, Institute for Color Science and Technology, Tehran 1668814811 (Iran, Islamic Republic of)

2015-05-15

Graphical abstract: This figure illustrates the inhibition mechanism. The film precipitation on the anodic and cathodic regions of the metal surface causes a drop in dissolution rate of steel. - Highlights: • We synthesized the ZP pigments via coprecipitation method. • Effect of KOH:ZnCl{sub 2} on phase formation, morphology and inhibitive performance of pigment. • KOH:ZnCl{sub 2} ratio is effective on phase formation and morphology of ZP pigments. • KZn{sub 2}H(PO{sub 4}){sub 2} phase showed superior corrosion inhibition behavior than KZnPO{sub 4}. - Abstract: Different types of potassium zinc phosphate (PZP) pigments were synthesized by a co-precipitation method. The PZPs were obtained through changing KOH:ZnCl{sub 2} mole ratio. The chemical composition of the pigments was studied by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy (SEM). Then, the extracts of the PZPs were prepared in 3.5% (w/w) NaCl solution. The inhibitive performance of the pigments was investigated by polarization technique and SEM surface analysis through dipping mild steel panels in the pigment extracts for different immersion times. Results showed that changing ZnCl{sub 2}/KOH mole ratio could influence formation of KZn{sub 2}H(PO{sub 4}){sub 2} and KZnPO{sub 4} phases. It was known that the KZn{sub 2}H(PO{sub 4}){sub 2} phase has a superior corrosion inhibition behavior in 3.5% NaCl solution than KZnPO{sub 4} phase.

On the phase formation of sputtered hafnium oxide and oxynitride films

International Nuclear Information System (INIS)

Sarakinos, K.; Music, D.; Mraz, S.; Baben, M. to; Jiang, K.; Nahif, F.; Braun, A.; Zilkens, C.; Schneider, J. M.; Konstantinidis, S.; Renaux, F.; Cossement, D.; Munnik, F.

2010-01-01

Hafnium oxynitride films are deposited from a Hf target employing direct current magnetron sputtering in an Ar-O 2 -N 2 atmosphere. It is shown that the presence of N 2 allows for the stabilization of the transition zone between the metallic and the compound sputtering mode enabling deposition of films at well defined conditions of target coverage by varying the O 2 partial pressure. Plasma analysis reveals that this experimental strategy facilitates control over the flux of the O - ions which are generated on the oxidized target surface and accelerated by the negative target potential toward the growing film. An arrangement that enables film growth without O - ion bombardment is also implemented. Moreover, stabilization of the transition sputtering zone and control of the O - ion flux without N 2 addition is achieved employing high power pulsed magnetron sputtering. Structural characterization of the deposited films unambiguously proves that the phase formation of hafnium oxide and hafnium oxynitride films with the crystal structure of HfO 2 is independent from the O - bombardment conditions. Experimental and theoretical data indicate that the presence of vacancies and/or the substitution of O by N atoms in the nonmetal sublattice favor the formation of the cubic and/or the tetragonal HfO 2 crystal structure at the expense of the monoclinic HfO 2 one.

Generation of a new spectral format, the lifetime synchronous spectrum (LiSS), using phase-resolved fluorescence spectroscopy

International Nuclear Information System (INIS)

Shaver, J.M.; McGown, L.B.

1994-01-01

A new fluorescence spectral format is introduced in which fluorescence lifetime is shown as a function of synchronously scanned wavelength to generate a Lifetime Synchronous Spectrum (LiSS). Lifetimes are determined in the frequency domain with the use of Phase-Resolved Fluorescence Spectroscopy (PRFS) to obtain the phase of the fluorescence signal. Theory and construction of the LiSS are presented and experimental results are shown for solutions of single components and simple binary and ternary mixtures. These results show how the lifetime information in the LiSS augments the steady-state intensity information of a standard synchronous spectrum, providing unique information for identification of components and resolution of overlapping spectral peaks. The LiSS technique takes advantage of noise reduction inherent in the extraction of lifetime from PRFS in addition to standard spectral smoothing techniques. The precision of phase determination through PRFS is found to be comparable to that of direct phase measurements at normal fluorescence intensities and superior for low-intensity signals

Effect of high temperature deposition on CoSi2 phase formation

International Nuclear Information System (INIS)

Comrie, C. M.; Ahmed, H.; Smeets, D.; Demeulemeester, J.; Vantomme, A.; Turner, S.; Van Tendeloo, G.; Detavernier, C.

2013-01-01

This paper discusses the nucleation behaviour of the CoSi to CoSi 2 transformation from cobalt silicide thin films grown by deposition at elevated substrate temperatures ranging from 375 °C to 600 °C. A combination of channelling, real-time Rutherford backscattering spectrometry, real-time x-ray diffraction, and transmission electron microscopy was used to investigate the effect of the deposition temperature on the subsequent formation temperature of CoSi 2 , its growth behaviour, and the epitaxial quality of the CoSi 2 thus formed. The temperature at which deposition took place was observed to exert a significant and systematic influence on both the formation temperature of CoSi 2 and its growth mechanism. CoSi films grown at the lowest temperatures were found to increase the CoSi 2 nucleation temperature above that of CoSi 2 grown by conventional solid phase reaction, whereas the higher deposition temperatures reduced the nucleation temperature significantly. In addition, a systematic change in growth mechanism of the subsequent CoSi 2 growth occurs as a function of deposition temperature. First, the CoSi 2 growth rate from films grown at the lower reactive deposition temperatures is substantially lower than that grown at higher reactive deposition temperatures, even though the onset of growth occurs at a higher temperature, Second, for deposition temperatures below 450 °C, the growth appears columnar, indicating nucleation controlled growth. Elevated deposition temperatures, on the other hand, render the CoSi 2 formation process layer-by-layer which indicates enhanced nucleation of the CoSi 2 and diffusion controlled growth. Our results further indicate that this observed trend is most likely related to stress and changes in microstructure introduced during reactive deposition of the CoSi film. The deposition temperature therefore provides a handle to tune the CoSi 2 growth mechanism.

Study of the formation of secondary phases in the composite LSM/YSZ

International Nuclear Information System (INIS)

Rodrigues, Ranieri Andrade

2007-01-01

The composite of strontium-doped lanthanum manganite (La 1-x SrxMnO 3 - LSM) and Yttria-stabilized zirconia (ZrO 2 /Y 2 O 3 - YSZ), is indicated as cathode of the Solid Oxide Fuel Cells (SOFC). It presents better acting as cathode due to the Triple Phase Boundary (TPB) formed in the interface area between the cathode and the electrolyte. For the temperatures up to 1100 deg C, LSM and YSZ can react producing lanthanum zirconate (La 2 Zr 2 O 7 - LZO) and strontium zirconate (SrZrO 3 - SZO). In this sense, the present work intends to contribute in the study of the formation of phases LZO and SZO, studying different massic proportions between LSM and YSZ with sintering temperatures varying between 1000 deg C and 1400 deg C. For the obtention of the precursory powders the co-precipitation routes were adopted to obtain YSZ and conventional powder mixture for the preparation of LSM. The composite LSM/YSZ, studied in this work, is prepared with two concentrations of Sr for LSM (30 mol por cent - LSM7 and 40 mol por cent - LSM6) and one concentration of Yttria for YSZ (10 mol por cent). The results obtained by X-ray fluorescence showed that the routes adopted for synthesis of powders were effective in the obtention of the compositions LSM6, LSM7 and YSZ, with close values to the stoichiometric. The studied massic proportions were: 50 por cent of LSM and 50 por cent of YSZ (1:1), 25 por cent of LSM and 75 por cent of YSZ (1:3), and 75 por cent of LSM and 25 por cent of YSZ (3:1). Such proportions of mixtures were conformed and submitted at different conditions of temperatures and times of sintering: 1000 deg C, 1200 deg C, 1300 deg C, 1350 deg C and 1400 deg C for 4 and 8 hours. The values of medium size of the particles and the specific surface area values for the mixture of LSM6/YSZ and LSM7/YSZ, are of the same order of largeness after the mixture in a attrition mill and in different massic proportions. Secondary phases like LZO and SZO were not found in the analysis for

Phase formation kinetics, hardness and magnetocaloric effect of sub-rapidly solidified LaFe11.6Si1.4 plates during isothermal annealing

Science.gov (United States)

Dai, Yuting; Xu, Zhishuai; Luo, Zhiping; Han, Ke; Zhai, Qijie; Zheng, Hongxing

2018-05-01

High-temperature phase transition behavior and intrinsic brittleness of NaZn13-type τ1 phase in La-Fe-Si magnetocaloric materials are two key problems from the viewpoint of materials production and practical applications. In the present work, the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation was introduced to quantitatively characterize the formation kinetics of τ1 phase in sub-rapidly solidified LaFe11.6Si1.4 plates during the isothermal annealing process. Avrami index was estimated to be 0.43 (∼0.5), which suggests that the formation of τ1 phase is in a diffusion-controlled one-dimensional growth mode. Meanwhile, it is found that the Vickers hardness as a function of annealing time for sub-rapidly solidified plates also agrees well with the JMAK equation. The Vickers hardness of τ1 phase was estimated to be about 754. Under a magnetic field change of 30 kOe, the maximum magnetic entropy change was about 22.31 J/(kg·K) for plates annealed at 1323 K for 48 h, and the effective magnetic refrigeration capacity reached 191 J/kg.

The impact of liquid-liquid-vapour phase behaviour on coke formation from model coke precusors

Energy Technology Data Exchange (ETDEWEB)

Minicucci, D.; Shaw, J.M. [Univ. of Toronto, Dept. of Chemical Engineering and Applied Chemistry, Toronto, ON (Canada)

2000-08-01

Catalysts used in the hydroprocessing of heavy feedstocks deactivate due to coke deposition. Although the mechanism for coke formation is not fully understood, condensation reactions of polynuclear aromatic compounds present in the feeds are a key aspect. The effect of coke deposition on catalyst performance is typically modelled using accelerated aging agents comprising model coke precursors. Mixtures employed in such studies polynuclear aromatic compounds such as anthracene as the coke precursor, and long chain alkanes such as hexadecane as a diluent. We show in this paper that binary and pseudo binary mixtures of polynuclear aromatic compounds and n-alkanes present TYPE II, TYPE IV, or TYPE III phase behaviour according to the van Konynenburg and Scott (1980) phase projection nomenclature, Incubation periods and the apparent autocatalytic effects associated with coke deposition in such systems are explained through a combination of high temperature phase equilibrium experiments and computations with the model systems n-alkane + anthracene + hydrogen, n-alkane + pyrene + hydrogen, and n-alkane + dibenzo[a,k]chrysene + hydrogen. (au)

Effects of the liquid-gas phase transition and cluster formation on the symmetry energy

International Nuclear Information System (INIS)

Typel, S.; Wolter, H.H.; Roepke, G.; Blaschke, D.

2014-01-01

Various definitions of the symmetry energy are introduced for nuclei, dilute nuclear matter below saturation density and stellar matter, which is found in compact stars or core-collapse supernovae. The resulting differences are exemplified by calculations in a theoretical approach based on a generalized relativistic density functional for dense matter. It contains nucleonic clusters as explicit degrees of freedom with medium-dependent properties that are derived for light clusters from a quantum statistical approach. With such a model the dissolution of clusters at high densities can be described. The effects of the liquid-gas phase transition in nuclear matter and of cluster formation in stellar matter on the density dependence of the symmetry energy are studied for different temperatures. It is observed that correlations and the formation of inhomogeneous matter at low densities and temperatures causes an increase of the symmetry energy as compared to calculations assuming a uniform uncorrelated spatial distribution of constituent baryons and leptons. (orig.)

Phase formation in as-solidified and heat-treated Al–Si–Cu–Mg–Ni alloys: Thermodynamic assessment and experimental investigation for alloy design

International Nuclear Information System (INIS)

Farkoosh, A.R.; Javidani, M.; Hoseini, M.; Larouche, D.; Pekguleryuz, M.

2013-01-01

Highlights: ► Phase formation in Al–Si–Ni–Cu–Mg–Fe system have been investigated. ► T-Al 9 FeNi, γ-Al 7 Cu 4 Ni, δ-Al 3 CuNi and ε-Al 3 Ni are formed at different Ni levels. ► Thermally stable Ni-bearing precipitates improved the overaged hardness. ► It was found that Ni:Cu and Ni:Fe ratios control the precipitation. ► δ-Al 3 CuNi phase has more contribution to strength compare to other precipitates. - Abstract: Thermodynamic simulations based on the CALPHAD method have been carried out to assess the phase formation in Al–7Si–(0–1)Ni–0.5Cu–0.35Mg alloys (in wt.%) under equilibrium and non-equilibrium (Scheil cooling) conditions. Calculations showed that the T-Al 9 FeNi, γ-Al 7 Cu 4 Ni, δ-Al 3 CuNi and ε-Al 3 Ni phases are formed at different Ni levels. By analyzing the calculated isothermal sections of the phase diagrams it was revealed that the Ni:Cu and Ni:Fe ratios control precipitation in this alloy system. In order to verify the simulation results, microstructural investigations in as-cast, solution treated and aged conditions were carried out using electron probe microanalysis (EPMA), scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Furthermore, cooling curve analysis (CCA) was also performed to determine the freezing range of the new alloys and porosity formation during solidification. Hardness measurements of the overaged samples showed that in this alloy system the δ-Al 3 CuNi phase has a greater influence on the overall strength of the alloys compared to the other Ni-bearing precipitates.

Phase formation in as-solidified and heat-treated Al-Si-Cu-Mg-Ni alloys: Thermodynamic assessment and experimental investigation for alloy design

Energy Technology Data Exchange (ETDEWEB)

Farkoosh, A.R., E-mail: amir.rezaeifarkoosh@mail.mcgill.ca [Department of Mining and Materials Engineering, McGill University, 3610 University, Aluminum Research Center - REGAL, Montreal, Quebec, Canada H3A 2B2 (Canada); Javidani, M. [Laval University, Department of Mining, Metallurgy and Materials Engineering, Aluminum Research Center - REGAL, 1065 Ave de la Medecine, Quebec, Canada G1V 0A6 (Canada); Hoseini, M. [Department of Mining and Materials Engineering, McGill University, 3610 University, Aluminum Research Center - REGAL, Montreal, Quebec, Canada H3A 2B2 (Canada); Larouche, D. [Laval University, Department of Mining, Metallurgy and Materials Engineering, Aluminum Research Center - REGAL, 1065 Ave de la Medecine, Quebec, Canada G1V 0A6 (Canada); Pekguleryuz, M. [Department of Mining and Materials Engineering, McGill University, 3610 University, Aluminum Research Center - REGAL, Montreal, Quebec, Canada H3A 2B2 (Canada)

2013-02-25

Highlights: Black-Right-Pointing-Pointer Phase formation in Al-Si-Ni-Cu-Mg-Fe system have been investigated. Black-Right-Pointing-Pointer T-Al{sub 9}FeNi, {gamma}-Al{sub 7}Cu{sub 4}Ni, {delta}-Al{sub 3}CuNi and {epsilon}-Al{sub 3}Ni are formed at different Ni levels. Black-Right-Pointing-Pointer Thermally stable Ni-bearing precipitates improved the overaged hardness. Black-Right-Pointing-Pointer It was found that Ni:Cu and Ni:Fe ratios control the precipitation. Black-Right-Pointing-Pointer {delta}-Al{sub 3}CuNi phase has more contribution to strength compare to other precipitates. - Abstract: Thermodynamic simulations based on the CALPHAD method have been carried out to assess the phase formation in Al-7Si-(0-1)Ni-0.5Cu-0.35Mg alloys (in wt.%) under equilibrium and non-equilibrium (Scheil cooling) conditions. Calculations showed that the T-Al{sub 9}FeNi, {gamma}-Al{sub 7}Cu{sub 4}Ni, {delta}-Al{sub 3}CuNi and {epsilon}-Al{sub 3}Ni phases are formed at different Ni levels. By analyzing the calculated isothermal sections of the phase diagrams it was revealed that the Ni:Cu and Ni:Fe ratios control precipitation in this alloy system. In order to verify the simulation results, microstructural investigations in as-cast, solution treated and aged conditions were carried out using electron probe microanalysis (EPMA), scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Furthermore, cooling curve analysis (CCA) was also performed to determine the freezing range of the new alloys and porosity formation during solidification. Hardness measurements of the overaged samples showed that in this alloy system the {delta}-Al{sub 3}CuNi phase has a greater influence on the overall strength of the alloys compared to the other Ni-bearing precipitates.

Formation of nanocrystalline and amorphous phase of Al-Pb-Si-Sn-Cu powder during mechanical alloying

International Nuclear Information System (INIS)

Ran Guang; Zhou Jingen; Xi Shengqi; Li Pengliang

2006-01-01

Al-15%Pb-4%Si-1%Sn-1.5%Cu alloys (mass fraction, %) were prepared by mechanical alloying (MA). Phase transformation and microstructure characteristics of the alloy powders were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the nanocrystalline supersaturated solid solutions and amorphous phase in the powders are obtained during MA. The effect of ball milling is more evident to lead than to aluminum. During MA, the mixture powders are firstly fined, alloyed, nanocrystallized and then the nanocrystalline partly transforms to amorphous phase. A thermodynamic model is developed based on semi-experimental theory of Miedema to calculate the driving force for phase evolution. The thermodynamic analysis shows that there is no chemical driving force to form a crystalline solid solution from the elemental components. But for the amorphous phase, the Gibbs free energy is higher than 0 for the alloy with lead content in the ranges of 0-86.8 at.% and 98.4-100 at.% and lower than 0 in range of 86.8-98.4 at.%. For the Al-2.25 at.%Pb (Al-15%Pb, mass fraction, %), the driving force for formation of amorphization and nanocrystalline supersaturated solid solutions are provided not by the negative heat of mixing but by mechanical work

Formation of integral asymmetric membranes of AB diblock and ABC triblock copolymers by phase inversion.

Science.gov (United States)

Jung, Adina; Filiz, Volkan; Rangou, Sofia; Buhr, Kristian; Merten, Petra; Hahn, Janina; Clodt, Juliana; Abetz, Clarissa; Abetz, Volker

2013-04-12

The formation of integral asymmetric membranes from ABC triblock terpolymers by non-solvent-induced phase separation is shown. They are compared with the AB diblock copolymer precursors. Triblock terpolymers of polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) (PS-b-P2VP-b-PEO) with two compositions are investigated. The third block supports the formation of a membrane in a case, where the corresponding diblock copolymer does not form a good membrane. In addition, the hydrophilicity is increased by the third block and due to the hydroxyl group the possibility of post-functionalization is given. The morphologies are imaged by scanning electron microscopy. The influence of the PEO on the membrane properties is analyzed by water flux, retention, and dynamic contact angle measurements. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Unusual polymorphism in new bent-shaped liquid crystals based on biphenyl as a central molecular core

Directory of Open Access Journals (Sweden)

Anna Kovářová

2014-04-01

Full Text Available Bent-shaped mesogens possessing a biphenyl as a central core have been synthesized and the role of the terminal chain and the orientation of the ester as a linkage group have been investigated. For the studied molecular core we have established that both parameters play an important role for the mesomorphic properties. The polyfluoroalkyl terminal chain supports the formation of mesophases, and the introduction of a chiral lactate terminal chain destabilizes mesophases for the first type of mutual orientation of ester groups, attached to the central core. On the contrary, for the opposite orientation of esters, the terminal chain has no effect on the mesomorphic properties, and columnar phases have been found for all compounds. A unique phase sequence has been found for the mesogen with the fluorinated chain. A generalized tilted smectics, SmCG, have been observed in a temperature interval between two different lamellar SmCP phases and characterized by X-ray and dielectric measurements. The dielectric spectroscopy data are unique and presented for the first time in the SmCG phase providing new information about the molecular dynamics.

Microstructures and phase formations in the surface layer of an AISI D2 steel treated with pulsed electron beam

International Nuclear Information System (INIS)

Zou, J.X.; Grosdidier, T.; Zhang, K.M.; Gao, B.; Hao, S.Z.; Dong, C.

2007-01-01

The nanostructures and metastable phase transformations in the surface layer of an AISI D2 steel treated with high current pulsed electron beam (HCPEB) were investigated. The surface structure is marked by two distinct features, i.e. the formation of sub-micrometer fine austenite γ grains (50-150 nm), and the disappearance of carbides via dissolution and crater eruption. The γ phase directly grows from the melt and is retained down to room temperature. Although the cooling rate is as high as 10 7 K/s in our case, the martensitic transformation could completely be suppressed. Such an effect is due to the increased stability of the austenite phase through grain refinement and chemistry modification

Average accelerator simulation Truebeam using phase space in IAEA format

International Nuclear Information System (INIS)

Santana, Emico Ferreira; Milian, Felix Mas; Paixao, Paulo Oliveira; Costa, Raranna Alves da; Velasco, Fermin Garcia

2015-01-01

In this paper is used a computational code of radiation transport simulation based on Monte Carlo technique, in order to model a linear accelerator of treatment by Radiotherapy. This work is the initial step of future proposals which aim to study several treatment of patient by Radiotherapy, employing computational modeling in cooperation with the institutions UESC, IPEN, UFRJ e COI. The Chosen simulation code is GATE/Geant4. The average accelerator is TrueBeam of Varian Company. The geometric modeling was based in technical manuals, and radiation sources on the phase space for photons, provided by manufacturer in the IAEA (International Atomic Energy Agency) format. The simulations were carried out in equal conditions to experimental measurements. Were studied photons beams of 6MV, with 10 per 10 cm of field, focusing on a water phantom. For validation were compared dose curves in depth, lateral profiles in different depths of the simulated results and experimental data. The final modeling of this accelerator will be used in future works involving treatments and real patients. (author)

Effect of Nb element content in U-Zr-Nb alloy on hardness, microstructure and phase formation

International Nuclear Information System (INIS)

Masrukan; M Husna Al Hasa; Jan Setiawan; Slamet Pribadi

2015-01-01

Experiments to determine the effect of Nb element in the U-Zr alloys on hardness, microstructure and phase formation has been done. The addition of Nb element would effect the hardness, microstructure and phase which formed. The U-Zr-Nb alloy was made with the variation of Nb 2%, 5% and 8% by melting in an electric arc melting furnace that equipped with water cooling and the argon atmosphere. The U-Zr-Nb alloy to be cut divided to some testing, such as hardness test, microstructure, and phase analysis. Hardness testing was done by Vickers hardness testing equipment, microstructure by an optical microscope, and diffraction pattern by XRD and phase analysis was done by GSAS. Hardness testing results showed that the addition of 2% to 5% Nb element in U-Zr alloys will increased in hardness, but the addition of Nb element over 5% the hardness was decreased. Observations the microstructure showed that the addition of 2% to 5% Nb element, grains were formed from fine into coarse. Phase analysis for diffraction pattern showed that the phase changed from αU and γU (Zr,Nb)at 2% Nb to be αU, γU (Zr,Nb) and δ1 (UZr_2) phase at 5% and 8% Nb. Phase changes was followed by changes in its compositions. The composition of αU at 2% Nb was 40% increased to 81% at 5% Nb and decreased to 3.9% at 8% Nb. The composition of γU decreased from 59,86% to 14,91% with increased Nb from 2% to 5% and further increased to 52,74% at 8% Nb. (author)

Liquid crystals with novel terminal chains as ferroelectric liquid crystal hosts

International Nuclear Information System (INIS)

Cosquer, G.Y.

2000-02-01

Changes to the molecular structure of liquid crystals can have a significant effect upon their mesomorphism and ferroelectric properties. Most of the research in liquid crystal for display applications concentrates on the design and synthesis of novel mesogenic cores to which straight terminal alkyl or alkoxy chains are attached. However, little is known about the effects upon the mesomorphism and ferroelectric properties of varying the terminal chains. The compounds prepared in this work have a common core - a 2,3-difluoroterphenyl unit with a nine-atom alkyl (nonyl) or alkoxy (octyloxy) chain at the 4-position, but with an unusual chain at the 4''-position. In some cases the terminal chain contains hetero atoms such as silicon, oxygen, chlorine and bromine or has a bulky end group. In total 46 final materials were synthesised in an attempt to understand the effect of an unusual terminal chains on mesomorphism and for some of these compounds the effect upon the switching times when added to a standard ferroelectric mixture were investigated. It was found that most compounds containing a bulky end group only displayed a smectic C phase, compounds with a halogen substituent as an end unit displayed a smectic A phase and that increasing the chain flexibility by introducing an oxygen atom in the chain reduces the melting and clearing points. The electro-optical measurements carried out on ferroelectric mixtures containing a bulky end group compound showed that shorter switching times were produced than for the ferroelectric mixture containing a straight chain compound. It is suggested that a bulky end group diminishes te extent of interlayer mixing in the chiral smectic C phase and therefore the molecules move more easily with ferroelectric switching. (author)

Determination of the positions and orientations of concentrated rod-like colloids from 3D microscopy data

International Nuclear Information System (INIS)

Besseling, T H; Hermes, M; Kuijk, A; De Nijs, B; Deng, T-S; Dijkstra, M; Imhof, A; Van Blaaderen, A

2015-01-01

Confocal microscopy in combination with real-space particle tracking has proven to be a powerful tool in scientific fields such as soft matter physics, materials science and cell biology. However, 3D tracking of anisotropic particles in concentrated phases remains not as optimized compared to algorithms for spherical particles. To address this problem, we developed a new particle-fitting algorithm that can extract the positions and orientations of fluorescent rod-like particles from three dimensional confocal microscopy data stacks. The algorithm is tailored to work even when the fluorescent signals of the particles overlap considerably and a threshold method and subsequent clusters analysis alone do not suffice. We demonstrate that our algorithm correctly identifies all five coordinates of uniaxial particles in both a concentrated disordered phase and a liquid-crystalline smectic-B phase. Apart from confocal microscopy images, we also demonstrate that the algorithm can be used to identify nanorods in 3D electron tomography reconstructions. Lastly, we determined the accuracy of the algorithm using both simulated and experimental confocal microscopy data-stacks of diffusing silica rods in a dilute suspension. This novel particle-fitting algorithm allows for the study of structure and dynamics in both dilute and dense liquid-crystalline phases (such as nematic, smectic and crystalline phases) as well as the study of the glass transition of rod-like particles in three dimensions on the single particle level. (paper)

Structural evolution in nanocrystalline Cu obtained by high-energy mechanical milling: Phases formation of copper oxides

International Nuclear Information System (INIS)

Khitouni, Mohamed; Daly, Rakia; Mhadhbi, Mohsen; Kolsi, Abdelwaheb

2009-01-01

Nanocrystalline copper with mean crystallite size of 18 nm was synthesized by using high-energy mechanical milling. The structural and morphological changes during mechanical milling especially, the formation of CuO and Cu 2 O phases were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy in transmittance mode (FTIR). Mechanical milling of Cu results in a continuous decrease in the Cu means crystallite size and an increase in microstrain. Moreover, milling of Cu, in air synthetic, results in partial oxidation to Cu 2 O and CuO. Prolonged milling supports the formation of CuO oxide. SEM results show that flattened Cu flakes were laid and welded on each other and tend to form a matrix of randomly welded thin layers of highly deformed particles.

MAX phase formation by intercalation upon annealing of TiCx/Al (0.4 ≤ x ≤ 1) bilayer thin films

International Nuclear Information System (INIS)

Abdulkadhim, Ahmed; Takahashi, Tetsuya; Music, Denis; Munnik, Frans; Schneider, Jochen M.

2011-01-01

TiC x /Al bilayer thin films were synthesized using combinatorial magnetron sputtering to study the influence of C content on the reaction products at different annealing temperatures. Based on energy-dispersive X-ray analysis calibrated by elastic recoil detection analysis data, x in TiC x was varied from 0.4 to 1.0. Film constitution was studied by X-ray diffraction before and after annealing at temperatures from 500 to 1000 deg. C. The formation of TiC x and Al in the as-deposited samples over the whole C/Ti range was identified. Upon annealing, TiC x reacts with Al to form Ti-Al-based intermetallics. At temperatures as low as 700 deg. C, the formation of MAX phases (space group P6 3 /mmc) is observed at x ≤ 0.7. Based on the comparison between the C content induced changes in the lattice spacing of TiC x and Ti 2 AlC as well as Ti 3 AlC 2 , we infer the direct formation of MAX phases by Al intercalation into TiC x for x ≤ 0.7.

Thermochemistry of methoxythiophenes: Measurement of their enthalpies of vaporization and estimation of their enthalpies of formation in the condensed phase

International Nuclear Information System (INIS)

Temprado, Manuel; Notario, Rafael; Roux, María Victoria; Verevkin, Sergey P.

2014-01-01

Highlights: • The enthalpies of vaporization of 2- and 3-methoxythiophenes have been measured by the transpiration method. • We have estimated the enthalpies of formation of methoxythiophenes in liquid phase. • The optimized geometries of methoxythiophenes have been tabulated and compared with the experimental crystal structures. - Abstract: Enthalpies of vaporization of 2- and 3-methoxythiophenes (48.32 ± 0.30 and 48.54 ± 0.22 kJ · mol −1 , respectively) have been measured by the transpiration method using nitrogen as the carrying and protecting stream. Combustion experiments leading to enthalpies of formation in the liquid phase, Δ f H 0 m (l), for both isomers failed due to rapid darkening of freshly distilled samples even under a protecting atmosphere. However, combination of experimental vaporization enthalpies with values of the gaseous enthalpies of formation, Δ f H 0 m (g), obtained by quantum-chemical calculations from our previous work Notario et al. (2012) [24] permits establishing estimated Δ f H 0 m (l) values of −(68.3 ± 4.2) and −(80.1 ± 4.2) kJ · mol −1 , for 2- and 3-methoxythiophene, respectively

MAX phase formation by intercalation upon annealing of TiC{sub x}/Al (0.4 {<=} x {<=} 1) bilayer thin films

Energy Technology Data Exchange (ETDEWEB)

Abdulkadhim, Ahmed; Takahashi, Tetsuya [Materials Chemistry, RWTH Aachen University, Kopernikusstrasse 10, 52074 Aachen (Germany); Music, Denis, E-mail: music@mch.rwth-aachen.de [Materials Chemistry, RWTH Aachen University, Kopernikusstrasse 10, 52074 Aachen (Germany); Munnik, Frans [Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrasse 400, 01328 Dresden (Germany); Schneider, Jochen M. [Materials Chemistry, RWTH Aachen University, Kopernikusstrasse 10, 52074 Aachen (Germany)

2011-09-15

TiC{sub x}/Al bilayer thin films were synthesized using combinatorial magnetron sputtering to study the influence of C content on the reaction products at different annealing temperatures. Based on energy-dispersive X-ray analysis calibrated by elastic recoil detection analysis data, x in TiC{sub x} was varied from 0.4 to 1.0. Film constitution was studied by X-ray diffraction before and after annealing at temperatures from 500 to 1000 deg. C. The formation of TiC{sub x} and Al in the as-deposited samples over the whole C/Ti range was identified. Upon annealing, TiC{sub x} reacts with Al to form Ti-Al-based intermetallics. At temperatures as low as 700 deg. C, the formation of MAX phases (space group P6{sub 3}/mmc) is observed at x {<=} 0.7. Based on the comparison between the C content induced changes in the lattice spacing of TiC{sub x} and Ti{sub 2}AlC as well as Ti{sub 3}AlC{sub 2}, we infer the direct formation of MAX phases by Al intercalation into TiC{sub x} for x {<=} 0.7.

Unveiling the Role of CNTs on the Phase Formation of 1D Ferroelectrics

KAUST Repository

Mahajan, Amit

2015-05-21

Carbon nanotubes (CNTs) have the potential to act as templates or bottom electrodes for three dimension (3D) capacitor arrays, which utilise one dimension (1D) ferroelectric nanostructures to increase memory size and density. However, growing a ferroelectric on the surface of CNTs is non-trivial. Here, we demonstrate that multi-walled (MW) CNTs decrease the time and temperature for formation of lead zirconium titanate Pb(Zr1-xTix)O3 (PZT) by ~100 ºC commensurate with a decrease in activation energy from 68±15 kJ/mol to 27±2 kJ/mol. As a consequence, monophasic PZT was obtained at 575 ºC for MWCNTs/PZT whereas for pure PZT traces of pyrochlore were still present at 650 ºC, where PZT phase formed due to homogeneous nucleation. The piezoelectric nature of MWCNT/PZT synthesised at 500 ºC for 1 h was proved. Although further work is required to prove the concept of 3D capacitor arrays, our result suggests that it is feasible to utilise MWCNTs as templates/electrodes for the formation of 1D PZT nano ferroelectrics.

Synthesis and mesomorphic properties of new heterocyclic liquid crystals with Central Ester–Chalcone linkages

Directory of Open Access Journals (Sweden)

Yong-Wei Cheryl Lim

2017-01-01

Full Text Available A series of new calamitic liquid crystals, 4-[3-(pyridin-4-ylprop-2-enoyl]phenyl 4-alkyloxybenzoates, comprising a pyridyl core, ester–chalcone central linkage and terminal alkyloxy chain were synthesized and characterized. This series consists of four members that differ by the length of the alkyloxy chain (CnH2n+1O, where n = 10, 12, 14, 16. The structures of the title compounds were elucidated using spectroscopic and spectrometric techniques, such as FT-IR, NMR (1H and 13C and EI-MS. The mesomorphic properties were studied using differential scanning calorimetry and optical polarizing microscopy. The decyloxy-containing compound was found to be non-mesogenic, whilst the compounds containing n-dodecyloxy to n-hexadecyloxy chains exhibited an enantiotropic smectic A phase with a fan-shaped texture. From the structure–property relationship study, it was proposed that the number of carbons in the alkyloxy chain must be at least 12 (n ≥ 12 to generate the smectic phase in the corresponding substituted ArCOOArCOCHCHC5H4N compounds.

Formation, structure, and evolution of boiling nucleus and interfacial tension between bulk liquid phase and nucleus

Science.gov (United States)

Wang, Xiao-Dong; Peng, Xiao-Feng; Tian, Yong; Wang, Bu-Xuan

2005-05-01

In this paper, the concept of the molecular free path is introduced to derive a criterion distinguishing active molecules from inactive molecules in liquid phase. A concept of the critical aggregation concentration (CAC) of active molecules is proposed to describe the physical configuration before the formation of a nucleus during vapor-liquid phase transition. All active molecules exist as monomers when the concentration of active molecules is lower than CAC, while the active molecules will generate aggregation once the concentration of the active molecules reaches CAC. However, these aggregates with aggregation number, N, smaller than five can steadily exist in bulk phase. The other excess active molecules can only produce infinite aggregation and form a critical nucleus of vapor-liquid phase transition. Without any outer perturbation the state point of CAC corresponds to the critical superheated or supercooled state. Meanwhile, a model of two-region structure of a nucleus is proposed to describe nucleus evolution. The interfacial tension between bulk liquid phase and nucleus is dependent of the density gradient in the transition region and varies with the structure change of the transition region. With the interfacial tension calculated using this model, the predicted nucleation rate is very close to the experimental measurement. Furthermore, this model and associated analysis provides solid theoretical evidences to clarify the definition of nucleation rate and understand nucleation phenomenon with the insight into the physical nature.

Formation of super disperse phase and its influence on equilibrium and thermodynamics of thermal dehydration

Energy Technology Data Exchange (ETDEWEB)

Polyachenok, O.G. [Department of Chemistry, Mogilev State University of Foodstuffs, 212027 (Belarus)], E-mail: polyachenok@mogilev.by; Dudkina, E.N.; Branovitskaya, N.V. [Department of Chemistry, Mogilev State University of Foodstuffs, 212027 (Belarus); Polyachenok, L.D. [Department of Chemistry, Mogilev State University of A.A. Kuleshov, 212022 (Belarus)

2008-01-30

New data on the dehydration and rehydration processes of calcium, manganese and copper dichlorides are presented that reveal surprising, in a certain sense, behaviour difficult to be explained for the last two chlorides in terms of the usual conception of thermodynamic equilibrium. A substantial role of a super disperse phase at studying the equilibrium of the thermal decomposition of a hydrate is postulated to explain the experimental results for manganese and copper dichlorides. It is shown that the formation of such a phase of the hydrate is able to change appreciably the experimental results, causing the increase of water vapour pressure and the decrease of the derived enthalpy of a reaction. The results obtained allow to understand the reasons for considerable differences of some literature data. They enable to receive more precise and reliable data for thermal dehydration and probably for some other decomposition processes.

Leading Formative Assessment Change: A 3-Phase Approach

Science.gov (United States)

Northwest Evaluation Association, 2016

2016-01-01

If you are seeking greater student engagement and growth, you need to integrate high-impact formative assessment practices into daily instruction. Read the final article in our five-part series to find advice aimed at leaders determined to bring classroom formative assessment practices district wide. Learn: (1) what you MUST consider when…

Analytical model of chemical phase and formation of DSB in chromosomes by ionizing radiation.

Science.gov (United States)

Barilla, Jiří; Lokajíček, Miloš; Pisaková, Hana; Simr, Pavel

2013-03-01

Mathematical analytical model of the processes running in individual radical clusters during the chemical phase (under the presence of radiomodifiers) proposed by us earlier has been further developed and improved. It has been applied to the data presented by Blok and Loman characterizing the oxygen effect in SSB and DSB formation (in water solution and at low-LET radiation) also in the region of very small oxygen concentrations, which cannot be studied with the help of experiments done with living cells. In this new analysis the values of all reaction rates and diffusion parameters known from literature have been made use of. The great increase of SSB and DSB at zero oxygen concentration may follow from the fact that at small oxygen concentrations the oxygen absorbs other radicals while at higher concentrations the formation of oxygen radicals prevails. It explains the double oxygen effect found already earlier by Ewing. The model may be easily extended to include also the effects of other radiomodifiers present in medium during irradiation.

Analytical model of chemical phase and formation of DSB in chromosomes by ionizing radiation

International Nuclear Information System (INIS)

Barilla, Jiři; Simr, Pavel; Lokajíček, Miloš; Pisaková, Hana