Sidorenko, G.A.; Zhil'tsova, I.G.; Moroz, I.Kh.
Uranyl phosphate is easily synthesized by adding a 0.36M solution of phosphorous acid of 60degC to a 0.5M solution of uranyle nitrate. The precipitate at pH 0.87-1.10 contains two morphologically different phases - one in the form of quadratic disks (''heavy'' phase) - the other in form of needle-crystals of size up to 0.1 mm (''light'' phase). X-ray analysis determined the ''heavy'' phase as meta-autunite, - the ''light'' phase as uranyl phosphate of composition (UO 2 ):(PO 4 )=3:2. Uranyl phosphate is straw-coloured, its specific weight is 3.45; the luminescence is similar to that of autunite; the refraction index is Nsub(g)=Nsub(m)=1.581; pr=1.570 with a slight pleochroism from light yellow to white; the interference colours are week; the extinction is direct. The chemical analysis of two independently obtained samples of uranyl phosphate was carried out. It led to the crystallo-chemical formula (UO 2 ) 3 (PO 4 ) 2 x 4,8H 2 O. The symmetry and the parameters of the elementary cell of the phosphate are determined: it is a rhombic cell with a=13.11+-0.01A, b=6.98+-0.01A, c=16.91+-0.03A and Z=3. The x-ray density is rho=3.53. The DTA curve shows a higher temperature at the beginning of the dehydration: nearly 120deg compared with the first endoeffect of N-metaautunite which occurs at 50deg. The i.r. spectrum gives a lower symmetry than for N-meta-autunite. The water in the uranyl phosphate is strongly orientated and coupled to the structure. Dumontite which has a ratio (UO 2 ):(PO 4 )=3:2 is found to have a analogous chemical composition to the uranyl phosphate. The parameters b and c are similar in both compounds. The formation of phosphate and the transformation into N-meta-autunite can take place even under natural coditions. The phosphoric analogue of troegerite has the same (UO 2 )/(PO 4 ) ratio but differs in the water content. The structural relations of the two compounds are still unknown