Why does uranium oxide phosphate contract on heating?

(U₂O)(PO₄)₂ is related to ultra-low expansion β-(Zr₂O)(PO₄)₂ ceramics, but shows a continuous thermal contraction. High-temperature neutron diffraction has allowed to follow accurately the thermal variations of its cell edges and to give a structural explanation to the phenomenon: like in β-(Zr₂O)(PO₄)₂, the dilatometric anomaly arises simultaneously from a contractive push-pull effect due to Coulombic repulsions and from a libration of the PO₄ and UO₇ polyhedra, but in the present case, the second mechanism predominates. The size of the tetravalent cation appears as a key parameter in monitoring the thermal expansion of ceramics of this family.     

Extraction of uranium into a third phase of thorium nitrate—tributyl phosphate

Extraction of 0.05–0.25M uranyl nitrate into 30% tributyl phosphate (TBP) in dodecane from nitric acid solutions of thorium nitrate at equilibrium with its salt has been studied. Under investigated conditions a third (second organic) phase is formed. As the heavy organic phase extracts uranium, the calculated ratio of TBP to thorium and uranium sum decreases from 2.7 to less than 7. Electronic spectra show that in heavy organic phase approximately 80% of uranium is found as trinitrate complex, while in the light organic phase this complex is not detected. The measurements of dielectric constant () of the heavy phase reveal a frequency dependence of . The data obtained point to the existence of an ordered structure in the heavy organic phase.     

The synthesis and crystal structure of a hydrated magnesium phosphate Mg3(PO4)2·4H2O

The synthesis and crystal structure of a novel hydrated magnesium phosphate is described. The crystal structure was solved from powder X-ray diffraction data. Mg₃(PO₄)₂·4H₂O crystallizes in the orthorhombic space group Cmc2₁ (No. 36) with a=8.41087(9) Å, b=17.3850(2) Å, c=12.8034(1) Å, V=1872.15(4) ų and Z=8. The structure consists of sheets stacked along [010], which are linked by edge sharing octahedral Mg₂O₆(H₂O)₄ dimers. Within the sheets there are infinite edge-sharing chains of Mg octahedra along [100]. The compound has been further characterized by ³¹P MAS NMR spectroscopy and thermogravimetric analysis. The crystal structure of two dehydrated variants existing around 200 (Mg₃(PO₄)₂·2.5H₂O) and 275 °C (Mg₃(PO₄)₂·2H₂O) remain unknown.     

Solid solutions of double phosphate hexahydrates in the MgNH4PO4 · 6H2O-Ni2+-H2O system and their dehydration products

Substitutional solid solutions Mg²⁺ ? Ni²⁺ of crystal hydrates Mg_{(1 ? x)}Ni _x NH₄PO₄ · 6H₂O and Mg_{(1 ? x)}Ni _x NH₄PO₄ · H₂O (where 0 < x ≤ 0.65), which have struvite structure and dittmarite structure, respectively, have been studied. Ion exchange Mg²⁺ ? Ni²⁺ influences the condition of M²⁺-H₂O (M²⁺ = Mg²⁺, Ni²⁺) coordination bonds and hydrogen bonds involving coordinated H₂O molecules, as probed by X-ray powder diffraction, thermal analysis, and FTIR spectroscopy. The coordination of water molecules to metal ions in those crystal hydrates is treated to be a factor that determines the propensity of the resulting crystal structures to polymorphism.     

Assay of uranium in crude diuranate cakes and MgF2 slag produced at the natural uranium conversion plants by γ-ray spectrometry

A transmission-corrected -ray counting method has been employed for the assay of uranium in crude Na₂U₂O₇ cakes produced at the Uranium Conversion Facilities. A 3×3 NaI(TI) detector was used in conjunction with a 400-channel analyzer. The observed count rate of the 1 MeV -ray emitted by the²³⁸U in the sample was corrected for sample self-attenuation, measured with a⁶⁵Zn (-energy 1115 keV) transmission source. A calibration factor determined by measuring a standard of known amount of radioactive material in the same form and geometry as the unknown sample was used to convert the transmission corrected count rate to the amount of uranium in the weighted sample. Another -spectrometric method is described for the assay of the U-content in the MgF₂ slag produced during the magnesiothermic reduction of UF₄ to U-metal ingots at the natural U-conversion plant.     

Quantitative extraction of uranium(VI) in aqueous solutions with n-alkylamine intercalates of γ-titanium phosphate

The intercalation compounds Ti(C₃H₇NH₂)(HPO₄)₂·H₂O (18.4 Å) (-TiP/n-Pr) and Ti(C₄H₉NH₂)(HPO₄)₂·H₂O (20.5 Å) (-TiP/n-Bu) have been prepared using -titanium phosphate, Ti(HPO₄)₂·2H₂O (11.6 Å), as precursor. The retention of UO ₂ ²⁺ , in aqueous solutions by -TiP is very low being only a superficial adsorption phenomenon. When the intercalated materials are used, the retention is quantitative until 95% of the cation exchange capacity in the -TiP/n-Pr case (c.e.c.=6.30 mequiv./g), and over 80% for the -TiP/n-Bu compound (c.e.c.=6.04 mequiv./g).     

The synthesis and applications of α-zirconium phosphate

The synthesis of α-ZrP with a range of crystallinity is of high importance due to the different requirements in various applications.Nanosized crystalline α-ZrP is typically obtained by refluxing amorphous ZrP in concentrated H3PO4 solutions.Microcrystalline α-ZrP are obtained by direct precipitation in the presence of either HF or oxalic acid which are used as complexing agents for zirconium.These larger crystals are useful as ion-exchangers in column-type applications as the back pressure can be significantly reduced.A novel minimalistic synthesis that is green,simple and fast is highlighted in this review.Both nano-sized and micro-sized α-ZrP can be prepared via this protocol to meet many potential applications.Applications of α-ZrP in ion-exchange,catalysis,lubricants,intercalation hosts,polymer fillers and fire retardants are discussed.     

Study of effect of phosphate and uranium ions on the thermal properties of surfactant-modified natural red clay using TG–FTIR–MS techniques

Products of sorption of uranyl ions on HDTMA-red clay in the presence of phosphates were characterized by thermal analysis. It was established on the basis of DTG curves of the sorption products and FTIR spectra of the gaseous phase of sorption products decomposition that the thermal stability of the mineral increased when P(V) ions were sorbed along with U(VI) ions, i.e., the temperature of defragmentation/oxidation of surfactant increased when going from U(VI)–HDTMA-clay to U(VI)–P(V)–HDTMA-clay to P(V)–HDTMA-clay. The DSC curves of the sorption products showed that defragmentation/oxidation was an exothermic process and dehydration and dehydroxylation had an endothermic character. The investigated sorption system has practical importance, since an evident increase in U(VI) sorption over the entire pH range is observed when going from U(VI)–HDTMA-clay to U(VI)–P(V)–HDTMA-clay.

     

Direct crystallization of silicate–phosphate glasses of NaCaPO4–SiO2 system

The subject of the study was silicate–phosphate glasses of NaCaPO₄–SiO₂ system which are precursors of glass–crystalline materials. Glass–crystalline materials of NaCaPO₄–SiO₂ system obtained via crystallization of glasses belong to a group of the so-called bioactive materials. In order to obtain glass–crystalline materials with pre-established parameters, it is necessary to conduct crystallization of glasses at specific conditions. In order to design direct crystallization process properly, it is necessary to know the structure and microstructure of the glassy precursor. Microscopic investigation showed that liquation takes place in all the studied glasses. Based on DSC examinations, it has been found out that crystallization of the glasses of NaCaPO₄–SiO₂ system is a multistep process. The presence of several clearly separated exothermic peaks in DSC curves of investigated glasses makes it possible to crystallize only the separated phase with the matrix remaining amorphous or vice versa. Conducted detailed X-ray and spectroscopic studies of the materials obtained by heating in a gradient furnace (in the temperature specified on the basis of DSC) showed that separated phase and matrix crystallizes separately. Therefore, bioactive glass–crystalline materials can be obtained due to the existence of the phase separation phenomenon and pre-established sizes of the crystalline phase.     

Extraction of moderate oxidation state technetium species between 30 % tri-n-butyl phosphate and H2SO4/HNO3

The extraction of technetium species at oxidation state lower than +7 has been examined in sulfuric and sulfuric/nitric acid solutions using UV–Vis spectroscopy and optically transparent thin layer cell (RVC-OTTLE). Soluble Tc(III), TcO²⁺ and [Tc₂O₂]³⁺ species with absorption bands at 420–450, 400, and 502 nm, respectively, were detected as products of pertechnetates electroreduction. The distribution ratios of ⁹⁹Tc with lower than +VII oxidation state ionic species between 4 M H₂SO₄ and 30 % TBP/kerosene were found and are significantly lower than for TcO₄ ^? in the same solution.     

Synthesis and phase formation in M 0.5(1+x) 2+ FexTi2−x (PO4)3 phosphate series

New complex phosphates of titanium, iron, and alkaline-earth metals have been synthesized. X-ray powder diffraction, differential thermal analysis (DTA), and IR spectroscopy are used to study phase formation in the series of M_0.5(1+x)Fe_xTi_2?x (PO₄)₃ (M = Mg, Ca, Sr, Ba) phosphates. Individual compounds and solid solutions are found to crystallize in the NaZr₂(PO₄)₃ and K₂Mg₂(SO₄)₃ structure types. Their crystal parameters are calculated. CaFeTi(PO₄)₃ is studied using Mössbauer spectroscopy. Its structure is refined by the Rietveld method: space group $R\bar 3$ c, Z = 6, a = 8.5172(1), Å, c = 21.7739(4) Å, V = 1367.91(4) ų.     

Intercalation of pyridine and quinoline intoα-zirconium phosphate

The uptake of pyridine and quinoline into-zirconium phosphate has been investigated by the batch method. The effect of solvent on the reactions was also studied. Pyridine was taken up from ethanol, chloroform, carbon tetrachloride, ethanol-water, and acetone-water solutions, but not from pure acetone at 25°C. Water accelerated the uptake of pyridine. These facts indicate that a water molecule was involved in the uptake reaction of pyridine.Quinoline was taken up easily in an ethanol-water solution at 25°C, and in an ethanol solution at the boiling point. Two reactions — ion exchange and intercalation — occur on taking up the quinoline. An IR spectrum of the quinoline form is reported.     

Simultaneous determination of uranium and thorium using 4-(2′-thiazolylazo)resacetophenone oxime as analytical reagent. A derivative spectrophotometric method

A first derivative spectrophotometric method has been developed for the simultaneous determination of uranium(VI) and thorium(IV) when present in the same solution using 4-(2-tiazolylazo)resacetophenone oxime (TARPO) as analytical reagent without prior separation of any of the metals or using masking agents, etc. The method allows the determination of uranium and thorium in their mixtures in the range of 0–10 ppm each. Many common anions and cations even in large quantities do not interfere.     

Electrochemical separation of uranium and cerium in molten LiCl–KCl

The electrochemical separation of uranium from cerium in LiCl–KCl eutectic and the electrochemical behavior of Ce(III) were studied. According to the cyclic voltammogram of Ce(III) and the former result of U(III), electrodeposition potential was determined at ?1.65 V (vs Ag/AgCl). The uranium metal was successfully deposited and separated from cerium. The morphology of deposit and cross section of electrode were investigated by SEM, firstly uranium deposit alloys with stainless steel and forms a thin transition layer, and secondly the uranium metal layer grows from the transition layer. The separation factors of uranium/cerium on different recovery ratios were determined through a series of steps. It was found that the content of cerium in the deposit and separation factors declined with increasing the initial concentration of U³⁺ in molten salts; the separation factors remained stable at around 20 in different uranium recovery ratios.     

The [CoN4(OH)(OH2)]2+ (N4 = trpn,cyclen and tren) promoted hydrolysis of the phosphotriester 2,4–dinitrophenyl diethyl phosphate

The [CoL(OH2)2]3+ (L=trpn, cyclen andtren)promoted hydrolysis of the phosphotriester 2,4–dinitrophenyl diethyl phosphate to give diethyl phosphate and 2,4–dinitrophenolate has been studied in detail over the pH range 3–7.5. The pK values of the various complexes have been determined at 25°C and I=0.1moldm–3 by potentiometric titration. The pH-rate profiles for the reactions are consistent with the hydroxoaqua complex [CoL(OH)(OH2)]2+ being the active species in the hydrolysis. No evidence for saturation kinetics was obtained and values of kcat determined at pH 7 and 25°C (I=0.1moldm–3) are 4.24×10–3dm3mol–1 s–1 (tren)<3.05×10–2dm3mol–1 s–1 (cyclen)<7.5 × 10–1dm3mol–1s–1 (trpn). Studies involving the more reactive phosphonate ester 2,4–dinitrophenyl ethyl methylphosphonate suggest that the rate-determining step in the reaction is the decomposition of the ternary complex between the cobalt(III) complex and the phosphotriester. The rate enhancement using 0.01mol dm–3 Co(trpn)3+ is some 4.6×104 fold at pH7 and 25°C.     

Liquid–liquid equilibria of aqueous two-phase systems containing polyethylene glycol and ammonium dihydrogen phosphate or diammonium hydrogen phosphate. Experiment and correlation

Phase diagrams and liquid–liquid equilibrium (LLE) data of the aqueous systems polyethylene glycol 6000 (PEG₆₀₀₀)–ammonium dihydrogen phosphate and aqueous PEG₆₀₀₀–diammonium hydrogen phosphate have been determined experimentally at 298.15, 308.15 and 318.15 K. Furthermore, the osmotic virial equation was used to correlate the phase behavior of these systems. Good agreement was obtained with the experimental data. Finally, the effect of temperature and the type of salt on the LLE are discussed.     

Direct and stepwise intercalation of alkylalcohols intoα-zirconium phosphate

Intercalation of alkylalcohols into -zirconium phosphate was investigated at 25°C and/or under reflux.n-Alcohols having two to five carbons and 2-propanol were taken up at 25°C. These alcohols, andn-hexanol and heptanol, also intercalated under reflux.n-Alcohols having eight to eighteen carbon atoms intercalated when a stepwise method was employed. 2-Butanol and tertiary amylalcohols intercalated under reflux using a butanol intercalate as a starting material. Ethanol-to-butanol intercalates were unstable at room temperature, losing alcohols and changing to -zirconium phosphate. The particle size of the -zirconium phosphate did not affect the intercalation of alcohols.     

Insertion, isomerization, and cascade reactivity of the tethered silylalkyl uranium metallocene (η(5)-C5Me4SiMe2CH2-κC)2U

Investigation of the insertion reactivity of the tethered silylalkyl complex (η(5)-C(5)Me(4)SiMe(2)CH(2)-κC)(2)U (1) has led to a series of new reactions for U-C bonds. Elemental sulfur reacts with 1 by inserting two sulfur atoms into each of the U-C bonds to form the bis(tethered alkyl disulfide) complex (η(5):η(2)-C(5)Me(4)SiMe(2)CH(2)S(2))(2)U (2). The bulky substrate N,N'-diisopropylcarbodiimide, (i)PrN═C═N(i)Pr, inserts into only one of the U-C bonds of 1 to produce the mixed-tether complex (η(5)-C(5)Me(4)SiMe(2)CH(2)-κC)U[η(5)-C(5)Me(4)SiMe(2)CH(2)C((i)PrN)(2)-κ(2)N,N'] (3). Carbon monoxide did not exclusively undergo a simple insertion into the U-C bond of 3 but instead formed {μ-[η(5)-C(5)Me(4)SiMe(2)CH(2)C(═N(i)Pr)O-κ(2)O,N]U[OC(C(5)Me(4)SiMe(2)CH(2))CN((i)Pr)-κ(2)O,N](2) (4) in a cascade of reactions that formally includes U-C bond cleavage, C-N bond cleavage of the amidinate ligand, alkyl or silyl migration, U-O, C-C, and C-N bond formations, and CO insertion. The reaction of 3 with isoelectronic tert-butyl isocyanide led to insertion of the substrate into the U-C bond, but with a rearrangement of the amidinate ligand binding mode from κ(2) to κ(1) to form [η(5):η(2)-C(5)Me(4)SiMe(2)CH(2)C(═N(t)Bu)]U[η(5)-C(5)Me(4)SiMe(2)CH(2)C(═N(i)Pr)N((i)Pr)-κN] (5). The product of double insertion of (t)BuN≡C into the U-C bonds of 1, namely [η(5):η(2)-C(5)Me(4)SiMe(2)CH(2)C(═N(t)Bu)](2)U (6), was found to undergo an unusual thermal rearrangement that formally involves C-H bond activation, C-C bond cleavage, and C-C bond coupling to form the first formimidoyl actinide complex, [η(5):η(5):η(3)-(t)BuNC(CH(2)SiMe(2)C(5)Me(4))(CHSiMe(2)C(5)Me(4))]U(η(2)-HC═N(t)Bu) (7).