Untitled

Черноруков, Н. Г.; Knyazev, A. V.; Kortikova, O. V.; Chuprov, L. A.

doi:10.1023/a:1022305131818

Cited by 3 publications

(6 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The first type includes the water molecules bound to an alkali metal ion by ion3dipole interactions. Water molecules of the second type, as we showed in [9], are strongly polarized to the H...OH state owing to the coordination with a boron atom. As a result, the boron coordination changes from trigonal planar (BO 3 ) in the anhydrous compounds to tetrahedral (BO 3 OH) in the crystal hydrates, forming a covalent bond with the oxygen atom of the water molecule.…”

Section: Thermodynamic Functions Of Dehydrationmentioning

confidence: 55%

Thermodynamics of Alkali Metal Uranoborates

et al. 2005

Self Cite

View full text Add to dashboard Cite

The standard enthalpies of formation of crystalline A I BUO 5 (A I = Li, Na, K, Rb, Cs) at 298.15 K were determined by reaction calorimetry. For these compounds, the heat capacities in the range 10 3300 K were determined by adiabatic vacuum calorimetry, and the thermodynamic functions were calculated. The standard entropies and Gibbs energies of formation at 298.15 K and the standard thermodynamic functions of solution of these compounds were calculated.Here we report on a thermodynamic study of the compounds A I BUO 5 (A I = Li, Na, K, Rb, or Cs).The compounds A I BUO 5 were prepared by a solidphase reaction between UO 3 , B 2 O 3 , and alkali metal carbonate or nitrate ( Table 1). The syntheses were performed in a platinum crucible, which was charged with the reactants (for the atomic ratio, see Table 1). The charge was calcined at 75031000oC for 8 h. Excess boron and alkali metal were washed out with boiling distilled water in the form of water-soluble borates, and the precipitate was dried in air for 24 h. Hydration of anhydrous alkali metal uranoborates to monohydrates in the case of Na, K, Rb, and Cs and to sesquihydrate in the case of Li was performed under hydrothermal conditions at 200oC in a hermetically sealed 50% filled pressure vessel for 15 h.The phase purity of the compounds was checked by X-ray diffraction (DRON-3.0 diffractometer, CoK a radiation). The elemental composition was determined photometrically using standard procedures. Boron(III) was determined by the reaction with quinalizarin in concentrated sulfuric acid (l max = 625 nm) [1]. The U(VI) content was determined from the absorption of its complex with arsenazo III (l max = 650 nm, pH 3) [2]. The alkali metal content w(A 2 O) (%) was determined from the difference: w(A 2 O) = 2[100% 3 w(UO 3 )] 3 w(B 2 O 3 ). The measurements were performed with a KFK-3 photocolorimeter and a pH-140 pH meter. According to elemental analysis, the compounds had the formula A I BUO 5 .According to the results of X-ray phase analysis, alkali metal uranoborates have a layered structure. As reported by Gasperin [3,4] for the lithium and sodium derivatives, the [BUO 5 ] n 2i layers are formed by pentagonal bipyramids UO 7 linked into infinite chains through common edges and by BO 3 triangles linking the chains into two-dimensional layers. The axial bonds in the uranium polyhedron are shortened and directed toward the interlayer space, in which the alkali metal ions are located. THERMOCHEMISTRY OF ALKALI METAL URANOBORATESThe experimental thermochemical data were obtained with an upgraded calorimeter of S.M. Skuratov's design [5]. All the experiments were performed in a thin-walled Teflon ampule consisting of two vessels: internal (V = 5 cm 3 ) into which weighed portions of the samples were placed and external (V = 40 cm 3 filled with an HF solution. The reactants were mixed by breaking the bottom of the internal vessel. The temperature in the experiments were measured with a platinum resistivity thermometer and an Shch-516 digital voltmeter. The adiabatic con...

show abstract

Section: Thermodynamic Functions Of Dehydrationmentioning

confidence: 55%

Thermodynamics of Alkali Metal Uranoborates

et al. 2005

Self Cite

View full text Add to dashboard Cite

show abstract

“…Next, we determined the solubility products of the studied compounds according to equation 3. The examples of the values are shown in Table 3.…”

Section: Resultsmentioning

confidence: 99%

“…The compounds studied were synthesized by methods described elsewhere [1][2][3]. The phases of individual compounds obtained before and after contact with aqueous solutions were established by X-ray analysis using DRON-3 diffractometer.…”

Section: Methodsmentioning

confidence: 99%

“…The subjects of our studies are compounds of the general formula M k (AnUO 2 ) k ⋅nH 2 O, where An are VO 4 3-, PO 4 3-, AsO 4 3-, HSiO 4 3-, BO 3 3-anions, M k are alkaline, alkaline earth and 3d-transition elements. Great majority of the substances were synthesized in our laboratory for the first time [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

“…Great majority of the substances were synthesized in our laboratory for the first time [1][2][3]. They have layered structures and can be characterized as high thermally and chemically resistant materials.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Physico-chemical study of heterogeneous equilibria in salt-aqueous systems of inorganic compounds of uranium(VI)

Черноруков

Нипрук

2006

Czech J Phys

Self Cite

View full text Add to dashboard Cite

The report presents results obtained in systematic investigation of the physico-chemical state of heterogeneous equilibrium systems of "aqueous solution -precipitate" in the case of the crystalline mineral-like uranium (VI) compounds with the general formula M k (AnUO 2 ) k ⋅nH 2 O, where positions denoted as "An" are occupied by VO 4 3-, PO 4 3-, AsO 4 3-, HSiO 4 3-, or BO 3 3-anions, and M k are alkaline, alkaline earth, and the 3d-transition elements. Chemical stabilities and solubilities of uraniumvanadates, uraniumphosphates, uraniumarsenates, uraniumsilicates, and uraniumborates have been experimentally determined. Detailed quantitative description of the physico-chemical processes and reactions involved in heterogeneous equilibrium in aqueous solutions of the salts by means of equilibrium thermodynamics is presented. The description gives us the possibility to predict the behaviour of the uranium compounds under different conditions and to calculate Gibbs functions of the formation of the compounds studied.

show abstract

Physico-chemical study of heterogeneous equilibria in salt-aqueous systems of inorganic compounds of uranium(VI)

Черноруков

Нипрук

2006

Czech J Phys

Self Cite

View full text Add to dashboard Cite

The report presents results obtained in systematic investigation of the physico-chemical state of heterogeneous equilibrium systems of "aqueous solution -precipitate" in the case of the crystalline mineral-like uranium (VI) compounds with the general formula M k (AnUO 2 ) k ⋅nH 2 O, where positions denoted as "An" are occupied by VO 4 3-, PO 4 3-, AsO 4 3-, HSiO 4 3-, or BO 3 3anions, and M k are alkaline, alkaline earth, and the 3d-transition elements. Chemical stabilities and solubilities of uraniumvanadates, uraniumphosphates, uraniumarsenates, uraniumsilicates, and uraniumborates have been experimentally determined. Detailed quantitative description of the physico-chemical processes and reactions involved in heterogeneous equilibrium in aqueous solutions of the salts by means of equilibrium thermodynamics is presented. The description gives us the possibility to predict the behaviour of the uranium compounds under different conditions and to calculate Gibbs functions of the formation of the compounds studied.

show abstract

Untitled

Cited by 3 publications

References 1 publication

Thermodynamics of Alkali Metal Uranoborates

Thermodynamics of Alkali Metal Uranoborates

Physico-chemical study of heterogeneous equilibria in salt-aqueous systems of inorganic compounds of uranium(VI)

Physico-chemical study of heterogeneous equilibria in salt-aqueous systems of inorganic compounds of uranium(VI)

Contact Info

Product

Resources

About