M. V. Sukhanov

Sintering mechanism for high-density NZP ceramics

We have studied the shrinkage kinetics and mechanism of NaZr2(PO4)3 containing inorganic additives. The sintering of NaZr2(PO4)3 containing ZnO microadditives is shown to follow a liquid-phase mechanism. Effective sintering aids include oxides of metals in the oxidation states 2+ and 3+ that are capable of reacting with sodium zirconium phosphate to form solid solutions. Ceramics having a relative density of 96–99% and isostructural with NaZr2(PO4)3 can be prepared by adding 0.75–2.0 wt % ZnO as a sintering aid capable of influencing the structure of grain boundaries in ceramic materials, pressing green bodies at 200–300 MPa, and sintering them at 1000–1100°C for 7–15 h.

Synthesis, structure, and thermal expansion of sodium zirconium arsenate phosphates

Sodium zirconium arsenate phosphates NaZr2(AsO4)x(PO4)3−x were synthesized by precipitation technique and studied by X-ray diffraction and IR spectroscopy. In the series of NaZr2(AsO4)x(PO4)3−x, continuous substitution solid solutions are formed (0 ≤ x ≤ 3) with the mineral kosnarite structure. The crystal structure of NaZr2(AsO4)1.5(PO4)1.5 was refined by full-profile analysis: space group R

Standard thermodynamic functions of CaNi0.5Zr1.5(PO4)3 crystalline phosphate in the range of T → 0 to 640 K

\bar 3

Development and synthesis of bulk and membrane catalysts based on framework phosphates and molybdates

c, a = 8.9600(4)Å, c = 22.9770(9) Å, V = 1597.5(1) Å3, Rwp = 4.55. The thermal expansion of the arsenate-phosphate NaZr2(AsO4)1.5(PO4)1.5 and the arsenate NaZr2(AsO4)3 was studied by thermal X-ray diffraction in the temperature range of 20–800°C. The average linear thermal expansion coefficients (αav = 2.45 × 10−6 and 3.91 × 10−6 K−1, respectively) indicate that these salts are medium expansion compounds.

Catalytic properties of zirconium phosphate and double phosphates of zirconium and alkali metals with a NaZr2(PO4)3 structure

The temperature dependence of the heat capacity Cp○ = f(T) of CaNi0.5Zr1.5(PO4)3 crystalline phosphate is studied by precision adiabatic vacuum and differential scanning calorimetry over the temperature range of 7–640 K. Its standard thermodynamic functions Cp○ (T), H○(T)-H○(0), S○(T), and G○(T)-H○(0) for the region T → 0 to 640 K and the standard entropy of formation at T = 298.15 K are calculated from the obtained experimental data. Using data on the low-temperature (30–50 K) heat capacity, the D fractal dimension of phosphate is determined and conclusions about the character of the topology of its structure have been made. The final results are compared to data from thermodynamic investigations of the structurally related crystalline phosphates Zr3(PO4)4, Ni0.5Zr2(PO4)3, and Ca0.5Zr2(PO4)3.

Synthesis and properties of LiZr2(AsO4)3 and LiZr2(AsO4) x (PO4)3 − x

The scientific principles were formulated that underlie an integrated approach to development and synthesis of bulk and membrane catalysts for methanol transformation to dimethyl ether and hydrogen which are environmentally friendly fuels. The results were summarized for studies into relationships in formation of phosphates MZr2(PO4)3 (M = Na, K, Rb, Cs, Mg0.5, Ca0.5, Sr0.5, Ba0.5, Zr0.25), Cu0.5(1+y)FeyZr2−y(Po4)3, molybdate phosphates Na1−yZr2(Moo4)y(Po4)3−y, and molybdate Ni0.3Cr0.4Fe1.4(Moo4)3 with the desired structure and properties controllable by variation of their chemical composition and synthesis parameters. The surface characteristics and catalytic properties of the resulting systems and the yields of the target product formed from methanol transformations in inert and oxidizing atmospheres were analyzed in relation to the catalyst synthesis condition.

The heat capacity and standard thermodynamic functions of Ni0.5Zr2(PO4)3 phosphate over the temperature range from T → 0 to 664 K

Zirconium orthophosphate Zr3(PO4)4 and double phosphates of zirconium and alkali metals AZr2(PO4)3 (A = Na, K, Rb, Cs) with a NaZr2(PO4)3 structure were synthesized and characterized by X-ray diffraction and electron microprobe analyses and capillary condensation of nitrogen. The catalytic properties of the phosphates in the dehydration of methanol were studied.

Crystal structures of double cesium zirconium and barium zirconium orthophosphates

The LiZr2(AsO4)3 arsenate and LiZr2(AsO4)x(PO4)3 − x solid solutions have been prepared through precipitation followed by heat treatment, and characterized by X-ray diffraction, X-ray structure analysis, IR spectroscopy, and impedance spectroscopy. We have established conditions for the crystallization of the arsenate and a continuous series of arsenate phosphate solid solutions (0 ≤ x ≤ 3), which have been obtained as two polymorphs: monoclinic and hexagonal. Using the Rietveld method, we have refined the crystal structures of the polymorphs of LiZr2(AsO4)3 (sp. gr. P21/n, a = 9.1064(2), b = 9.1906(2), c = 12.7269(3) Å, β = 90.844(2)°, V =1065.03(5) Å3, Z = 4; sp. gr. R

The heat capacity and thermodynamic functions of Ca0.5Zr2(PO4)3 crystalline phosphate from T → 0 to 650 K

\bar 3

Crystal structure of the double magnesium zirconium orthophosphate at temperatures of 298 and 1023 K

c, a = 9.1600(4), c = 22.9059(13) Å, V = 1664.44(14) Å, Z = 6) and LiZr2(AsO4)1.5(PO4)1.5. Their structural frameworks are built up of AsO4 tetrahedra—or (As,P)O4 tetrahedra occupied by arsenic and phosphorus atoms at random—and ZrO6 octahedra, with the lithium atoms in between. The ionic conductivity of the materials has been measured. The cation conductivity of monoclinic LiZr2(AsO4)x(PO4)3 − x with 0 ≤ x ≤ 1 has been shown to exceed the conductivity of lithium zirconium phosphate.