A structural study of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-partially stabilized zirconia ceramics

Partially stabilized zirconia ceramics ZrO₂ (Y₂O₃) of different structures and phase compositions are tested for thermal stability and thermal shock. The ceramics can be used as solid electrolytes in oxygen activity sensors for fluid heat transfer agents (lead).__________Translated from Novye Ogneupory, No. 10, pp. 56 – 59, October, 2004.     

A method for determining the charge state of chromium in Cr-doped Bi<Subscript>12</Subscript>SiO<Subscript>20</Subscript> and Bi<Subscript>12</Subscript>TiO<Subscript>20</Subscript> materials

A chemical method for determination of the charge state of chromium in B₂O₃-based materials (Bi₁₂SiO₂₀ and Bi₁₂TiO₂₀ single crystals) in a wide Cr concentration range (1 × 10^–5 – 2 × 10^–2 wt.%)is proposed. The method is based on a color reaction between Cr⁶⁺ and diphenylcarbazide in an acid medium.Translated from Novye Ogneupory, No. 8, pp. 61 – 63, August, 2004.     

The Structure of Fusion-Cast High-Chrome Oxide Refractories in the Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> - MgO - Al<Subscript>2</Subscript>O<Subscript>3</Subscript> System

The phase composition and structure of fusion-cast refractories composed of 57.0 – 84.2% Cr₂O₃, 4.3 – 36.1% MgO, 2.0 – 9.7% Al₂O₃, and 2.4 – 6.9% SiO₂ have been studied by petrographic and x-ray spectral microprobe analysis methods. Refractories high in MgO with modulus M = (Cr₂O₃ +Al₂O₃)/MgO = 1.64 – 3.1 are shown to consist of spinel phase Mg(Cr, Al)₂O₄ and silicate glass. Refractory materials (80.8 – 84.2% Cr₂O₃, 4.3 – 4.7% MgO, 2.0 – 9.7% Al₂O₃, and 2.7 – 6.9% SiO₂ with M = 18.7 – 20.2) are three-phase systems composed of spinel, escolaite, and glass phase. These materials, owing to their high corrosion resistance, have promising potentiality for practical applications.__________Translated from Novye Ogneupory, No. 12, pp. 69 – 74, December, 2004.     

Heat treatment of silica-fiber-reinforced BN-Si<Subscript>3</Subscript>N<Subscript>4</Subscript> matrix composite

A new wave-transparent composite reinforced by silica fibers with a hybrid matrix comprising BN and Si₃N₄ was prepared by precursor infiltration and pyrolysis, and it was heat-treated at elevated temperatures. The variations of the composite during heat treatments were characterized and investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The as-received composite exhibits good mechanical properties, and it is almost amorphous. When treated at 1600°C, it turned brittle, and silica fibers in it were fused; the composite showed a good crystalline form. When treated at 2100°C, the composite broke into pieces, and the composition showed only BN. Si₃N₄ was decomposed, and silica fibers were volatilized. The presence of BN probably affected the phase transitions of silica fibers. __________ Translated from Novye Ogneupory, No. 8, pp. 49–52, August 2007.     

Synthesis and electrochemical properties of layered LiNi<Subscript>1/2</Subscript>Mn<Subscript>1/2</Subscript>O<Subscript>2</Subscript>prepared by coprecipitation

Spherical LiNi_1/2Mn_1/2O ₂ powders were synthesized from LiOH . H₂O and coprecipitated metal hydroxide, (Ni_1/2Mn_1/2)(OH)₂. The average particle size of the powders was about 10 m and the size distribution was quite narrow due to the homogeneity of the metal hydroxide, (Ni_1/2Mn_1/2)(OH)₂. The tap-density of the LiNi_1/2Mn_1/2O₂ powders was approximately 2.2 g cm_–3, which is comparable to the tap-density of commercial LiCoO₂. The LiNi_1/2Mn_1/2 O₂electrode delivered a discharge capacity of 152, 163, 183, and 189 mA h g^–1 in the voltage ranges of 2.8–4.3, 2.8–4.4, 2.8–4.5, and 2.8–4.6 V, respectively, with good cyclability. Furthermore, Al(OH)₃-coated LiNi_1/2Mn_1/2O₂exhibited excellent cycling behavior and rate capability compared to the pristine electrode.     

Glass formation in the LiF-ZnSO<Subscript>4</Subscript> system

The glass-forming ability is investigated in the LiF-ZnSO₄ binary system. It is found that, upon cooling melts at a rate of 10³ K/s, the glass formation is observed in the concentration range 30–60 mol % ZnSO₄. The characteristic temperatures are determined using differential thermal analysis. The density of glasses is measured by hydrostatic weighing. The experimental results obtained are used to calculate the molar volumes and the thermal stability parameters of lithium-containing fluorosulfate glasses.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Nepomiluev, Reznitskikh.     

Crystallization Behavior of Amorphous Zr<Subscript>55</Subscript>Cu<Subscript>20</Subscript>Ni<Subscript>10</Subscript>Al<Subscript>10</Subscript>Ti<Subscript>5</Subscript> Alloy

In the present study, the crystallization behavior and thermal stability of amorphous Zr₅₅Cu₂₀Ni₁₀Al₁₀Ti₅ alloy, obtained by melt-spinning, have been investigated using X-ray diffraction (XRD), differential thermal analysis (DTA) and transmission electron microscopy (TEM). The activation energy for crystallization has been evaluated by the Kissinger method, and it has been found that E _x obtained from the crystallization onset temperature (T _x) is lower than E _p determined by the crystallization peak temperature (T _P). During the continuous annealing process, ZrO and h-Al₃Zr₅ phases firstly precipitate from the amorphous matrix, then Zr₂Ni_0.66O_0.33 phase forms continuously and its relative content increases with increasing annealing temperature. However, no crystalline phases have been observed during the isothermal annealing process at 733 K (below T _x) for 90 min. The atomic clusters can keep the stability state through adjusting the short-range ordering.     

Thermal and neutron shielding properties of <Superscript>10</Superscript>B<Subscript>2</Subscript>O<Subscript>3</Subscript>/polyimide hybrid materials

In this study, ¹⁰B₂O₃/polyimide (PI) hybrid materials were synthesized with the aim to improve their thermal stability and neutron shielding properties. 3,3′-Diaminodiphenyl sulfone (DADPS) reacted with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) in N-methyl-2-pyrrolidone (NMP) and mixed with amine functionalized ¹⁰B₂O₃ to prepare a series of poly (amic acid), meanwhile, corresponding PIs were obtained via the thermal imidization procedures. The morphologies and structures of the prepared hybrid materials were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The thermooxidative and flame retardancy properties of the PI films were examined by thermogravimetric analysis (TGA) and limiting oxygen ındex (LOI). The experimental results showed that as the amount of functionalized ¹⁰B₂O₃ was increased, flame retardant properties of the hybrid films were increased. Hybrid materials were also irradiated with thermal neutrons. The neutron shielding properties increasing depends on the amount and the distribution of the ¹⁰B isotope.     

Combustion of a Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript>-Al-C Powder Mixture in the SHS Regime and the Structure of the Combustion Products

The combustion of pressed specimens of a stoichiometric Fe₂O₃-TiO₂-Al-C powder mixture burning in the SHS regime is studied. It is found that the final product has the same shape and size as the initial specimen. The composition and structure of the final product, which is highly porous high-melting Al₂O₃-TiC-Fe(Ti) composite ceramics, are studied. The mechanism of phase and structure formation in the examined system is proposed.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 4, pp. 60–66, July–August, 2005.     

Synthesis,Characterization and Properties of One-dimensional Complexes of <Emphasis Type="Italic">cis-syn-cis</Emphasis>-Dicyclohexyl-18-crown-6 with K<Subscript>2</Subscript>[M(mnt)<Subscript>2</Subscript>] (M==Ni,Pd, Pt)

Three complexes [K(DC18C6-A)]₂[M(mnt)₂] (DC18C6-A=cis-syn-cis-dicyclohexyl-18-crown-6, isomer A; M=Ni, 1; Pd, 2; Pt, 3; mnt = 1,2-dicyanoethene-1,2-dithiolate, maleonitriledithiolate, [C₂S₂(CN)₂]²⁻) have been synthesized and characterized by elementary analysis, UV–vis, FT-IR spectroscopy and X-ray single crystal diffraction. They are isomorphous and all display infinite one-dimensional chain-like structure formed by [K(DC18C6-A)]⁺ complex cations and [M(mnt)₂]²⁻ (M=Ni, Pd, Pt) complex anions through K–N interactions. Thermal analysis indicates that three complexes are all thermal stable under 260 °C and experience the same decomposition process of dissociation and evaporation of crown ether molecules. Their electrochemical behaviors have been studied by cyclic voltammetry.     

Thermoelectric Properties of <Emphasis Type="Italic">x</Emphasis>PbTe/Yb<Subscript>0.2</Subscript>Co<Subscript>4</Subscript>Sb<Subscript>12</Subscript> Hot-Pressed Samples

The xPbTe/Yb_0.2Co₄Sb₁₂ compounds were prepared by the ball-milling and hot-pressed process. Electrical conductivity of the composite samples are reduced with a increase in PbTe content; and, their temperature dependence coefficients show the positive values. The maximum electrical conductivity of composite materials is ~80000 Sm⁻¹ at 800 K. The Seebeck coefficient (absolute value) of the composite material is obviously improved with an increase in the dispersed phase (PbTe) content; the Seebeck coefficient (absolute value) of the 10PbTe sample is ~260 μVK⁻¹ at 700 K, which increases by 13.6% relative to that of the Yb_0.2Co₄Sb₁₂ sample. The thermal conductivity of the composite samples is improved due to introduction of PbTe, and the thermal conductivity of the 10PbTe sample is ~3 Wm⁻¹ K⁻¹ at 550 K. The maximum value of ZT is 0.78 at 700 K for the 2.5PbTe sample.     

Effects of surface area on electrochemical performance of Li[Ni<Subscript>0.2</Subscript>Li<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>]O<Subscript>2</Subscript> cathode material

The effect of surface area on the electrochemical properties and thermal stability of Li[Ni_0.2Li_0.2Mn_0.6]O₂ powders was characterized using a charge/discharge cycler and DSC (Differential Scanning Calorimeter). The surface area of the samples was successfully controlled from ~4.0 to ~11.7 m² g⁻¹ by changing the molar ratio of the nitrate/acetate sources and adding an organic solvent such as acetic acid or glucose. The discharge capacity and rate capability was almost linearly increased with increase in surface area of the sample powder. A sample with a large surface area of 9.6–11.7 m² g⁻¹ delivered a high discharge capacity of ~250 mAh g⁻¹ at a 0.2 C rate and maintained 62–63% of its capacity at a 6 C rate versus a 0.2 C rate. According to the DSC analysis, heat generation by thermal reaction between the charged electrode and electrolyte was not critically dependent on the surface area. Instead, it was closely related to the type of organic solvent employed in the fabrication process of the powder.     

Thermomechanical properties of refractory materials of AL<Subscript>2</Subscript>O<Subscript>3</Subscript>–Si<Subscript>3</Subscript>N<Subscript>4</Subscript>–C compositions based on acpb after impregnation with a sol-gel composition

Comparative characteristics are presented for the physicomechanical properties and oxidation resistance of refractory materials of Al₂O₃–Si₃N₄–C composition based on an ACPB for the original materials (fired at 1400°C) and after impregnation with a sol-gel composition and heat treatment at 800°C. Areduction in material porosity, increase in strength and reduction in carbon burn-off are due to development of a glassy phase in the pore space and on graphite flakes due to SiO₂formation with thermal destruction of the organosilicon substance.     

Investigation into the phase formation in the ZrO<Subscript>2</Subscript>-CeO<Subscript>2</Subscript> system

Nanopowders of solid solutions with different compositions are prepared in the zirconia-enriched region of the ZrO₂-CeO₂ system. The crystallization of these powders and the formation of the monoclinic, cubic, and tetragonal solid solutions of the composition (Zr_{1 – x} Ce_x)O₂ are investigated. It is found that the unit cell parameters of the solid solutions increase as the cerium content increases. This confirms the fact that cerium ions [r(Ce⁴⁺) = 1.11 ] substitute for zirconium ions [r(Zr⁴⁺) = 0.98 ] in these solid solutions. The average size of crystallites of the solid solutions under investigation increases from 5 to 60 nm in the temperature range 500–1200°C.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Panova, Glushkova, Nefedova.     

Dependence of the optical properties of the 30.5K<Subscript>2</Subscript>O · 8.3Al<Subscript>2</Subscript>O<Subscript>3</Subscript> · 3.6SiO<Subscript>2</Subscript> · 57.6P<Subscript>2</Subscript>O<Subscript>5</Subscript> glass on the trivalent titanium content

An optical material, namely, the potassium aluminosilicophosphate glass activated with trivalent titanium ions, is synthesized and studied. The optimum concentration range (0.2–10.0 wt % Ti₂O₃) that provides the best physical, luminescent, and kinetic properties of glasses is determined. This makes it possible to use the sensitizing properties of Ti³⁺ ions to the greatest extent.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Batyaev, Leonov.     

Determination of the Specific Heat of the Normal Alkanes C<Subscript>7</Subscript>-C<Subscript>11</Subscript>

Using precise experimental data on the specific heat at constant pressure C _p of the normal alkanes C₇-C₁₁ over a wide parameter range, the C _p values are determined on the liquid and vapor branches of the boundary curve from the normal boiling point to 0.98T _c. In the coordinates C _p-P _s-T _s, orthogonal projections of the reduced phase diagram of these hydrocarbons are constructed and analyzed. Existing generalized expressions for C _p of the liquid and gas phases of the normal alkanes C₅-C₁₁ on the boundary curve as a function of temperature are evaluated, and new expressions for C _p are proposed.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 4, 2005, pp. 476–480.Original Russian Text Copyright © 2005 by Kuznetsov, Gorbachev.     

Properties of a melt of the eutectic composition in the NaPO<Subscript>3</Subscript>-Na<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>-LiF system

Physical (density, viscosity) and thermophysical (heat capacity, thermal conductivity) properties of a melt of the eutectic composition (wt %) 84NaPO₃ · 8Na₂B₄O₇ · 8LiF have been investigated. It has been demonstrated that this eutectic mixture is a promising material for the use as a high-temperature heat-transfer agent.     

Synthesis and Structure of Large AlPO<Subscript>4</Subscript>-5 Crystals

Large, high quality, perfect hexagonally shaped AlPO₄-5 crystals have been crystallized using hydrothermal synthesis. The crystallization was carried out at 447 or 457 K with a crystallization time from one to four days and tripropylamine (TPA) molecules as template. The morphology of the crystals was observed with SEM. For the first time, the structure of the AlPO₄-5 crystal together with TPA template molecules has been successfully refined in space group P6cc by single crystal X-ray diffraction. The parameters are a = b = 13.725(3) Å, c = 8.473(3) Å, and = 120.0. The size of some crystals is up to 2.2 mm in c direction, or up to 0.31 mm in a or b direction. All observed angles and distances are within acceptable ranges: P–O = 1.50–1.54 Å, Al–O = 1.62–1.72 Å, O–P–O = 107–111, O–Al–O = 103–113 and P–O–Al = 147–150.     

Sorption studies of CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript>, N<Subscript>2</Subscript>, CO,O<Subscript>2</Subscript> and Ar on nanoporous aluminum terephthalate [MIL-53(Al)]

Aluminum terephthalate, MIL-53(Al), metal–organic framework synthesized hydrothermally and purified by solvent extraction method was used as an adsorbent for gas adsorption studies. The synthesized MIL-53(Al) was characterized by powder X-Ray diffraction analysis, surface area measurement using N₂ adsorption–desorption at 77 K, FTIR spectroscopy and thermo gravimetric analysis. Adsorption isotherms of CO₂, CH₄, CO, N₂, O₂ and Ar were measured at 288 and 303 K. The absolute adsorption capacity was found in the order CO₂>CH₄>CO>N₂>Ar>O₂. Henry’s constants, heat of adsorption in the low pressure region and adsorption selectivities for the adsorbate gases were calculated from their adsorption isotherms. The high selectivity and low heat of adsorption for CO₂ suggests that MIL-53(Al) is a potential adsorbent material for the separation of CO₂ from gas mixtures. The high selectivity for CH₄ over O₂ and its low heat of adsorption suggests that MIL-53(Al) could also be a compatible adsorbent for the separation of methane from methane–oxygen gas mixtures.     

Kinetics of the nanocrystal formation in the ZrO<Subscript>2</Subscript>-In<Subscript>2</Subscript>O<Subscript>3</Subscript>-H<Subscript>2</Subscript>O system under hydrothermal conditions

The hydrothermal synthesis of nanocrystals in the ZrO₂-In₂O₃-H₂O system is investigated kinetically. The presence of indium hydroxide results in an increase in the dehydration temperature of this system. The size of nanocrystals is equal to 20–30 nm and virtually does not depend on the temperature and time of hydrothermal treatment or on the type of crystalline modification of ZrO₂. An increase in the synthesis temperature leads to an increase in the fraction of the monoclinic zirconia modification.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Artamonova, Almjasheva, Mittova, Lavrushina, Gusarov.