Synthesis and ionic conduction of sodium titanate Na<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>7</Subscript>

Chemical and phase transformations in the course of synthesis of sodium titanate Na₂Ti₃O₇ have been studied. Prepared sodium titanates have been characterized by X-ray powder diffraction analysis, scaning electron microscopy, and impedance spectroscopy, their electrochemical testing has been conducted. Mechanochemical interaction of titanium dioxide and sodium carbonate at the grinding stage has been revealed. The utilization of mesoporous titanium dioxide have been shown to provide a considerable decrease of final annealing temperature. Thus obtained titanates exhibit high electrochemical capacity.     

Effect of the composition of (Mo,Nb, V,Ti)/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> surface oxide structures on the oxidative dehydrogenation of ethane to ethylene

Molecular layering method was used to synthesize on the surface of γ-Al₂O₃ vanadium-titanium oxide structures of varied composition and structure from the gas phase and niobium- and molybdenum-containing additives from the liquid phase. The resulting composites and the starting aluminum oxide were studied by X-ray diffraction analysis and chemical-analytical and adsorption methods. The catalytic properties of the synthesized products were examined in the oxidative dehydrogenation of ethane. It was shown that the activity of the samples is affected not only by the composition and structure of surface structures, but also by the relative amounts of components in mechanical mixing of vanadium-titanium oxide and niobium oxide supported systems.     

Phase transitions in double molybdates K<Subscript>2</Subscript>M<Stack><Subscript>2</Subscript><Superscript>II</Superscript></Stack>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> with M = Mg or Co

Phase transitions and cation mobility in double molybdates K₂M ₂ ^II (MoO₄)₃ with M = Mg or Co and the products of their heterovalent doping with scandium(III) and vanadium(V) have been studied. The transition from low to high conductivity in K₂M ₂ ^II (MoO₄)₃ is the result of a two-stage phase transition, whose occurrence is significantly extended in time. Heterovalent substitutions noticeably decrease the heat of the phase transition. The transition to the low-temperature phase is not achieved even after long-term exposure.     

Lithium deintercalation/intercalation processes in cathode materials based on lithium iron phosphate with the olivine structure

This review describes the current state of the studies of lithium deintercalation/intercalation processes in cathode materials based on lithium iron phosphate with olivine structure. The limiting factors of LiFePO₄ charge/discharge processes, as well as the main methods for their acceleration are considered. A partial replacement of iron cations in the structure improves the electrochemical characteristics of the cathode materials, including the discharge capacity, charge/discharge rate, and, in some cases, changes the charge/discharge mechanism. The use of nanoscale phosphate LiFePO₄ with the olivine structure considerably increases the charge/discharge rate of cathode materials based on it by reducing the diffusion path length. Methods for LiFePO₄ surface modification are considered. Particular attention is paid to the development of composite materials with electron-conducting additives. Combining of various approaches to the modification of the material in question makes it possible to obtain materials with a discharge capacity close to the theoretical value (170 mA h g^–1) at a low charge/discharge rate and to considerably increase its capacity at high charge and discharge currents.     

High-enthalpy hot-shot wind tunnel with combined heating and stabilization of parameters

In the present paper, we consider instrumentation and the experimental procedure for conducting tests in a highenthalpy short-duration wind-tunnel facility, namely, a hypersonic hot-shot wind tunnel. We consider operation of the hot-shot wind tunnel with the test gas (TG) parameters kept constant during the regime and also operation of the tunnel as a traditional shock tube with a decay of the TG parameters that occurs as the TG leaves a constant-volume settling chamber. Stabilization of the TG parameters is achieved by using a pressure multiplier installed coaxially with the settling chamber, the configuration presenting a linear arrangement of the two components. Unloading of pressure multiplier dynamic component is achieved by using an equalizer whose piston moves in the opposite direction to the multiplier piston system. Several modes of wind tunnel operation with various combinations of different TG heating methods (electric arc, chemical energy, adiabatic compression, or heating in an external with respect to the settling chamber heat source) are possible. The design of a device responsible for diaphragm breakdown delay is considered. The design and dimensions of the wind tunnel provide for its normal operation under the following conditions: range of Mach numbers M = 4–20, range of settling-chamber temperatures T _ch1 = 600–4000 K, and settling-chamber pressure p _ch1 up to 200 MPa (in operation with a double settling chamber, the stagnation pressure p _0n = p _ch2 can be varied from 1 to 200 MPa). The settling chamber volume (80–100 dm³) is sufficiently large, allowing obtaining a 1-m diameter hypersonic stream in the test section during ～ 100 ms (in combination with a second settling chamber).     

Cation mobility in modified Li1 + xTi2 ? xGax(PO4)3 lithium titanium NASICON phosphates

Li_{1 +x} Ti_{2 − x} Ga _x (PO₄)₃(x= 0−0.2) NASICON double phosphates are prepared and studied by high-temperature X-ray diffraction, ⁷Li NMR spectroscopy, impedance spectroscopy, and calorimetry. Doping with Ga³⁺ cations increases cation mobility in LiTi₂(PO₄)₃. Ion conductivity, NMR spectroscopy, and calorimetry data imply the occurrence of a phase transition in LiTi₂(PO₄)₃ and in products of partial gallium-for-titanium substitution. Original Russian Text ? I.Yu. Pinus, I.V. Arkhangel’skii, N.A. Zhuravlev, A.B. Yaroslavtsev, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 8, pp. 1235–1239.     

Phase transitions and ion transport in NASICON materials of composition Li1 + xZr2 ? xInx(PO4)3(x = 0–1)

NASICON materials of composition Li_{1 + x} Zr_{2 − x} In _x (PO₄)₃(x = 0–1) were synthesized. The phase constitution, particle size, and conductivity of these materials were studied as s function of synthesis temperature. High-temperature X-ray powder diffraction was used to study phase transitions in the materials synthesized. Low levels (x ≤ 0.1) partial substitution of indium for zirconium considerably increase the lithium ion conductivity and reduce the activation energy for conduction compared to the parent compound.     

Magnetic and resonance properties of ferrihydrite nanoparticles doped with cobalt

Powders of undoped ferrihydrite nanoparticles and ferrihydrite nanoparticles doped with cobalt in the ratio of 5: 1 have been prepared by hydrolysis of 3d-metal salts. It has been shown using Mössbauer spectroscopy that cobalt is uniformly distributed over characteristic crystal-chemical positions of iron ions. The blocking temperatures of ferrihydrite nanoparticles have been determined. The nanoparticle sizes, magnetizations, surface anisotropy constants, and bulk anisotropy constants have been estimated. The doping of ferrihydrite nanoparticles with cobalt leads to a significant increase in the anisotropy constant of a nanoparticle and to the formation of surface rotational anisotropy with the surface anisotropy constant K _u = 1.6 × 10^–3 erg/cm².     

Effect of ultrasonic treatment on magnetic ferrihydrite nanoparticles in a suspended state

Dried sediments of magnetic ferrihydrite nanoparticles subjected to ultrasonic treatment in the cavitation mode are studied via Mössbauer spectroscopy. Fe ions are reduced to the metal state. In all experiments with detected metal reduction, the investigated suspensions contain organic components.