S. N. Mudretsova

Formation of nickel carbide in the course of deformation treatment of Ni-C mixtures

Nonequilibrium Ni(C) solid solutions supersaturated with carbon to 10.2 at % were synthesized by mechanochemical method. An analysis of diffraction patterns showed that the formation of Ni(C) solid solutions is accompanied by an increase in the probability of appearance of deformation stacking faults. When the carbon content in the initial Ni-C mixtures is above 20 at %, the fcc Ni(C) solid solution resulting from the mechanical synthesis transforms into the metastable Ni3C nickel carbide with a hexagonal structure. The thermal stability of nonequilibrium Ni(C) solid solutions was determined. The solid solutions formed from the mixtures with carbon contents from 7 to 15 at % undergo partial decomposition accompanied by the carbide precipitation upon heating to 300°C. The decomposition of the metastable Ni3C carbide starts at a temperature Ts ~ 464.8°C; the thermal effect is —ΔH=10–13 kJ/mol. The effective radius of carbon atoms in the Ni(C) solid solutions was determined; it is equal to Rceff=0.061 nm.

Thermoanalysis of the system BaO2BaOO2

Abstract Thermoanalysis of the system BaO 2 BaOO 2 has been carried out at oxygen pressures from 0.2 to 1.5 atmospheres using a Netzsch STA-409 simultaneous analyser. Measurements were made over the temperature range from 25 to 950°C. The thermogravimetric data obtained have been used to evaluate the non-stoichometric region boundaries for BaO 2 and to estimate the same region for BaO. The temperatures of the monovariant equilibrium BaO 1+ x 1 BaO 2− x 2 have been determined: T mon = 990, 1041, 1083 and 1109 K at P O 2 = 0.2, 0.5, 1.0 and 1.5 oxygen atmospheres, respectively. For the reaction BaO 1.0 + 0.5O 2 = BaO 2.0 , the values Δ G ⦵ T = −5.1, −2.1, 0.3, and 1.7 kJ mol −1 have been calculated for the above respective temperatures.

Thermochemical characteristics of nonstoichiometric Ba2Cu3O5: II. Thermal transformations

Abstract Thermoanalysis (TG-DSC) of the pure compound Ba2Cu3O5+δ (023) has been carried out at oxygen pressures of 0.21 and 1 atm in the temperature range 25–970°C. It was shown that 5.5 823°C at 0.21 atm O2; > 890°C at 1 atm O2) appeared. The liquid phase transition took place at temperatures higher than 860°C (0.21 atm) and 910°C (1 atm).

Investigation of the structure and magnetic and mechanical properties of textured substrates of an Ni-Cr-W alloy

Based on the data of X-ray diffraction, electron-backscatter diffraction, dilatometry, thermal analysis, and scanning electron microscopy, we determined the optimum regimes of heat treatment of cold-rolled tape substrates of an alloy Ni88.4Cr9.2W2.4 that permit obtaining a perfect cube texture. It has been shown that the use of two-stage annealings makes it possible to obtain in this ternary nickel alloy a cube texture in which the scatter about the rolling direction (RD) and the transverse direction (TD) of the substrates varied within 6.75°–7.20° and 4.8°–5.4°, respectively.

Mechanochemical activation of aluminum: 5. Formation of aluminum carbide upon heating of activated mixtures

The mechanical activation of thermal synthesis of aluminum carbide Al4C3 in Al-15 wt % C and Al-30 wt % C mixtures is studied with differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. It is found that the mechanical treatment of powders results in an essential reduction in the temperature of carbide synthesis. A correlation between the temperature of the onset of synthesis and size L of the coherent scattering region of aluminum is established. When the doses of absorbed mechanical energy exceed 15–20 kJ/g and, as a result, the L value decreases to 20 nm, the synthesis proceeds by a solid-phase mechanism at a temperature significantly lower than the melting point of aluminum and the synthesis temperature reduces by 800°C. The particle size of the formed aluminum carbide and unreacted aluminum after heating to 900°C is 20–40 nm. At doses D = 50–80 kJ/g, the heat of the formation of carbide from activated samples is about two times lower compared to the standard value. The possible sources of this discrepancy are discussed.

Thermochemical characteristics of BaCuO2

Abstract Using simultaneous thermal analysis (TG + DSC), the heat capacity and non-stoichiometry of BaCuO 2+ x in O 2 atmosphere have been investigated. The results are formulated as 2.11 ± 0.02 > 2 + x > 2.00 ± 0.02 for 600°C t C p = 0.405 + 1.05 × 10 −4 t (J/g −1 K −1 ) was measured in the temperature range 40°C t

Thermal analysis of mercury superconductor HgBa2CuO4 + x and its precursor Ba2CuO3 + y☆

The superconducting compound HgBa2CuO4 + x and its precursor Ba2CuO3 + y have been studied in an oxygen atmosphere by TG-DTA in the temperature interval 20–1100°C. It was supposed that the succession of chemical processes taking place during the heating (20° min−1, 1 atm O2) of HgBa2Cu1.05O4.12 is as follows: It was supposed that the Ba2CuO3.23 compound during heating (1° min−1, 0.21 atm O2) and cooling (20° min−1, 0.21 atm O2) undergoes following stages:

Chemical deposition of smooth nanocrystalline Y2O3 films from solutions of metal-organic precursors

A series of (Y(AcO)3·4H2O—Q—Solv) solutions (Q is monoethanolamine (MEA), diethanolamine (DEA), en, dien; Solv = MeOH, EtOH, PriOH, BuOH) was studied to choose the metal-organic precursor for surface smoothing treatment of metallic tapes by chemical deposition of nanocrystalline yttria films. Based on the results of viscosity, wetting angle, and thermal stability measurements, a solution (Y(AcO)3·4H2O—dien—PriOH) was proposed as a new metal-organic precursor. After chemical deposition of nanocrystalline yttria films about 300 nm thick on a Hastelloy C-276 metallic tape the surface roughness was reduced by a factor of 11 (from 9.0 to 0.8 nm on a surface area of 5×5 μm2).

Defective structure, plastic properties, and reactivity of mechanically activated magnesium

The genesis of a defective structure (particle size, size of coherent scattering regions (CSRs), dislocation concentrations, and two types of deformation and twin stacking defects (SDs)) of magnesium during its mechanical activation in a vibrating mill in the presence of liquid additions was studied by X-ray diffraction (XRD) analysis, microscopy, and adsorption (BET) method. The dynamic mechanical properties were checked for the activated samples using a K-44-2 vertical impact machine. The ability of magnesium to be oxidized in air was checked by heating it in the cell of a differential scanning calorimeter. At mechanical activation doses of less than 5 kJ/g, the accumulation of chaotically arranged dislocations and deformation SDs was accompanied by an increase in the plasticity of the material. At higher doses, polygonization of dislocations led to a drastic decrease in the CSR size and dislocation run, leading to embrittlement of the material. The changes in the mechanical properties were confirmed by symbatic changes in the outer particle size and showed themselves on the pressure oscillograms during the impulse loading of pressed Mg layers. Mechanical activation led to an increase in the level of oxidation of magnesium with oxygen, but did not affect the temperature of the start of oxidation. A method for activating magnesium with additions was suggested and led to the formation of highly disperse magnesium samples with the oxidation temperature lowered by 150°C.

Mechanochemistry of hexagonal boron nitride. 2. Reactivity upon interaction with water

Mechanical activation makes boron nitride chemically reactive with respect to water. The fact of the reaction proceeding, which is accompanied by a change in the structure of boron nitride, is confirmed by the data of IR spectroscopy, X-ray diffraction, transmission electron microscopy, differential thermal analysis, adsorption, and gravimetry. It is established that the most defective amorphous part of the material is primarily hydrolyzed. The reaction takes place at room temperature, with the conversion increasing to values of higher than 50% with the dose of mechanical energy supplied during the mechanical activation. In addition to ammonia, hydrolysis gives rise to the formation of ammonium pentaboride, NH4B5O6(OH)4 · 2H2O. After the reaction products are removed, residual boron nitride, which is dried at T ≤ 100°C, crystallizes to form nanosized rods.