The coating of cadmium compounds with nickel compounds

Micrometer-sized particles of cadmium carbonate (cores) were prepared by homogeneous precipitation from aqueous solution containing urea in the presence of cadmium sulfate. These particles were then homogeneously coated with a layer of nickel hydroxy carbonate by heating their dispersion in aqueous solution, containing nickel sulfate and urea, at 85 °C for 70 min with constant agitation. The same solution mixture produced spheroids of nickel hydroxy carbonate (coating precursors), when heated under similar conditions in the absence of the cadmium carbonate particles. The existence of the coated layer on the cores and its composition was confirmed by various physical methods. The as-prepared carbonated solids (cores, coating precursors, and coated particles) were converted into their oxide forms by calcination at 700 °C. The cores became porous, whereas the coating precursors and coating layer disintegrated into smaller particles during the calcination process.     

The coating of cadmium compounds with copper compounds

Fine particles of cadmium carbonate (CdCO₃) were prepared by heating aqueous solutions containing dissolved urea and cadmium sulfate at 85°C for 1 h. Effect of the composition of the reactant mixture on the morphology of the precipitated particles was investigated. It was found that the cadmium sulfate content of the reactant mixture significantly affected the shape and size of the precipitated particles. At certain range of reactant mixture composition, cauliflower-shaped uniform particles were obtained. The later particles were coated with basic copper carbonate (Cu₂(OH)₂CO₃) by heating aqueous dispersions, containing CdCO₃ particles, copper (II) nitrate, and urea at 85°C for various periods of time with constant stirring. The coating process was found sensitive to the experimental conditions and in most of the trials; mixtures of the coated and coating precursor particles were obtained. As such, extensive optimizations were carried out and conditions were established for the production of uniformly coated particles.On calcination at 700°C for 1 h, the CdCO₃ particles converted into CdO, whereas the coated particles (CdCO_{3 (core)}/Cu₂(OH)₂CO_{3 (coating)} transformed into CdO_(core)/CuO_(coating)) without sintering. In the coated particles, the core and coating materials stayed mutually inert during the calcination reaction and independently converted into their respective oxides.All the calcined and uncalcined products were characterized by various physical and chemical methods.     

Synthesis and characterization of uniformly coated particles (cobalt compounds on copper compounds)

Spherical particles (～3 μm) of copper(II) oxalate were produced in the form of precipitated solids by gently mixing aqueous solutions of oxalic acid and copper nitrate with predetermined concentrations at room temperature. These particles were isolated from the mother liquor and then coated with cobalt basic carbonate. The coating trials involved heating of the aqueous dispersions, containing known amounts of the dispersed copper oxalate particles (cores), urea, and cobalt nitrate, at 70–85 °C for various periods of time with constant stirring. The heating process decomposed urea, increased pH, liberated carbonate ions, which resulted in the precipitation of the dissolved cobalt ions in the form of shells of cobalt basic carbonate around each core particle. The coating process was sensitive to the applied experimental parameters, since uniformly coated particles were obtained under a narrow range of coating mixture composition. In the absence of the cores, the same reactants solutions produced coating precursor particles (cobalt basic carbonate), when subjected to similar heating conditions. Physical and chemical analyses indicated that the coating material of the coated particles and the coating precursor particles had the same chemical compositions. The as-prepared core, coating precursor, and coated particles were converted into oxide forms by heating their dry powders at elevated temperatures under controlled heating conditions. The heat treatment produced obvious changes in the surface morphology of these particles due to loss of material. Moreover, the heat-treated particles preserved shape integrity to a maximum extent, showing their thermal stability. Selected batches of the as-prepared and heat-treated products were characterized by various physical methods.     

The phase conversion of precursor powders for powder melting process YBa2Cu3O7−x superconductors

The effects of heating rate and holding time on the formation of YBa₂Cu₃O_7−x phase in precursor powders for YBa₂Cu₃O_7−x superconducting bulks prepared by powder melting process have been investigated. The phase conversion of the precursor powders is studied by X-ray diffraction and found to be different for different heating rates during heating. The YBa₂Cu₃O_7−x phase is formed during heating to peritectic temperature at 100 and 400 °C/h, but not at 6,000 °C/h. The longer the holding time, the more the amount of YBa₂Cu₃O_7−x phase between 880 °C and about 950 °C. The results are useful for understanding the mechanism of powder melting process and controlling the process conditions.     

Synthesis of B–C–N nanocrystalline particle by mechanical alloying and spark plasma sintering

B–C–N nanocrystalline particles have been synthesized by Spark plasma sintering (SPS) from the amorphous BC₂N (a-BC₂N) precursor, which were prepared by the mechanical alloying (MA) method from a mixture of graphite and hexagonal boron nitride (h-BN). The syntheses have been performed in the temperature range from 1200 to 1900 °C at the heating rate of about 300 °C min⁻¹ with loads of 30 MPa. The obtained product has been checked by X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron energy loss spectrum (EELS). It has been found that the B–C–N nanocrystalline particles can be synthesized at the temperature of 1600 °C with the grain size less than 50 nm, and at the temperature of 1900 °C, the a-BC₂N is decomposed into graphite and h-BN.     

Preparation of SiC–SiO<Subscript>2</Subscript>–CuO composites

SiC–SiO₂–CuO composite particles were prepared by double coating processes. SEM, DSC-TG, XRD techniques were carried out to characterize the coated composite particles and sintered compacts. It was found that a core-shell structure was constructed in the composite particles with the core of SiC and the shell of SiO₂–CuO. Cu–silicides were detected in hot-pressed compacts. SiO₂ might decompose at 1,300 °C. The decomposition product of Si would result in the transformation from Cu_6.69Si into Cu₃Si.     

Phosphorus-containing compounds of pollucite structure and radiochemical problems

New pollucite-like phosphorus-containing compounds with cesium and uni-, bi-, and trivalent cations (Li; Mg, Mn, Co, Ni, Cu, Zn, Cd, Sr, Ba; Al, Cr, Fe), many of which can be present in various combinations in wastes from radiochemical processes, were synthesized. The individual phases obtained were characterized by X-ray phase analysis and IR spectroscopy. The symmetry of the unit cells of the phosphorus-containing compounds decreases relative to the silicon analog (pollucite natural mineral) from Ia3d to I4₁32. The behavior of the compounds on heating to 1000°C, under hydrothermal conditions at 90°C, in aqueous systems (distilled water and seawater) at 25°C, and in a CsCl melt at 680°C was studied. The chemical and phase composition of the samples remained unchanged under all these conditions. The Cs leaching rates varied from 7.1 × 10⁻⁶ to 1.46 × 10⁻⁵ g cm⁻² day⁻¹. The “crystal-chemical modeling” of the new possible compositions of the compounds with the expected pollucite structure was performed.     

Spillover effect in the hydrogen absorption by the polycrystalline powder alloy FeNi1.75Cu1.5Mo0.5 and electric conductivity of the pressed powder

The process of hydrogen absorption by the FeNi_1.75Cu_1.5Mo_0.5 alloy in the polycrystalline form was investigated for both the pure and palladized forms (0.008 76% Pd) at temperatures from ambient to 600 °C in a hydrogen flow. Using differential scanning calorimetry, (DSC) thermogravimetry (TG) and X-ray diffraction, the influence of palladization on the hydrogen absorption was demonstrated. Kinetic analysis of the DSC thermograms, the kinetic and thermic parameters of hydrogen absorption were determined. The TG thermograms showed that on hydrogen absorption a weight change took place due to water formation and reduction of the oxide film at the surface of the powder particles. The activation energies of hydrogen absorption were 170 kJ mol⁻¹ for the original powder and 32 kJ mol⁻¹ for the palladized one. The enthalpies of the absorption ranged from ΔH = −5 to ΔH = −380 J g⁻¹ for the original and palladized powder, respectively. The rate constants of the absorption depended on the palladization and were found to be 0.03 and 1.20 s⁻¹, respectively, at 162 °C. The electric conductivity of the pressed powder (9 kbar) increases on heating in both air and a hydrogen atmosphere up to 600 °C, tending to a constant value. The changes of the parameters characteristic of the palladized form are ascribed to the mechanism of a hydrogen spillover effect due to the presence of palladium.     

Novel bromide anion conducting refractory solid electrolytes based on lanthanum oxybromide

A new type of high bromide anion conducting solid was artificially designed with the solids based on lanthanide oxybromide (LnOBr). LnOBr is selected as it is insoluble in water and also highly stable at temperatures around 800°C. The enhancement of Br⁻ anion conductivity was successfully realized by creating Br⁻ ion vacancies by doping divalent cation in the Ln site of the LnOBr host lattice. The Br⁻ anion conductivity was the highest among the conventional bromide anion conducting solids such as Pb_0.99K_0.01Br_1.99 (373°C) and CsPbBr₃ (500°C) which contain toxic lead in them. The Br⁻ anion conductivity of LnOBr based solid enters into the practically useful region (σ > 10⁻³ Sċcm⁻¹).     

The microstructure and fracture properties of MgO crystals containing a dispersed phase

MgO crystals containing up to 40% by volume of magnesioferrite and up to 2% by volume of iron and nickel were produced by a diffusion technique followed by appropriate heat treatments. Magnesioferrite precipitate did not significantly change the effective surface energy of a crack as measured by the double cantilever beam technique. Iron and nickel precipitate was produced in the form of platelets lying on {100}_MgO planes whose orientation relationships were [001]_MgO ∥[001]_Fe, [110]MgO ∥[100]_Fe with a spread of +10°, approximately, and [001]_MgO ∥[001]_Ni, [010]_MgO ∥[010]_Ni with negligible spread. Despite the crystallographic orientation relationships, the metal-MgO interface appeared to be very weak; the reasons for this are discussed. The effect of the metal precipitate on crack propagation was to markedly increase the density of cleavage steps. For a volume fraction of precipitate of 0.02, this led to a small increase in the effective surface energy, on the order of 1 Jm⁻².     

Effects of Steam Environment on Creep Behavior of Nextel™610/Monazite/Alumina Composite at 1,100°C

The tensile creep behavior of a N610™/LaPO₄/Al₂O₃ composite was investigated at 1,100°C in laboratory air and in steam. The composite consists of a porous alumina matrix reinforced with Nextel 610 fibers woven in an eight-harness satin weave fabric and coated with monazite. The tensile stress-strain behavior was investigated and the tensile properties measured at 1,100°C. The addition of monazite coating resulted in ~33% improvement in ultimate tensile strength (UTS) at 1,100°C. Tensile creep behavior was examined for creep stresses in the 32–72 MPa range. Primary and secondary creep regimes were observed in all tests. Minimum creep rate was reached in all tests. In air, creep strains remained below 0.8% and creep strain rates approached 2 × 10⁻⁸ s⁻¹. Creep run-out defined as 100 h at creep stress was achieved in all tests conducted in air. The presence of steam accelerated creep rates and significantly reduced creep lifetimes. In steam, creep strain reached 2.25%, and creep strain rate approached 2.6 × 10⁻⁶ s⁻¹. In steam, creep run-out was not achieved. The retained strength and modulus of all specimens that achieved run-out were characterized. Comparison with results obtained for N610™/Al₂O₃ (control) specimens revealed that the use of the monazite coating resulted in considerable improvement in creep resistance at 1,100°C both in air and in steam. Composite microstructure, as well as damage and failure mechanisms were investigated.     

Thermogravimetric method for determination of oxygen stoichiometry in superconducting 1:2:3 and metal-substituted 1:2:3 compounds

The paper presents a modified thermogravimetric method for determination of oxygen stoichiometry of the oxide superconductors YBa₂Cu₃O_7−δ and metal-substituted compounds of the type YBa_2−x La _x Cu₃O_7+δ and YBa₂(Cu_1−x M _x )₃O_7−δ (M=Mg/Zn) between 25° and 930°C.     

Thermal decomposition of β-FeOOH

β-FeOOH particles were prepared by a forced hydrolysis of the 0.1 M FeCl₃ + 5·10⁻³ M HCl solution, whereas sulfated β-FeOOH particles were prepared by forced hydrolysis of the 0.1 M FeCl₃ solution containing 5·10⁻³ M quinine hydrogen sulfate (QHS). β-FeOOH particles, as well as sulfated β-FeOOH particles, were thermally treated up to 600 °C. The samples were characterized using DTA, XRD, FT-IR and TEM. β-FeOOH particles showed a cigar-type morphology, whereas bundles of β-FeOOH needles were obtained in the presence of QHS. Heating of β-FeOOH particles at 300 °C and above yielded α-Fe₂O₃ particles. Specific adsorption of sulfate groups showed a strong effect on the thermal decomposition of β-FeOOH particles. Upon heating of sulfated particles between 300 and 500 °C the formation of an amorphous phase and a small fraction of α-Fe₂O₃ were observed. Needle-like morphology of amorphous particles in these samples was preserved. At 600 °C, α-Fe₂O₃ particles were obtained; however, they were much smaller than those obtained by heating a pure β-FeOOH.     

Synthesis,structure and characterization of ceramic Ca4Bi2Ti4Nb6O30

The polycrystalline samples of Ca₄Bi₂Ti₄Nb₆O₃₀ (herein designated CBTN) were synthesized by the conventional ceramic method. Preliminary X-ray structural study of the compound showed the formation of a single phase solid solution having orthorhombic structure in the paraelectric phase. Measurements of the dielectric constant (ε) and dielectric loss (tan δ) as a function of temperature (−180–200°C) at 1 kHz and 10 kHz and also as a function of frequency (10² Hz to 10⁴ Hz) at five different temperatures [−180°C, −40°C, − 10°C 26°C (room temperature) and 75°C] have shown a dielectric anomaly and a phase transition at − 13 ±1°C in CBTN.     

Investigation of the quasi-ternary system LaMnO3–LaCoO3–“LaCuO3”. II: The series LaMn0.25?xCo0.75?xCu2xO3?δ and LaMn0.75?xCo0.25?xCu2xO3?δ

This paper investigates the crystal structure, thermal expansion, and electrical conductivity of two series of perovskites (LaMn_0.25−x Co_0.75−x Cu_2x O_3−δ and LaMn_0.75−x Co_0.25−x Cu_2x O_3−δ with x = 0, 0.025, 0.05, 0.1, 0.15, 0.2, and 0.25) in the quasi-ternary system LaMnO₃–LaCoO₃–“LaCuO₃”. The Mn/Co ratio was found to have a stronger influence on these properties than the Cu content. In comparison to the Co-rich series (LaMn_0.25−x Co_0.75−x Cu_2x O_3−δ), the Mn-rich series (LaMn_0.75−x Co_0.25−x Cu_2x O_3−δ) showed a much higher Cu solubility. All compositions in this series were single-phase materials after calcination at 1100 °C. The Co-rich series showed higher thermal expansion coefficients (α_max = 19.6 × 10⁻⁶ K⁻¹) and electrical conductivity (σ_max = 730 S/cm at 800 °C) than the Mn-rich series (α_max = 10.6 × 10⁻⁶ K⁻¹, σ_max = 94 S/cm at 800 °C). Irregularities in the thermal expansion curves indicated phase transitions at 150–350 °C for the Mn-rich series, while partial melting occurred at 980–1000 °C for the Co-rich series with x > 0.15. I. Arul Raj—on leave from Central Electrochemical Research Institute, Karaikudi, 630006 India.     

Studies on tin oxide films prepared by electron beam evaporation and spray pyrolysis methods

Transparent conducting tin oxide thin films have been prepared by electron beam evaporation and spray pyrolysis methods. Structural, optical and electrical properties were studied under different preparation conditions like substrate temperature, solution flow rate and rate of deposition. Resistivity of undoped evaporated films varied from 2.65 × 10⁻² ω-cm to 3.57 × 10⁻³ ω-cm in the temperature range 150–200°C. For undoped spray pyrolyzed films, the resistivity was observed to be in the range 1.2 × 10⁻¹ to 1.69 × 10⁻² ω-cm in the temperature range 250–370° C. Hall effect measurements indicated that the mobility as well as carrier concentration of evaporated films were greater than that of spray deposited films. The lowest resistivity for antimony doped tin oxide film was found to be 7.74 × 10⁻⁴ ω-cm, which was deposited at 350°C with 0.26 g of SbCl₃ and 4 g of SnCl₄ (SbCl₃/SnCl₄ = 0.065). Evaporated films were found to be amorphous in the temperature range up to 200°C, whereas spray pyrolyzed films prepared at substrate temperature of 300– 370°C were poly crystalline. The morphology of tin oxide films was studied using SEM.     

Diffusion in the CuSn binary system: application to Nb3Sn composites

Non-parabolic growth of intermediate phases in CuSn binary diffusion couples has been observed at 220° C. The deviation from parabolic behaviour may be attributed to grain boundary diffusion. Diffusion coefficients for both the∈-(Cu₃Sn) andη-(Cu₆Sn₅) phases are typically of the order of 2×10⁻¹¹ cm² sec⁻¹, and are in general agreement with other published values.     

Superconducting YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−δ</Subscript> thick film (T<Subscript>c</Subscript>(0) = 92 K) on a newly developed perovskite ceramic substrate

A complex perovskite oxide, YbBa₂NbO₆, as a non-reacting substrate for YBa₂Cu₃O_7-° super-conducting film has been developed. The dielectric constant and loss factor values of the material are in the range suitable for its use as substrate for microwave applications. A YBa₂Cu₃O_7−δ superconducting thick film dip coated on YbBa₂NbO₆ substrate gave a T_c (0) of 92 K and current density of ∼ 1.3 × 10⁴ A cm⁻².     

High rate performance of LiFePO<Subscript>4</Subscript> cathode materials co-doped with C and Ti<Superscript>4+</Superscript> by microwave synthesis

Nanostructured LiFePO₄ powder with a narrow particle size (ca. 100 nm) for high rate lithium-ion battery cathode application was obtained by microwave heating and using citric acid as carbon source. The microstructures and morphologies of the synthesized materials were investigated by X-ray diffraction and scanning electron microscope while the electrochemical performances were evaluated by galvanostatic charge-discharge. The carbon coating and Ti⁴⁺ could improve the conductivity both between the LiFePO₄ particles and the intrinsic electronic conductivity. The LiFePO₄ doped with 5% C and 1% Ti⁴⁺ resulted in a specific capacity of 114·95 mAh·g⁻¹ and 102·4 mAh·g⁻¹ at discharge rates of 0·3C and 1C, respectively, and the cycle performance is very good.     

Structure and superconductivity of Gex Cu1−x alloy films

Structural studies of Ge_x - Cu_1?x alloy films show that for x >0.80 300 K deposited films are found to be amorphous. On in situ heating these samples to ～ 100°C, a discrete, crystalline, second phase particles of Cu₃ Ge (?) compound appear in the amorphous matrix of Ge. For x ? 0.8 crystallites of Cu₃ Ge can be detected in amorphous Ge at room temperature. At higher Cu concentration (x < 0.4) in addition to crystalline Cu₃ Ge and Ge, free copper is detected. These structural studies suggest that the superconductivity behavior observed in the quenched alloy films presumably arise from small crystallites of Cu₃ Ge embedded in the amorphous matrix of Ge.