Elastic properties of powders during compaction. Part 1: Pseudo-isotropic moduli

The elastic moduli of powdered materials undergoing uniaxial compaction was investigated, paying particular attention to effects of solid phase material properties and initial particle shape. Elastic properties were characterised by the isotropic elastic moduli Poisson’s ratio and Young’s modulus, calculated from elastic wave speeds measured in the axial (pressing direction). To isolate material property effects, three different ductile metal powders (copper, stainless steel, and aluminium) with equivalent particle shape (spheroidal) were tested. Comparison with similar measurements for a brittle spheroidal powder (glass) illustrated that solid phase yield mechanism affects the evolution of pore character, and hence bulk elastic properties of the powder compact. Pore character was also studied separately by comparing copper powders with differing particle shapes (spheroidal, irregular, and dendritic). For all powders, Young’s modulus increased monotonically with compaction (reducing porosity). For the ductile spheroidal powders, differences in evolution of Young’s modulus with compaction were accounted for by solid phase elastic properties. The different morphology copper powders showed an increase in compact compliance as particle (pore) ruggedness increased. Poisson’s ratio followed a concave porosity dependence: decreasing in the initial stages of compaction, then increasing as porosity approached zero. Comparison between powders indicated the initial decrease in Poisson’s ratio was insensitive to solid phase material properties. However, as the compact approached solid phase density, the Poisson’s ratio—porosity locus diverged towards corresponding solid phase values for each particle material, indicating an influence of solid phase elastic properties.     

Structural Studies of Nanocrystalline Nitrogen–Helium Solids by Raman Spectroscopy

Structural and thermal properties of nanocrystalline nitrogen–helium solids are studied by Raman spectroscopy at temperature range 1.8–41 K. The N₂ vibrational line possesses spectral structure very similar to what is observed in bulk solid nitrogen, indicating ordered structure inside the nanocrystallites. The spectral observations show that the structure of the solid is dependent on the N₂ content in the gas mixture used for sample preparation. Evidence for disordered nitrogen on the surfaces and interfaces of nanocrystallites can be extracted from the Raman spectra of the most diluted samples. Removing superfluid helium from the sample and annealing at 21 K did not affect the structure of the solid, whereas higher annealing temperatures yielded strong increase of density as evidenced by the up to ∼10-fold increase of Raman signal. The α-solid—β -solid transition, evidenced by a ∼0.8 cm⁻¹ shift in the peak position, was seen in the collapsed nitrogen samples approximately at the same temperature as in a solid nitrogen film.     

Growth mechanism and multiphoton-induced photoluminescence of crownlike zinc oxide

A crownlike zinc oxide crystal composed of a hexagonal cap and a towerlike shaft was synthesized by vapor-phase transport method. Based on vapor–liquid–solid and vapor–solid mechanism, the growth model of the crystal was proposed. Under the excitation of pulse laser with 1150-nm wavelength, strong ultraviolet emission at 388 nm was observed. The peak position and the relationship between the emission intensity and excitation intensity demonstrated that the ultraviolet photoluminescence was induced by three-photon absorption. The photoluminescence characteristic of the sample was investigated.     

Effect of compound organification of montmorillonite on the structure and properties of polypropylene/montmorillonite nanocomposites

In this paper, reactive organic montmorillonite (RMMT), prepared with compound alkylammoniums, were used in ternary-monomer solid phase graft copolymerization in order to enhance the melting intercalation of montmorillonite (MMT), stabilize the intercalated structure, and prepare the exfoliated polypropylene/montmorillonite (PP/MMT) nanocomposites (PPMN). The structure and properties of PPMN were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), etc. Results show that the compound organification, solid phase graft copolymerization really favored the melting intercalation. The compound organification and exothermic process of the solid phase copolymerization promoted the melting intercalation. The mechanical properties, melt flow rate and Vicat softening point of PPMN significantly had a preferable reinforced state at 6–8 phr PP/MMT graft copolymers (PPGM). The increase of the mechanical properties and thermal properties was owed to the reinforcement of the exfoliated MMT and the compatibilization of the oligomers built by the polar monomers during the solid phase graft copolymerization. The improvement of the fluidity of PPMN derived from the plasticization of the exfoliated MMT and oligomers. Translated from Chinese Journal of Materials Research, 2006, 20(2): 197–202 [译自: 材料研究学报]     

Role of dispersion conditions on grindability of yttria stabilized zirconia (YSZ) powders

A precursor for zirconia - 8 mole% yttria (YSZ-ZrO₂-8 m% Y₂O₃) powder was prepared by coprecipitation and the calcination temperature was fixed as 900°C from TG-DTA and XRD studies. The calcined powder could be dry ground only to a mean particle size (D₅₀) of 6 Μm containing substantial amount of coarse agglomerates in the size range 10–100 Μm. The dispersion conditions for its wet grinding were evaluated through zeta-potential and viscosity studies. The zeta-potential variation with pH of the aqueous suspensions of the powder exhibited maximum numerical values at 3 and 11 pH, exhibiting the ideal pHs for dispersion stability through electrostatic columbic repulsion mechanism. Slurries of dry ground powders with solid concentration in the range 15–30 vol.% exhibited pseudo-plastic flow characteristics, indicating presence of flocculates. With progress of grinding, the increase in viscosity of the slurries became less significant with decreasing solid concentration. Even though the particle size of the ground slurries decreased with decreasing solid content, there was little change in it for slurries with solid content < 20 vol.%. Grinding conditions for formation of sinter-active powders of YSZ with sub-micron size (D ₅₀ ∼ 0.7 Μm free of agglomerates of size > 5 Μm) were established. Compacts from this powder could be sintered at 1400°C to translucent bodies with 99% theoretical density.     

Phase transformation and precipitation hardening behavior of Cr and Fe in BS40CrFeSn alloy

Phase transformation and precipitation hardening behavior of the water atomized copper alloy powder was studied by aging treatment, to develop high strength Cu–40Zn–X (X: Cr, Fe, Sn) alloys by powder metallurgy process. Super-saturated solid solution elements of Cr and Fe are formed in the brass matrix, and single β phase was retained in the raw powder after water atomization. Solid solubility of Cr and Fe decreased with increase of aging temperature, and phase transformation evolved from single β phase to α + β duplex phase structure after aged at the elevated temperature of 773 K and over. It was clarified that Cr showed higher precipitation potential than Fe in the brass matrix. The hardness depended strongly upon solid solubility of Cr and Fe, and upon phase transformation.     

Synthesis of a lightweight Ti–10Al–5Mg (wt.%) alloy by mechanical alloying followed by compaction and sintering

A lightweight Ti–10Al–5Mg (wt.%) alloy was synthesized by mechanical alloying followed by cold compaction and sintering. A metastable hcp α-Ti(Al,Mg) solid solution was obtained after 5 h of milling. The c/a ratio of the hcp structure was found to increase with milling time. The particle size distribution of the mixture becomes broader and the dp50 value decreases as the milling time increases. The structure of the 900 and 1,100 °C sintered samples consist of an α-Ti(Al) solid solution matrix with α₂-Ti₃Al and MgO precipitates. Values of 11 and 188 GPa were obtained for the Hardness and Young’s modulus of 1,100 °C sintered sample, respectively, confirming the strength improvement of the Ti-based alloy.     

structure and transport properties of Li1-2xCo1+xVO4 lithium ionic conductors

Li_1-2xCo_{1 +x} VO₄ (0 ≤x ≤ 0.25) spinel solid solutions were synthesized and characterized by x-ray diffraction and IR spectroscopy. The materials were found to have a cubic structure in the composition range 0 ≤x ≤ 0.1 and an orthorhombic structure forx> 0.1. The observed lattice distortions were shown to correlate with Co content. The conductivity of the solid solutions was measured as a function of temperature and oxygen partial pressure. The ionic and electronic (n andp) conductivities were determined. The conduction in the solid solutions was shown to be dominated by Li⁺ ions.     

Electronic conductivity of Sr3-3xLa2x█x(VO4)2 solid solutions

The electronic conductivity of Sr_3-3xLa_2x█_x(VO₄)₂ solid solutions was measured at oxygen pressures from 10^-13 to 10⁵ Pa and temperatures from 1070 to 1270 K, and their band gap was determined as a function of composition. The activation energy (≏2.85 eV) and enthalpies of electron generation (≏4.2 eV) and migration (≏0.75 eV) were determined. A correlation between the band gap and electronic conductivity of the solid solutions was revealed     

Preparation of metal alloy powder by semi-solid processing

A laboratory study was carried out, using Pb–15 wt.% Sn alloy on self-made apparatus, to determine the solidification behavior of the semi-solid slurry with the solid fraction beyond 0.6. It is found that the solid–liquid separation is obvious in the samples with the solid fraction beyond 0.6. According to this character of semi-solid processing, a kind of single-crystal powder coated with Pb–Sn eutectic was made during continuous stirring and cooling processes. The analysis and discussion indicated that this approach can reduce the content of oxide and impurity in the powder.     

Thermal-Conductivity Measurements and Predictions for Ni–Cr Solid Solution Alloys

Thermal conductivities of Ni–Cr solid solution alloys have been measured to develop a prediction equation for thermal conductivities as functions of temperature and chemical composition. Samples used were Ni–x at% Cr (0 ≤ x ≤ 22) and commercial alloys of Nichrome Nos. 1 and 2. Thermal conductivity measurements were carried out using the transient hot-strip method over a temperature range from 293 K to 1273 K. The thermal conductivities of the alloys increased with increasing temperature and decreased with increasing Cr concentration at constant temperature. The Smith–Palmer equation has been examined to relate the thermal conductivities of the alloys to the electrical resistivities. The thermal conductivity and electrical-resistivity data, respectively, in the present work and in the literature have confirmed that the Smith–Palmer equation applies to Ni–Cr solid solutions and Nichrome alloys. On the basis of this equation, the thermal conductivity of Ni–Cr solid solution alloys has been expressed as a function of temperature and chemical composition. This analysis has also been applied to Ni–Fe and Cu–Ni solid solution alloys.     

Atmospheric pressure solvothermal synthesis of ceria–zirconia solid solutions and their large oxygen storage capacity

Ceria–zirconia solid solution has a function as an oxygen storage material, which keeps air to fuel ratio (A/F) on a stoichiometric composition at the surface of three-way catalyst (TWC) for automotive exhaust. When A/F could be kept stoichiometric, TWC shows good catalytic activity. At first, ceria which dissolves 20 mol% of zirconia was developed by Ozawa et al. in 1987. After that, the ceria–zirconia solid solution was improved to achieve a complete solubility in the solid state at nano-level by surfactant modified homogeneous coprecipitation (J catal 169:490, 1997). Nano-level solid solution of ceria and zirconia could have been made by various methods. Those materials have similar amount of oxygen storage capacity (OSC). The improvement of OSC comes from the larger amount of bulk oxygen that can contributes OSC by the larger amount of zirconia dissolving into ceria (Catal Lett 33(1–2):193–200 1995). Solvothermal synthesis is usually done in a higher temperature than that can be reached under atmospheric pressure. The higher temperature accelerates generation of precipitation; however, a pressure vessel is necessary, and such a hermetically closed system is unsuitable to the material synthesis of the low-value-added product. Atmospheric pressure solvothermal (APS) synthesis was applied to ceria-zirconia solid solutions in this study. The APS ceria-zirconia showed larger amount of OSC. The excellent OSC performance was presumed to come from further uniformity of zirconium ions in the ceria lattice.     

Synthesis and characterization of β type solid solution in the binary system of Bi2O3-Eu2O3

We have investigated Bi₂O₃-Eu₂O₃ binary system by doping with Eu₂O₃ in the composition range from 1 to 10 mole% via solid state reactions and succeeded to stabilize β-Bi₂O₃ phase which is metastable when pure. Stability of β-Bi₂O₃ polymorph was influenced by heat treatment temperature. Tetragonal type solid solution was obtained in 3–6 mole% addition range when annealed at 750°C and the range was 2–7 mole% when annealed at 800°C. We have also carried out investigations on lattice parameters, microstructural properties and elemental compositions of this β type solid solution for each doping ratio. Lattice parameters increased with amount of Eu₂O₃ addition. Our experimental observations strongly suggested that oxygen deficiency type non-stoichiometry is present in doped β type solid solutions.     

Thermoelectric power of ferroelectric potassium vanadate,cesium vanadate,lithium vanadate and their solid solutions

The thermoelectric power of the vanadates of potassium, cesium and lithium and their solid solutions was measured in the temperature range covering their transition points. The thermoelectric power measurement was carried out by the two-electrode technique for pellets of polycrystalline ceramic samples. The thermoelectric power increased with temperature initially, then decreased attaining a zero value at the transition temperature. As the concentration of KVO₃ increased the thermoelectric power decreased for the solid solutions (K _x − Cs_1−x )VO₃, whereas the thermoelectric power increased with increase in concentration of KVO₃ for the solid solutions (K _x − Li_1−x )VO₃. Vanadates of potassium, cesium, and lithium and their solid solutions showedP type semiconductor behaviour in ferroelectric state andn type semiconductor behaviour in paraelectric region.     

Deformation-driven formation of equilibrium phases in the Cu–Ni alloys

The homogeneous coarse-grained (CG) Cu–Ni alloys with nickel concentrations of 9, 26, 42, and 77 wt% were produced from as-cast ingots by homogenization at 850 °C followed by quenching. The subsequent high-pressure torsion (5 torsions at 5 GPa) leads to the grain refinement (grain size about 100 nm) and to the decomposition of the supersaturated solid solution in the alloys containing 42 and 77 wt% Ni. The lattice spacing of the fine Cu-rich regions in the Cu–77 wt% Ni alloy was measured by the X-ray diffraction (XRD). They contain 28 ± 5 wt% Ni. The amount of the fine Ni-rich ferromagnetic regions in the paramagnetic Cu–42 wt% Ni alloy was estimated by comparing its magnetization with that of fully ferromagnetic Cu–77 wt% Ni alloy. According to the lever rule, these Ni-rich ferromagnetic regions contain about 88 wt% Ni. It means that the high-pressure torsion of the supersaturated Cu–Ni solid solutions produces phases which correspond to the equilibrium solubility limit at 200 ± 40 °C (Cu–77 wt% Ni alloy) and 270 ± 20 °C (Cu–42 wt% Ni alloy). To explain this phenomenon, the concept of the effective temperature proposed by Martin (Phys Rev B 30:1424, 1984) for the irradiation-driven decomposition of supersaturated solid solutions was employed. It follows from this concept that the deformation-driven decomposition of supersaturated Cu–Ni solid solutions proceeds at the mean effective temperature T _eff = 235 ± 30 °C. The elevated effective temperature for the high-pressure torsion-driven decomposition of a supersaturated solid solution has been observed for the first time. Previously, only the T _eff equal to the room temperature was observed in the Al–Zn alloys.     

Method for increasing <Emphasis Type="Italic">β</Emphasis>-SiC yield on solid state reaction of coal fly ash and activated carbon powder

A novel process for increasing β-SiC yield on solid state reaction of coal fly ash and micro powder activated carbon powder has been proposed. β-SiC powder was synthesized at temperature 1300°C for 2 h under vacuum condition with 1 l/min argon flow. Cycling synthesis process has been developed for increasing β-SiC yield on solid state reaction of coal fly ash and activated carbon powder. Synthesized products were analyzed by XRD with Cu-Kα radiation, FTIR spectrometer and SEM fitted with EDAX. The results show that the amount of relative β-SiC is increased with the number of cycling synthesis.     

Measurement of Gibbs energies of formation of CoF2 and MnF2 using a new composite dispersed solid electrolyte

Gibbs energies of formation of CoF₂ and MnF₂ have been measured in the temperature range from 700 to 1100 K using Al₂O₃-dispersed CaF₂ solid electrolyte and Ni+NiF₂ as the reference electrode. The dispersed solid electrolyte has higher conductivity than pure CaF₂ thus permitting accurate measurements at lower temperatures. However, to prevent reaction between Al₂O₃ in the solid electrolyte and NiF₂ (or CoF₂) at the electrode, the dispersed solid electrolyte was coated with pure CaF₂, thus creating a composite structure. The free energies of formation of CoF₂ and MnF₂ are (± 1700) J mol⁻¹; {fx37-1} The third law analysis gives the enthalpy of formation of solid CoF₂ as ΔH° (298·15 K) = −672·69 (± 0·1) kJ mol⁻¹, which compares with a value of −671·5 (± 4) kJ mol⁻¹ given in Janaf tables. For solid MnF₂, ΔH°(298·15 K) = − 854·97 (± 0·13) kJ mol⁻¹, which is significantly different from a value of −803·3 kJ mol⁻¹ given in the compilation by Barinet al.     

Instability of solid–liquid interface in transitional metal–carbide systems

The instability of solid–liquid interface (ISLI) during the liquid-phase sintering was studied using carbide–Ni composites. Of the various transitional metal carbides TiC of 4th period is the only carbide that exhibits a strong ISLI with negative curvatures in molten Ni. No ISLI was observed for other carbides in the 5th and 6th periods. The origin of ISLI is strain developed at the interface between the carbides and the newly formed solid solutions. The difference in the size of the atoms involved can be used to predict the formation of a carbide–Ni solid solution when the Hume-Rothery rules are applied. Aside from the size factor, other factors in the rules are not effective in predicting this phenomenon.     

Low-temperature immobilization of liquid radioactive waste using silica from concentrated hydrothermal solutions

Experiments on vitrification of simulated liquid radioactive waste (LRW) were performed. To obtain solid glass-like phases, LRW components were treated with aqueous-alcoholic hydrochloric acid solutions containing hydrolyzates of alkyl silicates and aqueous silica sols obtained by membrane concentration of a natural hydrothermal solution. The pH of the mixture was 1.5–4. The characteristics of the solid samples obtained were studied by X-ray phase analysis, thermogravimetry, and scanning electron microscopy. A procedure was developed for low-temperature (5–60°C) immobilizaiton of low-level LRW using aqueous silica sols.     

High-temperature equilibrium between YBa2Cu3-xCoxO6+δ solid solutions and oxygen

The equilibrium oxygen content of YBa₂Cu_3-xCo_xO_6+δ (0.2 ≤x ≤ 0.8) solid solutions was determined by coulometric titration at temperatures in the range 600–850°C and oxygen pressures 1 ≤po ₂ ≤ 10⁵ Pa. The partial enthalpy and entropy of oxygen dissolution were evaluated as a function of composition. The thermodynamic functions were found to change sharply near the high- and low-oxygen limits of the solid solution. The results are interpreted in terms of a quasi-chemical model considering three inequivalent oxygen sites in the basal plane.