Ultrasound velocity and absorption in BeO,Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, ZrO<Subscript>2</Subscript>, and SiO<Subscript>2</Subscript> ceramics

We have measured the ultrasound velocity and absorption in BeO, Al₂O₃, ZrO₂, and SiO₂ ceramics. The results indicate that the ultrasound velocity in oxide ceramics depends on the nature of the basic oxide component, the density of the material, and the preferential alignment of the grains. The ultrasound velocity in ceramics is shown to correlate with their thermal conductivity: with increasing thermal conductivity, the ultrasound velocity increases. The ultrasound absorption in oxide ceramics decreases with decreasing temperature, and vice versa, with increasing temperature, the ultrasound attenuation coefficient increases.     

Mechanical properties of bovine hydroxyapatite (BHA) composites doped with SiO<Subscript>2</Subscript>, MgO,Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, and ZrO<Subscript>2</Subscript>

Biologically derived hydroxyapatite from calcinated (at 850 °C) bovine bones (BHA) was doped with 5 wt% and 10 wt% of SiO₂, MgO, Al₂O₃ and ZrO₂ (stabilized with 8% Y₂O₃). The aim was to improve the sintering ability and the mechanical properties (compression strength and hardness) of the resultant BHA-composites. Cylindrical samples were sintered at several temperatures between 1,000 and 1,300 °C for 4 h in air. The experimental results showed that sintering generally occurs at 1,200 °C. The BHA–MgO composites showed the best sintering performance. In the BHA–SiO₂ composites, extended formation of glassy phase occurred at 1,300 °C, resulting in structural degradation of the resultant samples. No sound reinforcement was achieved in the case of doping with Al₂O₃ and zirconia probably due to the big gap between the optimum sintering temperatures of BHA and these two oxides.     

Microstructure and high-temperature strength of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Er<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>/ZrO<Subscript>2</Subscript> ternary melt growth composite

A new Al₂O₃/Er₃Al₅O₁₂(EAG)/ZrO₂ ternary MGC (Melt Growth Composite) with a novel microstructure has been fabricated by unidirectional solidification. This ternary MGC has a microstructure consisting of continuous networks of single-crystal Al₂O₃, single-crystal EAG and fine cubic-ZrO₂ phases without grain boundaries. The ternary MGC has also characteristic dimensions of the microstructure of around 2–4 m for EAG phases, around 2–4 m for Al₂O₃ phases reinforced with around 0.4–0.8 m cubic-ZrO₂ phases. No amorphous phases are formed at interfaces between phases in the ternary MGC. The ternary MGCs flexural strength at 1873 K is approximately 700 MPa, more than twice the 330 MPa of the Al₂O₃/EAG binary MGC. The fracture manner of the Al₂O₃/EAG/ZrO₂ ternary MGC at 1873 K shows the same intergranular fracture as the Al₂O₃/EAG binary MGC, but is significantly different from the transgranular fracture of the sintered ceramic.     

Formation and structural phase transitions of mesoporous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and TiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> xerogels under hydrothermal conditions

We have studied the effect of the hydrothermal synthesis temperature on Al₂O₃ structure formation and examined the role of the phase composition of the precursor gel and surfactant in the formation of the pore structure of Al₂O₃. A technique has been proposed for the synthesis of TiO₂/Al₂O₃ binary xerogels, and the effect of TiO₂ content on the pore structure parameters and adsorption properties of TiO₂/Al₂O₃ has been investigated.     

Effects of TiO<Subscript>2</Subscript>, ZrO<Subscript>2</Subscript> and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> dopants on the compressive strength of tricalcium phosphate

Tricalcium phosphate (TCP) powders synthesised using the Ca(NO₃)₂ and Ca(OH)₂ routes were doped with TiO₂, ZrO₂ and Al₂O₃ in order to increase their compressive strength. An ultimate compressive strength (UCS) of 255 ± 6 MPa was achieved for approximately 10 vol% TiO₂ doping compared to 30 ± 3 MPa for an un-doped control processed and tested in the same manner. Higher levels of TiO₂ doping resulted in smaller increases in UCS with 30 and 50 vol% achieving 213 ± 9 and 178 ± 15 MPa, respectively. Very small amounts of Al₂O₃ doping (< 0.5 vol%) also resulted in a stronger materials. However, under the processing conditions employed, higher levels of Al₂O₃ and ZrO₂ doping resulted in no beneficial effect on the UCS. Polyvinyl alcohol (PVA) was used as binding agent to facilitate processing. As expected, higher levels of PVA were associated with smaller increases in UCS. Powders synthesised using the Ca(OH)₂ route had smaller particle size and resulted in larger increases in UCS compared to the Ca(NO₃)₂-synthesised powders. Although some powders contained α and β-TCP phases, no other calcium phosphate, CaO, CaTiO₃ or CaZrO₃ phases were detected. In conclusion, a significant increase in the UCS of TCP was achieved by doping with approximately 10 vol% TiO₂ which is expected to have little or no effect on the bioactivity or bioresorbability of the material.     

Temperature-Dependent Thermal Boundary Conductance at Al/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> interfaces

With the ever-decreasing size of microelectronic devices, growing applications of superlattices, and development of nanotechnology, thermal resistances of interfaces are becoming increasingly central to thermal management. Although there has been much success in understanding thermal boundary conductance at low temperatures, the current models applied at temperatures more common in device operation are not adequate due to our current limited understanding of phonon transport channels. In this study, the scattering processes in Al and Pt films on Al₂O₃ substrates are examined by transient thermoreflectance testing at high temperatures. At high temperatures, traditional models predict the thermal boundary conductance to be relatively constant in these systems due to assumptions about phonon elastic scattering. Experiments, however, show an increase in the conductance indicating potential inelastic phonon processes.     

Solubility of UF<Subscript>4</Subscript>, ThF<Subscript>4</Subscript>, and CeF<Subscript>3</Subscript> in a LiF-NaF-KF melt

The solubility of UF₄, ThF₄, and CeF₃ in fluoride melt of the composition 45 mol % LiF-12 mol % NaF-43 mol % KF in the temperature interval 773–973 K was determined. The solubility of the fluorides increases with an increase in the melt temperature. The CeF₃ solubility in the LiF-NaF-KF system is high: 19.9 mol % at 923 K and 23.3 mol % at 973 K. Experimental data on the solubility of CeF₃ (PuF₃ imitator) were compared to the calculated data on the PuF₃ solubility in the LiF-NaF-KF melt. The results showed that CeF3 can be considered as PuF3 imitator in FLINAK melt.     

Ceramics Based on Powder Mixtures Containing Calcium Hydrogen Phosphates and Sodium Salts (Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>, Na<Subscript>4</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>, and NaPO<Subscript>3</Subscript>)

Ceramic materials in the Na₂O–CaO–P₂O₅ system have been produced using powder mixtures containing calcium hydrogen phosphates (monetite/brushite: CaHPO₄/CaHPO₄ ? 2H₂O) and sodium salts (Na₂CO₃ ? H₂O, Na₄P₂O₇ ? 10H,O, and NaPO₃). These salts were used as precursors to the following high-temperature phases: Сa₂P₂O₇, Na₂O, Na₄P₂O₇, and NaPO₃. The amount of the salts in the powder mixtures was such that the oxide composition of the ceramics corresponded to 10 mol % sodium oxide for each mixture in the Na₂O–CaO–P₂O₅ system. The powder mixtures were prepared using mechanical activation in acetone, which was accompanied by monetite rehydration to brushite. X-ray diffraction characterization showed that, after firing, the phase composition of the ceramics produced from the powder mixtures thus prepared lay in the Сa₂P₂O₇–NaCaPO₄–Na₂СaP₂O₇–Са(РО₃)₂ phase field. The resultant ceramic materials contain biocompatible and bioresorbable phases and can be recommended for bone implant fabrication.     

Growth of Rare-Earth-Doped K<Subscript>2</Subscript>LaCl<Subscript>5</Subscript>, K<Subscript>2</Subscript>BaCl<Subscript>4</Subscript>, and K<Subscript>2</Subscript>SrCl<Subscript>4</Subscript> Single Crystals

Processes are described for the synthesis and melt growth of rare-earth-doped K₂LaCl₅, K₂BaCl₄, and K₂SrCl₄, using rare-earth oxides as starting materials. The solubility of rare-earth activators in Bridgman-grown crystals are determined, and the spectroscopic properties of K₂LaCl₅〈Nd〉 crystals are investigated.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 748–752.Original Russian Text Copyright © 2005 by Vinogradova, Galagan, Dmitruk, Moiseeva, Osiko, Sviridova, Brekhovskikh, Fedorov.     

Structural,Magnetic, and Optoelectronic Properties of TbNi<Subscript>5</Subscript>, TbNi<Subscript>3</Subscript>Ti<Subscript>2</Subscript> and TbNi<Subscript>3</Subscript>V<Subscript>2</Subscript> Compounds

The spin-polarized, electronic, magnetic, and optical properties of TbNi₅, TbNi₃Ti₂, and TbNi₃V₂ intermetallic compounds have been calculated by employing the full-potential linear augmented plane waves (FP-LAPW) within the density functional theory (DFT) and implemented in the WIEN2k package. In this approach, the generalized gradient approximation with Hubbard U-correction (GGA + U) was chosen as exchange-correlation potential. The electronic structure such as band structure and density of states have been investigated and compared among them. The frequency dependences of dielectric function, optical absorption, reflectivity, and optical conductivity are determined. The optical spectra are changed due to the substitution of nickel with titanium and vanadium. Total and local magnetic moments of Tb, Ni, Ti, and V are also estimated; it is shown that the total magnetic moment of the three alloys is vigorously contributed by the local magnetic moment of terbium.     

Fabrication of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite nanofibers by electrospinning

PVA(Polyvinyl alcohol)/chromium nitrate/aluminum nitrate composite nanofibers were prepared by using sol–gel processing and electrospinning technique. By high temperature calcinating the above precursor fibers, Cr₂O₃/Al₂O₃ composite nanofibers were successfully obtained. The fibers were characterized by XRD, IR, and SEM, respectively. The results showed that the crystalline phase and the morphology of the fibers depended on the calcination temperatures.     

Phase developments in Pb(Mg<Subscript>1/2</Subscript>W<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> and Pb(Zn<Subscript>1/2</Subscript>W<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> via B-site precursor route

Phase formation stages of MgWO₄ and ZnWO₄ (precursor compositions for following steps) were investigated by monitoring the reactions of oxide chemicals at various temperatures. Developed phases were examined by using X-ray diffraction (XRD). Successive attempts were also conducted for Pb(Mg_1/2W_1/2)O₃ (PMW) and Pb(Zn_1/2W_1/2)O₃ (PZW) by reacting PbO with the precursor compounds. Stages of phase development in the two compositions were also analyzed. The results are compared with those of another tungsten-containing perovskite Pb(Fe_2/3W_1/3)O₃ (PFW) and its B-site precursor Fe₂WO₆. After PbO addition to the precursor powders, a perovskite phase formed directly (i.e., without any intermediate phases) in the case of PMW. For PbO + ½ZnWO₄, in contrast, the decomposition of ZnWO₄ and preferential reaction with PbO resulted in Pb₂WO₅ and ZnO, instead of the perovskite PZW.     

Role of Ti diffusion on the formation of phases in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> brazed interface

Diffusivities of Ti, Cu, Al and Ag in the interface of Al₂O₃–Al₂O₃ braze joints using Ag–Cu–Ti active filler alloy, have been calculated by Matano–Boltzman method. The Matano plane has been identified for each elemental diffusion at various brazing temperatures. The diffusivities of Ag, Cu and Al are almost insignificant on formation of interface during brazing, whereas the diffusivity of Ti changes significantly with the brazing temperature and controls the formation of different reaction product in the interface. Presence of TiO and Ti₃Cu₃O phases in the interface has been confirmed by transmission electron microscopy (TEM).     

Directional solidification and growth characteristics of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Er<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>/ZrO<Subscript>2</Subscript> ternary eutectic ceramic by laser floating zone melting

Directionally solidified Al₂O₃/Er₃Al₅O₁₂/ZrO₂ ternary eutectic ceramic in situ composite rods with length of 110 mm have been fabricated by laser floating zone melting. The microstructural characteristics of steady growth zone, initial growth zone and solid/liquid interface are investigated under high temperature gradient. In the steady growth zone, the eutectic spacing (λ) is rapidly decreased as increasing the growth rate (V), and the corresponding relationship between growth rate and eutectic spacing is determined to be λ = 11.14 × V ^?1/2. The temperature gradient has been measured to be about 5.3 × 10³ K/cm. In the initial growth zone, the melting process and temperature distribution are recorded by infrared thermal imager, and several unstable complex microstructures are observed. In the quenched zone, the regular eutectics with minimum eutectic spacing of 200 nm are obtained. Moreover, the solid/liquid interface during solidification shows convex interface morphology and the interface height is gradually decreased as increasing the growth rate. The eutectic growth behaviors at the center and edge of the as-grown rod are compared and discussed.     

Valence-band offsets of InGaZnO<Subscript>4</Subscript>, LaAlO<Subscript>3</Subscript>, and SrTiO<Subscript>3</Subscript> heterostructures explained by interface-induced gap states

The intrinsic interface-induced gap states (IFIGS) which derive from the virtual gap states of the complex band structure are the fundamental mechanism that determines the band-structure lineup at semiconductor interfaces. The valence-band offsets of heterostructures are composed of a zero-charge-transfer term and an electrostatic-dipole contribution which are given by the difference of the p-type branch-point energies of the IFIGS and of the electronegativities, respectively, of the two semiconductors involved. The valence-band offsets of InGaZnO₄, LaAlO₃, and SrTiO₃ heterostructures are quantitatively and consistently explained by the IFIGS-and-electronegativity concept. The analysis of the experimental InGaZnO₄, LaAlO₃, and SrTiO₃ data yields the p-type branch-point energies as 2.37?±?0.18 eV, 2.59?±?0.13 eV, and 2.86?±?0.14 eV, respectively.     

Systematic investigation of the effect of oxygen mobility on CO oxidation over AgPt nanoshells supported on CeO<Subscript>2</Subscript>, TiO<Subscript>2</Subscript> and Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Here, we have systematically investigated how the nature of the support influenced the oxygen mobility and activities in catalysts comprised of AgPt nanoshells deposited over inorganic oxides. We first synthesized AgPt nanoshells by galvanic replacement reaction between Ag nanospheres and PtCl₆ ^2? _(aq) combined with Pt reduction using hydroquinone as an auxiliary reducing agent. The nanoshells were then supported over TiO₂, Al₂O₃ and CeO₂. Through this methodology, we prepared materials with similar metallic nanoparticle AgPt compositions (~0.99 wt% Pt), sizes (43 ± 2 nm diameter), spherical shapes, surface morphologies, number of active sites \( (\sim4.5\;\upmu{\text{mol}}\;{\text{g}}_{{{\text{cat}} .}}^{ - 1} ) \) and uniform distribution over the supports, differing only in terms of the nature of the support. The oxide reduction temperature, its capability of re-oxidation and the presence of oxygen mobility were strongly dependent on the metal–support interaction between AgPt nanoshells and oxide supports. These properties have significantly influenced their catalytic performances toward the CO oxidation. At 230 °C, the CO oxidation TOF was 40.4 ± 0.4, 6.9 ± 1, 1.4 ± 0.8 min^?1 for AgPt/CeO₂, AgPt/TiO₂, AgPt/Al₂O₃, respectively. These differences were attributed to the concentration of oxygen vacancies in each catalyst, which presented exactly the same trend as that of the catalytic activities. Our results may have important contributions to the design of highly active metal oxide-based catalysts toward gas-phase oxidation transformations.     

High-temperature thermodynamic properties of the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

High-temperature mass spectrometry is used to investigate vaporization processes and determine SiO₂ activity in the Al₂O₃-SiO₂ system between 1850 and 1970 K. The results are consistent with the known phase equilibria in this system.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 4, 2005, pp. 434–441.Original Russian Text Copyright © 2005 by Bondar, Lopatin, Stolyarova.     

Formation behavior of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> from CaTiO<Subscript>3</Subscript>, CuO and TiO<Subscript>2</Subscript>

The formation behavior of CaCu₃Ti₄O₁₂ (CCTO) had been investigated via solid state reaction from CaTiO₃, CuO and TiO₂ powders. In the temperature range from 750 to 1,200 °C, the reaction sequence was traced by XRD, and the microstructure evolution of calcined powders was also investigated by SEM. CCTO began to form owing to the reaction between CaTiO₃, CuO and TiO₂ at around 850 °C, and became the major phase at 1,000 °C. Finally, the single phase CCTO was obtained at 1,150 °C. However, CCTO was decomposed at CaTiO₃, CuO and TiO₂ when the temperature increased to 1,200 °C. In addition, no other intermediate phases occurred in the synthesized process. The formation behaviors indicated that CaTiO₃ prevented the formation and growth of CCTO.     

Thermochemical and luminescent properties of RbVO<Subscript>3</Subscript>, CsVO<Subscript>3</Subscript>, and Rb<Subscript>0.5</Subscript>Cs<Subscript>0.5</Subscript>VO<Subscript>3</Subscript>

RbVO₃, CsVO₃, and Rb_0.5Cs_0.5VO₃ have been synthesized by the Pechini process. The vanadates have an orthorhombic structure (sp. gr. Pbcm), melt congruently in the range 650–530°C, and undergo a reversible phase transition in the range 520–340°C. We have determined the onset temperatures and end points of the transformations at a temperature scan rate of 3°C/min and their enthalpies, and measured the photo-, roentgeno-, and cathodoluminescence and diffuse reflectance spectra of the vanadates. The luminescence spectra each are well fitted with three pseudo-Voigt functions. CsVO₃ has the highest integrated emission intensity. The emission intensity of the Rb_0.5Cs_0.5VO₃ solid solution is lower than that of the simple vanadates because of the optical absorption around its intrinsic luminescence band. This may be due to the presence of stable vacancy-type structural defects in Rb_0.5Cs_0.5VO₃.