Raman Spectra and the Structure of Melts in the Na2O–P2O5–SiO2System

Raman spectra of melts in the Na₂O–P₂O₅–SiO₂system are measured at high temperatures. The differences between the Raman spectra of melts and glasses with identical compositions are considered. It is demonstrated that the structural inhomogeneity of the system slightly increases with a decrease in temperature and vitrification of the melt.     

Ignition and phase formation in the Zr–Al–C system

The ignition mechanism and the dependence of the composition of the products of combustion or thermal explosion in a mixture of 2Zr + Al + C on the initiation temperature and heat transfer conditions were studied. Heat transfer conditions were changed by varying the size of the samples and the gaseous medium in which the experiments were performed. Two contusion regimes were found: a low-temperature regime, in which zirconium aluminides formed and carbon and part of the zirconium remained unreacted, and a high-temperature regime in which the reaction products were zirconium carbide and aluminide. Upon re-initiation, the low-temperature combustion products reacted in the high-temperature combustion regime. The observed dependences are due to parallel reactions in the three-component system.     

Relationship Between the Synthesis and Structure of Ceramic Precursors of the TiO2–CeO2–ZrO2 System

Refractories and Industrial Ceramics - Tetragonal solid solutions based on the TiO2–CeO2–ZrO2 system stable up to 1,350°C were obtained. A method of pH titration of the initial...     

Phase Equilibriums in the Al2O3–SiO2–ZrO2 System: Calculation and Experiment

Glass Physics and Chemistry - The phase equilibria in the Al2O3–SiO2–ZrO2 system up to a temperature of 2550.15 K, calculated using the Nuclea database, are considered in comparison...     

Thermal Stability and Crystallization Kinetics of MgO–Al2O3–B2O3–SiO2 Glasses

To support commercialization of the MgO–Al₂O₃–B₂O–SiO₂-based low-dielectric glass fibers, crystallization characteristics of the relevant glasses was investigated under various heat-treatment conditions. The study focused on the effects of iron on the related thermal properties and crystallization kinetics. Both air-cooled and nucleation-treated samples were characterized by using the differential thermal analysis/differential scanning calorimeter method between room temperature and 1200°C. A collected set of properties covers glass transition temperature (T_g), maximum crystallization temperature (T_p), specific heat (ΔC_p), enthalpy of crystallization (ΔH_cryst), and thermal stability (ΔT=T_p—T_g). Using the Kinssiger method, the activation energy of crystallization was determined. Crystalline phases in the samples having various thermal histories were determined using powder X-ray diffraction (XRD) and/or in situ high-temperature XRD method. Selective scanning electron microscope/energy-dispersive spectroscopy analysis provided evidence that crystal density in the glass is affected by the iron concentration. Glass network structures, for air-cooled and heat-treated samples, were examined using a midinfrared spectroscopic method. Combining all of the results from our study, iron in glass is believed to function as a nucleation agent enhancing crystal population density in the melt without altering a primary phase field. By comparing the XRD data of the glasses in two forms (bulk versus powder), the following conclusions can be reached. The low-dielectric glass melt in commercial operation should be resistant to crystallization above 1100°C. Microscopic amorphous phase separation, possibly a borate-enriched phase separating from the silicate-enriched continuous phase can occur only if the melt is held at temperatures below 1100°C, that is, below the glass immiscibility temperature. The study concludes that neither crystallization nor amorphous phase separation will be expected for drawing fibers between 1200°C and 1300°C in a commercial operation.     

Effect of Zr–Al Co-Doping on Structure and Photocatalytic Performance of ZnO Photocatalyst

利用水热处理结合焙烧的方法分别制备了Zr、Al掺杂及Zr–Al共掺的ZnO光催化剂。研究了制备的光催化剂样品的相结构和光谱性能;以紫外光（λ=254nm）为光源,酸性橙Ⅱ为降解对象,进行光催化活性测试;考察了Zr、Al掺杂对ZnO光催化剂反应活性的影响。研究表明,制备的产物均为六方晶系纤锌矿结构的ZnO;Zr、Al掺杂及Zr–Al共掺的ZnO样品的光催化活性相对于纯ZnO均有较大程度的提高,而且Zr–Al共掺的ZnO的光催化性能明显优于单一掺杂的。Zr–Al共掺可以明显改善ZnO表面状态,使ZnO具有更丰富的表面羟基,同时可以抑制光生电子–空穴对的复合,从而有利于光催化活性和稳定性的提高。     

Effect of Sitallization Conditions on the Hardness of Transparent Sitalls in the System ZnO–MgO–Al2O3–SiO2

Glass and Ceramics - Reliable protection of the screens of next-generation mobile devices requires the use of transparent materials which are stronger than glass. In the present work the influence...     

Heat-Insulating Properties of High-Alumina Materials Filament-Reinforced with Glass Fiber of the Al2O3–SiO2 and Al2O3–SiO2–ZrO2 Systems

Refractories and Industrial Ceramics - Refractory heat-insulating materials produced in Russia are characterized. The thermal stability of high-alumina heat-insulating materials filament-reinforced...     

Thermal Expansion of Melts and Glasses in the As–Se System

The bulk thermal expansion coefficients of glasses and melts in the As–Se system are measured in the temperature range 298–1200 K. In glass-forming melts containing 40–60 mol % As, an increase in the density is found at temperatures above 1000 K, which is assumed to be associated with changes in the structure and character of the chemical bonding.     

Thermal and devitrification behavior of CaO–Ga2O3–SiO2 glasses

A study of the influence of the substitution of Ga₂O₃ for CaO, at constant O/Si ratio, on thermal properties and non-isothermal devitrification of 2.5CaO.2SiO₂ is reported. Differential thermal analysis (DTA) and X-ray diffraction analysis were used. The X-ray diffraction pattern of the crystallized Ga₂O₃ base glass shows that the αCaO SiO₂, that should be stable only above 1125°C, forms in the temperature range 900–1000°C. A new ternary crystalline phase, whose reflections are not reported in the JCPDS cards, was found to form during crystallization of the glass. The glass transformation temperature, T_g, and softening, T_s, temperature decrease as Ga₂O₃ is substituted for CaO. This is the result of the substitution of the network modifying cation Ca²⁺, of higher coordination number, by a network forming cation Ga³⁺ in fourfold coordination, in a composition range of relative insensitivity to changes of covalent cross-linking density. The crystal growth activation energy, E_c, decreases with substitution; this is the consequence of the decrease of the structural rigidity and of the shift of crystallization to a higher temperature range. Devitrification involves a mechanism of surface nucleation; surface nuclei behaving as bulk nuclei in samples that soften and sinter before devitryfing.     

Integrated experimental phase equilibria study and thermodynamic modelling of the binary ZnO–Al2O3, ZnO–SiO2, Al2O3–SiO2 and ternary ZnO–Al2O3–SiO2 systems

Phase equilibria of the ZnO–SiO₂, Al₂O₃–SiO₂ and ZnO–Al₂O₃–SiO₂ systems at liquidus were characterized at 1340–1740 °C in air. The ZnO–Al₂O₃ subsolidus phase equilibria were derived from the experiments with the SiO₂- and CaO + SiO₂-containing slags. High-temperature equilibration on silica or platinum substrates, followed by quenching and direct measurement of Zn, Al, Si and Ca concentrations in the phases with the electron probe X-ray microanalysis (EPMA) was used to accurately characterize the system. Special attention was given to zincite phase that was shown to consist of two separate ranges of compositions: round-shaped low-Al zincite (<2 mol.% AlO_1.5) and platy high-Al zincite (4–11 mol.% AlO_1.5). A technique was developed for more accurate measurement of the ZnO solubility in the low-ZnO phases (corundum, mullite, tridymite and cristobalite) surrounded by the ZnO-containing slag, using l-line for Zn instead of K-line, avoiding the interference of secondary X-ray fluorescence. Solubility of ZnO was found to be below 0.03 mol.% in corundum and cristobalite, and below 0.3 mol.% in mullite. Present experimental data were used to obtain a self-consistent set of parameters of the thermodynamic models for all phases in this system using FactSage computer package. The modified quasichemical model with two sublattices (Zn²⁺, Al³⁺, Si⁴⁺) (O^2?) was used for the liquid slag phase; the compound energy formalism was used for the spinel (Zn²⁺,Al³⁺)[Zn²⁺,Al³⁺,Va]₂O^2-₄ and mullite Al³⁺₂(Al³⁺,Si⁴⁺) (O^2?,Va)₅ phases; the Bragg-Williams formalism was used for the zincite (ZnO, Al₂O₃); other solid phases (tridymite and cristobalite SiO₂, corundum Al₂O₃, and willemite Zn₂SiO₄) were described as stoichiometric. Present study is a part of the research program on the characterization of the multicomponent Pb–Zn–Cu–Fe–Ca–Si–O–S–Al–Mg–Cr–As–Sn–Sb–Bi–Ag–Au–Ni system.     

Characterization and sintering of gels in the system MgO–Al2O3–SiO2

Cordierite aerogels, made by supercritical drying, and xerogels, formed by ambient pressure drying, have been prepared by combining two different recipes. The chemical composition of the gels varied from stoichiometric cordierite 2MgO·Al₂O₃·5SiO₂ to 0·5MgO·1·4Al₂O₃·5SiO₂ due to different procedures for washing of the gels. The crystallization of nearly stoichiometric cordierite gels was shown to be relatively complex involving the formation of several metastable phases such as μ-cordierite (Mg₂Al₄Si₅O₁₈), spinel (Al₆Si₂O₁₃) and sapphirine (Mg₄Al₈Si₂O₂₀) before the equilibrium phase composition was obtained at around 1350°C. On the other hand, during crystallization of gels with stoichiometry close to 0·5MgO·1·4Al₂O₃·5SiO₂ the equilibrium phases mullite, cristobalite and α-cordierite were the major phases formed during heat treatment. A lower densification rate was observed for aerogels compared to xerogels due to a larger pore size. A lower crystallization temperature in aerogels probably due to heterogeneous nucleation reduced the densification. For gels with a composition near 0·5MgO·1·4Al₂O₃·5SiO₂ nucleation and densification occur simultaneously and large differences in the densification behavior was observed. ©     

Heat Loss Reduction in Combustion of Cu(Ni)–Al Powder Systems Due to Their Microstructural Transformation

The paper reviews published data on structural–phase changes in Cu–Al and Ni–Al metal powders during in situ combustion. The heatconservation properties of various structures located around reactive cells in the combustion wave zone are revealed. The mechanism providing for nearly adiabatic combustion conditions is discussed and a microstructural model for this mechanism is justified.     

Combustion of Ti–Al–C compacts in air and helium: A TRXRD study

Combustion of Ti–Al–C compacts in air and helium was investigated by time-resolved X-ray diffraction (TRXRD). The type of environment was found to markedly affect both SHS reaction and product structure. SHS reaction in helium yielded a product containing 80–85 wt % Ti2AlC, 15–20 wt % TiAl, and trace amounts of TiC admixture.     

Synthesis, Structure, and Photophysical Properties of Nanocomposites in the “Cu+ Organic Complex–SiO2” System

The possibility of synthesizing a series of nanohybrids in the Cu⁺ organic complex–SiO₂ system (with different contents of the organic component) by the sol–gel method is analyzed. It is shown that the organic component at a content of 10% provides optimum conditions for the formation of a nanocomposite in this system. The photophysical properties of the nanocomposites synthesized are investigated, and the photosensitivity and quantum yield of charge carrier photogeneration are determined.     

Reactive sintering behavior and enhanced densification of (Ti,Zr)B2–(Zr,Ti)C composites

Reactive hot pressing was used to prepare (Ti,Zr)B₂–(Zr,Ti)C composites from equimolar ZrB₂ and TiC powders. The reaction and solid-solution coupling effect and enhanced densification in ZrB₂-50 mol.% TiC were proposed as contrasted to conventional consolidation of TiB₂-50 mol.% ZrC. The (Ti,Zr)B₂–(Zr,Ti)C composite sintered at a temperature as low as 1750 °C exhibited negligible porosity and average grain sizes of 0.30 μm for (Ti,Zr)B₂ and 0.36 μm for (Zr,Ti)C. Complete reaction and rapid densification of ZrB₂-50 mol.% TiC was achieved at 1800 °C for only 10 min. The densification mechanism was mainly attributed to material transport through lattice diffusion of Ti and Zr atoms with an activation energy of 531 ± 16 kJ/mol. This study revealed for the first time novel insights into rapid densification of refractory fine-grained diboride–carbide composites by reactive hot pressing at relatively low temperatures.     

Structure and mechanical properties of the hybrid films of well dispersed SiO2 nanoparticle in polyimide (PI/SiO2) prepared by sol–gel process

Methyl methacrylate-butyl acrylate structural latexes were synthesized by two-stage seeded emulsion polymerization using 1,1-diphenylethylene (DPE) as a control reagent. In the first stage, the seed latex particles with the precursor poly (methyl methacrylate-DPE) (P(MMA-DPE)) were prepared, and then the second monomer n-butyl acrylate (nBA) was swollen into the seed latex particles under stirring at room temperature. In the second stage, the polymerization of nBA was thermally initiated at 80 °C, and the latex particles composed of block copolymer were synthesized. The size and morphology of the latex particles were investigated by light scattering and TEM. The contact angles of different latex films were also measured. The block copolymer was characterized by size exclusion chromatography, nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. Microphase separation of the block copolymer was examined using atomic force microscopy.