Rod-like eutectic structure of arc-melted TiB2–TiCxN1−x composite

TiB₂–TiC_xN_1−x composites were synthesized by arc-melting mixtures of TiB₂, TiC and TiN powders in a N₂ atmosphere at 60 kPa. TiB₂–TiC_xN_1−x composites were obtained at TiN contents below 20 mol%, whereas TiB formed in the composites at higher TiN contents. TiB₂–TiC_xN_1−x composites with a nominal composition of 36TiB₂–44TiC–20TiN (mol%) had a rod-like eutectic structure, where the TiC_xN_1−x single-crystal rods dispersed in the TiB₂ single-crystal matrix. The crystal orientation relationship between the TiB₂ matrix and the TiC_xN_1−x rods was TiB₂ (0 0 0 1)//TiC_xN_1−x (1 1 1). Vickers hardness (H_v) of the rod-like eutectic composite was 22.5 GPa.     

New catalyst of SO 4 2− /Al2O3–ZrO2 for n-butane isomerization

The catalytic behavior of Al-promoted sulfated zirconia for n-butane isomerization at low temperature in the absence of H₂ and at high temperature in the presence of H₂ was studied. The addition of Al enhances the activity and stability of the catalysts for reaction at 250°C and in the presence of H₂ significantly. After on stream for 120 h, the n-butane conversion of the catalyst containing 3 mol% Al₂O₃ keeps steadily at 88% of its equilibrium conversion and no observable trend of further deactivation has been observed. The difference in behavior of the promoted and unpromoted catalysts at low and high temperature is associated with a change of reaction mechanism from bimolecular to monomolecular. Experimental evidence is presented to show that the promoting effect of Al is different from that of the transition metals. Microcalorimetric measurements of NH₃ adsorption on catalysts reveal that the remarkable activity and stability of the Al-promoted catalysts are caused by an enhancement in the number of acid sites effective for the isomerization reaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

Enhanced thermoelectric efficiency of Cu2−xSe–Cu2S composite by incorporating Cu2S nanoparticles

The study of thermoelectric transport properties in Cu_2−xSe and Cu₂S has gained an importance in the thermoelectric research during last few years due to their superionic behavior and low cost. Here, we reported a facile method to enhance the thermoelectric efficiency of Cu_2−xSe by introducing Cu₂S nanoparticles (NPs) in the matrix of Cu_2−xSe. The observed efficiency is a direct result of simultaneous improvement of Seebeck coefficient (S) because of the external strain induced by Cu₂S nanoinclusions in Cu_2−xSe and decline in the total thermal conductivity by suppressing both electronic and lattice thermal contributions. Such higher S and lower thermal conductivity is realized for a composite structure with 10 wt% nanoinclusions of Cu₂S which effectively contributed to higher ZT value of 0.90 at moderate temperature of 773 K. Thus, it is believed that the proposed hybrid structure is a promising p-type thermoelectric material for mid-temperature range energy harvesting applications.     

Phase equilibria in the system CaO–SiO2–Nb2O5–La2O3 at 1473 K with pO2=10−15.47 atm

Phase equilibria in the CaO–SiO₂–La₂O₃–Nb₂O₅ system are important for the utilization of Nb and Rare Earth resources. In the present work, phase equilibria in the CaO–SiO₂–La₂O₃–Nb₂O₅ system at 1473 K in H₂ (pO₂ = 10^−15.47atm) were studied by the equilibrium experiment. SEM, EDS and XRD analysis were employed to identify the equilibrium phase relations. The isothermal spatial phase diagram of the CaO–SiO₂–La₂O₃–Nb₂O₅ system and the isothermal section of CaO–SiO₂–Nb₂O₅-(5%, 10%) La₂O₃ pseudo-ternary system were constructed. A total of eight equilibrium phase regions were determined, including Liquid + CaNb₂O₆+CaSiO₃+LaNbO₄ region, Liquid + CaNb₂O₆+SiO₂+CaSiO₃ region, Liquid + CaSiO₃+CaNb₂O₆ region, Liquid + CaSiO₃+SiO₂ region, Liquid + CaNb₂O₆+SiO₂ region, Liquid + CaSiO₃ region, Liquid + SiO₂ region and Liquid + CaNb₂O₆ region. Additionally, the influence of pO₂ on equilibrium composition and temperature was also investigated considering its significant effect on phase equilibria in the slag system with variable valence elements. The results indicated that higher external pO₂ can increase the equilibrium O content in a slag system, while higher equilibrium temperature corresponds to higher equilibrium pO₂. Besides, the relationship between phase equilibria shown in the traditional slag system and in the related generalized alloy system was also revealed. The present experimental data can help further study on Nb-bearing and RE-bearing slag systems, and the theoretical conclusions will help the development of thermodynamic models.     

Lamellar-interpenetrated Al−Si−Mg/Al2O3−ZrO2 composites prepared by freeze casting and pressureless infiltration

Using freeze casting and pressureless infiltration methods, we prepared lamellar Al−Si−Mg/Al₂O₃−ZrO₂ composites with initial ceramic loading of 30 vol% and different Al₂O₃:ZrO₂ weight ratios (Al₂O₃:ZrO₂=1:9, 3:7, 5:5, 7:3 and 9:1). The resultant composites inherited the lamellar structure of the Al₂O₃−ZrO₂ scaffolds, and the thickness of both metal and ceramic layers showed a trend of first increase and then decrease with increasing Al₂O₃ content. During pressureless infiltration, multiple chemical reactions took place between ZrO₂ and the Al−12Si−10Mg alloy and the main reaction products were (Al_1−m, Si_m)₃Zr, Al₂O₃ and ZrSi₂ phases. The degree of the reaction depended on the ZrO₂ content in the ceramic composition. In general, the compressive strength of the composites decreased with increasing Al₂O₃ content, but three-point bending strength showed a first decrease and then increase. When Al₂O₃:ZrO₂=1:9, the compressive and bending strength of the composites reached about 997±60 MPa and 426±10 MPa, respectively. A simple model was proposed to illustrate the fracture mode and toughening mechanism of the composites.     

Structural,morphological and electrical properties of Ce1−xRuxO2−δ (x=0.005–0.02) solid solutions

Nanoparticles of ceria–ruthenium oxide solid solutions with composition Ce_1−xRu_xO_2−δ (x=0.005–0.02) were successfully produced by self–propagating room temperature synthesis using reaction between metal nitrates and sodium hydroxide. These compositions were characterized by X–ray powder diffraction (XRD), Raman spectroscopy, specific surface area, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X–ray spectroscopy (EDX). The experimental measurements were complemented by calculations based on the ion–packing model. XRD analysis revealed the presence of single–phase solid solutions with CeO₂ fluorite structure (regardless of dopants concentration) and Raman spectroscopy confirmed the presence of the RuO₂ phase. Electrochemical impedance spectroscopy (EIS) measurements of sintered samples at different temperatures showed that the small ionic radius dopant reduces oxygen vacancies mobility that is responsible for the conductivity of these ceramics.     

Comparison of Mg–Al layered double hydroxides intercalated with OH− and CO32− for the removal of HCl,SO2, and NO2

Journal of Porous Materials - Two different Mg–Al layered double hydroxides (LDHs), OH?Mg–Al LDH and CO3?Mg–Al LDH, are prepared and utilized for the efficient removal...     

R_2O–RO–B_2O_3–SiO_2–Al_2O_3–P_2O_5–CaF_2系分相–析晶乳浊釉的形成机理

通过正交试验方法优化釉料组成和烧成工艺,制备了R_2O–RO–B_2O_3–SiO_2–Al_2O_3–P_2O_5–CaF_2多元系光亮无锆的分相–析晶乳浊釉。采用X射线衍射仪、透射电子显微镜/X射线能谱、场发射扫描电子显微镜等研究了釉的显微结构及分相与析晶的形成机理。结果表明析晶与分相结构并存,分相促进析晶;尺寸接近可见光波长的孤立液滴和所析出的钙钠长石晶体是釉面产生乳浊的根本原因。研究了不同烧成制度对分相–析晶乳浊釉显微结构的影响,发现缓冷釉样的分相液滴尺寸明显大于急冷釉样,急冷釉样中的第二相形貌表里存在明显差异,内部呈球形液滴状,表面则为蠕虫状。     

Visible-light-responsive photocatalysts xBiOBr–(1−x)BiOI

A new class of oxyhalide photocatalysts xBiOBr–(1−x)BiOI prepared by a soft chemical method were characterized by X-ray diffraction and UV–Vis diffuse reflectance spectra. They are all visible-light-responsive materials with the bandgaps ranging from 1.92 to 2.91 eV. Methyl orange (MO) photocatalytic degradation experiments showed that BiOBr possessed a higher photocatalytic activity than P25 (TiO₂) under UV illumination and iodine-modified BiOBr exhibited high photocatlytic activities under visible-light irradiation. The high photocatalytic activity is in close relation with the deep valance band edge position and the internal electric fields between [Bi₂O₂] slabs and halogen anionic slabs.     

Microstructure and dielectric properties of Ba0.4Sr0.6Ti1−yZryO3 sintered with SrO–B2O3–SiO2 glass additive

Ba_0.4Sr_0.6Ti_1−yZr_yO₃ (0y0.20) (BSTZ) ceramics were prepared via the solid state reaction route, followed by sintering at high temperature. SrO–B₂O₃–SiO₂ glass, as the sintering additive, was introduced to lower the sintering temperature. The effects of the amount of Zr substitution for Ti in Ba_0.4Sr_0.6Ti_1−yZr_yO₃ on the sintering temperature, microstructure and dielectric properties were investigated. Sintering temperature of Ba_0.4Sr_0.6Ti_1−yZr_yO₃ increases gradually with the increasing amount of Zr in Ba_0.4Sr_0.6Ti_1−yZr_yO₃. XRD phase analysis shows that all samples exhibit the desired perovskite structure, where the cell parameter a increases with the increasing amount of Zr substitution. Microstructural studies reveal a slow-down in grain growth by Zr substitution. Dielectric relaxation is observed in the dielectric loss versus temperature plots, where the relaxation time shows an increase with the increasing amount of Zr substitution. The slow-down in grain growth gives rise to the formation of more grain boundaries, which restrict the charge spreading and lead to an increase in the grain boundary barrier E_{a, 2}.     

Antibacterial and photocatalytic active transparent TiO2 crystallized CaO–BaO–B2O3–Al2O3–TiO2–ZnO glass nanocomposites

Transparent TiO₂ crystallized 5CaO–10BaO–65B₂O₃–Al₂O₃–20TiO₂–10ZnO (CBBATZ) glass nanocomposites were fabricated using melt-quenching technique followed by specific heat treatments. As-quenched glass samples were provided three different heat treatments at 630°C for 3, 5, and 10 hours in order to obtain different amounts of TiO₂ nanocrystals in the glass. The presence of rutile phase of TiO₂ nanocrystals in glass was confirmed by X-ray diffraction. The glass nanocomposite heat treated for 10 hours showed a hydrophobic nature with contact angle of 90.90°. Contact angle decreased from 90.90 to 22.20°, when irradiated under ultraviolet (UV) radiation for 45 minutes. This photoinduced hydrophilicity showed a photocatalytic and self-cleaning properties of glass nanocomposite. During photocatalytic ink test, the maximum change in color of Resurin (Rz) ink and 60% degradation in absorbance of ink within 150 minutes under UV radiation were found for glass nanocomposite heat treated at 10 hours. Also, 78% degradation in absorbance of methylene blue dye (pollutant) within 180 minutes under UV irradiation was found for glass naocomposite heat-treated at 10 hours. Antibacterial performance of transparent glass nanocomposite against Escherichia coli was evaluated as well. More than 95% of the bacterial cells were degraded with glass nanocomposite heat-treated at 10 hours. CBBATZ glass nanocomposite found to impart the antibacterial effect through generation of reactive oxygen species (ROS) in aqueous medium. ROS species which was confirmed in the bacterial cell through intracellular ROS generation kit. During evaluation of mechanical properties using nanoindentation technique, the values of hardness and reduced modulus increased by ~26% and 10%, respectively, for glass nanocomposite heat-treated at 10 hours as compared to as-quenched glass.     

Calcium fluorosilicates: The Ca6−0.5xSi2O10−xFx phase

The identity of Ca_6−0.5xSi₂O_10−xF_x with other germanate and silicate phases reported in the literature is confirmed by X-ray methods. The crystals exhibit superstructure which is interpreted as arising from ordering of Ca vacancies in the [203] direction. Its crystallochemical relationships with other fluorosilicate and germanates is discussed.     

电沉积α-PbO_2–TiO_2–CeO_2工艺研究

将TiO_2和CeO_2颗粒添加到由50 g/L PbO和4 mol/LNaOH组成的镀液中,通过阳极电沉积的方法在铝基体上制备了α-PbO_2-TiO_2-CeO_2复合镀层,用作铝基二氧化铅电极的中间层.通过研究镀液中固体颗粒的质量浓度和各种工艺条件对α-PbO_2-TiO_2-CeO_2复合镀层外观及结合力的影响,确定了最佳配方和操作条件为:TiO_2 15 g/L,CeO_2 10g/L,温度40℃,电流密度0.5 A/dm~2,电沉积时间3 h.在此条件下所得的复合镀层综合性能较好,其TiO_2和CeO_2含量(质量分数)分别为3.77%和2.13%.扫描电镜结果显示,固体颗粒的掺杂能抑制α-PbO_2晶胞的长大,起到细化晶粒的作用.X射线衍射分析表明,固体颗粒的加入改变了α-PbO_2镀层晶粒的择优取向,降低了其衍射峰强度.     

Hydrogen-storage properties of MgH2–10Ni–2NaAlH4–2Ti–2CNT milled in a planetary ball mill under H2

A sample with a composition of 84 wt% MgH₂–10 wt% Ni–2 wt% NaAlH₄–2 wt% Ti–2 wt% CNT (named MgH₂–10Ni–2NaAlH₄–2Ti–2CNT) was prepared by milling in a planetary ball mill under H₂. Activation of the sample was not required. At the first cycle, the sample absorbed 3.75 wt% H for 10 min, and 4.17 wt% H for 60 min at 593 K under 12 bar H₂. Reactive mechanical grinding of Mg with Ni, NaAlH₄, Ti, and CNT is thought to create defects on the surface and in the interior of Mg, as well as to reduce Mg particle size.     

Infrared GRIN GeS2–Sb2S3–CsCl chalcogenide glass–ceramics

Chalcogenide glasses show a unique potential for creating gradient refractive index (GRIN) lenses, which would reduce the size and weight of infrared thermal imaging system and remain/improve its performance. Here, we propose a new method that forms a GRIN chalcogenide glass–ceramics (GCs) by creating low refractive index (n) CsCl nanocrystals within a high n GeS₂–Sb₂S₃ glass matrix. After specific gradient thermal treatment, the GRIN structure of Δn ∼ 0.04 was formed through the gradient precipitation of CsCl. This work would pave a new path to design the GRIN chalcogenide GCs through a selective crystallization of halide crystals with low n.     

Bioactivity investigation of glass and glass ceramics in Li2O–SiO2–CaO–P2O5–CaF2 system

Abstract

Glass samples in Li₂O–SiO₂–CaO–P₂O₅–CaF₂ system with different contents of P₂O₅, CaO and CaF₂ in relative ratios responded to fluoroapatite (FA) composition (referred to P₂O₅ addition) have been prepared and heat treated at 550 and 750°C to obtain glass ceramics. Bioactivity of all samples has been proved in vitro by the presence of new layer of apatite-like phases formed after soaking in simulated body fluid (SBF). The development and the apatitic character of created layers have been demonstrated by Fourier transform infrared analysis. Scanning electron microscopy and electron probe microanalysis have demonstrated that the density and the thickness of new layer depend on P₂O₅ content, crystallisation temperature and immersion time. The bioactivity has been enhanced by P₂O₅ addition as well in the case of the base glasses as in the case of glass ceramics. The additional heat treatment appeared to inhibit the bioactive behaviour, though the longer SBF acting leads to the additional formation of apatite-like layer. The mechanical properties, expressed as Vicker hardness, have been found higher and increasing with P₂O₅ in glass ceramics treated at 750°C comparatively with base glass samples and the highest value of 7˙37 GPa has been achieved by 14 wt-%P₂O₅ addition. The same content of P₂O₅ in glass ceramics heat treated at 550°C resulted in a decrease in hardness to a minimum value from all samples. The increase and decrease in hardness responded to development and suppression of crystallisation respectively. The inhibition of crystallisation has been affected by the presence of 'amorphous' FA according to X-ray diffraction and differential thermal analysis results.     

Mechanical properties of (TixW1−x)C–Co cermet prepared by carbothermal reduction of high energy ball milled TiO2–WO3–C

A series of solid–solution carbides, (Ti_xW_1−x)C (x=0.9, 0.8, 0.7, 0.6), was prepared by the high-energy milling of TiO₂–WO₃–C mixtures via subsequent carbothermal reduction. With high-energy milling, only the size reduction of the constituent powders was apparent without any chemical reaction. The milled mixture powder was transformed to a single–phase (Ti_xW_1−x)C solid solution by heat treatment in a vacuum at 1200 °C. (Ti_xW_1−x)C–Co cermets were consolidated by isothermal sintering at 1300, 1400, and 1500 °C. The powders were fully densified by liquid-phase sintering at 1500 °C because the Co melted at 1430 °C. The mechanical properties of the (Ti_xW_1−x)C–Co cermet (H_v: ~24 GPa) were significantly better than those of the conventional WC–Co (H_v: ~13 GPa) or TiC–Co cermets (H_v: ~16 GPa). The use of a solid–solution carbide instead of conventional WC almost doubled its hardness values without a loss of toughness. It is indicated that the improved hardness of the (Ti_xW_1−x)C–Co cermet originates from the high hardness of (Ti_xW_1−x)C, and the solid–solution carbide would be a valuable substitute for conventional carbide cermets.     

Hydrothermal synthesis and characterization of nanorods “LixV2−δO4−δ·H2O”

Nanorods “Li_xV_2−δO_4−δ·H₂O” were hydrothermally synthesized with starting agents LiOH·H₂O and V₂O₅, and reducing agent hydrazine monohydrate (NH₂NH₂·H₂O) under alkaline condition at 160 °C. The samples were characterizated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The nanorods obtained have diameters from 80 to 100 nm with length up to several micrometers. Molecular coordination and assembly mechanism can be assumed to explain the formation of one-dimensional nanorods.     

Thermodynamic modeling and phase diagram prediction of salt lake brine systems. I. Aqueous Mg2+–Ca2+–Cl− binary and ternary systems

Salt lake brine is a complex salt-water system under natural environment. Although many models can express the thermodynamic properties and phase equilibrium of electrolyte aqueous solution, the multi-temperature characteristics and predictability are still the goals of model development. In this study, a comprehensive thermodynamic model system is re-established based on the eNRTL model and some improvements: (1) new expression of long-range electrostatic term with symmetrical reference state is proposed to handle the electrolyte solution covering entire concentration range; (2) the temperature dependence of the binary interaction parameters is formulated with a Gibbs Helmholtz expression containing three temperature coefficients, the liquid parameters, which associated with Gibbs energy, enthalpy, and heat capacity contribution; and (3) liquid parameters and solid species data are regressed from properties and solubility data at full temperature range. Together the activity coefficient model, property models and parameters of liquid and solid offer a comprehensive thermodynamic model system for the typical bittern of MgCl₂–CaCl₂–H₂O binary and ternary systems, and it shows excellent agreement with the literature data for the ternary and binary systems. The successful prediction of complete phase diagram of ternary system shows that the model has the ability to deal with high concentration and high non-ideality system, and the ability to extrapolate the temperature.     

Surface and bulk crystallization in Nd2O3–Al2O3–SiO2–TiO2 glasses

Neodymium aluminosilicate (Nd₂O₃–Al₂O₃–SiO₂; NdAS) glasses have been investigated for the effect of concentration of TiO₂ on the crystallization mechanism and for the effect of surface condition on crystal growth. NdAS glasses with 0–10 wt.% TiO₂ were heat-treated for nucleation and crystal growth and were examined for phase separation and morphology of surface crystals as well as for crystal growth rate. All the glasses exhibit surface crystallization, however, the glass having 8 wt.% TiO₂ also exhibits internal crystallization after a two-stage heat treatment. Surface crystallization was dependent on the condition of the glass surface and the amount of TiO₂. The crystal growth on the cut surface was faster than on the fractured surface and the growth rate in surface increased with increasing TiO₂. The phase separation found in NdAS glasses containing above 8 wt.% TiO₂, was confirmed to be an important factor controlling the internal crystallization process in Nd₂O₃–Al₂O₃–SiO₂–TiO₂ glasses.