Crystallization of glass of the system K2O(Na2O)Al2O3SiO2

In a whiteware composition, the glassy phase derives from the molten feldspar in which a portion of quartz, clay and other crystalline constituents are dissolved. This glass is the major and continuous phase in the whiteware body and is the potential source of the crystalline phase, viz. mullite. Synthetic glass has been prepared by melting mixtures of feldspar and quartz comparable to whiteware-glass in composition. Glasses were also synthesized by melting mixtures of feldspar, quartz and mineralizers. All of these glasses were heat-treated and their mullite contents were estimated by X-ray analysis supported by TEM & SEM study. Among thirtyone (31) different mineralizers tried, only thirteen (13) are found to be effective mullite is builders. The cation of the mineralizer helps replacement of the Al³⁺ ion from the glass which subsequently diffuses through the residual SiO₂ and mullite is formed. The replacement reaction and hence the degree of mullitization is dependent on factors, e.g. charge, radius, field strength of the cation as well as on the cation-oxygen bond strength. This last appears as the most predominant factor for mullitization.     

Phase equilibrium in binary La2O3-Dy2O3 and ternary CeO2-La2O3-Dy2O3 systems

Cerium oxide doped with oxides of rare earth elements is a multifunctional material, a wide range of uses which is associated with its unique physicochemical properties. Phase diagrams of multicomponent systems are the physicochemical basis for the creation of new materials with improved characteristics.In this work, phase equilibria in ternary CeO₂–La₂O₃–Dy₂O₃ and binary La₂O₃–Dy₂O₃ systems in the whole concentration range were studied. No new phases have been identified in these systems. An isothermal section of the phase diagram of the CeO₂–La₂O₃–Dy₂O₃ system at a temperature of 1500 °С is constructed. No new phases have been detected in the system. It was found that in the studied ternary system solid solutions are formed on the basis of (F) modification of CeO₂ with structure of fluorite type, monoclinic (B), cubic (C) and hexagonal (A) modifications of Ln₂O₃.In the La₂O₃–Dy₂O₃ binary system (1500–1100 °С) three types of solid solutions are formed: based on hexagonal modification A-La₂O₃, monoclinic modification B-Dy₂O₃ and cubic modification C-Dy₂O₃ separated by two-phase fields (A+B) and (B+C), respectively. The boundaries of the regions of homogeneity of solid solutions based on A-La₂O₃ are determined by compositions containing 35–40, 20–25, 15–20 mol% Dy₂O₃ at 1500, 1250, 1100 °C, respectively. From the obtained data it follows that the solubility of Dy₂O₃ in the hexagonal modification of lanthanum oxide is 39 mol% at 1500 °C, 23 mol. % at 1250 °C and 16 mol% at 1100 °C. The limits of existence of solid solutions based on monoclinic B-modification are determined by compositions containing 30–35, 65–60 (1250 °С), 35–40, 55–60 (1100 °С) 40–45, 70–75 (1500 °C) mol% Dy₂O₃.In the studied system, with a decrease in temperature from 1500° to 1100°C, there is a decrease in the solubility of La₂O₃ in the crystal lattice of cubic solid solutions of C-type from 16 to 10 mol%.     

Propylene metathesis over Re2O7/Al2O3-B2O3 catalysts

A series of alumina aluminum borate (AAB) with various Al/B molar ratios were prepared by the coprecipitation method. The supported rhenium oxide catalysts with various contents of Re₂O₇ were also prepared by the impregnation method with perrhenic acid. The catalytic activity and stability of Re₂O₇/AAB catalysts for the reaction of propylene metathesis were tested in a fixed-bed microreactor. It was found that Re₂O₇/AAB is more active, stable and regenerable than Re₂O₇/Al₂O₃ for propylene metathesis. The optimum Al/B molar ratio was found to be in the range of 4–10.     

La2O3的添加对P2O5-Al2O3-SiO2系微晶玻璃性能的影响

以ZrO2为晶核剂,根据DSC图谱制定合理的热处理制度,制备了磷扩散源P2O5-Al2O3-SiO2系微晶玻璃。采用XRD分析观察了P2O5-Al2O3-SiO2系微晶玻璃的析晶状况,热膨胀仪测试了该微晶玻璃的膨胀系数,分析La2O3的含量对P2O5-Al2O3-SiO2系微晶玻璃在高温下释放P2O5速率的影响。结果表明:随着La2O3含量增加,P2O5-Al2O3-SiO2系微晶玻璃中晶体含量增加,主晶相未发生改变,都为磷酸锆晶体;同时,该微晶玻璃的热膨胀系数相对降低,P2O5的释放速率也随之增加。     

Polycrystalline In2O3 and In2O3/Y2O3 photoanodes

Single crystal In₂O₃ shows promise as a photoanode for the decomposition of water. Because of various difficulties in the preparation of the single crystal material, two simple techniques were developed for the preparation of polycrystalline In₂O₃ anodes. One method involves the thermal decomposition of the nitrate while the other utilizes the chemical vapour deposition technique. Voltammograms and photoresponse spectra of these anodes are compared to the single crystal material. Among other observations, it is noted that the quantum efficiencies of the thermally decomposed films are comparable to the single crystal material. It is also shown that the on-set potential can be shifted to more negative values by forming the mixed oxide In₂O₃/Y₂O₃.     

UV-Enhanced Exchange of O2with H2O Adsorbed on TiO2

Ultraviolet light dramatically increases the rate of isotope exchange between gas-phase O₂and water adsorbed on TiO₂at room temperature, but it does not affect the rate of CO₂–water exchange. Both ethanol and acetaldehyde, when coadsorbed with H₂¹⁸O, dramatically decrease the rate of O₂exchange, but not CO₂exchange, with adsorbed H₂¹⁸O. This decrease is attributed to a combination of competition for adsorbed oxygen between exchange and photocatalytic oxidation of the adsorbed organic and blocking of the oxygen adsorption sites by the organic. The same oxygen species participate in O₂-H₂¹⁸O exchange and photocatalytic oxidation.     

Barium aluminate hydrates—VI. 2BaO.Al2O3.5H2O and 2BaO.Al2O3.H2O

The compound 2BaO.Al₂O₃.5H₂O has been synthesised and studied by infra-red, X-ray and thermal analytical techniques. The compound of approximate formula 2BaO.Al₂O₃.H₂O forms as a dehydration product. The results are interpreted in terms of the known structure.     

Thermal diffusion of alkali chlorides in H2O and D2O

Entropies of transport for very dilute aqueous alkaline chlorides solution at 25° have been determined by the potentiometric method. The limiting slopes were calculated and the molar entropies of transport at infinite dilution obtained by extrapolation.The standard transported entropy of Cl^? ion was also derived by extrapolating the steady state thermoelectric powers to infinite dilution. The ‘absolute’ ionic entropies of transport have been estimated from the standard transported entropy following Gurney's choice of the absolute standard partial molar entropy of H⁺ ion as ?5.5eu.Soret data obtained in H₂O are compared with that obtained in D₂O. Results are discussed in terms of the structure of the solvent and ionic hydration phenomena.     

Phase equilibrium studies in V2O5-Fe2O3 and V2O5-TiO2 systems

V₂O₅-Fe₂O₃ and V₂O₅-TiO₂ systems represent two important chemical systems with various applications, including energy, catalysts, and high-performance materials. In the present study, high-temperature phase equilibrium experiments were conducted at the temperature range of 670–1000°C in air. Electron probe X-ray micro-analyzer (EPMA) was used to analyze the microstructure and composition of the phases presented in quenched samples. Systematic experiments demonstrated that V₂O₅-containing systems should not be quenched by water-based quenching media. Phase diagrams in both systems were constructed, and the eutectic and peritectic points of the systems were confirmed and compared with previous studies. The present study improved the previous results and could be used as the base for thermodynamic modelings and further applications of the two systems.     

Bactericidal Effectiveness of O3, O3/H2O2 and O3/TiO2 on Clostridium perfringens

The purpose of this research is to evaluate the bactericidal capacity of different Advanced Oxidation Treatments (AOTs) based on ozone: ozone, ozone/hydrogen peroxide and ozone/titanium dioxide on a wild strain of Clostridium perfringens, a fecal bacterial indicator in drinking water. The dose of ozone consumed ranges from 0.6 mg L^?1 min^?1 to 5.13 mg L^?1 min^?1 depending on the process and on the sample. In the treatments combined with O₃, H₂O₂ dose utilized is 0.04 mM and TiO₂ dose, 1 g L^?1. In order to evaluate the influence of natural organic matter and suspension solids over the disinfection rate, treatments are performed with two types of water – natural water from Ebro River (Zaragoza, Spain) and NaCl solution 0.9%. To achieve 4 log units of inactivation, 3.6 mg O₃ L^?1 is necessary in O₃ treatment, 4.25 mg O₃ L^?1 in O₃/TiO₂ system and 2.7 mg O₃ L^?1 in O₃/H₂O₂ after processing the natural water. In NaCl solution, to get the same inactivation, 0.42 mg O₃ L^?1 is necessary in O₃ treatment, 1.15 mg O₃ L^?1 in O₃/TiO₂ system and 0.06 mg O₃ L^?1 in O₃/H₂O₂ process. Even though the three treatments studied have a high bactericidal activity due to the number of surviving bacteria decreases to non-detectable levels, O₃/H₂O₂ is the most effective system for eliminating C. perfringens cells in a lower contact time, followed by O₃ and finally O₃/TiO₂ system.     

Enhanced Bactericidal Effect of O3/H2O2 Followed by Cl2

With the appearance of chlorine resistant microorganisms such as Cryptosporidium parvum and Giardia lamblia in drinking water, significant attention has been drawn to the sequential application of multiple disinfectants including ozone, chlorine dioxide, and UV as a primary disinfectant. However, few studies have reported about the inactivation behavior of ozone-based AOP (advanced oxidation process) or its sequential application combined with other disinfectants. This is especially important since ozone itself experiences difficulty in the inactivation of these pathogens, especially at low temperatures: This study investigates the enhanced inactivation of Bacillus subtilis spores by the presence of an OH radical in the O₃/H₂O₂ system and the synergistically enhanced inactivation in the application of the O₃/H₂O₂ system followed by Cl₂. The results suggest that the O₃/H₂O₂ process can be considered as one of the viable alternatives when O₃ alone does not satisfy the disinfection requirement.     

固体超强酸催化剂S2O2-8/Fe2O3-Al2O3的制备及其酯化性能

以硝酸铁为铁源、硝酸铝为铝源,通过共沉淀法制备固体超强酸催化剂S₂O^2-₈/Fe₂O₃-Al₂O₃。通过催化剂样品的FT-IR谱图、不同焙烧温度催化剂样品的XRD谱图、不同陈化温度的N2吸附-脱附曲线以及催化剂样品的SEM照片,研究了其晶体的形成过程。催化剂样品红外谱图表明,催化剂中的S=O有较强的共价双键特征,诱导催化剂形成超强酸性;在XRD谱图中既无Al₂O₃的晶相峰,也无Fe₂(SO₄)₃晶相峰,说明Al₂O₃与Fe₂O₃ 在催化剂样品的表面形成了Al₂O₃-Fe₂O₃ 共价键的复杂结构。采用BET方程和BJH模型计算催化剂样品的比表面积和孔径分布,经冰水陈化的催化剂样品平均孔径为9.1 nm,最可几孔径为7.5 nm,比表面积为78.9 m²·g^-1,孔容0.149 cm³·g^-1。研究了催化剂的铁与铝物质的量比、(NH₄)₂S₂O₈浸渍浓度和不同焙烧温度对硬脂酸正丁酯酯化率的影响。在反应温度85 ℃、催化剂用量0.2 g (为反应物总质量的2%)和回流反应150 min的条件下,酯化率可达84.5%。     

热疗用Fe2O3-SiO2-Y2O3-Al2O3微晶玻璃微球的制备与性能

采用火焰漂浮法制备新型含钇铁磁微晶玻璃微球(ferromagnetic glass ceramic microspheres,FGCMs),用以放疗与热疗相结合的医疗用途.通过热分析和X射线衍射(X-ray diffraction,XRD)研究热处理温度对FGCMs性能的影响.使用偏光显微镜观察FC-CMs的形貌.用振...     

Lithium concentration effect on crystallization kinetics and spectral properties of Cr-doped Li2O–K2O–Al2O3–B2O3 glass-ceramics

Alkali-aluminaborate glass-ceramics doped with Cr ions are synthesized by volume crystallization. According to non-isothermal DSC method three parallel processes occur in material: 2D Avrami-Yerofeev nucleation, 2D and 3D crystallization. During the heat treatment, the LiAl₇B₄O₁₇ crystalline phase is formed. With Li₂O content rising crystallinity of the material increases from 27 to 69% and the crystalline field strength Dq/B of Cr³⁺ increases from 2.25 to 3.55. The photoluminescence spectra possess intense bands at 685, 700, and 715 nm for glass with 6.8 mol.% Li₂O and higher and its decay kinetics is described by the sum of two exponentials. The maximum luminescence QY obtained is 50% at 16.1 mol.% Li₂O. The highest conversion efficiency of the 532 nm LED luminescence obtained by glass-ceramics with chromium is 10%. Thus, Cr-doped alkali-alumina-borate glass-ceramics are a promising material for use in the design of radiation sources for the red and NIR spectral regions.     

Vitrification and crystallization of glasses in the SiO2-Al2O3-Fe2O3(FeO)-CaO-MgO-R2O system

A correlation dependence is established between the degree of cohesion of the silicon-oxygen skeleton of ash-slag glasses and their crystallizability. It is shown that the physicochemical properties of the investigated glasses are determined by the degree of cohesion of the silicon-oxygen skeleton and the presence of chemical and phase inhomogeneities in glasses.     

Self-organized nano-crystallisation of BaF2 from Na2O/K2O/BaF2/Al2O3/SiO2 glasses

In glasses with the compositions (100 ? x)(2Na₂O·16K₂O·8Al₂O₃·74SiO₂)xBaF₂ (with x = 0 to 6), the glass transition temperature decreases with increasing BaF₂-concentration. Samples with x = 6 were thermally treated at temperatures in the range from 500 to 600 °C for 5–160 h. This leads to the crystallisation of BaF₂. The quantity of crystalline BaF₂ increases with increasing time of thermal treatment, while the mean crystallite size remains constant within the limits of error. The glass transformation temperature of partially crystallised samples increases with increasing crystallisation time and approaches a value equal to the temperature, at which the samples were treated. This is explained by the formation of a highly viscous layer enriched in SiO₂ which is formed during crystallisation. This layer acts as a diffusion barrier and hinders further crystal growth.     

Na2O-Al2O3-Fe2O3系烧结过程中铝、铁的反应行为

以Al2O3, Fe2O3和Na2CO3为原料,对Na2O-Al2O3-Fe2O3系烧结过程中的反应行为进行了详细研究. 基于溶出率与时间、温度的关系,证明Na2O×Al2O3和Na2O×Fe2O3的生成反应动力学都服从Zhuralev-Lesokin-Tempelman模型,表观活化能分别为186.59和80.92 kJ/mol,表明Na2O×Fe2O3比Na2O×Al2O3在动力学上更易形成;Al2O3易与Na2O×Fe2O3反应形成Na2O×Al2O3和Fe2O3,在1273 K烧结30 min,所得熟料Al2O3溶出率达98.51%;Fe2O3对Na2O×Al2O3的形成有双重作用,在1273 K下可加速Na2O×Al2O3的形成,超过1323 K,促使Na2O×Al2O3分解成Na2O和b-Al2O3,且随着温度升高或时间延长,分解程度增高,从而导致熟料中Al2O3溶出率显著降低.     

Crystallization Hierarchy of CaO-P2O5-SiO2-Al2O3-TiO2 Glass-Ceramics

Glasses in the tricalcium phosphate-anorthite (Ca₃(PO₄)₂-CaAl₂Si₂O₈ or TCP-CAS₂) system with additional TiO₂ were melted. Crystallization was investigated using thermal analysis, X-ray diffraction, and transmission optical and electron microscopies. During the heat treatment, as the growth temperature increases, successive crystalline phases separate from the glass matrix. The phases present in the fully heat-treated glass-ceramic are ß-TCP, anor-thite (CAS₂), and rutile (TiO₂). Apart from TiO₂, these phases evolve from other polymorphs during the heat treatment. The metastable phases, pseudo-orthorhombic CAS₂ and alpha-TCP, appear first around 880°C and transform into the stable phases, triclinic anorthite CAS₂ and ß-TCP, around 940° and 1000°C, respectively. The material crystallizes in stages. The first stage is the separation from the glass matrix of rutile and what is believed to be a calcium phosphate phase, with crystal sizes varying from 20 to 200 nm. This is followed by the appearance of larger crystals (1-2 µm) of the metastable pseudo-orthorhombic CAS₂, surrounding the previously crystallized phases. Finally, this pseudo-orthorhombic CAS₂ phase transforms to anorthite (15-20 µm) spherulites. TiO₂ does not act as a direct nucleating agent in the glass composition studied: no sign of heterogeneous nucleation and growth from TiO₂ crystals has been found, and moreover, TiO₂-free base glass crystallizes in a manner similar to that of the glass containing TiO₂.     

Effect of temperature and heating rate on the sintering performance of SiC-Al2O3-Dy2O3 and SiC-Al2O3-Yb2O3 systems

Samples of SiC+10 vol%(Al₂O₃+Dy₂O₃) and SiC+10 vol%(Al₂O₃+Yb₂O₃) mixtures were obtained by cold isostatic pressing and sintered for one hour in a dilatometer at 1800 °C and 1900 °C, applying heating rates of 10, 20 and 30 °C/min. The results of the complete sintering cycle indicated that the heating rates do not significantly influence the shrinkage, but that temperature and total sintering time may be relevant factors. The compacts sintered at 1900 °C shrank on average 9% more than those sintered at 1800 °C, and it was found that the sintering time can be reduced by 40–50% at faster heating rates. The maximum shrinkage rates occurred at temperatures lower than those of the sintering thresholds for the two mixtures, two temperatures and three heating rates. It was also found that after formation of the liquid, the mechanisms of particle rearrangement and solution-precipitation were not as fast as reported in the literature, even at high heating rates, for example 30 °C/min, but they are responsible for much of the shrinkage occurring throughout the sintering cycle.