Time–Temperature–Transformation Diagrams with More than One Nose

The structures of time–temperature–transformation diagrams of glasses which crystallize by combined homogeneous and heterogeneous crystallization mechanisms are examined. Considerations are given to the factors which might produce more than one extremum in such diagrams. Specific nucleation and growth models are used, and the influence of the parameters which appear in the nucleation and growth rate expressions upon the structure of the diagrams is evaluated.     

Zirconia–Ceria Solid Solution Synthesis and the Temperature–Time–Transformation Diagram for the 1:1 Composition

Zirconia–ceria solid solutions of tetragonal symmetry ( t 'ZrO₂) containing 30 to 65 mol% ceria were prepared by annealing c '-ZrO₂ at 627°C samples sintered at 1660–1760°C, where c '-ZrO₂ is defined as a cubic or tetragonal phase whose axial ratio c/a (tetragonality) is equal to 1. The lattice parameters and the cube root of the unit cell volumes of the annealed samples increased linearly with the ceria content but, on the other hand, the axial ratio c/a (tetragonality) decreased to 1.000 at 70 mol%. During the annealing of each sample, the cell volume decreased because the residual Ce³⁺ ions were oxidized to the smaller Ce⁴⁺. The temperature–time–transformation (TTT) diagram of the 1:1 solid solution was investigated for the c'-t' diffusionless phase transition and the c'–(t + c) diffusional reaction. The c'–t' transformation was found to behave as a thermally activated process with an activation energy estimated to be 113 kJ/mol. This value may indicate that c'–t' transformation is controlled by oxygen diffusion accompanied by dimensional changes of the cerium ions.     

Development of Porous Antireflective Films on Borosilicate Glasses

Experiments were conducted to characterize the development of gradient-index antireflective (GIAR) films formed on a phase-separated alkali borosilicate glass. Solution chemistry, secondary-ion mass spectrometry, Auger electron spectroscopy, weight-loss, scanning electron microscopy, and specific surface area analyses were used to evaluate a proposed model for film formation. The results suggest that the film-forming process is more complicated than proposed. For near-optimum heat trcatments, the film-formation acid treatment was virtually nonselective; only for much longer than optimum annealing times was selectivity evident. The graded-index films may result from precipitation of dissolved glass. The analyses were complicated by major compositional variations existing in the as-received glass.     

Temperature–Time–Mechanical Properties of Glass–Ceramics Produced from Coal Fly Ash

Physical and mechanical properties of glass–ceramics fabricated from thermal power plant fly ash were analyzed and compared with suggest a temperature–time–mechanical (T–T–M) diagram. Coal fly ash with SiO₂–Al₂O₃–MgO–CaO as major components and TiO₂ as a nuclear agent were used to develop glass–ceramic materials which were heat treated at 900°–1050°C for 0.5–4 h for crystallization. It was verified that the high aspect ratio of unknown crystallines in the microstructure contributed high hardness, strength, fracture toughness, and wear resistance. These results are correlated with heat treatment conditions and microstructure and a T–T–M properties (hardness, strength, elastic constant, toughness, and wear rate) diagram on glass–ceramics produced from coal fly ash is proposed.     

硼硅酸锌玻璃的制备及其发光特性

由于发光玻璃独特的透明性,在激光、光学放大器、光通讯、储能和显示等光电子领域有着广泛的应用.本文利用高温固相法制备出了新型硼硅酸锌:铕掺杂的硼硅酸锌玻璃,讨论了掺杂离子浓度对玻璃发光特性的影响.结果表明Eu2+掺杂的硼硅酸锌玻璃在250～400 nm波长范围可以被很好地激发,有很宽的激发波长范围,发射谱为一个宽带峰,位于450 nm.掺杂不同浓度的Eu2+的硼硅酸锌发光玻璃的激发光谱有所不同,随着掺杂Eu2+浓度的增加,荧光强度增强,但发射光谱峰位置基本没有变化.另外,Eu2+掺杂硼硅酸锌玻璃较易合成,是一种很好的蓝色发光材料,具有较大的应用价值.     

Comparison of Bulk Properties of Mg-PSZ with Temperature–Time Contour Diagrams

The relationships of the precipitated metastable and stable phases with respect to the bulk properties of Mg-PSZ were analyzed versus time and temperature. An application of the temparature-time-transformation diagram method detailed in a previous study was used to analyze the data. A new methodology is presented to compare the complex property relationships between the bulk properties and precipitated phases. Fracture toughness ( K _IC ), Vickers hardness, as well as area fractions of unreacted secondary precipitate zones and grain boundary phase, were measured and plotted. For example, a maximum in fracture toughness was found to correlate with the disappearance of the unreacted secondary precipitate zones.     

Investigation of the Physicochemical Properties of Borosilicate Glasses for the Preparation of Glass-Fiber Materials

Borosilicate glasses of two compositions are synthesized and investigated with the aim of preparing glass microspheres from them. Using the Appen and Okhotin additive methods, the physicochemical properties of the glasses and melts are calculated, their crystallization ability and water stability are experimentally studied, their intrinsic temperatures are determined using dilatometry and differential scanning calorimetry, and their TLCE values are obtained.     

Birefringence and Microstructure of Anisotropic Borosilicate Glasses

Optically anisotropic glasses were obtained by the uniaxial stretching of phase-separated borosilicate glasses in the transformation temperature range. The sign inversion of the birefringence, induced by subsequent heat treatments, was correlated with microstructure. The positive birefringence is attributed to form birefringence and the negative birefringence to "distribution birefringence" caused by the anisotropic distribution of the separated phase.     

Viscosity and Microstructure of Phase-Separated Borosilicate Glasses

The viscosity of a sodium borosilicate glass (SiO₂ 70, B₂O₃ 23, and Na₂O 7 wt%) was measured as a function of heat-treatment temperature and time for phase separation. The viscosity was shown to approach an equilibrium value unique to the heat-treatment temperature. The magnitude of the equilibrium viscosity increased as the heat-treatment temperature decreased. These results, plus electron microscopy of microstructure development, established that the viscosity of phase-separated borosilicate glasses is primarily controlled by the composition of the continuous, high-viscosity phase and that the effect, if any, of the microstructure size is small. In contrast to previous reports, the heat-treatment time required to attain the equilibrium composition was extremely long.     

硼硅酸盐玻璃结构与其熔体性质研究

对硼硅酸盐玻璃结构及其熔体性质展开研究,通过红外光谱分析了Al2O3对硼硅酸盐玻璃结构的影响,测试了玻璃熔体的高温粘度和抗折强度.研究结果表明:当玻璃中Al2O3/SiO2物质的量比在1.2％～6.5％,(R2O-Al2O3)/B2O3的物质的量比在0.04 ～0.41范围内时,Al3+全部以[AlO4]形式存在,是玻璃网络形成体,B3+大部分以[BO3]的形式存在,是玻璃网络外体,少部分以[BO4]形式存在,是玻璃网络形成体.增加玻璃熔体中Al2O3的含量,玻璃中游离氧含量和[BO4]含量减少,[BO3]含量增加,玻璃的高温粘度增大,熔制温度升高,抗折强度降低.     

Structure and Electrical Properties of Iron Borosilicate Glasses

Glassesofnominal composition 25SiO₂- 30Na₂O-2Al₂O₃-x Fe₂O₃-(43- x)B₂O₃ (x = 1 to 6 mol%) were prepared by the ordinary melt quenching technique. The influence of Fe₂O₃ substitution at the expense of B₂O₃ on structure and electrical conductivity of sodium borosilicate glasses was investigated. The conductivity was found to increase with increasing Fe₂O₃ content. A double channel conduction mechanism was introduced to explain the electrical conductivity measurements. Moreover, the activation energy decreases considerably in the temperature range from 473 to 773 °K. The activation energies of conduction in various temperature regions were calculated. The conduction was best described by sodium ion migration and hopping between the two valence states of iron. FTIR absorption spectra in the spectral range 1600-400 cm^?1 were measured and a deconvolution analysis technique (DAT) using Gaussian peaks was introduced to analyze the studied glasses. Different characteristic bands were observed and attributed to different types of borate besides silicate vibrational groups.     

Preparation by a Sol-Gel Process of Borosilicate Glasses Containing Microcrystals of Tellurium and Zinc Telluride

Borosilicate glasses, 5B₂O₃· 95SiO₂ (mol%), containing TeO₂ and ZnO nominally equivalent to 10 wt% Te and ZnTe were prepared by a solgel method from Si(OC₂H₅)₄, B(OCH₃)₃, H₆TeO₆, and Zn(NO₃)₂. A study by electron spectroscopy for chemical analysis (ESCA) showed that glasses heated at high temperature (450°C) in air contained both Te⁶⁺ and Te⁴⁺ ions on the surface layer, but that mainly Te⁴⁺ ions occurred inside the bulk glass. When solgel-derived borosilicate glasses containing the TeO₂ compound were reduced at elevated temperature in a hydrogen atmosphere, Te crystallites ranging in size from 4 to 15 nm were produced at a lower temperature, between 200° and 250°C. The absorption edge moved from the infrared to the visible wavelength region as the particle size decreased to about 4 nm. For glasses containing both TeO₂ and ZnO, ZnTe crystallites formed at high temperature—over 300°C—and existed along with the Te phase.     

Corrosion of Borosilicate Sealing Glasses for Molten Carbonate Fuel Cells

The development of a new sealant for molten carbonate fuel cells (MCFC) requires a study of the attack of molten carbonates on selected materials. Silica and Pyrex® glasses have better corrosion resistance against molten carbonates than other glasses, but they have unsuitable thermal expansion coefficients. Comparisons have also been made between borosilicate glasses of suitable thermal expansion for sealants for MCFC and silica and Pyrex® glasses. The corrosion kinetics in molten carbonates follows two limiting relations and involves two corrosion mechanisms. The weight loss varied linearly with time, indicating a dissolution of the glass network at short times. Longer times show corrosion, depending on the square root of time, typical of a diffusion mechanism and indicating formation of a protective layer on the surface of the glass. The main crystalline corrosion product is lithium methasilicate. The glass-corrosion rate follows the well-known Arrhenius law. These studies used scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and chemical analysis. A general corrosion mechanism of borosilicate glasses in molten carbonates is proposed.     

Fracture- and Indentation-Induced Structural Changes of Sodium Borosilicate Glasses

It is known that indentation using a diamond indenter induces permanent densification to result in plastic or inelastic deformation of glass. However, it is still unclear whether a high tensile stress causes such a structural change or not. In this study, fracture- and indentation-induced structural changes of glasses with the compositions of 20 Na₂O − 40x B₂O₃ – (80−40x) SiO₂ (in mol%, x = 0, 0.5, 1, 1.5) are investigated. Two-point bending tests of the glass fibers are performed to apply a high tensile stress to the glasses, and Vickers indentation tests of the glasses are also carried out for comparison. The structural change of the glass is evaluated by using Raman spectroscopy. It is elucidated that a tensile side of the fractured fiber for every composition shows a permanent structural change, which is characterized by a lower wave number shift of Raman peak assigned to the Si-O-Si bending vibration mode. It is also found that the behaviors of Raman peaks of the fractured fiber are opposite to those of the indented glass under a high compressive stress.     

Exploring Internal Structure of Nanoporous Glasses Obtained by Leaching of Phase‐Separated Alkali Borosilicate Glasses

Mesoporous glasses – the leaching products of phase‐separated alkali borosilicate glasses – are widely used in fundamental research and practical applications. In this work, the option to control their internal mesopore structure by varying the conditions of microphase separation has been studied. Structure and transport characterization of a family of nanoporous glasses obtained under different conditions has been performed using a combination of several experimental techniques, including gas adsorption, nuclear magnetic resonance cryoporometry and diffusometry.     

化学强化玻璃的发展现状及研究展望

化学强化玻璃因其表面压应力层使玻璃的机械强度提高,被广泛用于电子产品显示屏领域。本文对钠钙玻璃、铝硅玻璃、磷铝硅玻璃、锂铝硅玻璃等的化学强化进行了综述,对进一步通过优化骨干网络结构来提高玻璃本征强度获得更高机械强度的玻璃做出了可行性探索。总结了目前化学强化玻璃面临的问题及发展方向,为相关科学研究和工业生产提供参考。     

Percolation Phenomenon for Dissolution of Sodium Borosilicate Glasses in Aqueous Solutions

A percolation phenomenon has been discovered for the dissolution of sodium borosilicate glasses in aqueous solutions under low-pH conditions (pH ∼2). The glasses fall into one of two categories which are markedly different in the dissolution behavior, in terms of whether the Si/B ratio in the glass network exceeds a threshold value or not. The transition from one of the categories to the other is very sharp when the Si/B ratio is changed as the key parameter. The qualitative aspects of the experimental observation can be explained very well by a simple model combined with the site percolation theory.     

In-Situ Surface-Roughness Measurements during the Preparation of Chemically Etched Porous Silicon

We have monitored the stain-etching of silicon in real time using neutron reflection. The etching process does not occur uniformly with time and possible dynamics of the process is under consideration. Distinct irregularities are produced on the PS surface and some gas bubbling from the cell is observed.     

Electron Micrographs of Some Borosilicate Glasses and Their Internal Structure

Many electron micrographs were obtained for borosilicate glass which had been subjected to chemical attack after heat-treatment at various temperatures and durations in order to study changes in internal structure, the so-called "phase separation." Both replica and direct-transmission methods were applied to Vycor-type glass. The two kinds of picture showed good agreement with each other. The conclusions obtained are as follows: (1) So-called quenched-state glass contains a glassy microphase of alkali borate, with dimensions less than 100 a.u., which corresponds to the so-called low-melting component; (2) the longer the heat-treatment time under constant temperature the larger the size of this glassy microphase becomes; (3) another kind of glassy microphase (SiO₂-rich) which corresponds to the so-called high-melting component is also enlarged with increasing heat-treatment time; (4) the size of both glassy microphases shows different values with different heat-treatment temperatures. Based on the experimental results described, a discussion of the relation between the internal structure and some physical properties of the glass is presented.     

Effect of Radiation on Glasses in Borosilicate and Boron-Lead-Silicate Systems

The effect of an electron flux and gamma radiation on glasses produced in a synthetic glass batch is considered. The origin of the radiation color centers arising in glasses and the disintegration of these centers in thermal and photodecolorization is investigated.