Metastable Immiscibility Surface in the System Na2O-B2O3-SiO2*

Opalescence and clearing techniques were used to determine the metastable immiscibility surface for sodium borosilicate solutions. These results indicate that a three-liquid region, which may or may not be metastable to two-liquid regions, underlies the immiscibility surface.     

Thermal Conductivity of Molten B2O3, B2O3–SiO2, Na2O–B2O3, and Na2O–SiO2 Systems

With the aid of the transient hot‐wire method, the thermal conductivity of molten B₂O₃, B₂O₃–SiO₂, Na₂O–SiO₂, and Na₂O–B₂O₃ systems was measured along with their temperature and composition. It was observed that the thermal conductivity of pure B₂O₃ increased with temperature, until about 1400 K, and then decreased subsequently. Using the MAS‐NMR, 3Q‐MAS, and Raman spectroscopy, the structure of B₂O₃ and SiO₂ in the B₂O₃–SiO₂ system was confirmed. Findings show that an addition of B₂O₃ into the pure SiO₂ system causes a significant decrease in thermal conductivity, due to the formation of boroxol rings. The thermal conductivity of the Na₂O–SiO₂ system was measured and its phonon mean free path was calculated. In addition, a positive linear relation between viscosity and thermal conductivity was observed. In the Na₂O–B₂O₃ system, it was found that a change in the relative fraction of 4‐coordinated boron has an influence on the thermal conductivity when the concentration of Na₂O is between 10 and 30 mol%, in which case the tetraborate unit is dominant.     

Vaporization and Thermodynamic Properties of Melts in the Na2O–B2O3–SiO2 System

The vapor composition, partial pressures of the molecular species of the vapor, and activities of the melt components in the Na₂O–B₂O₃–SiO₂ system at temperatures of 1300 and 1350 K are studied using the Knudsen effusion mass-spectrometric method. It is shown that the vapor composition depends on the concentration ratio of sodium and boron oxides in the condensed phase. When the content of boron oxide is larger than the content of sodium oxide in the condensed phase, the vapor contains NaBO₂, (NaBO₂)₂, and B₂O₃ molecules. At the ratio [Na₂O] : [B₂O₃] > 1, the gas phase contains atomic sodium. The activities obtained for NaBO₂ and B₂O₃ indicate substantial negative deviations from an ideal behavior.     

Metastable Liquid Immiscibility in Alkali Metal Oxide–Silica Systems

A search was made for evidence of metastable phase separation in binary alkali metal oxide-silica glasses which had been subjected to the usual glassmaking procedures of melting, relatively fast cooling, and annealing. Electron microscopy and electrical properties measurements were the principal tools of investigation. Evidence for phase separation in Li₂O and Na₂O silica systems is given together with critical temperature estimates. Although K₂O-SiO₂ glasses showed some slight evidences of structural segregation it is concluded that binary K₂O, Rb₂O, and Cs₂O silica glasses generally show simple solution behavior and allow reasonable correlations of properties with cation size, type, and separation.     

B2O3含量对SiO2-Al2O3-B2O3-RO体系玻璃的性能和微观结构的影响

针对B2O3含量的变化对SiO2-Al2O3-B2O3-RO体系玻璃的介电性能、失透温度和微观结构的影响进行研究分析.研究发现:随着B2O3含量的提高,玻璃的介电常数和介电损耗逐步下降,玻璃的失透温度范围变的更大.而且,B2O3含量升高后玻璃更易于失透,导致玻璃失透的主要原因是玻璃分相;FTIR光谱分析显示,随着B2O3含量的升高,B2O3在玻璃中存在的结构发生了转变,[BO3]逐步向[BO4]进行转变.     

Structure of glasses in the Na2O - Fe2O3 - B2O3 - SiO2 system

The structure of glasses of a local area of the Na₂O - Fe₂O₃ -B₂O₃ - SiO₂ system is studied. The sequence of formation of oxygen-containing tetrahedral groups in the presence of nonbridge oxygen ions is established. Formation of groups of a six-coordinated into cation facilitates crystallization of sodium-boron-silicate glass melts in cooling. Translated from Steklo i Keramika, No. 1, pp. 11–13, January, 2000.     

B2O3对SiO2-Al2O3-MgO系统高强玻璃纤维性能的影响

高强玻璃纤维具有质轻、高强、耐高温及性价比高等优异特性,广泛应用于复合材料领域.本文通过对不同B2O3含量的高强玻纤试样进行拉伸、侵蚀、粘度、红外等性能的测试,研究了B2O3含量对高强玻璃纤维各种性能的影响.结果表明在高强玻璃纤维中引入一定含量B2O3,提高了玻璃纤维的拉伸强度,降低了高温粘度,一定程度上改善了高强玻璃纤维的工艺性能和提高了力学性能.     

Immiscibility and Crystallization in A12O3-SiO2 Glasses

Metastable glass-in-glass separation was observed on rapid quenching of A1₂O₃-SiO₂ melts containing from 10 to 50 mol% A1₂O₃. Nucleation and subsequent crystallization of mullite within the high-alumina-dispersed glass phase may occur either during cooling from the melt or on reheating. The metastable binary two-liquid region is compositionally defined, and a structural interpretation of the phase separation and the effects of small oxide additions on it is offered. Evidence for both classical and possible spinodal nucleation mechanisms during liquid segregation in this system is presented.     

Selected Phase Equilibria Studies in the Al2O3–CaO–SiO2 System

The Al₂O₃–CaO–SiO₂ system provides the basis for describing many important chemical processes. Although the system has previously been extensively studied, recent advances in experimental technique have provided the opportunity to obtain accurate liquidus measurements in the low‐silica region at fixed temperatures. The experimental procedures involve equilibration of high‐purity oxide powder mixtures at selected temperatures, rapid quenching, and accurate measurement of phase compositions using electron probe X‐ray microanalysis. The liquidus isotherms have been determined at selected temperatures between 1503 and 1873 K in the anorthite, gehlenite, pseudowollastonite, corundum, CaAl₁₂O₁₉, CaAl₂O₆, lime, Ca₃SiO₃, and Ca₂SiO₄ primary phase fields. The results are compared with currently available thermodynamic model predictions of the phase chemistry.     

Physical,Mechanical, and Thermal Characteristics of B2O3 - SiO2- Li2O -Fe2O3 Glasses

Silicon - Glasses of compositions 50.4B2O3 - 30SiO2- $$(19.6-x)$$ Li2O - $$x$$ Fe2O3, $$x$$ = (0 ≤ $$x$$ ≤ 2) were fabricated with molar fraction utilizing the conventional process....     

Studies in Lithium Oxide Systems: III,Liquid Immiscibility in the System Li2O-B2O3-SiO2

Glasses within the ternary system Li₂O-B₂O₂SiO₂ containing less than 25.6% Li₂Ocan be broadly classified into three groups according to their behavior during cooling or heating. One group, containing either more than 18% Li₂Oor less than 20% SiO₂, yields clear glasses during slow or rapid cooling. The second group, containing approximately 5 to 15% Li₂O and 26 to 90% SiO₂, yields dense white opal glass during slow or rapid cooling. The third group, located at the outer edge of the second group, cools to room temperature as clear glasses but develops opacity when reheated to temperatures between 550° and 8800°C. It has been shown by electron microscopy that the opacity is due to liquid immiscibility, the matrix glass containing well-formed spheres of the dispersed phase. Some of the clear glasses of both groups have been shown to consist of two immiscible phases. The size of the dispersed units in the spontaneous opal glasses and also the reheat opal glasses can be controlled by the variation of the reheat treatments. The phase separation reported here is beyond the resolution of the petrographic microscope and can be detected only with the high resolution of the electron microscope. Accessory evidence is given to show that the phases are non-crystalline.     

0.20 R2O-0.45 CaO-0.35 ZnO-Al2O3-SiO2系统的相变

通过大量的配方实验,利用ＯＭ,ＴＥＭ和ＸＲＤ分析,研究了０.20R2O-0.45CaO-0.35ZnO-Al2O3-SiO2系统的分相与析晶,研究结果表明,在Ａl2O3含量高于0.30-0.45mole的区域可以获得乳浊程度和光泽度各异的析晶乳浊釉,在低铝区可获得分相乳浊和分相玻璃,且乳浊程度随Ａl2O3含量的降低,ＳiO2含量的提高而提高,用Ｎa2Ｏ取代Ｋ２Ｏ不利于系统的分相,试样中析出的晶体主要为硅锌矿,锌黄长石,白榴石笔锌铝尖晶石,当Ｒ２O全部由Ｋ２Ｏ引入且Ａl2O3含量较低时,主要为硅锌矿,白榴石和锌黄长石,Ａl2O3含量较高时则主要为白榴石,锌黄长石和锌铝尖晶石,用Na2O等摩尔取代Ｋ２O炒利于白榴石和硅 矿的析晶,而有利于锌黄长石的析晶,锌黄长石的析晶主要受组成的影响,对析晶保温度不敏感,通过设计合理的配方,采用适当的烧成温芳制度,可以获得结晶良好的析晶乳浊釉,分相乳浊釉,分相玻璃,硅锌矿或锌黄长石分相结晶釉或微晶玻璃。     

Investigation of the Phase Diagram of the Na2O–B2O3–SiO2 System by the Small-Angle X-ray Scattering Technique

Sodium borosilicate melts containing 60 mol % SiO₂ are investigated in the temperature range T _g–1100°C by the small-angle X-ray scattering (SAXS) technique. The temperature dependences of the SAXS intensity for the studied melts consist of two linear portions. A change in the slope of these portions is observed at temperatures that coincide, to within the accuracy of the SAXS experiment (±5–10 K), with the liquidus temperatures, which are usually determined to approximately identical accuracy. The change in the slope is associated with the change in the temperature coefficients of the isothermal compressibility upon transition from a liquid state to a supercooled liquid state. Similar results were obtained earlier for binary melts in the sodium borate system and a number of other systems. On this basis, it is assumed that the transition from a liquid state to a supercooled liquid state for melts in any glass-forming system can be revealed from the temperature dependences of the SAXS intensity, and the SAXS technique can be used to determine the liquidus temperatures, primarily for glass-forming melts with a low crystallization ability.     

Sm2O3掺杂对BaO-B2O3-Al2O3-SiO2玻璃形成及结构的影响

借助魔角旋转核磁共振技术,探讨掺Sm2O3后BaO-B2O3-Al2O3-SiO2(BBAS)玻璃(BBASS玻璃)的形成、结构及热处理条件下玻璃结构的变化情况.研究表明:随着稀土掺量的增加,BBASS玻璃的形成区域先扩大后缩小.在Sm2O3外掺摩尔分数为30%时BBASS玻璃具有最大的形成区域.在BBAS玻璃结构中,随着BaO含量的增加,硼氧三角体[BO3]逐渐向[BO4]转变,原先[AlO4],[AlO5],[AlO6]共存的铝氧多面体结构逐渐转变为大量[AlO4]和少量[AlO5]共存的结构.在BBASS玻璃结构中,随着5m2O3掺入量的增加,Sm2O3对铝氧多面体结构变化的影响与BaO类似;对硼氧多面体而言,Sm3 强大的积聚作用使玻璃结构中硼氧多面体形成了巨大的网络.以上差异说明了Al3 比B3 更容易进入稳定的四面体结构.热处理对玻璃结构影响甚微.     

NaCl在NaOH水溶液中的结晶介稳区宽度的理论计算

通过对成核机理决定介稳区宽度的计算模型进行修正,建立了适用于NaCl-NaOH-H2O体系的结晶介稳区宽度计算模型,得出NaCl结晶的介稳区宽度,与经典结晶理论相比,计算误差较小,可以对工业氯碱的结晶条件进行理论指导。     

SiO2-BaO-Fe2O3系统微晶玻璃的制备及其磁性能研究

选择SiO2-BaO-Fe2O3玻璃体系,采用分步晶化热处理方法制备出了以BaFe12O19为磁性主晶相的无变形硬盘用微晶玻璃,并利用XRD、SEM、VSM等测试手段对微晶玻璃进行了分析和性能检测。研究结果表明:采用分步晶化热处理方法制备的微晶玻璃性能优于传统的一步晶化热处理方法,并且样品在分步晶化热处理过程中不会产生变形。经700℃/5h 850℃/10h分步晶化热处理所制备出的微晶玻璃的主晶相为BaSiO3,BaFe12O19,晶粒尺寸在1.0μm以内,其比饱和磁化强度可达248.89Am2/kg,矫顽力可达142.44kA/m。