Corrections to the phase diagram of the Mg-O-Al2O3-SiO2 system

Translated from Steklo i Keramika, No. 10, pp. 11–12, October, 1992.     

Phase diagram of the system Al2O3-SiO2

Phase diagrams of the system Al₂O₃ - SiO₂ as presented in the domestic and foreign literature are analyzed. The congruent and incongruent states of mullite, liquation in the solid phase, and the structures of mullite and sillimanite are discussed.Translated from Ogneupory, No. 8, pp. 11 – 14, August, 1995.A lecture delivered to metallurgists and silicate producers at the Ural State Engineering University.     

镁铝硅系堇青石基微晶玻璃的制备及性能研究

采用高温熔融法制备了MgO-Al2O3-SiO2 (MAS)系堇青石基微晶玻璃.借助X射线衍射仪(XRD)、扫描电镜(SEM)及热膨胀系数仪研究了晶化热处理工艺、MgO/Al2O3质量比以及晶核剂种类(TiO2/ZrO2)与含量对MAS系堇青石基微晶玻璃理化性能和晶化特性的影响.结果表明:在核化温度750℃、保温时间1h,晶化温度1050℃、保温时间2.5h,升温速率5 ℃/min时,微晶玻璃中堇青石含量最高,析晶性能最好;当MgO/Al2O3质量比为1左右时,在30 ～ 700℃温度范围内,平均热膨胀系数最小,在4.4 ～4.8×10-6K-1范围内可调;TiO2是MAS系堇青石基微晶玻璃的有效晶核剂,而ZrO2的加入并不利于基础玻璃的晶化.     

Synthesis,Structure and Properties of MgO-Al2O3-SiO2-B2O3 Transparent Glass-Ceramics

Silicon - MgO-Al2O3-SiO2-B2O3 system transparent glass-ceramics have been prepared by conventional melt-quenching method followed by controlled crystallization, and their properties were also...     

MgO-Al2O3-SiO2系透明玻璃陶瓷研究进展

透明玻璃陶瓷具有热膨胀系数可调、强度高、化学稳定性好的优点,且兼具透光/发光的特性,是一种在光学信息、生物技术、激光技术、红外遥感及民用照明等领域有着广泛的应用前景的新型功能材料。本文简述了玻璃陶瓷的透光机制,对形核剂、过渡金属离子及稀土离子掺杂MgO-Al₂O₃-SiO₂(MAS)系透明玻璃陶的析晶及透光/发光性能方面的研究进展进行了介绍,并简要分析了开发具备透光/发光性质的高结晶度MAS透明玻璃陶瓷材料存在的问题,最后展望了透明玻璃陶瓷的发展趋势与前景。     

MgO-Al2O3-SiO2系统微晶玻璃晶化行为及性能研究

本文制备了MgO-Al2O3-SiO2系微晶玻璃,用XRD、DTA、SEM等方法对该系统微晶玻璃材料的析晶过程进行了研究。在此基础上,讨论了晶化行为对微晶玻璃的热学及力学性能的影响。结果表明：材料的热学性能及力学性能取决于热处理工艺。晶化温度950-980℃段,微晶玻璃试样的致密性好,力学强度优良。     

MgO-Al2O3-SiO2系统微晶玻璃晶化行为及性能研究

制备了MgO-Al2O3-SiO2系微晶玻璃，用XRD．DTA，SEM等方法对该系统微晶玻璃材料的析晶过程进行了研究。在此基础上，讨论了晶化行为对微晶玻璃的热学及力学性能的影响。结果表明：材料的热学性能及力学性能取决于热处理工艺。晶化温度950～980℃段，微晶玻璃武样的致密性好，力学强度优良。     

The phase conversions and properties of refractories based on the MgO-Al2O3-Cr2O3system

Conclusions An investigation of the phase conversions in the MgO-Al₂O₃-Cr₂O₃ system at a below-unity ratio MgO/R₂O₃ and varied content of sesquioxides showed that the magnesiochromite initially being formed in all mixtures interacts with the Al₂O₃ at temperatures above 1000°C with the result that two kinds of solid solutions are formed, viz., a spinel one Mg(Cr_xAl)_1–x)₂O₄ and (Al_xCr_1–x)₂O₃. The predominance of a given component in the original composition remains preserved in both phases.The presence was established of a solid solution of Al₂O₃ in the spinel phase which contained a signficant amount of MgAl₂O₄. No solid solutions of R₂O₃ are formed in the spinel when the chromite component predominates in both phases.The changes in the properties of the specimens correspond to the phase conversions. After high-temperature firing materials of the type Mg(Al, Cr)₂O₄-(Al, Cr)₂O₃ possess adequate property indices.The analysis is concerned with that part of the system for which MgO/(Al₂O₃ + Cr₂O₃) is less than unity.Translated from Ogneupory, No. 8, pp. 48–53, August, 1976.     

纳米尖晶石铁氧体在MgO-Al2O3-SiO2玻璃中的析晶研究

以正硅酸乙酯、醋酸镁、异丙醇铝、醋酸镍和硝酸铁为原料，通过溶胶一凝胶工艺合成了氧化镁一氧化铝一二氧化硅玻璃和微晶玻璃。采用DTA和XRD对凝胶玻璃的吸晶行为进行表征。DTA和XRD结果显示：凝胶体在500℃热处理后可以转变为透明玻璃体，在900℃热处理后，得到含有堇青石晶相的微晶玻璃；当5％(摩尔分数)氧化镍引入体系后，在800℃处理2h后，纳米尖晶石和堇青石同时从体系中析出；当氧化镍和三氧化二铁同时取代体系中的氧化镁和氧化铝时，纯纳米铁氧体尖晶石从玻璃体中析出。     

含Bi2O3的MgO-Al2O3-SiO2玻璃核化与晶化动力学研究

使用差热分析(DTA)的方法研究了含Bi2O3的MgO-Al2O3-SiO2玻璃粉末(粒度≤0．054mm)的核化与晶化动力学。由此方法确定了样品最大成核速度温度，同时计算出晶体生长的活化能和动力学参数。结果表明，含Bi2O3玻璃的晶化指数(n)和晶体生长维数(m)都为1．15(约等于1)，这说明该玻璃的晶化机制是表面晶化。由Kissinger和Augis—Bennett方程计算出的活化能较为接近，平均值为401kJ／mol。     

Effect of metastable phase on the crystallization and mechanical properties of MgO-Al2O3-SiO2 glass-ceramics without nucleating agents

Glass-ceramics without nucleating agents usually undergo surface crystallization, which deteriorates the overall performance of the products. In this paper, we evaluated the effects of the metastable MgAl₂Si₃O₁₀ crystalline phase on the crystallization behavior of a MgO–Al₂O₃–SiO₂ (MAS) glass without nucleating agents and mechanical properties of the glass-ceramics obtained. The results demonstrated that the precipitation of metastable MgAl₂Si₃O₁₀ crystallites promotes the crystallization mechanism transformed from surface crystallization into volume crystallization with two-dimensional crystal growth. Furthermore, the grain size of MgAl₂Si₃O₁₀ near the surface of the prepared glass-ceramics was larger than that of MgAl₂Si₃O₁₀ inside, which helps to generate compressive stress and improves its mechanical properties. The glass-ceramics containing metastable MgAl₂Si₃O₁₀ phase exhibited an enhanced hardness in the range of 7.6 GPa–9.5 GPa for indentation loads ranging from 2.94 N to 98 N, and indentation size effect behavior was observed in Vickers hardness tests of both MAS glass and glass-ceramics. The load-independent hardness values for MAS glass and glass-ceramics were reliably evaluated by the modified proportional specimen resistance (MPSR) model of 7.1 GPa and 7.6 GPa, respectively, with a high correlation coefficient of more than 0.9999. This work reveals the unexploited potential of the metastable phase in improving the crystallization ability and mechanical properties of glass-ceramics.     

Phase-microstructure-property relationship in high quality factor MgO-Al2O3-SiO2-TiO2-La2O3 glass-ceramics

MgO-Al₂O₃-SiO₂-TiO₂-La₂O₃ glass-ceramics were investigated with respect to the phase compositions and the microstructure as well as the microwave dielectric properties. Indialite, magnesium aluminum titanate (MAT, Mg₄Al₂Ti₉O₂₅), perrierite, and spinel were the main crystal phases in the studied 1.8MgO-1.2Al₂O₃-2.8SiO₂-1.4TiO₂-xLa₂O₃ (x=0.4, 0.3, 0.2) glass-ceramics. Mg₄Al₂Ti₉O₂₅ was detected inside the indialite domain as well as at the boundary while no decomposition product (rutile) is found, proving that Mg₄Al₂Ti₉O₂₅ is fully stabilized. After heat-treatment at 1200 °C, the quality factor (Q×f) of the glass-ceramics increases from 27,500 to 40,000 GHz with decreasing La₂O₃ concentrations. This is caused by the formation of more indialite and MAT. Meanwhile, the temperature coefficient (τ_f) shifts positively from −95 to −65 ppm/°C because of the smaller perrierite concentration. However, τ_f is still too negative due to the absence of rutile that possesses a high positive τ_f. For the 1.3MgO-1.2Al₂O₃-2.8SiO₂-1.4TiO₂-0.2La₂O₃ glass-ceramic with lower MgO molar composition, the peaks assigned to rutile is found and the chemical formula of MAT changes to MgAl₂Ti₃O₁₀ while spinel disappears. MgAl₂Ti₃O₁₀, which distributes mainly at the boundary, decomposes partially, leading to the precipitation of rutile inside the indialite domain. Thus, the τ_f of the glass-ceramic could be adjusted to near 0 ppm/°C with ε_r=9.9 and Q×f=28,600 GHz, which are favorable properties for microwave dielectric applications.     

MgO-Al2O3-SiO2系统微晶玻璃的析晶及热处理工艺研究

用XRD、DTA对MgO-Al2O3-SiO2系微晶玻璃材料的析晶过程进行了研究,讨论了热处理温度及时间对微晶玻璃热膨胀系数的影响,表明了各种晶体的析出特点.     

晶化时间对MgO-Al2O3-SiO2系微晶玻璃显微结构及性能的影响

通过差热分析(DTA)、X射线衍射分析(XRD)、扫描电子显微镜(SEM)等测试手段研究了不同晶化时间对MgO-Al2O3-SiO2系微晶玻璃析晶性能、微观结构及抗弯强度的影响。研究结果表明,随着晶化时间的加长,晶粒尺寸逐步增大,抗弯强度逐渐增高。     

组成对MgO-Al2O3-SiO2系统分相析晶的影响

对MgO-Al2O3-SiO2系统的分相与析晶进行了探讨,通过对不同组成点在热处理各阶段的试样进行XRD、TEM及DTA分析,研究了玻璃组成对玻璃的分相和析晶的影响.结果表明:当组成中MgO/Al2O3越大且同时SiO2含量越高,越利于该系统产生分相.当MgO/Al2O3大于3且SiO2含量大于68mol％时,水淬试样产生分相.SiO2含量较高时,分相液滴很容易聚集在一起,形成连通的蠕虫状分相粒子.随着SiO2含量的降低,玻璃的析晶放热峰温度逐渐降低,而且析晶放热峰变得尖锐,玻璃析晶趋势增强.当SiO2含量越低且MgO/Al2O3越大时,越利于该系统析晶.     

MgO-Al2O3-SiO2系统微晶玻璃的热处理工艺对其介电性能的影响

本文制备了MgO-Al2O3-SiO2系微晶玻璃,用XRD、DTA等方法对该系统微晶玻璃材料的析晶过程进行研究,通过正交试验,讨论了热处理温度及时间对微晶玻璃介电性能的影响.结果表明通过热处理工艺来控制晶相的析出,可以使样品的介电常数和介电损耗符合要求.获得较小介电常数的热处理制度为核化温度750℃,核化时间1h,晶化温度1100℃,晶化时间1.5h,所获得的微晶玻璃的介电常数为6.13,介电损耗4.22×10-3+可作为绝缘体等微波介质材料使用.     

Effects of MgO on Crystallization and Microwave Dielectric Properties of MgO-Al2O3-SiO2-TiO2-La2O3 Glass-Ceramics

A new glass-ceramic material with dielectric constant ε_r~9–12 and optimum quality factor Q × f~29000 GHz was fabricated from xMgO-1.2Al₂O₃-2.8SiO₂-1.2TiO₂-0.4La₂O₃ (x = 1.0, 1.4, 1.8 and 2.2) system. The effects of MgO on crystallization, microstructure, and dielectric properties of the material were investigated by differential scanning calorimeter(DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and network analyzer. The results show that the glass-ceramic consists of multicrystalline phases, including perrierite, cordierite, magnesium aluminotitanate (MAT), rutile, and spinel (MgAl₂O₄). Rising MgO content promotes the formation of MAT with compositions richer in magnesia, stabilizes spinel at high temperature, and at the same time suppresses the existence of rutile in the material. Quality factor Q × f value of the material is significantly improved with increasing MgO, which is mainly attributed to the existence of more MAT and spinel, while the drop of dielectric constant is related to the decrease in rutile.     

A coupled phase diagram experimental study and thermodynamic optimization of the Li2O-CaO-Al2O3 and Li2O-CaO-SiO2 systems,and prediction of the phase diagrams of the Li2O-CaO-Al2O3-SiO2 system

A coupled experimental phase diagram study and thermodynamic modeling of the Li₂O-CaO-Al₂O₃ and Li₂O-CaO-SiO₂ systems was conducted at 1 atm total pressure. Differential scanning calorimetry (DSC) measurements were performed in the Li₂O-CaO-Al₂O₃ and Li₂O-CaO-SiO₂ systems. In addition, the phase relations in the Li₂O-CaO-Al₂O₃ system were determined by equilibration/quenching experiments at 1643 and 1743 K, and the phases were characterized with X-ray diffraction (XRD) and Electron-probe micro analysis-wavelength dispersive spectroscopy (EPMA-WDS). The absence of ternary compounds or solid solutions was confirmed. Congruent melting of Li₂CaSiO₄ compound in the Li₂O-CaO-SiO₂ system was determined at 1350 ± 5 K. Thermodynamic optimization of the Li₂O-CaO-Al₂O₃ and Li₂O-CaO-SiO₂ systems was carried out based on new phase diagram experiments and critically evaluated literature data. The phase diagrams of the quaternary Li₂O-CaO-Al₂O₃-SiO₂ system were predicted using the thermodynamic models with optimized model parameters.