SiO2—MgO—Al2O3—F系玻璃陶瓷的析晶

本文应用TEM,XRD和EDAX等技术,系统研究了SiO2-MgO-Al2O3-F系玻璃陶瓷的析晶过程。结果表明：在玻璃熔体的冷却过程中,由于驰豫作用而形成晶核,在随后的热处理过程中,中间相Mg2FBO3和KAlSiO4以此核为中心析出,氟的存在促进了晶体的整体析出,而主晶相氟金云相在中间相的晶界处形核长大。     

SiO2-Al2O3-MgO-F系微晶玻璃的形变析晶

采用高温熔融法制备了SiO2 -Al2O3 -MgO-F系玻璃样品,应用X射线衍射(XRD)、扫描电子显微镜(SEM)研究了该微晶玻璃在自由形变时的析晶特征,得到了微晶玻璃自由形变析晶的规律.结果表明:在热处理过程中随着温度的升高,基础玻璃的黏度逐渐降低,可以在析晶前施加压力使之发生变形.在自由形变的前提下,微晶玻璃析出的晶体在垂直压力和平行压力方向上没有出现定向析晶.显微硬度测试结果也表明在微晶玻璃中没有明显的各向异性特征,不会带来材料性能在不同方向上的差异,为形状复杂、均质同性微晶陶瓷的制备提供了一个有效途径.     

SiO2-MgO-Al2 O3-F系玻璃陶瓷的析晶

本文应用TEM,XRD和EDAX等技术,系统研究了SiO2-MgO-Al2O3-F系玻璃陶瓷的析晶过程.结果表明:在玻璃熔体的冷却过程中,由于弛豫作用而形成晶核,在随后的热处理过程中,中间相Mg2FB3和KAlSiO4以此核为中心析出;氟的存在促进了晶体的整体析出,而主晶相氟金云母在中间相的晶界处形核长大.     

K2O—B2O3—SiO2玻璃成分对析晶性能的影响

本文利用ＤＴＡ、ＸＲＤ、ＴＥＭ、ＳＥＭ等技术研究了三种Ｋ２Ｏ－Ｂ２Ｏ３－ＳｉＯ２玻璃的析晶性能。结果表明，Ｋ２Ｏ３－Ｂ２Ｏ３－ＳｉＯ２玻璃的析晶由分相引起，分相和析昌能力受成分影响较大，随Ｂ２Ｏ３和Ｋ２Ｏ含量增多及Ｋ２Ｏ／Ｂ２Ｏ３比值的降低，析晶加强，析晶主晶相类别尚未查清，次晶相确定为α－方石英。     

CaO—MgO—Al2O3—SiO2—F系可切削微晶玻璃的晶化机理研究

在CaO-MgO-Al2O3-SiO2-F系可切削微晶玻璃体系中，本研究分析了K2O和ZrO2c对玻璃析晶和显微结构的影响，探讨了晶化机理。K^ 促使云母相的生成和球晶的形成，晶化过程中，云母和顽辉石互为外延生长，使球晶中条状晶解离为片状晶。ZrO2与F^-一起促使玻璃晶化后形成棒状云母晶粒，并具有晶粒长径比大、相互交换的显微结构。     

SiO2-Al2O3-MgO-K2O-(F,Cr2O3)玻璃陶瓷的析晶

为了研究形核剂氟化物、氧化铬及其复合作用对SiO2-Al2O3-MgO-K2O系玻璃陶瓷形核和析晶的影响,采用高温熔融法制备了不同氟化物和氧化铬含量的基础玻璃,并对该基础玻璃进行了差热分析、显微分析和X射线衍射分析.结果表明:在所研究的玻璃体系中,氟化物或氧化铬的加入,都不同程度地削弱了玻璃体的结构,降低了玻璃的转变温度;当基础玻璃只含有氟化物时,玻璃在表面析出云母晶体,内部发生分相现象,而玻璃中仅含有氧化铬时,玻璃中发生整体析晶;没有氟化物的存在,不能析出云母晶体;当同时加入两种元素的物质后,对玻璃体析晶的影响不是简单的加合,复合的作用更为突出,进一步降低了玻璃的转变温度和析晶温度,整体均匀析出云母晶体.     

B2O3-Al2O3-SiO2系微晶玻璃析晶动力学研究

采用差示扫描量热（DSC）分析法对B2O3-Al2O3-SiO2系统微晶玻璃的析晶动力学参数进行了测定，研究了该系统微晶玻璃的析晶动力学。结果表明：随着B2O3/SiO2比的降低，该系统玻璃的析晶活化能E呈先升高后降低的变化趋势，当B2O3/SiO2比为11：5时，析晶活化能最小，Emin=375．4kJ／mol，晶化指数n则先减小后增大，但均〉4，表明该系统玻璃可整体析晶。     

含AlF3和ZrF4氟化物玻璃的分相与析晶

以摩尔组成为8．7MgF2-17．4CaF2-8．7SrF2-13．3BaF2-13．0YF3-31．6．AlF3-7．3ZrF4的氟化物玻璃为对象，研究了玻璃的分相和析晶．研究表明，玻璃中同时含有AlF3和ZrF4时，玻璃产生明显的分相，玻璃在高温下对水比较敏感，容易产生表面析晶．玻璃内部的析晶主要来自稳定性较差的富Al相，受空气中水分的影响，玻璃表面的析晶首先产生于富Zr相．依据玻璃的分相和析晶表现，讨论了含AlF3和ZrF4氟化物玻璃的表面析晶机理．     

晶种对低温烧结BaO-Al2O3-SiO2系微晶玻璃析晶的影响

用烧结法制备了化学计量比和高Ba含量的两组BaO-Al2O3-SiO2(BAS)系微晶玻璃,研究了晶种对低温烧结BaO-Al2O3-SiO2系微晶玻璃析晶的影响.结果表明,玻璃的软化温度随着品种含量的增加而提高.在两组玻璃粉中添加晶种有助于降低析晶活化能,促进六方钡长石和单斜钡长石的析出;晶种含量为1%时活化能最小,成分为化学计量比的玻璃析晶峰值温度也最低.在850℃保温时间2 h,添加1%晶种的BAS系微品玻璃全部转变为单斜钡长石.在两组成分的BAS系微晶玻璃中,六方钡长石的析出表现为整体析晶.不加晶种时,单斜钡长石通过六方钡长石一单斜钡长石的晶型转变析出,表现为整体析晶;添加晶种后,单斜钡长石主要因"同构"效应直接从基础玻璃中析出,表现为表面析晶.     

CaO-MgO-Al2O3-SiO2-F系可切削微晶玻璃的晶化机理研究

在CaO MgO Al2 O3 SiO2 F系可切削微晶玻璃体系中 ,本研究分析了K2 O和ZrO2 对玻璃析晶和显微结构的影响 ,探讨了晶化机理。K+ 促使云母相的生成和球晶的形成 ;晶化过程中 ,云母和顽辉石互为外延生长 ,使球晶中条状晶解离为片状晶。ZrO2 与F- 一起促使玻璃晶化后形成棒状云母晶粒 ,并具有晶粒长径比大、相互交错的显微结构     

V2O5含量对SiO2-MgO-Al2O3-K2O-V2O5-F系玻璃陶瓷析晶的影响

应用扫描电子显微镜(SEM)、X射线衍射(XRD)及电子探针(EPMA)等技术研究了V2O5含量对SiO2-MgO-Al2O3-K2O-V2O5-F玻璃陶瓷析晶的影响.结果表明,在所研究的玻璃体系中,V2O5的加入促进了莫来石晶体在较低温度下的析出,而且随着玻璃中V2O5含量的提高,莫来石和云母晶体的析晶温度区间逐渐向低温方向移动.EPMA结果显示在析出的晶体中没有钒元素的聚集,表明V2O5的加入没有参与晶体的直接形核,而是以网络外体的形式存在于玻璃体系中,削弱玻璃的结构,导致晶体析出温度降低.同时发现VO含量尽管对析出晶体的种类没有明显的影响,但是对晶体的形态、大小及数量的影响较为显著.     

Laser processing of ceramics of the SiO2-Al2O3 system

An investigation has been made of the constitution of laser-processed ceramics from the SiO₂-Al₂O₃ system. Samples were produced in the form of pellets a few millimetres in diameter by pulsed laser melting of mixtures of silica and alumina powders containing 40, 60 and 70 mol % Al₂O₃. X-ray diffraction identified the main crystalline phases as Al₂O₃ in the pellets produced from the 70 mol % Al₂O₃ mixture and mullite from the 60 and 40 mol % Al₂O₃ mixtures. The proportion of glassy phase present increased with increasing SiO₂ content. Microstructural observations on the 60 mol % Al₂O₃ pellet showed primary mullite crystals and a lamellar structure interpreted as a eutectic of Al₂O₃ and mullite. Pellets prepared by melting kaolin powder consisted essentially of a glassy phase and much porosity. Cladding of an alumina substrate, carried out using a continuous powder feed into a laser-generated melt pool, was carried out using the same silica-alumina mixtures as those employed for pellet production. A clad layer was also produced by preplacing a kaolin coat on the alumina substrate prior to laser processing. The effects of traverse speed over the range 3.7 to 7.4 mm s^?1 inclusive, power density (44.4 and 111 W mm^?2) and powder flow rate (0.13 to 0.47 g s^?1 inclusive) were investigated. It was found that the phases present in the clad layer depended on the composition of the precursor powder and the processing conditions. Microstructural examination of the clad layers produced from SiO₂-60 mol % Al₂O₃ and kaolin that had completely melted during processing exhibited various growth morphologies.     

Combustion Synthesis of Glass (B2O3-Al2O3-MgO)-Ceramic (TiB2) Composites

The combustion synthesis, or self-propagating high temperature synthesis (SHS), technique has been used to produce glass ceramic composites that have a glass matrix based on B₂O₃-MgO-Al₂O₃and a crystalline ceramic phase of TiB₂. Conditions for producing glassy materials by the SHS technique are discussed and the thermodynamics of these combustion reactions are analyzed. The combustion characteristics, i.e., ignition energy, combustion temperature, and wave velocity have been determined. Green density of the pellets had a significant effect on the combustion characteristics. Green pellets with low density were used to reduce heat loss, thus enabling the synthesis of those compositions having low adiabatic temperatures. The glass-forming region of these SHS glasses was found to be in relatively good agreement with that of samples produced by the traditional furnace-melting method.     

Crystallization and microstructural behaviour of strontium titanate borosilicate glass ceramics with Bi2O3 addition

Glasses in the system (65 −x) [SrO·TiO₂] − (35) [2SiO₂·B₂O₃] − (x) [Bi₂O₃] wherex = 1, 5, 10 (wt%) prepared by melting in alumina crucible (1375–1575 K), were subjected to different heat treatment schedules followed by DTA studies. Crystallization study showed the formation of Sr₂B₂O₅ as major phase at low temperature (≈950°C) heat treatment. At high temperatures, TiO₂ and SrTiO₃ with or without Sr₂B₂O₅ crystallize out depending on heat treatment. In this paper, the influence of variation in composition, thermal treatment on the nature of crystallizing phases as well as on the resulting microstructures are investigated through XRD, IR and SEM. Uniform crystallization was achieved by suitable addition of Bi₂O₃ and proper heat treatment.     

Effect of 1 wt% CoO addition on dielectric and microstructural behaviour of (SrO·TiO2)-(2SiO2·B2O3) glass and glass ceramic

Glass of the nominal composition 64 wt%(SrO·TiO₂)·35 wt%(2SiO₂·B₂O₃)-1 wt%(CoO) was prepared. The glass samples were subjected to heat treatment at 900 and 950 C. The phase progression in these glass ceramics from X-ray diffraction studies shows the formation of Sr₂B₂O₅ as primary crystalline phase followed by rutile (TiO₂), Sr₃Ti₂O₇, SrB₂Si₂O₈ and Sr₃B₂SiO₈ as secondary phases. The first DTA exothermic peak of glass corresponds to the crystallization of Sr₂B₂O₅, rutile and Sr₃Ti₂O₇ phase while second crystallization peak may be assigned to the formation of SrB₂Si₂O₈ and Sr₃B₂SiO₈ phases. From microstructure studies we find that strontium borate grows with larger grain size whereas the other phases like Sr₃Ti₂O₇, TiO₂ appear smaller in size. Cobalt oxide content in the strontium titanate borosilicate glass ceramic gives the thermal stability to dielectric behaviour and decreases the dielectric loss. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

超重力熔铸Y2O3-Al2O3-SiO2玻璃的晶化行为研究

研究了以超重力熔铸方法制备的Y₂O₃-Al₂O₃-SiO₂玻璃的晶化行为, 并结合相图分析了热处理条件对晶化过程的影响规律。实验结果表明, Y₂O₃-Al₂O₃-SiO₂玻璃的晶化行为与热处理温度和SiO₂含量密切相关。当热处理温度为1050℃时, 晶化后样品的相组成沿超重力场方向呈现出梯度分布, 自上而下分别为Al₆Si₂O₁₃玻璃陶瓷、纯玻璃相、χ-Al₂O₃玻璃陶瓷。当退火温度为1100℃时, 析出晶相主要为Y₃Al₅O₁₂及Y₂Si₂O₇; 退火温度为1200℃时主要析出Y₃Al₅O₁₂。因此, 以超重力熔铸法制备YAS玻璃结合后续热处理的工艺, 提供了一种快速制备YAS基微晶玻璃的新方法。     

BaFe12O19-BaTiO3/SiO2-B2O3微晶玻璃陶瓷的sol-gel合成及微波性能

采用柠檬酸sol-gel工艺合成了BaFe12O19-BaTiO3／SiO2-B2O3微晶玻璃陶瓷，对其介电常数及其磁导率在1MHz－6HGz下的变化规律进行了研究。结果表明其复介电常数和复磁导率值基本随测试频率的增加而下降。     

SiO2-CaO-B2O3-Al2O3微晶玻璃在平板式ITSOFC中密封性能的研究

平板式中温固体氧化物燃料电池(ITSOFC)的密封材料在工作温度下,与其接触的电池材料应具备以下特性:(1)气密性;(2)尺寸稳定性;(3)热匹配性;(4)化学稳定性;(5)绝缘性.采用SiO₂-CaO-B₂O₃-Al₂O₃系统微晶玻璃制备出一种适用于850℃的密封材料.该材料在850℃保证一定尺寸的前提下,能够与8YSZ电解质和Ni-Cr双极板紧密黏附,热膨胀系数8.9×10^-6)/℃和8YSZ接近,电导率约为10^-8S/cm有良好的电绝缘性能,在O₂和H₂气氛下保温100h没有气体泄漏,且密封后的黏附界面边界分明,元素扩散层厚度<10μm.实验证明该材料适用于ITSOFC 850℃密封.