K2O-ZnO-Al2O3-B2O3-SiO2系掺Cr3+透明莫来石微晶玻璃的研究

采用了X射线衍射、透射电镜和吸收光谱及荧光光谱技术研究了K2O－ZnO-Al2O3-B2O3－SiO2系掺Cr^3 玻璃的析晶性能和光谱。研究结果表明：在K2O－Al2O3-B2O3-SiO2系掺Cr^3 玻璃的基础上引入ZnO后，析晶性能明显改善；析晶温度降低，析出的纳米莫来石微晶均匀、规则；微晶玻璃的发光强度明显增强。     

Formation of sol-gel nanostructured mullite by additions of fluoride ion

Summary The subject of this study was to investigate the effect of fluoride ions addition on the temperature of sol gel mullite formation based on the hypotheses that the presence of fluoride ions can decrease the temperature of mullite formation (in respect to common 980°C, in sol-gel processing). Polymeric sols were prepared by mixing TEOS and aluminum nitrate nanohydrate and by adding fluoride ions (from 2 to 5 mass%). DTA, TG, XRD and SEM were used for characterisation of mullite gel and crystalline mullite. The experimental results confirmed that the addition of fluoride ions decrease the temperature of mullite formation up to 890°C for the fluorine concentration of 3.5 mass%. Experimental results showed that the temperature of mullite formation is not a simple function of the fluoride ion content. The mechanism of fluorine effect was discussed in terms of the gelling process, gel structure and the phase separation before the mullite formation.     

New data on the thermal analysis of diphasic mullite gel

A diphasic mullite gel has been synthesized by using Ludox and Al(NO₃)₃-9H₂O in ammoniacal solution. Both DTA and DDTA studies have been performed with a sensitive differential thermal analyzer system. Besides usual exotherm due to mullite formation, a pronounced exotherm between 800–1300°C has been noted. Considering previous XRD data, it is explained as due to formation of Si-Al spinel phase, which is subsequently transformed exothermally at 1320°C to mullite.     

Preparation of Mullite Fibers by the Sol-Gel Method

Mullite fibers were synthesized from an aqueous solution of aluminum isopropoxide, aluminum nitrate and tetraethylorthosilicate by the Sol-Gel method. The starting solution was prepared by adding aluminum isopropoxide and tetraethylorthosilicate simultaneously to an aluminum nitrate aqueous solution. The spinnability of the starting solution was investigated by varying the molar ratio of aluminum isopropoxide/aluminum nitrate in the solution. Gel fibers were obtained from solutions in a composition range of aluminum isopropoxide/aluminum nitrate of 3 to 5. Gels obtained from spinnable solutions appeared to have high homogeneity in the mixing of the Al/Si components, leading to a sharp 980°C exothermic peak in the DTA curve and a mullitization temperature of 1000°C. However, in the case of gels obtained from unspinnable solutions, a small 980°C exothermic peak was detected, and the mullitization temperature was as high as 1200°C, probably due to greater heterogeneity in the mixing of the Al/Si components.     

Effect of Organic Ligands Used in Sol-Gel Process on the Formation of Mullite

The preparation of mullite by the sol-gel method using organic polydentate ligands and the effect of the raw materials and organic polydentate ligands on the formation of mullite were investigated. Two series of samples were prepared using tetraethoxyorthosilicate (TEOS) and aluminum nitrate nonahydrate, or dibutoxyethylacetoacetatoaluminum (Al(OBu)₂(AcAcEt)) as the silica and alumina sources, respectively, and using ethylene glycol (EG), 1,3-propanediol (PD), 1,3-butanediol (BD), 2-methyl-2, 4-pentanediol (MPD), diethlene glycol monoethyl ether (DEME) and ethoxyethanol as the ligands. When the alumina source was aluminum nitrate nonahydrate, mullite was apt to appear in the order of EG>PD>MPD. When Al(OBu)₂(AcAcEt) was the alumina source, the tendency toward the appearance of mullite crystalline phase was EG>BD>DEME>MPD. Between the two alumina sources, aluminum nitrate nonahydrate gave mullite much easier than Al(OBu)₂(AcAcEt). These relationships were discussed from the viewpoints of the coordination ability of the ligands and the miscibility between the silica and alumina.     

Preliminary Study on the Effect of pH on Thermal Transformation of Some Diphasic Al2O3-SiO2 Gels

Diphasic Al₂O₃-SiO₂ gels have been synthesized by hydrolyzing ethyl orthosilicate at three different pH ranges in presence of colloidal boehmite. Result shows that dominant mullitization process are sensitive to pH of the gelation process. At highly acidic pH range, solid state reaction between corundum and cristobalite occurs, and develops liquid phase for mullite nucleation. At moderately acidic pH, nucleation and crystallization are most operative for nucleation in aluminosilicate matrix. In highly basic pH region, Al-Si spinel phase develops by incorporation of Si in aluminous phase as intermediary phase. Polymorphic transformation of it may be the cause of sudden mullitization. The changes in crystallization sequence in three distinct processes may be due to variation in the nature and size of silicic acid particle formed by hydrolysis and condensation of TEOS at different pH.     

Hamaker 2: A Toolkit for the Calculation of Particle Interactions and Suspension Stability and its Application to Mullite Synthesis by Colloidal Methods

For modern processing of ceramics at the nanoscale, the influence of interparticle interactions in the suspended state becomes increasingly important. The Hamaker 2 program has been developed for the rapid prediction of these interactions, allowing us to gain important understanding of the often delicate balance of forces in ceramic powder suspensions. This article discusses the theoretical foundation of the implemented models and shows the benefit of this predictive approach applied to mullite production by colloidal methods.     

Preparation and Structural Defects of Al2-xZrx＋yTi1-yO5 and Al4.54Si1.46O9.73 Multiphase Material

In the study, sludge from the aluminum profile factory and kaolin were used as the raw materials. Through adding ZrO2 mineralizer in different contents, Al2-xZrx+yTi1-yO5 and Al4.54Si1.46O9.73 solid solution multiphase material was prepared to effectively inhibit the decomposition of aluminum titanate solid solution and optimize high temperature property of the multiphase material. With XRD and SEM means, crystalline structure and microstructure of each sample were characterized, and properties of each sample were tested. According to experimental results, the optimal addition amount of ZrO2 mineralizer was determined to be 1.5%. Correspondingly, contents for aluminum titanate solid solution, mullite solid solution and α-Al2O3 were 70.3%, 26.8% and 2.9% respectively, bulk density was 3.20 g/cm3, degree of porosity was 5.57%, water absorption rate was 1.74%, and the once thermal shock rupture strength retention rate was 90.52%.     

含氟体系中高性能T型分子筛膜的合成

含氟体系中,在负载晶种的大孔莫来石支撑体表面快速合成了高性能且取向生长的T型分子筛膜。采用XRD、SEM和MASNMR等手段对分子筛膜层和粉末进行表征。讨论了添加物、氟硅比、合成温度和合成时间等条件对膜生长与分离性能的影响,并阐述了含氟体系中T型分子筛膜快速晶化的机理。碱金属氟盐的加入促进了T型分子筛晶体层的晶化速率,并对晶体层形貌产生了一定的影响。膜应用于75℃、水/异丙醇（10：90,w/w）体系的平均渗透通量和分离因子分别为（4.91±0.18）kg·m^-2·h^-1和7060±1130。     

硼酸钙对电瓷结构和性能的影响

研究了硼酸钙掺量对电瓷的相结构、显微结构、电气性能和机械性能的影响.通过不同硼酸钙添加量的电瓷在不同烧结温度条件下的断裂强度、气孔率、电阻率,结合电瓷的晶相结构和显微结构的变化,探讨其构效关系.结果表明:硼酸钙含量的增加或烧结温度升高,电瓷的电阻率和气孔率降低.但当硼酸钙掺量超过10;,烧结温度超过1120℃之后,电阻率和气孔率的变化不明显.电瓷的断裂强度随着硼酸钙的添加而提高,当硼酸钙含量超过10;后开始降低,添加量为10;时电瓷的断裂强度随着烧结温度而提高,1120℃后无显著变化.硼酸钙促进莫来石相的析出,但硼酸钙含量过高时,会促进CaAl2Si2O8形成,降低莫来石相的析出量,并使其形貌从细针状向短柱状和粒状发生转变.硼酸钙掺量恒定时,提高烧结温度可促进细针状莫来石相的生成.