石英块料直接煅烧法生产方石英

阐述了石英块料直接煅烧法生产加工方石英的工艺特点。产品通过X射线衍射(XRD)、扫描电镜(SEM)、能谱仪(EDS)测试,说明块料直接煅烧法生产的方石英具有转化率高、加工性能好、成本低等特点。     

Reaction behavior of kaolinite with ferric oxide during reduction roasting

The pre-separation of silica and alumina in aluminosilicates is of great significance for efficiently treating alumina-/silica-bearing minerals for alumina production. In this work, the reaction behavior of kaolinite with ferric oxide during reduction roasting was investigated. The results of thermodynamic analyses and reduction roasting experiments show that ferrous oxide obtained from ferric oxide reduction preferentially reacts with alumina in kaolinite to form hercynite, meanwhile the silica in kaolinite is transformed into quartz solid solution and/or cristobalite solid solution. With increasing roasting temperature, fayalite formed by reaction of surplus ferrous oxide with silica at low temperature is reduced to silica and metallic iron in the presence of sufficient carbon dosage. However, increasing roasting temperature and decreasing Fe₂O₃/Al₂O₃ molar ratio favor mullite formation. The complete conversion of kaolinte into free silica and hercynite can be obtained by roasting raw meal of kaolin, ferric oxide and coal powder with Fe₂O₃/Al₂O₃/C molar ratio of 1.2:2.0:1.2 at 1373 K for 60 min. This work may facilitate the development of a technique for comprehensively utilizing silica and alumina in aluminosilicates.     

Investigation on cristobalite crystallization in silica-based ceramic cores for investment casting

In this work, cristobalite crystallization and its effects on mechanical and chemical behaviour of injection moulded silica-based ceramic cores were investigated. In order to simulate casting process condition, the sintered samples at 1220 °C were also heated up to 1430 °C. Flexural strength test was carried out on both sintered and heat treated samples. Chemical resistance of the cores was evaluated by leaching the samples inside 43 wt% KOH solution at its boiling point. Phase evolution and microstructure were investigated by thermal analyses (DTA and DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical microscopy (OM). Results showed that cristobalite was crystallized on the surface of fused silica grains at about 1380 °C. Flexural strength of the sintered cores was decreased after simulated casting heat treatment due to cristobalite phase transformation. The formed cristobalite on the surface of fused silica grains dramatically decreased the leachability of ceramic cores.     

α-石英方石英转变的研究

以SiO2含量高达98.2%的石英砂为原料,应用综合热分析仪分析了石英砂的方石英析出过程,采用X射线衍射仪对试样进行成分分析,利用万能材料试验机对烧结后试样进行强度测试。实验发现:DSC曲线中未出现明显的方石英析出放热峰。XRD测试表明,石英砂热处理后,产物中出现方石英相,随着温度的提高、保温时间的增加,方石英量不断增加。强度测试表明试样在1400℃热处理后耐压强度最高。     

粉煤灰中铝硅高效分离的动态扩大试验

为缓解我国氧化铝工业存在的铝土矿需求量大与国内铝土矿供应严重不足间的矛盾和粉煤灰大量堆积造成的环境问题,基于粉煤灰还原?氧化焙烧?碱浸实现铝硅分离的全新工艺路线,在已有静态小实验基础上,开展了实验室回转窑动态扩大试验研究。结果表明:在1100℃、配料比n(Fe):n(Al):n(C)=1.2:2:1.2、进料量75 g、还原焙烧1 h条件下得到的焙烧熟料,在Na₂O浓度为77.5 g/L的NaOH溶液中、液固比为20 mL/g时在130℃下溶出60 min,熟料中硅溶出率达92%;在Na₂O浓度100 g/L、模数为1.0的硅酸钠溶液中130℃溶出2 h,硅溶出率达60%以上,获得模数为2.4的硅酸钠溶液。对比分析物料焙烧过程和熟料溶出前后的形貌、粒度变化情况表明,物料粒度较大和溶液结构变化将导致硅溶出率下降。     

Effects of micro-sized mullite on cristobalite crystallization and properties of silica-based ceramic cores

Silica-based ceramic cores are extensively used in investment casting process, during which they must exhibit sufficient flexural strength and deformation resistance. In this study, micro-sized mullite was used as an additive to silica-based ceramic cores to optimize their high temperature properties. To investigate the effects of micro-sized mullite on cristobalite crystallization, mechanical and thermal properties of silica-based ceramic cores, ceramic cores with different amounts of micro-sized mullite were fabricated. The XRD results showed that additional micro-sized mullite diminished the crystallization of cristobalite at high temperatures, primarily caused by the mullite related compressive stresses on the surface regions of fused silica particles. Three-point bending tests and SEM results showed that micro-sized mullite had a more significant effect on the flexural strength of ceramic cores compared with conventional additives. Particularly, the fracture mechanism of silica-based ceramic cores had been changed from intergranular fracture into a mixed fracture consisting of both intergranular and transgranular fracture. The mechanical and thermal properties of ceramic cores were all reduced slightly as the mullite content exceed 4.6 wt%. Hence, to optimize the properties of silica-based ceramic cores, the micro-sized mullite content should not exceed 4.6 wt%.     

电子束辐照HDPE/绢英粉体系的热氧化及光氧化稳定性研究

通过电子束辐照改善了HDPE与无机填料绢英粉（STC）的界面相互作用，制得了强度韧性兼优的材料，为了开发应用这一新材料，有必要对其热氧及光氧稳定性进行研究，本文研究了电子束辐照HDPE（e-HDPE)放置后效应及其对e-HDPE/STC共混体系力学性能的影响，。采用人工加速热氧化及光氧化的方法，对e-HDPE/STC共混体系的热氧化及光氧化稳定性进行了研究，研究结果表明，电子束辐照HDPE加入稳定剂并造粒后性能比较稳定，对e-HDPE/STC共混体系的力学性能基本无影响，在本试验条件下，e-HDPE/STC共混体系具有较好的热氧化及光氧化稳定性，经过168h热氧化或光氧化以后，拉伸强度变化不大，冲击强度保持率分别为93％及84％。     

Synthesis of Chemically Stabilized Cristobalite

The synthesis of chemically stabilized cristobalite (CSC) by a wet-chemical route is described. CSC is a form of silica (containing small amounts of other oxides) which is similar in many ways to β-cristobalite, but does not invert to α-cristobalite upon cooling. The effects of changing the dopant levels and various synthetic parameters on the phases formed in the CaO-Al₂O₃-SiO₂ system have been investigated. Stabilization of cristobalite with a number of different dopant combinations has been attempted, with mixed results. The use of wet-chemical techniques has led to the synthesis of apparently phase-pure CSC in a composition region where traditional solid-state synthetic techniques yield a mixture of other phases.     

反应结合SiC电热材料的高温氧化特征

研究了反应结合SiC电热材料在1100～1580℃空气介质中加热时的氧化特征。结果表明：加热温度高于1420℃后，材料基体中的残留Si熔化并流动到表面形成SiO2。氧化后形成的SiO2与表面氧化层融为一体，提高了表面氧化层的致密度，有利于材料的抗氧化性能。1500℃左右为材料的抗氧化性能转折温度。在1500℃以下氧化时，反应结合SiC的抗氧化行为与重结晶SiC接近；高于1500℃氧化时，材料表面发生破坏性氧化，引起电热材料的失效。1500℃氧化后的表面氧化层中同时存在低温石英、方石英和非晶态SiO2。     

方石英的析晶与无定形化

石英是一种重要的结构和功能材料，在航天飞行器、半导体、电子通讯和光学器件等领域得到重要应用，但是高温下方石英的析晶限制了它的进一步应用．本文综述了不同研究人员对不同形态石英与石英基复合材料析晶行为及其差异的研究成果和所持的不同观点，再从“表面析晶”的角度分别对不同形态石英析晶行为的差异性与不同工艺因素对石英基复合材料的影响机制进行了系统阐述．最后，结合作者的工作，进一步介绍了方石英无定形化方面的最新研究成果．