Knowledge Management System Of Institute of process engineering,CAS
|关键词||多孔陶瓷 陶瓷膜 球形颗粒 烧结可控性 传质扩散|
多孔陶瓷具有耐高温、抗酸碱、耐有机腐蚀、良好的生物惰性、使用寿命长、再生性能好等优点，广泛应用在过滤、隔热、吸音及生物骨骼等领域中。目前，多孔陶瓷制备所用的原料多为形貌不规则的颗粒，这些颗粒在烧结过程中的可控性差，存在不均匀的团聚收缩，导致陶瓷中出现死孔、半通孔，并伴随孔率的烧结损失，影响了多孔陶瓷的实际应用效果。本论文针对陶瓷孔结构难以调控的问题，提出采用热等离子体制备的球形致密颗粒进行堆积造孔，通过烧结，球形颗粒间的接触点形成颈部连接，获得孔结构均匀、贯通、可调的多孔陶瓷。主要工作为：(1) 以球形致密的SiO2颗粒为原料进行紧密堆积造孔，球形颗粒堆积体经过烧结，相互接触的颗粒之间形成颈部连接，获得孔隙均匀贯通的多孔氧化硅陶瓷。结合动力学分析，对多孔陶瓷的烧结行为进行研究，结果发现球形致密的SiO2颗粒具有热稳定性，在颗粒间颈部强化过程中孔隙得到完好的保留，制备的多孔陶瓷具有很好的烧结可控性。研究了颗粒堆积紧密度对陶瓷结构和机械强度的影响，分析了球形颗粒造孔的特点。同时，获得了原料粒径对陶瓷孔径的调控规律。最后，开展了SiO2多孔陶瓷渗透性研究，并探索了其在固液分离、油水分离和颗粒粒径分级上的应用性能。(2) 为应用于高温环境，采用球形致密的Al2O3颗粒制备具有均匀贯通孔道的Al2O3多孔陶瓷。采用硅溶胶包覆原料颗粒的方法，有效降低了高强度氧化铝陶瓷的烧结温度，同时完好地保留了均匀、贯通、光滑的孔结构。分析了硅溶胶包覆层与氧化铝颗粒在烧结中生成莫来石颈部的过程，同时结合动力学分析开展了颈部生成的控制机理研究，结果表明莫来石颈部的生成受Al2O3颗粒表面Al3+释放速率的控制。根据陶瓷微观孔结构的烧结变化，优化了硅溶胶包覆量。同时，对莫来石强化陶瓷的作用机理进行了研究。最后，验证了氧化铝多孔陶瓷的高渗透性。(3) 以超细球形Al2O3颗粒为原料堆积造孔，制备孔径更小的Al2O3陶瓷膜。研究了超细球形Al2O3颗粒的烧结演化行为，发现球形颗粒堆积孔经过均匀的烧结演化，成为均匀贯通的孔结构，展现出良好的烧结可控性。从超细球形颗粒的传质机理研究中，发现球形颗粒通过表面扩散进行传质，烧结活化能达到721±12 kJ/mol，说明颗粒有很好的热稳定性。在膜层与过渡层的匹配研究中，得到了膜层的优化厚度4.8 μm和适宜的烧结区间1200 - 1400°C。通过膜层和过渡层的一步烧结机理研究，发现介稳相的纳米球形Al2O3颗粒转化为稳定的α相后才发生颗粒间的传质烧结，然而相转化温度与过渡层颗粒的烧结温度基本一致，使两层膜能够实现一步烧结。最后，将陶瓷膜用于悬浮颗粒分离，证明了其良好的应用性能。(4) 将孔结构的可控烧结技术运用到闭孔隔热陶瓷领域，利用SiO2空心颗粒壳体致密、高强的特点，制备了闭孔结构支撑的SiO2隔热陶瓷。通过调控烧结温度和烧结助剂，研究了隔热陶瓷孔结构的烧结可控性，结果发现致密的颗粒壳体能够很好地保护陶瓷闭孔结构，在高强颈部形成过程中，空心颗粒仅收缩<3.3%。同时，通过添加烧结助剂进行了陶瓷晶型结构的调控研究，揭示了方石英对隔热陶瓷性能的影响机理。通过调节空心颗粒的大小和壁厚，实现了多孔陶瓷结构和性能的调控。最后，建立了闭气孔支撑结构的隔热性能模拟模型，模拟结果与实验结果一致。
Porous ceramics is a very important material, which is widely used in filter, heat insulation, sound absorption and organic skeleton, ect. At present, the porous ceramics are mainly synthesized by irregular particles which have poor sintering controllability. The uneven contraction occurred among irregular particles can destroy the pore structure and limit the further improvement of the performance. In this work, inactive spheres synthesized by thermal plasma were used to synthesize porous ceramics through packing of spheres and sintering, the main work and results are listed as follows:(1) Amorphous SiO2 spheres with dense body were employed to synthesize porous SiO2 ceramics with uniform and interconnected pores through a new method combining close packing of spherical silica particles and sintering. Firstly, based on DSC analysis, the suitable sintering conditions for ceramics were set up. Then, the thermal stability of SiO2 spheres was studied according to kinetic analysis. Furthermore, the relation between sphere size and pore size was studied. Finally, the performances of the synthesized pores were researched, including the enhanced permeability for nitrogen and water, the consistence of filtration on solid/water separation, the performance in oil/water separation, and the employment in grading of particles.(2) The uniform and interconnected pore structures were extended to Al2O3 system which has better thermal resistance. A new method that coating the alumina spheres with silica sol was used to decrease the sintering temperature of ceramics while the pore structures were not be destroyed. Firstly, the pH regulation for silica coating and temperature control for gel-casting were studied to achive the two processes in one step. Then the formation process of mullite necks was reseached that Al3+ and O2- diffused from surface of spheres to necks and mullite could be formed after reaction. Furthermore, the Al3+ release controlled mullite formation mechanism was revealed according to the calculated activation energy and Avrami exponent n. Besides, the effect of thickness of coating layer on ceramic strength was sdutied, and the mechanism was revealed. Finally, the permeation flux of N2 and water was tested, and its well performance on pollution resistance was proved.(3) Then the uniform and sintering controllable pore structures were developed to Al2O3 membranes which has smaller pore size. Double-layered alumina membranes with interconnected uniform pores were synthesized by inactive sub-micrometer spheres through one-step sintering. Firstly, the mass transfer characterization of spheres and microstructure evolution of membrane were fully studied, the results showed that the interconnected uniform pores were formed after even evolution and the microstructure of membrane could be controlled by sintering conditions in a wide range. Then, the control of membrane thickness was studted, and a law between solid content of slurry and membrane thickness was established. Furthermore, the mechnism for one-step sintering was studied that mass transfer could not occur unless the metastable phases of spheres transform to stable α-Al2O3, and luckily the temperature for phase transformation of spheres and interlayer sintering was similar. Finally, the industrial waste water was processed by synthesized membrane and the result confirmed that the membrane was uniform without defects.(4) The technology of sintering controllability of pores was also needed in thermal insulation fields. Hollow SiO2 spheres with dense shells were employed to synthesize porous silica ceramics with closed-cell structure and high porosity. Firstlt, the influence of sintering temperature on the porous ceramic was studied and the suitable sintering conditions were determined. Then, the effect of different additives on crystal, structure and properties of porous ceramics was researched and the mechanism was revealed. Furthermore, it was revealed that α-cristobalite was negative both for ceramic strength and thermal insulation and it could be suppressed effectively by moderate Al2O3 and H3BO3. In addition, the thermal insulating performance and mechanical strength of ceramics could be controlled through changing the particle size or shell thickness of hollow spheres, and the regulation between them was set up. Finally, the simulation on relationship between porosity and thermal conductivity was set up according to effective medium theory.
|孙志强. 多孔氧化物陶瓷的可控烧结制备及性能研究[D]. 北京. 中国科学院研究生院,2017.|
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