【作者】 庞学满；

【导师】 徐明霞； 梁辉；

【作者基本信息】 天津大学 ， 材料学， 2008， 博士

【摘要】 本论文研究氮化硅基复相陶瓷材料凝胶注模成型工艺,从工艺设计的角度研究凝胶聚合过程、料浆制备以及坯体干燥等问题,寻求一条适用于非氧化物,尤其是适用于包括反应烧结氮化硅和液相烧结氮化硅基陶瓷材料制备的凝胶注模成型的技术路线,并对其中机理性的问题作深入的探讨。论文的主要工作及创新点包括以下几个方面:(1)以丙烯酰胺体系作为凝胶体系,研究该体系聚合过程的反应动力学,探讨引发剂和催化剂对聚合过程的作用机理,根据试差法得到聚合反应速率方程。综合考察单体与引发剂浓度对聚合反应速率以及聚合程度的影响。研究结果表明,聚合速率与引发剂浓度的平方根、单体浓度成正比;(2)以聚丙烯酸铵(PAA-NH4)作为分散剂,以聚乙二醇400(PEG400)为增润剂,采用球磨法制备了固相含量高达60% (vol),粘度低于1Pa·s,高稳定性的氮化硅料浆。研究了PAA-NH4对料浆稳定性的影响,探讨了PEG400在颗粒表面的吸附特性,以及提高颗粒润湿性的效果。根据液相中颗粒间以相切形式堆积的假设,建立了双球模型,解释了增润剂对于氮化硅料浆流变学性质的影响机理;(3)本论文采用浸泡法对金属硅粉进行表面改性,解决金属硅粉料遇水起泡和不易润湿的问题,同时选择合适的分散剂,采用高速分散工艺制备具有触变性的料浆。通过粘度法测试分散剂在颗粒表面的吸附等温线,研究其吸附状态,建立了触变网络模型,分析料浆流动过程中内部网络经历断裂-调整-重建的变化历程,解释了分散剂在料浆触变过程的作用机理;(4)以PAA-NH4和聚硅氧烷S-17为复合分散剂,采用球磨和高速分散相结合的工艺制备氮化硅-硅粉-烧结助剂复合料浆,以S-17作为料浆除泡剂,以达到工艺简单,同时具有较佳的除泡效果,同时利用S-17降低坯体内部液相表面张力,从而降低颗粒间毛细管力的作用,解决了坯体在干燥过程中的开裂问题;(5)根据颗粒堆积理论,以石英砂为粗颗粒粉料,氮化硅为细颗粒粉料,同时以纳米氮化硅作为超细粉,研究二元以及三元级配颗粒对料浆流变性和稳定性的影响。结果表明,通过掺入少量纳米氮化硅可以提高料浆稳定性,解决了以超细粉为原料制备料浆时不容易获得高固相含量的问题;(6)对坯体性能进行了表征,坯体未排胶前具有较高的强度(20MPa),当固相含量达到60vol%时,坯体的干燥收缩率接近为零,氮化硅坯体在排胶后仍然具有均匀紧密的内部结构。更多还原

【Abstract】 Gelcasting technology for silicon nitride based ceramics forming was researched in this dissertation. Gel polymerization process, slurry preparation and green body drying were studied in view of technical design. To seek a practical gelcasting technical route applied for non-oxides ceramic forming, particularly for silicon nitride-based ceramics, mechanism of the gelcasting process was discussed. The chief investigation and innovation in this dissertation were as follows: (1) The polymerization reaction kinetics and the effect mechanism of initiator and catalyst in acrylamide gel system were studied. Polymerization reaction rate equation was fitted by trial-and-error method. The factors affecting the rate of polymerization were analyzed, and the effect of monomer and initiator concentration on the polymerization reaction rate and extent was studied. The results show that the rate of polymerization is proportion to the square root of initiator concentration and the monomer concentration in premixed solution. (2) High property silicon nitride slurry with solid loading of 60vol% and viscosity of 1Pa·s was prepared using poly(acrylic acid) ammonium (PAA-NH4) as dispersant and polyethylene glycol 400 (PEG400) as wetting reagent. The effect of PAA-NH4 on stability of slurry was researched. The wetting ability of PEG400 on particles was studied and adsorption characteristic of PEG400 on particle surface were discussed. The mechanism of this impact was explained through double-sphere model based on particle tangent compacts. (3) In this dissertation, surface modification of Si particle was carried out to solve the problem of original powder foaming in water and badly wetting ability. Slurry with high solid loading and thixotropy was prepared by high speed dispersing process. The adsorption state of dispersant on the particle surface was studied by thixotropic network model and the mechanism of PAA-NH4 on thixotropic slurry process was discussed. (4) The various factors impacting rheology and stability of silicon nitride-silica-sintering additive composite slurry were studied in this work. PAA-NH4 and polysiloxane S-17 were used as composite dispersant to meet the stability requirements of the various powders. S-17 was used as slurry defoamer in order to eliminate bubbles. Since the introduction of surfactant S-17 into the slurry, lowering internal liquid surface tension, thus reducing capillary force between particles, the problem of cracking could be solved. (5) Based on the theory of particle accumulation, the effect of dual and ternary grain-composition on the rheology and stability of slurry were researched using quartz sand as coarse powder, silicon nitride powder for fine particles, the nano-silicon nitride as a superfine powder. The results of experiments show that the stability of slurry was improved due to the introduction of a small amount of nano-silicon nitride. And the problem of increasing the solid loading of slurry containing nano-powder was solved. (6) Performance of green body was characterized. High intensity (20 MPa) was presented before burning out the plasticity. Body shrinkage rate nearly became zero when the solid loading came up to 60vol%. Uniformity and compaction of the internal structure were remained after burning out the plasticity.更多还原