【作者】 王华；

【导师】 樊启晟； 李懋强；

【作者基本信息】 中国建筑材料科学研究总院 ， 材料学， 2007， 博士

【摘要】 在陶瓷材料先进成型技术中,室温冷凝浇注成型是近三年来发展的一种冷冻浇注成型工艺,它具有水基冷冻浇注成型的主要优点,如在干燥过程中没有收缩开裂,可以实现陶瓷近净尺寸成型,能够制备具有特殊孔结构的陶瓷坯体等,同时避免了通常水基冷冻浇注成型工艺需要昂贵专用设备以及具有较大体积变化等缺点。本文以炭黑、碳化硅为主要研究对象,采用莰烯作为悬浮介质,通过对陶瓷粉体在莰烯中的表面电性研究,高固相含量低粘度莰烯基炭黑料浆、高固相含量碳化硅料浆以及炭黑/碳化硅料浆的制备技术的研究,实现了反应烧结碳化硅素坯的室温冷凝浇注成型工艺,制备出了结构均匀、具有一定孔结构的反应烧结碳化硅素坯以及烧结体。主要获得的研究成果如下:研究了各种陶瓷粉体在莰烯中的表面电性,并对陶瓷粉体在莰烯中的表面电性进行了分析。偶联剂与分散剂的加入能够改变陶瓷粉体在莰烯中的表面电位,碳化硅、炭黑表面ZETA电位随偶联剂以及分散剂的加入量存在一个极值,此极值与陶瓷粉体表面对偶联剂以及分散剂的饱和吸附量密切相关。通过ZETA电位分析,可以初步判断分散剂以及偶联剂最佳加入量。系统研究炭黑莰烯基浓悬浮体的制备技术以及流变特性,阐明了炭黑的分散性与炭黑表面官能团含量的关系。研究发现:表面的酚羟基以及醌基含量高的炭黑在莰烯中的分散性能较好。超分散剂CH6是一种优良的炭黑分散剂,其最佳加入量为2mg/m²,分散机制为空间位阻稳定机制。采用超分散剂CH6分散的莰烯基炭黑料浆在固相含量为40vol%以下时,其流变特性接近于牛顿流体;当固相含量高于40vol%时,炭黑料浆呈现出塑性流体特征。系统研究了莰烯基碳化硅料浆的制备技术。通过对碳化硅表面改性可以有效提高碳化硅在莰烯中的分散性能,表面改性剂的种类以及改性工艺对分散性能有较大的影响,使用钛酸酯偶联剂TC27并采用干混法进行预处理的方式能够获得最好的分散效果。通过选用合适分散剂以及适当的表面改性以及采用合理级配,可以制备出固相分数达到70vol%,粘度为1.1Pa·s的莰烯基料浆,能够满足室温冷凝浇注成型工艺的要求。对莰烯基炭黑/碳化硅料浆制备技术以及流变特性进行了研究。研究表明:料浆的粘度与炭黑含量相关以及固相含量相关,通过优化制备出固相含量达到70vol%,50s^-1剪切速率下粘度小于0.9Pa·s的料浆,上述料浆能够较好地实现室温冷凝成型工艺。莰烯基碳化硅以及莰烯基炭黑/碳化硅料浆的流变学特性接近于宾汉流体。料浆存在剪切变稀现象,并存在一定的屈服值。研究了室温冷凝浇注成型的干燥过程,研究表明:冷凝成型样品的干燥可以分为升华干燥与解吸干燥两个阶段,其干燥速率随干燥时间的延长而呈指数下降。室温冷凝浇注成型工艺制备的炭黑/碳化硅坯体显微结构均匀,坯体中的气孔呈现树枝状结构,气孔尺寸分布为单峰分布,气孔尺寸与成型料浆的固相含量以及颗粒级配相关。可以通过调整固相分数、颗粒级配、炭黑含量等因素制备出致密或者一定孔结构的样品。经反应烧结后可制备出微观结构均匀的密度为3.0g/cm³的烧结体。更多还原

【Abstract】 Freeze casting at ambient temperature is a novel process for ceramics fabrication. It developed in past three years. Compared with conventional aqueous freeze casting, It uses a sublimable orgnic medium instead of water and provides a net shape forming method with less drying shrinkage caused by sublimation of frozen phase. This process does not need expensive freeze equipment and vacuum system which used in normal freeze casting process. In this study, camphene is used as suspending medium; carbon black and silicon carbide are dispensed in camphene. The Zeta potentials of ceramic powders in camphene are measured. Based upon the study on the rheology behavior of carbon black and silicon carbide slurries, high solid content and low viscosity slurries of carbon black, silicon carbide and carbon black/silicon carbide in camphene are obtained. The slurry of SiC/CB is casted in the mould and then freezed at room temperature to produce green parts for reaction bondend silicon carbide. After freeze drying, the green parts are sintered with liquid silicon at high temperature. The structure and properties of green body and sintered parts are investigated. The main results of these studies are as follows:The Zeta potentials of various ceramic powders in camphene have been measured and analyzed. It is found that the dispersant and coupling agent can change the surface potential. With adding of the dispersant and coupling agent, the surface potentials of carbon black and silicon carbide reach their peak values which closely related to there saturation absorbing capacities. Through Zeta potential analysis, the optimum addition quantity of dispersant and coupling agent can be forcasted.The rheological behavior of the slurry of high solid content of carbon black in camphene has been studied. It shows that the carbon black which contains higher phenolic hydroxyl group and quinonyl group on its surface has better dispersing capability. The hyper-dispersant CH6 is a superior one for carbon black, which reaches its best effect through the steric stability mechanism when the addition quantity is 2mg/m². With CH6 as dispersant, the rheological behavior of carbo black slurry in camphene changes from nearly Newtonian fluid, when its solid content is lower than 40vol%, to Plastic fluid, when its solid content is higher than 40vol%.The dissertation has conducted a systematic research on preparation of camphene based silicon carbide slurry. It can improve the dispersing capability of silicon carbide by using surface modification agent. The variety of the surface modification agent and the modification process influence the dispersing effect. The best dispersing result can be achieved by using titanate coupling agent TC27 and adopting dry process. By selecting suitable dispersant, conducting proper surface modification and adopting rational particle distribution, the slurry with 70vol% solid loading and viscosity of 1.1Pa·s can be prepared. Thus satisfies the requirement of freeze casting at room temperature.The dissertation has also conducted a systematic research on the preparing camphene based carbon black/silicon carbide slurry and its rheological behavior. The results show that the viscosity of the slurry is related to the content of carbon black and total solid content. The 70vol% solid loading slurry with viscosity less than 0.9Pa·s under 50s^-1shear rates can be prepared through optimization condition. This slurry can be adopted for freeze casting process at room temperature. The camphene based silicon carbide and carbon black/silicon carbide slurries are nearly Binham fluid.The carbon black/silicon carbide green bodies which fabricated by the room temperature freeze casting has homogeneous microstructure. There are exist dendritic pore in the green body, the size of the pore is nearly close, and the size of pore is related to the solid content and particle distribution. By regulating solid content, particle distribution, and the content of carbon black, dense samples or samples with particular pore can be produced. After sintering, the samples density can reach 3.0g/cm³ with homogeneous microstructure.更多还原