Study On The Preparation And Characteristics Of Cordierite Material With Low Coefficient Of Thermal Expansion

The life of ceramics used at high temperature or high temperature gradient field depend on the thermal shock resistance of materials, while the thermal shock resistance was influenced by many factors, and the coefficient of thermal expansion (CTE) was the most important one, so cordierite material was paid close attention and widely used because of its low CTE, it became a hot research topic that how to decrease the CTE of cordierite effectively.In this paper cordierite ceramic was prepared by using kaolin, talc and bauxite as starting materials, then pressed and sintered to obtain the samples. The optimal original formula, sintering condition, additive such as (TiO2+Al2O3), spodumene and pore-forming agent were studied. Besides the CTE of cordierite crystal and its thermal expansion anisotropy were studied by means of high temperature X-ray diffractmeter, the main results were:The optimal original formula of samples was:kaolin 41.5 wt%, talc 34.4 wt% and bauxite 24.1 wt%, the optimal sintering condition was 1350℃×4 h, then the CTE of sample prepared was 2.32×10-6℃-1; it could be decreased to 2.10×10-6℃-1 when 15 wt%(TiO2+Al2O3) was added, because a little aluminum titanate produced in sample had low CTE; it could be decreased to 2.20×10-6℃-1 when 8 wt% spodumene was added, because a little spodumene produced could promote preparation of cordierite; it could be decreased to 2.03×10-6℃-1 whenlO wt% starch was added, because the pore formed could hold a part of thermal expansion. When the additives mentioned above were added, the sample's sintering performance was well for use.The volume CTE and the liner CTE of cordierite crystal could be calculated accurately according to the method of high temperature X-ray diffractmeter, they were 2.33×10-6℃-1 and 0.84×10-6℃-1 respective at 800℃. The variation of CTE measured by this method was similar to that measured by standard method:there was a minimum at 300℃. That indicated there was a close relationship between the expansion of cordierite crystal and the expansion of sample. The linear CTE along a or b axis was similar to a linear ascending, the increased rate of it below 500℃was larger than that above 500℃, at 800℃the value reach the maximum 3.21×10-6℃-1; The linear CTE value along c axis decreased rapidly below 400℃, then decreased slowly above 400℃, and the value was -3.89×10-6℃-1 at 800℃. The linear CTE variation of crystal orientation [030] was similar to that of a axis, and crystal orientation [022] similar to c axis, the [122] was the most complicate. So the cordierite crystal had notable thermal expansion anisotropy.The different orientated crystal was distributed randomly in samples prepared by natural raw material, the expansion and shrinkage counteracted each other in a certain direction because of the notable thermal expansion anisotropy. So the linear CTE of cordierite material was relative low.