Study On Mechanism And Preparation Of Mullite-cordierite Refoactory

China is abundant of refractory resources, in which kyanite is one of importance and being developed recently. In the work, the application of kyanite in the preparation of mullite-cordierite refractory, the effect of composition and microstructure of the aforesaid material versus its properties are discussed. The goal in the present work is to develop high performance kiln furniture, which is saggar in particular, to match with the need in ceramics fabrication.50wt% raw kyanite was applied in the composition,±5wt% Zhimujie (a kind of secondary clay of high plasticity) as binder was added to compose matrices of 7:3 and 3:7 mullite/cordierite ratios. Besides a 50wt% of Jiaobaoshi (a kind of Shandong boxite) was added as aggregate. Experiments on different batch compositions and firing temperetures have been carried out. From the work it has shown that a synthesized mullite-cordierite of good performance can be obtained by using raw kyanite. MgO can be introduced by means of adding calcined talc or magnesia. Under the firing temperatures of 1300 and 1350 oC, by liquid phase sintering, the firing shrinkage will overcome the expansion process due to the formation of mullite. Through the tests of the as fired samples, batches of 1#, 2#, 3# and 4# have shown a high bending strength, it is due to fairly dense microstructure and even grains distribution, the needle like mullite garains has formed a skeletal structure. Owing to such a structure, crack will propagate along grain boundaries and transboundaries inside the material. Microstructures of samples 2#, 6#, 8# have shown the appearance of transgrain fracture, which have given rise to a conchoidal fracture surface. It has implied to a product of well-developed grain boundaries, and has given the samples of high bending strength. From the tests they have shown also that the particle size distribution and the nature of kyanite will affect the end result. By applying different particle size and different origin of kyanite there was quite a tremendous deviation of the result. The work has also carried out experiments on the role of additives and the effect of firing temperatures. An adequate additives (CaO, TiO₂, Fe₂O₃, R₂O) will help the formation of liquid phase, and enhanced the sintering process, however, the additives added should be in an adequate quantity, excessive additive will give rise to the increase of glass phase and will decrease the temperature shock resistivity. The optimum range of the additive is, CaO<2.0 wt%, TiO₂<2.0 wt%, it is necessary to avoid the existent of Fe₂O₃ and limits strictly the amount of R₂O.