| Cordierite ceramic material,owned good thermal stability,are widely used as refractory materials,foam ceramics,microwave ceramic substrates,etc.Cordierite ceramics must be glazed in order to improve the strength of the substrate,surface hardness,thermal stability and easy to clean,etc,when cordierite ceramics is used as microwave oven.LAS system material has low thermal expansion coefficient,excellent thermal stability and chemical stability,which make it become the main low expansion material.In this paper,the research objective is exploiting a low expansion glaze matching with cordierite ceramic substrates used as plate.Li2O-Al2O3-SiO2 system low thermal expansion glazes used on the low expansion ubstrates were prepared by preparation process of raw glaze.Mainly studies the influence of the composition of raw materials and process conditions on the glaze layer crystal phase composition,microstructure,thermal expansion coefficient and mechanical properties and thermal shock resistance of samples with glaze on surface.The glaze chemical corrosion resistance and the crystal formation mechanism of P-spodumene are studied.The main work and results of the thesis are as follows:1.Low expansion LAS glazes with different thermal expansion coefficient were prepared using adjusting the mole ratio of Li2O/Na2O,SiO2/Li2O and the content of MgO.The expansion coefficient of LAS glazes prepared can be adjusted in the range of 0.53?39.84×10-7/?.With the increase mole ratio of(m)Li2O/(m)Na2O,the melt temperature and crystallization temperature in cooling process of glazes ascends,the main crystalline phases of the glazes changes from ?-quartz solid solution and quartz into ?-quartz solid solution or P-spodumene solid solution,and the content of glass phase in the glaze layer and the thermal expansion coefficient of glazes decreases.With the increase ratio of SiO2/Li2O,the thermal expansion coefficient of glazes decreases(the mole ratio of SiO2/Li2O is between 6 and 10).When the SiO2/Li2O ratio is 8,the bending strength of the sample covering the glaze increased by 24%than the substrate,and the bending strength retention rate is as high as 96.7%after the 10 times thermal shock experiment.With the increase content of MgO,melting temperature of glazes decrease,while crystallization temperature of the glaze layer in cooling process ascends.The M4 glaze layer has a lot of rod-shaped grain,and has a low thermal expansion coefficient of-0.53×10-7/?.And the M4 sample is under a stress of 51 Mpa,which is not conducive to the increase of strength of the samples.2.The article uses the M2 formula as glaze formula.The influence of glaze slurry particle size,sintering temperature and the cooling method on the crystallization characteristics and the performance of the samples are studied.The results show that:if the glaze particle size is larger the surface roughness of the glaze will increase,however,if the glaze particle size is too small will result in the crack of the glaze layer in the process of drying.It is appropriate when particle size D50 is 4.26-5.16 um.With the increase of sintering temperature,the grain size in glazes increases,and the thermal expansion coefficient increase gradually.The strength retention of samples sintering at different temperature were above 90%after 10 times thermal shock experiments.3.The chemical resistance of glazes was studied.The results show that:the alkali resistance of the glazes containing P-spodumene solid solution crystalline phases is better than the glazes containing P-quartz solid solution crystalline phase.LAS glaze is superior to acid alkali resistance.Firing temperature glaze eased slightly lower chemical corrosion resistance.With the increase of sintering temperature,the chemical corrosion resistance of glaze weakened slightly.The chemical corrosion resistance of the quench glaze layer is less than furnace cooling. |
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