| In solar thermal power tower system, heat delivery mainly adopt alloy steel pipe. But alloy steel pipe can't resistance to high temperatures, and is easy to corrosion in high temperature condition, the development of new heat transport pipe material is of great significance.Based on the needs of solar thermal power tower, three kinds of materials were studied: mullite-cordierite composite ceramics, Mg-Al-Si system Al2O3-based composite ceramics and Ca-Mg-Al-Si system Al2O3-based composite ceramics, and cordierite-mullite Al2O3 composite ceramic material. Studied the relationship among composition, processing technology, micro structure and properties of the sample by modern testing technology, and discussed the mechanism of the thermal shock resistance.Used synthetic cordierite and synthetic powder as the main raw materials, Mullite-cordierite composite ceramic materials were prepared by no-pressure sintering process. The results showed that the best the best formula is 70%wt of synthetic cordierite and 30wt% of synthetic mullite, the sample sintered at 1440℃for 2h have the water absorption of 0.12%, the porosity of 0.30%, the bulk density of 2.487g/cm3, the bending strength of 68.49MPa and the sintering shrinkage of 29.93%. After 20times thermal shock resistance tests (quenching from 1100℃to 25℃in air medium), the bending strength is 87.13MPa, not only did not lose strength, but increased by 27.2%, and after 30 times thermal shock resistance test, circular sample did not crack. Because the open microstructure of cordierite prevented the densifying of samples, the sintering temperature of samples rised with the increase of synthetic cordierite,. The results of XRD showed that the major phases of all the samples were high -cordierite, low-cordierite, mullite and a-trydimite. The mechanism of thermal shock shows that when the amount of mullite was over 40wt%, there were lots of mullite grains in the form of bulk and needle bar. This structure was good to raise bending strength of the sample, but lowered the thermal shock resistance of samples. When the amount of synthetic mullite was 20%-30%, the major phase of samples was cordierite in the form of straitiform. with a little mullite among it. The sample has good thermal shock resistance because of this kind of structure. When the amount of synthetic mullite was less than 10%. there were lots of glass phase in samples, so the thermal shock resistance was bad. After comparing the phase composition and microstructure to the samples before thermal shock resistance test, discovered that the thermal shock wouldl promote the precipitation and growth of a-tridymiteof samples. And the tiny crack caused by the change of crystal form of quartz could improve the tenacity and thermal shock resistance of the samples. With -Al2O3 powder, Suzhou kaolin, talc, quartz as the main raw materials, Mg-Al-Si Al2O3-based composite ceramics materials were prepared by no-pressure sintering process. The results showed that the best formula isα-Al2O3 powder of 80wt%, Suzhou kaolin of 6wt%, talc of 9%, quartz of 5%. The sintering temperature of this formula was the lowest, and with the best thermal shock resistance. The sample sintered at 1480℃for 2h have the water absorption of 0.19%, the porosity of 0.57%, the bulk density of 3.06g/cm3, the bending strength of 99.59MPa, the sintering shrinkage of 12.72% and and the permanent linear shrinkage of 0.23%. After 20times thermal shock resistance tests (quenching from 1100℃to 25℃in air medium), the bending strength is 92.72MPa, only loss rate 6.9%. The study of the mechanism of thermal shock showed that when the amount of the Suzhou kaolin was more than 10wt%, the main phase were corundum, mullite and magnesia-alumina spinel. The secondary mullite in the sample led to the volume expansion and a higher sintering temperature, and abnormal growth of some grain, impeding the improvement of thermal resistance of the sample. When the amount of Suzhou kaolin was not more than 5wt%, the main phrase were corundum and a small amount of mullite, magnesia-alumina spine. The small amount of situ mullite and spinel in the sample can effectively suppress the grain growth and improved the thermal shock resistance of the samples.To further reduce the sintering temperature of the sample, added calcite in the Mg-Al-Si recipe. Withα-Al2O3 powder, Suzhou kaolin, calcite, talc, quartz as the main raw materials, Ca-Mg-Al-Si Al2O3-based composite ceramics materials were prepared by no-pressure sintering process. The orthogonal experimental results showed that the addition of calcite and talc in the formula introduced the sample with a good high-temperature fluxing agent CaO and MgO, which can reduce sintering temperature effectively. Taking the sintering temperature as the main index and through the orthogonal analysis, got the best formula, m(Suzhou kaolin):m(calcined talc):m(calcite):m(quartz):m(α-Al2O3)= 8:18:10:5:100. The sample sintered at 1340℃for 2h have the water absorption of 0.45%, the porosity of 1.87%, the bulk density of 2.32g/cm3, the bending strength of 110.28MPa, the sintering shrinkage of 13.42% and and the permanent linear shrinkage of 0.16%. After 20 times thermal shock resistance tests (quenching from 1100℃to 25℃in air medium), the bending strength is 139.66MPa, not only did not lose strength, but increased by 22.64%. The study of the mechanism of thermal shock resistance showed that the main phase in the samples were corundum and magnesia-alumina spine, a large number of grains close together, a small amount of glass phase filling the pores among the grains. Such a large number of crystalline phase and a small amount of glass phase gave the samples the smaller permanent linear shrinkage. Also observed by SEM analysis, sintering samples uniformly distributed closed pores small uniform size, which can partially eliminate the the stress of the sample, improving the thermal shock resistance of the samples. Most of the grains'diameter are about 1μm, and evenly distributed, closely integrated, which are very favorable to improve the bending strength and thermal shock resistance of the samples. The thermal shock resistance experiments showed, the thermal shock experiments may promote the growth of grains and small grains formation, which can increase the intensity of the sample. In the thermal shock process, the glass phase wrapped the grain surface will produce some residual compressive stress, which can increase the strength of the sample; also the sample surface residual stress in the thermal experiment process is one of the reasons to increase intensity.
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