| Energy shortage, low efficiency of the development, and environment pollution caused by the development and the use of energy are becoming main factors which limit the persistent development of the economy and the society of our country. Currently as far as our whole country is concerned, the low-cost convenient renewable energy technology is needed urgently to meet the demands of different areas. Solar energy is an inexhaustible and environmentally—friendly renewable energy source. Solar thermal power generation is an important direction of solar thermal utilization, and it is most likely to lead to a revolution in energy technology. At present, alloy steel pipe is used to transport the heat flow in the tower solar thermal power generation system. However, the alloy steel pipe existed some shortage, such as poor thermal shock resistance, short service life and high manufacturing cost, hindering the development of the solar thermal power generation. Therefore, the development of a high temperature heat pipe material with good thermal shock resistance has become an important research topic. Andalutsite-matrix composite ceramic heat pipe materials were prepared in response to this topic, the effects of different formulations and sintering temperature on microstructure and properties of the andalusite-matrix composition were investigated, the key physical properties were analyzed, relevant mechanism of thermal shock resistance was discussed, The methods of reducing sintering temperature and broadening the sintering temperature range of andalusite-matrix composition were investigated. The results indicated that the andalusite-matrix composition could be used as high temperature heat pipe material in solar power generation.The andalusite composite ceramic was fabricated from andalusite, PSZ(partially stabilized zirconia) and Su Zhou clay as raw materials. The effects of composition of raw materials and the sintering temperature on the sintering character and mechanical properties of the samples were also analyzed. Moreover, the composition, microstructure and mechanical properties of the samples were characterized by SEM, XRD and universal testing machine, respectively. The results show that the water absorption is0.41%, porosity is1.10%, bulk density is2.69g/cm3, bending strength is128.78MPa, when the samples were sintered at1490℃for2h. After30times thermal shock cycles from1100℃to room temperature in air, the bending strength increased from128.78to142.55MPa. X-ray diffraction peaks suggested fully developed mullite, zircon phases by reaction sintering of andalusite and PSZ. Microstructure consisting in mullite as a continuous predominant phase in which zircon grain was homogeneously distributed improved almost all the mechanical and fracture properties.In order to reduce the sintering temperature of andalusite-matrix ceramics, composite materials have been fabricated by using starting materials such as andalusite, PSZ, Su Zhou clay, and talc with addition of dolomite and spodumene. The effect of dolomite and spodumene content on the microstructure and mechanical properties of the andalusite-matrix composition was also analyzed. Moreover, the composition, microstructure and mechanical properties of the samples were characterized by SEM, XRD and universal testing machine, respectively. The results show that the water absorption is0.28%, porosity is0.74%, bulk density is2.61g/cm3, bending strength is96.08MPa, when the samples were sintered at1400℃for2h, After30times thermal shock cycles from1100℃to room temperature in air, the bending strength increased from96.08to117.61MPa. The densification of sample was improved with the increase of spodumene content. XRD analysis showed that the main phase of B5were mullite, Zircon and m-ZrO2. SEM results showed that the structure of B5sample is very compact, there is a small amount of pores in the sample, which is mostly closed pores. The columnar mullite crystals are intertwined together to form the skeleton, PSZ occupies both an intergranular and intragranular position in the mullite matrix, which improved the strength and toughness of sample. Relevant mechanism of reducing sintering temperature was discussed. The system generates low-melting point liquid with addition of spodumene, it can wet and dissolve the powder, sintering mechanism changed from solid phase sintering to liquid phase sintering. The sintering temperature is reduced. At the same time, the surface tension of glass softening makes the grain move closer, andalusite-matrix ceramics become desity at a lower temperature.In order to broaden the sintering temperature range of andalusite-matrix ceramics, composite materials have been fabricated by using starting materials such as andalusite, PSZ, Su Zhou clay, talc and spodumene with addition of boric acid. The effect of boric acid content on the microstructure and mechanical properties of the andalusite-matrix composition was also analyzed. Moreover, the composition, microstructure and mechanical properties of the samples were characterized by SEM, XRD and universal testing machine, respectively. The results show that the water absorption is0.30%, porosity is0.71%, bulk density is2.40g/cm3, bending strength is85.73MPa, when the samples were sintered at1420℃for2h. After30times thermal shock cycles from1100℃to room temperature in air, the bending strength reduced from85.73to73.08MPa. XRD analysis showed that the main phase of C1were mullite, Zircon, c-ZrO2and a-cristobalite. SEM results showed that the structure of Cl sample is very compact, there is a small amount of pores in the sample, which is mostly closed pores. The columnar mullite crystals are intertwined together to form the skeleton, PSZ grain was homogeneously distributed in the mullite matrix, which prevented crack propagation. Relevant mechanism of broadening the sintering temperature range was discussed. Adding B2O3is to let the melt have high temperature viscosity and improve the ability of deformation resistance at high temperature for porcelain body, as well as the viscosity reduced relatively gently with the temperature increasing.The optimal adhesive was prepared by using starting materials such as andalusite, PSZ, Su Zhou clay, talc, spodumene and low temperature flux A. The effects of low temperature flux content, phase composition and the micro structure on the properties of adhesive were also analyzed. Moreover, the composition, microstructure and mechanical properties of adhesive were characterized by XRD, SEM and universal testing machine, respectively. The results show that the bending strength is20.08MPa, when the adhesive was fired at1100℃for1h. After14times thermal shock cycles from1100℃to room temperature in air, the sample without crack. XRD analysis showed that the main phase of E2were Zircon, aluminium borate, andalusite and m-ZrO2. SEM results showed that the structure of E2is compact, there is a small amount of pores in the interface. There are a lot of liquid at the interface of adhesive/parent material. Liquid phase under capillary action, it is easy to diffuse to the parent material, and adhesion closely with matrix. The research of Joining mechanism showed that the liquid produces by low temperature flux could wet and diffuse into the parent material to form interface bond and intergrate them.The research of thermal shock resistance mechanism showed that andalusite composite ceramic material has good thermal shock resistance for its high inherent bending strength. The thermal shock resistance of the sample was significantly improved by the addition of ZrO2. The columnar mullite crystals improve the performance of thermal shock resistance of material. In addition, with the introduction of spodumene reduce the thermal expansion coefficient of the material, also greatly improved the thermal shock resistance of the material. |
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