| Energy technologies play an important role in human society, but human are faced with unexpected challenges because of uncontrolled exploitation and low efficient usage of resources. Solar energy resources become a worldwide research hotspot for the properties of limitlessness, universality and cleanability. High solar absorbing ceramic materials with low reflection were prepared in this paper which aimed at the solar receiver of core part of solar thermal power generation system.Mullite bonded SiC ceramics were prepared from synthetic mullite and silicon carbide powder in this paper. The physical and chemical properties of mullite bonded SiC ceramic such as the apparent porosity, water absorption, bulk density, bending strength and thermal expansion were measured. The results showed that the porosity, water absorption of samples decreased and then increased with the adding of mullite while the bulk density and bending strength increased fist and then decreased. The growth rate of samples increased with the adding of mullite and the arising of firing temperature. The lightness of samples decreased and then increased with the adding of mullite. The sample with mulllite 20% fired at 1380℃has the lowest porosity, water absorption, and the maximum bulk density which is 17%,10.88%, and 2.13g-cm-3, respectively. The bending strength is up to 69.62MPa and the coefficient of thermal expansion is 5.4×10-6℃-1. The samples did not crack through 30 times thermal cycling from room temperature to 1000℃, The bending strength of the samples after 30 times thermal shock cycling tests is 114.49MPa, and the increase rate of bending strength is 64.45%. The solar absorptivity (α) of best sample obtained on UV-Vis-NIR spectrophotometer (Lamda 750, USA) was 0.80, thermal emissivity(ε) was 0.91. The crystalline phases determined by the X-ray diffraction analysis (XRD) were a-SiC, mullite (3Al2O3-2SiO2), and a small amount of cristobalite. The oxidation weight gain and lightness of sample B2 are 7.49% and 46.61 respectively and the oxidation resistance is best. The microstructure was observed by scanning electron microscope (SEM) and the results showed that SiC were coated by three-dimensional network structure preventing the oxidation of SiC which were formed by mullite under the role of silica glass phase.Low thermal expansion ceramics were prepared from spodumene, Shandong quartz and Xingzi kaolin. The porosity and water absorption of samples decreased and then increased with the firing temperature arising. The bulk density increased with the adding of Xingzi kaolin. The bending strength of samples increased and then decreased with the firing temperature arising. Formula L3 with spodumene 70%, kaolin10% and quartz 20% fired at 1330℃have the best properties. The porosity, water absorption, bulk density, volume shrinkage and bending strength is 17%, 10.88%, and 2.13g·cm-3,17.2% and 45.83MPa, thermal expansion coefficient is 0.86×10-6℃-1 (0～900℃). The precipitated needle stick mullite and the formation of micro-cracks after thermal shock resistance cycling made the bending strength not decrease but increase. The bending strength of sample L3 fired at 1320℃is 46.38MPa after 10 times thermal shock cycling, and the increase rate of bending strength is 200.78%. Samples have good thermal stability. Main crystalline phases determined by XRD areβ-spodumene (Li2O·Al2O3·4SiO2). The microstructure was observed by SEM and the results showed that main crystalβ-spodumenes were bonded by glass phase. A mount of quartz were found on the surface ofβ-spodumene, needle or rod-like mulite distributed in the pores which play the role of toughening. Kaolin was decomposed into metakaolin at 400℃. Thenα-spodumene translated intoβ-spodumene accompanied by the 30% volume expansion at 800～900℃and kaolin continued to converse. After 1000℃, on one hand, metakaolin conversed into mullite, quartz and glass phase promoted sintering; on the other hand,β-spodumene dissolved free quartz which has the characteristic of low thermal expansion. The spodumenes were bonded by glass phase composed of mullite and quartz. Samples sintered density at 1330℃and spodumene solid solution crystallized completely which has the characteristic of low thermal expansion. The thermal expansion coefficients of the three formulas are less than 2×10-6℃-1 which reaches the request of low thermal expansion ceramic.SiC-spodumene composite ceramics were prepared from mixing L3 and B2. The porosity and water absorption of samples increased with the firing temperature arising. The bulk density trended in the opposite. The bending strength of samples decreased with the complex proportion increased. Formula BL2 with SiC 72%, mullite 18%, spodumene 7%, kaolin1% and quartz 2% fired at 1330℃have the best properties. The porosity, water absorption, bulk density, volume shrinkage and bending strength of sample BL2 is 24.67%,11.81%, and 2.09g·cm-3,-5.36% and 66.47MPa. The thermal conductivity of BL2 is 7.83W·(m·K)-1 at 35.3℃.The main crystalline phases determined by XRD areα-SiC, synthesized mullite and cristobalite andβ-spodumene. The microstructure was observed by SEM and the results showed that SiC as skeleton were bonded through meltingβ-spodumene filled in the gaps of SiC. The thermal expansion coefficient of best foumula BL2 is 4.55×10-6℃-1 (0-900℃), reached the purposes of adjusting the thermal expansion coefficient and improvement of thermal stability. Comparing to B2, the solar absorbance of sample BL2 were improved and the value of a andεare 0.83 and 0.91 respectively, but the values ofεare still high.SnO2 sol was prepared by sol-gel from SnCl4·5H2O as precursor in order to reduceε. And SiC-spodumene composite ceramics coated SnO2 film (BL2 as substrate) were prepared by spin-coating method and dipping method. The properties and microstructures of samples were tested by TG-DTA, XRD, SEM and UV-Vis-NIR reflectance spectroscopy respectively. The crystalline phase of the film is cassiterite (SnO2), and the optimal heat treatment temperature is at 600℃. Perfect crystallized SnO2 with thickness 0.5-1μm distributed on the substrate uniformly and well bonded with the substrate. SnO2 film had the role of reducingε. Appropriate sol viscosity and film layers can increase a. SnO2 film allows the visible and near-infrared lights transmit. But the transmition rate begins to decline for the infrared with wavelength greater than 4μm. These properties madeεof samples decrease. SnO2 film of sample A8 with proper thickness played the role of anti-flection film and thus increased a of samples. The optical property of sample A8 coated 3 layers are best and a andεare 0.853and 0.6531 respectively. Compared to BL2 of which the values of a andεare 0.83 and 0.91, a increased 0.83% andεdecreased 28.23%.SiC-spodumene composite ceramics coated SnO2 film are a promising material as high temperature coating used for the non-vocuum solar receiver tube.
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