| In recent years, with the rapid development of the building industry and the increasing energy consumption in buildings, building energy efficiency has become the future tendency. Therefore, the development of energy-efficient building materials and building energy-saving technology have become the fundamental way to slow down building energy consumption. Due to the rich resources, purity and non-regional restriction of emerging green solar energy, the combination of its product and building has become the new idea to achieve energy efficiency in buildings. Firstly, according to structure and performance requirements of thermal storage materials for solar heat utilization, formulas of thermal storage material of Ca-Al-Si system were designed. Coal slime, fly ash and other wastes were used as raw materials for sample preparation, to explore effects of coal slime addition on physical properties. Secondly, preparation process and formulas were changed to increase density and thermal shock resistance of samples. Then, honeycomb ceramic was prepared by extrusion technology, and the binding performance of encapsulants and honeycomb ceramics was studied. Finally, phase change materials were encapsulated in honeycomb ceramics to prepare latent-sensible thermal storage composite materials.In this paper, coal slime, fly ash, feldspar, dolomite and quartz were selected as raw materials for the preparation of L series samples. Semi-drying pressing technology and atmospheric sintering process were employed to prepare thermal storage ceramics for applying in energy-efficient buildings. The structure and performance of samples were characterized by different testing methods, such as XRD, SEM and so on. Effects of formula composition and firing temperature on properties of samples were discussed. The results indicated that the rational addition range of coal slime is 40%~60%, the total waste utilization rate of 70%, and the optimum sintering temperature is 1220℃.The bending strength of L1~L3 fired at 1220℃was with higher values(i.e. 54.92 MPa for L1, 61.00 MPa for L2, 64.24 MPa for L3), which could meet the strength demands for thermal storage ceramics. The water absorption of samples were 0.31%, 0.36% and 0.48%, all of which were lower than 0.5%. The bulk densities of samples were 2.25g/cm3, 2.09 g/cm3 and 2.03 g/cm3. Thermal shock resisitance tests showed that samples didn’t crack after 30 times thermal shock resistance(from 500℃ to room temperature, air-cooling), the strength loss rates of L1~L3 were-22.14%, 15.38% and 23.93%. XRD and SEM results manifested that crystal phases were anorthite, mullite and α-quartz. The existence of mullite can improve strength and thermal shock resistance of samples to exact extent.The storage density of sensible storage thermal ceramic is proportional to its bulk density. In order to improve the heat storage performance of samples, base on L2 and L3 formulas, the formula composition of F series was designed, with replacing10% dolomite in Ordos Mongolia by 5% albite in Yingde Guangdong province and 5% lithium porcelain stone in Xinyu Jiangxi province. The results revealed that the F1 formula fired at 1260℃ had the optimal performance. The bulk density of F1 and L2 were 2.32 g/cm3 and 2.09 g/cm3, which had magnified 11.00%. Comparing with the 61.00 MPa of L2 and 68.68 MPa of F1, the bending strength had increased 12.54%. Thermal shock resisitance indicated that the strength loss rate of F1 sample was only 6.79% after 30 times thermal shock resisitance, which were 55.85% less than that of L2, thus the performance of thermal shock resistance was proved. SEM and XRD analysis showed that the main crystal phases of F series samples were needle shaped mullite and particulate α-quartz, moreover the pore shape and its distribution on fratured surfaces had become more uniform, all of which gave samples a highter density and strength. The densification mechanism were that lithium porcelain stone, albite and feldspar formed a Li2O-Na2O-K2 O eutectic melt at high temperature, which filled the gaps and made samples dense.For further improving thermal shock resistance of samples, formulas of X series were designed base on the F1 formula by different fluxs, and the influences of fluxs on thermal shock resistance were discussed. Researchs found that the X3(10% lithium porcelain stone) formula fired at 1240℃had the optimal comprehensive performance. The water absorption, porosity, bulk density and bending strength were 0.24%, 0.56%, 2.32g/cm3 and 85.41 MPa, which were better than F series. The thermal expansion coefficient from room temperature to 300 ℃ was 5.97?10-6 ℃-1. Thermal conductivity and thermal storage density at 300℃ were 1.29 W /(m·K) and 519.35 kJ / kg. All the properties could meet requirements of basic performance of thermal storage ceramics used in energy-efficient buildings. Thermal shock tests indicated that the X series samples didn’t crack or had cracks after 30 times thermal shock resisitance; the strength and strength loss rate of X3 samples after 30 times thermal shock resistance were 83.74 MPa and 1.97%. the water absorption, porosity and bulk density were 0.25%, 0.57% and 2.33g/cm3, which demonstrated the excellent property of thermal shock resisitance compared with F and L series. SEM and XRD analysis showed that crystal phases of X series samples were needle shaped mullite and particulate α-quartz; and mullite crystals interwove a network structure, which gave samples a higher strength and perfect thermal shock resistance. The mechanism of thermal shock resistance indicated that the increased bending strength and three-dimensional network structure formed in samples improved thermal shock resistance of samples.Honeycomb ceramics were extruded with extrusion technology by selecting X3 formula composition. Latent-sensible thermal storage materials were prepared with PCM encapsulated in honeycomb ceramics by encapsulant. Test results showed that the water absorption, porosity and bulk density of honeycomb ceramics fired at 1240 ℃ were 9.18%, 18.32% and 1.81g/cm3; encapsulant of Y2 formula(water glass 40% wt)has the optimal binding performance with matrix, and the shear strength was 0.98 MPa. The storage density of composite heat storage materials with paraffin and potassium nitrate / sodium nitrate encapsulated were 133.54 kJ·kg-1 and 650.40 kJ·kg-1 at 50℃and 225 ℃. These composite materials could be used in energy-efficient buildings. |
