Synthesis And Application Of Xonotlite-type Calcium Silicate Hydrates Fibers

Energy is the most important issue for human survival and development. Since 21st century, energy conservation and emission reduction have become the common goal of nations in the world, so thermal insulation material was widely developed and applied. Xonotlite-type calcium silicate has become the most promising heat insulating material because of its low thermal conductivity, light weight, high intension, heat resistance properties, and so on. In this paper discussed the dynamic hydrothermal conditions on the formation of xonotlite-type calcium silicate, and the influence of different additives on the crystallinity and morphology of products. The thermal insulation property was tested by thermal analysis and thermal conductivity testing. Thermal insulation coating was prepared by adding the synthesized xonotlite into the emulsion. The main conclusions are as follows:The first: The activity of siliceous material on the formation of the hydrothermal products plays a key role when xonotlite was prepared with dynamic hydrothermal method. Crystalline xonotlite fiber is easily prepared with amorphous silica gel for its higher activity, but it is difficult to form secondary particles with a high hollowness. When Crystalline silica was used as raw material, longer time was required to synthesize xonotlite-type calcium silicate because of its poor activity, and it is more difficult to get the perfect crystalline xonotlite fiber. Calcareous materials have great influence on the crystallinity of xonotlite, Calcia obtained by new calcined calcium carbonate at 1000℃is conducive to form crystal xonotlite and higher crystallinity. Reaction temperature and reaction time have great influence on thydrothermal products too. Xonotlite fibers can be synthesized with silica gel at 220℃for 30 h, while the hydrothermal reaction with silica must be performed more than 50 h. Thermal analysis showed that the samples have good stability, good heat insulation properties at 100-1000℃.The second: The type and amount of additives have greatly impact on the crystallinity and morphology of the secondary particles of xonotlite-type calcium silicate. XRD and SEM show that the appropriate amount of CTAB, V₂O₅ can promote the formation of crystalline xonotlite good hollow secondary particles, CaCl₂ is not conducive to the formation of xonotlite when the silica gel was used as a silicon raw material. When the amount of CaCl₂, Sr(NO₃)₂, ZrOCl2 is a little excess, it is hard to obtained the crystalline xonotlite-type calcium silicate, CTAB, F127 and other surfactant is holdback to the formation of xonotlite, but the appropriate amount of KOH can promote the formation of xonotlite fibers and hollow secondary particles with the crystalline SiO₂ as a silicon raw material. This is because CTAB could reduce the infiltration properties of siliceous raw materials, which can reduce the reaction velecity so that is conducive to the formation of xonotlite hollow secondary particles and hamper to the reaction of crystalline silicat; while adding some KOH is favor dissolution of crystalline SiO₂ thus facilitating the formation of xonotlite.The third: Styrene-acrylic emulsion and pure acrylic emulsion were prepared by emulsion polymerization. Xonotlite fibers were added into styrene acylic emulsion to prepared thermal insulation coating. Thermal conductivity analysis showed that the thermal conductivities of xonotlite can be achieved 0.04888 W /( m·K) at room and the thermal conductivity of coating is about 0.050 W / (m·K) at 30℃. Other results showed that the performance of coating added xonotlite fibers is better than common coating.