No abstract

The possibility of using hollow ceramic microspheres and an organosilicon binder with silane and carbosilane links to obtain heat-resistant heat-insulating foam ceramics for construction purposes is demonstrated. The effect of the filler and the gaseous medium on the products of thermal destruction and the properties of the composite is considered. The thermophysical and physicomechanical characteristics of the heat-insulating materials are specified.Syntact materials (SM) are hollow microspheres bound by a mineral or organic binder, which are promising for use for heat insulation with enhanced physicomechanical and thermophysical characteristics. The study in [1] described compositions based on hollow inorganic microspheres and an organosilicon binder with the siloxane main chain. However, the disadvantage of these heat-insulating materials is their relatively low thermal resistance. Thus, the service temperature for SM with the most heat-resistant polyphenylsiloxane binder is not more than 450°C and after this temperature is exceeded the strength parameters deteriorate catastrophically.The thermal strength of SM can be increased by using fundamentally new organosilicon binders whose main chain in addition to siloxane links also contains carbosilane links. Until recently it was believed that such compounds can hardly ever be used in the industry [2]. However, it is currently established that the thermal destruction of such polymer binders at temperatures above 600°C produces heat-resistant silicon oxide and silicon carbide while retaining the initial polymer structure (USSR Inventors Certif. No. 1736979). Therefore, if the initial polymer contains a heat-resistant filler, it is possible after heat treatment to obtain a ceramic composite with high strength parameters.We investigated the problems of the development of heat-insulating SM based on an organosilicon binder for construction purposes with service temperature up to 1200°C. The filler consisted of hollow ceramic microspheres (frequently called cenospheres) produced by flotation treatment of flue gases from thermal power plants operating on solid fuel. The fractional composition of microspheres is given in Fig. 1. The binder is VKL-1 lacquer (TU 6-05-64-101-85) whose main component is oligooxidehydride-silmethylenesiloxysilane (OHSMS), which besides siloxane links also contains carbosilane and silane links.The technology of sample preparation consists in mixing the binder with hollow ceramic microspheres up to reaching the "moist sand" consistency, molding the composite at a low pressure, and subsequent thermal treatment. The detailed technology of producing this SM is described in [3].On the basis of theoretical principles, it can be assumed that intense thermal destruction processes which are accompanied by substantial modifications of the physicomechanical and thermophysical properties of the polymer and its transformation into a ceramic-like state occur at tempera-30 25 20 15 10 5 0 50 100 150 200 250 Size of fraction particles, m m Content of fraction...