The thesis presents the creation of a scientific foundation of microwave technology of manufacturing composite materials using liquid glass for thermal insulation. The technology is based on the established rules of formation of the structure and properties of materials depending on parameters of ultra-high-frequency radiation, modifiers of coagulation and crystallization, porogens, and foam stabilizers.
The author discovers the rules and quantitative dependences of the action of microwave radiation on the transformation of the liquid glass composition structure during its porization. The author also proves that due to the volume heating the degree of structural rearrangement is twice as important in comparison with convective heating, namely, at even temperatures for granular materials, and twice lower process temperature for composite materials. The paper establishes that the electromagnetic radiation is partially converted into heat, which contributes to intense porization with the volumetric expansion of the liquid-glass composition, and is partially aimed at structural changes in the material that improve its properties due to the effect of non-thermal action of microwave radiation.
The study reveals the peculiarities of the transition of the suspension based on liquid glass under the action of microwave radiation in the pyroplastic state under conditions of competing processes of dehydration and porization of the material structure. The value of the apparent activation energy is 13.05 kJ/mol for granular materials and 27.64 kJ/mol for composite materials in the first period of porization under the action of microwave radiation, and these values are respectively 136.07 kJ/mol and 116, 98 kJ/mol in the second period. Such low values indicate a high ability of microwave radiation to convert water into steam at relatively low temperatures, even in the bound state. On the contrary, during convective heating, the activation energy is zero in the first period of porization of granular materials, and it has a high value (115.72 kJ/mol) in the second period due to competing processes of porization and dehydration. During porization of composite materials, the values of the apparent activation energy are close (9.18 and 24.75 kJ/mol, respectively) at both stages of the process indicating slow evaporation of water resulting in mostly drying of the material without porization.
The research presents the developed formula for obtaining composite thermal insulation materials using modifiers of coagulation and crystallization, porogens, foam stabilizers, and studies their properties. It shows that such modification under the action of microwave radiation intensifies coagulation and crystallization. It leads to the predominance of compaction over pore growth by reducing open porosity, which allows obtaining the material with a closed porous structure and low average density (220-240 kg/m3), while maintaining a high level of strength (0.6-0.7 MPa for compression and 0.8-0.9 MPa for bending).
The author has developed the technology of granular and composite thermal insulation materials based on liquid glass under conditions of microwave radiation. The paper proposes to obtain granules by spraying the liquid glass composition using a spray for textured painting in a curing solution of calcium chloride using a mobile installation. The research develops a new process flow scheme for the manufacturing of composite materials in the form of thermal insulation products of various configurations by simultaneous porization with the volumetric expansion of granules and the binder under the action of microwave radiation. The work presents the optimal technological parameters of the process, namely, the output power of the installation is 650 W, atmospheric pressure, and the temperature is at the level of 115-120 0С. The proposed microwave technology allows obtaining materials with better performance at lower energy costs on their manufacturing compared to convective heating.
The author conducts the feasibility study and proves the advantages of microwave swelling of composite thermal insulation materials in comparison with the technology of manufacturing aluminosilicates and foam glass. These advantages include reducing the process duration and temperature, and the lack of need to introduce additional components to modify material properties. The feasibility study has shown that the price of the proposed composite thermal insulation material is 1.25 times lower than the price of the most common foam glass and it is at the price level of aluminosilicates.
