Investigation of Fibrous Heat-Shielding Ceramic Composite Materials on a Solar Furnace

The article considers the influence of a concentrated solar radiation flux at the focus of a Big Solar Furnace (BSF) on the formation of hierarchical structures of heat-shielding ceramic composite materials based on refractory oxide fibers. A flat front of irradiation with a concentrated solar flux in the focal spot of the BSF creates a uniform thermal field over the surface, which has a sharp temperature gradient deep into the sample along the z-axis, forming isothermal planes with a uniform temperature. It means that in these planes a certain hierarchical self-organization of a structure with a certain crystal structure takes place. At such concentrated solar irradiation, a high-density flux falls on the sample surface, a nonlinear, non-equilibrium temperature field arises, which shows that the processes in the solar furnace belong to the category of “Complexity” processes. Samples of heat-shielding materials were irradiated on the BSF at a concentrated solar radiation flux density of 380 and 460 W/cm2 until partial destruction in order to obtain a sintering and reflow zones on the samples to determine phase and structural changes in the samples. Investigations of microstructure of fused samples of VMK-5 and VMK-6 ceramic composite materials, heat-treated with a solar energy concentrated flow at T = 1800–1900°С, showed that a hierarchically self-organized structure with cubic and acicular crystals is formed in the samples. Studies of the microstructure of the fused VTI-17 samples showed that the structure of the samples passed to a new hierarchical level, from a chaotic distribution of fibers with non-fibrous inclusions in the initial samples to a hierarchically self-organized microstructure in the form of large grains. A further increase in temperature transfers the system to a new hierarchical level, crystals of cubic and lamellar shape grow from the grains.

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