Obtaining Titanium–Nickel Cermets on a Solar Furnace and Creation of Selectively Absorbing Coatings Based on Them for Solar Heat Receivers.

One intensively developing field in solar engineering is to increase the efficiency of solar photothermal heating installations. The main element of photothermal installations with solar heating is a vacuumed heat receiver with a selectively absorbing coating. Efficient selectively absorptive coatings make it possible to create vacuum pipes for the new generation of solar collectors able to operate year-round. The aim of our study is to create metal-ceramic materials and coatings with high selectively absorbing properties. The results on create metal-ceramic composite materials of TiO₂–NiO by partially reducing a metal of one oxide with the help of a solar furnace is given. Phase formation of cermet composite materials depending on technological modes is examined. It is shown that the phase composition of the synthesized cermet composite material depends mainly on melt temperature and the rate of its cooling. An optimal technological mode for synthesizing cermet is as follows: to obtain the overheated melt with temperature higher than 2000°C with further ultrafast quenching with a rate of ~10⁵–10⁶ °C/s. The dependence between spectral and optical properties of selectively absorbing coatings and the production technology and properties of the synthesized composite materials is given. The highest value of integral absorption α_s = 96.96%, emissivity ε = 3.48, and high selectivity coefficient α_s/ε = 27.86 are typical for cermet coating produced by melting in air with melt overheating under a cooling rate of ~10⁵–10⁶ °C/s. The experiments on coating heating in vacuum show that these coatings are the most heat resistant relative to coatings generated by other technological modes. Spectral and optical properties change insufficiently after heating under Т = 495°C and they are α_s = 91.69%, ε = 3.7, and α_s/ε = 24.78. [ABSTRACT FROM AUTHOR]