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The effect of a high-velocity flow of dissociated nitrogen on a sample of HfB2–30 vol % SiC ultrahigh-temperature ceramic materials modified with low amounts of reduced graphene oxide was studied to evaluate the potential of these materials in creating aerospace equipment intended for use in N2-based atmospheres. It was determined that, under the selected treatment conditions during a stepwise increase in the anode supply power of the plasma torch and, accordingly, in the acting heat flux at certain process parameters, the surface temperature of the sample sharply increases from ~1750 to 2000–2100°C. A further increase in the heat flux does not have an obvious and proportional effect on the surface temperature of the sample, which may indicate its high catalyticity with respect to surface recombination reactions of atomic nitrogen. It was shown that the surface layers of the material undergo a chemical transformation (removal of silicon-containing substances and formation of a new phase based on HfN), which is accompanied by a significant change in the microstructure (formation of dendrite-like structures), affecting the optical and catalytic characteristics of the surface. [ABSTRACT FROM AUTHOR]

The heat transfer to a cylindrical water-cooled copper model was experimentally investigated in an induction VGU-4 high-frequency (HF) plasmatron of the Institute for Problems in Mechanics of the Russian Academy of Sciences. The model, 30 mm in diameter, equipped with a calorimetric transducer with a heat-adsorbing graphite surface, 13.8 mm in diameter, was exposed to the surface heating in the combined regime by nitrogen plasma and laser radiation and in the cases of the heating with only laser radiation or a nitrogen plasma jet. The experiments in the HF-plasmatron jets were performed at the pressure in the setup low-pressure chamber p = 1 × 104 Pa, nitrogen mass flow rate G = 2.4 g/s, and the plasmatron HF-generator anode power Na.p. = 22 kW. It is established that in the chosen experimental regimes the dissociated-nitrogen jet and the high-frequency induction discharge do not produce a considerable effect on the laser beam passing through them. The values of the heat flux density are obtained as functions of the laser radiation power delivered. The subsonic nitrogen plasma flow in the quartz discharge channel and in the low-pressure chamber of the VGU-4 setup is numerically modeled under the experimental conditions basing on the solution of the complete Navier–Stokes equations using the Patankar–Spalding method. [ABSTRACT FROM AUTHOR]