Determination of graphite sublimation rate in high enthalpy plasma flow using 'laser knife' method

The experimental method to study a behavior of heat-resistant materials by the action of high-enthalpy plasma jets is developed. The main attention is focused on heating and thermal destruction of graphite samples. The argon plasma jet is generated by a plasmatron with an expanding anode channel providing a slightly divergent high-enthalpy laminar flow with the axial speed of 400-500 m/s, the diameter of 68 mm and high temperature which is not less than 10,000 K. The jet affects the isotropic graphite MPG-6 samples shaped in the form of a parallelepiped with the dimensions of 23 mm x 23 mm x 16 mm. A description of the method developed by the authors on the basis of the "laser knife" technique to determine the sublimation rate of heat-resistant materials is presented and the relevant time change in the sample material sublimation rate is analyzed. The shape and evolution of craters on the sample surface are analyzed. A nonmonotonic behavior in the sublimation is observed in the experiments. The maximum of sublimation rate is recorded when the initial warming up stage of the graphite sample is completed, which indicates the emergence and propagation of dislocations in graphite structure as it is heated to a temperature close to 3000 K. (C) 2016 Elsevier Ltd. All rights reserved.