Application of Gas Plasma Treatment for Testing of Structural Ceramic Composite Materials of the Discharge Chambers of Electrojet Engines

In this paper, the possibility of using gas plasma treatment for testing the samples of discharge chambers of electrojet engines is investigated. These discharge chambers were used for a prototype of the high-frequency ion engine. The model of a hemispherical discharge chamber was fabricated of Al$_2^{}$O$_3^{}$ – Si$_3^{}$N$_4^{}$ composite ceramics by the heat shrink molding method in such a way that a uniform wall thickness with an error of $0.2$ mm and a high accuracy of the forming surfaces and coupling sizes were achieved. A high-frequency ion engine, a modification of the electrojet engine, was employed to test the new composition and the new ceramics molding technology. When testing the boundary layer of the samples of the discharge chambers of electrojet engines by gas plasma treatment, the composition of the gas phase (consumption of components), power consumption, gas flow rate and the exposure time were varied. The tests revealed that the wear of ceramics in the engine’s exit section is nonlinear depending on the depth of the boundary layer and is an average of $0.1$ mm, which is less compared to quartz and corundum based materials used previously. The results of weighing the rings showed that the decrease in the weight of the inner ring was $1.25$ is in good agreement with the surface profile measurements. It is shown that the developed silicon nitride based ceramics obtained by three-dimensional modeling is a high-quality structural material resistant to ion-plasma erosion, and that the developed technological processes of heat shrink molding allow a fast manufacture of the functional prototypes of ceramic parts of electrojet engines. The application of new ceramics has the potential to increase the destruction time of the discharge chamber by a factor of no less than $1.2$, and hence the time of trouble-free operation of this model of the electrojet engine and the possibility of manufacturing relatively narrow rings widens the range of potential materials while relaxing the requirements concerning their structural strength. The gas plasma treatment that was used by us is suitable not only for testing of the structural elements of electrojet or plasma engines, but also for various technical machines operating under high-temperature, thermostressed or other loaded conditions.