Vaporization Behavior of Plasma Sprayed Y2SiO5 Coatings

The evaporation rates of plasma sprayed Y2SiO5 coatings were measured in a low pressure air; pair=4.6 Pa and 110 Pa, over a temperature range of 1943 to 2173 K. A xenon image furnace was used for heating specimens in a pressure-controlled chamber. The evaporation rate of the Y2SiO5 coating in pair=4.6 Pa at 1973 K was 3×10−7 kg/(m2·s), which is about 10−3 times of the evaporation rate of SiO2 calculated from the equilibrium pressure of SiO(g) and about 102 times of that of Y2O3 calculated from the equilibrium pressure of YO(g). The recession rate of the Y2SiO5 coating converted from the evaporation rate is 10−4 μm/s. A duplex coating consisting of an outer 100 μm-thick Y2SiO5 layer for erosion protection and an inner SiC layer, which we proposed for oxidation protection coating for C/C composites, is considered to be sufficiently resistant against recession due to evaporation during re-entry of the H-II orbiting plane-experimental (HOPE-X).