X-ray structural investigations of plasma-sprayed europium oxide

Conclusions

In the manufacture of a Eu₂O₃ powder for plasma-spraying, preparatory treatments such as sintering and plasma spheroidization have no effect on the chemical composition of the starting product. Plasma spheroidization of a Eu₂O₃ powder increases the amount of the high-temperature phase by 20% compared with sintering, but a spheroidized powder is more suitable for plasma-spraying. At specific plasma jet enthalpies in the range from 12 to 20 kW·sec/g no thermal dissociation of europium oxide or reaction between the compound and the plasma jet takes place. Plasma-deposited layers applied at specific enthalpies ranging from 12 to 15.2 kW·sec/g contain only the monoclinic high-temperature phase of europium oxide. Increasing the specific plasma jet enthalpy in deposition to above 15.2 kW·sec/g leads to the appearance of the cubic europium oxide phase in the coating. The grain size of plasma-deposited Eu₂O₃ coatings decreases with increasing specific enthalpy of the plasma jet. Increasing the specific enthalpy of the plasma jet from 12 to 15.2 kW·sec/g reduces the crystal lattice parameter c of europium oxide, but further increase in specific enthalpy produces no further change in this parameter. With increasing specific enthalpy of the jet, the crystal lattice parametera of Eu₂O₃ at first, between 12 and 16.2 kW·sec/g, decreases and then, between 16.2 and 20 kW·sec/g, steadily grows. No chemical reaction takes place between a europium oxide coating and a D16 aluminum alloy substrate.