Wettability and reaction of alumina with molten manganese

A basic research study for improvement of plasma-sprayed alumina coatings h as been conducted. The wettability of the molten manganese/alumina ceramic system was examined by the sessile drop method. A MnAl2O4 spinel layer was formed at the interface, suggesting the existence of wettability between th e molten manganese and the spinel. When the spinel was dense, the contact a ngle was about 88 deg for the temperature range from 1573 K to 1623 K. When there were open pores in the spinel layer and a sintered porous spinel sub strate was used, the contact angle exceeded 90 deg. Therefore, the effect o f interfacial conditions on the wettability was discussed. Owing to the rap id vaporization of manganese, the contact angle decreased with time at temp eratures of 1673 K and above.