A study of millimeter-wave sintering of fine-grained alumina compacts

A number of high-frequency microwave sintering studies of alumina have repo rted that sintering proceeds much faster in microwave furnaces when compare d to conventional furnaces, and that densification can occur at lower tempe ratures. These differences have motivated the search for a nonthermal micro wave enhancement effect such as the time-averaged microwave field-induced m ass transport effect proposed by Rybakov and Semenov. To assess the differe nce between microwave and conventional sintering, and the presence of a non thermal effect in microwave sintering, a study of millimeter-wave (mm-wave) (35 GHz) sintering has been conducted at the Naval Research Laboratory (NR L) using a well-studied fine-grained (submicron) commercial alumina with re producibly manufactured properties, Sumitomo AKP-50, This paper reports our results, which generally indicate no large differences in the required tem peratures for densification of conventionally and microwave sintered compac ts, or between the resulting microstructures, The nonthermal effect propose d by Ryakov and Semenov was evaluated for fine-grained alumina and found to be small compared to the surface energy driving force for sintering.