Silicon nitride glow plug with alumina corrosion and erosion protective coating

Abstract

A ceramic glow plug comprises a ceramic heater formed by embedding a metal wire in a sintered Si.sub.3 N.sub.4 -based ceramic. The ceramic heater is brazed to the inner surface of an axial bore of a metal tube and the metal tube is brazed to the inner surface of an axial bore of a metal holder. The tip of the ceramic heater extends from the metal tube and metal holder and is coated with highly heat and corrosion resistant material to minimize erosion and corrosion due to combustion gases. The coating consists essentially of a thin CVD film of alumina (Al.sub.2 O.sub.3) having a thickness of 2 .mu.m deposited on a precoating AlON layer having a thickness of 0.5 .mu.m formed on the exposed surface of the tip. Alternatively, the protective coating may consist of thin CVD film of silicon carbide (SiC) or silicon nitride (Si.sub.3 N.sub.4) formed directly on the exposed surface of the tip.

Dependencies are inferred from the claim text.