Degradation of Silicon Nitride Glow Plugs in Various Environments Part 1: dc Electric Field in Ambient Air

All‐ceramic glow plugs (GP) based on sintered‐silicon nitride are evaluated as hot surface ignition systems for natural gas and hydrogen direct injection combustion engines. This paper presents experimental results of the accelerated degradation tests of the GPs in air, wherein GP is heated solely by dc electricity. The complex degradation process has been linked mostly to the redistribution of the sintering additives in Si ₃ N ₄ /Yb ₂ O ₃ system under an influence of dc electric field and temperatures over 1300°C, as experienced by GP in‐service. Ytterbium ions migration varies with time, temperature, and voltage. The microstructural damage was studied primarily by SEM microscopy.