Precursor derived SiOC/MoSi₂-composites for diesel glow plugs: preparation and high temperature properties

抄録

In this study precursor derived SiOC/MoSi₂ composites were evaluated with respect to their potential for the application as glow plug material. In a first step, fully dense composite materials with different fractions of electrical conductive MoSi₂ were fabricated by field-assisted sintering technique (FAST). The percolation threshold, where the electrical properties change from insulating to a suitable level of conduction depends on the microstructure, which can be controlled by the initial particle size of the used SiOC particles. It becomes principally possible to fabricate both, the insulating part and the heater material with the same MoSi₂ content and therefore without thermal mismatch. Room temperature properties, high temperature strength, oxidation and creep behaviour depend strongly on the MoSi₂ volume fraction. MoSi₂ contents beyond the percolation threshold lead to significantly enhanced creep rates. At high temperatures, reactions between SiOC and MoSi₂ can be observed, which differ at the air exposed surface and in the interior of the samples. From these findings, an upper limit for the application temperature can be derived.