Entwicklung von Platin-MMC Elektrodenwerkstoffen für Zündkerzen

Abstract

Pt/MeO and Ag/MeO composites were investigated regarding their arcing stability in single break operations. The following materials were used: Pt/ZrO2, Pt/Y2O3, Pt/MgO, Pt/Al2O3, Pt/YAM, Pt/SnO2, Pt/CeO2 and pure platinum; Ag/SnO2, Ag/CeO, Ag/ZrO2 and pure silver. The craters produced on the surface were analysed using white light interferometry (WLI) and FIB/SEM techniques. The voltage- and current-versus-time characteristics of the arc were registered using an oscilloscope. The SEM observations showed that the arc root constricts with decreasing current and they pointed out that the oxides have a strong influence on the arc mobility at the surface. On Pt/MeO composites only a single depression is formed while on pure platinum, several craters are produced by the displacement of the arc. On silver and its composites, the numerous small craters and the arc path indicate high arc mobility. It was observed that the greater the arc mobility, the shallower the crater. Observations with FIB/SEM dual beam showed that the oxides melt and formed large plates on the crater surface for most of the Pt/MeO or they partially disappeared like for Pt/SnO2, Ag/SnO2 and Ag/CdO (vaporization, sublimation). The melting of refractory oxides indicates that the arc cathode root temperature should be very high. Ag/ZrO2 revealed to be the most stable material regarding its microstructure modification in the crater region and the hypothesis that the oxides remain stable if Tm Reinforcement ³ Tb Matrix is drawn. Nevertheless, WLI measurements pointed out that material stability does not imply necessarily a reduced crater size.