Due to the constantly required increase in the efficiency of engines, spark plug electrodes suffer from steadily increasing erosive stress. This results from the growing, demanding operating conditions such as a higher operation temperature. In addition to the stress on the engine components, considerations regarding cost-effectiveness and sustainability are important as well. To fulfil these material requirements, the currently used precious metals should be replaced by cheaper, easier available ceramic materials. With the use of ceramics their excellent high-temperature properties can be exploited. In addition to a high melting temperature and good resistance to erosion, which most ceramics have, also high strength and good thermal shock resistance are important for successful use of ceramics as electrodes in spark plugs.
The present work provides an overview of the requirements of the electrode materials. Those are compared with the property profile of ceramics in general and finally leads to the most important parameters, which form the basis for the selection of the ceramics. Based on the existing literature, molybdenum disilicide, silicon carbide and silicon nitride were selected for a comprehensive characterization regarding their suitability as electrode materials for spark plugs. Erosion resistance and thermal shock resistance were used as the main comparison criteria for the selected ceramics. To estimate these behaviours and the associated mechanical and thermal loads, different tests were carried out. Density, flexural strength, Young’s modulus, fracture toughness, hardness, thermal expansion, and oxidation resistance of the ceramics where determined. Four thermal shock parameters were calculated using the determined data and further material data taken from the literature. In the conclusion, all material data is compared with each other for a material’s selection for further possible test series. Molybdenum disilicide and silicon carbide have been selected for those next steps.