Nonlinear electroceramic components, e.g. varistors and thermistors, are well known examples for today's electroceramic applications. Their electrical behaviour makes them favourable components for a wide range of switching devices and overload protection. For varistors as well as for thermistors the strongly nonlinear change of the specific electrical resistance (depending on temperature and electrical field strength respectively) is the reason for the wide spread usage. This paper focuses on PTC-thermistors (i.e. PTCs are positive temperature coefficient resistors), which accompany us in our everyday life, well hidden in our refrigerators, cars etc.The resistivity of PTC-thermistors strongly increases within a small temperature range. For example the resistivity may change up to seven orders of magnitude (five orders of magnitude in Fig.

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PTCs are electrical resistors (thermistors) with a positive temperature coefficient. They change their resistivity up to seven orders of magnitude within a certain temperature range. Though these parts are only loaded electrically, they often fail due to thermo-mechanical stresses caused by Joule self heating. With the aid of an infrared camera system the temperature distributions of PTCs in service were investigated. They show a big variety in appearance, often strongly differing from the temperature distribution predicted by a model-calculation using homogenous material properties. The temperature distributions measured with the infrared system give information about gradients in material properties. Performing destructive tests by high electrical loading lead to fractures, which are initiated in the most stressed regions. Fractography was used to identify fracture origins. With the information of the fractography and thermal analysis of the infrared camera the FEM-model could be modified in order to understand different kind of fracture modes.

The Si3N4 is one of the leader high-tech ceramic nowadays. As a result of numerous developments excellent mechanical properties of the material are increased by carbon additives. In our previous investigation the electrical effect of the additives was examined. In our work thermo radiation measurements were used by infrared camera technique on conductor Si3N4 ceramic composites in infrared wavelength range. The thermal properties of the developed ceramic composites were determined. This is not easy with the ordinary methods because of the fashioning and geometrical parameters of the material. During the experiments the emissivity of our composites was determined by infrared thermography measurements. Based on a theoretical thermal conductivity model an evaluation method that allows a derivation of thermal conductivities of special geometry conductive materials from results of infrared measurements was established.