Pulse and Heating Technique Results of Platinum Alloys Compared with Modeling Results

Full text: Platinum, a very precious metal, along with its alloys have many applications technically and also in ornaments such as in jewellery. Their thermophysical properties like density, heat capacity, thermal conductivity and surface tension play an important role in casting processes and are required as input data for casting simulation. The goal of this work is to investigate these properties and to simulate them through modeling. Platinum and three typical jewellery alloys namely Pt-5Co, Pt-5Ru and Pt-4Cu were investigated by an ohmic pulse heating technique. This technique delivers thermophysical properties of electrically conducting materials deep into the liquid phase. Heating rates up to 108 K/s are achieved, and the liquid phase is achieved after about 30 μs. Within this short time the geometry of the sample will neither be destroyed through force of gravity, instabilities nor other effects, so that short-term measurements become possible on 'standing' liquid columns. These measurements allow the calculation of specific heat capacity and the temperature dependencies of electrical resistivity, enthalpy, and density of these alloys in the solid and liquid phase. Thermal conductivity and thermal diffusivity as a function of temperature are estimated from resistivity data using the Wiedemann- Franz-law at the end of the solid phase and at the beginning of the liquid phase. Based on the temperature-dependent experimental data listed above, model calculations have been performed to achieve a deeper insight into the thermodynamical behavior of these materials both within the high-temperature solid and liquid regime. For such calculations, it is of special importance to choose model functions that are both physically relevant and numerically robust. (author)