If anyone has any good ideas, I have a requirement to measure thermal conductivity at 1700 Deg C PLUS The electronics I can handle, the probe keeps melting.....

In fairly non-conductive systems, thermal conductivity is measured by a heated probe technique - Ap's reference leads to some papers on it AFAIR.

The answer to measuring electrical conductivity, like Kai says, depends on the material. In our high temperature measurement method, we have a co-axial probe, about 15mm id, with a 3mm centre, and measure the complex impedance at about half probe immersion. We then find the frequency at which the minimum impedance occurs. We immerse the probe fully, then, whilst removing the probe in steps, measure the resistance as a function of depth. The gradient of the resistance/depth line, plus some simple geometrical considerations of the probe, allows us to measure the sample conductivity.

The probe is made of high purity alumina, with molybdenum metal components.

We didn't invent the technique, it was invented by Professor Donald Sadoway at MIT.

Steve