  We present a non-invasive technique for measuring the thermal conductivity of
fragile and sensitive materials. In the context of planet formation research,
the investigation of the thermal conductivity of porous dust aggregates provide
important knowledge about the influence of heating processes, like internal
heating by radioactive decay of short-lived nuclei, e.g. 26Al, on the evolution
and growth of planetesimals. The determination of the thermal conductivity was
performed by a combination of laboratory experiments and numerical simulations.
An IR camera measured the temperature distribution of the sample surface heated
by a well-characterized laser beam. The thermal conductivity as free parameter
in the model calculations, exactly emulating the experiment, was varied until
the experimental and numerical temperature distributions showed best agreement.
Thus, we determined for three types of porous dust samples, consisting of
spherical, micrometer-sized SiO2 particles, with volume filling factors in the
range of 15% to 54%, the thermal conductivity to be 0.002 to 0.02 W/(m*K),
respectively. From our results, we can conclude that the thermal conductivity
mainly depends on the volume filling factor. Further investigations, which are
planned for different materials and varied contact area sizes (produced by
sintering), will prove the appropriate dependencies in more detail.
