Thermal conductivity measurements of porous dust aggregates: I. Technique, model and first results

TL;DR

This paper introduces a non-invasive method combining experiments and simulations to measure the thermal conductivity of porous dust aggregates, providing insights relevant to planet formation and the evolution of planetesimals.

Contribution

It presents a novel technique for measuring thermal conductivity of fragile porous materials using IR imaging and numerical modeling, with initial results for SiO2 dust samples.

Findings

Thermal conductivity ranges from 0.002 to 0.02 W/(m*K) for samples.

Thermal conductivity correlates strongly with volume filling factor.

Method enables non-invasive, accurate measurements of fragile materials.

Abstract

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.