Determination of heat capacity of carbon composites with application to carbon/phenolic ablators up to high temperatures

Simulations of atmospheric entry of spacecraft and satellites require accurate knowledge of thermophysical properties such as heat capacity in a wide temperature range. However, the characterization of this quantity is not straightforward for carbon composites at high temperatures, due to pyrolysis reactions that occur in the material. We develop a methodology for determining the heat capacity and required heat of pyrolysis for carbon composites in these conditions. The methodology consists of three steps: organic elemental analysis to determine composition, differential scanning calorimetry experiments on the different components to determine apparent heat capacity, and computations to separate the apparent heat capacity into heat capacity and heat of pyrolysis. This methodology is applied to the ZURAM (R) carbon/phenolic ablator from room temperature up to 1100 K. The results obtained were compared to separate analyzes of the different components of the material, assuming that heat capacity is an additive property. It was found that compressing the samples into disks provides improved resolution and repeatability for low density materials. This provided a determination of the heat capacity of the decomposing composite with a relative standard deviation < 10% and of < 20% for the heat of pyrolysis. The proposed methodology can directly be applied to other carbon composites such as carbon/epoxy systems. (C) 2020 Elsevier Masson SAS. All rights reserved.

Automated summary

A methodology was developed to determine the heat capacity and required heat of pyrolysis for carbon composites at high temperatures, providing improved resolution and repeatability. Results were compared to separate analyzes of different components, and compressing samples into disks was found to enhance measurement accuracy.