Spectral emissivity measurement for high-temperature applications: a systematic review

Measuring emissivity is pivotal for obtaining reliable high-temperature measurements through non-contact techniques such as pyrometry and thermal imaging. The interest in characterizing materials in terms of their radiant properties has increased in recent years due to the expanded application fields of these techniques, ranging from the process industry to aerospace and the energy industry. Various methods are available in the literature to assess material emissivity, but they are primarily classified into indirect and direct methods. This review also addresses different types of materials, various experimental conditions (e.g., heating technologies and measurement frequency bands), and different types of measurement outputs. The aim of this review paper is therefore to systematically examine the literature available on the topic, highlighting the pros and cons of the different methodologies used for measuring emissivity at temperatures up to 2500 °C.