Measurement Techniques for Determining the Thermal Conductivity of Bulk Samples and Thin Films

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Thermal conductivity is one class of basic transport properties of materials that characterizes the flow of heat through it. Over recent years, the transformation of smart materials of atomically thin layers to small-size bulk samples has further made it difficult to determine the thermal conductivity more accurately due to the second law of thermodynamics, which prevents full control over heat flux during measurement. Heat flux and small temperature gradients are the two most important parameters that need to be considered while measuring the thermal properties of small dimensional samples. The difficulty in thermal measurements is associated with the thermal anchoring and controlling the heat loss that takes place due to conduction, convection, and radiation processes. In addition, controlled temperature difference coupled with high-speed data acquisition allows to study the thermal properties in a more extensive way. In this chapter, some of the reliable and effective techniques are mentioned that can help us to measure thermal conductivity with the lowest possible error. The importance of maintaining a high vacuum, choosing a proper heat source, and selecting heat sinks with desirable electrical outlets is also discussed here. Moreover, depending on the nature and dimension of the samples, different measuring techniques need to be used to extract the thermal conductivity of samples accurately. In general, understanding these properties is significant for predicting the performance of electronic materials in real-world applications, such as heat exchangers, evaporators, thermocouples, refrigerators, gas turbine engine applications, automotive parts, and biomedical parts. Further, these properties can be helpful in analyzing carbon nanotubes, selecting suitable ceramic coatings, assessing polymers, etc.