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Thermal Diffusivity by The Laser Flash Technique

Thermal Analysis

  1. Stephen F. Corbin1,
  2. Dennis M. Turriff2

Published Online: 12 OCT 2012

DOI: 10.1002/0471266965.com102.pub2

Characterization of Materials

Characterization of Materials

How to Cite

Corbin, S. F. and Turriff, D. M. 2012. Thermal Diffusivity by The Laser Flash Technique. Characterization of Materials. 1–10.

Author Information

  1. 1

    Dalhousie University, Halifax, NS, Canada

  2. 2

    MEA Forensic Engineers and Scientists, ON, Canada

Publication History

  1. Published Online: 12 OCT 2012

Abstract

Thermal diffusivity is an important material thermophysical property. The most widely used method for measuring thermal diffusivity is the laser flash technique. In this technique, a sample is placed within a controlled atmosphere furnace and subjected to a finite impulse of radiant energy on its front surface, through the use of a laser. The transport of heat through the sample, as a result of the laser impulse, causes a transient temperature rise on the rear surface of the specimen. This temperature rise is measured by an IR detector placed above the rear sample surface. The net result is a “thermogram” which is a plot of the rear-face temperature versus time. Assuming a proper set-up and careful experimentation, the transfer of heat under these conditions approximates one-dimensional heat flow. Comparing the experimental data with one-dimensional heat flow theoretical predictions, allows an estimation of thermal diffusivity.

There are several methods available to determine thermal diffusivity based on experimental and theoretical comparisons. The simplest method is to determine the “half-rise time,” t0.5, which is the time at which the experimentally measured rear-face temperature reaches half of its maximum value. More accurate methods use sophisticated analysis algorithms to model and fit the entire experimental thermogram curve to an ideal theoretical curve by means of a nonlinear least-squares procedure. These approaches can include corrections that account for the fact that the experimental measurements only approximate one-dimensional heat flow conditions.

Using the thermogram curve fitting techniques, the measurement of thermal diffusivity of a range of material types including solid thermal insulators and conductors is possible. It is also possible to measure the apparent diffusivity of inhomogeneous samples such as composites and porous materials. Using two- and three-layer analysis methods allows the measurement of thermal diffusivity of liquids. The layer methods can be extended to a determination of the thermal contact resistance of interfaces encountered in coated or bonded materials.

Keywords:

  • thermal diffusivity;
  • thermal conductivity;
  • laser flash apparatus;
  • thermophysical properties