Thermal Diffusivity and Thermal Conductivity Testing
Laser Flash Analysis (LFA) is employed for measuring the thermal diffusivity and thermal conductivity of materials. The method was originally developed by Parker et al in 1961 using a laser as the energy pulse source. A detailed overview of the procedure for applying the method is outlined in ASTM E1461 and ASTM E2585. Instrument models using a xenon flash bulb for the energy source have also been developed and operate on a similar basis.
Figure 1 – TAL’s TA Laser Flash Analyzer
In flash diffusivity testing, a special graphite coating is applied to ensure the sample doesn’t reflect thermal radiation (in the case of transparent samples, a base layer of a precious metal is applied to make the sample opaque to IR radiation). A pulse of IR radiation is applied to one side of the sample. The IR radiation is absorbed by the sample and diffuses through the sample to the other side, where it is re-emitted. This radiation is detected by a camera, which monitors the temperature signal as a function of time. The temperature behavior as a function of time is then analyzed to give information on the thermal diffusivity of the material. If specific heat capacity and density are known, thermal conductivity may also be determined.
The method is particularly useful in characterizing high conductivity materials (e.g. metals) and in situations where a higher temperature range is sought. For a better understanding of the strengths and weaknesses of different methods for thermal conductivity check out this short video TAL co-produced.
Recently, TAL invested in a second LFA Analyzer, a TA Discovery DXF xenon flash unit with a operational temperature range up to 500°C. As part of commissioning the unit, it was qualified against a known standard of stainless steel. The results of this qualification can be found above. Experimental test results are plotted along the referenced data and lower and upper confidence intervals of 4.5%. The instrument performs within the uncertainty limits of the reference data at all points. This data is summarized also in the table below:
| Temperature °Celsius |
Measured Thermal Diffusivity (cm2/s) | Expected Thermal Diffusivity (cm2/s) |
% difference |
| 31 | 0.038 | 0.038 | 0.5% |
| 53 | 0.039 | 0.038 | 0.6% |
| 98 | 0.041 | 0.039 | 4.2% |
| 197 | 0.043 | 0.042 | 1.3% |
| 299 | 0.044 | 0.044 | -1.2% |
| 400 | 0.046 | 0.047 | -2.0% |
| 500 | 0.049 | 0.048 | 0.5% |
The stainless steel reference sample was provided by TA Instruments and the reference data was provided in report number R051201-08 Revision 1. The reference data was dated March 2013 and was described as “Anter qualified, data published”.
TAL offers contract testing services in LFA characterization of samples for thermal diffusivity & thermal conductivity. For further details or to receive a quotation please contact us here.