How to Perform a TMA Experiment

The thermal expansion value displayed by the instrument represents the total thermal expansion of the system (sample + the sample holder + the probe). However, the operator is interested in thermal expansion of the sample only, so the thermal expansion curve of the sample holder and probe should be subtracted from the sample run. In most cases, the sample holder and the probe are made of fused quartz, with CLTE = 0.6ppm/°C. This correction should be applied to materials with CLTE below 30ppm/°C but can be ignored for materials with higher expansivities. 

The expansion response of the TMA instrument can be checked with a standard reference material of defined thermal expansion. The Polymer Handbook (Brandrup 1999) and the Handbook of Chemistry and Physics (Lide 1998) provide tables of CLTEs versus temperature for numerous materials. Prime (1997) also lists CLTE values for three calibration standards (lead, aluminum, and copper) in the temperature range from -100 C to 180 °C. ASTM E831 describes the standard test method for measuring CLTE of solid materials by TMA. 

One advantage of TMA is that measurements can be carried out on actual manufactured parts with a variety of shapes, or on small pieces chipped off of a part. When using flat samples in compression and flexure, sample thicknesses between 0.5 and 2.5 mm are recommended in order to limit temperature gradients in the sample to -1 °C (Prime 1997).The heating rate should not exceed 5°C/min, and for thicker samples as low as 1 °C/min is recommended. Ideally, the minimum sample thickness should be around 0.5 mm, but if a thinner sample is used in the compression mode, the empty cell baseline should be subtracted from the actual run (Sircar and Chartoff 1994). 

In the tension mode, film thickness or fiber diameter from 20 to 200 m is preferred. The sample width or diameter should be chosen consistent with probe dimensions (see Section 4.5.6 for the required load levels). 

The measured properties in thermal analysis of polymers (e.g., Tg, Tn, crystallization temperature, CLTE) are often a function of the thermal and 

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