Thermophysical properties

Thermal diffusivity and conductivity

The thermal diffusivity and conductivity are the most important thermophysical parameters for describing the heat transfer properties of a material or component. The laser flash analysis (LFA) has been used as a fast, versatile and precise absolute method for the measurement of the temperature diffusivity. In principle, one side of the sample with a defined thickness is heated with a short laser pulse and the resulting temperature rise of the back side is determined by using an infrared detector. From this, the temperature diffusivity of the material can be determined. A reference sample can also be used to measure the specific heat capacity and, if the density of the material is known, the thermal conductivity of the material can be determined.

 

Normen: ASTM E1461, DIN EN 821

Heat deflection temperature (HDT) and Vicat softening temperature (VST)

The requirements for thermal stability of polymers increase in many applications. However, there is no strictly defined upper application temperature for plastics. A measure for this is the heat deflection temperature ( HDT ).

This is determined on a specimen which is under a bending load and is heated in an oil bath at a heating rate of 2 K / min. If the deformation exceeds 0.2 %, the temperature to be measured is reached.

The method is not applicable if the material is too soft and deforms too much even at temperatures below 27 ° C.

The Vicat softening temperature (VST) is measured with a needle-shaped indenter, which is loaded with a test force of 10 N or 50 N. The specimen is thereby heated with a defined heating rate. The temperature is determined when the needle reaches a penetration depth of 1 mm.

Normen: DIN EN ISO 75, DIN EN ISO 306