Possible data sources: evitherm, CINDAS

To access a data source click on "Finding data" in the left-hand menu.

Are the data relevant to my application?

Below are comments from the evitherm project team giving some guidance on selecting data that are suitable for the material and the application of interest, addressing each thermal property in turn.


Thermal conductivity and diffusivity of metallic alloys

The thermal conductivity/diffusivity (and electrical conductivity) of metals is generally high. However, the thermal and partly mechanical treatment of the material may change their thermal conductivity/diffusivity. There is a relation between thermal conductivity and electric resistivity of metals called the Wiedemann-Franz-Lorenz law. Depending on the type of alloy there is a deviation between the theoretical and the real Lorenz number. For molten metals the theoretical Lorenz number is usually valid. In addition to the detailed chemical composition of metals, it is useful to know thermal pre-treatment of the material. Because hardness is also affected by thermal treatment this easily determined value is an additional help to estimate the thermal conductivity/diffusivity.

Expansivity and density

Data may be a function of heat treatment condition. The presence of phase transitions, especially martensitic transitions which occur at different temperatures on heating and cooling, make data recording and interpretation difficult.

Emissivity and other infrared optical properties

The main features (variations of emissivity with direction, temperature, wavelength) given here are true in the infrared spectrum (wavelengths higher than 0.8 µm) for most metals. For shorter wavelengths (UV and visible spectrum) the behaviour is much more dependent on the nature of the metal. Smooth (polished) metals are characterised by low values of emissivity and consequently by high values of reflectivity. For variations of emissivity with direction, the typical behaviour is a slow increase of directional emissivity with increasing angle from the normal, but lower than 40°, and then a significant increase of directional emissivity with angle, reaching a maximum for an angle higher than 80 ° and then a very strong decrease of emissivity with angle, reaching zero at the direction 90°. For most metals the ratio of hemispherical emissivity to  normal emissivity is larger than 1 because of the variations of directional emissivity with angle.

Spectral emissivity tends to decrease with increasing wavelength. In most instances, the spectral emissivity of metals tends to increase with temperature. Total emissivity tends also to increase with temperature but this is mainly due to the displacement of the spectrum toward short wavelengths than to the increase of the spectral emissivity with temperature. The spectral emissivity of a metal increases with surface roughness. The surface is considered to be "rough" if the imperfections are not much smaller than the wavelength. The theory says that the emissive properties of a metal are related to the electrical properties. With some simplifications and for wavelengths that are not too short, the normal spectral emissivity is proportional to the square root of electrical resistivity (Hagen-Rubens emissivity relation).

The degree of oxidation has the greatest effect on the spectral emissivity of metals. If the oxide layer is thick, then the spectral emissivity of the surface is characterised by the oxide and is generally much higher than that of the underlying metal. If the oxide layer is thin, and so not opaque for all wavelengths, the value of spectral emissivity lies between that of the metal and the oxide and can depend strongly on the thickness of the oxide layer and wavelength value.

Specific heat capacity

Heat capacity data are available for all pure metals, including many metallic alloys. The main parameter affecting Cp data is the atmosphere around the sample, especially for reducing and oxidising atmospheres.