Possible problems and solutions

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This section tackles some common expansion and density mesurement problems and their possible resolution. You may also wish to see FAQs & Advice line.

Density

The density of a solid is difficult to obtain, since most materials contain imperfections at the atomic level (e.g. lattice displacements, lattice disorders) or, on the macroscopic level, ‘implants’ such as pores and cracks. Combining these factors makes it even more difficult to estimate or determine the actual density of a solid. For liquids and gases (as well as for solids) the pressure of the ambient atmosphere can affect the density.

Possible solutions to density determination are:

(i) knowledge of the phase diagram of the material,

(ii) use of literature or databases to get an estimate,

(iii) make your own measurements or, as always,

(iv) ask an expert (try a national measurement laboratory or your materials supplier, who may have access to unpublished property data).


Thermal expansion coefficient

Thermal expansion coefficient itself is a very small number (~ 10-6 / K) which often makes it difficult to determine accurately. Further, the expansion coefficient can be very sensitive to the actual composition (and for solids, on the crystalline structure) of the material of interest. Combining these two points, small amounts of impurities can drastically change the thermal expansion behaviour of a material.

Possible solutions to expansion determination are:

(i) make expansion measurements for the actual material

(ii) use literature or databases to get an estimate, or

(iii) contact experts (try a national measurement laboratory or your materials supplier, who may have access to unpublished property data).


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