Calcination of glass, silica, quartz and alumina fibre textiles
Calcination is a thermal treatment of a solid chemical compound whereby the compound is raised to a high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), generally for the purpose of removing impurities or volatile substances and/or to incur thermal decomposition.
The root of the word calcination refers to its most prominent use, which is to remove carbon from limestone (calcium carbonate) through combustion to yield calcium oxide (quicklime).
However in glass, silica, quartz or alumina fibre applications Calcination is referring to the removal of the ‘Size’, sometimes called ‘finish’ which is often a starch applied to the yarn to give it more structure and stability for processing.
Whilst these sizes or organic finishes represent only a tiny fraction of the product they can in some critical applications be undesirable.
Therefore, these high temperature textiles are calcinated to remove the finish only but not to a degree it impinges on the performance properties of the fibre.
Quartz and Alumina fibres are most commonly subjected to this process given they are used in critical applications within aerospace industries. Click here for examples of Quartz felts that have been calcinated.
Some glass fibres are heat processed for a limited period to simply carbonise the organic matter. This results in the fibre caramelising and tanning in colour. It also has the desired effect of ‘setting’ the yarns a little for added stiffness. Click here for examples of caramelised glass textiles.
- Tracy Barker
