REFRACTORY CERAMIC FIBRE (RCF)
RCFs are synthetic fibres produced from the melting and blowing or spinning of calcined kaolin clay or a combination of alumina (Al2O3) and silicon dioxide (SiO2). Oxides such as zirconia, ferric oxide, titanium oxide, magnesium oxide, calcium oxide, and alkalines may be added. The percentage of components (by weight) is as follows: alumina, 20% to 80%; silicon dioxide, 20% to 80%; and other oxides in smaller amounts.
RCF is produced in various grades and thicknesses. It is specified by several factors:
Density – 96Kg/cubic metre or 128Kg /cubic metre are common types. The more dense fibre is tougher but lees effective as an insulator. Kilns usually have high density fibre as the top layer or hot face, and lower density fibre as a back-up or second and/or third layers of insulation.
Thickness – 25mm or 50mm are common thicknesses
Length most rolls are approximately 7 metres in length
After some dubious test results, RCFs were aligned with asbestos as a danger to health and were judged to be possibly carcinogenic, due to the fact that tiny fibres were not soluble in bodily fluids. Sales of fibre were affected, and manufacturers created a soluble and supposedly safer fibre material, which however is not anywhere near as useful for pottery kiln use. Both these issues are discussed in a later items.