Characteristics and Applications of Commercial Refractory Ceramic Fibers (RCFs)

¨      RCFs are aluminosilicate glasses (non-crystalline), CAS RN 142844-00-6.

¨      RCFs were fully commercialized in the early 1960’s, largely replacing traditional insulating refractories (bricks and concretes) in high temperature process equipment, because of the large energy savings afforded by their low thermal conductivity and low thermal mass.

¨      RCFs’ chemical and physical characteristics provide excellent thermal insulation properties and energy savings for temperatures up to about 1400°C (2550°F).

¨      The manufactured fibers have diameters varying along their length from <0.5 µm to >10 µm, and lengths from 10’s to 100’s mm.  Additionally, as manufactured, RCF products contain 20 – 50% by weight of unfiberized glass particles, referred to as “shot”, with dimensions >75 µm.

¨      Airborne respirable RCF fibers encountered in occupational settings have dimensions significantly different from manufactured RCF fibers and airborne asbestos fibers.  Airborne RCFs have geometric mean diameters in the range 0.5 to 1.5 µm and geometric mean lengths of 10 to 50 µm.  Airborne asbestos fibers have geometric mean diameters <0.3 µm, and are usually shorter than airborne RCFs; few of these asbestos fibers would be detectable by phase contrast optical microscopy, the standard technique for counting respirable fibers.

¨      RCFs are sometimes referred to incorrectly as “asbestos substitutes.”  Asbestos – a term commonly used to describe a group of natural fibers, having a wide range of chemistries and physical characteristics – is only capable of a maximum use temperature of 850°C (1550°F), and was used mostly in construction and friction products, applications now replaced by alternative (non-RCF) fibers and non-fibrous materials.

¨      RCFs and asbestos fibers have very different chemical and physical characteristics.  Asbestos fibers are closer in composition to the lower temperature glass wool fibers than to RCFs.  RCFs are brittle materials having much lower tensile strengths than asbestos fibers; RCFs break transversely rather than cleave longitudinally into thinner fibers.  All synthetic vitreous fibers (SVFs) are more soluble in neutral pH (e.g. lung fluid) than all asbestos fibers, and RCFs are no less soluble than many other SVFs.