An industrial term for the fast (seconds to minutes) high-temperature heating (usually 900 – 1000°C) of porous clays or perlites to remove adsorbed water by volatilization, in addition to partial dehydroxylation (structural water) of the clay minerals present. For most clay minerals, the point where the rapid loss of structural water first occurs is often referred to as the onset of low volatile matter (LVM) characteristics. Termination of heating at this or a somewhat higher temperature commonly generates a material (e.g., calcium hydroxide) whose porous bulk fabric remains intact and which does not readily slake in water. Unlike calcination, which implies a complete dissociation reaction, superheating produces limited dehydroxylation without destroying plasticity (i.e., without destroying clay-like properties). Thus, LVM clays will still display a measurable weight loss on ignition.
Syn., flash heating,
Cf., low volatile matter (LVM); slake; calcine; loss on ignition; water, adsorbed; water, structural; water, zeolitic