A significant number of ceramic kilns producing clay-facing brick are fired with
sawdust fuel in North America. It has been long recognized that wood-fired
boilers experience potassium attack on refractories as K2O vapors are present
in the combustion atmosphere. These vapors penetrate the refractory, providing
for two types of deleterious wear processes. These are (1) glazing of the brick and
deposition of slag on the surface of the brick near the “burners” and (2) expansion
of the brick over a long period.
In tunnel kilns of length 50–100 meters, expansion progressed over a
period to the point that the interior walls made of fireclay brick typically buckle
inward. In about seven years of service, the brick must be replaced to continue
operation.
In the same kilns, crown (roof) brick (insulating firebrick) in flat, suspended
construction exhibited “sheet” spalling in seven years of service. Sheet spalling is
loss of refractory thickness of about 25 mm (1 in.) over a large area (many
bricks). The sheet spalling was apparently a result of expansion reactions
between the IFB and the alkali in the kiln atmosphere.