Ceramics are undoubtedly a form of art,
but there have always been endeavors to make ceramics into items of utility.
Indeed, ceramics were developed as objects for use, and not simply as
show pieces. Considering the heavy use of ceramic ware that is made in
the kitchens and furnaces, it becomes extremely necessary that ceramics
should become heat-resistant. There have been many attempts at making
ceramics heat-resistant, and these have evolved in the form of ceramics
that are known as thermal ceramics.
What are Thermal Ceramics?
Thermal ceramics are all those ceramics that need to be used in places
where the temperatures can get to be quite high. Such ceramics need to
be heat-resistant. In actuality, all ceramics are heat-resistant since
they are made by firing the clay once or twice at extremely high temperatures
in furnaces. They are later cooled down and then painted or glazed.
However, ordinary ceramics will crack if they are continuously subjected
to high temperatures, even though they may have been made by high temperature
firing. Also, there may be dunts, i.e. cracks when the ceramic was setting,
which could widen and break the whole ceramic article when subjected to
a high temperature again.
In order to overcome all these difficulties, thermal ceramics are needed
where they are to be used in high temperatures. Ceramics used for insulating
and refractory purposes come under this category.
There are three different classifications of thermal ceramics depending
on the use they are subjected to. The following are the three types:
I. Insulating Firebricks – Insulating firebricks
are extremely high heat resistant bricks that are used to make the inner
lining, the floor and the channels of the furnaces. In metallurgical operations
using the blast furnace (such as the one used in the smelting or iron),
there is a need for withstanding extremely high temperatures. This is
where insulating firebricks can be used in order to withstand the internal
temperature as well as to insulate the temperature from radiating outside.
Insulating firebricks are generally made in the shape of rectangular slabs.
II. Monolithics – These are thermal ceramics that
are used as castables. They are generally heavy and are quite versatile
in their uses. Castable ceramics can be made as low castables, dense castables,
castables with high amount of iron and alumina, etc. All castables are
insulating, but they can be made specially insulating by modifying the
processes in their manufacture.
III. Fibers – Fibers are a kind of plastic foam
such as Kevlar that has been made from ceramics clay. These are used in
manufacturing purposes in industries such as glass, iron and steel, incineration,
production of aluminum and in metallurgical operations for the manufacture
of other metals. One important property that is looked for in fibers is
that they should have a low shrinkage.
Markets where Thermal Ceramics are Used
Thermal ceramics are used in all areas where there is a requirement of
high temperature resistant ceramics. Some key industries in which they
are used are:
I. Manufacturing of scientific equipment
II. Manufacturing of aircraft and defense equipment
III. Semiconductor processing
IV. Thermal management
In these and other such industries, thermal ceramics are used to make
liners in refractory furnaces (firebricks), drying towers, baths, floors
and channels of the furnaces.
The insulating thermal ceramics ware also finds a lot of use in household
appliances like ovens, and in places like steam generators in saunas,