The high thermal and electrical resistance of kyanite makes it useful for porcelain used with spark plugs.
Kyanite is a mineral that has many industrial uses, such as the molding and formation of products that must withstand high temperatures. It is also added to the clay bodies of different clays and porcelains because it has unusual thermal and structural properties that can enhance the strength and change the shrinkage of fired clay. While kyanite is typically used in industrial settings, it can also be used for sculpture and small-scale productions of clay items.
Kyanite
Kyanite is a mineral composed of aluminum, silicon and oxygen. There are two other minerals with the same chemical composition as kyanite: andalusite and sillimanite. Kyanite forms at much higher pressures than andalusite and sillimanite and is often found in sedimentary rocks that contain clay. It is unusual in that it kyanite has different hardnesses, depending upon what part of the crystal is tested. It also expands when exposed to heat, unlike most other minerals. Kyanite is typically used for the formation of products which must withstand high heat, and is also used as an abrasive.
Green Clay
Kyanite has an unusual, needle-like grain and fibrous structure. When added to a clay body, these grains interlock with one another, forming a mesh or matrix. This matrix adds a significant amount of strength and durability to the clay body. With unfired clay, this matrix structure helps the clay maintain its form, which is helpful when making a large structure.
Fired Clay
Kyanite prevents cracking and warping during the firing process and increases the temperature at which an item can be fired. The same needle-like structures that maintain strength before firing also maintain strength during and after the firing process. This helps the finished product resist breaking afterwards and makes it more durable. At high temperatures, kyanite converts to mullite, which is an even stronger material.
Expansion
Clays shrink when fired, some significantly. This can be a problem, and it can be difficult to determine how large a piece should be at production in order to be the correct size once fired. Kyanite, unlike most other minerals, expands by about 2 percent when heated. This expansion helps maintain the volume of the clay object and effectively prevents significant shrinking in any type of clay. The predictability of kyanite expansion is also helpful when calculating the size of the initial item.
Tags: other minerals, added clay, also used, andalusite sillimanite, clay body, Clay Kyanite, firing process