Functions of Raw Materials in the Porcelain Tile Body
Porcelain tile raw materials are usually classified according to their functions during the manufacturing process. They are generally are divided into two basic groups that are plastic and non-plastic. Plasticity may be defined as a property which allows the deformation of the clay when an external force is removed. The large group of non-plastic raw materials includes minerals, rocks, and artificial chemicals that when mixed with water is not plastic. A part of the non-plastic porcelain raw materials acts as a filler, reducing high plasticity or shrinkage of the body when drying or firing. Other non-plastic raw materials are used for sintering, fluxing or melting.
Plastic raw materials include kaolin, clay, and bentonite while non-plastic raw materials are feldspar, quartz, limestone, dolomite, magnesite, calcium phosphate and talc. The classic porcelain body consists of three major components: clay, silica, and feldspar.
The most important component of a ceramic tile body is clay. Clay is a term for naturally occurring mineral aggregates consisting mainly of the hydrous silicate of alumina. There is considerable variation in the clay’s mineral content and degree of purity. Clay serves various functions such as a binder, a suspension aid and is an inexpensive source of alumina and silica. It produces a light coloring during firing and enhances mechanical characteristics.
Feldspar provides the glassy phase for the ceramic bodies and they are added to decrease the firing temperature. Especially fort he the porcelain tiles, feldspar plays an important role in achieving the vitreous nature of the body and the high mechanical resistance of the product. Besides acting as a flux, feldspars also facilitate drying and release of gas during firing like other non-plastics.
The other constituents besides the basic clay, feldspar and silica sand include a number of minerals that are used for modifications they create within the characteristics of the bodies themselves. The most important component in this group is talc which is used to increase the fusibility. Wollastonite, dolomite, magnesite, nepheline syenite are other minerals that are used to assist the vitrification process of the body.