Zirconium aluminium carbides

As we mentioned earlier in this chapter, fireclay, muUite, and alumina refractories have been used for the layer that is in contact with molten Al. There were trials of magnesia, zirconium, aluminium titanate, and silicmi carbide refractories. The results of these trials cannot be called tmsuccessful. Most likely, these trials were sustainable for the entire range of actions necessary at implementation of a new material. In a limited amount, these materials are used today (crucibles for secondary Al for low-pressure dye casting, runners between melting and holding furnaces for special alloys, burner blocks, tap hole blocks). Yet the existing technical decision is to use alumina silica refractories with a relatively sophisticated structure and antiwetting additives. 

The traditional or conventional ceramics are generally in monolithic form. These include bricks, pottery, tiles and a variety of art objects. The advanced or high-performance monolithic ceramic materials represent a new and improved class of ceramic materials where, frequently, some sophisticated chemical processing route is used to obtain them. Generally, their characteristics are based on the high quality and purity of the raw materials used. Examples of these high-performance ceramics include oxides, nitrides, carbides of silicon, aluminium, titanium and zirconium, alumina, etc. 

Ceramics can be elementary i.e., they may consist of only one element (carbon, for example, can exist in two different ceramic forms, as diamond or graphite), or they can be compounds of different elements. Of technical importance are silicate ceramics, containing silicon oxide (for example, porcelain or mullite), oxide ceramics i.e., compounds of metallic elements with oxygen (for example, aluminium oxide AI2O3, zirconium oxide Zr02, or magnesium oxide MgO), and non-oxide ceramics i. e., oxygen-free compounds like silicon carbide and silicon nitride. 

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