sialon

thumb|α-SiAlON parts SiAlON ceramics are a specialist class of high-temperature refractory materials, with high strength at ambient and high temperatures, good thermal shock resistance and exceptional resistance to wetting or corrosion by molten non-ferrous metals, compared to other refractory materials such as, for example, alumina. A typical use is with handling of molten aluminium. They also are exceptionally corrosion resistant and hence are also used in the chemical industry. SiAlONs also have high wear resistance, low thermal expansion and good oxidation resistance up to above ~1000 °C. They were first reported around 1971.

==Forms== {| Class = "wikitable" style = "text-align: center" |+SiAlON forms ! Form ! formula ! n ! symmetry ! space group ! No ! Pearson symbol ! Z |- | α | Si12–m–nAlm+nOnN16–n | | trigonal | P31c | 159 | hP28 | 4 |- | β | Si6–nAlnOnN8–n | 0–4.2 | hexagonal | P63 | 173 | hP14 | 2 |- | O' | Si2–nAlnO1+nN2–n | 0–0.2 | orthorhombic | Cmc21 | 36 | oS20 | 4 |} m and n are the numbers of Al–N and Al–O bonds substituting for Si–N bonds SiAlONs are ceramics based on the elements silicon (Si), aluminium (Al), oxygen (O) and nitrogen (N). They are solid solutions of silicon nitride (Si3N4), where Si–N bonds are partly replaced with Al–N and Al–O bonds. The substitution degrees can be estimated from the lattice parameters. The charge discrepancy caused by the substitution can be compensated by adding metal cations such as Li+, Mg2+, Ca2+, Y3+ and Ln3+, where Ln stands for lanthanide. SiAlONs exist in three basic forms, which are iso-structural with one of the two common forms of silicon nitride, alpha and beta, and with orthorhombic silicon oxynitride; they are hence named as α, β and O'-SiAlONs.