Sialon Advanced Ceramics – Evolution of Sialons from Silicon Nitride

Silicon nitride (Si₃N₄) was discovered in the mid-nineteenth century and caused no excitement among the engineering fraternity of the day. The problem was that Si₃N₄ does not lend itself to ease of fabrication. Over the next century two principle routes for fabricating Si₃N₄ ceramics were developed: hot pressing and reaction bonding.

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Hot Pressed Silicon Nitride Ceramics - HPSN

Hot pressed Si₃N₄ (HPSN), was made by adding a flux (usually magnesia, MgO) to a fine Si₃N₄ powder and then pressing the powder in a graphite die at high pressure and temperature. The resultant HPSN body, although fully dense and extremely strong, could only be made in to simple shapes which would then require expensive diamond grinding to obtain the desired profile.

Reaction Bonded Silicon Nitride - RBSN

Reaction bonded Si₃N₄ (RBSN), was made by carefully nitriding a silicon (Si) 'dough' to produce a formed piece of Si₃N₄. This RBSN body was porous and low strength, but it was refractory and could be formed in to relatively complex shapes.

Sialon Advanced Ceramics - Evolution

Both these materials therefore had significant drawbacks. Then, in the early 1970s came a revolutionary breakthrough which made scientists and engineers alike sit up and take notice. This discovery was made independantly at Newcastle University in the UK by Jack and Wilson (Ian Wilson was our late M.D.) and in Japan by Osana et al. This breakthrough was the discovery of sialon, an alloy of Si₃N₄. This was the first known man-made ceramic alloy and in 1972 the first Patent was granted for sialon materials under the names of Jack and Wilson.

Sialons - What Are They?

The term 'sialon' describes silicon-aluminium-oxynitride alloys of silicon nitride. Further work on these alloys soon showed that the days of having to hot press or reaction bond Si₃N₄ to get a useful body were over. By making additions of rare earth oxides such as yttria (Y₂O₃), fully dense, pressureless sinterable materials could be produced.

Over the next two decades the sialon system was meticulously studied resulting in the modern day sialons as manufactured by International Syalons under the trade name Syalon.

This information has been sourced, reviewed and adapted from materials provided by International Syalons.

For more information on this source, please visit International Syalons.