|Monthly Tech-Tip |
Man-made ceramic surfaces are among the most abrasion resistant materials known. Products made to abrade others are also made from bonded ceramic grains.
Abrasion ceramics can refer to two things: Products that resist abrasion because they are hard (more correctly these are actually abrasion-resistant ceramics) and products that abrade other materials because they are harder.
Of course, even every-day porcelain surfaces are very durable. The hardness of vitrified pottery and porcelain is largely dependent on the development of aluminum silicates during firing. This requires temperatures high enough to melt fluxes available and enable them to dissolve quartz and other minerals. Sufficient time is required for the growth of crystalline species like mullite (from clay crystals). Glazes can also be resistant to abrasion, this happens when they have the highest possible percentages of alumina and silica and are fired high and melted well. But ceramics can be made much more wear and abrasion resistant by using specialized materials (e.g. refractory powders and grains, nano particle sizes, non-oxides) and fired in special ways (e.g. to very high temperatures, special cooling curves). Sintered products are popular for abrasion resistance. If the individual particles are very hard and they can be bonded by sintering only, there is no weakness associated with the bonding glass). Calcined alumina, for example, can be cast and fired to very high temperatures to produce highly dense and surfaces with exceptional resistance to abrasion.
The abrasives industry makes products designed to abrade others. Manufacturers produce a range of angular particled sands having grains of very high hardness. Other manufacturers buy these and bond them into shapes (e.g. grinding wheels) using binder/bonding frit mixtures (or formulated glasses). During firing the binders burn away and the frits melt and bond the particles (thus they are called vitrified bonded abrasives). Firing temperatures need to be low enough not to damage the abrasive grains or cause shapes to warp but high enough to melt the bonding glass (this can be done below 850C). Soaking for considerable time is needed for penetration of the heat (e.g. three hours). Special low expansion bonding frits are produced for this (e.g. Ferro Frit 3249). Very low concentrations of zinc and iron are also important. If you do not have a frit available, study the chemistry of 3249 and create a mix of other frits and materials to duplicate it.
A densification process occurring within a ceramic kiln. With increasing temperatures particles pack tighter and tighter together, bonding more and more into a stronger and stronger matrix.
The term vitrified refers to the fired state of a piece of porcelain or stoneware. Vitrified ware has been fired high enough to make it very strong, hard and dense.
This term generally refers to the industry that produces the non-metallic objects we use every day (like porcelain, tile, glass, stoneware).
|Materials||Ferro Frit 3249|