Sintering - Ceramic Sintering

Ceramic Sintering

Sintering is part of the firing process used in the manufacture of pottery and other ceramic objects. Substances such as glass, alumina, zirconia, silica, magnesia, lime, beryllium oxide and ferric oxide. Some ceramic raw materials have a lower affinity for water and a lower plasticity index than clay, requiring organic additives in the stages before sintering. The general procedure of creating ceramic objects via sintering of powders includes:

• Mixing water, binder, deflocculant, and unfired ceramic powder to form a slurry;
• Spray-drying the slurry;
• Putting the spray dried powder into a mold and pressing it to form a green body (an unsintered ceramic item);
• Heating the green body at low temperature to burn off the binder;
• Sintering at a high temperature to fuse the ceramic particles together.

All the characteristic temperatures associated to phases transformation, glass transitions and melting points, occurring during a sinterisation cycle of a particular ceramics formulation (i.e., tails and frits) can be easily obtained by observing the expansion-temperature curves during optical dilatometer thermal analysis. In fact, sinterisation is associated to a remarkable shrinkage of the material because glass phases flow, once their transition temperature is reached, and start consolidating the powdery structure and considerably reducing the porosity of the material.

There are two types of sintering: with pressure (also known as hot pressing), and without pressure. Pressureless sintering is possible with graded metal-ceramic composites, with a nanoparticle sintering aid and bulk molding technology. A variant used for 3D shapes is called hot isostatic pressing.

To allow efficient stacking of product in the furnace during sintering and prevent parts sticking together, many manufacturers separate ware using Ceramic Powder Separator Sheets. These sheets are available in various materials such as alumina, zirconia and magnesia. They are additionally categorized by fine, medium and coarse particle sizes. By matching the material and particle size to the ware being sintered, surface damage and contamination can be reduced while maximizing furnace loading.