Sintering

Sintering
Sintering is a manufacturing process in which a fine powder that has been formed into a shape is subsequently fired at temperature below melting point. The compact, when fired, densifies and becomes non-porous . The powder particles form bonds at this temperatures and the contact points between particles, which were originally formed under the mechanical pressure during compaction, increase in size and strength, improving mechanical properties.
sintering is a thermal treatment that densification accompanies it. Densification almost always requires shrinkage. The shrinkage takes place as a result of materials being transported by one or more of several diffusion processes. This may involve a liquid or reactive liquid or diffusion at grain boundaries or through the volume of particle.
Therefore, it is a densification process where porosity is usually reduced and the grain size increases significantly through mass transport. This is important because it allows an engineer to form a dense ceramic body at temperatures below the often very high melting temperature of the ceramic. For many properties such as strength, thermal conductivity, and translucency, in order to reach a maximum value for a product, it is necessary to remove as much porosity as possible. A formed powder compact can be anywhere from 40% to 75% dense, with little strength. A sintered body can have much higher strengths and densities exceeding 99% .
The ability to achieve dimensional tolerances in powder metallurgy parts arises directly from the control of the sintering process and in particular shrinkage. Thus a detailed understanding of the sintering process and the associated shrinkage is of considerable importance.