Sintering is a production process for forming a mechanically strong body out of a ceramic or metallic powder.
This is achieved by applying heat (often in combination with higher pressure) but keeping the temperature below the Melting Temperatures and EnthalpiesThe enthalpy of fusion of a substance, also known as latent heat, is a measure of the energy input, typically heat, which is necessary to convert a substance from solid to liquid state. The melting point of a substance is the temperature at which it changes state from solid (crystalline) to liquid (isotropic melt).melting temperature of the main component. During sintering, shrinkage due to compaction and pore healing is usually observed. In addition, grain growth may occur. A distinction is made between solid-phase and liquid-phase sintering. For the latter, only partial melting takes place during heating.
The steps occurring during sintering are very complex. There are different factors that influence the sintering process like grain size or compaction. In addition, the conditions during sintering (temperature, time, and atmosphere) will also have an influence on the final product.
Sintering follows DebindingDebinding is one of the main production steps in the ceramic and powder-metallurgical industries. It refers to the thermal or catalytic removal of additives used in steps prior to production such as casting.debinding as the next step in the production chain. It is typically studied with a dilatometer to acquire information about shrinkage steps and final shrinkage. Another method of characterizing the sintering process is Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity, as neck formation and grain growth can result in a different thermal conductivity than a loose or just compacted powder.
As sintering takes usually place at higher temperatures, energy costs are high. Therefore, different approaches like Rate-Controlled Sintering (RCS)The properties of sintered products, such as density or particle size distribution, are determined by the sintering conditions (temperature, atmosphere, etc.) and especially by the sintering rates. Rate Controlled Sintering (Rate-Controlled Sintering (RCS)The properties of sintered products, such as density or particle size distribution, are determined by the sintering conditions (temperature, atmosphere, etc.) and especially by the sintering rates. RCS) or Kinetic Analysis are used to reduce time and if possible, also temperature, and additionally to optimize the densification of the sintered part.
See below for an example depicting the sintering of a porcelain green body.