ISO 21821 is the international standard on fine ceramics that covers the determination of densification properties of ceramic powders on natural sintering.
ISO 21821 specifies the test method to determine the extent to which ceramic powder compacts made of granulated or ungranulated ceramic powders are densified when they are sintered at a high temperature without the application of any external pressure or external densification force.
The test method is applicable to pure oxides, mixtures of oxides, and solid solutions, and is also applicable to non-oxides (e.g. carbides, nitrides) that can be sintered under vacuum or constant gas pressure (1 bar or less) to prevent oxidation or decomposition.
Note: The test method is not applicable to ceramics that can only be sintered using pressure-assisted sintering techniques such as hot pressing (HP), hot isostatic pressing (HIP), gas pressure sintering (GPS), or spark plasma sintering (SPS). Inorganic sintering additives can be used where their presence is reported.
ISO 21821 on the densification properties of ceramic powders is useful for:
Densification is the act of reducing porosity in a sample, thereby making it denser. Grain growth is the process of grain boundary motion and Ostwald ripening to increase the average grain size.
When ceramic powder compacts are heat-treated at high temperatures, they shrink and are densified due to sintering.
Sintering is the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction. Sintering happens as part of a manufacturing process used with metals, ceramics, plastics, and other materials.
The mass, dimensions (diameter and height), volume, and apparent density of a ceramic powder compact are measured before and after sintering through thermal treatment. The variations in mass, dimensions, volume, and apparent density depend on maximum temperature, dwell time, heating rate, and apparent density after compaction, and can be expressed as a function of these parameters.
ISO 21821 on the densification properties of ceramic powders specifies the test method to determine the extent to which ceramic powder compacts made of granulated or ungranulated ceramic powders are densified using sintering.
This can help you produce complex shapes without secondary machining operations and can be used for the shaping of materials with a high melting point.
ISO 21821