Why does alumina ceramics turn yellow in color?
Alumina ceramics is a ceramic material with Al2O3 as the main crystalline phase. Due to its high melting point, high hardness, heat resistance, corrosion resistance, and electrical insulation characteristics, it can be used under harsher conditions. Alumina ceramics have lower production cost and matured production technology. It is currently one of the ceramic materials with the largest exportation and the widest application range. It is mainly used in fields of cutting tools, wear-resistant parts and bio-ceramics. In addition, it is also widely used in energy, aerospace, chemical and electronic fields. In particular, alumina porcelain 95 porcelain and 99 porcelain, whether in structural ceramics or electronic ceramics, are one of the most widely used and most used ceramic materials.
The preparation of alumina ceramics will go through many production processes. During the process, there are more opportunities for materials to contact machinery, equipment, tools, utensils, and the environment. Therefore, there are more factors that cause pollution and porcelain quality problems. Vhandy Ceramic will analyze the yellowing of alumina ceramics.
Normally, alumina ceramics are white after firing, but often they appear pale yellow. The editor also learned from industry insiders that this phenomenon becomes more obvious with the higher the alumina content and the higher the density of the porcelain. Moreover, it will change color after exposure to sunlight. Compared with the non-irradiated porcelain, it will be slightly yellow, and with the increase of exposure time, the color will become darker.
Analysis on the Causes of the Yellowing of Alumina Ceramics
Many people have conducted detection tests on this and found that there is no obvious difference in internal trace elements. At present, no exact reason has been found for this phenomenon, but it is generally believed that there may be the following reasons:
(1) After the sun is irradiated, the internal composition changes, and this change is irreversible, so the color will also change.
(2) It may be that the alumina ceramic has deliquescent, which produces hydrated alumina. In fact, not only ceramic products have this characteristic, but other materials will also have it, so we can only overcome the discoloration of alumina precision ceramics by minimizing the influence of external factors.
(3) The ceramics with high alumina content above 99 are mainly solid-phase sintered, and the sintering aid is solid-melted into the oxide crystals and enriched on the grain boundaries, resulting in a decrease in crystal purity, showing a yellow-based color, and Due to surface lattice defects and other reasons, the surface is in a meta-stable state, which is easy to adsorb various fine substances and show discoloration.