Causes of spots on the surface of alumina ceramics

How do the spots, stains, and other defects caused by alumina ceramics?
Alumina ceramics is a ceramic material with a-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.
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. In general, the common color quality problems after alumina ceramics are fired are:

(1) There are spots on the surface of the porcelain piece, such as black spots, brown spots, and red spots;
(2) There are patches on the surface of the porcelain parts, such as dark spots (shade spots), black cloud spots, bright spots, etc.;
(3) Porcelain parts have color differences, such as overall yellowing or graying;
(4) Porcelain pieces are light yellow.

One, Spots

1. Common phenomenon: In the production process of alumina porcelain, there are often black, brown, brown and pink spots on the surface of the porcelain, and there are also some inside carefully. This spot is one of the main reasons for the failure of alumina porcelain products. .
2. Cause analysis: The above-mentioned spots are generally more obvious, and it is easier to collect samples for analysis. Electron microscopy, energy spectrum analysis or chemical analysis can be used, and general qualitative analysis is sufficient. The main impurities that produce black, brown and brown spots are Fe, and the main impurities of pink spots are Fe, Cr, and Ni. By analyzing the composition of the spots and tracking the production process and production process, it can be preliminarily determined that the black, brown, and brown spots are mainly caused by the mixing of mechanical iron particles during the production of raw materials and ceramics. The pink spot can be judged from the composition analysis to be caused by the fine particles of stainless steel material. There are two main aspects to the mixing of mechanical impurities: one is the raw material; the other is the production process.
3. Prevention and solution measures

Pay attention to the following during compression molding:

(1) Raw materials: try to choose high-quality raw materials with low iron content, and perform magnetic separation to remove iron if necessary.

(2) Grinding: drop the bricks, pay attention to observe whether the lining bricks of the ball mill fall off, and repair them in time.

(3) Granulation: The slurry transportation is equipped with magnetic separation, iron removal, hot blast stove, and hot blast filtration to prevent rust from entering the material in the hot blast system. The granulated powder undergoes magnetic separation and iron removal before the final product is packaged.

(4) Piping: All pipelines should be lined with polyurethane as much as possible.