During preparation, the MgO raw materials are processed and then mixed according to the composition. To promote sintering and make the grains grow slightly, and to reduce the hydration tendency of the preparation, some additives such as TiO2, Al2O3, V2O3, etc. can be added. If high-purity MgO ceramics are required, the method of adding additives cannot be used to promote sintering and grain growth, but the method of activated sintering is used, that is, Mg(OH)2 is calcined at an appropriate temperature to obtain active MgO with many lattice defects, which is used to make sintered magnesium oxide ceramics. It is generally appropriate to calcine and decompose Mg(OH)2 at 1200℃.
MgO has strong chemical activity, is easily soluble in acid, and has a large hydration capacity. Therefore, the manufacturing process of MgO ceramics must consider this characteristic of the raw materials. To reduce the activity of MgO, it should be pre-burned to 1100~1300℃. The grinding lining and grinding balls used for grinding raw materials should be made of ceramic materials, and steel balls cannot be used. Dry grinding is used to prevent water hydration. It is best to use vibration grinding to obtain more fine particles. The molding method can be semi-dry pressing, slip injection, hot die casting and hot pressing. The binder used in the semi-dry pressing method is glycerol, polyvinyl alcohol, carbon tetrachloride solution of beeswax, etc., and fine-grained ingredients are selected and molded at a pressure of 50~70MPa. To prepare the slurry for slip injection molding, anhydrous ethanol is required as a medium to prevent MgO from hydrating and expanding. It is best to add 2%~3% oleic acid (generally about 14%) when preparing the raw materials for hot die casting. The fine grinding time should not be too long to prevent MgO particles from agglomerating. The volume density of the product obtained by hot pressing can be close to the theoretical density value. The general pressure is 20~30MPa, the temperature is 1300~1400℃, and the pressurization time is 20~40min.
MgO ceramics are mostly produced by slip injection. However, since MgO is easily hydrated, its process is relatively complicated. When preparing the slurry, to prevent MgO from contacting with water, anhydrous ethanol and other organic liquids are required as suspension media. The widely used process is as follows: Mix the MgO raw material with a sufficient amount of distilled water to form a paste and fully hydrate it into Mg(OH)2. After being stored for a certain period, dry it below 100°C, calcine it under sealed conditions at 1450~1600°C, and keep it warm for 8 hours to decompose the magnesium hydroxide back into MgO. Then ball mill it for 45~90 hours, then add water (the amount of water added is 50%~60%) and continue grinding for 70~90 minutes. Form a suspended slurry for casting. To improve the performance of the slurry, the pH value can be adjusted to 7~8.
After demolding, the blank is dried at 70°C. In order to quickly remove the moisture in the blank, the wet air should be removed as soon as possible.
The firing of ceramics is first bisque fired at 1250°C, and then placed in a corundum porcelain sagger and sintered at 1750~1800°C for 2 hours.
Edgetech offers a wide range of MgO ceramic products such as MgO crucibles, MgO tubes, and MgO stabilized ceramic products.