Reasons for Reducing Sintering Shrinkage of Alumina Ceramics
Alumina is an important ceramic substance for both structural and practical purposes. It is frequently employed as a component in contemporary industry, high technology, and other sectors. The rate of fire shrinkage for alumina ceramics is relatively high. There is a correlation between the technique of formation and the particle size of the raw materials in terms of the shrinking rate. The shrinking rate typically falls between 10% and 25%. Large sintering shrinkage immediately results in serious product deformation. The sintered products frequently need to undergo post-processing including grinding, cutting, and polishing in order to meet the dimensional precision standards of parts assembly. A product with significant deformation requires extensive post-processing, and the post-processing of the high-hardness alumina ceramic material is exceedingly complex and extremely expensive. Therefore, this article introduces a method to reduce sintering shrinkage of alumina ceramic materials.
In the implement process of reducing sintering shrinkage, metal aluminum powder is substituted for some of the aluminum oxide powder in order to generate alumina ceramic products by solid-phase sintering while maintaining the same aluminum ratio in the raw materials. The raw material has an average particle size of 10μm, and its sintering temperature is between 1200 and 1450 degrees Celsius. The rate at which the temperature rises is 500 degrees Celsius per hour, and the water absorption rate of the product after sintering ≤0.5%.
Specific Methods to Reduce Sintering Shrinkage of Alumina Ceramics
Method one:
In a wet ball mill, weigh industrial aluminum oxide powder (94.7%), kaolin (1.04%), talc (2.14%), and calcium carbonate (1.11%), according to a specified weight percentage, and then add 0.5wt% methylcellulose. After that, the recipe calls for the addition of metal aluminum powder (1.01%), followed by mixing, grouting, drying, biscuit firing, finishing, and fire to generate the final product. After fire, the alumina product that was generated using this approach experiences a shrinkage rate of 5%, and its other qualities are identical to those of ceramics made from 95 alumina that were formed by grouting.
Method two:
Mix a given weight percentage of methylcellulose (0.5wt%) with a known weight percentage of industrial aluminum oxide powder (92.17%), kaolin (2.05%), talc (2.14%), and calcium carbonate (1.11%), then wet ball mill the mixture. Spray granulation, dry pressing, drying, biscuit firing, finishing, and firing are next performed before the final product is obtained. After the formula has been followed and the metal aluminum powder (2.71%) has been added and mixed, the process is complete. The alumina product made using this process has the same qualities as dry-pressed 95 alumina ceramics, including a shrinkage rate of only 2% after fire.
Method three:
Mix a first batch of industrial aluminum oxide powder (96.83%) and magnesium oxide powder (1.02%) by weight, then ball mill dry once before adding 0.3wt% oleic acid for a second round of milling. The next step is to follow the formula and add 2.15% of metal aluminum powder, followed by grinding the mixture, drying it, adding paraffin and oleic acid to the mix, hot die casting, removing the wax, performing fine trimming, and finally burning the products.The process produces 99 alumina ceramics with the same other qualities as hot die-casting 99 alumina ceramics, with a shrinkage rate of 1% after fire.
Conclusion
To sum up, the sintering shrinkage of alumina ceramic materials can be reduced by adjusting the formula of the alumina ceramics and replacing a portion of the powdered aluminum oxide with powdered metal aluminum. This results in the alumina ceramic product having the same dimensions and precision as the green body. As a result, high-precision products are able to be immediately obtained by machining high-precision blanks, and the manufacture of high-precision alumina ceramic components is able to be accomplished in a straightforward and cost-effective manner.