There are pores and impurities inside ceramic products, and their grain boundaries and crystal structures produce reflection losses and absorption losses to light, so it is opaque. To make ceramics transparent, it is necessary to try to make the scattering and absorption of light by ceramics as little as possible. At this time, ceramics can become transparent. Using Al2O3 with a purity of more than 99.99%, adding a small amount of pure magnesium oxide, lanthanum trioxide, or yttrium trioxide and other additives, using isostatic pressing, or extrusion molding/injection molding, etc., after atmosphere sintering or hot pressing sintering, strictly controlling the grain size, a high-density transparent alumina tube can be obtained. It is mainly used to manufacture the light-emitting tube of high-pressure sodium lamps (the working life can exceed 20,000 hours). It can also be used as microwave-integrated circuit substrates, bearing materials, wear-resistant surface materials, and infrared optical component materials.
High-purity alumina usually refers to alumina with a purity of more than 99.99% (4N). Alumina with a content of 60% can be used in the production of high-voltage electric porcelain. The purity of 99.5% alumina used in semiconductor preparation equipment has been greatly improved compared to 60%, but it is generally believed that alumina above 4N is called high-purity alumina.
-What are the main impurities that need to be removed from high-purity alumina? What effect do these impurities have on the performance of the material?
There are five main impurities: silicon, calcium, iron, sodium, and potassium. The presence of iron impurities will make the sintered material dark and dark; sodium and potassium impurities will affect the electrical properties of the material, causing its electrical properties to deteriorate; silicon and calcium impurities will cause abnormal grain growth during the sintering process. So we require that the content of these impurities be reduced as much as possible, for example, to below 20 ppm.
-What are the important values of high-purity alumina materials?
High-purity alumina is widely used. It is a key raw material in many high-tech fields. For example, it can be used to manufacture precision ceramic components for semiconductor equipment and various transparent ceramics.
-What are the requirements for the purity of raw materials and other performance indicators of transparent alumina ceramics?
Transparent alumina ceramics have relatively high requirements for the purity of materials. If the iron impurity content is too high, the fired alumina transparent ceramic will be dark and black; high impurity content such as silicon and calcium will affect the microstructure of the material. Another problem is the dispersion of powder particles. If the particles are severely agglomerated, even if you use 99.99% pure raw materials, you cannot produce qualified transparent ceramics. In addition, there is a key point that there are strict requirements for the sintering activity of alumina powder.
-There is a granulation step in the industrial production of ordinary alumina ceramics. Is granulation still required when preparing transparent ceramics?
-It depends on which molding method is used. We can use dry pressing or isostatic pressing to process the flat product. In this case, granulation is required. If you make tubular products such as high-pressure sodium lamp tubes, you can use extrusion molding. In this case, granulation is not required. There is also a molding method called injection molding. After we disperse the ceramic particles evenly in water, we add organic matter to form a network structure and directly solidify it. This process does not require a granulation step.
-What are the main processes for industrial production of high-purity alumina? What are the technical difficulties?
The main processes for industrial production of high-purity alumina are ammonium aluminum sulfate thermal decomposition, ammonium aluminum carbonate thermal decomposition, alcohol salt hydrolysis, and high-purity aluminum direct hydrolysis. At present, the ammonium aluminum sulfate thermal decomposition method has been eliminated. Its calcination process will produce sulfur dioxide and sulfur trioxide, which is more serious for air pollution; while the other three methods are still widely used by manufacturers. At present, it is not difficult to achieve the indicator of “high purity”. The key lies in achieving high dispersion performance of the powder. How to solve the agglomeration problem and improve its dispersion is the current technical difficulty.
Edgetech supplies alumina ceramic products of various purities, and can also process customized products according to your drawings. We use advanced equipment and exquisite craftsmanship to make each product, and strictly inspect and control it layer by layer to provide you with the best quality ceramic products.