SiC single crystal is a Group IV-IV compound semiconductor material composed of two elements, Si and C, in a stoichiometric ratio of 1:1. Its hardness is second only to diamond.
The carbon reduction of silicon oxide method to prepare SiC is mainly based on the following chemical reaction formula:
The reaction process of carbon reduction of silicon oxide is relatively complex, in which the reaction temperature directly affects the final product.
In the preparation process of silicon carbide, the raw materials are first placed in a resistance furnace. The resistance furnace consists of end walls at both ends, with a graphite electrode in the center, and the furnace core connects the two electrodes. On the periphery of the furnace core, the raw materials participating in the reaction are first placed, and then the materials used for heat preservation are placed on the periphery. When smelting begins, the resistance furnace is energized and the temperature rises to 2,600 to 2,700 degrees Celsius. Electric heat energy is transferred to the charge through the surface of the furnace core, causing it to be gradually heated. When the temperature of the charge exceeds 1450 degrees Celsius, a chemical reaction occurs to generate silicon carbide and carbon monoxide gas. As the smelting process continues, the high-temperature area in the charge will gradually expand, and the amount of silicon carbide generated will also increase. Silicon carbide is continuously formed in the furnace, and through evaporation and movement, the crystals gradually grow and eventually gather into cylindrical crystals.
Part of the inner wall of the crystal begins to decompose due to the high temperature exceeding 2,600 degrees Celsius. The silicon element produced by decomposition will recombine with the carbon element in the charge to form new silicon carbide.
When the chemical reaction of silicon carbide (SiC) is complete and the furnace has cooled down, the next step can begin. First, the walls of the furnace are dismantled, and then the raw materials in the furnace are selected and graded layer by layer. The selected raw materials are crushed to obtain the granular material we want. Next, impurities in the raw materials are removed through water washing or cleaning with acid and alkali solutions, as well as magnetic separation and other methods. The cleaned raw materials need to be dried and then screened again, and finally pure silicon carbide powder can be obtained. If necessary, these powders can be further processed according to the actual use, such as shaping or fine grinding, to produce finer silicon carbide powder.
Specific steps are as follows:
(1) Raw materials
Green silicon carbide micro powder is produced by crushing coarser green silicon carbide. The chemical composition of silicon carbide should be greater than 99%, and free carbon and iron oxide should be less than 0.2%.
(2)Broken
To crush silicon carbide sand into fine powder, two methods are currently used in China, one is the intermittent wet ball mill crushing, and the other is crushing using an airflow powder mill.
(3)Magnetic separation
No matter what method is used to crush silicon carbide powder into fine powder, wet magnetic separation and mechanical magnetic separation are usually used. This is because there is no dust during wet magnetic separation, the magnetic materials are completely separated, the product after magnetic separation contains less iron, and the silicon carbide powder taken away by the magnetic materials is also less.
(4)Water separation
The basic principle of the water separation method is to use the different settling speeds of silicon carbide particles of different diameters in water to perform particle size sorting.
(5) Ultrasonic screening
With the development of ultrasonic technology, it has also been widely used in ultrasonic screening of micro-powder technology, which can basically solve screening problems such as strong adsorption, easy agglomeration, high static electricity, high fineness, high density, and light specific gravity.
(6)Quality inspection
Micropowder quality inspection includes chemical composition, particle size composition and other items. For inspection methods and quality standards, please refer to “Silicon Carbide Technical Conditions.”
(7) Grinding dust production
After the micro powder is grouped and screened, the material head can be used to prepare grinding powder. The production of grinding powder can reduce waste and extend the product chain.
Post time: May-13-2024