# Fabrication of Silicon Carbide from Recycled Silicon Wafer Cutting Sludge and Its Purification
## 1 Introduction  
Silicon carbide (SiC) is an inorganic compound that has been considered an important structural material, along with silicon nitride [1]. Depending upon its structure, it is classified as various polytypes phases; for instance, \(\beta\)-SiC (or 3C-SiC) has a cubic crystal structure, whereas \(\alpha\)-SiC (or 6H-SiC) has a hexagonal structure [2]. SiC is also known as a rigid material, which has very high thermal, chemical, and mechanical properties. In addition to high mechanical strength and high thermal conductivity, SiC also possesses a low thermal expansion coefficient, large band gap, low density, high hardness, and excellent corrosion resistance [3; 4; 5]. SiC can also be used as an antacid and an antalkali, in sandpaper, grinding wheels, disks, wire saws, as well as many abrasive products. Also, it can be used for composite material applications with steel [6]. In many manufacturing processes that produce abrasive pipes, impellers, and pumping chambers, SiC is the preferred raw material because of its high hardness, abrasion, and strength stability over a wide temperature range [7]. Recently, it has been used in the production of ferroalloys using an electric furnace in order to improve the efficiency. Furthermore, SiC can be used to produce manyother products, including fixed and moving turbine components, suction box covers, seals, bearings, ball-valve parts, hot gas flow liners, heat exchangers, and semiconductor process equipment. Various methods such as the Acheson method, Chemical Vapor Deposition (CVD), direct carbonization method, sol-gel method, gas-phase reactions, and self-propagation high-temperature synthesis have been used in the production of SiC [8]. Historically, [PERSON], while searching for a strong material by reacting clay and carbon, produced a small amount of SiC [9]. Clay and coke were mixed in an iron bowl, and a strong electric current flow was applied to the mixture through the electrode. After analyzing the product and working out the formula, it was confirmed that SiC had been synthesized. This method is known as the Acheson method, which uses high temperature, is suitable for producing \(\alpha\)-SiC on an industrial scale, and remains the most common method in the world. However, for high-purity synthesis, the sol-gel method is more reliable than the Acheson method, as Si and C powders are used to produce a hybrid gel [10; 11; 12]. Moreover, [PERSON] has done a lot of work on the synthesis of SiC and its composites. Most of his work was done by reactive infiltration, as they mention that this process is low-cost and is made in a low processing temperature [13; 14; 15]. Nevertheless, among all methods, direct carbonization is the most economical and effective as less energy is required when high-volume production is required. In the carbonization method, metallic silicon is mixed with carbon powder to produce \(\beta\)-phase SiC. This is the most beneficial and approachable method [16; 17; 18]. The reaction formula is given as:  
\[\text{Si(s)}+\text{C(s)}\rightarrow\text{SiC(s)}. \tag{1}\]  
On the other hand, the silicon sludge discharged from the silicon ingot cutting process can be used as a silicon source in this reaction. Currently, in the semiconductor and photovoltaic industries, a high-purity silicon ingot is being sliced for manufacturing Si wafers, and more than 40% of the ingot is lost to sludge in the cutting process [19; 20; 21]. The discharged silicon sludge is expected to be increasing worldwide, owing to the development of electronic devices and the growth of the photovoltaic industry. Two types of Si sludge are generated according to the cutting method. The first one is obtained by a slurry method in which a certain ratio of SiC powder is serving as an abrasive, and water and ethylene glycol are serving as a lubricant and a coolant. The slurry is continuously supplied to the sawing wire during the cutting process. Thus, the sludge consists of SiC, Si, iron powder, and cooling oil.