Synthesis and environmental applications of silicon carbide

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Silicon carbide (SiC) is a material produced through the high-temperature smelting of quartz sand, petroleum coke (or coal coke), and wood chips in a resistance furnace. With its stable chemical properties, high thermal conductivity, low coefficient of thermal expansion, and excellent wear resistance, silicon carbide has various applications beyond its use as an abrasive material.

Low-grade silicon carbide (containing approximately 85% SiC) is an excellent deoxidizer in the steel-making industry. It accelerates the steel refining process, facilitates control over chemical composition, and improves steel quality. Additionally, silicon carbide is widely used in the production of electric heating elements, such as silicon carbide rods.

Silicon carbide exists in two crystal forms: β-SiC, which has a cubic structure similar to zinc sulfide; and α-SiC, which has a densely packed hexagonal crystal structure. β-SiC transforms into α-SiC at around 2100°C.

Synthesis of Silicon Carbide

1. Synthesis using silicon dioxide and carbon (coal):

Reaction: SiO2 + 3C → SiC + 2CO

The materials are mixed in a mixer, with the moisture content controlled at 2%-3%. After mixing, the bulk density of the mixture should be around 1.4-1.6 g/cm3. The loading sequence involves first laying a layer of unreacted material on the bottom of the furnace, then adding new ingredients to a certain height (about half the height from the furnace core to the bottom), followed by a layer of amorphous material. The process continues with the addition of ingredients up to the level of the furnace core.

The furnace core is placed on a base made of mixed ingredients, slightly raised in the middle to accommodate possible collapse during the furnace operation. The mixed ingredients are spread on the upper part of the furnace core, along with amorphous material or unreacted material. Once the furnace is loaded, the synthesis process begins by applying electric current and controlling the reaction process with current voltage and intensity. β-SiC starts forming when the furnace temperature reaches 1500°C, transforming into α-SiC starting from 2100°C. Complete conversion to α-SiC occurs at 2400°C. The synthesis process takes approximately 26-36 hours, followed by a 24-hour cooling period. Afterward, water cooling can be applied, and the product is layered, graded, and sorted. The synthesized material is crushed and then washed with sulfuric acid to remove impurities such as iron, aluminum, calcium, and magnesium.

2. Synthesis using metallic silicon:

Reaction: Si + C = SiC

This method involves heating high-purity metallic silicon powder and high-purity carbon powder (graphite powder) in a vacuum or protective atmosphere. At temperatures between 1150°C and 1250°C, silicon (Si) and carbon (C) react to form β-SiC, which has an amorphous structure. Crystallization of β-SiC begins at 1350°C, and β-SiC crystals are formed at 2000°C. Above 2000°C, α-SiC can be produced. Although this method is costlier, it allows the production of high-purity silicon carbide materials.

3. Synthesis using the gas-phase method:

The gas-phase method involves the reaction between silicon tetrachloride (SiCl4) and hydrocarbon (toluene) at temperatures ranging from 1200°C to 1800°C, which is the most suitable temperature for SiC formation. By using silicon-organic compounds with a stoichiometric Synthesis and Application Environment of Silicon Carbide.

Silicon carbide (SiC) has a wide range of applications due to its unique properties. Here are some additional details about its synthesis and application environment:

4. Synthesis of Silicon Carbide Using Aqueous Solution:

Silicon carbide can be synthesized using an aqueous solution of silicon compounds, such as sodium silicate (Na2SiO3) or silica sol (SiO2). The process involves the hydrolysis of silicon compounds followed by carbonization. This method enables the synthesis of silicon carbide with controlled particle size and morphology. It is often used for producing silicon carbide powders or coatings.

It's worth noting that ongoing research and development continue to explore new applications for silicon carbide in areas such as quantum computing, optoelectronics, and sensors.

Overall, silicon carbide's unique combination of properties makes it a versatile material with applications in diverse industries, ranging from manufacturing and electronics to energy and environmental sectors.