Carborundum

Carborundum is the trade name for silicon carbide (SiC), a hard, crystalline compound made of silicon and carbon. It is one of the hardest known synthetic materials, ranking just below diamond and boron carbide on the Mohs scale. Carborundum is widely used as an abrasive, refractory, and semiconductor material, making it highly valuable in both industrial and technological applications.

Chemical Composition and Structure

• Chemical formula: SiC (Silicon Carbide)
• Molecular weight: 40.10 g/mol
• Crystal structure: Tetrahedral arrangement of silicon and carbon atoms.

Silicon carbide occurs naturally in extremely small quantities as a rare mineral known as moissanite, first discovered in a meteorite by Henri Moissan in 1893. However, almost all carborundum used today is synthetically produced.

Discovery and History

Carborundum was first synthesised in 1891 by the American inventor Edward Goodrich Acheson while attempting to create artificial diamonds. He mixed silica (sand) and carbon (coke) and heated them in an electric furnace at high temperatures. Instead of diamonds, he obtained shiny, crystalline particles of silicon carbide.
Recognising its extreme hardness, Acheson patented the process and established the Carborundum Company in 1894 to produce the material commercially for use as an abrasive.
The process he developed, known as the Acheson Process, remains a key method for industrial production of SiC.

Physical and Chemical Properties

These unique properties make carborundum suitable for harsh industrial conditions and high-performance applications.

Manufacturing Process (Acheson Process)

1. Raw Materials:
   • Silica sand (SiO₂)
   • Carbon (in the form of coke or anthracite)
2. Process Steps:
   • The materials are placed in an electric resistance furnace with a graphite core.
   • A high electric current (around 2,000°C–2,500°C) passes through the mixture.
   • The reaction forms silicon carbide and carbon monoxide gas:

     SiO2+3C→SiC+2COSiO₂ + 3C \rightarrow SiC + 2COSiO2​+3C→SiC+2CO

3. Cooling and Crushing:
   • The furnace is allowed to cool for several days.
   • The solid mass of SiC is removed, crushed, and graded by grain size.
4. Purification:
   • Impurities are removed by acid leaching or further heating.

Types of Silicon Carbide

Depending on purity and application, SiC is classified into different grades:

1. Black Silicon Carbide:
   • Contains about 98% SiC.
   • Used mainly as an abrasive and for refractory applications.
2. Green Silicon Carbide:
   • Higher purity (~99%) with sharper edges.
   • Used for precision grinding and polishing of hard metals and ceramics.
3. Beta Silicon Carbide (β-SiC):
   • Formed below 2000°C; cubic crystal structure.
   • Used in semiconductors and electronic applications.
4. Alpha Silicon Carbide (α-SiC):
   • Formed above 2000°C; hexagonal or rhombohedral crystal structure.
   • Used in structural and refractory materials.

Industrial Applications

Carborundum’s exceptional hardness, thermal stability, and electrical properties make it useful in diverse industries:

1. Abrasives and Cutting Tools:

• Grinding wheels, sandpapers, and cutting tools.
• Used in machining metals, stones, glass, and ceramics.

2. Refractory Material:

• Used in high-temperature furnaces, kiln linings, and crucibles due to its heat resistance and low thermal expansion.

3. Electronics and Semiconductors:

• Silicon carbide semiconductors are used in high-voltage and high-temperature electronic devices, power converters, and electric vehicle systems.
• SiC-based diodes and transistors are more energy-efficient than traditional silicon-based electronics.

4. Automotive Industry:

• Components in electric vehicles (EVs), such as inverters and power modules.
• SiC ceramics are also used in brake discs and mechanical seals.

5. Aerospace and Defence:

• Used in advanced composites for armour and heat shields due to its strength and light weight.

6. Solar Energy:

• SiC wafers are used as substrates for LED lights and photovoltaic cells.

7. Structural Materials:

• Used in bulletproof vests, turbine parts, and corrosion-resistant pipelines.

Advantages of Carborundum

• Extremely hard and wear-resistant.
• Chemically inert and corrosion-resistant.
• High thermal conductivity and resistance to thermal shock.
• Stable at very high temperatures.
• Recyclable and environmentally stable.

Limitations

• Brittle nature: Can fracture under heavy impact.
• High cost compared to conventional abrasives or metals.
• Processing difficulty: Requires specialised tools for shaping or machining.

Environmental and Economic Significance

Carborundum contributes to energy efficiency and sustainability in several industries:

• In electronics, SiC devices reduce power losses and carbon emissions.
• In metallurgy and manufacturing, its reusability and durability lower material waste.
• Its role in renewable energy systems (solar, electric vehicles) supports the transition to cleaner technologies.