Mat Sci Report on Boron Carbide

Boron Carbide is one of the hardest materials in the world, it has many uses due to its extreme hardness and resistance to wear. Boron Carbide was first discovered by Henri Moissan in 1899 when he reacted Boron Oxide and fused it with Carbon in an electric arc furnace, it was not until the 1930’s that its chemical composition was estimated to be B4C. It is also known as black diamond because of its dark colour and extreme hardness.

Physical structure of boron Carbide

Boron Carbide is an advanced non-oxidized ceramic material, it has the chemical composition of B4C, however this is just an estimate because in practical situations Boron Carbide has a slight deficiency in the Carbon content, the structure of Boron Carbide is highly complex. Boron Carbide known as an icosahedron based boride, icosahedron is a solid shape with 20 sides and 30 edges, the icosahedra form a rhombohedral lattice. A rhombohedral is a 3 dimensional solid shape that looks like a rhombus. According to the company FELDCO international the composition of Boron Carbide powder is: 74% - 79% Boron, 17% - 24% Carbon, 0. 1% - 1% B203, 0. 2% - 0. 5% Iron, 0. 1% - 0. 3% Silicon.

Boron Carbide has a high capability to absorb neutrons and is resistant to wear as being a semi-conductor, which means that it has the conductivity between that of an insulator and conductor, semi-conductors are often used as components in electric circuits. Boron Carbide has a relatively low density of 2520 kg/m3 which means that the material is very lightweight, the hardness value of Boron Carbide is rated between 9 and 10 on the Mohs hardness scale, which ranks a material on a scale between 1 and 10, with 10 being the hardest material (diamond). Although the Mohs scale is useful to quickly see the hardness of a particular material the scale is inaccurate because it was created long ago. The hardness value of Boron Carbide is 2900-3580 kg/mm2. Boron Carbide has a young’s modulus of 450-470 GPa, and melting point of 2445 degrees Celsius, however it begins to oxidize once the temperature has exceeded 500 degrees Celsius, so the material should not be used if the temperature exceeds this temperature. Boron Carbide has an electrical conductivity of 140 seconds at 25 degrees Celsius, and thermal conductivity of 30-42 W/m. K at 25 degrees Celsius, and a thermal expansion co-efficient of 5x10

-6 degrees Celsius.

Summary of physical properties:

Density: 2520 Kg/m3

Hardness: 2900-3580 Kg/mm2

Young’s modulus: 450-470 GPa

Melting point: 2445 °C

Electrical conductivity: 140 s

Thermal conductivity: 30-42 W/m.

K Thermal expansion co-efficient: 5x10

-6 °C

Boron Carbide characteristics:

• Extremely hard
• Resistant to chemicals
• Low density
• Good nuclear ability to absorb neutrons
• Difficult to sinter to relatively high densities.

Manufacturing processes

Boron Carbide is produced when Boron Trioxide (B2O3) reacts with Carbon (C) in the oxidation reduction process. This reaction occurs above the melting temperature of Boron Carbide, this temperature is obtained by an Electric Arc Furnace, large amounts of Carbon Monoxide are produced as a by-product of the reaction: 2B2O3 + 7C □(→┴ ) B4C + 6COIn commercial use, Boron Carbide usually needs to be purified and milled to remove metallic impurities. Boron Carbide is difficult to sinter to full density because of its low self-diffusion co-efficient which is caused from its strong covalent bonds between its atoms, high resistance to grain boundary growth, and its low surface tension. Sintering is the process of making a compacted powder denser by eliminating the interparticle pores by thermal energy driven atomic diffusion, the diffusion can cause grain growth to be inevitable, grain growth is a process which competes against densification of the compacted powder. The densification increases the strength and toughness of the material but the grain growth results in the toughness and strength to degrade, therefore it is ideal to try reduce the grain growth as much as possible. The grain growth can be reduced, however this involves using pressure to assist the sintering process but this would involve a greater cost in the manufacturing process and therefore isn’t always economically viable.

Applications

Anti-ballistic armour: Boron Carbide has the physical properties of high hardness, high young’s modulus, as well as a low density. The combination of all these properties make the material ideal in having the excellent ability of being able to stop projectiles that are traveling at a high velocity. The low density and high hardness of Boron Carbide makes it a lightweight material that makes it possible to make a bullet proof vest from the material. A bullet proof vest made out of Boron Carbide has the potential to completely shatter a bullet on impact, leaving nothing more than a bruise on the person wearing the bullet proof vest. The material can also be used on tank and similar vehicles to act as armor plating.

Nozzles for water jet cutters: The extreme hardness and resistance to wear of Boron Carbide allows it to be used as a nozzle for high velocity and high pressure water jet cutters. The water jet is able to cut through metals and other materials, so the nozzle needs to be extremely resistant to wear so that the water jet stream is not distorted after continuous use.

Neutron absorbing material: Boron Carbide has the ability to capability to capture neutrons, Boron Carbide is typically used in nuclear power plants to protect the workers inside the power plant from neutrons that are being released during the nuclear power production process.

Abrasives: Boron Carbide is an extremely hard ceramic material, and because of this physical property it is often used as an abrasive in the lapping and polishing process. Lapping is the process of rubbing an abrasive in between two surfaces, the one material is the material that needs to be flattened and smoothened, and the other material is called the lap and can either be a hard or soft material. Lapping is used when a particular surface roughness and flatness is required that is beyond the ability of standard grinding.

Padlocks: Boron Carbide has the physical properties of being very hard and wear resistant which would make it an ideal material to choose in padlocks because of its ability to resist the action of cutters and sawing that may be used by a person intending to break the lock.

Replacement for Barium Nitrate: In green coloured fireworks the toxic metal Barium Nitrate, although Barium Nitrate is not harmful in small amount after continued use of fireworks such as in a theme park or military training ground the amount of Barium Nitrate may build up and become harmful to humans. Boron Carbide is a suitable replacement for Barium Nitrate because of its ability to burn for a long time and has a high light intensity when being burned.

Environmental impacts and sustainability

Environmental impact and sustainability refers to Boron Carbide’s ability to be recycled or reused after use, as well as its effects on the environment and people. Environmental impacts refers to the substance’s ability to negatively harm the surrounding environment or potentially harm people. Boron carbide’s sustainability refers to the material’s ability to be used reliably for a long period of time, if the material had a poor ability to be maintained or used at a certain level then it would not be a good material to use because it would wear or break easily. Sustainability also refers to the materials ability to be manufactured without depleting the natural resources used to create the substance.

Environmental impacts: Boron Carbide in general is an unreactive material and isn’t harmful to the environment, however Boron Carbide powder is known to be irritate the human skin and eyes. Boron Carbide powder is non-lethal to humans and can be easily treated if irritation occurs such as flushing the eyes and washing the skin with soap and water. Boron Carbide is odourless and insoluble in water so if exposed to the environment it will not cause an unpleasant smell and will not mix in water so can be easily filtered out.

Sustainability: Boron Carbide is made out of the elements Carbon and Boron, both of which are readily available materials, so creating Boron Carbide does not pose a risk to the depletion of the Carbon and Boron. As discussed previously Boron Carbide is an extremely hard and wear resistant material which means that it has a high resistance to wearing down or breaking and therefore has the property of being very sustainable as it would take a great amount of stress and energy to cause the material to become unstable. Increasing the concentration of B10 in Boron Carbide can improve the control efficiency of the Boron material. Material efficiency is trying to minimize the amount of raw materials used and select raw materials that are the most economical, as well as maximise the lifetime of the material. Material efficiency is important because it ensures that natural resources aren’t depleted and ensures the product being made from the raw materials is sustainable.