Diamond is the hardest naturally occurring material. Over 70% of diamonds are used in industrial applications, and demand for this material is constantly increasing. Natural diamond is composed of carbon crystals that form under high temperature and pressure conditions found only about 100 miles beneath the earth’s surface. It is usually 99.95 percent carbon. The remaining 0.05 percent may contain one or more trace elements, which are atoms that aren’t essential to the diamond’s chemistry. Diamond has an isometric crystal structure, which means that the carbon atoms are bonded in the same way in all directions. Graphite, another mineral that only contains carbon, has a very different formation process and crystal structure. As a result, graphite is so soft that it can be written on, whereas diamond is so hard that it can only be scratched with another diamond. Besides the hardness of diamond, we will discuss other properties of diamond, along with diamond vs graphite properties.
What is a diamond?
Diamond is a rare, naturally occurring carbon mineral. Each carbon atom in a diamond is surrounded by four other carbon atoms and is linked to them via strong covalent bonds, the strongest type of chemical bond. This simple, uniform, tightly-bonded arrangement results in one of the most durable and versatile materials known. The structure of diamond is shown:
Diamond is the hardest natural substance, known to man. Thermal conductivity of diamond is highest than any natural material and is it chemically resistant too. These properties of diamond make it suitable for use as a cutting tool and other applications requiring durability. There are many unique optical properties of diamond, including a high index of refraction, high dispersion and adamantine luster. These characteristics contribute to diamond’s popularity as the world’s most popular gemstone and allow it to be used in specialty lenses where durability and performance are required. Many people believe that diamond formed from coal because it is composed of the element carbon. This is still taught in many classrooms despite the fact that it is false!
How diamonds are formed?
Diamonds are not naturally occurring on Earth’s surface. Instead, diamonds are formed at high temperatures and pressures found in the Earth’s mantle, about 100 miles below the surface. The majority of diamonds discovered were brought to the Earth’s surface by deep-source volcanic eruptions. These eruptions start in the mantle and travel up, tearing out pieces of mantle rock and delivering them to the Earth’s surface without melting. These mantle blocks are known as xenoliths. They contain diamonds formed in the mantle’s high temperature and pressure conditions. Diamonds are mined from the rock that contains the xenoliths or from the soils and sediments that formed as the diamond-bearing rocks weathered away.
Properties of diamond
Besides the hardness, diamond provides an impressive combination of chemical, physical and mechanical properties, as given below:
- Diamonds come in a variety of colors, including black, brown, yellow, gray, white, blue, orange, purple, pink, and red. Colored diamonds have crystallographic defects, such as substitutional impurities and structural flaws, which cause the coloration. Pure diamonds, in theory, would be transparent and colorless.
- Because of their flatness, reflections on properly cut diamond facets are undistorted. The refractive index of diamond is 2.417 (measured by sodium light at 589.3 nm).
- Diamond is isotropic due to its cubic structure.
- Diamond is an excellent electrical insulator, with a resistivity of 10 x 1011 to 10 x 1018 Ω Due to substitutional boron impurities, replacing carbon atoms, most natural blue diamonds are semiconductors.
- Diamond, unlike most electrical insulators, is a good heat conductor due to its strong covalent bonding and low phonon scattering. Thermal conductivity of diamond is about 2200 W / (mK), which is five times that of silver, the most thermally conductive metal.
- Diamond, as a form of carbon, oxidizes in air when heated above 700 °C. Diamond can be heated to around 1700 °C in the absence of oxygen, such as in a flow of high-purity argon gas.
- Diamonds are prone to breakage due to their perfect and easy cleavage. When struck with a regular hammer, a diamond will shatter. Toughness of a diamond is measured to be 2 M Pa m1/2, which is good when compared to other gemstones like aquamarine, but poor when compared to most engineering materials.
- Diamond reacts with some materials, such as steel, and c-BN wears less when cutting or abrading them.
Other properties of diamond include its:
- Low thermal expansion coefficient
- High strength
- Low coefficient of friction
- Broad optical transparency from ultra violet to infrared
- Resistant to chemical corrosion
- Biologically compatibility
How hard are diamonds?
Diamonds are discovered as rough stones and must be processed before they can be purchased as a gleaming gem. Diamonds are the crystallized form of carbon, formed under extreme heat and pressure. This is the same process that makes diamonds the hardest mineral known to man. On the Mohs Hardness Scale, a diamond is rated a ten. The Mohs Scale of hardness is used to assess the hardness of solids, particularly minerals. From softest to hardest, here’s the scale:
- Talc: Finger nails can easily scratch it.
- Gypsum: Only fingernails can scratch it.
- Calcite: It is scratched by a copper coin.
- Fluorite: It is not scratched by a copper coin and cannot scratch glass.
- Apatite: It can only scratch glass and is easily scratched by a knife.
- Orthoclase: It easily scratches glass and is just scratched by a file.
- Quartz: It cannot be scratched by a file even.
- Topaz: It can only be scratched only by corundum and diamond.
- Corundum: It is scratched only by a diamond.
- Diamond: It can be scratched only by another diamond.
Hardness of diamond is due to the molecular structure of diamond. Diamonds are made up of carbon atoms that are linked in a lattice structure. Each carbon atom shares electrons with four other carbon atoms, resulting in the formation of a tetrahedral unit. This tetrahedral bonding of five carbon atoms creates a molecule that is extremely strong. Graphite, another type of carbon, is not as strong as diamond because the carbon atoms in graphite form rings, with each atom only linked to one other atom.
Diamond vs graphite
Organic compounds are defined as the carbon-containing substances. Carbon is an element in Group 4 of the periodic table. The number of protons in carbon is 6, similarly number of electrons in carbon is also 6. One carbon atom can form four covalent bonds. This means that carbon atoms can combine to form families of similar compounds with chains or rings. Carbon can also form massive covalent structures such as diamond and graphite. Diamond and graphite have obviously very different properties. Although both are made up of carbon, but the difference in their structure makes a distinctions between their appearance and other properties.
- Diamond is one of the hardest materials known, while graphite is a soft material.
- Diamond is transparent while graphite is gray colored.
- One of the most asked question about diamond is that, is diamond a conductor and the answer is no. Diamond is an electric insulator but the graphite is an electric conductor.
- In the structure of diamond, 4 carbon atoms are covalently attached to a single carbon atom. On the other hand, structure of graphite consists of 3 covalently bonded carbon atoms to a single carbon atom.
- In diamond structure, carbon atoms make a regular lattice arrangement whereas, in graphite structure, carbon atoms form layers to make a hexagonal arrangement.
- There is no free electron present in diamond structure while in graphite structure, each carbon atom provides a free electron, which together cause electric conduction.
- Since diamond is very hard due to strong covalent bonds so it is used in cutting tools like glass cutters. While the graphite layers can slide over each other so it is slippery and is used as a lubricant.
All of the carbon atoms in graphite have strong chemical bonds to three other carbon atoms, resulting in sheets that resemble chicken wire; weak forces hold the sheets together in stacks that can easily slide past each other. When you write with a pencil on paper, these sheets slide apart, leaving the graphite chunks behind as a mark on the paper.
Uses of diamond
Since World War II, the use of diamond has increased dramatically, owing to its unique combination of properties and increased availability as synthesis methods improved. The majority of industrial diamonds are used as abrasives. Besides it, there is a long list of the uses of diamond, some of which are given below:
- Thin diamond membranes are used to create diamond windows. They are used to fill gaps in lasers, x-ray machines, and vacuum chambers. They are clear, long-lasting, and resistant to heat and abrasion.
- Diamond speaker domes improve the sound quality of high-end speakers. Diamond is a very stiff material, and when formed into a thin dome, it can vibrate rapidly without deforming, thereby improving sound quality.
- Material that absorbs or transmits excess heat is referred to as a heat sink. The thermal conductivity of diamond is much higher than any material. It’s used to keep heat away from heat-sensitive components in high-performance microelectronics.
- Diamonds are used where extreme abrasion resistance, durability, and reliability are required, just as some watches have jewel bearings in their movements.
- Wear-resistant parts can be created by applying a thin layer of diamond to surfaces. Carbon is converted into a vapor in this process, which deposits diamond on the surface of wearable parts.
Other uses of diamond include various fields like:
- Wear components
- Cutting tools
- Thermal management
- Semiconductor devices
- Optical components
- Other high performance applications