When we talk about the hardest material, the first thing that comes to our mind is Diamond. The Diamond is the hardest thing known to almost every common man in the world. But recently, this precious and expensive gem had to give away its title for the hardest substance and few other compounds are discovered which are harder than diamond. There are rare and are natural substance and thus, not used as widely as diamond. Apart from diamonds and those rare substances, there are other materials which are very hard and can bear a lot of pressure and prove to be very useful for science and to man. Few of the most hard substance known to man are:
The Aluminum oxide, commonly known as Alumina, is chemically formed as Al2O3. The most commonly known form of this is the crystalline polymorphous form (known as corundum as well as alpha-aluminum oxide) but other varieties of this compound are precious and hard gems named ruby and sapphire, the color is due to the presence of some impurities. The most common use of the crystalline Alumina is the extraction of aluminum. But due to its high melting point, it is also used as a refractory material. Other properties of this compound include high resistance towards electricity, but thermal conductivity is high, water insoluble, etc. It is also used in cutting tools and as an abrasive because of its hardness.
9. Zirconium Carbide:
Zirconium carbide, chemically ZrC, is one the extremely hard materials. This is again a ceramic material which usually looks like grey metallic powder. The material is sued in tool bits for manufacturing cutting tools. This compound has high resistance towards corrosion. The material has a cubic crystal lattice structure formed by a very strong covalent bond between Zr and C. Therefore, the material is used in jet engines, rocket engines, supersonic vehicles and its parts, etc. This is because of its property of high load bearing capacity at high temperature and its low density. Hafnium-free of this compound is also used in coating the refractory in nuclear reactors.
8. Titanium carbide:
Titanium carbide (chemically known as TiC) is a compound which is hard and made from ceramic material and resembles tungsten carbide. The structure is like that of a NaCl cubic crystal and appears like black powder. The compound is used in tool bits for commercial reasons and also used for preparing cermet; cermets are used in high speed cutting of machine steel material. The best apart about the compound is that it is resistant towards getting corroded or oxidized or worn. The TiC is also used like a heat shield in space crafts as it has a melting point of 3160 degree Celsius. By adding 6-30% more titanium, we can make a solid solution of the substance which is more brittle than the original TiC.
7. Titanium diboride:
Formed by titanium and boron, TiB2, is a very hard ceramic substance. But unlike ceramic, it is a great electric conductor and has high resistance for mechanical erosion. Due to its property to conduct electricity, the titanium diboride is helpful in aluminium smelting process as a cathode. Its properties are very much like that of titanium carbide but are obviously superior to those of TiC. The hardness of this compound is three times more than the fully hardened steel. Chemically also, this substance is more stable than TiC and even more stable than pure iron which is because of its property of resistance to oxidation. The substance is not available naturally and is therefore, manufactured in the laboratories using some high temperature and high pressure techniques.
6. Rhenium diboride:
This compound was firstly synthesized in the year 1962. Rhenium diboride or ReB2, became the strongest man made compound. This synthetic compound is a very cheaper one because the procedure to produce this compound will not take high pressure. In spite of not being formed with high pressure, the compound is super hard. But note that only the production process is cheaper and rhenium is an expensive metal all by itself. The hardness of this compound is found comparable to that of a diamond. In physical appearance, this substance is of the form of a black powder which is insoluble in water. The hardness is mainly because of the density of valance electron is high and covalent bonds are short.
5. Boron Carbide:
Discovered in 19th century, Boron Carbide is a very hard substance with the chemical formula B4C, i.e., the ratio of boron to carbon is 4:1. This ceramic product is very had and is the major compound used in manufacturing bullet-proof vests, tank armor, and many other industrial uses. The compound has a unique property to absorb neutron radiation and thus, it is used in the nuclear power plants for shielding purposes. The compound has a property of being stable in the presence of ionizing radiations and other chemicals. It is also used in padlocks, high-pressure jet cutter nozzles, blasting nozzles, wear resistant coating, anti-ballistic armor plating, cutting tools, in the brake linings for many vehicles.
Borazon is also called the cubic boron nitride (CBN) and is the commercial brand name for the cubic form of Boron Nitride. When boron and nitrogen are taken in equal amount and are heated at a temperature of more than 1800 degree Celsius at 7 GPa, then the resulting compound will be borazon. The best thing about borazon is that it is available in abundance and is very cheap. Thus, most of the drillers prefer borazon over diamond as diamonds are expensive. Apart from being a substitute to the diamond, borazon is also used for making cutting tools, saw blades, knives, needles, rollers, engine, gears, aerospace parts, turbine parts, blades, even surgical knives, grinding steel, paper mill rolls, etc.
Diamond is made of carbon atoms. When carbon atoms are pressurized for about 1 to 3.3 billion years, then diamonds are formed. As, diamonds are formed under very high pressure, they are very hard. Also, the bonds between the carbon atoms in a diamond are hexagonal and thus are unbreakable. Because of property of diamond of being hard, diamonds are commercially used in industries for drilling efficiently and also used for adornment. And the structure of diamond being very beautiful, they are used in jewelry after proper cutting and polishing. The diamond can reflect light as well as refract and entraps the light in it, and thus, they shine beautifully.
The mineral Lonsdaleite is a translucent, brownish yellow and is made from the atoms of carbon but the arrangement of these atoms in Lonsdaleite is different from the arrangement of carbon atoms in a diamond. The simulation of this mineral has shown that it can survive 58% higher stress as compared to diamond. The mineral is very rare and is formed naturally whenever the graphite containing meteorites fall on the earth and hit the surface. As the mineral is rare and there is not enough of this mineral present on earth, researchers are trying to find a way to produce this in a laboratory by some feasible way. The Lonsdaleite is very rare and thus cannot be wasted in tests and studies; therefore, more of it must be produced in the lab.
1. Wurtzite Boron Nitride:
The structure of Wurtzite is very much same as that of a diamond but the difference is it is not made up of carbon but some other atoms. The structure of Wurtzite is more complex than diamond and thus makes it stronger than diamond. The mineral do exist naturally but in a very small amount that cannot be risked in laboratory tests. It is formed during those volcanic eruptions with high pressure and high temperature. Simulation has shown that it can survive 18% more stress if compared to diamonds. Scientists believe that the strength is because of the re-orientation process of the flexible bonds. The structure of Wurtzite boron nitride becomes 80% stronger after the re-orientation process, and this makes it the hardest substance found on earth.