Introduction:
One of the advanced ceramic materials making waves in the manufacturing sector is Silicon carbide ceramic. The world of science is thrilled by this discovery. It is an advanced ceramic material which has provided answers to many needs of industrialists particularly the power electronics sector.
Origin of silicon carbide
The advanced semiconductor known today as silicon carbide was discovered by accident in the year 1891 by Acheson Ed. He was an American scientist who wanted to provide an alternative to diamonds. His intention was clear, but the result of his experiment produced silicon carbide, which gave him popularity, as no one had ever made such a discovery.
Silicon carbide was also found to occur naturally as a mineral, in a meteorite in 1893, by Moissan Henri. This birthed its other name, Moissanite. Due to this discovery and resemblance of its components to stardust, silicon carbide was named gemstone from the sky4.
FIG 1: A piece of meteorite
Commercial Preparation of Silicon Carbide
Silicon carbide ceramic can be synthetically produced in commercial quantities. There are two known methods of the synthetic production of silicon carbide. The Lely method initiated by Anthony Lely in 1955, also known as crystal growth technology, and the Chemical vapor method.
FIG. 2: Covalent bonding of silicon carbide
-
Lely method: This is a process of commercial production of silicon carbide crystals for the semiconductor industry. Here, silicon carbide powder is sublimed and heated in a crucible at very high temperatures with argon gas. Thereafter, the crystals cling to a rod in the middle of the crucible which is at a lower temperature.
-
Chemical vapor method: This is a method that was adopted by metallurgical and extractive industries to generate highly pure products8. The chemical vapor method involves the breakdown of silicon and carbon atoms in a controlled environment. The incomplete breakdown resulting from this method produces silicon carbide substrates, used by the semiconductor industry7.
The many dimensions of silicon carbide as a semiconductor ceramic
Silicon carbide is a substance which is also known as carborundum. Other names by which it is known are silicon carbide semiconductor, sic, ceramic sic and silicon carbide substrate. We will often interchange the use of the names in our discussion of the various characteristics of this advanced ceramic.
Nevertheless, and no matter what name you choose to call the substance, its basic features remain the same. The features of sic ceramic which will be examined further are the chemical, physical and mechanical features (properties).
Chemical properties of Silicon carbide (Sic): Silicon carbide is a chemical compound which is made up of silicon and carbon ions that are strongly bonded together. The strong bonds possessed by this advanced ceramic, makes it chemically inert. The band gap of its chemical structure is strong, thereby making it highly effective as a semiconductor ceramic (sic ceramic).
In other words, sic cannot be easily disintegrated by other chemical substances, particularly acids and alkalis. The tetrahedral bonding of silicon and carbon atoms produce silicon carbide substrate1. As a result, sic has the required internal composition which fits well in the manufacturing sector, especially as semiconductors.
It is also highly resistant to salts and alkalis and cannot be dissolved in water. Rather, it can be dissolved in molten iron as well as some forms of hydrofluoric acid.
Electronically, the intrinsic carrier density of ceramic sic is very low, and this enhances its suitability to high temperature operations.
Physical Properties: These are easily reflected in the color, shape and texture of the substance. Carborundum is a gem and this is reflected in its various shades of colors. Just like diamonds, they are highly valued for their luster, and the colors are graded from 4 to 7. It is also important to note that its greenish brilliance can make one mistake for diamonds.
Known also as Sic cte as a result of its thermal characteristics, since sic cte defines its thermal coefficient, silicon carbide materials are reputed to conduct a high amount of electricity. It has a very high boiling point as well as a high melting point.
Mechanical properties of silicon carbide: Silicon carbide is a very hard material. In fact, it is the hardest substance2. Silicon carbide is a reputably hard material, second only to diamond. The covalence in the bonds of the silicon and carbonic atoms in silicon carbide, makes it very hard8. Sic ceramic is considered highly resistant to corrosiveness and impact.
Sic ceramic has a lot of weight, as well as a high absorption capacity.
Carborundum and polytypism: Sic ceramic crystallizes in different structures through a process known as polytypism2, which produces polytypes of the advanced ceramic. The formation of polytypes in silicon carbide is attributed to the differences in the surface characteristics of both carbon and silicon5.
Polytypes of sic ceramic have distinguishing features in terms of mobility, bandgap and electronic properties. They are also differentiated with respect to the stacking of their crystals2. The crystalline characteristics of silicon carbide gave root to its form as carborundum, a highly valued gemstone.
Mobility of sic ceramic polytypes are exhibited in the uses of silicon carbide for the development of acoustic materials.
FIG 3: Sic ceramic crystals
Uses of sic ceramic (silicon carbide):
-
Sic ceramic is considered as one of the best advanced ceramic materials used for the production of ballistic equipment. These include body protecting apparel such as bullet proof vests. Most bullet proof vests use advanced ceramic materials as the front layer of the outfit. This is as a result of the capacity of the semiconductor to deflect high velocity projectiles such as bullets9.
-
Sic cte is used as coating for micro electro mechanical systems (MEMS) technology deployed in biomedical and biochemical systems10. Electrical products resulting from the MEMs technology such as generators and acoustic require such attributes of sic cte. The objective regarding choice of sic cte is to achieve cost effectiveness in production as well as reliability8.
FIG 4: Silicon carbide semiconductors in generator parts
-
Silicon carbide is a trusted advanced ceramic material used in the production of durable bricks, used for building. Silicon that is present in clay which is used in the production of bricks, lends it the advanced ceramic attribute. Bricks are used in construction to achieve strength, durability and good ventilation in building structures11.
FIG 5: Silicon carbide semiconductor (Bricks)
-
The aviation sector is renowned for its emphasis on quality, and durability of their equipment. This informs the use of silicon ceramic coating in the materials used to construct aircrafts. This ensures that airplanes are strong enough to resist the force of high velocity winds and crafts. The appropriate weight of the sic ceramic used also ensures that aircrafts remain afloat.
FIG 6: Aircraft parts fabricated from sic ceramic
-
The physical and microstructural characteristics of advanced ceramic materials such as sic ceramic make them first choice. They are appropriately deployed in the manufacture of critical components of electrical equipment such as generators as well as surgical implements. Their use as thin films keep the materials long lasting and resistant to wear and tear.
FIG 7: Sic use in electronics.
-
We had mentioned at the beginning of this article that silicon carbide is also known as carborundum. The term carborundum is particularly applied to sic ceramic when it applies to its use for jewelries. As a good alternative to diamonds, carborundum is highly favored for the fabrication of engagement rings. It is less expensive as diamonds, but just as impactful!
-
The ability of silicon carbide to support high electricity voltages, makes it suitable for electric and solar powered vehicles. Silicon carbide has very high thermal conductivity and promotes the dissipation of heat among component parts of electric vehicles12. Sic ceramic used in electric vehicle (EV) chargers promotes efficiency by reducing requirements for other component parts12.
-
Sic ceramic is useful for photocatalytic processes. These are methods which are used to increase thermodynamic processes by using light energy for photosynthesis. Photocatalytic processes help to reduce the exposure of the environment to chemicals and toxins from industrial activities. In this way, silicon carbide is a useful tool for protecting our environment13.
-
The hardness of sic ceramic materials makes them disposed for use as abrasives. Abrasives on their own need to possess tensile strength as well as durability. Abrasives such as sic ceramic are used in diverse sectors such as construction and technological sectors. Examples of abrasives include sandpaper, which is used to smoothen softer rough surfaces14.
FIG 8: Silicon carbide abrasive - sandpaper
-
Silicon carbide is also used for the fabrication of cutting materials. It is very hard and as such, can withstand corrosion, while cutting other objects. Materials which are coated with sic ceramic offer potential for precision and hardness when used for cutting hard materials. Also, silicon carbide ceramic used for cutting do not easily wear off or corrode despite repeated uses.
Challenges in the use of silicon carbide include the following:
Ø Silicon carbide is a very rare material. As a result of this, its availability is dependent on commercial production, which in most cases, results in impure forms of the compound.
Ø Production costs of silicon carbide are high and this is reflected in the high cost of purchase by industrialists who need them.
Conclusion:
Silicon carbide is a very good discovery and has continued to make an impact in the various forms of its use. We hope that further technological advancements will emerge to innovate cheaper methods to make it available for more industrialists.