Silicon carbide (SiC). It is a synthetic material of exceptional hardness , highly resistant to wear and chemically inert to alkalis and acids . It is also known as carborundum or carborundium, it has a covalent structure of 1: 1 stoichiometry and a hardness similar to that of diamond , despite the different size of C and Si.
Summary
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- 1 Discovery
- 1 Combination
- 2 Features of silicon carbide
- 3 Obtaining
- 1 Manufacturing technology
- 4 Applications
- 5 Risk of manipulation
- 6 Protection measures
- 7 Sources
Discovery
It was discovered in 1893 by French Henri Moissani as he examined samples of rocks from the crater of a meteorite located in the Canyon Diablo ( Arizona , USA ) and then obtained accidentally by the Swedish chemist Jons Jacob Berzelius in 1894 while conducting an experiment to synthesize diamonds.
Almost at the same time, the American Edward Goodrich Acheson designed a method to make from clay and coke a material that could replace diamond as abrasive and cutting material (Acheson method); he named the product obtained (silicon carbide) carborundum. In 1894 he created the company Carborundum Co for its commercialization.
Combination
Silicon carbide comes from a combination of petroleum coke , and highly pure quartz or sand , which are melted at high temperatures in an electronic furnace. In general, they remain at a temperature of 2000 ºC , for 36 hours, and their crystallization can be observed from 1400 ºC or 1800 ºC.
Features of silicon carbide
- Silicon carbide has a black color, although it also acquires a hue similar to that of [sand], that is, it goes from yellowto transparent. In addition, it can be found in green .
- It is considered a solid alloyon the host structure (C in the form of a diamond), atoms of this are exchanged for Silicon atoms, as long as the hole left is similar to the size of the atom that will occupy it.
- It has great capacity to tolerate wear and corrosion.
- It reaches hardnesses on the Mohs scale from 9 to 9.5.
- It is a semiconductor(~ 2.4V) and refractory material that has many advantages to be used in devices that involve working in extreme conditions of temperature, voltage and frequency , Silicon Carbide can withstand a voltage or electric field gradient of up to eight times greater than silicon or gallium arsenide without breaking, this high value of breaking electric field makes it useful in the manufacture of components that operate at high voltage and high energy such as: diodes , transistors , suppressors , and even high microwave devicesenergy . Added to this is the advantage of being able to place a high [density] of packaging on integrated circuits.
- Thanks to the high speed of saturation of charge carriers (2 × 107 cm − ¹) it is possible to use SiC for devices that work at high frequencies, be they Radio frequencies or Microwaves. Finally, a hardness of ~ 9 on the Mohs scale provides it with mechanical resistance that, together with its electrical properties, make SiC-based devices offer numerous benefits compared to other semiconductors.
- The characteristics of the elastic modulus and thermal expansion are given by the characteristics of the SiC crystal itself, and the thermal conductivity or thermal diffusivity of silicon carbides tends to be substantially higher than that of other structural ceramics. The combination of a high elastic modulus and moderate coefficient of thermal expansion makes SiC susceptible to damage from thermal shock.
- Thermal shock resistance is significantly lower than that of silicon nitride, but higher than zirconia structural ceramics. Thermal shock behavior is also highly application dependent. For example, very rapid temperature changes can lead to a preference for Si3N4 over SiC, while for moderate rates of temperature change the high thermal conductivity of SiC can lead to better performance.
- The fracture resistance of SiC tends to be lower than that of other structural ceramicsleading to some concern about the use of SiC in certain combustion engines , such as turbine rotors that may be susceptible to impact from objects. strangers.
- The angular abrasion resistance of the particle or mixture. Reaction bonded SiC tends to be the most susceptible to erosive wear due to preferential wear of the free grains attached to the silicon surface. Reaction bonded SiC also appears much less resistant to acids, alkalis, and high-temperature products of combustion than single-phase sintered material.
- In contact with sodium sulfate, or acidic or basic coal slags from coal gasification, SiC tends to corrode slightly. Sintered silicon carbide has also been shown to corrode at elevated temperatures in atmospheres containing hydrogen .
Obtaining
The renowned Acheson method is currently used for the preparation of silicon carbide. Each material for this process goes through an exhaustive selection, which includes grinding, washing, drying and magnetically separating the inappropriate traces. Subsequently, it is necessary to extract the powder, carry out the screening, mix and package. Usually this silicon carbon is produced in different types of grain, with different thicknesses and additives.
Silicon carbide is obtained from high purity sands or quartz and petroleum coke fused in an electric arc furnace at more than 2000 ° C with the following composition:
SiO 2 + 3 C → SiC + 2 CO
Then it goes through a process of: Selection, grinding, washing, drying, magnetic separation, dust absorption, screening, mixing and packaging. Then with this product in different grains (or grain thicknesses) and different additives, supports and binders, sandpaper , metal cutting discs, polishing pastes, among others, are made.
manufacturing technology
Silicon carbides for structural use can be classified as: sintered reaction bonded, liquid phase, and sintered solid state. Reaction bonded SiC4 is a compound of a continuous SiC matrix that has 5 to 20% silicon, and metal that fills the remaining volume. To form this material, a preform of the powder that contained the added carbon as a powder or as the product of decomposition of a resin from the carbon source, is infiltrated with silicon around 1500 ºC with direct contact or using silicon vapor.
Silicon reacts with the carbon preform to form a bridging structure on SiC. The remaining excess silica fills the residual pore space and gives a completely dense product that has structural integrity up to 1370 ºC. Silicon melts at 1410 ºC. The preform can be manufactured by any of the traditional ceramic processes. On the other hand, the low temperatures (1500 ºC) used during reaction bonding, combined with the flexibility of size and purity of the powder, provide a good quality product at a reasonable cost.
Applications
Silicon carbide has been the most widely used material for structural ceramic uses. Characteristics such as relatively low thermal expansion, high radius force-weight, high thermal conductivity, hardness, resistance to abrasion and corrosion, and most importantly, the maintenance of elastic resistance at temperatures up to 1650 ºC, have led to a wide range of uses.
They are used more for low temperature wear operation than for high temperature behavior. The uses of SiC are such as sandblasting injectors, automotive water pump seals , bearings, pump components, and extrusion dies that use carbide’s high hardness, abrasion resistance, and corrosion resistance. silicon.
Structural uses at high temperatures extend from the rocket injector grooves to furnace rollers, and the combination of high thermal conductivity, hardness, and high temperature stability causes the components of the exchanger tubes to be manufactured of silicon carbide.
This thermal ceramic is resistant and strong against heat shock, and provides great thermal conductivity, ideal for the manufacture of furnace linings and fittings.
It is used in the manufacture of pencils, sandpaper, ceramics and as an abrasive for cutting or polishing.
Risk of manipulation
Current law indicates that employers need to inform their workers that they will be handling this type of material during their workday. In addition, the company must instruct personnel on the proper handling of silicon carbide.
The labeling of each container will ensure a quick identification of the content. Similarly, it is prudent for employees to receive a complete medical evaluation, periodically, to rule out potential health risks. These tests may include collecting air samples individually or in the vicinity of the facility.
Inhaling silicon carbide can cause excessive irritation to the eyes and nose, and constant closeness to the mixture can make the individual susceptible to chronic lung disease, changes in the chest , choking and wheezing, or excessive coughing .
In addition, it has been said that exaggerated exposure to silicon carbide can cause serious diseases such as cancer , infertility, or increase the chances of contracting tuberculosis. The effects of this material can last from six months to a year in the body.
Protection measures
It is important to take control regarding the protection of health when exposed to silicon carbide:
- Operating in a ventilated area is vital to reduce chemicalexposure . If the location does not have these characteristics, the use of respirators is essential.
- The worker should take a shower immediately after handling silicon carbide. You have to be precise in this regard, because health could be at stake.
- Wear protective clothing, which completely prevents contact with your skin of silicon carbide. This includes: gloves, shoes, head protection . It must be cleaned daily and available for use.
- The use of impact lenses is recommended, which have side covers to prevent any part of silicon carbide from coming into contact with the eyes.
If you are using a respirator, but you can smell, feel or taste silicon carbide, you should leave the premises immediately and contact the medical service as soon as possible.
