Technical ceramics has been explored and studied for high temperature applications since many years. With the development in technology, the material and its favorable properties has travelled long way to offer superior benefits. Interestingly, the below given write up covers this property of Silicon Carbide (Sic) and Aluminum Oxide (Al2O3).
Temperature properties of Ceramic
High temperature ceramic always outperforms metals and alloys. Thermal resistance, wide working temperature range and high thermal conductivity make them an ultimate choice in specific applications. Technical ceramics are basically tailored by controlling either its structure or formulations to obtain the desired property.
Thermal shock resistance
Shock resistance stands for the materials capability of withstanding sudden or sharp changes in high temperature. Ceramic melting temperature has its relation with this very property .Hence evaluating the ceramic melting point is crucial in designing systems. The common ceramic melting point is generally considered at 2000 degC. However, since ceramic is a brittle material any sudden fluctuation in temperature causes the material to shatter at undesirable thermal shock.
Thermal conductivity
Thermal conductivity tells us the temperature behavior through a material body .For instance, cooking pan are known for its uniform heat distribution throughout.
Which metal has higher thermal conductivity? What about technical ceramics?
Higher thermal conductivity is assigned at a value of 400 W/Mk or above which is for Silver. In technical ceramics silicon Carbide always tops the chart which is in turn known for its durability and strength. The thermal conductivity of Silicon Carbide is greater than 200 W/Mk
Coefficient of thermal expansion
The movement of atoms through a material makes it swell rapidly under applied temperature. The low coefficient of thermal expansion of ceramic makes them ideal to be used in several applications. They tend to remain stable in a wide variety of working temperatures.
Prominent temperature applications of technical Ceramic
High temperature ceramic Vs Ultra-high temperature ceramic
High temperature ceramic works in a range of around 650 degC Above. Ultra-high temperature ceramic works at even greater temperature. The melting temperature range is around 1500 degC or below. Hence, they often find place in application such as semiconductor devices and aerospace components.
The popular ultra-high temperature ceramic are especially group IV materials such as Titanium Zirconium and Hafnium. They possess extreme melting point at the range above 4000 degC. The thermal conductivity value is generally greater than 140 KW/Mk.
High temperature ceramic coatings: A new age technology
High temperature ceramic coatings ensure protection and are resistant towards corrosion and rust. High temperature ceramic coatings retard the energy transfer through the material. The nearest parts are saved from heat damage. The coatings also grant a lustrous look and aids in providing glossy, visual and appealing aesthetics to the surfaces where it is applied.
Silicon Carbide Vs Aluminum Oxide
Aluminum Oxide and Silicon Carbide has been names often heard in ceramic due to its exceptional properties. Aluminum Oxide has better material properties. They offer good strength, and are tear resistant and are chemically stable. Silicon Carbide on the other hand is known for its high electrical and thermal conductivity and good temperature resistance. Some of the Key differences and detailed information of Silicon Carbide and Aluminum Oxide is delineated below.
Physical Properties of Aluminum Oxide and Silicon Carbide
The physical properties of a material are crucial to understand and select the material for desired applications. It includes the basic data of the material and its morphological value or behaviors with temperature electricity or heat.
Some of the prominent physical properties of Aluminum Oxide are given below:
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ALUMINUM OXIDE (AL2O3) |
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Aluminum Oxide formula: Al2O3 |
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Alumina Density :3.95 g /cm3 |
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Al2O3 Molecular Weight / or the Aluminum Oxide molar mass value : 101 g/mol |
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Al2O3 melting point: 2072 degC |
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Alumina Thermal conductivity: 30W /mK |
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Alumina specific heat capacity :0.9 J/gC |
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Alumina Electrical conductivity :10-12 - 10-14 S/cm |
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Alumina Hardness: 9 mohs scale |
Some of the prominent physical properties of Silicon Carbide are given below:
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SILICON CARBIDE (SIC) |
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Silicon Carbide formula: SiC |
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Silicon Carbide density: 3.21 g/cm3 |
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Silicon Carbide Molecular weight: 40 g/mol |
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The melting point of silicon carbide ceramic : 2700 degC |
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Silicon Carbide Thermal conductivity: 120- 180 W /mK |
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Silicon carbide specific heat capacity: 750 J/kgK |
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Silicon Carbide Electrical conductivity: 107 ohm-cm |
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Silicon Carbide hardness: 9.5 mohs |
Silicon Carbide and its heat resistance
SiC thermal conductivity is in the range of 130 – 260 W / MK. It is also known in the name of carborundum. The thermal expansion is around 4 x 10-6 degC-1. The thermal expansion values are considered generally lesser than the common semi-conductor devices.
Silicon Carbide crystal structure is tetrahedral in nature. The very nature of its crystal makes it harder with low density. The higher thermal conductivity along with lower thermal expansion makes silicon carbide stay effective under induced thermal stresses. The high thermal shock resistance makes SiC a popular material in nozzles manufacture of rockets, valve components, heat exchanger etc.
Silicon Carbide and its thermal applications
Silicon Carbide holds tends to remain elastic even at elevated temperatures, say 1600 or above. This is a prime factor that contributes to its high temperature nature. The shock resistance of SiC in comparison with Nitride and Zirconia is different. It is higher than Zirconia. Hence Silicon Carbide is preferred in ordinary temperature applications.
Silicon Carbide is of immense potential in power electronic industry due to its high thermal conductivity and high bandgap. Silicon Carbide ceramic is capable of withstanding higher voltage fluctuations. Sic devices also work well with lesser heat losses.
Alumina and its heat resistance
Alumina and its exceptional properties are named after their strong inter atomic ionic bonds. Aluminum Oxide, Alumina possesses many structural forms such as Alpha Al2O3 basically stable at higher temperature of application. Alpha phase aluminum Oxide are strong and known for its dielectric strength.
Aluminum Oxide of high purity are majorly used both in oxidizing and reducing environments of 1920 degC. Aluminum Oxide resists mostly all solvents. They are never damaged by acids such as hydrofluoric acid. The weight loss of Alumina is in the range of 10-6 to -7 in vacuum ranges when subjected to a temperature of 1700 or above degC.
Aluminum Oxide and its thermal applications
Being a highly heat-resistant material aluminum oxide is basically used as refractory lining. They are also used for heat insulation inside furnaces. Alumina, Aluminum Oxide also serves as better catalysts in petrochemical industries due to their ability to work under higher temperature. It is also inert and stays away from being reactive with the reactants taking part in the process.
The electrical insulation properties of alumina make them an ideal fit for semiconductor industries and dielectric application. They ensure good dielectric values when converted from DC to frequencies. The purity of alumina also has ranges in which the most widely used one is 99.8%. 99.8% pure alumina is majorly deployed in high temperature applications.
Bottom Line
A brief on major differences between aluminum Oxide and silicon Carbide is written for understanding. Aluminium Oxide is known for its hardness and other material benefits. It resist abrasion and holds good strength. When it comes to thermal properties Silicon Carbide is superior with excellent heat resistance and thermal stability.