Aluminium Oxide is a favorite of engineers due to the wide range of properties they offer. It offers high thermal conductivity and better insulating properties. The resistance to extreme fracture is some among the noteworthiest one. Here in this article, we give the differences between 95% and 99% alumina grade.
What is Alumina?
Alumina ceramic, known in the name of Al2O3 is the oxide of Alumina made generally from bauxite. Their excellent thermal conductivity, durability and high hardness makes them an ideal choice in many applications. The popular methods of manufacturing Alumina ceramic constitutes injection moulding, casting – slip or dry and extrusion. They possess high compressive strength and are good in extremely corrosive environments or cases exposed to large wear and tear.
Alumina Structure
Alumina structure is majorly called as corundum. The O2 atoms are arranged in hexagonal forms in the lattice. Aluminium occupies octahedral spaces which is 2/3rd of the material. The lattice of corundum is trigonal Bravais. The Al3+ which is present at the centre of the lattice always adopts 8 phase arrangement.
Alumina has other metastable phases as well such as for cubic forms. The phases such as
are monoclinic and hexagonal. The phase such as
Orthorhombic and tetragonal or orthorhombic. Of which
- Al2O3 is technically important in terms of engineering applications.
Properties of Aluminum Oxide, Alumina
Properties of Al2O3 includes, generic, morphological such as hardness or strength dependant and temperature . A brief overview of all the relevant properties is given below
Density of Aluminum Oxide Ceramic
The general structure of Aluminum Oxide has the proportion of voids very less that leads to higher density. For example, at a standard temperature of 25 degC, the al2O3 density remains at 3.76 g/cm3. This will give an indication oh how much mass is present in any cubic volume of the material.
The grain size is another factor that influences the alumina density. On the other hand, 85% of Alumina has grain size of 3 – 4 microns post firing, which is more durable and functional.
Temperature resistance of Alumina
Alumina Ceramic can withstand high temperature. 2000 degc or above is the melting temperature of alumina . They thrive in oxidising and reducing environments of around 2000 degF and vacuum situations in the range of 2000 degC. Unlike other ceramic, Aluminum Oxide tend to maintain their inherent structure at elevated temperatures.
Alumina ceramic works well at a service temperature of around 1300 to 2100 degC. The alumina thermal conductivity value is around 12 – 40 W/mK and alumina cte is in the range of 10-6 /K. It also displays excellent resistance to strong acids, water, alkalis, UV and several other factors. The latent heat of fusion of Alumina is determined to be 620 – 1360 KJ/Kg and the heat capacity of alumina around 451 -955J/KgK.
Alumina Oxide Hardness
By hardness we get to know if the material withstands any damage or impact. In terms of hardness. Aluminum Oxide is quite above tungsten or conventional metal such as steel with hardness in the range of 9.
Electrical Property of Alumina
Alumina possesses excellent dielectric properties. Alumina ceramic offers best electrical insulation. The electrons or in other way electric current finds it unable to pass or penetrate through Aluminum Oxide. The alumina electrical resistivity is accounted around 1014 power Ohm-Cm.
Aluminum Oxide has a dielectric constant ranging from 8 to 11. It is a poor conductor of electricity as the elements of alumina and Oxygen are arranged in a tightly packed manner. Alumina electrical conductivity lies in the range of 10-12 Scm-1 or above.
Grades of Alumina, Al2O3
There are different grades of Alumina. Depending upon the desired application, we utilise the functionality of different grades. A generic information of some relevant types is indicated below.
Smelter Grade
Smelter grades of alumina are used to make Alumina metal either in fluidised beds or calcifiers by using Aluminium hydroxide. This process removes free water to reduce the bulk surface of alumina. The process gives a alumina quarter in its order. The surface area ranges in the value of 50 m2 or more per Kg.
Reactive grade Alumina
Reactive alumina grades refer to technical ceramics of high purity with crystal size of less than 1 micrometre. This type of alumina sinters to a completely denser form on low temperature. This grade of alumina is useful for inert applications at high temperature or the applications that causes wear and tear.
High Purity Alumina
99.9% or more is the purity that we will obtain for high purity alumina. The manufacturers usually produce high purity alumina by using hydrate of Bayer or chloride.
Fused Alumina
Fused alumina is generally formed in furnaces. Due to severe heat impact the material between melts producing densely packed alumina that’s useful as refractory alumina grade.
95% alumina and 99% alumina
Alumina grades are common names in the field of ceramic science. They excel in providing good strength, wear and corrosion resistance and are suitable to be used at high temperature applications.
Properties and compositional differences
95% of alumina consists majorly Al2O3. The remaining 5% constitute compounds such as Oxides of Calcium, Magnesium and Silicon. The components added help increase the strength and reduces the sintering temperature of final formed Aluminum Oxide.
99% alumina has more than 99% of alumina in its very constitution with lesser additive, the alumina gets the name of the purest grade among all the other types. It offers greater hardness, better electrical properties and superior wear and tear resistance.
Material data sheet of 95 % and 99% Alumina grade
Material data sheet is a comprehensive one in place reserve to obtain all the relevant data of 95 and 99 % of alumina.
|
Properties of Materials |
95% of Alumina |
99% of Alumina |
| Purity (%) |
95% |
99% |
| Appearance |
White or Pink Colour |
Ivory |
| Capacity of Water absorption |
0 |
0 |
| Density (g /cm3) |
3.7 |
3.9 |
| Fracture toughness (MpaM1/2) |
3 to 4 |
3 to 4 |
| Flexural strength at 25 degC |
300 |
330 |
| Moh’s hardness scale |
9 |
9 |
| Thermal conductivity at 25 degC (W/Mk) |
18-22 |
27 |
| CTE at 25 degC (10-6 mm/degC) |
8 |
8 |
| Compressive strength at 25 degC (MPa) |
2200 |
2350 |
| Maximum Working temperature (degC) |
1500 |
1700 |
The usages of 95% and 99% Alumina
95% of Alumina is good in terms of mechanical strength. They offer better wear and tear resistance and are in turn cost efficient. The suitable applications where they are subjected to are given below:
- Mechanical seals
- Electronic substrate applications
- Ceramic parts of textiles and pump accessories
- Wear resistant coating or liners in industries
99% of Alumina Oxide, high purity offers better electrical resistance or insulation properties and good hardness. The below given lists delineate on the different usages of Alumina oxide high purity grade
- Semiconductor manufacturing and high-performance electrical components
- Biomedical implants
- High temperature refractories or linings inside furnaces
- Mechanical parts for precision manufacturing.
Bottom Line
Alumina ceramic, Al2O3 has always excelled in ceramic science due to their superior properties and multi-functional usages. The different alumina manufactured are intended to cater more centric services to each industry on which they are focused. Be it 95% and 99% of Alumina likewise has property benefits subject to distinct applications.