Aluminum Oxide – Everything You Need to Know

November 21, 2024

What is Aluminum Oxide?

Aluminum oxide, abbreviated as alumina, is a tough Technical ceramic material with the perfect combination of mechanical, electrical, and thermal properties. Thanks to its superior cost-to-price performance, alumina has been universally utilized in various industrial applications.

Industrial alumina materials are crafted from bauxite and diaspore. The chemical formula of alumina is Al₂O₃. In most cases, alumina has three kinds of crystal structure, which are α-Al₂O₃, β-Al₂O₃, and γ-Al₂O₃, respectively. The inherent structures present different properties but are almost entirely converted into α-Al₂O₃ at temperatures above 1300℃.

Alumina Benefits

● Perfect electrical Insulation: It’s ideal for various high-voltage uses

● High dielectric strength, dielectric constant, and volume resistivity

● Remarkable mechanical strength, even if in high-temperature operation

● Superb wear resistance and durability with self-lubrication attribute

● High-temperature resistance even works up to 1750℃ in the air

● Good thermal conductivity with quick dissipation and thermal shock resistance

● Transparent of over 99.99% purity alumina to microwave radio frequencies

● Fabulous chemical stability and no corrosion in a variety of harsh conditions

Alumina Grades

Alumina is classified into many grades to reach different fields and diverse application needs.

1. By particle size: alumina powder is classified as nano, fine, medium, and coarse.

2. By uses: alumina can be divided into high purity grade, industrial, and special.

3. By production process: aluminum oxide can be divided into electrolytic alumina, hydrothermal, and alumina sol methods.

4. By application fields: metallurgical grade alumina and high purity grade

The nano, fine, and medium grades of alumina are regularly used in JingHui Industry production. We have four variations per alumina purity: 95%, 99%, 99.5%, and 99.7% al2o3. In these different purities of al2o3, the targeted additives with specific dosages can be mixed with the alumina material to obtain the designated properties.

Alumina Ceramic Material Properties

Physical properties

Item	Unit	99.7% al₂o₃	99.5% al₂o₃	99% al₂o₃	95% al₂o₃
Density	g/cm³	≧3.95	≧3.90	≧3.85	≧3.65
Hardness	GPa	14.1	14.1	13.7	11.5
Tensile strength	MPa	279	262	248	221
Compressive strength	MPa	2650	2240	2240	2000
Flexural Strength @ 25℃	MPa	390	379	338	320
Fracture Toughness	MPam^1/2	4~5	4~5	4~5	3~4
Elastic modulus	GPa	380	370	350	303

Thermal Properties

Item	Unit	99.7% al₂o₃	99.5% al₂o₃	99% al₂o₃	95% al₂o₃
Thermal conductivity @ 25℃	W/m.k	31	30	29	24
Specific heat capacity	J.kg*k @100℃	780	780	780	780
Thermal expansion coefficient @ 25℃ to 700℃	10-6/K	6.5~8.2	6.5~8.0	6.2~8.0	5.0~8.0
Thermal shock	℃	≧200	≧200	≧200	≧220
Max. service temperature (In the air)	℃	1750	1650	1600	1450

Electrical properties

Item	Unit	99.7% al₂o₃	99.5% al₂o₃	99% al₂o₃	95% al₂o₃
Dielectric strength @ 25℃	KV/mm	20	19	18	18
Dielectric constant @1MHz	(E)	9.8	9.7	9,5	9.5
Dielectric loss @ 25℃	1MHz	＜0.0001	0.0001	0.0002	0.0002
Volume resistivity @ 25℃	ohm. cm	＞1* 10¹⁴	＞1* 10¹⁴	＞1* 10¹⁴	＞1* 10¹⁴

Alumina Ceramic Machining

Industrial ceramics have stringent requirements on dimensional accuracy and surface quality in applications requiring high-tech fields and extreme environments.

Since the ceramic body will shrink approximately 20% after sintering, holding the tight tolerance before machining is almost impossible. That’s why ceramic machining is essential to conduct after being fired and sintered. Because of the extraordinary hardness of alumina ceramic, single-crystal diamond tools and diamond grinding wheels are required in the machining process. The typical alumina ceramic machining covers fine grinding, honing, chamfering, CNC machining, milling, threading, tapping, drilling, engraving, polishing, etc. The dimensional tolerance can achieve +/-0.005mm or better and a mirror effect.

Our factory has advanced machining facilities, including 4-axis and 5-axis machining centers, internal and external grinding machines, flat grinding machines, honing machines, and polishing machines. The machined Ceramic Components not only realize the desired fitting relationship but also enhance the devices' performance and reliability.

Aluminum Oxide (Al2O3) Uses

In modern industrial applications, aluminum oxide (Al2O3) takes a far cry position of the advanced ceramic family others, and you can easily find them in the following fields:

1. Electrical and Electronics

Alumina offers excellent electrical insulation, high dielectric strength, high heat conductivity, high mechanical strength, and transparency, making it suitable for electrical and electronic devices. The primary forms of alumina are alumina insulators, alumina substrates, insulation tubes， semiconductor package ceramics, and transparent ceramics.

2. Machinery

Because of its excellent high hardness and wear resistance, high-temperature stability, chemical inertness, and other physical properties, alumina is usually a wise choice for Engineered Ceramics in machinery, such as ceramic bearings and shafts, Ceramic Seals, ceramic grinding mechanisms, ceramic cutting inserts, and tools, wear parts, thread/yarn guides, etc.

3. Refractories

As the strengths of high melting point, resistance to high temperature, and good thermal shock, ceramic setter plates, ceramic crucibles, labware, refractory tubes, and ceramic thermal protection tubes for industrial high-temperature furnaces.

4. Automobile industry

Due to its high heat resistance, hardness, and good wear resistance, alumina produces engine combustion chamber components and piezoelectric elements in sensors and actuators. It can also be used in exhaust gas treatment systems.

5. Petrochemicals

Alumina can resist corrosion from various acids and alkalis and extend the service life of equipment. Thus, They are often used for corrosion-resistant coatings, inorganic microfiltration ceramic membranes, and chemical seasoning balls.

6. Energy

Since alumina can withstand the harsh environments of high temperature, high pressure, corrosion, and high wear, alumina-based nozzles, combustion chambers, and turbine blades are widely used in thermal power plants, metal smelting, and nuclear reactor structural parts.

7. Biomedical material

Considering its excellent biocompatibility, biological inertness, physical and chemical stability, and high hardness, alumina is often used to make artificial bones, joints, and teeth.

8. Aerospace

Given their ability to withstand high temperature, high pressure, high strength, high wear, strong corrosion resistance, and good thermal insulation, precisely machined alumina products are used as ultra-high-precision structural components in engines, combustion chambers, solar panels, satellite antennas, and casings in spacecraft and satellites.‌

Conclusions‌

As the most essential material in modern industry, alumina ceramics have been recognized as the most commercially valuable product in the advanced ceramic industry. With the emergence of powder preparation technology, new production processes, new manufacturing technologies, and composite modification and surface treatment of alumina ceramics, its performance can be further improved, and its application areas can be broadened and deepened.

Author:

Mr. Andy Chen

E-mail:

andy@jinghui0738.com

Phone/WhatsApp:

+86 13760126904