Semi-finished products in C799 alumina
Alumina semi-finished products are products partially processed from alumina, which will be finished later (by our hard material customers). There are different types and forms of semi-finished products in order to be able to adapt to the demand. The choice of alumina as a raw material for these components is due to its many properties which offer a wide range of possibilities in terms of applications.
Why choose alumina as a material?
Alumina is a ceramic that has many advantages allowing a wide choice in terms of field of application. Indeed, aluminum oxide has a good resistance to high temperatures (up to 1950 °C for example for Kyocera DEGUSSIT AL23, 99.7% pure). This makes it a material of choice for high temperature applications. Alumina is a very good electrical insulator, even at high temperatures. It also has excellent dimensional stability, even under heat (creep starts only at 1400 °C), and therefore allows the manufacture of components whose shape and size will remain stable despite high temperatures. In addition to its heat properties, alumina is extremely resistant to corrosion. This ceramic can be used with the vast majority of chemicals without the risk of the aluminum oxide being attacked or interacting with the chemical with which it is brought into contact. Finally, this ceramic offers a high resistance to wear and abrasion, so objects made of alumina are durable and can be used for a long time. All these properties make alumina an ideal material in many fields. Alumina also provides a good surface finish after machining.
Why alumina instead of MACOR®?
The choice of alumina semi-finished products rather than MACOR® is explained by the "superior" properties of aluminum oxide. MACOR® is a remarkable technical ceramic because of its unique combination of properties. The material can withstand temperatures of up to 1000 °C and is easy to machine with conventional tools. However, alumina can withstand much higher temperatures (up to 1950 °C for DEGUSSIT AL23). Aluminum oxide is more resistant to high temperatures, corrosion and wear. This makes alumina a better choice of material when the conditions of use are very demanding. On the other hand, the thermal conductivity of alumina is high, while that of MACOR® is low, which can be a factor of choice depending on the intended application.
The different types of semi-finished products
Alumina semi-finished products come in different forms:
- Rods or sticks which are cylindrical in shape (like a bar). Their diameter and length can vary from 0.5 mm to 90 mm maximum.
- Plates which are flat semi-finished products that can be square or round with very variable dimensions and a maximum thickness of 50 mm
- Strips which are flat rectangular parallelepipeds (with a low height/width ratio)
In addition to Kyocera pure alumina and MACOR®, we offer other technical ceramics depending on the application. Semi-finished products are also available in 95% alumina (C795), porous mullite (C530), dense mullite (C610), zirconium oxide or zirconia (3Y-TZP, Mg-PSZ, 8Y-FSZ), silicon nitride (Si3N4), sapphire, or silicon carbide. All these materials have more or less good machinability and varied mechanical properties.
How are alumina semi-finished products manufactured?
Alumina semi-finished products are manufactured either by extrusion, uniaxial pressing, or isostatic pressing and green machining. The resulting shapes are then sintered at a very high temperature of around 1800 °C. Rods, small tubes and strips are obtained by extrusion with possible lengths up to 2 meters. Plates as well as rods and large tubes are usually obtained by cold isostatic pressing (CIP).
Areas of application for semi-finished products
Alumina semi-finished products are generally available from stock, mainly as standard products, but they can be customized on request, especially for large sizes or for optimized shapes for machining. Semi-finished products can be used in the glass industry, in metallurgy, in research and development, in laboratories, in aeronautics, but also by our customers and machining partners. For example, the bars can be used as blanks for machining.