In certain situations, a conventional material like metal (even the notably durable tungsten carbide) or ceramic can withstand the rigors that they are put through. However, there is a way to engineer what is referred to as an “advanced ceramic” that takes on enhanced properties that are especially suited for extreme environments most commonly found in industrial settings.
One such material is Alumina, which we’ve covered in the past. One of the most common uses of Alumina is in the common tube furnace, which requires the use of an advanced material to withstand the extreme temperatures produced by the furnace. With that said, let's dive into Alumina as a material and why it's commonly used in alumina furnace tubes.
Alumina is the abbreviated term for “aluminum oxide”. Commonly derived from bauxite (found primarily in topsoil), Alumina’s raw form resembles a grainy powder like common table salt.
As a powder, Alumina can enhance conventional ceramic is a process known as “sintering”, where the powdered Alumina is pressed into the ceramic giving it enhanced properties like increased hardness, higher density, low thermal conductivity, and low electrical conductivity to name a few.
These properties make it a great material for use in hollow ceramic tubes and almost any high-temperature ceramic tube application.
Alumina grades are also referred to as “purities”. In the process of sintering Alumina to ceramic, there can be an acceptable level of other substances that transfer over such as talc. Alumina purity can start at around 88% and go up to 99.5% pure. To put it simply, the higher the purity of Alumina ceramic, the better its performance.
The two most standard “high-purity” grades of Alumina ceramic are 99.80% and 99.5%. As you can see in the table below, their specific performance differs. In a laboratory or industrial setting sometimes a tenth of a percentage makes all the difference.
The two most common uses for Alumina ceramic rods are in a high-temperature kiln application. Yet, those two uses have completely different functions.
Roller Kilns: a roller kiln is a kiln or furnace that operates like a conveyor belt. A material that needs to be fired is placed at one end where it rolls through a heated tunnel. By the time the material exits the conveyor, it has been completely fired. Alumina ceramic tubing is perfect for this process due to its ability to withstand not just high temperatures but drastic temperature changes. Moreover, the hardness factor of Alumina means that the aforementioned tubing is less prone to breakage or even standard wear-and-tear.
Tube Furnace: while it sounds similar, a tube furnace functions in an entirely distinct way from a roller kiln. Think of your countertop convection oven at home. When you peer inside while it’s on you may see one or more red-hot tubes on display. This function is very similar to a tube furnace; a tubular heating element is super-heated through electrical conduction. Because Alumina ceramic tubing is dielectric it can transmit this electricity without conducting it, making it a safe material for this purpose.
There are many types of Alumina ceramic tubing as well as sizes. They can also be referred to under different names like alumina cylinders or alumina ceramic rods; both products share the same properties. Let’s discuss three of the most popular types and three of their most popular ranges. Of course, we can create custom alumina ceramic tube sizes for your specific application.