Floating Zone Oven
A floating zone oven is a type of furnace used to produce monocrystalline ingots, or large pieces of a single-crystal material, out of normally polycrystalline materials. It utilizes a zone, typically a zone of molten material, that “floats” between two rods, both containing the raw material in the form of a solid, which is melted and remelted as the rods are moved in and out of the molten zone. Depending on the particular material, the oven can operate at temperatures ranging from 700 to 2000 degrees Celsius.
In terms of its structure, a floating zone oven is typically composed of a vertical chamber that is equipped with several furnaces, depending on the type of application and size of the project. The lower portion of the chamber contains a vacuum system, while the upper portion contains multiple layered heaters. The materials to effectively heat the new crystalline material can be specified in order to ensure a uniform heating, as well as a controlled cooling and solidification rate.
The operation of the oven begins by first placing two graphite rods in the heating chamber, with each one containing the raw material inside. The rods are then moved in and out of the molten zone in order to heat it, both rods continuing to move at opposite directions from each other, almost like a seesaw. As this happens, the zone of molten material inches toward the rod that is being “lowered” in the chamber, remelting the raw material into liquid form and thus creating a single crystalline structure in the process.
The movement of the rods is usually accomplished by a mechanical or electric motor, depending on the application, allowing the radius of the molten zone to remain constant while the single-crystal ingot continues to grow. When the desired crystalline structure is reached, the rod can be lifted out of the furnace, and the ingot can be removed.
Floating zone ovens are preferred for applications requiring large, single-crystal ingots. This is in contrast to other furnaces, such as directional solidification furnaces, which can only produce ingots of several centimeters in length at most. It also allows for the production of high-longitude single-crystal parts, which can be difficult if not impossible to produce with other furnaces. Additionally, the process is automated and requires no manual intervention, making it an efficient option for producing single crystal parts.
Due to their electric and/or mechanical mechanisms, floating zone ovens require regular maintenance and repairs to ensure its correct and efficient operation. Not only must the heater and vacuum system be specifically calibrated depending on the material and desired output, but it is also necessary to periodically inspect and replace the graphite rods in order to prevent any potential damage due to the repeated movement inside the chamber.
In conclusion, floating zone ovens can be a great choice for the production of large and high precision single-crystal ingots and parts, as it is highly automated and efficient. Its use however, requires proper and constant maintenance in order to ensure the proper and safe operation of the oven.
