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Unlike traditional sintering furnaces, where reduction is provided by either hydrogen gas or carbon monoxide, the operation of the new furnace is based on the technology of metal refining, as described by the Ellingham or Richardson Diagram. Figure 1 shows the relationship between metals and metal oxides and their relative stability. As the partial pressure of oxygen is reduced, the ability for heat dissociation of oxides becomes greater.
In vacuum processing, applying a vacuum reduces the partial pressure of oxygen; however, this can result in the evaporation of high-vapor-pressure metals. The new furnace works by reducing the partial pressure of oxygen within the furnace-not by vacuum, but rather by the oxidation of the graphite within the furnace. The graphite essentially acts as a "getter" for any residual oxygen that is present in the process gas. From a physical chemistry standpoint:
C + ? O2 ?CO
The low-oxygen atmosphere will thus reduce even difficult-to-reduce oxides, such as MnO, SiO2, and TiO2, without evaporation.
*The KYK Oxynon(r) sintering furnace, supplied by Kanto Yakin Kogyo, Hiratsuka, Kanagawa, Japan.
Many other materials-including tungsten carbide, niobium, molybdenum, tungsten, silicon nitride and alumina-have also been evaluated in the furnace and are still under development, but the results are expected to be equally positive.
Furnace Features* Operating temperature: 2200°C (3992°F)
* Number of hot zones: four
* Belt type: graphite composite
* Opening size: 10 in. wide x 4 in. high
* Gases: nitrogen, argon and potentially helium
For more information about the new furnace or to arrange an evaluation of its performance in a specific application, contact CISP at (814) 865-7346 or e-mail firstname.lastname@example.org . More information about the furnace can also be found at http://www.oxynon.com .