Ceramic Industry

ONLINE EXCLUSIVE- Case Study: New Furnace Shows Promise at PSU

June 1, 2004
A new ultra-high-temperature, ultra-low-oxygen thermal processing furnace installed at The Pennsylvania State University is providing positive results in a range of industrial applications

Figure 1. Free energy of metallic oxide formation and the zone of the furnace operation.
A new continuous furnace* capable of heating to 2200°C has been installed at the Center for Innovative Sintered Products (CSP) at The Pennsylvania State University (PSU) in University Park, Pa. The furnace allows metals and alloys to be sintered and brazed at a reduced oxygen partial pressure without the use of vacuum or hydrogen. This is particularly desirable for sintering and brazing materials with high-vapor-pressure elements, such as chromium and manganese.

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.

A CISP researcher sets up the gas flow on the new furnace.
Test results from the new furnace to date have been positive. For instance, titanium has successfully been sintered continuously with an elongation of 15%, and superalloys have been successfully brazed. Additionally, manganese-containing braze has been used to sinter-braze powder metal components with good bond strength.

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 dfh100@psu.edu . More information about the furnace can also be found at http://www.oxynon.com .