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Book Review: Advanced Ceramics in the Aluminum Industry
12-13-02
While conventional ceramic materials are widely utilized in aluminum production, advanced ceramics are used very little compared to their potential. This is due to their higher cost relative to traditional materials, lack of experience in aluminum processing applications, and durability concerns. To address the potential for expanded application of advanced ceramics in the aluminum industry, a workshop was held in September 2000 sponsored by USACA (United States Advanced Ceramics Association) and DOE-OIT with cooperation of The Aluminum Association. In February 2001, a report of the conclusions from that workshop was published under the title "Applications for Advanced Ceramics in Aluminum Production: Needs and Opportunities", and represents what is hoped to be a first step in a collaborative partnership between the two industry groups.
First, a definition of "advanced ceramics" is needed. The report states "advanced ceramics are distinguished (from traditional ceramics, presumably) by their purity and performance. They include oxides and non-oxides and various particulate, whisker, and continuous fiber-reinforced ceramic composites. High purity ceramic coatings are also part of the advanced ceramics family." Typical monolithic advanced ceramics are aluminum oxide, alumina-zirconia-silica (AZS), transformation-toughened zirconia, silicon carbide, boron carbide, and silicon nitride. Ceramic coatings applied by a range of processes are now commercially used, for example as thermal barrier coatings in gas turbine engines. Continuous fiber ceramic composites (CFCCs) are engineered ceramics in which fibers are used to increase the toughness of the ceramic. These advanced ceramics are said to be best suited for high temperature, corrosive applications where their superior performance can justify their higher cost.
Opportunities for application of advanced ceramics were considered in three areas of the aluminum industry: smelting, melting, and molten metal handling. In each area, an assessment of the performance requirements, current technology used, most promising advanced ceramic solutions, R&D needed, and implementation steps was made by the group involved in the workshop, which is reported in chapters devoted to the respective areas. In the smelting area, the most critical needs related to materials of construction as well as anodes and cathodes. Specifically the non-consumable anode and wettable cathode that have been the focus of R&D attention in the area of improved smelting processes were also considered here. One additional area that appears to hold promise in the smelting area is in the area of sensors. Initially, the improved protection of current sensors that could be achieved by advanced ceramics followed by the development of new ceramic sensors for measuring alumina content in the molten electrolyte were identified.
In the melting and molten metal handling areas, the key barrier to further use of advanced ceramics appears to be the lack of standardized test results for these materials under the conditions relevant to aluminum processing. Critical properties are listed as thermal shock, corrosion, mechanical impact, and erosion on the scale found in actual aluminum production. The suggestion is made that a demonstration facility similar to one developed by the glass industry is needed to enable this larger-scale testing. Enhanced surface properties of the ceramics facilitated by a better understanding of the aluminum-ceramic interface were also identified as an area for future development. Included in this section is an excellent summary chart showing material needs in aluminum furnaces and molten metal handling processes. This chart details the performance requirements in a number of areas including operating temperature and other properties of interest for each process step, and discusses current and future materials options.
The goal of the workshop was to be the first step in collaboration, and to further define future directions a section entitled "Initial Implementation Steps" is included in the report. Three key points made are the need to 1) establish partnerships between the advanced ceramics and aluminum companies and industries as a whole, 2) collect and organize baseline data and existing efforts, and 3) educate and train workers to handle advanced ceramic components. The latter need comes from the fact that because advanced ceramics are significantly more expensive than traditional materials, inadvertent damage to the ceramic component by worker mishandling which would significantly degrade or break the material would have a higher cost impact than for traditional ceramics.
The report is available from the Aluminum Association (www.aluminum.org),
USACA (www.advancedceramics.org),
or the DOE Office of Industrial Technologies (www.eere.energy.gov/industry).
Article provided courtesy of The Aluminum Association - www.aluminum.org
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