Research Results on Molten Aluminum-Water Explosions Published
12-26-02


Casthouse safety is an important priority for the aluminum industry. Avoiding molten aluminum-water explosions is one area of ongoing interest. Recent research sponsored by DOE-OIT and the aluminum industry to investigate alternative coating materials as well as to explore different methods of reducing explosion tendency has been reported publicly.

During the direct chill casting of aluminum ingots, the potential for contact between molten aluminum and the water used to cool the solidifying ingot exists and, under certain conditions, an explosion can occur. Gaining a better understanding of the conditions for molten aluminum-water explosions and developing methods to prevent them has been a focus of effort for the aluminum industry in general and the Aluminum Association in particular for decades. Summaries of the results of this work are in the Light Metals proceedings volumes, available from TMS (www.tms.org).

Beginning in the 1960's, the Aluminum Association has sponsored a series of studies of the causes and prevention of molten aluminum-water explosions at government, industry, and academic laboratories. These studies led to a better understanding of molten aluminum reactions with water, and for a number of years a practical commercial solution was available. Called Tarset Standard, a coal tar-based epoxy, this material was essentially a coating used in casting pits. This coating was pulled off the market for environmental and other reasons and an alternative had to be identified that would carry out the same function. In mid-1995, the Aluminum Association directed a project with industry support to develop replacement coatings. This research, performed at the Alcoa Technical Center, identified three alternative coating materials that showed efficacy in preventing molten aluminum-water explosions. These coatings (Intertuf 132HS, Multi-Gard 955CP, and WiseChem E-115a), while effective, had unacceptably long cure times from an industry perspective. This area had to be addressed.

In addition, through a CRADA arrangement with Oak Ridge National Laboratory, a parallel effort to study the fundamentals of the interactions occurring at a submerged surface in contact with molten aluminum was initiated. The ORNL program, described in a 1998 article (JOM, v.50, no. 2, 1998, pp. 35-38), addressed phenomenological issues such as surface wettability, gas generation from coatings, charring of coatings, inertial constraint, melt temperature, water temperature, and external shocks for their relative impact on triggering surface-assisted steam explosions. In addition, a safe, versatile, instrumented facility for studying these reactions was established, called the Steam Explosion Triggering Studies (SETS) facility. Test results from the SETS facility indicated that explosion suppression is governed by three main factors: surface wettability, paint wear-off, and pyrolysis of paints, during which non-condensable gases are generated.

It is with this background that a follow-on project was initiated with funding support from the Department of Energy-Office of Industrial Technology Aluminum Industries of the Future program. The project sought to address questions related to the new coating options, specifically whether these coatings could be protective at shorter cure times than specified by the manufacturers as well as whether they were protective when applied to concrete surfaces. In addition, the finding that the evolution of non-condensable gases had an important role in explosion prevention in the SETS test was to be further exploited by doing larger scale testing in what is termed the Standard Molten Metal Explosion Test at Alcoa. With Alcoa and ORNL working collaboratively, the research effort has demonstrated that all the coatings can prevent explosions at curing times below the original vendor recommendations, different for each coating. Extensive information on coating characterization and performance as a function of curing time is included in the project final report. In the area of using non-condensable gases to prevent explosion, the ORNL results showing prevention ability in the SETS test were not duplicated in larger scale tests. This is an area requiring further study.

A Fact Sheet is available from DOE-OIT at www.eere.energy.gov/industry/aluminum/pdfs/explosions.pdf.

Article provided courtesy of The Aluminum Association - www.aluminum.org