In 1999, EPA and the U.S. magnesium industry, with the support of the International Magnesium Association (IMA), launched a voluntary partnership to better understand and reduce emissions of sulfur hexafluoride (SF6), a very potent greenhouse gas. EPA’s partnership with the magnesium industry promotes technically feasible and economically attractive actions aimed at minimizing SF6 emissions and reducing the threat of global climate change.
SF6 has been widely used by the magnesium industry for more than 25 years. Magnesium producers, casters, and recycling companies commonly use a cover gas of dilute SF6 in dry air and/or carbon dioxide (CO2) to protect the molten metal from oxidation and potentially violent burning. Without protection, molten magnesium will oxidize in the presence of air and form magnesium oxide (MgO) deposits that greatly reduce the quality and strength of the final product. In contrast, an effective cover gas, such as SF6, modifies and stabilizes the MgO surface film to form a protective layer that prevents further oxidation (see Molten Magnesium images).
Although studies are underway to characterize the reaction byproducts of SF6 and molten magnesium, it appears most of the SF6 introduced to the molten metal surface is emitted to the atmosphere and that only a small portion reacts or decomposes. With a global warming potential (GWP) 23,900 times as strong as CO2 and a 3,200-year atmospheric lifetime, reducing SF6 emissions will have significant environmental benefit for many future generations. In 2002, the U.S. magnesium industry’s SF6 emissions were equal to 2.4 million metric tons of CO2, a 42% improvement since launching the partnership in 1999.
EPA conducted its first measurement study of magnesium die casting emissions in September 2002.
Measured SF6 Emissions From Magnesium Die Casting Operations (PDF) (5 pp, 118K, About PDF) by S. Bartos, J. Marks, R. Kantamaneni, and C. Laush. This paper was presented at The Minerals, Metals, and Materials Society’s (TMS) 132nd Annual Conference, held in San Diego, California, in March of 2003. The paper describes a study conducted at Product Technologies, one of EPA’s magnesium die casting partners, to measure SF6 degradation and by-products in typical hot-chambered die casting equipment.
In just a few short years, EPA and its magnesium industry climate protection partners have made tremendous progress, reducing emissions intensity by more than 40% from 1999 to 2002. The industry is succeeding in cost effective pollution prevention stories by optimizing equipment designs and operation and improving SF6 gas management practices. These activities and technological innovations have directly contributed to the partnership’s success and provided both economic and environmental benefits. More detailed information on the costs of reducing SF6 emissions from magnesium operations is available at EPA’s High GWP Home Page.
In February 2003, EPA’s partners and the International Magnesium Association added their support to the President’s Climate VISION Climate VISION , initiative by establishing a goal to eliminate SF6 emissions by year-end 2010. To meet this technically aggressive commitment, the industry will need to further evaluate and implement alternative cover gases such as HFC-134a, 3M’s fluorinated ketone, Novec™ 612, and possibly sulfur dioxide (SO2). Table 1 shows the atmospheric lifetimes and GWPs of these chemicals compared to SF6.
Table 1: Global Warming Potential (100 year)*
|Compound||Atmospheric Lifetime (years)||Global Warming Potential (100 Year)|
|3M™ Novec™ 612(C3F7C(O)C2F5)||0.014**||~1**|
* IPCC 1995
EPA & Partner Responsibilities
Under the agreement, EPA will:
- Assist the Partner to review GHG emission reduction strategies and technologies;
- Serve as a clearinghouse for technical information on successful strategies to reduce SF6 emissions;
- Provide partners with recognition for their achievements in protecting the climate;
- Seek to establish agreements with all magnesium casting companies operating in the United States and to host international technical conferences to discuss emissions reduction efforts being made by the industry and its affiliates; and
- Support the development of high-quality emissions data.
Partners agree to:
- Strive to eliminate SF6 emissions by evaluating and installing more environmentally friendly cover gas systems;
- Estimate SF6 use and SF6 usage rate (kg SF6/metric ton of Mg processed) in 1999 and earlier if possible using historical records;
- Track and record annual SF6 use and usage rate with one of the techniques developed by the Partnership;
- Optimize casting processes and machinery to achieve lower SF6 usage rates.
- Share with EPA and other Partners non-confidential information about successful SF6 emission reduction processes and technologies.
- Employ tracking and reporting scheme implemented under the SF6 Partnership to help avoid contributing to the atmospheric build-up of long-lived chemicals, and to document early contributions to global climate protection.
- Partner companies and/or individuals excelling in their efforts to protect the climate are eligible for EPA’s prestigious Climate Protection Award.
- Cover Gas Emissions Measurement Study. EPA’s partner companies are invited to collaborate on studies seeking to better understand cover gas degradation and by-product emissions. The following paper describes the partnership’s first cover gas study. Measured SF6 Emissions From Magnesium Die Casting Operations (PDF) (5 pp, 118K, About PDF) by S. Bartos, J. Marks, R. Kantamaneni, and C. Laush. This paper was presented at The Minerals, Metals, and Materials Society’s (TMS) 132nd Annual Conference, held in San Diego, California in March of 2003. The paper describes a study conducted at Product Technologies, one of EPA’s magnesium die casting partners, to measure SF6 degradation and by-products in typical hot-chambered die casting equipment.
- International Conference on SF6 and the Environment. The global magnesium industry, its equipment and material suppliers, and customers are invited to this biennial technical conference to share the latest information on emission reduction strategies, climate science, and environmental policies.