October 30, 2006 — Lunt Manufacturing Co. Inc., a magnesium diecaster in Hampshire, IL, recently hosted a pilot test of various cover-gas systems to evaluate possible replacements for SF6 as magnesium's basic method for protecting their melts from oxidation. Testing was coordinated with the EPA's SF6 Emission Reduction Partnership for the Magnesium Industry.
Molten magnesium may be highly volatile when it oxidizes, and magnesium-oxide formation can reduce the finish quality and or strength of the finished products. Magnesium diecasters and others have used SF6, sulfur hexafluoride, for several decades as a cover gas to shield the molten metal from air.
EPA states that studies are underway to characterize the reaction byproducts of SF6 and molten magnesium, and that 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. It says that reducing SF6 emissions may lead to significant environmental benefits.
Sulfur hexafluoride is the most potent green gas, according to the Intergovernmental Panel on Climate Change: it assigns to SF6 a “global warming potential” of 22,200 times that of CO2 over a 100 year period, though its mixing ratio in the atmosphere is far lower than that of CO2.
The tests conducted at Lunt included AM-Cover™, MTG-Shield™ with Novec 612™ and dilute sulfur dioxide (SO2). Technicians used sophisticated analysis equipment to monitor the rates of reaction, potential creation of any by-product gases, and the melt-surface conditions. And, the SF6 was analyzed as a proper benchmark.
EPA and U.S. magnesium producers formed the SF6 Emission Reduction Partnership in 1999, with support of the International Magnesium Association (IMA), to gain a better understanding of sulfur hexaflouoride and reduce its emissions. The Partnership is co-sponsoring the 4th International Conference on SF6
Other companies co-sponsoring the tests with Lunt and the EPA were Advanced Magnesium Technologies (Australia), Matheson Tri-Gas (U.S), Taiyo Nippon Sanso Corp. (Japan), 3M (U.S.) and Polycontrols (Canada).