Alternatives to SF6 for
Magnesium Melt Protection
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I • ••**•• i I !**••*-• i * •*•* tit »*•• i i nmt urn-
SR, Emission Reduction
Partnership ft* the Magnesium Industry
Japan Magnesium Association
lightweight and recyclable magnesium
have the potential to grow significantly
in the future as consumers, businesses,
and national governments seek to reduce
greenhouse gas emissions. The global
magnesium industry is working together
with governments to demonstrate its
environmental stewardship and eliminate
SF6 emissions. New melt protection
technologies are cleaner and cost effec-
tive, and will help further improve the
industry's environmental performance.
EPA-430-R-06-007
Photo courtesy of Mark S. Johnson Photography
www.msjphotography.com v***^ '
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Alternative (non-SF6) melt protection
can provide:
• Excellent performance
• Potential cost savings
• Worker safety and environmental benefits
Why Does Molten Magnesium (Mg) Need Protection?
Today's automobiles, aerospace technologies, and portable electronics all use
magnesium (Mg) for its advantageous light weight and structural properties.
While being produced and when used in manufacturing other products, molten
Mg will oxidize (burn) on contact with ambient air. Therefore Mg producers and parts
manufacturers use melt protection on the metal's surface to prevent burning. In the
past, salt fluxes or concentrated sulfur dioxide (S02) gas were used for this purpose.
While these chemicals provided adequate melt protection, they also reduced the qual-
ity of the metal, corroded equipment, and presented workplace and environmental
hazards. Since the 1970s, the international magnesium industry has largely used SF6
for melt protection for its nontoxic, nonflammable, and non-corrosive characteristics.
China's rapidly growing Mg industry employs sulfur powder for melt protection but is
transitioning to SF6 cover gas systems to improve product quality.
Molten Mg without melt protection
Molten Mg with melt protection
1
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Why Eliminate SF6?
Although it is an effective Mg cover gas, SF6 is a very potent and persistent
greenhouse gas,1 which means its release to the atmosphere contributes to global
warming for thousands of years. Many national governments and companies around
the world are seeking to reduce or eliminate SF6 use in molten Mg processes. For
example in the United States, members of the SF6 Emission Reduction Partnership
for the Magnesium Industry have committed to voluntarily eliminate SF6 emissions
by 2010. Also, the European Union will prohibit the use of SF6 in Mg die-casting
beginning in 2008, except when used in quantities less than 850 kg per year.
Many end users of Mg worldwide will continue to demand consistently high-quality
Mg products and will seek improved environmental conditions that alternative flux-
less melt protection other than SF6 can provide.
from 240 cars
= CO, from 210 acres of forest
One standard 52 kg (115 Ib) cylinder of SF6 is equivalent to 1,243 tonnes of C02. Therefore, the
climate benefit of eliminating emissions of one standard cylinder is similar to eliminating C02
emissions from 240 U.S. passenger cars for one year or planting roughly 210 acres of
forest land.2
SF6 has a 100-year global warming potential of 23,900 and an atmospheric lifetime of 3,200 years.
Climate Change 1995: The Science of Climate Change. Intergovernmental Panel on Climate Change
(IPCC). Cambridge University Press, Cambridge, U.K.
• EPA ENERGY STAR conversion factor (11,560 Ibs C02 / U.S. car), http://www.energystar.gov
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2004 Estimated Worldwide Mg Primary Production/Capacity3
Israel
24,000
Kazakhstan
16,000
Brazil
11,000
Serbia &
Montenegro
- Reported in metric tons. 2 000
Source: U.S. Geological Survey and Hydro Magnesium estimates.
U.S. Geological Survey- URL: http://minerals.er.usgs.gov/minerals/pubs/commodity/
magnesium/mgmetmcsOS.pdf
Hydro Magnesium - Magnesium Supply and Demand 2004, IMA Annual Conference, Berlin 22-24.5.2005
China's magnesium industry presents a
unique opportunity for climate protection
in the world's fastest growing production
center. The magnesium industry in China
is opening new plants and beginning to
transition from flux-based melt protection
to cover gas technologies. Instead of
using the potent global warming gas SF6
for melt protection, these firms can
"leapfrog" beyond SF6 and choose the more environmentally friendly options dis-
cussed in this brochure. By adopting alternative melt protection technologies, China
has an opportunity to avoid releasing annual greenhouse gas emissions equal to
roughly 9.6 million metric tons of carbon dioxide (MMTC02)—more than three
times the total emissions released by the entire U.S. Mg industry, production and
casting combined, in 2004.3
Based on U.S. Geological Survey estimates of China's 2004 primary Mg production of 400 kt. See URL:
http://minerals.er.usgs.gov/minerals/pubs/commodity/magnesium/mgmetmcs05.pdf. Assumes 1 kg
SF6/mt of Mg produced.
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What Alternatives to SF6 are Available for Mg Melt Protection?
Several alternative melt protection technologies are commercially available that pro-
vide comparable performance to SF6. The most technically proven alternatives to
date include:
+ AM-cover™ -Patented fluorine-based blended gas technology consisting of an
active gas (such as HFC-134a) and a carrier gas such as nitrogen or carbon-
dioxide.
• Novec™ 612 Magnesium Protection Fluid—Patented blended liquid-to-gas
system using a fluorinated ketone as the active ingredient and a carrier gas
such as carbon dioxide or nitrogen and dry air.
+ Dilute S02—An approximately 1.5% S02 mixture that uses nitrogen, carbon
dioxide, and/or dry air as a carrier gas.
Other alternatives have been developed but are not currently commercialized or
readily available. One technique known as "COOLCOM" generates solid C02 (i.e., dry
ice) for melt protection.4 Another technique is a boron trifluoride (BF3) system that
uses solid fluoroborate as a feedstock to generate a small amount of BF3 gas in-line
when needed for melt protection.5 A third technique under investigation uses S02F2
for melt protection.
What are the Benefits of Mg Melt Protection Alternatives to SF6?
By using fluxless melt protection other than SF6, the global Mg industry can benefit
from improved metal quality, potential cost savings, and increased workplace safety
while reducing greenhouse gas emissions.
Potential Cost Savings
Companies can potentially reduce their costs using Mg melt protection other than
SF6. Using alternative fluorine-based blended melt protection in place of an SF6-
based cover gas process can reduce metal loss (% dross) due to oxidation and pro-
vide associated cost savings, as shown in the hypothetical example in the graph on
page 5. This example also shows that as the incoming Mg raw material price
increases, the resulting cost savings also increase.
When considering dilute S02 systems, the cost of S02 per kg is usually less than the
cost of SF6; however, equipment and process upgrades often must be made to safe-
ly use sulfur-based systems, and associated worker safety and environmental risks
4 Bach et al, 2005. See URL: www.tms.org/Meetings/Annual-05/AM05-TechProg.pdf
5 Revankar et al, no date. See URL: http://www.hatch.ca/LighUVIetals/Articles/
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are necessary considerations. Dilute S02 systems also do not reduce metal loss,
and thus may not offer the additional cost savings possible with fluorine-based sys-
tems shown in the graph below.
Mg producers or casters should note that the potential for the cost savings shown
in the graph depends on the use of appropriate gas distribution systems, furnace
lid designs and maintenance, and other production factors. Also, magnesium melt
protection costs depend on many factors, including the price of Mg raw materials,
the cost of a specific melt protection, the ratio of blended gas used, and the flow
rate needed.
Potential Cost Savings from Reducing Metal Losses:
Alternative fluorine-based melt protection vs. SF6 cover
% Metal Loss Reduction Vs. Die Cast Ingot Price
(Die Cast Process Only)
$60
0.25%
0.50%
1.25%
1.50% 1J5o/o
Initial Mg
Die Cast
Ingot Price
USD1.40/lb.
USD1.20/lb.
USD1.00/lb.
USD0.80/lb.
2.00%
Est. % Metal Loss Reduction from Normal SF6
Based Cover Gas Process
USD0.80/IIJ.
IUSD1.00/lb.l=IUSD1.20/lb.^USD1.40/lb.
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Workplace Safety and Environmental Benefits
Alternative non-SF6 Mg melt protection can provide important workplace safety and
environmental benefits. These systems:
*• Produce less smoke and fumes—making the workplace safer for workers'
health
Are non-flammable
Reduce or eliminate greenhouse gas emissions—A typical diecasting facility
that processes 2,000 tonnes of Mg per year using alternative melt protection
other than SF6 may reduce greenhouse gas emissions by over 60,000 tonnes
of C02 equivalent emissions per year compared to an SF6-based system.
*• Do not deplete stratospheric ozone
The alternative melt protection technologies can potentially produce toxic or corro-
sive byproducts, as does SF6 (see Table 1). However, if these technologies are man-
aged and operated correctly, the byproducts can be maintained at acceptable levels.
Mg casting operation using SF6; alternative fluorine-based melt protection may
substantially reduce the workplace fume and smoke emissions shown above.
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Table 1. Summary of Magnesium Melt Protection Options
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1 1
Compound
SF6
FK (Novec™
612)
HFC-134a
(AM-cover)
Dilute S02
BF3
S02F2j
Atmospheric
Lifetime"
(yrs)
3,200
0.014
14.6
Several
days
?
?
Global
Warming
Potential
(GWP)a
(100 yrs)
23,900
~r
1,300
0
Not
measured
~1
Potential
Climate
Benefit
(% reduction
in overall
global
warming
vs. SF6)b
-
95-99%
95-99%
NA
?
?
Selected
Potential
Byproduct
Emissions
of Concern0
S02d, HFe
HFe, PFIB9,
PFCsh
HFe, PFCsh
S02d
BF31
S02d, HFe
Equipment and
Process Upgrades
(from SF6 system)
-
Moderate (e.g., same
as "minimal" plus liq-
uid processing equip-
ment & monitoring)
Minimal (e.g., recali-
brate mixing units;
possibly add entry
point to improve
distribution)
Significant (e.g.,
replace all mixing
equipment & distri-
bution system pip-
ing with stainless
steel/corrosion-
resistant materials;
monitoring)
Moderate (see
above)
Significant' (see
above)
a Global Warming Potential (GWP) reflects the potential for contributing to the heating of the earth's atmosphere over a
specified time frame. C02 has a GWP of 1. The GWP figures listed above are from: Climate Change 1995: The Science of
Climate Change. Intergovernmental Panel on Climate Change (IPCC), Cambridge University Press, Cambridge, U.K.
b Potential Climate Benefits are from: Characterization of Cover Gas Emissions from U.S. Magnesium Die Casting, U.S. EPA,
May 2004, pp. ES-4, ES-5, 5-7. EPA430-R-04-004, www.epa.gov/highgwp/magnesium-f6/pdf/covergas_may2004.pdf
= This category does not reflect a comprehensive list of potential byproduct emissions, but rather those most commonly
identified; other byproduct emissions may also be produced.
1S02 must be used with care. It is toxic to humans at 2 parts per million (ppm) (based on American Conference of
Governmental Industrial Hygienists Threshold Limit Values) and can corrode steel equipment. At levels produced in the
magnesium industry, it contributes minimally to acid rain.
3 HF (hydrogen fluoride) is toxic at low levels and can accelerate corrosion of equipment. HF levels may be minimized to
acceptable levels by using good operating practices.
' Taniguchi, N. et al. "Atmospheric Chemistry of C2F5C(0)CF(CF3)2: Photolysis and Reaction with Cl atoms, OH radicals, and
Ozone." J. Phys Chem. A., 107(15): 2674-2679.
9 PFIB (perfluorisobutylene) is toxic; good operating practices can eliminate PFIB byproduct emissions.
11 PFCs (perfluorocarbons) are potent greenhouse gases and have long atmospheric lifetimes ranging from 1,000 to 50,000
years (see www.ipcc.ch//press/SPM.pdf). Adding oxygen to the cover gas mixture can minimize PFC production to non-
detectable levels (see www.epa.gov/highgwp/electricpower-sf6/pdf/milbrath.pdf).
1 BF3 (boron trifluoride) gas is highly reactive, toxic (1 ppm workplace exposure limit, U.S. DOL/OSHA), and corrosive; good
operating practices may maintain BP3 at acceptable levels.
' S02F2 is toxic and thus poses potential workplace hazards; these hazards must be addressed with the use of alarms or
odorization, equipment upgrades, and establishment of a safe supply chain.
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Retrofitting for Alternative Melt Protection Technologies
In most cases, conversion from an SF6-based or (older) S02-based system to
a non-SF6 alternative melt protection system is relatively easy. It is important that
melt protection users carefully follow the manufacturer's recommended best prac-
tices to achieve good performance, maintain product quality, and achieve workplace
and environmental improvements. Table 1 (previous page) briefly summarizes the
environmental and operational concerns. When installing a new melt protection
technology, companies should use careful advance planning and good operating
practices, such as:
• Proper choice and grade of carrier gases—Pay attention to the final blended
product (active ingredient plus carrier gas) and how efficiently it is applied to
the molten Mg surface. For example, some alternatives perform better in carri-
er gas mixtures of nitrogen or carbon dioxide rather than dry air alone.
Correct concentrations and flow rates—Know exactly how much of the final
product has been delivered; consider the need for improving current gas
blending equipment. With some alternatives, Mg is best protected at lower
concentrations and higher flow rates than those used with SF6.
• Good distribution systems and practices—Available melt protection alterna-
tives are more reactive and thus less thermally stable than SF6, making good
gas distribution essential.
• Appropriate operating conditions—Monitor process parameters such as
molten metal level, and variations in temperature and alloy chemistry.
The detailed information needed to convert a facility to use an alternative melt pro-
tection technology is available from the respective technology providers - please
see the list of suppliers' contact information on the back cover.
8
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Globally, the magnesium industry can avoid annual
greenhouse gas emissions equal to more than 15 million
metric tons of C02 by eliminating SF6 emissions.
The environmental benefit from choosing climate-
friendly Mg melt protection technologies is equivalent
to the C02 absorbed by planting 2.5 million acres
(10,117 km2) of forest3, an area larger than the United
States Yellowstone National Park.
:-TJlii'r- ' ' :
irest per
Photo of Yellowstone National Park courtesy of U.S. National Park Service
Contact Information:
U.S. EPA: www.epa.gov/magnesium-sf6
IMA: www.intlmag.org
CMA:
JMA:
www.chinamagnesium.org
www.chinamagnesium.org/english.htm
www.kt.rim.or.jp/~ho01 -mag
Product Information:
www.am-technologies.com.au/metal.htm
AM-cover:
Novec™612:
www.3M.com; dsmilbrath@mmm.com
mixing equipment:
christian.domanyi@rauch-ft.com (outside N. America)
kurt.brissing@rauch-ft.com (N. America)
www.tn-sanso.co.jp/en/index.html (Japan)
Dilute S02 (Europe): www.aski-gasetechnik.de
Dilute S02 (N. America): www.polycontrols.com
COOLCOM: www.linde-gas.com
S02F2: www.halidegroup.com
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