Finding New Materials
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These electric cars will generate electricity onboard in a fuel cell powered by hydrogen and air. The
reforming of natural gas (methane) to produce hydrogen can be made more efficient, but new alloys are
needed.   |
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Some of the challenges facing tomorrow's metallurgists
Nickel magazine, Dec. 00 -- The Nickel Development Institute (NiDI) believes that the proposed
"hydrogen economy" of the 21st centrury poses significant materials-related challenges for the current crop
of metallurgists and material engineers making their way through university.
In the U.S. alone, hundreds of millions of dollars could be saved in the production of hydrogen if new
materials for natural gas (methane) reformers were available. For example, significant savings could be
realized if these petrochemical plants could operate at a higher temperature say, 200°C higher than is now
the case. Such an operation would consume less natural gas, owing to the more efficient use of energy.
The materials currently used in reformers are subject to "metal dusting," a form of rapid, often catastrophic carburization that occurs at elevated temperatures in conditions of high carbon activity and low oxygen.
To develop new materials that are resistant to metal dusting, more research is required. Existing materials include special stainless and nickel-based alloys. Still, researchers continue to study new nickel-containing compositions, as well as surface treatments. Examples include various intermetallics, such as nickel-aluminum systems. Unfortunately, all these materials have properties that render fabrication a challenge.
Metal dusting affects many other systems, including synthetic natural gas plants, coal gasification, fired heaters handling hydrocarbons, and even metallurgical processes, such as direct iron reduction.
Metal dusting is not the only high-temperature challenge. Other high-temperature environments (of 500°C or more) involve corrosives, such as chlorine and fluorine, that require materials that perform well yet are cost-effective. These have yet to be developed. Ideally, such materials must have not only high corrosion resistance, but high ductility, strength, and ease of fabrication.
Alloy research is also needed to find suitable metals for the containment of the electrolyte in fuel cells, even if the various technologies are still being developed. Safety and reliability of fuel cells will be necessary for quick acceptance by consumers. The proposed hydrogen economy will likely require safe materials for the long-distance transport of liquid hydrogen at 20°K. Even if some nickel-containing stainless steel wrought materials are suitable, the welds must remain ductile -- yet another engineering challenge. And although not directly related, there is a need for further development of superconducting materials.
Although nickel will continue to be used in the development of many of these new materials, the nickel industry itself faces its own metallurgical challenges. Consider the development of hydrometallurgical processes for lateritic ores. These corrosive and abrasive aqueous processes use sulphuric acid and operate at elevated temperatures and pressures. Small changes in process conditions can radically alter the corrosion resistance of the various materials used. Much work, including alloy development, still needs to be done to determine the most economic materials for use in these processes.
Another promising technology is supercritical water oxidation (SCWO), which could be used in the destruction of hazardous wastes. SCWO, too, operates at elevated temperatures and pressures. Researchers are trying to understand how to control the corrosivity of these and other systems. The cost of the materials used to contain the reaction could determine how extensively the technologies will be used.
In virtually every industry, there is a need for a high-strength stainless steel with high resistance to corrosion. Such a material could be used in pumps and valves, fasteners, and various structural components for severe corrosive services. An alloy is needed with an equivalent corrosion resistance of the 6% molybdenum stainless steels but with a minimum yield strength of 700 megapascals.
The superduplex alloys come the closest to meeting that requirement, though they have minimum yield strengths of less than 600 megapascals. The current precipitation-hardenable stainless steels have the strength, but not the corrosion resistance. A fully weldable version, if one could be found, would be in demand for pressure vessels and piping systems.
NiDI supports research designed to help solve these materials challenges and provides information, technical assistance and education to assist materials specifiers.
To tackle these and other challenges, students need a broad materials background involving all aspects of production and fabrication. The underlying goal must be to find high performance materials that render technological processes both economical and environmentally safe.
Gary Coates is technical director of NiDI
Photo: NiDI
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Gary Coates |
