NICKEL

DAVID HANSON, C&EN WASHINGTON

If there ever was a utilitarian metal, it's nickel. This well-known transition element may have more varied applications than any other metal. It is used in everything from our coins to our automobiles and from jewelry to paper clips, and new uses are found all the time.

Basically, nickel is a hard, malleable, ductile, lustrous, silver-white metal that takes a high polish. It conducts heat and electricity and is slightly magnetic. It forms numerous compounds, many of them blue or green, and finely divided nickel can adsorb hydrogen.

But it is as an alloy with other metals that nickel really shines. The first reported use of nickel was in a nickel-copper-zinc alloy produced in China in the Middle Ages. It is believed that some alloys were produced in prehistoric times. Today, an estimated 85% of nickel ends up as alloys.

The largest use is in making stainless steel. As much as 70% of nickel goes to make stainless or other steel alloys. With concentrations of up to 45%, nickel adds strength and corrosion resistance. Surprisingly, 16% of stainless steel goes into the chemical process industry. Electronics consume 18%; auto manufacturing, 15%; and the food and beverage industry, 13%.

In addition to its use in steel alloys, nickel forms useful alloys with other metals. Copper-nickel alloys offer a good compromise between strength and ductility and resist corrosion in saltwater, nonoxidizing acids, and alkalies. These alloys are used in industrial plumbing and petrochemical equipment.

Nickel-copper is also the alloy of which coins are made. The U.S. nickel is 25% nickel and 75% copper.

Other useful alloys include nickel-chromium and nickel-molybdenum combinations that are the basis for materials that can withstand extremely corrosive chemical plant environments, such as hot sulfuric and phosphoric acids, hydrogen chloride gas, and other oxidative conditions.

Electroplating is the second largest use for this versatile metal. The process is used to produce corrosion-resistant and decorative finishes, as well as substrates for chromium coatings. Nickel can be plated on many surfaces, including plastics. Automobile trim, bathroom fittings, and electronic connectors are just a few of the many applications.

There is also a process for plating nickel without an electric current. This "electroless" process makes very uniform plating. Other materials can be added to improve the finish, such as Teflon to increase lubricity or silicon carbide for wear resistance. This process is used on computer hard drives for a smooth, nonmagnetic base for the magnetic recording layer.

Nickel also happens to be an excellent catalyst for many chemical reactions. By itself or combined with other metals, nickel is used for a myriad of industrial and research applications. The most famous nickel catalyst is called Raney nickel. Developed by Murray Raney in the 1920s, it is 90% nickel and 10% aluminum.

	FIREBALL A 3-mm droplet of nickel-zirconium, heated to incandescence, hovers between electrically charged plates inside the Electrostatic Levitator at NASA's Marshall Space Flight Center in Huntsville, Ala. NASA PHOTO

All of these uses demand a lot of nickel. The U.S. consumes more than 195,000 metric tons of nickel yearly. But the last nickel mine in the U.S. closed in 1987. Most new nickel comes from Canada and Australia. The two most common ores are nickel-iron-sulfide pentlandite, (Ni,Fe)₉S₈, and a nickel silicate contained in hydrated magnesium, usually garnierite, (Ni,Mg)₆ Si₄O₁₀(OH)₈.

But at a cost of $8,000 per ton, nickel is not cheap. So there is an efficient recycling system to recover and reuse nickel. More than 110,000 tons of nickel were recovered from scrap in the U.S. last year, about 57% of total consumption, according to the U.S. Geological Survey.

Unfortunately, nickel comes with an evil side. Several nickel compounds are known human carcinogens. Nickel refiners had a number of health problems in the past, but current exposures to nickel in the workplace are much lower. Still, caution is taken with nickel refinery dust and especially nickel subsulfide (Ni₃S₂). Another compound of concern is nickel carbonyl, a highly toxic, volatile liquid used to purify nickel or to produce fine nickel particles. U.S. and international health agencies have set exposure standards for these and other nickel compounds.

Another health issue is contact dermatitis from exposure to nickel. Reactions to nickel alloys in earrings used for pierced ears are the most frequent, but itchy rashes can occur on any body part that comes into prolonged contact with nickel. The European Union has banned earrings with more than 0.05% nickel and some nickel-plated jewelry. The American Academy of Dermatology says that nickel allergies are the most common chemical allergy causing skin problems.

Nickel use continues to grow as new applications are found. Nanotechnology, electronics, and catalysis are areas of exciting nickel research. Use of the metal is rising each year, and the industry is confident about its future. This is one element where you don't have to exaggerate when you say that you're getting your nickel's worth.

David J. Hanson is assistant managing editor for government and policy at C&EN. He has worked for the magazine since 1977.

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