Lofty Uses for Lowly Elements – Mechanix Illustrated
This piece was a sort of editorial compromise… as I was getting more into sci/tech writing, I thought it would be nice to get a column or two going. I pitched “Element of the Month” to Mechanix Illustrated, figuring it would be good for about 8.5 years, but the editor told me to just pick seven and do it as a feature. These were particularly fun, and in some cases a bit prophetic in terms of our wasteful habits as a species…
by Steven K. Roberts
IF YOU’RE like most people, you probably sat through your share of high-school science classes listening to descriptions of various elements, compounds and natural phenomena. You probably yawned a time or two, wondering if everything in the world of science was really that dull.
You know by now that it isn’t, of course, with such complex undertakings as the space shuttle and designer genes making headlines daily. But with all this attention to the products of high technology, the lowly elements at the heart of it all are commonly ignored—and unappreciated.
Some elements—fundamental substances that in combination make up all that exists—have such dramatic impact on our technology (or economy) that they are in the spotlight constantly. Everyone knows about gold’s seductive sheen and even a child knows that it is helium that makes balloons rise.
Yet every element has its own unique characteristics, and with the increasing specialization of our various technologies, all of them have been put to use in ways that could hardly have been imagined by the science teachers of yesteryear.
Let’s consider these seven well-known elements and some of their intriguing new uses: gold, lead, aluminum, silver, tin, helium and silicon.
The king of metals has sparked wars, economic booms, love affairs and murders—not to mention madness. Fortunes have been won and lost over the magical substance, and in 1979 alone there were over 309 tons of new gold coinage issued in 80 countries.
But there are a host of uses for gold that have nothing to do with its beauty or its economic significance. Consider, for example, the electronics industry. Gold’s superior conductivity and resistance to corrosion make it ideal as a plating material on connectors. RCA alone uses over one-half pound of pure gold each day for just this purpose. On more of a micro scale, the same characteristics make tiny gold wires the preferred method of interconnection between an integrated-circuit chip and the pins that connect it with the outside world.
The lustrous metal is also used for bonding in another high-technology environment: the rocket engines of the space shuttle and the jet engines of most modern aircraft. Special gold alloys with a bonding strength of 75 tons per square inch are the only materials researchers have found that can reliably withstand the intense heat of the engines without losing strength or corroding.
Speaking of intense heat, gold is also being used in the face masks designed for firemen. With an exterior film on a mylar substrate, the heat of a close fire can be reflected before it has a chance to melt the clear plastic material of the mask itself.
The transparency of thin films of gold is paying off in some other interesting applications. The windshields of such diverse transportation machines as Alpine locomotives and jet aircraft make use of gold for two reasons. First, the film reflects most of the solar heat that would otherwise have to be dissipated within the cabin by an air-conditioning system and, second, the conductive layer heats uniformly upon application of an electric current, quickly and effectively defogging or deicing the windshield.
Gold-bearing glass isn’t limited to planes and trains. It can be found in a growing number of buildings, saving thousands of dollars in construction and operation costs. Sure, the glass costs two to three times as much as the normal variety, but its ability to block out over 90 percent of the solar heat in the summer and reflect heat back into the building in the winter allows the builder to get away with much smaller heating and air-conditioning plants, while doing away with heavy drapes. Operating costs over the life of the structure are reduced as well.
These windows, such as PPG’s Solarban 490 reflective insulating units, consist of two pieces of glass sealed together and separated by an airspace. A gold film is deposited on either interior airspace surface. On a typical summer day, such units reduce solar gain on a building’s south side up to 89 percent compared to standard 1/8-inch clear glass—all with only 1 ounce of gold per 400 to 1,000 square feet!
Then there is laser fusion, precision humidity measurement, gas-sample analysis and high-power vacuum tubes. . . Gold, which once shone primarily as a decorative and economic material, is now the key to a number of new technologies. Hold onto your ring.
Lead, three doors up from gold in the periodic table of the elements, hasn’t nearly the luster or magic of the king of metals. But it is far more pervasive in our modern technology, solving some major problems with its unique characteristics.
We all know of lead’s universal presence in automobile batteries, of course, and its usefulness in the energy-storage arena is making it a key element in the design of electric cars, solar-power systems and power-backup facilities for computers. But the most awesome lead-based batteries of all must certainly be those being investigated in a New Jersey research center: Weighing in at 122 tons each, the 2-megawatt units are intended for load averaging at electric-power utilities. By storing some excess power overnight and delivering it to the power grid during periods of heavy use, the batteries can decrease the probability of brownouts.
But lead’s most obvious characteristic is probably its weight. This made it the ideal ballast material in the August, 1978, crossing of the Atlantic by the helium balloon Double Eagle II. It is also the reason that the Japanese fishing industry recently started making nets from lead-cored yarn. The fishermen have found markedly improved performance with the uniformly heavy netting, along with greater reliability and resistance to fouling.
The softness of lead makes it useful for acoustical insulation; so over 17,000 square feet of lead sheeting were recently stapled into the walls of the luxurious Meadowlands Hilton in Secaucus, New Jersey, for just that reason. The same principle applies in the numerous factories that use lead curtains or leaded foam sheet to surround particularly noisy processes. In such diverse operations as the Learjet plant in Wichita, Kansas, and the Dow Jones printing plant in Orlando, Florida, the use of lead for industrial noise reduction has been demonstrated to improve employee health and morale.
The metal’s radiation-shielding properties are well-known, and one of the more unusual applications of this characteristic involves the use of lead putty during radiation therapy for cancer patients. The material, which comes in 10-pound cans, is simply molded to the patient’s body wherever exposure is not desired.
Unlike some other elements, lead doesn’t lend itself to very many gee-whiz applications. But its unique characteristics make it indispensible to a number of technologies.
Aluminum comprises one-twelfth of the earth’s crust and offers a rare combination of abundance and utility.
The catch, of course, is that the raw material needs to be about 45-percent aluminum oxide before it is considered practical for conversion into aluminum, a process that requires prodigious amounts of electricity. In fact, it wasn’t until the middle of the last century that it even became possible to isolate the pure metal from the clays in which it is most commonly found. It went for about $545 a pound back then, but fell a thousandfold after an Ohio inventor named Charles Hall hit upon a process involving high-current electrolysis.
In the nearly 100 years since Hall’s discovery, aluminum has grown from a substance of almost jewel-like rarity (the 100-ounce casting that caps the Washington Monument sat for a time in the window of Tiffany & Co.) to something modern technology would be hard-pressed to do without. Its extremely useful combination of characteristics—light weight, high thermal and electrical conductivity, workability, strength, corrosion resistance, reflectivity and nonmagnetic character—makes it indispensable.
Consider, for example, the transportation industry. The first airplane that ever left the ground had some aluminum components in the engine, and nearly 100 tons of the substance can be found today in each Boeing 747. But light weight is useful for more than just flying machines. The Bay Area Rapid Transit (BART) system in San Francisco depends heavily upon aluminum as a structural material in its cars, allowing electricity cost to average 2.2 kilowatt-hours per car per mile.
This compares rather favorably with typical steel units such as those used by New York City’s transit system, which require 5.4 kilowatt-hours to do the same job.
None of this has gone unnoticed by automakers. At first only such critical parts as pistons were made from aluminum, but as our energy-squandering habits came face to face with reality, it began to make sense to do something more with the stuff. Every pound of aluminum that can be used in place of steel knocks 2.25 pounds off a car’s weight—saving five to seven times the energy (over the vehicle’s life) that was needed to make that pound of aluminum in the first place. The value of this was demonstrated a few years ago by the Viking Project, which produced a practical two-passenger car that consistently attained 59 mpg at highway speeds. Of the vehicle’s 1,200 pounds, 425 were aluminum.
This lightweight metal also puts another old standard to shame: copper. Twice as conductive but one-third the weight, aluminum has all but replaced copper for power transmission and distribution lines. It saves money, not only in lower transportation and installation costs, but throughout its exceedingly long operating life as well. Since the power lost in the form of heat is dependent upon the electrical resistance of the wire (along with the square of the current), aluminum can cut energy waste in half.
That’s a good thing because the process of extracting aluminum from bauxite ore requires about 1 percent of America’s generated electrical power. (It is this, not scarcity, that makes aluminum such a recyclable metal. The cost of recycling is about 5 percent of that required to produce an equivalent amount from the raw ore.)
If gold is the king of metals, then aluminum would have to be the queen—they team up beautifully. A century ago, the two could be found together in the helmet of King Frederick VII of Denmark and the baby rattle of Napoleon III; today you can find them in close partnership in such diverse places as the construction industry and the suits of firefighters. The well-dressed fireman of today wears not only a faceplate covered with gold film,
but an aluminum-coated asbestos suit that keeps inside temperatures at 85° to 100°F while he’s confronting a 2,000°F fire.
Fine stuff, aluminum, Americans tore over 225 million pounds of it along the serrated edges of foil boxes last year; they also ate out of it, pumped electricity through it, drove around in it, sunbathed on it, flew in it, carried clothing in it, hit baseballs with it, drank beer out of it, painted with it, rubbed it under their arms. . . and recycled it.
Silver has decorative and monetary uses certainly, but it’s easy to forget the pervasiveness of this shining metal in a variety of industries. Photography would still be in the dark ages were it not for silver halides, and the pursuit of a reliable electrical-contact material would still be plagued by corrosion and high resistance were it not for the availability of silver-nickel alloys.
Silver teams up well with other metals also. Adding as little as .5 percent yields the strongest aluminum-casting alloy yet discovered— used extensively in the Trident missiles. Mixing a dollop of silver with lead and tin produces a solder capable of holding up under the high temperature and pressure of modern auto radiators.
There’s another automotive application that might come as a surprise: the electrode tips of spark plugs. Since 1980, silver-tipped plugs with a 30,000-mile life have been standard in Peugot, BMW, Volvo, Audi and Renault automobiles, and Bosch’s new Silver Sport plugs are the units of choice for high-RPM engines such as those found in snowmobiles. The secret is better heat conductivity, allowing a longer insulator, thinner electrode and lower firing voltage. This all adds up to less chemical corrosion and physical wear.
Silver’s remarkable thermal conductivity even landed it a job in carbide grinding wheels, where its ability to conduct heat rapidly away from the working surface dramatically increases wheel life.
When one thinks of batteries, the usual names that come to mind are carbon-zinc, lead-acid, nickel-cadmium, mercury and so on. But in the aircraft industry, it is silver-zinc that takes the prize for light weight and high performance. Quite a few commercial jetliners use 22-pound silver batteries as power-backup units capable of delivering 6,700 watts (about 9 hp) continuously for three minutes if main power fails. With a shelf life of 10 years, the batteries represent a significant safety feature in an industry that cannot afford to take too many chances.
Silver, with the highest electrical and thermal conductivity of any metal, is guaranteed an important role in our increasingly electronic society. Like aluminum, it is eminently recyclable, with over half of all U.S. production coming from coins and used photographic materials. But unlike aluminum, it is anything but plentiful, and we can expect prices to climb as demand gradually outstrips supply.
Tin, like the other elements we have discussed so far, has progressed into a number of interesting new applications from its traditional and unexciting ones. It is losing ground to new food-packaging technologies that are slowly rendering the tin can obsolete, and techniques such as soldering, while constantly being refined and developed, are merely extensions of old methods.
One clever new application of this whitish metal has been developed by Dunlop for their 150Gram tennis racket. The company needed to produce a foam-cored frame of carbon-fiber-reinforced polymer, so began with a die-cast skeleton of tin-bismuth alloy around which the plastic material was injection-molded. The core was then melted out and replaced with two different densities of polyurethane foam (low density for the head, high for the handle). The result is a lightweight and very high-performance unit which outperforms traditional materials. The value of the tin-bismuth alloy lies in its low melting point and dimensional stability upon temperature change.
Tin’s corrosion resistance is the reason it was adopted decades ago as the lining for food and beverage cans, and that same characteristic has recently found application as a fuel-tank lining for alcohol-powered vehicles. Standard steel tanks would quickly suffer from exposure to some of the more cheaply produced alcohol fuels (which contain acidic by-products of the fermentation process).
Other automotive uses of tin include a number of plain bearings— one of the metal’s classic uses. Standard engine bearings are an alloy of aluminum, tin and copper bonded to a steel shell. Other bearings (gearbox, clutch, steering and so on) are composites of bronze (copper plus tin) and low-friction plastic.
But the most surprising new uses of tin are in a class of chemicals known as the organotin compounds. They have found uses as pesticides and antifeedants for plant protection, water-repellent treatments for clothing and building materials, wood preservatives and stabilizers for PVC plastics that prevent decomposition and brittleness upon exposure to high temperatures or ultraviolet light. These new compounds are being widely used in agriculture and construction and show promise in a variety of other fields.
Tin can be found in woolen fabrics, glassware, computers and even sleeping bags. Such uses, not at all obvious upon examination of the pure metal, demonstrate once again the applicability of each element’s unique characteristics in at least some corner of our increasingly specialized technology.
Helium is an endangered resource. For decades, drillers of natural gas have been venting what they call “wind gas” to the atmosphere. It is of virtually no value compared with the fuel that accompanies it to the wellhead.
This waste product is helium, a nonrenewable and very limited resource upon which a rapidly growing new technology depends. Once used only for balloons, deep-sea diving and aluminum welding, helium is the key to cryogenics and superconductivity.
Many gases can be reduced to a supercold liquid state, but only helium remains a liquid no matter how deeply it is chilled. At least one research lab has succeeded in reducing it to within .001 degree of absolute zero.
This is all very interesting, but it is also incredibly useful. At such temperatures, normal physical principles are abandoned and such phenomena as superconductivity—zero electrical resistance—become commonplace. It is this that allows the prodigious currents to drive magnets powerful enough to propel artillery shells every bit as effectively as gunpowder. Or, if you’re not in a military frame of mind, allows frictionless trains to scoot along at 300 to 500 mph—or accelerate particles to a speed necessary for nuclear fusion.
Computers made of superfast Josephson junctions and immersed in a bath of liquid helium can offer, at the very least, 100 times the speed of the fastest machines currently available. It is clear that quite a variety of new technologies will be looking to helium as a key element: transportation, armaments, computing, power generation and storage—yet the United States still vents about 13 billion of its roughly 700 billion cubic feet every year as a waste product of natural-gas drilling. Even though helium is the universe’s second most plentiful element, there is a limited supply on earth and it cannot be produced by any known economical means.
Silicon, the primary component of common sand, has become during the last quarter-century the very heart of the solid-state revolution that has brought us everything from digital watches to space-shuttle avionics.
The second most abundant element in the earth’s crust (being exceeded only by oxygen), silicon was found to have some unusual electrical properties when refined to an ultrapure form and doped with a tiny amount of another material such as arsenic. In particular, it could be made to amplify an electrical signal.
From this, it was just a matter of time and ingenuity before the basic transistor grew into the integrated circuit—then into successively more complex ones which eventually incorporated entire computer systems on single low-cost chips.
By now, these microprocessors are so thoroughly integrated with modern technology that it is difficult to imagine a world without them. Yet not so very long ago, silicon’s primary uses were as abrasives and components of structural steel, glass and pottery.
Silicon is also the key to another new technology: photovoltaic power conversion. The direct production of electricity from solar energy is something that has been plagued by problems of high cost and low efficiency, but recent advances in the creation of continuous ribbons and ever-larger wafers of silicon are bringing the price of solar-power systems down to a level that is competitive with standard techniques.
All this leads to an observation or two. We have spoken here about seven more-or-less randomly chosen elements, all of which have taken on some remarkable new roles in the last decade or so. Each of them (and each of the other 96 as well) has a set of characteristics that makes it uniquely appropriate for certain applications. The difference
of one orbital electron spells the difference between aluminum and silicon, between gold and mercury or between helium and lithium.
As our technology continues to grow more and more specialized, we will come to appreciate even further the rich palette of materials we have to work with. We may also frequently find ourselves in difficult situations, as strategically significant elements upon which we have grown to depend become suddenly unavailable due to wars, economic boycott or our own wasteful habits.
STEVEN K. ROBERTS is a free-lance science writer and industrial-systems consultant from Dublin, Ohio.
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