Stone Age, Bronze Age, Iron Age - humanity's history is outlined in terms of characteristic basic materials. However, for experts such as George F. Mechlin, our present time would be better called the Age of Materials Science.
''Technology remains our best deterrent to dependence upon unstable foreign sources of critical minerals,'' says Dr. Mechlin, vice-president for research and development at Westinghouse Electric Corporation. He and fellow materials experts see knowledge - scientific understanding of materials' properties and the know-how to turn this to practical use - as the essential ''raw material'' the United States needs to conserve, recycle, and substitute its way out of that dependence.
Conserving and recycling critical minerals and finding substitutes for them wherever feasible will be as important as finding new reliable sources of mineral supply, such experts believe. However, conservation and substitution mean more than just finding more efficient processes and alternative minerals. They also mean developing revolutionary new alloys and other artificial substances that require less of the scarce minerals or dispense with them entirely. Materials scientists call them ''synterials,'' by analogy with the ''synfuels'' that may one day replace petroleum and natural gas.
''We are learning things that may enable us to reduce the amount of cobalt needed in superalloys (used in jet engines, for example) and permanent magnets. And fiber-reinforced plastics are already being used to replace metals in many applications from tennis racket shafts to aircraft,'' Dr. Mechlin explained at a press briefing last year. ''Many of our new materials will be stronger, lighter, easier to shape, more corrosion-resistant, and will require less energy to produce,'' he added.
The United States today depends heavily on imports for more than 10 metals and minerals essential for its industry and defense. They include antimony, bauxite (for aluminum), cadmium, chromium, cobalt, columbium, manganese, nickel, platinum-group metals, tin, and tungsten.
Recycling can help conserve what is imported. It also can sometimes save on energy. The National Research Council of the US National Academy of Sciences notes that ''for magnesium, the remelt energy is only 1.5 percent of the energy required to win the metal from virgin ore; for aluminum, it is 3 to 4 percent; and for titanium, it is 30 percent.''
Aluminum, certainly, has been a recyling success. Billions of aluminum beverage cans, as well as other scrap, are recycled every year. Much stainless steel also is recovered. But there are severe economic and engineering limits on what recycling can do. It wouldn't be feasible, for example, to try to recover the tungsten from the burned out filaments of electric light bulbs. Nor is it possible to rescue the tin washed down the drain when people brush their teeth with fluoride (and tin-containing) toothpaste.
For recyling to play a truly meaningful role over the range of critical minerals requires restructuring the whole materials cycle, from mining to discard, and almost mineral by mineral to accommodate a recycling economy. While many experts believe this is desirable and eventually will be necessary, it may be many years in coming.
For example, iron and steel recycling has scarcely begun to realize its potential. For Herschel Cutler, executive director of the Institute of Scrap Iron and Steel, the much publicized ''garbage into gold'' vision of recovering metals from trash is a hollow promise. He points out that you don't have to fish in the dump for iron and steel scrap. There already is something like 700 million tons of it on hand with more added each year. ''We are nowhere near using it,'' he says, partly for economic reasons and partly because of technical difficulties.
To begin with, the economic structure favors using virgin ore over recycling scrap in the iron and steel business. Tax benefits encourage mining. Freight rates - far higher for scrap than ore - discourage recycling. ''We have fashioned laws that discriminate against scrap,'' Mr. Cutler says.
Also, national policy made for other purposes can backfire. Under pressure to increase gasoline mileage, auto makers are using new high strength low alloy (HSLA) steel to make thinner, lighter-weight parts along with the traditional carbon steels in car bodies. The alloying materials include critical imported metals which should be recycled. Beneficial as these elements are in strengthening the new specialty steels, they are generally considered a metallurgical ''poison.'' Even the small amounts of these materials in HSLA steels are enough to ruin a meltdown for recycling. Unless the scrap were recycled to make the particular steel from which it came, the product would be so degraded it could only be used at the lowest level of steelmaking. Thus, in what Mr. Cutler calls a ''hypothetical but very realistic scenario,'' HSLA scrap could end up in reinforcing bars with its precious imported alloying elements locked away inside concrete.
To make matters worse, he explains, it presently is impossible to tell the difference between the HSLA steel in, say, a car fender, and ordinary carbon steel in the door. This is true both at the scrap yard and in the recycling facility. There is need for a basic research program to find economical ways to identify HSLA steel, especially to identify the alloying elements in the molten state. But, Mr. Cutler asks, who is to do this? There would not be enough financial return for any private company to undertake the study and the federal government has not taken it up either, he says.
This brings up the question of public vs. private benefit, which is central not only to recycling but to US minerals policy in general. The country as a whole would benefit by recycling the alloying minerals in HSLA steel. Yet any private company that took on the research task would probably lose money. ''There are costs where the benefit is public, not private,'' Mr. Cutler observes. ''Attempting to justify cost for public good where there is no direct private benefit can be hard to do. Maybe this is an area where government action is needed.''
Meanwhile, materials scientists, who see great promise in the new synterials, are concerned with the state of materials research in the US. Oleg D. Sherby of Stanford University warned Congress two years ago: ''Metalworking research facilities are either primitive or nonexistent at universities in the United States. And education in metal forming is not being emphasized. . . . The leadership for initiating such activities should be considered by Congress. . . .''
Very little has been done to heed this warning since then, either for metallurgy specifically or for materials science generally. Where industry and a few university departments such as that of Dr. Sherby have followed specific research lines, often with Department of Defense funding, great progress has been made in developing new materials. But this does not cover the US need for new knowledge.
Citing what he called ''dangerous complacency,'' Dr. Mechlin has warned: ''Where research has been funded, we have been able to find substitutions for critical materials. . . . But where research has not been funded, we could be in real trouble. Chromium is perhaps the classic example. Without chromium, we could not produce stainless steel. We could not build power plants or jet engines, refine gasoline or process certain foods. Yet despite the fact that we import 92 percent of the chromium we use in this country, we have done very little research to find substitutes.''
Still, the opportunities for developing new materials seem enormous to materials scientists. There are, for example, the superplastic metals with which Dr. Sherby and many materials scientists around the world now are working. These metallic alloys have a structure that allows them to become quite plastic at high temperatures. They can be stretched like chewing gum to hundreds of times their starting length or easily pressed into molds to take on complex forms. Yet at normal working temperatures they retain high strength and ductility.
In this way, a complete turbine wheel, blades and all, can be formed with virtually none of the metal wasted and with almost no additional machining to make the part ready for service. This contrasts with making such a wheel in parts and adding the turbine blades one by one.
To cite another example, superplastic titanium alloys can be made into light-weight, very strong parts that can carry structural loads in aircraft frames. In one research project, British Aerospace has found it can reduce labor in making titanium parts by up to 70 percent, cut the part's weight by up to 40 percent, and lower costs by 60 percent using superplastic technology. And while up to 90 percent of an aluminum block can become scrap in aircraft part manufacture, there is little wastage with superplastic titanium.
Superplastic techniques allow formation of alloys not possible with older technology. Also, they confer properties on metals that can reduce the need for critical alloying minerals. The ultra-high carbon steels (UHC) with which Dr. Sherby works at Stanford demonstrate this. Medium and mild carbon steel, such as those used in automobile bodies, typically have less than 0.25 percent carbon. Dr. Sherby's high carbon steels run between 1 and 2 percent. Above 2 percent, you have cast iron.
Superplastic technology allows Dr. Sherby to shape and work these steels into complex parts which, instead of being brittle like cast iron, are stronger and more ductile than the HSLA steels without needing any of the HSLA critical alloying elements. Moreover, superplasticity allows metals to be bonded by diffusion of their atoms. This bonding is stronger than normal welding, whose heat often slightly damages the adjacent metal. Using this technique, Dr. Sherby has been able to produce metal laminates that can be formed into complex shapes without breaking and in which UHC steel of extreme hardness is bonded to a softer mild steel.
Superplastic metals promise both to conserve critical materials and to substitute for them in many uses. However, Dr. Sherby warns that humility is in order. He and his colleagues at Stanford have found that the famed old Damascus swords were made of UHC steel and probably were formed with the help of superplasticity. Also, he knows of a Middle Eastern adz blade from 400 BC which is made of two parts joined by diffusion bonding. Thus, while superplastic technology promises to have a big future, it may also have had an glorious, if now little known, past.
Then there are the metal glasses. If a metal is very quickly cooled well below its normal freezing point, it can solidify with an amorphous structure more like that of glass than the crystalline regularity of normal metals. These amorphous metals, or metal glasses, are the strongest, toughest, most corrosion-resistant and easily magnetized materials known. The cost of producing them is relatively low, for they are formed directly from the molten state without additional processing.
These metal glasses, which already are used in phonographs, promise to have wide application. Yet again, knowledge is a critical factor, Robert Mehrabian of the National Bureau of Standards says, ''Our understanding of the basic phenomena at play is lagging.'' The same could be said for many other promising materials science fields - high strength plastics and plastic composites, ceramics that may replace steels in many uses, or other synterials.
Research engineers and scientists need to know much more about the inner structure of materials at the atomic level, about surface properties, and similar basic factors. For example, learning to implant atoms of chromium, cobalt, or other critical alloying metals only where they are needed on the surface, rather than mixing them throughout the metal, can conserve these vital materials.
Thus, to materials experts, US dependence on imported minerals is not so much a threat as a challenge to develop materials that remove the country's minerals vulnerablity. While acknowledging that finding stable sources of supply is important, to them, the critical raw material is knowledge.