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close this bookEco-restructuring: Implications for sustainable development (UNU, 1998, 417 pages)
close this folderPart I: Restructuring resource use
close this folder4. Materials futures: Pollution prevention, recycling, and improved functionality
View the document(introductory text...)
View the documentEditor's introduction
View the documentBackground
View the documentStrategies to increase materials productivity
View the documentMaterials technology
View the documentMaterial attributes
View the documentMaterial performance trends
View the documentConclusions
View the documentNotes
View the documentReferences

(introductory text...)

Pradeep Rohatgi, Kalpana Rohatgi, and Robert U. Ayres

Editor's introduction

This chapter addresses a key problem in the context of eco-restructuring, namely the extent of technological possibilities for radically increasing materials productivity. It will be recalled that two premises of the book are (1) that economic growth must continue, at least for the foreseeable future, and (2) that the nature of that growth must change radically in order to satisfy the basic requirements of long-run sustainability. That change has two fundamental implications. First, the fact that non-renewable resource stocks are finite dictates that the rate of extraction of non-renewable materials cannot increase significantly over its present level, globally, and must eventually approach zero. Second, the fact that the habitability of the earth for humans depends on the health of the biosphere dictates that the rate of emissions of chemically active - hence potentially harmful - wastes into the environment must be decreased even more drastically, and even sooner.

There are two generic strategies for reducing waste emissions. The first is known as "end-of-pipe" treatment. It is the strategy that has been favoured overwhelmingly up to now. And it will remain essential. But it is ultimately limited in its effectiveness by the fact that wastes can never be completely inert as long as they differ chemically or physically from the composition of the environmental medium into which they are discarded. The other generic approach is to reduce the use of materials, especially non-renewable extractive materials. This is often taken to imply a reduced standard of living, even reversion to a sort of Gandhian lifestyle. It need not imply any such thing. What it does imply is that the economy must generate much more output (GDP) for each unit of physical materials and energy input. In other words, the productivity of materials and energy must be sharply increased and must continue to increase over time.

To increase materials and energy productivity there are several approaches. One that has been discussed frequently in the past is "dematerialization", i.e. to use less material for a given function than in the past. This approach depends partly on scientific progress in materials science, enabling materials to perform better. It also depends on more mundane changes to encourage less wasteful practices in the materials cycle itself - especially less dependence on dissipative uses of materials (such as solvents, cleaning agents, pigments, lubricants, etc.) and more efficient re-use, recovery, and remanufacturing of durable goods. This approach is sometimes called "clean technology," to distinguish it from waste treatment.

When the use of materials is considered from a lifecycle perspective, it is clear that efficient recovery, repair, renovation, remanufacturing, and recycling depend very strongly on how the material is utilized in the first place. Products that are dissipated in use (such as solvents or detergents) cannot be recovered for re-use. Products that are very difficult to disassemble cannot be repaired, renovated, or remanufactured. Clearly, these "end-of-life" issues must be taken into account at the beginning, i.e. at the stage of product design. Design for environment (DFE) is an emerging discipline that attempts to deal with this aspect of the problem. DEE requires that products be designed not only for performance and low manufacturing cost, but also for long life, efficient disassembly, and remanu facturability, and - where remanufacturing is not possible - for efficient recycling.

Clearly the problem of increasing materials productivity raises an enormous number of peripheral issues with respect to needed material performance characteristics. The present chapter deals primarily with the latter.


As a point of departure, we begin with a truism: every substance extracted from the earth's crust, or harvested from a forest or fishery or from agriculture, is a potential waste. Not only is it a potential waste; in almost all cases it soon becomes an actual waste, with a delay of a few weeks to a few years at most. The only exceptions worth mentioning are long-lived construction materials. In other words, materials consumed by the industrial economic system do not physically disappear. They are merely transformed into less useful forms.1

Table 4.1 World production of metal ores, 1993


Gross weight of ore(million m.t.)

Metal content (%)

Net weight of metal (million m.t.)

Mine and mill wastea (million m.t.)









































Platinum groupb

» 50



» 50

Uranium (1978)c










Data source: Minerals Yearbook 1993.

a. Extrapolated from US data on ore treated and sold vs marketable product for 1993, using same implied ore grade.
b. Based on ore grades mentioned in text for mines in South Africa only.
c. Based on Barney (1980). No current data available.

In some cases (as with fossil fuels) they are considerably transformed by combination with atmospheric oxygen. In other cases (such as solvents and packaging materials) they are discarded in more or less the same form as they are used. It follows from this simple relationship between inputs and outputs a consequence of the laws of physics 2- that economic growth in the past has been accompanied by growth in waste generation and pollution.

Apart from fossil fuels, however, enormous quantities of minerals and metal ores are extracted from the earth's crust. Table 4.1 shows world consumption of concentrated (or selected) metal ores and metals,3 and the rate of extraction is increasing rapidly (fig. 4.1).

Annual production (i.e. extraction) of metals in the United States is more than 1.5 tonnes per capita (down from a maximum of close to 2 tonnes in the early 1970s). However the decline merely reflects the fact that the United States is increasingly dependent on imported ores or metals. Allowing for ores processed elsewhere, the real US consumption level is now more than 2.5 tonnes per capita. Consumption levels in Europe cannot be much less, though figures are harder to find.

Each tonne of refined metal involves the removal and processing of at least 4 tonnes of ore (in the case of aluminium) and up to several thousand tonnes of gangue and overburden, in the case of uranium, platinum group metals, or gold. These figures rise over time because the best grades of ore are used first. Thus, other factors remaining equal, energy consumption and costs of exploration, extraction, and beneficiation per unit would tend to rise over time. Only technological progress could compensate for this trend. The fact that resource prices have, on average, declined over many decades is regarded by resource economists as a strong indication of the power of technology - called forth by free markets - to keep resource scarcity at bay (see Barnett and Morse 1962; Smith 1979). It must be said that the neo-Malthusian worries about resource scarcity do not appear to be a near-term threat to economic growth, as has been suggested at times in the past.

Fig. 4.1 World metals mining, 1700-1980 (Note: * denotes continuous production without historical data. Source: Josef Pacyna, "Atmospheric trace elements from natural and anthropogenic sources," in J. O. Nriagu and C. 1. Davidson (eds), Toxic Metals in the Atmosphere, New York: Wiley, 1986)

Other threats are more immediate. The mining, beneficiation, and smelting of metal ores are inherently dirty. Even though modern technology permits the capture of most toxic waste pollutants from the process, these materials must still be disposed of somehow. A number of very toxic metals are byproducts of copper, zinc, and lead, for instance. These include arsenic, bismuth, cadmium, cobalt, selenium, silver, tellurium, and thallium. Although many of these metals are recovered for use in other commercial products, the products in question - from pesticides, herbicides, fungicides, and wood preservatives to pigments and batteries- are almost entirely dissipated or discarded after use. (Toxic heavy metals are also dispersed into the environment via coal ash, which contains significant quantities of them.)

Non-metallic chemicals too are dissipated and lost either in use or after use. Such materials also constitute increasing pollution loads, with unknown environmental and health implications.

Until recently the only response to increasing pollution of the environment has been essentially localized "end-of-pipe" treatment. However, traditional approaches to pollution control seldom eliminate the wastes. They normally attempt to shift the wastes from a place where they can do harm to a place where they are less likely to do so. In some cases they are converted from a dangerously harmful form to a less potentially harmful form or location. Indeed, regulation has, in some cases, encouraged the recovery and treatment of wastes from one medium, only to find them reappearing in another. For instance, the burning of solid wastes may generate air pollution. Air pollutants, especially particulates and oxides of nitrogen and sulphur, can be (re)deposited on land via rainfall, only to be carried into rivers and streams via surface runoff.

The only possible way to reach a sustainable state is to find ways of using materials more efficiently in the first place, i.e. to begin to evolve closed (or nearly closed) materials cycles. In other words, we must learn how to get much more functional "bang for the buck" from materials - and not just the "high-tech" materials that get most of the attention. In this paper we adopt an engineering-technological perspective to increasing materials productivity, as described in the next section.

Strategies to increase materials productivity

In brief, there are three elements to the long-term materials productivity programme. The first is to reduce, and eventually eliminate, inherently dissipative uses of non-biodegradable materials, especially toxic ones (such as heavy metals). This involves process change and what has come to be known as "pollution prevention" via "clean technology." The second is to design products for easier disassembly and re-use, and for reduced environmental impact, known as "design for environment" (DFE). The third is to develop much more efficient technologies for recycling consumption waste materials, so as to eliminate the need to extract "virgin" materials that only make the problems worse in time.

It is not really necessary to describe in detail how this can be accomplished. It is sufficient to know that it is technically and economically feasible. (It remains, still, for policy makers to create the appropriate incentives to harness market forces. But this is a separate topic.) Of course, specific "scenarios" might be helpful in making such a conclusion more credible to doubters. However this would serve a communications purpose rather than an analytic one.

Returning to the specifics, we note four basic strategies for raising the productivity of material resources. These four generic strategies are:

1. "Dematerialization": more efficient use of a given material for a given function. This can be achieved by increasing performance, reducing the need for materials by means of improved processing quality control, and/or better design. For instance, the need for built-in safety factors in many applications was established many years ago in terms of crude "rules of thumb." Computeraided design (CAD), together with improved quality control, now permits significant reductions in materials thickness (and weight) for many structural purposes - from engines to aircraft wings to buildings without compromising safety. In addition, there has been very rapid progress in recent years in micro-electronics and micromachines. The minimum scale of electronic devices has decreased by at least a factor of 104 (to 0.5 microns) while the scale of machines has fallen by a factor of 100 (to 100 microns). The density of information storage capacity (i.e. computer memories) has increased by around two orders of magnitude per decade for the past four decades, and the rate of progress has not yet shown any tendency to decline.

2. Substitution of a scarce or hazardous material by another material. Again, either technology or policy can drive such a shift. For instance, cadmium has been largely eliminated from PVC stabilizers and pigments. Lead pipes for water were replaced long ago by copper pipes. Lead arsenate has been eliminated as a pesticide for orchards; lead has also been phased out (to a large extent) as a pigment for exterior paints, and as an anti-knock additive for gasoline. It is also gradually being phased out of applications for soldering compounds and bearings. Similarly, mercury has been phased out of most uses as an anti-mould or anti-fungal agent (e.g. in paint) and in batteries - formerly its biggest use. It is also slowly being phased out of chlorine manufacturing.

3. Repair, re-use, remanufacturing, and recycling. For convenience we refer to this simply as the "recycling" strategy. Obviously all of these variants tend to reduce the need for virgin materials and (indirectly) all of the environmental damage and energy consumption associated with the extraction and processing of virgin materials, including their toxic byproducts. Diesel engines are routinely remanufactured. The same could be done for automobile engines and other complex subassemblies, such as universal gears, transmissions, and compressors. One of the most attractive underutilized candidates for remanufacturing is tyres. Aluminium cans, stainless steel automotive components, copper wire, and galvanized iron/steel are particularly good examples of candidates for more recycling. Arsenic and cadmium exemplify toxic by-products (of copper and zinc mining) that could be reduced thereby.

4. "Waste mining": utilization of waste streams from (currently) unreplaceable resources as alternative sources of other needed materials. This strategy simultaneously reduces (a) the environmental damage due to the primary waste stream, (b) the rate of exhaustion of the second resource, and (c) the environmental damage due to mining the second resource. One attractive possibility is the use of so-called flue gas desulphurization (FGD) "scrubber" waste, which is virtually the same as natural gypsum, to manufacture plasterboard. Metallurgical slag is used for paving roads, but it can also be reprocessed into insulation competitive with fibre glass. Coal ash can be used in concrete products, or even as a source of aluminium and ferro-silicon. Phosphate rock processing waste can be a source of fluorine chemicals used in the aluminium industry (it already is in the United States). And so on.

All of the above strategies can be further subdivided into two categories, namely technology (and economics) driven or policy driven. They are summarized, with examples, in the 4 x 2 matrix below. The choice of materials productivity strategy in each case will depend on economics and the available technology. We now review some areas of changing materials technology.

1A De-materialization, technology driven Example: microminiaturization in the electronics industry.

1B De-materialization, policy driven Example: imposition of Composite Average Fuel Economy (CAFE) standards for automobiles in the 1970s (USA) led to significant reductions in vehicle weight.

2A Material substitution, technology driven Examples: substitution of PVC for cast iron or copper water/ sewer pipe in buildings; substitution of optical fibres (glass) for copper wire for point-to-point telecommunications

2B Material substitution, policy driven Examples: ban on CFCs leading to replacement by HCFCs or HFCs in air conditioners and refrigerators; ban on tetraethyl lead (TEL) leading to substitution by aromatics and alcohols (e.g. MTBE) as octane enhancers in gasoline.

3A Recycling, technology driven Examples: recycling of lead from starting-lighting-ignition (SLI) batteries used in motor vehicles; recovery of catalysts from catalytic convertors.

3B Recycling, policy driven Mandatory minimum levels of recycled pulp in paper products, e.g. in Germany; recycling of aluminium cans, Sweden; recovery of mercury from fluorescent lights, Sweden.

4A Waste "mining, " technology driven FGD for oil and gas refineries with recovery of elemental sulphur; recovery of fluosilicic acid from phosphate rock processing wastes in the Unites States.

4B Waste "mining," policy driven Enforcement of FGD in non-ferrous metal smelters, with recovery of sulphuric acid; enforcement of FGD for electric power plants, with recovery of lime/limestone scrubber waste for use in wallboard production, Denmark

Materials technology

Diversity is the most noteworthy characteristic of materials. It seems sensible, therefore, to begin this section with a taxonomy. The following is taken from the Table of Contents of a standard reference work (Lynch 1975):

Ferrous Alloys
Light Metals
Aluminum-Base Alloys
Nickel-Base Alloys
Other Metals
Glasses and Glass Ceramics
Alumina and other Refractories
Electronic Materials
Nuclear Materials
Biomedical Materials
Graphitic Materials

The list can be further expanded. For instance, composites can be subdivided into metal matrix composites, ceramic matrix composites, and polymer matrix composites. Even a cursory summary of all these technologies in a short chapter is bound to be unbalanced and, in many ways, unsatisfactory. One can scarcely hope to do more than pick out a few salient topics.

A selection principle is urgently needed. It is therefore probably useful to start with the observation that the present economic importance of the material categories is virtually inverse to their present day interest from a research perspective. Natural materials such as wood, paper, rubber, leather, cotton, wool, stone, and clay are still enormously important in the world economy, but they are declining in importance, if only because newer alternatives are increasingly available (Larson et al. 1986). The same is true of the "old" metals copper (bronze, brass), lead, zinc (pewter), tin, silver, and gold.

From the research perspective, iron and steel, too, have largely had their day in the sun. The technology of iron smelting was essentially fully developed by the 1830s. The steel industry burst into prominence after 1860, after a long accumulation of incremental improvements in furnace design and metallurgy culminated in the great innovations of Bessemer, Kelley, Mushet, Siemens, Martin, and Thomas.

The metallurgy of steel and ferro-alloys progressed rapidly for the next half century or so. However, although significant process improvements have continued since World War II, illustrated in figure 4.2, the potential of iron based alloys technology has been largely (albeit not entirely) exhausted.4 Newer technologies in this area include direct casting of strip (which cuts energy consumption) and wider use of high-strength low-alloy (HSLA) steels, which cuts the weight of structures such as auto and truck chassis.

Aluminium was a curiosity metal until the simultaneous invention in the 1880s (by Hall in the United States and Heroult in France) of a practical electrolytic reduction process. This process is still universal in the industry, though improved processes have been developed to the pilot stage. The problem for aluminium is that - aside for aircraft and structural components that can be produced by rolling, bending, or extrusion without machining (such as roof panels, window frames, and cans) - it is currently too expensive to substitute for steel for most uses. However, this limitation is now gradually being overcome in the auto sector, where aluminium is beginning to substitute for steel and even cast-iron (for engines). This substitution would likely accelerate in the event that light-weight battery-powered electric cars become more popular. The fact that aluminium is relatively easy to recycle (for example, cans) is a positive indicator for this development.

Since World War II, research emphasis in materials science has shifted to polymers, ultra-light composites, and special materials for limited applications such as semiconductors, supermagnets, superconductors, hard surfaces, and nickel- or cobalt-based "super-alloys." Most of these developments have been driven by military or aerospace requirements (for electronic equipment, airframes, and jet engines, for instance). In any case, copper, steel, and aluminium metallurgy - whether moribund or not - will not be considered further in this chapter. Nor will we discuss the properties or production processes of other old materials, including concrete, glass, wood, or paper.

To be sure, any of the "old" materials may enjoy a revival, in terms of research interest, because of either a new method of processing (e.g. plywood or fiber board) or a new use (e.g. the superconducting properties of certain tin alloys). But, given the necessary brevity of this chapter and the enormous scope of its coverage, it seems justified to start by eliminating this group from further consideration.

Fig. 4.2 Process improvements in metallurgy, 1953-1974 (Source: NAS/NRC 1989)

Material attributes

In general, material science is all about performance. It is tempting, at times, to try to measure technological progress for materials in terms of simple measures such as "tensile strength." Yet, even a moment's thought suggests that there are many other properties of importance. Each application calls for a different combination of properties. Generally speaking, it is the combination that matters. One of the attractive virtues of plastics - apart from light weight - is that customization of desired combinations has proven to be relatively easy (as compared, for instance, with metals or ceramics).

This point is especially well illustrated in the case of synthetic fibres. By and large, polymer-based materials have not (to date) competed significantly with metals. They do compete, in general, with wood, paper, natural rubber, and natural fibres. Recent developments in so-called "engineering" plastics have extended their range of competitiveness. Polymers that conduct electricity now appear to be very close to commercial realization.

The first "synthetic" fibres in the 1893-1895 era were cellulose based (viscose rayon and cellulose acetate). The rayon industry boomed in the 1920s and 1930s. Later, completely man-made fibres were introduced, beginning with nylon (1935); see table 4.2. An effort to discern some meaningful trend was made by a "futures" consulting organization (Gordon and Munson 1982). A panel of experts identified four parameters as being "important" for synthetic fibres. The panel weighted the four attributes as follows:


Panel weight

Tensile strength (g/denier)


Elastic recovery (% recovery from % stretch)


Modulus (g/denier)


Moisture regain (%)



A comparison of the major man-made fibres is given in table 4.2 and figure 4.3. It is obvious that the index constructed from the above parameters, weighted as indicated a priori by the panel, does not explain the success of newer fibres. In fact, an early form of rayon (cuprayon) introduced in 1894 is superior to all the more recent fibres but one in terms of the composite index. Clearly, a number of other (perhaps less quantifiable) factors such as "feel" are important. Moreover, the optimum "mix" of factors evidently varies significantly from one fibre use to another. The salient feature of recent developments in this field is probably diversity itself.

Table 4.2 Man-made fibres data


Year of introduction

Tensile strength (g/denier)

Elastic recovery (% recovery from % stretch)

Modulus (g/denier)

Moisture regain (%)















































































Arnel 60






























Source: Textile World, Man-made Fiber Chart, various years.

Much the same point can be made about other categories of materials. Although alloy steels have not been getting significantly stronger or harder, in recent decades the number of specialized steel alloys with different combinations of properties continues to grow. The same trend is even more pronounced for other metal alloys, refractories, and ceramics, and for polymers and composites. In many instances properties such as fracture toughness have significantly increased owing to improvements in processing.

Material performance trends

We have noted already that the areas of greatest research interest in materials science and engineering are not necessarily the areas of greatest current economic importance. Having said this, however, it is of interest to look at recent trends in three of the areas of current economic interest, namely high-temperature materials, light weight materials, especially high-strength composites, and "electronic" materials. Potential areas of future application will be noted.

Fig. 4.3 Man-made fibres performance index when values are non-dimensionalized by scaling between 0 and 1 (Source: Gordon and Munson 1982)

High-temperature materials

A requirement common to many material uses is a combination of toughness (i.e. ductility), strength at high temperatures, inflammability, corrosion and oxidation resistance, and minimum weight. Early uses for such materials were mainly for high-speed drilling and cutting tools (hence, "high-speed" steels). Jet engines and gas turbines currently exemplify this requirement. The essential point is that increased fuel economy and higher thrust-to-weight ratio are achieved by operating at higher temperature and pressures. A 150°F increase in inlet temperatures yields a 20 per cent increase in thrust (Clark and Flemings 1986). (For comparison, the thrust-to-weight ratio for large jet engines has somewhat more than doubled in the past 30 years; Steinberg 1986.) Airframes and re-entry vehicles (RVs) also require a combination of high strength and low weight at high temperatures. Increased fuel economy for aircraft is obviously very important in terms of increasing long-term resource productivity.

Two radically different cases can immediately be distinguished, depending on whether exposure to air is also essential or not. Thus carbon fibre, one of the strongest and lightest of all materials, cannot be used in engines, for instance, because of its combustibility. On the other hand, non-metallic refractories such as oxides, carbides, or nitrides are quite strong and not affected by the presence of oxygen. On the other hand, they tend to be brittle, i.e. they lack ductility. Thus, two major lines of development can be discerned. The first is metallurgical. The problem is to find metallic alloys with better combinations of strength and ductility for applications in oxidizing environments, especially for turbine engines.

Here again, a panel of experts identified three relevant parameters (taking non-flammability for granted) and weighted them (Gordon and Munson 1982):


Panel weight

Rupture strength


Creep strength





Table 4.3 High temperature materials: Non-dimensionalized parameters and performance index



Rupture strength

Creep strength















Nimonic 80A






Nimonic 90












M 252






Rene 41












GMR 235






Alloy 713c






Udimet 700






Nimonic 105






Nimonic 115


















Alloy 7131C






MM 509






MM 246












MM 200 (DS)












Source: Gordon and Munson (1982).
Note: Index weight factors 1/3 each.

Data for a number of high-temperature alloys introduced since World War II are shown in table 4.3. In this case (since the application is relatively unchanged), the single composite index, illustrated in figure 4.4, seems to have some explanatory power. However, even here there were two different applications, namely turbine blades and vanes.

For turbine blades, nickel-based alloys were preferred because of higher strength and stress resistance, whereas for vanes, cobalt-based alloys were preferred (because of reduced environmental degradation). The only three cobalt-based alloys in the study were S-816, MM 509, and HA-188. They show almost no upward trend in the composite index. There was a clear and rapid upward trend in the index of performance for nickel-based alloys, on the other hand, up to the mid-1960s. Since then, improvements have been achieved mainly by the use of directional crystallization techniques in the investment casting process. Incremental improvements in high-temperature metallurgy have permitted gas turbine operating temperatures to increase at the rate of 10-12°F (about 6-7°C) per year since the 1960s (Clark and Flemings 1986). The development of gas turbines in the 120-150 MW range with turbine inlet temperatures of 2,600°F is envisioned, thanks to developments in advanced casting systems.

Fig. 4.4 High-temperature materials performance index (Source: Gordon and Munson 1982)

Fig. 4.5 The steep climb m operating temperatures made possible by modern materials

The alternative line of research in high-temperature materials is focusing on advanced ceramics, such as silicon carbide, silicon nitride, and lithium aluminium silicate. Concern over possible shortages of cobalt, chromium, and other so-called "strategic" metals played a major role in accelerating the research effort in this field in the 1970s. Figure 4.5 shows the continuing trend in high-temperature materials capabilities. Based on their known properties, ceramic-matrix composites seem to offer a potential of raising turbine inlet temperatures from about 1,850°F (1,000°C) to as much as 2,700°F or about 1,500°C (Clark and Flemings 1986). This would increase theoretical maximum turbine fuel efficiency, if realized, by around 27 per cent.

As of 1996, the major applications of structural ceramics are still for cutting tools and mechanical seals. However, a decade ago ceramic automobile turbochargers were already being produced by Nissan in Japan and ceramic glow plugs and pre-combustion chambers for diesel engines are being made by Isuzu (Robinson 1986). Ford and Garret Corporation were about to test a 100 hp gas turbine engine with a metal housing and ceramic parts in contact with the hot gases (Robinson 1986). However, little further progress has been reported since then, at least in terms of practical applications.

Fig. 4.6 Typical strength variability curve for a ceramic (Source: NMABNRC 1975)

The problems of utilizing advanced ceramics such as silicon nitride for engines or other purposes where they compete with metals are not so much their well-known brittleness (i.e. lack of ductility) as their low fracture toughness and tendency to fail unpredictably. This, in turn, is because the distribution of microscopic defects - which concentrate and propagate stress cannot be predicted a priori, owing to scatter in the experimental data, as shown in figure 4.6. A theoretical possibility is to "proof test," namely to test all ceramic parts up to a certain level of performance and throw away those that fail. This greatly decreases the odds of random failure among the survivors, as shown in figure 4.7. However, under present conditions, yields are likely to be less than 20 per cent, which is far too low. Until yields of 70 per cent or better can be achieved in practice, the economics of advanced ceramics will remain unfavourable.

Part of the problem of unpredictability may have its origin in the traditional techniques of compaction and hot pressing (sintering). The quality of the product is dependent on the size of distribution and uniformity of the starting material. New processing techniques such as "sol-gel" processing may offer hope. A "sol" is a colloidal suspension of particles in sizes from 1 to 100 nanometers. As the "sol" loses liquid, it gradually becomes a "gel." Although the concept is old, this technique has been widely practiced for only about three years, and its popularity is growing rapidly (Robinson 1986). New approaches in the field of ceramic matrix composites are enhancing the fracture resistance of ceramics.

Fig. 4.7 Effect of a uniform tensile proof test on failure probability of a bar in bending (Source: NMABNRC 1975)

However, this growing interest in chemical-based techniques can be interpreted as evidence that the older physics-based techniques are reaching a dead end. At present, it appears safe to predict that advanced ceramics will rapidly grow in economic importance, but that they will not become serious competitors with metals (e.g. in auto, diesel, or jet engines) for at least another decade. This means that major technical improvements in engine performance - hence fuel economy - especially in large-scale applications cannot be expected for at least another 10 years, if not more. In the interim period, metal-matrix composites that contain ceramic particles or fibres will result in small incremental improvements in engine performance.

Strong light materials

De-materialization depends to some extent on the substitution of lighter materials for conventional ones, especially in structural applications. Strength-to-weight and (Young's) modulus-to-weight are obviously important characteristics in this context. For most practical purposes "strength" is a combination of two characteristics, namely resistance to stretching and resistance to bending (stiffness). The first is commonly measured in terms of the amount of pulling or tensile stress required to cause the sample to break (usually measured in psi, or pounds per square inch, of cross-section). The second is measured in terms of the tensile stress required in principle to stretch the sample to twice its original length, also measured in psi. This number is called "Young's modulus." For purposes of comparison, typical values of breaking strength and stiffness for standard engineering materials are as follows:

Tensile strength (x103) psi

Stiffness (modulus) (x103) psi

Wood (spruce, along grain)






Glass (window or bottle)






Carbon steel (mild)



In principle, it seems obvious that these numbers must bear some relation to the attractive forces between atoms of the material. But if only inter-atomic forces were involved, materials should be 10 to 50 times stronger than they actually are. Very careful experiments in the 1940s and 1950s showed that flawless microscopic crystals or whiskers or very thin fibres of glass approached theoretical breaking strength much more closely than macro materials (Gordon 1973). Figure 4.8 shows that the strength-to-density ratios of today's engineering materials have increased by more than 50-fold, as compared with materials available at the beginning of the industrial revolution. This trend can be expected to continue for some time to come.

In the 1950s, theory (supported by newly available empirical data from Xray microscopy and other new research tools) began to catch up' and the essential mechanisms of defect propagation in brittle materials and "crack-stopping" behaviour in ductile metals and natural composites (such as wood and bone) were finally understood (Gordon 1973). "Composites" are composed of two or more components, namely very strong small fibres (oriented or not) embedded in a much weaker matrix. A factor of 5 or so difference in strength between the two components is actually essential. This insight opened the door to synthetic composites, of which the first commercially important one was fiber glass-reinforced plastic (FRP). FRP is still by far the most important composite commercially, but by the beginning of the 1970s a large family of new high-performance composites had been developed, largely by the aerospace industry.

Fig. 4.8 Progress in materials strength-density ratio, showing a 50-fold increase (Source: NAS/NRC 1989)

The key to a practical composite material is the stronger and stiffer component, which can be a glass fibre, a mineral crystal such as sapphire (Al2O3), or boron (B), or graphite (C) fibre, a metallic crystal ("whisker"), or even a complex structure consisting of a silicon carbide-coated boron fibre or a core of thin (e.g. tungsten) wire on which a coating of boron (B) or a boron carbon compound (B4C) has been vapour-deposited.

For almost all commercial applications, the matrix or binder is an epoxy or phenolic resin that can be easily moulded. However, if the composite material must also be heat resistant and non-inflammable, only mineral materials or metals can be used. In such cases, manufacturing techniques may be similar to those used in ceramic manufacturing (casting, powder compaction, followed by isostatic compression and sintering). As noted above, recent trends in advanced structural ceramic applications research suggest that physical techniques may be supplanted by chemical methods, such as the "solgel" method (Robinson 1986).

Another approach to the creation of metallic composites is to arrange a two phase system of metallic crystals with the requisite difference in strength and stiffness. Such a system can be created by powder-forming techniques (metalmatrix composites) or by dissolving one metal in another and allowing it to crystallize as a separate phase within the melt under controlled conditions. The result is called a eutectic or "intermetallic" alloy. A number of combinations have been identified that have the requisite characteristics (e.g. Lynch 1975). In recent years a great deal of attention has been given to composites with intermetallic compounds as matrix materials reinforced by strong fibres. The most promising example at present is nickel aluminide (Ni3Al), with small amounts of boron added to increase cohesion and small amounts of hafnium to increase yield strength (Claasen and Girifalco 1986). Other promising matrix materials include NiAl and TiAl.

The list of possible metal-matrix composites and eutectics may get much longer in time, but it is difficult to say whether significant improvements in absolute performance are likely. In any case, the primary objective of R&D over the next few years is to improve predictability, consistency, and formability, in order to decrease the cost per unit performance. Well over a decade after their initial introduction into the aerospace industry (for specialized uses in military aircraft and spacecraft), ultra-strong graphite-based composites finally appeared in a few selected commercial products such as tennis rackets, skis, and golf clubs in the late 1970s. They are gradually increasing market share as prices come down and designers learn how to utilize the new materials to best advantage. However, there are many other potential "civil" applications where strength, light weight, and corrosion resistance will make a difference. Bicycle frames, motorcycles, and small light aircraft would probably be the next obvious applications, followed by substantial use in commercial aircraft.

In principle, composites can replace aluminium for most of the structural parts of any aircraft, including the exterior "skin," and a significant part of the engine. Even small savings in weight in aircraft (or spacecraft) have a significant pay-off in terms of fuel economy or, equivalently, increased payload.

Undoubtedly, these materials will ultimately have a significant impact on the economics of air transportation. Commercialization has been slow, up to now, because of the long product "life cycle" in the aircraft industry, the specialized knowledge involved, and the fact that most of it was initially proprietary to the aerospace industry. All of these factors result in rather high costs. However, most of the basic patents have already expired and the key "process'' patents are currently expiring. This will open up the field to more intense competition. It can be expected that the ratio of "composites" to metals in newly designed subsonic aircraft will rise rapidly through the 1990s. For example, all the control surfaces on the Boeing 757 and 767 aircraft are made of graphite-epoxy composites, yielding a saving of 856 lb in weight and a 2 per cent saving in fuel (Clark and Flemings 1986).

Beyond aircraft applications, there will eventually also be important applications in automobiles. Until 1980 or so, only fiber glass (FRP) had found a significant automotive use (in the Chevrolet Corvette body). But an increasing number of bumpers and body panels and some complete metal automobile bodies are being replaced by unreinforced thermoplastic polymers, so the first major opportunity for lightweight composites may be to replace steel in the chassis and frame. The overall proportion of plastics in the weight of an average auto has increased quite sharply in recent years - it is now between 10 and 15 per cent - and this ratio can be expected to continue to grow in the future. Use of plastics in automobiles will accelerate if ways are developed to recycle the plastics more effectively than at present. (Currently, the plastics from junked cars are mainly dumped in landfills or incinerated, whereas the metals are largely recycled.)

Meanwhile, as noted above, ceramics may ultimately replace much of the metal in the conventional auto engine, and high-strength low alloy steel will continue to replace mild steel in chassis and frame. The benefits of weight reduction in automobiles (and trucks) are not as great as in the case of aircraft but are nevertheless significant. Most of the increased fuel economy observed in automobiles since 1970 is attributable to lighter weight and better tyres - not to more efficient engines. However, it is clear that a great deal remains to be learned about large-scale manufacturing with composite materials before they can replace metals in mass-produced products.

Up until now, the auto industry has not invested much effort in this field. In view of the long lead-times in the industry, polymer-matrix composites (except FRP) cannot be expected to begin to replace steel in major automobile structural parts such as the chassis and frame until probably after 2010. However, ultra light metal-matrix composites such as aluminium-silicon carbide are beginning to replace old materials such as cast-iron in brake rotors, brake calipers, and engine blocks. The use of aluminium and magnesium will significantly increase in the next generation of motor vehicles, which will be half to two thirds the weight of the current generation of cars. The weight reductions, together with engine performance improvements and continuing aerodynamic improvements (thanks to CAD) and continuing tyre performance improvements, will cut fuel consumption per vehicle-kilometre by at least a factor of two.

Another application would be for second-generation supersonic aircraft, now being developed by several countries. Such an aircraft would probably utilize up to 50 per cent polymer-matrix composites, plus 10 per cent meta-matrix composites, 15 per cent aluminium lithium alloy, and 25 per cent other metals such as steel, aluminium, and titanium (Steinberg 1986).

Electronic materials

The category of electronic materials includes "ordinary" conductors, semiconductors, superconductors, photoconductors, photoelectrics, photovoltaics, photomagnetics, ferromagnetics, diamagnetics, paramagnetics, magnetostrictives, piezo-electrics, laser materials, and a host of others. Even a brief summary of the physical phenomena involved would be far too long for a chapter such as this.

Since the development of the transistor in 1947 - as a substitute for the electron tube or "vacuum tube" - research in the field of semiconductors has grown spectacularly. The rapid growth of basic knowledge about the materials has been driven by burgeoning demand for electronic devices, from telephone switchboards to radio, television, radar, sonar, and computers. The last application has proved the most important, especially after the successive development of integrated circuits (c. 1960) followed by the "microprocessor" (c. 1970), and then large-scale integration (LSI), very large-scale integration (VSLI), and now ultra large-scale integration (ULSI). Table 4.4 summarizes these dramatic changes.

One of the key technological driving forces, whose impact seems to have been consistently underestimated, is the close relationship between operating speed, power consumption, cost, and scale. The original motivation for the invention of the transistor was to cut down on the electric power consumption of the telephone switching systems. Miniaturization and large scale required the solution of many difficult technological problems such as controlling even smaller line widths (fig. 4.9). However, as these technical problems were solved, it proved to be a powerful cost-cutting strategy, because manufacturers' sharply declining semiconductor circuitry costs, in turn, generated steady increases in demand, including wholly new applications (fig. 4.10).

Table 4.4 The development of semiconductors

Integrated circuit

Period of diffusion

Vacuum tube to 1945










lntegration (elements per unit or per chip)

1 unit

1 unit








Functions per unit or per chip






Reliability per function






Price per function(per chip or per unit)






Source: NIRA (1985).

Fig. 4.9 Changes in the scale of integration and minimum line width (Data source: Electronic Industries Association of Japan)

The growth of demand for more "computer power" seems to be continuing unabated, as costs continue to fall. In fact, major new categories of computer and communications applications, such as voice processing, vision processing, and "artificial intelligence," are just beginning to emerge (table 4.5). The silicon chip continues to dominate all challengers; its eventual replacement by other more exotic materials continues to be delayed into the indefinite future. However other (faster) semiconductor materials, such as gallium arsenide, may eventually have their day.

Fig. 4.10 Changes in computing power and computer usage (Source: Moravec 1991)

It is literally impossible to forecast with any confidence the "winners" and "losers" in this intense competition. A few conclusions can be drawn, however:

- Switching speeds and micro-miniaturization can still be increased by orders of magnitude, in principle, exploiting optical technologies now becoming ever more important (table 4.6).

- Manufacturing techniques are becoming more and more critical. The need for microscopic tolerances and ultra-low levels of impurity contamination require increasingly sophisticated (and expensive) and totally automated robotics facilities.

- Design complexity is becoming the limiting factor. Sophisticated CAD is already essential for "chip" design and every successive generation of more powerful memory or microprocessor chips5 will certainly require correspondingly more powerful CAD software, probably including artificial intelligence (AI) to perform some of the functions performed by human designers at present. This, in turn, will emphasize the role of the very few research institutions capable of assembling a "critical mass" of front-rank AI researchers, applied mathematicians and logicians, and electronics and software specialists.

For the above reasons, the semiconductor, telecommunications, computer, and software industries are now inextricably linked and marching together. "New starts," small firms, and small countries are now essentially out of the game, as far as leading-edge microelectronics technology is concerned. (This is not true for software, of course.)

One of the major apparent opportunities for research in the field of electronic materials has been superconductors.6 The advent of a practical commercial helium liquefied in the early 1950s resulted in an explosion of exploratory research in this field. Only a few superconductors were known up to that time, but by 1970 several hundred superconducting compounds and alloys had been identified. Moreover, by that time superconducting magnets were being sold commercially (by Westinghouse). Such magnets are now standard laboratory research tools, and will be used for any new large particle accelerators or, probably, for future magnetic levitation ("mag-lev") rail systems.

Table 4.5 Breakthroughs expected in electronics


Technological need

Current technology

New technology

Performance comparison


Large-volume transmission



10 times


High-speed processing

Silicon LSI


5-6 times

Josephson-junction device

At least 10 times

High-density memory

Horizontal magnetic recording

Perpendicular magnetic recording

At least 10 times

Larger-scale integration devices

Planar integration

Three dimensional circuit devices


Instrumentation and control

Improved sensitivity


Josephson junction device


Improved resolution


Ultrasonics (microscope)

(1 An or less)

Source: Hitachi Research Institute (n.d.).

Table 4.6 Breakthroughs expected in optics


Technological need

Current technology

New technology

Performance comparison


Large-volume transmission

Milliwaves (1011 Hz)

Laser light (1014 Hz)

1,000 times

Long-distance transmission (relaying distance)

Electromagnetic waves (1 km)

Laser light (10-100 km)

10-100 times

Transmission cost reduction (cable weight)

Coaxial cable (130 kg/m)

Optical fibre cable (70 g/m)

About 1/2000


High-speed processing

Josephson junction device (6-7 pieoseconds)

Laser light (10 picoseconds)

0.6 times

Intra-CPU transmission (data volume/second)

Sequential processing

Parallel processing

Several dozen times

Spatial image information- processing

Unidimensional development needed

Parallel processing of two-dimensional image possible

Advantageous for image information processing

High-density recording

Perpendicular magnetic recording (TOM bits/cm2)

Magneto-optic recording (20M bits/cm2 minimum)

At least 2 times

Instrumentation and control

High reliability:

Light is advantageous

Electromagnetic interference






Short circuits



Source: NIRA (1985).

On the other hand, the cost of liquid helium has not fallen significantly since 1960 and is not likely to. Many once active projects such as the development of a superconducting computer (IBM) have been dropped. As of 1975 the highest known critical temperature (Al0.8Ge0.2Nb3) was only 20.7°K, which was still below the boiling point of liquid hydrogen (22.7°K).

The first sign of a major breakthrough was the discovery in 1986 of a new class of barium-copper-lanthanum oxide superconductors, which achieved superconductivity at 35°K. In January 1987 partial superconductivity in a similar compound was reported at 52°K, under very high pressure. Only a few weeks later another metallic oxide compound was reported to be super conductive at 98°K. More discoveries are to be expected. Dozens of laboratories around the world are now said to be searching for new compounds capable of superconductivity at even higher temperatures, and many physicists are now optimistic about the possibility of achieving superconductivity at room temperature (Sullivan 1987).

However the 77°K barrier, which has now been exceeded, was the truly significant one. Below that temperature only liquid helium is a feasible coolant (except in space), whereas above that point liquid nitrogen (77°K) can be used. Liquid nitrogen is available in industrial quantities as a by-product of the production of liquid oxygen used by the steel industry and for rocket propulsion. It costs only 10 per cent as much as liquid helium and is far less volatile. Thus, it is now realistic to think in terms of large-scale applications of superconductivity, e.g. power generation and transmission and magnetic levitation of high-speed trains. Neither of these applications is imminent. However, on a time scale of 50 years, both are rather good bets.

Photovoltaic (PV) materials are another category of potential importance as solar cells. Major candidates include silicon (crystalline or amorphous) and thin films. The latter may be made from gallium arsenide, copper indium diselenide, cadmium telluride, or other combinations not yet discovered. Silicon is by far the most widely used, at present, with achievable solar conversion efficiency of nearly 20 per cent for the crystalline form. Amorphous silicon has achievable conversion efficiency of at least 15 per cent, but it can be manufactured at much lower cost. Laboratory cells have already achieved over 30 per cent conversion efficiency, using concentrator cells, and 40 per cent or more is now regarded as likely by the end of the 1990s.

Some experts think that an 80 per cent conversion rate for sunlight to electricity is ultimately conceivable. This development is of the greatest possible importance. Each unit of electricity generated by photovoltaics instead of coal-burning eliminates emissions of sulphur and nitrogen oxides, volatile organics, coal ash carrying toxic trace metals, and carbon dioxide into the atmosphere.

Apart from progress in the fundamental science, there has been very rapid progress on the technological side. A number of new techniques for coating thin films of semi-conductive materials onto a glass (or other) substrate have been developed, e.g. by Mobil-Tyco, Westinghouse, and Honeywell. Spectacular progress has also been made in reducing film thickness by a factor of 100, as compared with early cells (Zweibel 1987).

NASA, DOD, and Bell Laboratories supported much of the early R&D work in this field to obtain long-lived solar cells for application in satellites. The first solar cells, used mainly by NASA, cost US$1,000 per watt. An array of solar cells in 1975 cost about US$75 per watt of peak capacity (Wp) compared with US$5 per watt for a large nuclear power plant in 1975US$. The "energy crisis" of 19731974 precipitated an accelerated programme of R&D in this area, focused mainly on bringing down the cost of manufacturing. The US R&D programme was cut back sharply in the 1980s (from US$150 million in 1980 to US$43 million in 1987), but not before major progress had been made, as shown in figure 4.11 (Maycock 1982). The modest goals of US efforts to tap solar energy in recent years have been to achieve a competitive final price level of 6 cents per kWh by the year 2010, with module efficiencies of 15-20 per cent. Up until 1990 or so, the market for solar PV power had been restricted to remote locations and special purpose applications (although the market was clearly growing). But the energy utility industry had not shown much interest. However it now appears likely that some big firms (notably Enron Corp.) have decided to invest in mass production of solar cells with the deliberate intention of bringing the price down more rapidly, perhaps even by 2000. More recent progress in this field is discussed in chapter 7 in this book.

Another important category that is worth discussing briefly is ferromagnetic materials (White 1985). In a way, this is surprising, because the phenomenon of ferromagnetism has been known for such a long time. However, as in the case of "strong materials," the relationship between magnetic fields on the micro (inter-atomic) scale and the macro scale was not adequately understood until the 1940s when Neel, Kittel, and others developed the basic physical concepts that have dominated subsequent R&D in magnetism. The progress in basic physics of ferromagnetism was rapidly translated into increased practical interest, especially because of the growing importance of magnetic materials.

Photovoltaic module and system price goals (Source: Maycock 1982)

Ferrites- a new class of magnetic oxide materials, mainly Fe2O3 were first used for data recording in the 1930s.7 Ferrites also rapidly found applications in transformers, radar, communication equipment, and (by the late 1950s) computer memories. Discrete ferrite "core" memories have long been superseded by high-speed semiconductors; but ferrite-based magnetic tapes and disks remain the major form of read-in/read-out medium- to long-term data storage system. (It is not yet clear to what extent optical storage devices will ultimately replace magnetic devices, if ever.)

New non-iron-based ferromagnetic alloys for permanent magnets also began to be discovered in the 1930s, beginning with the Al-Ni-Co family. This was mainly research by trial and error. In the 1950s Phillips Laboratories produced permanently magnetized ferrites based on iron oxides combined with strontium or barium, aligned in powder form, then compacted and sintered. The rare-earth-cobalt (SmCo5) based permanent magnets (REPMs) were discovered in 1967 and first commercialized by 1970. A second generation series based on Sm2Co17 was introduced around 1981, and an important boron-based compound Fe14Nd2B appeared in 1983.

For permanent magnets there are two important parameters, namely energy product (the amount of stored magnetic energy8) and coercivity (the resistance to reversal or demagnetization by an external field, Hc). Progress since 1900 in these two areas is shown in figures 4.12 and 4.13, respectively. It is interesting to note that the theoretical maximum value of stored magnetic energy for iron would be 107 mega-gauss oersteds (MGOe) (if all the microdomains could be completely aligned), and in the case of other alloys it may well be much higher. Thus, there is still room for significant progress in this area.

Applications of permanent magnets are widespread in many types of devices, but perhaps the most important single application is for special purpose electric motors. Recent improvements in magnet performance can be expected to be reflected in improved electric motor performance. In fact, a whole new class of compact motor designs now appears practical (White 1985). This, in turn, will result in at least some significant new applications. For instance, compact high-power electric motors could replace hydraulic motors in robots, resulting in a substantial increase in speed of operation. However, the most attractive application for new types of powerful compact electric motors would be to propel electric vehicles. This is a major topic in itself, however, and we cannot discuss it at length here.

Fig. 4.12 Change in energy of various permanent magnet materials (Source: NAS/NRC 1989)

Fig. 4.13 Change in coercivity of various permanent magnet materials (Source: NAS/NRC 1989)

One final example of electronic materials worth mentioning is a class of organic liquids whose viscosity is strongly dependent on the imposed electric field. When a transverse field (voltage) is imposed, such a liquid becomes extremely viscous - almost glassy; yet when the field is removed it flows freely. This class of materials could conceivably become the basis for electrically controlled clutches, brakes, or robotic grippers, thus eliminating much of the mechanical complexity that now plagues such devices. However, much research remains to be done, primarily in the optimization of the molecular synthesis and the scale-up of manufacturing technology.


Materials are the underpinnings of technology - not only figuratively but literally. Some of the most important of all technological "breakthroughs" were associated with materials. The ability to make hard, impervious ceramic pots for the storage of liquids and seeds was one of the first requisites of urban civilization, around 8000 BC. The "Bronze" age and the "Iron" age were major technological milestones. The discoveries of paper and glass (not only for windows but, perhaps more important, for lenses) were only a little less significant in their time. Iron tools and weapons are an enormous improvement over bronze tools, but require much more advanced methods of smelting and working. Steel is as much an improvement over older forms of iron as iron was over bronze. The historian Elton Morrison called steel "almost the greatest invention," with some justice.

However, in some sense the "age of materials" is now past and the "age of information" is upon us. To be sure, most traditional uses of basic materials will continue for many decades, with gradual but cumulative reductions in the sheer mass of materials required for most purposes. Materials of all kinds are becoming more sophisticated and "information intensive," in the sense that they offer more service to the end-user.

But greatly overshadowing this rather broad trend is the enormously rapid increase in the uses of materials specifically for purposes of energy conversion (e.g. magnets, photovoltaics) and processing or storing information. The semiconductors and ferrites constitute the two obvious examples of the latter, but it can be argued that the dominant trend of the future is toward the development of materials that are "information intensive" in this narrower sense. A rough tabulation of the materials of greatest research interest today is given in table 4.7. The degree of sophistication and information content of these materials is continually increasing (fig. 4.14). But they will also be more difficult to produce and to recycle. This will induce increasing interest in re-use and remanufacturing in coming decades.

Table 4.7 Breakthroughs expected in serials


Technological need

Breakthrough technology



Large-volume transmission

Milliwaves, laser beams

Compound semiconductors (InP, GaAIAs, etc.)

Long-distance transmission

Low-loss optical fibre

Non-silicic material


High-speed operations

Compound semiconductors ICs

Compound semiconductors (GaAs, InP, etc.)

Josephson junction device

Superconductive materials (alloys, compounds)

High-density recording

Perpendicular magnetic recording

Perpendicular magnetized film

Magneto-optic recording

Magneto-optic recording materials

Molecular memory

High polymers, biological substances (protein)

Instrumentation and control

Improvement in sensing performance

Josephson junction device

Superconductive materials (alloys, compounds, etc.)


Biological (micro-organisms, enzymes, etc.)

Improved resistance to environmental conditions

Devices more resistant to environmental conditions

Compound semiconductors (GaAs, InP, etc.)

Energy conversion

Solar energy, especially in remote areas


Silicon (crystalline or amorphous) Ga-As, Cd-Te, Cu-In, Se

More efficient generators, transmission lines


Cu-Ba-La-O. Other methane oxygen compounds


Magnetic levitation


Sm-Co, Nd-Fe-B


Cu-Ba-La-O. Other metallic oxygen compounds

Fig. 4.14 Relation between the quantity of materials in a product and its information content


1. Each tonne of fossil fuel burned results in the ultimate release of roughly 3 tonnes of CO2 to the atmosphere, not to mention significant quantities of sulphur oxides (SOx) and oxides of nitrogen (NOx) - the main causes of environmental acidification. Atmospheric carbon dioxide concentration has increased by about 20 per cent since the nineteenth century.

2. Specifically, the first law of thermodynamics, i.e. the law of conservation of mass.

3. The quantities of ore removed from the earth are normally much larger, but physical separation techniques leave much of the excess material at the mine, where it is piled up into small mountains, but not put back into the ground. For instance, copper ores mined in the western United States contain less than 0.4 per cent copper, whereas concentrates delivered to refineries average 20 per cent copper. Thus, for every tonne of concentrate, at least 50 tonnes of crude ore were dug up and processed (by flotation ponds) at the mine. For I tonne of refined copper 250 tonnes of ore are processed. In some cases the quantities of ore processed are much larger. For example, roughly 140,000 tonnes of ore must be processed to yield 1 tonne of platinum group metals.

4. Applications of high-strength low-alloy (HSLA) steels are still continuing to increase how ever, especially in the auto industry. Major process innovations, notably the Basic Oxygen Process (BOF) and continuous casters, also appeared after World War II.

5. A 16 megabyte chip was announced in early 1987 by NTI (Nippon Telephone and Telegraph Co.). As of 1997 we are in the gigabyte range.

6. These are materials that lose all electrical resistivity at a temperature below some "critical", level so long as the magnetic field strength (including the field induced by the superconductive current itself) is below a critical level.

7. Data recording requires "soft" magnetic materials, i.e. materials that can easily be magnetized and demagnetized at high frequency without large "eddy current" losses. The latter requirement cannot be met by metals, but oxides fill the bill because of very high electrical resistivity.

8. Magnetic energy is measured in mega-gauss oersteds (MGOe).


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