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Background

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

Ore

Gross weight of ore(million m.t.)

Metal content (%)

Net weight of metal (million m.t.)

Mine and mill wastea (million m.t.)

Aluminium 106 19 19.8 86
Chromium 10 30 3.0 7
Copper >2,500 0.4 9.4 >2,490
Gold 466 0.0005 0.002 466
Iron 989 52 517.0 472
Lead >45 6.5 2.9 >42
Manganese 22 33 7.2 15
Nickel >130 0.7 0.9 >129
Platinum groupb 50 0.0005 0.0002 50
Uranium (1978)c 1,900 0.002 0.04 1,900
Zinc >219 3.2 6.9 >212

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
Composites
Polymers
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:

Parameter

Panel weight

Tensile strength (g/denier) 0.2581
Elastic recovery (% recovery from % stretch) 0.2903
Modulus (g/denier) 0.2903
Moisture regain (%) 0.1613
  1.0000

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

Fibre

Year of introduction

Tensile strength (g/denier)

Elastic recovery (% recovery from % stretch)

Modulus (g/denier)

Moisture regain (%)

Visrayon 1892 2.40 74 11.10 13.00
Acerayon 1894 1.50 65 5.50 6.50
Nylon 1935 5.70 100 24.00 3.80
Orlon 1949 5.00 84 24.00 0.90
Dacron 1951 5.00 95 25.00 1.38
Vicara 1953 1.25 99.5 3.50 10.00
Acrilan 1953 3.00 75 30.00 1.70
Dynel 1953 3.00 87 9.70 0.40
Arnel 1955 1.40 84 5.20 3.20
Zefran 1959 3.50 92 11.00 2.50
Darvan 1959 2.00 75 7.00 3.00
Kodel 1959 3.00 87 11.00 0.40
Vycron 1962 8.00 60 0.16 0.60
Arnel 60 1962 2.30 70 10.00 4.00
Zefkrome 1964 4.20 84 11.30 2.50
Encron 1968 5.00 70 5.30 4.00
Sef 1972 2.60 99 3.00 2.50
Triacetate 1980 1.30 70 5.20 3.20

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.


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