While higher currents increase production, they also create more heat (leading perhaps to ventilation problems) and stronger magnetic fields (which can disturb the aluminum pool). (Brubaker, 94) If currents are increased, without changing pot size, there is faster corrosion of the cathode, and fluorocarbon formation at the anode.

A small amount of the current is wasted, as a result of side reactions, concentration gradients, transient short circuits, and so forth. (Prasad, Kirk-Othmer, Choate) In the first commercial cells, the current efficiency (the percentage of the current which actually resulted in net production of aluminum) was only 75-78%. (Choate, 25) For modern cells, it is 85-95%. So a 180,000 ampere pot which was 90% efficient would produce 1,305 kilograms daily.

Don't confuse current efficiency with energy efficiency (the percentage of the electrical energy entering the smelter which actually is used to reduce aluminum). Because additional voltage must be used to overcome electrical resistance, energy efficiency is only about 26%. (Choate, 31) The total amperage useable by a smelting operation in Grantville may be limited by the power generation and transmission equipment, or by allowable current densities in the pots. At that point, adding pots is the only way to increase capacity. Modern potlines usually don't exceed 300 pots, but of course you can add potlines.

The total size of the smelter is limited by the local availability of electricity, land, building supplies and labor.

Subsequent Processing The molten aluminum is transported to a holding furnace. If the intent is to make an aluminum alloy, the alloying elements are added at this point. When the composition is correct, the alloy is poured into a mold, in which it cools to form an ingot. The ingot can then be further manipulated.

Aluminum (and its alloys) can be cast by melting it and then pouring it into a packed sand mold or a permanent iron or steel mold. Aluminum has a relatively low melting point (660 deg. C.), which facilitates casting.

Molten aluminum dissolves iron, so if it is cast in an iron receptacle, the latter needs a protective coating.

If silica is present, perhaps as a binder, the aluminum will reduce it, producing elemental silicon.

The molten aluminum can be worked in a variety of ways, depending on the alloy, including rolling (into sheets or foils), forging (hammering), extrusion (pushing through a hole) or drawing (into wires).

Heat-strengthening a suitable aluminum alloy (e.g., aluminum-copper) requires controlled temperatures and uniform heating of the furnace. (Hultgren, 297-8) The modern EB describes the process (which it calls "solution heat treatment") in general terms: (1) heating the metal for 6-24 hours at temperatures of 370-535 deg. C., (2) quenching, in hot (66-100 deg. C.) water for casting alloys, or in water at room temperature for wrought alloys; and (3) "aging" the metal, either at room temperature or, to accelerate the process, at a higher one (the encyclopedia says, "somewhat above the boiling point of water"). (IEP 392, 395).

The optimal time-and-temperature conditions are alloy-specific. More detailed specifications may appear in the personal library of one of Grantville's engineers or machinists-for example, treatments for five common alloys appear in Walsh'sMachinists' and Metalworkers' Pocket Reference (9-25).

Of course, to make sure the temperature is correct in practice, we will need pyrometers.

Welding aluminum, especially to other metals, can be somewhat tricky but hopefully the welders of Grantville already know something about this.

Quality Control An important consideration in aluminum production is the minimization of impurities, whether you are engaged in primary production (from ore) or secondary production (recycling of foundry scrap or aluminum articles).

The basic problem is that, of the common metallic elements, only potassium, sodium, calcium and magnesium are more reactive than aluminum. Once a less reactive element is associated with the aluminum, it is "practically impossible" to remove it. (NAP, 53) Hence, impurities-at least those which adversely effect the properties of the desired alloy-must be minimized. That means that the raw materials should be as pure as possible. The impurities come primarily from the anodes and the alumina. (Kirk-Othmer, 2:196) The most common impurity in aluminum is iron. In general, it is considered undesirable (note that the Bayer process deliberately removes iron oxide), and the iron content of commercially pure aluminum is typically 0.08-0.5%. (Belov, 185-6) If iron content is excessive, iron aluminide crystals form, which have an undesirable effect on formability, fatigue resistance and surface finish. (Key to Metals) Iron also interferes with heat hardening. (Hultgren, 302) Next most common is silicon, which is problematic because it can render the aluminum more brittle.

However silicon is deliberately added to some alloys to increase castability. The other principal impurities in "primary" aluminum are titanium, vanadium and manganese.

Calcium, lithium and sodium are derived from the fluoride electrolyte. Hydrogen and oxygen can also be troublesome, and are found in the raw materials and in the air. In recycling "secondary" aluminum, elements (e.g., zinc, magnesium) deliberately added when making the original alloy may be undesirable if the desired alloy is different.

If the ultimate goal is to manufacture an aluminum alloy, then the quality of the source of the alloying element must also be known, and, the melt will be tested, and adjusted, until the desired alloy composition is achieved.

Modern chemists and metallurgists are accustomed to relying on instrumental methods. After the Ring of Fire, the up-timers have access to two appropriate instruments. The power plant has a "Metallurgist XR,"

which is a portable X-ray fluorescence spectrophotometer specifically designed for alloy analysis.

(Boyes) And, even more surprisingly, the high school has a $300,000 atomic absorption spectrophotometer given to them in October 1997 by LaFarge Corp.

Neither of these instruments is going to remain in working order for very long. However, while they last, we can assay a lot of ores from different suppliers, and also reconstruct the compositions of the many different aluminum alloys which are available in Grantville. Just analyzing the parts of an automobile could allow reconstruction of the composition of representative alloys of all of the major types, including the high strength aluminum-magnesium 7000 series. (www.autoaluminum.org) After they fail, we'll have to rely on wet chemical techniques and microscopic examination of etched metal sections. Fortunately, the two spectrophotometers allow us to assemble a library of photographs of the microscopic appearance of alloys of known composition.

Uses for Pure Aluminum The uses for pure aluminum are constrained by its relatively low hardness and tensile strength.

Nonetheless, there are significant markets for it.

Historically, the first uses of aluminum were as jewelry and novelty articles (e.g., aluminum knives and forks for court banquets). Perhaps the most dramatic prestige pieces were the Eros statue in London and the cap of the Washington Monument. For these uses, the high cost of aluminum was actually part of the attraction. The first significant use for aluminum was in steel foundries; aluminum could be used in small quantities to scavenge oxygen, and thereby reduce blow holes and occluded gases that would otherwise weaken the steel. (Wallace, 10) Prior to 1900, the largest market (30-50%) for aluminum was in cooking utensils, where aluminum's heat conductivity, lightness, and corrosion resistance were all big advantages. The de-oxidant market was about half the size of this one.

Aluminum gradually infiltrated other markets, including bicycle parts and locomotive headlights.

However, the next major development was the adoption of aluminum for long-distance electrical lines.

Aluminum has only 63% the conductivity of copper, but it weighs only 30% as much. Thus, by making the aluminum wire thick enough, you can equal the current-carrying capability of copper wire with wire which weighs only 48% as much. This in turn meant that as soon as the price (by unit weight) of aluminum dropped to double that of copper, it would have a price advantage. By 1903, 37% of aluminum sales were for conductor use, even though in that year the price ratio was actual 2.5. (Bear in mind that with lighter transmission lines, the supporting structures could be scaled down.)(Wallach, 15-17) While aluminum wire was not as strong as copper wire, this problem could be overcome (as it was in 1908) by wrapping aluminum strands around a steel core. This increased the weight (e.g., to 80% that of copper) but the composite was 57% stronger.

Aluminum could be rolled much thinner than tin, so that allowed it to make inroads into the foil industry before 1908. (Wallace, 18) Ultimately, this led to the use of aluminum foil in electrolytic capacitors.

(Calvert) Aluminum was also used in paints, beginning in 1900. (Wallace, 18) The aluminum flakes reflect both visible and ultraviolet light, and protect the substrate from corrosion (Calvert).

Another important use of unalloyed aluminum was in the "thermite" process. Aluminum was added to an oxide of another, less reactive metal, such as chromium, manganese, vanadium, tungsten, or molybdenum. The aluminum would reduce the oxide, liberating the elemental metal and producing a great deal of heat in the process.

Aluminum was also used to make reciprocating parts for machinery (where lightness was important), and vessels for handling chemicals (think corrosion resistance). A surface coating of aluminum could also be applied to other metals ("calorizing," developed in 1911).

Finally, metallic aluminum could be reacted to form various useful aluminum compounds, such as aluminum nitrate (used in explosives).

Aluminum Alloys The impetus for alloying aluminum with other metals came from the automotive industry. They had to research the properties of the alloys, and also figure out how to cast or otherwise handle them. Bear in mind that there was relatively little use of any alloys (other than brasses and bronzes) prior to World War I. Nonetheless, duralumin (a copper-magnesium-manganese wrought alloy of aluminum) was commercially available by 1909. By 1915, one-quarter of aluminum production was used to make alloys,and most of this went into motor vehicles. (Wallace, 20) Aluminum alloys can be divided into two categories, casting alloys and wrought alloys. Casting alloys are formed into their final shape by, surprise, casting. That is, the molten metal is poured into a mold, the metal is allowed to harden, and the mold is removed. Wrought alloys are cast, initially, but can be further worked, by rolling, hammering, etc., "hot" or "cold." Most production is of the more versatile wrought alloys.

There is a standard classification for aluminum alloys. It is not in the encyclopedias, but it may be known to the engineers and machinists of Grantville (and even to the auto buffs). Wrought alloys are given 4 digit numbers, in which the first digit indicates the principal alloying element, as follows: 1xxx (No major alloying element, i.e., aluminum of 99% or higher purity) 2xxx (Copper) 3xxx (Manganese) 4xxx (Silicon) 5xxx (Magnesium) 6xxx (about equal amounts of silicon and magnesium) 7xxx (Zinc) 8xxx (Other) * * *

Aluminum alloys can be light, hard and strong, thereby endearing themselves to the USE's transportation industry. Unfortunately, there are some practical problems with recreating the standard aluminum alloys in Grantville.

First, we need to know the composition of the alloy. EA says that aluminum can be alloyed with copper, magnesium, manganese, chromium, silicon, iron, nickel, and zinc. It also mentions tin, cadmium, lead, bismuth, cobalt, titanium, vanadium, boron, sodium and zirconium as special purpose additives.

EA gives the specifications for several alloys: 2024: "duralumin type," 4.5% copper, 0.6% manganese, 1.5% magnesium. (EA also explains how to heat-strengthen this alloy) 3003: 1.25% manganese 7075: magnesium, zinc, copper, chromium (unspecified amounts) "Alclad" is described by EA as a composite material having an "alloy core" which is "coated" with "aluminum or an aluminum alloy." This allows for the combination of the strength of the alloy core (which can be aluminum, such as 2024, or steel) with the corrosion resistance of the aluminum. The cladding is usually high purity aluminum rather than an alloy. EA doesn't describe the coating method. It isn't electroplating or vapor deposition, as one might guess.

Rather, the aluminum is hot-rolled onto the alloy. (Engineering Metallurgy, 284) In its article on "Bronze," EA lays out the composition of four aluminum bronze alloys, and suggests uses for each (e.g., gears). It also explains how to heat treat them to increase their hardness.

The modern EB describes several casting alloys in general terms: (1) 5-10% silicon, (2) 7-10% copper, (3) 4-5% copper and 10% magnesium, (4) 5% silicon, 0.5% magnesium, 1.5% copper.

With respect to wrought aluminum alloys, it suggests adding (not at the same time!) about 1% manganese for strength, about 10% silicon for low melting point alloys suitable for welding wire, and 5-6% magnesium for strength, hardness, weldability, and corrosion resistance. It says that aluminum-zinc alloys are hard, strong, and heat treatable, but doesn't suggest a particular zinc content.

Finally, it provides compositions for aluminum bronzes (which are primarily copper, but up to 11% aluminum), "superplastic zinc" (which is 22% aluminum), and two aluminum-tin alloys suited for bearings use.

EB1911 is less useful, as aluminum was relatively new at the time of publication. It generally speaks about light alloys with 1-2% of other metals, and heavy alloys in which the aluminum content is just 1-10%. In the latter category, it specifically mentions the aluminum bronzes (90-97.5% copper, 2.5-10% aluminum).

There are engineers in Grantville, and they are likely to own handbooks which provide some information.

For example,Perry's Chemical Engineer's Handbook (1963) has nominal compositions for the wrought alloys 1100, 3003, 2017, 2024, 5052, 6063, and 7075, and cast alloys (these are old designations) 13, 380, 43, 195, 214, and 220.

I would be very surprised if Hal Smith, the retired aeronautical engineer (1633, Chap. 11) didn't have a book with the formula for the premiere aircraft alloy, 7075-assuming he didn't have it memorized. And he probably knows the proper heat treatments, too.

Secondly, we need to be able to purify the alloying element. That may mean that before we can make, say, aluminum-manganese alloys, we have to develop manganese refining technology to the point that we have a consistent material free of impurities which could adversely affect the properties of the alloy.

Generally speaking, the specifications for aluminum alloys specify that there not be more than 0.05 percent of individual "mystery" elements, and that such elements not total more than 0.15 percent of the alloy.

If you are adding just 1% of a second metal to aluminum, then if the second metal is at least 85% pure, then no more than 15% of it will be unknowns, and that will introduce no more than 0.15 percent of unknowns into the alloy. On the other hand, if the second metal is 5% of the final alloy, it had best have a purity of 97%.

My gut reaction is that the first practical aluminum alloys will be those using copper. It is my understanding that even the ancients were able to produce copper with a purity of 98 to 99%. (Garrison, 91) Pure zinc is of particular interest, and, by the seventeenth century, it was already being produced, by smelting calamine, in China and India. (Habashi) In Europe, pure zinc was first deliberately manufactured in the 1740's. While an analysis of zinc technology is way outside the scope of this essay, that leads me to believe that the jump to zinc distillation is not a huge one for the down-time Europeans to make.

According to "Canon," Doctor Gribbleflotz succeeded in first isolating zinc from premium quality Harz Mountains sphalerite (zinc iron sulphide) by December, 1633 and, by February, 1634, had processed five tons of ore. (Offord, "Dr. Phil Zinkens a Bundle,"Grantville Gazette, Volume 7) Thus, a zinc smelter was a "going concern" at that point.

In April, 1634, not knowing of Dr. Phil's triumph, Magda and Sharon arranged for Grantville to receive two hundred tons of Japanese zinc by midsummer, 1635. (1634: The Galileo Affair, Chap. 29) It is unclear whether what they ordered was zinc ore or zinc metal.

The upshot is that I think that at least the aluminum-copper, aluminum-zinc, and aluminum-copper-zinc alloys could be made in Grantville as soon as pure aluminum was available.

What about manganese and magnesium? There are known sources of magnesium and manganese in existing mines, or in areas friendly to the USE. (Runkle, "Mente e Malleo,"Grantville Gazette, Volume 2).

Manganese dioxide (pyrolusite) can be reduced with carbon, and pure manganese was first produced in 1774. The 1911 EB notes that at the end of the nineteenth century pyrolusite was "extensively minded at Ilmenau and several other places in Thuringia . . ." and it describes a method used in 1893 to prepare 97% manganese from pyrolusite.

John Leggett has written a series of "USE Steel reports," which envision that, in December 1632, manganite (another manganese ore) will be imported for conversion into "spiegeleisen," a pig iron which, because of its manganese content (about 12%) is useful in the removal of oxygen and sulfur from steel (especially in the Bessemer process). The 1911 EB also mentions use of ferromanganese, which is 80% manganese.

While even ferromanganese has too much iron to be used as is in the preparation of aluminum alloys, it can certainly be refined further, perhaps electrolytically, for that purpose. Or prepared from pyrolusite, by the 1893 method.

Manganese of purity suitable for use by the aluminum industry is likely to be available two or three years after the first large-scale use of ferromanganese in the steel industry.

There are two standard methods of making magnesium, and both are briefly discussed in Encyclopedia Americana. The more common method is to obtain it electrolytically from magnesium chloride (as was done in 1808), since magnesium is even more reactive than aluminum.

It is actually easier to recover magnesium than aluminum (as I hope to elaborate upon in a future article).

And magnesium has some interesting uses in its own right, for example, in pyrotechnics. I would expect that there will be small-scale production of magnesium by alchemists like Dr. Gribbelflotz (he would fall in love with the burning magnesium ribbon experiment), but that large-scale extraction would come much later, perhaps not until two to four years after the aluminum industry commences ingot production. (In the long-term, magnesium could be serious competition for aluminum.) In short, I am expecting that manganese and magnesium will be available for alloying use sometime in the 1640's.

Predecessors of the Hall-Heroult Process The first method (Wohler, 1845) used to make aluminum was to pass aluminum chloride over molten potassium (an even more reactive metal). The aluminum was produced in the form of globules, each weighing ten to fifteen milligrams. Unfortunately, both aluminum chloride and metallic potassium were expensive.

In 1854, St. Claire Deville chose to reduce aluminum chloride with sodium rather than potassium. The reducing power of sodium was greater, and sodium was also less expensive. Later, he replaced the simple chloride with a double chloride of sodium and aluminum. So reformulated, the Deville process became the dominant commercial process for making pure aluminum until Hall and Heroult's simultaneous discovery of the feasibility of electrolytic reduction of alumina in a cryolite bath.

There are two other early methods which warrant discussion. One used a different ore, cryolite, already familiar to us as a flux. In water-free form, it has an aluminum content of 12.85%.

In 1855 and thereafter, John Percy, Allan Dick, and Heinrich Rose all advocated reducing it, rather than aluminum chloride, with sodium.

Deville himself experimented with cryolite, perhaps as early as late 1855, but by 1856, had received a discouraging report concerning the practicality of mining cryolite in Greenland, and probably ceased using it after 1857. In 1859 he wrote a book on aluminum which warned against using cryolite.

There were two aluminum smelters in France in the late 1850s, one at Amfreville-la-mi-Voie, near Rouen, and the other in Nanterre. Kragh says that "most" of the aluminum produced at Amfreville was made from cryolite. However, the only cryolite purchase made by the Amfreville facility was of ten tons, in late 1855. Thus, its maximum possible production of aluminum from cryolite was about 1,300 kilograms, The plant in Nanterre, it only acquired five tons of cryolite.

Most sources (e.g., EB11-Al; Johnson's; Wagner 113; Freer, 21-22; Hiorns, 347) consider the Deville method, using chemical reduction of aluminum double chlorides, to have been the dominant method of making aluminum prior to Hall-Heroult.

It is possible to electrolytically reduce cryolite, rather than alumina, to obtain aluminum. Unfortunately, as pointed out by 1911 EB, a slight variation in voltage can result in the reduction of the sodium, as well as the aluminum, producing a sodium-aluminum alloy. * * *

Eugene and Alfred Cowles found (1885) that copper reduced the melting point of alumina to the point that it could be melted in an electric furnace and reduced with carbon. This produced a copper-aluminum alloy, called "aluminum bronze," with an aluminum content of up to 10%. The effective cost per pound of the aluminum content was one-third of that of the Deville aluminum (Wallace, 509). Unfortunately, the copper could not be separated from the aluminum, and that limited the use of the method.

The difficulties attendant on the early methods of producing pure aluminum can be judged by charting its price. Note that no attempt has been made to express these amounts in constant dollars. Prices are per pound unless otherwise stated.

Wohler method: "more expensive than gold" (Raymond, 224) "twice as much as platinum or gold"

http://www.arkansaspreservation.org/historic-properties/national-register/siding_materials.asp?page=theo 1852: $545 (presumably Wohler method)(Ammen, 12) 1852: $1200/kg (CRC) 1854: 3000 francs/kg (Raymond, 224) Note: in 1854, price of potassium was 17 pounds sterling (EB11-Al)

Early Deville method: 1855: $155 (Ammen, 12) 1000 francs/kg (Raymond, 224) 1856: 300 francs/kg Deville double chloride method: 1859: $ 17 (Ammen, 12) 1884: $ 12 (Wallace, 4) $16 (Binczewski-same as the 1884 price of silver; laborer paid $1/day) 1886: $25/kg (CRC) 1889: $ 10 (Wallace, 9), 16s/pound (EB11-Al) 1880s: 40 francs/kg (Raymond, 224)

Hall-Heroult method: 1889: $ 5 1890: $ 2 (in 1,000 pound lots) 1891: $ 0.50 (Wallace, 13); 4s/pound (EB11-Al) 1899: $ 0.33 1910: $ 0.22 (Brubaker, 59) 1920: $ 0.31 1930: $ 0.24 1940: $ 0.19 1942-45: $0.15 1950: $ 0.17 1960: $ 0.26 1970: $ 0.29 (USGS) 1980: $ 0.76 1990: $ 0.74.

1999: $ 0.66 20C high, $1.10 (1988), low 0.15 (1942-5) Recycling Aluminum Some writers have dubbed the twentieth century "the Aluminum Age." Because of the pervasive use of aluminum in our society, it is safe to assume that a substantial amount of aluminum was in Grantville at the time of the Ring of Fire. Some articles (e.g., aluminum wiring and some aluminum foil) will be fairly pure, others (e.g., siding, automotive parts) will be alloys containing significant amounts of other elements.

Which articles will be offered for recycling? Those for which there are reasonable (cheap, functional) substitutes available down-time.

Which articles will be accepted for recycling? Those which can be processed without unreasonable expense. The acceptability ultimately depends on how easily the aluminum alloy can be separated from the other materials with which it is now associated, and how similar that alloy is to the one which is now desired.

In general, the alloys used to make aluminum articles fall into two categories, wrought alloys and cast alloys. If you are making wrought alloys, impurities can be a serious problem, and hence even cast alloyscrap direct from the foundry isn't usually recycled to make wrought alloys.

While wrought alloy scrap from the foundry can be recycled to make either wrought or cast alloys, once wrought alloy is incorporated into a consumer product, its recycling potential is dependent on what contaminants it has acquired.

If scrap from diverse sources is melted together to make a secondary alloy, it will limit the latter's strength and other qualities. The only common alloying element that can be removed from aluminum scrap is magnesium. (Hultgren, 298)

Aluminum Articles in Grantville Aluminum Cans. Used beverage cans are 80% aluminum packaging. The typical contaminants for cans are dirt, moisture, plastic, glass, and other metals. Some of these were part of the can and others were mixed in with it before recycling. Lead is one of the more troublesome contaminants. (Miller) Cans are made of wrought aluminum alloys. They may have sides made of manganese-rich alloys 3004 or 3104, ends made of alloy 5182, and tabs made of magnesium-rich alloys 5042 or 5082. (NAP, MatWeb, etc.) Kitchen foil. Reynolds' aluminum foil is made from alloy 8111; it is about 97% aluminum, but contains 0.4-1% iron, 0.3-1.1% silicon.

Siding. Aluminum siding is one of the more obvious articles to recycle. (On Feb. 14, 2006, UPI reported that in response to increased scrap metal prices, Indianapolis thieves were stripping siding off houses.) The usual siding alloy is 3105, which is 0.2-0.8% magnesium, 0.3-0.8% manganese, and up to 0.7% iron, 0.6% silicon, 0.4% zinc, 0.3% copper, 0.2% chromium, and 0.1% titanium. I have also found reference to use of 3003, another manganese-rich alloy.

Air conditioning condensers. One heavy household or light commercial unit provides several hundred pounds of aluminum alloy. In OTL, condensers are sold for scrap when houses are remodeled or the air conditioning system is upgraded. (Knox, private communication) Wheel Rims. These are likely to be alloys of the 6xxx series, such as 6082. Thus, they will contain silicon and magnesium.

Aluminum wire. These tend to be 1xxx series (unalloyed aluminum), such as 1350.