Aluminum

The ALCOA Building in Pittsburgh, built from 1951-1953 by the architectural firm of Harrison and Abramovitz, incorporates aluminum throughout to showcase the company's products.

Aluminum is one of the most abundant metallic elements. It occurs naturally as alum and is not metallic in its natural state. Aluminum (Al on the Periodic Table, atomic number 13) is lightweight, resist corrosion, and is among the most used metals on Earth (second only to iron).

History

Ancient Greeks and Romans used aluminium salts as dyeing mordants and as astringents for dressing wounds; alum is still used as a styptic. In 1761, Guyton de Morveau suggested calling the base alum alumine. In 1808, Humphry Davy identified the existence of a metal base of alum, which he at first termed alumium and later aluminum (see etymology section, below).

The metal was first produced in 1825 (in an impure form) by Danish physicist and chemist Hans Christian Ørsted. He reacted anhydrous aluminium chloride with potassium amalgam and yielded a lump of metal looking similar to tin. Friedrich Wöhler was aware of these experiments and cited them, but after redoing the experiments of Ørsted he concluded that this metal was pure potassium. He conducted a similar experiment in 1827 by mixing anhydrous aluminium chloride with potassium and yielded aluminium. Wöhler is generally credited with isolating aluminium (Latin alumen, alum), but also Ørsted can be listed as its discoverer. Further, Pierre Berthier discovered aluminium in bauxite ore and successfully extracted it. Frenchman Henri Etienne Sainte-Claire Deville improved Wöhler's method in 1846, and described his improvements in a book in 1859, chief among these being the substitution of sodium for the considerably more expensive potassium. Deville likely also conceived the idea of the electrolysis of aluminium oxide dissolved in cryolite; Charles Martin Hall and Paul Héroult might have developed the more practical process after Deville.

Before the Hall-Héroult process was developed, aluminium was exceedingly difficult to extract from its various ores. This made pure aluminium more valuable than gold. Bars of aluminium were exhibited at the Exposition Universelle of 1855. Napoleon III, Emperor of France, is reputed to have given a banquet where the most honoured guests were given aluminium utensils, while the others made do with gold. The Washington Monument was completed, with the 100 ounce (2.8 kg) aluminium capstone being put in place on December 6, 1884, in an elaborate dedication ceremony. It was the largest single piece of aluminium cast at the time, when aluminium was as expensive as silver. Aluminium has been produced in commercial quantities for just over 100 years.

Aluminium was selected as the material to be used for the apex of the Washington Monument in 1884, a time when one ounce (30 grams) cost the daily wage of a common worker on the project;[51] aluminium was about the same value as silver.

The Cowles companies supplied aluminium alloy in quantity in the United States and England using smelters like the furnace of Carl Wilhelm Siemens by 1886. Charles Martin Hall of Ohio in the U.S. and Paul Héroult of France independently developed the Hall-Héroult electrolytic process that made extracting aluminium from minerals cheaper and is now the principal method used worldwide. Hall's process, in 1888 with the financial backing of Alfred E. Hunt, started the Pittsburgh Reduction Company today known as Alcoa. Héroult's process was in production by 1889 in Switzerland at Aluminium Industrie, now Alcan, and at British Aluminium, now Luxfer Group and Alcoa, by 1896 in Scotland.

By 1895, the metal was being used as a building material as far away as Sydney, Australia in the dome of the Chief Secretary's Building.

Many navies have used an aluminium superstructure for their vessels; the 1975 fire aboard USS Belknap that gutted her aluminium superstructure, as well as observation of battle damage to British ships during the Falklands War, led to many navies switching to all steel superstructures. The Arleigh Burke class was the first such U.S. ship, being constructed entirely of steel.

Aluminium wire was once widely used for domestic electrical wiring. Owing to corrosion-induced failures, a number of fires resulted. This dicontinuation thus illustrates one failed application of the otherwise highly useful metal.

In 2008, the price of aluminium peaked at $1.45/lb in July but dropped to $0.70/lb by December

Metallurgy

The most popular process for manufacturing aluminum has been extrusion. In 1894 G.A. Dick designed a press to extrude hot brass rods, which he lent to the experimentation of aluminum extraction. 6 years later, a hydraulic press had been developed that could extrude aluminum and other metals. With the extrusion process being so efficient, aluminum was soon being used to create windows, doors, and even decorative accents. Strength and hardness were of the most importance so aluminum alloys were created to enhance these properties. Aluminum alloys can be cast or wrought iron as well as heat treatable and non-heat-treatable. Non-heat-treatable was used for roofing and had small amounts of manganese, whereas heat-treatable has other elements (such as silicone or copper) and are best for structural means.

Uses and Installation

Aluminum was used for doors, railings, trim and signs following World War I. The aluminum and aluminum alloys were popular because of its color, its ease of use, and its abundance. The first building that was completely covered in aluminum was the A.O smith Corporation Research and Engineering Building. This building was created using pressed aluminum for the walls, and extruded aluminum for the windows and doors. The use of aluminum on the inside for trim and decorative purposes could also be found. Aluminum fell in popularity during the Great Depression and continued until World War II. New processes for extracting aluminum were found during World War II which increased the amount of aluminum use extensively.

Conservation

Aluminum oxide seems to be resistant to corrosion in part to the aluminum oxide film that can be found on its surface. Aluminum alloys can contain silicon, magnesium, or manganese which are also highly resistant to corrosion. If an aluminum alloy contains large amounts of copper, the aluminum is more likely to experience some corrosion because of copper’s susceptibility to corrosion.

Identification

• Simple methods
  • visual examination
  • spot testing
  • specific gravity

• Scientific methods
  • xrf
  • xrd
  • pixe
  • libs
  • electrochemical techniques
  • metallography

Deterioration

Elements such as hydrochloric acid, dirt, humidity, and sulfates can break down the oxide film that occurs naturally on the aluminum. Alkalinity is also a contributing factor the speed of which the aluminum will deteriorate. Soils and some forms of wood can also wreak havoc on the aluminum’s film, causing extensive corrosion. Most acid based chemicals should also be removed from areas that may contain aluminum or its alloys. If the oxide film becomes permeable, dirts, oils, and pollutants prevent the oxide film from reforming and protecting the aluminum.

Conservation Techniques - architecture

The preservation of aluminum relies heavily on the application of a watertight coating. Unsealed aluminum tends to take on a gray cover and may be in danger of corrosion. Unsealed aluminum is difficult to clean because the damage is irreversible. On sealed aluminum, a mild cleaner will only remove loose soil but will have no effect on the stains in the oxide film. Heavy-duty cleaners are effective in removing these stains but may cause damage to the aluminum alloys. Using plastic abrasives lightly have been proven to remove broken oxide layers without damaging the aluminum or its alloys. In order to find the best cleaning technique, a sample or test piece should be used. Maintaining aluminum after it has been cleaned requires a wax or varnish, though wax may cause excessive buildup. Painting aluminum is a difficult task and is not usually recommended because it could alter the surface’s appearance.

Conservation Techniques - historical objects

Cleaning

• Mechanical

• Chemical

1.Saponaria Officinalis(soapwort) extract

100 gms soapwort root

1 lit water

Pour boiling water on dry root,cover and after 10 minutes you can use it.Fresh solution is pH neutral.

Can be used on chemically/electrochemically oxidized,chromated or phosphated objects!

According to:

Personal experience

2.Sodium carbonate/waterglass solution

10-40 gm sodium carbonate

5-10 gm waterglass

1 lit water

Immerse object in solution.Can be used only on objects that are not electrochemically or chemically oxidized,chromated or phosphated! Rinse well!

3.Sodium tetraborate solution

30 gm sodium tetraborate

1 lit water

add few drops of ammonia

pH of solution is 10.If we correct pH to 7 solution can be used on electrochemically/chemically oxidized,chromated and phosphated objects. Rinse well!

• Electrochemical

Electroclytic cleaning

6 gm Na2CO3

6 gm sodium phosphate

1 lit water

stainless steel anode,12v,1A/dm2

Object must be connected to negative terminal of current source ,and immersed in solution,anode must be immersed before. Can be used only on objects that are not chemically/electrochemically oxidized,chromated or phosphated! Rinse well!

• Ultrasonic

4-6 gms sodium carbonate

6-8 gms trisodium phosphate

10-12 gms sodium silicate

1 lit distilled water

2-5 minutes,then rinse well and repeat if needs

• Laser

There are well documented examples of laser cleaning aluminium objects.

Structural consolidation

• mechanical joining

• cementing/gluing

• soldering / hard / soft

• welding /electric arc / tack / oxyacetilene / laser

Stabilization

• Conversion coatings

1.Tannic acid treatment

1 gm tannic acid

1 lit water

Immerse object in solution,duration 30 seconds.We must correct pH to 4(with phosphoric acid or NaOH solution) For better paint bonding and corrosion resistance. If we add 0,003% potassium titanium fluoride protection can be even better.

2.Phosphating

180 mll butyl alcohol

140 mll isopropyl alcohol

45 mll phosphoric acid

90 mll distilled water

Immerse objects in solution(60-120 seconds).Rinse well,dry, lacquer or paint. For better paint bonding and corrosion protection. Try to avoid any contact with solution,use rubber gloves!

Protective coatings

• Clearcoats/ Paraloid B 72/ Paraloid B 67 / Paraloid B 44 / Paraloid B 48 N / ORMOCER

• Waxes / Renaissance Wax / Cosmolloid 80 H/ Dinitrol 4010 / DIY mixtures

• Combinations / Paraloid B 72 + Renaissance wax etc.

Replacement

Finding replacement pieces for aluminum is possible in most of its forms, though certain shapes may no longer be available and recreation will be expensive. Also, replacing sections may affect the aluminum’s performance. Some aluminum pieces are capable of being welded if they are either pure aluminum or low-manganese alloys. Also, alloys that are heat treated tend to lose strength during welding so test pieces are strongly recommended.

References

• Kelley, Stephen J. "Aluminum." Twentieth-century Building Materials: History and Conservation. By Thomas C. Jester. New York: McGraw-Hill, 1995. 46-50. Print.

Examples

Aluminum is commonly used as "siding" to clad the exterior walls of buildings.   Aluminum entrance, ALCOA Research Laboratory (b. 1929), New Kensington, PA.   Hand-hammered aluminum doors and aluminum light fixture, ALCOA Research Laboratory.   Aluminum marquee in the streamline moderne Columbia, SC Greyhound Bus Station (b. 1938-39).

Further reading

• Selwyn,L. Metals and Corrosion - A Handbook for Conservation Professional, Ottawa 2004.
• Bailey, G. (2004) “The stabilization of A wrecked and corroded aluminium aircraft”, in the proceedings of the ICOM-CC Metal interim meeting METAL 04, 453-464.
• Degrigny, Christian (1995). "Stabilisation de moteurs d'avion immergés". Studies in Conservation 40, 10-18.
• Hallam, David L., Adams, C.D., Bailey, G. and Heath, Graham, A. (1997). "Redefining the electrochemical treatment of historic aluminium objects", in: Metal 95, Ed. Ian D. Macleod, Stéphane L. Pennec and Luc Robbiola, James & James, London, 220-222.

External links

• H. Ward Jandl, "With Heritage So Shiny: America's First All-Aluminum House," APT Bulletin, vol. 23 no. 2 (1991): 38-43. Available online at: http://www.jstor.org/stable/1504383
• Institut pour l`historie de l`aluminium / Institute for the history of aluminium
• Gujarathi ,K. Corrosion of Aluminium Alloy 2024 Belonging to The 1930s in Seawater Environment-thesis(2008.)
• Degrigny,C. Stabilization of submerged BMW 801 D2 engine from a Focke Wulf 190 +some other similar articles
• Bailey,G.T. Stabilization of wrecked and corroded aluminium aircraft