Aluminium foil
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Aluminium foil (or aluminum foil in American English; also called tinfoil) is aluminium prepared in thin metal leaves. The foil is pliable and can be readily bent or wrapped around objects. Thin foils are fragile and are sometimes laminated with other materials such as plastics or paper to make them stronger and more useful.
Annual production of aluminium foil was approximately Template:Convert in Europe in 2014,<ref>Template:Cite web</ref> and Template:Convert in the U.S. in 2003.<ref name=aausa>"Foil & Packaging". Template:Webarchive. The Aluminum Association (USA).</ref> Approximately 75% of aluminium foil is used for packaging of foods, cosmetics, and chemical products, and 25% is used for industrial applications (e.g., thermal insulation, electrical cables, and electronics).<ref name=aausa/> It can be easily recycled.
Aluminium foil supplanted tin foil in the mid-20th century. In the United Kingdom and United States it is often informally called "tin foil", just as steel cans are often still called "tin cans". Metallised films are sometimes mistaken for aluminium foil, but are actually polymer films coated with a thin layer of aluminium.
History
Precursors
Foil made from a thin leaf of tin was commercially available before its aluminium counterpart. Tin foil was marketed commercially from the late nineteenth into the early twentieth century. The term "tin foil" survives in the English language as a term for the newer aluminium foil. Tin foil is less malleable than aluminium foil and tends to give a slight tin taste to food wrapped in it. Tin foil has been supplanted by aluminium and other materials for wrapping food.<ref>Template:Cite web</ref> The first audio recordings on phonograph cylinders were made on tin foil.<ref>Template:Cite web</ref>
Invention
Tin was first replaced by aluminium in 1910, when the first aluminium foil rolling plant, Template:Nobr was opened in Emmishofen, Switzerland. The plant, owned by Template:Nobr, the aluminium manufacturers, was founded in 1886 in Schaffhausen, Switzerland, at the foot of the Rhine Falls, whose energy powered the process. In December 1907, Neher's sons, along with Dr. Lauber, had invented the endless rolling process, by which they discovered that aluminium foil could be used as a protective barrier.<ref>Template:Cite web</ref> Bern-based Tobler began wrapping its chocolate bars in aluminium foil in 1911, including the unique triangular chocolate bar, Toblerone.<ref>Template:Cite web</ref>
Properties
Aluminium foil has a thickness less than Template:Convert; thinner gauges down to Template:Convert are also commonly used.<ref name="EAFA facts1">Template:Cite web</ref> Standard household foil is typically Template:Convert thick, and heavy-duty household foil is typically Template:Convert. Foil may have a non-stick coating on only one side.<ref>Template:Cite web</ref>
Although aluminium is non-magnetic, it is a good conductor, so even a thin sheet reflects almost all of an incident electric wave. At frequencies more than 100 MHz, the transmitted electric field is attenuated by more than 80 decibels (dB), that is less than 10−8 = 0.00000001 of the power gets through.<ref>Template:Citation. Template:Harvtxt graphs reflection loss for copper and shows electric field and plane wave losses at greater than 90 dB.</ref> Thin sheets of aluminium are not very effective at attenuating low-frequency magnetic fields. The shielding effectiveness is dependent upon the skin depth. A field travelling through one skin depth will lose about 63% of its energy (it is attenuated to 1/e = 1/2.718... of its original energy). Thin shields also have internal reflections that reduce the shielding effectiveness.<ref>Template:Harvnb.</ref>
Manufacture
The continuous casting method is much less energy-intensive and has become the preferred process.<ref name="Robertson">Robertson, G. (2006). 2nd ed. Food Packaging, Principles and Practice, Boca Raton, FL, Taylor & Francis Group: Template:ISBN. Chapter 7: Metal Packaging Materials.</ref> It is difficult to produce rollers with a gap fine enough to cope with the foil gauge, and to avoid this, as well as reducing tearing, increasing production rates, and controlling thickness,<ref name="degarmo">Template:Cite book</ref> for the final pass when producing thicknesses below Template:Convert, two sheets are rolled at the same time, doubling the thickness of the gauge at entry to the rollers. After the rollers, the two sheets are separated, which produces foil with one shiny side and one matte side.
The two sides in contact with each other are matte, and the exterior sides become shiny. The difference in thermal properties between the two sides is imperceptible without instrumentation. By Kirchhoff's law of radiation, increased reflectivity decreases both absorption and emission of radiation.
Uses
Aluminium foil is widely sold into the consumer market,<ref>Examples of products Template:Webarchive</ref> such as for barbecuing delicate foods.<ref>Template:Cite book</ref>
As with all metallic items, it reacts to being placed in a microwave oven. This is because of the electromagnetic fields of the microwaves inducing electric currents in the foil and high potentials at the sharp points of the foil sheet; if the potential is sufficiently high, it will cause electric arcing to areas with lower potential, even to the air surrounding the sheet. Modern microwave ovens have been designed to prevent damage to the cavity magnetron tube from microwave energy reflection, and aluminium packages designed for microwave heating are available.<ref>Huss, G. (1997) Microwaveable Packaging and Dual-Ovenable Materials in The Wiley Encyclopedia of Packaging Technology, 2nd ed., edited by Brody, A. and Marsch, K. New York, John Wiley and Sons</ref>
Submerged in a baking soda solution, it can be used to polish metals such as silver and gold via electrolytic cleaning, as it is a more reactive metal than either.<ref>Template:Cite web</ref> A similar method can be used to produce silver substrates for Raman spectrography.<ref>Template:Cite journal</ref>
Environmental issues
Some aluminium foil products can be recycled at around 5% of the original energy cost.<ref>Template:Cite web</ref>
See also
References
External links
- European Aluminium Foil Association
- Aluminum Association (USA)
- Aluminum Foil from How Products Are Made, vol. 1, Thomson Gale (2005).
- How It's Made: Aluminium Foil - HowItsMadeEpisodes channel on YouTube.
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