Aluminium foil (oraluminum foil inAmerican English; also calledtinfoil) isaluminium prepared in thinmetal leaves. Thefoil is pliable and can be readily bent or wrapped around objects. Thin foils are fragile and are sometimeslaminated with other materials such asplastics orpaper to make them stronger and more useful.
Annual production of aluminium foil was approximately 850,000 tonnes (940,000 tons) in Europe in 2014,[1] and 600,000 tonnes (660,000 tons) in the U.S. in 2003.[2] Approximately 75% of aluminium foil is used forpackaging offoods,cosmetics, and chemical products, and 25% is used for industrial applications (e.g.,thermal insulation, electrical cables, and electronics).[2] It can be easilyrecycled.
Aluminium foil supplantedtin foil in the mid-20th century. In theUnited Kingdom andUnited States it is often informally called "tin foil", just assteel cans are often still called "tin cans".Metallised films are sometimes mistaken for aluminium foil, but are actually polymer filmscoated with a thin layer of aluminium.
Foil made from a thin leaf oftin 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 lessmalleable 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.[3] The first audio recordings onphonograph cylinders were made on tin foil.[4]
Tin was first replaced by aluminium in 1910, when the first aluminium foil rolling plant,Dr. Lauber, Neher & Cie. was opened inEmmishofen,Switzerland. The plant, owned byJ. G. Neher & Sons, the aluminium manufacturers, was founded in 1886 inSchaffhausen, Switzerland, at the foot of theRhine 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.[5]Bern-based Tobler began wrapping its chocolate bars in aluminium foil in 1911, including the uniquetriangular chocolate bar,Toblerone.[6]
Aluminium foil has a thickness less than 0.2 mm (7.9 mils); thinner gauges down to 6 μm (0.24 mils) are also commonly used.[7] Standard household foil is typically 0.016 mm (0.63 mils) thick, and heavy-duty household foil is typically 0.024 mm (0.94 mils). Foil may have a non-stick coating on only one side.[8]
Although aluminium is non-magnetic, it is a goodconductor, 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.[9] Thin sheets of aluminium are not very effective at attenuating low-frequency magnetic fields. The shielding effectiveness is dependent upon theskin 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.[10]
The continuous casting method is much less energy-intensive and has become the preferred process.[11] 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,[12] for the final pass when producing thicknesses below 0.025 mm (1mil), 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. ByKirchhoff's law of radiation, increased reflectivity decreases both absorption andemission of radiation.
Aluminium foil is widely sold into theconsumer market,[13] such as forbarbecuing delicate foods.[14]
As with all metallic items, it reacts to being placed in amicrowave oven. This is because of theelectromagnetic fields of the microwaves inducing electric currents in the foil and highpotentials at the sharp points of the foil sheet; if the potential is sufficiently high, it will causeelectric arcing to areas with lower potential, even to the air surrounding the sheet. Modern microwave ovens have been designed to prevent damage to thecavity magnetron tube from microwave energy reflection, and aluminium packages designed for microwave heating are available.[15]
Submerged in abaking sodasolution, it can be used to polish metals such as silver and gold viaelectrolytic cleaning, as it is a morereactive metal than either.[16] A similar method can be used to produce silver substrates forRaman spectrography.[17]
Some aluminium foil products can berecycled at around 5% of the originalenergy cost.[18]
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