Aluminium foil is
aluminiumAluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
prepared in thin
metal leavesMetal leaf, also called composition leaf or schlagmetal, is a thin foil used for decoration. Metal leaf can come in many different shades. Some metal leaf may look like gold leaf but not contain any real gold...
, with a thickness less than 0.2 millimetre, thinner gauges down to 6 micrometre are also commonly used. In the USA, foils are commonly gauged in mils. Standard household foil is typically 0.022 millimetre thick and heavy duty household foil is typically 0.033 millimetre.The
foilA foil is a very thin sheet of metal, usually made by hammering or rolling a piece of metal. Foils are most easily made with malleable metals, such as aluminium, copper, tin, and gold. Foils usually bend under their own weight and can be torn easily. The more malleable a metal, the thinner foil can...
is pliable, and can be readily bent or wrapped around objects. Thin foils are fragile and are sometimes
laminateA laminate is a material that can be constructed by uniting two or more layers of material together. The process of creating a laminate is lamination, which in common parlance refers to the placing of something between layers of plastic and gluing them with heat and/or pressure, usually with an...
d to other materials such as
plasticA plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
s or
paperPaper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
to make them more useful. Aluminium foil supplanted
tin foilTin foil, also spelled tinfoil, is a thin foil made of tin. Actual tin foil was superseded by cheaper and more durable aluminium foil after World War II, and aluminium foil is sometimes confused with "tin foil" because of its similarity to the former material.-History:Foil made from a thin leaf of...
in the mid 20th century.
Annual production of aluminium foil was approximately 800000 tonne in Europe and 600000 tonne in the USA in 2003. Approximately 75% of aluminium foil is used for packaging of
foodFood is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
s,
cosmeticsCosmetics are substances used to enhance the appearance or odor of the human body. Cosmetics include skin-care creams, lotions, powders, perfumes, lipsticks, fingernail and toe nail polish, eye and facial makeup, towelettes, permanent waves, colored contact lenses, hair colors, hair sprays and...
, and chemical products, and 25% used for industrial applications (e.g. thermal insulation, cables and electronics).
In
North AmericaNorth America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, aluminium foil is known as
aluminum foil. It is also sometimes called
Reynolds wrap after
Reynolds MetalsReynolds Group Holdings is an American packaging company with its roots in the Reynolds Metals Company, was the second largest aluminum company in the United States, and the third largest in the world...
, the leading manufacturer in North America. In the
United KingdomThe United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
and
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
it is, informally, widely called
tin foil, for historical reasons.
Metallised filmMetallised films are polymer films coated with a thin layer of metal, usually aluminium. They offer the glossy metallic appearance of an aluminium foil at a reduced weight and cost...
s are sometimes mistaken for aluminium foil, but are actually polymer films coated with a thin layer of aluminium.
Before aluminium foil
Foil made from a thin leaf of
tinTin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
was commercially available before its aluminium counterpart. It 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 maleable 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.
The first audio recordings on phonograph cylinders were made on tin foil.
The first aluminium foil
Tin was first replaced by aluminium in 1910, when the first aluminium foil rolling plant, "Dr. Lauber, Neher & Cie." was opened in
EmmishofenKreuzlingen is a municipality in the district of Kreuzlingen in the canton of Thurgau in north-eastern Switzerland. It is the seat of the district and is the second largest city of the canton, after Frauenfeld, with a population of over 18,000...
,
SwitzerlandSwitzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
. The plant, owned by J.G. Neher & Sons, the aluminium manufacturers, started in 1886 in
SchaffhausenSchaffhausen is a city in northern Switzerland and the capital of the canton of the same name; it has an estimated population of 34,587 ....
, Switzerland , at the foot of the
Rhine FallsThe Rhine Falls is the largest plain waterfall in Europe.The falls are located on the Upper Rhine between the municipalities of Neuhausen am Rheinfall and Laufen-Uhwiesen, near the town of Schaffhausen in northern Switzerland, between the cantons of Schaffhausen and Zürich. They are 150 m ...
- capturing the falls' energy to produce aluminium. Neher's sons together with Dr. Lauber discovered the endless rolling process and the use of aluminium foil as a protective barrier in December 1907.
The first use of foil in the United States was in 1913 for wrapping
Life SaversLife Savers is an American brand of ring-shaped mints and artificially fruit-flavored hard candy. The candy is known for its distinctive packaging, coming in aluminum foil rolls....
, candy bars, and gum. Processes evolved over time to include the use of print, colour, lacquer, laminate and the embossing of the aluminium.
Manufacture
Aluminium foil is produced by rolling sheet ingots cast from molten aluminium, then re-rolling on sheet and foil rolling mills to the desired thickness, or by continuously casting and cold rolling. To maintain a constant thickness in aluminium foil production, beta radiation is passed through the foil to a sensor on the other side. If the intensity becomes too high, then the rollers adjust, increasing the thickness. If the intensities become too low and the foil has become too thick, the rollers apply more pressure, causing the foil to be made thinner.
The continuous casting method is much less energy intensive and has become the preferred process. For thicknesses below 0.025 millimetre, two layers are usually put together for the final pass and afterwards separated which produces foil with one bright side and one matte side. The two sides in contact with each other are matte and the exterior sides become bright, this is done to reduce tearing, increase production rates, control thickness, and get around the need for a smaller diameter roller.
Some
lubricationLubrication is the process, or technique employed to reduce wear of one or both surfaces in close proximity, and moving relative to each another, by interposing a substance called lubricant between the surfaces to carry or to help carry the load between the opposing surfaces. The interposed...
is needed during the rolling stages; otherwise the foil surface can become marked with a herringbone pattern. These lubricants are sprayed on the foil surface before passing through the mill rolls.
KeroseneKerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...
based lubricants are commonly used, although oils approved for food contact must be used for foil intended for food packaging.
Aluminium becomes work hardened during the cold rolling process and is
annealedAnnealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...
for most purposes. The rolls of foil are heated until the degree of softness is reached, which may be up to 340 °C (644 °F) for 12 hours. During this heating, the lubricating oils are burned off leaving a dry surface. Lubricant oils may not be completely burnt off for hard temper rolls, which can make subsequent coating or printing more difficult.
Properties
Aluminium foils thicker than 25 micrometre are impermeable to oxygen and water. Foils thinner than this become slightly permeable due to minute pinholes caused by the production process.
Aluminium foil has a shiny side and a matte side. The shiny side is produced when the aluminium is rolled during the final pass. It is difficult to produce rollers with a gap fine enough to cope with the foil gauge, therefore, for the final pass, two sheets are rolled at the same time, doubling the thickness of the gauge at entry to the rollers. When the sheets are later separated, the inside surface is dull, and the outside surface is shiny. This difference in the finish has led to the perception that favouring a side has an effect when cooking. While many believe that the different properties keep heat out when wrapped with the shiny finish facing out, and keep heat in with the shiny finish facing inwards, the actual difference is imperceptible without instrumentation. The
reflectivityIn optics and photometry, reflectivity is the fraction of incident radiation reflected by a surface. In general it must be treated as a directional property that is a function of the reflected direction, the incident direction, and the incident wavelength...
of bright aluminium foil is 88% while dull embossed foil is about 80%.
Packaging
As aluminium foil acts as a complete barrier to
lightLight or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
and
oxygenOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
(which cause
fatFats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
s to oxidise or become rancid), odours and flavours,
moistureHumidity is the amount of moisture the air can hold before it rains. Moisture refers to the presence of a liquid, especially water, often in trace amounts...
, and
bacteriaBacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, it is used extensively in food and pharmaceutical packaging. Aluminium foil is used to make long life packs (
aseptic packagingAseptic processing is the process by which a sterile product is packaged in a sterile container in a way that maintains sterility...
) for
drinkA drink, or beverage, is a liquid which is specifically prepared for human consumption. In addition to fulfilling a basic human need, beverages form part of the culture of human society.-Water:...
s and
dairyA dairy is a business enterprise established for the harvesting of animal milk—mostly from cows or goats, but also from buffalo, sheep, horses or camels —for human consumption. A dairy is typically located on a dedicated dairy farm or section of a multi-purpose farm that is concerned...
products which enables storage without refrigeration. Aluminium foil laminates are also used to package many other oxygen or moisture sensitive foods, and
tobaccoTobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...
, in the form of pouches, sachets and tubes, and as tamper evident closures. Aluminium foil containers and trays are used to bake pies and to pack
takeawayTake-out or takeout , carry-out , take-away , parcel , or tapau , is food purchased at a...
meals, ready snacks and long life
petA pet is a household animal kept for companionship and a person's enjoyment, as opposed to wild animals or to livestock, laboratory animals, working animals or sport animals, which are kept for economic or productive reasons. The most popular pets are noted for their loyal or playful...
foods.
Aluminium foil is widely sold into the
consumerConsumer is a broad label for any individuals or households that use goods generated within the economy. The concept of a consumer occurs in different contexts, so that the usage and significance of the term may vary.-Economics and marketing:...
market, often in rolls of 500 mm (19.7 in) width and several metres in length. It is used for wrapping food in order to preserve it, for example when storing leftover food in a
refrigeratorA refrigerator is a common household appliance that consists of a thermally insulated compartment and a heat pump that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room...
(where it serves the additional purpose of preventing odour exchange), when taking
sandwichA sandwich is a food item, typically consisting of two or more slices of :bread with one or more fillings between them, or one slice of bread with a topping or toppings, commonly called an open sandwich. Sandwiches are a widely popular type of lunch food, typically taken to work or school, or...
es on a journey, or when selling some kinds of take-away or
fast foodFast food is the term given to food that can be prepared and served very quickly. While any meal with low preparation time can be considered to be fast food, typically the term refers to food sold in a restaurant or store with preheated or precooked ingredients, and served to the customer in a...
.
Tex-MexTex-Mex is a regional American cuisine that blends food products available in the United States and the culinary creations of Mexican-Americans influenced by the cuisines of Mexico.Tex Mex may also refer to:...
restaurants in the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
, for example, typically provide take-away burritos wrapped in aluminium foil.
Insulation
Aluminium foil is widely used for
thermal insulationThermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...
(barrier and reflectivity), heat exchangers (
heat conductionIn heat transfer, conduction is a mode of transfer of energy within and between bodies of matter, due to a temperature gradient. Conduction means collisional and diffusive transfer of kinetic energy of particles of ponderable matter . Conduction takes place in all forms of ponderable matter, viz....
) and cable liners (barrier and electrical conductivity). Aluminium foil's heat conductive qualities make it a common accessory in
hookahA hookah A hookah(Gujarati હૂકાહ) A hookah(Gujarati હૂકાહ) (Hindustani: हुक़्क़ा (Devanagari, (Nastaleeq) huqqah) also known as a waterpipe or narghile, is a single or multi-stemmed (often glass-based) instrument for smoking in which the smoke is cooled by water. The tobacco smoked is referred to...
smoking: a sheet of perforated aluminium foil is frequently placed between the coal and the tobacco, allowing the tobacco to be heated without coming into direct contact with the burning coal.
EMF shielding
The typical shielding effectiveness of aluminium foil for a 100 MHz Spectrum is 80 dB per standard mil.
Cooking
Aluminium foil is also used for
barbecuingBarbecue or barbeque , used chiefly in the United States, Canada, the United Kingdom, New Zealand and Australia is a method and apparatus for cooking meat, poultry and occasionally fish with the heat and hot smoke of a fire, smoking wood, or hot coals of...
more delicate foods such as mushrooms and vegetables; food is wrapped in foil then placed on the grill, preventing loss of moisture that may result in a less appealing texture.
As is the case with all metallic items, aluminium foil reacts to being
microwavedA microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...
. This is due to the effect of electric fields of the microwaves causing a build up of charge to form between the sharp points in the aluminium; if enough charge accumulates it will discharge to a different place on the foil, creating a spark (
i.e., arcing). The design of modern microwave ovens has been corrected so microwave energy cannot be reflected back into the magnetron, and aluminium packages designed for microwave heating are available.
Art and decoration
Heavier foils made of aluminium are used for art, decoration, and crafts, especially in bright metallic colours. Metallic aluminium, normally silvery in colour, can be made to take on other colours through anodization. Anodizing creates an oxide layer on the aluminium surface that can accept coloured dyes or metallic salts, depending on the process used. In this way, aluminium is used to create an inexpensive gold foil that actually contains no gold, and many other bright metallic colours. These foils are sometimes used in distinctive packaging.
Geochemical sampling
Foil is used by organic/petroleum geochemists for protecting rock samples taken from the field and in the lab, where the sample is subject to biomarker analysis. While plastic or cloth bags are normally used for a geological sampling exercise, cloth bags are permeable and may allow organic solvents or oils (such as oils imparted from the skin) to taint the sample, and traces of the plastics from plastic bags may also taint the sample. Foil provides a seal to the ingress of organic solvents and does not taint the sample. Foil is also used extensively in geochemical laboratories to provide a barrier for the geochemist, and for sample storage.
Polishing steel
Aluminum foil is used to remove rust from steel and polishes steel surfaces by hand by rubbing it with aluminium foil dipped in water. The aluminium foil is softer than steel, and does not scratch the surface. Heat is generated by rubbing friction, the aluminium oxidizes to produce
aluminium oxideAluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...
. Aluminium has a higher
reduction potentialReduction potential is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. Reduction potential is measured in volts , or millivolts...
than iron, and therefore leaches oxygen atoms away from any rust on the steel surface. Aluminium oxide is harder than steel, and the microscopic grains of aluminium oxide produced create a fine
metal polishingPolishing and buffing are finishing processes for smoothing a workpiece's surface using an abrasive and a work wheel. Technically polishing refers to processes that use an abrasive that is glued to the work wheel, while buffing uses a loose abrasive applied to the work wheel...
compound that smoothes the steel surface to a bright shine.
Ribbon microphones
The material used in many
ribbon microphoneA ribbon microphone is a type of dynamic microphone that uses a thin aluminum, duraluminum or nanofilm ribbon placed between the poles of a magnet to generate voltages by electromagnetic induction...
s is aluminium leaf or "imitation silver leaf" as it is sometimes called. This is pure aluminium and is around 0.6-2.0 micrometres thick. It is in fact virtually the same material that the BBC used on Coles ribbons, with the exception that they also hand beat the leaf even more. They did this by sandwiching the ribbon between toilet paper and beating with a ball peen hammer. This "cold forges" the leaf. Corrugations must also be imparted into the ribbon, Coles used 25 per inch (1 mm cycle), RCA 44BX has 19 per inch (0.7 mm cycle) and is around 50 mm (2 in) long. RCA 77 has 13 corrugations per inch (0.5 mm cycle). RCA ribbon material is around 1 - 1.5 micrometers (0.00005 inch). The new Nady ribbon plus AEA both clearly advertise the fact they use 2 micrometre aluminium ribbon in their mics.
Environmental issues
The extensive use of aluminium foil has been criticized by
environmentalistsEnvironmentalism is a broad philosophy, ideology and social movement regarding concerns for environmental conservation and improvement of the health of the environment, particularly as the measure for this health seeks to incorporate the concerns of non-human elements...
because of the high resource
costIn production, research, retail, and accounting, a cost is the value of money that has been used up to produce something, and hence is not available for use anymore. In business, the cost may be one of acquisition, in which case the amount of money expended to acquire it is counted as cost. In this...
of extracting aluminium, primarily as a result of the large amount of
electricityElectricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
used to process
bauxiteBauxite is an aluminium ore and is the main source of aluminium. This form of rock consists mostly of the minerals gibbsite Al3, boehmite γ-AlO, and diaspore α-AlO, in a mixture with the two iron oxides goethite and hematite, the clay mineral kaolinite, and small amounts of anatase TiO2...
ore. This cost is reduced via
recyclingRecycling is processing used materials into new products to prevent waste of potentially useful materials, reduce the consumption of fresh raw materials, reduce energy usage, reduce air pollution and water pollution by reducing the need for "conventional" waste disposal, and lower greenhouse...
, reduced energy requirements during transport due to lighter weight packages, and the fact that many foods that would otherwise perish can be protected over long periods without refrigeration. Some aluminium foil products can be recycled at around 5% of the original
energyIn physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
cost, although many aluminium laminates are not recycled due to difficulties in separating the components and low yield of aluminium metal.
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