What is Aluminium Foil ?
Foil is a very thin sheet of rolled aluminium supplied in its pure form (`commercial purity`) or in a variety of alloys and tempers which give a wide choice of tensile properties. The thickness of foil ranges from the thinnest currently produced commercially at about 0.0065 mm (or 6.5 µm) to the defined upper limit of 0.2 mm (or 200 µm). Material thicker than 0.2 mm is defined as sheet or strip.
What are its Attributes?
Abundance – aluminium is plentiful with no danger of world depletion
Barrier efficiency to light, gases, oils and fats, volatile compounds and water vapour
Temperature resistance from deep-freeze to oven processing
Heat conductivity and reflectivity
Strength and durability
Compatibility with foods and pharmaceuticals
Ease of lamination and coating
Formability and non-returning dead-fold
Decorative potential, brilliant or matt surface
Printability by flexo, gravure and offset litho
Cost-effectiveness – optimum performance yet resource economy
As aluminium foil acts as a complete barrier to light and oxygen (which cause fats to oxidise or become rancid), odours and flavours, moisture, and bacteria, it is used extensively in food and pharmaceutical packaging. Aluminium foil is used to make long life packs (aseptic packaging) for drinks and dairy products which enables storage without refrigeration. Aluminium foil laminates are also used to package many other oxygen or moisture sensitive foods, and tobacco, 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 takeaway meals, ready snacks and long life pet foods.Aluminium foil is widely sold into the consumer market, usually in rolls of around 50 centimetres 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 refrigerator (where it serves the additional purpose of preventing odour exchange), when taking sandwiches on a journey, or when selling some kinds of take-away or fast food. Tex-Mex restaurants in the United States, for example, typically provide take-away burritos wrapped in aluminium foil.
Aluminium foil is also widely used for thermal insulation (barrier and reflectivity), heat exchangers (heat conduction) and cable liners (barrier and electrical conductivity). Foils in special alloys are even used for structural honeycomb components for aircraft. Aluminium foil`s heat conductive qualities make it a common accessory in hookah 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.
The typical shielding effectiveness of aluminium foil for a 100 MHz Spectrum is 80 dB per standard mil. It will block all broadcast radio waves when completely surrounding the receiver and absorb free standing waves when grounded.
Aluminium foil is also used for barbecuing 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 microwaved. 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). Due to frequent use in food services, this commonly leads to kitchen fires. 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.
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.
A simple and inexpensive way to remove rust from and polish steel surfaces by hand is to rub it with aluminium foil dipped in water. The aluminium foil is softer than steel, and will not scratch the surface. As heat is generated by rubbing friction, the aluminium will oxidize to produce aluminium oxide. Aluminium has a higher reduction potential than iron, and will therefore leach oxygen atoms away from any rust on the steel surface. Aluminium oxide is harder than steel, and the microscopic grains of aluminium oxide produced creates a fine metal polishing compound that smoothes the steel surface to a bright shine.
The material use in many ribbon microphones is aluminium leaf or “imitation silver leaf” as it is sometimes called. This is pure aluminium and is around .6-2.0 micron 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, RCA 44BX has 19 per inch (and is around 2″ long) and the RCA 77 has 13 corrugations per inch. RCA ribbon material is around 1 – 1.5 micrometers (microns) or .00005 inch. The new Nady ribbon plus AEA both clearly advertise the fact they use 2 micron aluminium ribbon in their mics.