Thursday, March 6, 2014



STAINLESS STEEL
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is a steel alloy with a minimum of 10.5% chromium content by mass.
Stainless steel does not readily corrode, rust or stain with water as ordinary steel does, but despite the name it is not fully stain-proof, most notably under low-oxygen, high-salinity, or poor-circulation environments. There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel is used where both the properties of steel and resistance to corrosion are required.
Stainless steel differs from carbon steel by the amount of chromium present. Unprotected carbon steel rusts readily when exposed to air and moisture. This iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide, and due to the greater volume of the iron oxide this tends to flake and fall away. Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion by blocking oxygen diffusion to the steel surface and blocks corrosion from spreading into the metal's internal structure, and due to the similar size of the steel and oxide ions they bond very strongly and remain attached to the surface.
Passivation only occurs if the proportion of chromium is high enough and oxygen is present.

Sumber :  http://en.wikipedia.org/wiki/Stainless_steel




ALUMINIUM
Aluminium is a chemical element in the boron group with symbol Al and atomic number 13. It is a silvery white, soft, ductile metal. Aluminium is the third most abundant element (after oxygen and silicon), and the most abundant metal, in the Earth's crust. It makes up about 8% by weight of the Earth's solid surface. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals. The chief ore of aluminium is bauxite.
Aluminium is remarkable for the metal's low density and for its ability to resist corrosion due to the phenomenon of passivation. Structural components made from aluminium and its alloys are vital to the aerospace industry and are important in other areas of transportation and structural materials. The most useful compounds of aluminium, at least on a weight basis, are the oxides and sulfates.
Despite its prevalence in the environment, no known form of life uses aluminium salts metabolically. In keeping with its pervasiveness, aluminium is well tolerated by plants and animals. Owing to their prevalence, potential beneficial (or otherwise) biological roles of aluminium compounds are of continuing interest.

Sumber :  http://en.wikipedia.org/wiki/Aluminium





COPPER

Copper is a chemical element with the symbol Cu (from Latin: cuprum) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; a freshly exposed surface has a reddish-orange color. It is used as a conductor of heat and electricity, a building material, and a constituent of various metal alloys.
The metal and its alloys have been used for thousands of years. In the Roman era, copper was principally mined on Cyprus, hence the origin of the name of the metal as сyprium (metal of Cyprus), later shortened to сuprum. Its compounds are commonly encountered as copper(II) salts, which often impart blue or green colors to minerals such as azurite and turquoise and have been widely used historically as pigments. Architectural structures built with copper corrode to give green verdigris (or patina). Decorative art prominently features copper, both by itself and as part of pigments.
Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the respiratory enzyme complex cytochrome c oxidase. In molluscs and crustacea copper is a constituent of the blood pigment hemocyanin, which is replaced by the iron-complexed hemoglobin in fish and other vertebrates. The main areas where copper is found in humans are liver, muscle and bone. Copper compounds are used as bacteriostatic substances, fungicides, and wood preservatives.

Sumber : http://en.wikipedia.org/wiki/Copper




BRONZE
Bronze is an alloy consisting primarily of copper, usually with tin as the main additive. It is hard and tough, and it was so significant in antiquity that the Bronze Age was named after the metal. However, historical pieces were often made interchangeably of brasses (copper and zinc), and bronzes with different compositions, so modern museum and scholarly descriptions of older objects increasingly use the more inclusive term "copper alloy" instead. Historically the term latten was used for such alloys.
The discovery of bronze enabled people to create metal objects which were harder and more durable than previously possible. Tools, weapons, armor, and various building materials, like decorative tiles, made of bronze were harder and more durable than their stone and copper ("Chalcolithic") predecessors. Initially bronze was made out of copper and arsenic to form arsenic bronze, or directly from naturally or artificially mixed ores of those. It was only later that tin was used, becoming the sole type of major non-copper ingredient of bronze in the late 3rd millennium BC. Tin bronze was superior to arsenic bronze in that the alloying process itself could more easily be controlled and the alloy was stronger and easier to cast. Also, unlike arsenic, tin is not toxic.
The earliest tin-alloy bronze dates to 4500 BCE in a Vin
ča culture site in Pločnik (Serbia). Other early examples date to the late 4th millennium BC in Susa (Iran) and some ancient sites in China, Luristan (Iran) and Mesopotamia (Iraq).
Ores of copper and (far rarer) tin are rarely found together (exceptions include one ancient site in Thailand and one in Iran), so serious bronze work has always involved trade. Tin sources and trade in ancient times had a major influence of the development of cultures. In Europe, a major source for tin was England's deposits of ore in Cornwall, which were traded as far as Phoenicia in the Eastern Mediterranean.
Though bronze is generally harder than wrought iron, with Vickers hardness of 60–258 vs. 30–80, the Bronze Age gave way to the Iron Age because iron was easier to find and to process into a poor grade of metal; although it can be made into higher grades, doing that takes significantly more effort and skill. Bronze was still used during the Iron Age. For many purposes, the weaker wrought iron was found to be sufficiently strong.

Sumber :  http://en.wikipedia.org/wiki/Bronze






BRASS
Brass is an alloy made of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties. It is a substitutional alloy: atoms of the two constituents may replace each other within the same crystal structure.
By comparison, bronze is principally an alloy of copper and tin. Bronze does not necessarily contain tin, and a variety of alloys of copper, including alloys with arsenic, phosphorus, aluminium, manganese, and silicon, are commonly termed "bronze". The term is applied to a variety of brasses and the distinction is largely historical, both terms having a common antecedent in the term latten.
It is used for decoration for its bright gold-like appearance; for applications where low friction is required such as locks, gears, bearings, doorknobs, ammunition casings and valves; for plumbing and electrical applications; and extensively in brass musical instruments such as horns and bells for its acoustic properties. It is also used in zippers. Brass is often used in situations where it is important that sparks not be struck, as in fittings and tools around explosive gases.

Sumber :  http://en.wikipedia.org/wiki/Brass



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