Archive for November, 2012

Sodium (Na)

Natrium

Sodium is a chemical element with the symbol Na (from Latin: natrium) in the periodic table and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. The free metal does not occur in nature, but instead must be prepared from its compounds; it was first isolated by Humphry Davy in 1807 by the electrolysis of sodium hydroxide.

Sodium is the sixth most abundant element in the Earth’s crust, and exists in numerous minerals such as feldspars, sodalite and rock salt. Many salts of sodium are highly water-soluble, and their sodium has been leached by the action of water so that chloride and sodium are the most common dissolved elements by weight in the Earth’s bodies of oceanic water.

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Hydrogen Cracking

What is Hydrogen cracking ?

Hydrogen cracking also known as cold cracking or delayed cracking. The main feature of this type of crack is that it occurs in ferritic weldable steels, and generally occurs immediately on welding or after a short time after welding, but usually within 48hrs. The mechanism starts with lone hydrogen atoms diffusing through the metal.

At high temperatures, the elevated solubility of hydrogen allows hydrogen to diffuse into the metal (or the hydrogen can diffuse in at a low temperature, assisted by a concentration gradient). When these hydrogen atoms re-combine in minuscule voids of the metal matrix to form hydrogen molecules, they create pressure from inside the cavity they are in. This pressure can increase to levels where the metal has reduced ductility and tensile strength up to the point where it cracks open (hydrogen induced cracking, or HIC). High-strength and low-alloy steels, nickel and titanium alloys are most susceptible. Austempered iron is also susceptible.

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Kevlar

History of Armor

Kevlar is five times stronger than steel but very light weight  and half the wieght of fiberglass which made it ideal  for making bulletproof vests. It is resistant to impact and abrasion damage. In seawwater its strength is 20 times more than steel which made it excellent for offshore drilling operations. Kevlar is made by Dupont Corporation.

Kevlar is a chemical compuned polyparaphenylene terepthalamide which belongs to the class aromatic polyamide is a para-aramid synthetic fibre. Aramides belong to class of nylons. The aramide ring and the para structure is what gives kevlar its high strength and thermal stability.  Kevlar was developed in 1965 by Stephanie Kwolek and Roberto Berendt at DuPont Laboratories. Kevlar is a very strong synthetic fiber that can be spun into cloth to make body armor. Kevlar cloth was first used to make body armor in the 1970′s. Kevlar went through a number of government tests until finally a “bullet-resistant” vest was developed.

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