User:Sm8900/Chemicals

Chemicals in manufacturing refers to the use of various chemical elements in manufacturing, as well as important compunds of those chemicals.

Metals

Metals can be categorised according to their physical or chemical properties. Categories described in the subsections below include ferrous and non-ferrous metals; brittle metals and refractory metals; white metals; heavy and light metals; and base, noble, and precious metals. One common approach categorises the elemental metals on the basis of their chemical properties into alkali and alkaline earth metals; transition and post-transition metals; and lanthanides and actinides. Other categories are possible, depending on the criteria for inclusion. For example, the ferromagnetic metals—those metals that are magnetic at room temperature—are iron, cobalt, and nickel.

Iron

In the modern world, iron alloys, such as steel, stainless steel, cast iron and special steels are by far the most common industrial metals, because of their mechanical properties and low cost. The iron and steel industry is thus very important economically, and iron is the cheapest metal, with a price of a few dollars per kilogram or per pound (see Metal#uses).

Chromium

Chromium metal is valued for its high corrosion resistance and hardness. A major development in steel production was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel. Stainless steel and chrome plating (electroplating with chromium) together comprise 85% of the commercial use.

Industrial production of chromium prodeeds from chromite ore (mostly FeCr₂O₄) to produce ferrochromium, an iron-chromium alloy, by means of aluminothermic or silicothermic reactions. Ferrochromium is then used to produce alloys such as stainless steel. Pure chromium metal is produced by a different process: roasting and leaching of chromite to separate it from iron, followed by reduction with carbon and then aluminium.

Chrome plating

Hard chrome, also known as industrial chrome or engineered chrome, is used to reduce friction, improve durability through abrasion tolerance and wear resistance in general, minimize galling or seizing of parts, expand chemical inertness to include a broader set of conditions (such as oxidation resistance), and bulking material for worn parts to restore their original dimensions. It is very hard, measuring between 65 and 69 HRC (also based on the base metal's hardness). Hard chrome tends to be thicker than decorative chrome, with standard thicknesses in nonsalvage applications ranging from 0.02 to 0.04 mm (20 to 40 μm), but it can be an order of magnitude thicker for extreme wear resistance requirements, in such cases 0.1 mm (100 μm) or thicker provides optimal results.

Selenium

Selenium is found in metal sulfide ores, where it partially replaces the sulfur. Commercially, selenium is produced as a byproduct in the refining of these ores, most often during production. Minerals that are pure selenide or selenate compounds are known but rare. The chief commercial uses for selenium today are glassmaking and pigments. Selenium is a semiconductor and is used in photocells. Applications in electronics, once important, have been mostly replaced with silicon semiconductor devices. Selenium is still used in a few types of DC power surge protectors and one type of fluorescent quantum dot.

• Glassmaking. The largest commercial use of Se, accounting for about 50% of consumption, is for the production of glass. Se compounds confer a red color to glass. This color cancels out the green or yellow tints that arise from iron impurities typical for most glass. For this purpose, various selenite and selenate salts are added. For other applications, a red color may be desired, produced by mixtures of CdSe and CdS. Larger amounts of ammonium selenite are used to make ruby red glass, such as those that are used in traffic lights, as well as in the manufacturing of art glass and black glass. The presence of selenium in plate glass is important to architects, as it reduces the amount of solar radiation that is transmitted through the glass.

External links

• Videos for each element by the University of Nottingham
• "Chemical Elements", In Our Time, BBC Radio 4 discussion with Paul Strathern, Mary Archer and John Murrell (25 May 2000)

Category:Chemistry