Pickling (metal)

Pickling is a metal surface treatment used to remove impurities, such as stains, inorganic contaminants, rust or scale from ferrous metals, copper, precious metals and aluminum alloys. A solution called pickle liquor, which contains strong acids, is used to remove the surface impurities. It is commonly used to descale or clean steel in various steelmaking processes.

Process

Many hot working processes and other processes that occur at high temperatures leave a discoloring oxide layer or scale on the surface. In order to remove the scale the workpiece is dipped into a vat of pickle liquor.

The primary acid used is hydrochloric acid, although sulfuric acid was previously more common. Hydrochloric acid is more expensive than sulfuric acid, but it pickles much faster while minimizing base metal loss. The speed is a requirement for integration in automatic steel mills that run production at high speed; speeds as high as 800 ft/min (≈243 metres/min) have been reported.

Carbon steels, with an alloy content less than or equal to 6%, are often pickled in hydrochloric or sulfuric acid. Steels with an alloy content greater than 6% must be pickled in two steps and other acids are used, such as phosphoric, nitric and hydrofluoric acid. Rust- and acid-resistant chromium-nickel steels are pickled in a bath of hydrochloric and nitric acid. Most copper alloys are pickled in dilute sulfuric acid, but brass is pickled in concentrated sulfuric and nitric acid mixed with sodium chloride and soot.

Metal

A metal (from Greek μέταλλον métallon, "mine, quarry, metal") is a material (an element, compound, or alloy) that is typically hard, opaque, shiny, and has good electrical and thermal conductivity. Metals are generally malleable — that is, they can be hammered or pressed permanently out of shape without breaking or cracking — as well as fusible (able to be fused or melted) and ductile (able to be drawn out into a thin wire). About 91 of the 118 elements in the periodic table are metals, the others are nonmetals or metalloids. Some elements appear in both metallic and non-metallic forms.

Astrophysicists use the term "metal" to collectively describe all elements other than hydrogen and helium. Thus, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium.

Many elements and compounds that are not normally classified as metals become metallic under high pressures; these are formed as metallic allotropes of non-metals.

Structure and bonding

Metal: A Headbanger's Journey

Metal: A Headbanger's Journey is a 2005 documentary directed by Sam Dunn with Scot McFadyen and Jessica Wise. The film follows 31-year-old Dunn, a Canadian anthropologist, who has been a heavy metal fan since the age of 12. Dunn sets out across the world to uncover the various opinions on heavy metal music, including its origins, culture, controversy, and the reasons it is loved by so many people. The film made its debut at the 2005 Toronto International Film Festival, and was released as a two-disc special edition DVD in the US on September 19, 2006.

A follow-up to the film titled Global Metal premiered at the Bergen International Film Festival on October 17, 2007, and saw limited release in theatres in June 2008. Dunn has also elaborated upon his "Heavy Metal Family Tree" in the VH1 series Metal Evolution, which focuses on one subgenre per episode.

Contents

The film discusses the traits and originators of some of metal's many subgenres, including the New Wave of British Heavy Metal, power metal, nu metal, glam metal, thrash metal, black metal, and death metal. Dunn uses a family-tree-type flowchart to document some of the most popular metal subgenres. The film also explores various aspects of heavy metal culture. Notable segments include Dunn taking a trip to the Wacken Open Air festival, an interview with Dee Snider providing an analysis of the PMRC attack on heavy metal music, and an interview with several Norwegian black metal bands.

Heavy metal music

Heavy metal (or simply metal) is a genre of rock music that developed in the late 1960s and early 1970s, largely in the United Kingdom and the United States. With roots in blues rock and psychedelic rock, the bands that created heavy metal developed a thick, massive sound, characterized by highly amplified distortion, extended guitar solos, emphatic beats, and overall loudness. Heavy metal lyrics and performance styles are often associated with masculinity, aggression, and machismo.

The first heavy metal bands such as Led Zeppelin, Black Sabbath and Deep Purple attracted large audiences, though they were often derided by critics, a status common throughout the history of the genre. During the mid-1970s, Judas Priest helped spur the genre's evolution by discarding much of its blues influence;Motörhead introduced a punk rock sensibility and an increasing emphasis on speed. Beginning in the late 1970s, bands in the New Wave of British Heavy Metal such as Iron Maiden and Saxon followed in a similar vein. Before the end of the decade, heavy metal fans became known as "metalheads" or "headbangers".