Precious Metals: Noble Metals & Basic Metallurgy
Precious Metal
The word "metal" is derived from the Greek word metallin, or "to search after," and from the Greek word metallon, or the Latin word metallum which both mean "mine or metal." The earliest known metal employed by humans was native, or "free" gold that was found in Spanish caves, and dates back to the late Paleolithic period (c.40,000 BC).
Basic Metallurgy
Metallurgy is a category of materials science that studies the physical and chemical behavior of the metallic elements, as well as their intermetallic compounds, and the mixing of various metals into "alloys." The science of metallurgy is commonly used in the trade of metalworking and jewelry making. The term "extractive metallurgy" refers to the practice of removing valuable metals from an ore body and refining the extracted raw metal into a purer form.
In chemistry, a "metal" is a chemical element whose atoms readily lose electrons to form positive ions (cations), and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms - also described as a lattice of positive ions surrounded by a cloud of delocalized electrons. Metals are divided into two main groups: "ferrous" and "non-ferrous." Ferrous metals contain Iron (Fe, ferrum), and non-ferrous metals include "nobel" or "precious metals," base metals, or light metals.
Noble Metals
A noble metal or "precious metals" is a rare metallic chemical element that has a high surface luster, is softer or more ductile than other metals, is less chemically reactive than most elements, and has high economic value due to its rarity.
The physical characteristics of elemental metals such as gold and silver are described as:
Plastic: The metal can be bent and worked without rupturing (not brittle).
Malleable: The metal can be compressed, deformed, extruded, hammered, and rolled.
Ductile: The metal will permit 'plastic' elongation (wire drawing) without fracturing.
The noble metals would include: gold, silver, and the platinum group (aka: "platinum group metals," or "PGMs") which includes platinum, palladium, rhodium, iridium, osmium, and ruthenium. These metals are considered "noble" primarily because of their corrosion and oxidation resistance, as well as their chemical stability. The noble metals are also extremely rare in nature, and prized for their suitability for jewelry making and other fine crafts.
Base Metals
Base metals are found in great abundance throughout the earth's crust. Base metals include: aluminum, copper, lead, mercury, nickle, tin, and zinc.
Light Metals
The term "light metals" refers to any metal that has a low density and light weight. These types of metals would include: aluminum, magnesium and titanium.
Transition Metals
Many metals are inclined to oxidize through electron loss, reacting with oxygen in the air to form oxides over time. Transition metals (such as iron, copper, zinc, and nickel) take longer to oxidize, and some (gold, palladium, platinum) do not react with the atmosphere at all. Some metals form an oxide barrier layer on their surface (copper, titanium) which cannot be penetrated by further oxygen molecules.
Ductile Fracture in Metals
A "ductile fracture" occurs when extensive plastic deformation takes place prior to the mechanical rupture. Noble metals with a high purity can withstand large amounts deformation (plasticity) before fracture will occur.
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