Interesting Facts About Metal Alloys

Chances are you often encounter metal alloys in your everyday life in the form of jewelry, cookware, tools, and most other items made of metal. Examples of alloys include white gold, sterling silver, brass, bronze, and steel. Here are some interesting facts about metal alloys.

Facts About Common Alloys

An alloy is a blend of two or more metals. The blend can form a solid solution or can be a simple mixture, depending on the size of the crystals that form and how homogeneous the alloy is. Here are some distinctive alloys:

• Although sterling silver is an alloy consisting mainly of silver, many alloys with the word "silver" in their names are only silver in color. German silver and Tibetan silver are examples of alloys that have the name but don't contain any elemental silver.
• Many people believe steel is an alloy of iron and nickel, but it consists primarily of iron, carbon, and any of several other metals.
• Stainless steel is an alloy of iron, low levels of carbon, and chromium. The chromium gives the steel resistance to "stain," or iron rust. A thin layer of chromium oxide forms on the surface of stainless steel, protecting it from oxygen, which is what causes rust. However, stainless steel can be stained if you expose it to a corrosive environment, such as seawater. That environment attacks and removes the protective chromium oxide coating more quickly than it can repair itself, exposing the iron to attack.
• Solder is an alloy used to bond metals to each other. Most solder is an alloy of lead and tin. Special solders exist for other applications. For example, silver solder is used in the manufacture of sterling silver jewelry. Fine silver or pure silver is not an alloy and will melt and join to itself.
• Brass is an alloy consisting primarily of copper and zinc. Bronze, on the other hand, is an alloy of copper with another metal, usually tin. Originally, brass and bronze were considered to be distinct alloys, but in modern usage, "brass" means any copper alloy. You might hear brass cited as a type of bronze or vice versa.
• Pewter is a tin alloy consisting of 85 to 99 percent tin with copper, antimony, bismuth, lead, and/or silver. Although lead is used much less often in modern pewter, even "lead-free" pewter typically contains a small amount of lead. "Lead-free" is defined as containing no more than 0.05 percent (500 ppm) lead, which remains appreciable if the pewter is used for cookware, dishes, or children's jewelry.

Facts About Special Alloys

These alloys have interesting properties:

• Electrum is a naturally occurring alloy of gold and silver with small amounts of copper and other metals. Considered by the ancient Greeks to be "white gold," it was used as far back as 3000 B.C. for coins, drinking vessels, and ornaments.
• Gold can exist in nature as a pure metal, but most of the gold you encounter is an alloy. The amount of gold in the alloy is expressed in terms of karats, so 24-karat gold is pure gold, 14-karat gold is 14/24 parts gold, and 10-karat gold is 10/24 parts gold or less than half gold. Any of several metals can be used for the remaining portion of the alloy.
• An amalgam is an alloy made by combining mercury with another metal. Almost all metals form amalgams, with the exception of iron. Amalgam is used in dentistry and in gold and silver mining because these metals readily combine with mercury.