Keith P. Walsh is spreading drivel again (August 25, 2007). As usual he is confused, and he may be confusing readers of both the sci.med.dentistry and sci.materials newsgroups. He needs to take some lessons rather than try to give them.
Point 1: The technical definition for an alloy (a noun describing a material)
The Merriam-Webster OnLine Dictionary defines an alloy as: "a substance composed of two or more metals or of a metal and a nonmetal intimately united usually by being fused together and dissolving in each other when molten". Note the qualification "usually" to describe the process of melting.
The Random House Unabridged Dictionary has a similar definition: "a substance composed of two or more metals, or of a metal or metals with a nonmetal, intimately mixed, as by fusion or electrodeposition".
Mr. Walsh prefers to use a narrower, crankier definition that: "An alloy is formed by raising each of the constituent metals to be alloyed to a temperature above its melting point, mixing the metal constituents thoroughly whilst they are all in their molten states, and allowing the mixture to solidify by cooling at a controlled rate."
By Mr. Walsh's definition an amalgam is not a "true alloy", since the process used for making it (transient liquid phase sintering) does not involve complete melting.
All the above definitions complicate matters by trying to describe both a material and the process of mixing used to make it.
A sensible place to find a technical definition for an alloy is in the ASM Materials Engineering Dictionary, which was published in 1992 by ASM International (The Materials Information Society). This dictionary defines an alloy as: "A substance having metallic properties and being composed of two or more chemical elements of which at least one is a metal". This definition simply describes an alloy as a material, without limiting the process used to make it.
The definition comes from the ASM Metals Handbook. It is right out of the Glossary of Metallurgical Terms at the beginning of the Metals Handbook, Desk Edition (page 1.3 of the first 1985 edition, or page 5 of the second 1998 edition).
The exact same definition appeared fifty years earlier on page 1 in the Definitions of Metallurgical Terms at the beginning of the 1948 edition of the Metals Handbook (published by the American Society for Metals, the predecessor of ASM International).
A similar definition also appears earlier on page 3 in the 1939 edition of the Metals Handbook, which defines an alloy as: "a mixture with metallic properties composed of two or more elements of which at least one is a metal".
Similar definitions appear in textbooks. One example is Materials Science and Engineering: An Introduction, by William D. Callister, Jr. The glossary on page 810 of the fourth edition, John Wiley & Sons,
1997 defines an alloy simply as: "a metallic substance that is composed of two or more elements".The Oxford English Dictionary (1989 edition) also defines an alloy broadly as: "a mixture of metals; a metallic compound, an amalgam."
I believe that the time-tested (almost sixty year old) Metals Handbook definition is a sensible description for what an alloy is.
Pittsburgh Pete
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