Lessons on Alloys, Amalgams, and Pleonasms (1)

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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On Aug 29, 2:55 pm, snipped-for-privacy@hotmail.com wrote:

So it's OK for me to call those mixtures of metals made with liquid gallium "amalgams" then Pete?
Keith P Walsh
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On 29 Aug, 14:55, snipped-for-privacy@hotmail.com wrote:

Hey Pittsburgh Pete where are you?
Don't go all shy on us now - things are just getting interesting.
I've found some more people who call gallium amalgams "gallium amalgams". And they mean "gallium amalgams with no mercury in them".
It's Giles Humpston and David M Jacobson in their book, "Principles of Soldering", published by ASM International (April 2004) and endorsed by The Materials Information Society.
You can read it yourself by following this link:
http://books.google.com/books?id=cQ6khQScBF4C&pg=PA103&dq=%22gallium+amalgam%22&sig=Um_AAj4cKineMZPCpE4sXOWq3Uw#PPP1,M1
The parts which are of interest to us are:
Page 115 - Section 5.4.1 - Amalgams Based on Mercury
Page 116 - Section 5.4.2 - Amalgams Based on Gallium
"Gallium melts at 29 deg C and is therefore a potential base for formulating very low-process-temperature amalgams without the toxic hazard associated with mercury"
(Note, there's no mercury in these amalgams.)
Page 117 - Section 5.4.3 - Amalgams Based on Indium
"Indium is another liquid metal that can be considered as a base for amalgam systems. "
(There's no mercury in these amalgams either.)
So I think this just about settles it. The term "mercury amalgam" is NOT a pleonasm, because on its own the word "amalgam" is not sufficient to distinguish between mercury amalgams, gallium amalgams and indium amalgams.
Maybe the lesson to learn is that we shouldn't so easily allow ourselves to be misled by dentists who were misled by their professors in dental schools.
Keith P Walsh
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The repeated repeatedly deleted.
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that's rich coming from you
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