Lessons on Alloys, Amalgams, and Pleonasms (2)

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 2: The technical definition for an amalgam (a noun describing a material)
The Metals Handbook, Desk Edition (2nd, 1998) defines an amalgam as: "a dental alloy produced by combining mercury with alloy particles of silver, tin, copper, and sometimes zinc".
The single volume, 1948 edition of the Metals Handbook, defines an amalgam more simply just as: "a mercury-base alloy".
I believe that the time-tested (almost sixty year old) Metals Handbook definition is a sensible description for what an amalgam is.
Based on the above definitions:
Point 3: An amalgam is an alloy, and an amalgam implies the presence of mercury.
The Metals Handbook started out as a single volume. It grew over ten editions into a rather authoritative collection of about two dozen thick reference books that take up an entire shelf. You can typically find it in a university library or a large public library.
More recently the Metals Handbook was renamed simply as the ASM Handbook, since its coverage is being broadened to include other materials that formerly were covered in another series called the Engineered Materials Handbook. These handbooks are the consensus result of a large collective enterprise involving many committees and the volunteer efforts of hundreds of members.
The Desk Editions are affordable versions condensed down to single volume. I cited it because I have it on my bookshelf.
Pittsburgh Pete
DISCLAIMER
We do not believe what we write, and neither should you. Information furnished to you is for topical (external) use only. This information may not be worth any more than either a groundhog turd, or what you paid for it (nothing). The author may not even have been either sane or sober when he wrote it down. Do not worry, be happy.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Keith is a wonder, of sorts, isn't he.
There are some people in life that are best avoided, and Keith P. Walsh is one of them.
Good luck, Pete.
Good to see you still posting, and doing your best to mitigate the misinformation and distortion.
Jim
snipped-for-privacy@hotmail.com wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That may be because I have a habit of embarrassing people by exposing their ignorances.
I'll try an example.
Pittsburgh Pete says, "An amalgam is an alloy, and an amalgam implies the presence of mercury."
That "an amalgam" has come to imply mercury (note that even Pete only says "implies" and not "requires"), especially in the dental profession, is because mercury amalgams are the most common.
But mercury amalgams are NOT the only type of amalgam, as you can see by extracts from the book, "Principles of Soldering", by Giles Humpston and David M Jacobson, published by ASM International (April 2004) and endorsed by The Materials Information Society.
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.)
You can read all this at:
http://books.google.com/books?id=cQ6khQScBF4C&pg=PA103&dq=%22gallium+amalgam%22&sig=Um_AAj4cKineMZPCpE4sXOWq3Uw#PPP1,M1
So Jim, it is clear from the above that the term "mercury amalgam" is NOT a pleonasm, because on its own the word "amalgam" is not sufficient to distinguish between "mercury amalgams" in which the liquid metal amalgamating agent is mercury, "gallium amalgams" in which the liquid metal amalgamating agent is gallium, and "indium amalgams" in which the liquid metal amalgamating agent is indium.
Now, do you agree with this?
Go on, answer that one simple question.
Do you agree that the term "mercury amalgam" is NOT a pleonasm?
How about you Pittsburgh Pete?
(Or even you Steven Bornfield?)
Keith P Walsh
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I see you are still the same fellow, boring in with the same standard challenging responses.
You are truly one of the people in life best avoided.
PLONK !
I've created a special kill filter just for you.
Jim
Keith P Walsh wrote:

http://books.google.com/books?id=cQ6khQScBF4C&pg=PA103&dq=%22gallium+amalgam%22&sig=Um_AAj4cKineMZPCpE4sXOWq3Uw#PPP1,M1
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Kill yourself, delusional shithead.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Read and learn Jimbo. Read and learn.
If you mix together different metals at a temperature which is above the melting point of only one of the metals in the mix, and you allow the mixture to harden, then what you end up with is an inhomogeneous mixture of dissimilar metals, an example of which is shown at:
http://book.boot.users.btopenworld.com/setting.htm
If you want to create such a material working at room temperature then you have to use mercury as the molten (liquid) metal component in the mix, because mercury is the only metal that is in the liquid state at room temperature.
However, if you work at a little over 30 degrees celsius then it is possible to use liquid gallium to mix with solid pieces of other metals and create a mixture of metals which, because of the way in which it has been formed, will have a similarly inhomogeneous microstructure to that described above.
And of course if you can work at a temperature around 160 degrees celsius (not much use for patients in dental surgeries) then you can produce other solid metal mixtures, again with similarly inhomogeneous microstructures to those described above, by using liquid indium to "amalgamate" solid bits of other metals.
If on the other hand you mix together different metals at a temperature which is well above the melting points of ALL of the metals in the mix, and you mix them thoroughly before allowing the mixture to solidify by cooling at a controlled rate, then what you get is a solid mixture of metals which does not have the same degree of material inhomogeneity as the materials desgribed above. What you get is a different type of mixture of metals which has a much more homogeneous microstructure whereby it would not be possible to show the relative positions of the atoms of the different metals at the scale of the diagram indicated above.
Now, one important point to note is that it doesn't really make any difference what we call these materials, because of their different physical structures the two different types of material will distinguish themselves naturally by differences in their physical behavior. And these differences are determined by Nature, not by the names which anyone might prefer to give them.
For example, you would expect the thermoelectric behavior of these two types of material to be different as a consequence of the differences in their internal sctructure.
However, at this point it would be convenient to be able to identify the two different types by giving them different labels, or "names".
I think it makes sense to call the first ype of material, (where bits of solid metal are "amalgamated" by mixing them with a liquid metal "amalgamating agent" - which might be mercury, gallium or indium) an "amalgam". And in fact I do rather suspect that this usage may actually be the true origin of the word amalgam - even if it did arise through the discovery and use of mainly "mercury amalgams".
And I think it also makes sense to call the other type of material, where all of the metals are mixed in their liquid states, true alloys - or simply "alloys".
Remember that it doesn't make any difference if Pittsburgh Pete wants the "amalgams" to be called "alloys" as well ( - at least he appears to have given up on the idea that an amalgam must have mercury), the amalgams will distinguish themselves naturally from the true alloys by the differences in their physical behaviors.
And you can see that this must be true by considering the thermoelectric properties of the materials.
A quick reminder of the thermoelectric effect can be seen at:
http://book.boot.users.btopenworld.com/thermo2.htm
The relevant point to understand here is that if you put dissimilar metals in contact with each other and maintain the contact points at different temperatures then an electrical current will flow, and the current will continue to flow for as long as the temperature difference is maintained. This phenomenon of course runs contrary to the popular myth that in order for dissimilar metals in contact with each other to produce an electrical current they must become involved in an electrolytic reaction. (A myth which seemed particularly prevalent amongst members of the dental profession by the way - at least before I came along and started pointing out that it isn't true.)
This thermoelectric effect is also the explanation for what happens when bits of one metal are encased within another metal and subjected to a temperature gradient. You can see a graphical representation of this effect at:
http://www.elektrotechnik.hs-magdeburg.de/Mitarbeiter/hinken/news/N6.htm
(figure d is particularly instructive)
The temperature gradient shown induces a thermoelectric eddy current around the inclusion, and this produces an electromagnetic field which extends outside the surfaces of the surrounding material and can be detected using sensitive instruments.
The presence of this phenomenon in Nature is used to detect inclusions of metals inside other metals.
It works if the inclusion and the surrounding material are both pure (but dissimilar) elemental metals.
And it also works if the inclusion and the surrounding material are dissimilar alloys.
But it doesn't work for a single true alloy if there is no inclusion of a dissimilar metallic composition inside it. This is because the component metals in a true alloy are too homogeneously mixed for the effect being detected to arise.
Now, because of their inhomogeneous internal structures you would expect this effect to arise in amalgams (including dental amalgams made with mercury). But, as I have already said, you would not expect it to arise in a true alloy.
Get the message?
At this point I should ask if you know whether or not experimental investigations have ever been carried out in order to measure the thermoelectric behavior of a typical dental amalgam, and to compare it with the thermoelectric behavior of a true alloy.
But I already know that you don't, so I shall just point out to you that therein lies your ignorance.
Keith P Walsh
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Keith:
Your combination of ignorance and arrogance is truly appalling. The phrase you can't find to describe a "mixture of metals which has a much more homogeneous microstructure whereby it would not be possible to show the relative positions of the atoms of the different metals" is simply called a phase. A particular alloy that starts out from a homogeneous liquid may not be a single phase once it solidifies.
Why don't you just step away from the keyboard, go down to the library, and learn something about materials before you go pontificating to the world? Michael F. Ashby and D.R. H. Jones have written two good books on Engineering Materials. Engineering Materials 2 (An introduction to microstructures, processing, and design) is worth reading, if you want to actually learn about how nature works.
Pittsburgh Pete
DISCLAIMER
We do not believe what we write, and neither should you. Information furnished to you is for topical (external) use only. This information may not be worth any more than either a groundhog turd, or what you paid for it (nothing). The author may not even have been either sane or sober when he wrote it down. Do not worry, be happy.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 2 Sep, 23:09, snipped-for-privacy@hotmail.com wrote:

Pete,
Experience has led me to believe that there isn't any book in any library anywhere in the world which contains any scientific information at all concerning the thermoelectric properties of the inhomogeneous mixtures of dissimilar metals commonly used in restorative dentistry.
I would be delighted if you could prove me wrong.
Keith P Walsh
PS, can I take it we are now agreed that the term "mercury amalgam" is NOT a pleonasm?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I forgot to say, principal amongst the thermoelectric properties of any material is its seebeck coefficient - measured in volts per kelvin.
(Perhaps you already knew that.)
Keith P Walsh
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.