The Difference Between an Alloy and an Amalgam - It's Thermoelectric!

The following statement was made by Professor Xu Wang of the University of Akron in response to a question regarding the
relationship between the thermoelectric properties and the electromagnetic behavior of metal amalgam dental fillings.
"Theoretically electromagnetic field will be generated by thermal gradient. But the thermoelectric coupling parameter in most metals is very low (0.001-0.01). So I don't think the induced electromagnetic field is significant enough to influence the neurological tissue nearby."
Amalgams, including dental amalgams, are not like most other metals in at least one crucial respect; they have a much greater degree of material inhomogeneity.
This is true when compared either with pure metals, such as copper, silver, etc., or with true alloys such as brass.
The explanation for the difference in the material homogeneities of amalgams and true alloys lies in the difference between the methods by which the two types of material are formed.
When a true alloy is formed, the component metals are mixed together at a temperature which is greater than the melting point of all of them. Then, after having been mixed thoroughly in its fully liquid state, the mixture is allowed to solidify by cooling at a controlled rate.
By contrast, in an amalgamation process, bits of solid metal, which may themselves be of either pure metal or an alloy, are mixed together with a liquid metal at a temperature which is BELOW THE MELTING POINT of the solid component(s). (And in the case of dental amalgam, where mercury is used as the liquid metal amalgamating agent, this process is normally performed at room temperature.)
In the setting process of such an amalgam, the liquid mercury becomes part of the solid material not as a result of any subsequent reduction in temperature, but by joining in solid solution with the outer layer of the solid particles of metal with which it was mixed. But of course, not all of the volume of the solid particles is involved in this process and, as a result, the microstructure of the resulting solid amalgam is as depicted in the schematic diagram at:
http://book.boot.users.btopenworld.com/setting.htm
In this diagram the lumps of "unreacted alloy" (denoted "gamma") are the cores of the original grains of solid silver-tin alloy which have not mixed with any of the mercury during the amalgamation process.
At this scale it is not possible to show the spatial relationship between the atoms of silver and the atoms of tin in these alloy "cores". The alloy has too great a degree of homogeneity for this to be done.
However, the relative inhomogeneity of the "amalgam" is clearly depicted by the sizes of the unreacted alloy cores. (These being held together by a solid matrix of a dissimilar mixture of metals (denoted "gamma-1") which does have mercury in it, and which may be presumed therefore to have dissimilar physical properies.)
Now, I have it on good authority from Professor David B Mahler of The Oregon Health & Science University School of Dentistry that the median size of the "unreacted" grains of original solid alloy in dental amalgams is in the order of 30 microns. Scientists with experience of electrical phenomena at the nano scale might provide some testimony to the significance of this figure.
The question which remains unanswered is this; whilst it may be appropriate to quote a "coupling parameter" for the local electromagnetic effect arising purely from temperature difference in a homogeneous metallic material, such as a pure metal or an alloy of metals (for example the type of alloy which may be mixed with liquid mercury to form an amalgam), is it not the case that the dominant (and potentially much larger) electromagnetic effect arising as a result of temperature differences in a more inhomogeneous mixture of dissimilar metals, such as an amalgam, is more likely to be that caused by the establishment of thermoelectric eddy currents which would be necessary for maintaining physical equilibrium against temperature gradient in such an inhomogeneous medium?
Can anyone think of any experimental procedure which might be employed in order to demonstrate the case either way?
And is it possible that Professor Wang was failing to take into account the degree of inhomogeneity of metal amalgams, which is much greater than "most metals", when estimating the size of the electromegnetic disturbance produced by thermoelectric effects in dental amalgams?
Professor Wang's home page is at:
http://www.ecgf.uakron.edu/~pan/wang /
Keith Walsh
PS, Any dentists out there who don't know anything about the thermoelectric behavior of dental amalgams can always quote professor Wang's "coupling parameter" statement if pressed. But I would strongly advise you to make sure that he knows what he's talking about first.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Keith P Walsh wrote, On 1/28/2009 4:34 AM:

Keith, Yes, I can think of an experimental procedure. Several people on these newsgroups (myself included) have described to you exactly how to measure the thermoelectric properties of metal amalgam dental fillings. But it has been a complete waste of time. In the last 15+ years that I've been reading your posts, you have never once made even the slightest effort to test your hypothesis.
Look, this is not that difficult. I will help you if you are willing purchase some materials, borrow or rent a good digital volt meter, construct a test apparatus, and then run your experiment. Otherwise, feel free to continue shouting in the wilderness.
--

Paul D Oosterhout
I work for SAIC (but I don't speak for SAIC)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Hell, a couple of years ago I found what he needed on e-bay for well under $100 and offered to buy it for him if he made and published the measurements.
--
Jim Pennino

Remove .spam.sux to reply.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I think that by definition, an amalgam has to have mercury in it.
Al
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That's a common misconception.
That "an amalgam" has come to imply mercury, particularly 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 find details of this book at:
http://books.google.com/books?id=cQ6khQScBF4C&pg=PA103&dq=%22gallium+amalgam%22&sig=Um_AAj4cKineMZPCpE4sXOWq3Uw#PPP1,M1
When I first quoted these pages (see message in thread "Lessons on Alloys, Amalgams, and Pleonasms (2)" of 1 September 2007) they were available for reading at the above URL.
Unfortunately it looks like since then they've been made unavailable! (I tell ya, if I were a conspiracy theorist ... ).
Anyway the quotes are genuine.
So come on Al. Please don't simply ignore this post just because you've been proved wrong.
Get typing and give us your opinion now (and don't be shy about cross- posting to the other groups).
Keith P Walsh
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sorry to labor the point Al, but I found my other favorite reference for gallium amalgams (i.e. where the liquid metal used to formulate the amalgam is gallium and not mercury - so there's no mercury in 'em).
This is from the Institute of Physics document service website at:
http://www.priorartdatabase.com/IPCOM/000137544 /
"Hermetic Sealing of Electronic Hardware Using Gallium Amalgams
In this proposed invention, the gallium amalgam is mixed in a ball mill, but the mixing action is minimized to limit the abrasion of the metal particles so as not to have the liquid gallium wet the metal particles. Since the metal particles are not wetted by the liquid gallium, they will not dissolve in the liquid gallium. The pot life is thus much extended. The liquid gallium, laden with metal particles, is placed on the surfaces to be joined. The faying surfaces are pressed together and then vibrated with respect to each other. The compressive stresses and relative motion between the surfaces cause the metal particles to abrade against each other and the faying surfaces. The particles and the faying surfaces become clean and thus wettable by the liquid gallium. The amalgamation process begins solidifying the amalgam and joining the two surfaces. When the amalgamation process is complete, the amalgam becomes solid and holds the faying surfaces together.
The amalgam can be a ternary alloy having 5-35% Cu and 15-30% Ni in liquid gallium. The nickel and copper particle size has to be less than about 0.05 mm so that the faying surfaces are not kept excessively apart by the particles. The relative motion between the faying surfaces to initiate the amalgamation action can be achieved by..."
So you see there really are amalgams with no mercury in them - but it is still correct to call them amalgams because of the nature of the process by which they are formed.
But like I said, yours is a common misconception, so there's no need to feel stupid.
On the other hand, if you begin to wonder whether the idea that "there's nothing wrong metal amalgam dental fillings" might also be a common misconception let me know and I'll give you some pointers on how you might find out.
Keith P Walsh
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
It seems to me that we go for several months without hearing from Mr. Walsh, and then he resurfaces with a post of basically the same stuff he posted the previous time around.
Has anyone determined the period of the Walsh function? Is it correlated with the phase of the moon, perhaps?
At any rate, during a previous iteration, Mr. Walsh gave us a reference to a paper on the eddy currents induced inside a metallic conductor which contains an inclusion of a different metal and is subjected to a temperature gradient.
Let's see, when was that ... ah yes, it was back in October 2006.
In the paper Mr. Walsh referred us to then, the authors considered a copper-constantan system. If one had a block of copper with a constantan inclusion, and if that block were subjected to a temperature gradient, then there would be a steady, DC eddy current flowing inside the block of metal, due to the thermoelectric effect and the fact that one end of the inclusion would be at a different temperature than the other end due to the temperature gradient.
This would presumably occur inside any conductor which was not of homogeneous composition (i.e., a dental amalgam) and was subjected to a temperature gradient.
I pointed out at the time that the external manifestation of this eddy current was a very, very small (pT, that's right -- PICO-Tesla -- PICO, as in 10^-12) steady magnetic field. This result was stated in the very paper Mr. Walsh referred us to, but somehow he seemed to have missed it in his reading. This is an extremely tiny magnetic field, many orders of magnitude less than the earth's magnetic field, and it is hard to see how it would have any effect whatsoever on the human body.
In fact, the authors of Mr. Walsh's reference stated that "only the most sensitive magnetometers have a significant chance to detect the expected magnetic field values at a proper signal to noise ratio." This magnetic field is so tiny that you would need a SQUID detector to have any chance of even measuring it.
So, how could this extremely weak DC magnetic field, many orders of magnitude less than the already existing DC magnetic field of the earth, possibly have any effect on the human body?
I seem to recall that Mr. Walsh ignored this question back in 2006.
Olin Perry Norton
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

By analogy, it would be hard for you to "see" how a pebble could topple a boy on a skateboard (any effect whatsoever) when a boulder or brick wall would stop him dead. Perhaps you do not want to see.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:
Mr Norton.
Thank you for your contribution.
In reply, first of all, can I take it that you agree with my description of the difference between an amalgam and an alloy (which is not dependent upon whether or not the thermoelectric eddy currents generated by the amalgams are detectable by human neurological tissue.)? And also, for the benefit of my friend alchazz, that amalgams may be formed using liquid gallium as the amalgamating agent rather than liquid mercury, with the consequence that there is no mercury in the resulting gallium amalgams?

OK then, I'll address it now.
There is a basic inconsistency in the argument that you have presented here (OK I know, you've really only presented a question).
The inconsistency which you imply in your question is that, although the SQUID detector is sensitive enough to detect a very weak local electromagnetic effect in the presence of the Earth's magnetic field, which may be considered much stronger, human neurological tissue is not sensitive enough to do the same.
I do not believe that you actually know whether or not this apparent implication is correct. At least, I do not believe that you are able to provide any direct scientific (i.e. experimental) evidence in support of any such assertion.
And there in lies the rub. It appears that, in this "science obsessed" world of ours, no-one has ever bothered to even try to find out (by experiment) whether or not human neurological tissue is capable of detecting the electromagnetic disturbances generated by the lumps of inhomogeneous mixtures of metals that dentists routinely place in children's teeth.
So a word of warning, if you want to set yourself up as some sort of expert on the electromagnetic behavior of amalgam dental fillings, you might first wish to consider why there doesn't appear to be anyone in that role ahead of you (just think, with a little work you could be a hero! And I'm sure that the American Dental Association would be most generous in its gratitude for your expertise - but perhaps only if you are able to tell them what they want to hear.)
My answer to your question is this. Perhaps human neurological tissue detects weak local electromagnetic disturbances, even in the presence of much stronger magnetic fields, in a similar way to that in which the SQUID detector does. In the absence of any experimantal evidence to the contrary why shouldn't it? Perhaps that's a question which you might like to address (although I understand perfectly well that in the absence of any relevant experimental evidence at all you'd only be able to guess your answer anyway).
Electric, magnetic and electromagnetic fields are all manifestations of the fundamental energy that makes up the Universe. They are not characterised by field strength alone. Their nature is much more complex than that. In the modern technique of nuclear resonance imaging, the strength of the signal is largely irrelevant with regard to the degree by which it is attenuated by the target. It's the frquency/wavelength of the signal that matters most crucially, and if it doesn't match the resonant frequency/wavelength of the target then the attenuation doesn't happen, no matter how strong the signal is.
That's just an example to establish the principle that in certain circumstances a weak signal may have a significant effect, whereas a much stronger signal which has different characteristics might have no effect at all in otherwise identical circumstances (a principle which I believe that "Androcles" may have been alluding to in his response to your contribution - thank's for the prompt Androcles).
If you would prefer to believe that there isn't any analogous principle which might apply in our topic of interest well fine, go ahead, but as I say, in the absence of any authoritative scientific evidence on the matter, you're still only guessing.
There was another thread concerning this subject which I left uncompleted a few years ago. I'd asked how one would know that the process by which the local electromagnetic field generated by thermoelectric eddy currents is not reversible, and I was presented with the answer, "Elementry (sic) physics" - I'll just go and find it (isn't Google Groups wonderful. In centuries to come they'll look back on these arguments and laugh - or cry.)
Found it. Jim Pennino, 24 October 2006, in thread, "Electromagnetic Effects in Inhomogeneous Materials", the relevant part of which went like this:
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ +

A static magnetic field will not generate a current.

Elementry physics. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ++
I'll start this one back up again now as well.
I agree that the influence of a static magnetic field is not able to drive an electric current in a homogeneous electrical conductor. That much is "elementary physics". However, having said that, at the moment of establishing the new local magnetic field in the vicinity of the conductor the charge carriers (electrons) in the conductor will be disturbed momentarily, and may adopt a new static arrangement in order to maintain equilibrium with the newly established local field, although no further movement of the electrons will take place once this static equilibrium condition is reached.
This situation is analogous to the effect of the application of a temperature differential to a homogeneos electrical conductor, in that on the establishment of the temperature differential the charge carriers in it must adjust their position (thereby creating a momentary "current" - i.e. displacement of charge) in order to maintain equilibrium with the new temperature gradient. And that on reaching the new equilibrium position, no further displacement of of charge (current) can be induced or maintained by the static temperature differential.
However, where inhomogeneous conductors are involved, such as a circuit comprising elements of, say, two dissimilar metals, then a static temperature differential applied between the contact points of the two dissimilar metals DOES induce an electric current in the circuit, and this current continues to flow for as long as the static temperature differential is maintained. And of course the equivalent of this phenomenon when applied to an inhomogeneous material such as a dental amalgam is that the static temperature differential should be expected to induce and sustain "thermeoelectric" eddy currents around the inclusions of dissimilar metal which are internal to the material itself.
I don't know whether this stuff is included under the description "elementary physics" or not. Though it does appear that dental students in dental schools are never taught it. Nevertheless, it makes me wonder whether or not the reverse analogy is also true for static magnetic fields when applied to inhomogeneous mixtures of metals, and that these too might be able to induce eddy currents in dental amalgams.
Food for thought.
If only we had some experimental evidence which might settle the issue either way.
Whatever the case, I'd advise anyone who might be feeling the urge to step into the role of "expert on the electromagnetic behavior of dental amalgams" at this point to be very careful.
Because I for one can feel the rumblings of a next question which might be on the lines of, "and are you presuming that static electromagnetic fields are the only kind that metal dental restorations are subjected to?".
"Elementry physics" my eye!
Keith P Walsh
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Keith P Walsh wrote:

    I will accept your use of the term "gallium amalgam" though it is seldom used and hence can be misinterpreted.     In fact, dental restoratives have been made using gallium as a major component; unfortunately their performance has been disappointing:
http://www.cda-adc.ca/jcda/vol-64/issue-9/645.html
Steve
--
Mark & Steven Bornfeld DDS
http://www.dentaltwins.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Dear Steve,
I think that the main reason why the term "gallium amalgam" might be misinterpreted is because of the widespread misconception that, by definition, an "amalgam" must have mercury in it.
This also explains why the the types of gallium amalgams that we are talking about here, which do not have any mercury in them, are sometimes erroneously referred to as "gallium alloys", e.g.:
http://www.cda-adc.ca/jcda/vol-64/issue-9/645.html
Of course, it may be argued that, whilst establishing a consistent nomenclature is important in any scientific discipline (including that of dental materials science), the names that we actually give to physical entities is perhaps of secondary importance to the correct identification of their physical properties and behaviors.
However, I do think that in this instance it might be helpful, as well as perfectly correct, for us to establish that the true origin of the word "amalgam", as applied to certain types of mixtures of metals, is NOT dependent upon there being mercury included in the mix, but is in fact defined by the general process by which they are formed; i.e. that of mixing a quantity of a liquid metal "amalgamating agent" together with solid particles of another metal at a temperature which is below the melting point of the solid metal, and then allowing the mixture to harden by a process which might reasonably be termed "amalgamation".
The metallic element gallium melts at around 30 degrees celsius. It can therefore be used in amalgamation processes such as this to form amalgams by mixing it together with bits of solid metals or alloys at a temperature slightly above that of room temperature (say, below 40 degrees celsius). The type of material that you get from such a process could not be accurately described as an alloy (or what I sometimes call a "true alloy) because a significant part of its volume would remain as the "unreacted", or "undissolved" cores of the original grains of solid alloy used in the mix, and these would not have any gallium in them at all.
So it wouldn't be "an alloy". It would be "bits of an alloy all held together in a matrix of a dissimilar metallic composition formed by the liquid gallium in dissolving the outer layers only of the original solid particles". Or, more generally, an inhomogeneous mixture of dissimilar mixtures of metals.
It is from the requirement to distinguish materials of this type that the term "amalgam" originates.
Primarily such materials are distinguished in the physical sense by their much greater degree of material inhomogeneity, as compared with that of true alloys, and this distinction comes from the complementary fact that true alloys have a much greater degree of material homogeneity due to their being formed by mixing together the constituent metals at a sufficiently high temperature such that they are ALL in the liquid state.
By this definition, therefore, a gallium amalgam may be considered no more a true alloy than a mercury amalgam is.
I am already aware that attempts are been made to formulate suitable gallium amalgams for use as restorative dental materials.
However, as far as I can tell the principal motivation for this is to find a viable alternative to the use of mercury amalgams.
And, again to the best of my knowledge, the reason for this is concern for the possible toxic effects that the mercury in mercury amalgams may have on the human body.
Since I know that you have read, and often responded to, many of my enquiries to sci.med.dentistry over the years, I presume that you will be aware that my own particular interest in this topic is not the toxic properties of mercury, but rather the electrical behavior of amalgams. And in fact my interest in the subject dates back to the early 1990s, beginning with a series of letters which I wrote towards the end of 1992 enquiring about the electrical properties of dental amalgams. You can read them at:
http://book.boot.users.btopenworld.com/intro.htm
As a result of the response to these letters, and of my own personal experiences both before and after they were written, I have come to believe that the electrical potentials generated by metal amalgam dental fillings are able to dissipate electrical energy through the nerves in people's heads and, in so doing, make them unhappy.
And in extreme though not unusual cases they are also able to cause permanent neurological injury which cannot be repaired simply by the removal of the fillings.
Scientific evidence for the existence of amalgam potentials is well documented.
And from my knowledge of the electrical behavior of mixtures of metals, I have no reason to expect that the electrical potentials generated by dental restorations constructed using gallium amalgams, rather than mercury amalgams, will be any less significant in magnitude.
I remember reading a comment some years ago that if dental (mercury) amalgams were being invented right now their use would never be approved by the US Food and Drug Administration (the implication being that the implied approval that their use has now is only due to the application of the somewhat unscientific principle that "we've been using them for so long that there can't possibly be anything wrong with them!").
My hope on the advent of gallium amalgams is that someone, perhaps the FDA, or the ADA, or an erudite young scientist in a university materials science lab somewhere, will recognise that the interaction of the electrical (not only galvanic, but also thermoelectric and electromagnetic) behaviors of these new materials with the human body ought to be investigated thoroughly first before they can be approved for this use. Something which has still never been done with mercury amalgams.
Keith P Walsh
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Keith P Walsh wrote, On 2/4/2009 3:47 AM:

Mr Wash Your knowlege of the electrical behavior of mixtures of metal is purely speculative. You have never attempted to make even the most basic measurements to back up your claims. Purchase some amalgam materials, fabricate some test samples, assemble a test fixture, rent (or borrow) a good digital volt meter and take some measurements. Then you will KNOW the thermal electrical behavior of dental amalgams.

There you go again, trying to get someone else to do your work for you. Do your own work, publish your results, and then bask in praise that will befall unto you.
Best of luck,
--

Paul D Oosterhout
I work for SAIC (but I don't speak for SAIC)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The measurements which can be made with a good digital voltmeter have already been demonstrated, see,
http://book.boot.users.btopenworld.com/potentials.htm
(These were taken by Dr Jack Levenson, hero of the mercury-free dentistry movement in the UK, but sadly now deceased.)
The potentials measured here showed up even though the fillings were not in contact with any saliva - which shouldn't be surprising since it was first demonstrated that this is the case way back in 1952, see:
http://jdr.sagepub.com/cgi/reprint/31/2/205
Experimental procedures to confirm whether or not these electrical potentials do in fact excite neurological synapses in the vicinity of dental fillings would have to positively detect the occurrence, or the lack of occurrence, of such excitation in the nerve fibers.
I believe that instruments do exist which are sensitive enough to be able do this. But a "good" digital voltmeter costing less than $100 is not one of them.
I'm sure I've explained all this to you before. (Perhaps it's you who is habitually failing to retain the significant parts of the argument here.)
Keith P Walsh
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Keith P Walsh wrote, On 2/5/2009 5:02 AM:

Keith, Stop being such a cheapskate! If you really felt strongly about the health of children you wouldn't let a few measly dollars stand in the way of this important research. Now take a crowbar, open up your wallet, an get that DVM.
Besides, you don't need to purchase a DVM they are readily available for lease at any test equipment rental store. See: <http://www.testequipmenthq.com/ <http://www.livingston.co.uk/ <http://www.etestdirect.com/ Do a web search, you will be able to find dozens more.
Another way to go is to purchase a used DVM. You will not need the latest and greatest equipment for your experiment. Just a good, reliable meter that can measure in the microvolt range.
Good luck. We are all waiting to hear about your results.
--

Paul D Oosterhout
I work for SAIC (but I don't speak for SAIC)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You're beginning to sound desperate Paul.
The reason why I keep returning to these newsgroups with the same old questions is because those questions have never been answered.
I recognise that people like you and Jim Pennino are able to convince yourselves that you have answered my questions, but you are mistaken. All you ever do is simply make up excuses for ignoring them because you don't know what the answers are.
Olin Perry Norton even appeared to have convinced himself that he had conclusively dealt with my questions by asking me one of his own which I couldn't answer!
How obtuse is that!?
Some of the earliest questions I posted to sci.med.dentistry were concerned with the physical properties of dental amalgams, and why it appears that properties such as their electrical conductivity and magnetic susceptibility had ever been measured. And those questions are still not resolved today.
I still bother to check. (I doubt very much whether any of you guys ever do.) And on a recent search I found a paper with the following title:
"Magnetic susceptibility and electrical conductivity of metallic dental materials and their impact on MR imaging artifacts"
- the summary of which can be seen at:
http://www.demajournal.com/article/S0109-5641 (07)00199-6/abstract
I was sufficiently interested to pay the online fee to buy the complete article (see, I'm not such a cheapskate after all!), and do you know what I discovered? I discovered that the "amalgams" which the paper claims to have tested were not amalgams at all. They were simply samples of the various ALLOYS which are supplied to dentists for mixing with liquid mercury to form amalgams.
As it happens, two of those alloys do have some mercury in them - Starfill NG2 (3% Hg) and Ana 2000 Duet (2% Hg). However, despite their mercury content, these materials are NOT amalgams. They are ALLOYS. Dentists will appreciate perfectly well that you can't make amalgams with those proportions of mercury. These materials would have been formed by mixing ALL of the constituents (Ag 70%, CU 15%, Hg 3%, Sn 12%; and; Ag 43%, Cu 25.4%, Hg 2%, Sn 29.6%, respectively) in their molten states, i.e. at a temperature well above room temperature, and then allowed to cool at controlled rate.
The other "amalgams" tested, i.e. those with 0% mercury content, were not amalgams either, they too were ALLOYS (Safargam Plus, Safargam NG2, Safargam Special and Ana 70 Duett).
These alloys are purposely formulated for use in amalgams. It may make sense therefore to refer to them by the term "amalgam alloys", in which term the word "amalgam" serves as an adjective.
But they are NOT amalgams. And in the physical world, regardless of what anyone calls them, they do not accurately represent the physical composition of any material that would be found in anyone's mouth in the form of an amalgam dental filling.
The discovery of this paper therefore does not answer any of my questions regarding the physical properties of amalgam fillings.
On the contrary, it raises more questions.
Such as, if someone can get a Phd measuring the electrical and electromagnetic properties of the alloys used for mixing amalgams, why hasn't anyone bohered to do the same with samples of actual amalgams (i.e. after the alloys have been turned into powder and mixed with liquid mercury to form the actual amalgams which are placed in peopl's teeth.)?
The same paper also presents the results of measurements for a range of other metal alloys, those used for crowns, bridges, braces, etc,.
So we have the properties of electrical conductivity and magnetic susceptibility for just about every type of metallic material that dentists place in people's mouths, and for the ALLOYS used for mixing amalgams, but NOT for the mixed amalgams themselves.
And with regard to the actual amalgams themselves, i.e. as they appear in people's teeth, we are still ignorant.
How do you explain that?
And don't tell me that it's up to me to do the measurements myself.
That's just the same old excuse that you always use simply to avoid the question.
Keith P Walsh
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Keith P Walsh wrote:

    Sorry Keith. I'm not interested in the semantics of what your definition of amalgam vs. alloy is. I'm a clinical dentist, and I want my materials to work on planet earth.
Carry on, Steve
--
Mark & Steven Bornfeld DDS
http://www.dentaltwins.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

It has been demonstrated on planet earth that (mercury) amalgam dental fillings generate electrical potentials with magnitudes of up to 350 millivolts. See:
http://book.boot.users.btopenworld.com/dutch.htm
It has also been demonstrated that these potentials can be detected even when the amalgams are not in contact with any saliva in the mouth. See:
http://jdr.sagepub.com/cgi/reprint/31/2/205
And another research study carried out in Poland (which I believe is also on planet earth) has even demonstrated experimentally that the electrical potentials generated by amalgam fillings are quickly regenerated after being discharged. See:
http://www.ncbi.nlm.nih.gov/pubmed/2103035?dopt=Abstract
Do you think that it should be possible to carry out (on planet earth of course) research studies to compare the electrical behavior of amalgams made with liquid gallium (gallium amalgams) with that of mercury amalgams?
Keith P Walsh
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Keith P Walsh wrote:

(snip--sorry).
    I'm sure it's possible. I've watched for years as the denizens of sci.materials and perhaps sci.physics have encouraged you to conduct your tests.     You can try it with plutonium, for all I care. I'm not using gallium, and I'm neither a physicist nor a metallurgist. And I'm not going to use gallium "alloys" in my practice.     You should know though that I'm the type of guy who tests 9-volt batteries by touching them to my tongue. Maybe that's my problem right there.
Steve
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

How about mercury amalgams?
Do you use them?
(And remember, it's NOT a pleonasm.)
Keith P Walsh
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Keith P Walsh wrote:

Take it up with Webster:
http://www.merriam-webster.com/dictionary/amalgam

--
Mark & Steven Bornfeld DDS
http://www.dentaltwins.com
  Click to see the full signature.
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.