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An Amalgam is not an Alloy - Proof

The Austrian company Ogussa manufactures an alloy called Starfill NG2. This alloy is intended for use by dentists in mixing solid particles of it together with liquid mercury to form a dental amalgam.

Starfill NG2 is not the amalgam. It is an alloy which must be mixed with liquid mercury in order to form the amalgam.

The composition of the alloy Starfill NG2 is as follows:

Ag - 70% Cu - 15% Hg - 3% Sn - 12%

Since it contains 3% mercury, Starfill NG2 can be accurately described as "an alloy of mercury with other metals".

However, as we have already established, it is NOT an amalgam.

Even dentists (in fact, especially dentists) will recognise that you cannot make an amalgam with only 3% mercury.

Therefore, logically, it must be concluded that "an alloy of mercury with other metals" is NOT an adequate definition of an amalgam.

In spite of this, it appears that many dentists, as well as a significant number of editors of various types of dictionary, have been misled into believing that an accurate definition of an amalgam is ""an alloy of mercury with other metals".

In fact this definition is inaccurate on two counts.

Firstly, an amalgam is not an alloy. True metallic alloys are formed by heating ALL of the constituent metals to a temperature which is higher than the melting point of each of them. The molten metals are mixed together thoroughly and then allowed to solidify by cooling at a controlled rate. That's how the "alloy of mercury with other metals" called Starfill NG2 is produced.

In contrast, an amalgam is formed by mixing bits of a solid metal, or solid metal alloy, together with a liquid metal at a temperature which is below the melting point of the solid component.

Secondly, it is perfectly possible to form an amalgam in which the amalgamating agent is a liquid metal other than mercury, so that the resulting amalgam does not have any mercury in it at all.

Do we have any examples of such amalgams?

Well of course we do. If you go to:

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- you will find a paper describing amalgams formed by mixing liquid gallium (melting point 29.7 celsius), with different amounts of aluminium (that's "aluminum" to Americans).

There is NO MERCURY in these amalgams.

Amalgams can also be formed by using indium as the liquid metal amalgamating agent. There is NO MERCury in these amalgams either.

And therefore the widely supported definition of an amalgam which is given as "an alloy of mercury with other metals" is at best inadequate, and at worst downright wrong.

So I would suggest that any dozy dim-witted dunce in the dental pofession who has been fooled into believing this definition should stop believing it, and stop using it, now.

And they should also recognise that because there are different types of amalgams, formed by using different liquid metal amalgamating agents, then it makes perfect linguistic, scientific and logical sense to differentiate between them by referring to them as gallium amalgams, indium amalgams and MERCURY AMALGAMS, etc.

And those dozy dim-witted dunces in the dental pofession who are in the habit of telling people that the term "mercury amalgam" is a pleonasm should realise that the teachers who taught them to believe this in dental school were confused and ignorant, and they have simply passed on their confusion and ignorance to you.

(When I use the term "mercury amalgam" it doesn't mean that I think that I can form an amalgam by mixing liquid mercury with liquid mercury - it means I'm referring to an amalgam formed using liquid mercury rather than liquid gallium, or liquid indium, etc. - by the way, I'm sure that this is all very obvious to you guys at sci.materials - It's the DDS dopes at sci.med.dentistry who appear to have difficulty in accepting that what they were taught in dental school was garbage.)

However, this is not simply an argument about semantics.

The reason why it is important to distinguish between amalgams and an alloys is because these are two distict types of mixtures of metals. When you mix liquid mercury together with a powdered metal alloy at room temperature what you end up with is a solid which has a much more inhomogeneous microstructure than any true alloy has. A large proportion of that microstructure consists of solid cores of unreacted alloy which has not fused with any mercury at all, see:

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This material would be more accurately described as a mixture of at least two different alloys. But it cannot be accurately described as "an alloy".

And, because of its significantly different microstructure, you might also expect such a material to differ from a true alloy in its electrical, electromagnetic and thermoelectric behaviour (that's "behavior" to Americans).

In 2007 a team of Czech researchers set out to measure the magnetic susceptibility and electrical resistivity of a range of metallic dental materials (a bit late in the day don't you think?).

You can read their report at:

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At the top of page 717 they list 6 different materials included in the study which are describerd as "Amalgams".

These materials are not amalgams. They are the alloys used to form dental amalgams by mixing them with liquid mercury. And as a matter of fact it is not obvious from the report whether it was in fact amalgams or just samples of the alloys that were measured in the tests. (You would expect the physical properties of an amalgam to vary significantly from point to point within the material according to the inhomogeneous nature of the material's microstructure. It appears that the researchers made no attempt to take account of this variation in their study. Also - there is no mention anywhere of the % Hg content of the "amalgams" that they measured. Did they simply receive samples of the alloys from the manufacturers - and their results were from measurements of the alloys and not representative of the properties of amalgams at all? I'm trying to find out and I'll report later.)

Anyway the case is made pretty clearly. An amalgam is not an alloy.

If anyone has any opinions on the Czech study I'd be interested to hear them. (Remember that you wouldn't be able to repeat this study without knowing what percentages of Hg were used in the "Amalgams" tested.

Keith P Walsh.

PS, I have noticed in recent years that attempts have been made to develop amalgams ustilising liquid metal amalgamating agents other than mercury (e.g. gallium) for use in dentistry. I also gather that these attempts are generally inspired by the perception that mercury should not be used in dental materials because of its toxic properties. My own belief is that any "gallium amalgam" intended for use in dentistry would, as a newly developed dental material, have to satisfy rigorous testing for its physical properties to satisfy public bodies, such as the US FDA, that it is acceptable from the point of view of bio-compatibility. And, presuming that such tests would include a thorough examination of its electrical, electromagnetic and thermoelectric behaviour, it would be unlikely to gain the required approval. The principal reasons why the electrical, electromagnetic and thermoelectric properties of mercury amalgams have never been subjected to similar scrutiny are because, firstly, when mercury amalgams were first developed for use in restorative dentistry the significance of these properties was not as well recognised as it is today; and, secondly, in the case of mercury amalgams there appears to apply a wholly unscientific principle that, because they have been used for so long in dentistry now, if they were causing any significant problem it would have been widely recognised (remember that the widespread adoption of mercury amalgams for use in restorative dentistry was quickly followed by the rise to prominence of psychiatric "medicine" in our societies, and at present there is insufficient scientific evidence to support any assertion that the two are not significantly linked by the relationship of cause and effect.)

Reply to
Keith P Walsh
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It's the DDS dopes at sci.med.dentistry who appear to

Keith:

The fifth edition (1994) of the McGraw-Hill Dictionary of Scientific and Technical Terms has the following definition for amalgam (metallurgy): an alloy of mercury.

For mineralogy it similarly says amalgam: a silver mercury alloy occurring in nature.

Pittsburgh Pete

Reply to
metalengr

- It's the DDS dopes at sci.med.dentistry who appear to

Reply to
Keith P Walsh

- It's the DDS dopes at sci.med.dentistry who appear to

Yes you are right.

Amongst the the people who don't understand that amalgams can be formed without any mercury in them at all are the editors of some technical dictionaries.

My advice would be to treat the information that you read in these dictionaries with caution.

Keith P Walsh

Reply to
Keith P Walsh

:

ls- It's the DDS dopes at sci.med.dentistry who appear to

ASM International is the materials information society. Volume 2 of the ASM Handbook is titled Properties and Selection: Nonferrous Alloys and Special-Purpose Materials. It contains a brief section on Dental Amalgam which begins with the following sentence:

=93Dental amalgam is a silver-mercury alloy used for restoring lost tooth structure.=94

Pittsburgh Pete

Reply to
metalengr

Thank you for your contribution.

It highlights very well the confusion and inconsistancy that exists regarding this issue, even amongst the supposedly learned.

The website of the Copper Development Agency carries the following definition for "Alloy":

"A homogeneous mixture or solid solution of two or more metals, the atoms of one replacing or occupying interstitial positions between the atoms of the other."

It's a definition which also crops up in several dictionaries.

Dental amalgam does not match this definition, most obviously because dental amalgam is an INHOMOGENEOUS mixture of metals.

You can see the inhomogeneous nature of the microstructure of a typical dental amalgam at:

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The cores of unreacted alloy don't have any mecury in them at all (i.e. there are no atoms of Hg there, neither interstitial nor otherwise). However they are all held together in a solid matrix which DOES have mercury in it. This is what defines the INHOMOGENEITY of the amalgam. No alloy has this type of microstructure.

And it is therefore not accurate to describe dental amalgam as an alloy.

I think that this fact is best explained by considering the materials listed in table 1 of the scientific paper on the electrical properies of dental amalgams which can be seen at:

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The six materials listed at the top of this table are described as "Amalgams", but they are not amalgams, they are alloys. In order to make dental amalgams with these materials they must all be mixed with approximately 50% mercury.

However, if you look at the composition of the first material, Starfill NG2, you will see that this alloy already has 3% mercury in it.

So this material may be accurately described as "an alloy of mercury with other metals", and I would propose that it would indeed match with the definition of an alloy given above (i.e., "A homogeneous mixture or solid solution of two or more metals, the atoms of one replacing or occupying interstitial positions between the atoms of the other.")

But Starfill NG2 is NOT an amalgam.

Dentists in particular will recognise that you cannot make a dental amalgam with only 3% mercury.

The key to understanding this issue accurately lies in recognising that the use of the word "amalgam" originated as a means of DISTINGUISHING amalgams from alloys.

In other words, type of mixture of metals known as an amalgam is DIFFERENT from the type of mixture of metals known as an alloy. And the differences between the two arise from the differences in the methods by which they are formed.

This isn't just an argument about semantics.

If someone says, "we understand perfectly well the thermoelectric behavior of alloys", then another person who has been misled into believing that an amalgam is an alloy might easily, but wrongly, conclude from this that "we therefore understand perfectly well the thermoelectric behavior of amalgams".

And they might further presume that there is therefore no reason to independently investigate the thermoelectric behavior of dental amalgams.

But the consequence of the fact that the homogeneity of amalgams is different from that of alloys is precisely that you would expect their thermoelectric behaviors to be DIFFERENT ALSO.

And therefore (if you are able to think scientifically) it is not appropriate to deduce the thermoelectric behavior of an amalgam simply by assuming it to be similar to that of an alloy.

I would suggest that the apparent confusion and inconsistency regarding the correct descriptions of these mixtures of metals would best be solved if materials scientists, dentists, dictionary editors and newsgroup contributors could all acknowledge and agree that the type of mixture of metals known as an amalgam is not an alloy, and the type of mixture of metal known as an alloy is not an amalgam.

Keith P Walsh

PS, I have heard of attempts, mainly by materials scientists concerned about the toxic properties of dental amalgams formed by mixing solid alloys with liquid mercury, to develop amalgams formed by mixing solid alloys with liquid gallium instead (gallium melts at about 30 degrees C).

The idea that this is a worthwhile endeavor is, as I understand it, based on the assumption that a gallium amalgam would be more "bio- compatible" with regard to its toxic properties.(Some appear to have been persuaded that it is correct to refer to the material as gallium "alloy", on account of the fact that it has no mercury in it.)

However, my own view is that any new material developed such as this for use in dentistry would be required to satisfy strict tests to ascertain the bio-compatibility of its thermoelectric behavior. And it is my guess that it might not pass.

There is of course no requirement for amalgams made with mercury to pass such tests, as a result of the wholly unscientific presumption that "they have been in use for so long now that it can be reasonably assumed that there is nothing wrong with them". Wholly unscientific.

Reply to
Keith P Walsh

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