Resistivity of amalgams still a mystery

There is no theoretical derivation of resistance of materials.

It is a measured property.

I suspect a resistivity measurement is not as simple as it appears. The topology of the amalgam micro structure, impurities, grain boundaries, individual grain composition would all effect the the measured resistivity. The applied voltage may also cause ion migration in the solid that would effect resistivity with time. Performing a full blown impedance measurements and then the appropriate circuit analysis (not an easy task) may provide some clues to the amalgam stability, but it would need to be correlated with measured compositional changes. Other issues such as crystallographic defects induced by pressure (chewing) may also effect the resistivity (and impedance) of the amalgam.

Gregg

Certainly you can attempt to theoretically estimate the conductivity of materials. I don't know how successfull those attempts have been with amalgam. However I do agree that resistance is a measureable property. By definition V=RI, R=V/I and the current and voltage across any material are obviously real, meaurable quantities for any material, including amalgam.

I have a rope.

Attempt to theoretically estimate how long it is.

And the universe trembles at the astounding insight.

FYI, measuring the resistance of something with a resistance in the sub-Ohm range requires some attention to detail to have any meaning.

In message , Simplicio writes

Sure. "A function of" covers almost anything.

Not when you try to "apply it to non-ideal, or non-typical conditions which would exist in practice".

Quite. Have you considered that the changes might not even have the same sign?

Interesting assumptions. Can you justify them? And don't you want some decay rate constants in there?

With the stated assumptions, it's a power law. With different assumptions it would be something else.

Sure. Anything you say. But I know the difference between correlation and causality. "Both vary with time" says nothing significant about their relationship.

Did you?

I can postulate any theoretical relationship I want. You don't make the rules.

Have you considered that it wouldn't matter because the total resistance of the amalgam would still be a function of time. I don't know what you are getting at but you should be able to understand that as an amalgam loses Hg the rate of vaporizaton will change as well the structure of the amalgam itself changes leading to changes in resistance. In other words, as the amalgam becomes "less dense" by losing Hg, the rate of vapor emission and resistance will change. I don't really give two cents whether the changes are large or even measurable. I only stated that a relationship exists with is worth understanding, because, if you can theoretically predict the change in resistance as a funtion of rate of vaporization, you can (although I know this is years away) theoretically predict the rate of Hg loss from the amalgam under all circumstances.

Dosen't every equation having to do with circuits and solid state end up being e to the something or other? (and it does seem to fit the bill since the vaporization slowly decreases but never goes to 0)

sure

measure it. Put an amalgam in a circuit next to an Hg vapor meter, and measure the change in the total resistance of the amalgam and rate of change of vaporization as a function of time.

The point is that more research should be done to understand the relationship of all the physical properties of amalgam. If you want to derive a full blown solid state theory of Hg vaporization from amalgam go ahead. (I know that no current theory comes close to being able to do this).

Since you appear to have some science background you should agree that the amount of remaining Hg in the amalgam would directly affect the rate of vaporization and the resistance to some degree, establishing the "causality". No aristotilian reflection on the nature of correlation and existence is required.

-------------------- You can postulate any relationship that you want. Astrologers and tea cup readers do that.

The problem is in getting data that fits the postulation rather than fitting the postulation to the data. (and doing more testing). --

Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer