Tools to differentiate silver from molybdenum

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Discussion Overview

The discussion revolves around methods to differentiate silver from molybdenum, particularly in the context of counterfeit coins and bars. Participants explore various tools and techniques that could leverage differences in thermal and electrical conductivities, as well as magnetic properties.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that counterfeiters may use molybdenum to create fake silver due to its lower cost and suggests that differences in electrical and thermal conductivities can be used for differentiation.
  • Another participant proposes using a 4 terminal resistance meter to test resistivity, mentioning the method of dropping a coin through a magnetic field to observe differences in fall rates due to eddy currents.
  • A different participant highlights the magnetic properties, stating that silver is diamagnetic while molybdenum is paramagnetic, suggesting that measuring the detuning of a resonant circuit could help differentiate the two metals.
  • One participant mentions the use of a galvanic cell with a known silver electrode as a potential method for differentiation.
  • There is a request for clarification on the concept of measuring detuning in a resonant circuit, indicating some participants may not fully understand the technical aspects involved.
  • A later reply elaborates on the resonant circuit concept, explaining how passing a coin through a coil can change the oscillator frequency, which could help discriminate between silver and molybdenum.

Areas of Agreement / Disagreement

Participants express various methods for differentiating silver from molybdenum, but there is no consensus on a single best approach. Some methods are more technical and may not be fully understood by all participants, indicating a range of expertise and understanding in the discussion.

Contextual Notes

Some participants express uncertainty about specific technical terms and concepts, such as "detuning of a resonant circuit," which may limit the clarity of the discussion for those less familiar with the underlying physics.

bluemoonKY
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I remember reading on a blog or a news article on the internet once that sometimes counterfeiters have made fake silver coins and silver bars out of molybdenum. Silver is worth far more than molybdenum. Counterfeiters made fake silver out of molybdenum because they could acquire the molybdenum for a low price and then sell the molybdenum at silver prices. The source said that the electrical and thermal conductivities of molybdenum are far different than the electrical and thermal conducitivities of silver, and that is how one can use certain tools to differentiate silver from molybdenum. I cannot find the old source on the internet.

What tools can be used to differentiate silver from molybdenum by looking at thermal and electrical conductivities?
 
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To test the resistivity would require a 4 terminal resistance meter, two far terminals to inject a current, with the two closer terminals to measure the voltage drop proportional to resistivity.

You might drop or roll a coin through the poles of a strong magnet. Conductive material will fall slower than a resistive material due to higher eddy currents in the good conductor.

There are electro-magnetic gauges, (NOT ultrasonic), used to measure the thickness of steel plate from one side. Maybe they will give a significantly different reading for a fake coin.
 
Silver is diamagnetic, molybdenum is paramagnetic. So maybe you could measure the detuning of a resonant circuit, when a coin is brought into the coil.
 
Galvanic cell with one known silver electrode .

Actual coins by weight .
 
Last edited:
DrDu said:
Silver is diamagnetic, molybdenum is paramagnetic. So maybe you could measure the detuning of a resonant circuit, when a coin is brought into the coil.

Could you translate the second sentence in a less technical way please? I don't know what measuring the detuning of a resonant circuit even means.
 
bluemoonKY said:
I don't know what measuring the detuning of a resonant circuit even means.
An inductor has an inductance, L, and a loss or Q determined in part by the core material.
If you have a free running LC oscillator and pass the coin through the coil there will be a change of oscillator frequency. The degree of change will discriminate between the two metals. It is like a simple metal detector.
https://en.wikipedia.org/wiki/Electronic_oscillator#Feedback_oscillator
 

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