3 ms·

Ultrasound testing is probably a weakness. Edit: Sound passes through tungsten and gold at significantly different rates. Also, a "mixed media" type material

by tyingq 4y ago

Ultrasound testing is probably a weakness. Edit: Sound passes through tungsten and gold at significantly different rates. Also, a "mixed media" type material would have extra "echos" that a homogenous thing would not.

ajot 4y ago
Maybe a Differential Thermal Analysis/Thermomechanical Analysia? I suspect gold and tungsten have different behaviours when heated, and that should tell both apart. https://en.wikipedia.org/wiki/Differential_thermal_analysis https://en.wikipedia.org/wiki/Differential_thermal_analysis https://en.wikipedia.org/wiki/Thermomechanical_analysis https://en.wikipedia.org/wiki/Thermomechanical_analysis
- deleted 4y ago
  [deleted]
- speakeron 4y ago
  They have different magnetic susceptibilities. Gold is diamagnetic (repelled by magnetism); tungsten is paramagnetic (attracted). A strong magnetic field (neodymium magnets) and sensitive scales can tell them apart. I built a small rig a few years ago with parts from Aliexpress that worked for coins and for bars it's just scaling it up.
ginko 4y ago
Looks like tungsten has more than twice the electric resistivity of gold. Setting up a conductivity test shouldn't be too hard.
- daneel_w 4y ago
  Because of electrical current preferring the path of least resistance (the gold instead of the tungsten), and because of the Skin effect (https://en.wikipedia.org/wiki/Skin_effect https://en.wikipedia.org/wiki/Skin_effect), I suspect such a test would be inaccurate. Especially given how thick the plating is in these particular bars.
  - tyingq 4y ago
    A high current test might work, albeit with some undesirable side effects :)
  - upofadown 4y ago
    No skin effect for the direct current you could normally use to measure resistance. Accurately measuring the resistance of something as large as a metal bar can be tricky, but the gold would help as it does not oxidize on the surface.
  - marcosdumay 4y ago
    The skin effect happens exclusively on alternating currents, and you will need a fairly high frequency for it to become a problem on the size gold bars usually have. So, no, it's completely irrelevant here.

by tyingq 4y ago

ajot 4y ago

Maybe a Differential Thermal Analysis/Thermomechanical Analysia? I suspect gold and tungsten have different behaviours when heated, and that should tell both apart. https://en.wikipedia.org/wiki/Differential_thermal_analysis https://en.wikipedia.org/wiki/Differential_thermal_analysis https://en.wikipedia.org/wiki/Thermomechanical_analysis https://en.wikipedia.org/wiki/Thermomechanical_analysis

deleted 4y ago
[deleted]
speakeron 4y ago
They have different magnetic susceptibilities. Gold is diamagnetic (repelled by magnetism); tungsten is paramagnetic (attracted). A strong magnetic field (neodymium magnets) and sensitive scales can tell them apart. I built a small rig a few years ago with parts from Aliexpress that worked for coins and for bars it's just scaling it up.

ginko 4y ago

Looks like tungsten has more than twice the electric resistivity of gold. Setting up a conductivity test shouldn't be too hard.

daneel_w 4y ago
Because of electrical current preferring the path of least resistance (the gold instead of the tungsten), and because of the Skin effect (https://en.wikipedia.org/wiki/Skin_effect https://en.wikipedia.org/wiki/Skin_effect), I suspect such a test would be inaccurate. Especially given how thick the plating is in these particular bars.
- tyingq 4y ago
  A high current test might work, albeit with some undesirable side effects :)
- upofadown 4y ago
  No skin effect for the direct current you could normally use to measure resistance. Accurately measuring the resistance of something as large as a metal bar can be tricky, but the gold would help as it does not oxidize on the surface.
- marcosdumay 4y ago
  The skin effect happens exclusively on alternating currents, and you will need a fairly high frequency for it to become a problem on the size gold bars usually have. So, no, it's completely irrelevant here.