The other approach for doing elemental analysis is EDX, energy dispersive x-ray spectroscopy. In this method an electron beam is accelerated to 5-30KV and focused on the sample. This basiHe
2+
cally replaces the x-ray excitation with e-beam. From there, a pulse height detector is used to generate the x ray spectrum, very much like the XRF system. The equipment is (naturally) expensive, so why would you go that route instead of XRF? Simple--spatial resolution. Your typical EDX tool is installed on a scanning electron microscope, which has very high resolution. Not needed to analyze a hunk of unknown alloy.
Back down to earth, I started wondering if it might be possible to update the old spark test by aiming a home-brew spectrometer at the trail of sparks and see what spectral lines show up.
Here is a web site that sells inexpensive spectrometer kits.
Iron and carbon would burn and generate light but it's not clear to me if nickel, chrome, vanadium, molybdenum etc. would.
Again, even if the "new age spark test" scheme is able to detect the different metals in your alloy, it would be a challenge to get quantitative results. Still, it might be good enough to aim you in the right direction -- and if augmented with other data (magnetic/nonmagnetic etc) you MIGHT be able to narrow down the field of possibles even more.
An interesting discussion!
A spark is a short-duration plasma
Suggesting one does it with a plasma instead of a spark- almost the equivalent of the Bunsen burner flame test, but much hotter, and with a wavelength detector (usually diffraction grating) to let you see more "colours".
OK - let us pick out the possibles.
To resolve first the X-Ray thing. Yes indeed, you can excite the metal atoms with X-Rays, but you can also use other primary excitation sources.
1) β- radiation is, as I understand it,
an electron beam. It will do. β+ is positrons. We won't do that!
2)
Protons. The stuff left over when we ionize hydrogen to get electrons. Hmm.. That is the stuff they use in the LHC. The hydrogen they use for many weeks supply is the size of a in-car fire extinguisher.
3)
α Alpha particles. These are helium nuclei. 2 protons + 2 neutrons. Among other things, they come from smoke detectors. Written as He2+ or He2+ with energy 5MeV, and they move fast - like about 15,000 km/sec.
I can do, and have done X-Rays. Expensive, awkward to use, risky, needing high energy evacuated kit.
I once used a hospital X-Ray machine to put a beam through a 1mm thick little square of copper which I used as a neutral density filter to cut down the brightness of the beam, so I could develop an auto-focus video device for the photomultiplier display to allow continuous X-Ray diagnosis. The only way I could get my face close enough to the eyepiece was to sit on the machine, and let the beam go down onto the copper quite close to where I was ..er. sitting. I had the heavy white apron and all, but the beam was to the side of me, and I had it switched on for 20 seconds and longer at a time. X-Rays is not what we (OK - I) would want to use.
Electron beam guns is also something I have got to grips with. The up to 40kW kind where the beam is focused onto the top of the (titanium) being vaporized, using scan coil magnets to move it around. Huge vacuum pumps, and 35kV power supplies (variable), running up to near 1Amp. All is OK unless you lose control of the beam. If it ever hit the side of the chamber and broke through, that would be a huge dose of X-Ray.
I came to dislike electron beams. I still have two of the old Leybold Hereaus electron guns intact with cooling jackets and a high-isolation filament transformer. They are nice big chunks of beautifully shaped stainless steel that can be re-purposed. Alternatively, if any HM member wants them, even for a door stop or boat anchor, they are there for the taking, but you have to fund the shipping - and remember, I am in the UK! We can throw in the safety isolation filament transformer and a length of molybdenum filament wire. This stuff is a bit heavy.
We don't need X-rays, nor electron beams.
Americium is an Alpha (α) source, and a weak gamma (γ) source that is unknown in nature, the only artificially produced element, made by neutron bombardment of plutonium or uranium, so it is, in fact, a component of reactor waste. The tiny amount needed for a steel analyzer can come from a few smoke detectors.
Can we use the light as @homebrewed suggests?
Perhaps one can, though I think this is still the stuff of a small vacuum chamber. Perhaps of stainless pipe about 50mm diameter, and having quartz windows. A cheap plastic diffraction grating, and one of those "line array", or matrix photodiodes. The carbon arc can be started with a spark, stabilize the light, and the sample being tested is in fact one of the electrodes, or is placed on a piece of carbon. We only need a brief flare - perhaps 400mS.
The photodiodes can be sampled much faster, perhaps at 20 - 100kHz, and the outputs put through a calibration scaling before display. A Raspberry Pi fitted with an e-Bay A-D converter add-on board (about $10 to$40) might do.
So far, for me, this version is just a mad, free thinking, possibly stupid speculation. Like designing on the back of a napkin while the food is arriving! I have no idea whether this high speed, high tech, version of a Bunsen flame test will work. Feel free to trash the musings if you like.
The radioactive way - a proven design exists!
That is why I like it. None of the bits are outrageously expensive. Much of the design outline is already in this thread. It has some nice science in it.
How we get the spectrum plot out of it is something I did not quite understand. I (think) the energy that excites the metal atom is released as the electrons return to their un-hyped-up quantum state, and the wavelength of what is released is related to the wavelength by Planck's Constant, which is extremely er.. constant. So measuring the relative brightness of the scintillation leads to a place on the plot.
We surely do not need a build as clunky as this!
The smoke detector set looks like this. Again, I am thinking it need not be like this.
OK - not fully checked out yet, but this last option looks so very feasible that it is surely worth a scrutinize by HM Forum crowd critique.