4
$\begingroup$

I am a master student of nuclear physics. Due to some measurements I'd like to make, I have to use Magnesium as a beam target. Searching through the net to see it's properties I found that it can be easily oxidized. In addition I've read that it's highly flammable.

I have in hand two forms of Magnesium:powder and ribbon. In order to make the targets I have two alternatives.

  1. Use the powder to make highly pressured pellets. I thought of flushing a bottle with Argon or Nitrogen, making the pellet as fast as possible using this procedure(which involves acetone) in the atmosphere and then after the pellet is formed put it in the Argon or Nitrogen bottle.
  2. Use the ribbon as is. The only problem is that it not wide enough, so I will have to make a spiral of this ribbon around something(I don't yet know what the "something" will be, so any idea is welcome!). The ribbon I have has a width of 3mm but I want a width of 6mm. So I thought of spinning the ribbon around an item, to form a spiral.

The goal is to make the target as safely as possible and avoid Magnesium oxidizing, because I don't want to have Oxygen in my target. So my question has three parts.

  1. How to safely treat magnesium powder/ribbon so as to avoid any possible accident and preventing it from oxidizing?
  2. Which of the above would be the most effective way to make the target?
  3. How to store the target until the experiment will be held?

Note that after the target is made, it will go to an evaporator, in order to evaporate some gold. Any advice, help or direction is more than welcome!

$\endgroup$
3
$\begingroup$

Magnesium powder and ribbon are relatively stable in air at normal conditions, probably because of thin protective layer of oxide. However, ribbon can burn in air with blinding light and powder gives self-burning (i.e. not needing external oxygen sources like air) mixtures with many common substances, some of them explosive. Moreover, burning magnesium may continue to burn in $\ce{CO_2}$ atmosphere, under quartz sand and especially under water (producing hydrogen, that can form explosive mixture). The only common material that can safely extinguish burning magnesium is iron powder. Surprising enough, being stable in cold water for short time, magnesium readily react with methanol (and probably ethanol), chlorinated hydrocarbons and hot water.

The good thing is that magnesium ribbon is not easy to lit up, and powder is almost impossible to lit up when on surface of some massive object (common gas lighter flame lit magnesium ribbon after 15-60 seconds of heating)

Magnesium must not be heated on air or under nitrogen. Period. Technical grade argon probably contain significant amount of nitrogen, so it should not be used either.

Magnesium theoretically can be melted under eutectic mixture of $\ce{NaCl}$-$\ce{KCl}$-$\ce{CaCl_2}$, but by doing so without experienced supervision you ask troubles. Still, theoretically speaking, if you find an iron (not silicate, porcelain or corundum) crucible you probably can melt magnesium in it under mentioned mixture of dry salts, let it crystallize and then carve it out.

However, magnesium alloy sheets are available on the market, so maybe you can find something and cut needed form from commercially available sheets. Try this first before doing anything requiring heating magnesium. I have doubts, that you will be able to press good tablets from magnesium powder, so if commercially available sheets and maybe some magnesium compounds (oxide, sulfide and others) won't not work for you, you probably will end with melting magnesium. I hope you won't need it, it is dangerous.

$\endgroup$
  • $\begingroup$ Thank you very much for your answer! I also want to avoid melting Magnesium, because I don't have equipment to do so, let alone safety. The ribbon I have has a width of 3mm but I want a width of 6mm. So I thought of spinning the ribbon around an item, to form a spiral. Can this be achieved? $\endgroup$ – Thanos Mar 7 '14 at 10:26
  • $\begingroup$ Probably it won't keep form. However, magnesium is relatively soft, so if you need relatively small widening, may be cold forging or press on ribbon will work? $\endgroup$ – permeakra Mar 7 '14 at 10:32
  • $\begingroup$ I need a widening but I also need the thickness to remain as is. $\endgroup$ – Thanos Mar 7 '14 at 10:37
  • $\begingroup$ Let me ask. What elements are tolerable in the target? $\endgroup$ – permeakra Mar 7 '14 at 10:40
  • $\begingroup$ That's not trivial to answer! It certainly must not have Oxygen or near elements(in atomic number). It will also have evaporated gold on it. Which elements do you have in mind? $\endgroup$ – Thanos Mar 7 '14 at 10:45
0
$\begingroup$

You can buy magnesium fabrications any way you like. It does surface air oxidize, but only divided metal is hazardous - powder, shavings, chips - unless you grind or saw on it. Magnesium burns under air, nitrogen, carbon dioxide, and water; and sand. Near anything containing oxygen or halogen will feed it. An argon flood should kill it. Also look at Metal-X extinguisher ratings.

If surface oxidation is a problem, ion mill it clean in vacuum, then deposit a micron of Parylene. Parylene C may be reactive toward naked magnesium. Parylene as such should work... but ask the coating vendors or test it.

http://en.wikipedia.org/wiki/Parylene
http://www.paryleneengineering.com/why_use_parylene.html
http://scscoatings.com/what_is_parylene/parylene_properties.aspx
https://www.google.com/patents/US5156919

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.