# Can osmium react with oxygen at room temperature?

I’m an avid collector of elements (I love shiny rocks - don’t judge).

I’m looking to buy some osmium, as it’s one of the heaviest and hardest metals out there.

However, people online told me to avoid buying it, because it could react with oxygen naturally and become its acute toxic oxide.

However, from doing my own research, it seems it only oxidizes at 200 °C, which I doubt my metal vials will ever reach.

Can this be confirmed? Would it be safe to just store 99.99% pure osmium out in the open?

• See also episodictable.com/osmium // ... it’s [OsO4] also extremely poisonous. The molecule easily binds with oils in our body, irritating the skin, nose, and throat. It’ll also burn the eyes, but it won’t stop there: it also permanently stains the corneas, rendering a person blind. Even at concentrations too low to smell — roughly two parts per billion — it can cause a fatal buildup of fluid in the lungs or damage the kidneys.... you’ll need to store it carefully — inside a sealed glass container, preferably with secondary containment on top of that ... in an inert environment.. Dec 2, 2021 at 15:49
• Osmium powder is clearly dangerous but it is less clear whether bulk osmium is a major hazard (but probably best to only store in a closed container.) Dec 2, 2021 at 17:36
• @matt_black I have family members and many small animals. Id rather not endanger them. Ill just stick to chromium, tungsten and gold. Honestly it was very tempting, extremely heavy blue-hued metal. It just looks like something alien. However, I already have heavy metals and blue metal (silicon) so Im good. Dec 2, 2021 at 18:39
– Ed V
Dec 2, 2021 at 19:42
• Dec 3, 2021 at 2:51

Of the platinum metals, osmium is the most rapidly attacked by air. The powdered metal, even at room temperature, exudes the characteristic odour of the poisonous, volatile tetroxide, OsO4.

Osmium tetroxide is remarkably toxic and is not good stuff to have out in the open. Do not do this!

• thanks for the information. Thats too bad. I guess tungsten and gold will have to do then, since I cant have osmium Dec 2, 2021 at 18:33
• Why OsO4 is toxic? chemistry.stackexchange.com/questions/151649/… (@MisterSirCode) Dec 3, 2021 at 2:53
• Sometimes I wonder how many crisis-aversions can be directly attributed to Stack Exchange users. Dec 4, 2021 at 7:46

As the others already stated, handling pure Osmium is too dangerous at home, but there are shops that offer small samples of elements sealed in acrylic glass, which is supposed to be safe. Maybe this would satisfy your collectory needs ;-)

They may look like these cubes:

I'm not promoting this specific shop, this was just the first google hit.

According to Wikipedia:

Finely divided metallic osmium is pyrophoric[1] and reacts with oxygen at room temperature, forming volatile osmium tetroxide. Some osmium compounds are also converted to the tetroxide if oxygen is present.[1]

Osmium does not really differ from most metals by reacting with air at room temperature. But in most cases such as iron the oxide remains solid on the metal surface and -- if we avoid conditions that may break down the oxide chemically such as moisture, or trigger electrochemical reactions such as residual salts -- the solid oxide film will provide protection against extensive reaction. In contrast, the volatile oxide formed by osmium when it reacts with air vaporizes off and provides no such protection, and thus formation of the toxic oxide fumes continues. Most osmium is used in the form of alloys whose base metals form solid oxides.

You may just want to extract the writing point from a fountain pen and call it a day.

Cited reference

1. Smith, Ivan C.; Carson, Bonnie L.; Ferguson, Thomas L. (1974). "Osmium: An Appraisal of Environmental Exposure". Environmental Health Perspectives 8: 201–213. https://doi.org/10.2307/3428200, JSTOR 3428200. PMC 1474945. PMID 4470919.

• thanks, I was sincerely hoping itd be a little safer to have, but it appears not. I can use tungsten and gold instead Dec 2, 2021 at 18:39

It can! Please think twice before ordering osmium. The oxide is volatile and extremely toxic: one good huff is enough to give you severe pulmonary edema, and make you drown in your own body fluids several hours after the exposure. Contact with eyes will make you permanently blind by turning your corneas black and opaque.

However, the most danger is in handling osmium powder. The real danger is in handling osmium powder. Meanwhile, the question explicitly suggests that the bulk form of osmium is being considered: OP says "I love shiny rocks", not "I love dull gray powders". Also, all the sellers of elements for collection that I know of tend to sell osmium in the bulk form: cubes, pellets and nuggets, not in powdered form. I wish more people were actually reading the questions, instead of just quickly glancing over the title and copy-pasting two sentences from the first Google hit.

Formation of $$\ce{OsO4}$$ from osmium metal in room temperature is thermodynamically unfavorable. Handling bulk osmium is not nearly as dangerous. Be careful, though! While the majority of metals is ductile and malleable, some exceptions -- including osmium -- are brittle. Instead of deforming under mechanical stress, they shatter into small pieces, greatly increasing the surface area that could react with oxygen in the air!

Here is a video of a man handling bulk osmium nugget. Notice that he is wearing gloves. He has since been recently active, and is alive and well.

$$\ce{OsO4}$$ is formed slowly when osmium powder reacts with $$\ce{O2}$$ at ambient temperature. Reaction of bulk solid requires heating to 400 °C.

It is a bit of a shame that the accepted answer does not really make any effort to actually answer your question and does not even differentiate between powdered and bulk osmium. Instead, it just copies two short sentences from an external source.

• Hmmm - while I agree that the accepted answer could be better for the reasons you give, the reference used, Encyclopedia Britannica, is not one I would characterise as "of questionable quality and reputation" Dec 3, 2021 at 22:47
• In the English speaking world it has arguably been the premier publication of its type for over two centuries en.wikipedia.org/wiki/… Dec 3, 2021 at 22:55
• I don't think that starting an answer with "It can!" is a good way to introduce the horrors that come after. || "The claim of osmium being able to react with air at room temperature is about the osmium powder." That is incorrect. You might want to read the quote again. || I also wouldn't want to bank on the comparison with aluminium or iron. These metals form (in absence of moisture) quite strong protective surface oxides. It is one key difference to osmium. || So while this answer states facts, I find it particularly less helpful than the answers already given. Dec 4, 2021 at 0:18
• From the link of the 1st comment under Q: In the 1980s, NASA wanted to conduct spectroscopy in the extreme ultraviolet range using instruments on board the space shuttle. Element 76 is one of the few materials that’s capable of reflecting light in this highly energetic range — more than twice as good as gold or platinum. So the folks in charge of the mission sent up mirrors with a coating of pure osmium… and when they came back down, the osmium was gone. Dec 4, 2021 at 7:22
• @IanBush - that wiki link is impressive; I didn't realize Britannica's been around 250+ years... although I'd argue that Wikipedia has itself far surpassed all other encyclopedias. Britannica covers 288,274 topics, while Wikipedia has 54,739,246 pages (6,417,116 in English)...and that's in only 20 years. (Can you imagine what Wikipedia will be like, a couple centuries from now!) 😉 Dec 4, 2021 at 8:06