Would armor made out of molybdenum(Mo) protect from any kind of damage and would it cause any harm to the person wearing it?

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    $\begingroup$ Pure metal or some kind of alloy? $\endgroup$ – Joe Kissling Mar 24 '17 at 20:08
  • $\begingroup$ Why are you asking this - why molybdenum? $\endgroup$ – user3106 Mar 24 '17 at 20:25
  • $\begingroup$ Are you asking about molybdenum disulfide as in a super slippery coating or just the raw element? $\endgroup$ – Blackbeagle Mar 24 '17 at 21:28

No Molybdenum armour would not be worth wearing.

While Molybdenum is often used in alloys of iron, only rarely is it used on its own.

With a Mohs hardness of 5.5 Molybdenum is a bit harder than steel (4.5) it would probably have a similar protective value to steel. It would be significantly heavier having a density of 10.28 g/cm³ compared to iron's 7.874 g/cm³.

While Molybdenum has lots of interesting chemical properties all you really want out of armor is the ability to withstand a beating without deformation or shattering.

Since it is much more expensive than steel and provides similar protection, stick to your preferred steel alloy for all your defensive needs. Who knows it may have a small amount of Mo in it already.

  • $\begingroup$ Yeah -- it seems that most US RHA is made using an alloy similar to 4340, which is a Mo-bearing steel $\endgroup$ – Shalvenay Mar 25 '17 at 1:13
  • $\begingroup$ @shalvenay what is US RHA? $\endgroup$ – sphennings Mar 25 '17 at 17:52
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    $\begingroup$ RHA = Rolled Homogenous Armor (think WWII era tank armor, or some armor components on lesser armored vehicles nowadays) $\endgroup$ – Shalvenay Mar 25 '17 at 17:55

As @sphennings explained, molybdenum is around 20% heavier, but it is also more than 20% harder.

This makes molybdenum armor more useful than iron armor.

The problems with it:

  • Its melting point is 2600°C, compared to iron's 1500°C. This means, it is probably not processable with medieval technology, and it is totaly impossible for them to produce it from ores. We produce it by burning its sulfide in air, and then reducing the resulting oxide with ammonia. This has been possible with the chemical technology of the XIX century.
  • If your civilization has this technology level, they can use molybdenum more effectively than iron (although it will be much more costly for them).
  • $\begingroup$ This assumes an equal benefit between the lightness of an armor and its strength. Seems a bold assumption – while armor is by most accounts already very heavy it also offers very good protection. The increase in protection which is likely minor given the context is probably not worth the increase in weight. Agility and endurance are worth something too. $\endgroup$ – Greenstick Aug 1 '17 at 20:28
  • $\begingroup$ Why are you discussing "medieval technology"? I don't see anything in the question to indicate the technology level at all, and certainly nothing about it being "medieval" level (whatever that means; "medieval" is a very broad term already). $\endgroup$ – user Oct 9 '17 at 18:27
  • $\begingroup$ If I recall, higher density also makes it more effective at protecting against blunt trauma. The wearer feels less of the shock from being hit by, say, a giant club. Of course, you have to assume that mobility isn't compromised despite the weight for this to make sense. $\endgroup$ – Xenocacia Oct 10 '17 at 2:04

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