Science Forums 2

[CraigD]

Gardamorg, you have edited your post to completely remove all of its original contents, which asked about the potential of osmium, the densest naturally occurring element, as a structural material, compared to carbon! Because changing posts in such a way can be confusing, please don’t do it in the future.

The following is my answer to your original post.

As best I can tell, unalloyed osmium is slightly less hard than typical metal alloys, such as steel, and much less hard and practically less strong than regular crystal materials, such as sapphire and diamond.

Before discussing this thread’s question, it’s important to understand the difference between hardness and strength. Hardness is, basically, a measure of what materials can scratch and cut others. Strength can be measured in many ways, such as shear strength, how difficult a material is to bend, tensile strength, how hard it is to pull a material apart, and compression strength, a measure of how hard a material is to compress.

Osmium hardness is 7.0 on the Mohs scale, a bit softer than most steel tools and machine parts, which have typical Mohs scale hardness of 7-8. The wikipedia article’s summary history of the use of osmium notes that it was at one time used for phonograph needles, before being replaced with much harder sapphire and diamond needles as techniques to make such needles became available.

Osmium has high shear strength, a shear modulus or 222 GPa, compared to 79 for steel and 478 for diamond.

Osmium has a very high compression strength, a bulk modulus likely between 395 and 462 GPa, possibly higher than diamond’s 442, (eg: Phys. Rev. B 70 (2004): Takemura Kenichi - Bulk modulus of osmium:...).

As far as making nanotubes or similar structures of osmium, I suspect there’d be a big problem, because it’s very chemically reactive, oxidizing very readily. I suspect that, like steel wool, fine osmium wire would burn. Oxidized into its most common form, Osmium tetroxide, it sublimates into a deadly poison gas (it’s name is literally latin for ). This reaction can be avoided is osmium is alloyed with other metals, or, of course, kept out of contact with oxygen.

Another drawback with large-scale use of osmium is that it’s fairly rare, and expensive, about US$100/g, or roughly 4 times as expensive as platinum.

In short, I think osmium is mostly good for what it’s currently used for, an ingredient in metal alloys, and a chemical used in synthesizing certain unusual compounds.

Originally Posted by Gardamorg

What could possible be the hardest strongest most durable substance?

Because strength and durability are not absolute qualities of materials, and, as noted above, are not synonyms, I don’t think this question can meaningfully be answered. Some materials are stronger and more durable in one application than ones that are stronger and more durable in another application. Some very strong materials are fragile, while some very durable materials are not very strong.