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Gallium is a metal that melts at room temperature.

I have a character who has the ability to manipulate matter and temperature to some degree. Is it possible for her to carry around a sheathe full of gallium and alter it into an effective sword?

Her environment is usually lower than gallium's melting point

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    $\begingroup$ Somebody smarter than me can decode this, but it appears the tensile and compression strength of the material is extremely low: azom.com/properties.aspx?ArticleID=1132 $\endgroup$ – Ranger Sep 6 '16 at 18:43
  • $\begingroup$ Well, if somebody snatches it away, it becomes useless, so that's nice. But honestly why doesn't she just matter-manipulate it into steel when fighting and then back again when done? $\endgroup$ – Superbest Sep 7 '16 at 6:22
  • $\begingroup$ @Superbest, that would involve splitting atoms $\endgroup$ – One Normal Night Sep 7 '16 at 11:37
  • $\begingroup$ I was thinking about an assassin's weapon, and a gallium knife/sword would melt on a hot day once discarded. But a stab in the throat with a knife made of ice would probably be better for baffling the detectives. He'd need to get the carotid with the first thrust, though. $\endgroup$ – nigel222 Sep 7 '16 at 16:13
  • $\begingroup$ why not just carry steel to begin with? $\endgroup$ – Azor Ahai Sep 8 '16 at 0:18
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Regardless of the temperature, Gallium is a poor choice for a sword.

Decoding its properties from Nex Terren's comment link:

http://www.azom.com/properties.aspx?ArticleID=1132

Some of Gallium's mechanical properties:

Tensile Strength - How strong is it, or how much force does it take to pull it until it breaks:

15-40 MPa (compare to polyethylene [AKA plastic] 12-43 vs steel 500-2000)

Hardness - If you poke or scratch it does it deform:

50 on the Vickers scale (most hardness comparisons start at 80, it's a pretty soft solid - easily deforms or scratchs)

Young's Modulus - how easy is it to deform:

9.6-10 GPa (Most comparable to wood 11, again easily deformable. Most metals are 100+ steel is around 200)

Poisson's Ratio A measure of how much it deforms, ranging from 0 to 0.5:

0.47 (Most hard metals are much lower 0.2-0.3, it's similar to saturated clay 0.40–0.49, or Gold 0.42–0.44.)

Conclusion

Your sword would be solid but would easily bend if put under stress and would likely break if swung or used to block. I don't think it would be likely to shatter (it's not hard enough), it would just bend and break more like a plastic or gold sword than a glass sword.

Beyond its general weakness, I'm not even sure if you could sharpen it using any traditional means (it would likely melt from friction heat at the edge if you tried a whetstone). You could cast it into a blunt pointed/edged shape, but I'm not sure it would be worth it, as any minor handling would quickly bend or blunt it.

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    $\begingroup$ @JDługosz Thanks for the fixes. Me and grammar never got along; or is it grammar and I? $\endgroup$ – Josh King Sep 6 '16 at 20:49
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    $\begingroup$ My edit concerned homonyms (sound alike words) ot grammar, and the availability of header formatting. As for I vs me, that’s subject vs object. subject verb object so you say I got something, never Me got something. Ignore the example of Cookie Monster; that is an affectation not a good example to follow! $\endgroup$ – JDługosz Sep 6 '16 at 20:54
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    $\begingroup$ A gallium weapon would be great at piercing aluminum armor, since gallium has strange interactions with aluminum. That is the only case where I can see it being useful as a weapon in any form. $\endgroup$ – Cody Sep 6 '16 at 21:57
  • $\begingroup$ It still has density, so getting whacked with it could result in some nasty blunt trauma (like gold and very unlike plastic). $\endgroup$ – Superbest Sep 7 '16 at 6:23
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    $\begingroup$ So, a sword is a no-no but what about bullets? Like "it pierces and melts inside you" or something $\endgroup$ – Loupax Sep 7 '16 at 14:25
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Melting point is not among the first concerns when picking materials for a weapon, ductility, malleability, and brittleness are. In the case of gallium, where you run into trouble is with the brittleness. Even if your heroine is able to keep her sword as chilled as she can, as soon as she strikes something hard with it, it will fracture in her hands.

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One issue is cost. Google says gallium is around \$220 per 100g, so around 3-4 times more expensive than silver. Reckoning on around 1kg for a rapier, that's going to set you back around \$2k. This seems excessive.

The obvious question your character is going to be asked is "why do you have a bagful of this relatively expensive metal?" If you're trying to sneak around without your weapon being noticed, this is a bad idea. Plus metal detectors, if we're in a modern-day setting.

A much better solution is simply to carry a water bottle. A couple of litres of water can then be turned into a very effective mace. For an even better version of this, flow the water over a rolled-up newspaper to make a pykrete weapon which is very much stronger than pure ice. With a rolled-up newspaper, you could shape this as a club/mace, or taper the newspaper to make yourself a rapier.

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    $\begingroup$ Clever idea with the pykrete. What's even cooler is the newspaper idea you suggested would technically be "super pykrete" (according to the Mythbusters tests) which is actually even stronger than the original material. $\endgroup$ – thanby Sep 7 '16 at 13:17
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You can always say it's Gallium alloy. I doubt anyone knows every and single Gallium alloy properties; and the alloy in question doesn't even have to be Gallium majority, it's enough for it to be the most interesting metal in a bunch to be called so.

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I wouldn't think this would be practical. If her sword is in contact with an enemy (skin, blood, organs, other gross stuff) for even a short period of time, it would start to melt. If an enemy could get a hand on the sword's blade, he/she could hold it for 2-3 seconds and then remove the blade from the hilt.

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  • $\begingroup$ I don't think this is a real issue, because she could alter it while it's touching skin, arguably making it more dangerous. The real problem would the brittleness, mentioned above $\endgroup$ – One Normal Night Sep 6 '16 at 19:07
  • $\begingroup$ Only if the enemy is from our neck of the woods. $\endgroup$ – Ash Aug 5 '17 at 18:58
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I would think the ability to keep the sword cool enough to be used would be a more effective weapon than the sword itself.

Gallium, like water, expands when in solid form (instead of contracting/shrinking, like most everything else), and as a metal it would be too brittle to strike or slash. Maybe stabbing would be fine. Consider a dagger.

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At room temperature it's rubbish but I can't find any information on it's physical properties at low, like liquid helium low, temperatures. It could perform very well if you were fighting a goo monster on Triton where the summers are a balmy negative two thirty Celsius but no-one's ever been interested to test that weirdly enough.

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