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Old 2017-02-23, 10:28   #1
fivemack
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Default Unwise chemistry question

Aluminium, famously, is a reactive metal protected by an oxide layer; I've done the experiment where you apply liquid gallium to aluminium, and it removes the oxide layer and diffuses between the grains and the aluminium disintegrates impressively. I have seen the equivalent experiment with mercury done by a chemistry teacher, but am obviously unwilling to possess elemental mercury as an individual because the clean-up costs can get rapidly astronomical.

Chromium definitely has an oxide layer; do you get similarly interesting effects applying Ga or Hg to chromium? It seems worth asking before sacrificing several pounds worth of Cr and Ga to the gods of non-reactivity (though if they don't react, separating Ga, with a melting point less than 100C, and Cr with a melting point of 1900C is probably a matter of boiling water and a couple of sacrificial chopsticks)
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Old 2017-02-23, 12:53   #2
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Looks like the answer may be no: http://nvlpubs.nist.gov/nistpubs/Leg...report4313.pdf

Quote:
The possibility of using gallium as a liquid
metal to replace mercury in dental restorations was
investigated. It was found that gallium would not
combine at room or mouth temperature with bodycentered'*
cubic metals such as tantalum, chromium
and molybdenum.
Also, gallium's melting point is just above room temperature. You could separate it out by holding it in your hand for a few minutes!
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Old 2017-02-23, 16:28   #3
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Quote:
Originally Posted by wombatman View Post
Looks like the answer may be no: http://nvlpubs.nist.gov/nistpubs/Leg...report4313.pdf



Also, gallium's melting point is just above room temperature. You could separate it out by holding it in your hand for a few minutes!
Thanks! Gallium's melting point is only just above room temperature, and (for some reason connected I think with surface tension) the metal is extremely sticky, so if you try holding it in your hand you end up with an annoyingly mirror-plated patch on your hand, quite a lot of vigorous scrubbing, a worry about whether there's any aluminium in your plumbing or in your taps, and a slight worry about how good gallium might not be for your skin.
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Old 2017-02-23, 16:37   #4
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"When these mixtures of gallium and chromium were heated over an open flame the two metals combined with an exothermic reaction causing the mass suddenly to become bright red. The combination, after cooling, was a black friable powder"

is an odd line from that dentistry report; I wonder if the same thing happens under nitrogen or argon, or if you're just seeing the chromium burn. But gallium oxide is white, and I think the obvious oxide from burned chromium is dark green.

I don't have the kit to prepare a nitrogen- or argon-purged vessel to do the experiment in, nor is it probably wise to do so. I do have an eighth of a kilogram of chromium on order from eBay for no particular reason.

It does report doing the gold-gallium experiment, which they see producing a blue intermetallic; gold-indium is also supposed to be a nice blue, and indeed I have 100mg of Au in a box somewhere set aside for performing that experiment once I've found a decent tiny crucible.

Last fiddled with by fivemack on 2017-02-23 at 16:40
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Old 2017-02-23, 18:39   #5
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Quote:
Originally Posted by fivemack View Post
... for performing that experiment once I've found a decent tiny crucible.
Make your own. Get a graphite stick of, say, 10mm diameter, and carve a hole in it with a sharp knife, or a drill bit, or a small chisel. The drill is almost certainly the easiest. It's how I used to make high-temperature crucibles back when I was a practising spectroscopist.

A lump of coal or BBQ charcoal will do at a pinch but the latter tends to be a bit porous.

I can't answer the original question OTTOMH, the one about Cr and Ga and/or Hg. I do have a small bottle of Hg so, in principle, could perform that experiment. The toxicity of the metal is grossly over-exaggerated IMAO. I would drink (a small amount of) the liquid. I wouldn't like to eat more than a gram of inorganic Hg and I'd expect to be extremely ill indeed, possible fatally so, from a few milligrams of organo-mercury compounds inhaled or applied to the skin.
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Old 2017-02-23, 19:36   #6
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Quote:
Originally Posted by fivemack View Post
Thanks! Gallium's melting point is only just above room temperature, and (for some reason connected I think with surface tension) the metal is extremely sticky, so if you try holding it in your hand you end up with an annoyingly mirror-plated patch on your hand, quite a lot of vigorous scrubbing, a worry about whether there's any aluminium in your plumbing or in your taps, and a slight worry about how good gallium might not be for your skin.
This is probably good practice in general , but I was thinking of the gallium spoon prank. I've not personally held gallium metal, so I was unaware of its stickiness. I'm a bit surprised it wouldn't run off given typical body temperature, but that's good to know!
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Old 2017-02-23, 20:24   #7
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Quote:
Originally Posted by xilman View Post
Make your own. Get a graphite stick of, say, 10mm diameter, and carve a hole in it with a sharp knife, or a drill bit, or a small chisel. The drill is almost certainly the easiest. It's how I used to make high-temperature crucibles back when I was a practising spectroscopist.
The best heating mechanism I have is one of those kitchen blowtorches, so I would worry about igniting a carbon crucible - is that a meaningful concern with graphite? eBay offers a fair variety of silica crucibles, I don't know whether a kitchen supply shop would offer an enormous variety of porcelain goods usable as crucibles.
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Old 2017-02-24, 07:22   #8
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Quote:
Originally Posted by fivemack View Post
The best heating mechanism I have is one of those kitchen blowtorches, so I would worry about igniting a carbon crucible - is that a meaningful concern with graphite? eBay offers a fair variety of silica crucibles, I don't know whether a kitchen supply shop would offer an enormous variety of porcelain goods usable as crucibles.
I used to wind my own electric heating elements as well. In my case tungsten as I needed to get really hot. W bending is an art. It's brittle at room temperature and at red heat. When it's hot enough it's as malleable as Cu. Some people have the skill to know when it is hot enough, the majority do not. I happen to be a natural tungsten bender, probably the least useful of what few skills I do possess.

I'll think about alternative solutions.
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Old 2017-02-24, 07:50   #9
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Quote:
Originally Posted by xilman View Post
natural tungsten bender
Aren't they playing Glastonbury this year?
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Old 2017-02-24, 16:40   #10
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Quote:
Originally Posted by xilman View Post
I used to wind my own electric heating elements as well. In my case tungsten as I needed to get really hot. W bending is an art. It's brittle at room temperature and at red heat. When it's hot enough it's as malleable as Cu. Some people have the skill to know when it is hot enough, the majority do not. I happen to be a natural tungsten bender, probably the least useful of what few skills I do possess.

I'll think about alternative solutions.
Wow! Another special quality for tungsten, and one which seems rather unusual, too. Thanks for that bit of stray knowledge!
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Old 2017-02-24, 19:20   #11
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On the subject of unwise chemistry, this occurred last week:
Quote:
A university building was evacuated after a student accidentally made the same explosive that was used in the Paris terror attacks.
https://www.theguardian.com/educatio...xplosive-scare
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