[80nine]

Hi,

Im new to this forum and i will be greatful if someone could help me with my questions.

I dont know much about chemistry but my mission is to mix a liquid fuel that burns with a red flame and it cant be too toxic or highly flammable.

So i have to mix a fuel that burns with a non yellow flame with a salt of lithium that is soluble in that fuel.

Maybe i can use one of this as fuel/solvent?

* Propylene glycol
* Tripropylene glycol
* Ethylene glycol (too toxic, can not use)
* Triethylene glycol
* Glycerol
Other?

Maybe i can use one of this as a solute?

* Lithium Nitrate
* Lithium Acetylacetonate
* Lithium Sulfide
* Lithium Iodide
* Lithium Acetate
* Lithium Sulfate / monohydrate
* Lithium Perchlorate
* Lithium Bromide
* Lithium Chloride (can not use, fouling of wick)


I have tried solutions of propylene glycol with lithium chloride but the light went out because the wick got dirty very quickly.
Also tried propylene glycol with lithium bromide but i think it was not very soluble?

Grateful for any help.
Thank you.

[rolnor]

I think you should avoid lithium perchlorate, it can explode with organic material.
Maybe you can just try, trial and error.

[Arkcon]

For a red flame, lithium is too weak.  What you'd like is strontium salts.  Perhaps these sort of flame compounds are available from vendor who supply theater productions.  They may have some compositions ready to go.

[Enthalpy]

Rather than dissolving a salt in a fuel, I'd try an organic salt of the colouring metal. Something like strontium dipropanoate: adjust the acid if the salt shall be liquid. A well chosen such salt should be soluble in petroleum distillates, nice advantage. Fatty acids are cheap.

In case lithium's colour suffices, some lubricating greases contain it already, as a fatty acid salt, often stearate. If not, maybe strontium can replace it.

[FlaskBreaker]

I agree with Arkcon, strontium would be the best element for the job. Usually strontium chloride is used for red flames. Most chemical suppliers have strontium chloride, so I recommend you shop around and find the best price/quantity.

Of course, you could use other strontium salts, however strontium chloride is the one I use.

[80nine]

For a red flame, lithium is too weak.  What you'd like is strontium salts.  Perhaps these sort of flame compounds are available from vendor who supply theater productions.  They may have some compositions ready to go.

I have used propyleneglycol as solvent and tried to mix with both lithium chloride and strontium chloride.
The flame becomes fairly red with both but with chloride in the fuel the wick gets all black and dirty and the flame get choked out.

Is it the chloride that makes the wick dirty and flame go out when burned?
If its the chloride, im thinking of trying with lithium/strontium iodide?

Boric acid works for a green flame and there is no dirt on the wick.


Thanks everyone for the answers

[billnotgatez]

Did you use
propyleneglycol as solvent
for the
Boric acid
test?

[Enthalpy]

You dissolve SrCl₂, which is not volatile, in a fuel that is somewhat volatile, and send the solution in a wick to evaporate them at the flame's heat so their vapour burns.

I'd would find logic (but this has little value versus experimental evidence!) that the wick evaporates only the fuel but very little of the salt, which accumulates on the wick.

Salts can color a flame made by burning powders. These don't rely much on evaporation, and they provide intense heat immediately at the powder.
But in a fuel burnt gently with air, I would not use such a salt, because it's not volatile enough.

Search for strontium compounds that are volatile if some exist. Could be small organic salts like diformate or diethanoate, or Sr(OCH₃)₂  -if they exist and can be purchased or synthesized. The chemists here may hopefully bring more ideas. Then, the dissolving fuel (if any!) would better be about as hard to evaporate as the strontium-bearing molecule, to avoid segregation at the wick. This was my attempt with strontium distearate, but the distearate may not be volatile enough even if used alone, hence the smaller molecule.

With iodide, I fear the heat destroys the compound before evaporation. You'd get iodine or its compound in the air and a strontium compound on the wick. This may even happen a bit with the chloride.

The other path would be to introduce the metal, as a salt or metallic, directly in the flame at a location hot enough to evaporate some. Like it's done with a crystal of table salt. But does this fit your needs?

If you succeed, you'll get a strontium compound (the oxide, a salt...) in the air. Depending on the use, please check the toxicity.

[Enthalpy]

And in case lithium gives a color intense enough in a situation where you evaporate and burn a compound, finding volatile compounds of lithium should be easier than of strontium. Maybe lithium butanoate (=butyrate), predicted to evaporate around +166°C, or a slightly heavier compound.

Again, please check the toxicity! Lithium compounds are drugs for the brain. After a flame, LiOH is expected, which is caustic.

[Enthalpy]

This lightest oil fraction safely burnable with a wick is petroleum or kerosene, which boils around +210°C. That would match lithium hexanoate better, for a similar behaviour and for simultaneous vaporization of a mixture.

Heavier liquids, or solids like candles, have a boiling point matched by heavier lithium (or strontium?) organic salts. Lithium palmitate or stearate are soaps commonly used in technical lubrication greases, so that would make an easy try.

Again, LiOH in the air is unhealthy. The good point is you'll feel pain before your lungs are deadly hurt, but for the eyes I don't know. Absorbed lithium also changes the mood.

[Enthalpy]

Lithium stearate, palmitate and co seem to decompose before they boil under normal pressure, so shorter organic acids are preferable.

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A use for intense colored flames of volatile metal compounds could be emergency signalling rockets (they must bear a special name) to call for help, for instance in a shipwreck. Presently they use standard pyrotechnics with a solid oxidiser and a radiating metal; burning in the air with a wick may last longer. These lights use to fall for minutes under a parachute. A balloon, to fly longer?

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I've seen no volatile strontium compound. All checked organic salts decompose before they evaporate. But maybe a ligand does it better? Like cyclooctatetraene (COT) or an aza crown ether? COT is known to complex two Li atoms, which releases 2*200kJ, so Li₂C₈H₈ must have some heat stability, but the metal outside raises the boiling point.

One banal volatile organometallic is PbEt₄, boiling around +80°C because the hydrocarbyls surround the metal. Ti and Zr are known for intense white light and might make similar compounds, or heavier compounds to burn with a wick. Ti-C and Zr-C bonds are stronger than Pb-C hence the compounds may survive higher temperatures. PbEt₄ was cheaply produced, but silanes instead may inspire the synthesis of the more reactive Ti and Zr compounds.

TiCot₂ and ZrCot₂ sandwiches would expose only hydrocarbons, and C₁₆ can match wax' boiling point.

I emphasize that TiO₂ nanoparticles are a respiratory carcinogen, proven at mice and suspected at humans, as are nearly all mineral fine powders, so I'd mistrust ZrO₂ equally. If such a brilliant coloured candle is ever produced, it shouldn't serve for a garden dinner.

Marc Schaefer, aka Enthalpy

[Enthalpy]

Flare is a better name than "emergency signalling rockets":
https://en.wikipedia.org/wiki/Flare
they serve on land too, an easier application for a fuel burning in air with or without a wick.

Glass fibres make nice wicks too, working with wax, and they resist the flame better than organic fibres do. Possible advantage if metal in a fuel makes the flame hotter.

[Enthalpy]

A possible use for coloured flames is a grave candle
https://en.wikipedia.org/wiki/Grave_candle
it's very common in some countries, generally red in Germany.

A metal flame expectedly emits more light than a candle in a tinted glass, so it might burn longer, definite advantage in this use. Solar cells, batteries and LED burn even longer but aren't as symbol-loaded nor traditional.

Lamps can also signal an improvised aircraft runway, work at a road or a railway... for which an efficient flame may be more convenient than a battery and optionally a solar panel.

Such candles or lamps would be enclosed. Something to catch the metal oxides in the fumes would be nice.

Marc Schaefer, aka Enthalpy