24 replies to this topic

[pyrotrev]

Funny, I've just had similar problems with some glitter mixes using a medium bright flake. It seems to depend a bit on how much flake you use, and how intimately it's mixed with the other ingredients, large amounts and/or rough mixing (best for glitter) cuased the stars to split at right angles to the direction of pumping, due to alignment of layers of flake with no binder between. It would likely not be such a problem with rolled stars. The only sure cure I found was to use an acetone based binder that cut through the stearin

[dr thrust]

hmmm.... errrrr... this may sound a silly question, but ive got some of this stearin coated aluminium and uncoated to, i find the uncoated makes much better "silver wave" cores, so is there a way of dissolving the stearin off the aluminium?

[pyrotrev]

Adding it to some petroleum spirit or acetone, a good stir then filtering/decanting off the liquid should do the trick. Due to the leafing nature of flake I suspect it will rapidly clog most filters known to man, so patience and decanting may be the better bet. It will obviously considerably increase its vulnerability to corrosion, so make sure you've some boric acid at hand!

[pyromaniac303]

Page 4 of this data sheet gives detailed information about solubility in different solvents:
Stearic Acid MSDS

Stearic acid and stearin are apparently the same thing, according to several candle makiing websites.

[digger]

Page 4 of this data sheet gives detailed information about solubility in different solvents:
Stearic Acid MSDS

Stearic acid and stearin are apparently the same thing, according to several candle makiing websites.

We make these where I work, and strictly speaking they are different things. Stearine is (up to) three stearic acid molecules attached to a glycerin backbone, whereas stearic acid does not have the glycerin, however many people outside of the industry use both terms to describe either compound mainly due to ignorance of lipid chemistry.

[pyromaniac303]

We make these where I work, and strictly speaking they are different things. Stearine is (up to) three stearic acid molecules attached to a glycerin backbone, whereas stearic acid does not have the glycerin, however many people outside of the industry use both terms to describe either compound mainly due to ignorance of lipid chemistry.

Do you know which one is most likely used to coat the aluminium? And also would they both have similar solubility properties? I actually have some stearin I found in a hobby shop years ago, though I'm unsure which type I have as it was sold in a plastic bag with a scribbled label saying 'stearin 99p'. Should be getting some chrome steel media soon (well they seem to be lost in the post...) so I may add this as I mill aluminium.

[GalFisk]

Petroleum spirit works well for dissolving stearine, paraffin and similar, acetone is not nearly as efficient. I suspect it's the same way with stearic acid, but I haven't tested it.

[digger]

Do you know which one is most likely used to coat the aluminium? And also would they both have similar solubility properties? I actually have some stearin I found in a hobby shop years ago, though I'm unsure which type I have as it was sold in a plastic bag with a scribbled label saying 'stearin 99p'. Should be getting some chrome steel media soon (well they seem to be lost in the post...) so I may add this as I mill aluminium.

They have differnent properties (even the purity of varies due to the process used to fractionate it, hence stearin can be described by its Iodine value to represent its melting point range).

However this aside I would imagine that Stearin would be the chemical used to coat the aluminium as stearic acid is corrosive (well I have seen it eat carbon steel valve gear in weeks when at elevated temperatures).

Yes most non polar solvents should disolve the stearin easily (acetone, toluene, xylene etc), and to a lesser extent they are soluble in some polar protic solvents such as isopropanol, ethanol etc.

So you should be able to remove it relativly easily, however I have to ask the question as it seams allot of effort to go to. Why not just buy some without the stearine coating for the certain applications that require it and use the stearin coated stuff for less sensitive formula?

Edited by digger, 12 June 2008 - 11:17 AM.

[Pretty green flames]

A weak solution of Sodium carbonate might also work, that way you would change the "Stearine" (provided it's stearic acid) into Sodium stearate (Soap) which could then be simply washed away from the aluminium. Although I don't know how the aluminium would react to a slightly alkaline solution (would it completely destroy the aluminium?)

The only problem i see with the use of nonpolar solvents is the cost and safely disposing them, you can tolerate something like acetone going down the sink but petrolium spirits is something that shouldn't go down the drain.

Both of these methods are a waste of time though, messy, time consuming and relatievly expensive.

[digger]

A weak solution of Sodium carbonate might also work, that way you would change the "Stearine" (provided it's stearic acid) into Sodium stearate (Soap) which could then be simply washed away from the aluminium. Although I don't know how the aluminium would react to a slightly alkaline solution (would it completely destroy the aluminium?)

Unfortunately sodium carbonate is unlikely to work as I am sure it is stearin that is used as in tri stearic acid glycerol ester. In which case sodium hydroxide at elevated temperature would have to be used to make soap leaving Nil change of any of the aluminium remaining. I am also sceptical whether sodium carbonate would react with stearic acid unless at elevated temperature due to its high melting point. As you say it would also probably react with aluminium anyway under these conditions.

P.S. I agree absolutley no flamable or polar solvents should be going down the drain under any circumstances, they can cause explosions within the drain system as a worst case or poison organic waste treatment beds.

Edited by digger, 12 June 2008 - 11:21 AM.