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| Restoring dried solder flux paste |
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| tooki:
--- Quote from: uli12us on February 04, 2021, 11:46:07 pm ---The tacky flux in syringes contain petroleum jelly as well. Unfortunately the fraction of it is a secret. I think a third of the weight can not be bad. So you have 1 part rosin, 1part IPA or other alcohol and 1 part petroleum jelly. --- End quote --- There's more to it. (Though I don't know what it is.) I tried some experiments with making flux paste from rosin, and nothing I did ever resulted in it actually mixing with the petroleum jelly. With alcohol, it just formed a separate liquid layer. Without alcohol, the rosin could be melted, but always separated back out, so just rosin particles suspended in grease. Awful to solder with. Various commercial fluxes I've looked at use processed rosin (polymerized or various other processes I've forgotten). So I don't think they're actually just mixing in raw rosin. |
| jpanhalt:
Kester (MSDS, SDS) shows that its rosin is 40% to 55% rosin ( CAS:8050-09-07) with an empirical formula of C19H29COOH and isopropy alcohol 55% to 70% (IPA). The rosin is soluble in "alcohol," benzene, and ether. "Alcohol" probably refers to ethanol (absolute). If one searches on that CAS number you may get two different structural formulas (see here: https://www.sigmaaldrich.com/catalog/search?term=8050-09-7&interface=CAS%20No.&N=0&mode=partialmax&lang=en®ion=US&focus=product). Of the two, only abietic acid has the empirical formula of C19H29COOH. Moreover, it is commonly said that rosin flux is mostly abietic acid. Wikipedia lists the solubility of abietic acid as very soluble in ethanol, acetone, diethyl ether, and petroleum ether. The latter is a distillation product from petroleum and is mostly aliphatic hydrocarbons, but can contain other hydrocarbons as impurities. Whether it is soluble in petroleum jelly is not clear. Rate of dissolution is temperature dependent. If heated above abietic acid's melting point, it may well dissolve or form a cloudy mixture. I know you can dissolve it in paraffin wax that way. (I used it as a vacuum sealer in high school.) I suspect any relatively short chain alcohol or any of the substitutes* mentioned earlier will dissolve it. Kester does list the principle component of its flux thinners as isopropyl alcohol, e.g,. 85% to 100%. Since abietic acid is insoluble in water, I'd expect its solubility in "alcohol" to be highly dependent on whether the alcohol was absolute or had water in it. For example, absolute ethanol is an excellent solvent for fats, but 95% ethanol is not. Same goes for IPA. *Even with a 10% to 30% water, cellosolves will dissolve rosin flux. |
| SilverSolder:
--- Quote from: jpanhalt on February 15, 2021, 04:49:00 pm --- [...] For example, absolute ethanol is an excellent solvent for fats, but 95% ethanol is not. Same goes for IPA. [...] --- End quote --- That is very interesting, wonder why that is? Do the water molecules somehow block the alcohol molecules by being more attracted to them than fat, or something like that? |
| tooki:
--- Quote from: jpanhalt on February 15, 2021, 04:49:00 pm ---Kester (MSDS, SDS) shows that its rosin is 40% to 55% rosin ( CAS:8050-09-07) with an empirical formula of C19H29COOH and isopropy alcohol 55% to 70% (IPA). The rosin is soluble in "alcohol," benzene, and ether. "Alcohol" probably refers to ethanol (absolute). If one searches on that CAS number you may get two different structural formulas (see here: https://www.sigmaaldrich.com/catalog/search?term=8050-09-7&interface=CAS%20No.&N=0&mode=partialmax&lang=en®ion=US&focus=product). Of the two, only abietic acid has the empirical formula of C19H29COOH. Moreover, it is commonly said that rosin flux is mostly abietic acid. Wikipedia lists the solubility of abietic acid as very soluble in ethanol, acetone, diethyl ether, and petroleum ether. The latter is a distillation product from petroleum and is mostly aliphatic hydrocarbons, but can contain other hydrocarbons as impurities. Whether it is soluble in petroleum jelly is not clear. Rate of dissolution is temperature dependent. If heated above abietic acid's melting point, it may well dissolve or form a cloudy mixture. I know you can dissolve it in paraffin wax that way. (I used it as a vacuum sealer in high school.) I suspect any relatively short chain alcohol or any of the substitutes* mentioned earlier will dissolve it. Kester does list the principle component of its flux thinners as isopropyl alcohol, e.g,. 85% to 100%. Since abietic acid is insoluble in water, I'd expect its solubility in "alcohol" to be highly dependent on whether the alcohol was absolute or had water in it. For example, absolute ethanol is an excellent solvent for fats, but 95% ethanol is not. Same goes for IPA. *Even with a 10% to 30% water, cellosolves will dissolve rosin flux. --- End quote --- We all know it dissolves in most solvents. It definitely does not readily dissolve in petroleum jelly. Again, I've tried. Both with and without the help of alcohol (>99% IPA, specifically). I melted it to the point the rosin was fully liquid (and the petroleum jelly, too, of course, since its melting point is far lower). Oddly, the wiki article on abietic acid lists two wildly different melting points: "as low as 85 °C" in the body text, "172–175 °C" in the infobox, each with a citation. I'm pretty sure I exceeded 85 °C, but no way did I reach 172 °C. When melted, they'd appear to mix, but as it cooled, it separated into two distinct phases. :( It might be interesting to try dissolving it with a hydrocarbon solvent and petroleum jelly, since I would expect each of those to be miscible with each other. |
| jpanhalt:
Even pure substances can crystalize or form glasses from "solutions" of themselves. We "all know that." For example, you can purify hexadecane (cetane, a major component of diesel fuel) simply by crystallization from liquid hexadecane. I would not necessarily assume petroleum jelly and rosin are miscible at all temperatures. If the rosin precipitates, increase the amount of petroleum jelly, or reverse the ratios (i.e., more rosin, less petroleum jelly). Maybe that is the reason the composition is a secret. |
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