Post by coastalrocketeer on Dec 2, 2018 20:49:44 GMT -8
I was trying to figure out how much KOH would be needed for dissolution of a certain number of grams of Aluminum foil for Aluminate enrichment of potential refractory mixes and found this in my searches:
“ Al (s) + KOH(aq) --> K+(aq) + Al(OH)4-(aq) This reaction is strongly exothermic and is the reaction that takes place when crystal Drano (which is primarily a metal hydroxide with bits of Al in it) is added to a drain.
Stoichiometry involves the ratio of the reactants and products. These ratios are given by the coefficients in a balanced equation. The balanced equation for the above reaction would be:
2Al + 2KOH + 6H20 —> 2 K[Al(OH)4] + 3 H2
For NaOH the balanced equation is:
2Al + 2NaOH + 6H20 —> 2 Na[Al(OH)4] + 3 H2
I wanted to be adding close to the right amount of lye for the amount of aluminum I want to dissolve, so as not to have significant amounts of excess lye, unreacted aluminum, or too much extra water.
You can see how much Lye and how much water will be consumed, And can calculate these as a ratio to your desired Aluminum input.
I expect one would need significantly more water to make it go smoothly and not boil and spatter excessively... balancing this with not having SO much water that it can’t be part of your mix water, presumably added near the end, as I believe Karl has stated that it will act as an accelerator to curing.
In my experience, I disolved Al in NaOH. Manny more variables contribute to the reaction. First of all , the result of the Al+H2O reaction is not a homogenus Na Al(OH)4. One might get manny more compouns frome it (FE: Al(OH)3, Al(OH)5/6 ect, also some chemists claim in there studies a "Al-O-Al brdge". So far the theory. As for the practical part, the released heat can be reuced by performing the dissolution in a cold environment or by applying cooling to the liquid. Also by reducing the reactive surface of the Al (I use 2mm sheet aluminium, not pure like Al food grade foil). Also adding smaller bits of Al (dont put all Al at once). One can completely eliminate boiling of the aquatios solution. My dissolution of 50g of Al lasts about 40hours, but no "boubles", splater or much visible vapor. Also the pH of the Na(K) solution is important, in the texts I fond it is mainly 16M+ , even 18M , so water/alkali ratio is crucial.
How about just adding some aluminum oxide to the mix? I use 200 mesh white aluminum oxide blast media in my custom face coats and it works really well as a kind of grog. I have used it up to 90 percent with 10 precent fire clay with really good results. I fuse it with an acetylene torch. I try not to get it to hot avoiding lots of glass formation. How about fumed alumina if your looking for some crystalline structure/growth??? I'm not sure what grain size the ceramics glaze industry offers but that should be a good source too.
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