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06/09/2004 09:55   Metal Acid Wash   [Body]

Acid metal wash is a mix of phosphoric acid and solvents and inhibitors and probably a whole load of other crap. It's also damn expensive (Bunnings wanted $23 for 500ml of the stuff). So we're making our own.

The recipe I outline below has come about from processes of deduction and is probably not perfect. It will, however, be a good starting point and we can modify the mix over time.

The raw resources we have are:

85% w/w Phosphoric Acid (H3O4P)
100% Methanol (CH3OH)
Chromium Oxide (Cr2O3)

Some handy (but not all are necessary to make the required calculations) physical properties of these chemicals are listed below. Any of these values could be easily verified on the web or in a high school chemistry text:

M(H3O4P) = 97.977 g/mol
D(H3O4P) = 1.7 @ 85%
85% H3O4P w/w = 15 mol/L
M(Cr2O3) = 151.866 g/mol
M(CH3OH) = 32.026 g/mol
D(CH3OH) = 0.792

The products on the market that I have used as a guide are shown below. These values are printed on the packaging:

Wattyl Kill Rust: 383 g/L of Hydrocarbons.
Dulux Quit Rust: 30% Phosphoric Acid and 2 g/L of Cr2O3

That's all you need to work out:

1 L of our Acid Metal Wash =

333ml of H3O4P
383g of CH3OH === 484ml of CH3OH
2g of Cr2O3
and 184ml H2O

I'm just going to mix this up as we need it in 1L batches. Obviously the numbers can all be scaled to give larger or smaller amounts. I have no idea how stable the mix is (I'd expect some of the methanol to get away if it's left out) so I'll just make it up as we go.

So 1L of the commercial product will cost $45 but 1L of our mix will cost $3. We have the resources to make 15L...damning awesome.

 
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