- Joined
- Apr 23, 2018
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Since y'all are in learning mode, I'll put out a little more prep talk.
Ionic cleaners/surfactants like trisodium phosphate (TSP) and butyl cellosolv (stuff with names like blahblah-monobutyl-ether/diol, aka simple purple spray) are best at removing particles from the work's surface. In fact, they are exceedingly good at it. Take a piece of surfaced iron and clean it until the rag comes clean using whatever method you want. Then spray on some TSP or cellosolv cleaner, wait a minute or two, and wipe that off- the rag will come back gray/black, because those little metal particles carry a net positive charge in the natural environment (but not in a vacuum and not in your general chemistry text). That big electro-negative phosphate anion will dump a sodium on it's head to hook up with a metal cation with a higher charge density (sound familiar?). It's really incredible to see, you gotta try it. Lots of particles can be freed from what appears to be a very clean surface this way.
Ionic cleaners don't do much at all against oils. For that you need either a solvent (for removal and dilution) or a medium chain amphoteric, which is a fancy name for soap. The amphoteric forms micelles around the hydrophobic oil that can be carried away with a water rinse.
How clean is clean, and how clean is necessary? For epoxy paints, there is no such thing as clean enough, they rely on mechanical adhesion. Oil paints are tolerant of light-medium oils, and can still displace heavy oils well enough to stick. Spray paints are full of somewhat neutral reducers that don't displace oil well regardless of paint film chemistry. Acetone is great for a final wipe, as are all VOCs, but so is any member of the BTEX group (benzene, toluene, ethylbenzene, xylene). Be careful with simple alcohols (methyl, ethyl, propyl), alcohol is a strong nucleophile and will react with (as in break) some polymers, can etch steel, and will oxidize the surface if left in contact too long. Butoxyethanol not so much of a problem.
Ionic cleaners/surfactants like trisodium phosphate (TSP) and butyl cellosolv (stuff with names like blahblah-monobutyl-ether/diol, aka simple purple spray) are best at removing particles from the work's surface. In fact, they are exceedingly good at it. Take a piece of surfaced iron and clean it until the rag comes clean using whatever method you want. Then spray on some TSP or cellosolv cleaner, wait a minute or two, and wipe that off- the rag will come back gray/black, because those little metal particles carry a net positive charge in the natural environment (but not in a vacuum and not in your general chemistry text). That big electro-negative phosphate anion will dump a sodium on it's head to hook up with a metal cation with a higher charge density (sound familiar?). It's really incredible to see, you gotta try it. Lots of particles can be freed from what appears to be a very clean surface this way.
Ionic cleaners don't do much at all against oils. For that you need either a solvent (for removal and dilution) or a medium chain amphoteric, which is a fancy name for soap. The amphoteric forms micelles around the hydrophobic oil that can be carried away with a water rinse.
How clean is clean, and how clean is necessary? For epoxy paints, there is no such thing as clean enough, they rely on mechanical adhesion. Oil paints are tolerant of light-medium oils, and can still displace heavy oils well enough to stick. Spray paints are full of somewhat neutral reducers that don't displace oil well regardless of paint film chemistry. Acetone is great for a final wipe, as are all VOCs, but so is any member of the BTEX group (benzene, toluene, ethylbenzene, xylene). Be careful with simple alcohols (methyl, ethyl, propyl), alcohol is a strong nucleophile and will react with (as in break) some polymers, can etch steel, and will oxidize the surface if left in contact too long. Butoxyethanol not so much of a problem.
