Given the difficulty of rinsing Ospho off, would it not help to neutralize it with a base before rinsing?
How to neutralize Ospho
- Thread starter Barry
- Start date
Lizer
Mad Scientist
No because then you have contamination from whatever base you’re using. The base simply accepts hydrogen ions and reduces pH. It doesn’t contribute to removal of an acid film at all. The film needs an effective SOLVENT to remove it. Itself or water would be the best solvent in this case. It needs to be rehydrated by more acid (for some reason water doesn't rehydrate it well), but once rehydrated, water (not WGR or another chemical solvent uncapable of further solubilizing it) would be the best solvent to carry it away.
In fact a base may do a worse job at removing it. Because the acid resolubilizes very readily when you put more acid on it, this suggests that solubilization is pH driven to some extent. This is not uncommon in the work I do. Something like casein or EDTA both require pH adjustments of the solvent to get them to go into solution.
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Lizer
Mad Scientist
I was referring to dried, but all the same, you then have residue of whatever base you used on the metal which is still undesirable. I don't know what you'd gain by neutralizing the pH if the material itself is still there.
Obviously water seems to be effective since many have done so without issue, but if I lived in a vacuum and had no knowledge of the outside world, intuitively I probably would have used Dawn and water to wash it off while still wet.
Obviously water seems to be effective since many have done so without issue, but if I lived in a vacuum and had no knowledge of the outside world, intuitively I probably would have used Dawn and water to wash it off while still wet.
Thanks for your thorough and very informative comments. It occurs to me from digesting your statements that if we took the word ACID out of ACID FILM about 98% of the confusion could be eliminated.
@shine: Would you recommend in favor or against using Dawn in water to wash the panel after reapplying the Ospho ahead of a final thorough rinse with running water? I need to de-phosphoric acid my entire car, inside and out.
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Emil
Lizer
Mad Scientist
"Why would acid in anything else be different?"
The holes referenced are a property of being corrosive, not acidic. Both strong acids and strong bases can be corrosive.
To the second point, acids are not created equal. Some acids are very strong (like hydrochloric/muriatic or sulfuric/battery acid) whereas other acids are weak, like Phosphoric acid or citric acid. You drink phosphoric acid in your pop, but it's clearly not burning holes in you from the inside out, nor is molasses.
For only those that are actually interested, I post a link here that shows strengths of various acids. The pKa is a value that tells how strong an acid is; it is inversely related to the Ka of an acid, which is its dissociation constant. An acid that readily dissociates and donates hydrogen ions is a strong acid, whereas an acid that does not dissociate as easily and likes to hold on to its hydrogen ions will have a lower dissociation constant. In other words, one is charitable whereas the other is not. That's a lot of boring background most of you will never need to ever care about. But it puts these numbers in the link in context. The lower the pKa, the stronger the acid. pKa values less than 0 are very strong, while those above 0 get progressively weaker as the number gets higher. Inversely, the higher the Ka, the stronger the acid.
So look at where HCl and sulfuric (H2SO4) sit on the chart, vs phosphoric acid H2PO4.
It's also interesting to see where other acids sit as well.
Good point. My question was relating to the following. The parts were sandblasted. however I notice, in some hard to reach places, there is some pitting. Based on this, I'm asking the pro's (Barry) and the experienced the question.