How to neutralize Ospho

Lizer

Mad Scientist
Given the difficulty of rinsing Ospho off, would it not help to neutralize it with a base before rinsing?
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.
 

Evil_Fiz

Promoted Users
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.
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.

-----
Emil
 

Lizer

Mad Scientist
Those of us old enough to remember the car batteries that weren't sealed also remember the holes left in our clothes and skin from the acid that got on us. Why would acid in anything else be different?
"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.

 

elwood

Promoted Users
Thanks Lizer, I always learn something new from you. You seem to give a different perspective on what most of us have gotten used to and take for granted and never understood the what and whys of the way things are. Cool, very cool.
 

mga1600

New Member
Not a criticism directed at anyone, more just an observation. For the life of me I don't understand why so many folks want to use epoxy, but don't want to follow the directions for it's use. There are no shortcuts to quality.
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.
 

bigstar

New Member
Hello all. I appreciate all of your expertise and knowledge. I have a question on the Ospho… on areas that I am not planning to paint should I just paint on a couple coats of the Ospho and leave it? Will this be a suitable permanent coating or do I really have to clean it off and prime it? This will be on an exterior structure. Thank you
 
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cmfisher4

Promoted Users
I got a thumbs up when I asked a similar questions, Bigstar. Not sure how well it will hold up to the elements, but you should be okay (better than nothing)! In intend to use it inside areas where I can't get to to paint.
 

Dean Jenkins

Promoted Users
Will this be a suitable permanent coating or do I really have to clean it off and prime it? This will be on an exterior structure. Thank you
The instructions on the ospho container assume the surface will be painted after treatment. They are OK with painting over dried ospho, obviously the folks here are not.

You say it is an "exterior structure" and I assume it has some rust since you are using ospho. If it rusted before, it will rust again.

If you don't want to go the full ospho - neutralize - epoxy route (which would be best), why not at least treat it with ospho and then some rustoleum rattle can paint?

Not trying to be critical or complicate things, I just don't think the ospho will be a "suitable permanent coating," which is what you asked.
 
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bigstar

New Member
Thanks ya’ll I kindof knew the answer already. I’m doing a steel frame for a bunkhouse and was looking for the best way to get rid of surface rust on the frame before I build wood wall framing around it. My search lead me here. I will Ospho, clean, prime and paint. Thank you again
 
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