chemistry question

Actually, what was stated was that using a sodium caustic to neutralize hydrochloric acid would leave salt which would lead to corrosion. Also, just using HCl and rinsing it will leave a surface so clean that rust will begin immediately.

Bob

I have difficulty believing anything else is in a box labeled as Trisodium Phosphate! If it does, then it violates laws related to labeling products. I have two boxes, one old one fairly new that are labeled TSP and both do not mention any other compound, nor would I expect them too. Now if you have a product that is labeled as a cleaner, or a cleaner with TSP, who knows what would be in it. Recheck the label on the box. If it is labeled as TSP, it better be TSP.

Anyway sodium carbonate is known commonly as washing soda. There is no more relationship between sodium carbonate and trisodium phosphate than there is between TSP and sodium chloride.

On 31 Oct 2003 17:15:12 -0800, jim rozen wrote something ......and in reply I say!:

That swampy smell sure do get around!

BTDT!

And now I am _GLAD_ I use REYNOLDS.

See! The cooking people CARE more than the tansmission people!

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On Fri, 31 Oct 2003 14:17:45 -0800, "Harold & Susan Vordos" wrote something ......and in reply I say!:

Producing a salt solution on the metal = rust????

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I have a tub of Red Devil brand cleaner labeled TSP/90. The "TSP/90" is printed in a bold font about 3/4" tall. Above that, in a much smaller and lighter font, it says "phosphate free". The ingredients are "sodium metasilicate". The instructions for use say it is "a trisodium phosphate substitute".

Any that spends 30 seconds reading the label would know that this is not real TSP, but I could see where someone in a hurry could mistake it for the real thing.

R, Tom Q.

I keep hearing that same response, but how much salt would be in question? One would have rinsed the parts in clear water, then in a solution of sodium hydroxide. When the items in question are introduced to the lye solution the amount of HCL remaining on the parts should be down to next to nothing, and would most likely already have been neutralized by the iron itself. If you've not put any steel in HCL, perhaps you should do so to understand the speed at which it reacts, especially if heated.

Please read the post by Koz, which is in keeping with my personal experiences as well. I have no argument with the theory of salt being a by-product, but one might consider the reality of the situation at hand. In this instance, the part(s) would be protected by the residual lye. It would be highly unlikely that any salt would have been formed.

Harold

Grant where have you found the real TSP?

Dan

What we said was that using caustic soda, or baking soda, or any other alkali metal base to *neutralize* HCl remaining on the steel from an acid dip produces a salt (in this case NaCl, table salt). Unless the water is very hot, some of that salt residue will settle in any pores, cracks, threads, or other feature of the part. *That* will promote corrosion of the steel.

Obviously, if there is no HCl present, for example your potato conveyor, adding caustic to the water does not produce salt, and thus doesn't leave a residue on the steel which promotes corrosion.

In combination with the starch in the potatos, caustic *should* produce a carbonate scale on the metal which will in fact offer some protection from rusting. But scale is what the original poster is trying to remove, he wants bright metal ready for galvanizing. So caustic is not advised.

Gary

Doesn't the plating shop have a reverse current bath they use for cleaning parts just before the plating bath?

John

I suspect the plating process won't worry if the part is wet with a little HCL on it - I suspect there is HCL in the plating and if not, the zinc will become zinc chloride in short time. And then the Hydrogen bubbles off in gas form.

Martin

Dang...long day and the HCL thing didn't sink in. Spud plants usually neutralize with sulphuric or similar during clean-up. BTW, no starch build-up to be seen on these units. Funny to see em brand new and painted by the fabricator...paint lasts about 15 minutes :)

Koz

Gary Coffman wrote:

I suspect dipping anything wet into molten zinc would get a bit exciting. We are talking about parts that will be hot dip galvanized, not plated.

Gary

My PERSONAL EXPERIENCE is this: I found a charge-driving nail gun at the dump. Nice, but badly rusted. I took it all apart and put it in HCl. I then neutralized with lye (or maybe TSP). I rinsed really well, oiled it, and reassembled. I couple of days later I noticed quite a bit of rust. "Dang!", I thought, "I guess that I didn't neutralize well enough." I repeated the entire process and was _really_ careful about neutralizing. It rusted again, badly.

Bob

I think the standard, visceral demonstration for this is the one typically done in a beginning chemistry class. The instructor demonstrates some NaOH solution, how it will be terribly causting and then the same with some concentrated hydrochloric acid, again a piece of metal or whatnot dropped in the beaker,

Then you mix the correct proportions and the result is then imbibied in front of the audience. Salt water, see?

Almost as good as the milk carton full of oxy hydrogen mix from electrosis of water...

Jim

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On Sat, 1 Nov 2003 18:17:53 -0800, "Harold & Susan Vordos" wrote something ......and in reply I say!:

But if you have removed the HCl to the point where the salt will not matter, what is the point of "neutralising" it with the lye?

Smart-sounding question, but genuine. I have always used simple rinsing and then oil (WD40 or whatever) if needed rather than NaCl, because of the salt argument.

_Does_ the lye protect the steel in any way?

I have done it. Yes it rusts anyway if left.

Actually burying the steel in lye, as those conveyors apparently are, is quite different from having dipped them for a short while and then left them out to air.

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I used Brownell's water displacing oil after rinsing when hot bluing firearms, which I haven't done in decades. The bluing solution was a hellish mix of caustic, sodium nitrite, and sodium nitrate, kept at

295 deg F by back-adding water (very carefully). Very nasty. The hot rinse was to remove the caustic (lye), etc. In theory, the oil displaced the water to prevent rusting. Bluing is a form of oxide which is relatively stable. Without a good rinse and oil, it'll still rust.

Pete Keillor

I have difficulty with it too, but it happens. You used to be able to buy pure Calgon at the super market, but all the boxes I have looked at for some years say Sodium Carbonate and Calgon.

As you say Sodium Carbonate is washing soda, and as such it is milder than TSP but used for many of the same things.

Dan