So I'm going to buy some citric acid so that I can passivate some stainless. I was all set to buy some on line, but the shipping is a little pricey. I don't know how much I'll use, so I don't want to buy in bulk quite yet. I thought I'd see where I can buy it locally.

So, I'm in San Diego. If anyone knows any place specific that would be great. But I don't expect anyone will know my local options that well, so I'm looking for some ideas. What else is it used for? What kind of places will carry it?

Don't they sell Citrus juice in California?

You're right! And in San Diego, think of all the limes being sold for fish tacos!

How much of that is a joke, and how much are you being serious? I was figuring on pure citric acid so that I wouldn't have all the other junk that comes with citrus juices.

Amazon sells it in 5# containers, the grocery store has it by the ounce in the spice section, restaurant supply stores may have bigger containers, and that is food grade citric acid.

Phil

Beer and wine making store should have it.
Rob

health food stores carry it as well. in San Diego that should be easy to find . :lol:

Amazon sells it in 5# containers, the grocery store has it by the ounce in the spice section, restaurant supply stores may have bigger containers, and that is food grade citric acid.

Phil

I saw it on Amazon, but the descriptions on the food-supplement items wasn't very clear about whether it was just plain citric acid. The laboratory-grade items were very specific, but wanted like $8 for shipping a pound. I suppose I'll go and buy a five-pound bag of the stuff from the food section.

Thanks.

And teenylittlemetalguy, don't you know that in San Diego every store is a health food store? That's how we roll.

Quote-"And teenylittlemetalguy, don't you know that in San Diego every store is a health food store? That's how we roll."


I thought that may be the case. funny how 7-11 is now a health food store because they painted it green. I remember when there was only healthy food in those stores.
But back to citric acid, depending on what you are doing pure grades are typically not needed, especially in the shop.
Cheap alternatives often have good effect. What are you using it for?

First line in the thread "So I'm going to buy some citric acid so that I can passivate some stainless".

As lots of acids can be used to passivate stainless I don't think a bit of a mix will cause problems. Citric acid is liked as it's relatively safe to have around compared to the mineral acids.

You're right! And in San Diego, think of all the limes being sold for fish tacos!

How much of that is a joke, and how much are you being serious? I was figuring on pure citric acid so that I wouldn't have all the other junk that comes with citrus juices.

I have used lemon juice. so I am serious

Why go to the expense & effort of passivation? Is there a lot of iron imbedded in your surface somehow? :huh:

Why go to the expense & effort of passivation? Is there a lot of iron imbedded in your surface somehow?

If the old finish is stripped with a chlorine bearing chemical (muriatic acid, vinegar, saltwater, a number of paint strippers) then the chrome oxide will be stripped and passivation will be necessary. I ran into this with a vinegar spill on a stainless stove top, and ended up using a citrus cleaner (Orange clean I think) after removing the rust (getting citric acid was the next step, but I didn't need to). I wet the surface and kept it wet for some time before finish cleaning and it has been in good shape since.

Phil

If the old finish is stripped with a chlorine bearing chemical (muriatic acid, vinegar, saltwater, a number of paint strippers) then the chrome oxide will be stripped and passivation will be necessary. I ran into this with a vinegar spill on a stainless stove top, and ended up using a citrus cleaner (Orange clean I think) after removing the rust (getting citric acid was the next step, but I didn't need to). I wet the surface and kept it wet for some time before finish cleaning and it has been in good shape since.

Phil

Phil, thanks, I didnt realize that is what was going on. Very helpful.

I didn't know about the differences in acids with regards to the chromium oxide prior to reading these threads. However, I have been doing some small-scale forging with stainless, and have been a little disappointed in my inability to brush it to a lustrous finish. I'm not sure how accurate my understanding is, but I gathered that I needed to treat the steel with a certain type of acid after forging to restore it's surface qualities.

So, I'm not sure how Phil's statement fits in to my understanding, but I'm hoping that, in addition to the effects he described above, that I'll be able to brush it to a nice finish after treatment.

My wife just brought me a 500ml graduated cylinder. It's nice, because I can fill it to an easily-known quantity, and then add in my citric acid (measured by weight on a kitchen scale) to get to my 10% solution. It's tall, so I can completely cover some of the items I've forged, like a cocktail spoon, without having a huge volume of acid solution. I won't heat the solution, as I've seen in recipes, but I will be able to control my solution pretty well. First test will be a stainless key fob I made recently; I'll drop it in, and check out the results.

Expect to see another thread, with some background, details, observations, and hypotheses.

Now if you want a "forge finish" without the pickle, and possible scale left in place you can simply heat and air cool the metal as if you are normalizing. This will burn off any free iron on the surface and produce a passivated stainless steel part. I am unsure about the best temperature to use for this process.

Phil

That's interesting.

I know you say you are unsure about the temperature, but what kind of ballpark are we talking about? If it's similar to normalizing, It would be below critical, right? I'd assume that we're also talking about something over a black heat. Think that's in the ballpark?

I'll still start with the pickle. As I mentioned in another thread, I just bought a project of a house, so I don't have a forge outside of the one at CBA Vista for a while. It will be easier to pickle at home than heat to anything over 500 or 600 degrees.

2000F was mentioned in another thread followed by a cold water quench (my bad on the air cool)



Phil

I have been doing some small-scale forging with stainless, and have been a little disappointed in my inability to brush it to a lustrous finish. I'm not sure how accurate my understanding is, but I gathered that I needed to treat the steel with a certain type of acid after forging to restore it's surface qualities.

Have you tried abrasives?

Some abrasives, yes. Wire wheels and brushes. They can get most of the scale off, but the color is still closer to black than that nice satiny slivery stainless color. Also, part of the issue is spots of rust on the items, as well as fire scale. I'm hoping to remove both at the same time.

My citric acid came in a plastic bag. I haven't tracked down a suitable container yet, so I'm avoiding opening the bag for my scale removal test until I can store it. I admit that I'm not trying too hard to look, but having bought two fixer houses recently, I'm kind of full up on projects right now. I do have motivation to get it done, though: I am putting in a new kitchen soon, and I want to fab the hardware out of stainless.

Grocery stores have citric acid in the coffee supply section as well , and poultry farms use it , and poultry farm suppliers have it in 5 gal. buckets if you need more .
Its quite a bit cheaper at the supply store or from a farmer . ;)

I get mine from the store that sells water softener supplies

Some pool supply stores would have it for water adjustments.

other sources would include citrus juice.
brewery shops
some hardware stores
Pharmacy - we keep citric acid in our pharmacy, but worst case scenario you might have to settle for vitamin C (ascorbic acid) The chemical difference is so slight that it will not matter in terms of normalizing (citric acid has 1 extra molecule of oxygen)

It is exceptionally cheap at our pool supply store.

Grocery stores have citric acid in the coffee supply section as well , and poultry farms use it , and poultry farm suppliers have it in 5 gal. buckets if you need more .
Its quite a bit cheaper at the supply store or from a farmer .

I've seen it in TSC farmer supply stores with the drugs - it acidifies the water for tetracycline, or something like that.

topic is a little dated but citric acid is available in the canning section of most grocery stores.