5 ms·

So there’s several details and questions that I think might be important for interpreting this study! 1) all stainless steels need to be “passivated” in order

So there’s several details and questions that I think might be important for interpreting this study! 1) all stainless steels need to be “passivated” in order to be properly stainless. These days that process involves putting the stainless steel in a hot water bath with like a pound of citric acid for every gallon of water used. (I actually do this at home with any cookware or steel bottles where I notice a metallic taste). Chips of stainless steel that aren’t passivated will leach and or corrode! 2) I think most cookware is 304 steel. I’m not sure how often it’s 316. But also unless you control for passivation it’s still pretty uninformative.

yumraj 5y ago
> all stainless steels need to be “passivated” in order to be properly stainless. Does the passivated layer survive scrubbing and dish washing?
- cyounkins 5y ago
  It can be damaged physically or chemically but the oxide layer is self-healing upon contact with oxygen.
  - jeffbee 5y ago
    The depth of the chromium-rich top layer would be measured in nanometers at most, while a visible scratch would have to be tens of microns in size.
    - Tade0 5y ago
      Isn't stainless steel a uniform alloy of chrome, nickel and iron?
      - jeffbee 5y ago
        It would be if you made it in space, but in the presence of oxygen, or when the factory dips it in acid which is what they do, the surface is depleted of iron and enriched of chromium to a depth of a few molecules. Below that is a thicker nickel-rich region. Nobody really knows how this migrating is happening at a low level, by the way. Mystery of material science.
brador 5y ago
Soda is acidic and comes in Aluminum cans. Why don't the cans develop holes?
- slater 5y ago
  "The inside of the can is lined by spray coating an epoxy lacquer or polymer to protect the aluminum from being corroded by acidic contents such as carbonated beverages and imparting a metallic taste to the beverage." https://en.wikipedia.org/wiki/Aluminum_can https://en.wikipedia.org/wiki/Aluminum_can
  - pleb_nz 5y ago
    I often wonder how good that coating is for consumers. I'd be surprised if it doesn't leach into the produce.
    - Caspy7 5y ago
      Certainly a belief among some that soda from a glass bottle tastes notably better.
      - throwntoday 5y ago
        That has more to do with the use of cane sugar vs corn syrup
        boomboomsubban 5y ago
        Mexican Coke, which uses cane sugar, comes in a glass bottle, but you can also get US coke presumably with corn syrup in a glass bottle and some people do think it tastes better.
        ac29 5y ago
        > Mexican Coke, which uses cane sugar This is at least partially a myth. Here's a study which found no sucrose in Mexican coke: https://onlinelibrary.wiley.com/doi/full/10.1038/oby.2010.255 https://onlinelibrary.wiley.com/doi/full/10.1038/oby.2010.25... Though, it is complicated because there are multiple bottlers making multiple different coke products, and even the same bottlers could shift what sweeteners they use over time, presumably based on pricing.
hammock 5y ago
Does occasionally cleaning my cookware with Barkeeper's Friend (oxalic acid) accomplish the same?
- carterschonwald 5y ago
  I don’t know! With citric acid and it’s predecessors, they only dissolve iron atoms but don’t react with the chromium and nickel alloying elements, which is an important combo!
  - hammock 5y ago
    I found this passage. Doesn't really explain the process though.. natural oxidation completes in the air 1-2 weeks? >To passivate stainless steel at home without using a nitric acid bath, you need to clean the surface of all dirt, oils and oxides. The best way to do this is to use an oxalic acid based cleanser like those mentioned below, and a non-metallic green scrubby pad. Don't use steel wool, or any metal pad, even stainless steel, because this will actually promote rust. Scour the surface thoroughly and then rinse and dry it with a towel. Leave it alone for a week or two and it will re-passivate itself. You should not have to do this procedure more than once, but it can be repeated as often as necessary. https://spaco.org/Passivate.htm https://spaco.org/Passivate.htm
luma 5y ago
When welding stainless used in food service, you then need to re-passivate all the joints. Can be a bit of a pain for long pipelines. You'll often see acrylic piping used in food plants partially for this reason (another reason is that it's easy to see any blockages or growths etc through the pipe walls).

yumraj 5y ago

> all stainless steels need to be “passivated” in order to be properly stainless. Does the passivated layer survive scrubbing and dish washing?

cyounkins 5y ago
It can be damaged physically or chemically but the oxide layer is self-healing upon contact with oxygen.
- jeffbee 5y ago
  The depth of the chromium-rich top layer would be measured in nanometers at most, while a visible scratch would have to be tens of microns in size.
  - Tade0 5y ago
    Isn't stainless steel a uniform alloy of chrome, nickel and iron?
    - jeffbee 5y ago
      It would be if you made it in space, but in the presence of oxygen, or when the factory dips it in acid which is what they do, the surface is depleted of iron and enriched of chromium to a depth of a few molecules. Below that is a thicker nickel-rich region. Nobody really knows how this migrating is happening at a low level, by the way. Mystery of material science.

brador 5y ago

Soda is acidic and comes in Aluminum cans. Why don't the cans develop holes?

slater 5y ago
"The inside of the can is lined by spray coating an epoxy lacquer or polymer to protect the aluminum from being corroded by acidic contents such as carbonated beverages and imparting a metallic taste to the beverage." https://en.wikipedia.org/wiki/Aluminum_can https://en.wikipedia.org/wiki/Aluminum_can
- pleb_nz 5y ago
  I often wonder how good that coating is for consumers. I'd be surprised if it doesn't leach into the produce.
  - Caspy7 5y ago
    Certainly a belief among some that soda from a glass bottle tastes notably better.
    - throwntoday 5y ago
      That has more to do with the use of cane sugar vs corn syrup
      - boomboomsubban 5y ago
        Mexican Coke, which uses cane sugar, comes in a glass bottle, but you can also get US coke presumably with corn syrup in a glass bottle and some people do think it tastes better.
        ac29 5y ago
        > Mexican Coke, which uses cane sugar This is at least partially a myth. Here's a study which found no sucrose in Mexican coke: https://onlinelibrary.wiley.com/doi/full/10.1038/oby.2010.255 https://onlinelibrary.wiley.com/doi/full/10.1038/oby.2010.25... Though, it is complicated because there are multiple bottlers making multiple different coke products, and even the same bottlers could shift what sweeteners they use over time, presumably based on pricing.

hammock 5y ago

Does occasionally cleaning my cookware with Barkeeper's Friend (oxalic acid) accomplish the same?

carterschonwald 5y ago
I don’t know! With citric acid and it’s predecessors, they only dissolve iron atoms but don’t react with the chromium and nickel alloying elements, which is an important combo!
- hammock 5y ago
  I found this passage. Doesn't really explain the process though.. natural oxidation completes in the air 1-2 weeks? >To passivate stainless steel at home without using a nitric acid bath, you need to clean the surface of all dirt, oils and oxides. The best way to do this is to use an oxalic acid based cleanser like those mentioned below, and a non-metallic green scrubby pad. Don't use steel wool, or any metal pad, even stainless steel, because this will actually promote rust. Scour the surface thoroughly and then rinse and dry it with a towel. Leave it alone for a week or two and it will re-passivate itself. You should not have to do this procedure more than once, but it can be repeated as often as necessary. https://spaco.org/Passivate.htm https://spaco.org/Passivate.htm

luma 5y ago

When welding stainless used in food service, you then need to re-passivate all the joints. Can be a bit of a pain for long pipelines. You'll often see acrylic piping used in food plants partially for this reason (another reason is that it's easy to see any blockages or growths etc through the pipe walls).