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Kelly
971 posts
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in about 12 years
in about 12 years
Treating Metal Against Rust Using Tannic Acid and/or Phospheric Acid
On the issue of rabbit trails:
" Tannin baths, commonly using tannic acid, interact with iron and steel to form a protective, blue-black ferric tannate layer that converts active rust into a stable, corrosion-resistant surface. This process, acting as a natural chelating agent, adheres well, improves corrosion resistance, and is used for conservation and surface modification.
Key Effects of Tannin Baths on Metal:
" Tannin baths, commonly using tannic acid, interact with iron and steel to form a protective, blue-black ferric tannate layer that converts active rust into a stable, corrosion-resistant surface. This process, acting as a natural chelating agent, adheres well, improves corrosion resistance, and is used for conservation and surface modification.
Key Effects of Tannin Baths on Metal:
- Corrosion Inhibition/Passivation: Tannins act as inhibitors, especially on steel and iron, by forming insoluble iron-tannate complexes that deposit onto the metal surface, forming a protective, dense film.
- Rust Conversion: On rusted iron objects, tannic acid reacts with iron ions to turn rust into a black-blue, stable protective layer, halting further corrosion.
- Surface Modification: Tannin treatment turns iron surfaces dark blue, gray, or black, which is highly desirable in art and textile applications (e.g., printing and dying).
- Corrosion Rate Regulation: While tannins reduce corrosion by forming a protective layer, the effectiveness depends heavily on the concentration and the pH of the bath, with lower pH often required to enhance passivation in certain environments.
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Metal Affinity: Tannic acid has a high affinity to chelate with metals, particularly iron, but can also work with aluminum alloys and other transition metals.
Common Application:
- Surface Preparation: Before treatment, iron objects should be cleaned of dirt and grease.
- Concentration: A typical tannic acid solution used for treating iron objects is around 2% to 10% weight/volume, often applied in water.
Disclaimer: Tannin treatments are often used to stabilize rust, but extreme concentrations or high pH can alter the coating's effectiveness."
* FROM THE ABOVE, WE CAN GO TO using phosphoric acid in place of tannic acid for it's different effect, when treating rust, or to combining tannic and phosphoric acid to take advantage of the properties of both, which is what many commercial suppliers do.
* Both tannic acid and phosphoric acid are easy to come by. The former can be made by just soaking, for example, oak chips to extract the tannins. Metal workers of old used other items to produce their tannic acid too. Even pomegranates.
*SIDE NOTE: There are some good quality commercial products too. Some both alter the rust and coat the product. Project Farm did a review and the two spendy versions worked really well (Eastwood's encapsulator and O_____).
I keep a bottle of Corrosion X around. It's pretty remarkable stuff.
Car buffs used and may still use Penetrol, and additive for oil based paints sold in paint stores or paint sections of stores, to get into and protect hard to reach places.
* FROM THE ABOVE, WE CAN GO TO using phosphoric acid in place of tannic acid for it's different effect, when treating rust, or to combining tannic and phosphoric acid to take advantage of the properties of both, which is what many commercial suppliers do.
* Both tannic acid and phosphoric acid are easy to come by. The former can be made by just soaking, for example, oak chips to extract the tannins. Metal workers of old used other items to produce their tannic acid too. Even pomegranates.
*SIDE NOTE: There are some good quality commercial products too. Some both alter the rust and coat the product. Project Farm did a review and the two spendy versions worked really well (Eastwood's encapsulator and O_____).
I keep a bottle of Corrosion X around. It's pretty remarkable stuff.
Car buffs used and may still use Penetrol, and additive for oil based paints sold in paint stores or paint sections of stores, to get into and protect hard to reach places.
