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topic 10502

Electro-chemistry of Stainless Steel


We build small saline filled chambers for biological purposes. It is required to supply a voltage to a stainless steel electrode which is placed in direct contact with the saline. The saline consists of 150 millimoles NaCl and 16 millimoles of Na2HPO4 (Sodium dibasic Phosphate) which acts as a buffer. If a stainless steel electrode and a copper electrode are placed in this solution and a voltage of about 3.5 volts is applied, the cathode (copper) discharges gas, which we assume to be hydrogen. The anode begins to form a light green soluble substance which fits the description of ferrous chloride. However if we instead use 16 millimoles of NaH2PO4 (monobasic) we see a colorless gas (oxygen ?)at the anode and no green substance at all. Can someone help us with the electro-chemistry of this phenomenon?

George C. Malachowski
- Fort Collins, Colorado, USA.


At the anode you are generating Oxygen and Chlorine and Hydrogen at the cathode. The metals in the Stainless Steel are forming Chloride salts. Nickel Chloride, Ferrous Chloride and Chromic Chloride. If the pH is above 8.0, the Nickel will probably precipitate. In time, you may find deposited Iron on the cathode with traces of Chrome. The deposit will be smutty brown with possibly a slight green tint. If you continue electrolysis, the SS will dissolve completely. The Di Sodium Phosphate used alone should be OK. If you require the Sodium Chloride for some reason, I recommend you use either a Platinum metal anode, or a Platinum clad or Platinum plated Titanium material. Carbon can also be used but will eventually fall apart. Iridium Oxide is the best of all but may be cost prohibitive.

Rick Armstrong
- Anaheim, CA, U.S.A.

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