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Topic: chromic acid vs potassium dichromate  (Read 95 times)

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Offline pcm81

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chromic acid vs potassium dichromate
« on: March 14, 2019, 10:38:34 AM »
Usually chromic acid CrO3 is used in chomium electroplating and Potassium di-Chromate K(CrO3)2 is used in chromate conversion of zinc plating. I am wondering if Aqueous solutions of these two chemicals can be used interchangeably for these 2 processes. I believe Sulfuric acid is also used i the solutions and naturally concentration for electroplating bath will be different from concentration for zinc/chromium conversion bath.

Offline chenbeier

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Re: chromic acid vs potassium dichromate
« Reply #1 on: March 14, 2019, 11:43:44 AM »
Pottasium dichromate is K2Cr2O7, what is equal to K2CrO4*CrO3 (pottassium chromate  plus one (chromic-VI-oxid) chromic acid molecule.
In plating industry the solution is acidified with sulfuric acid and its call chromic sulfuric acid.

K2CrO4*CrO3 + H2SO4 => 2 CrO3 + K2SO4 + H2O

Higher concentration of the compound is produced directly using CrO3


Offline pcm81

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Re: chromic acid vs potassium dichromate
« Reply #2 on: March 14, 2019, 01:09:19 PM »
Pottasium dichromate is K2Cr2O7, what is equal to K2CrO4*CrO3 (pottassium chromate  plus one (chromic-VI-oxid) chromic acid molecule.
In plating industry the solution is acidified with sulfuric acid and its call chromic sulfuric acid.

K2CrO4*CrO3 + H2SO4 => 2 CrO3 + K2SO4 + H2O

Higher concentration of the compound is produced directly using CrO3

Tanks. That actually makes sense. I actually have chomium plating solution CrO3 inH2O (33oz of CrO3/Gal + 0.33oz of H2SO4/gal of H2O) and was debating if i can use that for chromium conversion coating of zinc.

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