Authoritative Answers, Fun, & Aloha -- no cost, no passwords, no popups
(as an eBay Partner & Amazon Affiliate we earn from qualifying purchases)

Home /
T.O.C.
Fun
FAQs
Good
Books
Ref.
Libr.
Adver-
tise
Help
Wanted
Current
Q&A's
Site 🔍
Search
pub     mobile?
Metal finishing Q&As since 1989

-----

Chromic anodise analysis problem




Q. We process parts in a chromic acid anodise solution. We recently had a chrome replenishment unit installed to reduce the chromic acid additions we make. However, it is causing problems with our analysis of the solution. We have two methods, both of which do not appear to be reliable. A pH titration method now no longer works as the chrome recovery unit does not give back any acidity, just free chrome. Our method using ferrous ammonium sulphate also gives unreliable results as it gives us higher results when the free chrome is clearly depleting (ie, when the unit has been out of order and coating weight values are decreasing).

Are there any other reliable methods for free chrome analysis in a chromic acid anodising bath?

Paul Fulford
Chemist - Southampton, UK
March 6, 2008


A. FREE CHROME ANALYSIS?

Use AAS [on eBay or Amazon affil links] , it is easy.

Jose Castellanos
- Minneapolis, MN, USA


A. I must respectfully differ with the last poster.

The way to do this analysis is via a titration. Diluting by a factor of 10,000 and then using a trace analysis technique is a shortcut that I'd use as a last resort.

You might try an iodometric method - add an excess of KI under acid conditions, then titrate to an emerald green endpoint with 0.1N sodium thiosulphate [on eBay or Amazon affil links] solution. Use plenty of fresh starch indicator solution.

You might also try adding more sulfuric acid to the mix when you do your FAS titration. Also...very important! FAS has to be restandardized virtually each time it is used, because the air oxidizes it and it loses titer no matter how carefully you seal it up.

dave wichern
Dave Wichern
Consultant - The Bronx, New York




(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

Finishing
Jobshops
Capital
Equipment
Chemicals &
Consumables
Consult'g,
& Software


About/Contact  -  Privacy Policy  -  ©1995-2024 finishing.com, Pine Beach, New Jersey, USA  -  about "affil links"