No passwords, no registration, no paywalls, no popups, no AI

As an Amazon Associate & eBay Partner we earn from affil links

finishing.com -- The Home Page of the Finishing Industry

Search our quarter-million Q&As

Home of the finishing HOTLINE since 1989

-----

Sulphuric Acid LR Vs CP grade

Q. Dear Sir / Madam,

We seek expert guidance regarding the use of sulphuric acid in pretreatment for nickel - hard chrome plating.

Component: Mild steel cylindrical hollow tube
Plating process: Semi-bright Nickel - Bright Nickel - Hard Chrome (duplex Ni + Cr)
Industry: Automotive / industrial application

Pretreatment sequence:
Soak degreasing - Water rinse - Anodic cleaning1 - Water rinse -
Anodic cleaning - Three water rinses -
Sulphuric acid dip (4-5 %, 30-40 seconds) - Water rinse -
Semi-bright Nickel - Bright Nickel - Hard Chrome

"Sulfuric acid Manufacture"
(2013)
by King, Moats,
& Davenport
sulfuric_acid_mfg_2013

on Amazon or eBay
or AbeBooks
(affil link)

Currently, we are using LR grade sulphuric acid for this activation dip, H2SO4

Query:
What would be the expected impact - positive or negative - if we replace LR grade sulphuric acid with CP grade sulphuric acid at the same operating conditions (4-5 %, 30-40 seconds)?

Specifically, we would appreciate expert views on:

1. Effect on MS surface activation and cleanliness
2. Impact on nickel adhesion (especially for duplex Ni followed by hard chrome)
3. Any risk of over-activation or adverse effects
4. Whether CP grade provides practical benefits in industrial plating, or if LR grade is sufficient with proper bath control

Your guidance will help us decide whether a change in acid grade is technically justified.

Thank you in advance for your valuable time and expertise.

Regards,
Rajkamal
Chh.SambhajiNagar, MS, India

Rajkamal
Shop In-charge - Chh. Sambhaji Nagar, Maharashtra, India.
January 8, 2026

"Sulfuric Acid Use and Handling"
(1965)
by Oscar T. Fasullo
sulfuric_acid_usehandling1965

on Amazon or eBay
or AbeBooks
(affil link)

A. Hi Rajkamal

I don't think the purity of the acid used in pretreatment matters much and, as you say, there is a rinse before plating anyway. As a practical matter, however, if there is lead in your sulfuric acid it will cause you problems with your water disposal permits before it causes problems with your nickel plating.

LR is surely good enough.

Luck & Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.

Sorry! Finishing.com is temporarily Read-Only.
Ted Mooney is retiring but I have several offers to take it over.
We're working hard to make sure we find it the best new home.

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: