Pitting in Acid Zinc Plating
What causes pitting on steel part surfaces after acid zinc plating?
Q. We acid zinc plate steel parts in-house. The parts are rack-plated. Our problem: The parts show pitting on the surface after the plating. Our chemical vendor suggested that we dump a third of the plating solution and add one-third fresh solution. This has partially solved our problem, but has not eliminated it. Do you have any suggestions on how to solve this issue?—P.J.
A. You mentioned in a subsequent e-mail that you monitor the chemistry of the bath on a daily/weekly basis. That's a great start!
There are a number of things that can cause surface pitting:
1. Bath temperature is too high.
2. Brightener concentration is too high.
3. Chloride concentration is low.
4. Carrier is low.
5. "Tramp" metals are present in the bath.
6. Organic contamination in the bath.
The analysis numbers you sent indicate that the first four items are well within the control limits specified by your chemical vendor. Item five can be determined by doing an analysis for heavy metals. You may have a high concentration of iron that can cause pitting.
I think what you have to concentrate on is organic contamination. The brighteners and carriers that are used in your plating bath are primarily organic in nature, and they break down and decompose in use. The best way to remove these organic contaminants is to treat with activated carbon. This process removes a lot of the organic trash that forms when the brighteners and carriers break down. Keep in mind that treatment with activated carbon does remove some of the brighteners and carriers used in the plating bath. After the treatment, you must reconstitute the brighteners and carriers used in the plating bath.
Related Content
-
NASF/AESF Foundation Research Project #120: Electrochemical Destruction of Perfluorooctanesulfonate in Electroplating Wastewaters – January – December 2023
This NASF-AESF Foundation research project report covers quarterly reporting for the year 2023 at the University of Illinois at Chicago. The objective of this work is to utilize a cost-effective reactive electrochemical membrane (REM) for the removal of PFAS from synthetic electroplating wastewater. Discussed here are the oxidation of PFOA with three different catalysts, development of a method for detecting PFAS, as well as work on 6:2-fluorotelomersulfonic acid (6:2 FTS) and electrodeposited bismuth/tin oxide catalysts.
-
NASF/AESF Foundation Research Project #122: Electrochemical Approaches to Treatment of PFAS in Plating Wastewater - 12th Quarterly Report
This NASF-AESF Foundation research project report covers the 12th quarter of project work (October – December 2023) at the University of Georgia. In our previous report, we described our work on performance and effect of surface fluorinated Ti4O7 anodes on PFAS degradation in reactive electrochemical membrane (REM) mode. This quarter, our experiments involved utilizing porous Ti4O7 plates serving both as anodes and membranes. Tests compared pristine and F-18.6 Ti4O7 anodes at current densities of 10 mA/cm2 and 40 mA/cm2. This 12th quarterly report discusses the mechanisms of the effects on EO performance by anode surface fluorination.
-
NASF/AESF Foundation Research Project #122: Electrochemical Approaches to Treatment of PFAS in Plating Wastewater - 9th Quarterly Report
The NASF-AESF Foundation Research Board selected a project addressing the problem of PFAS and related chemicals in plating wastewater streams. This report covers the ninth quarter of work (January-March 2023). In this report, we describe our work on evaluating the performance of PFAS degradation by electrooxidation using surface fluorinated Ti4O7 anodes in batch mode.