Have you ever heard the expression “the devil is in the details”? How many times do we think we have covered everything only to find out that some of the basic things get overlooked? One of the details that I find frequently overlooked is accounting for ALL components that make up a process tank.
Standard Components in a Watt’s Nickel Plating Bath
For example, let’s take a look at a standard Watt’s nickel plating bath. The components that are commonly tested for are nickel metal, nickel sulfate, nickel chloride, boric acid, surface tension, carrier concentration, pH, and secondary brightener. That is a fairly long list of things to test for and control. Certainly, the chemical suppliers will have quality control procedures to ensure the products meet expected quality standards, but let’s take a closer look at the bath components.
How’s the H20?
What is the largest component in a nickel plating bath? The answer is water. But how often is the water used to make up a bath or add to the tank for evaporation losses truly analyzed? Do we assume the water coming from the tap is of acceptable quality, and not really scrutinize it like we do our proprietary additives or commodity chemicals? Ions such as calcium, magnesium, sodium and potassium can have an impact on the long-term quality of a nickel plating process.
Assessing Added Chemical Components
The pH is something that is monitored throughout the day in a nickel plating bath. Normally, the pH rises during the plating process when using soluble nickel anodes. The pH is lowered by additions of sulfuric acid. What is your procedure for storing sulfuric acid for making additions to the plating tank? Is it stored in open containers near the plating line? Does it have any color to it, other than water white? Do we assume that all sulfuric acid is the same and not take the time to check it out?
I have seen instances of sulfuric acid that looked perfectly good in the drum, but it gets stored in a bucket for a period of time and leaches the plasticizer, causing the acid to turn a darker color. This can be the cause of organic contamination in the bath, and possibly be the cause of excessive use of activated carbon to deal with this issue. Also, does your supplier use recycled drums and if so, what is their procedure for determining the degree of cleanliness of the drums?
Another chemical that is occasionally added to the bath is hydrogen peroxide to deal with iron and organic contamination. It is rare for this to be a problem, but it certainly can be if we just assume it is good and could never cause an issue.
Of course, there are other plating baths that this can be applied to. For example, acid chloride zinc uses a brightener and starter as proprietary components. But other components added, depending on the bath chosen, are boric acid, ammonium chloride, potassium chloride, hydrochloric acid and water. Once again, acid and water are variables that are normally not controlled for quality.
Rethinking Process Issues
When issues arise with your process, think about the things that are introduced to the tank that could be a cause for problems. Having samples available in the lab to test these things in hull cells can be a benefit. Performing periodic water quality checks with a simple test kit is also a good idea to keep track of your plant’s tap water quality. Your Asterion representative can assist you with methods to stay on top of your process.
So, what really is in your tank?