Plating Resources recently announced the development of a new and safe way to add sulfate to hexavalent chrome plating baths, Buffered Sulfate Adjuster.

The product can be used for both hard and decorative plating, either when making up a new solution or when raising the sulfate level in an existing bath. Traditionally the sulfate has been increased using hazardous concentrated sulfuric acid.

We spoke with Eric Svenson Sr., president of Plating Resources, about the Buffered Sulfate Adjuster

F&C: Your newest addition to your product line is Buffered Sulfate Adjuster to add sulfate to hexavalent chrome plating baths. Tell us what that product does and the advantages it brings to shops.

ES: Hexavalent chrome baths require a small amount of sulfate in order to deposit chromium. The sulfate ion (SO₄) is a true catalyst as it’s not consumed in the electrochemical reaction. The amount needed varies with the bath type but is generally a ratio of chromic acid: sulfate between 80 – 260:1, with 100:1 being typical for a standard bath without any other catalyst. The traditional way to add sulfate is by using sulfuric acid. But there’s a problem because sulfuric acid is:

• Very corrosive and dangerous to store and handle.
• Very exothermic, which means it gives off heat whenever added to a water-based solution like a chrome bath. 
• Very concentrated and difficult to measure accurately. This makes it incredibly easy to overshoot the sulfate needed for its desired ratio, and adding too much really messes up the bath.

Regarding the exothermic issue with sulfuric acid, it gives off so much heat that adding it too fast actually causes the bath to boil at its surface and literally explodes back onto the operator’s face. This becomes even worse and more dangerous when adding sulfuric acid to an already hot chrome bath which typically operates at 130 - 140° F.  

We struggled with these problems for years, looking for a safer alternative to using sulfuric acid. First, we tried instructing workers to only add it to a cold bath, to add it very slowly, and to distribute it evenly across the bath’s surface using plenty of agitation. This helped in some cases, but not in others as the platers always seemed to be in a hurry to get things done, and that’s when accidents often seem to happen. Then we tried pre-diluting the sulfuric acid to help eliminate some of its exothermic properties, but this became overly expensive and didn’t address its corrosive or measurement issues. 

Our laboratory staff was finally able to solve this dilemma by developing a unique dry powder substitute for sulfuric acid. They then combined this with a buffer that improves the chrome bath’s performance. There are four major advantages to using Buffered Sulfate Adjuster:

• It isn’t exothermic, so it can be safely added to a chrome bath, even a hot one. 
• It isn’t corrosive, so there’s no danger with storing or handling it. 
• It’s a dry powder that’s very easy to measure accurately. This means the plater can zero in on the exact amount needed to hit the precise sulfate ratio.
• It’s combined with a buffer that helps the bath perform better by smoothing the deposit and increasing its tolerance to impurities.

F&C: What are the steps for new bath makeup?

ES: Making up a new bath properly can be a little more involved than some may think. This is because there’s a preparation phase and then the actual bath makeup phase. Here’s what we recommend:

Preparation Phase 

• Start by donning any required Personal Protective Equipment.
• Remove and clean the anodes. 
• Clean out the tank and remove any debris like anode sludge, dropped parts, etc.
• Inspect the equipment used, like the heaters, cooling coils, and agitation system. 
• Inspect the tank liner (a spart tester is handy for this) and make any needed repairs. 
• Clean the buss bars and retorque their connections. 

Bath Make-Up Phase

• Fill the tank only 2/3 full using pure RO/DI water.
• Turn on the ventilation and agitation systems.
• Add the chromic acid.
• Add the catalysts and bath additives that will be used. 
• Add only 90% of the required sulfate using Buffered Sulfate Adjuster. This should be carefully weighed; using only 90% of this accounts for excess sulfate that’s typically in the water supply and the chromic acid that’s used) 
• Fill the tank to its operating volume with the RO/DI water. Be sure to leave enough space for the volume displacement from the anodes and any abnormally large parts that get plated. 
• Turn on the bath heaters; be sure the liquid level is above the heater’s ‘hot’ zone)
• Heat the bath to the desired 130-140° F. while allowing enough time for all the chemicals to dissolve fully. This usually takes around 30-45 minutes, depending on the amount and type of agitation used.
• Take a bath sample and have it analyzed for chromic acid, sulfate and the catalysts used. Then make any small chemical additions needed based on this analysis. The sulfate may be slightly low as we only initially added 90% of the calculated quantity needed.
• An option at this point is to electrolyze the anodes using dummy rods to activate them and build a small amount of trivalent chrome. The bath is now ready for plating.

As a final note: all bath chemical quantities should be accurately calculated and measured.   

F&C: How did you come up with this product? What were shops asking of you — or what were you seeing — that brought upon this product?

ES: As I mentioned earlier, it was developed in our laboratory at Plating Resources. We observed several instances where employees got burned from contact with sulfuric acid and several splash-back accidents over the years while helping platers make up their baths. These accidents occurred in spite of the warnings and special instructions about the dangers involved. Sometimes it’s hard to change a person’s habits, especially if they are old-school and have done things a certain way for decades or are in a hurry to get things done. We realized there had to be a better way. There were several sulfate options besides sulfuric acid, but the trick was developing one that was relatively non-hazardous and then improving it by combining it with a buffer. 

The Buffer helps the bath by increasing its tolerance to impurities like excessive trivalent, iron, and copper. It also provides a smoother finish without changing the micro-crack structure. The result of using Buffered Sulfate Adjuster in the chrome bath instead of sulfuric acid is using a much safer chemical to store, is safer for the operators to handle, and even improves the plating quality and extends the bath life.    

F&C: What is the best way to control the sulfate level, and why is this important?

ES: One of the most important bath control issues in hard chrome plating is maintaining the optimum sulfate ratio. This relates to the amount of chromic acid vs. the amount of sulfate (SO4) in the bath. The ideal ratio for a standard bath is 100:1, while a Dura-3000 High-Efficiency bath is 120:1. That’s 100-120 times the amount of chromic acid as there is sulfate. This ratio changes over time as the bath is used because chromic acid is consumed or as excess sulfate is introduced.  Maintaining the desired ratio is important because small variations in either the chromic acid or sulfate levels change the ratio, and this has a significant effect on the quality of the resulting chrome deposit. 

We recommend the bath ingredients chrome and sulfate be controlled within a maximum +/- 5% variance, with a 2% variance being even better. This is best done by bath analysis using professional equipment and procedures, not a box-type test kit. Most operations find that weekly testing is adequate for maintaining these control points. This should be done in-house with monthly backup samples sent to an outside laboratory that specializes in hard chrome plating so the catalysts and impurity levels can also be tested. The ratio can be adjusted by adding chromic acid or sulfate or by lowering the sulfate with barium carbonate. Bath additions should be made only based on reliable analysis, never by guesstimate. Religiously following this protocol eliminates the quality peaks and valleys. This results in a much smoother operation with enhanced quality and efficiency. There will be less rework to process, deliveries will be improved, and profits will increase.

Visit www.plating.com for additional information.