Determining the Proper Material for an Electroless Nickel Plating Tank

Q: We are an existing plating shop in the Midwest and we are considering purchasing an additional electroless nickel plating tank for our facility. What suggestions do you have for the ideal EN tank material?

A: That is an excellent question and careful consideration should be made on what material is ideal for both the EN chemistry and your company.

Because most EN chemistries operate at elevated temperatures exceeding 185°F and also have a tendency to plateout on the tank walls, the choice of material that can be used is limited.

The most popular construction materials used today are solid propylene, stainless steel or steel tanks with a liner such as 25 mil PVC.

Other materials have been used in the past, but with limited success. These include fiberglass-reinforced resins, polyethylene and steel coated with various coatings.

Each of the most popular materials used in the field do have their own advantages and disadvantages. Depending on your company's requirements or concerns, one tank material may be more advantageous than another.

A comparison of the advantages and disadvantages of each material is as follows:

Stress-Relieved Polypropylene

Advantages	Disadvantages
1. Inexpensive to fabricate	1. Tends to oxidize and become brittle
2. Minimizes plateout	2. Needs to be stripped by nitric acid periodically
	3. Expands with high temperatures, leading to leaks and cracks
	4. Short tank life

Stainless Steel

Advantages	Disadvantages
1. Ideal for larger tanks greater than 500 gallons	1. Expensive to fabricate
2. Long tank life	2. Parts must not come into contact with tank walls
3. Reduces nitric stripping
4. Thermal expansion not an issue
5. Reduces the waste treatment costs associated with nitric acid

PVC Bag Liners in Steel Tanks

Advantages	Disadvantages
1. Low cost to manufacture	1. Replacement of bag liners is an ongoing expense
2. Eliminates nitric stripping completely	2. Filtration is difficult
3. Lower waste treatment costs	3. Limits type of heat source
	4. Disposed liners may become a problem in the future

All three construction materials work and are used successfully in the field today. If cost is your main concern, then polypropylene or PVC liners may be best for you. If the elimination or reduction of nitric acid is important to you, then stainless steel or PVC liners may be best for you.

Stainless steel tanks offer the most advantages. The cost may be 20-25% more, but the longevity of the equipment will pay for itself over time.

Recent advancements, such as adding a passivation system to a stainless steel tank, can further minimize the use of nitric acid and, in some cases, nearly eliminate its use completely.

As always, it is wise to discuss with your EN supplier what type of tank is best for their chemistry. The stability of their EN bath may require one type of tank over another.

Mike Aleksinas is the president of MetalChem. He can be reached at mike@metalchem-inc.com or 864-877-6175.