We heat our electroless nickel plating solutions using stainless steel electric heaters. We find that the nickel metal plates out on our heaters. Is there anything we can do to eliminate this problem? A.R.
Electroless nickel is a heat sensitive process. As the temperature of the plating bath increases, the reactivity of solution increases and more metal is deposited out of the solution. The areas around the heaters tend to be hotter than other areas of the plating solution and as a result metal will deposit on the heater surfaces.
The first thing you should do is investigate the agitation of the plating bath. Most likely you are not getting sufficient mixing of the plating solution in the area of the heaters. With good mixing temperature, buildup around the heaters will be minimized.
Passivation of the stainless steel heaters is also recommended. The classic method for doing this is to use a 50% nitric acid solution for a minimum of one hour. A word of caution: If the concentration of the nitric acid drops much below 50%, you will not achieve good passivation.
A somewhat different approach is to use anodic protection on the stainless steel surface of the heaters. An 8-12 watt DC anodic charge is applied continuously to the surface.
Last but not least, I recommend the following two papers for learning more about good electroless nickel plating methods: Plating & Surface Finishing, Volume 87, October, 2000, 40-43, November, 2000, 29-31.