Contaminant Removal from Plating Baths. Volume 4. Bench-Scale Evaluation of Electroless Nickel Bath Rejuvenation.

Abstract : Electroless nickel (EN) plating is performed at all U.S. Air Force ALCs as part of depot level maintenance of aircraft parts. EN baths are frequently (once a month) dumped due to reaction byproduct (orthophosphite) build-up in the bath. Battelle was contracted by Armstrong laboratory/Environics Directorate (AL/EQS) to identify, test, and implement a suitable technology to rejuvenate spent EN baths. After a technology review, three different technologies were considered for the rejuvenation of EN baths. After initial testing, one of them, the Stapleton Enfinity process, was selected for detailed bench scale testing. Plating tests with continuous bath rejuvenation were performed for 10 metal turnovers. Bath constituents were continuously monitored to determine the efficacy of orthophosphite (contaminant) removal from the bath. Plating quality, phosphorous content of deposit and deposit stress characteristics were analyzed and were found to meet the required specifications. Waste generated from the process (calcium orthophosphite filter cake) was collected and analyzed. The filter cake was successfully washed to reduce the nickel content to less than 5 ppm by TCLP. Alternate methods to monitor nickel content of the bath (in the presence of calcium) were developed. Plating rate, deposit characteristics, and waste generation were favorably compared to conventional EN processes. Based on results of these tests, it was recommend that a full-scale prototype unit of the Stapleton process with filter cake washing be designed, installed, and demonstrated at Tinker AFB OC-ALC.