A study of corrosion performance of electroless Ni–P and Ni–W–P coatings on AZ91D magnesium alloy

The autocatalytic nature of the electroless nickel‐based alloy coating process will inevitably produce H₂ bubbles which may be left in electroless nickel‐based alloy coating. If the H₂ cannot be removed and left in the coating, it can lead to its poor corrosion resistance due to hydrogen cracks. So, the post treatment is an essential step for electroless deposition process. In this paper, electroless Ni–P and Ni–W–P coatings with chromium‐free pretreatment and dehydrogenation post treatment have been successfully prepared on AZ91D magnesium alloy, and the corrosion behaviors of the two kind coating samples in NaCl solution, HCl solution, and H₂SO₄ solution have been investigated. Both the polarization test and immersion tests show that the electroless Ni–W–P coating has better corrosion resistance than that of electroless Ni–P coating.     

Electroless deposition of the copper sulfide coating on polyacrylonitrile with a chelating agent of triethanolamine and its EMI Shielding Effectiveness

In this study, an effective deposition of CuS on PAN film was proposed by an electroless plating method with the reduction agents NaHSO₃ and Na₂S₂O₃·5H₂O and a chelating agent (triethanolamine, TEA). A variety of concentrations of TEA were added to obtain the anchoring effect and chelating effect in the electroless plating bath. The GIA-XRD and laser Raman analysis indicated that the deposited layer consisted of CuS. The mechanism of the copper sulfide (CuS) growth and the electromagnetic interference shielding effectiveness (EMI SE) of the composite were studied. It was found that the vinyl acetate remained in PAN substrate would be purged due to the swelling effect by TEA solution. Then the anchoring effect occurred due to the hydrogen bonding between the pits of PAN substrate and TEA. Consequently, the copper sulfide layer was deposited effectively by the electroless plating reaction. The swelling degree (S_d) was proposed and evaluated from the FT-IR spectra. The relationship between swelling degree of the PAN composite and TEA concentration (C) is expressed as: S_d = 0.07 + 1.00 × e^(− 15.15C). On the other hand, the FESEM micrograph showed that the average thickness of copper sulfide increased from 76 nm to 247 nm when the concentration of TEA increased from 0.00 M to 0.60 M. As a result, the EMI SE of the composites increased from 10-12 dB to 25-27 dB.