| Wood is a natural organic polymer material with light weight and renewable properties. However, dry wood is electrical insulator, which limits its application in many fields. Endowing a metal layer on the wood surface is an important way to expand the application field of wood. Electroless plating is the most effective approach to prepare wood-based composite via metal or alloy coating deposition on wood surface. In recent years, the research of electroless plating on wood surface has been rapidly improved. It has been focused on electroless deposition of copper or binary alloy on wood surface to endow wood with new properties. But copper or binary alloy deposits have the disadvantage of poor corrosion resistance, which limits the application of materials for a long time. Therefore, electroless deposition of Ni-based ternary alloy on wood surface is an important way to improve corrosion resistance. In this work, triplochiton sclexcylon and birch veneer were used as substrates and the metal deposition rate and surface resistivity were as the reference value to obtain the optimal plating solution of Ni-based ternary alloy. The coating properties were characterized and tested. The results are as follows:(1) In the process of electroless Ni-Fe-P plating on APTES-treated triplochiton sclexcylon veneer, sodium hypophosphite as reducing agent, the optimal pretreatment conditions are as follows:1.5% APTES stored for five hours, wood samples were dipped into PdCl2 (2 g/L) solution for 10min, next, the resulting samples were immersed in NaH2PO2 solution (2 g/L) for 10 min. The suitable plating bath composition and plating conditions are as follows:45 g/L of nickel sulfate,17.5 g/L of ammonium ferrous sulfate,27.5 g/L of sodium hypophosphite,70 g/L of potassium sodium tartrate,40 g/L of ammonium sulfate, pH value 9.2,90 ℃ for 40 min. The shielding effectiveness value of plated veneer exceeded 45 dB in frequencies from 9 kHz to 1.5 GHz. VSM results showed that the veneer-based composite exhibits higher magnetism. SEM results showed that the coatings were uniform, continuous and compact, and the special structure of wood was still seen clearly. XPS results investigated that the coating was consisted of Ni0, Fe0 and P0, Ni was the main component with 92.51 wt.%, but the contents of Fe and P were 5.57 wt.% and 1.92 wt.%, respectively. The XRD analysis indicated that the coating was crystalline. Adhesion test results showed that the adhesion strength between Ni-Fe-P alloy coating and wood surface was high. The contact angle of single plate was 104°, and decreased 6° after 15 s. The corrosion potential of Ni-Fe-P ternary alloy coating was -0.301 V, the corrosion current density was 7.58×10-6 A/cm2, and the polarization resistance was 3652.9 Ω/cm2. Corrosion resistance of Ni-Fe-P coating was obviously higher than that of Ni-P coating.In the process of electroless Ni-Fe-P plating by using Pd-free activation method, the pretreatment for triplochiton sclexcylon veneer is that the veneers were immersed in 4g/L of KBH4 (3 g/L NaOH) solution for 8min. The plating solution composition and conditions for triplochiton sclexcylon veneer are as follows:45 g/L of nickel sulfate,17.5 g/L of ammonium ferrous sulfate,25 g/L of sodium hypophosphite,70 g/L of potassium sodium tartrate,25 g/L of ammonium sulfate, pH value 9.4,90 ℃ for 60 min. The shielding effectiveness value of plated veneer exceeded 50 dB in frequencies from 9 kHz to 1.5 GHz. VSM results showed that the veneer-based composite exhibits higher magnetism. SEM results showed that the coatings were uniform, continuous and compact, and the special structure of wood was still seen clearly. XPS results verified that the coating was consisted of Ni0, Fe0 and P0, Ni was the main component with 93.60 wt.%, but the contents of Fe and P were 4.71 wt.% and 1.69 wt.%, respectively. The XRD analysis indicated that the coating was crystalline. Adhesion test results showed that the adhesion strength between Ni-Fe-P alloy coating and wood surface was high. The contact angle of single plate was 110°, and decreased 2° after 15 s. The corrosion potential of Ni-Fe-P ternary alloy coating was -0.3610 V, the corrosion current density was 7.89×10-6 A/cm2, and the polarization resistance was 4160.9 Ω/cm2. The coating obtained by this method exhibited excellent corrosion resistance.(2) Ni-W-P coatings were plated by using Pd-free activation and birch as substrate. The suitable bath composition and plating conditions are as follows:22.5 g/L of nickel sulfate,17.5 g/L of sodium tungstate,27.5 g/L of sodium hypophosphite,25 g/L of sodium citrate,5 g/L of lactic acid,30 g/L of ammonium chloride, pH value 8.8,88 ℃ for 40 min. XPS results show that the coating was consisted of Ni0, W0 and P0, Ni was the main component with 89.80 wt.%, but the contents of W and P 4.48 wt.% and 5.72 wt.%, respectively. The XRD analysis indicated that the coating was microcrystalline crystalline. SEM results showed that the coatings were uniform, continuous and compact, and the special structure of wood was still seen clearly. The shielding effectiveness value of plated veneer exceeded 40 dB in frequencies from 9 kHz to 1.5 GHz. Adhesion test results showed that the adhesion strength between Ni-W-P alloy coating and wood surface was high. The contact angle of single plate was 119°, and decreased 2° after 15 s. The corrosion potential of Ni-W-P ternary alloy coating was -0.3400 V, the corrosion current density was 2.163 ×10-6 A/cm2, and the polarization resistance was 20106 Ω/cm2. Compared with Ni-P coating, Ni-W-P coating showed better corrosion resistance.(3) Ni-Mo-P coatings were obtained by using APTES-Pd activation and birch as substrate. The suitable bath composition and plating conditions are as follows:27.5 g/L of nickel sulfate,0.6 g/L of ammonium molybdate,24 g/L of sodium hypophosphite,27.5 g/L of sodium citrate,12.5 g/L of sodium acetate, pH value 9.5,85 ℃ for 50 min. The shielding effectiveness value of plated veneer exceeded 45 dB in frequencies from 9 kHz to 1.5 GHz. SEM results showed that the coatings were uniform, continuous and compact, and the special structure of wood could be still seen clearly. XPS results show that the coating was consisted of Ni0, Mo0 and P0, Ni was the main component with 92.05 wt.%, but the contents of Mo and P 6.86 wt.% and 1.09 wt.%, respectively. The XRD analysis indicated that the coating was crystalline. Adhesion test results showed that the adhesion strength between Ni-Mo-P alloy coating and wood surface was high. The contact angle of single plate was 115°, and decreased 1° after 15 s. The corrosion potential of Ni-Mo-P ternary alloy coating was-0.3100 V, the corrosion current density was 4.522 × 10-6 A/cm2, and the polarization resistance was 8244.0 Ω/cm2, the corrosion resistance improved significantly.The wood-based composites with corrosion resistant and electromagnetic shielding effectiveness were obtained by using electroless Ni-based ternary alloy plating on wood surface. This method provides a new way for wood surface metallization, and plays a positive role for the development of wood science and technology. |
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