Study On Preparation And Properties Of Ni-Mo-P Coating

By adding complex agents in the bath formulation improves plating Ni-Mo-Pdeposition rate, and solves the problem of high bath temperature. The effect ofsolution constituents on the deposition rate and deposit composition of electrolessNi-Mo-P plating is examined. The preparation Ni-Mo-P coating formulationcomposition and processing conditions are studied. It is studied that the effects of theconcentration of sodium molybdate Mo content of the coating, the coatingmorphology by scanning electron microscopy (SEM), energy spectrum analysis(EDS), etc. The polarization curves of Ni-Mo-P coatings with different concentrationsof sodium molybdate are measured to study the effects of sodium molybdateconcentration on the corrosion resistance of Ni-Mo-P coating.The results show that with sodium citrate as a complexing agent in theelectroless plating bath can achieve a good Ni,Mo,P co-deposition. With theconcentration of sodium citrate, the deposition rate of Ni-Mo-P increases, thendecreases.When the concentration of sodium citrate is30g/L,the deposition rate ofNi-Mo-P is fast; the deposition rate of Ni-Mo-P increases with the concentration ofnickel sulfate and sodium hypophosphite; the Mo contents increase with increasingconcentration of sodium molybdate in the plating bath, but the plating rate decreases.The concentration of the solution constituents in the following experiment: nickelsulfate30—35g/L, sodium hypophosphite30—35g/L, sodium citrate27—32g/L,complex agent A15—20ml/L, sodium molybdate0.2—0.8g/L, pH8—9, temperature70—80℃. Under this condition, the availability of the plating rate stability and goodperformance of the coating. When the concentration of sodium molybdate is0.2g/L,the deposition rate is fast up to17.6μm/h. When the concentration of sodiummolybdate0.6g/L, the obtained Ni-Mo-P plating layer have good corrosion resistance.Under sodium pyrophosphate system, screening experiments to optimize theadditive formulation, to obtain a low-temperature fast the bath formulation: nickelsulfate30—35g/L, sodium hypophosphite30—35g/L, sodium pyrophosphate27—32g/L, ammonium sulfate35—40g/L, complex agent B10—15ml/L, sodium molybdate0.2—1.6g/L, pH8.5—9.5, temperature65—70℃. Under this condition, thedeposition rate can be obtained a stable and good performance of the coating; Whenthe concentration of sodium molybdate is0.2g/L, the deposition rate is fast up to15.25μm/h, and the sodium molybdate1.6g/L, the Mo content is6.88wt%in theobtained the Ni-Mo-P coating, and the layer have good corrosion resistance.