Investigation Of Electroless Ni-P Plating On Carbon Fiber And Electroless Ni-P-MoS₂Composite Plating On Titanium Alloy

In this paper, electroless Ni-P coatings with good performance were successfullyobtained on carbon fiber surface, glue removing, coarsening and activation processingwere studied. Preferable technology formula of electroless Ni-P plating on carbon fiberwas determined by orthogonal experiment. Effects of temperature, pH value, sodiumhypophosphite concentration and lactic acid concentration on deposition rate wereanalysed through single factor experiment. Effects of Saccharin and lauryl sodiumsulfate on electroless Ni-P plating were discussed. Reaction mechanism of electrolessNi-P was preliminarily explored. Furthemore, electroless Ni-P-MoS2composite coatingswere successfully obtained on titanium alloy. Adhesion of electroless Ni-P coatingsobtained on zinc film, tin film and phosphating film, respectively, were tested. Effectsof pH value, stirring ways, surfactant type and concentration on depositon rate, MoS2content and distribution in Ni-P-MoS2composite coatings were analysed. Codepositionmechanism of MoS2partical, Ni and P was explored.Carbon fibers firing at400℃for30minutes works better at glue removing thanthat of putting the carbon fibers into soxhelt extraction device or nitric acid for it makesthe weight loss ration of canbon fibers2.14%, firing can remove the glue completelyand keep the carbon fibers in good condition. Superficial area of carbon fibers issignificantly enlarged by coarsening processing which is beneficial to adhesion betweenelectroless Ni-P coatings and carbon fibers. More catalytic crystal nucleus adsorb uponcarbon fibers by activated in AgNO3solution than that in PdCl2solution, which meansAgNO3had a better effect on activation than PdCl2.Preferable technologyl formula for electroless Ni-P plating on carbon fiber is:NiSO4·6H2O0.1mol/L, NaH2PO2·H2O0.25mol/L, NaAC·3H2O0.055mol/L,Na3C6H5O7·2H2O0.1mol/L, C3H6O30.2mol/L, C4H6O50.065mol/L, CH4N2S1.0mg/L,pH value=5.4, temperature=85℃. Deposition rate accelerates as the bath temperatureor pH value increases.however,deposition rate stops increasing when sodiumhypophosphite concentration reaches0.19mol/L, and it decreases when the lactic acidconcentration reaches0.22mol/L. Results above were also proved by reaction potentialand current density revealsed from electroless Ni-P plating polarization curves. Forsaccharin has the ability of refining grain and brightening coatings, finer grains, strong adhesion and lower utilization ratio of sodium hypophosphite can be observed whensaccharin is added to the solution. However, lauryl sodium sulfate will enter into thecoatings in the process of electroless Ni-P plating, hence the unfavorable influences,such as slower deposition rate, weaker adhesion, lower utilization ratio of sodiumhypophosphite are taken to the electroless Ni-P plating.Cathodic reduction of nickel is irreversible, and it is catalyzed by the appearance ofatomic hydrogen, meanwhile, there is an irreversible chemical conversion before theanodic oxidation of sodium hypophophite. Cathodic reaction and anodic reaction ofelectroless Ni-P plating influence each other, reduction potential of nickel become lowerwhen sodium hypophophite is added to the solution, that is conducive to the reductionof nickel; moreover, oxidation potential of sodium hypophophite become higher whennickel ion is added, produce of crystalline nickel has the ability of catalysis and that ishelpful to the oxidation of sodium hypophophite.Experiment results of electroless Ni-P-MoS2composite plating on titanium alloywere as follows: adhesion between electroless Ni-P coatings obtained upon zinc filmand titanium alloy is stronger in constrast to tin film and phosphating film, there are nocracks between the coating and titanium alloy, the coatings can bear40N loading forceat least. Deposition rate of electroless Ni-P-MoS2composite coatings goes up as the pHvalue increases under acidic condition, while the MoS2content of the compositecoatings increases first and then decreases, distribution condition and content of MoS2are both the best when pH value was6.0; fast deposition rate, high MoS2particlecontent and uniform distribution are all achieved by using interval stirring; depositionrate and MoS2content of electroless Ni-P-MoS2composite coating are both guaranteedby adding single cationic surfactant to the bath, MoS2particles are evenly distributed inthe coexistence of cationic and anionic surfactant; MoS2particles which are activateddeliver to the surface of Ni-P coatings by stirring and electric force, while MoS2particles which are not activated reached the surface of Ni-P coatings only by stirring.After catalysis, MoS2particles which are completely or partly activated are completelyor partly packed by nickel coatings,while MoS2particles which are not activated areadhered to the surface of Ni-P coatings.