Study On The Structure And Property Of Nickle Based Alloy-Nano TiO₂Composite Coatings

Nano titanium dioxide is a kind of semi-conductor having good photo catalytic activity andpractical value. Various kinds of methods were employed to improve its photo catalytic activity. Itsapplication fields were restricted because of the difficulties of separating and recycling nano titaniumdioxide powders. Nano titanium dioxide particles can be loaded by electroless deposited coatings.Electroless plating Ni-P binary alloys have been achieved extensive application in industry, for thecoatings process excellent physical and chemical properties. Recent researches show that, byintroducing another constituent in the electroless deposited nickel-based binary alloys, the nickelbased ternary alloys can be obtained with the improved properties and performance. To add insolubleparticles in electroless plating bath and make them co-deposited with electroless deposited alloys, wecan obtain composite coatings which have excellent properties. As the nano-particles have quantumsize effect, small size effect, surface and interface effects, they have special physical and chemicalproperties. Nano composite coatings have specific functions such as hardenability, good wearresistance and good corrosion resistance. In this paper, Ni-P-nanometer TiO₂composite coatingswere prepared by electrophoretically deposite and electroless plating Ni-P alloy to improve thecontent of nano TiO₂particles in the coatings.Zinc doped nano TiO₂particles were prepared by sol-gel method. The test of light degradatingmethyl orange showed that, the highest photo catalytic occurred when the concentration of zinc inTiO₂particle was0.8wt%and had been calcined at500℃.The TiO₂particles containing0.8wt%zinc were nitrided. The test of light degradating methyl orange showed that, the TiO₂particles dopedwith zinc and nitron have excellent photo catalytic property. This showed that zinc and nitron canimprove photo catalytic property of nano titanium dioxide simultaneously.The composition and operating conditions have great effect on the deposition rate andconstituent of electroless deposited Ni-Zn-P alloys. With the bath content of ZnSO4increased, thedeposition rate and the content of P in the coating decreased. With the bath content of NaH2PO2increased, the deposition rate and the content of phosphorus in the coating increased. With pH valueand temperature of the bath increased, the deposition rate increased and the content of phosphorus inthe coating decreased. The electroless deposited Ni-Zn-P alloy is composed with amorphour phaseand solid solution of nickel. Ni₃P phase appears and the coating is crystallized completely when ithas been heated to400℃. The Ni₅Zn₁₂phase appears when it has been heated to600℃.The greatestmicrohardness value appears when it has been heated to500℃. The results of erosion test show that,the mass loss of electroless deposited Ni-Zn-P alloy increased with corrosive medium flow rateincreased and erosion angle decreased. The results show that the electroless deposited Ni-Sn-P ternary alloy is amorphous. Thedeposition rate and the tin content in the coating increase, but the phosphorus content in the coatingdecreases with increasing the stannic chloride and sodium hypophosphite contents in the bath. Thedeposition rate increases with the pH value of the bath in the range of3to6. Mass loss of the coatingincreases with increasing the erosion time and the flow velocity of erosion solution, which has itsmaximum value as the coating impacted at an angle of60°.Electroless deposited Ni-Zn-P-TiO₂nano-composite coatings were prepared by adding nanoTiO₂particles into electroless plating bath. The content of TiO₂in the composite coatings is10.76wt%at the optium technological conditions.The hardness values of electroless depositedNi-Zn-P-TiO₂nano-composite coatings are higher than that of electroless plating Ni-Zn-P alloy atthe same conditions. The composite coatings have the highest hardness value when they are heattreated at400℃for one hour. The results of erosion test show that, the mass loss of coatings areincreasing with corrosive medium flow rate increasing and erosion angle decreasing. Electrolessdeposited Ni-Zn-P-TiO₂nano-composite coatings have better anti errosion property than Ni-Zn-Palloy coatings.The effect of the applied electric field strength, electric current and deposition durations onelectrophoretically depositing were studied. Suitable technological parameters of electroless platingNi-P solution were obtained.The microstructure of the composite coating was analyzed by XRD andSEM. The microhardness values of the composite coatings were tested.The methyl orange solutionwas used as the reactant to evaluate the photocatalytic activity of the catalyst samples. The resultsshow that, nanometer TiO₂particles are distributed uniformly in the composite coating. Themicrohardness values of the composite coatings are higher than that of Ni-P alloy coatings. Thecomposite coating processes better photocatalytic activity.