Anodic spark deposition of P, Me(II) or Me(III) containing coatings on aluminium and titanium alloys in electrolytes with polyphosphate complexes

The aim of this study was to characterise the correlation between the molar ratio n = [polyphosphate]/[metal cation] in aqueous electrolyte and the gr owth parameters, composition and surface distribution of elements of anodic coatings on aluminium and titanium alloys. Coatings were formed in electro chemical cell using the anodic spark deposition method. The two-component e lectrolytes contained sodium hexametaphosphate (Na6P6O18) or sodium tripoly phosphate (Na5P3O10) and acetates of Mg(II), Zn(II), Ba(II), Mn(II), Ni(II) , Pb(II), Y(III), Eu(III) were used. Coatings were characterised by electro n probe microanalysis, laser mass spectrometry and X-ray diffraction. It wa s shown that the n value essentially affects the composition and thickness of coatings when lower than a certain value n(0), which lies in the range f rom 2.5 to 10 depending on the metal cation in the electrolyte. Coatings fo rmed in electrolytes of n < 1 consist mostly of electrolyte species. The in fluence of n on composition and parameters of the coatings is explained in terms of deposition and thermolysis of polyphosphate complexes on the anode surface owing to electric breakdown. (C) 2001 Elsevier Science B.V. All ri ghts reserved.