Interphase Study by XPS of Sol-Gel ZrO 2 Coatings On Stainless Steel
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ABSTRACT ZrO2 coatings were obtained by the the ailkoxide route and deposited onto stainless steel using the dip coating technique. The starting solutions were prepared by mixing zirconium tetrabutoxide, isopropanol, acetylacetone. The water content for the hydrolitic reaction arose from the atmosphere moisture. Useful information for the structural organization of the zirconia/steel interphase is given by
XPS analysis.
It is found that during firing treatment, the main components (Fe, Cr, Ni) of the stainless steel diffuse into the ceramic coating. XPS data allow to describe the chemical composition variation from the bulk substrate to the outer coating surface.
INTRODUCTION For many reasons, the sol-gel process is an efficient method for preparing ceramic coatings on different substrates[ 1,21. Much attention has been focused on zirconia coatings because of
the superior properties of this oxide, such as chemical durability, high hardness, refractoriness, and ionic conductivity . A number of reports concerning ZrO2 coatings on glass[3,4], or on stainless steel[5-7] has been already published. In a recent work, the present authors have been studying the protective action and the deformation capability of zirconia coatings prepared on stainless steel substrates[8]. In the present paper, the structural organization of the interphase of this composite system is investigated thoroughly by the XPS technique.
EXPERIMENTAL Zirconia coatings were prepared by mixing zirconium tetrabutoxide with isopropanol in a 1:5 weight ratio. Then, acetylacetone was added in a 1:1 molar ratio with the zirconium tetrabutoxide. The water content for the hydrolitic reaction arose from the atmosphere moisture above the coating bath. The substrate used was 304 stainless steel .Its composition is given in table I. Table I: 304 stainless steel composition (wt%) nISi ICu IC IMo 8.48 . 0.43 0.08 0.05 0.16
ICr INi I 17.4
S 0.3
703 Mat. Rlea. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
I
The stainless steel plates are polished with abrasive paper up to 11im in order to obtain a polymiror like surface state. After degreasing ultrasonically in acetone, they were dipped into the solution and withdrawn at a rate of 10 cm/mn. Then, the coated plates were thermally treated at 500'C for a short period. Zirconia coatings onto stainless steel studied by XPS were designated by the labels A and B.Their chararacteristics are reported in table II.Xray photoelectron spectra of these coatings were measured using Al Ka(1486.6 eV) as the excitation source and referenced to the CQls) lines at 284.8 eV. Depth profiling curves of main elements analysed(Zr,Fe,Cr,Ni,O) were obtained by sputtering progressively the samples over an area of 12mm2 with an Ar' ion beam; the sputtering rate was about 1.6 nm/min.
I
Table 11: Characteristics of zirconia coatings onto stainless steel investigated b Sample A Sample B Dipping number
Firing period at 5000C
5 min
1
2 2*10 min
Thickness
35 nmn
65 nmn
XPS
RESULTS AND DISCUSSION Figure 1 shows XPS
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