Controlled preparation and characterization of multilayer sol-gel zirconia dip-coatings
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cribe a method for controlled preparation of sol-gel ceramic multilayer coatings obtained by dip-coating. The proposed fabrication routine guarantees obtaining crack-free multilayer coatings with control of the thickness and porosity of individual layers. The procedure is applied to obtain a 10-layer ZrO2–3 mol% Y2O3 coating deposited on AISI 310 stainless steel. The microstructure of this coating was investigated by using x-ray powder diffractometry and atomic force microscopy, and special consideration was given to the mechanical characterization of this thin film using ultramicrohardness indentation tests. Our results suggest that these zirconia coatings have good properties for use as protection barriers. Implications concerning general tailoring design of sol-gel dip-coatings are also considered.
I. INTRODUCTION
The sol-gel method is widely used for preparing inorganic materials from solutions containing metals, being usually referred to as a wet chemical method of producing ceramic materials.1,2 The most attractive feature of this processing route is the possibility of tailoring unique materials by polymerization of organometallic compounds (metal alkoxides, metal acetylacetonates, etc.) to a polymer gel. Two chemical reactions are involved in this process, hydrolysis and polycondensation. These reactions are usually simultaneous and are controlled by employing an appropriate acid or base catalyst agent. Because organometallic compounds and water are not miscible, a common solvent (alcohol) must be used in the process. However, it is possible to eliminate the use of the additional solvent by exposing the mixture to intense ultrasonic irradiation (sonogels).3 Nowadays the sol-gel process is used by a growing number of researchers for the preparation of an extensive variety of new materials, including bulk materials, films, membranes, or fibers. Coating is an important application of the sol-gel process because it presents certain advantages over other techniques: simple equipment and low cost, possibility of coating large areas, high optical quality of films, etc. The chemical processing and applications of sol-gel films have been reviewed by Schmidt4 and Sakka et al.,5 respectively. In addition, starting from precursor sol-gel a)
Guest scientist from Instituto de Fı´sica Rosario (CONICETUNR), Avenida 27 de Febrero, 210 bis. 2000 Rosario, Argentina. b) Address all correspondence to this author. J. Mater. Res., Vol. 16, No. 8, Aug 2001
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solutions, a large variety of deposition techniques can be used (dip-coating, spin-coating, spray-coating, electrophoresis, etc.).6,7 Sol-gel zirconia coatings have technological importance for applications as protection barriers.8 Indeed, zirconia has a large thermal expansion coefficient (10 × 10−6 °C−1) which is of the same order as those of metallic substrates (from 10 × 10−6 to 20 × 10−6 °C−1) and its thermal conductivity (0.05 cal cm−1 °C−1 s−1) is 1 order of magnitude less than those of metals, enabling its use as a
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