Investigation of Structural and Mechanical Properties of UV and Microwave-Irradiated Al 2 O 3 / ZrO 2 Multilayers by Sol
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Investigation of Structural and Mechanical Properties of UV and Microwave-Irradiated Al2O3 / ZrO2 Multilayers by Sol-Gel Coating A. R. Phani and H. Haefke Micro and Nanomaterials Section CSEM Swiss Center for Electronics and Microtechnology, Inc.,CH-2007 Neuchâtel, Switzerland ABSTRACT Thin film multilayers of Al2O3 / ZrO2 have been deposited on quartz and AISI 440C steel substrates at room temperature by sol-gel dip coating technique followed by annealing at different temperatures ranging from 200oC to 800oC for 5h. Prior to annealing the deposited films have been exposed 10 min to ultraviolet radiation (248 nm wavelength) and microwave (2.45 MHz at 800 W power) respectively. Unlike conventional annealing methods, microwave heating is generally quite faster, simpler, and very energy efficient. The lower temperature and shorter time with microwave irradiation might be ascribed to the activating and facilitating effect of microwave on solid phase diffusion. X-ray diffraction (XRD) and scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analyser techniques have been employed to characterize structural, morphological and elemental composition of the thin films. Adhesion strength failure measurements on films have shown critical loads up to 35 N. Nanohardness indentation tests of the films exposed to microwave have shown hardness of 10 GPa with elastic modulus of 85 GPa compared to the annealed films hardness of 4.5 GPa with elastic modulus 57 GPa. INTRODUCTION Microwave irradiation is becoming an increasingly popular method of heating samples in the laboratory to synthesize biological1, organic2 and inorganic materials3. Unlike conventional annealing process, this technique offers a clean, cheap, and convenient method of heating, which often results in higher yields and shorter reaction times. Coatings with surface laser treatments4 or microwave exposure5 leads to enhanced mechanical and tribological properties. There has been less attention in literature that sol-gel films treatment with microwave radiation. In the last decade, many investigators have utilized microwave technique to synthesize powder perovskite solid compounds such as La2CuO46, and high temperature superconducting materials such as YBa2Cu3O7-x7. In present work ceramic oxides such as Al2O3, ZrO2, have been chosen because they are widely used in many optical, microelectronic and protective coating applications due to their excellent properties such as chemical resistance, good mechanical strength, and high hardness, transparency, high abrasive and corrosion resistance as well as insulating materials. In order to combine the properties of Al2O3 and ZrO2, multilayers of these oxides have been deposited by sol-gel dip coating technique. Deposited thin films have been exposed to UV or microwave radiations followed by annealing in order to investigate their structural and mechanical properties.
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EXPERIMENTAL PROCEDURE Fig 1 shows the preparation process for aluminium oxide and zirconium oxide multilayered thin films by sol
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