| Summary: | 碩士 === 國立中央大學 === 能源工程研究所 === 97 === Thin films of pure Al and Al-Sc alloys prepared by direct current (DC) magnetron sputtering technique were considered as the candidate of reflective films of the auto-lamp. Stable and good optical reflectivity is the major concern during the performance of auto-lamp for a number of thermal cycles under a corrosive environment. The optical reflectivity and corrosion behavior may depend upon the composition and structure of the films. Examination through electron probe microanalysis(EPMA), the Sc-contents of the Al-Sc films are at 0.19、0.22、0.48、0.53wt.%, respectively. Observation using field emission scanning electron microscope (FESEM), we found that the grains decrease their size with increasing the Sc-content in the films. Al-0.53wt.% Sc film exhibits the finest grains (roughly at 50 ±5 nm) among the five films. The stress exerted to a specific film in a thermal cycle (heating the film from room temperatue to 450℃and cooling down naturally to the ambient) was estimated by measuring the curvature change on the film in terms of a Laser beam. A compressive stress was induced in the heating stage but a tensile stress induced in the cooling stage. The compressive stress increases to a maximum and deceases to zero with increasing the temperature. However, the tensile stress increases with decreasing the temperature. The temperature in response to maximal compression is higher for the film containing greater Sc-content, i.e., 290℃(0.53wt.% Sc) > 225℃ (0.48wt.% Sc) > 220℃(0.22wt.% Sc) > 190℃ (0.19wt.% Sc) > 110℃(Al). The average and maximum surface roughness (Ra & Rmax.) of the films were determined by atomic force microscope (AFM). Among the five films, Al-0.53wt.% Sc film indicated the smallest Ra & Rmax (Ra= 4.729nm; Rmax= 6.481nm ) and revealed the smoothest surface where no any hillock could be found and result in the highest optical reflectivity. The corrosion behavior of the films annealed at 85, 185 and 450℃ for 1 h was electrochemically investigated in 5wt.% NaCl solution. The open circuit potential (OCP) of the Al-Sc films displays a noble value -0.700 (±0.05V) compared to the pure Al-film (at -1.10V). The corrosion-resistance increases with increasing the Sc-content in the films. The Al-0.53wt.% Sc is the most suitable candidate for the reflective material of auto-lamp due to its highest resistance to corrosion (lowest corrosion current at 1.07nA/cm2). The films containing higher Sc-content tend to have higher optical reflectivity and the reflectivity loss is much less when the film post corrosion test.
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