Fabrication of Al sub(2)O sub(3)-W Functionally Graded Materials by Slipcasting Method

• Published in: IOP conference series. Materials Science and Engineering 2011-01, Vol.18, p.1-4
• Main Authors: Katayama, Tomoyuki, Sukenaga, Sohei, Saito, Noritaka, Kagata, Hajime, Nakashima, Kunihiko
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Discharge lamps; Functionally gradient materials; Heat treatment; Materials science; Oxidation; Polished; Scanning electron microscopy
• ISSN: 1757-8981; 1757-899X
• DOI: 10.1088/1757-899X/18/20/202023

We have successfully fabricated a functionally graded material (FGM) from tungsten and alumina powders by a slip-casting method. This FGM has applications as a sealing and conducting component for high-intensity discharge lamps (HiDLs) that have a translucent alumina envelope. Two types of W powder, with different oxidizing properties, were used as the raw powders for the Al sub(2)O sub(3)-W FGM. "Oxidized W" was prepared by heat-treatment at 200 [degrees]C for 180 min in air. Alumina and each of the W powders were mixed in ultrapure water by ultrasonic stirring. The slurry was then cast into a cylindrical acrylic mold, which had a base of porous alumina, under controlled pressure. The green compacts were subsequently dried, and then sintered using a vacuum furnace at 1600 [degrees]C for a fixed time. The microstmctures of the FGMs were observed by scanning electron microscopy (SEM) of the polished section. The Al sub(2)O sub(3)-W FGM with the "oxidized W" powder resulted in a microscopic compositional gradient. However, the FGM with "as-received W" showed no compositional gradient. This result was mainly attributed to the difference between the [zeta]-potentials of the W powders with the different oxidizing conditions; basically "oxidized W" powder tends to disperse because of the larger [zeta]-potential of the oxide layer coated on the W powder core.