• PDF / 2,539,551 Bytes
• 12 Pages / 593.972 x 792 pts Page_size
• 17 Downloads / 262 Views

DOWNLOAD

REPORT

---

UCTION

THERMOELECTRIC devices have attracted worldwide attention, primarily due to their ability to convert heat directly into electricity and the possibility of their applications in waste heat recovery to improve energy usage efficiency. CoSb3 is a skutterudite structure compound with good thermoelectric properties and is among the most promising thermoelectric materials.[1–4] Furthermore, various studies have indicated that the thermoelectric properties of CoSb3 can be further enhanced with indium alloying.[5–11] The solubility of indium in CoSb3 and the formation of the InSb phase with excess indium alloying have also been examined.[5–11] Phase diagrams are fundamental to material systems and can be determined by experimental measurements and calculation.[12–14] However, only three recent studies have investigated the Co-In-Sb phase equilibria,[5,6,15] while no studies have reported thermodynamic modeling of the Co-In-Sb system. This study experimentally determines the CoSb3-InSb vertical section. The ternary-phase equilibria determined in this study and those in

WOJCIECH GIERLOTKA is with the Department of Materials Science and Technology, National Dong Hua University, Hualien, Taiwan. Contact e-mail: [email protected] SINN-WEN CHEN, SSU-MING TSENG, and PO-HAN LIN are with the Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan. Manuscript submitted August 16, 2017. Article published online May 29, 2019 METALLURGICAL AND MATERIALS TRANSACTIONS A

the literature[5,6,15] are used for the thermodynamic modeling of the Co-In-Sb ternary system using the Calphad method,[12–14] and the Co-In-Sb phase diagrams are calculated with the developed models.

II.

EXPERIMENTAL PROCEDURES

Pure elements of Co foils (99.95 wt pct, Alfa Aesar, Ward Hill, MA), In shots (99.99 wt pct, Alfa Aesar, Ward Hill, MA), and Sb shots (99.999 wt pct, Alfa Aesar, Ward Hill, MA) each with a total weight of one gram were weighed and encapsulated in 6 9 8 mm quartz tubes at 105 bar vacuum. The sample capsules were placed at 1000 °C for three days to ensure complete mixing and melting of the elements and then quenched in water. The samples were heat treated at different temperatures for predetermined lengths of time and then quenched in water. The lengths of heat-treatment time varied with the heat-treatment temperatures. They were 14, 28, 60, and 90 days when the temperatures were 850 °C, 800 °C and 825 °C; 700° C and 750 °C; 650 °C; and 450 °C, respectively. The quenched ingots were cut into two parts. One half was examined using powder X-ray diffraction analysis (XRD, Rigaku Ultima IV/ED2802N, Japan) with a Cu-Ka radiation source, and then compared with the JCPDS (Joint Committee on Powder Diffraction Standard) database. The other half was mounted in epoxy and polished for metallographic examination. Optical microscope (Olympus, BH, Japan) and scanning electron microscope (SEM, Hitachi, s-2500, Japan) were

VOLUME 50A, AUGUST 2019—3891

used to analyze the microstructures. The phase compositions were characte