The Kinetics of the Chlorination of Yttrium Oxide

Abstract

The chlorination kinetics of Y 2 O 3 with chlorine to produce YOCl was studied by thermogravimetry over a temperature range from 575°C to 975°C. The influence of convective mass transfer into the boundary layer surrounding the sample, gaseous diffusion into the sample pores, partial pressure of chlorine, and temperature on the reaction rate were analyzed in order to determine the rate-controlling step. The thermogravimetric and scanning electron microscopy (SEM) results showed that the process follows a model of nucleation and growth, and the process is chemically controlled for temperatures lower than 800°C, with an activation energy (Ea) of 187 ± 3 kJ/mol. In the 850°C to 975°C range the reaction rate was affected by diffusion of Cl 2 through the gas film surrounding the sample, with apparent Ea of 105 ± 11 kJ/mol.A global rate equation that includes these parameters has been developed R ¼ da=dt ¼ 10 5 kPa À1 Á exp À 187 kJÁmol À1 RÁTÁpCl 2 Á1:51Á 1 À a ð ÞÁÀln 1 À a ð Þ ½

Activity and Stability of Carbon Supported PtxY Alloys for the ORR Determined by RDE and Single-Cell PEMFC Measurements

“…35 Interestingly, Y 2 O 3 was not found to be the major crystalline side phase at the given reaction conditions, although metallic yttrium is expected to be oxidized upon exposure to ambient air after completion of the synthesis. The formation of YOCl from Y 2 O 3 in the presence of Cl 2 , was, e.g., reported by Gaviria et al, who studied YOCl formation between 575-975 • C. 36 The formation of minor amounts of oxidized yttrium species during the preparation process might originate from the transfer of the sample from the glove box to the tube furnace during which a short air exposure (< 10 s) could not be avoided.…”

Chlorination of Lanthanum Oxide

“…The aim of this work is to continue with the kinetic research on direct chlorination of rare earth oxides, − and to study the chlorination of La 2 O 3 in order to determine the rate equation, the mechanism of the reaction, and the kinetics parameters.…”

Sintering of Titanium with Yttrium Oxide Additions for the Scavenging of Chlorine Impurities

“…A substantial increase in sintered density during liquid phase sintering results from the gettering of the chlorine and the prevention of chloride vaporization. [36] Sintering to near full density (~99.5 pct) can be achieved with 500 ppm Y 2 O 3 additions in compacts that would otherwise swell to~77 pct relative density. The sintered density can be similarly improved by vacuum degassing for periods up to 12 hours at intermediate temperatures prior to sintering.…”

“…We therefore assume that Reaction [1], supported by the YOCl product observed in the assintered microstructure, has occurred during sintering at 1573 K (1300°C). In addition, the Ellingham diagram of the Y 2 O 3 -Cl 2 -O 2 system up to 1273 K (1000°C) (Figure 12), produced by Gaviria and Bohe, [36] indicates that when Y 2 O 3 is exposed to a chlorine gas-containing environment, the most stable product should be YOCl.…”

“…Gaviria and Bohe [36] studied chlorination of Y 2 O 3 up to a temperature of 1248 K (975°C). In brief, they heated Y 2 O 3 powder in a flowing gas mixture of argon and chlorine at a rate of 3.8°C/min-a similar heating rate as used in this study.…”