Phase stability of noble metal loaded WO3 for SO2 sensor applications

Dongwon Shin, Theodore M. Besmann, Beth L. Armstrong

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

A thermodynamic phase stability investigation of semiconductor oxide materials for SO2 gas sensing applications has been performed to provide insight into understanding the working principles for SO2 sensing. Complex phase stabilities of noble metals (Au, Ag, Pd, and Pt) loaded WO3 semiconductor oxides for SO2 sensors have been investigated through the use of the CALPHAD (CALculation of PHAse Diagram) computational thermodynamics approach. Thermodynamic descriptions for the individual phases, i.e. SO2 gas, oxides, sulfides, and metal sulfates, are obtained from the Scientific Group Thermodata Europe (SGTE) Substance Database. Calculated isothermal sections of W-S-O show a significant phase transformation for WS2 at 400 °C. This phase transformation agrees with the previously reported experimental findings that the SO2 response of WO3 increases notably at that temperature. Ag-loaded WO3 in equilibrium with the SO2 gas exhibits very complex phase stabilities for the binary sulfide and ternary sulfate, while the other metals (Au, Pd and Pt) did not exhibit any notable phase transformations. The thermodynamic model predicts an allotropic phase transformation of the Ag2S phase near 500 °C in Ag/WO3-SO2 regardless of the Ag content, which differs from the reported experimental observation that 1.0 wt% Ag/WO3 exhibited SO2 sensor response at 450 °C. This discrepancy may be attributed to the fact that the solubility of Ag in the WO3 phase has not been considered in the thermodynamic model.

Original languageEnglish
Pages (from-to)75-80
Number of pages6
JournalSensors and Actuators, B: Chemical
Volume176
DOIs
StatePublished - 2013

Funding

The authors would like to thank the Oak Ridge National Laboratory (ORNL) sensor research team, David West, Fred Montgomery, and Dane Wilson, for their helpful discussions. This research was sponsored by the US Department of Energy Office of Fossil Energy, National Energy Technology Laboratory . This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.

Keywords

  • CALPHAD
  • Semiconductor gas sensor
  • Thermodynamics

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