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Lee AC, Qin M, Li H, Shi Z, Xu J, Gao F, Chen Y. Annealing of Strontium Titanate Based Thermoelectric Materials by Graphite: Mechanistic Analysis by Spectroscopic and Chromatographic Techniques. Chempluschem 2020; 85:734-741. [PMID: 32286741 DOI: 10.1002/cplu.202000113] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Revised: 03/25/2020] [Indexed: 11/12/2022]
Abstract
Strontium titanate (SrTiO3 ) based materials are promising for high-temperature thermoelectric applications. In order to enhance their performance, annealing is usually required and carried out under various atmospheres. Annealing with graphite is quite effective, but the mechanism is not yet clear. In this work, we use IR spectroscopy and gas chromatography (GC) to monitor the chemical environment under the annealing conditions (1350 °C for 8 h under 16.9 mL/min N2 with graphite) and quantify the various gases evolved in the process. It is shown that reducing agents, H2 and CO (concentrations peaked at ca. 0.4-0.5 %), are generated from graphite in the annealing process. H2 is produced in carbon gasification reaction, which also generates CO. Additional CO is produced from incomplete combustion of carbon. In the annealing of a La-doped SrTiO3 -based ceramic with graphite, higher levels of H2 O and CO2 are detected, which is resulted from the reduction of the ceramic by H2 and CO, respectively. About 67 % of the oxygen vacancies were created by CO reduction while about 33 % by H2 reduction. The conclusions are well supported by direct weight loss measurements with a difference of less than 6 %.
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Affiliation(s)
- Alex Chinghuan Lee
- Energy and Catalysis Laboratory, Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, P. R. China.,Hierarchical Green-Energy Materials (Hi-GEM) Research Center, National Cheng Kung University, Tainan, 70101, Taiwan, P. R. China
| | - Mengjie Qin
- State Key Laboratory of Solidification Processing, MIIT Key Laboratory of Radiation Detection Materials and Devices, USI Institute of Intelligence Materials and Structure, NPU-QMUL Joint Research Institute of Advanced Materials and Structure, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, 710072, P. R. China
| | - Haoran Li
- Energy and Catalysis Laboratory, Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, P. R. China
| | - Zongmo Shi
- State Key Laboratory of Solidification Processing, MIIT Key Laboratory of Radiation Detection Materials and Devices, USI Institute of Intelligence Materials and Structure, NPU-QMUL Joint Research Institute of Advanced Materials and Structure, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, 710072, P. R. China
| | - Jie Xu
- State Key Laboratory of Solidification Processing, MIIT Key Laboratory of Radiation Detection Materials and Devices, USI Institute of Intelligence Materials and Structure, NPU-QMUL Joint Research Institute of Advanced Materials and Structure, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, 710072, P. R. China
| | - Feng Gao
- State Key Laboratory of Solidification Processing, MIIT Key Laboratory of Radiation Detection Materials and Devices, USI Institute of Intelligence Materials and Structure, NPU-QMUL Joint Research Institute of Advanced Materials and Structure, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, 710072, P. R. China
| | - Yongsheng Chen
- Energy and Catalysis Laboratory, Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, P. R. China
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