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Effects of phase transition of added TiO2 on characteristics of SnO2-based hydrocarbon-gas sensors
517
Senwrs and Actuators 8, 13-14 (1993) 517-518
Effects of phase transition of added TiO, on characteristics of SnO,-based hydrocarbon-gas sensors Wan-Young Chung and Duk-Dong Lee Departmentof Ekxrronics, Kyungpook National Universi~ Taegu 702-701 (South &rea) Dong-Han
Choi
Department of Semiconduchx Engineering, Chorqju University, Chongiu 360-764 (South Korea)
Intrurluction Recently, there have been increased demands for sensors to detect hydrocarbon gases as they become a promising fuel in industry and the home. Metal oxide, such as SnO,, ZnO, Fe,O, have been used as raw materials for hydrocarbon-sensing devices [l-3]. In this study, Pt and Sb-doped SnO-TiO raw materials were prepared by coprecipitation method. The effects of drying methods of precipitated powder and TiO, addition to the thick film on the microstructure and gassensing characteristics of the thick tihn were investigated.
Experimental A coprecipitation method was used for preparing SnO,-based material with added TiO> The preparation of SnOz-TiO, powders doped with Sb and Pt, started with SnCl,, TiCI,, SbCl, and H2PtC&-6H,O. At tist, SnC&, TiCi, and H,PtC!&.6H,O were &solved in deionized water, separately. SbCl, was dissolved in 30% HCl solution and diluted with deionized water. After that, the precipitate was dried by two methods, that is, freeze-drying and air-drying method. The dried powder was calcined at 600 “C for 1 h in Nz atmosphere. The thick tihns using these powders were prepared by screen-printing method. The thick films were sintered at various temperatures for 2 h in ambient NZ atmosphere.
The effect of the drying method on the microstructure of SnO,TiO,(Sb, Pt) raw material was investigated by TEM. The grain size of freeze-dried powder was about 50 A, and that of air-dried powder was much smaller; the powder seems to be amorphous, which is confirmed by XRD. From the AES and ESCA analyses, we infer that titanium-doped above 1 mol% exists in the form of TiOZ on the surface of the films. In this study, 1 wt.% platinum was added to a SnO,-TiO,(Sb, Pt) thick film by the addition of H,PtCI,+6H,O aqueous solution during coprecipitation process to get homogeneously dispersed Pt. The crystallite size of SnO, in the 5 mol% TiO,-added thick film was increased up to the heat treatment temperature of 900 “C!, and was decreased in the range of 900 and 1000 “C. This decreasing range corresponded well with the range of phase-transition temperature of the added TiO,. Adhesiveness of SnOi based thick films on the alumina substrate was improved by TiOZ addition. The crystallite size of the thick film heat treated at 1000 “C was equal to that of films heat treated at 800 “C. The sensitive layer heat-treated at higher temperature had better adhesiveness to substrate in the temperature range of 600 and 1000 “C. In this study, in order to decrease the resistivity of the film, Sb(V) was used as donor dopant. The Sb addition to the film lowered the resistivity but the i20
Results and discussSon Synthesized TiO, by precipitation method have two polymorphic phases: auatase and rutile. The trausformation temperature of freeze-dried powder was 60& 800 “C and that of air-dried powder was 70&1000 “C from XRD data.
0925-4005/93/$6.00
0
5 10 15 20 25 30 35
TiO, (mol%)
Fig. 1. Gas sensitivities of the thick film as a function of Ti02 content (heat treatment temperature: 700 “C).
@ 1993 - Elsevier Sequoia. AI1 rights resewed
518
sensitivity to CH, as not impaired in the range of 0.1-l wt.%. The film made from air-dried powder showed higher sensitivity to CH, than that of freeze-dried. The thick film with a TiO, content in the range 3-5 mol% showed relatively high sensitivities to CH4 and C,H,, (Fig. 1).
powder. TiO, addition enhanced the sensitivity of the film to hydrocarbon gases in the range of 3-5 mol%. Addition of Pt by simultaneous precipitation improved considerably the sensitivity of the film to hydrocarbon gases. The films made of air-dried powder showed higher sensitivity to CI& than freeze-dried films.
Conclusions
References
SnO,-TiO,(Sb, Pt) raw materials were prepared by coprecipitation method. This precipitate was dried by two drying methods: freeze-drying and air-drying. The phase transition of added Ti02 from anatase to rutile affected the microstructure and sensing characteristics of the thick film. The drying method affects not only the morphology of the calcined powder but also the sensing characteristics of the film made from that
T. Seiyama, A. Kato, K Fuji&i and M. Nagatanui, A new detector for gases components using semiconductive thin films, AMI. Chern., 34 (1962) 1502-1503. D.-D. Lee and D.-H. Chui, Thick-l?hnhydrocarbon gas sensors, Sensors and Achutors, Bl (1990) 231-235. Y. S. Shen, X. C. He, B. Q. Lii X. Q. Liu and X. Shen, Preparation,structureandgassensingpropextiesofSnOrZnO complex oxide, Pmt. 3rd Inf. Meet. on Chemical Sensors, Cleveland, OH, USA, 1990, pp. 35-38.
Senwrs and Actuators 8, 13-14 (1993) 517-518
Effects of phase transition of added TiO, on characteristics of SnO,-based hydrocarbon-gas sensors Wan-Young Chung and Duk-Dong Lee Departmentof Ekxrronics, Kyungpook National Universi~ Taegu 702-701 (South &rea) Dong-Han
Choi
Department of Semiconduchx Engineering, Chorqju University, Chongiu 360-764 (South Korea)
Intrurluction Recently, there have been increased demands for sensors to detect hydrocarbon gases as they become a promising fuel in industry and the home. Metal oxide, such as SnO,, ZnO, Fe,O, have been used as raw materials for hydrocarbon-sensing devices [l-3]. In this study, Pt and Sb-doped SnO-TiO raw materials were prepared by coprecipitation method. The effects of drying methods of precipitated powder and TiO, addition to the thick film on the microstructure and gassensing characteristics of the thick tihn were investigated.
Experimental A coprecipitation method was used for preparing SnO,-based material with added TiO> The preparation of SnOz-TiO, powders doped with Sb and Pt, started with SnCl,, TiCI,, SbCl, and H2PtC&-6H,O. At tist, SnC&, TiCi, and H,PtC!&.6H,O were &solved in deionized water, separately. SbCl, was dissolved in 30% HCl solution and diluted with deionized water. After that, the precipitate was dried by two methods, that is, freeze-drying and air-drying method. The dried powder was calcined at 600 “C for 1 h in Nz atmosphere. The thick tihns using these powders were prepared by screen-printing method. The thick films were sintered at various temperatures for 2 h in ambient NZ atmosphere.
The effect of the drying method on the microstructure of SnO,TiO,(Sb, Pt) raw material was investigated by TEM. The grain size of freeze-dried powder was about 50 A, and that of air-dried powder was much smaller; the powder seems to be amorphous, which is confirmed by XRD. From the AES and ESCA analyses, we infer that titanium-doped above 1 mol% exists in the form of TiOZ on the surface of the films. In this study, 1 wt.% platinum was added to a SnO,-TiO,(Sb, Pt) thick film by the addition of H,PtCI,+6H,O aqueous solution during coprecipitation process to get homogeneously dispersed Pt. The crystallite size of SnO, in the 5 mol% TiO,-added thick film was increased up to the heat treatment temperature of 900 “C!, and was decreased in the range of 900 and 1000 “C. This decreasing range corresponded well with the range of phase-transition temperature of the added TiO,. Adhesiveness of SnOi based thick films on the alumina substrate was improved by TiOZ addition. The crystallite size of the thick film heat treated at 1000 “C was equal to that of films heat treated at 800 “C. The sensitive layer heat-treated at higher temperature had better adhesiveness to substrate in the temperature range of 600 and 1000 “C. In this study, in order to decrease the resistivity of the film, Sb(V) was used as donor dopant. The Sb addition to the film lowered the resistivity but the i20
Results and discussSon Synthesized TiO, by precipitation method have two polymorphic phases: auatase and rutile. The trausformation temperature of freeze-dried powder was 60& 800 “C and that of air-dried powder was 70&1000 “C from XRD data.
0925-4005/93/$6.00
0
5 10 15 20 25 30 35
TiO, (mol%)
Fig. 1. Gas sensitivities of the thick film as a function of Ti02 content (heat treatment temperature: 700 “C).
@ 1993 - Elsevier Sequoia. AI1 rights resewed
518
sensitivity to CH, as not impaired in the range of 0.1-l wt.%. The film made from air-dried powder showed higher sensitivity to CH, than that of freeze-dried. The thick film with a TiO, content in the range 3-5 mol% showed relatively high sensitivities to CH4 and C,H,, (Fig. 1).
powder. TiO, addition enhanced the sensitivity of the film to hydrocarbon gases in the range of 3-5 mol%. Addition of Pt by simultaneous precipitation improved considerably the sensitivity of the film to hydrocarbon gases. The films made of air-dried powder showed higher sensitivity to CI& than freeze-dried films.
Conclusions
References
SnO,-TiO,(Sb, Pt) raw materials were prepared by coprecipitation method. This precipitate was dried by two drying methods: freeze-drying and air-drying. The phase transition of added Ti02 from anatase to rutile affected the microstructure and sensing characteristics of the thick film. The drying method affects not only the morphology of the calcined powder but also the sensing characteristics of the film made from that
T. Seiyama, A. Kato, K Fuji&i and M. Nagatanui, A new detector for gases components using semiconductive thin films, AMI. Chern., 34 (1962) 1502-1503. D.-D. Lee and D.-H. Chui, Thick-l?hnhydrocarbon gas sensors, Sensors and Achutors, Bl (1990) 231-235. Y. S. Shen, X. C. He, B. Q. Lii X. Q. Liu and X. Shen, Preparation,structureandgassensingpropextiesofSnOrZnO complex oxide, Pmt. 3rd Inf. Meet. on Chemical Sensors, Cleveland, OH, USA, 1990, pp. 35-38.