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Sonochemically prepared tin-dioxide based composition for methane sensor
Materials Letters 60 (2006) 991 – 994 www.elsevier.com/locate/matlet
Sonochemically prepared tin-dioxide based composition for methane sensor Nandini Das ⁎, Asim K. Halder, Jalaluddin Mondal A. Sen, H.S. Maiti Electroceramics Division, Central Glass and Ceramic Research Institute, Kolkata 700 032, India Received 24 June 2005; accepted 17 October 2005 Available online 28 November 2005
Abstract Nanosized (3.5–14.0 nm) tin dioxide based powders containing antimony oxide and palladium have been prepared by sonication-assisted simultaneous precipitation. Thick film sensors made with these powders showed good sensitivity towards methane and their resistance values are optimum for practical applications. This contrasts with the film made with the powders prepared without sonication, which showed higher resistance in the ambient. © 2005 Elsevier B.V. All rights reserved. Keywords: Nanosize; SnO2; Sonochemical; Sensor; Methane sensitivity
1. Introduction Metal oxide based sensors have been widely used for the detection of gases, which include toxic and pollutant gases like CO, H2S, CH4, H2, etc. [1]. Many metal oxides viz. ZnO, TiO2, SnO2, WO3, and Ga2O3 have been examined for gas sensing [2–4]. Amongst them, tin dioxide has been widely used for gas sensing applications. Incidentally, sensors made with nanosized powder showed low operating temperature and high sensitivity [5,6]. Nanosized SnO2 powders have been prepared by different routes [7–13] like vapour deposition, sputtering, sol–gel processing, coprecipitation, spray pyrolysis, etc. Currently, sonochemical technique has emerged as a cheap, simple and alternative route of fine powder preparation [14]. The chemical effects of ultrasound arise out of acoustic cavitation, which is the formation, growth and implosive collapse of bubbles in a liquid [15]. There are two regions of sonochemical reactivity, the inside zone of the collapsing bubble and the interface between the bubble and the liquid. The cavitation can generate a temperature of around 5000 K and a pressure over 1800 kPa [16], which enable many chemical reactions to occur. In this study, nanosized SnO2 based powders containing antimony and palladium have been prepared by sonicationassisted simultaneous precipitation. The powder composition was selected [17] keeping in view the role of Pd as a catalyst ⁎ Corresponding author. E-mail address: [email protected] (N. Das). 0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.10.058
and the role of Sb (an “n” type dopant which goes into solid solution [17] with SnO2) in lowering the sensor resistance within acceptable limit for real life applications. The gas (methane) sensing characteristics of the powders in thick film form were compared with those of the powders prepared without sonication under identical conditions. 2. Materials and methods Batches containing tin dioxide, 0.25% (with respect to tin dioxide) antimony oxide and 10 wt.% palladium were prepared by sonication-assisted simultaneous precipitation technique. In this technique, reagent grade SnCl2·2H2O, Sb2O3 and PdCl2 were used to prepare the composition. In a typical synthesis procedure, SnCl2, Sb2O3, PdCl2, solutions were prepared [17] and mixed in the calculated ratio, and the mixture was taken in a beaker. The solution was sonicated (Ultrasonic processor, model—VPL P2, Vibronics, India, 1.25 stainless steel horn, 25 kHz, 250 W) for 30 min. NH4OH solution was then added slowly to the reaction mixture under sonication. The pH of the solution was kept at around 9. The sonication was continued for 4 h and the warm solution was allowed to cool. At the end of the reaction, black precipitate was obtained. The precipitate was centrifuged, washed by distilled water and ethanol in a sequence. The precipitate was sonicated in ethanol for 10 min and finally the ethanol was evaporated by slow heating to obtain a dry product. The filtrate after centrifuging was checked for the presence of any dissolved salt by further adding NH4OH
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solution. The dried powder was calcined at different temperatures (up to 600 °C) for 2 h in air. For comparison, similar composition was prepared under identical conditions excluding the sonication steps. The dried and calcined powders were examined using X-ray diffraction (Philips, PW, 1710 with Cu Kα radiation). The average grain sizes of the powders were calculated using Debye–Scherrer formula [18] D ¼ 0:9k=bcosh;
ð1Þ
where D is the average grain size, λ = 1.541 Å (X-ray wave length), and β = √(B2 − b2), B being the width of the diffraction peak at half maximum for the diffraction angle 2θ and b is the same for very large crystallites. The value of b was determined from XRD of large grained sample prepared by calcining the powder at a high temperature (1000 °C). In addition, further information about the particle size and shape was obtained from scanning electron microscope (SEM, LEO, 30i). Thermogravimetric analysis of the powders was carried out in air at a heating rate 10 °C/min using a Simadzu thermal analysis system. For gas sensing study, thick pastes of the powders were prepared in an aqueous medium containing a small amount of (1%) PVA binder. The pastes were painted on the outer surface of thin alumina tubes (length 3 mm, outer diameter 2 mm and
Fig. 2. XRD patterns of powder prepared by sonication-assisted simultaneous precipitation followed by calcination at 400 and 600 °C.
thickness 0.5 mm) with gold electrodes and platinum lead wires already attached to the ends by curing at a high temperature [17]. Kanthal heating coils were placed inside the tubes. After applying the coatings (thickness ∼ 100 μm), the assembly was dried in an oven followed by curing at 600 °C. The electrical resistance and methane sensitivity of the coatings were measured at 350 °C by using a digital multimeter (Solatron), a constant voltage/current source (Keithley 228 A) and an X–Y recorder. All the fired samples were initially preheated at 350 °C for 72 h to achieve the desired stability before measurements. 3. Results and discussion The XRD patterns of the powders (both uncalcined and calcined at 400 and 600 °C) prepared by conventional precipitation as well as sonication-assisted precipitation have been given in Figs. 1 and 2 respectively. The peaks of SnO2 (slightly shifted) due to solid solution Table 1 Particle size of the powders after calcination at different temperatures
Fig. 1. XRD patterns of powder prepared by simultaneous precipitation followed by calcination at 400 and 600 °C.
Powder calcination temperature (°C)
Particle size (nm) Conventional
Sonochemical
Uncalcined 400 600
4.67 10.57 11.81
3.45 6.41 14.0
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Table 2 Resistance and sensitivity values of sensors made by using different powders Powder preparation method
Calcination Resistance Resistance Sensitivity temperature (air) at (CH4) at (%) (°C) 350 °C 350 °C
Conventional precipitation Sonication-assisted precipitation
400 600 400 600
2.91 MΩ 3.1 MΩ 416 MΩ 30.15 kΩ
0.395 MΩ 0.524 MΩ 99 MΩ 3.23 kΩ
86 85 76 90
tivity of the thick films prepared by the powders showed interesting results. The sensitivity (S) of the films in 1000 ppm methane was calculated from the following relation: Sð%Þ ¼ ðRA −RG Þ=RA 100
Fig. 3. SEM image of the powder prepared by sonication-assisted precipitation.
[17] of Sb2O3 have been marked in the traces of Figs. 1 and 2. The peaks of PdO merged with those of SnO2. Incidentally, the powder precipitated under sonication showed orthorhombic phase of SnO2 along with the tetragonal phase as depicted in Fig. 2 (bottom trace). However, the other peaks of the orthorhombic SnO2 could not be clarified probably because of the broad and noisy X-ray traces owing to very fine particle size of the powders. After calcinations, only the peaks of tetragonal SnO2 were found. The average particle sizes of the powders determined by Debye–Scherrer method have been furnished in Table 1. Though the average particle size of the powder prepared by sonication-assisted precipitation is marginally smaller than that of the powder prepared by simple precipitation, the powder prepared by this methods contains large agglomerates. However, no such spherical isolated agglomerates were observed in case of powders prepared by sonication-assisted precipitation (Fig. 3). The extent of agglomeration in conventionally precipitated powder seems to be quite high because the weight loss (up to 110 °C) for such powder due to adsorbed moisture on the exposed surface is less (∼5.11%) than that (∼ 8.09%) of the powder prepared by the sonication-assisted precipitation (Fig. 4(a) and (b)). The electrical resistance and methane sensi-
Fig. 4. TGA curves of the powders prepared by a) conventional precipitation and b) sonication-assisted precipitation.
ð2Þ
where RA is the sensor resistance in air at 350 °C (at this temperature optimum sensitivity is normally achieved) and RG is the sensor resistance in 1000 ppm methane at the same temperature. Table 2 shows the resistance and sensitivity values for the sensors made by using different powders. It is evident from Table 2 that the RA value for sonicationassisted powder after calcinations at 600 °C (where only the expected tetragonal phase is present) is much less (by two orders of magnitude) than that of the powder prepared without sonication. To understand this behavior, we have to first consider that due to adsorption of oxygen ions from the atmosphere, the grains of n-type semiconductors like SnO2 form electron depleted surface layers up to a depth of Debye length LD given by [19,20]. LD ¼ ðe0 KB T =n0 e2 Þ1=2
ð3Þ
where ε0 is the dielectric permittivity of the free space, KB the Boltzman constant, n0 the total carrier concentration, T the absolute temperature and e the charge of the carrier. It may be noted that the resistance of a film may be either grain boundary controlled or neck controlled depending on the grain size [21,22]. For large grains (grain size, D >> 2LD, where LD ∼ 5 nm for SnO2 [19]), the neck cross section is large (Fig. 5a, Ref. [21]) and the resistance should be grain boundary controlled. For small grains (D ∼ 2LD, Fig. 5b), the resistance becomes neck controlled and can be very high because the depletion region or the space charge region of high resistivity controls the overall resistance, where the core region of low resistivity occupies a small portion of the neck area. In the present case, as discussed earlier, the powders prepared by simple precipitation contain large agglomerates and the intra-agglomerate sintering in this case should be much faster than [23] interagglomerate sintering and this should lead to intra-agglomerate bonding having small neck regions leading to very high resistance. For the
Fig. 5. A schematic to explain the grain size effect on the resistivity. Hatched part shows core region (low resistivity), while unhatched part shows spacecharge region (high resistivity).
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powders prepared by the sonication-assisted precipitation process (containing less agglomerates), the intra-agglomerate sintering should be less prominent and hence unlike conventionally prepared powders, the resistance values should be much lower. Indeed, such composition, showing lower resistance, preclude the necessity of adding more antimony to adjust the resistance of the sensors (at the cost of sensitivity) [17] for practical applications. Incidentally, for powders prepared by calcining at 400 °C, the sonication-assisted route showed much higher resistance. This may be due to the presence of high resistance [24] orthorhombic phases in such powders and the orthorhombic phase vanished (Fig. 2) at a calcination temperature of 600 °C. The gas sensitivity values of the films (Table 2) were quite satisfactory and such sonication-assisted precipitated powders should be very useful for fabrication of sensors.
4. Conclusion It has been observed that nanosized (3.5–14.0 nm) tin dioxide based powders can be prepared by sonication-assisted simultaneous precipitation. Thick films prepared by using such powders show very good methane sensitivity and above all, the resistance of the films in air at the operating temperature (350 °C) is much less (and optimum for sensor instrumentation) than that of the films prepared by using conventionally precipitated powder. Also such sonication-assisted precipitated powder needs a lower amount of antimony doping (with consequent improved sensitivity) for fabrication of real life gas sensors. References [1] F. Lu, Y. Liu, M. Dong, X. Wang, Sensors and Actuators. B, Chemical 66 (2000) 225. [2] T.G. Nenov, S.P. Yordanov, Ceramic Sensors—Technology and Applications, Technomic Publishing, Lancaster, PA, 1996.
[3] H. Meixner, U. Lampe, Sensors and Actuators. B, Chemical 33 (1996) 198. [4] L.M. Cukrov, P.G. Mc Cornick, Sensors and Actuators. B, Chemical (2001) 491. [5] N. Yamazoe, N. Miura, Some basic aspects of semiconductor gas sensors, in: T. Seiyama (Ed.), Chem. Sens. Technol., vol. 4, Elsevier, Amsterdam, 1992, p. 30, Koanha, Japan. [6] N. Sergent, P. Gelin, L.P. Camby, H. Praliaud, G. Thomas, Sensors and Actuators. B, Chemical 84 (2002) 176. [7] T. Oyabu, Journal of Applied Physics 53 (1982) 2785. [8] R.M. Geatches, A.V. Chadwick, J.D. Wright, Sensors and Actuators. B, Chemical 4 (1991) 472. [9] H.P. Hubner, S. Drost, Sensors and Actuators. B, Chemical 4 (1991) 463. [10] R. Puyane, I. Kato, Proceedings of SPIE 401 (1983) 190. [11] S. Kanefuse, M. Haradome, Solid-State Electronics 27 (1984) 533. [12] Z. Jin, H.J. Zhou, Z.L. Jin, R.E. Svinell, C.C. Liu, Sensors and Actuators. B, Chemical 52 (1998) 188. [13] T.J. Maffeis, G.T. Owen, M.W. Penny, T.K.H. Starke, S.A. Clark, H. Ferkel, S.P. Wilks, Surface Science 520 (2002) 29. [14] K.S. Suslick, G.J. Price, Annual Review of Material Science (1999) 295. [15] G. Pang, X. Xu, V. Markovich, S. Avivi, O. Palchik, Y. Koltypin, G. Gorodetsky, Y. Yeshurun, H.P. Buchkremer, A. Gedanken, Materials Research Bulletin 38 (2003) 11. [16] K.S. Suslick, Scientific American 260 (1989) 80. [17] K. Chatterjee, S. Chatterjee, A. Banerjee, M. Raut, N.C. Pal, A. Sen, H.S. Maiti, Materials Chemistry and Physics 81 (2003) 33. [18] A. Taylor, “X-ray Metallography” John Wiley, New York (1961) pp. 678, 686. [19] Z. Chen, L. Lai, C.H. Shek, H. Chen, Journal of Materials Research 18 (6) (2003) 1289. [20] F. Cosandey, G. Sekandan, A. Singhal, JOM-E 52 (10) (2000). [21] N. Yamozoe, Sensors and Actuators. B, Chemical 5 (1991) 7. [22] X. Wang, S.S. Yee, W.P. Carey, Sensors and Actuators. B, Chemical 24–25 (1995) 454. [23] M.N. Rahaman, Ceramic Processing and Sintering, Marcel Dekker, New York, 1995. [24] J.P. Ahn, S.H. Kim, J.K. Park, M.Y. Huh, Sensors and Actuators. B, Chemical 94 (2003) 125.
Sonochemically prepared tin-dioxide based composition for methane sensor Nandini Das ⁎, Asim K. Halder, Jalaluddin Mondal A. Sen, H.S. Maiti Electroceramics Division, Central Glass and Ceramic Research Institute, Kolkata 700 032, India Received 24 June 2005; accepted 17 October 2005 Available online 28 November 2005
Abstract Nanosized (3.5–14.0 nm) tin dioxide based powders containing antimony oxide and palladium have been prepared by sonication-assisted simultaneous precipitation. Thick film sensors made with these powders showed good sensitivity towards methane and their resistance values are optimum for practical applications. This contrasts with the film made with the powders prepared without sonication, which showed higher resistance in the ambient. © 2005 Elsevier B.V. All rights reserved. Keywords: Nanosize; SnO2; Sonochemical; Sensor; Methane sensitivity
1. Introduction Metal oxide based sensors have been widely used for the detection of gases, which include toxic and pollutant gases like CO, H2S, CH4, H2, etc. [1]. Many metal oxides viz. ZnO, TiO2, SnO2, WO3, and Ga2O3 have been examined for gas sensing [2–4]. Amongst them, tin dioxide has been widely used for gas sensing applications. Incidentally, sensors made with nanosized powder showed low operating temperature and high sensitivity [5,6]. Nanosized SnO2 powders have been prepared by different routes [7–13] like vapour deposition, sputtering, sol–gel processing, coprecipitation, spray pyrolysis, etc. Currently, sonochemical technique has emerged as a cheap, simple and alternative route of fine powder preparation [14]. The chemical effects of ultrasound arise out of acoustic cavitation, which is the formation, growth and implosive collapse of bubbles in a liquid [15]. There are two regions of sonochemical reactivity, the inside zone of the collapsing bubble and the interface between the bubble and the liquid. The cavitation can generate a temperature of around 5000 K and a pressure over 1800 kPa [16], which enable many chemical reactions to occur. In this study, nanosized SnO2 based powders containing antimony and palladium have been prepared by sonicationassisted simultaneous precipitation. The powder composition was selected [17] keeping in view the role of Pd as a catalyst ⁎ Corresponding author. E-mail address: [email protected] (N. Das). 0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.10.058
and the role of Sb (an “n” type dopant which goes into solid solution [17] with SnO2) in lowering the sensor resistance within acceptable limit for real life applications. The gas (methane) sensing characteristics of the powders in thick film form were compared with those of the powders prepared without sonication under identical conditions. 2. Materials and methods Batches containing tin dioxide, 0.25% (with respect to tin dioxide) antimony oxide and 10 wt.% palladium were prepared by sonication-assisted simultaneous precipitation technique. In this technique, reagent grade SnCl2·2H2O, Sb2O3 and PdCl2 were used to prepare the composition. In a typical synthesis procedure, SnCl2, Sb2O3, PdCl2, solutions were prepared [17] and mixed in the calculated ratio, and the mixture was taken in a beaker. The solution was sonicated (Ultrasonic processor, model—VPL P2, Vibronics, India, 1.25 stainless steel horn, 25 kHz, 250 W) for 30 min. NH4OH solution was then added slowly to the reaction mixture under sonication. The pH of the solution was kept at around 9. The sonication was continued for 4 h and the warm solution was allowed to cool. At the end of the reaction, black precipitate was obtained. The precipitate was centrifuged, washed by distilled water and ethanol in a sequence. The precipitate was sonicated in ethanol for 10 min and finally the ethanol was evaporated by slow heating to obtain a dry product. The filtrate after centrifuging was checked for the presence of any dissolved salt by further adding NH4OH
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solution. The dried powder was calcined at different temperatures (up to 600 °C) for 2 h in air. For comparison, similar composition was prepared under identical conditions excluding the sonication steps. The dried and calcined powders were examined using X-ray diffraction (Philips, PW, 1710 with Cu Kα radiation). The average grain sizes of the powders were calculated using Debye–Scherrer formula [18] D ¼ 0:9k=bcosh;
ð1Þ
where D is the average grain size, λ = 1.541 Å (X-ray wave length), and β = √(B2 − b2), B being the width of the diffraction peak at half maximum for the diffraction angle 2θ and b is the same for very large crystallites. The value of b was determined from XRD of large grained sample prepared by calcining the powder at a high temperature (1000 °C). In addition, further information about the particle size and shape was obtained from scanning electron microscope (SEM, LEO, 30i). Thermogravimetric analysis of the powders was carried out in air at a heating rate 10 °C/min using a Simadzu thermal analysis system. For gas sensing study, thick pastes of the powders were prepared in an aqueous medium containing a small amount of (1%) PVA binder. The pastes were painted on the outer surface of thin alumina tubes (length 3 mm, outer diameter 2 mm and
Fig. 2. XRD patterns of powder prepared by sonication-assisted simultaneous precipitation followed by calcination at 400 and 600 °C.
thickness 0.5 mm) with gold electrodes and platinum lead wires already attached to the ends by curing at a high temperature [17]. Kanthal heating coils were placed inside the tubes. After applying the coatings (thickness ∼ 100 μm), the assembly was dried in an oven followed by curing at 600 °C. The electrical resistance and methane sensitivity of the coatings were measured at 350 °C by using a digital multimeter (Solatron), a constant voltage/current source (Keithley 228 A) and an X–Y recorder. All the fired samples were initially preheated at 350 °C for 72 h to achieve the desired stability before measurements. 3. Results and discussion The XRD patterns of the powders (both uncalcined and calcined at 400 and 600 °C) prepared by conventional precipitation as well as sonication-assisted precipitation have been given in Figs. 1 and 2 respectively. The peaks of SnO2 (slightly shifted) due to solid solution Table 1 Particle size of the powders after calcination at different temperatures
Fig. 1. XRD patterns of powder prepared by simultaneous precipitation followed by calcination at 400 and 600 °C.
Powder calcination temperature (°C)
Particle size (nm) Conventional
Sonochemical
Uncalcined 400 600
4.67 10.57 11.81
3.45 6.41 14.0
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Table 2 Resistance and sensitivity values of sensors made by using different powders Powder preparation method
Calcination Resistance Resistance Sensitivity temperature (air) at (CH4) at (%) (°C) 350 °C 350 °C
Conventional precipitation Sonication-assisted precipitation
400 600 400 600
2.91 MΩ 3.1 MΩ 416 MΩ 30.15 kΩ
0.395 MΩ 0.524 MΩ 99 MΩ 3.23 kΩ
86 85 76 90
tivity of the thick films prepared by the powders showed interesting results. The sensitivity (S) of the films in 1000 ppm methane was calculated from the following relation: Sð%Þ ¼ ðRA −RG Þ=RA 100
Fig. 3. SEM image of the powder prepared by sonication-assisted precipitation.
[17] of Sb2O3 have been marked in the traces of Figs. 1 and 2. The peaks of PdO merged with those of SnO2. Incidentally, the powder precipitated under sonication showed orthorhombic phase of SnO2 along with the tetragonal phase as depicted in Fig. 2 (bottom trace). However, the other peaks of the orthorhombic SnO2 could not be clarified probably because of the broad and noisy X-ray traces owing to very fine particle size of the powders. After calcinations, only the peaks of tetragonal SnO2 were found. The average particle sizes of the powders determined by Debye–Scherrer method have been furnished in Table 1. Though the average particle size of the powder prepared by sonication-assisted precipitation is marginally smaller than that of the powder prepared by simple precipitation, the powder prepared by this methods contains large agglomerates. However, no such spherical isolated agglomerates were observed in case of powders prepared by sonication-assisted precipitation (Fig. 3). The extent of agglomeration in conventionally precipitated powder seems to be quite high because the weight loss (up to 110 °C) for such powder due to adsorbed moisture on the exposed surface is less (∼5.11%) than that (∼ 8.09%) of the powder prepared by the sonication-assisted precipitation (Fig. 4(a) and (b)). The electrical resistance and methane sensi-
Fig. 4. TGA curves of the powders prepared by a) conventional precipitation and b) sonication-assisted precipitation.
ð2Þ
where RA is the sensor resistance in air at 350 °C (at this temperature optimum sensitivity is normally achieved) and RG is the sensor resistance in 1000 ppm methane at the same temperature. Table 2 shows the resistance and sensitivity values for the sensors made by using different powders. It is evident from Table 2 that the RA value for sonicationassisted powder after calcinations at 600 °C (where only the expected tetragonal phase is present) is much less (by two orders of magnitude) than that of the powder prepared without sonication. To understand this behavior, we have to first consider that due to adsorption of oxygen ions from the atmosphere, the grains of n-type semiconductors like SnO2 form electron depleted surface layers up to a depth of Debye length LD given by [19,20]. LD ¼ ðe0 KB T =n0 e2 Þ1=2
ð3Þ
where ε0 is the dielectric permittivity of the free space, KB the Boltzman constant, n0 the total carrier concentration, T the absolute temperature and e the charge of the carrier. It may be noted that the resistance of a film may be either grain boundary controlled or neck controlled depending on the grain size [21,22]. For large grains (grain size, D >> 2LD, where LD ∼ 5 nm for SnO2 [19]), the neck cross section is large (Fig. 5a, Ref. [21]) and the resistance should be grain boundary controlled. For small grains (D ∼ 2LD, Fig. 5b), the resistance becomes neck controlled and can be very high because the depletion region or the space charge region of high resistivity controls the overall resistance, where the core region of low resistivity occupies a small portion of the neck area. In the present case, as discussed earlier, the powders prepared by simple precipitation contain large agglomerates and the intra-agglomerate sintering in this case should be much faster than [23] interagglomerate sintering and this should lead to intra-agglomerate bonding having small neck regions leading to very high resistance. For the
Fig. 5. A schematic to explain the grain size effect on the resistivity. Hatched part shows core region (low resistivity), while unhatched part shows spacecharge region (high resistivity).
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powders prepared by the sonication-assisted precipitation process (containing less agglomerates), the intra-agglomerate sintering should be less prominent and hence unlike conventionally prepared powders, the resistance values should be much lower. Indeed, such composition, showing lower resistance, preclude the necessity of adding more antimony to adjust the resistance of the sensors (at the cost of sensitivity) [17] for practical applications. Incidentally, for powders prepared by calcining at 400 °C, the sonication-assisted route showed much higher resistance. This may be due to the presence of high resistance [24] orthorhombic phases in such powders and the orthorhombic phase vanished (Fig. 2) at a calcination temperature of 600 °C. The gas sensitivity values of the films (Table 2) were quite satisfactory and such sonication-assisted precipitated powders should be very useful for fabrication of sensors.
4. Conclusion It has been observed that nanosized (3.5–14.0 nm) tin dioxide based powders can be prepared by sonication-assisted simultaneous precipitation. Thick films prepared by using such powders show very good methane sensitivity and above all, the resistance of the films in air at the operating temperature (350 °C) is much less (and optimum for sensor instrumentation) than that of the films prepared by using conventionally precipitated powder. Also such sonication-assisted precipitated powder needs a lower amount of antimony doping (with consequent improved sensitivity) for fabrication of real life gas sensors. References [1] F. Lu, Y. Liu, M. Dong, X. Wang, Sensors and Actuators. B, Chemical 66 (2000) 225. [2] T.G. Nenov, S.P. Yordanov, Ceramic Sensors—Technology and Applications, Technomic Publishing, Lancaster, PA, 1996.
[3] H. Meixner, U. Lampe, Sensors and Actuators. B, Chemical 33 (1996) 198. [4] L.M. Cukrov, P.G. Mc Cornick, Sensors and Actuators. B, Chemical (2001) 491. [5] N. Yamazoe, N. Miura, Some basic aspects of semiconductor gas sensors, in: T. Seiyama (Ed.), Chem. Sens. Technol., vol. 4, Elsevier, Amsterdam, 1992, p. 30, Koanha, Japan. [6] N. Sergent, P. Gelin, L.P. Camby, H. Praliaud, G. Thomas, Sensors and Actuators. B, Chemical 84 (2002) 176. [7] T. Oyabu, Journal of Applied Physics 53 (1982) 2785. [8] R.M. Geatches, A.V. Chadwick, J.D. Wright, Sensors and Actuators. B, Chemical 4 (1991) 472. [9] H.P. Hubner, S. Drost, Sensors and Actuators. B, Chemical 4 (1991) 463. [10] R. Puyane, I. Kato, Proceedings of SPIE 401 (1983) 190. [11] S. Kanefuse, M. Haradome, Solid-State Electronics 27 (1984) 533. [12] Z. Jin, H.J. Zhou, Z.L. Jin, R.E. Svinell, C.C. Liu, Sensors and Actuators. B, Chemical 52 (1998) 188. [13] T.J. Maffeis, G.T. Owen, M.W. Penny, T.K.H. Starke, S.A. Clark, H. Ferkel, S.P. Wilks, Surface Science 520 (2002) 29. [14] K.S. Suslick, G.J. Price, Annual Review of Material Science (1999) 295. [15] G. Pang, X. Xu, V. Markovich, S. Avivi, O. Palchik, Y. Koltypin, G. Gorodetsky, Y. Yeshurun, H.P. Buchkremer, A. Gedanken, Materials Research Bulletin 38 (2003) 11. [16] K.S. Suslick, Scientific American 260 (1989) 80. [17] K. Chatterjee, S. Chatterjee, A. Banerjee, M. Raut, N.C. Pal, A. Sen, H.S. Maiti, Materials Chemistry and Physics 81 (2003) 33. [18] A. Taylor, “X-ray Metallography” John Wiley, New York (1961) pp. 678, 686. [19] Z. Chen, L. Lai, C.H. Shek, H. Chen, Journal of Materials Research 18 (6) (2003) 1289. [20] F. Cosandey, G. Sekandan, A. Singhal, JOM-E 52 (10) (2000). [21] N. Yamozoe, Sensors and Actuators. B, Chemical 5 (1991) 7. [22] X. Wang, S.S. Yee, W.P. Carey, Sensors and Actuators. B, Chemical 24–25 (1995) 454. [23] M.N. Rahaman, Ceramic Processing and Sintering, Marcel Dekker, New York, 1995. [24] J.P. Ahn, S.H. Kim, J.K. Park, M.Y. Huh, Sensors and Actuators. B, Chemical 94 (2003) 125.