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Gas response of tin oxide film sensor to varying methane gas concentration
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 5 (2018) 11140–11143
www.materialstoday.com/proceedings
NanoThailand2016
Gas response of tin oxide film sensor to varying methane gas concentration Emmanuel A. Florido*, Brainerd D. Cruz, Yc A. Pasion Institute of Mathematical Sciences and Physics, University of the Philippines Los Baños, Los Baños 4013, Philippines
Abstract This study was aimed to determine the effect of methane gas concentration on the voltage response of tin oxide (SnO2) film. The sensing circuit of the tin oxide film was interfaced to a laptop computer throug an arduino microcontroller for data acquisition. Real time data table and graph can be visualized on the laptop screen during the gas sensing process. The sensor was enclosed in an airtight plastic jar container connected to a gas source and a water trap that maintained atmospheric pressure in the chamber. A mixture of 1% methane in helium was introduced into the chamber at a rate of 2 liters per minute (LPM) using a mass flow controller. The gas mixture was introduced intermittently at several stages. Each stage was followed by a standby stage during which there was no gas flow and the sensor was allowed to equilibrate with the gas mixture. It was observed that during the introduction of gas at each stage the voltage output of the sensor was increasing. During the standby stage there was no observed change in the voltage output as indicated by a flat response in the graph of voltage output versus time. The added quantity of gas can be computed from the flow rate and time duration of each stage. The incremental concentration of gas was also computed after each succeeding stage. The computed concentration in parts per million (ppm) was plotted with the measured voltage output per stage. Results showed a linear relationship between gas concentration and voltage output in the range of 3.75 to 7.8 ppm with a linearity of 0.99 and sensor sensitivity of 140 mV/1000 ppm. The sensitivity and linearity were 161 mV/1000 ppm and 0.98, respectively in the range 1000 to 9000 ppm. It is recommended to conduct more trials at different concentration ranges, different methane input mixture percentages, and different flow rates. © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 5th Thailand International Nanotechnology Conference (NanoThailand2016). Keywords: tin oxide, sensor, methane, gas concentration, gas response, sensitivity Introduction
* Corresponding author. Tel.: +63-049-536-6610; fax: +63-049-536-6610. E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 5th Thailand International Nanotechnology Conference (NanoThailand2016).
Emmanuel A. Florido et.al./ Materials Today: Proceedings 5 (2018) 11140–11143
11141
1. Introduction Methane gas is odorless and non-toxic but the danger lies in the possibility of asphyxiation in enclosed spaces due to its ability to replace oxygen [1] as well as combustion within 5 to 15% concentration in air at room temperature. It has a lifespan of several hours but its effectivity as a green house has qlobal warning potential which is twenty times that of carbon dioxide [2]. For the past several years efforts have been focused on developing semiconducting metal oxides for gas sensing and measurement for use in portable instruments [3,4]. Some of these materials ZnO, In2O3, Cd2SnO4 or SnO2 have exhibited good sensor characteristics like high sensitivity, fast response non-toxicity and stability [4,5]. Adsorption of oxygen on the surface of the metal oxides raises the resistivity of the surface due to immobilization of electrons as shown in Eq 1.
2O e O2 [300 C 1500 C]
(1)
Adsorbed oxygen can be removed from the surface by reacting with a reducing gas such as methane. The reaction shown in Eq. 2 results to a decrease in resistivity of the material [6]. CH4 4O(ads) CO2(air) 2H2O 4bulk
(2)
Tin oxide is a wide-band gap n-type semiconductor similar in electrical and gas sensing properties to zinc oxide. Different methods of fabrication have been studied including sol-gel method, spray pyrolysis, precipitation, and screen printing [6,7] This study was done to determine the response of a commercial tin oxide film to intermittent but successive increment in methane gas concentration in a single set of measurements in an airtight gas chamber in order to determine its capability as a preliminary study prior to laboratory fabrication of tin oxide films using various methods. The result would be helpful in optimizing fabrication parameters to extend the sensing range capability of the sensor to methane gas concentration. The commercial tin oxide film used has a theoretical range of 200 to 10,000 ppm. 2. Methodology The gas sensing set-up (Fig.1) was assembled using a commercial screen printed tin oxide sensor film connected to a circuit bridge interfaced to a computer through a microcontroller. The sensor was enclosed in a 1-liter airtight gas chamber of known volume. The chamber was kept airtight to maintain the total amount of oxygen inside the container as well as to contain the introduced gas mixture. Anaytical grade methane gas was introduced to the gas chamber using a programmable mass flow controller. Methane gas was mixed with pure nitrogen gas resulting to a concentration of 1% methane. The flow rate was set to 2 liters per minute (LPM). The gas mixture was fed into the gas chamber intermittently in stages. Each stage lasted for 20 seconds after which was gas flow was switched off. This was followed by an 80-sec resting period during which the sensor was allowed to equilibrate with the gas concentration. The added amount of the gas can be computed from the flow rate and time duration of each flow stage. The voltage response for each stage was detected by the microcontroller. The whole process lasted for a total of 2000 seconds resulting to an incremental increase in chamber gas concentration with corresponding voltage response increment. Real time data can be viewed on the computers display during gas sensing.
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Emmanuel A. Florido et.al./ Materials Today: Proceedings 5 (2018) 11140–11143
Fig. 1. Part of the gas sensing set-up showing the front and back of the mass flow controller (left and middle photo,respectively) and the microcontroller (right photo). 3. Results and Discussion The voltage response with time of tin oxide film sensor to an incremental increase in methane gas concentration is shown in Fig. 2. The horizontal part of the curve corresponds to the voltage output during 80-second stage described in the methodology during which the sensor was allowed to equilibrate with the gas. The vertical part corresponds to the voltage response when an additional amount of methane gas was introduced into the gas chamber. It can be observed that there is a decreasing voltage response at higher concentrations which can be attributed to the onset of saturation of the film surface when the adsorbed oxygen gets depleted from the surface. Even with replenishment of oxygen from the air inside the airtight container, the free oxygen supply eventually gets depleted. Fig. 3 shows the voltage response of the tin oxide sensor to methane gas concentration. The sensitivity and linearity of the sensor was 161 mV/1000 ppm and 0.98, respectively in the range 1000 to 9000 ppm. Another set of data was obtained for the range 3.75 to 7.8 ppm with a linearity of 0.99 and sensor sensitivity of 140 mV/1000 ppm.
Fig. 2. Voltage response with time of tin oxide gas sensor to intermittent increment in methane gas concentration.
Emmanuel A. Florido et.al./ Materials Today: Proceedings 5 (2018) 11140–11143
a
11143
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Fig. 3. a. Voltage response of tin oxide gas sensor to increasing methane gas concentration in the range 1000 to 9000 ppm. b. Voltage response of tin oxide gas sensor to increasing methane gas concentration in the range 3.75 to 7.8 ppm. 4. Summary and Conclusion Results showed that the voltage response and sensitivy of a commercial tin oxide film to methane concentration were 161 mV/1000 ppm and 0.98, respectively in the range 1000 to 9000 ppm and 140 mV/1000 ppm.for the range 3.75 to 7.8 ppm with a linearity of 0.99. The sensing range given in the data sheet of the sensor is 300 ppm to 10000 ppm. The result of this study would help the researcher in the optimization of parameters and method in film fabrication to enhance the sensing range and sensitivity of the film for low-cost film fabrication. Acknowledgements The authors would like to acknowledge the Philippine Council for Industry, Energy, and Emerging Technlogy Research and Development, Department of Science and Technology for funding the project through which this study was conducted and the Institute of Mathematical Sciences and Physics, University of the Philippines for the laboratory facilities. References [1] P. Bhattacharyya, P.K. Basu, H. Saha, S. Basu, Sensors and Actuators B 124 (2007) 62–67. [2] Q. Schiermeier, Methane finding baffles scientists, Nature 439 (2006) 128(News). [3] S. Basu and P. K. Basu, J. Sens. Stud, Article ID 861968, (2009) 1-20. [4] P. Bhattacharyya, P.K. Basu, H. Saha, S. Basu, Sensors and Actuators B 124 (2007) 62–67. [5] H. Moon, S. Kim and W. Choi, Transactions On Electrical And Electronic Materials 13-2, (2012)106-109. [6] S. Chakraborty, A. Sen , H.S. Maiti, Sensors and Actuators B 115 (2006) 610–613. [7] L. De Angeles, R. Riva, Sensors and Actuators B 28 (1995) 25-29.
ScienceDirect Materials Today: Proceedings 5 (2018) 11140–11143
www.materialstoday.com/proceedings
NanoThailand2016
Gas response of tin oxide film sensor to varying methane gas concentration Emmanuel A. Florido*, Brainerd D. Cruz, Yc A. Pasion Institute of Mathematical Sciences and Physics, University of the Philippines Los Baños, Los Baños 4013, Philippines
Abstract This study was aimed to determine the effect of methane gas concentration on the voltage response of tin oxide (SnO2) film. The sensing circuit of the tin oxide film was interfaced to a laptop computer throug an arduino microcontroller for data acquisition. Real time data table and graph can be visualized on the laptop screen during the gas sensing process. The sensor was enclosed in an airtight plastic jar container connected to a gas source and a water trap that maintained atmospheric pressure in the chamber. A mixture of 1% methane in helium was introduced into the chamber at a rate of 2 liters per minute (LPM) using a mass flow controller. The gas mixture was introduced intermittently at several stages. Each stage was followed by a standby stage during which there was no gas flow and the sensor was allowed to equilibrate with the gas mixture. It was observed that during the introduction of gas at each stage the voltage output of the sensor was increasing. During the standby stage there was no observed change in the voltage output as indicated by a flat response in the graph of voltage output versus time. The added quantity of gas can be computed from the flow rate and time duration of each stage. The incremental concentration of gas was also computed after each succeeding stage. The computed concentration in parts per million (ppm) was plotted with the measured voltage output per stage. Results showed a linear relationship between gas concentration and voltage output in the range of 3.75 to 7.8 ppm with a linearity of 0.99 and sensor sensitivity of 140 mV/1000 ppm. The sensitivity and linearity were 161 mV/1000 ppm and 0.98, respectively in the range 1000 to 9000 ppm. It is recommended to conduct more trials at different concentration ranges, different methane input mixture percentages, and different flow rates. © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 5th Thailand International Nanotechnology Conference (NanoThailand2016). Keywords: tin oxide, sensor, methane, gas concentration, gas response, sensitivity Introduction
* Corresponding author. Tel.: +63-049-536-6610; fax: +63-049-536-6610. E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 5th Thailand International Nanotechnology Conference (NanoThailand2016).
Emmanuel A. Florido et.al./ Materials Today: Proceedings 5 (2018) 11140–11143
11141
1. Introduction Methane gas is odorless and non-toxic but the danger lies in the possibility of asphyxiation in enclosed spaces due to its ability to replace oxygen [1] as well as combustion within 5 to 15% concentration in air at room temperature. It has a lifespan of several hours but its effectivity as a green house has qlobal warning potential which is twenty times that of carbon dioxide [2]. For the past several years efforts have been focused on developing semiconducting metal oxides for gas sensing and measurement for use in portable instruments [3,4]. Some of these materials ZnO, In2O3, Cd2SnO4 or SnO2 have exhibited good sensor characteristics like high sensitivity, fast response non-toxicity and stability [4,5]. Adsorption of oxygen on the surface of the metal oxides raises the resistivity of the surface due to immobilization of electrons as shown in Eq 1.
2O e O2 [300 C 1500 C]
(1)
Adsorbed oxygen can be removed from the surface by reacting with a reducing gas such as methane. The reaction shown in Eq. 2 results to a decrease in resistivity of the material [6]. CH4 4O(ads) CO2(air) 2H2O 4bulk
(2)
Tin oxide is a wide-band gap n-type semiconductor similar in electrical and gas sensing properties to zinc oxide. Different methods of fabrication have been studied including sol-gel method, spray pyrolysis, precipitation, and screen printing [6,7] This study was done to determine the response of a commercial tin oxide film to intermittent but successive increment in methane gas concentration in a single set of measurements in an airtight gas chamber in order to determine its capability as a preliminary study prior to laboratory fabrication of tin oxide films using various methods. The result would be helpful in optimizing fabrication parameters to extend the sensing range capability of the sensor to methane gas concentration. The commercial tin oxide film used has a theoretical range of 200 to 10,000 ppm. 2. Methodology The gas sensing set-up (Fig.1) was assembled using a commercial screen printed tin oxide sensor film connected to a circuit bridge interfaced to a computer through a microcontroller. The sensor was enclosed in a 1-liter airtight gas chamber of known volume. The chamber was kept airtight to maintain the total amount of oxygen inside the container as well as to contain the introduced gas mixture. Anaytical grade methane gas was introduced to the gas chamber using a programmable mass flow controller. Methane gas was mixed with pure nitrogen gas resulting to a concentration of 1% methane. The flow rate was set to 2 liters per minute (LPM). The gas mixture was fed into the gas chamber intermittently in stages. Each stage lasted for 20 seconds after which was gas flow was switched off. This was followed by an 80-sec resting period during which the sensor was allowed to equilibrate with the gas concentration. The added amount of the gas can be computed from the flow rate and time duration of each flow stage. The voltage response for each stage was detected by the microcontroller. The whole process lasted for a total of 2000 seconds resulting to an incremental increase in chamber gas concentration with corresponding voltage response increment. Real time data can be viewed on the computers display during gas sensing.
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Emmanuel A. Florido et.al./ Materials Today: Proceedings 5 (2018) 11140–11143
Fig. 1. Part of the gas sensing set-up showing the front and back of the mass flow controller (left and middle photo,respectively) and the microcontroller (right photo). 3. Results and Discussion The voltage response with time of tin oxide film sensor to an incremental increase in methane gas concentration is shown in Fig. 2. The horizontal part of the curve corresponds to the voltage output during 80-second stage described in the methodology during which the sensor was allowed to equilibrate with the gas. The vertical part corresponds to the voltage response when an additional amount of methane gas was introduced into the gas chamber. It can be observed that there is a decreasing voltage response at higher concentrations which can be attributed to the onset of saturation of the film surface when the adsorbed oxygen gets depleted from the surface. Even with replenishment of oxygen from the air inside the airtight container, the free oxygen supply eventually gets depleted. Fig. 3 shows the voltage response of the tin oxide sensor to methane gas concentration. The sensitivity and linearity of the sensor was 161 mV/1000 ppm and 0.98, respectively in the range 1000 to 9000 ppm. Another set of data was obtained for the range 3.75 to 7.8 ppm with a linearity of 0.99 and sensor sensitivity of 140 mV/1000 ppm.
Fig. 2. Voltage response with time of tin oxide gas sensor to intermittent increment in methane gas concentration.
Emmanuel A. Florido et.al./ Materials Today: Proceedings 5 (2018) 11140–11143
a
11143
b
Fig. 3. a. Voltage response of tin oxide gas sensor to increasing methane gas concentration in the range 1000 to 9000 ppm. b. Voltage response of tin oxide gas sensor to increasing methane gas concentration in the range 3.75 to 7.8 ppm. 4. Summary and Conclusion Results showed that the voltage response and sensitivy of a commercial tin oxide film to methane concentration were 161 mV/1000 ppm and 0.98, respectively in the range 1000 to 9000 ppm and 140 mV/1000 ppm.for the range 3.75 to 7.8 ppm with a linearity of 0.99. The sensing range given in the data sheet of the sensor is 300 ppm to 10000 ppm. The result of this study would help the researcher in the optimization of parameters and method in film fabrication to enhance the sensing range and sensitivity of the film for low-cost film fabrication. Acknowledgements The authors would like to acknowledge the Philippine Council for Industry, Energy, and Emerging Technlogy Research and Development, Department of Science and Technology for funding the project through which this study was conducted and the Institute of Mathematical Sciences and Physics, University of the Philippines for the laboratory facilities. References [1] P. Bhattacharyya, P.K. Basu, H. Saha, S. Basu, Sensors and Actuators B 124 (2007) 62–67. [2] Q. Schiermeier, Methane finding baffles scientists, Nature 439 (2006) 128(News). [3] S. Basu and P. K. Basu, J. Sens. Stud, Article ID 861968, (2009) 1-20. [4] P. Bhattacharyya, P.K. Basu, H. Saha, S. Basu, Sensors and Actuators B 124 (2007) 62–67. [5] H. Moon, S. Kim and W. Choi, Transactions On Electrical And Electronic Materials 13-2, (2012)106-109. [6] S. Chakraborty, A. Sen , H.S. Maiti, Sensors and Actuators B 115 (2006) 610–613. [7] L. De Angeles, R. Riva, Sensors and Actuators B 28 (1995) 25-29.