Chlorine Gas Sensor Research Articles

Chlorine gas sensors with high sensitivity using Mg-phthalocyanine thin films

High sensitivity chlorine (Cl 2) gas detection has been realized by newly developed gas sensors using Mg-phthalocyanine (MgPc) thin films. The MgPc thin film gas sensors exhibited an increase of conductivity with exposure to Cl 2 gas. The sensing properties of the MgPc thin film gas sensors were strongly dependent on the preparation conditions of MgPc thin films. The highest sensitivity for Cl 2 gas was obtained in the gas sensor using MgPc thin film prepared under the optimized preparation conditions; substrate temperature of 180 °C, evaporation temperature of 475 °C and film thickness of 40 nm. It was obtained that at operating temperature of 200 °C, the sensitivity of the MgPc thin film gas sensor linearly increased with the Cl 2 gas concentration in the range of 0.18–35 ppm.

Development and evaluation of a micro chemical gas sensor with an inner-circulation diffuser pump

A micro chlorine gas sensor with an inner-circulation diffuser pump is newly developed. The sensor based on electro-chemical principle, only has the size of one-tenth in comparison with the conventional one. The sensor consists of an air–liquid separation membrane, a PZT-driven diffuser pump and micro electrodes which were manufactured by micro machining. The inner-circulation is generated by driving the diffuser pump with trapped air working as a buffer, in order to preserve the condition of internal reagent. The properties of the sensor were evaluated by circulation rate of the pump, pressure-proof of the membrane, and responsibility to chlorine gas.

High sensitivity chlorine gas sensors using CdSnO 3 thick film prepared by co-precipitation method

This paper reports the gas-sensing properties to Cl 2 in CdSnO 3 thick film sensor. The raw powders of CdSnO 3 were prepared by co-precipitation method. The phase compositions and particle morphology were examined by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Effects of calcining temperature on gas-sensing properties, sensitivity ( R g/ R a) -operating temperature, and sensitivity-gas concentration were investigated. The results demonstrated that the CdSnO 3 sensor prepared by using the powder calcined at 900 °C showed high sensitivity to dilute Cl 2 at 250 °C. Especially, the CdSnO 3 sensor showed the sensitivity as high as 8 even to 0.1 ppm Cl 2.

High sensitivity chlorine gas sensors using CdIn 2O 4 thick film prepared by co-precipitation method

Gas-sensing properties to dilute Cl 2 have been investigated for CdIn 2O 4 thick film sensors prepared by co-precipitation method. Cadmium nitrate and indium nitrate were mixed in de-ionized water. The 0.1 M NaOH was added to the mixed solution. The co-precipitate obtained was washed, filtered, dried, and calcined at 600–900 °C for 4 h. The CdIn 2O 4 sensor prepared using the powder calcined at 600 °C showed high sensitivity ( S= R g/ R a) to dilute Cl 2 at 250 °C. In particular, the CdIn 2O 4 sensor showed the sensitivity as high as 1200 even to 0.2 ppm Cl 2. The crystal structure and surface morphology were examined by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively.

New chlorine gas sensor fabricated from chlorine anion- and scandium(III) cation-conducting solid electrolytes

A chlorine gas sensor was fabricated from monovalent Cl − anion- and trivalent Sc 3+ cation-conducting solid electrolytes. The sensor exhibited reproducible response, and time to reach 90% response was less than 3 min. Good linearity was observed between the sensor EMF output and the logarithm of the chlorine gas concentration, and the results obey ideal Nernst equation.

A new type of chlorine gas sensor with the combination of Cl− anion and Al3+ cation conducting solid electrolytes

A chlorine gas (Cl2) sensor was fabricated with the combination of monovalent Cl− anion and trivalent Al3+ cation conducting solid electrolytes. The time necessary to obtain a 90% response was less than several minutes, and also reproducible response was continuously demonstrated. An exact 1:1 relationship was observed between the sensor output and the logarithm of the chlorine gas concentration, and the relation exactly obeys the Nernst theoretical equation.

A chlorine gas sensor based on the combination of Mg 2+ cation conducting and O 2− anion conducting solid electrolytes with lanthanum oxychloride as an auxiliary electrode

A chlorine gas sensor was fabricated with the combination of divalent Mg 2+ ion conducting Mg 1−2x( Zr 1−x Nb x) 4 P 6 O 24 (x=0.15) solid solution and divalent oxide anion conducting stabilized zirconia with calcium-doped lanthanum oxychloride as an auxiliary electrode. The response time necessary for the attainment of 90% response was within several min and a rapid and reproducible response was continuously achieved. The relation between the sensor output and the logarithm of chlorine gas concentration was exactly 1–1 and obeys the Nernst theoretical relation.

Stability and sensing mechanism of high sensitivity chlorine gas sensors using transparent conducting oxide thin films

Newly developed semiconductor thin-film gas sensors with a high sensitivity for Cl2 gas using (Zn2In2O5)x–(MgIn2O4)1−x multicomponent transparent conducting oxide thin films are described. The sensitivity of (Zn2In2O5)x–(MgIn2O4)1−x thin-film gas sensors could be controlled by altering the composition. The highest sensitivity was obtained using (Zn2In2O5)0.6–(MgIn2O4)0.4 thin films prepared by magnetron sputtering; when operated at 300°C, they were able to detect Cl2 gas at a minimum concentration of 0.01 ppm. The resistivity, carrier concentration and Hall mobility of the thin-film sensors were measured under operating conditions using the van der Pauw method. An increase or decrease of resistivity in thin-film sensors resulted from an decrease or increase, respectively, of both carrier concentration and Hall mobility. Our experiments showed that carrier transport in thin-film gas sensors is dominated by grain boundary scattering. The adsorption of chlorine results in a free electron trap, the same as that produced by adsorption of oxygen. The sensitivity and the resistance of (Zn2In2O5)0.6–(MgIn2O4)0.4 multicomponent oxide thin-film gas sensors exhibited very stable long term operation in air containing high concentrations of Cl2 gas.

Investigations on the electrochemical behaviour of the phase boundary counter electrode/electrolyte of amperometric solid electrolyte gas sensors based on Ag β-alumina

Amperometric gas sensors based on solid silver ion conductors, e.g. chlorine gas sensors, usually contain silver electrodes as counter electrodes or common counter/reference electrodes. The electrochemical kinetic behaviour of the system Ag electrode/Ag β-alumina solid electrolyte has been investigated in the temperature range between 275 and 375°C. The measurements have been carried out using different types of solid-state electrochemical cells. By appropriately combining the results of quasi-stationary galvanostatic and impedance measurements received from the different cells, the resistance behaviour of the electrode reaction occurring at the phase boundary Ag/Ag β-alumina has been evaluated. This behaviour is described in good approximation by an ohmic resistance R* referred to the geometrical area of the phase boundary, the value of which is given by an equation as a function of the temperature. Typical values are R*=264 Ω cm2 (quasi-stationary) and R*=143 Ω cm2 (100 kHz) at 275°C, and R*=97 Ω cm2 (quasi-stationary) and R*=71 Ω cm2 (100 kHz) at 375°C.

SnInO-based chlorine gas sensor

The dependence of the resistance of InSnO (ITO) layers on a small amount of chlorine gas in air is studied here. The chlorine-sensitive ITO films have been fabricated by reactive sputtering of In and Sn from a metal alloy target (In and Sn in the proportion 0.94:0.06 by weight) on silicon substrates. It is found that the chlorine gas in the ambient atmosphere makes the ITO resistance increase. The dependence of the resistance on chlorine concentration tends to saturate at concentrations above 3 ppm. The sensitivity maximum is observed at 300 °C. The addition of Pt significantly increases the sensitivity and reduces the temperature of the sensitivity maximum. The response time is ≈ 150 s at 90 °C and decreases exponentially with increasing temperature. The results obtained are typical for gas sensors based on tin oxide or ITO and can be explained in terms of electron localization at surface adsorption centres dominated by chlorine molecules and the electric transport features at the polycrystalline film grain boundaries.

Limiting-current chlorine gas sensor based on β″-alumina solid electrolyte

A new type of limiting-current solid-state ionic gas sensor for gases that may not be transferred in solid electrolytes is presented. The sensor is based on the reaction of the gaseous species with the electroactive component under the condition of limited access of the gas by a kinetic barrier. The technique allows the presently available fast solid alkali metal, silver and copper ion conductors to be used at ambient and moderately increased temperatures. A linear relationship between the electrical current and the gas concentration is observed for chlorine gas. The device may be operated at lower temperatures than the potentiometric chlorine gas sensor, is sensitive to low partial gas pressures and may also overcome problems of cross-sensitivity. Sensors for gases other than chlorine may be based on the same principle.

Limiting-current type surface modified gas sensor based on ??-alumina fast solid ionic conductor

A new type of limiting current solid state ionic gas sensor is presented. The sensor is based on the reaction of the gaseous species with the electroactive component under the condition of limited access of the gas by a kinetic barrier. This allows one to employ the available fast solid alkali metal, silver and copper ionic conductors at ambient, and moderately increased temperatures. Theoretical considerations are presented and compared to experimental results of this type of limiting-current surface modified solid state electrochemical chlorine gas sensors. A linear relationship between the electrical current and the gas concentration is observed. The device may be operated at low temperatures, is sensitive to low partial gas pressures and may also overcome problems of cross-sensitivity. Sensors for gases other than chlorine may be based on the same principles.

Selectivity, response time and chemical aspects of gas sensitive AgCl layers for gas sensors

The cross sensitivity of potentiometric solid electrolyte chlorine gas sensors based on AgCl modified electrodes against H 2S is caused by a kinetic interaction under metastable formation of Ag 2S. The thermodynamically more stable AgCl is subsequently formed without an influence on the cell voltage. The response of the sensor to changes in the chlorine partial pressure appears to be rate-determined by the chlorine transfer across the interface gas/AgCl.