Combustion Monitor Sensor Based on Tin Dioxide

Ihokura, Kousuke; Murakami, Nobuaki

doi:10.5796/kogyobutsurikagaku.51.672

Cited by 1 publication

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“…Ihokura (9) observed similar results in the variation of gas sensitivity with surface area of SnO2 in that with CO and isobutane there was an increase of sensitivity with increase of surface area. With methane, on the other hand, he observed an increase of sensitivity with a decrease of surface area.…”

Section: Table II Analysis Of Chloride Ion Content After Two Years St...mentioning

confidence: 57%

The Effects of Residual Chlorides on Gas Sensing Characteristics of Tin Oxide Gas Sensors

Son

Kwon

Roberts

1991

J. Electrochem. Soc.

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In an investigation on carbon monoxide sensors, the effect on electrical conductivity of residual chloride content of tin oxide materials have been studied to provide information relating to the sensitivity and selectivity in the detection of carbon monoxide. The starting material was a-stannic acid, precipitated in the reactidn between tin chloride and ammonia, which was calcined at 650~ for 2 h. The lower the chloride content of the original dried precipitate, the greater was the surface area and the greater was the sensitivity to carbon monoxide of the calcined material. Conversely, the higher the chloride content, the smaller was the surface area and lower the sensitivity to carbon monoxide and higher the sensitivity to propane and methane. The residual chloride content in the calcined material, whatever the amount of chloride in the original precipitate, was invariably about 0.2 weight percent.The high conductivity of SnO2 is believed to arise from the presence of native defects, i.e., oxygen vacancies and/or interstitial tin ions associated with the nonstoichiometric composition. The effect of chloride in oxide has been studied mainly in respect of films. In the case of pure SnO2 films, i.e., undoped material but containing residual chlorides, conductivity has been attributed to a combination of chloride ions and oxygen vacancies remaining from the incomplete decomposition of SnC14 and the incomplete oxidation of the film to stoichiometric SnQ (1-4). Most of the investigations concerned with residual chloride deal with the effect of the impurity on electrical properties. In the present work, however, the emphasis has been on the different physical properties of heat-treated materials, differences apparently related to the chloride content of the precipitates.Selectivity to different gases appears to be associated with different physical properties, i.e., the grain size and surface area of the sensing materials which, whatever the chloride content in the original precipitate, invariably contained the same amount of chloride after heat-treatment. The most useful analytical data on chloride in SnO2 was that on a film made by vapor deposition from SnC14 (5). According to this work, the lowest residual chloride content, 0.3 weight percent (w/o), was established after heat-treatment in hydrogen; it was 0.8-1.2 w/o following that treatment in nitrogen or oxygen. This may be compared with the residual content of 0.2 w/o after heat-treatment found in the present work. This chloride content, 0.2 w/o, justified a comparison in the electrical properties between the film and the sintered materials of the present work.The effect of operating temperature, residual chloride contents, and calcination atmosphere on sensitivity to CO are examined. Measurements on propane and methane were also carried out for comparison purposes.

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Section: Table II Analysis Of Chloride Ion Content After Two Years St...mentioning

confidence: 57%