Takeshi Nakahara

A carbon dioxide gas sensor based on solid electrolyte for air quality control

Abstract A practical CO 2 gas sensor for air quality control is developed by using a combination of a Na 3 Zr 2 Si 2 PO 12 (NASICON) as a solid electrolyte and Li 2 CO 3 as a carbonate phase. The sensors electromotive force (emf) shows a linear relationship with the logarithm of CO 2 concentration. Zeolite is chosen as a filter material in order to minimize the effect of interfering gases on the sensors emf and shows very little sensor response deterioration to CO 2 . Under continuous energizing, both the emf and a change in the emf (defined as Δemf) are stable over a period of 2 years. However, after the sensor is exposed to a high humidity atmosphere in an unpowered state, the emf decreases, but Δemf stays constant. A new data selection method for renewing the standard of the emf is investigated in order to monitor CO 2 concentration using Δemf. The output of the CO 2 monitor corresponds to a conventional non-dispersive infrared (NDIR) analyzer.

Titania NOx sensors for exhaust monitoring

Abstract Oxide semiconductors have been examined to develop NOx sensors for exhaust monitoring. Titania doped with trivalent elements, such as Al3+, Sc3+, Ga3+ or In3+, has a good sensitivity and selectivity to NO between 450 and 550 °C, and shows rapid response. A sensor probe for monitoring exhaust NOx has been fabricated. Many kinds of interference gases, such as C3H6, CO and SO2, have been found to have only a slight influence on the sensor response to NO. The influence of O2 and H2O is also negligible, except for the cases of 0% H2O and fuel-rich conditions. In accordance with these results, the sensor probe operates satisfactority in the exhaust gas of various combustion conditions without interference from the various kinds of gas species in the exhaust gases.

Polyaddition of bifunctional spiro orthoesters with bifunctional acid chlorides accompanying double ring-opening isomerization

Polyaddition of bifunctional spiro orthoesters (SOEs) with bifunctional acid chlorides was examined to develop zero-shrinkage polymerization. The polyaddition afforded the corresponding polyether-esters by repeating the addition reaction accompanying the double ring-opening isomerization of the SOE moiety in a manner similar to the reaction of monofunctional SOEs with acid chlorides. The polyaddition accompanied a slight shrinkage or expansion in volume.

Addition reaction of spiro orthoesters with electrophiles: A model reaction for the development of novel polyaddition accompanying ring‐opening isomerization

The addition reaction of spiro orthoesters (SOEs) with electrophiles accompanying ring-opening isomerization was investigated as a model reaction for polyaddition of bifunctional SOEs with bifunctional electrophiles. Among several electrophiles such as carboxylic acids and carboxylic anhydrides, acid halides showed particularly high reactivities to SOEs. An equimolar reaction of SOEs with acid chlorides took place selectively, leading to the corresponding 1: 1 adducts. SOEs with seven-membered cyclic ether rings-1,4,6-trioxaspiro[5.6]undecane derivatives-showed higher reactivities than SOEs with six- and five-membered cyclic ether rings. The reaction accompanied zero shrinkage in volume.

Ring-opening isomerization addition reaction of bicyclo ortho esters with acid chlorides. Model reaction for development of a novel polyaddition reaction accompanying ring-opening isomerization

The reaction of bicyclo ortho esters (BOEs) with acid chlorides was examined. The BOEs readily reacted with acid chlorides to give the corresponding adducts via ring-opening isomerization. The order of the reactivities of the acid chlorides is as follows, sebacoyl chloride > adipoyl chloride > succinyl chloride and 1,3,5-benzenetricarbonyl chloride > isophthaloyl chloride ≥ benzoyl chloride. It is considered that the ring-opening isomerization of the BOEs with acid chlorides proceeds by a similar mechanism as that of the homopolymerization of the BOEs.

Polyaddition of bifunctional bicyclo ortho esters with acid chlorides accompanying double ring‐opening isomerization

Polyaddition of bifunctional bicyclo ortho esters (BOEs) with bifunctional acid chlorides were carried out to afford quantitatively the corresponding polymers via a double ring-opening isomerization process. Polyaddition of bifunctional BOEs with a trifunctional acid chloride, 1,3,5-benzenetricarbonyl chloride. also proceeds satisfactorily to yield crosslinked polymers quantitatively. The mixtures of BOEs and acid chloride show zero to low shrinkage (0.6%) during the polyaddition reaction.

Limiting current type oxygen sensor using new rate-determining method

Abstract A limiting current type oxygen sensor in which the inflow of oxygen is controlled by an electrochemical method, that is a solid electrolyte cell instead of a physical diffusion controlled method such as pores in the usual sensors, has been developed. As a result of a study on the mechanism of the sensor by using model sensors, it is suggested that the limiting current of the sensor is determined by the resistance of the cell for controlling the inflow of oxygen. A practical type oxygen sensor was also fabricated and the fundamental properties were examined. The sensor exhibited good limiting current characteristics over a wide oxygen concentration range. The output current of the sensor was scarcely affected by interfering gases such as CO and H 2 , and by the temperature and absolute humidity of the surrounding atmosphere. The 90% response time of the sensor was about 7 s.

Overview of Gas Sensors for Environmental Use

Publisher Summary This chapter presents an overview of gas sensors for environmental use. The needs of gas sensing for controlling air pollution can be classified in three cases. The first one is for grasping the actual circumstances of the air pollution, for example, understanding the details of the generation and consumption of CO2 and CH4 on global scale. The second is the routine watching of pollutant gases in the atmosphere and in combustion exhaust gases. For this purpose, conventional analytical instruments are used at present; however more simple and easy methods are desired to increase the number of monitoring stations and emission sources. The third need of gas sensing is for closed-loop control of combustion engines, boilers and furnaces. The application of oxygen sensors to the feedback control of the air-fuel ratio of automobile engines is the only one example in which gas sensors are widely used at present for the use of closed-loop control. Conventional analytical methods for environmental use have been established for the routine watching of pollutant gases in the atmosphere and in combustion exhaust gases. Equipments based on various analytical methods have been put into practice and are widely used in the field. Classifying various kinds of these methods, there are three main types—that is, optical type which utilize the change of absorption spectrum or luminescence spectrum of gas, chemical analysis based on the chemical reaction of an absorbed gas with a specific reagent, and gas chromatography which use a variety of detectors.