Kenzo Fukuda

A fiber-optic evanescent-wave hydrogen gas sensor using palladium-supported tungsten oxide

A new optical-fiber hydrogen sensor has been developed. The sensor utilizes the absorption change of the evanescent field in the clad region. The platinum- or palladium-supported tungsten oxide was used as sensing media. Two different approaches were adopted for the fiber fabrication. One used Pd/WO3 containing silicone resin as the clad. The other utilized the sol–gel process to form a thin Pd/WO3 clad. In the presence of hydrogen, strong evanescent-wave absorption was observed as a result of the formation of tungsten bronze. The sensor sensitively and immediately responded to hydrogen. It was found that the characteristics of the sensor were easily controlled by the amount of catalysts. The sensor developed in this study has potential to measure the spatial distribution along the fiber line, unlike the traditional hydrogen sensors that measure the concentration of a certain spatial point.

Re-activation of an amperometric organophosphate pesticide biosensor by 2-pyridinealdoxime methochloride

Abstract Inhibitions and re-activation characteristics of a biosensor by the organophosphate pesticides were investigated. The amperometric enzyme sensor co-immobilized on a platinum electrode by crosslinking was fabricated. Inhibition of the biosensor by dimethyl 2,2-dichlorovynyl phosphate (Dichlorvos, DDVP) as a model organophosphate pesticide was tested. The relative inhibition parameter (RI) was proportional to the concentration over a wide range. It was found that a nearly reversible inhibition process was observed if the inhibition is weak. However, irreversibility was appeared when the strongly inhibition took place. In this case, only 2-pyridinealdoxime methochloride (PAM) successfully regenerated the enzyme activity. PAM treatment guaranteed almost stable recovery rate and sensitivity. The results clarified that proposed re-activation procedures could realize inexpensive and reliable continuous monitoring of organophosphate pesticides.

An automated car ventilation system

Abstract A prototype of an automated car ventilation system that inhibits the intake of exhaust gas was constructed to explore suitable choices and application methods of gas sensors. The requirements for the gas sensors were discussed and the sensing characteristics of candidate sensors were investigated. The system adopted three metal-oxide semiconductor-type gas sensors. A CO/HC (hydrocarbon) gas sensor and an NO 2 sensor were utilized for the detection of exhaust fume in outside-air, and an odor sensor for the monitoring of inside-air. The sensing characteristics of these sensors, including humidity effects were investigated. It has been found that the humidity interference is not negligible, and computer algorithm to cope with the interference was presented. The prototype system satisfactorily shut out exhaust-containing air when the pollution level was high. The data collected on highways indicated that the wind efficiently reduces pollution level.

The interference elimination for gas sensor by catalyst filters

Abstract The method to eliminate alcohol interference for CO gas sensor using oxide semiconductor is explored. Some oxidizing agents and reducing agents were tested as the filtering materials. Nafion was found to be the most effective. This property was improved by the treatment to form the Nafion into complete H-type before measurement. The elimination capability is correlated with the acidities of the filtering materials.

THE PARTIAL OXIDATION OF METHANE TO METHANOL WITH NITRITE AND NITRATE MELTS

Abstract The effect of reduced oxygen species on the partial oxidation of methane to methanol was examined with nitrite melts. The experimental results support the suggestion that the formation of methanol or C2 compounds depends on different reduced oxygen species, as observed in our previous work using nitrate melts. It has been suggested that the partial oxidation of methane proceeds to CH3OH or C2 compounds via parallel pathways. This suggestion was verified by increasing the oxygen concentration to carry out the partial oxidation of methane in 25 mol% NaNCO3 -75 mol% KNO3 melts. A methanol selectivity of 8.2% and a methanol yield of 0.43% were observed with CH4/O2 = 15/1 at 575 °C, whereas with CH4/O2 = 7/1 methanol selectivity and yield increased to 23.7% and 1.1%, respectively. The results further confirm the contribution of the superoxide ion O2- on methanol formation.

Nitrate-sensitive corroding metal electrode

Abstract The electrode potential of Devardas alloy in phosphate solutions buffered at pH = 12 containing different amounts of nitrate ions has been measured. A proportional relation between the electrode potential and the concentration of nitrate ions [NO3−] is observed when [NO3−] is less than 40 mg 1−1. When [NO3−] is larger than 200 mg 1−1, log[NO3−] is linearly related to the electrode potential, with a slope of about 120 mV decade−1 up to [NO3−]=10 000 mg 1−1. The presence of chloride sulfate and perchlorate ions has almost no effect on the above relations. The sensitivity and selectivity of the above metal electrode exceed those of nitrate-ion-selective electrodes. Since the electrical impedance of the corroding metal/solution interface is much lower than that of other methods, the potential measurement should be easier.

Application of bistable nature of metal surface in aqueous solution to an oxygen sensor

A new oxygen sensor is proposed. It utilizes the electrochemically bistable nature of an iron surface in neutral buffer solutions. Iron placed in neutral solutions takes two discrete and stable states. The electrode potential is about -0.75 V (always versus SCE) in one state and about -0.25 V in the other. Dissolved-oxygen concentrations, as well as pH, govern the surface states. When the oxygen concentration and pH are low, the electrode stays at the former potential. The electrode potential indicates whether the oxygen concentration is above or below a threshold value. The exact dissolved-oxygen concentration can be determined from the transient time of an externally polarized electrode.

THE PROMOTIVE PROPERTIES OF ALKALI METAL NITRATE MELTS FOR THE PARTIAL OXIDATION OF METHANE TO METHANOL

Abstract (Na, K)NO3 melts of various ratios were used as promoters for the partial oxidation of methane to methanol. Experiments were performed in a flow reactor system under atmospheric pressure and at various temperatures in the range of 525-600 °C. The influence of reaction temperature, melt composition, and reduced oxygen species on methane conversion and methanol selectivity were investigated systematically. The major reaction products were CH3OH, CO, CO2, and trace amounts of C2H6 and C2H4. A methane conversion of 1.8-12.4% and a methanol selectivity of 0.4-14.1% were obtained under these reaction conditions. Binary melts could achieve higher methanol selectivity than a single melt. The amounts of reduced oxygen species O2- and O22-were estimated from thermochemical data according to the ion equilibrium in molten nitrates. The promotive effect of nitrate melts was confirmed and the results indicate that superoxide O2- plays an important role for methanol formation.