Masuo Nakagawa

A new chemiluminescence-based sensor for discriminating and determining constituents in mixed gases

Chemiluminescence (CL) is observed during the catalytic oxidation of various combustible vapours on layer of aluminium oxide (λ-Al2O3) powder in air. A new chemiluminescence-based sensor has been prepared applying this phenomenon. The working mechanisms of the sensor is based on the production of chemiluminescent species, e.g., formaldehyde and carbon, as intermediate species of catalytic oxidation of the vapours. Three methods of detection by the sensor are demonstrated: (i) continuous determination and discrimination of a vapour by CL spectrum measurements; (ii) determination and discrimination of a vapour by CL glow-curve measurements; and (iii) separate determination of constituents in mixed vapours. Ethanol, butanol, acetone, n-butyric acid and xylene are determined by the sensor. The lower limit of the vapours is the order of 1 ppm or less, except for xylene.

A new method for recognizing organic vapor by spectroscopic image on cataluminescence-based gas sensor

Abstract ‘Cataluminescence’ is a kind of chemiluminescence emitted during catalytic oxidation of combustible gas. This paper describes a new method using a system which can measure spectroscopic images on a cataluminescence-based sensor to discriminate and determine concentrations of organic vapors in air. Using this equipment, we can measure continuously the image of ‘cataluminescence’ intensity, which reflects the type and concentration of organic vapor, as a function of wavelength and catalyst temperature. Not only the difference between alcohol and ketone, but also the kind of alcohol, e.g. ethanol and butanol, can be distinguished and determined quantitatively by means of this system.

Analytical detection system of mixed odor vapors using chemiluminescence-based gas sensor

Abstract A chemiluminescence(CL)-based gas sensor made of γ-Al2O3 emits CL during catalytic oxidation of a combustible odor vapor. The CL intensity is proportional to the concentration of ethanol or acetone vapor in air. The algebraic sum rule is applicable to the CL intensities by the mixed gas of these two kinds of vapors, when the sensor is heated above 450°C. The CL intensities are measured in periodic temperature cycles between 650 and 450°C. The concentrations of vapor components can be detected analytically by measuring total CL intensities during the high and low temperatures for air containing mixed vapors of various concentrations of ethanol below 400 ppm and acetone below 200 ppm.

High sensitive hydrocarbon gas sensor utilizing cataluminescence of γ-Al2O3 activated with Dy3+

A new method using cataluminescence (CTL)-based gas-sensor detecting hydrocarbon in air is proposed. CTL is a kind of chemiluminescence (CL), which is emitted during catalytic oxidation of organic vapors, e.g., ethanol and acetone. By depositing Dy on the γ-Al2O3 catalyst, we measured the extra CTL spectrum due to Dy3+ during the catalytic oxidation of hydrocarbon gas, while no such CTL was emitted from the γ-Al2O3 catalyst without Dy. By investigating the luminescence mechanism of Dy, the existence of active species produced in a course of catalytic oxidation to excite Dy directly was clarified. The CTL-based gas-sensor using γ-Al2O3 activated with Dy3+ has high sensitivity and linear characteristic. The detection limit of iso-butane in air is 0.2 ppm.

Cataluminescence-Based Gas Sensors

Cataluminescence (CTL) is chemiluminescence emitted in a course of catalytic oxidation. Since 1990, the present authors and coworkers have observed CTL during the catalytic oxidation of various organic vapors in air. This phenomenon has been applied to the CTL-based sensors for detecting combustible vapors. THE CTL response is fast, reproductible and proportional to the concentration of the combustible vapors of ppm orders in air. Based on two types of models of the CTL, the relationship between the CTL intensity and the rate of catalytic oxidation have been investigated analytically. In this article, the effects of catalyst temperature, gas flow-rate and gas concentration on the CTL intensity are demonstrated. Finally, various types of sensing system using the CTL-based sensor are proposed. The results of discrimination and determination of more than ten types of vapors of various concentrations are shown.

Discrimination and determination of gases utilizing adsorption luminescence

Thermoluminescence caused by adsorbates (adsorption thermoluminescence) appears in the process of heating Al2O3 powder that had previously adsorbed the vapour of an organic solvent, such as ethanol or acetone, at room temperature. The profiles of the thermoluminescence spectrum and glow curve depend on the kind of adsorbed vapour. The total amount of emitted light L depends on the concentration of the vapour in air, and L increases with an increase in the duration of adsorption. The adsorbates that act as the origin of the thermoluminescence are accumulated through a Langmuir-type adsorption process of very low activation energy (about 0.02 eV). These characteristics of the adsorption thermoluminescence enable us to discriminate and determine very low concentrations of these vapours. For example, L is proportional to the concentration of acetone vapour below 20 ppm for an adsorption time of 10 min, and the 1 ppm of vapour can be measured with good reproducibility.

Anomalous temperature dependence of the electrical conductivity of zinc oxide thin films

Abstract The temperature dependence of the conductivity of Ga-doped ZnO thin films was examined in humid and dry atmospheres. The conductivity initially increases to the maximum (range 1) and then decreases to the minimum (range 2) and again increases (range 3) in the heating run under humid air atmosphere. The subsequent cooling reduces the conductivity to less than that for the heating run. The extent of the reduction becomes large as the cooling rate increases. The extrema character in the conductivity versus temperature curves does not disappear under nitrogen gas atmosphere provided it is humid. On the other hand, the conductivity in the ranges 1 and 2 decreases so significantly that the extrema character disappears in the driest air as possible. These behaviors are explained by assuming that the dissociatively chemisorbed states of water vapor act as electron donors and desorb at the higher temperature, and the desorption as well as the chemisorption require a time for attaining equilibrium. With this in view, a theoretical analysis is given of semiconducting films thinner than the depletion boundary layer thickness, and numerical curves fitting to the experimental results are obtained. The heat of chemisorption of nonionized water q ° is 1.35 eV and the energy levels of water chemisorption donors and oxygen chemisorption acceptors are at 0.66 and 0.59 eV below the conduction band edge, respectively.

Continuous determination and discrimination of mixed odour vapours by a new chemiluminescence-based sensor system

Abstract A gas sensor that utilizes chemiluminescence (CL) during the catalytic oxidation of odour vapours on a sintered aluminium oxide (γ-Al 2 O 3 ) layer is proposed. A new technique is applied to determine continuously the concentration of each constituent in a mixed vapour by a single CL-based sensor. The sensor is heated and cooled periodically in a temperature cycle between 200 and 740 °C at constant heating and cooling rates of ±9 °C s −1 . By measuring the total CL intensities in the heating and cooling courses, we can obtain the concentration of each constituent for a mixed vapour of ethanol and acetone in air. The lowest detection limit of the concentration of these vapours is of the order of 1 ppm.

Red thermoluminescence of volcanic glass fractions from tephras

Abstract The thermoluminescence (TL) spectra of the volcanic glass fractions from tephras collected in Japan were investigated by a TL time-resolving spectroscopy system. As a result, a broad, intense and red emission band at 620 nm with a glow peak at 330°C was obtained from the glass fractions and it was found to be grown by γ irradiation. Based on the correspondence between the TL emission spectra of the glass fractions and those of quartz and plagioclase crystals, we have attributed the high TL intensity of the glass fractions to quartz and plagioclase microcrystals included in the glass shards. In particular, the red TL of quartz is so strong that even a small content of quartz microcrystals in glass shards can be detected. Therefore the red TL of volcanic glass fractions will be applied to the dating.

Photoluminescence and Thermoluminescence of MgSO4, CaSO4, SrSO4 and BaSO4 Powder Phosphors Activated with Tb3+

The photoluminescence (PL) spectra and optical excitation spectra of phosphors were obtained at temperatures of 10, 80, 300 and 370 K. Many narrow bands were observed in both the spectra, and were attributed to the transitions within the 4f8 electron configuration in Tb3+. The quenching of the 5D3 emission series assigned to the transitions 5D3→7FJ (J=6,5,4,3,2,1 and 0) is characteristic of the PL emission spectra. The thermoluminescence (TL) glow curves, TL emission spectra and TL fading properties of the same samples were also observed. The quenching of the 5D3 emission series is not observed in the TL emission spectra. The large differences between the features of the TL emission spectrum and the PL emission spectrum are contradictory to the conventional model of the TL emission process. The addition of Na+ to the phosphors as a charge compensator is effective in enhancing the PL efficiency, but causes TL fading because of the shallow electron traps due to Na+.