Impedancemetric gas sensor based on Pt and WO3 co-loaded TiO2 and ZrO2 as total NOx sensing materials

Pt-loaded metal oxides [WO₃/ZrO₂, MO_x/TiO₂ (MO_x = WO₃, MoO₃, V₂O₅), WO₃ and TiO₂] equipped with interdigital Au electrodes have been tested as a NO_x (NO and NO₂) gas sensor at 500 °C. The impedance value at 4 Hz was used as a sensing signal. Among the samples tested, Pt-WO₃/TiO₂ showed the highest sensor response magnitude to NO. The sensor was found to respond consistently and rapidly to change in concentration of NO and NO₂ in the oxygen rich and moist gas mixture at 500 °C. The 90% response and 90% recovery times were as short as less than 5–10 s. The impedance at 4 Hz of the present device was found to vary almost linearly with the logarithm of NO_x (NO or NO₂) concentration from 10 to 570 ppm. Pt-WO₃/TiO₂ showed responses to NO and NO₂ of the same algebraic sign and nearly the same magnitude, while Pt/WO₃ and WO₃/TiO₂ showed higher response to NO than NO₂. The impedance at 4 Hz in the presence of NO for Pt-WO₃/TiO₂ was almost equal at any O₂ concentration examined (1–99%), while in the case of Pt/WO₃ and WO₃/TiO₂ the impedance increased with the oxygen concentration. The features of Pt-WO₃/TiO₂ are favorable as a NO_x sensor that can monitor and control the NO_x concentration in automotive exhaust. The effect of WO₃ loading of Pt-WO₃/ZrO₂-based sensor is studied to discuss the role of surface W-OH sites on the NO_x sensing.     

Stress-Induced Resistivity Anomaly in Semiconducting Barium Titanate Ceramic Wire

Thin, semiconducting BaTiO₃ ceramic wires prepared in the present study exhibited reversible stress-induced, nonlinear current—;voltage characteristics across several grain boundaries. A remarkable change in resistance with the application (by the three-point bending method) of only ∼1% tensile deformation indicated that the BaTiO₃ wires may have potential as stress-sensing devices. Resistance in the BaTiO₃ wires bot increased and decreased with increasing tensile stress parallel to the electric fields, far below the ferroelectric transition temperature, T _c; in Sr-substituted wires near T _c, on the other hand, resistance only increased. Detailed studies of the patterns and fluctuation of polarization at grain boundaries could be meaningful, because stress-sensing characteristics may be induced by changes in the relative angle between polarization vectors of adjacent grains.     

Zeta potential measurement on the surface of blue-green algae particles for micro-bubble process.

Any kind of blue-green alga produces metabolites of musty substances and toxins. Therefore, it is necessary to remove the blue-green algae, and processing also including nutrient removal is desired for the water quality improvement of eutrophic lakes. The purpose of this study has been to investigate the possibility of a flotation system using a hybrid technique (chemical compounds and electrostatic bridge) applied to raw water containing phytoplankton with high pH of water, and to examine the zeta potential value of phytoplankton surface and the removal efficiency for phytoplankton, ammonia, nitrogen, and phosphoric acid.The results were as follows: firstly, zeta potential of M. aeruginosa particles was observed to achieve charge neutralization on their surface by adhesion of magnesium hydroxide precipitation with increasing pH. Secondly, maximum removal efficiency concerning chlorophyll-a was observed as 84%, and this efficiency was obtained in the condition of pH > 10, and magnesium hydroxide precipitation was observed. Thirdly, in the pH condition that the maximum removal efficiency of chlorophyll-a was obtained, the removal efficiency and the amount of decrease of NH(4)-N and PO(4)-P before and after the change of pH values were observed as 6.7% (0.04 mg-P/L) and 63.6% (0.07 mg-N/L), respectively.     

Surface temperature of Pd/C catalyst under microwave irradiation in dechlorination process of PCBs

In recent years, a new effective method of processing for polychlorinated biphenyls (PCBs) has been developed: It enables PCBs to become harmless by dechlorinating them using a 2.45 GHz microwave (MW). Compared with conventional thermal heating, MW processing hardly produces any harmful byproduct materials, and has high reaction velocity. To investigate such promotion of chemical reaction by MW irradiation, the surface temperature of the catalyst is measured by an infrared camera just after the irradiation by MW. It is recognized that there are some heated regions on the catalyst and the temperature is not uniform. It is natural to say that chemical reaction is promoted well on such a heated region. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Dielectrics loss of PCBs leading to microwave heating

A new effective processing for polychlorinated biphenyls (PCBs) has been recently developed. PCBs become harmless by dechlorination using 2.45 GHz-microwave (MW). To investigate such chemical reaction by MW irradiation, the dielectric loss of pure PCBs solutions and an isomer mixture in MW band is measured. Some PCBs and isopropyl alchol, added as a source of hydrogen supply have high dielectric loss in MW band. This suggests that MW heats PCBs and isopropyl alchol, and then the temperature of the solvent consisting mainly of insulating oil rises by the thermal conduction. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

On-board digital signal processing technologies for present and future SCPC systems

Devices and architectures for on-board SCPC (single channel per carrier) multi-carrier demodulators suitable for use in satellites to be launched between the present and the year 2000 are discussed in the light of trends in the development of device technology towards lower on-board weight and power consumption. It is shown that at the present time (equivalent to about 1990 for on-board use). The choice of demodulation scheme depends on the number of channels available for regeneration on board the satellite. The total weight and power consumption for several suitable on-board multicarrier demodulation schemes are predicted for 1990, 1995 and 2000, as functions of the number of channels to be regenerated.     

CO2 absorption and desorption of Bi2O3-La2O3 powders prepared by mechanical synthesis

In order to obtain CO₂-absorbents to eliminate CO₂ concentration locally, Bi₂O₃-La₂O₃ mixed powders were prepared by mechanical alloying (MA) method using a planetary ball-milling machine. CO₂-absorption and desorption properties were checked by TG-DTA for the obtained powder samples. As a result, the sample shown by (Bi₂O₃)_1−x(La₂O₃)_x [x≤0.50] was found to form α-Bi₂O₃-solid solution with repeated CO₂-adsorption and desorption around 400- 500 °C. Absorbed and desorbed CO₂ contents varied with MA time: the 72 h MA’ed sample had a larger CO₂ content than the 24 h MA’ed sample. The performance depended on the sample composition, and (Bi₂O₃)_0.70(La₂O₃)_0.30 was found to have the highest performance in the present system.     

Temperature Dependence of Anelastic Deformation in Polycrystalline Silicon Nitride

The influence of grain-boundary sliding on the evaluation of the apparent Young's modulus and plastic-deformation (flow) stress was investigated by bending tests for two types of silicon nitrides sintered with Y₂O₃-based additives The apparent Young's moduli measured at high temperatures are consistent with those predicated from a theory based on polycrystalline anelasticity due to grain-boundary sliding. The temperature dependence of the critical bending stress for the onset of plastic deformation shows viscoplastic properties of the interglanular glass. The ductile-to-brittle transition of fracture is discussed by the bending strengths normalized by the measured Young's modulus.