Potentiometric-Type Gas Sensor Using MgFe2O4 Sensing Electrode for Detection of Hydrocarbon Based on Carbon Number.

Hydrocarbon (HC) monitoring is necessary for safe and effective operations in industries such as petroleum and gas. In this study, total hydrocarbons can be detected by using yttria-stabilized zirconia (YSZ)-based potentiometric-type gas sensor using MgFe2O4 sensing electrode (SE). The sensor was found to generate a similar response magnitude to those of hydrocarbons that have the same carbon number, irrespective of the type of carbon bond (total hydrocarbon detection). Aside from being capable of detecting total hydrocarbons sensitively and selectively with rapid response time, the sensor using MgFe2O4-SE also exhibited a linear relationship between sensor responses and carbon number. In addition to that, the developed sensor showed a logarithmically linear relationship between sensor responses and HC concentration in the range 20-700 ppm. These sensing characteristics were confirmed to be reproducible, and sensor responses toward HC were found to be repeatable and gradually decreased with increasing in O2 concentration in the range of 3-21 vol %.

Significant Enhancement of Piezoelectric Response in AlN by Yb Addition.

This study employs first-principles calculations to investigate how introducing Yb into aluminum nitride (AlN) leads to a large enhancement in the material's piezoelectric response (d33). The maximum d33 is calculated to be over 100 pC/N, which is 20 times higher than that of AlN. One reason for such a significant improvement in d33 is the elastic-softening effect, which is indicated by a decrease in the elastic constant, C33. The strain sensitivity (du/dε) of the internal parameter, u, is also an important factor for improving the piezoelectric stress constant, e33. On the basis of mixing enthalpy calculations, YbxAl1-xN is predicted to be more stable as a wurtzite phase than as a rock salt phase at composition up to x ≈ 0.7. These results suggest that Yb can be doped into AlN at high concentrations. It was also observed that the dielectric constant, ε33, generally increases with increasing Yb concentrations. However, the electromechanical coupling coefficient, k332, only increases up to x = 0.778, which is likely because of the relatively lower values of ε33 within this range.

Polarity Inversion of Aluminum Nitride Thin Films by using Si and MgSi Dopants.

Polarity is among the critical characteristics that could governs the functionality of piezoelectric materials. In this study, the polarity of aluminum nitride (AlN) thin films was inverted from Al-polar to N-polar by doping Si into AlN in the range of 1-15 at.%. Polarity inversion from Al-polar to N-polar also occurred when MgSi was codoped into AlN with Mg to Si ratio was less than 1. However, the polarity can be reversed from N-polar to Al-polar when the ratio of Mg and Si was greater than 1. The effect of Si and MgSi addition was investigated with regards to their crystal structure, lattice parameters, polarity distribution and the oxidation state of each elements. Furthermore, the effect of intermediate layer as well as the presence of point defect (i.e. aluminum vacancy) were investigated and how these factors influence the polarity of the thin films are discussed in this report.

Adhesive bonding of alumina air-abraded Ag-Pd-Cu-Au alloy with 10-methacryloyloxydecyl dihydrogen phosphate.

The aim of this paper is to study changes in the Ag-Pd-Cu-Au alloy surfaces by alumina air-abrasion process and effect of those changes on the adhesive bonding characteristic. Surface roughness, surface composition and chemical state of the alumina air-abraded alloys were analyzed by a confocal laser scanning microscope, an energy dispersive X-ray spectroscopy and an X-ray photoelectron spectroscopy. The results showed that the alumina air-abrasion changed the alloy surface by mechanical roughening, alumina remain and copper oxidation. Effect of the changes in the alloy surface on the adhesive bonding characteristic was examined by using a methyl methacrylate/tri-n-butylborane derivative (MMA/TBB) resin cement with the 10-methacryloyloxydecyl dihydrogen phosphate (MDP) contained primer. The shear bond strength test results indicated that the surface oxidation by the abrasion is the main contributor that improved the adhesive bonding rather than other effects such as mechanical roughening or alumina remain.

First-Principles Study of Piezoelectric Properties and Bonding Analysis in (Mg, X, Al)N Solid Solutions (X = Nb, Ti, Zr, Hf).

The enhancement mechanism of piezoelectric properties by codoping Mg + X (X = Nb, Ti, Zr, Hf) into aluminum nitride (AlN) was investigated by first-principles calculations. Theoretically, the piezoelectric constant (d 33) can be increased when the elastic constant (C 33) is decreased and the piezoelectric stress constant (e 33) is increased. All components of e 33, which consists of the clamped e 33, the Born effective charge (Z 33), and the strain sensitivity (du/dε) of the internal parameter, were improved by the addition of Mg + X into AlN. The decrease in C 33 and the increase in du/dε that were observed in Mg + X-codoped AlN indicate the occurrence of elastic softening which was considered to be influenced by changes in the interatomic bond in the wurtzite structure. The bonding analysis of metal-nitrogen (Me-N) pairs in the Mg + X-codoped AlN system which was carried out by crystal orbital Hamilton populations showed that the covalent bonding (Me-N) was weaker than in pure AlN. Therefore, this weaker covalent bond is considered to be one of the origins of the elastic softening. Similar phenomena were also found for Sc-doped AlN which has higher piezoelectric response than that of pure AlN.

YSZ-based sensor using Cr-Fe-based spinel-oxide electrodes for selective detection of CO.

A selective carbon monoxide (CO) sensor was developed by the use of both of CuCrFeO4 and CoCrFeO4 as the sensing electrode (SE) for yttria-stabilized zirconia (YSZ)-based potentiometric sensor. The sensing-characteristic examinations of the YSZ-based sensors using each of spinel oxides as the single-SE sensor showed that CuCrFeO4-SE had the ability to detect CO, hydrocarbons and NOx gases, while CoCrFeO4-SE was sensitive to hydrocarbons and NOx gases. Thus, when both SEs were paired as a combined-SEs sensor, the resulting sensor could generate a selective response to CO at 450 °C under humid conditions. The sensor was also capable of detecting CO in the concentration range of 20-700 ppm. Its sensing mechanism that was examined via polarization-curve measurements was confirmed to be based on mixed-potential model. The CO response generated by the combined-SEs sensor was unaffected by the change of water vapor concentration in the range of 1.3-11.5 vol% H2O. Additionally, the sensing performance was stable during 13 days tested.

Insight into the aging effect on enhancement of hydrogen-sensing characteristics of a zirconia-based sensor utilizing a Zn-Ta-O-based sensing electrode.

A significant enhancement in the hydrogen (H2) sensitivity as well as selectivity after aging for more than 40 days has been observed for a mixed-potential-type sensor using ZnO (+84 wt % Ta2O5) as the sensing electrode (SE) and yttria-stabilized zirconia (YSZ) as the solid electrolyte. The effect of the aging process in enhancing the sensing characteristics of the sensor using ZnO (+84 wt % Ta2O5)-SE was studied here by investigating the changes in the morphology, crystal structure, chemical surface state, and catalytic properties of the SE material before and after aging at 500 °C for 80 days. X-ray diffraction measurements confirmed that the crystal structure of the SE material was found to be unaffected by aging, while the morphological change observed via scanning electron microscopy imaging indicated a decrease in the porosity and an increase in the particle size after aging. A significant change, particularly in the binding energy of Ta 4f, was also observed for the SE material after long-term aging. Although the catalytic activities toward the anodic reaction of H2 and the other examined gases were moderately stable after aging, a significant decrease in the heterogeneous catalytic activity of the gas-phase reaction (oxidation) of H2 was observed. Such a trend presumably resulted in a higher fraction of H2 reaching the triple-phase boundary, where the electrochemical reactions generate a sensing signal (mixed potential), resulting in high H2 sensitivity as well as high H2 selectivity after long-term aging of the present sensor.