Gas sensing properties of p-type hollow NiO hemispheres prepared by polymeric colloidal templating method

This work presents a simple and versatile route to produce macroporous p-type metal oxide thin films. Two-dimensional arrays of p-type NiO films with a hollow hemisphere structure were fabricated by colloidal templating and RF-sputtering followed by a subsequent heat treatment. The diameter and shell thickness of the NiO hemisphere were 800 nm and 20 nm, respectively. X-ray diffraction and high-resolution transmission electron microscopy analysis indicate that the pure NiO phase with grain size of 10 nm was obtained at calcination temperatures that exceeded 450 °C. Close-packed arrays of hollow NiO hemispheres were found to exhibit p-type gas sensing properties against (CO, H₂, C₃H₈, CH₄, NO₂, and C₂H₅OH), leading to significantly enhanced responses to C₂H₅OH (R_gas/R_air = 5.0 at 200 ppm).     

Preparation and properties of borosilicate glass-coated Cu powder for internal electrode of multilayer ceramic device

In this study, a process was proposed which allows a base metal electrode to be burnt-out in an oxidative atmosphere for fabrication of multilayer ceramic device. To protect Cu in an oxidative atmosphere, the Cu powder was coated with borosilicate glass via a sol-gel process. The oxidation resistance and shrinkage of the glass-coated Cu were investigated. When a 10% glass-coated Cu was heated up to 500°C under an oxidative atmosphere, the Cu could survive without formation of copper oxide. The oxidation of the Cu was observed when heating at temperatures above 700°C. This might be due to exposure of Cu to oxidative atmosphere related to softening behavior of glass. The glass-coated Cu exhibited a shrinkage behavior which follows the shrinkage behavior of glass in the low temperature range and the shrinkage of pure Cu in the high temperature range. To measure the electrical conductivity of the glass-coated Cu electrode, the Cu pastes were prepared and printed onto alumina substrate. The binder-burn-out process of the glass-coated Cu was carried out at 550°C under an air atmosphere, and was then sintered at 1000°C under a nitrogen atmosphere. The electrical conductivity of the Cu electrode measured was above 10⁴ /Ωcm which means that it can be used as the internal electrode of a multilayer device.     

Effects of copper addition on the formation of inclusions and the resistance to pitting corrosion of high performance duplex stainless steels

To elucidate the effects of copper addition on the formation of inclusions and the resistance to pitting corrosion of alloys, potentiodynamic and potentiostatic polarization tests, a SEM-EDS analysis of inclusions, and thermodynamic calculations of the formation of inclusions were conducted. The addition of copper to the base alloy increased the number and area of numerous (Mn, Cr, (Al), (Fe)) oxides and oxy-sulfides due to an increase in the activity of chromium and resulted in decreased pitting resistance. The thermodynamic prediction of the formation of inclusions was in good agreement with the experimental results.     

Intermediate space for housing design learned from tradition of Korean maru and Turkish sofa

The study examines traditional design approaches for intermediate spaces of residential buildings to support environmentally driven design strategies of current practices. For the evaluation of the potential of traditional design strategies, traditional houses of Korea and Turkey are explored by making a detailed comparison of maru and sofa according to theoretical considerations on intermediate spaces. After examining the concept of the intermediate space and the general characteristics of Korean and Turkish traditional housing, 10 cases from 17th to 19th centuries are selected and compared to clarify the features of maru and sofa as intermediate spaces. Based on the results, the arrangement of maru shows characteristics of contradiction between interior rooms and intermediate spaces in a monotonous structural repetition, while sofa presents an apparently hierarchical spatial composition. Sofa has the placeness quality, while maru has the quality of plurality, actively mixing both inside and outside environments. While maru allows various free access with clear spatial continuity, sofa produces a sequential spatial experience with the pleasure of different architectural qualities. Finally, the study suggests opened type and closed type of intermediate space as two possible strategies for modern houses based on the results of comparative analyses. Recent environmental studies in architecture should consider intermediate spaces of various traditional houses due to the insights and possibilities these spatial elements may potentially provide to both architectural practice and theory, especially in a pandemic era.     

Transient Analysis and Leakage Detection Algorithm using GA and HS algorithm for a Pipeline System

The impact of leakage was incorporated into the transfer functions of the complex head and discharge. The impedance transfer functions for the various leaking pipeline systems were also derived. Hydraulic transients could be efficiently analyzed by the developed method. The simulation of normalized pressure variation using the method of characteristics and the impulse response method shows good agreement to the condition of turbulent flow. The leak calibration could be performed by incorporation of the impulse response method with Genetic Algorithm (GA) and Harmony Search (HS). The objective functions for the leakage detection can be made using the pressure-head response at the valve, or the pressure-head or the flow response at a certain point of the pipeline located upstream from the valve. The proposed method is not constrained by the Courant number to control the numerical dissipation of the method of charac teristics. The limitations associated with the discreteness of the pipeline system in the inverse transient analysis can be neglected in the proposed method.     

Leakage currents in Ti−O/Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> thin film deposited on Ta/Ti/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The electrical characteristics of Ta/Ta₂O₅ films and Ta/Ti−O/Ta₂O₅ films deposited by RF reactive sputtering on Ta/Ti/Al₂O₃ substrates were investigated. Ta was used for the bottom and upper electrodes in order to simplify the fabrication process. Dielectric materials were annealed at 700°C for 60 sec under vacuum. XRD analysis showed that Ta was crystalline and Ta₂O₅ was amorphous in an as-deposited state, but amorphous Ta₂O₅ was transformed to a crystalline state by rapid thermal heat treatment. We compared lnJ-E², C−V, and C−F of both as-deposited and annealed dielectric thin films deposited on the Ta bottom electrode. From these results, we concluded that introducing a Ti−O buffer layer could reduce the leakage current. The conduction mechanisms of Ti−O/Ta₂O₅ could be interpreted appropriately by hopping conduction and space-charge-limited current.     

Novel fabrication of an SnO(2) nanowire gas sensor with high sensitivity

We fabricated a nanowire-based gas sensor using a simple method of growing SnO(2) nanowires bridging the gap between two pre-patterned Au catalysts, in which the electrical contacts to the nanowires are self-assembled during the synthesis of the nanowires. The gas sensing capability of this network-structured gas sensor was demonstrated using a diluted NO(2). The sensitivity, as a function of temperature, was highest at 200?°C and was determined to be 18 and 180 when the NO(2) concentration was 0.5 and 5?ppm, respectively. Our sensor showed higher sensitivity compared to different types of sensors including SnO(2) powder-based thin films, SnO(2) coating on carbon nanotubes or single/multiple SnO(2) nanobelts. The enhanced sensitivity was attributed to the additional modulation of the sensor resistance due to the potential barrier at nanowire/nanowire junctions as well as the surface depletion region of each nanowire.     

Highly conductive coaxial SnO(2)-In(2)O(3) heterostructured nanowires for Li ion battery electrodes

Novel SnO(2)-In(2)O(3) heterostructured nanowires were produced via a thermal evaporation method, and their possible nucleation/growth mechanism is proposed. We found that the electronic conductivity of the individual SnO(2)-In(2)O(3) nanowires was 2 orders of magnitude better than that of the pure SnO(2) nanowires, due to the formation of Sn-doped In(2)O(3) caused by the incorporation of Sn into the In(2)O(3) lattice during the nucleation and growth of the In(2)O(3) shell nanostructures. This provides the SnO(2)-In(2)O(3) nanowires with an outstanding lithium storage capacity, making them suitable for promising Li ion battery electrodes.     

Evaluation of defects in aluminum piston castings by using ultrasonics and computer tomography

Pistons used in automobile engines are made of aluminum alloy; and endurance of high pressure and high temperature is required. Recently, high strength pistons are needed to cope with the increase of pressure and temperature in the engine cylinder. A high strength piston is possible when the piston casting has little or no casting defects, such as micro-pores and cracks. Generally the defects can be evaluated by non-destructive testing (NDT), and the most efficient ways for evaluation are using ultrasonics and computer tomography. In the present study, two NDT methods were compared and evaluated to investigate the defects in the aluminum piston castings. Artificial defects were machined by using very small drill bits with diameters 1, 0.5, 0.3, 0.2 and 0.1 mm. The defects were investigated by using an ultrasonic tester and a computer tomography system. Defects smaller than 0.3 mm may not be found by using the ultrasonic test, but the defects may be found by using the computer tomography system. The investigation conditions for detecting small defects and the scanning time for in-line defect analysis are discussed in the present study.     

Conformational-induced doping effect of sodium dodecyl benzene sulfonate on single walled carbon nanotubes

The doping behavior of single-walled carbon nanotubes (SWCNTs) was investigated with an emphasis on the control of the conformation of sodium dodecylbenzene sulfonate (NaDDBS) with sulfonate groups acting as an electro-withdrawing group. The conformation of adsorbed NaDDBS on SWCNTs was controlled as a function of the amount of NaDDBS. The doping behavior of SWCNTs was significantly affected by the dosing amount of NaDDBS due to the conformational change of NaDDBS adsorbed on the SWCNT surface, which affected the spatial distance between the SWCNT surface and the sulfonate groups in NaDDBS. At a higher concentration, the spatial distance between the sulfonate group in NaDDBS and SWCNT was not sufficiently close enough to dope SWCNT due to the repulsive forces between the sulfonate groups in NaDDBS. Alternatively, at a lower concentration, NaDDBS acted as a p-type dopant for SWCNTs. To this end, this paper demonstrates a new tendency of doping that is related to the adsorbed behavior of a dispersant.