• Journal of the Microelectronics and Packaging Society
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• v.16 no.4
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• pp.55-60
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• 2009

Porous silicon film is fabricated by electrochemical etching in a chemical mixture of HF and ethanol. Effects of Si type, Si resistivity, ultrasonic frequency, current density and etching time on surface morphology of PS film were studied. Electrochemical etching in ultrasonic bath promotes the uniformity of porous layer of Si. Frequency of ultrasonic was increased from 40 kHz to 130 kHz to obtain uniform pores on the Si surface. When current density was higher, the sizes of pores were larger. The new etching cell using back contact metal and current shield help to overcome nonhomogeneity and current crowding effect, and then leads to fabricate uniform pores on the Si surface. The distribution of pore size shows no notable tendency with etching time.

• Steel and Composite Structures
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• v.43 no.6
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• pp.821-837
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• 2022

This research is devoted to study the effects of humidity and temperature on the bending behavior of functionally graded (FG) ceramic-metal porous plates resting on Pasternak elastic foundation using a quasi-3D hyperbolic shear deformation theory developed recently. The present plate theory with only four unknowns, takes into account both transverse shear and normal deformations and satisfies the zero traction boundary conditions on the surfaces of the functionally graded plate without using shear correction factors. Material properties of porous FG plate are defined by rule of the mixture with an additional term of porosity in the through-thickness direction. The governing differential equations are obtained using the "principle of virtual work". Analytically, the Navier method is used to solve the equations that govern a simply supported FG porous plate. The obtained results are checked by comparing the results determined for the perfect and imperfect FG plates with those available in the scientific literature. Effects due to material index, porosity factors, moisture and thermal loads, foundation rigidities, geometric ratios on the FG porous plate are all examined. Finally, this research will help us to design advanced functionally graded materials to ensure better durability and efficiency for hygro-thermal environments.

• Structural Engineering and Mechanics
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• v.76 no.3
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• pp.413-420
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• 2020

Considering inverse cotangential shear strain function, the present paper studies nonlinear stability of nonlocal higher-order refined beams made of metal foams based on Chebyshev-Ritz method. Based on inverse cotangential beam model, it is feasible to incorporate shear deformations needless of shear correction factor. Metal foam is supposed to contain different distributions of pores across the beam thickness. Also, presented Chebyshev-Ritz method can provide a unified solution for considering various boundary conditions based on simply-supported and clamped edges. Nonlinear effects have been included based upon von-karman's assumption and nonlinear elastic foundation. The buckling curves are shown to be affected by pore distribution, geometric imperfection of the beam, nonlocal scale factor, foundation and geometrical factors.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.1
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• pp.23-29
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• 2007

Pitch-coated anatase $TiO_2$ typed was prepared by $CCl_4$ solvent mixing method with different mixing ratios. Since the carbon layers derived from pitch on the $TiO_2$ particles were porous, the pitch-coated $TiO_2$ sample series showed a good adsorptivity and photo decomposition activity. The BET surface area for the carbon layer in the sample increases to increasing with pitch contents. The SEM results present to the characterization of porous texture on the pitch-coated $TiO_2$ sample and pitch distributions on the surfaces for all the materials used. From XRD data a weak and broad carbon peak of graphene with pristine anatase peaks were observed in the X-ray diffraction patterns for the pitch-coated $TiO_2$. The EDX spectra show the presence of C, O and S with strong Ti peaks. Most of these samples are richer in carbon and major Ti metal than any other elements. Finally, the excellent photocatalytic activity of pitch-coated $TiO_2$ with slope relationship between relative concentration of MB ($c/c_o$) and t could be attributed to the homogeneous coated pitch on the external surface by $CCl_4$ solvent method.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.16.1-16.1
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• 2011

Gas sensor properties of $WO_3$ nanowire structures have been studied. The sensing layer was prepared by deposition of tungsten metal on porous single wall carbon nanotubes followed by thermal oxidation. The morphology and crystalline quality of $WO_3$ material was investigated by SEM, TEM, XRD and Raman analysis. A highly porous $WO_3$ nanowire structure with a mean diameter of 82 nm was obtained. Response to CO, $NH_3$ and $H_2$ gases diluted in air were investigated in the temperature range of $100{\sim}340^{\circ}C$ The sensor exhibited low response to CO gas and quite high response to $NH_3$ and $H_2$ gases. The highest sensitivity was observed at $250^{\circ}C$ for $NH_3$ and $300^{\circ}C$ for $H_2$. The effect of the diameters of $WO_3$ nanowires on the sensor performance was also studied. The $WO_3$ nanowires sensor with diameter of 40 nm showed quite high sensitivity, fast response and recovery times to $H_2$ diluted in dry air. The sensitivity as a function of detecting gas concentrations and gas sensing mechanism was discussed. The effect of dilution carrier gases, dry air and nitrogen, was examined.

• Journal of the Korean Ceramic Society
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• v.41 no.2
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• pp.176-181
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• 2004

EAF (Electric Arc Furnace) dust is classified as special wastes containing heavy metal contaminants may cause to damage an environment such as underground water contamination if they were not treated properly. For reutilizing the EAF dust, the porous body was made from EAF dust/clay composition system, and analyzed pore characteristics. It was found that a light-aggregate body was made up two different microstructures. One was non-black and dense microstructure which located near surface, and the other was black and porous microstructure (black coring) which located inner part. For systematizing the relationship of the black-coring area and the bloating degree, we defined the Ic(core index) and Is(shell index). It was found that the optimal bloating conditions of artificial light-weight aggregate were more than 0.5 of Ic and 0.4 of Is.

• Journal of Sensor Science and Technology
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• v.17 no.1
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• pp.9-14
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• 2008

In this paper, the gas responses of tungsten oxide films prepared by anodic reaction was discussed. Sensing electrodes and heating electrodes were patterned by photolithography method on quartz substrate. Porous tungsten oxide was fabricated in electrolyte solutions of 5 % HF (HF :$C_2H_6OH:H_2O$=3 : 2 : 20) by anodic reaction. The anodic reaction with metal (platinum wire) as a cathode and the sensing device as an anode was conducted under the various reaction times (1-10 min) at 10 mA/$cm^2$ The surface structure and morphology of the fabricated sensor have been analysed by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). All the peaks of XRD results were well indexed to the pure phase pattern. The average diameter of the porous tungsten oxide surface were ranged about 100 nm. The fabricaed sensor showed good sensitivity to 200 ppm toluene at operating temperature of $250^{\circ}C$.

• Journal of Surface Science and Engineering
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• v.51 no.1
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• pp.1-10
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• 2018

Anodic oxidation treatment of metals is one of typical surface finishing methods which has been used for improving surface appearance, bioactivity, adhesion with paints and the resistances to corrosion and/or abrasion. This article provides fundamental principle, type and characteristics of the anodic oxidation treatment methods, including anodizing method and plasma electrolytic oxidation (PEO) method. The anodic oxidation can form thick oxide films on the metal surface by electrochemical reactions under the application of electric current and voltage between the working electrode and auxiliary electrode. The anodic oxide films are classified into two types of barrier type and porous type. The porous anodic oxide films include a porous anodizing film containing regular pores, nanotubes and PEO films containing irregular pores with different sizes and shapes. Thickness and defect density of the anodic oxide films are important factors which affect the corrosion resistance of metals. The anodic oxide film thickness is limited by how fast ions can migrate through the anodic oxide film. Defect density in the anodic oxide film is dependent upon alloying elements and second-phase particles in the alloys. In this article, the principle and mechanisms of formation and growth of anodic oxide films on metals are described.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.12S
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• pp.1232-1236
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• 2003

In this work, we fabricated a gas-sensing device based on porous silicon(PS), and its C-V properties were investigated for sensing alcohol vapor. The structure of the sensor consists of thin Au/oxidized PS/PS/P-Si/Al, where the p-Si is etched anisotropically to be prepared into a membrane-shape. We used alcohol gases vaporized from different alcohol (or ethanol) solutions mixed with pure water at 36$^{\circ}C$, similarly with an alcohol breath measurement to check drunk driving. As the result, I-V curves showed typical tunneling property, and C-V curves were shaped like those of a MIS (metal-insulator-semiconductor) capacitor, where the capacitance in accumulation was increased with alcohol vapor concentration.

• Journal of Aerospace System Engineering
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• v.8 no.3
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• pp.1-5
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• 2014

An inner flow of a porous cylinder with partial slots was visualized to study fluidic phenomena in a solid rocket motor. A high-pressure chamber and an air supply system for high flow rate were used. In order to visualize the inner flow, the smoke generator with a cam-driven pump and heaters and high speed camera were adopted. The results of the cylinder type and the partial slot type were compared. As a result, the injected smoke flow in the partial slot type had circumferential fluctuations unlike the cylinder type. It was found that the circumferential flow induced from the partial slots could be the cause of combustion instability and roll torque.