Advances in Precision Engineering

Volumes 447-448

doi: 10.4028/

Paper Title Page

Authors: Aukkaravittayapun Suparerk, Wai Tat Kerk, Hu Wu, Hai Jing Lu
Abstract: Flexible transparent conducting (TC) film is a key element as the transparent electrode of the flexible electronics such as touch screen, solar cell, display or lighting. Current commercial flexible sputtered ITO films have shown some limitations; high sheet resistance (> 10 ohm/sq), deterioration of ITO film during repeatedly bending, indium scarce, and expensive fabrication process (sputtering). In this report, a new simple and cheap process to make such flexible TC film by using hot embossing and forming micro metal mesh underneath transparent conducting layer is proposed. This simple process has yielded a promising result with sheet resistance as low as 4 ohm/sq and the light transmission of 68% (@550nm). Future improvement on light transmission is discussed.
Authors: Hamid Farrokhi, Wei Zhou, Hong Yu Zheng, Zhong Li Li
Abstract: We studied the feasibility of micromachining of silicon wafer using 200 W fiber laser of 1090 nm in wavelength. Irradiated area was observed and analyzed using scanning electron microscope and surface profiler. It was found that micromachining of silicon could not be carried out efficiently. Careful analyses revealed possible causes for the poor machinability: first, very weak plasma formed during the fiber laser-material interaction, leading to low evaporation or melt ejection; second, formation of large amounts of SiO2 resulted in expansion of volume. It is further demonstrated that the surface oxidation can be made use of for the purpose of surface texturing.
Authors: Linda Y.L. Wu, Y.Y. Feng, G.J. Qi
Abstract: Polymer materials are sometimes molded to aluminum alloy to form integrated industrial parts for special applications, such as high strength, heavy duty applications. To ensure the bonding strength for long term applications, chemical treatment of aluminum surface is a quick and efficient method prior to polymer injection molding onto aluminum part. In this study, chemical etching and anodizing processes were studied to obtain suitable surface roughness and porous structures to enhance the penetration of polymer into the pores leading to interfacial anchoring and high bonding strength. Surface roughness, surface contact angles, and surface porous structures were investigated by surface Profilometer, contact angle tester, and scanning electron microscopy. Bending tests and cracking analyses were carried out to determine the bonding strength. Optimized chemical treatment recipe and process parameters were established. Preferred surface characteristics are defined. The failure mechanism of bending test was analysed and correlated to the bending fracture phenomina.
Authors: Jhun Yew Cheong, Xing Zhao Ding, Beng Kang Tay, Xian Ting Zeng
Abstract: In this paper, CrAlSiN coatings are deposited by a lateral rotating cathode arc technique. The high temperature oxidation behaviors of these coatings are studied in ambient atmosphere at temperatures ranging from 800°C-1000°C for an hour. The ternary TiAlN coating is used as the benchmark in this study. The surface morphology and chemical composition of the coating samples before and after oxidation at different temperatures are analyzed by scanning electron microscopy (SEM) equipped by energy dispersive X-ray spectrometer (EDX), glow discharge optical spectrometry (GDOS) and X-ray diffraction (XRD). The CrAlSiN coatings show much better oxidation resistance than the TiAlN coatings. TiAlN starts to oxidize from 800oC and forms a complete surface oxide layer after oxidation at 1000oC for an hour. However, CrAlSiN shows a relatively good oxidation resistance below 1000oC and only is oxidized to form a thin oxide scale with a thickness of 0.3 µm at 1000oC for one hour. It is found that the oxidation of both coatings is triggered from the surface metallic droplets generated by the arc deposition process.
Authors: R. Cai, W.K. Tan, Fern Lan Ng, Chang Q. Sun
Abstract: In this paper, three types of titanium dioxide structures (anatase, heated amorphous and amorphous) from peroxo titanium complex were deposited on glass and wafer substrates by spraying technique. Influences of crystal structure, morphology and sodium ion on UV induced hydrophilicity were studied. X-ray diffraction revealed that crystalline anatase coatings are extremely hydrophilic (<10°) under UV irradiation (indoor) while the amorphous coatings are still hydrophobic on both glass and wafer substrate with contact angles as high as 70º. When amorphous coating was heated at 450°C, its structure was converted into crystalline anatase, and hence its UV induced hydrophilicity behavior on wafer substrate became similar to that of anatase. However, this UV induced hydrophilicity was inhibited on heated glass (450°C), suggesting that sodium ions in the glass might be responsible for the differences between silicon wafer and glass. With increasing coating thickness, such inhibition effect was reduced, but the hydrophilicity still could not reach the level of anatase. After 6 months of outdoor exposure, water contact angle for amorphous, heated amorphous and anatase were 61°, 26.6° and 12.1°, respectively. Also, X-ray diffraction suggested that amorphous is not converted into anatase after long period of UV exposure, although coating morphologies are changed based on Scanning Electron Microscopic observation. It is concluded that the crystal structure, coating morphology and sodium ion concentration have key impact on the photocatalytic properties on glass substrate.
Authors: Xiao Zhang, Min Qian, Yu Chan Liu, Hong Xie
Abstract: In this paper we report the fabrication of hydrophobic hard coatings using sol-gel processing and cured at room temperature by an ammonia-assisted process. The coating thickness can be tuned from several hundreds of nanometer to several microns. These coatings show both high transparency (better than PMMA or glass substrates) and high hardness (pencil hardness 2H-4H on PMMA). The coatings are very smooth with surface roughness Ra less than 2 nm for coatings with different thicknesses from 200 nm to 2 m. The water contact angle (WCA) of the coating is about 115 to 120o and the sliding angle for a 20 l water drop is less than 10o. The advantage of this process is the ease for larger area application and especially suitable for plastic surface treatment due to the low temperature curing process.
Authors: Gui Jun Bi, Sum Huan Ng, Khin Thet May, Cong Zhi Chan
Abstract: This study aims to investigate laser welding process for the bonding of micro-fluidic devices. PMMA was selected for the investigation. The devices consist of an opaque substrate with micro-channels and a transparent cover. The welding process was optimized according to laser power, welding speed and clamping pressure. The cross-sectional analysis, flow and pressure tests, as well as the lap-shear test were conducted on the samples welded with the optimized process parameters. The results show that the laser welding can meet the requirements for bonding the plastic micro-fluidic devices.
Authors: A. Liu, J. An, Chee Kai Chua, Kah Fai Leong
Abstract: Engineered tendon and ligament scaffolds are ideally a bunch of biocompatible and biodegradable microfibers that are three-dimensionally aligned with no fusion between individual fibers. In this paper, a simple yet effective device that is able to fabricate this nearly native structure is presented, including design and operation method. Briefly, the device is die-free and requires only simple components such as a plate with an orifice, an aluminum holder, a ring heater and a rotating mandrel. The fabrication is done by a single step with microfiber (10 µm diameter) bundles being directly obtained at a very low take-up speed. The as-spun microfiber bundles appear silvery and shiny, apparently similar to a native tendon. This device and the method associated opens up a new way to diversify the structure of biomaterials.
Authors: Jia En Low, Wei Xiang Koh, Joon Kit Lai, Yan Jie Lee, Xu Li, Ge Chen, Yang Kay Juay, Jian Hong Zhao
Abstract: Poly(lactic acid) (PLA) is a biodegradable and biocompatible aliphatic polyester whose lactic acid monomers are derived from renewable resources such as corn and sugar beet. As a thermal plastic it can be processed through compounding and injection. As such, we have developed a microfludic device using PLA aimed at blood dialysis application. To quantify the degradation of PLA, its hydrolysis at different pH value was studied. To study the bioresorbable property of these fabricated devices, its decomposition was tested by morphology observation and weight change measurements after embedding in soil under simulated environmental conditions. Upon contact with a hydrophobic surface, platelets and prothrombin are always activated to attach to the surface, resulting in blood clot. This would block the blood flow through the dialysis channels in the microfluidic device. To improve the hydrophilicity, hence the blood compatibility, chemical grafting of a hydrophilic polymer, poly(ethylene oxide) methacrylate (PEGmA), onto the surface of PLA microfluidic device was carried out and the changes in hydrophilicity was monitored through measuring the water contact angle. Our results indicate that chemical grafting of PEGmA significantly improves the hydrophilicity of the device surface.
Authors: Keiji Ogawa, Toshiki Hirogaki, Eiichi Aoyama, Mitsuaki Taniguchi, Sachiko Ogawa
Abstract: Bamboo grows faster than other renewable natural materials. Bamboo fiber, in particular, has attracted attention as an environmentally superior material. Therefore, we proposed a sustainable manufacturing system using bamboo. An extraction method of bamboo fibers end-milled using a machining center with in-situ measurement is proposed. Bamboo fibers with high precision shape are efficiently acquired. In the present report, we propose the fabrication of binder-free composite by a hot press forming method that only uses bamboo fibers extracted by a machining center. We experimentally demonstrated various hot press forming conditions and achieved proper forming conditions to optimize the forming process. We also made various three-dimensional shapes considering the practical applications of the formed binder-free bamboo fiber moldings.

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