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Chen Y.-T.,National Central University | Lee S.-L.,National Central University | Bor H.-Y.,Electro-Mat | Lin J.-C.,National Central University
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2013

This research investigates the effects of natural aging and cold working prior to artificial aging on microstructures and mechanical properties of Al-4.6Cu-0.5Mg-0.5Ag alloy. Mechanical properties relative to microstructure variations were elucidated by the observations of the optical microscope (OM), differential scanning calorimeter (DSC), electrical conductivity meter (pct IACS), and transmission electron microscopy (TEM). The results showed that natural aging treatment has little noticeable benefit on the quantity of precipitation strengthening phases and mechanical properties, but it increases the precipitation strengthening rate at the initial stage of artificial aging. Cold working brings more lattice defects which suppress Al-Cu (GP zone) and Mg-Ag clustering, and therefore the precipitation of Ω phase decreases. Furthermore, more dislocations are formed, leading to precipitate the more heterogeneous nucleation of θ′ phase. The above-mentioned precipitation phenomena and strain hardening effect are more obvious with higher degrees of cold working. © 2013 The Minerals, Metals & Materials Society and ASM International. Source


Kim Y.K.,Korea Aerospace University | Park I.S.,Electro-Mat | Choi J.,Korea Aerospace University
Microelectronics Reliability | Year: 2010

The objective of this study is to analyze a warpage development mechanism by simulating a strip type packaging for plastic ball grid array. Molding compound and substrate materials were thermo-mechanically tested to obtain the mechanical properties by several test methods. Samples were fabricated using the same materials, and warpage developments were measured at room temperature after molding compound cure. Based on the tested materials property, the warpage developments were simulated by numerical calculations during cooldown process. The results were compared with the measurement data of the samples, and the warpage mechanism was investigated based on the elastic and viscoelastic simulation results. It was found that the relaxation behaviors of the molding compound and the substrate materials had significant effect on the warpage development. It was also found that the warpage development was dependent on the packaging geometry. The development mechanism was analyzed through the simulation calculations by combining different material properties modeling and geometries, and the results showed comprehensive consideration of the materials and the packaging design are essential to control the warpage. © 2010 Elsevier Ltd. All rights reserved. Source


Thiruvasagam P.,SASTRA University | Vijayan M.,Electro-Mat
High Performance Polymers | Year: 2012

Two new diacid monomers 4,4′-bis[5-(trimellitimido)napthyloxy] diphenyl sulfone and 4,4′-bis[5-(trimellitimido)napthyloxy]benzophenone were synthesized and characterized by spectroscopic analysis. A series of poly(amide-imide)s (PAIs) were prepared from these diacids and aromatic diamines through phosphorylation reaction. The structures of the PAIs were characterized by infrared and 1H-NMR. The PAIs were characterized by X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, electrical properties, solution viscosity and solubility test. The flexible linkages and pendant groups in the PAIs chain will disturb chain-chain packing and their effects on solubility, thermal stability and electrical properties were investigated. PAIs showed excellent thermal stability and good solubility. The dielectric constants of the PAIs were in the range 4.15-4.77. The PAIs have electrical insulation character and the film can be used in insulation of electrical items operating at elevated temperatures. © The Author(s) 2012. Source


Moghimi N.,University of Waterloo | Abdellah M.,University of Waterloo | Thomas J.P.,University of Waterloo | Mohapatra M.,Electro-Mat | Leung K.T.,University of Waterloo
Journal of the American Chemical Society | Year: 2013

Concave nanostructures are rare because of their thermodynamically unfavorable shapes. We prepared bimetallic FeNi concave nanocubes with high Miller index planes through controlled triggering of the different growth kinetics of Fe and Ni. Taking advantage of the higher activity of the high-index planes, we then fabricated monodispersed concave nanocages via a material-independent electroleaching process. With the high-index facets exposed, these concave nanocubes and nanocages are 10- and 100-fold more active, respectively, toward electrodetection of 4-aminophenol than cuboctahedrons, providing a label-free sensing approach for monitoring toxins in water and pharmaceutical wastes. © 2013 American Chemical Society. Source


Kalem S.,TUBITAK - Marmara Research Center | Arthursson O.,Chalmers University of Technology | Romandic I.,Electro-Mat
Applied Physics A: Materials Science and Processing | Year: 2010

The surface of a single-crystal germanium wafer was transformed to crystals of germanium fluorides and oxides upon exposure to a vapor of HF and HNO 3 chemical mixture. Structure analysis indicates that the transformation results in a germanate polycrystalline layer consisting of germanium oxide and ammonium fluogermanate with preferential crystal growth orientation in 〈101〉 direction. Local vibrational mode analysis confirms the presence of N-H and Ge-F vibrational modes in addition to Ge-O stretching modes. Energy dispersive studies reveal the presence of hexagonal α-phase GeO2 crystal clusters and ammonium fluogermanates around these clusters in addition to a surface oxide layer. Electronic band structure as probed by ellipsometry has been associated with the germanium oxide crystals and disorder-induced band tailing effects at the interface of the germanate layer and the bulk Ge wafer. The acid vapor exposure causes Ge surface to emit yellow photoluminescence at room temperature. © 2009 Springer-Verlag. Source

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