Science and Technology of Nanomaterials

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Authors: Xiao Ping Li, H.L. Seet, Z.J. Zhao, Y.K. Kong
Abstract: For the purpose of developing a composite micro sensor for weak magnetic field, fabrication of high permeability ferromagnetic material is needed. The magnetic properties of the pulse-plated samples depend greatly on the chemical composition and nanocrystalline grain size of the ferromagnetic layer. In this study, the effect of the pulse plating parameter: duty cycle on the chemical composition and grain size of the deposited layer was investigated. A layer of soft ferromagnetic material Ni-Fe was deposited onto copper wires of 20µm diameter by means of pulse and dc plating and tested under XRD for grain size measurement. It was found that variations in duty cycle do not affect the thickness of the plated layer, but affect significantly the chemical composition. There is an optimum duty cycle for getting the minimum grain size of plated layer in pulse plating with saccharin. The results from the magnetic measurement showed that the permeability of the plated material increased greatly as the grain size decreased in the range of 10 – 55 nm.
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Authors: Xiao Ping Li, Z.J. Zhao, T.B. Oh, H.L. Seet
Abstract: In order to develop high sensitivity micro sensors for bio-magnetic field using NiFe electroplated composite sensing elements, it is important to study how different plating processes can affect the magnetic properties in terms of the chemical composition and magnetic structure of the plated layer. In this study, to study the effect of the magnetic field on the magnetic structure of the electroplated NiFe layers, magnetic controlled plating in which a longitudinal magnetic field ranging from 0 to 400 Oe is applied during nanocrystalline electroplating of permalloy Ni80Fe20 layer of 2 µm thick onto a 20 µm diameter Cu wire. The magnetic structure of the plated layers is studied by investigating the Giant magneto-impedance (GMI) effect of the plated layer. GMI has been measured from a frequency range of 100 kHz to 50 MHz. It is observed that under conventional electroplating without an external magnetic controlling field, the anisotropy of the plated layer is generally circumferential as indicted by the double peaks of the MI curves in testing at high frequency. When a longitudinal magnetic field is applied during electroplating, the plated layer shows single peak MI curves, suggesting that the anisotropy is changed from circumferential to longitudinal. The results also show that the sensitivity and resolution of a magnetic field sensor is improved greatly by changing the anisotropy of the plated layer from circumferential to longitudinal.
167
Authors: X.L. Zhong, Manoj Gupta
Abstract: In present study, elemental magnesium was reinforced with nano-size alumina particles (50-nm). The composite samples were synthesized using the technique of powder metallurgy and the effect of extrusion temperature and sintering on the end properties was particularly investigated. The results of microstructural characterization studies confirmed the presence and reasonably uniform distribution of alumina particles. Results obtained from extruded unsintered samples revealed that the hardness and dimensional stability of magnesium increases with an increasing presence of alumina particles while the 0.2%YS, UTS and ductility deteriorated. Results further revealed that including sintering step and extruding at higher temperature lead to an increase in dimensional stability, hardness, 0.2%YS, UTS and ductility for an alumina content as low as one percent by weight.
171
Authors: Sam Zhang, Deen Sun, Yong Qing Fu, H. Du, Qing Zhang
Abstract: Nanocrystalline TiN (or nc-TiN) has been imbedded in amorphous silicon nitride (a-SiNx)matrix to form a nanocomposite thin film (nc-TiN/a-SiNx) via magnetron sputtering deposition on silicon wafer. Two important effects of the Si3N4 sputtering target power on the formation of nc-TiN/a-SiNx have been studied: (1) Aside from forming a-SiNx in the matrix, Si atoms also imbed into TiN to form (Ti,Si)N solid solution crystallites. At low target power, the solid solution is substitutional. With increase of power, the amount of silicon “dissolved” in the TiN crystallite increases, and in the meantime, the interstitial components increase which is manifested in the increase in the TiN lattice parameter. (2) The crystallites have a preferred orientation varying with the deposition target power. As conveniently described by the coefficient of texture, the degree of preferred orientation along [111] direction decreases and finally tails off with increase of power. At the same time, the crystallites orient along [200] and [220] direction and eventually [220] direction dominants.
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Authors: Xinglong Tan, Shaoyu Qiu, Wenyan He, Daifu Lei
Abstract: The properties of nano WC/Co hardmetals prepared by different Spark Plasma Sintering processes were measured. A 4-layer Functionally Graded Materials (FGM) was also obtained by Spark Plasma Sintering technology (SPS), starting from powders of nano WC/10%Co, nano WC/12%Co, micro WC/15%Co and stainless steel disk. The other 3-layer FGM was made from powders of nano 21%Al2O3/ZrO2, nickel and stainless steel. The SPS processing led to FGM free of internal stress, which was measured using Vickers indentations.
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Authors: S. Bansal, A.M. Saxena, T. Hartwig, Rao R. Tummala
Abstract: Bulk nanocrystalline copper and nickel (average grain size ~ 50 nm) with high purity and density were synthesized by equichannel angular extrusion (ECAE). Both nanohardness and microhardness measurements revealed a significant increase in hardness of the bulk sample. The tensile strength of these materials has been found to be 5-6 times higher than conventional forms and our experiments show that Cu is extremely stable up to temperatures of 100 oC and Ni to temperatures of 250 oC. The fracture toughness, measured by the value of JIC for nc-copper and nickel have been found to be 21.66 KJ/m2 and 12.13 KJ/m2, respectively which are high for these strength levels.
183
Authors: H.F. Li, R.V. Ramanujan
Abstract: Mechanical alloying (MA) is a widely used processing technique to prepare metastable or nanophase materials in a cost effective fashion. In this study, mechanically alloying FeCo based nanomagnetic alloys was included. Scanning electron microscope (SEM), X-ray diffractometer (XRD), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) were used to characterize the as milled powders. The effect of additional elements P and B on the powder size, microstructures and magnetic properties is discussed. It showed that the addition of P and B could reduce the powder size more effectively. The addition of elements P and B during MA of FeCo magnetic alloy also led to the formation of spherical nanocrystallines instead of banded microstructures in MA FeCo without these additions.
187
Authors: Qing Feng Wang, Peng Cheng Zhang, Xiao Hong Wang, Da Peng Ren, Ding Mu Lang, Yan Zhi Zhang
Abstract: Microstructure of nickel deposit ,which was prepared with pulse-plating technology on depleted uranium surface, has been studied by X-ray diffractometry(XRD),Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). The results indicate that the crystallographic structure of the deposit is face centered cubic; the deposit has a highly preferred orientation of (200), the relative orientation density of (200) is 3.44; the average grain size is about 45.5nm. The deposit is fine and has multi-crystal nature as well as crystallographic defects as dislocation, stacking and twin. It’s feasible to prepare nanocrystalline nickel deposit on depleted uranium surface with pulse plating technology.
191
Authors: Tatsuo Ohgushi, Mayumi Nagae
Abstract: Na-X zeolite easily caused a thermal runaway by microwave radiation of 500W but Ca-X zeolite merely reached ca. 300°C. Mixtures of Ca-X and Na-X reached lower heating temperature with increasing the content of Ca-X and the heating temperature could be controlled (>300°C) by adjusting the content. Since water in X zeolite almost completely desorbs by 400°C, conditions realizing the heating temperature of ca. 400°C were studied. The mixture with the ratio of Ca-X/Na-X=0.9/0.1 was quickly heated to ca. 400°C by the radiation of 10-20 min in the 500 W power and reached the dehydration state up to >90 %. A degradation degree of adsorption capacity of the mixture for water was examined after two and three treatments with the microwave heating. The average degradation degree was 1.4 % per treatment. The properties of the zeolite desiccant with microwave treatment were compared with those of commercial CaCl2 desiccant. It was found that the zeolite desiccant is superior to the commercial desiccant and an application of zeolite to a domestic reusable desiccant, through the heating technique, is promising.
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Authors: Xing Yi Ling, Zhaolin Liu, Jim Yang Lee
Abstract: The rapid synthesis of platinum nanoparticles using ethylene glycol and microwave dielectric heating is reported here. The Pt nanoparticles after synthesis were transferred to a toluene solution of dodecanethiol (DDT) to form DDT-encapsulated Pt nanoparticles. The TEM examinations showed nearly spherical platinum nanoparticles. The particles were in the size range of 2~8 nm and exhibited narrow size distribution. They were stable in the toluene solution for at least 10 months. Larger particles were formed with longer microwave heating time, higher metal precursor salt concentrations, and lower pH values. XPS measurements revealed >80% of Pt was in the zero valent state and the S 2p signal showed strong adsorption of sulfur species on the surface of platinum nanoparticles. FTIR spectroscopy also confirmed the interactions of thiol groups and the platinum surface.
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