Defects and Diffusion, Theory & Simulation II

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Authors: M. Rizwan Malik, Tie Lin Shi, Zi Rong Tang, Shi Yuan Liu
Abstract: It is critical to understand multiphase flow applications with regard to dynamic behavior. In this paper, a systematic approach to the study of these applications is pursued, leading to separated flows comprising the effects of free surface flows and wetting. For the first time, wetting phenomena (three wetting regimes such as no wetting, 90 º wetting angle and absolute wetting) are added in the separated flow model. Special attention is paid to computational fluid dynamics (CFD) in order to envisage the relationship between complex metallurgical practices such as mass and momentum exchange, turbulence, heat, reaction kinetics and electromagnetic fields. Simulations are performed in order to develop sub-models for studying multiphase flow phenomena at larger scales. The outcomes show that a proper mixture of techniques is valuable for constructing larger-scale models based upon sub-models for recreating the hierarchical structure of a detailed CFD model applicable throughout the process.
Authors: Deepika Sharma, Kamlesh Chandra, Prabhu Shankar Misra
Abstract: Iron-Phosphorus based soft magnetic materials are known for their hot and cold shortness. The present investigation deals with the development of high-density Fe-P based alloys in the form of very thin sheets (0.1mm) by proper soaking of them at a high temperature so as to eliminate Iron-Phosphide eutectic and bring the phosphorus entirely into solution in the iron. It has also been possible to eliminate the use of a hydrogen atmosphere during sintering by using carbon to form CO gas within the compact by reaction with the oxygen of the iron powder particles. A glassy ceramic coating applied over the compact serves as a protective coating in order to avoid atmospheric oxygen attack over the compact held at high temperature. The Fe-0.3wt% P- 0.4wt% Si alloy so formed yielded coercivities as low as 0.42 Oe, resistivities as high as 28.4 µΩcm and total losses as low as 0.132 W/Kg. Such a combination of properties may make the alloy suitable for application in magnetic relays and transformer cores.
Authors: M. El-Hofy, A.H. Salama
Abstract: Two samples of ZnO doped Ba with the chemical composition, 97ZnO-3BaO, have been prepared via oxalate co-precipitation. During precipitation the first sample, A, was stirred by magnetic stirrer while the second sample, B, was stirred via 40KHz ultrasonic wave. The obtained powders were decomposed at 400°C for 3h, then pressed and sintered at 1200°C for 1.5h. Then XRD, SEM and J-E measurements were performed and analysed. The grain sizes of the obtained ceramics were (0.5-2.26) µm and (80-119) nm for samples A and B, respectively. The J-E measurements revealed that the obtained ceramic has voltage switching characteristics, and that the switching voltage could be controlled by the stirring process.
Authors: S.S. Kanmani, K. Ramachandran
Abstract: Self-diffusion, both cationic and anionic, in ZnO nanoparticles was studied here in accord with reaction coordinate theory. The jump frequencies at various temperatures were computed. The isotope effect revealed that self-diffusion occurred mainly via a vacancy mechanism in nano ZnO; a result not previously reported in the literature.
Authors: R.N. Mariammal, K. Ramachandran
Abstract: An experimental and theoretical investigation of defect modes in tin-doped cupric oxide (Sn-doped CuO) nanoparticles synthesized via a one-step solid-state reaction was reported. The defect mode at 455 cm-1 due to Sn doping in CuO nanoparticles, calculated using a molecular model, was compared with the experimental value of 458 cm-1 obtained from the FTIR vibrational spectrum. The Debye-Waller factor (DWF) of CuO nanoparticles was determined using Rietveld refinement of the XRD pattern and the Wilson’s plot, and the results were discussed on the basis of the number of surface atoms and thermal vibrations. The effect of defect modes upon the DWF of Sn-doped CuO nanoparticles was also discussed.
Authors: B.I. Ugheoke, Othman Mamat, B. Ariwahjoedi
Abstract: Silica refractory research and development has taken a down-turn; perhaps due to the problems associated with it, or because of concerns regarding earth conservation, earth being a major source of the raw material - quartz - which is used for silica refractory manufacture. In this review, the authors have pin-pointed the problems associated with silica refractory use from the researches of the early era (1913 to 1990) and have assessed the themes of current research, in order to ascertain how well these current researches have attended to the problems raised in the early research era. The review shows that the gaps identified in the early research era still remain unattended to. It concludes by making a case for nanostructured silica obtained from rice husk ash (RHA), for the production of silica refractory, as a way of solving these problems and making silica refractory production a booming industry once again.
Authors: Frank Wirbeleit
Abstract: Boron in silicon has presented challenges for decades because of clustering and so-called transient enhanced diffusion [1-2]. An understanding of boron diffusion post rapid thermal annealing in general, and out of in situ doped epitaxially grown silicon-germanium films in particular, is essential to hetero junction engineering in microelectronic device technology today. In order to model boron diffusion, post-implantation, the local density diffusion (LDD) model has been applied in the past [3]. Via mathematical convolution of the diffusion model slope and the initial boron concentration profile, these former results were transferred to this work. In this way, non-diffusing boron was predicted to exist in the center of the presented in situ boron-doped films. In addition, boron diffusion control by co-implanted carbon was demonstrated and the applied LDD model was completed and confirmed by adapting A. Einstein’s proof [4] for this purpose.
Authors: Dmitri V. Lioubtchenko, Tatiana A. Briantseva, Z.M. Lebedeva, Tim J. Bullough
Abstract: GaAs surface composition changes occurring during Al film growth using the CBE method with laser assistance were investigated in situ by means of laser reflectivity. The results were compared with data on precise chemical analyses and X-ray microanalyses carried out after film deposition. It was found that the peculiarity of film formation depended upon the laser power. Physicochemical interactions of the Ga atoms from the GaAs surface, with atoms and molecules from the surrounding media, are determinative reactions at a laser power of 2W. At a power of 0.02W, the laser reflectivity changes were mainly due to reactions with Al. The appearance of “free” Ga and As in the region outside of the laser spot indicated the destruction of GaAs islands weakly connected with the GaAs surface.
Authors: S.B. Shrivastava, Aman Deep Acharya, R. Sharma
Abstract: The diffusion trapping model has been applied to slow positron annihilation in He+ irradiated polystyrene and polystyrene – polystyrene bilayers. The S-parameter and the positron lifetime have been calculated as a function of the incident positron energy. The effect of the fluence upon the nature of the S-parameter curve has been discussed. It has been found that a change in fluence affects positronium formation. The transition rate for surface to positronium formation has been found to be dependent upon the fluence and the atomic number of the irradiated ion. The lifetime results show that, at low energy, the o-Ps annihilates mainly at the polymeric surface. The free volume hole concentration is found to decrease at low energy, and becomes constant at higher energies.
Authors: M.Rizwan Malik, Tie Lin Shi, Zi Rong Tang, Shi Yuan Liu, M. Haseeb
Abstract: Engineering medical applications are enriched by the fabrication potential of the growing technology of Micro-Electro-Mechanical Systems (MEMS). Within this technological expansion, device manufacturing costs, failure and long-term performance reliability are critical issues that have to be resolved using basic probabilistic design methodologies which are yet largely unexploited by industrial and service companies at the mature innovation level. Modeling and testing of high-performance MEMS is a promising route, based upon these methodologies, to enhancing reliability and preventing surface failure. In this paper, we focus on the modeling of the mechanical properties of MEMS, as exemplified by a capacitive accelerometer, using probabilistic techniques. The accuracy of these techniques is also evaluated for the accelerometer with regard to those parameters that affect mainly reliability and failure. The simulated analysis of the mechanical properties is performed with easy-to-use probabilistic software known as “NESSUS”. It is concluded that probabilistic design methodologies are very effective and balanced for making design decisions that can, with both reliability and ease, ensure component or system efficiency.

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