bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Combined Addition of Silicon Carbide Whiskers and Fullerene Nanoparticles on Properties of Thermoelectric Zinc Antimonide
Authors: Itoh Takashi , Asari Nobuhisa , Kanetake Nobuyuki , Okada Akira 
Published: April 2011

AbstractThermoelectric power generation is a hopeful method harnessing waste thermal energy particularly covering a middle temperature range between 500 and 800K. A Zn4Sb3 compound is a promising “phonon glass electron crystal” material applicable to thermoelectric power generation around 700K. This material, however, has a problem of its brittleness. In this research, the silicon carbide whiskers were added into the Zn4Sb3 compound for overcoming the brittleness, and the fullerene nanoparticles were also added for improving the thermoelectric performance. The Zn4Sb3 compound was synthesized from mixture of pure zinc and antimony powders by a liquid-solid phase reactions method. Firstly, the synthesized compound powder was mixed with the fullerene nanoparticles. The planetary ball milling method was used in order to disentangle the fullerene agglomerate and to obtain a uniform mixture. Subsequently, the mixture was uniformly mixed with the SiC whiskers by the planetary ball milling. The final mixture was consolidated by the pulse discharge sintering. The synthesized phases were identified by XRD. The morphology of the whiskers after mixing was observed. The flexural strength and the thermoelectric properties of the sintered samples were measured. The length of SiC whiskers and the flexural strength were decreased with the mixing time. Though the addition of SiC whiskers lowered the thermoelectric performance, the combined addition of SiC whiskers and fullerene nanoparticles restored the performance by especially decrease of the thermoelectric conductivity owing to the phonon scattering.
Thermoelectric Oxides and Oxynitrides with Perovskite-type Structure
Authors: Weidenkaff Anke , Bocher Laura , Robert Rosa , Aguirre Myriam , Logvinovich Dmitry 
Published: April 2011

AbstractTransition metal oxides and oxynitrides with perovskite-type structures are potential high temperature stable thermoelectric materials. With innovative soft chemistry synthesis procedures the crystallite size in complex oxide ceramics with perovskite-type structure can be decreased compared to classical synthesis routes and allows to lower the heat conductivity dramatically while a large power factor can be maintained at the same time. Submicron crystallites are beneficial to lower the lattice thermal conductivity without influencing the electron mobility.In this work, perovskite-type cobaltates, molybdates and manganates are studied. The influence of heterostructures and nanocrystalline domains in perovskite oxides/oxynitrides and the correlation with transport properties and Seebeck coefficient will be discussed.
Thermoelectric properties of Bi2Te3 based thin films fabricated by pulsed laser deposition
Authors: Higomo Shun , Yagi Takashi , Obara Haruhiko , Yamamoto Atsushi , Ueno Kazuo , Iida Tsutomu , Taketoshi Naoyuki , Baba Tetsuya 
Published: April 2011

AbstractBi2Te3-based thin films were fabricated on glass substrates by the pulsed laser deposition (PLD) method. The vapor pressures of Bi and Te are significantly different, so controlling the stoichiometric composition is difficult when using conventional physical vapor deposition techniques, and the thermoelectric properties of Bi2Te3 films are sensitive to the film composition. PLD is a promising technique for the fabrication of telluride-based films such as Bi2Te3 due to its superior capability for controlling the film composition. Another advantage of PLD is the flexibility that it allows in terms of atmosphere in the reaction chamber; high concentrations of gases such as oxygen or argon can be introduced. We have measured various compositions of Bi2Te3 based films, and have identified the optimal compositions for both n-type and p-type material. The thermal conductivities of these Bi2Te3 films were evaluated by an exact measuring system, and the results were twice as low as those of conventional bulk materials. These results suggest that PLD has significant advantages for the deposition of in-plane Bi2Te3-based thin films.
Application of the Thermal Quadrupole Method in the Characterization of Thermoelectric Modules
Authors: Hatzikraniotis Euripides , Samaras Ioannis , Georgakaki Dimitra , Paraskevopoulos Konstantinos M 
Published: April 2011

AbstractMeasurements of assembled thermoelectric (TE) modules commonly include investigations of the module output power versus load resistance. Using an AC electrical measurement for TE modules, a model of equivalent passive RC circuit has been developed and tested for both the thermal and electrical characteristics of the module. In this work we present and analyze data of a commercially available module, using equivalent passive RC circuit, to examine, explain and model the electro-thermal activity in the module. In addition data we analyzed by thermal quadrupole theory. Measurements were taken over the frequency range of 0,5mHz to 50 Hz and the device performance (ZT) was evaluated from measured data.
New Thermoelectric Arsenides and Antimonides for High Temperature Applications
Authors: Xu Hong , Soheilnia Navid , Zhang Huqin , Alboni Paola N. , Tritt Terry M. , Kleinke Holger 
Published: April 2011

AbstractThree different materials crystallizing in the cubic Ir3Ge7 type are under investigation in our group, namely Mo3(Sb,Te)7, Nb3(Sb,Te)7, and Re3(E,As)7 (with E = Si, Ge, Sn). Our electronic structure calculations reveal a band gap to occur at 55 valence-electrons in all three cases, namely Mo3Sb5Te2, Nb3Sb2Te5, and Re3EAs6. Cubic holes exist in these structures that may be filled with small cations such as 3d transition metal atoms. Ni0.06Mo3Sb5.4Te1.6 is a degenerate p-type semiconductor that reaches ZT = 0.96 at 750°C, while Re3Ge0.6As6.4 is a degenerate n- type semiconductor with slightly lower ZT values. Preliminary results indicate that the Re3(Sn,As)7 system may be the most promising of the rhenium arsenides.
Converting Traditional Materials Labs to Project-based Learning Experiences: Aiding students' Development of Higher-order Cognitive Skills
Authors: Vanasupa Linda , Chen Katherine C , Stolk Jonathan , Savage Richard , Harding Trevor , London Blair , Hughes William 
Published: April 2011

AbstractAgainst a backdrop of compelling societal needs, graduates in science and engineering now must master their disciplines and demonstrate a sophisticated level of cognitive, affective and social development. This has lead a number of national and international commissions on science and engineering to urge educators to re-think the way in which STEM disciplines are taught. We have chosen to “repackage” a traditional undergraduate materials engineering curriculum in a form designed to promote the development of higher-order cognitive skills like self-directed learning and design. Classic metallurgy experiments have been converted to project-based learning experiences where students are put in the role of “designers” of problem solutions and faculty play the role of coaches. These include: designing, prototyping and marketing of a cast metal object; systems designing, building and testing of a fiber optic spectrometer; product improvement of a prosthetic device; design and evaluation of a heat treatment process for roller bearings. Projects were designed to leverage known relationships within the educational psychology literature that enable deeper learning. Evaluation of 36 juniors in a project-based learning course (i.e., the test cohort) against a quasi-control group in traditional engineering courses showed that the test cohort scored significantly higher on two motivation scales shown to be critical components in self-directed learning (p<0.001). The test cohort also reported a significantly higher use of peers as learning resources than the quasi-control group. Their motivation scores also correlate highly with self-reported comfort with several aspects of design, implying that their motivation contributes significantly to students' ability to effectively engage in the design process. In this paper, we present examples of the materials engineering projects that were designed and implemented, and the design features that enable them to promote the development of sophisticated cognitive functioning.
The Use of A Multidisciplinary Project to Expand the Materials Science Curriculum
Authors: Heard Robert , Matthews Deanna 
Published: April 2011

AbstractA special interdisciplinary project course was offered in the Fall of 2006 within the Carnegie Institute of Technology at Carnegie Mellon University. The course was open to students from across the university, it drew participants from Civil and Environmental Engineering, Engineering and Public Policy, Materials Science and Engineering, Architecture, the School of Design. This multidisciplinary collection of students formed the necessary knowledge base to approach the various tasks of the project. Each student was to rely on their academic experience and talents to contribute to the work, while simultaneously learning from those in other disciplines. The participating material science and engineering were juniors acquainted with fundamental of materials. Some students were taking courses involving steel making process and steel mechanical properties concurrently. Students in civil and mechanical engineering and architecture are familiar with structural design and construction processes. Students in engineering and public policy and environmental engineering have experience with life cycle assessment and environmental impacts. The collaborative group experience introduced students to how disciplines interact in the real world, encouraging them to pursue their own interests in broader areas.The project consisted of three efforts assessing life cycle impact in terms of energy consumption, greenhouse gas emissions, and economic costs of equivalent products made from both steel and wood The first effort involved comparison of steel products versus wood products in existing designs. The second, looked at the optimization of steel products to improve design options and the third tried to identifying opportunities to leverage the use of steel materials in green building design and construction, based on certification requirements established by the US Green Building Council and the Leadership in Energy and Environmental Design (LEED) rating system.At Carnegie Mellon, the Green Design Initiative researchers have been leaders in life cycle assessment methodology development and assessment, and have a history of merging students and faculty from across the university into research teams. This multidisciplinary project was good example of how common topics can be exploited to provide excellent discovery opportunities for undergraduate engineering programs.
Thermal Expansion and Residual Stress in Ancient Chinese Bronze Castings
Authors: Taube Michelle , McCarthy Blythe 
Published: April 2011

AbstractAncient Chinese bronze vessels from the Shang to Zhou dynasties (c. 1500 - 221 BCE) were cast using piece molds. Several large vessel shapes, especially those with legs, have been found to be made in several steps with the vessel body cast onto previously-made legs or other appendages. In this situation the molten metal contacts and must attach to the solid pieces from the first casting. Similar interfaces are found at solid metal mold spacers or chaplets used in the casting process. Previous researchers showed that the casting can exhibit concentration gradients and evidence of slip in the regions around these interfaces. In this work, we studied the thermal expansion of the bronze at cast-on joints in ancient Chinese bronzes using thermomechanical analysis (TMA). The results are compared with those from reference lead-tin bronze alloys.
Fabrication of PdxNiyP100-x-y Metallic Glass Film by Electroless Alloy Plating and its Catalyst Activity
Authors: Imamura Yoshihide , Sone Masato , Shibata Akinobu , Ishiyama Chiemi , Higo Yakichi 
Published: April 2011

AbstractPd-Ni-P films were systematically plated using a mixture of Pd and Ni-P plating solutions. The films were plated by electroless alloy plating using three Pd/Ni-P mixture ratios (1/1, 3/1, and 1/3) at plating temperatures adjusted within a range from 303 to 333K. An increase in the Ni-P mixture ratio or in the plating temperature led to an increase in the Ni content of the plated film and a decrease in the Pd content. The P content of the plated film remained almost constant. These results indicate that the composition of the fabricated film can be effectively controlled by adjusting the plating temperature and mixture ratio. The plated film had a flat surface morphology without defects such as pinholes or nodules. TEM observation of the film revealed an amorphous structure. DSC analysis during heating revealed an endothermic peak and exothermic peak corresponding to the glass transition and crystallization, respectively. On the basis of these results, we concluded that the plated Pd-Ni-P film was metallic glass. The plated Pd-Ni-P film was also confirmed to have catalytic activity, as the Ni-P alloy was plated directly onto the film without catalyzation by electroless plating. The high flatness and uniformity of the surface of the Ni-P film plated onto the Pd-Ni-P film suggests that the Ni-P film grew via a one-dimensional growth mechanism.
Free Volume Relaxation Process in Zr50Cu40Al10 Bulk Metallic Glass Studied by Positron Annihilation Techniques
Authors: Ishii Akito , Hori Fuminobu , Iwase Akihiro , Yokoyama Yoshihiko , Konno Toyohiko J 
Published: April 2011

AbstractStructural relaxation around free volume in Zr50Cu40Al10 bulk metallic glass (BMG) during isothermal annealing at 473, 573 and 673 K which are below glass transition temperature Tg =675 K have been investigated by positron annihilation lifetime (PAL) and coincidence Doppler broadening (CDB) measurements. The trends of change in positron lifetime, which correspond to the size of free volume at each annealing temperature, have a good correlation with their density change. These annealing processes obey a stretched exponential relaxation function (KWW: Kohlrausch-Williams-Watts law). Fitting parameters of KWW function, with relaxation time t0 and β, in each temperature were determined. These relaxation parameters depend on the annealing temperature, suggesting the distribution of activation energy for structural relaxation. Moreover, the profile of electron momentum distribution around free volume derived by CDB spectrum during annealing showed no appreciable change at each temperature. These facts suggest that long range chemical ordering, particularly around the free volume, dose not take place essentially.
Molecular Dynamics Simulations of Glassforming Network Fluids
Authors: Binder Kurt , Horbach Juergen , Hawlitzky Michael 
Published: April 2011

AbstractMolecular Dynamics simulations of molten oxides, such as fluid silicon dioxide and germanium dioxide, based on simple classical pair potentials, are compared with corresponding Car-Parrinello “ab initio” Molecular Dynamics (CPMD) work and with experiment. It is shown that CPMD provides a significantly better account for properties on short length scales, but classical MD is still indispensable to deal with larger scales of length and time. The behavior of the mean square displacement of the particles as well as the incoherent intermediate scattering function is compatible with a mode coupling description, at least at very high temperatures, while the diffusion constants show a crossover to Arrhenius behavior near the mode coupling critical temperature of these systems. Finally, the results for the network forming liquids are compared to those from simulations of binary metallic alloys such as Al80Ni20, which form a structure similar to densely packed hard spheres.
Analysis of Indentation Creep
Authors: Stone Donald , Elmustafa A. A. 
Published: April 2011

AbstractIncreasingly, indentation creep experiments are being used to characterize rate-sensitive deformation in specimens that, due to small size or high hardness, are difficult to characterize by more conventional methods like uniaxial loading. In the present work we use finite element analysis to simulate indentation creep in a collection of materials whose properties vary across a wide range of hardness, strain rate sensitivities, and work hardening exponents. Our studies reveal that the commonly held assumption that the strain rate sensitivity of the hardness equals that of the flow stress is violated except for materials with low hardness/modulus ratios like soft metals. Another commonly held assumption is that the area of the indent increases with the square of depth during constant load creep. This latter assumption is used in an analysis where the experimenter estimates the increase in indent area (decrease in hardness) during creep based on the change in depth. This assumption is also strongly violated. Fortunately, both violations are easily explained by noting that the “constants” of proportionality relating 1) hardness to flow stress and 2) area to (depth)2 are actually functions of the hardness/modulus ratio. Based upon knowledge of these functions it is possible to accurately calculate 1) the strain rate sensitivity of the flow stress from a measurement of the strain rate sensitivity of the hardness and 2) the power law exponent relating area to depth during constant load creep.
A Thermo-Magneto-Mechanical Free Energy Model for NiMnGa Single Crystals
Authors: Morrison Phillip , Seelecke Stefan , Kohl Manfred , Krevet Berthold 
Published: April 2011

AbstractThe paper extends the authors' recent model for one-dimensional rate-dependent magneto-mechanical behavior of NiMnGa single crystals to account for temperature-dependent effects including austenite/martensite and ferro-/paramagnetic phase transitions. The magneto-mechanical model is based on the Helmholtz free energy landscape constructed for a meso-scale lattice element with strain and magnetization as order parameters. This two-dimensional energy landscape includes three paraboloidal wells representing the two easy-axis and one hard-axis martensite variants relevant for the structurally one-dimensional case. Phase transformations resulting from applied stresses and magnetic fields follow from a system of evolution laws based on the Gibbs free energy equations and the theory of thermally activated processes, which in the low-thermal-activation limit appropriately reproduce the athermal transformation behavior observed in these materials. The phase fractions subsequently determine the macroscopic strain and magnetization of a sample of NiMnGa by means of a standard averaging procedure. To account for the first-order phase transitions to austenite, additional temperature-dependent wells representing the stable states of austenitic NiMnGa are introduced into the Helmholtz energy landscape. The transition from ferromagnetic to paramagnetic states is modeled as a second order transformation based on the gradual degeneration of the ferromagnetic wells with increasing temperature.
Fast Characterization of Silicon Membrane Structures by Laser-Doppler Vibrometry
Authors: Gerbach Ronny , Ebert Matthias , Bagdahn Joerg 
Published: April 2011

AbstractMicromechanical structures were investigated nondestructively via laser-Doppler-vibrometry to determine defect structures. Therefore, silicon membrane structures were characterized by their measured resonant frequencies and mode shapes. The influence of defects on the micromechanical structures is shown on the measured dynamic properties. Defect samples were indentified on the basis of the ratios of measured resonant frequencies and the quantified comparison of mode shapes without an identification of unknown parameters. The investigations showed that a fast determination of defect structures is possible by measured dynamic properties.
A Direct Method of Determining Complex Depth Profiles of Residual Stresses in Thin Films on a Nanoscale - Mechanics of Residually Stressed Systems
Authors: Massl Stefan , Keckes Jozef , Pippan Reinhard 
Published: April 2011

AbstractThe basic ideas behind the calculation procedure of the developed ion beam layer removal method (ILR method) to determine complex depth profiles of residual stresses are explained. In order to give the readers an understanding of the mechanics of films on substrates and the corresponding stresses in cantilevers fabricated from such systems, the equations necessary for the calculations are explained by means of a residually stressed model system.
Aligned Low Temperature Wafer Bonding for MEMS Manufacturing: Challenges and Promises
Authors: Dragoi Viorel , Matthias Thorsten , Mittendorfer Gerald , Lindner Paul 
Published: April 2011

AbstractThe increased complexity of current generations of MEMS devices imposes new requirements for wafer bonding. Among these can be mentioned low process temperature (<400°C), precise optical alignment of substrates, ability to bond a large variety of substrates and the possibility to bond with defined intermediate layers. An important aspect in aligned wafer bonding is that alignment accuracy needs to be correlated to the type of bond process. Especially in case of processes using bonding layers the post-bond alignment accuracy will be given by the behavior of the bonding layers. This paper aims to review the main criteria to be considered in defining aligned wafer bonding processes. Particularly bonding of substrates containing electronics (e.g. CMOS wafers) is currently of high technological interest.
RF MEMS Behavior, Surface Roughness and Asperity Contact
Authors: Rezvanian O. , Zikry M. A. , Brown C. , Krim J. 
Published: April 2011

AbstractModeling predictions and experimental measurements were obtained to characterize the electro-mechanical response of radio frequency (RF) microelectromechanical (MEM) switches due to variations in surface roughness and finite asperity deformations. A Weierstrass-Mandelbrot fractal representation was used to generate three-dimensional surface roughness profiles. Contact asperity deformations due to applied contact pressures, were then obtained by a creep constitutive formulation. The contact pressure is derived from the interrelated effects of roughness characteristics, material hardening and softening, temperature increases due to Joule heating, and contact forces. The numerical predictions were qualitatively consistent with the experimental measurements and observations of how contact resistance evolves as a function of deformation time history. This study provides a framework that is based on an integrated modeling and experimental measurements, which can be used in design of reliable RF MEMS devices with extended life cycles.
A Miniature Silicon Condenser Microphone Improved with a Flexure Hinge Diaphragm and a Large Back Volume
Authors: Kim Hyejin , Lee Sung Q , Lee Jaewoo , Lee Sangkyun , Park Kangho 
Published: April 2011

AbstractWe have developed a miniature silicon condenser microphone improved with a spring supported hinge diaphragm and a large back volume, which is designed in order to increase sensitivity of microphones. MEMS Technology has been successfully applied to miniature silicon capacitive microphones, and we fabricated the smallest condenser silicon microphone in the presented reports. We used the finite-element analysis (FEA) to evaluate mechanical and acoustic performances of the condenser microphone with a flexure hinge diaphragm. From the simulation results, we confirmed that the sensitivity of a flexure hinge diaphragm can be improved about 285 times higher than a flat diaphragm. The first and second modes occurred at 15,637Hz and 24,387Hz, respectively. The areas of the miniature condenser microphones with a hinge diaphragm are 1.5 mm × 1.5 mm. We measured the impedance characteristics and sensitivities of the fabricated condenser microphones. The sensitivities of microphones are around 12.87 μV/Pa (-60 dB ref. 12.5 mV/Pa) at 1 kHz under a low bias voltage of 1 V, and the frequency response is flat up to 13 kHz.