bluuebunny/crossref_metadata_2025 huggingface dataset:
Macro Machined Photoacoustic Non-Resonant Cell
Authors: Zhao Jun Juan , Zhao Zhan , Du Li Dong , Wu Shao Hua
Published: July 2011

Photoacoustic spectroscopy (PAS), which is widely used in gas sensing applications, is capable of a wide dynamic range, simplicity of use, high selectivity and sensitivity and also possesses novel detection characteristics when the cell are scaled into a micro system design. In a PAS system which is based on the photoacoustic effect, if the parameters of light power, chopper frequency, and absorption coefficient of the target analyte were decided, the level of the acoustic signal is inverse proportional to the radius square of the cell in which the sample is laid. So, miniaturizing the size of the cell can improve the system’s sensitivity. In our experiment, we initially designed a macro photoacoustic non-resonant cell (PNC) using stainless steel. As the macro cell is scaled to a dimension approaching the microelectromechanical systems (MEMS) level, the basic information gained from these initial tests is a special reference to fabricating a MEMS scale device. The non-resonance test conducted at 100 Hz demonstrated large signals (15.89mV) for CO2concentrations at 600 ppm and high signal-to-noise (S/N) values (~ 85:1). Then a structure of monolithic MEMS photoacoustic cavity was proposed which incorporate a three-wafer.
An AD7746-Based Data Acquisition System for Capacitive Pressure Sensor in Weather Detection Application
Authors: Huang Zhen , Zhu Jian , Lu Le
Published: July 2011

Data acquisition system for barometric capacitive pressure sensor with high accuracy is present. The precision of the data acquisition system is less than 1fF, which improves the pressure sensor with high accuracy of 0.1hPa in the pressure range from 5hPa to 1080hPa. The data acquisition system consists of an AD7746 chip, an ATmega16 microprocessor, a 1602 LCD display and a pair of wireless modules. The capacitance data acquired by the AD7746 are transferred to a host computer using RS232 port via wireless module and display on the LCD in real-time. Preliminary results obtained from experiments show that this system fulfills the requirements of the weather observation and can be used in upper-air weather detection applications.
A High-Performance Interface ASIC for Quartz Rate Sensor
Authors: Chen Wei Ping , Wang Qing Yi , Yin Liang , Zhou Zhi Ping
Published: July 2011

In this work, an ASIC interface for quartz rate sensor (QRS) is introduced. Based on 0.6μm 18V N-well CMOS process, it is the first to be realized in the domestic. This chip has a minimized size of 5×4.4mm2. Compared with traditional interface constructed by separate devices, such interface implemented with integrated circuits is advantageous in size and power consumption. This satisfies the requirements of miniature and low power consumption in space industry and military domain. The test results show that this interface features low noise, high linearity, and stable operation. Integrated with the sensor, the entire system presents high performance in short term bias stability, nonlinearity, output noise, bias variation over temperature, and power consumption.
New Style Four-Electrode MEMS Conductivity Chip
Authors: Wu Shao Hua , Zhao Zhan , Fang Zhen , Du Li Dong , Geng Dao Qu , Xu Jing , Zhao Jun Juan
Published: July 2011

MEMS sensor for solution conductivity measurement has been applied widely which has many advantages such as cheap, accurate, batch fabricate, and good consistent etc. Existent MEMS conductivity sensors usually have planar structure with four short parallel electrodes so that the two voltage electrodes are tend to be polluted and consequently lead to mistakes for the conductivity test system. A new pattern of conductivity chip with an annular voltage electrode to enhance the ability of anti-pollution based on MEMS technology is going to be introduced in this article; the ANSYS simulation is applied to help demonstrate the reasons why the new pattern of conductivity chip has good ability of anti-pollution and the experiment results are also presented to show the performance of the conductivity sensor.
A Four-Quadrant Analog Multiplier Based on CMOS Source Coupled Pair
Authors: Chen Wei Ping , Wang Tian Yang , Xu Hong Lei , Liu Xiao Wei
Published: July 2011

A novel structure for CMOS four-quadrant analog multiplier is presented. The multiplier is based on the square law of MOSFET. To enlarge the input impedance and improve the linearity, CMOS source coupled pair was employed. Also active attenuator was used to enhance the input range. Compared with the traditional multipliers based on Gilbert cell, the proposed circuit features high linearity, high input range. Circuit simulation using HSPICE with 0.5μm CMOS technology shows that under ±2.5V supply the proposed multiplier provides linear range of more than 50% of the voltage supply, THD is 0.3% at 100kHz and 0.8% at 1MHz, -3dB bandwidth is 2.5MHz, and the power consumption is 5mW.
Characterization of Contact and Bulk Piezoresistive Properties of Carbon Nanotube/Styrene-Butadiene-Styrene Composite
Authors: Wang Zhi Feng , Yang Ji Min , Ye Xiong Ying , Liu Li Tao , Xie Xu Ming
Published: July 2011

Carbon nanotube (CNT) filled polymer nanocomposites are increasingly regarded as a realistic alternative to conventional smart materials. In this paper, we studied the contact and bulk piezoresistive properties of multi-walled carbon nanotube/styrene butadiene styrene (MWNT/SBS) composite. Measurements of resistance change under pressure utilizing an Au plate PCB electrode and a sputtered Au layer electrode for same samples were implemented to examine bulk piezoresistivity of the composites and the influence of contact resistance. The results showed that the contact resistance responses to stress for separated electrodes are more remarkable than bulk resistance responses in the MWNT/SBS composite films, but not so stable.
DFT Study of Structure, Electronic, Optical and Magnetic Properties of ZnO and Cu-Doped ZnO Clusters
Authors: Ding Jian Ning , Wang Xiu Qin , Yuan Ning Yi
Published: July 2011

The structure, polarizability and magnetic properties of ZnnOn and Cu-doped Znn-1On (n=2-12, 16) clusters are theoretically investigated using density-functional theory (DFT) at B3LYP/LanL2DZ level. For pure ZnnOn clusters, Zn3O3, Zn8O8 and Zn12O12 are relatively more stable unit, and the ZnnOn clusters with bigger HOMO-LUMO gap tends to have larger <α>/2n. For Cu-doped Znn-1On clusters, the substitution of Zn by Cu atom narrows the HOMO-LUMO gaps and enhances polarizability. In single-doped CuZnn-1On clusters, the magnetic moments of O atoms bonded with Cu atoms are ferromagnetically coupled to the moments of the Cu atoms.
Effect of Wet Etching Parameter on the Diameter and Length of Silicon Nanowires
Authors: He Yang , Jiang Cheng Yu , Yin Heng Xu , Jun Chen , Yuan Wei Zheng
Published: July 2011

A wet etching method for preparing silicon nanowires on silicon substrates at near room temperature is presented. The effect of experiment parameter on the silver nanoparticle forming including concentration of AgNO3, immersing time and solution temperature, and the effect of etching time on the length of silicon nanowires are investigated. It is concluded that solution temperature has more impact to diameter of silicon nanowires than concentration of AgNO3 and immersing time and longer etching time may result in longer silicon nanowires.
A Novel Assembly Method for a Micro Direct Methanol Fuel Cell Using Multi-Layer Bonding Technique
Authors: Zhu Yi Ming , Wang Xiao Hong , Zhou Yan An
Published: July 2011

A novel assembly method for a micro direct methanol fuel cell (μDMFC) using multi-layer bonding is developed. The anode and cathode plates of the μDMFC are fabricated by using MEMS technologies. PDMS gaskets are introduced to fill the gap between the silicon plate and the membrane electrode assembly (MEA) to prevent fuel or oxidant leaking. To assemble a μDMFC, adhesive tapes and oxygen plasma treatment of the PDMS gasket for surface activation are introduced. In this method, the PDMS gasket with adhesive tapes is bonded to the silicon plate then bonded to the MEA, which fixes the movable components of the μDMFC to simplify the assembly operation. The novel assembly method shows good maneuverability and reliability. The μDMFC shows great performance due to the low internal resistance attributing to this novel assembly method. With thermal insulated holders, the μDMFC generates a power density of 20.29mW/cm2. This assembly method is applicable for the assembly of the μDMFC stack.
Multidisciplinary Design Optimization of the 2-D Microaccelerometer
Authors: Liu Yu , Wen Zhi Yu , Chen Li , Yang Hong Yun
Published: July 2011

Multidisciplinary design optimization of a 2-D microaccelerometer is discussed. Considering the influence of microstructure design, fabrication process and detection circuit, as well as the constraints of fabrication limitations, damp design and adhesion factor, a multidisciplinary optimization model is developed by global criterion method, where the sensitivity, resolution, resonant frequency and damping ratio are selected as objective functions. Furthermore, the multi-objective optimum of the model is obtained by genetic algorithm.
Assessing the Validity of Quantum Corrections to Molecular Dynamics Simulations of Bulk Silicon
Authors: Zhou Qi Ming , Bi Ke Dong , Chen Yun Fei
Published: July 2011

Thermal conductivities of bulk silicon are calculated by equilibrium molecular dynamics (MD) simulations. Applying common used quantum corrections to the MD results, does not bring them into better agreement with the theoretical predictions or experimental data, while the uncorrected values are closer to the theoretical predictions and experiments below 400K. By assessing the validity of quantum corrections according to theoretical calculations and MD simulations, we demonstrate that the hypothesis of equating the heat fluxes is not reliable. In addition, we explore that the rations of thermal conductivities of MD simulations and quantum calculations are approximate to 1. Then a modified quantum correction for mapping MD simulations to quantum systems is proposed.
Fabrication of Nano-Grating by Focused Ion Beam / Scanning Electron Microscopy Dual-Beam System
Authors: Yao Bao Yin , Luo Hu , Feng Li Shuang , Zhou Zhen , Wang Rong Ming , Chi Yuan Yuan
Published: July 2011

The uniform, well designed nano-gratings have been successfully fabricated by using a dual beam focused ion beam (FIB)/scanning electron microscopy (SEM) system on the silicon substrates coated with 15 nm thick Au layer. The nano-gratings were designed with period of 840 nm, groove of 425 nm and beam of 415 nm. By adjusting the FIB parameters of milling like beam current, dwell time and scanning model, the fabricated nano-gratings were uniform in width and the side wall had good verticality. The currently fabricated nano-gratings using focused ion beam can be adjusted to serve as sub-wavelength optical resonant sensor which can be extended to nano-grating accelerometer with resolution of 10-9g.
Rapidly Identify the Critical Parameter of MEMS Device Based on Element Model Library
Authors: He Yang , Jiang Cheng Yu , Yuan Wei Zheng , Yung Kai Leung , Xu Yan
Published: July 2011

The purpose of this paper is to introduce a simplified yet efficient method to identify the critical parameter of MEMS device based on rapid computer experiments instead of expensive physical experiments. The prototype model of MEMS device is rapidly established by connecting reusable and parameterized element models based on developed element model library. Critical parameters are identified and optimal parameter assemblies are obtained using Taguchi method based on computational experiments of the prototype model. A typical MEMS device--micro resonator is used for demonstrating the design methodology. The method enables the designer to rapidly identify critical parameter of a new MEMS device in early stage of design.
Analysis of Capillary Condensation of Vapor in Multi-Wall Carbon Nanotubes
Authors: Wang Wei , Wang Xin , Li Tuo , Chen Wei Ping
Published: July 2011

Multi-wall Carbon Nanotubes (MWNTs) is the new hotspot material as the active sensing element, but there is no certain theory on the phenomenon of the vapor's capillary condensation in MWNTs for the present. This paper presents a new theory that the capillary condensation of vapor in MWNTs mostly occur in the internal hollow tube, according to the calculation of equivalent model of MWNTs. A kind of carbon nanotubes (CNTs) humidity sensor based on quartz crystal microbalance was fabricated, CNTs employed as adsorption materials. The sensor was put in 11% and 97% relative humidity environment in experimental, and the value of MH2O/MCNT was calculated. The theory in this paper is proved by the comparison between the experimental and the analysis results.
Stability Analysis in High-Order Electromechanical Sigma-Delta Accelerometer
Authors: Liu Yun Tao , Liu Xiao Wei , Chen Wei Ping , Wu Qun
Published: July 2011

A nonlinearity model including distortion components for sigma-delta (ΣΔ) accelerometer that allows stability analysis is described. Based on this model, closed-loop stability and signal dependent stability are analyzed detailedly. To verify the conclusions, Matlab/Simulink model for a fourth-order ΣΔ accelerometer is designed. The simulation results indicate that high-order system needs a large compensation coefficient, and it will not affect the performance due to the very high low-frequency gain of the loop filter. High-order system is conditionally stable, and stability is affected by the input signal.
Tribological Properties of Magnesium Silicate Powders Prepared by Ball Milling
Authors: Xiao Zhou , Su Xun Jia , Hou Gen Liang , Bi Song , Liu Zhao Hui
Published: July 2011

Hydroxyl magnesium silicate powders were prepared by planetary-milling machine and a certain amount of No.46 mechanical oil was canned into the stainless steel vial in order to investigate its influence on the size of particles. The tribological properties of the powders in the oil were investigated on a four-ball machine. The morphologies and the chemical components of the worn surfaces were characterized by means of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The ball milling results showed that the adding of mechanical oil decreased the cold welding and agglomeration, finally, fine silicate powders of 2μm in mean size were made. The tribological test results showed that the extreme pressure and antiwear properties of No.46 mechanical oil were improved by the additive obviously. The lubrication mechanism is inferred that a boundary lubrication film is formed and the tribochemical reactions occur on the friction surfaces due to the active agents in the silicate crystal, thus it can be seen that the silicate powders is a new and enviroment friendly lube additive.
Microelectronics Package Design Using Experimentally-Validated Modeling and Simulation
Authors: Young Nathan , Johnson Jay , Ewsuk Kevin G.
Published: July 2011

Packaging high power radio frequency integrated circuits (RFICs) in low temperature cofired ceramic (LTCC) presents many challenges. Within the constraints of LTCC fabrication, the design must provide the usual electrical isolation and interconnections required to package the IC, with additional consideration given to RF isolation and thermal management. While iterative design and prototyping is an option for developing RFIC packaging, it would be expensive and most likely unsuccessful due to the complexity of the problem. To facilitate and optimize package design, thermal and mechanical simulations were used to understand and control the critical parameters in LTCC package design. The models were validated through comparisons to experimental results. This paper summarizes an experimentally-validated modeling approach to RFIC package design, and presents some results and key findings.
Microwave-Accelerated Curing of Cement-Based Materials: Compressive Strength and Maturity Modeling
Authors: Makul Natt , Agrawal Dinesh Kumar
Published: July 2011

Microwave energy is applied to cure cement-based materials with microwave power and time of application. First, the dielectric permittivity of them during a 24-hour first-hydration period at a frequency of 2.45 ± 0.05 GHz is measured and analyzed. Second, the characteristics of hardened cement paste as subjected to microwave energy with multi-mode rectangular wave guide, with specific attention to temperature rise, microstructure and development. This article presents a theoretical analysis to relate the compressive strengths of the CBM when subjected to microwave energy at an operating frequency of 2.45 GHz with a multi-mode cavity. The effects of water-to-solid mass ratios, aggregates, pozzolan materials, microwave power levels, application times, sequential processes, delay times, and comparisons with conventional curing (lime saturated-deionized water) were taken into account. The results indicated that for increasing the compressive strength, the main coefficient (a) as the Richards model are up to the highest value, the optimal energy level (microwave power × application time) should be in the range of 2.0 to 3.0 KJ when the specimen size was of  70.0 mm  40.0 mm in order to avoid the position of highest electric field strength within the cavity. Furthermore, the calculated compressive strengths based on the maturity concept overestimated the strength during 28 day first hydration time of the microwave-cured cement-based materials using the formula:
Optimisation of the Ceramic Phase for Ceramizable Silicone Rubber Based Composites – Microstructural Aspect
Authors: Pędzich Zbigniew , Bieliński Dariusz M. , Dul Jan , Zarzecka-Napierała Magdalena
Published: July 2011

The paper presents results of investigation on composition of mineral components used for ceramizable silicone rubber-basing composites. Using different crystalline phase additives it is possible to assure the proper course of the composite degradation and its transformation during ceramization process. Three crystalline components were tested as an additive to silicone rubber – bentonite, kaolinite and wollastonite. They were added simultaneously with a glassy phase. These compounds during firing evolved (decomposed) and introduced into ceramized material polycrystalline structure, responsible for its properties. Characteristic of ceramized composite body created during heating was investigated by mercury porosimetry. The porosity evolution was described in the range of 600 – 1050°C.
Hybrid, Nano-Structurized Materials of Special Purpose on the Basis of Silicon Dioxide
Authors: Mansurov Z. , Mofa N.N. , Shabanova T.A.
Published: July 2011

Highly disperse powders of complex morphology, micro- and nanostructure were obtained by treatment of quartz in a planetary-centrifugal mill of a dynamic action in the presence of different organic substances. The surface layer with the thickness of 10-70nm modifying the particle of quartz after mechanochemical treatment is a polymer with encapsulated nanosized particles of iron. Powder material from such highly disperse composition particles of modified quartz is characterized by ferromagnetic and electroconducting properties. A galvanic effect in a nanosize scale is possible to take place on the surface of particles consisting of a polymer nanostucturized film with sites supersaturated with metallic and carbon clusters. The practical realization of such structures is promising when producing highly active sorbents as well as for collecting of oil products spills on the surface of water.
The SH – Synthesis of Ceramic Based on Titanium Carbide and Silicon Carbide Composite Materials
Authors: Mansurov Zulkhair A. , Vongai I.M. , Chervyakova O.V. , Zavalishina T.A. , Aknazarov S.H.
Published: July 2011

The processes of SHS synthesis ceramic materials with the using of titanium oxide and silicon were investigated. The ceramic materials with the high operating characteristics were obtained.
Young’s Modulus and Poisson’s Ratio of Liquid Phase-Sintered Silicon Carbide
Authors: Okuzono Yasushi , Hirata Yoshihiro , Matsunaga Naoki , Sameshima Soichiro
Published: July 2011

The compressive stress-strain relation (room temperature) of SiC compact (75 vol% 800 nm SiC- 25 vol% 30 nm SiC) hot-pressed with 1.6 vol% Al2O3- 0.83 vol% Gd2O3 at 1950 °C was examined at a crosshead speed of 0.05 mm/min. The dense SiC (97.8 ± 1.5 % theoretical density) possessed 796 MPa of average flexural strength, 5.27 MPa・m1/2 of fracture toughness, 8.1 of Weibull modulus, and 475 GPa of average flexural Young’s modulus. The strains of SiC compacts along directions of height and width changed nonlinearly with applied compressive stress. The apparent Young’s modulus and Poisson’s ratio decreased with increasing strain along the direction of height and reached constant values of 275 ± 59 GPa and 0.214 ± 0.05, respectively. The steady-state compressive Young’s modulus was independent of the flexural strength.
Synthesis and Electrochemical Properties of C/LiMnPO4 Cathode Materials by Complex Polymerized Method
Authors: Fujita Atsushi , Isobe Fuminari , Kodera Takayuki , Ogihara Takashi
Published: July 2011

C/LiMnPO4 materials were synthesized by the complex polymerized method. An orthorhombic olivine type structure was obtained by calcination at temperatures over 973 K under an argon/hydrogen (5%) atmosphere. Differential thermogravimetric analysis showed that the carbon content of C/LiMnPO4 was about 65 wt%. The initial discharge capacity of C/LiMnPO4 calcined at 973 K was 135 mAh/g at 0.1 C and 60 mAh/g at 1 C.
Characterization of Samarium Doped Ceria Powders Having High Specific Surface Area Synthesized by Carbon-Assisted Spray Pyrolysis
Authors: Myoujin Kenichi , Ichiboshi Hiroki , Kodera Takayuki , Ogihara Takashi
Published: July 2011

Spherical samarium doped ceria (Ce0.8Sm0.2O1.9, SDC) powders having high specific surface area (SSA) were successfully synthesized by carbon-assisted spray pyrolysis (CASP). Saccharides, such as monosaccharides and disaccharides, or organic acids were used as carbon sources. The physical and chemical properties of these powders were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Thermo gravimetry-Differential Thermal Analysis (TG-DTA), and BET. Decarbonized powders obtained by this method exhibit spherical morphologies and nano- and submicron-sizes. The SSA of SDC obtained from CASP was more than seven times higher than that obtained from conventional spray pyrolysis (CSP). The SSA of the decarbonized SDC powders obtained by calcination at 900 °C was estimated to be approximately 70 m2/g by using the BET method. The relative density of SDC obtained from CASP was higher than that obtained from CSP. The relative density of the SDC pellet was highest (96 %) when it was sintered at 1400 °C.
First-Principles Calculations of Structural Changes Induced by Oxygen Vacancies in Tetragonal Phase BaTiO3
Authors: Iwazaki Yoshiki , Sakashita Tatsuo , Suzuki Toshimasa , Mizuno Youichi , Tsuneyuki Shinji
Published: July 2011

Structural changes induced by oxygen vacancies in tetragonal phase BaTiO3are studied with first principles calculations within density functional theory. In our calculations, the incorporation of oxygen vacancies greatly decreases c/a ratio of the tetragonal phase BaTiO3, and a phase transition from tetragonal to cubic phase occurs when the incorporation of the oxygen vacancies reaches about 4%. Our results also shows that the generation of the oxygen vacancies slightly increases the volume of BaTiO3, and the increases are typically less than 0.5% even in heavily reduced conditions.
Planarization of Zinc Oxide Surface and Evaluation of Processing Damage
Authors: Miyazaki Hiroki , Adachi Yutaka , Sakaguchi Isao , Ishigaki Takamasa , Ohashi Naoki
Published: July 2011

The processes for polishing a ZnO surface were investigated with the aim of establishing a process for obtaining an atomically flat surface with high crystalline quality. The defects in a layer undergoing mechanical polishing were monitored through photoluminescence measurements, and the purity of the polished surface was characterized by SIMS. An atomicallyfishing process.
Relationship between the Crystallinity and Magnetic Properties of Cr2O3/LiNbO3/Cr2O3 Multi-Layer Materials
Authors: Yokota Takeshi , Tsuboi Yasutoshi , Kito Shinya , Imura Rempei , Gomi Manabu
Published: July 2011

The magnetic properties of an artificial multiferroic material, a Cr2O3/LiNbO3/Cr2O3 hetero structure with various-thickness LiNbO3 layers, were investigated. All samples showed ferromagnetism due to the existence of oxygen deficiency or an excess of the Cr2O3 layer in the LNO/Cr2O3 interface. The ferromagnetism of the samples was affected by the crystal orientation of the LiNbO3 layer, and seemed to have a major impact on the magneto-electric behavior of this hetero system.
Electrical Properties of La(Cr,Mn)O3 NTC Materials
Authors: Fujita Toshiaki , Fujiwara Kazutaka , Yamaguchi Takashi
Published: July 2011

We investigated the electrical properties of the perovskite R(Cr,Mn)O3(where R is selected from various rare earth elements and Y), which is suitable for use in negative temperature coefficient (NTC) thermistors. The substitutions of Mn for Cr in La(Cr,Mn)O3and larger ions for R3+decreased both the resistivities (r) and thermistor constants (B values) estimated from measurements at 25°C and 50°C according to r = r0exp(B/T). The activation energies of the carrier number (Eg) and carrier mobility (WH) were estimated by measuring the thermoelectric power and resistivity. A change in WHcorresponded to a change in the B value. We discussed the relationship between the grand state electronic configuration of the M3+ions and the local lattice distortion around the M3+ions. The change in WHcould be qualitatively linked to the M3d– O2p transfer energy, which is corresponding to the hybridization between the M3d and O2p orbital (M: transition metal elements, O: oxygen).
Characterization of Grain Boundaries of Lead-Free Semiconducting Ceramics Using BaTiO3-(Bi1/2K1/2)TiO3 System
Authors: Takeda Hiroaki , Joong Sang Han , Tateishi Takashi , Kunej Spela , Leach Colin , Freer Robert , Hoshina Takuya , Tsurumi Takaaki
Published: July 2011

BaTiO3–(Bi1/2K1/2)TiO3 (abbreviated as BT-BKT) solid solution ceramics, as a lead-free PTC (positive temperature coefficient of resistivity) thermistor material usable over 130°C, has been synthesized by sintering in N2 atmosphere and after annealing in air over 1200°C. In the BT-BKT ceramics with PTC property, the impedance/modulus spectroscopic plots have revealed that a third resistance-capacitance (RC) response besides grains and grain boundaries. Using the remote electron beam induced current (REBIC) configuration, imaging has revealed EBIC contrast consistent with the presence of negatively charged electrostatic grain boundary barriers in the BT-BKT semiconducting ceramics.
Multilayer Varistor with Low-Voltage Characteristics from ZnO + ACoO3 Ceramics (A = Ca, Sr and Ba)
Authors: Koga Eiichi , Sawada Noriko , Amisawa Mikinori
Published: July 2011

The non-linear properties provided from ZnO + ACoO3 ceramics (A=Ca,Sr and Ba) and their application to MLCV for ESD-suppression were studied. Their ceramics showed excellent non-linear I-V properties in lower voltage region. Especially, ZnO + SrCoO3 ceramics intrinsically had about 20 % lower Vgb than those of Pr and Bi-based ZnO varistors. MLCV using ZnO + SrCoO3 ceramics demonstrated extremely low-voltage property of V1mA= 5.6 V with maintaining excellent non-linearity and reliability performance against ESD.
Resistivity of Thin Films of MoSi2–Si Composites
Authors: Hikita Shinya , Hayashi Teppei , Sato Yuuki , Yoshikado Shinzo
Published: July 2011

Thin films of the composite of molybdenum silicate (MoSi2) and silicon (Si) were fabricated by radio frequency magnetron sputtering using a target made of a powder mixture of MoSi2 and Si. The composite thin film consisted of two types of molybdenum silicate with hexagonal and unknown crystal structures. The temperature dependence of the resistivity of a thin film was measured using the four-probe method. The sign of the temperature coefficient of the resistivity changed from positive to negative with increasing molar ratio of Si to Mo. It was suggested that molybdenum silicate with the hexagonal structure had both positive and negative temperature coefficients of resistivity, whereas the unknown structure showed only a negative temperature coefficient of resistivity.
Molecular Dynamics Study on Dielectric Properties of Silicon Oxynitride: Composition and Microstructure Dependence
Authors: Tomita Munemasa , Tsuruta Kenji
Published: July 2011

Extra-long molecular-dynamics simulations are performed to study the interplay between dielectric properties and microstructures of silicon oxynitride. We quantitatively obtained the ionic permittivity and its linear dependence on nitrogen concentration. Analyses on microstructure of the oxynitride show that, as the N concentration increases, N atoms enter Si-O networks creating smaller-sized rings. While overall tendency of dielectric constant is monotonic increase on the N concentration, microscopic characteristics, such as local displacement of atoms, are strongly depend on local bonding environments.
Development of Gas-Solid Phase Hybrid Synthesis Method of Single Crystal Ba2SiO4:Eu2+
Authors: Sakamoto Tatsuya , Uematsu Kazuyoshi , Ishigaki Tadashi , Toda Kenji , Sato Mineo
Published: July 2011

We succeeded in the single crystal growth of Ba2SiO4:Eu2+ by novel synthesis method which was gas (SiO) and solid (Ba - Sc - Al - Eu - O) phase hybridized. The Ba2SiO4:Eu2+ single crystal was synthesized by interfacial crystal growth after the reaction of the SiO gas with the surface of Ba - Sc - Al - Eu - O substrate in the reductive atmosphere. The single crystals were plate-like crystals with about 500 μm sizes and emitted green light around 500 nm under 300 - 450 nm excitation.
High-Temperature Depolarization of Alkali Niobate Lead-Free Piezoceramics
Authors: Matsudo Hitoshi , Kakimoto Kenichi , Kagomiya Isao
Published: July 2011

Na0.5K0.5NbO3 (NKN) lead-free piezoelectric ceramics was synthesized by a mixed oxide reaction method. The ceramics was poled under an electric field of 3 kV/mm at 150 °C for 0.5 h. The thermally stimulated depolarization current (TSDC) measurement was carried out at the heating rate of 1 °C/min from room temperature up to 500 °C under an applied voltage of 0 and 0.5 V. The zero-bias TSDC pattern showed broad patterns around at 365 and 375 °C. These temperatures corresponded to the temperatures showing bending points in the Arrhenius plot of TSDC measured under 0.5 V. The oxygen vacancy related electrical conduction was changed at 313 °C at the heating step. The mobile oxygen vacancy in NKN ceramics was piled up under the poling field, and the oxygen vacancy was diffused at temperature higher than 313 °C.
Description of Crystallographic Morphologies of Product Phases with Singularity and Δg Distribution
Authors: Zhang Wen Zheng , Shi Zhang Zhi
Published: July 2011

Product phases from various phase transformations often exhibit fascinating morphologies. Facets of unique crystallographic orientations are characteristic of the morphologies. Based on a comparison of facets in the surfaces and interfaces of crystals, this paper proposes to use singularity as the common features of facets on a crystal. While association of facets with energy singularity has been established from the Wulff construction, we defined singularity in structure with an absence of one or more types of defects common to a vicinal surface or interface. Singularity in an interfacial structure is described in terms of both ledges and dislocations. When dislocations are involved, the candidates of the singular interfaces derive mainly from the principal O-lattice planes. The orientations of these planes are defined by Δg’s, which are measurable in diffraction patterns. Singularity with respect to the orientation relationship results from further eliminating defects, which is permitted by a special arrangement of Δg’s. The candidates of singular interface confined by the arrangement of discrete Δg’s are helpful for understanding the crystallographic morphology. One example from an Mg alloy is provided to show the association of the singular interfaces with Δg’s. The effect of the potential presence of a long-range strain and kinetic effects are briefly discussed.
Stochastic Statistical Theory of Precipitation in Metastable Alloys with Application to Fe-Cu and Fe-Cu-Mn Alloy Systems
Authors: Khromov Konstantin , Soisson Frederic , Stroev Andrey , Vaks Valentin
Published: July 2011

The consistent and computationally efficient stochastic statistical approach is suggestedto study kinetics of decomposition of metastable alloys. An important parameter of the theory is thesize of locally equilibrated regions at the nucleation stage which is estimated using the ``maximumthermodynamic gain'' principle suggested. For several realistic models of Fe-Cu alloys studied, the re-sults obtained agree well with kinetic Monte Carlo simulations. Application of methods developed tostudies of decomposition of Fe-Cu-Mn alloys revealed a great sensitivity of evolution to both the con-figurational and kinetic interatomic interactions in an alloy. Using for these interactions the availablefirst-principle and CALPHAD estimates, we can well reproduce the peculiar features of decomposi-tion of Fe-Cu-Mn alloys observed in experiments.
Distribution of Dislocations in Nanostructured Bainite
Authors: Cornide J. , Miyamoto Goro , Caballero Francisca G. , Furuhara Tadashi , Miller Michael K. , Garcia-Mateo Carlos
Published: July 2011

The dislocation density in ferrite and austenite of a bainitic microstructure obtained by transformation at very low temperature (300 °C) has been determined using transmission electron microscopy. Observations revealed that bainitic ferrite plates consist of two distinctive regions with different substructures. A central region in the ferrite plate is observed with dislocations that may result from lattice-invariant deformation at the earlier stage of bainite growth. As plastic deformation occurs in the surrounding austenite to accommodate the transformation strain as growth progresses, the Ferrite/Austenite interface has also a very distinctive dislocation profile. In addition, atom-probe tomography suggested that dislocation tangles observed in the vicinity of the ferrite/austenite interface might trap higher amount of carbon than single dislocations inside the bainitic ferrite plate.
Modeling of Growth and Formation of Pearlite Colonies for Simple Models of Alloys Iron-Carbon
Authors: Khromov Konstantin , Stroev Andrey , Vaks Valentin
Published: July 2011

Growth and formation of pearlite colonies are simulated for some simple models of alloysiron-carbon. The steady-state growth is shown to be possible only via the interfacial but not the volumecarbon diffusion mechanism. The model of formation of pearlite colonies based on assumptions ofstrong enhancement of carbon diffusion near grain boundaries is suggested.
Understanding of the Bainite Transformation in a Nano-Structured Bainitic Steel
Authors: Hodgson Peter , Timokhina Ilana , Xiong Xiang Yuan , Adachi Yoshitaka , Beladi Hossein
Published: July 2011

A 0.79C-1.5Si-1.98Mn-0.98Cr-0.24Mo-1.06Al-1.58Co (wt%) steel was isothermally heat treated at 200°C for 10 days to form a nano-scale bainitic microstructure consisting of nanobainitic ferrite laths with high dislocation density and retained austenite films. The crystallographic analysis using TEM and EBSD revealed that the bainitic ferrite laths are close to the Nishiyama-Wassermann orientation relationship with the parent austenite. There was only one type of packet identified in a given transformed austenite grain. Each packet consisted of two different blocks having variants with the same habit plane, but different crystallographic orientations. The presence of fine C-rich clusters and Fe-C carbides with a wide range of compositions in bainitic ferrite was revealed by Three-dimensional Atom Probe Tomography (APT). The high carbon content of bainitic ferrite compared to the para-equilibrium level of carbon in ferrite, absence of segregation of carbon to the austenite/bainitic ferrite interface and absence of partitioning of substitutional elements between the retained austenite and bainitic ferrite were also found using APT.
Effects of Transformation Temperature on Variant Grouping of Bainitic Ferrite in Low Carbon Steel
Authors: Takayama Naoki , Miyamoto Goro , Furuhara Tadashi
Published: July 2011

Effects of transformation temperature on variant grouping tendency of bainitic ferrite in a low carbon low alloy steel transformed isothermally are investigated by means of electron backscatter diffraction analysis. Baintic variants of Kurdjumov-Sachs (K-S) orientation relationship belonging to the same Bain correspondence tend to form adjacently in the bainite structure formed at 823K, while the K-S variants sharing the same close-packed plane parallel relation form adjacently in the bainite structure formed at 723K and lath martensite formed by quenching.
Neutron Diffraction Study of a CuAlBe Shape Memory Alloy
Authors: Dubois Matthieu , Mathon Marie Hélène , Klosek Vincent , Andre Gilles , Lodini Alain
Published: July 2011

This work presents the texture evolution of the austenitic phase of a copper based shape memory alloy by neutron diffraction. The Cu-11%Al-0.62%Be (in mass %) alloy was subjected to cold and hot rolling processes. The texture of the rolled samples at reduction rates of 5%, 10% and 15% respectively were compared to those of the raw material. A <001> partial fiber is observed for the raw material and cold rolled samples whereas the texture of the hot rolled sample is mainly characterized by a <111> fiber. The influence of these mechanical treatments on the transition temperatures and the hysteresis evolution was also analysed by following the integrated intensity of the {220} reflection of the austenitic phase. A shift towards low temperatures of martensitic transition temperatures is observed with the increasing of the rolling rate.
Effects of Cooling Rate and Sn Addition on the Microstructure of Ti-Nb-Sn Alloys
Authors: Aleixo Giorgia T. , Lopes Eder S.N. , Contieri Rodrigo , Cremasco Alessandra , Afonso Conrado Ramos Moreira , Caram Rubens
Published: July 2011

Ti-based alloys present unique properties and hence, are employed in several industrial segments. Among Ti alloys, β type alloys form one of the most versatile classes of materials in relation to processing, microstructure and mechanical properties. It is well known that heat treatment of Ti alloys plays an important role in determining their microstructure and mechanical behavior. The aim of this work is to analyze microstructure and phases formed during cooling of β Ti-Nb-Sn alloy through different cooling rates. Initially, samples of Ti-Nb-Sn system were prepared through arc melting furnace. After, they were subjected to continuous cooling experiments to evaluate conditions for obtaining metastable phases. Microstructure analysis, differential scanning calorimetry and X-ray diffraction were performed in order to evaluate phase transformations. Depending on the cooling rate and composition, α” martensite, ω phase and β phase were obtained. Elastic modulus has been found to decrease as the amount of Sn was increased.
Martensite Fraction Determination Using Cooling Curve Analysis
Authors: Marcano Diana , Mendez Patricio , Gibbs John W. , Kannengiesser Th.
Published: July 2011

This work presents a method of calculating the martensite fraction of an Fe-alloy, usingcooling curve analysis (CCA). It is based on a differential heat balance equation which takes intoaccount only convective exchange with the surroundings. By measuring a T(t) curve of an Fe-alloyand solving numerically the differential heat balance equation the martensite fraction can be calcu-lated. It is found that calculated martensite fraction using this methodology is comparable with resultsobtained using electron backscattering diffraction (EBDS).
Zêta Hydride Precipitation in Zirconium Alloys: an Example of Elastically Driven Morphology of Coherent Trigonal Precipitates inside a Сlose-Packed Hexagonal Matrix
Authors: Thuinet Ludovic , Legris Alexandre
Published: July 2011

The influence of a crystallographic symmetry break on the morphology of precipitates during the coherent precipitation of a trigonal phase in a close packed hexagonal matrix is analyzed. It is pointed out that in spite of the isotropy of the stress free strain of the precipitate in the basal plane, the existence of an extra elastic constant in the precipitate (associated to the loss of symmetry) induces a morphological evolution from a shape having a symmetry of revolution around the threefold axis to a needle-like one oriented along the compact directions in the basal plane. These general considerations are applied to the case of zêta zirconium hydrides the crystallography of which has been recently identified to be coherent with that of the alpha Zr matrix. The influence of symmetry break and elastic heterogeneity on precipitation morphology has been numerically addressed by using different approaches. An analytical approximation to the elastic energy based on Eshelby equivalent inclusion method allows obtaining a qualitative criterion to determine the occurrence of a shape bifurcation of zêta hydrides.
First-Principles and Genetic Modelling of Precipitation Sequences in Aluminium Alloys
Authors: De Jong Maarten , Dutta Rangan K. , Sluiter Marcel H. F. , Miroux Alexis G. , van der Zwaag Sybrand , Sietsma Jilt , Rivera-Díaz-del-Castillo Pedro E.J.
Published: July 2011

Aluminium alloys display complex phase transitions to achieve their desired properties.Many of these involve elaborated precipitation sequences where the main role is not played by ther-modynamically stable species, but by metastable precipitates instead. An interplay between phasestability, crystal symmetry, diffusion, volume and particle/matrix interfaces sets the pace for the ki-netics. Thermodynamic modelling, which focuses on stable precipitates, is not an aid in describingsuch processes, as it is usually transitional phases that achieve the desired properties. The model pre-sented here combines first--principles to obtain the transition precipitate energetics (both at the bulkand at the interface with the matrix) with thermochemical databases to describe the overall kineticsof stable precipitates. Precipitate size and number density are captured via the Kampmann--Wagnernumerical approach, which is embedded in a genetic algorithm to obtain optimal compositional andheat treatment scenarios for the optimisation of the mechanical properties in aluminium alloys of the 7000 series.
Effect of Mn on the Nanoprecipitation in Binary Fe-Cu alloys
Authors: Shabadi Rajashekhara , Taillard Roland , Radiguet Bertrand , De Baerdemaeker Jérémie , Leunis Elke
Published: July 2011

Effect of the third alloying element Mn on Cu-precipitation was studied in a binary Fe-1.3% Cu alloy. Precipitation in both the alloys was investigated after homogenization treatment and subsequent artificial aging. Advanced characterization techniques such as Positron Annihilation Spectroscopy (PAS) and Tomographic Atom Probe (TAP) were used to establish the chemical composition, morphology, size and number density of the Cu-rich phases. Combined results of PAS and TAP were particularly useful in order to follow the Cu precipitation in the binary alloy. At short aging times, addition of Mn significantly increased the kinetics of hardening while its effect on the magnitude of precipitation strengthening is only marginal. It further increases the over-aging kinetics.
The β'-α' Interaction: a Study of early Stages of Phase Separation in a Fe-20%Cr-6%Al-0.5%Ti Alloy
Authors: Capdevila Carlos , Miller Michael K. , Russell K.F. , Chao J. , López F.A.
Published: July 2011

The temporal evolution of the microstructure resulting from phase separation into Fe-rich (α), Cr-rich (α¢), and Fe(Ti,Al) (β¢) phases of a Fe-20Cr-6Al-0.5Ti alloy has been analyzed by thermoelectric power measurements (TEP). The early stages of decomposition and the evolution of the three-dimensional microstructure have been analyzed by atom probe tomography (APT). The roles of Cr, Al, and Ti during the decomposition process have been investigated in terms of solute partitioning between the phases. Analysis of proximity histograms revealed that significant Al and Ti partitioning occurs, which is consistent with theoretical calculations. The results indicate that as the α-α¢ phase separation proceeds, Al and Ti are rejected into the α phase, which causes the β¢ phase to nucleate on the surface of the α¢ phase.
Study by Differential Thermal Analysis of Reverse Spinodal Transformation in 15-5 PH Alloy.
Authors: Herny Emilie , Andrieu Eric , Lacaze Jacques , Danoix Frédéric , Lecoq Nicolas
Published: July 2011

Alloy 15-5 PH is a stainless steel with 15 wt.% Cr and 5 wt.% Ni that is precipitation hardened by addition of Cu. In its semi-finished state, this alloy consists in Cu-supersaturated soft martensite; its high specific properties come from a final tempering consisting in a heating to 550-600°C, holding for 4 hours, and then air cooling. This treatment leads to nanometric Cu precipitation that hardens the material and to transformation of some martensite to reverted austenite which is then stable and provides ductility. While a' embrittlement of such steels is known to occur at temperature in the range 450-520°C, it has been reported that they can be sensitive to the same phenomenon after long term ageing at temperature as low as 300°C, with a significant loss of ductility and an increase of the ductile-to-brittle transition temperature. Atom probe studies showed that this degradation is related to demixtion of martensite into Fe-rich and Cr-rich phases. Depending on the ageing temperature, demixtion can proceed through a nucleation and growth precipitation or by spinodal decomposition of the martensitic matrix. The present study reports differential thermal analyses (DTA) performed upon heating samples of material held at various temperatures (290-525°C) for various times (410 h to 8500 h) that have been characterized by atom probe. A clear DTA signal is obtained upon the reverse spinodal transformation that is further found to depend on ageing conditions.
Phase Transformation Near Dislocations and Cracks
Authors: Massih Ali R.
Published: July 2011

A generic model for nucleation of oriented second-phase in alloys in the vicinity of cracksand dislocations, is considered. The model employs the Ginsburg-Landau approach, which accountsfor the elasticity of crystalline solid and the interaction of structure/composition with the elastic ﬁeldin the vicinity of the defect and in the crystalline bulk. We examine the nature of the structural phasetransition and construct its phase diagram.
Precipitation of Co in Supersaturated Au-Based Au-Co Alloys; Microstructural Evolution and Transformation Kinetics
Authors: Bauer Rico , Bischoff E. , Mittemeijer Eric Jan
Published: July 2011

Natural formation of the unusual bcc modification for Co was demonstrated to occur upon precipitation of Co in supersaturated Au90Co10 alloy, applying high resolution transmission electron microscopy. The bcc Co phase precipitates as thin (0.5 – 1 nm) plates along {100} habit planes, exhibiting the orientation relationship: {100}Au,fcc//{100}Co,bcc and <001>Au,fcc//<011>Co,bcc. Prolonged annealing induces a Bain type transformation from bcc Co into fcc Co. The precipitation kinetics of Co in supersaturated solid solutions of Au90Co10 was investigated by DSC upon isothermal annealing at temperatures in the range 567 K to 612 K and upon isochronal annealing at heating rates in the range 5 to 40 K·min‑1. Results of the fitting of a modular model of transformation kinetics to, simultaneously, all isothermal DSC runs and to, simultaneously, all isochronal DSC runs, could be discussed in terms of the different extents of the effects of quenched‑in defects on isothermally and isochronally conducted transformations.