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In order to achieve enhancements in thermoelectric efficiency, microstructures that can form numerous interfaces have been investigated intensively for controlling the transport of charge carriers and heat-carrying phonons. In this paper, we report the heterogeneous microstructure of Mg2Si0.6Sn0.4 thermoelectric materials synthesized by a simple B2O3 encapsulation method and investigation of its influence on thermoelectric properties. The addition of Sb causes the evolution of a Sn-rich secondary phase and a heterogeneous microstructure consisting of Sn-deficient grains and a Sn-rich boundary phase, with coherent interfaces between them. The secondary phase induced by Sb doping suppressed the bipolar effect and reduced the thermal conductivity because of minority carrier blocking and phonon scattering at phase boundaries. However, high concentration of Sb in Sn-rich phase led to insufficient doping in Si-rich main phase and electron-hole compensation by Mg vacancies, resulting in decrease of the doping efficiency of Sb.

Bi2Te2.7Se0.3 bulk materials containing x vol% MgO nanoparticles (average particle size ≈ 100 nm, x = 0, 0.5, 1.0, 1.5) were synthesized by using high-energy ball milling and plasma- activated sintering (PAS) without any special process for nanoparticle dispersion. A microstructure investigation using a scanning electron microscope (SEM) confirmed that MgO nanoparticles were properly dispersed in the Bi2Te2.7Se0.3 matrix and that the grain size was smaller in MgO-containing samples due to suppressed grain growth. The resistivity and the maximum Seebeck coefficient of Bi2Te2.7Se0.3 increased with increasing MgO content whereas the thermal conductivity decreased in the measurement temperature range of 298 K - 573 K. As a result, the maximum dimensionless figure of merit, ZT max, increased about 8.5% in this study, from 0.806 for pristine Bi2Te2.7Se0.3 to 0.875 when x = 1.5. The ZT max was observed to shift to lower temperature, the electron concentration to decrease, and the electron mobility to increase with increasing x, which were explained using a hypothesis that the Te Bi antisite defect concentration decreased as the MgO content increased. In summary, the addition of MgO nanoparticles has been shown to be a simple and effective method to improve the low-temperature thermoelectric properties of n-type Bi2Te3 materials.

Miniature thermoelectric modules (TEMs) are required for micro power generation as well as local cooling, and they should have small size and high performance. However, conventional bulk TEMs generally have in-plane dimensions of a few centimeters, and empty space between the legs for electrical isolation makes efficient miniaturization difficult. In this study, a miniature TEM with footprint of about 0.35 cm2 and leg height of 0.97 mm was fabricated by reducing the dimensions of the legs and attaching them together to form a closely packed assembly, without using microelectromechanical processes. First, Bi0.4Sb1.6Te3 (BST) and Bi2Te2.7Se0.3 (BTS) ingots were made by ball milling and spark plasma sintering, and the ingots were cut into thin plates. These BST and BTS plates were then attached alternately using polyimide tapes, and the attached plates were sliced vertically to produce thin sheets. This process was repeated once again to make chessboard-like assemblies having 20 p–n pairs in an area of 0.35 cm2, and electrical contacts were formed by Ni sputtering and Ag paste coating. Finally, thermally conductive silicone pads (~500 μm) were attached on both sides of the assembly using electrically insulating interface thermal tapes (∼180 μm). The maximum output power (Pmax) from the miniature module was about 28 μW and 2.0 mW for temperature difference (ΔT) of 5.6°C and 50.5°C, respectively. Reducing the contact resistance was considered to be the key to increase the output power.

We found that Na is a good source to develop twin structures in the Bi-Te system, such as Ag as noted in a previous study. The twin boundaries had a considerable influence on reductions of the lattice thermal conductivity due to phonon scattering by the nano-ordered layers and on reductions of the electrical resistivity owing to the defects generated by the substitution of Na into the cation sites. Here, we report the enhanced thermoelectric properties of a Na-doped p-type Bi0.5Sb1.5Te3 alloy. Measurements show that the electrical resistivity and the Seebeck coefficient decrease with Na doping due to an increase in the free carrier (hole) concentration and that the lattice thermal conductivity decreases with Na doping. The achieved maximum ZT value was 1.20 at 423 K, which is approximately 20% higher than that of Bi0.5Sb1.5Te3 under the same fabrication conditions. These results were achievable by controlling the morphology of the twin structure and the carrier concentration by means of Na doping.

Density functional calculations are performed to study the band structures of Bi2Te3-related binary (Bi2Te3, Sb2Te3, Bi2Se3, and Sb2Se3) and Sb/Se-doped ternary compounds [(Bi1−x Sb x )2Te3 and Bi2(Te1−y Se y )3]. The band gap was found to be increased by Sb doping and to be monotonically increased by Se doping. In ternary compounds, the change in the conduction band structure is more significant as compared to the change in the valence band structure. The band degeneracy of the valence band maximum is maintained at 6 in binaries and ternaries. However, when going from Bi2Te3 to Sb2Te3 (Bi2Se3), the degeneracy of the conduction band minimum is reduced from 6 to 2(1). Based on the results for the band structures, we suggest suitable stoichiometries of ternary compounds for high thermoelectric performance.

Ag(Sb1−x La x )Te2 compounds (x = 0, 0.01, 0.02, 0.03, and 0.05) were fabricated to study the effect of La-doping on the thermoelectric properties by using a spark-plasma-sintering process. All specimens were nearly single-phase AgSbTe2 with a small amount of Ag2Te. The La doping in AgSbTe2 resulted in a reduction in the electrical and the thermal conductivity but increased the Seebeck coefficient. A small amount of La doping increased the Seebeck coefficient because of the electron filtering effect. The maximum figure of merit was 1.50 due to the enhanced power factor and extremely low thermal conductivity.

Bi2Te3 thermoelectric thin films were deposited on the flexible polyimide substrates by RF magnetron co-sputtering of a Bi and a Te targets. The influence of the substrate temperature and RF power on the microstructure, chemical composition, and the thermoelectric properties of the sputtered films was investigated by using scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and in-plane resistivity/Seebeck coefficient measurement. It was shown that the thermoelectric properties of the films depend sensitively on the Bi/Te chemical composition ratio and the substrate temperature, and the layered structure was clearly observed from the cross section of the (00L)-oriented, nearly stoichiometric Bi2Te3 films when the substrate temperature is higher than 250 °C. As-deposited Bi2Te3 films deposited at 300 °C show the highest power factor of 0.97 mW/K2m and the Seebeck coefficient of −193 μV/K at 32 °C, which also have (00L) preferred orientation and the layered structure. The durability of the Bi2Te3 films on polyimide against repeated bending was also tested by monitoring the film resistance, and it was concluded that the Bi2Te3 films are applicable reliably on the curved surfaces with the radius of curvature larger than 5 mm.

We investigated the microstructure of GeTe-based thermoelectric materials by using transmission electron microscopy. GeTe-based materials with a rhombohedral structure showed a herringbone structure, which is described as a regular arrangement of domain structures. The crystal region with different rhombohedral axis formed a domain. Domains with different variants showed alternative white and black contrast. We proposed a parallelepiped domain unit surrounded by (0 0 1), ( 1 1 ¯ 0 ) and ( 1 1 1 ¯ ) planes. Domain units were arranged along a specific direction 〈0 0 1〉 and 〈1 1 0〉, which formed many colonies. Well-aligned colonies comprised various kinds of herringbone structures. Several herringbone structures were described in detail based on the transmission electron microscopy results.

We report the enhanced thermoelectric properties of Ce-doped AgSbTe2 (AgSb1−xCexTe2) compounds. As the Ce contents increased, the proportion of heterophase Ag2Te in the AgSbTe2 gradually decreased, along with the size of the crystals. The electrical resistivity and Seebeck coefficient were dramatically affected by Ce doping and the lattice thermal conductivity was reduced. The presence of nanostructured Ag2Te heterophases resulted in a greatly enhanced dimensionless figure of merit, ZT of 1.5 at 673 K. These findings highlight the importance of the heterophase and doping control, which determines both electrical and thermal properties.

Non-Newtonian fluid mechanics takes charge of an important role in the oil industries. Especially in the oil well drilling process, the drilling fluid such as mud keeps the drill bit cool and clean during drilling, with suspending drill cuttings and lubricating a drill bit. The purpose of this study is to examine the effect of fluid mud rheological properties to predict different characteristics of non-Newtonian fluid in the mud mixing tank on offshore drilling platforms. In this paper, ANSYS fluent package was used for the simulation to solve the hydrodynamic force and to evaluate mud mixing time. Prediction of the power consumption and the pumping effectiveness has been presented with different operating fluid models as Newtonian and non-Newtonian fluid. The comparison between Newtonain mud model and non-Newtonian mud model is confirmed by the CFD simulation method of drilling mud mixing tank. The results present useful information for the design of the drilling mud mixing tanks and provide some guidance on the use of CFD tool for such non-Newtonian fluid flow.

A hash function is an essential cryptographic algorithm primitive that is used to provide integrity to many applications such as message authentication codes and digital signatures. In this paper, we introduce a concept and test method for a Cryptographic Algorithm Validation Program (CAVP). Also, we design an SHA-3 CAVP program and implement an SHA-3 algorithm in 16bit-UICC. Finally, we compare the efficiency of SHA-3 with SHA-2 and evaluate the exellence of the SHA-3 algorithm.

The thermoelectric properties of the Ge1−xMnxTe compounds were investigated in the temperature range from 300 K to 773 K. The crystal structure of the compound was gradually changed with Mn, changing from a rhombohedral to a cubic-like cell. The Seebeck coefficient and the electrical resistivity were increased with Mn. From the Hall coefficient measurement, the reduction of the carrier concentration was confirmed and was responsible for the change of the electrical properties. The thermal conductivity was also reduced with Mn. The maximum dimensionless figure of merit, ZT, was obtained for x = 0.05 composition, where the value was ZT = 1.3 at 773 K. The evolution of the crystal structure with Mn attributed to the change of the thermoelectric properties. The Mn-doped compound which has a more cubic phase than a rhombohedral exhibited superior thermoelectric properties to the pure rhombohedral phase. Open image in new window

The Bi-doped Mg2Si powder was fabricated with solid state reaction method and consolidated with hot pressing method and then its thermoelectric properties were investigated. The n-type transport properties were measured in all samples and temperature dependence of the electrical properties shows a behavior of degenerate semiconductors for Bi-doped samples. The electrical resistivity and the Seebeck coefficient were greatly reduced with Bi, which was mainly due to the increment of the carrier concentration. The samples have maximum carrier concentration of 8.2 × 1018 cm−3. The largest ZT value of 0.61 was achieve at 873 K for Mg2.04SiBi0.02. The Bi-doping was found to be an effective n-type dopant to adjust carrier concentration.

In drilling process of oil wells, the drilling fluid such as mud keeps the drill bit cool and clean during drilling, with suspending drill cuttings and lubricating a drill bit. In this paper, a commercial CFD package(ANSYS Fluent 15.0) was used to solve the hydrodynamic force and evaluate mud mixing time in the mud mixing tank on offshore drilling platforms. Prediction of power consumption in co-rotating and counter-rotating models has been compared with results of Nagata's correlation equation. This research shows the hydrodynamic effect inside the two phase mud mixing tank according to rotating directions(co-rotating and counter-rotating). These results, we can conclude that the co-rotating direction of the two shafts with mixing blade in the mud mixing tank can be a preferable in power consumption and mixing time reduction.

P-type (Bi,Sb) 2 Te 3 compounds were fabricated with high energy ball-milled powder and their thermoelectric properties were investigated as a function of the ball milling time. The fine grain sizes were confirmed with the X-ray analysis and the microscopy images in the samples fabricated with powders from long ball milling time. The values of the lattice thermal conductivity of the samples at high temperature show smaller values for long milling time (>24 h) than those for short time, resulted from the finer grain sizes of the samples. As well as the microstructural change, the Seebeck coefficient and the electrical resistivity of the compounds were significantly altered with the ball milling time. The carrier concentration was dramatically increased in the samples after 24 h milling, which was attributed to the formation of the antisite defects introduced by the accumulated thermal energy. The formation of antisite defects may be also promoted by the unintentional Fe doping from jars and balls. The highest value of ZT = 1.14 was achieved at 323 K for the samples with 10 h. The temperature where the value of ZT was maximized and the values of ZT was varied with the ball milling time, which implies that the ball milling time should be carefully optimized for the suitable application of this compounds.

Non-stoichiometric Mn x Te1−x (x = 0.48–0.52) has been prepared by a melt-quench process followed by spark-plasma-sintering to investigate its thermoelectric properties. Polycrystalline Mn x Te1−x with x > 0.51 has a nearly single MnTe phase. The measured Seebeck coefficient and electrical conductivity show a similar trend, in which a transition occurs near 473 K with increasing temperature. The thermal conductivity of Mn x Te1−x compounds shows a tendency to decrease with increasing Mn content. Along with a low thermal conductivity and a high power factor, the samples with x > 0.51 have a high figure of merit, which reaches 0.41 at 773 K. The results indicate that production of a homogenous MnTe single phase is an effective way to improve the thermoelectric properties of p-type non-stoichiometric Mn x Te1−x compounds.

The effect of Sb addition on the thermoelectric properties of the AgPb18Sb1+xTe20 (x = 0 − 1) compounds (LAST-18 compounds) has been investigated in a temperature range between 323 K and 723 K. The measured thermoelectric properties were compared with LAST-18 (x = 0 composition) previously reported and fabricated using the same procedure. All samples showed a negative Seebeck coefficient, which implies the major carrier is the electrons. The carrier concentration of the samples with additional Sb was larger than that of the LAST-18 compounds, indicating that Sb is acting as a donor element in the LAST compounds. From the results of XRD, the Seebeck coefficient, and Hall measurement, the solubility limit of Sb in LAST was estimated. The maximum dimensionless figure of merit, ZT, was obtained for the x = 0.2 composition, where the value was ZT = 1.33 at 723 K. The enhancement of ZT was attributed to the increment of the carrier concentration, resulting in a dramatic reduction of electrical resistivity compared with LAST-18.

The purpose of this paper is to investigate the doping effect of La, as a substituent against Sb, on the transport properties of the AgSbTe2 thermoelectric compounds. The samples were fabricated by spark plasma sintering (SPS). The intended compound was Ag(Sb1−xLax)Te2, in which the doping content was x = 0∼0.05. Un-doped and La-doped compounds were revealed a nearly single phase of AgSbTe2, containing a very small amount of Ag2Te. With an increase in La content, the fractured surfaces of Ag(Sb1−xLax)Te2 changed from an irregular morphology to a laminar morphology, indicating a transition from ductile to brittle cleavage fracture. The Seebeck coefficient of the Ag(Sb1−xLax)Te2 compound was, as its highest value, 358 μV/K for Ag(Sb0.98La0.02)Te2 (i.e. x = 0.02) at 150°C. Electrical resistivity exhibited higher values for the compound with the value of x=0.02 than for other compounds. Power factor was higher for the doped sample (x = 0.01) than for the un-doped compound at the temperature region of 25∼300°C. Desirably, the carrier concentration of the Ag (Sb1-xLax)Te2 compound was optimized from 1020/cm3 to 1019 /cm3 by La doping, regardless of doping content.

Polycrystalline specimens of the thermoelectric material Zn4Sb3 were prepared by the hot-pressing method at various temperatures and pressures and their thermoelectric properties were evaluated in a temperature range from 298 K to 673 K. A single phase of Zn4Sb3 was obtained in the samples prepared at 673 K with a pressure above 150 MPa, whereas ZnSb was placed in the Zn4Sb3 matrix for the samples prepared at 100 MPa. The electrical transport properties of the single phase compound showed p-type conduction and metallic transport behavior based on the temperature dependence. The sample produced at 673 K under a pressure of 200 MPa exhibited the highest ZT value of 1.36 at 673 K. This study suggests that the dense and single-phase Zn4Sb3 compound is a route to achieve a high thermoelectric performance.

(GeTe)x(AgSbTe2)1−x(x=80, 85) compounds were fabricated by melting-hot press and RSP-hot press processes. The (GeTe)85(AgSbTe2)15 compound, which composed of mainly crystalline and partly amorphous structures, was produced in part by rapid solidification. X-ray diffraction analysis showed that the (GeTe)x(AgSbTe2)1−x compounds represented a single phase of GeTe. The electron transport properties were evaluated over the temperature range of RT∼773K, and then systematically changed with compositions x in (GeTe)x(AgSbTe2)1−x compounds. The maximum Seebeck coefficient was 227 μV/K at 673K in the (GeTe)80(AgSbTe2)20 compounds fabricated by melting and hot-press process. The minimum resistivity was shown in the (GeTe)85(AgSbTe2)15 by melting and hot-press process.

In this study, the thermoelectric properties of the Ag-doped Bi0.5Sb1.5Te3 compounds were investigated in the temperature range from 323 K to 573 K. Ingots were fabricated by a conventional melting process and the powder crushed from ingots was then sintered using a hot-pressing method. The temperature dependence of the Seebeck coefficient and the electrical conductivity of the Ag-doped Bi0.5Sb1.5Te3 compound are characteristic of degenerate semiconductors, which is fairly different from the conventional Bi0.5Sb1.5Te3 compound. The power factor (α2σ) of the quaternary compound was larger than that of the ternary, which is mainly due to the increase in the electrical conductivity with doping content of Ag. The thermal conductivity was greater than that of the Ag-free Bi0.5Sb1.5Te3 compound in the temperature range from 323 K to 523 K. The lattice thermal conductivity showed low values throughout the temperature range. The maximum value of the dimensionless figure of merit (ZT) of the 0.05 wt. % Ag-doped compound and the ternary alloy were 1.2 at 373 K and 0.88 at 323 K, respectively. Each of the maximum peak ZT shifts to a higher temperature region with increases in the doping content of Ag. This is likely due to the control of the lattice thermal conductivity by the twin structure, which had a nano-ordered layer.

The influence of the cooling condition after solution treatment on the high temperature fatigue resistance of 23Cr-26Ni heat resistant steel was investigated. Two different cooling conditions were applied to the steel after solution treatment at 1230oC for 3 hours. One specimen was water quenched immediately after the solution treatment. The other one was furnace cooled at a rate of 0.5oC/min down to 750oC after the solution treatment. Then, both specimens were aged at 750oC for 5 hours. The low cycle fatigue (LCF) test was conducted to investigate the influence of high temperature on the LCF behaviors of the heat-resistant 23Cr26Ni alloy. Under two different heat treatment conditions, the LCF test was performed at total strain amplitudes ranging from ±0.4~0.9% at room temperature (RT) and 600°C. During the test, initial cyclic hardening occurred at both experimental temperatures. This phenomenon was attributed to the increase in the dislocation density due to cyclic deformation, which resulted in the interaction between the newly created dislocations and precipitates. Cyclic softening was observed in the later stages of the LCF test at RT. The formation of precipitates and increase in the dislocation density were observed using TEM. Also, the XRD and EDS techniques were used to verify the type and composition of the precipitates.

A realistic model for the electrical output power from a thermoelectric device has been developed. The electrical contact resistivity, the thermal contact conductivity, and the thickness of an insulating layer and an electrode were considered to enhance the theoretical model. The maximum output power was achieved in the specific length of a thermoelement, which was largely dependent on the contact properties and the thickness of the insulating layer and the electrode.The measured output power from the fabricated thermoelectric device was understood and compared with the developed model. It was also seen that the derived model can be used to estimate the output power as a function of the dimension of the thermoelectric device. The optimized design was essential to enhance the performance of the thermoelectric device for waste heat recovery.

The electronic states of Mn15O56 and Mn14FeO56 cluster models were theoretically calculated by the DV-Xα method, a first principle molecular orbital method that adopts the Hartree-Fock-Slater approximation. The Mn14FeO56 cluster model, wherein an Fe atom is substituted for the centermost Mn atom, shows a lower energy band gap than Mn15O56. The Fe atom substituted for the centermost Mn atom in the Mn15O56 model affects the interaction of Mn-3d and O-2p, as well as Fe-3d and O-2p. It is concluded that the electrical conductivity of Mn14FeO56 is improved over that of Mn15O56 by the substitution of the Fe atom for the Mn atom.

The electronic structure of HfTe5 has been calculated within density functional theory using a self-consistent full-potential linearized augmented plane wave plus a local orbital method incorporated in WIEN2k. Spin–orbit interaction (SOI) was incorporated using a second variational procedure. The exchange correlation potential was computed with the Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation (GGA). The obtained density of states indicates that HfTe5 is a semimetal, which is in accordance with the experimental results. The valence bands near the Fermi level originate primarily from the Te atoms. The valence charge density was also obtained to understand the bonding characteristics.

Colloidal silica/silane sol solutions were prepared in variation with the amount of silane and reaction time. Such sol solutions were synthesized from colloidal silica/tetramethoxysilane(TMOS)/methyltrimethoxysilane(MTMS). Sol solutions were prepared by sol-gel method through two step reactions. In order to understand their physical and chemical properties, dip coating of sol solutions was performed on the glass substrates. The effects of amount of MTMS and reaction time on the formation of coating films were studied. Coating films became transparent as the reaction time increased. Contact angle of coating films increased with increasing the amount of MTMS. Contact angle of coating films decreased with increasing reaction time. Surface free energy of coating films decreased with increasing the amount of MTMS. Surface roughness of coating films decreased with increasing the amount of MTMS when the reaction time was 6 h. When the reaction time was 24, 48 and 72 h, surface roughness of coating films decreased with increasing the amount of MTMS in the beginning, and then increased when further amount of MTMS was added. Plastic hardness increased with increasing the amount of MTMS. Elastic portion inversely decreased with increasing the amount of MTMS. Coating films were stable until 550°C. Thermal degradation temperature of coating films decreased with increasing the amount of MTMS.

The effect of molybdenum substitution in electronic structures of manganese dioxide has been calculated by the DV-Xα molecular orbital method. The molybdenum atom substituted for manganese atom located in center-sited of (Mn15O56)-52 cluster model. By the molybdenum substitution the energy band gap between the highest occupied molecular orbital (HOMO) of valence band and the lowest unoccupied molecular orbital (LUMO) was decreased, also the interaction of Mn-3d and O-2p was weakened but that of Mo-4d and O-2p was intensified. Both bonds of (Mn15O56)-52 and (Mn14MoO56)-52 was composed of not only ionic but also partially covalent.

This paper presents the effects of fillers on electrical properties of PTFE composites for nozzle of circuit breaker. PTFE has been used widely as a material for circuit breaker nozzle. Adding some filler into PTFE material is expected to be efficient for improving the endurance against arc radiation. In this experiment, effects of fillers on electrical properties such as dielectric constant, dissipation factor, electrical resistivity, dielectric strength and corona resistance of PTFE composites were investigated.

We find that Ag-interstitial ($Ag_I$) acts as an electron donor and plays an important role in Ag-excess doped polycrystalline PbTe thermoelectric materials. When Ag is heavily doped in PbTe, the neutral (Ag-Ag) dimer defect is formed at the Pb-site and the environment becomes Pb-rich/Te-poor condition. Then the positively ionized Ag interstitial ($Ag_I^+$) defect becomes the major defect under Pb-rich condition. Due to the small formation energy and small diffusion barrier of $Ag_I^+$, Ag can be easily dissolved into the PbTe matrix. The temperature behavior of the Ag defect formation energy well explains the $Ag_I^+$ solubility, the electron carrier generation, and the increasing electrical conductivity in Ag-excess doped polycrystalline PbTe at high temperature. This abnormal doping behavior by forming interstitial defects is also found for Au-doped PbTe., 18 pages, 4 figures

In the present works, the change of a rolling texture by La or Mm (Misch metal) addition in high Mg content (>5wt%) Al - Mg alloy was investigated. By Mm addition, B (Brass) orientation {011} 〈112〉 was typically developed with Mg contents and it was accelerated by La , Mm additions. TC (twin copper) orientation {255} 〈511〉 and G (Goss) orientation {110} 〈001〉 orientations closely related mechanical twinning were decreased in intensity and development of coarsen share bend was suppressed by Mm addition in Al -10wt% Mg alloy. And it caused improvement of formability by Mm addition in high Mg content Al - Mg alloy.

The electronic states of manganese dioxide substituted with transition metals were theoretically calculated by DV-Xα method, cluster model was Mn 15 O 56 and Mn 14 XO 56 (X = transition metal). The energy band gap of manganese-X oxides is lower than that of manganese dioxide from theoretical calculation. Also it is identified that the electrical conductivity of manganese-tungsten oxide is better than that of manganese dioxide from experiment of anodic deposition method. It is confirmed that the theoretical calculation coincides with experimental results.

Organic-inorganic hybrid blends were prepared in variation with the ratio of sol solution to urethaneacrylic resin. Such sol solutions were synthesized from colloidal silica (CS)/ methyltrimethoxysilane(MTMS)/vinyltrimethoxysilane(VTMS) by sol-gel reaction through two step reactions. Thin films of organic-inorganic hybrid blends were prepared using spin coater on the glass and aluminum sheets. In order to understand surface properties of thin films, contact angle and roughness were measured. Surface contact angle and roughness of thin films increased as the amount of sol solution increased. Thermal dissociation temperature of thin films was observed using TGA. Thin films were stable until 270 oC. Thermal dissociation temperature of thin films improved with increasing sol solution. In order to observe insulation property of thin films, electrical resistance measurements were performed. Surface and volume resistance of thin films increased as the amount of sol solution increased.

Electric conducting behavior, sectional residual stress and texture in deformed Al-Zr alloy were investigated in order to investigate effect of deformation on electric conductance. {111} textures were developed in the wire of deformed Al-Zr alloy and most strong intensity of {111} texture was observed at the core in the cross section of the wire. Residual stress was mainly measured at the surface and , especially, measured at the core in the case of 4.5Φ wire, also, electric conductance was higher at the surface than at the core. This means that electric conductance might be affected by distribution of the residual stress.

The optimum design of a die shape for Pilger mill process was carried out using FEM analyses considering various processing factors. The important design parameters of the Pilger mill machine are feed rate and profile of the grooved die. Optimum design procedure was conducted in order to investigate effects on forming load and the deformed shape of a material depending on the die surface profiles. Profiles of the die surface for the optimum design were testified with linear, cosine and quadratic curves considering physical forming process. The results of the analyses provided that the model of the quadratic profile gave the lowest forming load and the proper deformed shape.

In general micro alloy steel have the higher strength relative to conventional steels, which limits the utilization of conventional plastic forming processes. Incremental forming processes are more suitable for cold forming of such a high strength material. In particular, cold cross wedge rolling (CWR) can be a potential tool to fabricate axi-symmetric components with multi steps using high strength micro alloy steel. Obviously, optimization of die shape design is a crucial factor to apply cold cross wedge rolling to micro alloy steels. In this regards, a simulation-based process design using an elasto-plastic FEM has been carried out in order to obtain an optimum die shape for cold cross wedge rolling in this paper. Analysis results provided that the stretching angle and the shoulder angle at knifing and guiding zones were significant parameters for the stable forming process. It was demonstrated that proper stretching and shoulder angles reduced an excessive slip between a work piece and die in CWR process despite the condition of the low friction coefficient.

As a way to expand electric capacity in power line with hovering of electric power demand, STACIR/AW (super thermal-resistant Al alloy conductors Al-clad Invar-reinforced) overhead conductor which cans double ampacity has been developed. The STACIR/AW power line is mechanically composite stranded wire composed of INVAR/AW stranded wire as core for sag control and heat-resistant aluminum alloy for delivering doubled electric current. Recently, in order to ensure stable line operation and to predict its span of life, the changes of thermal properties for STACIR/AW have been investigated. In the present work, the changes of strain with temperature and the creep behavior as important factors in sag control will be presented. The transition temperature of STACIR/AW 410sqmm was estimated approximately 130°C and the creep rates were decreased with temperatures.

A microalloyed (MA) forging steel is non-heat-treated materials that have been replacing for conventional quenched and tempered (Q/T) structural steels since the MA forging steels are very cost-effective compared with Q/T steels for the production of automotive parts. However, due to a high strength and low elongation, it has been difficult to apply the MA cold forging steel to the ball stud for automobile. In this study, finite element analyses were carried out to investigate the forming loads, the stress and strain distributions of the workpiece in the cold forging processes of the ball stud using the MA cold forging steel. Compression test at room temperature and fatigue test were also performed to obtain the flow stress and fatigue life, respectively. From these results, it was found that the fatigue life was greatly affected by the strength in the neck region of the ball stud and the cold forging processes should be designed to improve the fatigue life of the ball stud used the MA cold forging steel.

Fatigue properties of INVAR/AW wires have been investigated under the heat exposure in order to ensure stable operation and to estimate life span of their power line. In the case of heat exposure for 1000hr, fatigue life and limit increased. For further heat exposure, fatigue limit decreased due to the decrease in yield strength. The variation fatigue of strand wire was strongly dependent on its amplitude. Also, cracks in wires of 7 strands were caused by stress concentration at the outer surface and fretting between each wire during vibration.

We have fabricated Mn-doped Bi2Te3 and Sb2Te3 single crystals by the vertical gradient solidification method. The compositions and crystal structures of Bi2−xMnxTe3 and Sb2−xMnxTe3 were determined using Electron Probe Micro-Analyzer (EPMA) and powder X-ray diffraction (XRD) patterns, respectively. Both crystal structures were rhombohedral with smaller lattice constants because of the smaller atomic radius of Mn than those of Bi and Sb. Based on the magnetization measurements, Mn-doped Bi2Te3 and Sb2Te3 compounds have ferromagnetic ordering at TC = 10 and 17 K, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The thermoelectric generation is the direct energy conversion method from heat to electric power. The conversion method is a very useful utilization of waste energy because of its possibility using a thermal energy below 423K. This research objective is to establish the thermoelectric technology on an optimum system design method and efficiency, and cost effective thermoelectric element in order to extract the maximum electric power from a wasted hot water. This paper is considered in manufacturing a thermoelectric generator and manufacturing of thermoelectric generator with 32 thermoelectric modules. It was also found that the electric voltage of thermoelectric generator with 32 modules slowly changed along temperature differences and the maximum power of thermoelectric generator using thermoelectric generating modules can be defined as temperature function.

The objective of this study is to develop a thermoelectric generation system which converts unused energy from close-at-hand sources such as garbage incineration heat and industrial exhaust etc. into electricity. This paper presents applicability of a commercially available thermoelectric generator f3r waster heat recovery. The test facility consists of water heater, pump, thermoelectric module and aluminium tubes and hot and cold water is used as heat source and sink fluids. It is shown that the three components of thermoelectric research exist in manufacturing a thermoelectric generator. The first component is fabrication of thermoelectric materials, the second is manufacturing of thermoelectric generator with 32 thermoelectric modules. The last one is characteristic measuring of thermoelectric generator with 32 thermoelectric modules of two types, cooling and power purpose. It was found that the rate of cold and hot water is 25 and 37 liter per minute and the maximum power of thermoelectric generator is 28Watts and its efficiency is 1.04%.

The oxidation behavior of Fe-30% Ni-12.5%Co Invar alloy possessing low thermal expansion-high strength has been studied by exposing it in temperature ranges of 1000–1200 in an air atmosphere. The formed oxide scale consisted of two layers, an outer layer and an inner layer, and the oxidation mechanism showed uniform growth for all oxidation conditions. The growth rate of the scale had a parabolic relationship with oxidation time, and the estimated activation energy for the growth of the whole oxide layer was approximately 19.84 kcal/mol. The outer scale consisted of five oxide layers, whose outermost scale consisted of major phase CoFe2O4 containing a particulate Fe2O3 phase. The oxide scale of Fe-30 Ni-12.5% Co had different compositions and phases from the Fe-30%Ni alloy investigated in previous studies. Especaally, when the alloy was exposed for a longer oxidation time and at a higher temperature, the volume fraction ratio of CoFe2O4 to Fe2O3 was found to increase

The segregation (distribution) of nickel and the composition of its constituents influence the low thermal expansion characteristics (Invar effect) in Fe−30 wt.% Ni−12.5wt.% Co−×C Invar alloy. The change of coefficient of the thermal expansion and magnetic properties were studied as an aspect of carbon addition causing the segregation of Ni in primary austenite of as-cast Fe−30wt.% Ni−12.5wt.% Co Invar alloy. The coefficient of thermal expansion of Fe−30 wt.% Ni−12.5 wt.% Co−×C Invar alloy showed its lowest value at 0.08 wt.% carbon, increased with increasing carbon content in the range of 0.08–1.0 wt.%C, kept constant at 1.0–2.0 wt.%C and decreased at carbon higher than 2.0 wt.%. The effective distribution of the coefficient of nickel in as-cast Fe−30 wt.% Ni−12.5 wt.% Co−×C Invar alloy increased with increasing carbon content. The volume fraction of the γ phase of Fe−30 wt.% Ni−12.5 wt.% Co−×C alloy increased with increasing carbon content. The microstructure of Fe−30 wt.% Ni−12.5 wt.% Co−×C alloy changed with the carbon content was independent of the coefficient of thermal expansion. The Curie temperature changed linearly with the carbon content and was similar to the change of the coefficient of thermal expansion. Moreover, the coefficient of thermal expansion decreased when the ratio of saturation magnetization to Curie temperature (σs/Tc) increased, decreasing the Curie temperature and showed a specific relationship with the magnetic properties of the Fe−30 wt.% Ni−12.5 wt.% Co−×C Invar alloy.

The progress spinodal decomposition in aged Co10Cu90 ribbons is closely correlated with giant magnetoresistance (GMR). In the phase decomposition, the MR ratio due to spin dependent scattering increases with the increase in the interface area in the constant wavelength regime. A maximum MR ratio of 8.1% in 15 kOe is obtained in the Co10Cu90 ribbon aged at 673 K for 166 h. By further aging, the MR ratio in high fields decreases with the increase of the wavelength, while the susceptibility of the MR ratio in low fields becomes larger due to the coarsening of ferromagnetic particles.