Analysis of composition dependence of some thermal transport properties in glassy Se80−xTe20Snx (0 ⩽ x ⩽ 10) alloys using transient plane source measurements

In the present work, we have studied simultaneous measurements of thermal transport properties (effective thermal conductivity, diffusivity, specific heat per unit volume, thermal inertia I_T) of glassy Se_80−xTe₂₀Sn_x (0 ? x ? 10) system using their twin pellets. The glassy system is prepared under a load of 5 tons and measurements have been made at room temperature using Transient Plane Source (TPS) technique. The composition dependence of the thermal transport properties of given glassy system is also discussed.     

Polypyrrole-NiO hybrid nanocomposite: Structural,morphological, optical and electrical transport studies

Polypyrrole (PPy)-nickel oxide (NiO) hybrid nanocomposite thin films have been prepared by spin coating method. The PPy–NiO hybrid nanocomposites were characterized for structural, morphological, optical and electrical analysis, and the results were compared with the pure PPy films. The structural and optoelectronic properties of PPy–NiO hybrid nanocomposites are quite different from those of pure PPy and NiO nanoparticles, which were attributed to the strong interaction between the PPy and NiO nanoparticles. The XRD pattern shows that broad peak of PPy becoming weaker on increasing the content of NiO nanoparticles in the PPy–NiO hybrid nanocomposites. Also the diffraction peaks of NiO nanoparticles in PPy–NiO (10–50 wt%) nanocomposites were found to shift to lower 2θ values. The morphological studies revealed that the transformation of granular morphology of PPy to the nanospheres and clusters in the PPy–NiO hybrid nanocomposites. FTIR spectra of PPy–NiO hybrid nanocomposites, revealed that the main absorption at 1204 cm⁻¹ and 1559 cm⁻¹ are affected by the presence of NiO nanoparticle in pure PPy and get shifted to 1216 cm⁻¹ and 1570 cm⁻¹ respectively indicates, insertion of NiO nanoparticles in the PPy–NiO hybrid nanocomposite. UV–vis absorption spectrum of PPy corresponding to λ_max = 442 nm is blue shifted to λ_max = 375 nm in the PPy–NiO hybrid nanocomposites, reveals strong interaction between PPy and NiO nanoparticles. The room temperature dc electrical conductivity is increased from 8.66 × 10⁻⁹ to 4.08 × 10⁻⁷ (Ω/cm)⁻¹ as the content of NiO nanoparticles increased from 10 to 50 in wt% in the PPy–NiO hybrid nanocomposites.     

Measurement of thermal conductivity of fluid using single and dual wire transient techniques

A modified measurement device to measure thermal conductivity of fluids using transient hot-wire technique has been designed, developed, tested and presented in this paper. The equipment is designed such that the thermal conductivity could be measured using both single wire sensor of different length and dual wire sensor. The sensor, which is also a heater, is a platinum micro-wire of 50 μm diameter. The influence of wire length on the measurement of thermal conductivity of fluids is tested using two single wires of length 50 mm and 100 mm. The thermal conductivity is also measured using a dual hot wire arrangement; which is achieved by placing the 100 mm and 50 mm wires in a Wheatstone bridge with the 100 mm wire as the sensor and 50 mm wire as a compensation wire. The apparatus requires a 100 ml of test fluid to perform the experiment. The testing temperature of the test fluid during the experimentation can be suitably varied by the choice of heat exchange fluid used in the apparatus. Water is chosen as testing fluids for primary standards. When compared to single wires, the thermal conductivity of the fluids measured is consistent with dual-wire method with an uncertainty of ±0.25%.     

Microstructural evolution of Cu-1 at% Ti alloy aged in a hydrogen atmosphere and its relation with the electrical conductivity

Copper alloys with titanium additions between 1 and 6 at% Ti emerge currently as attractive conductive materials for electrical and electronic commercial products, since they exhibit superior mechanical and electrical properties. However, their electrical conductivity is reduced owing to the residual amount of Ti solutes in the Cu solid solution (Cu_ss) phase. Since Cu shows only poor reactivity with hydrogen (H), while Ti exhibits high affinity to it, we were inspired by the idea that hydrogenation of Cu–Ti alloys would influence their microstructure, resulting in a significant change of their properties. In this contribution, the influence of aging under a deuterium (D₂) atmosphere of Cu-1 at% Ti alloys on their microstructure is investigated to explore the effects on the electrical conductivity. The specimens were investigated by means of transmission electron microscopy (TEM), field ion microscopy (FIM), computer-aided field ion image tomography (cFIIT), and atom probe tomography (APT).     

Effect of pre-readout annealing treatments on TL mechanism in tellurite glasses at therapeutic radiation doses level

The higher sensitization for thermal annealing on TL mechanism in the region 550–600 °C for 80(TeO₂)–5(TiO₂)–(15 − x) (WO₃)–(x) A_nO_m where A_nO_m = Nb₂O₅, Nd₂O₃, Er₂O₃ and x = 5 mol% has been measured. The behavior of trap centers and luminescence centers has been investigated for tellurite glasses doped with rare earth oxides irradiated at 0.5 up to 2 Gy and annealed at different temperatures in the range 350–700 °C. The behavior of the three types of tellurite glasses is analyzed regarding to their kinetic parameters and luminescence emission which enhance the claim of tellurite glasses for use as TLD material at therapeutic radiation doses.     

Column-by-column compositional mapping by Z-contrast imaging

A phenomenological method is developed to determine the composition of materials, with atomic column resolution, by analysis of integrated intensities of aberration-corrected Z-contrast scanning transmission electron microscopy images. The method is exemplified for InAs_xP_1−x alloys using epitaxial thin films with calibrated compositions as standards. Using this approach we have determined the composition of the two-dimensional wetting layer formed between self-assembled InAs quantum wires on InP(0 0 1) substrates.     

The influence of Cu addition on precipitation in Fe–Cr–Ni–Al–(Cu) model alloys

Precipitation in Fe–Cr–Ni–Al–(Cu) model alloys was investigated after ageing for 0.25, 3, 10 and 100 h at 798 K. Characterization of nanoscale precipitates was performed using three-dimensional atom probe microscopy and transmission electron microscopy. The precipitates are found to be enriched in Ni and Al (Cu) and depleted in Fe and Cr. After 0.25 h of ageing the number density of precipitates is ∼8×10²⁴ m⁻³, their volume fraction is about 15.5% and they are near-spherical with an average diameter of about 2–3 nm. During further ageing the precipitates in the both alloys grow, but the coarsening behaviour is different for both alloys. The precipitates of the Cu-free alloy grow much faster compared with the Cu-containing alloy and their density decreases. Precipitates in Cu-free alloy change to plate shaped even after 10 h of ageing, whereas those of Cu-containing alloy remain spherical up to 10 h of ageing. The influence of Cu addition on precipitation in these model alloys is discussed with respect to the different coarsening mechanisms.     

Effect of extrusion temperature on the physical properties of high-silicon aluminum alloy

Light-weight high-silicon aluminum alloys are used for electronic packaging in the aviation and spaceflight industry. Al-30Si and Al-40Si are fabricated with air-atomization and vacuum-canning hot-extrusion process. The density, thermal conductivity, hermeticity and thermal expansion coefficients of the material are measured, and the relationship between extrusion temperature and properties is obtained. Experimental results show that the density of high-silicon aluminum alloys prepared with this method is as high as 99.64% of the theory density, and increases with elevating extrusion temperature. At the same time, thermal conductivity varies between 104–140 W/(m·K); with the extrusion temperature, thermal expansion coefficient also increases but within 13 × 10⁻⁶ (at 100°C) and hermeticity of the material is high to 10⁻⁹ order of magnitude. __________ Translated from Chinese Journal of Mechanical Engineering, 2006, 42 (6): 7–10 [译自: 机械工程学报]     

Magneto-transport properties of Fe-doped LSMO manganites

Magneto-transport measurements have been performed on La_0.67Sr_0.33Mn_1−xFe_xO₃ (x = 0.0, 0.05 and 0.07) manganites synthesized by solid state route. The overall nature of AC susceptibility is found to be frequency independent. With the substitution of Mn by Fe, the transport properties dramatically change suppressing the double-exchange interaction. This in turn weakens the ferromagnetism and consequently decreases the paramagnetic to ferromagnetic transition temperature (T_c). However, DC electrical resistivity of the samples show board hump at metal-insulator transition temperature (T_MI) in contrary with sharp transition at T_c and T_MI < T_c indicating decoupling of electrical and magnetic properties. Resistivity behavior of these samples can be well explained by the consideration of bond percolation model which is basically developed from effective approximation method.     

Charge compensation by in-situ heating for insulating ceramics in scanning electron microscope

With a steady temperature increase under high vacuum (HV) in an environmental scanning electronic microscope, we observed charge-free characterization and fine secondary electron (SE) images in focus for insulating ceramics (alumina (Al₂O₃), aluminum nitride (AlN), pure magnesium silicate (Mg₂SiO₄)). The sample current I_sc increased from −8.18×10⁻¹³ to 2.76×10⁻⁷ A for Al₂O₃ and −9.28×10⁻¹² to 2.77×10⁻⁶ A for AlN with the temperature increased from 298 to 633 K. The surface conductance σ increased from 5.6×10⁻¹³ to 5.0×10⁻¹¹/Ω for Al₂O₃ and 1.1×10⁻¹² to 1.0×10⁻⁷/Ω for AlN with the temperature increased from 363 to 593 K. The SE image contrast obtained via heating approach in high vacuum with an Everhart–Thornley SE-detector was better than that via conventional approach of electron–ion neutralization in low vacuum (LV) with a gaseous SE-detector. The differences of compensation temperatures for charge effects indicate dielectric and thermal properties, and band structures of insulators. The charge compensation mechanisms of heating approach mainly relate to accelerated release of trapped electrons on insulating surface and to increase of electron emission yield by heating.     

Thermal sensors based on p-Pb0.925Yb0.075Te:Te and n-Pb0.925Yb0.075Se0.2Te0.8 thin films grown using thermal evaporation method

We utilize p-Pb_0.925Yb_0.075Te:Te and n-Pb_0.925Yb_0.075Se_0.2Te_0.8 ingots in a standard solid-state microwave synthesis route to fabricate thermally evaporated thin films. The nanostructure and composition of the films were studied through X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDX). The Seebeck coefficient and electrical conductivity were measured at a temperature range of 298–523 K. The micro-thermoelectric devices were composed of 20 pairs and 10 pairs of p-Pb_0.925Yb_0.075Te:Te and n-Pb_0.925Yb_0.075Se_0.2Te_0.8 thin films on glass substrates, respectively. The dimensions of the thin films thermoelectric generators which comprised of 10-pair were 12 mm × 10 mm, whereas, 20-pair were 23 mm × 20 mm, respectively of legs connected through aluminum electrodes. The serial 20-pair p–n thermocouples generated a maximum output open-circuit voltage of 275.3 mV and a maximum output power of 54.37 nW at a temperature difference of ΔT = 162 K; the values are 109.4 mV and 16.68 nW at ΔT = 162 K for the 10-pair thermocouples, respectively.     

Improvement in electrical and thermal behavior of polystyrene/multiwalled carbon nanotubes nanocomposites

Polystyrene (PS)/multiwalled carbon nanotubes (MWCNTs) nanocomposite has been prepared by solvent evaporation technique  and . Tetrahydroforan (THF) has been used as a solvent. Its electrical and thermal properties have been investigated by using LCR meter, 2-probe mechanism and Thermo Gravimetric Analysis Differential Thermal Calorimeter (TGA/DTA) respectively. Increase in dielectric constant and loss is observed with the increase of MWCNTs content in the nanocomposites. Frequency dependent AC conductivity follows the universal power law. Increase in AC conductivity with temperature has been attributed to hopping of π electrons in the MWCNTs. Temperature dependent DC conductivity was found to be a typical of a semi conducting behavior following Mott’s 3-D variable range hoping model. Best fitted Mott’s parameters were determined from the observed data.     

Simple apparatus for the multipurpose measurements of different thermoelectric parameters

A simple apparatus for the simultaneous measurement of Seebeck coefficient (α) and electrical resistivity (ρ) in the temperature range 100-600 K, Hall coefficient (R_H) and transverse Nernst-Ettingshausen coefficient (N) in the temperature range 300-600 K of the bar shaped samples has been fabricated. The instrument has been designed so simply that the sample can be easily mounted for the fast measurements of different thermoelectric parameters. The sample holder assembly of the apparatus has been designed so cleverly that any part of that section can be replaced in case of any damage; and so it can be regarded as a modular based system. The apparatus is relatively cheaper in cost and also portable.     

Inhomogeneity correction in calibration of electrical conductivity standards

The method for inhomogeneity investigation of measurement standards for electrical conductivity has been studied in the conductivity range from 2 MS/m to 14 MS/m. For this purpose a planar spiral coil has been developed and characterized. The impedance values of the coil are measured in the air and with a conducting plate above the coil at discrete frequencies from 2 kHz to 70 kHz. By selecting the corresponding operating frequency, relative changes in the conductivity value throughout the sample thicknesses have been measured. It was revealed that inhomogeneity of measurement standards has an effect on further measurements with calibrated conductivity meters. The relative conductivity changes of 0.1% due to inhomogeneity can be detected with the measurement uncertainty (k = 2) of less than 0.3% of the measured value.     

Temperature measurement in orthogonal metal cutting

Orthogonal cutting experiments were carried out on steel at different feedrates and cutting speeds. During these experiments the chip temperatures were measured using an infrared camera. The applied technique allows us to determine the chip temperature distribution at the free side of the chip. From this distribution the shear plane temperature at the top of the chip as well as the uniform chip temperature can be found. A finite-difference model was developed to compute the interfacial temperature between chip and tool, using the temperature distribution measured at the top of the chip.Nomenclature contact length with sticking friction behaviour [m] - c specific heat [J kg^–1 K^–1] - contact length with sliding friction behaviour [m] - F _P feed force [N] - F _V main cutting force [N] - h undeformed chip thickness [m] - h _c deformed chip thickness [m] - i,j denote nodal position - k thermal conductivity [W m^–2 K^–1] - L chip-tool contact length [m] - p defines time—space grid, Eq. (11) [s m^–2] - Q _C heat rate entering chip per unit width due to friction at the rake face [W m^–1] - Q _T total heat rate due to friction at the rake face [W m^–1] - Q _% percentage of the friction energy that enters the chip - q ₀ peak value ofq(x) [W m^–2] - q _e heat rate by radiation [W] - q(x) heat flux entering chip [W m^–2] - t time [s] - T temperature [K] - T _C uniform chip temperature [°C] - T _max maximum chip—tool temperature [°C] - T _mean mean chip—tool temperature [°C] - T _S measured shear plane temperature [°C] - x,y Cartesian coordinates [m] - V cutting speed [m s^–1] - V _C chip speed [m/s] - rake angle - ,, control volume lumped thermal diffusivity [m² s^–1] - emmittance for radiation - exponent, Eq. (3) - density [kg m^–3] - Stefan-Boltzmann constant [W m^–2 K⁴] - (x) shear stress distribution [N m^–2] - shear angle     

Three dimensional atom probe imaging of GaAsSb quantum rings

Unambiguous evidence of ring-shaped self-assembled GaSb nanostructures grown by molecular beam epitaxy is presented on the basis of atom-probe tomography reconstructions and dark field transmission electron microscopy imaging. The GaAs capping process causes a strong segregation of Sb out of the center of GaSb quantum dots, leading to the self-assembled GaAs_xSb_1−x quantum rings of 20-30 nm in diameter with x∼0.33.     

APT analyses of deuterium-loaded Fe/V multi-layered films

Interaction of hydrogen with metallic multi-layered thin films remains as a hot topic in recent days. Detailed knowledge on such chemically modulated systems is required if they are desired for application in hydrogen energy system as storage media. In this study, the deuterium concentration profile of Fe/V multi-layer was investigated by atom probe tomography (APT) at 60 and 30 K. It is firstly shown that deuterium-loaded sample can easily react with oxygen at the Pd capping layer on Fe/V and therefore, it is highly desired to avoid any oxygen exposure after D₂ loading before APT analysis. The analysis temperature also has an impact on D concentration profile. The result taken at 60 K shows clear traces of surface segregation of D atoms towards analysis surface. The observed diffusion profile of D allows us to estimate an apparent diffusion coefficient D. The calculated D at 60 K is in the order of 10⁻¹⁷ cm²/s, deviating 6 orders of magnitude from an extrapolated value. This was interpreted with alloying, D-trapping at defects and effects of the large extension to which the extrapolation was done. A D concentration profile taken at 30 K shows no segregation anymore and a homogeneous distribution at c_D=0.05(2) D/Me, which is in good accordance with that measured in the corresponding pressure–composition isotherm.     

A calibration system for PTU devices

Devices measuring pressure, temperature and humidity simultaneously are known as PTU devices. There are hardly any commercial calibration systems for the PTU devices available for low temperatures (<0 °C). To obtain more comprehensive data on the performance of PTU devices, a new calibration system is developed at MIKES. In this PTU Apparatus, pressure, temperature and humidity can be controlled simultaneously so that all combinations over the ranges are possible. The nominal ranges of the system are the following: absolute pressure 500–1100 hPa, temperature −52 °C to +80 °C and relative humidity 10–95%. The target uncertainties (k = 2) of the pressure, temperature and humidity are 10 Pa, 0,1–0,3 °C and 1–3% RH, respectively. The construction and operation as well as the results of operational tests of the PTU Apparatus are reported in this paper.     

Simultaneous measurement of CO and CO2 at elevated temperatures by diode laser wavelength modulated spectroscopy

One single semiconductor distributed-feedback (DFB) laser is used to demonstrate the possibility of simultaneous measurements of CO and CO₂ at elevated temperatures. Wavelength modulation spectroscopy with second-harmonic detection is used to improve the detection sensitivity and accuracy. The concentrations of CO and CO₂ are determined from the WMS-1-normalized absorption-based WMS-2f signal peak heights of a proper line pair of CO and CO₂ near 6357.814 cm⁻¹ and 6357.312 cm⁻¹, which are selected using some line-selection criterions for the target temperature range of 300–1000 K. The CO and CO₂ concentrations measurements are within 2.86% and 2.69% of the expected values over the tested temperature range 300–1000 K. The minimum detectable concentrations of CO and CO₂ at 1000 K are 250 ppm m and 280 ppm m respectively.     

Behaviour of TEM metal grids during in-situ heating experiments

The stability of Ni, Cu, Mo and Au transmission electron microscope (TEM) grids coated with ultra-thin amorphous carbon (α-C) or silicon monoxide film is examined by in-situ heating up to a temperature in the range 500–850 °C in a transmission electron microscope. It is demonstrated that some grids can generate nano-particles either due to the surface diffusion of metal atoms on amorphous film or due to the metal evaporation/redeposition. The emergence of nano-particles can complicate experimental observations, particularly in in-situ heating studies of dynamic behaviours of nano-materials in TEM. The most widely used Cu grid covered with amorphous carbon is unstable, and numerous Cu nano-particles start to form once the heating temperature reaches 600 °C. In the case of Ni grid covered with α-C film, a large number of Ni nano-crystals occur immediately when the temperature approaches 600 °C, accompanied by the graphitization of amorphous carbon. In contrast, both Mo and Au grids covered with α-C film exhibit good stability at elevated temperature, for instance, up to 680 and 850 °C for Mo and Au, respectively, and any other metal nano-particles are detected. Cu grid covered Si monoxide thin film is stable up to 550 °C, but Si nano-crystals appear under intensive electron beam. The generated nano-particles are well characterized by spectroscopic techniques (EDXS/EELS) and high-resolution TEM. The mechanism of nano-particle formation is addressed based on the interactions between the metal grid and the amorphous carbon film and on the sublimation of metal.