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.     

Investigation of some dielectric properties of phosphate glasses doped with iron oxides,by a microwave technique

The effects of iron ions on dielectric properties of lithium sodium phosphate glasses were studied by non-usual, fast and non-destructive microwave techniques. The dielectric constant (ε′), insertion loss (L) and microwave absorption spectra (microwave response) of the selected glass system xFe₂O₃·(1 − x)(50P₂O₅·25Li₂O·25Na₂O), being x = 0, 3, 6, … , 15 expressed in mol.%, were investigated. The dielectric constant of the samples was investigated at 9.00 GHz using the shorted-line method (SLM) giving the minimum value of ε′ = 2.10 ± 0.02 at room temperature, and increasing further with x, following a given law. It was observed a gradual increasing slope of ε′ in the temperature range of 25 ? t ? 330 °C, at the frequency of 9.00 GHz. Insertion loss (measured at 9.00 GHz) and measurements of microwave energy attenuation, at frequencies ranging from 8.00 to 12.00 GHz were also studied as a function of iron content in the glass samples.     

Effect of molybdenum tri-oxide molar ratio on the optical and some physical properties of tellurite-vanadate-molybdate glasses

Glasses with composition (60 − x)V₂O₅-40TeO₂ − x MoO₃ with 20 ? x ? 60 (in mol%) have been prepared using the usual melt quenching method. The optical absorption spectra of the glasses have been recorded in the wavelength range 300-800 nm. The position of the absorption edge and therefore the optical band gap values were found to be depend on the glass composition. For these glasses, the optical band gap was found to be in the range 2.03-2.86 eV with increasing of MoO₃ concentration. The absorption spectrum fitting method was employed to obtain the energy gap. In this method, only the measurement of the absorbance spectrum of the glass is needed. For each sample, the width of the band tail was determined. Also, the density and glass transition temperature values indicate that the rigidity and packing of the samples increase with increase in MoO₃ concentration as a network former.     

Mechanical behaviour of iron oxide scale: Experimental and numerical study

The paper addresses the identification of constitutive parameters of thick, brittle layers on metal substrates. Application is to the iron oxide behaviour during hot rolling processes of steel, where oxide scale breaking and embedding is one of the major causes of surface defects. Contact management of a FEM software has been adapted in order to address the transitions corresponding to transverse oxide fracture, along with two other mechanisms, namely delamination and interfacial stick/slip. It is applied to the hot strip rolling process to show pre-bite cracking and its consequences (“micro-extrusion” of the metal). To approximate the stress state prevailing at roll bite entry, the Four-Point Hot Bending Test (4PHBT) has been selected for the measurement of oxide properties. Oxidation is made in situ in the test rig under conditions similar to a hot strip mill (HSM) environment. Comparison of load-deflection curves for oxidized and non-oxidized samples allows the mechanical properties of the oxide to be determined. Above a critical temperature T_c - around 700 °C, but depending on strain rate - the oxide is ductile (with a very narrow plastic strain range, ?_p < 10⁻²) and elastic-viscoplastic (EVP) constitutive parameters are identified numerically. Below T_c, brittleness is manifested by an array of transverse, through-thickness cracks. Acoustic emission (AE) has been used to help detect the onset of fracture, while numerical simulation gives the critical fracture stress at the corresponding point of the load-deflection curve. Results for four low carbon steel grades are compared.     

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.     

Pawley and Rietveld refinements using electron diffraction from L1₂-type intermetallic Au₃Fe₁-x nanocrystals during their in-situ order-disorder transition

During the in-situ order-disorder transition of intermetallic L1₂-type Au₃Fe_1−x nanocrystals, structural information has been retrieved from their electron diffraction patterns based on the Pawley refinement that is unrelated to the electron kinematical or dynamical scattering nature as well as the Rietveld refinement using a kinematical approximation. At room temperature, it was found that the nanocrystals contain approximately x=40% vacancies at the Fe site. Based on in-situ heating this phase displayed an irreversible order-disorder transition, with the transition temperature between 553 and 593 K. A sudden increase in lattice parameter was detected during the first heating from the ordered phase, while the second heating of the disordered phase showed only a linear relationship with temperature. From the lattice parameter measurement of the disordered phase, the coefficient of thermal expansion was estimated as 1.462×10⁻⁵ K⁻¹. The long-range order parameter S was determined by the refined site occupancies, as well as the integrated intensities of the superlattice (1 0 0) and fundamental (2 2 0) reflections using the Pawley and Rietveld refinements during the order-disorder transition. Considering the dynamical scattering effect, Blackman two-beam approximation theory was applied to corrected S, which slightly attenuated after the correction. A comparison of the electron diffraction with X-ray diffraction data was made. It was demonstrated that elemental and structural information could be retrieved through quantitative electron diffraction studies of the nanomaterials. Since the Pawley refinement algorithm does not include the electron scattering event, it is especially useful to refine the electron diffraction data regardless of the sample thickness.     

The measurement of thermal conductivity variation with temperature for solid materials

An apparatus was designed to routinely measure the thermal conductivity variation with temperature for solid materials. The apparatus was calibrated by measuring the thermal conductivity variations with temperature for aluminum, zinc, tin and indium metals. The variations of thermal conductivity with temperature for the Zn-[x] wt.% Sb alloys (x = 10, 20, 30 and 40) were then measured by using the linear heat flow apparatus designed in present work. From experimental results it can be concluded that the linear heat flow apparatus can be used to measure thermal conductivity variation with temperature for multi component metallic alloys as well as pure metallic materials and for any kind of alloys. Variations of electrical conductivity with temperature for the Zn-[x] wt.% Sb alloys were determined from the Wiedemann–Franz (W–F) equation by using the measured values of thermal conductivity. Dependencies of the thermal and electrical conductivities on composition of Sb in the Zn–Sb alloys were also investigated. According to present experimental results, the thermal conductivity and electrical conductivity for the Zn-[x] wt.% Sb alloys decrease with increasing the temperature and the composition of Sb.     

Antimicrobial food packaging prepared from poly(butylene succinate) and zinc oxide

This article reports antibacterial activity, mechanical, thermal and physical properties of poly(butylene succinate) (PBS)/zinc oxide (ZnO) composite films for food packaging applications. The composite films were successfully prepared by using a blown film extruder at five ZnO levels ranging from 2 to 10 wt%. Under tension, PBS was stiffer due to the strengthening effect derived from rigid ZnO particles. However, the tear strength of the composite films was lower than the film without ZnO. Minimum ZnO content required to inhibit the Escherichia coli and the Staphylococcus aureus growths were observed at 6 wt% with the clear zone of 1.31 and 1.25 cm respectively. Thermal test results indicated the increased degree of crystallinity (X_c) and the decreased crystallization temperature (T_c) while the melting temperature (T_m) remain unchanged. Loss modulus curves informed the reduction of the glass transition temperature (T_g) of the film with ZnO at all concentrations. Release test indicated that Zn²⁺ migrated over 15 days studied while the maximum migration was observed when acetic acid was used as a food simulant.     

Fragility, DSC and elastic moduli studies on tellurite–vanadate glasses containing molybdenum

Ternary xMoO₃–40TeO₂–(60 − x)V₂O₅ glasses with 0 ? x ? 60 (in mol%) have been prepared by normal melt quenching method. DSC curves of these glasses have been investigated. The glass transition properties that have been measured and reported in this paper, include the glass transition temperature (T_g), glass transition width (ΔT_g), heat capacity change at glass transition (ΔC_P) and calculated fragility (F). Thermal stability, Poisson’s ratio, fragility and glass forming tendency of these glasses have been evaluated, to determine relationship between chemical composition and the thermal stability or to interpret the structure of glass. In addition, Makishima and Makenzie’s theory was applied for calculation of Young’s modulus, bulk modulus and shear modulus, indicating a strong relation between elastic properties and structure of glass. Generally, results of this work show that glass with x = 60 has the highest shear, bulk and Young’s moduli which make it as suitable candidate for the manufacture of strong glass fibers in technological applications; but it should be mentioned that glass with x = 20 has higher handling temperature and super resistance against thermal attack.     

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.     

“Magic size” effect in the packing of n-alkanes on Au(1 1 1): evidence of lowered sliding force for molecules with specific length

Molecular structure of monolayers formed at the interface between Au(1 1 1) surfaces and solutions containing n-alkanes has been studied by in situ scanning tunneling microscopy at room temperature. Increasing the C_nH_2n+2 length from n=10 up to 50 with even n numbers alternates rectangular and tilted arrangement of alkanes within the self-organized layers. This alternation is related to the dramatically lowered sliding force for molecules with a length close to mT (m-integer), where T is the period of commensurability between the CH₂-CH₂-CH₂ period along alkyl chains and the interatomic distance along Au〈1 1 0〉 direction.     

Qualitative evaluation of the germination frequency in Zr–Fe binary alloy

Major thermo-physical properties data are of fundamental importance to accurate and reliable design of melting and casting processes. In this paper, we show that we can control the germination process using thermodynamics data. These data must be known for the entire period of time and temperature range of interest in any given condition. In addition, a kinetic approach is employed to predict the microstructure of alloys. Viscosity data for Zr₇₆Fe₂₄, are fitted with an empirical relation. The best fit allows to estimate, through the resistance to germination factor, thermodynamic proprieties of interest (i.e., namely the enthalpy of fusion, the surface tension, the molar volume and the glass temperature). From the values of these quantities, the parameters (T, t) can be estimated. The temperature T is found between 930 K and 1194 K and the time t can be derived from the plateau of the germination frequency–temperature profile.     

Fabrication and characterization of ZnO thin film for hydrogen gas sensing prepared by RF-magnetron sputtering

A ZnO thin film-based gas sensor was fabricated using a SiO₂/Si substrate with an integrated platinum comb-like electrode and heating element. The structural characteristics, morphology, and surface roughness of the as-grown ZnO nanostructure were investigated. The optical properties were examined by UV–vis spectrophotometry. The film revealed the presence of a c-axis oriented (0 0 2) phase of 20.8 nm grain size. The sensor response was tested for hydrogen concentrations of 50, 70, 100, 200, 400, and 500 ppm at operating temperatures ranging from 250 °C to 400 °C. The sensitivity toward 50 and 200 ppm of hydrogen at the optimum operating temperature of 350 °C were about 78% and 98%, respectively. The response was linear within the range of 50–200 ppm of hydrogen concentration. Our results demonstrated the potential application of ZnO nanostructure for fabricating cost-effective and high-performance gas sensors.     

Friction, wear and N2-lubrication of carbon nitride coatings: a review

Recent results of tribological properties of carbon nitride (CN_x) coatings are reviewed. CN_x coatings of 100 nm thickness were formed on Si-wafer and Si₃N₄ disks by the ion beam mixing method. Friction and wear tests were carried out against Si₃N₄ balls in the environments of vacuum, Ar, N₂, CO₂, O₂ or air by a ball-on-disk tribo-tester in the load range of 80-750 mN and in the velocity range of 4-400 mm/s.It was found that friction coefficient μ is high (μ=0.2-0.4) in air and O₂, and low (μ=0.01-0.1) in N₂, CO₂ and vacuum. The lowest friction coefficient (μ<0.01) was obtained in N₂. It was also found that N₂ gas blown to the sliding surfaces in air effectively reduced the friction coefficient down to μ≈0.017. Wear rate of CN_x coatings varied in the range 10⁻⁹-10⁻⁵ mm³/N m depending on the environment.The wear mechanisms of CN_x in the nanometer scale were studied by abrasive sliding of an AFM diamond pin in air. It was confirmed that the major wear mechanism of CN_x in abrasive friction was low-cycle fatigue which generated thin flaky wear particles of nanometre size.     

Study of the heating rate effect on the glass transition properties of (60 − x)V2O5–xSb2O3–40TeO2 oxide glasses using differential scanning calorimetry (DSC)

The glass-transition temperature (T_g) and crystallization temperature (T_Cr) have been determined for the system (60 − x)V₂O₅–xSb₂O₃–40TeO₂ with 0 < x < 10 (in mol%) using differential scanning calorimetry (DSC) at heating rates φ = 3, 6, 9 and 13 K/min. The effect of the heating rate and the Sb₂O₃ content on T_g is discussed. It was observed that the transition region shifts to higher temperatures when the measuring time is reduced (or, conversely, when the applied temperature rate is increased). Using differential scanning calorimetry, the compositional dependence of T_g has been determined and so, an empirical equation has been deduced which relates the glass-transition temperature with the Sb₂O₃ content.     

Energy Spectra Of Dislocations In Silicon And Germanium

The properties of edge-type dislocations are strongly dependent on the temperature at which they have been introduced into the crystal. Dislocations produced at T < 0·6 T_m (T_m melting point) exhibit a richer variety of properties than those introduced at T > 0·6 T_m: in germanium a strong increase of the hole density, in silicon an electron para-magnetic resource (EPR)-signal, showing many fine details, and several peaks in the deep level transient spectroscopy (DLTS)-signal, are only found after low-temperature deformation. The increase in the hole density has been ascribed to point defect clouds, which surround the dislocation, and seem to control their mobility. The clouds are not stable at the deformation temperature. The electrical and optical properties of edge-type dislocations, introduced at T > 0·6 T_m into germanium, can be interpreted in terms of a half-filled one-dimensional band (for T ≥ 50 K), which might be due to dangling bonds in the dislocation core. In silicon the experimental data indicate a similar form of the local energy spectrum at dislocations.     

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.     

Relation between low temperature fluidity and sound velocity of lubricating oil

Low temperature fluidity is important for lubricating oil. Viscoelastic solid transition temperature at atmospheric pressure T_VE0 represents the low temperature fluidity of lubricating oil, which is estimated from the occurrence of photo elastic effect by lowering the temperature using liquid nitrogen. Sound velocity in lubricating oil is measured using Sing around technique. Then the adiabatic Bulk modulus K is calculated from the measured sound velocity. A relation is found between the adiabatic bulk modulus and the viscoelastic solid transition temperature of lubricating oil. The relation depends on the molecular structure of lubricating oil. The oils of a group belong to almost same molecular structure, follows the same relation. For same molecular structure T_VE0 decreases as decreasing the adiabatic bulk modulus of lubricating oil. It is also found that, the viscoelastic solid transition temperature of blend oils can be predicted from the base oils’ T_VE0 and K.     

The geometric dynamic errors of CMMs in fast scanning-probing

Quasi-stiffness model is effective for the compensation of the geometric errors of coordinates measuring machines (CMMs) in slow probing, but degrade the error compensation accuracy due to the generation of dynamic errors in fast probing. It is usually regarded that acceleration is the major origin of dynamic errors; and yet the dynamic effects that rise from the quick fluctuation of geometric errors in fast probing had attracted little attentions. This paper presents a model for the dynamic effects of the geometric errors of CMMs in fast probing, and investigates their properties with experiments. The error model is built with recursive least squares (RLS) identification technique by taking probing acceleration and the 6 geometric errors of X slideway for the inputs while the positioning error of probe tip for output. Then the positioning error of probe tip is decomposed into 7 components corresponding to the 7 inputs. Analyses on the experiments show that the angular errors around Y and Z axes, ε_Y(x) and ε_Z(x), can induce remarkable dynamic effects, especially in a CMM with low stiffness air bearing. Error compensation with RLS identification seems feasible theoretically, but it is not recommendable due to the veracity uncertainty of identification. Nevertheless smoothening the sharp corners of the curves of geometric errors, especially ε_Y ∼ x and ε_Z ∼ x, in terms of probing speed and Y coordinates of probe tip is considered as a simple but effective and reliable method to improve the accuracy of CMMs errors compensation in fast probing.     

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.