Simple apparatus to measure Seebeck coefficient up to 900 K

An apparatus for measuring Seebeck coefficient (S) has been designed that allows measurement of S from room temperature to 900 K. It is constructed from readily available equipment and instrumentation with parts that can be easily fabricated. The details of instrument fabrication, sources of errors, method of calibration, typical measurement in test sample are described. We report the Seebeck coefficient measurement of Ca-cobaltite (Ca₃Co₄O₉) a p-type thermoelectric material. The obtained results from the fabricated setup are well matched with the reported and standard instrument data with standard deviation of ±3%.     

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.     

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.     

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.     

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.     

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.     

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.     

Friction of molybdenum disulfide-titanium films under cryogenic vacuum conditions

The tribological behavior of steel and sapphire sliding on a sputtered MoS₂+Ti coating was studied in ultra-high vacuum as a function of temperature over the range of 4-300 K. The coefficient of kinetic friction for the steel/moly interface was determined to be approximately 0.05 from room temperature to 240 K, and increased monotonically to 0.125 at 4 K. The sapphire/moly friction coefficient was measured to be 0.15±0.05 at room temperature and increased monotonically to 0.25 at 4 K. We also analyze in detail the flash temperature due to frictional heating at the sliding contacts. Flash heating is a particularly strong effect at cryogenic temperatures.     

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.     

Computer simulation of a 1.0 GPa piston–cylinder assembly using finite element analysis (FEA)

The paper reports a preliminary study of the behavior of a high performance controlled-clearance piston gauge (CCPG) in the pressure range up to 1 GPa through finite elemental analysis (FEA). The details of the experimental characterization of this CCPG has already been published (Yadav et al., 2007 [1]). We have already pointed out that the use of Heydemann–Welch (HW) model for the characterization of any CCPG, has some limitation due to the fact that the linear extrapolation of the cube root of the fall rate versus jacket pressure (v^1/3–p_j) curve is assumed to be independent of the rheological properties of the pressure transmitting fluids. The FEA technique addresses this problem through simulation and optimization with a standard ANSYS program where the material properties of the piston and cylinder, pressure dependent density and viscosity of the pressure transmitting fluid etc. are to be used as the input parameters. Thus it provides characterization of a pressure balance in terms of effective area and distortion coefficient of the piston and cylinder. The present paper describes the results obtained on systematic studies carried out on the effect of gap profile between piston and cylinder of this controlled-clearance piston gauge, under the influence of applied pressure (p) from 100 MPa to 1000 MPa, on the pressure distortion coefficient (λ) of the assembly. The gap profile is also studied at different applied jacket pressure (p_j) such that p_j/p varied from 0.3, 0.4 and 0.5.     

The frictional behavior of mild steel under horizontal vibration

The present paper investigates experimentally the effect of external horizontal vibration on friction property of mild steel. To do so, a pin-on-disc apparatus having facility of vibrating the test samples in horizontal direction was designed and fabricated. Horizontal vibration is created along the sliding direction of vibration and perpendicular to the direction of vibration. The experimental setup has the facility to vary the amplitudes and frequencies of vibration while velocity of vibration is kept constant. During the experiment, the frequency and amplitude of vibration were varied from 0 to 500 Hz and 0 to 200 μm, respectively. Results show that the friction coefficient increases with the increase in amplitude and frequency of vibration for mild steel. The horizontal vibration can be of two types: one along the direction of sliding (longitudinal direction) and the other along the perpendicular direction of sliding (transverse direction). For both the cases, test sample slides horizontally. It is found that the magnitude of friction coefficient for longitudinal vibration is less than that for under transverse vibration. These results are analyzed by dimensional analysis to correlate the friction coefficient with sliding velocity, frequency and amplitude of vibration. The experimental results are also compared with those available in literature and simple physical explanations are provided.     

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.     

A tribometer for measurements in hostile environments

A tribometer at the National Institute of Standards and Technology in Boulder, Colorado is used to measure the coefficient of friction and the wear rate for various specimens in a controlled atmosphere of oxygen or non-corrosive gas. The wide range of demonstrated operating temperature of 80 to 1030 K is presently unavailable in any commercial apparatus. The machine uses ball-on-flat or ring-on-flat specimen geometries for comparison of conforming and non-conforming contacts. The tribometer can be loaded to produce a hertzian contact stress in excess of 12 GPa (1.7×10⁶ Ibf in⁻²) and surface velocities from 0.06 m s⁻¹ to 4.0 m s⁻¹. A range of environmental conditions this wide is unusual, especially the temperature range. The apparatus is described and some test results are compared with known values.     

Simultaneous measurement of emissivity and temperature of silicon wafers using a polarization technique

The emissivity of a silicon wafer under various conditions was theoretically and experimentally investigated. A quantitative relationship between the ratio of p-polarized to s-polarized radiances, and the polarized emissivity was obtained, irrespective of the emissivity change of silicon wafers due to oxide film thickness under wide variations of impurity concentration. We propose a new radiation thermometry method that can measure both the temperature and the spectral polarized emissivity of a silicon wafer, and we estimate the uncertainty of these measurements. Currently, the expanded uncertainty of the temperature measurement is estimated to be 3.52 K (2k) and 3.80 (2k) for p-polarization and s-polarization, respectively, at temperatures above 900 K.     

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.     

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.     

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.     

Field emission techniques for studying surface reactions: applying them to NO-H2 interaction with Pd tips

The adsorption of NO and its reaction with H₂ over Pd tips were investigated by means of field ion microscopy (FIM) and pulsed field desorption mass spectrometry (PFDMS) in the 10⁻³ Pa pressure range and at sample temperatures between 400 and 600 K. By varying the H₂ partial pressure while keeping the other control parameters constant, the NO+H₂ reaction over Pd crystallites is shown to exhibit a strong hysteresis effect. The hysteresis region narrows with increase in temperature and the H₂ pressures delimiting this hysteresis decrease as well. Abrupt transformations of the micrographs are observed by FIM from bright to dark patterns and vice versa. These transformations define the hysteresis region. The collected data allow establishing a novel kinetic phase diagram of the NO+H₂/Pd system within the range of temperatures and pressures indicated. The observed features are correlated with a local chemical analysis by means of field pulses. NO⁺ seems to be the dominating imaging species under all conditions. At high relative H₂ pressures (the “hydrogen-side”), H atoms seem to diffuse subsurface. This process is blocked at lower H₂ pressure (the “NO-side”) due to NO_ad and O_ad accumulation on the surface. Probe-hole measurements with field pulses indicate that the Pd surface undergoes oxidation as revealed by the occurrence of PdO₂⁺ species in the mass spectra.     

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.