Showing papers on "Atmospheric temperature range published in 2003"

Thermal conductivity of individual silicon nanowires

Abstract: The thermal conductivities of individual single crystalline intrinsic Si nanowires with diameters of 22, 37, 56, and 115 nm were measured using a microfabricated suspended device over a temperature range of 20–320 K. Although the nanowires had well-defined crystalline order, the thermal conductivity observed was more than two orders of magnitude lower than the bulk value. The strong diameter dependence of thermal conductivity in nanowires was ascribed to the increased phonon-boundary scattering and possible phonon spectrum modification.

High-Resolution X-Ray Spectroscopic Constraints on Cooling-Flow Models for Clusters of Galaxies

Abstract: We present high-resolution X-ray spectra of 14 putative cooling-flow clusters of galaxies obtained with the Reflection Grating Spectrometer on XMM-Newton. The clusters in the sample span a large range of temperatures and mass deposition rates. Various of these spectra exhibit line emission from O VIII, Ne X, Mg XII and XI, Al XIII and XII, Si XIV and XIII, N VII, and C VI as well as all Fe L ions. The spectra exhibit strong emission from cool plasma at just below the ambient temperature, T0, down to T0/2, but also exhibit a severe deficit of emission relative to the predictions of the isobaric cooling-flow model at lower temperatures (

Influence of temperature on thermal conductivity, thermal capacity and thermal diffusivity for different types of rock

Abstract: Thermal modeling down to great depth, e.g. down to the Mohorovicic discontinuity, requires representative values of thermal conductivity and thermal capacity at an appropriate depth. Often there is a lack of data, especially concerning temperature and pressure dependence of thermal conductivity and thermal capacity, due to missing or questionable data from boreholes. Studies of the temperature and pressure dependence of thermal conductivity and thermal capacity showed that temperature is dominating. Thus measurements on a set of magmatic, metamorphic and sedimentary rocks sampled from different depth levels of the Eastern Alpine crust were used to obtain an estimate of the temperature dependence of both properties––at least for the area of investigation––and to give a review of the temperature dependence of thermal conductivity ( λ ), thermal capacity ( ρ × c p ) and thermal diffusivity ( κ ) for different types of rock. The temperature dependence of thermal conductivity for crystalline (magmatitic and metamorphic) rocks is different to that of sedimentary rocks. Using the approach that the thermal resistivity (1/ λ ) is a linear function of temperature whose slope increases with λ (0), the conductivity at a temperature of 0 °C, two general equations were determined. The equation for crystalline rocks was verified in the temperature range of 0–500 °C and the equation for sedimentary rocks was tested in the temperature range from 0 to 300 °C. A general equation for the temperature dependence of λ for Eastern Alpine rocks can thus be formulated: λ(T)= λ(0) 0.99+T(a−b/λ(0)) with empirical constants and corresponding uncertainties a =0.0030±0.0015 and b =0.0042±0.0006 for crystalline rocks. The constants for corresponding sedimentary rocks are a =0.0034±0.0006 and b =0.0039±0.0014. λ is given in W m −1 K −1 , T in °C. At ambient conditions thermal diffusivity ( κ ) and thermal conductivity ( λ ) for Eastern Alpine crystalline rocks show the relationship: κ=0.45×λ.

Influence of processing conditions on the thermal and mechanical properties of SU8 negative photoresist coatings

Abstract: The thermal and mechanical properties of a new negative photoresist, SU8, were characterized. The influence of curing conditions, such as baking temperature, baking time and UV dosage, on the thermal and mechanical properties of the resultant coatings was studied in detail. It was found that the glass-transition temperature (Tg) of the coatings was coincident with the baking temperature over the temperature range of 25 °C–220 °C for coatings being baked for just 20 min. However, the Tg reached a limiting value (about 240 °C) once the cross-linking reaction was complete, and would not increase further with the baking temperature. The peak temperature of the dimension versus temperature plots, where heat shrinkage occurred, was about a factor of 1.16 times higher than the baking temperature for the temperature range studied. Both the Tg and the shrinkage temperature were affected by the baking time. The thermal expansion coefficients (TEC), including the volumetric TEC (αv), the in-plane TEC (α1) and the out-of-plane TEC (α2), were measured by a pressure–volume–temperature (PVT) apparatus and thermal–mechanical analyzer (TMA). Great residual stress could be generated during the process, and the change in residual stress with the environmental humidity was investigated using vibrational holographic interferometry.

Thermal conductivity of Si/SiGe superlattice nanowires

Abstract: The thermal conductivities of individual single crystalline Si/SiGe superlattice nanowires with diameters of 58 and 83 nm were measured over a temperature range from 20 to 320 K. The observed thermal conductivity shows similar temperature dependence as that of two-dimensional Si/SiGe superlattice films. Comparison with the thermal conductivity data of intrinsic Si nanowires suggests that alloy scattering of phonons in the Si–Ge segments is the dominant scattering mechanism in these superlattice nanowires. In addition, boundary scattering also contributes to thermal conductivity reduction.

High-Temperature Oxidation Behavior of Ti2AlC in Air

Abstract: The isothermal oxidation behavior of bulk Ti2AlC in air has been investigated in temperature range 1000–1300°C for exposure time up to 20 hr by TGA, XRD, and SEM/EDS The results demonstrated that Ti2AlC had excellent oxidation resistance The oxidation of Ti2AlC obeyed a cubic law with cubic rate constants, kc, increasing from 238×10-12 to 213×10-10 kg3/m6/sec as the temperature increased from 1000 to 1300°C As revealed by X-ray diffraction (XRD) and SEM/EDS results, scales consisting of a continuous inner α-Al2O3 layer and a discontinuous outer TiO2 (rutile) layer formed on the Ti2AlC substrate A possible mechanism for the selective oxidation of Al to form protective alumina is proposed in comparison with the oxidation of Ti–Al alloys In addition, the scales had good adhesion to the Ti2AlC substrate during thermal cycling

Effect of temperature on thermal properties of high-strength concrete

Abstract: For use in fire resistance calculations, the relevant thermal properties of high-strength concrete (HSC) were determined as a function of temperature. These properties included the thermal conductivity, specific heat, thermal expansion, and mass loss of plain and steel fibre-reinforced concrete made of siliceous and carbonate aggregate. The thermal properties are presented in equations that express the values of these properties as a function of temperature in the temperature range between 0 and 1,000°C. The effect of temperature on thermal conductivity, thermal expansion, specific heat, and mass loss of HSC is discussed. Test data indicate that the type of aggregate has a significant influence on the thermal properties of HSC, while the presence of steel fiber reinforcement has very little influence on the thermal properties of HSC.

Hot and solid gallium clusters: too small to melt.

Abstract: A novel multicollision induced dissociation scheme is employed to determine the energy content for mass-selected gallium cluster ions as a function of their temperature. Measurements were performed for Ga(+)(n) (n=17 39, and 40) over a 90-720 K temperature range. For Ga+39 and Ga+40 a broad maximum in the heat capacity-a signature of a melting transition for a small cluster-occurs at around 550 K. Thus small gallium clusters melt at substantially above the 302.9 K melting point of bulk gallium, in conflict with expectations that they will remain liquid to below 150 K. No melting transition is observed for Ga+17.

Temperature-dependent low-frequency vibrational spectra of purine and adenine

Abstract: Terahertz time-domain spectroscopy has been used to measure the vibrational spectra of polycrystalline purine and adenine over the temperature range 4–290 K. A number of well-resolved absorption peaks were observed in the frequency range 0.2–3.0 THz, which are interpreted as originating from intermolecular vibrational modes mediated by hydrogen bonds. We find that as the temperature is reduced, the observed absorption bands resolve into narrower peaks and some shift towards higher frequencies. We explain the temperature dependence of the spectra by the anharmonicity of the vibrational potentials and give an empirical expression to describe the frequency shift.

Polarized Raman study of the phonon dynamics in Pb ( Mg 1 / 3 Nb 2 / 3 ) O 3 crystal

Abstract: Pb(Mg 1 / 3 Nb 2 / 3 )O 3 is one of the simplest members of the class of lead relaxors and often serves as a model system for more complicated compounds. In this paper, we analyze both polarized and depolarized Raman-scattering spectra, measured in the temperature range between 1000 and 100 K, using a multiple-peak decomposition. Based on this analysis, we propose a comprehensive picture of the structural transformations in the crystal and associated dynamics. According to our model, the formation of the Fm3m symmetry in the chemically ordered regions as well as the appearance and freezing of the polar nanoregions are the consequences of the same phenomenon: the off-centered displacements of ions and their fast reorientational thermal motion. Short-lived dynamic lattice distortions are present even at the highest measured temperatures. From the Burns temperature, T d ∼620 K, their motion becomes progressively more restricted. Temperature T* ∼350 K marks the beginning of the freezing process which continues down to the temperature of the electric-field-induced phase transition, T d 0 ∼210 K. Raman scattering exists due to the presence of local lattice distortions. It is characterized by phonons with different wave vectors interacting with dynamic and static disorder.

Nature of the first-order phase transition in fluid phosphorus at high temperature and pressure.

Abstract: An in situ x-ray diffraction experiment has been performed on phosphorus to characterize the liquid-liquid transition which occurs at high temperature and pressure. The transition line has been measured over an extended temperature range up to 2200 degrees C at 0.3 GPa. From the shape of this line, a thermodynamic characterization of the transition is obtained in terms of latent heat and internal energy change. Moreover, the addition of the high-pressure high-temperature data to the known phase diagram of phosphorus allows us to conclude that this is a first-order transition between a dense molecular fluid and a polymeric liquid.

Characterisation of semiconducting V2O5–Bi2O3–TeO2 glasses through ultrasonic measurements

Abstract: Tellurite containing vanadate (50−x)V2O5–xBi2O3–50TeO2 glasses with different bismuth (x=0, 5, 10, 15, 20 and 25 wt%) contents have been prepared by rapid quenching method. Ultrasonic velocities (both longitudinal and shear) and attenuation (for longitudinal waves only) measurements have been made using a transducer operated at the fundamental frequency of 5 MHz in the temperature range from 150 to 480 K. The elastic moduli, Debye temperature, and Poisson’s ratio have been obtained both as a function of temperature and Bi2O3 content. The room temperature study on ultrasonic velocities, attenuation, elastic moduli, Poisson’s ratio, Debye temperature and glass transition temperature show the absence of any anomalies with addition of Bi2O3 content. The observed results confirm that the addition of Bi2O3 modifier changes the rigid formula character of TeO2 to a matrix of regular TeO3 and ionic behaviour bonds (NBOs). A monotonic decrease in velocities and elastic moduli, and an increase in attenuation and acoustic loss as a function of temperature in all the glass samples reveal the loose packing structure, which is attributed to the instability of TeO4 trigonal bipyramid units in the network as temperature increases. It is also inferred that the glasses with low Bi2O3 content are more stable than with high Bi2O3 content.

Dual luminophor pressure sensitive paint. II. Lifetime based measurement of pressure and temperature

Abstract: Two newly synthesized luminescent compounds provide a lifetime based dual pressure and temperature sensor when jointly dissolved in a polymer matrix. The temperature sensor is a tris(β-diketonate) phenanthroline europium complex, with a broad absorption peaked at 370 nm and a characteristic but relatively sharp 615 nm europium emission. The lifetime of this compound varies between 260 and 120 μs over the temperature range 5–45 °C for a derivative of −3.50 μs/°C. Our pressure sensor is a porphyrin compound called platinum tetra(pentafluorophenyl)porpholactone (PtTFPL) developed recently in our labs. This compound has a principal absorption band at 390 nm and a red-shifted phosphorescence at 730 μm. In silicone polycarbonate co-polymer, PtTFPL has a lifetime range of 42.7–6.6 μs in going from 0 to 1 atm at 1 atm. The two sensors have maximum absorption in the range 370–400 nm but non-overlapping emission spectra upon excitation with a broadband illumination at 400 nm. As a result, with appropriate band pass optical filters, the two emission lines can be detected separately. In addition to the high photostability of the dual system, our studies show that the luminescence properties of one sensor are independent of the presence of the other sensor. We note that measurement of decay rate is more robust than measuring intensity, since it is unaffected by changes in the light source, the index of refraction of the medium, optical geometry variations and fluctuations in film thickness and dye concentration. Hence the two compounds afford the possibility of a dual luminophor lifetime measurement of pressure and temperature.

High performance new MgB2 superconducting hollow wires

Abstract: MgB2 hollow wires have been produced with a new technique which uses a conventional wire manufacturing process but is applied to composite billets containing the elemental B and Mg precursors in an appropriate shape. The technique has been applied to the manufacture of both monofilamentary and multifilamentary wires of several tens of metres in length. The superconducting transport properties of the MgB2 hollow wires have been measured in a magnetic field and in the temperature range from 4.2 to 30 K. Promising results are obtained, which indicate the possibility of the application of these wires as superconductors in the temperature range of 15–30 K and at medium-high values of magnetic field.

Growth of Vertically Aligned Nitrogen-Doped Carbon Nanotubes: Control of the Nitrogen Content over the Temperature Range 900−1100 °C

Abstract: Nitrogen-doped carbon nanotubes were grown vertically aligned on the iron nanoparticles deposited on silicon substrates, by thermal chemical vapor deposition of methane/ammonia and acetylene/ammonia mixtures in the temperature range 900−1100 °C. The concentration of the nitrogen atoms has been controlled in the range 2−6 atomic %, by the flow rate of ammonia. All nanotubes exhibit a bamboo-like structure over this temperature range. The growth rate is insensitive to this nitrogen content, but the structure is strongly dependent on it. As the nitrogen content increases, the thicker compartment layers form uniformly at a regular distance and the relative amount of crystalline graphitic sheets is notably reduced. Electron energy-loss spectroscopy reveals the higher nitrogen concentration and the lower crystallinity for the compartment layers compared to the wall. The growth of nitrogen-doped carbon nanotubes has been explained using a base growth mechanism proposed for carbon nanotubes. We suggest that the n...

Surface Tension of Pure Liquids and Binary Liquid Mixtures

Abstract: The pendant drop method, combined with efficient temperature control of the measuring cell, allows high precision in surface tension measurements. The surface tensions of heptane, toluene, N,N-dimethylformamide, cyclohexane, N-methyl-2-pyrrolidone, and propanone were measured as a function of temperature using the pendant drop method. The results were compared with literature data. The surface tension and density of toluene + heptane and N,N-dimethylformamide + toluene at atmospheric pressure were measured over a temperature range. Gibbs excess surface concentrations are derived from the experimental surface tensions, and the influence of activity coefficients is discussed.

Ferroelectric transition in an epitaxial barium titanate thin film: Raman spectroscopy and x-ray diffraction study

Abstract: We have performed x-ray diffraction and Raman spectroscopy measurements in the temperature range of 300–873 K on a single phase epitaxially oriented BaTiO3 thin film grown by pulsed laser deposition on a single crystal MgO substrate. The θ–2θ room temperature diffraction measurements and asymmetric rocking curves indicate that the film is very weakly tetragonal with the c-axis parallel to the plane of the film. X-ray diffraction measurements up to high temperature reveal only a change in slope in the perpendicular to the plane lattice parameter around 450 K (in bulk Tc=395 K) indicating that a diffuse-like of phase transition is taking place. Room temperature polarized Raman spectra show that the film is indeed tetragonal with C4v symmetry and with the a-axis perpendicular to the film plane. Monitoring of the overdamped soft mode and the 308 cm−1 mode confirms that the phase transition is taking place over a wide temperature range according to the x-ray results. The increase of the phase transition temper...

Temperature and pressure study of Brillouin transverse modes in the organic glass-forming liquid orthoterphenyl.

Abstract: Transverse Brillouin spectra of orthoterphenyl are measured in the (250-305 K; 0.1-100 MPa) temperature-pressure range, which corresponds to the supercooled phase of this organic glass former. We show that the analysis of these spectra combined with an extrapolation of the reorientation times under pressure leads to an estimate of the static shear viscosity in a pressure range whose validity extends beyond the range of the Brillouin measurements. The relative contributions of temperature and of density to the change of this reorientation time measured along an isobar are extracted from our results in a large temperature range extending from the liquid to the low temperature supercooled state. They appear to be always of the same order of magnitude. It is also shown that in the range of the experiment, the orientational time is depending on a unique parameter built on temperature and density.

Temperature-dependent dispersion equations for KTiOPO4 and KTiOAsO4.

Abstract: We have measured the thermal expansion and the temperature dependence of z and y components of the refractive index for KTiOPO4 and KTiOAsO4, in the wavelength range 532-1585 nm and temperature range 25-200 degrees C, using an interferometric technique. The measurements were used to derive temperature-dependent Sellmeier equations for the two materials. These equations predict with good agreement the temperature dependence of quasi-phase-matched nonlinear frequency converters.

ZnO sol–gel derived porous film for CO gas sensing

Abstract: Fine powder of ZnO was synthesized by the sol–gel method, which was then calcined followed by spin coating on an alumina substrate and tested for CO gas sensing. With variation in the calcination temperature, the shape of gel powder changed into various morphologies: sheet, needle, and sphere. The grain growth rate increased above 700 °C and the larger grains showed higher degree of crystallization. The organic element in gel powders evaporated below 300 °C. The temperature dependence of the electrical conductance showed the sigmoidal shape, but the temperature range of the constant conductance narrowed with the decrease in the calcination temperature. The optimum sensing properties were observed for the specimen calcined at 500 °C, and it degraded with the increase in calcination temperature because of the larger grain size that limits the surface area for gas–solid reaction.

Temperature dependence of thermal expansion and elastic constants of single crystals of ZrB2 and the suitability of ZrB2 as a substrate for GaN film

Abstract: Coefficients of thermal expansion (CTE) and elastic constants of single crystals of ZrB2 have been determined in the temperature ranges from room temperature to 1073 K and from room temperature to 1373 K, respectively. The elastic constants of ZrB2 are best characterized by the large value of the Young modulus (as high as 500 GPa) and the small values of the Poisson ratio (0.13–0.15), indicating the high stiffness and hardness and the brittleness, respectively. The values of CTE along the a- and c-axis directions are 6.66×10−6 and 6.93×10−6 K−1, respectively, when averaged over the temperature range from room temperature to 1073 K. The CTE value along the a-axis direction of ZrB2 is only moderately larger than the corresponding value for GaN. This together with the small lattice mismatch along the a-axis direction between ZrB2 and GaN in the heteroepitaxial orientation relationship of (0001)GaN//(0001)ZrB2 and 〈1120〉GaN//〈1120〉ZrB2 indicate that only a small compressive stress develops in the GaN thin-film crystal grown on the (0001) surface of the ZrB2 substrate. The stresses developed in the GaN thin-film crystal are evaluated with the values of CTE and elastic constants of ZrB2 determined in the present study. The evaluation verifies the suitability of ZrB2 as a substrate for heteroepitaxial growth of GaN.

The microstructure and the thermal expansion characteristics of Cu/SiCp composites

Abstract: Copper/silicon carbide composites (Cu/SiC p ) were made by the powder metallurgy method. Electroless plating was employed to deposit a copper film on SiC p powder before mixing with Cu powder in order to improve the bonding status between Cu and SiC particles during sintering. Thermal expansion property of as-formed product was measured in the temperature range from 50 to 550 °C. The results showed that copper coating on silicon carbide particles could render uniform distribution of SiC p in the copper matrix. The composites exhibited positive thermal hysteresis behavior when cooled down from the peak temperature to room temperature, which can be explained in terms of the residual stresses and the interfacial bonding between copper and silicon carbide. The magnitude of this strain was a function of the SiC p volume fraction and the number of thermal cycles. The thermal expansion property of composites was measured and compared with those predicted from various theoretical models.