Showing papers on "Atmospheric temperature range published in 1991"
TL;DR: In this article, the fractionation factor between the 18O/16O ratio in calcite and CO2 gas produced as a result of reaction with phosphoric acid has been determined as a function of temperature for two of the most widely used variations of the dissolution technique, reaction in a sealed vessel and reaction in an acid bath.
Abstract: The fractionation factor (α) between the 18O/16O ratio in calcite and CO2 gas produced as a result of reaction with phosphoric acid has been determined as a function of temperature for two of the most widely used variations of the dissolution technique, reaction in a sealed vessel and reaction in an acid bath. Although these methods show approximately the same relationship between temperature and α, they are offset from one another by between 0.2 and 0.4% over the temperature range 25–90°C. There appears to be no temperature- or technique-dependent fractionation on carbon over the range of temperatures examined in this study. The difference between these two methods arises from three main processes: (1) isotopic exchange between the CO2, the phosphate polymers in the acid and water produced in the reaction; (2) dissolution of CO2 in the acid; and (3) incomplete removal of CO2 during the extraction process. Of these two methods the “acid bath” method probably provides the most accurate isotopic composition of the calcite. As a result of the fact the original fractionation factors were determined using the “sealed vessel” method, we have calculated our temperature [T (K)] - dependent fractionation factor (αT) taking into account the difference between the two methods at 25°C. For the “sealed vessel” method: (a) αT= [5.60 (± 0.33) × 102] T−2 + 1.003943 (± 0.000067). For the “common acid bath” technique: (b) αT = [5.25 (± 0.08) × 102] T −2 + 1.003970 (± 0.000034).
348 citations
TL;DR: In this paper, the authors investigated the tensile and compressive total (thermal and intrinsic) stress in diamond films prepared by microwave plasma CVD, as a function of methane concentration (0.2% −3.0%) and deposition temperature (600-900°C).
Abstract: The stress in diamond films prepared by microwave plasma CVD was investigated as a function of methane concentration (0.2%–3.0%) and deposition temperature (600–900 °C). Tensile and compressive total (thermal and intrinsic) stress were observed, depending on the deposition conditions. The thermal stress is compressive and relatively constant (0.215–0.275 GPa) over the temperature range investigated. The intrinsic stress is tensile and its origin is interpreted in terms of the grain boundary relaxation model. Calculations indicate a value of 0.84 GPa, using the grain boundary model, which is in fair agreement with the measured value. For the methane series, the tensile intrinsic stress decreases with increasing the methane fraction. The increasing compressive stress is ascribed to increased impurity (hydrogen and nondiamond phase carbon) incorporation with increasing methane fraction. 15N nuclear reaction analysis shows a linear correlation between hydrogen in the film and methane in the supply gas while spectroscopic ellipsometry shows a direct correlation between optically absorbing nondiamond (sp2) carbon incorporation and methane. For the temperature series, the intrinsic tensile stress increases with deposition temperature. The increase is ascribed to decreasing sp2 C incorporation with temperature, as confirmed by spectroscopic ellipsometry measurements.
248 citations
TL;DR: In this article, a new group contribution method, GCVOL, is proposed for the prediction of liquid densities as a function of the temperature, which is able to describe densities for the complete molecular range, covering solvents, oligomers, and polymers.
Abstract: A new group contribution method, GCVOL, for the prediction of liquid densities as a function of the temperature is proposed. A table for 36 different group volume increments for a wide variety of chemical families (noncyclic alkanes, aromatics, alkenes, ketones, ethers, esters, chlorides, and siloxanes) is given. Using the proposed method liquid densities for even strongly polar solvents can be predicted with an error of approximately 1% in the temperature range between the melting temperature and the normal boiling point. Densities of amorphous polymers in the temperature range of 277-571 K are predicted with an average error of 2.7%. The proposed method is able to describe densities for the complete molecular range, covering solvents, oligomers, and polymers
201 citations
01 Jan 1991
TL;DR: In this article, the authors measured the CO2/CO ratio formed by the heterogeneous reaction on the char surface for temperatures up to 1670 K and found an exponential decrease with a temperature coefficient of 3100/K.
Abstract: The ratio CO2/CO from oxidation of Spherocarb char has been measured over a wide temperature range making use of the electrodynamic balance where single particles are heated by laser irradiation but are immersed in room temperature gas. This has allowed measurement of the CO2/CO ratio formed by the heterogeneous reaction on the char surface for temperatures up to 1670 K. For these conditions, an exponential decrease with a temperature coefficient of 3100/K is found. The CO2/CO ratio is proportional to the oxygen partial pressure raised to a power of 0.21. These results are in substantial agreement with work reported at lower temperatures. At normal combustion temperature the CO2/CO ratio from heterogeneous reaction is less than 0.1. Gas phase oxidation of CO to CO2 near the char surface, however, can become important at high char temperatures, even in a gas maintained at room temperature, and can have an important impact on surface temperature. The temperature at which gas phase reactions begin to contribute to CO2 formation and surface temperature was found to be reduced by the presence of water vapor.
165 citations
TL;DR: Measurements of the attenuation of longitudinal-acoustic phonons in amorphous SiO{sub 2} for frequencies between 76 and 440 GHz, and in the temperature range 80--300 K show some evidence that the frequency dependence is faster than quadratic, thus indicating that the attenuations cannot be explained by classical relaxation theory.
Abstract: We report measurements of the attenuation of longitudinal-acoustic phonons in amorphous ${\mathrm{SiO}}_{2}$ for frequencies between 76 and 440 GHz, and in the temperature range 80--300 K. The samples are chemical-vapor-deposited films grown on tungsten substrates, and the phonons are generated and detected using picosecond optical techniques. The phonon attenuation is found to depend only weakly on temperature. In the upper part of the frequency range, there is some evidence that the frequency dependence is faster than quadratic, thus indicating that the attenuation cannot be explained by classical relaxation theory. A discussion of the relation between these results and the analysis of thermal-conductivity measurements is given.
149 citations
TL;DR: In this article, ZnO:Al films were deposited on (1210) oriented sapphire substrates heated up to 400°C by rf magnetron sputtering from a znO target mixed with Al2O3 of 2 wt%.
Abstract: ZnO:Al films were deposited on (1210) oriented sapphire substrates heated up to 400 °C by rf magnetron sputtering from a ZnO target mixed with Al2O3 of 2 wt%. Films deposited on a substrate heated to a temperature in the range 50–350 °C were (0001) oriented single crystals but those grown at 400 °C consisted of crystallites with the (0001) and (1101) orientation. The former films had relatively smooth surfaces whereas the latter exhibited very rough surfaces. Electrical properties such as resistivity, carrier concentration, and the Hall mobility were measured as a function of substrate temperature. The carrier concentration decreased as the substrate temperature was increased up to 300 °C, although the Al content remained unchanged in this temperature range. From these measurements, it was found that the native donors were important as a source of carriers, even in ZnO:Al films. However, it was found that the Hall mobilities for films with a thickness of more than 200 nm experienced minor changes over a...
142 citations
TL;DR: In this paper, an experiment to determine the electronic state of Cu in a ZnO crystal is performed using the admittance spectroscopy technique at the frequency range from 100 Hz to 100 kHz and the temperature range from -160 to +80°C.
Abstract: An experiment to determine the electronic state of Cu in a ZnO crystal is performed using the admittance spectroscopy technique at the frequency range from 100 Hz to 100 kHz and the temperature range from -160 to +80°C. The results obtained are summarised as follows: Cu behaves as an acceptor in ZnO and its energy level locates at 0.17 eV below the bottom of the conduction band. The values of the electron capture cross section are found to decrease with increasing Cu concentration, and they are determined as 2-12×10-17 cm2.
139 citations
TL;DR: A free space microwave measurement system that is used for the high-temperature measurement of dielectric constants and loss tangents of homogeneous materials and that is applicable to composite materials as well is discussed in this paper.
Abstract: A free-space microwave measurement system that is used for the high-temperature measurement of dielectric constants and loss tangents of homogeneous materials and that is applicable to composite materials as well is discussed. The system is capable of operating in the 5.85-40-GHz frequency range and ambient to 850 degrees C temperature range. A computer is used to control and coordinate furnace temperature, network analyzer functions, and data storage. Dielectric constants and loss tangents of the materials are calculated from the measured values of S/sub 21/. The measurement system, including the high-temperature furnace and the calibration technique, is described. Dielectric constants and loss tangents are presented for fused quartz and boron nitride grade HP in the frequency range 13.0-17.4 GHz and the temperature range from ambient to 850 degrees C. >
137 citations
TL;DR: In this article, the thermoelectric properties and Hall effects of a number of undoped Bi 2 Te 3 -Sb 2 Te3 pseudo-binary and Sb 2 Se 3 pseudo-ternary single crystal alloys grown by the Bridgman method were measured over the temperature range from 77 to 580 K. All of the alloys showed p -type extrinsic conduction and the analysis of the Seebeck coefficient and electrical conductivity indicated partial degeneracy at lower temperatures.
135 citations
TL;DR: In this article, the authors developed a technique which permits high yield fabrication of microbridges and low noise YBa2Cu3O7 superconducting quantum interference devices (SQUIDs) in epitaxial thin films.
Abstract: We have developed a technique which permits high‐yield fabrication of microbridges and low noise YBa2Cu3O7 superconducting quantum interference devices (SQUIDs) in epitaxial thin films. These SQUIDs operate over a wide temperature range extending from 4 K to close to the superconducting transition temperature. Measurements of an rf SQUID operating at 77 K give a peak‐to‐peak flux sensitivity of 36 μV/Φ0 and a flux noise at 10 Hz of 1.5× 10−4 Φ0/√Hz. Device yields over 80% have been obtained.
134 citations
TL;DR: In this article, the critical temperature of Bi 2 Sr 2 CaCU 2 O 8+δ (2212) was mapped to the (p, T ) plane for 10 −5 ≤ p ≤ 80 bar (O 2 ) and 300 ≤ T ≤ 840°C.
Abstract: We have mapped the critical temperature of Bi 2 Sr 2 CaCU 2 O 8+δ (2212) in the ( p, T ) plane for 10 −5 ≤ p ≤ 80 bar (O 2 ) and 300 ≤ T ≤ 840°C. Equilibrium conditions are frozen by quenching the samples into liquid gallium. The DC diamagnetic transitions remain sharp, and span an unusual temperature range for the 2212 phase (51.5 K to 94.4 K). This variation is attributed to a measured 2.5% change of the oxygen content ( Δδ ⋍ 0.2 ) in the structure. At the same time, we do not observe any significant variation of the lattice parameters. The Meissner effect, measured in an external magnetic field of 20 Oe, increases with T c . The slope of the normal-state susceptibility ∂ χ / ∂T becomes markedly less negative with decreasing oxygen concentration. It vanishes for the optimum doping that leads to T c ⋍ 94 K .
TL;DR: A relatively simple printed sensor, based on 7,7,8,8-tetracyano quinodimethane-modified graphite and immobilised butyrylcholinesterase, which operated at a potential of 100 mV versus Ag/AgCl (printed) and was sensitive to inhibition by organophosphates.
TL;DR: In this article, the effects of controllable network parameters on the important properties (degree of swelling, transition temperature and sharpness of transition) of the gels obtained were investigated. But the results were limited to a limited temperature range.
TL;DR: The structures of the antifluorite-type copper chalcogenides Cu 2 Se and Cu 1.8 S were studied using single crystal X-ray diffraction data both below and above the transition point.
TL;DR: In this article, the hydrogen solubilities of vanadium-nickel alloys were determined using a volumetric method in the temperature range 473-673 K and in the hydrogen pressure range 1×10 2 -3×10 6 Pa.
Abstract: Hydrogen permeation characteristics of palladium-plated vanadium and vanadium-nickel alloy membranes have been investigated using gas permeation technique in the temperature range 423-673 K and in the hydrogen pressure range 1×10 4 -3×10 5 pa, hydrogen solubilities of vanadium-nickel alloys have been determined using a volumetric method in the temperature range 473-673 K and in the hydrogen pressure range 1×10 2 -3×10 6 Pa
TL;DR: The results of measurements of solubility S and diffusivity D of hydrogen isotopes in Pb17Li in the temperature range from 508 K to 700 K are presented in this paper.
TL;DR: In this article, the authors measured the solubility and diffusivity of 2 and 3 M AMP (2-amino-2-methyl-1-propanol) solutions and correlated with temperature.
Abstract: The solubility and diffusivity of N 2 O in 2 and 3 M AMP (2-amino-2-methyl-1-propanol) solutions were measured and correlated with temperature. The N 2 O analogy was used to estimate the solubility and diffusivity of CO 2 in AMP solutions. The density of aqueous AMP solutions was determined over a wide range of temperatures and compositions. The viscosity of 2 and 3 M AMP solutions was measured over the temperature range 23-77°C
TL;DR: In this paper, the authors examined the active oxidation behavior of chemically vapor-deposited silicon carbide in an O2 atmosphere at 0.1 MPa in the temperature range between 1840 and 1923 K.
Abstract: Active oxidation behavior of chemically vapor-deposited silicon carbide in an Ar─O2 atmosphere at 0.1 MPa was examined in the temperature range between 1840 and 1923 K. The transition from active oxidation (mass loss) to passive oxidation (mass gain) was observed at certain distinct oxygen partial pressures (PO2t). The values of PO2t increased with increasing temperature and with decreasing total gas flow rates. This behavior was well explained by Wagner's model and thermodynamic calculations. Active oxidation rates (ka) increased with increasing O2 partial pressures and total gas flow rates. The rate-controlling step of the active oxidation was concluded to be O2 diffusion through the gaseous boundary layer.
TL;DR: In this article, the authors defined explosion limit temperatures for near stoichiometric mixtures of CO/H2O/O2 and H2O2 systems at atmospheric pressure without the presence of surfaces.
Abstract: New data on the kinetics of CO/H2O/O2 and H2/O2 mixtures in the temperature range of 852—1138 K and at I atmosphere pressure are reported. The data were obtained from adiabatic. constant pressure flow reactor experiments for variations in the initial carbon, hydrogen, and oxygen contents of the mixture and also for variations in the initial temperature. In particular, the results define explosion limit temperatures for near stoichiometric mixtures of CO/H2O/O2 and H2/O2 systems at atmospheric pressure without the presence of surfaces and also demonstrate the complex relationship between water vapor concentration and the carbon monoxide oxidation rate.
TL;DR: In this paper, the elastic constants on a single crystal of the shape-memory alloy NiTi in a wide temperature range are measured and step-like anomalies and hysteresis are detected at the austenitic-martensitic phase transition.
Abstract: The authors present measurements of the elastic constants on a single crystal of the shape-memory alloy NiTi in a wide temperature range. Step-like anomalies and hysteresis are detected at the austenitic-martensitic phase transition which provide evidence for the strain-order parameter coupling in the pre-martensitic phases. The results are discussed in the framework of existing Landau theory models.
TL;DR: In this paper, a power dissipation map for alpha-zirconium in the temperature range of 650 °C to 850 °C and in the strain-rate range of 10-3 to 102 s-1 was developed.
Abstract: The hot deformation characteristics of alpha-zirconium in the temperature range of 650 °C to 850 °C and in the strain-rate range of 10-3 to 102 s-1 are studied with the help of a power dissipation map developed on the basis of the Dynamic Materials Model.[7,8,9] The processing map describes the variation of the efficiency of power dissipation (η =2m/m + 1) calculated on the basis of the strain-rate sensitivity parameter (m), which partitions power dissipation between thermal and microstructural means. The processing map reveals a domain of dynamic recrystallization in the range of 730 °C to 850 °C and 10−2 to 1−1 with its peak efficiency of 40 pct at 800 °C and 0.1 s-1 which may be considered as optimum hot-working parameters. The characteristics of dynamic recrystallization are similar to those of static recrystallization regarding the sigmoidal variation of grain size (or hardness) with temperature, although the dynamic recrystallization temperature is much higher. When deformed at 650 °C and 10-3 s-1 texture-induced dynamic recovery occurred, while at strain rates higher than 1 s-1, alpha-zirconium exhibits microstructural instabilities in the form of localized shear bands which are to be avoided in processing.
TL;DR: It is shown that doping with potassium-thallium and rubidium- thallium alloys in the 400 to 430�C temperature range increases the Tc of C60/C70 mixtures to 25.6 K and above 45 K, respectively.
Abstract: The appearance of superconductivity at relatively high temperatures in alkali metal—doped C60 fullerene provides the challenge to both understand the nature and origin of the superconductivity and to determine the upper limit of the superconducting transition temperature (Tc). Towards the latter goal, it is shown that doping with potassium-thallium and rubidium-thallium alloys in the 400 to 430°C temperature range increases the Tc of C60/C70 mixtures to 25.6 K and above 45 K, respectively. Similar increases in Tc were also observed upon analogous doping of pure C60. Partial substitution of potassium with thallium in interstitial sites between C60 molecules is suggested by larger observed unit cell parameters than for the K3C60 and K4C60 phases. Contrary to previous results for C60 doped with different alkali metals, such expansion does not alone account for the changes in critical temperature.
TL;DR: In this article, phase formation and growth kinetics have been investigated with lateral diffusion couples in Cu•Si and Cu•Ge systems using analytical electron microscopy to determine the crystal structures and chemical compositions of the growing phases.
Abstract: Phase formation and growth kinetics have been investigated with lateral diffusion couples in Cu‐Si and Cu‐Ge systems. Analytical electron microscopy was used to determine the crystal structures and chemical compositions of the growing phases. Cu3Si is found to be the dominant phase in the Cu‐Si system. The growth of the silicide follows a (time)1/2 dependence with an activation energy of 0.95 eV in the temperature range of 200–260 °C. Cu3Ge is the only phase observed in Cu‐Ge lateral diffusion couples with its length up to 20 μm. The growth of Cu3Ge is a diffusion controlled process at a rate similar to that of Cu3Si. The activation energy of Cu3Ge growth is 0.94 eV at 200–420 °C. In Cu‐silicide or Cu‐germanide formation, Cu appears to be the dominant diffusing species.
TL;DR: In this article, the authors studied the two-stage oxidation mechanism of the intermetallic compound β-NiAl and Fe-23Cr-5Al-0.2Zr alloys modified by reactive element additions in the temperature range 1273-1473 K by using the oxygen isotope18O as a tracer.
Abstract: The oxidation mechanism of the intermetallic compound β-NiAl and Fe-23Cr-5Al-0.2Zr alloys modified by reactive-element additions was studied in the temperature range 1273–1473 K by means of the two-stage oxidation method using the oxygen isotope18O as a tracer.
TL;DR: In this article, the thermal diffusivity of MgSiO3 perovskite has been measured in the temperature range of 160 K to 340 K using a sample synthesized in a uniaxial split-sphere high-pressure apparatus.
Abstract: Thermal diffusivity of MgSiO3 perovskite has been measured in the temperature range of 160 K to 340 K using a sample synthesized in a uniaxial split-sphere high-pressure apparatus. At 300 K the thermal diffusivity of perovskite is 1.72 × 10−6 m2s−1, from which the thermal conductivity is evaluated to be 5.1 Wm−1K−1. Our model calculation shows that lattice thermal conductivity of the perovskite increases by a factor of 4 with depth throughout the lower mantle and reaches to 12 Wm−1K−1 in the vicinity of the mantle-core boundary. The D″ layer might not be a thermal boundary layer insulating the high core-temperature, if this layer mainly consists of the perovskite.
TL;DR: Novax as mentioned in this paper is a polyimide graphite graphite film with a high degree of graphitization, high value of magnetoresistance and very low anisotropy ratios.
TL;DR: The formation of iron silicides has been monitored by a variety of surface sensitive techniques such as Auger electron spectroscopy, electron energy loss spectrography, and low energy electron diffraction (LEED) as discussed by the authors.
Abstract: The formation of iron silicides has been monitored by a variety of surface sensitive techniques such as Auger electron spectroscopy, electron energy loss spectroscopy, and low energy electron diffraction (LEED). The deposition of Fe onto Si(100) at room temperature results in layer‐by‐layer growth of polycrystalline Fe with some Si interdiffused into the growing film. The extent of the reaction of silicide formation is very limited at room temperature. These two observations contradict previous reports. Formation of iron silicide by solid phase epitaxy occurs at low temperature (325 °C). The first compound formed can be identified as FeSi—with an additional Si layer at the surface. At 450 °C the silicide film transforms to FeSi2, maintaining a layer of Si at the outer surface. In view of the low formation temperature and some LEED observations the disilicide is probably in the β‐phase. We have determined the temperature range of stability of the FeSi2 film. Thermal treatments at temperatures around 600 °C produce the lateral disruption of the FeSi2 film. Iron disilicide can also be grown by evaporating Fe onto a Si substrate maintained at 350 °C.
TL;DR: In this paper, the authors studied the oxidation behavior of HfC at different temperature ranges between 1200-2200°C and showed that scale-growth kinetics are dominated by bulk (ambipolar) diffusion of oxygen and electrons through the oxide.
Abstract: The oxidation behavior of HfC, HfC-25 wt. % TaC, and HfC-7 wt.% PrC2 has been studied between 1200–2200° C. Parabolic growth of the oxide layer has been observed for both HfC and HfC-TaC over the entire temperature range. A break in the temperature dependence of the oxidation kinetics occurs around 1600°C. At lower temperatures, the kinetics are limited by gaseous diffusion via pores in the oxide. Above 1800°C, gaseous diffusion through pores becomes less important as scale-growth kinetics are dominated by bulk (ambipolar) diffusion of oxygen and electrons through the oxide.
TL;DR: The second-order rate coefficients of NH(X3Σ−) with NO, O2, and O have been studied in reflected and incident shock wave experiments as mentioned in this paper, where the source of NH was the thermal dissociation of isocyanic acid, HNCO.
Abstract: The reactions of NH(X3Σ−) with NO, O2, and O have been studied in reflected and incident shock wave experiments. The source of NH in all the experiments was the thermal dissociation of isocyanic acid, HNCO. Time-histories of the NH(X3Σ) and OH(X2Π) radicals were measured behind the shock waves using cw, narrow-linewidth laser absorption at 336 nm and 307 nm, respectively. The second-order rate coefficients of the reactions:
were determined to be:
and
cm3 mol−1 s−1, where ƒ and F define the lower and upper uncertainty limits, respectively.
The branching fraction of channel
defined as k3b/k3total, was determined to be 0.19 ± 0.10 over the temperature range of 2940 K to 3040 K.