Showing papers on "Atmospheric temperature range published in 1972"

Elastic Moduli of Diamond as a Function of Pressure and Temperature

Abstract: Values of wave velocities and elastic moduli at 25°C were measured for hydrostatic pressures to 20 000 psi (excess over 1 atm). Variations of velocities and moduli at 1 atm were obtained over a temperature range of +50°C to −195.8°C. Adiabatic stiffness moduli (units of 1012 dyn/cm2), their pressure derivatives, and their temperature coefficients (units of 10−5/C), are shown below for 1 atm and 25°C. ModulusValuePressure derivativesTemperature coefficientc1110.79±0.055.98±0.7−1.37±0.2c12 1.24±0.053.06±0.7−5.70±1.5c44 5.78±0.022.98±0.3−1.25±0.1

Thermal conductivity of Earth materials at high temperatures

Abstract: The total thermal conductivity (lattice plus radiative) of several important earth materials is measured in the temperature range from 500 to 1900 K. A new technique is used in which a CO2 laser generates a low-frequency temperature wave at one face of a small disk-shaped sample, and an infrared detector views the opposite face to detect the phase of the emerging radiation. Phase data at several frequencies yield the simultaneous determination of the thermal diffusivity and the mean extinction coefficient of the material. The lattice, radiative, and total thermal conductivities are then calculated. Results for single-crystal and polycrystalline forsterite-rich olivines and an enstatite indicate that, even in relatively pure large-grained material, the radiative conductivity does not increase rapidly with temperature. The predicted maximum total thermal conductivity at a depth of 400 km in an olivine mantle is 0.020 cal/cm/sec/deg C, which is less than twice the surface value.

Permittivity of Strontium Titanate

Abstract: The permittivity of single‐crystal single‐domain strontiumtitanate has been measured in detail in the [001], [011], and [111] directions, as a function of temperature (from 4.2 to 300 °K), electric field (from −23 000 to +23 000 V/cm, and frequency (from 1 kHz to 50 MHz). The free energy of the crystal is determined as a function of polarization with temperature as a parameter. The Curie‐Weiss law is satisfied in the temperature range 60–300 °K, giving a Curie temperature of 30 ± 2 °K for the three crystal orientations. The Lyddane‐Sachs‐Teller (LST) relation is satisfied for temperatures between 30 and 300 °K and for electric fields between 0 and 12 000 V/cm. A generalized LST relation is used to calculate the permittivity of strontiumtitanate from zero to optic frequencies. Two active optic modes are important. The lower‐frequency mode is attributed mainly to motion of the strontium ions with respect to the rest of the lattice, while the higher‐frequency active mode is attributed to motion of the titanium ions with respect to the oxygen lattice. The restoring forces that act on the Ti ions begin to "harden" when these ions are displaced approximately 0.002 A from their equilibrium positions.

Anomalous Viscoelastic Behavior of Metallic Glasses of Pd–Si‐Based Alloys

Abstract: The temperature and the stress dependence of viscoelastic properties of metallic glasses of three compositions: Pd0795Au004Si0165, Pd0795Ag004Si0165 and Pd0775Cu006Si0165 have been studied near the glass temperature The total retarded tensile compliance of these alloy glasses, Jd0 is small at low temperature (of the order of glass compliance Jg) but increases rapidly in a narrow temperature range when the temperature approaches Ta, at which the viscosity of the glass attains 1012 P, and attains a value as high as 200 times the glass compliance Jg for the Pd0775Cu006Si0165 glassy alloy, at T > Ta + 15°K Concurrent with an increase in Jd0 near Ta, the alloy liquids become non‐Newtonian in the stress range employed (σ varies from 6×106 to 3×108 dyn/cm2) The apparent shear activation volume for the viscous flow deduced from the non‐Newtonian behavior increases with temperature and attains a value as high as 100 times the atomic volume These results have been compared with viscoelastic beha

Electrical properties of nickel-low-doped n-type gallium arsenide Schottky-barrier diodes

Abstract: The forward current characteristics of nickel-low-doped n-type gallium arsenide Schottky-barrier diodes are measured over the temperature range 905-434 K The ideality factor and its temperature dependence is determined and found to decrease with increasing temperature according to the relationship n(T) = 114T^{-1/2} +0444 to within ±4 percent This is in agreement with the theoretical analysis of Strikha, who predicted a temperature dependence law between T-1and T^{-1/2} The barrier height is determined from both the saturation current and the capacitance methods A modification is made to the forward current expression, which results in good agreement between the values of the barrier height obtained from both methods over a wide temperature range The barrier height is found to decrease with increasing temperature at a rate of 58 × 10 -4 V/K Comparison with the dependence of the energy gap on temperature in GaAs suggests that the observed change in the barrier height is equal to that of E g

Carbon Monoxide Oxidation on a Pt(110) Single Crystal Surface

Abstract: The catalytic reaction between CO and O2 on a Pt (110) surface is investigated by residual gas analysis for different partial pressures of CO and O2 and various temperatures. The surface cleanliness of the Pt crystal is monitored by Auger electron spectroscopy. The results of the reaction study are generally in agreement with previous studies for polycrystalline Pt catalysts. The temperature dependence of the formation rate of CO2 exhibits a maximum whose position depends on the composition of the gas phase. At T=215°C two different rate laws are valid. For PO2>PCO the rate of CO2 formation is proportional to PO21.1PCO−0.6, while for PO2>PCO it is proportional to PO20.25 PCO0.75. These observations support the idea that the reaction obeys an Eley-Rideal mechanism in the pressure and temperature range investigated, and the results are evaluated accordingly. The influence of segregated Si on the CO oxidation reaction is investigated and found to be small.

The influence of oxygen concentration on the internal stress and dislocation arrangements in α titanium

Abstract: The temperature dependence of the long range (internal) and thermally activated components of the flow stress have been measured by a stress relaxation technique over the temperature range 200 to 550 K in α titanium containing five different levels of oxygen. In addition, the dislocation arrangements have been studied using thin foil electron microscopy techniques. In the higher oxygen materials it has been found that a transition from wavy to planar slip occurs towards lower temperatures. The internal stress varies more strongly with temperature than would be predicted by the temperature dependence of the elastic modulus; simultaneously, the thermally activated component of the flow stress (t*) obtained as the difference between the flow and internal stresses, goes through a maximum at the temperature where the internal stress (Tint) becomes strongly temperature dependent. An increase in t* and rise of Tint accompany the onset of planar slip.

Electrical conductivity of olivine

Abstract: The electrical conductivity σ of single crystals of olivine of 0, 7.7, 8.2, 9.4, and 26.4 mole % fayalite has been measured up to 1200°C and 7.5 kb. Samples from different localities with approximately the same fayalite content and impurity levels have electrical conductivities that differ by 2–3 orders of magnitude. It is proposed that the oxidation state of the iron in the natural olivines determines σ below 1100°C. No reversible change in activation energy was noted for any sample below 1100°C. In this temperature range activation energies for different samples vary from 0.7 to 2.0 ev. At 1150°C there is a reversible increase in σ, with a poorly determined activation energy of 7–8 ev. Mantle temperatures calculated from the present data on olivines with almost the same fayalite content differ by more than 700°C at any depth. The temperature difference becomes even larger with depth if the pressure effects noted in this study are used.

Magnetic susceptibility and expansion coefficient of the intermetallic compounds YbAl2 and YbAl3

Abstract: Magnetic susceptibilities and lattice constants of the intermetallic compounds YbAl2 and YbAl3 have been measured in the temperature range −180 °C to 550 °C. YbAl3 shows a behavior closely resembling that of an isomorphous trivalent REAl3 compound but YbAl2 appears to contain a percentage of YbIII which increases with temperature.

The crystal growth and thermoelectric properties of chromium disilicide

Abstract: Single crystals of chromium disilicide about 8 mm in diameter and 35 mm long were grown using the floating zone technique. Measurements of electrical resistivity ρ, Hall coefficient R and thermoelectric power α were carried out in the temperature range from 85 to 1100 K. The values of ρ and α showed the anisotropy over the temperature range studied. The ratios parallel and perpendicular to the c-axis were ρ ‖/ρ ⊥=1.9 and α ‖/α⊥=1.7 respectively, at room temperature. It was found to be a degenerate semiconductor having the hole concentration of 6.3×1020 cm−3 below 600 K. The effective masses of holes parallel and perpendicular to the c-axis determined from the thermoelectric power and the hole concentration near room temperature were estimated to be five and three times as large as a free electron mass, respectively. The calculation on the values of α ‖ and α ⊥ was made using those effective masses. These values showed good agreement with the observed values in the temperature range from 150 to 1100 K.

Semiconducting properties of nonstoichiometric manganese silicides

Abstract: Electrical resistivity, Hall coefficient and thermoelectric power were measured on manganese silicides of composition MnSi2−x withx ranging from 0.25 to 0.28 in the temperature range from 80 to 1100K. At higher temperatures a forbidden energy gap estimated from the resistivity data was about 0.40 eV. It was confirmed that MnSi2−x was a degenerated semiconductor and that the hole concentrations in the degenerated state varied from 1.8 to 2.3×1021 cm−3. The ratio of electron to hole mobility was less than unity. The intrinsic resistivity and the hole mobility varied with temperature as 3.6×10−4 exp(2320/T) and 1.2×104T−3/2 respectively. The value of Hall coefficient calculated by using a mobility ratio of 0.02 was in good agreement with that observed in the intrinsic region. From the relationship between hole concentration and thermoelectric power for MnSi1.73 near room temperature, the hole effective mass was estimated to be twelve times as large as the free electron mass. The calculation of the thermoelectric power was carried out based on the assumptions that the scattering of carriers is dominated by acoustic lattice scattering and that the carriers obey Fermi-Dirac statistics. The calculated results were in reasonable agreement with the observed thermoelectric powers in the temperature range from 150 to 1100K.

Electrical and Optical Properties of Ni S 2

Abstract: Optical absorption measurements on semiconducting Ni${\mathrm{S}}_{2}$ are analyzed to determine the energy gap and its temperature dependence. Electrical conductivity measurements made over a large temperature range exhibit three distinct regions of conduction, each with a different activation energy. The combination of electrical and optical measurements are interpreted in terms of a model in which partial carrier compensation pins the Fermi energy in the acceptor band.

The high-temperature creep behavior of nickel-rich Ni-W solid solutions

Abstract: The steady-state creep behavior of four nickel-rich Ni-W solid solutions (1, 2, 4, and 6 wt pct W) was investigated in the temperature range 850° to 1050°C. Constant stress tensile creep tests were performed in vacuum in the stress range 3000 to 7000 psi. Activation energies for creep were observed to be 71.4 ± 2.0, 74.4 ± 3.0, and 75.8 ±2.0 kcal per mole, after correcting temperature dependence of the elastic modulus, for alloys containing 2,4, and 6 pct W respectively. These values closely approximate the activation energies for the weighted diffusion coefficient, $$\bar D$$ =DNiDW/(XWDNi) whereX Ni andX w are the atom fractions of nickel and tungsten respectively, andD Ni andD w are the diffusion coefficients of nickel and tungsten in the alloy. The steady-state creep rates exhibit a power law stress dependence with an exponent,n, equal to 4.8 ±0.2 for all of the alloys studied. For tests conducted at temperatures and stresses such that both the diffusivity, $$\bar D$$ , and the ratio of the applied stress to the elastic modulus, σ/E, are. held constant, the steady-state creep rate, $$\dot \varepsilon _\mathcal{S} $$ , was found to vary with the stacking fault energy, γ, according to the empirical relation $$\dot \varepsilon _\mathcal{S} $$ ∼ γ4 2±4 over the range of creep rates studied.

Viscosity of the Binary Gaseous Mixtures He–Ne and Ne–N2 in the Temperature Range 25–700°C

Abstract: The paper presents new relative measurements of the viscosity of the binary mixtures He–Ne and Ne–N2, as well as repeated determinations of the viscosity of the pure gases. The experiments were performed using an oscillating‐disk viscometer; they were made at atmospheric pressure and in the nominal temperature range 25–700°C. The accuracy of the measurements is one of ± 0.1% at 25°C, deteriorating to ± 0.3% at 700°C. Tables of the thermal conductivity of the monatomic‐gas mixture are provided together with values for pure nitrogen. The binary diffusion coefficients for the mixtures have also been computed.

Absolute Rate Constants for the Reaction of Atomic Oxygen with Ethylene over the Temperature Range 232–500°K

Abstract: Rate constants for the reaction of atomic oxygen with ethylene were measured over a temperature range of 232–500°K using the flash photolysis‐resonance fluorescence technique. The rate constant at room temperature was also determined using a flash photolysis‐kinetic absorption spectroscopy system and a discharge‐flow system coupled to a mass spectrometer. Within the experimental errors of the three techniques, good agreement was found for the rate constant at 298°K. The bimolecular rate constant was also found invariant to changes in both total pressure and reactant concentration. Over the temperature range of the experiments, the rate data could be fitted by a simple Arrhenius expression of the form, k=5.42± 0.30× 10−12 exp[(−1130± 32 cal mole−1)/RT]cm3molecule−1· sec−1.

Thermal expansion of InxGa1−xP alloys

Abstract: The coefficient of thermal expansion has been determined for a series of InxGa1−xP alloys in the temperature range 15–650 °C. This parameter was found to increase linearly from (4.75±0.1)×10−6/°C for InP to (5.91±0.1)×10−6/°C for GaP.

Dielectric behaviour in a vanadium phosphate glass

Abstract: The dielectric constant and conductivity of 80% V 2 O 5 : 20% P 2 O 5 glass has been measured in the frequency range 10 2 to 10 9 Hz and in the temperature range 80 to 350°K. It is shown that the dielectric behaviour over these ranges is described by a Debye type relaxation process with distribution of relaxation times. A method is proposed to determine the width of distribution from the data at fixed frequencies and different temperatures. The width of distribution increases at frequencies ω > 10/ τ , which leads to an a.c. conductivity at these frequencies almost linearly proportional to frequency and independent of temperature. The estimated value of the static dielectric constant of about 30 was found to decrease with temperature while the infinite frequency dielectric constant of 10 was independent of temperature. The carrier concentration calculated from the dielectric relaxation time and the d.c. conductivity through a thermal diffusion model shows reasonable agreement with direct measurement using electron paramagnetic resonance.

The oxidation behavior of some Ni-Cr-Al alloys at high temperatures

Abstract: Oxidation of ternary Ni-Cr-Al alloys containing different Cr/Al ratios has been studied in the temperature range 800° to 1300°C. Most of the studies were performed in 1 atm oxygen or air, but the oxygen pressure dependence for one of the alloys was also investigated. The experimental methods included thermogravimetric measurements of oxidation rates and studies on reacted specimens by means of X-ray diffraction, metallographic techniques, electron microprobe analysis, and electron microscopy. In general, the oxidation rates decrease faster with time than that for an ideal parabolic behavior. The major reaction products were NiO, Cr2O3,α-Al2O3, and Ni(Cr,Al)2O4. The relative amounts of these were a function of composition, temperature, oxygen pressure, and reaction time. The Ni-9Cr-6Al alloy has the best oxidation resistance due to the formation ofα-Al2O3 at all temperatures investigated. The oxidation mechanism of the alloy is discussed.

Crystal Growth and Properties of Boron Monoarsenide

Abstract: Boron arsenide, a semiconductor with an energy gap of 1.46 eV, decomposes irreversibly at temperatures above 900 °C, thus limiting the temperature of the crystal growth process. In this work, single crystals of boron arsenide, identified by the x‐ray diffraction method, have been prepared by the chemical transport of polycrystalline boron arsenide in the presence of a temperature gradient. The transported crystals are p type and have a resistivity of approximately 0.01 Ω cm in the temperature range 77–500 °K. The hole concentration and Hall mobility, essentially independent of temperature in the range 77–300 °K, have been estimated to be in the ranges of 1018–1019 cm−3 and 100–400 cm2V−1sec−1, respectively. In spite of the high carrier concentrations, the transported crystals are suitable as substrates for the epitaxial growth of boron arsenide with controlled dopant distribution.

Mass diffusion in polycrystalline copper/electroplated gold planar couples

Abstract: The Au/Cu system is common to electrical connectors and recent trends toward higher ambient temperatures and thinner gold electroplates focuses attention on a new failure mode. This mode is degradation of thin gold electroplates by mass diffusion of the base metal (copper) to the surface of the electroplate at low temperatures (less than 250°C). Therefore, diffusion experiments were conducted for polycrystalline copper/electroplated gold planar couples over the temperature range of 50° to 750°C. The chemical interdiffusion coefficients, ~D, were calculated using the Boltzmann-Matano solution on the concentration-distance profiles which were determined using an electron microprobe. Results of this study show that ~D is a small function of concentration, generally with a variation of less than a factor of 3 to 5. The correlation of the temperature dependence of ~D between 250° and 750°C with existing data is excellent. The data conform to an Arrhenius equation: ~D= 1.5×10−5 e−23,600/RT At temperatures below 250°C the values of ~D deviate from this equation and below 150°C are significantly greater than would be predicted by extrapolating the high temperature Arrhenius equation. No correlation was found between electroplate thickness and diffusion rate.

The Influence of Quantum Effects on the Low-Temperature Creep of Zinc Crystals

Abstract: The creep of single crystals of Zn deformed by simple shear along the basis plane (0001) has been investigated in the temperature range 1.5 to 80 °K. It is shown that the influence of temperature on the creep in the investigated temperature range is weaker than that predicted by the classical theory of thermally activated creep. A peculiar temperature run of parameters describing the creep process has been discovered and proved anomalous as compared with the classical run. A mechanism for the influence of zero-point vibrations of the dislocation line on its motion through an aggregate of local obstacles is suggested and analyzed. The results obtained in this way show a satisfactory agreement with the experimental data. [Russian Text Ignored.]