Showing papers on "Atmospheric temperature range published in 1982"

Electron and hole mobilities in silicon as a function of concentration and temperature

Abstract: An analytical expression has been derived for the electron and hole mobility in silicon based on both experimental data and modified Brooks-Herring theory of mobility. The resulting expression allows one to obtain electron and hole mobility as a function of concentration up to \sim 10^{20} cm-3in an extended and continuous temperature range (250-500 K) within ± 13 percent of the reported experimental values.

Revised TIPS for simulations of liquid water and aqueous solutions

Abstract: An intermolecular potential function for the water dimer (TIPS2) has been developed and used in Monte Carlo simulations of liquid water in the NPT ensemble at 1 atm and −30, 25, and 75 °C. A simple four‐site model is employed for the monomers with one Lennard‐Jones term acting between oxygens and Coulomb terms for the intermolecular interactions between the charged sites. The function yields excellent thermodynamic results for the liquid across the temperature range; the average error in the computed densities and energies is 1.2% and a temperature of maximum density is indicated in the vicinity of 25 °C. Futhermore, the structural results are in reasonable agreement with Narten’s x‐ray data. Specifically, the oxygen–oxygen radial distribution function shows three well‐resolved peaks at 25 °C and a reduction in structure with increasing temperature. The simplicity of the TIPS2 potential,its success in describing liquid water, and the availability of TIPS parameters for hydrocarbons and for various organic functional groups provide a framework for computer simulations of aqueous solutions.

The Effect of Solutes on the Gelatinization Temperature Range of Potato Starch

Abstract: The gelatinization behaviour of potato starch in an excess of water or solutions of sugars, other organic hydroxy compounds, or various inorganic salts was studied The distribution of water and solutes between the external phase and the starch granules was measured by refractometry and a dye exclusion technique When the limited water uptake of native starch granules is taken into account, the cooperative nature of gelatinization and the effect of water content on gelatinization behaviour can be explained solely on the basis of the Flory theory of polymer melting Following the same argument, the effect of many solutes can be approximately described by the derived relationship between initial gelatinization temperature, water activity of the system and volume fraction of water in the granules Die Wirkung geloster Stoffe auf den Verkleisterungstemperatur-Bereich von Kartoffelstarke Das Verkleisterungsverhalten von Kartoffelstarke in einem Uberschus von Wasser oder Losungen von Zuckern, anderen organischen Hydroxyverbindungen oder verschiedenen anorganischen Salzen wurde untersucht Die Verteilung von Wasser und gelostem Stoff zwischen der externen Phase und den Starkekornern wurde durch Refraktometrie und ein Farbausschlusverfahren gemessen Wenn die begrenzte Wasseraufnahme der nativen Starkekorner mit in Betracht gezogen wird, kann die mitwirkende Natur der Verkleisterung und die Wirkung des Wassergehalts auf das Verkleisterungsverhalten ausschlieslich auf der Basis der Flory-Theorie des Polymerschmelzens erklart werden Den gleichen Argumenten folgend, kann die Wirkung vieler geloster Stoffe annahernd durch die Beziehung zwischen Anfangs-Verkleisterungstemperatur, Wasseraktivitat des Systems und Volumenanteil des Wassers in den Kornern beschrieben werden

Optical absorption of silicon between 1.6 and 4.7 eV at elevated temperatures

Abstract: The optical absorption coefficient of silicon for photon energies between 1.65 and 4.77 eV (750– 260 nm) has been determined at elevated temperatures (up to 700 °C) using polarization modulation ellipsometry. For photon energies below ∼3 eV (∼410 nm), the absorption coefficient increases exponentially with temperature from room 24° C to 700 °C, increasing by a factor of approximately 5 over that temperature range. The threshold for direct band‐gap absorption moves to lower energies with increasing temperature.

Solubilities of inert gases and methane in H2O and in D2O in the temperature range of 300 to 600 K

Abstract: The solubility of inert gases and methane in H2O and D2O has been measured between room temperature and 600 K. The calculation of Henry’s constants kH, from the solubility data is analyzed in detail; if due account is taken of the nonideality in the gas phase, they can be determined unambiguously up to 520 K. Above this temperature, the ambiguity in kH increases sharply as contributions of third and higher order virial coefficients to the equation of state of the gaseous mixture become more important. The differences of gas solubilities in light and heavy water essentially disappear above the temperature of minimum solubility of the gases. The characteristic thermodynamic features of the aqueous solutions of gases (i.e., large values of −ΔS02 and of ΔC0p2) are still present at 520 K. It is shown that mean‐field theories can account for the

X-ray study of phase transitions in efrroelectric Na0.5Bi0.5TiO3

Abstract: The temperature dependence of the lattice constant in Na0.5Bi0.5TiO3 single crystal was studied by means of X-ray diffraction. Two structural phase transitions were found in the temperature range 293-920 K: the cubic-to-tetragonal at 793 ± 5 K and the tetragonal-to-rhombohedral at 533 ± 5 K. The dielectric permittivity was measured and a considerable dispersion was observed. The shift of the dielectric permittivity maximums are linear in coordinates 1/T = F(In f).

Temperature dependence of the enthalpy and the heat capacity of the liquid-crystal octylcyanobiphenyl (8CB)

Abstract: An adiabatic scanning calorimeter has been used to study the thermal behavior of the liquid-crystal octylcyanobiphenyl (8CB) in the temperature range between 10 and 50\ifmmode^\circ\else\textdegree\fi{}C. The solid---to---smectic-$A$ ($\mathrm{KA}$), the smectic-$A$---to---nematic ($\mathrm{AN}$), as well as the nematic-to-isotropic (NI) phase transitions, which fall in this temperature range, have been investigated in great detail. From our measuring procedure the enthalpy behavior (including latent heats) as well as the heat capacity have been obtained. For the KA transition the latent heat was 25.7\ifmmode\pm\else\textpm\fi{}1.0 kJ/mol and for the NI transition it was 612\ifmmode\pm\else\textpm\fi{}5 J/mol. Within the resolution of our experiment we find that the $\mathrm{AN}$ transition is a continuous one. For the latent heat, if any, we arrive at an upper limit of 0.4 J/mol (or 1.4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ J/g). The observed anomaly in the heat capacity for the $\mathrm{AN}$ transition is not consistent with a nearly logarithmic singularity as predicted by the $\mathrm{XY}$ model, instead we obtain a critical exponent $\ensuremath{\alpha}={\ensuremath{\alpha}}^{\ensuremath{'}}=0.31\ifmmode\pm\else\textpm\fi{}0.03$. This result is consistent with the anisotropic scaling relation ${\ensuremath{ u}}_{\ensuremath{\parallel}}+2{\ensuremath{ u}}_{\ensuremath{\perp}}=2\ensuremath{-}\ensuremath{\alpha}$. The pretransitional effects near the NI transition are in qualitative agreement with the hypothesis of quasitricritical behavior.

Temperature dependence of silicon Raman lines

Abstract: The one‐phonon and two‐phonon Raman spectra have been measured in the temperature range 20–900 °C. The rate of decrease of the normalized frequencies with increase of temperature for the zone center, TO at L and TA at X, is 5.4×10−5/°C, while for TO at X and TA at L is lower, being 3.6×10−5/°C. We have also found that the relative intensity of Stokes and anti‐Stokes components of the Γ‐point optical phonon deviates significantly from the value involving only the phonon occupation number, particularly at high temperatures. The decrease of the Γ25′ phonon from 521 cm−1 at 20 °C to 493 cm−1 at 900 °C should provide an unambiguous determination of the surface temperature due to laser heating.

Controlled wettability of quartz surfaces

Abstract: The wettability of flat quartz-crystal surfaces has been assessed by measurement at 25 °C of contact angle at the water-vapour/water-drop/quartz-plate three-phase line. Plates pretreated by heating in vacuum gave angles, measured through the drop 1 min after removal from vacuum, of 0–44 ° as pretreatment temperature was increased from 200 to 1000 °C. Fully hydroxylated, therefore hydrophilic, quartz surfaces are progressively rendered hydrophobic by mutual condensation of surface hydroxyls to form siloxane bridges. Hysteresis was at a maximum after heating at 700–800 °C, indicating that maximum surface chemical heterogeneity was produced by heating in this temperature range. Plates methylated subsequent to heat treatment gave angles that were constant at ca. 80° up to treatment at 600 °C and that decreased from 80 to ca. 47 ° as the pretreatment temperature was further increased to 1000 °C. This variation with temperature is consistent with a mechanism for methylation in which only non-hydrogen-bonded surface hydroxyl groups on quartz are reactive towards the methylating reagent. Contact angles on both heat-treated and methylated plates were observed to decrease following extended exposure to water vapour.

Diffusivity of oxygen in silicon during steam oxidation

Abstract: The diffusivity of oxygen in silicon during steam oxidation at 700–1240 °C was measured on as‐oxidized Si wafers. To provide greater analytical sensitivity 18O was introduced into the float‐zone Si wafers from 1‐atm H2 18O steam, and the 18O depth profiles were measured by Cs+ secondary ion mass spectrometry. Over the entire temperature range studied, the diffusivity is governed by a single activation energy, 2.44 eV, and the prefactor is 7×10−2 cm2 s−1. Our results are compared with previous literature values measured only at high temperature.

Ion beam mixing at nickel‐silicon interfaces

Abstract: Ion‐beam mixing at Ni‐Si interfaces was studied as a function of dose, temperature, and dose rate. In the temperature range 10–443 K, the thickness of the mixed Ni‐Si layer grew proportionally to the square root of dose for 250‐keV Ar+ and 280‐keV Kr+ irradiations. The apparent diffusion coefficient for mixing during irradiation comprises temperature‐dependent and independent contributions. The activation enthalpy for the temperature‐dependent part is ∼0.09 eV. Varying the dose rate by a factor of ∼20 had little effect upon mixing at either 80 or 368 K. Analysis of these results using chemical rate theory showed that the low activation enthalpy for diffusion was not associated with point‐defect motion. More likely the temperature dependence of mixing in Ni‐Si is associated with the effect of temperature on compound formation. The results for mixing at 10 K in Ni‐Si were compared with those in Ni‐Al, at 10 K, to study the effect of crystal structure on displacement mixing.

Temperature Dependence of Electron-Irradiation Induced Amorphization of NiTi Alloys

Abstract: Electron-irradiation induced amorphization of NiTi alloys has been investigated in a temperature range from 50 to 393 K by high voltage electron microscopy with the following results: A crystalline-amorphous transition occurs when the total dose of electrons reaches a certain value. The critical value decreases with decreasing irradiation temperature and becomes almost constant with about 2×1025 e/m2 below 100 K. Process of the transition is also revealed.

Temperature dependence of three‐body association reactions from 45 to 400 K. The reactions N+2+2N2→N+4+N2 and O+2+2O2→O+4 +O2

Abstract: The temperature dependences of the three‐body ion–molecule association reactions N+2+2N2→N+4+N2 (1) and O+2+2O2→O+4+O2 (2) have been studied in a recently constructed liquid‐helium cooled ion drift tube in the temperature range 45–400 and 51–340 K, respectively. The results can be approximated over a wide temperature range by the expressions k1=6.8 × 10−29 (300/T)1.64 and k2=4 × 10−30 (300/T)2.93 although deviations at low temperatures are apparent. The influence of the electric drift field on the measured rate coefficients has been investigated in detail. Experimental effects which might be of importance in the low temperature measurements are discussed.

Effects of humidity on stress in thin silicon dioxide films

Abstract: The stresses of thermally grown as well as chemically vapor deposited (CVD) silicon dioxide were measured by the cantilever beam technique using x‐ray diffraction. Thermally grown oxide shows reversible stress changes upon heating or cooling of the films. The linear thermal expansion of such films is similar to that of bulk vitreous silica, 5×10−7 °C−1, the biaxial elastic modulus was found to be 6.3×1011 dyn/cm2. CVD oxides show extensive hysteresis in the stress‐temperature curves when tested in ambient air. From stress measurements of such films, deposited on Si and GaAs, it was concluded that their average linear thermal expansion coefficient in the temperature range of −170–115 °C is 4×10−6 °C−1, much higher than that of thermally grown oxide, while their biaxial elastic modulus is only 4.6–5.1×1011 dyn/cm2. The stress in such films was found to increase when the films were exposed to a dry ambient or vacuum. The time constant for this change was found to be several minutes at room temperature.

Thermal conductivity and density of toluene in the temperature range 273–373 K at pressures up to 250 MPa

Abstract: New experimental data on the thermal conductivity and the density of liquid toluene are presented in the temperature range 0–100°C at pressures up to 250 MPa. The measurements of thermal conductivity were performed with a transient hot-wire apparatus on an absolute basis with an inaccuracy less than 1.0%. The density was measured with a high-pressure burette method with an uncertainty within 0.1%. The experimental results for both properties are represented satisfactorily by the Tait-type equations, as well as empirical polynomials, covering the entire ranges of temperature and pressure. Furthermore, it is found that simple relations exist between the temperature dependence of thermal conductivity and the thermal expansion coefficient, and also between the pressure dependence of thermal conductivity and the isothermal compressibility, as are suggested theoretically.

High Pressure Oxidation of Silicon in Dry Oxygen

Abstract: The effects of oxidant pressure on the kinetics of thermal oxidation of (100) and (111) oriented silicon wafers in dry ambients were investigated over the temperature range of 800°–1000°C and the pressure range of 1–20 atm. The parabolic and linear rate constants were found to be proportional to oxygen pressure to the power of 1 and 0.7, respectively. A change in activation energy similar to that observed for pyrogenic steam oxidation occurs around 900°C. Oxide charges in oxides prepared in high pressure dry ambients were characterized and found to be compatible with present technological requirements for VLSI device fabrication, although increases in electron trapping due to neutral traps have been observed.

Enhanced diffusion of oxygen during internal oxidation of nickel-base alloys

Abstract: The depths of internal oxidation of Ni-Al (0.5–4 wt.%) alloys oxidized in the temperature range 800–1100°C in either Ni/NiO packs or in 1 atm oxygen are virtually independent of the alloy compositi...

Clathrate and other solid phases in the tetrahydrofuran–water system: thermal conductivity and heat capacity under pressure

Abstract: Solid phases in the tetrahydrofuran–water (THF–H2O) system were investigated in the temperature range 100–260 K and at pressures up to 1.5 GPa. Thermal conductivity, λ, and heat capacity per unit v...

Static fatigue of granite at 200°C

Abstract: Cylinders of Barre and Westerly granites have been compressed to failure in static fatigue tests under dry and wet conditions at 1 Kb confining pressure and temperatures of 24/sup 0/ and 200 /sup 0/C. The effect of increasing temperature and water content is, as expected, to weaken the rocks appreciably and to reduce the time to failure, at constant stress, by about two orders of magnitude. The activation energy estimated for dry Barre granite deformed in temperature range 24/sup 0/ to 200 /sup 0/C is 10.2 Kcal/mol which seems reasonable and is consistent with other work at higher temperatures. Extrapolation of the static fatique equations obtained for specimens deformed at 200 /sup 0/C, both wet and dry, to 10/sup 8/ years yields maximum stress differences near 3 Kb. While such extrapolations may be reasonable for intact material over time-spans of interest to national concerns, the stresses obtained seem unreasonably high for tectonic deformations. The discrepancy probably results from the very short durations of the tests which do not permit effective operation, at these low temperatures, of the several thermally-activated weakening effects of H/sub 2/O on silicates.

Kinetics of the reaction of hydroxyl radical with methane and with nine chlorine- and fluorine-substituted methanes. 1. Experimental results, comparisons, and applications

Abstract: The rates of reaction of OH with CH/sub 4/ and with all nine Cl- and F-substituted methanes that contain at least one abstractable H atom are measured over wide temperature ranges (mainly 250-480 K) by the discharge-flow method under strictly comparable experimental conditions. Curvature is found in all but one Arrhenius plot, that of CHF/sub 3/, which is slower reacting and was studied over a smaller temperature range. Optimized three-parameter expressions require a temperature exponent, n, of 2.0-2.2. They are reduced to Arrhenius A's and E's centered at 300 K. Substantial variation is found in the A's for related compounds, less so in the E's which correlate roughly with the bond energy of the abstracted C-H. The results are compared with all published data, and their use in atmospheric science and combustion is briefly discussed.

The influence of superficially applied oxide powders on the high-temperature oxidation behavior of Cr2O3-forming alloys

Abstract: The effects of superficially applied CeO2, mixed rare earth oxides, Co3O4, and Cr2O3 powders on the isothermal and cyclic oxidation of Ni-Cr alloys and the effects of CeO2 and MgO powders on the isothermal oxidation of Fe-25 wt.% Cr have been studied over the temperature range 940–1150°C in pure oxygen and dry air. The rates of oxidation of both the Ni- and Fe-base alloys were markedly reduced by the application of CeO2 powder. The presence of CeO2 also improved the scale adherence and resulted in marked changes in the oxidation morphology. The presence of Co3O4 or Cr2O3 powders on Ni-Cr alloys or MgO on Fe-Cr also produced changes in the oxidation morphology but did not decrease the rate of oxidation. These results are interpreted in terms of the influence of the oxide powders on the development of scale microstructure and their effectiveness in decreasing grain boundary transport in Cr2O3.

Ferroelectric Conversion of Heat to Electrical EnergyA Demonstration

Abstract: The conversion of heat to electricity by means of the pyroelectric effect is demonstrated here. The basic thermal-electrical cycle is described. The production of 100 mj of electrical energy per cubic centimeter of ferroelectric material (PZST) per thermal cycle (with a temperature span of 20°C) has been observed. This observation is discussed in terms of using regeneration to approach Carnot efficiency. The staging of ferroelectrics to increase the temperature range (and hence efficiency) is also explained.