Showing papers on "Atmospheric temperature range published in 1985"

Experimental determination of the nature of diffusive motions of water molecules at low temperatures.

Abstract: Extensive and high-quality quasi-elastic incoherent neutron scattering data were obtained for water in the temperature range extending from room temperature down to -20 \ifmmode^\circ\else\textdegree\fi{}C in the supercooled state. The analysis generally confirms findings of our previous experiment [S. H. Chen, J. Teixeira, and R. Nicklow, Phys. Rev. A 26, 3477 (1982)], but in particular three new results have been obtained: (a) two relaxation times are clearly identified, which are related to the short-time and intermediate-time diffusion of water molecules, respectively, and their temperature dependence has been determined; (b) one of these relaxation times is associated with jump diffusion of the protons, and the temperature dependence of the jump length has been qualitatively determined; (c) the Q dependence of the scattering intensity integrated over the quasi-elastic region gives a Debye-Waller factor which is temperature independent.

Ionic conductivity and mobility in network polymers from poly(propylene oxide) containing lithium perchlorate.

Abstract: Ionic conductivity σ and mobility μ in the amorphous network polymers from poly(propylene oxide) (PPO) containing lithium perchlorate (LiClO4) at the concentration of [LiClO4]/[PO unit]=0.042 and 0.076 were investigated by means of complex impedance and time‐of‐flight methods. The σ values of the PPO–LiClO4 complexes reached 10−5 S cm−1 at 70 °C. The temperature dependence of σ deviated from a single Arrhenius behavior above a critical temperature (−1 °C and 11 °C) which approximately corresponded to the glass transition temperature Tg. The μ values were relatively high and changed from 10−6 to 10−5 cm2 V−1 s−1 in the temperature range of 40–100 °C. The Nernst–Einstein equation correlated μ with the ionic diffusion coefficient D. The Williams–Landel–Ferry equation with C1≂5 and C2≂30–50 held with a temperature dependence of D in the order of 10−8–10−7 cm2 s−1. The change in the number of ionic carriers n with temperature obeyed the Arrhenius equation with the activation energy of 0.26 and 0.34 eV. The deg...

Transformation of yttria partially stabilized zirconia by low temperature annealing in air

Abstract: The tetragonal-to-monoclinic phase transformation of yttria partially stabilized zirconia by low temperature annealing in air was investigated in the temperature range 100 to 650° C using a sintered body of zirconia containing 2 to 4 mol% Y2O3. The amount of monoclinic phase formed was maximum at about 200° C. Both the decrease in grain size and increase in the yttria concentration were effective in decreasing the critical temperature below which the monoclinic phase was formed. The relationship between the critical temperature (T c) and the grain size was experimentally determined.

Solution crystallization of polyethylene at high temperatures

Abstract: Single crystals of polyethylene have been grown from solution in various solvents at temperatures between 70 and 120° C. This represents an overlap in crystallization conditions with those used for melt growth, where substantial isothermal thickening is known to occur during growth. The crystal thicknesses have been measured by Raman spectroscopy. Values of the equilibrium dissolution temperature and fold surface free energy are calculated for each solvent and the results analysed using the kinetic theory. Variations in crystal properties with time of crystallization are also investigated. A specific dependence of fold length on supercooling has been found to apply over the whole temperature range, consistent with predictions by the kinetic theories of crystallization in spite of changes in morphology which are incompatible with assumptions underlying the theoretical model. No evidence for isothermal thickening has been observed, except possibly for a small marginal effect at the highest temperature of 120° C investigated, over the same temperature range where melt crystallized material shows the effect prominently. Crystals grown at all temperatures displayed a rise in dissolution temperature with time which could be associated with an increase in surface perfection. All these findings have wider implications for our picture of polymer crystallization and crystal structure which are discussed here. A further, explicit, correlation with melt crystallization is deferred to a subsequent publication.

High-temperature structure refinements of calcite and magnesite

Abstract: Crystal structure parameters have been determined from X-ray intensity data collected for single crystals of calcite at24,200,400,600,750, and 800'c, and magnesite at24,2N,3(f|., 400, and 500"C. Refinements utilizing a rigid-body model and an anisotropic thermal model show good agreement in thermal parameters and R values, suggesting that the rigid-body model is valid over the temperature range studied. Comparison between the two minerals' response to temperature shows markedly different behaviors of the CO3 group. The negative thermal expansion along a for calcite is explained in terms of the large libration parameters and thermal expansion coeffrcients. Mean thermal expansion coeflicients are calculated for selected interatomic distances. A libration correction was applied to bonds within the carbonate group, and the corrected C-O interatomic distance increased more rapidly in calcite than in magnesite. Mean thermal expansion coeflicients for the Ca-O interatomic distance fc""_o : 15.9 x 10-6.C-1) in calcite and the Mg-O distance in magnesite fa"r_o:15.g x 10-6"C-l) are comparable to those found in other CaOu and MgOu octahedra. At 800"C the I : odd reflections of calcite are unobserved preferentially (I < 2o), possibly indicating the onset of orientational disorder. However, no phase transitions were found, and the decrease in intensity may be a result of increased thermal motion of the oxygen atoms.

Moisture diffusion in poltimide films in integrated circuits

Abstract: This paper reports the use of planar aluminum-PI-aluminum capacitors, in which the variation of low frequency dielectric permittivity is shown to be proportional to absorbed moisture, to carry out in-situ studies of moisture uptake and diffusion in PMDA-ODA device-grade polyimide films. It is found that the equilibrium amount of moisture uptake depends on ambient relative humidity in the temperature range 20-80‡C, and that the diffusion kinetics obey a Fickian model with a diffusion coefficient in the range 3-5 x 10-9 cm2 /sec at room temperature. The diffusion coefficient is temperature dependent, with an activation energy of 0.32-0.34 eV, and is weakly dependent on absorbed moisture at fixed temperature. An asymmetry is observed between absorption and desorption kinetics which correlates with the moisture-dependent diffusion coefficient.

1/f noise and grain-boundary diffusion in aluminum and aluminum alloys.

Abstract: We have measured the $\frac{1}{f}$ noise in polycrystalline films of Al, Al-Si(1%), and Al-Cu(4%) in the temperature range of 300 to 600 K. The temperature dependence indicated activation energies of 0.69, 0.80, and 0.89 eV, respectively. These energies are similar to the activation energies found for Al diffusion along grain boundaries for films of the same size and composition measured in the same temperature range. Measurements of samples with identical compositions but differing widths and thicknesses revealed significant departures from the usual inverse volume dependence of the $\frac{1}{f}$ noise.

Interdiffusion at the polyimide-Cu interface

Abstract: Interdiffusion at the polymide‐Cu interface has been studied with high resolution medium energy ion scattering (MEIS) and cross section transmission electron microscopy (TEM). Cu was evaported on polyimide in UHV and studied in situ with ion scattering. In the temperature range from 293 to 593 K Cu is found to diffuse into polyimide and form small spherical particles. The size of these spheres and the depth at which they occur increase with increasing temperature. Once the Cu spheres have been formed they become relatively immobile. It is argued that the kinetics of Cu‐polyimide interdiffusion is determined by atomic diffusion of Cu. Chemical effects do not appear to play an important role.

Thermal expansion and length stability of Zerodur in dependence on temperature and time

Abstract: The lengths and the thermal expansion values of the glass ceramic Zerodur show a reversible dependence on the thermal history within two temperature intervals. Typical effects associated with this dependence are, for example, isothermal length changes within and permanent length changes below the temperature intervals. It is assumed that relaxation causes the observed effects. The phenomena in the upper temperature range from 130°C to 300°C are related to the MgO content. The reversibility of the relaxation effects allows adjustment for lengths and thermal expansion values by appropriate cooling processes.

Low-temperature glass transition in proteins

Abstract: The viscoelastic properties of solid samples (crystals, amorphous films) of hen egg white lysozyme, bovine serum albumin, and sperm whale myoglobin were studied in the temperature range of 100–300 K at different hydration levels. Decreasing the temperature was shown to cause a steplike increase in the Young's modulus of highly hydrated protein samples (with water content exceeding 0.3 g/g dry weight of protein) in the temperature range of 237–251 K, followed by a large increase in the modulus in the broad temperature interval of 240–130 K, which we refer to as a mechanical glass transition. Soaking the samples in 50% glycerol solution completely removed the steplike transition without significantly affecting the glass transition. The apparent activation energy determined from the frequency dependence of the glass-transition temperature was found to be 18 kcal/mol for wet lysozyme crystals. Lowering the humidity causes both the change of the Young's modulus in response to the transition and the activation energy to decrease. The thermal expansion coefficient of amorphous protein films also indicates the glass transition at 150–170 K. The data presented suggest that the glass transition in hydrated samples is located in the surface layer of proteins and related to the immobilization of the protein groups and strongly bound water.

The AC conductivity and dielectric constant of lithium niobate single crystals

Abstract: The AC conductivity sigma ( omega ) and dielectric constant epsilon ' of lithium niobate single crystals have been measured along the ferroelectric c-axis in the temperature range 77-700K and in the frequency region 0.1-100 kHz. At low temperatures, below 400K, the AC conductivity can be expressed as sigma ( omega )=A omega s, where the slope s is close to unity and decreases with increasing temperature. The dielectric constant in this temperature region shows a weak frequency and temperature dependence. At higher temperatures, above 400K, the AC conductivity shows a strong temperature dependence and weak frequency dependence. The dielectric constant in this region also shows a strong frequency dispersion. The mechanism of conduction in low and high temperature regions is discussed in the light of existing theoretical models.

Temperature dependence of the energy gap of InSb using nonlinear optical techniques

Abstract: We report the first use of the resonant two‐photon photo‐Hall effect as a nonlinear optical technique to measure the temperature dependence of the energy gap of InSb. Values of Eg for the temperature range 2–210 K are determined and compared with theoretical predictions and past experimental work. The technique is shown to provide an accurate, straightforward means of measuring Eg as a function of temperature in semiconductor materials.

The viscosity of nitrogen, oxygen, and their binary mixtures in the limit of zero density

Abstract: The paper presents a concise and accurate representation of the viscosity of nitrogen, oxygen, and their binary mixtures at the limit of zero density and in the temperature range 110–2100 K, which can be programed easily on a computer. The correlation is founded upon the semiclassical kinetic theory of polyatomic gases and a body of critically evaluated experimental data. Use is also made of the principle of corresponding states to extend the correlation outside of the temperature range for which direct experimental results exist. The optimum correlation has an associated uncertainty of ±0.3% around room temperature, but it rises to a maximum of ±2% at either extreme of the temperature range. A secondary representation of the viscosity of the same gases, providing some saving in computational effort and a further extension of the temperature range at the expense of a small loss of accuracy, is also presented. The relationship of this second representation to similar correlations for other gases makes it attractive for some purposes.

Molecular relaxations in a rigid molecular glassy crystal

Abstract: The dielectric permittivity and loss of 1-cyanoadamantane have been measured under isothermal conditions in the frequency range, 100-2*105 Hz and the temperature range, 80-350K in the glassy crystal, supercooled (metastable) and stable (disordered) crystals and partially ordered crystalline states. Two relaxation regions were observed, one above the glass-like transition temperature (170K) and the other below it. (The latter finding is contrary to the observations of Amoureux et al., for which reasons are given.) The characteristics of the two relaxations are remarkably similar to those found in other isotropic and anisotropic glasses and glassy crystals. The implications of this similarity for concepts of the glass transition and configurational states are pointed out. The static permittivity of 1-cyanoadamantane shows that it is only partially disordered even at high temperatures and that its disorder-order transformation occurs over a wide temperature range. Isothermal measurements in this range show no time dependence of the ordering process.

STS-8 atomic oxygen effects experiment

Abstract: A flight experiment was performed on the eighth Space Shuttle mission to measure reaction of surfaces with atomic oxygen in the low earth orbital environment. More than 300 individual samples were exposed to ram (normal to surface) conditions for 41.75 hr leading to a total atomic oxygen fluence of 3.5 x 10 to the 20th atoms/sq cm. Reaction rates for surface recession measured primarily by mass change of several organic films were in the range of 3.0 x 10 to the -24th cu cm/atom, and less than 5 x 10 to the -26th cu cm/atom for Teflon. Effects of parameters such as temperature and solar radiation were assessed, as was the importance of atmospheric ionic species on surface recession. In an experiment performed on the fifth Space Shuttle flight, no temperature dependence of reaction rate for the organic films studied was found in the temperature range of 25 to 125 C. Preliminary findings indicate that the reactivity of organic films is not affected by temperature (in the range of 65 to 125 C), solar radiation, or ionic species. Significant surface morphology changes led to a carpet-like appearance also consistent with previous findings.