Showing papers on "Atmospheric temperature range published in 1989"

Shape-memory alloy micro-actuator

Abstract: A method of producing an integral piece of thermo-sensitive material, which is responsive to a shift in temperature from below to above a phase transformation temperature range to alter the material's condition to a shape-memory condition and move from one position to another. The method is characterized by depositing a thin film of shape-memory material (11 and 12), such as nickel titanium (Ni-Ti) onto a substrate (10) by vacuum deposition process such that the alloy exhibits an amorphous non-crystalline structure. The coated substrate is then annealed in a vacuum or in the presence of an inert atmosphere at a selected temperature, time and cool down rate to produce on ordered, partially disordered or fully disordered BCC structure. Also disclosed are actuator devices employing 'shape-memory material' (1) actuators.

Effects of Deformation Induced Phase Transformation and Twinning on the Mechanical Properties of Austenitic Fe–Mn–Al Alloys

Abstract: Structure and mechanical properties of austenitic Fe–(20 and 30)Mn–(0 to 7) Al alloys in the temperature range between 77 and 295 K have been investigated in relation to the occurrences of phase transformation and deformation twinning. Additions of aluminum to the 20 wt% Mn alloys significantly decreased the γ→e transformation temperature. The yield stress of these alloys increased with increasing aluminum content, whereas the strain hardening of them decreased. This tendency is prominent at low temperatures. In the 30 wt% Mn alloys the yield stress and strain hardening were almost identical regardless of aluminum contents. Additions of aluminum strongly suppress the γ→e transformation and give birth to the occurrence of deformation twinning. Calculated stacking fault energy based on a regular solution approach shows that the austenitic Fe–Mn–Al alloys which have the stacking fault energy approximately larger than 20 erg/cm2 favor the deformation twinning leading to the increase in low temperature ductility.

Measured elastic moduli of single-crystal MgO up to 1800 K

Abstract: Using the rectangular parallelepiped resonance method we measured the temperature dependence of the adiabatic elastic moduli of single-crystal MgO over the temperature range 300–1800 K. The high temperature limit of our measurements extends by 500 K the upper limit over which elasticity data on MgO are now available. Although our measured temperature dependence of C ij s are generally in good agreement with previous measurements over a more narrow range in temperature, we found that C 44 s decreases more rapidly with temperature, for T > 1000 K, than previous studies suggest. We also found that each of the slopes (ϱC 11 s /ϱT)p, (ϱKs/ϱT)p, and (C 44 s /ϱT)p become less negative with increasing temperature for T > 1400 K. From our measurements on elasticity we are able to confirm that the Gruneisen parameter at zero pressure is nearly constant with temperature up to 1800 K, with only a slight decrease above 1000 K. Utilizing our new data we present calculations showing the temperature dependence of thermodynamic parameters important in studies of earth's interior.

Elasticity of single‐crystal forsterite measured to 1700 K

Abstract: Measurements of the nine adiabatic elastic constants of single-crystal forsterite are reported for the temperature range 300–1700 K at ambient pressure. The measured room temperature Cijs and their first temperature derivatives at ambient conditions are generally consistent with previous measurements, which were taken over a narrower temperature range. Slight nonlinear behavior is observed in the temperature dependence of the C11s, C22s, and C33s moduli. The resulting Hill-averaged bulk and rigidity moduli Ks and G are lower at 1700 K than predicted by linear extrapolation of low-temperature data. At 1700 K the new data give Ks = 103.8 ± 1.1 GPa and G = 61.3 ± 0.5 GPa. Isotropic elastic wave velocities have been calculated using the Hill averaging scheme over the range of temperatures measured. At T = 1700 K and ambient pressure we find vp = 7.79 ± 0.04 km s−1 and vs = 4.48 ± 0.03 km s−1. The parameter (∂lnvs/∂lnvp)P is near to 1.2 and independent of temperature. Calculations are presented for elastic properties and other parameters important for the equations of state and anharmonicity of forsterite. Recent high-temperature thermal expansion measurements on a forsterite specimen from the same boule are used in this analysis. Effects of uncertainties in high-temperature thermal expansion data on these parameters have been evaluated and are discussed.

In situ processing of epitaxial Y‐Ba‐Cu‐O high Tc superconducting films on (100) SrTiO3 and (100) YS‐ZrO2 substrates at 500–650 °C

Abstract: We report the formation of excellent quality epitaxial YBa2Cu3O7 films on (100) SrTiO3 and (100) ZrO2 (yttria stabilized) substrates in the temperature range of 500–650 °C by XECl excimer laser ablation in a 0.2 Torr oxygen ambient. By applying a dc bias voltage of +300 V to an interposing ring, we were able to reduce the substrate temperatures from 650 to 500 °C for obtaining epitaxial films. The quality of the epitaxial films was found to decrease with temperature, particularly below 550 °C. The thickness of the superconducting films was varied from 500 to 5000 A with superconducting transition temperatures Tc (zero resistance) varying from 87 to 90 K for 650 °C deposits. The critical current density Jc of films was found to vary linearly with temperature with values of (zero magnetic field at 77 K) 5.0×106 and 1.0×106 for films deposited at 650 °C on (100) SrTiO3 and (100) yttria‐stabilized zirconia substrates, respectively. X‐ray diffraction, transmission electron microscopy, electron channeling patte...

Aryltrimethylammonium trifluoromethanesulfonates as precursors to aryl [18F]fluorides: Improved synthesis of [18F]GBR‐13119

Abstract: Aromatic nucleophilic substitution of various trimethylammonium trifluoromethanesulfonates with [18F]fluoride has been evaluated. Fluorinations were studied over a temperature range of 45–165°C, with decay corrected yields ranging from 20–80%. [18F]GBR 13119, 1-[2-{(4-[18F]fluorophenyl)(phenyl)methoxy}ethyl]-4-(3-phenylpropyl)piperazine, a potential radio-tracer for the dopamine uptake system, has been prepared in no-carrier-added form from 4-N,N,N,-trimethylaniliniumphenylmethanone trifluoromethanesulfonate. Purification by solid-phase techniques yielded the product in 20% decay corrected radiochemical yield and >98% radiochemical and chemical purity without HPLC.

Conformational change of bovine serum albumin by heat treatment.

Abstract: The thermal denaturation of bovine serum albumin (BSA) was studied at pH 2.8 and 7.0 in the range of 2-65 degrees C. The relative proportions of alpha-helix, beta-structure, and disordered structure in the protein conformation were determined as a function of temperature, by the curve-fitting method of circular dichroism spectra. With the rise of temperature at pH 7.0, the proportion of alpha-helix decreased above 30 degrees C and those of beta-structure and disordered structure increased in the same temperature range. The structural change was reversible in the temperature range below 45 degrees C. However, the structural change was partially reversible upon cooling to room temperature subsequent to heating at 65 degrees C. On the other hand, the structural change of BSA at pH 2.8 was completely reversible in the temperature range of 2-65 degrees C, probably because the interactions between domains and between subdomains might disappear due to the acid expansion. The secondary structure of disulfide bridges-cleaved BSA remained unchanged during the heat treatment up to 65 degrees C at pH 2.8 and 7.0.

Thick Film ZnO Resistive Gas Sensors Analysis of Their Kinetic Behavior

Abstract: Thick film polycristalline ZnO gas sensors for hydrogen partial pressure determination in hydrogen-air mixtures present at very complex kinetic behavior that demands to be thoroughly clarified in order for them to be used in practical applications. For this reason a systematic investigation has been carried out on the time and temperature dependence of the electrical conductivity of ZnO films deposited via spray pyrolysis on ceramic substrates in the temperature range 498-573 K in the presence of dispersed Pt as the catalyst

High‐Temperature Passive Oxidation of Chemically Vapor Deposited Silicon Carbide

Abstract: The oxidation behavior of chemically vapor deposited (CVD) SiC at high temperature was investigated using a thermogravimetric technique in the temperatures range of 1823 to 1948 K. The specimens were prepared by chemical vapor deposition using SiCl4, C3H8, and H2 as source gases. The oxidation behavior of the CVD-SiC indicated “passive” oxidation and a two-step parabolic oxidation kinetics over the entire temperature range. The crystallization of the SiO2 film formed may have caused this two-step parabolic behavior. The parabolic oxidation rate constant (Kp) varied with the square root of the oxygen partial pressure (P1/2O2). The activation energy for the oxidation was determined to be 345 and 387 kJ · mol−1. These values suggest that the diffusion process of the oxygen ion which passes through the SiO2 film is rate-controlling.

Temperature-induced magnetism in LaCoO 3

Abstract: Polarized and unpolarized neutron measurements have been performed on ${\mathrm{LaCoO}}_{3}$ in a temperature range between 10 and 295 K. A drastic decrease in the magnetic cross section is observed below 150 K. This is the first concrete experimental evidence for the temperature-induced magnetic moment of Co ions in this oxide as proposed in the thermally populated high-spin model. The temperature dependence of the moment is in qualitative agreement with that calculated from the magnetic-susceptibility data.

Diffusion of Water into Silica Glass at Low Temperature

Abstract: Diffusion of water into silica glass was measured in the temperature range of 200{degrees} to 750{degrees}C by treating the glass in air containing a constant water vapor pressure and analyzing the concentration profile using a Fourier transform infrared spectrometer. In the short-time diffusion heat treatments, the surface concentration was lower and the apparent diffusion coefficient was higher than the corresponding steady-state values. The temperature dependence of the steady-state diffusion coefficient showed two different activation energies. Above {approximately}550{degrees}C the diffusion coefficients were similar to the published results with an activation energy of {approximately}80 kJ/mol, while below {approximately}550{degrees}C, the diffusion coefficient was higher than the value obtained by extrapolation from higher temperatures, and the activation energy was {approximately}40kJ/mol. Correspondingly, the water solubility- temperature relation showed a sudden change at around the same temperature: at temperatures above this temperature the solubility increased with decreasing temperature, while at lower temperatures the trend was reversed. It is suggested that this observed peculiarity was caused by the initial nonequilibrium reaction between water and SiO{sub 2} glass and a change in enthalpy of the glass-water reaction.

Chemical Vapor Deposition of Copper from Copper (II) Hexafluoroacetylacetonate

Abstract: Thermally activated decomposition of the vapor phase of copper (II) hexafluoroacetylacetonate was studied. It was found that the temperature at which the decomposition is carried out influences dramatically the chemical composition of deposits; the higher the temperature, the more carbon is incorporated. Pure copper deposits having resistivities of 3–7 μΩ cm were obtained at substrate temperatures of 340°–390°C. It is believed that in this temperature range, breaking of the metal‐ligand bond of the copper compound takes place while at higher temperatures the onset of the ligand decomposition itself becomes significant. The vapor pressure of liquid copper (II) hexafluoroacetylacetonate was determined over the temperature range 97°‐120°C. The standard enthalpy of evaporation was found to be .

Domain-wall dynamics in organic charge-transfer compounds with one-dimensional ferroelectricity.

Abstract: It has been widely observed in ionic donor-acceptor charge-transfer (CT) compounds that kink-type domain walls between one-dimensional ferroelectric molecular domains show strong dielectric response with a thermally activated relaxation frequency over a wide temperature range. The domain walls can carry spin and electric charge, which produce anomalous charge-transport phenomena observed in this type of CT dielectrics.

Semiconducting and Thermoelectric Properties of Sintered Iron Disilicide

Abstract: The electrical resistivity, thermoelectric power, and Hall coefficient of sintered iron disilicide, Fe1−xMnxxSi2, and Fe1−yCoySi2 are measured over the temperature range from 77 to 1400 K. Regardless of the purity of raw materials, Fe1−xMnxSi2 and Fe1−yCoySi2 show semiconducting properties below the semiconductor-to-metal transition temperature Tc. Min and Co atoms in iron disilicide act as acceptor and donor, respectively. The energy gap of FeSi2 at 0 K is 1.00 eV, deduced from the temperature dependence of the Hall coefficient in the intrinsic region. The energy gap of Mn-doped FeSi2 decreases from 0.95 to 0.83 eV with increasing Mn amount. Above 150 K the lg ϱ versus 1/T dependence of Mn-doped FeSi2, exhibits an S-like decaying curve. This cannot be explained completely by ordinary band conduction, but can be done by small polaron conduction with crystalline distortions. An den gesinterten Eisendisiliziden Fe1-xMnxSi2 und Fe1−yCoySi2 werden spezifischer Widerstand, Thermospannung und Hallkoeffizient im Temperaturbereich zwischen 77 und 1400 K gemessen. Unabhangig von der Reinheit der Ausgangsmaterialien zeigen Fe1−xMnxSi2 und Fe1−yCoySi2 unterhalb der Temperatur Tc beim Halbleiter-Metall-Ubergang halbleitende Eigenschaften. Mn-bzw. Co-Atome im Eisendisilizid wirken als Akzeptor bzw. Donator. Die Energielucke von FeSi2 betragt bei 0 K 1,00 eV, was aus der Temperaturabhangigkeit des Hallkoeffizienten im Eigenleitungsgebiet ermittelt wird. Die Energielucke von FeSi2 vermindert sich von 0,95 auf 0,83 eV mit der Zunahme der Mn-Dotierung. Oberhalb 150 K zeigt die 1/T-Abhangigkeit von lg ϱ einen S-formigen Verlauf. Dieses Verhalten des spezifischen Widerstandes ist im Rahmen des gewohnlichen Bandermodells schwer verstandlich, es kann jedoch durch kleine Polaronen und Kristalldeformationen gedeutet werden.

On theCp toCv conversion of solid linear macromolecules II

Abstract: A modification is proposed for the Nernst-Lindemann equation that is used to convert calculated heat capacities at constant pressure (C p ) to heat capacities at constant volume (C v ) for solid, linear macromolecules. the constant A0 per mole of repeating unit in this equation is derived by taking into account the variable number of vibrators excited at different temperatures. With the new equation it is possible to calculateC p for solid polymers over a wider temperature range. The constant is calculated for solid polymers from experimental thermal expansivity, isothermal compressibility and heat capacity data obtained from the literature. An average value of (3.9±2.4)×10−3(K mol)/J was obtained for A0 (new) from data on 22 solid polymers. This average value may be used as a universal constant in case no experimental data on compressibility and expansivity are available for computation ofA 0. The remaining variation of A0 (new) with temperature is discussed and example calculations are shown for polyethylene. Effects of premelting and possibly large-amplitude motion are discovered for polyethylene in the temperature range 290 to 410 K.

Kinetics of Layer Growth and Multiphase Diffusion in Ion-Nitrided Titanium

Abstract: Pure titanium specimens were ion nitrided in a nitrogen plasma in the temperature range of 800 ‡C to 1080 ‡C at various nitrogen partial pressures. During ion nitriding, titanium nitrides TiN and Tiin2N and nitrogen solid solution layers (α and Β) were formed consistent with the equilibrium phase diagram. The kinetics of growth of these layers were studied as a function temperature and ion-nitriding parameters. An analytical diffusion model for multiphase diffusion was used to calculate the diffusion coefficients of nitrogen in the phases of the Ti-TiN system from layer growth experiments. Using the layer growth data, the temperature dependence of nitrogen diffusion in TiN (δ), Ti2N (e), and α titanium was found to obey the following relations: Dinδ=4.4±1.62 × 10su-5 exp-36,500±1400/RT Dine=2.7±1.05 ×10su-3 exp-35,760±2500/RT Dinα=0.96±0.08 × exp-51,280-505/RT

Spinodal decomposition and mechanical properties of an austenitic Fe-30wt.%Mn-9wt.%Al-0.9wt.%C alloy

Abstract: The microstructure and mechanical properties of an austenitic Fe-30wt.%Mn-9wt.%Al-0.9wt.%C alloy after aging in the temperature range between 743 and 873 K have been investigated. The occurrence of spinodal decomposition was confirmed by transmission electron microscopy observation of a modulated structure with superlattice reflections and identification of the X-ray sidebands. The rapid increase in the yield stress in the early stage of aging was proportional to the increase in the modulation amplitude and independent of the wavelength. The observed hardening has been examined using a theory dealing with the coherency strain produced by the spinodal decomposition.

On the non-linear properties of TlInX2 (X = S, Se, Te) ternary compounds

Abstract: Optical and electrical properties of the TlInX 2 (X = S, Se, Te) were studied. The selenides and tellurides are of chain-like structure while the sulfides are layered. The measurements ( I-U characteristics and optical absorption) seem to have a direct connection with the main structural features. The I-U -curves of the first two compounds are S-type with characteristic oscillations in the negative differential resistance (NDR) region while the sulfides show an Ohmic behavior. The optical absorption measurements in the temperature range 15–300 K for Se- and Te-compounds show a positive temperature coefficient of the gap while for the S-compound it is negative. Possible explanations are mentioned.

Molecular dynamics study of the structural and thermodynamic properties of MgO crystal with quantum correction

Abstract: We have applied the constant temperature and pressure molecular dynamics technique to the simulation of structural and thermodynamic properties of the MgO crystal in the temperature range between 300 and 2000 K, using empirical pair potential functions consisted of the Coulomb, dispersion, and repulsion interactions. Quantum corrections are included, based on the Wigner–Kirkwood expansion of the free energy in powers of Planck constant h. In the present study, only the first nonvanishing term with the order h2 is considered. As expected, quantum effects on the properties are found to become increasingly important with decreasing temperature. In view of the simplicity of the potential used, our simulation is quite successful in reproducing a wide range of measured properties of MgO, including the crystal structure, bulk modulus, thermal expansion coefficient, heat capacity, and mean‐square atomic displacements over a wide temperature range above 500 K. However, at lower temperatures, both the heat capacity...

Thermal decay of laser-induced long living metastable electronic states in Na2[Fe(CN)5NO] · 2H2O single crystals

Abstract: And the decay was measured in the temperature range of 106 K-300 K. All metastable states decay thermally according to an exponential law. We could not observe any emission of radiation in the energy range of 5 eV-0.3 eV during the thermal decay. We have evaluated the activation energies E A and frequency factors Z assuming the validity of the Arrhenius law and a first order reaction for three different metastable states. They all can be completely annihilated with red light. A strong temperature dependence with respect to the generation of the metastable states was observed

Insect sex pheromones : Effect of temperature on evaporation rates of acetates from rubber septa.

Abstract: The half-lives (t1/2) for evaporative loss ofn-alkyl andn-alkenyl acetates from rubber septa were determined at temperatures varying from 15 to 35 °C. The changes int1/2 with temperature gave high correlations with the equation, Int1/2 = ΔH/RT+yo where ΔΔH is the heat of vaporization,R is the gas constant,T is the absolute temperature, andyo is a constant. Half-lives changed dramatically with temperature and the degree of change with temperature increased with increasing molecular weight. For mixtures, component ratios changed with temperature, but the degree was modest. At 20 °C there was a 7.5-fold ratio oft1/2 between members of the homologousn-alkyl orn-alkenyl acetates differing by two carbon atoms. The large change int1/2 with temperature and with number of carbon atoms is a consequence of the thermodynamic relationships and the temperature range of pheromone usage. Therefore, a similar degree of change inf1/2 with temperature and number of carbon atoms will apply to other formulations of the same type (those in which the rate of evaporation is first order). The values oft1/2 at 20 °C mainly agreed very well with those reported previously at room temperature. However, our previously reported values for pentadecyl and hexadecyl acetate were revised. Half-lives were shown to depend on the vapor pressure of a compound in the formulation substrate, but not on the vapor pressure of the pure compound.