Complete Temperature Range Research Articles

Effect of freezing on the viscoelastic behaviour of whey protein concentrate suspensions

The effect of freezing on viscoelastic behaviour of whey protein concentrate (WPC) suspensions was studied. Suspensions with total protein content of 5% and 9% w/v were prepared from a commercial WPC (unheated suspensions). A group of unheated suspensions was treated at two temperatures (72.5 and 77.5 °C) during selected times to obtain 60% of soluble protein aggregates (heat-treated suspensions). Unheated suspensions and heat-treated suspensions were frozen at −25 °C (frozen unheated and frozen heat-treated suspensions). Frequency sweeps (0.01–10 Hz) were performed in the region of linear viscoelasticity at 10, 20, 30, 40, and 50 °C. Mechanical spectra of all studied suspensions at 20 °C were similar to viscoelastic fluids and complex viscosity increased with the frequency ( ω). Elastic ( G′) and viscous ( G″) moduli were modelled using power law equations ( G′ = aω x , G″ = bω y ), using fitted parameters a, x, b, and y for statistical analysis. Exponent y was the most influenced by freezing, indicating the existence of a higher degree of arrangement in frozen unheated suspensions and a lower degree of arrangement in frozen heat-treated suspensions. Only characteristic relaxation times (inverse of the crossover frequency) of suspensions with 5% w/v of total protein content were significantly influenced by freezing. Time–temperature superposition was satisfactory applied in unheated whey protein concentrate suspensions only in the range of high temperatures (30–50 °C). However, this principle failed over the complete temperature range in most of the frozen suspensions. It is possible that freezing produced an increase in the susceptibility to morphological changes with temperature during the rheological measurements.

A novel calibration method for an infrared thermography system applied to heat transfer experiments

In heat transfer measurements with highly non-uniform wall heat fluxes, high spatial resolution of wall temperatures is required to fully capture the complex thermal situation. Infrared thermography systems provide that spatial resolution. To meet the thermal accuracy, they are usually calibrated in situ using thermocouples embedded in the test surface, which have to cover the complete temperature range of interest. However, thermocouples which are placed in regions of high temperature and heat flux gradients often cannot be used for the calibration and the overall accuracy of the calibration decreases significantly. Therefore, in the present work a novel in situ calibration method is presented which does not require thermocouples over the complete surface temperature range. The number of free parameters of the calibration function is reduced by an optimized insensitivity of the system with respect to changes in operating conditions. Reference measurements demonstrate the advantages of the new method.

Ethylbenzene Transformation over a ZSM-5-Based Catalyst in a Riser Simulator

The transformation of ethylbenzene has been studied over a ZSM-5-type catalyst in a riser simulator that mimics the operation of a fluidized-bed reactor. The study was conducted at 350, 375, 400, 450, and 500 °C for reaction times of 3, 5, 7, 10, 13, and 15 s. The effect of reaction conditions on the ratio of cracking to disproportionation products (C/D), the distribution of diethylbenzene (DEB) isomers (m-DEB and p-DEB), and the ratio of benzene/diethylbenzenes (B/DEB) are reported. The experimental results were modeled using quasi-steady-state approximation. Disproportionation was determined to dominate at low temperatures (350−400 °C), while cracking reaction becomes significant as higher temperatures (>400 °C). Thus, two mechanisms were postulated to represent the disappearance of ethylbenzene during the transformation reaction (one mechanism for low temperature, and another for the complete temperature range considered). Kinetic parameters that were used for the disappearance of ethylbenzene during t...

Microstructuration induced differences in the thermo-optical and luminescence properties of Nd:YAG fine grain ceramics and crystals

The temperature and compositional dependences of thermo-optical properties of neodymium doped yttrium aluminum garnet (YAG) crystals and fine grain ceramics have been systematically investigated by means of time-resolved thermal lens spectrometry. We have found that Nd:YAG ceramics show a reduced thermal diffusivity compared to Nd:YAG single crystals in the complete temperature range investigated (80-300 K). The analysis of the time-resolved luminescent properties of Nd(3+) has revealed that the reduction in the phonon mean free path taking place in Nd:YAG ceramics cannot be associated with an increment in the density of lattice defects, indicating that phonon scattering at grain boundaries is the origin of the observed reduction in the thermal diffusivity of Nd:YAG ceramics. Finally, our results showed the ability of the time-resolved thermal lens to determine and optimize the thermo-optical properties of Nd:YAG ceramic based lasers.

Effect of the internal stress relaxation during the post-annealing on the photo-induced properties of TiO 2 coatings reactively sputtered

Photocatalyst TiO 2 coatings have been reactively sputtered at high pressure on cold glass substrates pre-coated by a SiN x sodium diffusion barrier. The as-deposited coatings were amorphous and the TiO 2/SiN x /glass samples were subsequently heated at different temperatures under air. The TiO 2 films crystallise in the anatase structure above temperatures of 250 °C with a [001] preferential orientation. The structural analyses have demonstrated that the crystallites are elongated following the c axis direction, perpendicularly to the surface. No modifications of grain size and texture have been observed over the complete temperature range studied (250–550 °C). However, the lattice parameters evolution shows a decrease of the tensile stress with a rise in annealing temperature. The microstructure is then completely relaxed around 400 °C and finally compressive stress is observed at higher temperature. The study of the photo-induced (photocatalytic and hydrophilic) properties shows an activity maximum at 400 °C. These results suggest that the photo-induced properties would be favoured by a relaxed microstructural state of titanium dioxide.

A climatological view of HNO3 partitioning in cirrus clouds

AbstractA new in situ climatology of cirrus ice water content (IWC) is used, together with observed molar ratios of HNO3/H2O in cirrus ice particles, to estimate the range of HNO3 content in cirrus ice in the temperature interval 185–240 K. We find that nearly over the complete temperature range HNO3 percentages in ice between 0.01 and 100% are possible in cirrus clouds and that IWC is a major parameter determining the content of HNO3 in ice at given temperatures. Considering average conditions, the HNO3 content increases with decreasing temperature from 1% to about 10% in the range 240–200 K. For colder ice clouds, the average HNO3 content again decreases down to 6%. At higher temperatures, less efficient HNO3 uptake limits the HNO3 content in cirrus ice, while at low temperatures small IWCs permit only little HNO3 in ice, thus causing the convex‐shaped average HNO3 content curve. The highest HNO3 content is expected in tropical ice clouds with very large IWCs, especially at temperatures between 190 and 210 K. Thus, tropical cirrus clouds show the highest potential to vertically redistribute HNO3. Copyright © 2008 Royal Meteorological Society

Ab initio potential energy curve for the neon atom pair and thermophysical properties for the dilute neon gas. II. Thermophysical properties for low-density neon

A neon–neon interatomic potential energy curve determined from quantum-mechanical ab initio calculations and described with an analytical representation (R. Hellmann, E. Bich, and E. Vogel, Molec. Phys. 106, 133 (2008)) was used in the framework of the quantum-statistical mechanics and of the corresponding kinetic theory to calculate the most important thermophysical properties of neon governed by two-body and three-body interactions. The second and third pressure virial coefficients as well as the viscosity and thermal conductivity coefficients, the last two in the so-called limit of zero density, were calculated for natural Ne from 25 to 10,000 K. Comparison of the calculated viscosity and thermal conductivity with the most accurate experimental data at ambient temperature shows that these values are accurate enough to be applied as standard values for the complete temperature range of the calculations characterized by an uncertainty of about ±0.1% except at the lowest temperatures.

Ab initio potential energy curve for the helium atom pair and thermophysical properties of the dilute helium gas. II. Thermophysical standard values for low-density helium

A helium–helium interatomic potential energy curve determined from quantum-mechanical ab initio calculations and described with an analytical representation considering relativistic retardation effects (R. Hellmann, E. Bich, and E. Vogel, Molec. Phys. (in press)) was used in the framework of the quantum-statistical mechanics and of the corresponding kinetic theory to calculate the most important thermophysical properties of helium governed by two-body and three-body interactions. The second pressure virial coefficient as well as the viscosity and thermal conductivity coefficients, the last two in the so-called limit of zero density, were calculated for 3He and 4He from 1 to 10 000 K and the third pressure virial coefficient for 4He from 20 to 10 000 K. The transport property values can be applied as standard values for the complete temperature range of the calculations characterized by an uncertainty of ±0.02% for temperatures above 15 K. This uncertainty is superior to the best experimental measurements at ambient temperature.

Activity of rhodium-based catalysts for CO preferential oxidation in H2-rich gases

The CO preferential oxidation (CO-PROX) process can lead to a reduction of the CO concentration in the hydrogen-rich gas from WGS process of hydrocarbons reformate down to at least 10 ppmv or below, so as to enable its direct feeding to standard PEM fuel cells. Rh-based catalysts supported on 3A zeolite, alumina, titania or ceria were prepared and tested for potential application in CO-PROX operating in a temperature range compatible with PEM FCs (80–100 °C). Among the prepared catalysts, 1% Rh-3A zeolite catalyst was found to be the most suitable one for the CO-PROX at low temperature: it reduced the inlet CO concentration below 10 ppmv within a temperature range of at least 80–120 °C without the appearance of undesirable side reactions. In order to improve the oxygen selectivity toward the CO complete oxidation with a lowest as possible hydrogen parasitic oxidation, the oxygen amount in the feed gas composition was decreased. With 1% Rh-3A zeolite catalyst the lowest O2 feed concentration was found to be 3 times the corresponding value of the CO stoichiometric oxidation (λ = 2O2/CO = 3). Finally, with the goal to reduce the noble metal costs, tests at lower Rh load (from 1 to 0.5%) were carried out. No significant variations in both activity and width of complete CO conversion temperature range resulted for 0.5% Rh-3A catalyst. Therefore, this catalyst operating at λ = 3 could potentially be used for the CO-PROX reaction at low temperature.

ANALYTICAL DYNAMICS OF NEURON PULSE PROPAGATION

The four-dimensional Hodgkin–Huxley equations describe the propagation in space and time of the action potential v(z) along a neural axon with z = x + ct and c being the pulse speed. The potential v(z), which is parameterized by the temperature, is driven by three gating functions, m(z), n(z) and h(z), each of which obeys formal first order kinetics with rate constants that are represented as nonlinear functions of the potential v. It is shown that this system can be analytically simplified (i) in the number of gating functions and (ii) in the form of associated rate functions while retaining to close approximation quantitative fidelity to computer solutions of the exact equations over the complete temperature range for which stable pulses exist. At a given temperature we record two solutions (T < T max ) corresponding to a high-speed and a low-speed branch in speed-temperature plots, c(T), or no solution (T > T max ). The pulse is considered as composed of two contiguous parts: (i) a pulse front extending from v(0) = 0 to a pulse maximum v = V max , and (ii) a pulse back extending from V max through a pulse minimum V min to a final regression back to v(z → ∞) = 0. An approximate analytic solution is derived for the pulse front, which is predicted to propagate at a speed c(T) = 1203 Θ⅜ (T° C ) cm/sec, [Formula: see text] in close agreement with computer solution of the exact Hodgkin–Huxley equations for the entire pulse. These results provide the basis for a derivation of two-dimensional differential equation systems for the pulse front and pulse back, which predict the pulse maximum and minimum over the operational temperature range 0 ≤ T ≤ 25° C , in close agreement with the exact equations. Most neuron dynamics studies have been based on voltage clamp experiments featuring external current injection in place of self-generating pulse propagation. Since the behaviors of the gating functions are similar, it is suggested that the present approximations might be applicable to such situations as well as to the dynamics of myelinated fibers.

Assessing friction characteristics of liquid lubricants

A reduction in friction in tribological contacts will lead to reduced energy requirements. It is therefore important to be able to measure the frictional characteristics of various liquid lubricants. Current laboratory tests measure friction, but the test rigs invariably induce wear between the mating contacts. A new test rig, the wire-on-capstan rig, is presented which measures friction without inducing wear between the wire and the rotating capstan. All seven lubricants tested (three without additives and four proprietary hydraulic oils) exhibit a reducing coefficient of friction with increasing temperature. Temperatures ranged from 25°C to 100°C. The mineral-based oil showed the lowest friction coefficient and the three synthetic ester based oils produced the highest friction coefficient over the complete temperature range. Future testing will extend the range of operating conditions and product types. Copyright © 2006 John Wiley & Sons, Ltd.

Low-Temperature Deposition of TiN by Plasma-Assisted Atomic Layer Deposition

Titanium nitride () films were deposited by a plasma-assisted atomic layer deposition (PA-ALD) process, based on precursor dosing and remote plasma exposure, at temperatures ranging from 100 to . The plasma, the PA-ALD process, and the resulting material properties were extensively investigated. The plasma was studied by optical emission spectroscopy and Langmuir probe, revealing an ion density of and an electron temperature of just above the substrate. Under floating conditions there is thus a considerable ion flux towards the substrate per ALD cycle with a typical ion energy of . film growth was studied by in situ spectroscopic ellipsometry, revealing self-limiting surface reactions for the complete temperature range. At the growth rate of was found to be significantly lower than the growth rate of at . The stoichiometry of the films varied with the plasma exposure time, while the Cl content was mostly affected by the deposition temperature ( at to at ). Resistivities as low as were obtained at a temperature of , while at a fair resistivity of was reached. These results show that PA-ALD with and plasma is well suited for low-temperature deposition of high-quality films.

Modeling the suppression of boron diffusion in Si∕SiGe due to carbon incorporation

We used the process simulator FLOOPS-ISE to implement a consistent model describing the diffusion behaviors of boron and carbon in silicon and silicon germanium. In particular, our model successfully accounts for boron and carbon behaviors in a wide range of sample structures and experimental conditions over the complete temperature range of 750–1070°C in inert and oxidizing ambients, and in the presence of implant damage. The structures studied include cases where the boron and carbon profiles are separated as well as cases where profiles overlap, cases with carbon in silicon and in SiGe, and our own recent experiments where boron diffusion within a SiGeC region has been characterized. We model carbon diffusion by the kickout and Frank-Turnbull mechanisms, and interstitial capture by substitutional carbon, and demonstrate that a model must incorporate all three effects to satisfactorily explain published data. We also include standard models for boron-interstitial clusters and {311} defects.

Simulation of aluminium sheet forming at elevated temperatures

The formability of aluminium sheet can be improved by increasing the temperature in some parts of the sheet and cooling other parts. Simulation of this process requires an accurate material model for the yield function and the temperature and strain-rate dependent hardening. In simulations of cylindrical cup deep drawing, the quadratic Hill yield criterion results in too much thinning in the bottom of the cup. The Vegter yield function is more flexible and gives better predictions. The model for work hardening and the temperature and strain-rate sensitivity needs to be accurate over the complete temperature range between the cooled and the heated parts of the sheet. It is demonstrated that the Bergström model is able to model the flow stress of Al–Mg alloys up to 200 °C and medium strain rates. For higher temperatures and low strain rates the deviations with experiments increase.

Speed of sound in nitrogen as a function of temperature and pressure

Speed of sound measurements in nitrogen by Younglove and McCarty [J. Chem. Thermodynam. 12, 1121–1128 (1980)] are revisited and an empirical polynomial equation for the speed of sound is derived. The polynomial coefficients differ from those given by Wong and Wu [J. Acoust. Soc. Am. 102, 650–651 (1997)] with the result that discrepancies between predicted and measured values at low temperatures are reduced. The maximal error over the complete temperature and pressure range from 80 to 350 K and 0.031 to 0.709 MPa is reduced from 5.38% to 0.78%.

Proton spin–lattice relaxation time in ordering VH x alloys

Proton spin–lattice relaxation time is determined in VH 0.68 and VH 0.73 alloys in the temperature range of β 1, β 2 and δ ordered phases (400–100 K). Experimental results are described in terms of dipole–dipole interaction mechanism. On comparing calculated and experimental data in the complete temperature range the values of temperature dependent activation energy E a and time constant τ 0 are estimated.

Structured porous Ni- and Co-YSZ cermets fabricated from directionally solidified eutectic composites

NiO-YSZ and CoO-YSZ eutectic rods were produced by directional solidification using the laser floating zone method (LFZ). This technique produces highly structured material consisting of alternate lamellae of transition metal oxide and zirconia with variable interlamellar spacing depending on growth conditions. We have chosen conditions for interlamellar spacing of about 1 μm. The microstructure is homogeneous and mechanically stable during thermochemical reduction. Complete reduction of the transition metal oxide produces a lamellar porous cermet with porous metallic lamellae alternated with the YSZ phase. The thermal expansion coefficients of the cermets are those of the YSZ skeleton. Reaction kinetics at different temperatures during the reduction process were studied by gravimetric methods. The reduction process within the complete temperature range studied for NiO-YSZ, and at high temperatures for CoO-YSZ seems to be controlled by the O 2− diffusion through the YSZ phase. The amount of Ni 2+ and Co 2+ ions dissolved in the YSZ phase is 2 and 5 mol%. Resistivity values for the cermets along the solidification axis are 50 μΩ cm for Co-YSZ and 130 μΩ cm for Ni-YSZ. These materials are porous, ionic and electronic conductors and could be used as textured anodes for solid-oxide fuel cells (SOFC).

Viscosity of glass at high contact pressure during indentation experiments

The mechanism of plastic deformation of glasses by indentation near room temperature has not been understood completely up to now. For the analysis of indentation experiments with a Vickers pyramid and spherical indenter, respectively, viscoelastic deformation behaviour is assumed for the complete temperature range from room temperature to the transformation temperature. Therefore, the rheological analysis of all experiments was performed with the help of a simple Maxwell model. The results of indentation experiments were compared with cylinder compression experiments, which were analysed by the same rheological principles. Additionally, some indents were analysed by topographical investigation to get the first hints of viscoelastic deformation behaviour below the transformation temperature of glass.

Determination and Study on the Solubility of Methane in Heptane + Cyclohexane and Heptane + Ethanol at High Pressures

It is known that the use of natural gas as a vehicular fuel is advantageous, but the storage limitation of natural gas is a severe drawback to the use. In this paper, a method for storing natural gas at moderate temperatures and pressures by dissolving natural gas in solvents is studied. A set of experimental equipment for measuring gas solubility in liquids under high pressures was established. The solubilities of methane in heptane + cyclohexane and heptane + ethanol were measured over the temperature range from 291.15 K to 313.15 K and pressures to 12.00 MPa. The new solubility measurements are believed to have uncertainties of 0.002 in the mole fraction. The data were analyzed using the Peng−Robinson equation of state with two kinds of mixing rules. In general, the equation coupled with the simple mixing rule represents the experimental data of methane + heptane + cyclohexane well over the complete temperature and pressure range when the interaction parameters kij for methane + heptane and methane + c...

Supersaturation and temperature dependency of gibbsite growth in laminar and turbulent flows

The temperature and supersaturation dependencies of gibbsite crystal growth rates in caustic aluminate solutions were experimentally investigated in both the laminar (Taylor–Couette precipitator) and turbulent (stirred tank) mixing regimes. The gibbsite precipitation experiments were conducted batchwise in a temperature range from 55°C to 90°C, but all with the same initial liquor composition and seed type. At low supersaturation it was found that gibbsite crystal growth could be described satisfactorily by a screw dislocation growth mechanism over the complete temperature range, irrespective of the flow regime. At higher supersaturation and lower temperatures, i.e. 55°C and 60°C, it is proposed that two-dimensional polynuclear growth is the dominant growth mechanism in turbulent flows. Any differences observed in the measured growth rate estimates from the laminar and turbulent systems were explained by error analysis.