Depolarization Thermocurrents in Ice Ih at Low Temperature

1981 ◽  
Vol 36 (4) ◽  
pp. 321-328 ◽  
Author(s):  
P. Pissis ◽  
G. Boudouris ◽  
J. C. Garson ◽  
J. L. Lévêque
Keyword(s):  
Low Temperature ◽  
Heating Rate ◽  
Relaxation Times ◽  
Relaxation Processes ◽  
Heating Rates ◽  
Temperature Range ◽  
Polycrystalline Ice

Polycrystalline ice samples frozen from highly purified water have been investigated by means of the depolarization thermo-current (DTC) technique in the temperature range 85-250 K. Three peaks have been observed at temperatures about 125, 165, and 225 K at a heating rate of 3.5 K/min. The measurements confirm most of the results reported by Johari and Jones. The characteristics of the low temperature DTC peak have been examined extensively for different samples, different heating rates and different polarization conditions. This peak has been found to be non-Debye. Its multiplicity has been studied experimentally using the possibilities offered by the DTC method. It may be better represented by a continuous ditribution of relaxation times than by a sum of discrete relaxation processes

The Effect of Thermal History on Porcelain Expansion Behavior

1989 ◽  
Vol 68 (9) ◽  
pp. 1313-1315 ◽  
Author(s):  
C.W. Fairhurst ◽  
D.T. Hashinger ◽  
S.W. Twiggs
Keyword(s):  
Thermal Expansion ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Heating Rate ◽  
Room Temperature ◽  
Heating Rates ◽  
Thermal Expansion Data ◽  
Temperature Range ◽  
Expansion Behavior

Porcelain-fused-to-metal restorations are fired several hundred degrees above the glass-transition temperature and cooled rapidly through the glass-transition temperature range. Thermal expansion data from room temperature to above the glass-transition temperature range are important for the thermal expansion of the porcelain to be matched to the alloy. The effect of heating rate during measurement of thermal expansion was determined for NBS SRM 710 glass and four commercial opaque and body porcelain products. Thermal expansion data were obtained at heating rates of from 3 to 30°C/min after the porcelain was cooled at the same rate. By use of the Moynihan equation (where Tg systematically increases in temperature with an increase in cooling/heating rate), the glass-transition temperatures (Tg) derived from these data were shown to be related to the heating rate.

Characteristic Relaxation Times of Low-temperature Semiconductor Breakdown Kinetics

1989 ◽  
Vol 44 (7) ◽  
pp. 629-632 ◽  
Author(s):  
J. Peinke ◽  
J. Parisi ◽  
U. Rau ◽  
W. Clauß ◽  
M. Weise
Keyword(s):  
Low Temperature ◽  
Characteristic Time ◽  
Relaxation Times ◽  
System Response ◽  
Relaxation Processes ◽  
Nonlinear Transport ◽  
Response Behavior ◽  
Slowing Down ◽  
Critical Phase ◽  
Spatio Temporal

The nonlinear transport behavior during low-temperature avalanche breakdown of extrinsic germanium is associated with the self-generated formation of spatio-temporal current structures. Very close to the critical phase transition between different conducting states, the underlying physical relaxation processes develop on relatively slow macroscopic time scales in the ms range. We have evaluated the slowing down of the characteristic time constants from independent measurements of the system response behavior to external pulsed excitations.

scholarly journals The Formation of the Oxides of Carbon by the Pyrolysis of Tobacco

1975 ◽  
Vol 8 (1) ◽  
Author(s):  
R. R. Baker
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
High Temperature ◽  
Low Temperature ◽  
Heating Rate ◽  
Temperature Region ◽  
High Temperature Region ◽  
Heating Rates ◽  
Carbon Oxides ◽  
Decomposition Reactions

AbstractFlue-cured Virginia tobacco has been heated in nitrogen and nitrogen/oxygen mixtures under flow conditions, and the rate of formation of carbon monoxide and carbon dioxide has been determined as a function of temperature, heating rate, and proportion of oxygen in the gas. When the tobacco is heated in nitrogen at heating rates comparable to those in a smouldering cigarette, 27 % of the carbon content of the tobacco is converted to carbon oxides. Both carbon oxides show two distinct formation regions: a low-temperature region (about 100°-450°C), and a high-temperature region (about 550°-900°C). These temperature limits are almost identical to those predicted from studies on the combustion coal of a cigarette burning in air. When tobacco, or the carbonaceous residue remaining after the pyrolysis experiments, is heated in nitrogen / oxygen mixtures, the total amount of carbon converted to carbon monoxide and carbon dioxide is independent of heating rate, but the relative proportions of the two oxides are strongly dependent on heating rate. At the lower heating rate, proportionally less carbon monoxide, and more carbon dioxide, is produced. Under oxidation conditions, about 70 % of both carbon oxides formed in the low-temperature region (100°-450°C) are produced by tobacco decomposition reactions, whereas in the high-temperature region about 10-20 % of the carbon monoxide, and 2-9 % of the carbon dioxide, are produced by tobacco decomposition.

Hardness of polymeric glasses in the TG region: a-Se

1988 ◽  
Vol 3 (4) ◽  
pp. 609-612 ◽  
Author(s):  
S. O. Kasap ◽  
M. Winnicka ◽  
S. Yannacopoulos
Keyword(s):  
Heating Rate ◽  
Structural Relaxation ◽  
Inflection Point ◽  
Relaxation Processes ◽  
Relaxation Model ◽  
Sharp Drop ◽  
Vickers Hardness Number ◽  
Temperature Range ◽  
Glass Transformation ◽  
Polymeric Glasses

The Vickers hardness number Hv of a typical glassy inorganic polymer, a-Se, is studied as a function of temperature with the heating rate varied as a parameter from 0.032 to 3 °C/min, over two decades. It is shown that Hv(T), as a function of temperature, goes through a sharp drop in the glass transformation region following the similar drop for the shear modulus G(T) reported previously. By defining an empirical glass transition temperature TG at the inflection point of Hv vs T behavior, the heating rate dependence of TG is examined and interpreted via the kinetic structural relaxation model of glass transformation. It is shown that over the temperature range 36–50 °C the rate of structural relaxation processes controlling the mechanical properties obeys an Arrhenius type of temperature dependence with an activation energy ∼2.75 cV/atom. Furthermore, over the temperature range accessed, the structural relaxation rate seems to follow the viscosity-temperature behavior.

Mechanical relaxation processes of wood in the low-temperature range

2001 ◽  
Vol 81 (13) ◽  
pp. 3338-3347 ◽  
Author(s):  
Eiichi Obataya ◽  
Misato Norimoto ◽  
Bunichiro Tomita
Keyword(s):  
Low Temperature ◽  
Mechanical Relaxation ◽  
Relaxation Processes ◽  
Temperature Range

High-Temperature Dielectric Properties of Goethite From 400 to 3000 MHz

2005 ◽  
Vol 20 (1) ◽  
pp. 18-29 ◽  
Author(s):  
C.A. Pickles ◽  
J. Mouris ◽  
R.M. Hutcheon
Keyword(s):  
Dielectric Properties ◽  
Thermogravimetric Analysis ◽  
Perturbation Technique ◽  
Relaxation Times ◽  
Relaxation Processes ◽  
Heating Rates ◽  
Hydrogen Atoms ◽  
Debye Relaxation ◽  
The Real ◽  
Thermally Activated

The dielectric properties of goethite and, in particular, the changes during the topotactic conversion of goethite to hematite were studied from room temperature to about 800 °C in the frequency range of 400 to 3000 MHz using the cavity perturbation technique. The complex permittivity, that is, both the real and the imaginary or absorptive parts (έ and ἕ), were measured under various heating regimens. In addition, thermogravimetric analysis (TGA) was performed to characterize the transformation of goethite to hematite. The Debye relaxation formalism was applied to the processes occurring both during and after the main dehydroxylation reaction to calculate the relaxation times. The Arrhenius equation for thermally activated relaxation times was used to determine the activation energies. Both the real and the absorptive parts of the permittivity exhibited a significant peak during the main part of the goethite to hematite decomposition reaction. Above the transformation, there was another, less dramatic, thermally activated increase in the permittivity values. The increase in the permittivities during the goethite to hematite transformation was attributed to the formation of quasi-free migrating radicals, for example, hydroxyl ions, oxygen ions, or hydrogen atoms, during the dehydroxylation of goethite. The derivative thermogravimetric analysis (DTGA) curve was found to be directly related to the transient values of the real and the imaginary permittivities. Higher heating rates resulted in an accelerated rate of dehydroxylation and therefore higher values of the transient permittivities. In the temperature range of 400 °C to 500 °C (i.e., just above the dehydroxylation peak), the real permittivity exhibited a varying frequency dependence, which suggested that changes were occurring in the newly formed, highly defected hematite structure, which is referred to as hydrohematite. During the reaction there were multiple relaxation processes and thus the Debye relationship could not be applied. However, at temperatures above about 500 °C, the structure stabilized, the Debye relationship was more closely followed, and the relaxation times could be determined as a function of temperature. The activation energy for the relaxation process above 500 °C was determined to be 0.47 kJ/mol.

scholarly journals The Effect of Rapid Heating and Fast Cooling on the Transformation Behavior and Mechanical Properties of an Advanced High Strength Steel (AHSS)

Metals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 545 ◽  
Author(s):  
Juan Pablo Pedraza ◽  
Rafael Landa-Mejia ◽  
Omar García-Rincon ◽  
C. Isaac Garcia
Keyword(s):  
Mechanical Properties ◽  
Heating Rate ◽  
Volume Fraction ◽  
Rapid Heating ◽  
Transformation Behavior ◽  
Heating Rates ◽  
Austenite Grain Size ◽  
Initial Microstructure ◽  
Temperature Range ◽  
Fast Cooling

The major goal of this work was to study the effect of rapid heating and fast cooling on the transformation behavior of 22MnB5 steel. The effect of the initial microstructure (ferrite + pearlite or fully spheroidized) on the transformation behavior of austenite (during intercritical and supercritical annealing) in terms of heating rates (2.5, 30 & 200 °C/s) and fast cooling, i.e., 300 °C/s rate, were studied. As expected, the kinetics of austenite nucleation and growth were strongly related to the heating rates. Similarly, the carbon content of the austenite was higher at lower intercritical annealing temperatures, particularly when slower heating rates were used. The supercritical temperatures used in this study were similar to those used during commercial hot stamping operations, i.e., 845 and 895 °C, respectively, followed by a fast cooling rate. The prior austenite grain size (PAGS) was not strongly influenced by the nature of the initial microstructure, heating rate, reheating temperatures (845 or 895 °C), at 30 s holding time. The decomposition of austenite using fast cooling rates was examined. The results showed that 100% martensite was not obtained. The observed low temperature transformation products consisted of mixtures of martensite-bainite plus undissolved Fe3C carbides and small amounts of martensite-austenite (M-A). At higher supercritical temperatures, i.e., 1000 °C and 1050 °C, the final microstructure showed an increase in the volume fraction of martensite and a decrease in the volume fraction of bainite. The Fe3C and the M-A microconstituent were not observed. The best combination of tensile properties was obtained on samples reheated in the lower temperature range (845 to 895 °C). Interestingly, when the samples where reheated at the higher temperature range (1000 to 1050 °C) and fast cooled, the results of the mechanical properties did not exhibit significantly higher strength levels independent of heating rate or initial microstructural condition. This can be attributed to the change in the microstructural balance %martensite+%bainite as the reheating temperature increases. The results of this study are presented and discussed.

Features of radiothermoluminescence of polypropylene and ethylene propylenediene elastomer SKEPT-4044 compositions with nanoscale metal-containing fillers

2020 ◽  
pp. 66-73
Author(s):  
A.M. Magerramov ◽  
◽  
N.I. Kurbanova ◽  
M.N. Bayramov ◽  
N.A. Alimirzoyeva ◽  
...  
Keyword(s):  
Transition Temperature ◽  
Molecular Mobility ◽  
Fe3o4 Nanoparticles ◽  
Low Temperatures ◽  
Frost Resistance ◽  
Relaxation Processes ◽  
Ethylene Propylene ◽  
Temperature Range ◽  
Β Relaxation

Using radiothermoluminescence (RTL), the molecular mobility features in the temperature range of 77-300 K were studied for the polypropylene (PP)/ethylene propylene diene elastomer SKEPT-4044 with NiO, Cu2O and Fe3O4 nanoparticles (NPs) based on ABS-acrylonitrile butadiene or SCS-divinyl styrene matrices. It has been shown that the introduction of nanofillers in PP significantly affects the nature and temperature of γ- and β-relaxation processes, while the region of manifestation of the β-process noticeably shifts to the region of low temperatures. Composites with Cu2O NPs have a higher β-transition temperature Tβ than composites with other NPs. It was found that PP/SKEPT-4044 composites with Cu2O NPs with a dispersion of 11-15 nm and acrylonitrile butadiene thermoplastics have optimal frost resistance compared to other compositions.

Relaxation processes of some simple aliphatic molecules in dilute solutions

1977 ◽  
Vol 55 (4) ◽  
pp. 297-301 ◽  
Author(s):  
M. P. Madan
Keyword(s):  
Carbon Tetrachloride ◽  
Dielectric Relaxation ◽  
Thermodynamic Parameters ◽  
Relaxation Times ◽  
Relaxation Processes ◽  
Dilute Solutions ◽  
Microwave Region ◽  
Nonpolar Solvents ◽  
Dielectric Data ◽  
Intramolecular Rotation

The dielectric relaxation processes of acetone, cyclohexanone, 4-methyl-2-pentanone, and 4-heptanone in dilute nonpolar solvents, n-heptane, cyclohexane, benzene, and carbon tetrachloride have been studied in the microwave region over a temperature range 10 to 60 °C. The relaxation times and the thermodynamic parameters for the activated states have been determined using the measured dielectric data. The results have been discussed in terms of dipole reorientation by molecular and intramolecular rotation and compared, wherever possible, with other similar studies on aliphatic molecules.

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