Eyring activation parameters for the relaxation processes of some asymmetric diaryl molecules in a polystyrene matrix

1980 ◽  
Vol 73 (7) ◽  
pp. 3467-3472 ◽  
Author(s):  
M. A. Desando ◽  
S. Walker
Keyword(s):  
Activation Parameters ◽  
Relaxation Processes ◽  
Polystyrene Matrix

Relaxation mapping analysis with an hyperbolic heating rate

2002 ◽  
Vol 754 ◽  
Author(s):  
C. J. Dias
Keyword(s):  
Activation Parameters ◽  
Activation Entropy ◽  
Relaxation Processes ◽  
Complex Materials ◽  
Cooperative Phenomena ◽  
Relaxation Parameters ◽  
A Value ◽  
Polarization Temperature ◽  
Free Activation Energy ◽  
Map Analysis

ABSTRACTThermally stimulated discharge currents (TSDC) together with the Relaxation Map Analysis (RMA) method is a convenient method to study relaxation processes in complex materials. In the RMA technique, one performs repeated TSDC runs while selecting polarization states through the use of a fixed polarization time schedule and a sucessively higher polarization temperature. Each peak has an associated polarization strength and a pair of activation parameters which can be the Gibbs free activation energy and the activation entropy. In the present paper we propose a different approach to RMA. It consists of a global heating of the sample in an hyperbolic manner to determine the activation parameters as a function of temperature. This determination is done by first selecting a value for the activation entropy for each temperature and then calculating the implied activation enthalpy or Gibbs free energy.We have reasoned that normal relaxation processes usually proceed with a null or close to zero activation entropy and that only relaxations associated to the glass transitionand/or cooperative phenomena involve large values of the activation entropy. In those cases and based on the curvature of the TSDC curve one can select a minimum activation entropy value which will fit the TSDC curve at a particular temperature. Using this data one determines the polarization strength associated to each pair of activation parameters. Results for the TSDC relaxation parameters spectra of a liquid crystal polymer will be presented together with comparisons between the thermal sampling method and the proposed method.

Relaxation Processes at High Temperature in TiAl-Nb-Mo Intermetallics

2012 ◽  
Vol 1516 ◽  
pp. 41-46 ◽  
Author(s):  
Pablo Simas ◽  
Thomas Schmoelzer ◽  
Svea Mayer ◽  
Maria L. Nó ◽  
Helmut Clemens ◽  
...  
Keyword(s):  
High Temperature ◽  
Relaxation Process ◽  
Activation Parameters ◽  
Relaxation Processes ◽  
Thermal Treatments ◽  
Intermetallic Alloys ◽  
Mechanical Spectroscopy ◽  
Responsible Mechanism ◽  
Defect Mobility

ABSTRACTIn the last decades there was a growing interest in developing new light-weight intermetallic alloys, which are able to substitute the heavy superalloys at a certain temperature range. At present a new Ti-Al-Nb-Mo family, called TNM™ alloys, is being optimized to fulfill the challenging requirements. The aim of the present work was to study the microscopic mechanisms of defect mobility at high temperature in TNM alloys in order to contribute to the understanding of their influence on the mechanical properties and hence to promote the further optimization of these alloys. Mechanical spectroscopy has been used to study the internal friction and the dynamic modulus up to 1460 K of a TNM alloy under different thermal treatments. These measurements allow to follow the microstructural evolution during in-situ thermal treatments. A relaxation process has been observed at about 1050 K and was characterized as a function of temperature and frequency in order to obtain the activation parameters of the responsible mechanism. In particular, the activation enthalpy has been determined to be H= 3 eV. The results are discussed and an atomic mechanism is proposed to explain the observed relaxation process.

Dielectric relaxation processes of some dialkyl disulfides

1983 ◽  
Vol 61 (9) ◽  
pp. 2107-2111 ◽  
Author(s):  
H. A. Khwaja ◽  
S. Walker
Keyword(s):  
Dielectric Relaxation ◽  
Relaxation Processes ◽  
Alkyl Chains ◽  
Polystyrene Matrix ◽  
Segmental Relaxation ◽  
Higher Temperature ◽  
Dialkyl Disulfides ◽  
Intramolecular Rotation ◽  
Two Temperature ◽  
Low Temperature Process

Dielectric relaxation studies have been performed for dimethyl, diethyl, di-isopropyl, di-n-butyl, di-tert-butyl, and di-n-octyl disulfides in a polystyrene matrix. For the last five compounds the absorption appears in two temperature regions. The relaxation data for the higher temperature regions are consistent with intramolecular rotation around the S—S bond with accompanying flexibility in the alkyl chains. The enthalpy barrier to this relaxation process is ~29 kJ mol−1 and is the trans (lower) barrier. This value is typical for all six dialkyl disulfides. The most likely interpretation of the low temperature process is that there is segmental relaxation of the alkyl chains which also involves movement of the main dipoles (S—S and S—C).

The Effect of Annealing on the Internal Friction in ECAP-Modified Ultrafine Grained Copper

2012 ◽  
Vol 184 ◽  
pp. 289-294 ◽  
Author(s):  
Igor S. Golovin ◽  
P.P. Pal-Val ◽  
L.N. Pal-Val ◽  
E.N. Vatazhuk ◽  
Yuri Estrin
Keyword(s):  
Activation Energy ◽  
Activation Parameters ◽  
Coarse Grained ◽  
Relaxation Processes ◽  
Exponential Factor ◽  
Mean Values ◽  
Thermally Activated ◽  
Ultrafine Grained ◽  
Relaxation Loss ◽  
The Mean

A detailed study of anelastic effects in submicrocrystalline copper using resonance (~70 kHz, 2 K to 320 K) and sub-resonance (0.05-100 Hz, 300 K to 675 K) techniques was carried out. Several relaxation processes were found in the temperature range of 2 K - 675 K: the relaxation loss peaks (Q-1) near 35 (P1) and 90K (P2) with the activation energy and the pre-exponential factor (H1≈ 0.02 eV,το1≈ 10-9s andH2≈ 0.09 eV,το2≈ 10-11s) similar to those of the Bordoni and the Niblett-Wilks peaks in coarse-grained Cu. This suggests that the peaks are due to the thermally activated motion of dislocation kinks in the primary and secondary Peierls relief. The mean values of activation parameters (H3≈1.4-1.6 eV,το3≈10-17s) of a third thermally activated peak (P3), which was significantly broadened, can be interpreted as a grain boundary peak with uncoupled activation parametersH3*≈0.45 eV andτο3*≈10-14s. A pseudo peak PRis associated with irreversible recrystallization processes. The influence of annealing on the observed effects is also discussed.

Relaxation processes of some aromatic sulfides, sulfoxides, and sulfones in a polystyrene matrix

1980 ◽  
Vol 73 (7) ◽  
pp. 3460-3466 ◽  
Author(s):  
M. A. Desando ◽  
S. Walker ◽  
W. H. Baarschers
Keyword(s):  
Relaxation Processes ◽  
Polystyrene Matrix

Dielectric relaxation in 2-acetylnaphthalene and related compounds

1978 ◽  
Vol 56 (4) ◽  
pp. 567-573 ◽  
Author(s):  
J. Crossley ◽  
M. A. Mazid ◽  
C. K. McLellan ◽  
P. F. Mountain ◽  
S. Walker
Keyword(s):  
Activation Parameters ◽  
Low Frequencies ◽  
Microwave Frequencies ◽  
Dielectric Absorption ◽  
Free Energy Of Activation ◽  
Polystyrene Matrix ◽  
The Matrix ◽  
Acetyl Group ◽  
Related Compounds ◽  
Xylene Solution

The dielectric absorption of 2-acetylnaphthalene and 2- and 3-acetylphenanthrene has been studied in p-xylene solution at several microwave frequencies and in a polystyrene matrix at low frequencies. Acetyl group relaxation has been established from both sets of data. A clear separation of the dielectric absorption of the molecule and the group has been achieved for both 2- and 3-acetylphenanthrene in the matrix. The Eyring activation parameters have been established for acetyl relaxation in these molecules in the matrix. The free energy of activation values for group relaxation increase in the sequence acetophenone < 2-acetylphenanthrene < 3-acetylphenanthrene < 2-acetylnaphthalene. For the p-xylene solution data the weight factor for group relaxation, C2, is appreciably lower than the theoretical value, so that C2 < C1, bearing out the findings of Fong and Smyth for 2-acetylnaphthalene. In polystyrene matrices, the data for 2- and 3-acetylphenanthrene also indicated that C2 < C1. The enthalpy of activation for acetyl relaxation in 2- and 3-acetylphenanthrene is similar to that for acetophenone and 1,4-diacetylbenzene whereas that for 2-acetylnaphthalene would seem somewhat larger.

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