Structural Relaxation, “Memory Behaviour”, Specific Heat Anomaly and Localized Motions in Amorphous Solids

1990 ◽  
Vol 215 ◽  
Author(s):  
G. P. Johari
Keyword(s):  
Specific Heat ◽  
Chemical Reactions ◽  
Structural Relaxation ◽  
Amorphous Solids ◽  
Glassy Matrix ◽  
Mechanical Relaxation ◽  
Mechanical Spectroscopy ◽  
Scanning Calorimetry ◽  
Glassy Material ◽  
Β Relaxation

AbstractDielectric and mechanical relaxation spectroscopy of thermoplastics and thermosets show that, in the former, ageing is related only to the spontaneous structural relaxation towards a lower energy, but still disordered, structure and decreases the strength of the β- relaxation process. Ageing of a thermoset initially increases the strength of its (dielectric) β-relaxation as a result of diffusionallowed chemical reactions, which increase the number of dipolar groups, and later decreases it towards a limiting value. The decrease in the strength of β-relaxation on ageing of polymers and other amorphous solids suggests that structural relaxation causes a collapse of low-density, high-entropy, regions or “soft-sites” randomly distributed in the structure of a glassy material. The increase in the strength of β-relaxation observed in thermosets is higher than calculated from the extent of chemical reactions that occur during their structural relaxation at T<Tg. It is suggested that these effects should be included in the phenomenological theories for both the physical ageing and “memory behaviour” - the latter can be conveniently studied by both dielectric and mechanical spectroscopy and by differential scanning calorimetry. Structural relaxation also decreases the magnitude of the specific heat anomaly in amorphous solids and can be used to experimentally test the postulate that tunneling centres involved in the low-temperature phonon properties are related to the presence of “islands of mobility” or “soft-sites” in an otherwise rigid glassy matrix.

High-Temperature Mechanical Relaxation due to Dislocation Motion inside Dislocation Networks

2008 ◽  
Vol 137 ◽  
pp. 21-28 ◽  
Author(s):  
Andre Rivière ◽  
Michel Gerland ◽  
Veronique Pelosin
Keyword(s):  
Internal Friction ◽  
Relaxation Effect ◽  
Dislocation Motion ◽  
Relaxation Peak ◽  
Mechanical Relaxation ◽  
In Situ Tem ◽  
Mechanical Spectroscopy ◽  
Internal Friction Peak ◽  
First Case ◽  
Dislocation Walls

Internal friction peaks observed in single or polycrystals are clearly due to a dislocation relaxation mechanism. Because a sample observed by transmission electron microscopy (TEM) often exhibits in the same time various dislocation microstructures (isolated dislocations, dislocation walls, etc.) it is very difficult to connect the observed relaxation peak with a particular dislocation microstructure. Using isothermal mechanical spectroscopy (IMS), it is easier to compare, for instance, the evolution of a relaxation peak with measurement temperature to the microstructural evolution observed by in-situ TEM at the same temperatures. IMS was used to study a relaxation peak in a 5N aluminium single crystal firstly 1% cold worked and then annealed at various temperatures. TEM experiments performed in the same material at various temperatures equal to the temperatures used for the damping experiments made possible to link this internal friction peak with a relaxation effect occurring inside dislocation walls. In two other experiments in a 4N aluminium polycrystal and in a metal matrix composite with SiC whiskers, it is shown that the observed relaxation peaks are connected to the motion of dislocations inside polygonization boundaries in the first case and in dislocation pile-ups around each whisker in the second one. Theoretical models proposed to explain such relaxation peaks due to a dislocation motion inside a dislocation wall or network are discussed.

Specific heats of polymer powders by differential scanning calorimetry

1982 ◽  
Vol 60 (14) ◽  
pp. 1853-1856 ◽  
Author(s):  
Eva I. Vargha-Butler ◽  
A. Wilhelm Neumann ◽  
Hassan A. Hamza
Keyword(s):  
Differential Scanning Calorimetry ◽  
Specific Heat ◽  
Scanning Calorimetry ◽  
Temperature Range ◽  
Specific Heats ◽  
Powdered Form ◽  
Polymer Powders

The specific heats of five polymers were determined by differential scanning calorimetry (DSC) in the temperature range of 300 to 360 K. The measurements were performed with polymers in the form of films, powders, and granules to clarify whether or not DSC specific heat values are dependent on the diminution of the sample. It was found that the specific heats for the bulk and powdered form of the polymer samples are indistinguishable within the error limits, justifying the determination of specific heats of powders by means of DSC.

scholarly journals The effect of structural changes during sintering on the electric and magnetic traits of the Ni96.7Mo3.3 alloy nanostructured powder

2009 ◽  
Vol 41 (2) ◽  
pp. 175-184 ◽  
Author(s):  
L. Ribic-Zelenovic ◽  
M. Spasojevic ◽  
A. Maricic ◽  
M.M. Ristic
Keyword(s):  
Electrical Resistivity ◽  
Magnetic Permeability ◽  
Structural Relaxation ◽  
Crystalline Phase ◽  
Structural Changes ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Fcc Lattice ◽  
Lower Permeability ◽  
Structural Powder

Ni96.7Mo3.3 powder was electrochemically obtained. An X-ray diffraction analysis determined that the powder consisted of a 20% amorphous and 80% crystalline phase. The crystalline phase consisted of a nanocrystalline solid nickel and molybdenum solution with a face-centred cubic (FCC) lattice with a high density of chaotically distributed dislocations and high microstrain value. The scanning electronic microscopy (SEM) showed that two particle structures were formed: larger cauliflower-like particles and smaller dendriteshaped ones. The thermal stability of the alloy was examined by differential scanning calorimetry (DSC) and by measuring the temperature dependence of the electrical resistivity and magnetic permeability. Structural powder relaxation was carried out in the temperature range of 450 K to 560 K causing considerable changes in the electrical resistivity and magnetic permeability. Upon structural relaxation, the magnetic permeability of the cooled alloy was about 80% higher than the magnetic permeability of the fresh powder. The crystallisation of the amorphous portion of the powder and crystalline grain increase occurred in the 630 K to 900 K temperature interval. Upon crystallisation of the amorphous phase and crystalline grain increase, the powder had about 50% lower magnetic permeability than the fresh powder and 3.6 times lower permeability than the powder where only structural relaxation took place.

Structural Relaxation Process in CuHfTi Amorphous Alloys

2009 ◽  
Vol 283-286 ◽  
pp. 533-538 ◽  
Author(s):  
Kazumasa Yamada ◽  
N. Shinagawa ◽  
M. Sogame ◽  
I.A. Figueroa ◽  
Hywel A. Davies ◽  
...  
Keyword(s):  
Activation Energy ◽  
Relaxation Process ◽  
Structural Relaxation ◽  
Amorphous Alloys ◽  
Melt Spinning ◽  
Amorphous Materials ◽  
Ternary Alloys ◽  
Relaxation Processes ◽  
Scanning Calorimetry ◽  
Structure Relaxation

The aim of this research is to clarify a quantitative evaluation in the structural relaxation processes focusing on the activation energy in Cu based amorphous alloys. The activation energy for structural relaxation process in a metal type amorphous CuHfTi ternary alloys, with cross sections of typically 0.03 mm x 2.0 mm, prepared by chill-block melt spinning has been investigated by Differential Scanning Calorimetry (DSC) with a cyclically heating technique. Activation energies for structural relaxation with a spatial quantity in amorphous materials have been discussed by use of a relaxed ratio function that depends on annealing temperature and time. In the present work, the distributions for the Activation Energy Spectrum (AES) were observed almost 152 kJmol-1 (1.58 eV). Another result has been also established that the “reversible” AES model energy distribution though the cyclically structure relaxation occurs even in amorphous Cu60Hf20Ti20 alloy.

scholarly journals EFFECT OF STRUCTURAL RELAXATION ON THE DEFORMATION BEHAVIOR OF A Zr64.13Cu15.75Ni10.12Al10 BULK METALLIC GLASS UNDER NANOINDENTATION

2010 ◽  
Vol 24 (15n16) ◽  
pp. 2320-2325 ◽  
Author(s):  
JIANSHENG GU ◽  
BINGCHEN WEI ◽  
TAIHUA ZHANG ◽  
YIHUI FENG ◽  
YANPING HU ◽  
...  
Keyword(s):  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Structural Relaxation ◽  
Deformation Behavior ◽  
Isothermal Annealing ◽  
Flow Behavior ◽  
Thermal And Mechanical Properties ◽  
Scanning Calorimetry ◽  
Obvious Effect ◽  
Dsc Curves

Structural relaxation by isothermal annealing below the glass transition temperature is conducted on a Zr 64.13 Cu 15.75 Ni 10.12 Al 10 bulk metallic glass. The effect of structural relaxation on thermal and mechanical properties was investigated by differential scanning calorimetry and instrumented nanoindentation. The recovery of the enthalpy in the DSC curves indicates that thermally unstable defects were annihilated through structural relaxation. During nanoindentation, the structural relaxation did not have a significant influence on the serrated plastic flow behavior. However, Structural relaxation shows an obvious effect in increasing both the hardness and elastic modulus, which is attributed to the annihilation of thermally unstable defects that resulted from the relaxation.

scholarly journals Competition between Structural Relaxation and Crystallization in the Glass Transition Range of Random Copolymers

Polymers ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 1778
Author(s):  
Jürgen E. K. Schawe ◽  
Claus Wrana
Keyword(s):  
Glass Transition ◽  
Structural Relaxation ◽  
Random Sequence ◽  
High Sensitivity ◽  
Random Copolymers ◽  
High Time Resolution ◽  
Scanning Calorimetry ◽  
Transition Range ◽  
Glass Transition Range ◽  
And Control

Structural relaxation in polymers occurs at temperatures in the glass transition range and below. At these temperatures, crystallization is controlled by diffusion and nucleation. A sequential occurrence of structural relaxation, nucleation, and crystallization was observed for several homopolymers during annealing in the range of the glass transition. It is known from the literature that all of these processes are strongly influenced by geometrical confinements. The focus of our work is copolymers, in which the confinements are caused by the random sequence of monomer units in the polymer chain. We characterize the influence of these confinements on structure formation and relaxation in the vicinity of the glass transition. The measurements were performed with a hydrogenated nitrile-butadiene copolymer (HNBR). The kinetics of the structural relaxation and the crystallization was measured using fast differential scanning calorimetry (FDSC). This technique was selected because of the high sensitivity, the fast cooling rates, and the high time resolution. Crystallization in HNBR causes a segregation of non-crystallizable segments in the macromolecule. This yields a reduction in mobility in the vicinity of the formed crystals and as a consequence an increased amount of so-called “rigid amorphous fraction” (RAF). The RAF can be interpreted as self-assembled confinements, which limit and control the crystallization. An analysis of the crystallization and the relaxation shows that the kinetic of both is identical. This means that the Kohlrausch exponent of relaxation and the Avrami exponent of crystallization are identical. Therefore, the crystallization is not controlled by nucleation but by diffusion and is terminated by the formation of RAF.

scholarly journals Uncovering β-relaxations in amorphous phase-change materials

2020 ◽  
Vol 6 (2) ◽  
pp. eaay6726 ◽  
Author(s):  
Si-Xu Peng ◽  
Yudong Cheng ◽  
Julian Pries ◽  
Shuai Wei ◽  
Hai-Bin Yu ◽  
...  
Keyword(s):  
Phase Change ◽  
Amorphous Phase ◽  
Amorphous Materials ◽  
Phase Change Materials ◽  
Special Kind ◽  
Relaxation Processes ◽  
Glass Transitions ◽  
Mechanical Spectroscopy ◽  
Characteristic Features ◽  
Β Relaxation

Relaxation processes are decisive for many physical properties of amorphous materials. For amorphous phase-change materials (PCMs) used in nonvolatile memories, relaxation processes are, however, difficult to characterize because of the lack of bulk samples. Here, instead of bulk samples, we use powder mechanical spectroscopy for powder samples to detect the prominent excess wings—a characteristic feature of β-relaxations—in a series of amorphous PCMs at temperatures below glass transitions. By contrast, β-relaxations are vanishingly small in amorphous chalcogenides of similar composition, which lack the characteristic features of PCMs. This conclusion is corroborated upon crossing the border from PCMs to non-PCMs, where β-relaxations drop substantially. Such a distinction implies that amorphous PCMs belong to a special kind of covalent glasses whose locally fast atomic motions are preserved even below the glass transitions. These findings suggest a correlation between β-relaxation and crystallization kinetics of PCMs, which have technological implications for phase-change memory functionalities.

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