Authors:Slobodan Stojadinovic, Jasmina Pekez, and Nikola Bajic
recrystallization; (b) by precipitation of dispersed carbides of microalloyed elements and (c) increasing the dislocation density by reducing the temperature of austenite transformation [ 7 – 9 ].
Grain refining is the consequence of combined effect of
Authors:Traian Florin Marinca, Ionel Chicinaş, and Olivier Isnard
other exothermic peak present in the sample milled for 12, 20 and 24 h is associated with the recrystallisation of the Fe 2 O 3 and is observed at about 593 °C for the 12 and 20 h milled samples recrystallisation and at 596 °C for the 24 h milled sample
Authors:R. C. Mehrotra, S. N. Varma, and B. K. Singh
DTA techniques were employed to study the thermal and structural characteristics of hydrated aluminium oxides and aluminous clays of the Pipra pelitic rocks from district Sidhi, India. Detailed microscopic investigations, X-ray and chemical analyses reveal that these clays were derived by the localized weathering of arkosic metasediments. The chemical and normative behaviours have confirmed their formation by the isochemical metamorphism of arkose, aided by a little granitization and followed by minor retrogression. A tentative correlation between the thermal and structural changes of these oxides and clay minerals at various transition temperatures has nicely displayed the presence of kaolinite, diaspore and gibbsite. The exothermic curves of kaolinite confirm the recrystallization. The presence of kaolinite in the clay fractions indicates the detrital origin.
The phase behavior of semicrystalline, aliphatic nylons is analyzed on the basis of differential scanning calorimetry, DSC,
and quasi-isothermal, temperature-modulated DSC, TMDSC. The data of main interest are the apparent heat capacities, Cp, in the temperature range from below the glass transitions to above the isotropization. Based on the contributions of the
vibrational motion to Cp, as is available from measurements in our laboratory, the ATHAS Data Bank, and multifaceted new TMDSC results, as well as
on information on the crystal structures, NMR, molecular dynamics simulation of paraffin crystals, and quasi-elastic neutron
scattering, the following observations are made: (a) In semicrystalline nylons the glass transition of the mobile-amorphous
phase is broadened to higher temperature. The additionally present rigid-amorphous phase, RAF, undergoes a separate, broad
glass transition at somewhat higher temperature. (b) The transition of the RAF, in turn, overlaps usually with an increase
in large-amplitude motion of the CH2-groups within the crystals and latent heat effects due to melting, recrystallization, and crystal annealing. (c) Above the
glass transitions of the two non-crystalline phases, Cp of the crystals approaches and exceeds that of the melt. This effect is due to additional entropy contributions (disordering)
within the crystals, which may for some nylons lead to a mesophase. In case a mesophase is formed, the Cp drops to the level of the melt as is common for mesophases. (d) Some locally reversible melting is present on the crystal
surfaces, but seems to be minimal for the mesophase. (e) The increasing amount of large-amplitude motion in the crystals is
described as a third glass transition, occurring over a broad temperature range below the melting or disordering transition
from crystal to mesophase.
The assumption of a separate glass transition in ordered phases was previously discovered on analyzing aliphatic poly(oxide)s
such as poly(oxyethylene), POE, and in the broad class of mesophase-forming small and large molecules. To attain a full description
of the globally-metastable, semicrystalline phase-structure of nylons and to understand its properties, one needs quantitative
information about the glass transitions of the two non-crystalline phases and that of the crystal, as well as the various
irreversible and locally reversible order/disorder transitions and their kinetics. Finally, with different substitutions in
the α-position of the backbone structure of nylon 2, one describes poly(amino acid)s which on proper copolymerization yield
proteins. This links the present study to the earlier thermal analyses of all naturally occurring poly(amino acid)s, a number
of copoly(amino acid)s, and globular proteins in their dehydrated states. It will be of importance to check by quantitative
thermal analysis if similar glass transitions and phase structures as seen in the aliphatic nylons are also present in the
poly(amino acid)s to possibly gain new information about the nanophase structure of proteins.
Tricalcium silicate characteristically exhibits the most intense reversible transition at a temperature of about 915‡. The intensity of this effect can be used to estimate the amount of C3S in mixtures and to calculate the degree of hydration of C3S. Low sensitivity forδT up to 800‡ and higher sensitivity between 800‡ and 1000‡ enable estimation of both Ca(OH)2 and C3S. Interference effects at higher temperatures owing to decarbonation, recrystallization toΒ-wollastonite, and dehydration of the calcium silicate hydrate can be overcome by heating to 1000‡, cooling to 800‡, and reheating. A determination of the degree of hydration of C3S obtained at different periods by DTA correlates well with that using the X-ray method.
Authors:T. Fukumoto, P. S. Thomas, B. H. Stuart, P. Simon, G. Adam, R. Shimmon, and J.-P. Guerbois
current paper, is carried out using a program based on the Simpson method that was devised for calculating the induction periods for the vulcanisation of rubber [ 8 ] and recrystallisation of nickel(II) sulphide [ 10 ]. Once the kinetic parameters have
, the magnitude of T m significantly decreased, together with a slight position shift toward higher temperatures, so indicating that recrystallization was significantly prohibited upon incorporation of WF with the matrix. The more contents the WF, the
Authors:Florin Popa, Ionel Chicinaş, Olivier Isnard, and Viorel Pop
exothermic peak emerges with an onset at 485 °C. This second peak is attributed to the sample re-crystallization, as expected for the nanometric powders obtained by milling. The difference between these two temperatures (internal stress removal peak and re-crystallization
Authors:Bernadett Bajnóczi, Zoltán May, Anna Ridovics, Máté Szabó, Géza Nagy, and Mária Tóth
M OLERA , J. – P RADELL , T. – S ALVADÓ , N. – V ENDRELL-SAZ , M. 1999 : Evidence of tin oxide recrystallization in opacified lead glazes . Journal of the American Ceramic Society, 82 , 2871 – 2875 .
M ÜHLERTHALER , Bruno – T HISSEN