Summary A pseudo-isothermal method for the kinetic analysis was applied to the recrystallisation of a to ß nickel sulphide based on the Ozawa model for non-isothermal crystallisation in the presence of pre-existing nuclei. The aim of the analysis was to determine the number of steps involved in the recrystallisation and, hence, determine the applicability of the kinetic equation based on a single step mechanism, as is commonly applied in the kinetic analysis of solid-state processes using thermal methods. The kinetic analysis yielded evidence of at least two processes indicating that physical and mechanistic significance should not be drawn from the use of a single step approximation of the rate equation.
The principles of selective separations by recrystallization are explained and formulae for the calculation of decontamination
factors are presented. Experiments with strontium sulfate and radioactive strontium ions demonstrate the validity of the theoretical
considerations. Similar or higher decontamination factors are found than those calculated for a uniform distribution of the
radioactive strontium ions between crystals and solution. The high values are explained by assuming a recrystallization mechanism
which consists of dissolution and redeposition of crystal layers. The half-times of recrystallization increase sharply with
Sr2+ or SO
concentration in the solution. In nitric acid solutions as well as in mixtures containing nitrates and nitric acid the solubility
of strontium sulfate is rather high, accordingly the decontamination factors are low under these conditions and furthermore
the recrystallization half-times are long.
recrystallization of amorphous sample [ 25 – 27 ]. Thus it might be proposed that MCP H 2 O after dehydration became a fully or partially amorphous form and then recrystallized with temperature.
TG curve and DSC
Toughened glass panels used as a glazing material in multistorey buildings are known to fracture prematurely when they contain
nickel sulfide inclusions as a result of the α-β phase recrystallisation in nickel sulfide. The kinetics of this recrystallisation
were studied by differential scanning calorimetry (DSC) under isothermal and non-isothermal conditions. The recrystallisation
was observed to be a two-step process with an induction period followed by the phase change. A two-stage kinetic model was
used to estimate the recrystallisation time under ambient conditions. These values were found to correlate well with the observed
time to failure for glass panels installed in multistorey buildings.
The thermal evolution of a very fine-grained hydrated cobalt molybdate, CoMoO4 · · 0.9H2O, has been studied by dilatometry, DTA, X-ray crystallography and scanning electron microscopy. Four principal stages have been detected between 25 and 1000°: dehydration, polymorphism (or precipitation), recrystallization, and high-temperature phase change. Such phenomena also occurred with some other hydrated molybdates (Ni, Mn).
Bisphenol-A polycarbonate (BAPC) was crystallised by exposure to acetone vapours for a period of 9 h; it developed a 20% crystallinity
according to WAXS measurements. The samples of semi-crystalline BAPC were then submitted to a series of thermal treatments
including annealing, self-nucleation and subsequent isothermal crystallizations. The results showed that the polymer possesses
a remarkable crystalline memory and a much faster recrystallization and reorganization capacity (lamellar thickening) than
its very low thermal crystallization rate. This peculiar crystallization behaviour probably stems from its rigid backbone
Plastically deformed samples of ultra high purity iron (UHP) doped with 150 ppm of niobium were investigated by differential
temperature scanning calorimetry (DTSC) determining the stored energy and the activation enthalpy of recovery and recrystallization.
Any oxidation effects were successfully prevented with a newly constructed device for cleaning the specimens by ion-etching
and enclosing them hermetically in noble metal capsules without any contact to air. Compared with pure iron the stored energy
and the activation enthalpy are increased in the Fe–Nb alloy resulting in a large shift of the recrystallization temperature.
The effect of thermal treatment, in air and in vacuum, on51Cr(III)-doped potassium chromate and on post-irradiation-recrystallized potassium chromate has been studied. The51Cr(VI) yield was found to increase and the M yield to decrease in all samples, while the DP yield remained constant up to 180 °C and decreased at higher temperatures. The results were not affected by the presence of oxygen.
The DSC characterisation of the morphology of the metastable a phase of stoichiometric nickel sulphide was carried out using
two calorimeters; a TA Instruments 2920 MDSC and a Perkin Elmer DSC-7, and two quenching histories. Based on these quenching
histories, significant differences were observed in the heat flow curves, including the observation of a second exothermic
peak which is tentatively assigned to be a metastable phase to metastable phase transformation. The kinetic constants for
the a to b recrystallisation were determined as a function of degree of conversion using a mechanism free isoconversional
model. Variations in the values of the kinetic constants were also ascribed to the quenching histories. Although the differences
in morphology observed were ascribed to the processing history, the shift in the position of the a to b recrystallisation
peak was partially attributed to the thermal resistances of the instruments used.
The thermal and crystal morphological properties of poly[ethylene teraphthalate] (PET) and poly(ethylene-2,6-naphthalenedicarboxylate) (PEN) biaxially oriented films were compared to amorphous and other isotropic semi-crystalline samples. Crystal melting as a function of temperature was characterized by temperature modulated DSC (TMDSC) and found to begin just above the glass transition for both oriented films. About 75°C above the glass transitions, substantial exothermic recrystallization begins and continues through the final melting region in oriented films. The maximum in the non-reversing TMDSC signal for the oriented films signifies the maximum recrystallization exothermic activity with peaks at 248°C and 258°C for PET and PEN, respectively. The final melting endotherm detected was 260°C and 270°C for PET and PEN, and is shown by the TMDSC data and by independent rapid heating rate melting point determinations to be due to the melting of species recrystallized during the heating scan. The results are compared with TMDSC data for initially amorphous and melt crystallized samples. The volume fraction of rigid species (Frigid=total crystal fraction plus rigid amorphous or non-crystalline species) were measured by TMDSC glass transition data, and contrasted with the area fraction of rigid species at the oriented film surface characterized with very high resolution atomic force microscopy (AFM) phase data. The data suggest that the 11 nm wide hard domains in PET, and 21 nm wide domains in PEN film detected by AFM consist of both crystal and high stiffness interphase species.