The nucleating efficiency and selectivity of different
β-nucleating agents was characterised and compared by differential scanning
calorimetry, (DSC) and temperature-modulated DSC (TMDSC). The nucleating agents
were the calcium salts of pimelic and suberic acid (Ca-pim and Ca-sub), linear trans-γ-quinacridone (LTQ), a commercial nucleator
NJ Star (NJS) and an experimental product (CGX-220). The efficiency and the
selectivity of Ca-sub and Ca-pim are extremely high. NJS is efficient above
a critical concentration, which is connected with its partial dissolution
in polypropylene melt. LTQ and CGX-220 possess strong overall nucleating ability
and moderate selectivity. Using TMDSC, we found that three consecutive processes
take place during the heating of β-nucleated samples cooled down to room
temperature: reversible partial melting of the β-form, irreversible βα-recrystallisation,
and the melting of the α-modification formed during βα-recrystallisation
or being present in samples prepared with non-selective β-nucleators.
Melting of the α-phase contains both reversible and irreversible components.
Authors:S. H. Murphy, G. A. Leeke, and M. J. Jenkins
The infrared spectrum of polycaprolactone has been recorded as a function of temperature in the range where melting and crystallisation of the polymer can occur. Examination of the carbonyl band of the spectra reveals a clear morphological sensitivity; heating the semi-crystalline polymer through the melting region results in a decrease in the intensity of the crystalline component of the carbonyl band. Accordingly, there was a subsequent increase in intensity of the crystalline carbonyl band on cooling. To enable comparison of these findings with a more conventional method of thermal analysis, similar experiments were conducted using a differential scanning calorimeter. The heated ATR accessory adopted for use in the FTIR spectrometer imposed significant limitations in the range of possible heating and cooling rates, but when these rates were carefully matched between FTIR and DSC, close correlation between the melting point and onset of re-crystallisation was observed. The results confirm that FTIR can be used as an alternative, if more laborious, way of investigating melting and re-crystallisation.
Authors:Shmuel Yariv, Isaak Lapides, and Mikhail Borisover
peaks do not appear in the diffractograms. Trace amounts of spinel and cristobalite are obtained from thermal recrystallization. Quartz is present as an impurity in the Wyoming bentonite and after the amorphization of MONT its X-ray peak becomes very
Authors:T. Belopolskaya, G. Tsereteli, N. Grunina, and O. Smirnova
DSC studies of melting process of annealed native structures and postdenatured ones in low-amylose starches with different
degrees of hydration were carried out. The starch recrystallization at different thermal treatments of the samples was studied
both after the complete and partial destroy of native structures. It has been shown that native structures as well as postdenatured
ones possess the ability to perfection, which is most clearly seen at the annealing at temperatures inside their melting ranges.
The results obtained demonstrate that at the same duration of annealing the process of crystal perfection for secondary starch
structures proceed more intensively compared to the native ones. The presence of the remained native structures in partial
melt in contrast to the remained gel ones restricts the ability of the recrystallized structures to perfection.
Controlled heating (in air) of clay minerals leads to transformations into disordered structures and recrystallization into new phases at high temperatures. These phase transformations are of topotactic nature. On the other hand, prolonged dry-grinding treatments of the same silicates causes structural amorphization with no recrystallization into new phases. The mechanical energy relaxation mechanism, invoked to explain these differences, accounts for the particle size changes and the large growth of dislocations. The latters affect sensibly the reactivity of the materials submitted to such solid-state treatments.
These processes are monitored mostly by XRD, DTA and IR spectroscopy. The latter method allows to study in some silicates submitted to progressive grinding the location and nature of OH groups and water molecules.
Authors:G. Bruni, V. Berbenni, C. Milanese, A. Girella, P. Cofrancesco, G. Bellazzi, and A. Marini
In this work the solid-state characterization of anhydrous D-mannitol has been performed: α and β modifications can be distinguished only by XRPD and FTIR as they show melting temperature
and enthalpy that are the same within the standard deviation. The understanding of the thermal behaviour of the δ form (obtained
by re-crystallization in acetone) has required XRPD experiments performed at variable temperature. This form during heating
undergoes a solid phase transition to α modification. By cooling a melted sample, under a wide range of experimental conditions,
a very fast crystallization occurs. Independently of the starting crystal form (β or δ form), the re-crystallization of D-mannitol from melt always leads to α form.
Authors:Ildikó Gyollai, Ildikó Gyollai, Szaniszló Bérczi, Krisztián Fintor, Szabolcs Nagy, and Arnold Gucsik
The Mócs chondrite was studied by optical microscopy, element mapping, as well as scanning electron microscope backscattered electron (SEM—BSE) imaging, in order to gain a better understanding of the thermal metamorphic as well as post-shock annealing evolution and the mineralogical signatures in this meteorite. The studied thin section of Mócs meteorite contains 26 chondrules with a variety of chondrule textures, which are characterized by a blurry rim. The chondrules mostly consist of pyroxene and olivine, whereas feldspars occur only in the recrystallized groundmass, chondrule mesostasis, and mineral melt inside and beyond the shock veins. It was found that the matrix was completely recrystallized. According to the scanning electron microscope and optical microscope observations mentioned above, it can be concluded that the Mócs chondrite is a 6.5 petrographic type.
New EGA findings revealed that the small endothermal event preceding that of the main decomposition of commercial NaHCO3 involves the simultaneous evolution of water and CO2. At very high sensitivity, EGA experiments evidenced that the above (limited) evolution of gases also took place from the
recrystallized material for which thermal methods gave no indication of endotherms.
Careful reexamination of previous DSC results indicated that for one kind of recrystallized material a very small endotherm
had been neglected. Renewed experiments revealed that this endotherm can be enhanced if the samples are prepared by crushing
and sieving in a wet atmosphere. Parallel FT-IR experiments on commercial and recrystallized materials demonstrated the presence
of carbonate in samples that had previously been taken just beyond the first small endotherm; this confirmed the EGA results.
SEM experiments showed that surface texture changes take place when samples are heated to temperatures just above that of
the preliminary endotherm. On the basis of these new findings, the interpretation previously given to the small endotherm
is revised and detailed knowledge is gained on the mechanism of decomposition of NaHCO3.
The Pleistocene travertine of Buda Vár-hegy (Castle Hill) has been studied in subsurface galleries and cellars. Lithological variations, sedimentary features of the travertine and the underlying friable chalky carbonates and calcareous clays were described in the field. Four lithotypes and several microfacies types of travertine have been identified. The stratal pattern of travertine, distribution of lithotypes, the macrofauna, and the presence of microbial sediments suggests that the travertine was deposited in a shallow lake environment. The lake was fed by lukewarm springs from the central part (probably from Szentháromság-tér [Szentháromság Square] area), where the thickest travertine deposits are found. Direct evidence of cascade deposits or terraced tetarata deposits have not been found in the studied sections. The intense cementation and recrystallisation appear in the form of at least four, mostly phreatic, cement generations, including micrite envelopes, thin fibrous rims, thick radiaxial spars and pore occluding mosaics.
Thermal behaviour of sodium oxo-salts of sulphur: Na2SO4, Na2S2O7, Na2S2O6, Na2SO3, Na2S2O5, Na2S2O4, Na2S2O3, Na2S3O6 and of sulphides Na2S and Na2S2 was studied on heating up to 1000°C. The experiments were performed with anhydrous compounds obtained from commercial products
by recrystallisation and dehydration. The stage mechanisms of decomposition of anionic sub-lattices of the salts have been
proposed basing on the Górski’s morphological classification of simple species. The thermal stability and the stage decomposition
mechanisms were correlated with the structure and the potential chemical properties of the salt anions. The thermal decomposition
processes were studied by means of thermal analysis, and the decomposition products were identified by means of X-ray phase