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.
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.
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
Authors:M. Chatterjee, S. Bhattacharyya, A. Bhattacharyya, M. Banerjee, G. Muthukrishnan, and S. Banerjee
A method is described for the recovery of NH499TcO4 from its reaction waste. From the collected waste solution99Tc was precipitated as99Tc2S7 which on digestion with ammoniacal hydrogen peroxide produced a mixture of NH499TcO4 and (NH4)2SO4 from which the latter was removed by treatment with Ba(OH)2. The solution fumished NH499TcO4 as a crystalline material in 54% overall yield and with 96–98% purity after chromatographic purification over Dowex 50W column. Recrystallisation of this material from aqueous ammoniacal ethanol gave the analytical material which compared well with a standard sample and with literature data in terms of its -counts/mg and its molar extinction co-efficients () at 244 and 286 nm.
Authors:A. Cvetkovskii, R. Bettini, Lj. Tasic, M. Stupar, I. Casini, A. Rossi, and F. Giordano
The thermal behaviour of binary mixtures between β-cyclodextrin (β-CD) and either carbamazepine polymorphic Form I (CBZ I),
Form III (CBZ III) or dihydrate was investigated in order to assess possible interactions of CBZ solid phases with β-CD. Physical
mixtures and kneaded binaries of β-CD and different CBZ crystal forms were studied by differential scanning calorimetry, thermogravimetric
analysis and hot stage microscopy. The pattern of transition of CBZ Form III into Form I is strongly influenced by β-CD. The
liquid-solid transition is practically absent when anhydrous CBZ/β-CD mixes are tested, as a consequence of an interaction
between β-CD and liquid CBZ that hinders CBZ recrystallisation as Form I occurring after CBZ Form III melting.
Water loss on heating of CBZ dihydrate in the presence of β-CD leads in all cases to the formation of CBZ Form I.
The compound BR-A657 is an angiotensin II receptor antagonist. The objective of this work was to investigate the existence
of polymorphs and pseudopolymorphs of BR-A657 and the transformation of crystal forms. Three crystal forms of BR-A657 have
been isolated by recrystallization and characterized by powder X-ray diffractometry, differential scanning calorimetry, and
thermogravimetric analysis. After storage of three days at 0% RH (silica gel, 20°C), 52% RH (saturated solution of Na2Cr2O7·2H2O/20°C) and 95% RH (saturated solution of Na2HPO4/20°C), Forms 2 and 3 were transformed to Form 1.
Temperature-modulated DSC (TMDSC) was used to enhance the perfection of crystals of different poly(p-phenylene sulfide) samples formed during slow cooling from the melt. The sample preparation was made with modulated cooling using a cool-heat mode. Re-heating the samples prepared by slow conventional and modulated coolings indicated that the melting point of the samples prepared by modulated cooling is considerably higher than the melting point of the samples crystallized with conventional cooling. Thus, the perfection of crystallites can be improved if the outer layers just deposited on their surface are re-melted and re-crystallized immediately.
Thermal characterization is proposed as analytical methodology for the purity assay of lapachol, and for determination of
the quality parameters of capsules containing this molecule. The TG data revealed that lapachol is more stable in the presence
of adjuvants, showing the good quality of the formulation. The kinetic parameters obtained were lower for lapachol drug than
for the formulated lapachol. The DSC data demonstrated good compatibility between lapachol drug and the adjuvant in the formulated
lapachol, and did not reveal impurities such as secondary products of the isolation and recrystallization processes. The data
were confirmed by the DSC-photovisual findings.