Authors:T. M. Carvalho, A. T. Adorno, A. G. Magdalena, and R. A. G. Silva
-isothermal kinetics of the reverse eutectoid reaction in the Cu–9 mass%Al, Cu–10 mass%Al, and Cu–11 mass%Al alloys were studied using differential scanning calorimetry (DSC), X-raydiffraction (XRD), and scanning electron microscopy (SEM
Authors:N. Cohen, M. Odlyha, D. Ucko, and Q. Pankhurst
Mechanical alloying is a versatile technique for the solid state synthesis of many materials, including alloys such as iron-copper
where the elements are immiscible under equilibrium conditions. The structural and magnetic state of these alloys, and their
thermal stability, have been investigated by means of thermomagnetometry, DSC, X-ray diffraction and Mssbauer spectroscopy.
Comparison of the thermomagnetometry curves for the various alloys together with analysis of intermediate reaction products
enabled the individual thermal processes to be identified. The Curie temperature of the alloys was measured, and it was found
that on heating the metastable alloys underwent phase segregation between 300-400C.
Authors:M. Bernardi, E. Antonelli, A. Lourenço, C. Feitosa, L. Maia, and A. Hernandes
The results reported here based on a study
(x=0, 0.2 and 1) nanometric powders prepared
by the modified Pechini method. The powder samples annealed from 600 to 1000C/2
h were characterized by thermogravimetric analysis (TG), differential scanning
calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy
(SEM) techniques. The decomposition reactions of resins were studied using
thermal analysis measurements. The barium titanate zirconate system presented
just one orthorhombic phase. Furthermore, this study produced BaTiO3
powders with a tetragonal structure using shorter heat treatments and less
expensive precursor materials than those required by the traditional methods.
Authors:M. Niyaz Ahamad, Rahul Vaish, and K. B. R. Varma
Glasses of the composition 2TeO2–V2O5 were fabricated via the conventional melt-quenching technique. The amorphous and the glassy nature of the as-quenched samples were confirmed by X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC), respectively. The glass transition and crystallization parameters were evaluated under non-isothermal conditions using DSC. X-ray diffraction studies confirmed the presence of partially oriented crystallites in the heat-treated glasses. Kauzmann temperature (lower bound for the kinetically observed glass transition) was deduced from the heating rate dependent glass transition and crystallization temperatures.
Authors:Marcelo Kobelnik, Douglas Lopes Cassimiro, Clóvis Augusto Ribeiro, Diógenes dos Santos Dias, and Marisa Spirandeli Crespi
The Ca–diclofenac compound was prepared. Thermogravimetry (TG), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), X-ray diffraction powder patterns, and microscopy analysis were used to characterize this compound. Details concerning the stages of dehydration, transition phase, and thermal decomposition as well as data of the kinetic parameters of these stages have been described here. The kinetic study of these stages was evaluated from several heating rates with a sample mass of 2 and 5 mg in open crucibles under nitrogen atmosphere. The obtained data were evaluated with the isoconversional kinetic method, where the value of activation energy (Ea/kJ mol−1) was evaluated in function of the conversion degree (α). The results show that this compound is hygroscopic. The obtained data lead to a dependence on the sample mass, which results in two kinetic behavior patterns.
Thermal analysis methods are well-established techniques in research laboratories of pharmaceutical industry. The robustness
and sensitivity of instrumentation, the introduction of automation and of reliable software according to the industrial needs
widened considerably the areas of applications in the last decade. Calibration of instruments and validation of results follow
the state of the art of cGMP as for other analytical techniques. Thermal analysis techniques are especially useful for the
study of the behavior of the poly-phasic systems drug substances and excipients and find a unique place for new delivery systems.
Since change of temperature and moisture occur by processing and storage, changes of the solid state may have a considerable
effect on activity, toxicity and stability of compounds. Current requirements of the International Conference of Harmonisation
for the characterization and the quantitation of polymorphism in new entities re-enforce the position of thermal analysis
techniques. This challenging task needs the use of complementary methods. Combined techniques and microcalorimetry demonstrate
their advantages. This article reviews the current use of thermal analysis and combined techniques in research and development
and in production. The advantage of commercially coupled techniques to thermogravimetry is emphasized with some examples.
Authors:L. Sobrados, S. Goni, J. L. Sagrera, and M. J. Martinez
Reactivity of solid mixtures of crystalline V2O5 and basic compounds strongly increases at room temperature by means of water molecules adsorption process from a saturated atmosphere (100% RH). This is due, firstly, to a crystalline-amorphous V2O5 transformation and secondly to the formation of strongly acid V2O5 gels. In the present paper the evolution with time of the CaCO3-V2O5 (1∶1) mixture in the aforementioned conditions was studied by thermal analysis (TG, DTG and DSC), X-ray diffraction (XRD) and infrared spectroscopy (IR). The results confirmed the V2O5 gels formation which decomposed the basic CaCC3 at room temperature through an acid-base mechanism reaction. A new crystalline compound was obtained which corresponded to a hydrated calcium metavanadate.
Behaviours of drawn semi-crystalline poly(ethylene terephthalate) films are investigated by DSC, X-ray diffraction and birefringence
measurements. The comparison of the different results confirms the coexistence of two structures into the amorphous part of
the material: a completely disordered amorphous phase and a mesomorphic amorphous one. Moreover, for the strongest draw ratio,
the calorimetric results show that the drawing effect on the strain induced crystalline structure proceeds by a better orientation
of this structure rather than by nucleation and growth of new oriented crystallites.
melting and crystallisation behaviour of poly(m-xylene
adipamide) (MXD6) are investigated by using the conventional DSC, X-ray diffraction
and polarised light microscopy. Triple, double or single melting endotherms
are obtained in subsequent heating scan for the samples after isothermal crystallisation
from the melt state at different temperatures. The lowest melting peak can
be ascribed to the melting of secondary crystals. The melting of primary crystals
causes the medium melting peak and the highest melting peak is attributed
to the melting of recrystallised species formed during heating. Following
the Hoffman–Weeks theory, the equilibrium melting temperature is equal
to 250C and the equilibrium melting enthalpy ΔHm0
to 175 J g–1. Then, using the Lauritzen–Hoffmann
theory of secondary crystallisation, the analyse of the spherulitic growth
shows that the temperature of transition between the growing regimes II and
III is equal to 176C. Finally the Gibbs-Thomson relationship allows the
determination of the distribution function of crystalline lamellae.