Authors:Edward Mikuli, Marta Liszka-Skoczylas, Joanna Hetmańczyk, and Janusz Szklarzewicz
of picoseconds. On cooling, several phasetransitions take place in these compounds [ 7 – 11 ]. For example, [Ni(NH 3 ) 6 ](NO 3 ) 2 displayed four low temperature phases [ 8 – 10 ]. The phasetransition at T C1 , associated with the largest change
Authors:V. A. Drebushchak, S. N. Dementiev, and Yu. V. Seryotkin
stellerite, with two close peaks one by one. The first one (∼200 °C) is narrow and high and the second one (∼250 °C) is broader and smaller. The first peak was reported to be the first-order phasetransition with the step change of 3.24% in the UC volume and
There are several approaches for the description of phase transitions (PT). leading to different classification schemes:ApproachClassification scheme bythermodynamicorder (after Ehrenfest)kineticreversibility, quenchability, hysteresisstructuralrelationship of crystallographic axes before and after PTmechanisticactual migration path of atoms during PT The most important techniques for investigating PT include DTA and DSC thermo-optical analysis, melastic neutron scattering, IR and Raman spectroscopy and elastic X-ray and neutron diffraction. The latter, as dependent on the temperature, can give indications on the mechanism of PT. The appropriate application of these techniques is demonstrated on the example of the polymorphism of KPO3.
Authors:M. Arai, T. Sakuma, T. Atake, and H. Kawaji
The phase transition and the crystal structures of CuITe were investigated by differential thermal analysis and X-ray powder
diffraction measurements in the temperature range between 300 and 683 K. The new phase transition in CuITe was observed at
592 K. The enthalpy of transition is ΔH=0.125 kJ mol-1. The new phase above 592 K belongs to tetragonal system with the space group I41/amd.
Authors:George G. G. de Oliveira, Humberto G. Ferraz, Patrícia Severino, and Eliana B. Souto
The aim of this article was to analyse the phasetransition and dehydration processes of nevirapine using DSC and thermogravimetry differential thermal analysis (TG-DTA).
Materials and methods
Nevirapine was provided by the
The aim of this study was to correlate the results of experimental data using DTA method and predictions of artificial neural
network (ANN) and multivariate linear regression (MLR). Thermal decomposition of polymers was analyzed by simultaneous DTA
method, and kinetic parameters (critical points, the change of enthalpy and entropy) of polymers were investigated. A computer
model based on multilayer feed forwarding back propagation and multilayer linear regression model were used for the prediction
of critical points, phase transitions of low-density polyethylene (LDPE) and mid-density polyethylene. As a result of our
study, we concluded that ANN model is more suitable than MLR about prediction of experimental data.
orthoborate crystallizes in the vaterite-type structure and has two polymorphous
forms, viz. a low- und a high temperature one. DTA measurements of YBO3
confirmed a reversible phase transition with a large thermal hysteresis. The
phase transition has been accurately characterized by the application of different
heating and cooling rates (β). Consequently, the extrapolation of the
experimental data to zero β yields the transition points at 986.9C
for the heating up and at 596.5C for the cooling down cycle. These values
correspond to samples just after treatment at 1350C. For samples with
a different ‘thermal history’ other phase transition temperatures
are observed, (e.g. after having performed several heating and cooling cycles).
The linear relationship between the associated DTA signal ΔT=Tonset–Toffset and the square root
of the heating rate β was confirmed, but the relation between Tonset and square root of β
is not found here.
From the empirical data a good linear fitting
between Tonset and
ln(β+1) can be derived.
From the kinetic analysis (Kissinger
method) of the phase transformation of YBO3 an apparent
activation energy of about 1386 kJ mol–1
for heating and of about 568 kJ mol–1 for
cooling can be determined
Authors:Bedřich Smetana, Simona Zlá, Aleš Kroupa, Monika Žaludová, Jaromír Drápala, Rostislav Burkovič, and Daniel Petlák
investigation is focused on the area close to the monovariant line in the phase diagram of Sn–Zn–Al ternary system ( Fig. 1 ). As this region of the Sn–Zn–Al phase diagram still deserves a lot of attention [ 3 – 11 ], the temperatures of phasetransitions were
Authors:Ke Liu, Xiao-Lin Zhou, Hai-Hua Chen, and Lai-Yu Lu
]. Although several research groups have experimental and theoretically investigated the pressure induced phasetransitions in TiN using different methods. For example, Zhao et al. [ 13 ] investigated the behavior of TiN using axial X-ray diffraction under