Search Results

You are looking at 21 - 30 of 668 items for :

  • "phase transition" x
  • Refine by Access: All Content x
Clear All

Abstract  

The phase transitions of α,α-trehalose dihydrate (T h) were investigated by either differential thermal analysis (DTA) with an in-house apparatus of variable-pressure type equipped with an open sample holder or commercially available TG (thermal gravimetry)-DTA apparatus for comparison under the same experimental conditions as to the heating rate (2°C min−1), the type of pan (open), and the particle size of T h (63 μm). The former DTA measurements were carried out under five different total pressures, 101, 75, 61, 48 and 35 kPa, which provided quite helpful information necessary for confirmative assignments of the endothermic peaks due to either melting or dehydration of T h. The usage of largely different amount of T h, 126 and 14 mg for the DTA and TG-DTA measurements respectively, led to their different DTA traces, showing that there were largely different extents of the influence by the measured sample surface exposed to the surrounding atmosphere on its dehydration behavior. In addition the high thermal sensitivity achieved with such mass of T h gave rise to an interesting discovery of an unidentified thermal event at 92°C prior to either melting or dehydration of T h.

Restricted access
Journal of Thermal Analysis and Calorimetry
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 phase transitions were

Restricted access

of picoseconds. On cooling, several phase transitions take place in these compounds [ 7 – 11 ]. For example, [Ni(NH 3 ) 6 ](NO 3 ) 2 displayed four low temperature phases [ 8 – 10 ]. The phase transition at T C1 , associated with the largest change

Restricted access

]. Although several research groups have experimental and theoretically investigated the pressure induced phase transitions in TiN using different methods. For example, Zhao et al. [ 13 ] investigated the behavior of TiN using axial X-ray diffraction under

Restricted access

Abstract  

Differential scanning microcalorimetric measurements on phase transitions in water-oil-surfactant mixtures are presented, demonstrating that this method is highly sensitive towards small heat changes connected with structural transitions in the samples. The values for the latent heat of phase transitions are determined and the results are compared with predictions from mean field theory, emphasizing the role calorimetric experiments can play to identify the most important contributions to the free energy describing the mixtures. Doing this, the present status of the understanding of temperature dependent phase transitions in microemulsions is reviewed.

Restricted access

Using an ac calorimetric method, detailed behaviour of the heat capacity in dipalmitoyl-phosphatidylcholine-cholesterol system was studied in the cholesterol concentration less than 5 mol%. It was revealed that the heat capacity near the main transition was composed of at least four anomalies, i.e., multipeak took place in the heat capacity. This fact indicates that a simple theory explaining coexistence of two phases in two component systems does not work in the multipeak region. Then, relation between the multipeak heat capacity and the change of the ripple structure with the cholesterol concentration should be taken into account, when we consider thermodynamical behaviour of the systems.

Restricted access

has been investigated for almost two decades and its ambient and sub-ambient phases have been well characterized: it has an orthorhombic structure with space group Fdd 2 below its ferro-paraelectric phase transition at T c = −126 °C, and a

Restricted access

properties and phase transition temperatures of (NH 4 ) 2 Co(SO 4 ) 2 ·6H 2 O crystals have not previously been reported. Further, some questions about Tutton salts are still open, especially those related to the nature of their structural changes and their

Restricted access

Abstract  

Phase transitions in ternary caesium lead bromide (CsPbBr3) were studied by means of DSC, TMA and high temperature X-ray diffraction. The samples were prepared from the solution by water evaporation and from the melt. on the DSC curves as well as on the temperature dependence of the lattice constants of CsPbBr3 only two effects were found belonging to the earlier published phase transitions at 88 and 130C and no further effects. Linear thermal expansion coefficient α of individual CsPbBr3 modifications were calculated from both TMA and high temperature X-ray diffraction. The structural parameters of the room temperature orthorhombic phase were refined and the results are presented. CsPbBr3 prepared from the solution contained about 10% of CsPb2Br5 and so the DSC curve of pure CsPb2Br5 was also measured and an effect at a temperature of 68.5C was found.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: G. Wolf, E. Königsberger, H. Schmidt, L.-C. Königsberger, and H. Gamsjäger
Restricted access