Thermal phases transformation

The maximum stress is obtained after each cycle and so no stress relaxation occurs. Note that the deflection measurements start with a dried membrane which already shows a certain deflection which is equivalent to a tensile stress level of 30 0 MPa. It is not clear at the moment whether it is allowed to sum up these two contributions or that the drying stress relaxes during heating and is replaced by stresses originating in the phase transformation/thermal mismatch processes. In any case when summing up is allowed the final stress in the y-alumina after cooling down is not greater than 30 MPa in the other case it is zero. 

Freedom from phase transformations (thermal and/or irradiation-induced)... 

V.V. Martynov, X-ray diffraction study of thermally and stress-induced phase transformations in single... 

It is evident that dedicated studies are required for each structure to optimize the template oxidation protocol. Many structures, in particular nonsiliceous, are thermally very sensitive [14, 15]. Calcination can result in a complete breakdown due to hydrolysis, redox processes, and phase transformations. The removal of templates in those systems is critical, making the development of mild detemplation techniques necessary [16]. 

The existence of more than one crystal phase for a given material, and the fact that only one form can be the most stable, naturally leads to studies of the interconversion between the various phases. Most often, such phase transformations are either by thermally initiated or solution mediated. 

The phase transformation relationships for the solvatomorphs of naproxen sodium have been reported [71], The dihydrate phase is obtained upon crystallization from water, and a monohydrate phase could be prepared by the dehydration of the dihydrate phase in a desiccator (RH = 0%) for two days. The anhydrate phase could be obtained from either the monohydrate or dihydrate by drying the substance in an oven at 120 °C for two hours. Thermal analysis data was used to demonstrate the existence of two types of water in the dihydrate phase, and that each could be removed at a characteristic temperature. 

Differential thermal analysis (DTA) consists of the monitoring of the differences in temperature existing between a solid sample and a reference as a function of temperature. Differences in temperature between the sample and reference are observed when a process takes place that requires a finite heat of reaction. Typical solid state changes of this type include phase transformations, structural conversions, decomposition reactions, and desolvation processes. These processes may require either the input or release of energy in the form of heat, which in turn translates into events that affect the temperature of the sample relative to a nonreactive reference. 

Chemical solution deposition (CSD) procedures have been widely used for the production of both amorphous and crystalline thin films for more than 20 years.1 Both colloidal (particulate) and polymeric-based processes have been developed. Numerous advances have been demonstrated in understanding solution chemistry, film formation behavior, and for crystalline films, phase transformation mechanisms during thermal processing. Several excellent review articles regarding CSD have been published, and the reader is referred to Refs. 5-12 for additional information on the topic. Recently, modeling of phase transformation behavior for control of thin-film microstructure has also been considered, as manipulation of film orientation and microstructure for various applications has grown in interest.13-15... 

TG analysis also represents a powerful adjunct to DTA or DSC analysis, since a combination of either method with a TG determination can be used in the assignment of observed thermal events. Desolvation processes or decomposition reactions must be accompanied by weight changes, and can be thusly identified by a TG weight loss over the same temperature range. On the other hand, solid-liquid or solid-solid phase transformations are not accompanied by any loss of sample mass and would not register in a TG thermogram. 

In another study, thermodiffractometry was used to study phase transformations in mannitol and paracetamol, as well as the desolvation of lactose monohydrate and the dioxane solvatomorph of paracetamol [56]. The authors noted that in order to obtain the best data, the heating cycle must be sufficiently slow to permit the thermally induced reactions to reach completion. At the same time, the use of overly long cycle times can yield sample decomposition. In addition, the sample conditions are bound to differ relative to the conditions used for a differential scanning calorimetry analysis, so one should expect some differences in thermal profiles when comparing data from analogous studies. 

Using Differential Scanning Calorimetric and Roentgen-phase analyses methods it has been established that synthesized polymers are amorphous systems. Thermal (phase) transformation temperatures of synthesized polymers have been determined. Thermooxidation stability of the synthesized polymers has been studied. There was shown that their thermooxidation stability exceeded the analogical characteristic of polyorganocarbosiloxanes. 

Various in situ methods require post-treatments to induce crystallization or phase transformation. In some cases, however, the required temperatures for these treatments may be close to or even higher than those for the thermal oxidation of the nanocarbons themselves. Furthermore, it has been shown that the oxidation temperature of CNTs can be drastically reduced to as low as 330 °C, when coated with reducible metal oxides such as Bi203 [180], This process is thought to occur via a Mars van Krev-elen mechanism and may severely reduce the potential operating temperatures for various applications such as fuel cells. 

Based on DSC and TGA experiments in combination with XRD examination and comparison with thermal events observed by other authors [173,174,178,183] who also investigated the thermal behavior of Mg(BH )j we proposed the following scheme of phase transformations taking place during milling and subsequent thermal experiments [175] ... 

I. Miroshnyk, L. Khriachtchev, S. Mirza, J. Rantanen, J. Heinamaki and J. Yliruusi, Insight into thermally induced phase transformations of erythromycin A dihydrate, Cryst. Growth Des., 6, 369-374 (2006). 

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