Investigation DSC and XRD on the Crystallization Kinetics in the Phosphate Li2O−Li2WO4−TiO2−P2O5 Glassy Ionic System

This work aims to investigate the prepared glasses within the 20Li2O−(50−x)Li2WO4−xTiO2−30P2O5 system, with 0≤x≤15 mol%. The bonds constituting the framework of these glasses were studied by Raman spectroscopy. The data analysis of the chemical durability showed that the dissolution rates depend on the composition of each glass. Thermal analysis by DSC technique was used to determine the activation energy of crystallization, it found in the glass of composition (x= 5) that Ec= 184.482 kJ/mol. The determinate Avrami parameter is around 1.7 which allows suggesting the mechanism is surface crystallization. The crystallization process of the prepared glasses is carried out by heating samples at 550°c for 4 hours and 12 hours. The crystallized phases are identified by XRD. The results of X−ray diffraction analysis confirm that TiO2 acts mainly as network forming units. The crystalline phases Li2WO4 (JCPDS# 01−072−0086) and (JCPDS# 01−087−0409) are formed during the crystallization process. The formation of these crystalline phases into the glasses depends on the time of heating at fixed crystallization temperature. FTIR spectra of the glass–ceramics show nearly the same IR vibrational modes as their parent glasses.

Generalised kinetics of overall phase transition useful for glass crystallisation when assuming non-isothermal conditions

The modelling of reaction kinetics is a fashionable subject of publications. We developed an analogue of the KJMA equation under non-isothermal conditions α(T)=1−exp(−(T/θ)N) that describes the dependence of degree of transformation α(T) at a constant rate, q, of heating with characteristic temperature θ(q) and power N, proportional to the Avrami parameter, n. This equation is valid even when the activation energy of the process is not constant. We demonstrate that reliable information about the activation energy is obtained when the experimental data are plotted in coordinates: logq (heating rate) against logTp (peak temperature).

Effect of Grain Size Distribution on Recrystallisation Kinetics in an Fe-30Ni Model Alloy

This paper discusses the role of grain size distribution on the recrystallisation rates and Avrami values for a Fe-30 wt. % Ni steel, which was used as a model alloy retaining an austenitic structure to room temperature. Cold deformation was used to provide uniform macroscopic strain distributions (strains of 0.2 and 0.3), followed by recrystallisation during annealing at 850–950 °C. It was shown that the Avrami parameter was directly related to the grain size distribution, with a lower Avrami exponent being seen for a larger average and wider grain size distribution. A method to predict the Avrami exponent from the grain size distribution was proposed. In situ heating in an SEM with EBSD showed the recrystallisation kinetics to be affected by differences in stored energy and nucleation in the different grain sizes supporting the proposed relationship.

Preparation and Properties of CaO-MgO-Al2O3-SiO2 Glass-Ceramics from Granite Wastes

Granite process industry generates a large amount of wastes, which pollute and damage the environment. This work aims to investigate the possibilities of using the granite sawing wastes in the production of glass-ceramics. Granite wastes with other components were used to prepare glass-ceramics. The crystallization behavior and properties of the glass-ceramics were investigated. The results showed that the activation energy for crystallization (Ec) was 463 kJ/mol and Avrami parameter (n) was 2.68, suggested a two dimension crystal growth mechanism. The main crystalline phase of all the obtained glass-ceramics was diopside. With the increase of heat treatment temperature, the diffraction peak intensity of diopside firstly increased and then decreased slightly. The minor crystalline phases spinel and Mg4Al2Ti9O25 were observed above 970°C. When heated at 970 °C for 1h, the sample exhibited the highest Vicker's hardness and bending strength values, 7.3 GPa and 151 MPa, respectively. And the glass-ceramics showed better acid resistant than alkali resistant.

Crystallisation Kinetics of aβ-Spodumene-Based Glass Ceramic

LZSA (Li2O-ZrO2-SiO2-Al2O3) glass ceramic system has shown high potential to obtain LTCC laminate tapes at low sintering temperature (<1000°C) for several applications, such as screen-printed electronic components. Furthermore, LZSA glass ceramics offer interesting mechanical, chemical, and thermal properties, which make LZSA also a potential candidate for fabricating multilayered structures processed by Laminated Objects Manufacturing (LOM) technology. The crystallization kinetics of an LZSA glass ceramic with a composition of 16.9Li2O⋅5.0ZrO2⋅65.1SiO2⋅8.6Al2O3was investigated using nonisothermal methods by differential thermal analysis and scanning electronic microscopy. Apparent activation energy for crystallization was found to be in the 274–292 kJ⋅mol−1range, and an Avrami parameternof 1 was obtained that is compared very favorably with SEM observations.

Nonisothermal Crystallization Kinetics of HDPE/UHMWPE/n-HA Composites

The influence of compatibilizer and dispersant on the nonisothermal crystallization behavior of HDPE/UHMWPE/HA is investigated here by differential scanning calorimetry (DSC). It has been analyzed by Jeziorny method. For different composites, the Jeziorny plots shows the linear portion. The small deviations from linearity only appear at higher relative crystallinity because of the secondary crystallization. The value of Avrami parameter n is between 2.7 and 3.5. At the same temperature, Zcand Sibecome bigger after adding compatibilier and dispersant while tmax is decreasing. The activation energy of crystallization also have been studied by Kissinger equation. The result shows that the addition of compatibilizer and dispersant can decrease the activation energy. In addition, the compatibilizer and dispersant also improve the mechanical properties of composites.

Crystallization Kinetics in Liquid Crystals with Hexagonal Precursor Phases by Calorimetry

Design and characterization of Schiff based liquid crystalline nO.m compounds exhibiting hexagonal smectic phases are reported. Crystallization kinetics investigations are carried out in the liquid crystals (LCs) exhibiting hexagonal ordered orthogonal and tilted precursor LC phases by calorimetry. The Avrami theory is referred and results are analyzed. Influence of molecular ordering, structure, and dimensionality of the LC precursor phase on kinetics is studied. Effect of shape and flexibility of the molecule for nucleation and growth processes is investigated. Varying rate of kinetics reflects upon the transit of the system from constant type to independent type of nucleation. The trends in the Avrami parameter b and exponent n suggest sporadic nucleation. Crystal growth is interpreted as heterogeneous permeation of layered domains (or aggregates) formed by needle shaped calamitic molecules. Calorimetric observations at different crystallization temperatures CT and hold time t infer diffusion mediated crystallization

DSC Kinetic Studies on Glass Ceramic System Crystallizing Indialite (Mg2Al4Si5O18)

A formulation belonging to the CaO-MgO-SiO2-Al2O3 system was characterized in order to found a monophase system based on indialite (Mg2Al4Si5O18), known for its good mechanical characteristics. The classical kinetic studies performed in the muffle kiln show an initial surface crystallization followed from immediate bulk crystallization. The kinetic results obtained via differential scanning calorimetry (DSC) were treated with isothermal method, Kissinger, Ozawa and Matusita and Sakka approaches and compared. These results partially explain the macroscopic behavior, because the studies performed on sample of different grain size show a typical trend for a surface crystallization, while the value of Avrami parameter calculated from the kinetics is 2.3, demonstrating a bi-dimensional crystallization. The value of crystallization energy EC calculated with the isothermal method is 517.8 kJmol-1 and the comparison with nonisothermal studies suggests bulk crystallization to occur with an increasing number of nuclei and a two-dimensional growth of crystals.