Activation Energy For Crystal Growth Research Articles

Effect of Alkali Oxides on Crystallization in CaO–SiO2–CaF2 Glasses

In the initial solidification stage in continuous steel casting, controlled crystallinity of the slag film is essential for regulating the horizontal heat flux from the strand to the mold. The effects of alkali oxides on the formation of cuspidine 13CaO·2SiO 2 ·CaF 2 ), which is the primary crystalline phase in the flux film in CaO-SiO 2 -CaF 2 -M 2 O glasses (M=Li, Na, K), were investigated in both isothermal and heating conditions. Addition of alkali oxides enhances crystallization of cuspidine by lowering the glass transition temperature and lowering the apparent activation energy of crystal growth. However, single excess addition of alkaline oxide (M 2 O) hinders the formation of cuspidine as CaF 2 is substituted by M 2 O.

Dependence of Apoferritin Crystal Growth on Temperature and Cadmium Concentration

Static light scattering and multiwell microbatch crystallization experiments have been used to determine how apoferritin crystal growth kinetics and final crystal size depend on temperature, pH, and cadmium concentration. The experiments were conducted on a linear thermal gradient covering a range from 30 to 40 °C. Crystal growth was monitored in situ under a microscope without disturbing the thermal environment. A dependence of apoferritin crystal formation and growth on temperature and cadmium concentration was observed. The range of cadmium concentrations that resulted in apoferritin crystal growth was evaluated and found to be consistent with the osmotic second virial coefficients determined via static light scattering. For the domain of conditions where apoferritin crystal formation occurred, the initial molar growth rate of apoferritin crystals increased linearly with temperature. It was observed that increasing cadmium concentration decreased the dependence of the final crystal size on temperature. The measured dependence of growth kinetics on temperature allowed the estimation of an activation energy for crystal growth. By comparing the value of this activation energy with that for nucleation (obtained from the literature), it became possible to explain the observation of larger, but fewer, apoferritin crystals at higher temperatures, which has also been reported in the literature for other proteins.

Influence of capping layers on the crystallization of doped SbxTe fast-growth phase-change films

Isothermal crystallization of doped SbxTe fast-growth phase-change films, with and without capping layers, was investigated using transmission electron microscopy, which provided direct and quantitative information on nucleation and growth processes separately. Two types of amorphous dielectric layers, ZnS–SiO2 and GeCrN, were used for sandwiching the SbxTe films to form typical trilayer stacks, which are the active part in applications. The nucleation and growth parameters of SbxTe films were found to be influenced by the dielectric capping layers. The crystal growth rate is temperature dependent and it reduces when the film is sandwiched between the dielectric layers. The reduction in growth rate differs with the capping layer type. The capping layer influence on the growth rate is pronounced at lower temperatures ∼160°C, but tends to vanish at higher temperatures ∼200°C. The activation energy for crystal growth is 2.4±0.3eV for an uncapped film and it increases ∼40% when the capping layers, GeCrN or ZnS–SiO2, are added. A temperature and time dependent nucleation rate is found and it is accelerated ∼1.7 times by GeCrN layers, whereas it is retarded ∼5 times by ZnS–SiO2 layers. The activation energy for crystal nucleation is 6.1±0.4eV for an uncapped film and it is not noticeably altered by the capping layers. These variations observed in the crystallization kinetics are attributed to variations in interface energy between the phase-change film and the capping layers or vacuum and the confinement effect by the capping layers on the phase-change film.

Crystallization kinetics and thermal stability of the Zr 60Al 7.5Cu 17.5Ni 10Si 4B 1 amorphous alloy studied by isothermal differential scanning calorimetry and transmission electron microscopy

The Zr 60Al 7.5Cu 17.5Ni 10Si 4B 1 (numbers indicate at.%) amorphous alloy was selected for an investigation of its crystallization kinetics and thermal stability because of its high activation energy of 370 kJ/mol for crystallization and its extended incubation time during isothermal annealing in the supercooled temperature region. The crystallization behavior and microstructure development during isothermal annealing were examined by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy (TEM). When annealing the Zr 60Al 7.5Cu 17.5Ni 10Si 4B 1 alloy isothermally at 714 K, Zr 2Cu crystals with average size about 5 nm were first observed at the early stage of 1% crystallization by TEM. The Zr 2Cu crystal size increases with annealing time, then reaches an average size of about 25 nm at the stage of 72% crystallization. In addition, the grain growth time as a function of the cube of particle size of the Zr 2Cu type crystalline phases presented a good linear relationship. This indicates that the crystal growth of the Zr 60Al 7.5Cu 17.5Ni 10Si 4B 1 alloy is a thermally activated process. The activation energy for growth of Zr 2Cu particles in the Zr 60Al 7.5 Cu 17.5Ni 10Si 4B 1 amorphous alloy is found to be 210 ± 25 kJ/mol. The lower activation energy of crystal growth during crystallization in comparison with 440 kJ/mol for crystallization in Zr 65Cu 35 corresponds to the rearrangement of other smaller atoms in the glass, such as Al or Si (compare to Zr).

Effect of silicon dioxide on crystallization and melting behavior of polypropylene

AbstractThe crystallization and melting behavior of isotactic polypropylene (iPP) and polypropylene copolymer (co‐PP) containing silicon dioxide (SiO2) were investigated by differential scanning calorimeter (DSC). SiO2 had a heterogenous nucleating effect on iPP, leading to a moderate increase in the crystallization temperature and a decrease in the half crystallization time. However, SiO2 decreased the crystallization temperature and prolonged the half crystallization time of co‐PP. A modified Avrami theory was successfully used to well describe the early stages of nonisothermal crystallization of iPP, co‐PP, and their composites. SiO2 exhibited high nucleation activity for iPP, but showed little nucleation activity for co‐PP and even restrained nucleation. The iPP/SiO2 composite had higher activation energy of crystal growth than iPP, indicating the difficulty of crystal growth of the composite. The co‐PP/SiO2 composite had lower activation energy than co‐PP, indicating the ease of crystal growth of the composite. Crystallization rates of iPP, co‐PP, and their composites depended on the nucleation. Because of its high rate of nucleation, the iPP/SiO2 composite had higher crystallization rate than iPP. Because of its low rate of nucleation, the co‐PP/SiO2 composite had lower crystallization rate than co‐PP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1889–1898, 2006

The glass to NZP crystal transformation in a mixed alkali germano-phosphate glass matrix

A mixed alkali germano-phosphate glass composition (Li0.5Na0.5Ge2(PO4)3) has been prepared and characterized. The crystallization mechanism of a NZP-type phase, the nucleation rate and the non-isothermal kinetic parameters have been studied by differential thermal analysis (DTA).The plot of the DTA peak height versus the glass particle size has shown a great tendency for surface crystallization. The nucleation rate type curves have given a maximum at 465±2°C and confirmed that nucleation was instantaneous at this temperature. Furthermore, the average value of the Avrami exponent (5.4±0.4) has revealed a tri-dimensional growth controlled by the development of the glass–crystal interface with a decreasing nucleation rate in the temperature range explored. From non-isothermal experiments, the apparent activation energy for the overall crystallization phenomenon has been founded in the range 260–273kJ/mol whereas the activation energy for crystal growth was 488±6kJ/mol.

Synthesis, characterization and devitrification behaviour of an yttrium containing boroaluminate glass

The glass forming region in the B2O3-Al2O3-Y2O3 composition diagram has been determined by a melting and quenching procedure at temperatures up to 1800°C. Different physical characteristics (density, coefficient of thermal expansion, glass transition and crystallization peak temperatures) have been determined for a 35B2O3-40Al2O3-25Y2O3 glass composition (in mol.%). By using a predictive model and some NMR structural data, different elastic moduli (Young's modulus, bulk modulus, shear modulus and Poisson's ratio) have been calculated. The devitrification behaviour has also been studied. Internal crystallization is the dominant mechanism and a new (Y, Al)BO3 ternary phase has been characterized by X-ray powder diffraction. The temperature and time nucleation dependence have been determined from DTA experiments as well as the crystallization kinetics (i.e. the Avrami exponent and the activation energy for crystal growth).

Crystallization kinetics of magnetic glass–ceramics prepared by the processing of waste materials

The objective of the present investigation was to study the feasibility of conversion of an intimate mixture of blast furnace slag and blast furnace flue dust generated by a single industrial company into magnetic glass–ceramic product. Blast furnace slag (BFS) and blast furnace flue dust (BFD) are generated at a rate of 300,000 and 30,000 tons/year, respectively, from iron and steel factory. The crystallization mechanisms of a composition containing BFS and BFD in a 50/50 proportion were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The crystallization temperature was found to vary from 900 to 1100 °C and two phases appeared in the crystallized samples: pyroxene Ca(Mg, Fe, Al)(Si, Al) 2O 6 and magnetite/maghemite. Heating rate and particle sizes effects on crystal growth of powdered samples were studied by DTA. The apparent activation energy of crystal growth using the particle size 180–315 μm was determined to be 355 and 329 kJ/mol for the first and second peak, respectively. The presence of sharp and broad crystallization peaks indicate simultaneous surface and internal crystallization mechanism. Good wear resistance and chemical durability particularly in alkaline environment, combine with good hardness and magnetic properties make this glass–ceramic material potentially useful for various industrial applications.

Effect of nucleation temperatures and time on crystallization behavior and properties of Li 2O–Al 2O 3–SiO 2 glasses

The crystallization behavior of Li 2O–Al 2O 3–SiO 2 glasses samples nucleated at different temperature and time (745 °C/2 h, 745 °C/6 h and 760 °C/6 h) was investigated by DTA, XRD and SEM. After nucleated at 745 °C for 2 and 6 h, the Avrami constants for the glass samples were 3.5–3.6 and activation energies of crystal growth were 276 ± 3 and 280 ± 5 kJ mol −1. The Avrami constant was 2.8 and activation energy of crystal growth was 302 ± 6 kJ mol −1 for samples nucleated at 760 °C for 6 h. The crystallized phase was identified as h-quartz solid solution and SEM observations indicated that glass–ceramic samples have fine grained microstructure which indicates bulk crystallization. With increasing nucleation temperature to 760 °C, the grain size increased and the values of flexural strength, hardness and fracture toughness decreased.

In situ Transmission Electron Microscopy Study of the Crystallization of Fast-growth Doped SbxTe Alloy Films

Crystallization of amorphous thin films composed of doped SbxTe with x = 3.0, 3.6, and 4.2 and constant dopant level was studied by in situ heating in a transmission electron microscopy. Magnetron sputtering was used to deposit 20-nm-thick films sandwiched between two types of 3-nm-thick dielectric layers on 25-nm-thick silicon-nitride membranes. One type of dielectric layer consists of ZnS–SiO2 (ZSO), the other of GeCrN (GCN). Crystallization was studied for temperatures in-between 150 and 190 °C. The type of dielectric layer turned out to strongly influence the crystallization process. Not only did the nucleation rate appear to depend sensitively on the dielectric layer type, but also the growth rate. The velocity of the crystalline/amorphous interface is about 5 times higher for the x = 4.2 film than for the x = 3.0 film if ZSO is used. In case of GCN, the interface velocity is about 2 times higher for the x = 4.2 film than for the x = 3.0 film. The activation energy for crystal growth is not significantly dependent on the Sb/Te ratio but is clearly different for ZSO and GCN—2.9 eV and 2.0 eV, respectively. The incubation time for the crystal nuclei formation is longer for ZSO than for GCN. Although the effects of the Sb/Te ratio and the dielectric layer type on the growth rates are strong, their effects on the nucleation rate are even more pronounced. A higher Sb/Te ratio results in a lower nucleation rate and the use of GCN instead of ZSO leads to higher nucleation rates.

Crystallization Kinetics of the LiBO2–Nb2O5 Glass Using Differential Thermal Analysis

The crystallization kinetics in the glass system (100−x)LiBO2−xNb2O5 (5≤x≤20, in molar ratio) prepared via the conventional metal‐plate quenching technique have been studied by isothermal and non‐isothermal methods using differential thermal analyses. X‐ray powder diffraction studies carried out on heat‐treated (500°C) glasses reveal the evolution of lithium niobate crystalline phase along with a minor phase of LiBO2. The exponent n in the Jhonson–Mehl–Avrami (JMA) equation applied to the isothermal process is 2.62, which is in excellent agreement with that obtained under the non‐isothermal process (2.67). The activation energies for crystal growth obtained from JMA equation under isothermal condition, modified Ozawa and Kissinger equations under non‐isothermal conditions, are 293, 311, and 306 kJ/mol, respectively.

Growth mechanisms of CuSCN films electrodeposited on ITO in EDTA-chelated copper(II) and KSCN aqueous solution

Electrodeposition of β-CuSCN films was investigated on transparent conducting ITO substrates in an aqueous electrolyte containing EDTA-chelated Cu(II) and KSCN. It has been observed that the instability of CuSO 4 and KSCN aqueous solution without EDTA is due to the formation of Cu(SCN) 2 precipitation, which can transform into CuSCN and (SCN) x at room temperature. Research results illuminate that the deposited film at −0.5 V versus Ag/AgCl sat at 298 K is uniform and dense and composed of nanocrystals. The film is p-type with stoichiometric excess of SCN and a direct transition gap of 3.7 eV. Deposition mechanisms of CuSCN films at varied temperatures are studied based on the proposed energetic model. At or below room temperature, the electron quantum tunnel through deposition layer is predominant at the very beginning. However, the growth is limited when the thickness of CuSCN film reaches the size comparable to the diffusion length of electrons. Above room temperature, the thermal activation of surface states plays an important role in the continuous growth of large crystals through holes transport in the valence band. The calculated activation energy for crystal growth is 0.5 eV.

Growth Phenomena of Single Crystals of Naphthalene in Supercritical Carbon Dioxide

The growth behavior and growth rates of naphthalene single crystals in supercritical carbon dioxide were observed and measured at temperatures 307.7, 312.7, and 317.7 K and pressures 15, 17.5, and 20 MPa to highlight the behavior of crystal growth in the supercritical phase. The morphology of naphthalene crystals did not change during the steady growth in the supercritical phase. The crystal growth rates from the supercritical phase were almost independent of pressure and higher with increasing temperature or supersaturation and were approximately between 4 × 10-9 and 2.5 × 10-8 m s-1 as supersaturation varied from 0.018 to 0.073, values which were found to be intermediate between those from a liquid or vapor phase at the same supersaturation. The activation energy for crystal growth from the supercritical phase was determined as 70.9 kJ mol-1, which showed that the crystal growth mechanism in the supercritical phase is almost similar to that in the liquid or vapor phase and that the growth rates were governed by the surface integration step.

Hydrothermal Synthesis of Submicrometer α‐Alumina from Seeded Tetraethylammonium Hydroxide‐Peptized Aluminum Hydroxide

Submicrometer α‐alumina powder was successfully synthesized from seeded aluminum hydroxide peptized with tetraethylammonium hydroxide (TENOH) and hydrothermally treated at 200°C, using α‐alumina particles as seeds. The powders were characterized by XRD, SEM, DTA‐TG, and BET analyses. Results showed that seeding could greatly enhance the transition to α‐alumina at 200°C without formation of other transient alumina phases. α‐Alumina with some amount of boehmite formed in the seeded samples, whereas boehmite was the exclusive phase formed in the nonseeded sample. The morphology of α‐alumina embedded in the boehmite matrix for the seeded samples suggests a direct transition from aluminum hydroxide to α‐alumina without the formation of transient alumina phases. The formation of α‐alumina in the seeded samples at temperatures as low as 200°C could be attributed to a favored nucleation in the TENOH‐peptized aluminum hydroxide and to the subsequent hydrothermal treatment that supplies the necessary activation energy for crystal growth. Transition of boehmite to α‐alumina in the hydrothermally treated samples with low‐seed contents was significantly promoted by heat‐treating the samples at 500°C.

Activation energy for crystal growth in stoichiometric CaAl2Si2O8 and Ca2Al2Si2O9 glasses

Activation energy for crystal growth in stoichiometric CaAl2Si2O8 and Ca2Al2Si2O9 glasses

Kinetic phenomena in non-crystalline materials studied by thermal analysis

Abstract The structural relaxation and viscosity behavior of Ge38S62 glass has been studied by thermomechanical analysis. The relaxation response to any thermal history is well described by the Tool-Naraynaswamy-Moynihan model. The apparent activation energy of structural relaxation is very close to the activation energy of viscous flow (Eη=47812 kJ mol-1). However, the activation energy of crystal growth obtained by optical microscopy is about one half of this value. Similar result has been obtained from isothermal DSC measurement (Ea=22020 kJ mol-1). The kinetic analysis of these data reveals interface controlled crystal growth with zero nucleation rate.

Crystallization behaviour of glasses produced from fly ash

Abstract The crystallization behaviour of fly ash based glass samples annealed at 600°C for 2 and 10 h was investigated by DTA, XRD and SEM. On the basis of DTA, nucleation experiments of two glass samples were carried out at 680 and 687°C for 5 h and crystallization experiments were performed at 924 and 892°C for 20 min. The Avrami constant for both glass samples was calculated as 4, which indicates bulk crystallization, predicted by the Ozawa equation. Using the modified Kissinger equation, activation energies of crystal growth were determined as 318 and 312 kJ/mol for samples annealed at 2 and 10 h, respectively. Single peak analysis technique proved that the activation energy is independent of DTA heating rate. SEM observations indicated that the produced glass–ceramic samples have fine grained microstructure. The crystallized phase was identified as diopside [Ca(Mg,Al)(Si,Al)2O6] by X-ray diffraction analysis. The results of Vickers microhardness tests showed that the hardness values of the produced glass–ceramic samples decreased with the increase in holding time at the annealing temperature.

Isothermal and non-isothermal crystallization kinetics of zinc-aluminosilicate glasses

Isothermal and non-isothermal differential thermal analysis (DTA), and X-ray diffraction (XRD) were used to study the nucleation and crystallization behavior of multicomponent Li 2O–ZnO–Al 2O 3–B 2O 3–SiO 2 glasses with ZrO 2 and TiO 2 as nucleating agents. The temperature of maximum nucleation rate for investigated glasses was found to be 1028 K. The crystallization of two phases (mullite s.s. and gahnite) occurs in a narrow temperature and time interval, respectively, therefore, the DTA curves are characterized by the superposition of exothermic peaks. Recently derived mathematical models have been applied for resolving the overlapping. The models enabled establishing the kinetic parameters for crystal growth of individual phases. The activation energies for crystal growth were found to be in the range of 459–471 and 368–386 kJ mol −1 for mullite and gahnite, respectively. Avrami exponent n reveals three-dimensional growth of both phases.

Influence of the nucleation time-lag on the activation energy in non-isothermal crystallization

In the present work, the influence of the nucleation time-lag on the non-isothermal glass crystallization is discussed. Differential thermal analysis (DTA) results of an iron-rich glass nucleated by Cr 2O 3 were obtained at different heating rates. The activation energy of crystallization, E c, and the Avrami parameter, m, estimated by Kissinger's and Ozawa's equations were shown to be dependent on the heating rate. The value of E c, obtained at 2.5, 5 and 7.5 K/min heating rates was calculated as 299 kJ/mol, while the value of E c, obtained at 10, 15 and 20 K/min was as 499 kJ/mol. The value of m for `low' and `high' heating rates were 2.57 and 1.45, respectively. The results were interpreted on the basis of the non-steady state nature of the nucleation process. It was assumed that at high heating rates no nucleation takes place and the crystals grow on a existing fixed number of nuclei; the activation energy of crystal growth, E g, can be estimated by applying the Kissinger equations. At low heating rates nucleation occurs and the number of nuclei formed is influenced by the heating rate; E g can be estimated by the Matusita and Sakka equation.

Thermal and devitrification behavior of (2.5− x)CaO·( x/3)In 2O 3·2SiO 2 glasses

A study of the influence of the substitution of In 2O 3 for CaO at constant O/Si ratio on thermal properties and non-isothermal devitrification of 2.5CaO·2SiO 2 is reported. Differential thermal analysis (DTA) and X-ray diffraction analysis were used. The X-ray diffraction pattern of the crystallized In 2O 3 base glass shows that the α-CaO·SiO 2, that should be stable only above 1125°C, forms in the temperature range 900–1000°C. A new ternary crystalline phase whose reflections are not reported in the JCPDS cards, was found to form during crystallization of the glass. As their intensity progressively increases with substitution, they should refer to a In 2O 3 rich phase. The glass transformation temperature T g results can be explained on the basis of the increased structural rigidity when Ca 2+ ions are substituted by In 3+ with the formation of stronger bond to the oxygen, while crystal growth activation energy ( E c) values can be explained considering the increasing of the crystallization temperature T p. Devitrification involves a mechanism of surface nucleation; surface nuclei behaving as bulk nuclei in samples that soften and sinter before devitryfing.