Activation Energy For Crystal Growth Research Articles

A Kinetic Study on Crystallization in TiO2-SiO2-CaO-Al2O3 Glass under Nucleation Saturation Conditions for the High Value-Added Utilization of CaO-SiO2-Based Solid Wastes.

A kinetic study of the non-isothermal crystallization of CaO-SiO2-Al2O3-TiO2 glass was carried out using the Matusita-Sakka equation and differential thermal analysis. As starting materials, fine-particle glass samples (<58 µm), case defined as ''nucleation saturation'' (i.e., containing such a large number of nuclei that the nucleus number is invariable during the DTA process), became dense bulk glass-ceramics through heat treatment, demonstrating the strong heterogeneous nucleation phenomenon at the juncture of particle boundaries under "nucleation saturation" conditions. Three types of crystal phase are formed during the heat treatment process: CaSiO3, Ca3TiSi2(AlSiTi)3O14, and CaTiO3. As the TiO2 content increases, the main crystal shifts from CaSiO3 to Ca3TiSi2(AlSiTi)3O14. The EG values (activation energy of crystal growth) are in the 286-789 kJ/mol range. With increasing TiO2, EG initially decreases (the minimum appears at 14% TiO2), and then, increases. When added within 14%, TiO2 is shown to be an efficient nucleating agent that promotes the growth of wollastonite in a two-dimensional mechanism. As TiO2 further increases to exceed 18%, it is no longer just a nucleating agent but becomes one of the major components in the studied glass, so, in turn, it undermines the crystallization of wollastonite by forming Ti-bearing compounds, resulting in a tendency toward surface crystallization and higher activation energy of crystal growth. For glass samples with fine particles, it is important to note the "nucleation saturation" case for a better understanding of the crystallization process.

Investigation on crystal growth behavior of La0.8Sr0.2FeO3 nanopowders fabricated with different organic additions

The crystal growth behavior of the perovskite-type La0.8Sr0.2FeO3 nanopowders fabricated via sol–gel process was controlled by adjusting the addition of acetic acid (HAc) and ethanol. As a result, the La0.8Sr0.2FeO3 with a stable orthorhombic structure was fabricated with high ethanol content after heat treatment at 1200 °C. Based on the relationship between the crystal size and heat-treatment temperature, the crystal growth rate of La0.8Sr0.2FeO3 powders at the low-temperature stage was much larger than that at the high-temperature stage. Correspondingly, the activation energy for crystal growth of the La0.8Sr0.2FeO3 powders was increased firstly and then decreased with the increase of HAc or ethanol content in the raw solution, owing to different hydrolysis rates in the H2O/ethanol system. The lowest activation energy for crystal growth at the low-temperature stage ((15.25 ± 0.23)kJ/mol) and high-temperature stage ((5.74 ± 0.01)kJ/mol) were obtained by controlling the molar ratio of HAc/Metal ions with 4:1 and the volume ratio of ethanol/H2O with 3:1.

Crystal growth behavior and fluorescence properties of LaMgAl11O19:Eu3+ nano-powders prepared via sol-gel process

LaMgAl11O19:Eu3+ (LMA:Eu3+) nano-powders were prepared via sol-gel process by controlling the amount of ethanol and AcOH in the raw solution. With the addition of ethanol, the activation energy for crystal growth of LMA:Eu3+ nano-powders was decreased from 69.10 ± 3.74 kJ/mol to 57.95 ± 2.62 kJ/mol, while the lowest activation energy of 57.95 ± 2.62 kJ/mol was obtained with the water/ethanol volume ratio of 1:3 and the AcOH/metal ions molar ratio of 1:1. However, there is less influence on the phase composition and microstructure of the powders after adding the organic additives. The LaMgAl11O19:Eu3+ powders exhibit a group of orange-red emission peaks from D05→FJ7 (J = 0, 1, 2, 3, 4) of Eu3+ under the excitation of ultraviolet light with a wavelength of 254 nm.

Comparative Research on the Thermophysical Properties of Nano-Sized La2(Zr0.7Ce0.3)2O7 Synthesized by Different Routes.

La2(Zr0.7Ce0.3)2O7 has been regarded as an ideal candidate for the next generation of thermal barrier coatings (TBCs) due to its prominent superiority. In this paper, the nano-sized La2(Zr0.7Ce0.3)2O7 was synthesized using two different synthetic routes: sol-gel and hydrothermal processes. Various techniques were utilized to assess the differences in the relevant thermophysical properties created by the different synthetic methods. According to the investigations, both samples exhibited pyrochlore structures with an excellent thermal stability. The sample synthesized via the hydrothermal method showed a more uniform particle size and morphology than that obtained through the sol-gel technique. The former also possessed a better sinter-resistance property, a more outstanding TEC (thermal expansion coefficient) and thermal conductivity, and a larger activation energy for crystal growth than the latter. The micro-strain of both samples showed an interesting change as the temperature increased, and 1200 °C was the turning point. Additionally, relative mechanisms were discussed in detail.

Effect of B2O3, K2O and Li2O as modifiers on crystal phase transition and crystallite growth of TiO2 in calcination of titanyl sulfate

Thermal phase transformation and crystal growth in calcination of titanyl sulfate with addition of B2O3, K2O and Li2O have been studied, and the structure and morphology of TiO2 product has been characterized by XRD, SEM, TEM and size analyzer. It is found that B3+ ions being doped interstitially into crystal lattice of rutile TiO2 tend to form compound of TiB0.024O2 with TiO2, which leads to increase in unit cell volume and henceforth, an increase in growth rate of the crystal plane (110) or reduction in growth rate of crystal plane (001). Change in growth rate in different crystal planes contributes to development of the plate shape and rod shape microcrystals and improvement in grain sphericity. Doping of K2O tends to inhibit the transformation of crystal form and inhibit particle sintering at high temperatures mainly by adsorption of the dopants onto crystal plane (110) and plane (100) of rutile TiO2. Li2O, which is mainly adsorbed on the surface of rutile TiO2, is found to have a weak effect on crystal phase transformation. The apparent activation energy for crystal growth of rutile TiO2 doped with B2O3, K2O and Li2O has been calculated to be 73.16 ​kJ/mol, 103.21 ​kJ/mol, and 187.24 ​kJ/mol respectively.

Defect-mediated crystal growth from deeply undercooled melts

In this work, a strong correlation between the density of defected atom pairs at the crystal-liquid interface and the activation energy for crystal growth from deeply undercooled melts is established. Using molecular dynamics simulations we study the intermediate interstitial pairs at the crystal-melt interfaces of both BCC and FCC pure metals. It is found that the pairs have preferred orientations, and two important types of interstitial pairs at the interfaces are identified according to their orientations. We demonstrate that the relative amount of these two kinds of interstitial pairs varies greatly for different systems and dominates the activation energy for crystal growth. The dependence of local structure and energy on the orientation of the interfacial interstitial pairs are revealed and the connections of these features with crystal growth kinetics are disclosed.

Effects on the crystallite growth behavior of LaPO4 nanopowders and its mechanical properties

The effects of pH of the reaction solution and the concentration of phosphoric acid on the crystal growth behavior of LaPO4 crystallites were investigated and the mechanical properties of rare-earth phosphates were compared. As a result, the concentration of phosphoric acid of 10% was beneficial to the crystal growth of LaPO4 nanocrystalline. When the pH value of the reaction solution was 2, the size of LaPO4 crystallites increased gradually with the increasing reaction temperature, and the smallest crystallite size of 43.27 nm was obtained after heat-treatment at 1000 °C. Simultaneously, the activation energy for crystal growth of LaPO4 nanocrystalline was relatively lower (26.82 kJ mol−1). With the decreasing radii of rare-earth ions, the hardness, Young's modulus and fracture toughness of the bulk rare-earth phosphates exhibited a reduced tendency, resulted from the increase of porosity under the same preparation process.

Effect of organic additions on crystal growth behavior of La0.8Sr0.2MnO3 nanopowders prepared via sol–gel process

The effects of the addition of AcOH and ethanol on phase composition and crystal growth behavior of La0.8Sr0.2MnO3 nanopowders prepared via sol–gel process were investigated. As a result, the phase composition of final products was not affected by the addition of ethanol or AcOH in the raw solution. The activation energy for crystal growth was firstly decreased and then increased with the continuous addition of ethanol or AcOH, while it was obviously influenced by the content of AcOH. After the addition of AcOH, the activation energy for crystal growth was reduced from 26.60 kJ/mol to 23.59 kJ/mol, and then was gradually augmented to 39.75 kJ/mol with the continuous increase. Correspondingly, the crystallite size of final products was controlled to be 48.5 nm, and the lowest activation energy for crystal growth of La0.8Sr0.2MnO3 nanopowders was obtained with water as the solvent and the AcOH/Mn molar ratio of 1:2, which was beneficial to the crystallization of La0.8Sr0.2MnO3 grains.

An Insight into the Correlation between Chemical Composition Changes of Aluminum-Iron-Polyphosphate Glasses and Thermal Properties.

The present study aimed to investigate the influence of the gradual substitution of Fe2O3 by Al2O3 on the thermal properties of polyphosphate glasses. The conducted considerations based on differential scanning calorimetry (DSC) and heating microscopy thermal analysis provided much essential information about the correlation between glass chemical composition and its characteristic parameters, such as transformation temperature, specific heat, crystallization temperature, crystallization enthalpy, the activation energy of crystal growth, melting temperature, and Angell glass thermal stability. The obtained estimation of viscosity changes as a function of temperature could be very helpful for researchers to correctly plan the vitrification process and thus radioactive waste immobilization. A precise analysis of DSC curves and X-ray diffraction patterns revealed the possibility of crystallization process design in order to create materials with different levels of crystallinity and phase composition. The drawn conclusions allow choosing the glass with the optimal concentration of Al2O3 and Fe2O3, which ensures the relatively low melting temperature, viscosity, and glass crystallization ability, with application potential in nuclear waste immobilization.

Influence of particle size and manufacturing conditions on the recrystallization of amorphous Enzalutamide

Non-isothermal differential scanning calorimetry was used to study the influences of particle size and mechanically induced defects on the recrystallization kinetics of amorphous Enzalutamide. Enzalutamide prepared by hot melt extrusion and spray-drying was used as a model material. The recrystallization rate was primarily accelerated by the presence of the processing-damaged surface of the powder particles. The actual surface/volume ratio associated with decreasing particle size fulfilled only a secondary role. Interestingly, higher quench rate during the extrusion led to a formation of thermally less stable material (with the worse stability being manifested via lower activation energy of crystal growth in the amorphous matrix). This can be the consequence of the formation of looser structure more prone to rearrangements. The recrystallization kinetics of the prepared Enzalutamide amorphous materials was described by the two-parameter autocatalytic kinetic model. The modified single-curve multivariate kinetic analysis (optimized for the data obtained at heating rate 0.5 °C•min−1) was used to calculate the extrapolated kinetic predictions of long-term isothermal crystal growth. The predictions were made for the temperatures from the range of drug shelf-life and processing for each particle size fraction. By the combination of the mass-weighted predictions for the individual powder fractions it was possible to obtain a very reasonable (temperature-extrapolated) prediction of the crystallization rate for the as-prepared unsieved powdered amorphous Enzalutamide.

Crystal growth behavior and sintering-resistance property of nano-sized β-Yb2Si2O7 for environmental barrier coatings

In this article, as an attractive candidate of EBCs for SiC-based ceramic matrix composites, nano-sized β-Yb2Si2O7 was synthesized by hydrothermal method. The sintering-resistance property and crystal growth behavior of β-Yb2Si2O7 powders and compacted bodies were evaluated via various techniques. Quantity analyses demonstrate that β-Yb2Si2O7 was formed at about 1100 °C, and possessed well thermal stability at even higher temperatures. The determined coefficient of thermal expansion and thermal conductivity are 4.63 × 10-6 K-1 and 1.72 W m-1 K-1, respectively. The microstructures of compacted bodies under different temperatures reveal the critical temperature of anti-sintering is about 1400 °C. Based on different growth mechanisms, the activation energy of crystal growth (Q) can be segmented into two sections with a turning point of 1076 °C. Furthermore, the relative relationship between activation energy and sintering was bridged.

Crystallization kinetics of pentaerythritol tetranitrate (PETN) thin films on various materials

The nature of the crystal growth process in explosives can dramatically impact their safety and performance. Thin films are a commonly used tool for investigating the fundamental crystallization behavior in many systems, and the interfacial physics between a crystallizing species and the substrate can significantly affect many factors associated with the crystal growth process. In this work, atmospheric vapor deposition was used to prepare thin films of supercooled PETN droplets on the surfaces of copper, gold, and silicon. The gold and copper surfaces were prepared on silicon substrates using ultra-high vacuum vapor deposition. Crystallization of the supercooled PETN droplets was induced by scanning the surface of each substrate type with an atomic force microscope upon which crystallization occurred in the form of compact, circularly shaped dendrites reminiscent of spherulites. All three substrates were characterized relative to their respective surface roughness and surface energy. The surface energy was assessed from contact angle measurements with three liquids: water, ethylene glycol, and dodecane. High-resolution, time-lapse images of the crystal growth process were acquired under high magnification on each material surface, and the crystal growth rates were measured based on the radial distance of “ring” features that appeared in the crystal growth patterns after inducing changes in the substrate temperature. The growth rates were used to determine the Arrhenius activation energy of crystal growth on each surface, and the results indicate that there is a significant correlation between the surface energy and the crystallization behavior of the supercooled PETN droplets.

Kinetic Processes in Amorphous Materials Revealed by Thermal Analysis: Application to Glassy Selenium

It is expected that viscous flow is affecting the kinetic processes in a supercooled liquid, such as the structural relaxation and the crystallization kinetics. These processes significantly influence the behavior of glass being prepared by quenching. In this paper, the activation energy of viscous flow is discussed with respect to the activation energy of crystal growth and the structural relaxation of glassy selenium. Differential scanning calorimetry (DSC), thermomechanical analysis (TMA) and hot-stage infrared microscopy were used. It is shown that the activation energy of structural relaxation corresponds to that of the viscous flow at the lowest value of the glass transition temperature obtained within the commonly achievable time scale. The temperature-dependent activation energy of crystal growth, data obtained by isothermal and non-isothermal DSC and TMA experiments, as well as direct microscopic measurements, follows nearly the same dependence as the activation energy of viscous flow, taking into account viscosity and crystal growth rate decoupling due to the departure from Stokes–Einstein behavior.

A study of phase evolution and crystal growth for nano-sized monoclinic Y4Al2O9 as a novel thermal barrier coatings

Nano-sized monoclinic Y4Al2O9 was produced by sol-gel process as a novel potential candidate material for thermal barrier coatings. The thermal behavior, structural evolution of the products and the morphological characteristics of the compacted bodies were investigated by Thermogravimetric analysis and differential scanning calorimeter (TG-DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Field emission scanning electron microscopy (FESEM). Qualitative analyses indicate that monoclinic Y4Al2O9 was formed at about 1000 °C, and exhibited good phase stability throughout the annealing temperature ranging from 1000 °C to 1400 °C. The thermophysical properties of Y4Al2O9 ceramics were also evaluated compared with 8YSZ and La2Zr2O7. The determined activation energy of crystal growth is about 72.71 ± 0.31 kJ mol−1. Meanwhile, Y4Al2O9 represents low thermal conductivity (1.71 W m−1 K−1), moderate thermal expansion coefficient (8.73 × 10−6 K−1), and high sintering-resistance ability. Such results reveal that nano-sized Y4Al2O9 is favorable for the application of TBCs.

Thermodynamics and up-conversion of Cr3+/Ho3+ Co-doped 12CaO·7Al2O3 synthesized in argon

A thorough study for thermodynamics characters and optical properties of pure 12CaO·7Al2O3 (C12A7) prepared under “argon” (Ar) and Cr3+/Ho3+ co-doped C12A7 (C12A7-Cr3+/Ho3+) derivatives have been made by using XRD, DSC/TG, Raman spectra and fluorescence spectrophotometer analysis, respectively. The precursor powders were calcined from 298 K to 1473 K under Ar atmosphere for studying their thermodynamics behaviors after co-precipitation. The relative chemical reactions for C12A7 were confirmed and determined by XRD, DSC/TG, Raman, FTIR and EDX analysis. Activation energies of crystal growth and extraction of free “O2−” for C12A7 polycrystals sintered under Ar atmosphere were measured to be (687/666) and (230/208) kJ/mol according to Ozawa/Kissinger methods, respectively. Crystallization parameters of pure C12A7 polycrystals in “Ar” gas were evaluated to be m = 3 and n = 3 with a 3D growth mechanism of constant nuclei. Visible up-conversion emissions at 470 nm and 540 nm were observed from C12A7-Cr3+/Ho3+ powders under 808 nm Xe lamp excitation. We proposed four relaxations and cooperative transformation mechanisms of Cr3+/Ho3+ to explain those up-conversion processes, which are one for 470 nm and three for 540 nm light respectively.

Crystal Growth in Mesoporous TiO2 Optical Thin Films

Synthesizing mesoporous TiO2 films with tunable crystallized content, using rapid and facile hydrolytic sol–gel routes, is of interest for developing optical and photocatalytic applications on different substrates. Here, the crystallinity and the porosity of TiO2 is fine-tuned, starting from low annealing temperatures. We further investigate the role of crystal seeds in temperature-induced crystalline phase changes in mesoporous TiO2 thin films by Raman spectroscopy, which is interpreted in the framework of a phonon quantum confinement model. The presence of crystal seeds in the films and the high atomic diffusion in the porous structure lead to the lower activation energy of crystal growth and stabilization of the anatase phase above 700 °C. The film nanostructural and optical properties emphasize the role of complexation by acetylacetone in the formation of nanocrystals and pores. Such fine-tuned optical thin films with varying crystallite and porosity content offer promising perspectives of application...

Study of the Non-Isothermal Crystallization Kinetics of Lithium Disilicate Glass Ceramic

The glass ceramic with the crystals of lithium disilicate Li2O · 2SiO2 (LS2) as the main crystal phase is one of the prospective materials in the field of restorative dentistry. In this study, the crystallization kinetics of LS2 glass ceramic obtained from the base glass of the system SiO2–Li2O–Al2O3–K2O–P2O5 were investigated by the non-isothermal method using differential thermal analysis at four different heating rates. The DTA curves showed different exothermic crystallization peaks over the temperature ranges of 645–683 and 807–845°C. The lithium metasilicate, Li2O · SiO2 (LS), and the lithium disilicate, crystallized over these respective temperature ranges, was established by XRD technique. The crystallization kinetic parameters were calculated by the Kissinger plot and Augis-Bennett equations for non-isothermal analysis. The calculated activation energy of crystal growth, EC1= 236 kJ/mol, EC2 = 340 kJ/mol, and the Avrami parameters, n1 = 1.46–1.67, n2 = 2.73–2.91, together with the results from SEM observations, indicated that the crystallization mechanism of LS was substantial surface crystallization while the crystallization mechanism of LS2 was dominant bulk crystallization. The calculated activation energy of glass transition was also determined EV = 516 kJ/mol.

Impact of chemical diffusion on crystal growth in sodium borosilicate glasses

The link between multicomponent diffusion and crystal growth has been investigated in a sodium borosilicate glass of interest to the nuclear industry. The growth rate of cristobalite, the principal crystal formed in this system, was studied between 700 °C and 900 °C. The growth rate was found to be linear with time and had an activation energy of 60 ± 12 kJ.mol−1 which is close to the activation energy of sodium self-diffusion. Analysis of compositions around crystals and in the bulk of the glass revealed compositional gradients assigned to multicomponent diffusion. A diffusive mechanism involving exchange between silicon and boron appears to drive melt compositions near the crystals while in the bulk of the glass, another diffusive mechanism is predominant, consisting of exchange of silicon and sodium, justifying the value calculated for the activation energy of crystal growth. These results were then used for modeling growth rates in our glass.

Acid-Promoted Crystallization of Amorphous Solid Water

In this study, the effect of externally added hydrogen chloride (HCl) on the crystallization of amorphous solid water (ASW) has been examined. ASW films containing small amounts of HCl, which dissociated into H+ (excess protons) and Cl– ions, and having a thickness of 90–360 monolayers (ML) were prepared on a Pt(111) substrate under an ultrahigh vacuum environment. The location of HCl in the samples was varied by controlling the stacking sequence of H2O and HCl during the film growth. Crystallization kinetics of these samples were examined by conducting temperature-programmed desorption experiments and isothermal kinetic measurements with reflection–absorption infrared spectroscopy for the temperature range of 137–145 K. Crystallization behaviors of pure and NaCl-doped ASW films were also examined for comparison. The results indicated that the excess protons accelerated the crystallization of the ASW films, in contrast to the retardation effect of Na+. In the presence of 0.1 ML HCl, the overall activation energy of ASW crystallization was reduced from 63.4 kJ·mol–1 in the absence of HCl to 48.5 kJ·mol–1, which is close to the activation energy of crystal growth. The crystallization started near the location of HCl injection in the samples, regardless of whether it was the vacuum/ASW interface or the film interior. These observations indicated that the excess protons facilitated the nucleation process and changed the rate-limiting step of ASW crystallization from nucleation to growth. An explanation based on thermodynamics has been proposed, that is, the configurational entropy of the excess protons in ice likely reduces the free-energy barrier of nucleation for the acid-doped ASW samples.

Crystal growth kinetics of unseeded high silica chabazite

Crystal growth of high silica chabazite using N,N,N-1-adamantammoniumhydroxide (TMAdaOH) as structure directing agent (SDA) were studied at 140–170 °C between 24 and 168 h using a direct method. Crystal growth rate increased when the temperature increased. The systems linear crystal growth rates were constant between 24 and 72 h at 150–160 °C. This allowed crystal growth data to be fitted with an empirical method for solid state kinetic processes and subsequent calculation of the systems apparent crystal growth activation energy. The magnitude of the activation energy indicates that the systems crystal growth is controlled by surface kinetics. At 170 °C the zeolite system displayed a non-constant linear crystal growth rate. The linear non-constant growth rate was attributed to surface processes resulting in transformation of spherical to cubic crystals as observed with scanning electron microscopy.