Crystallization Activation Energy Ec Research Articles

Tuning energy storage and light transmittance properties in ZrO2-modified Na2O–K2O–Nb2O5–SiO2 glass-ceramics

Crystallization kinetics in ZrO2-modified glass-ceramics, (35-x)Na2O–5K2O–40Nb2O5–20SiO2-xZrO2 (x = 0, 1, 3, 5, 10 mol%), is analyzed by crystallization activation energy Ec and kinetic parameter k. A large kinetic parameter k of 1.657 × 1025 is found for the sample with x = 1, which indicates a high tendency toward crystallization. NaNbO3 is formed as the major phase, and its crystallinity changes significantly by the addition of ZrO2. It is found that the dielectric permittivity and maximum polarization are affected by crystallinity. Large domains are formed, and a relaxation process appears at high frequencies. In addition, the breakdown strength (BDS) is affected by the strong electric field distortion rather than the resistance in this system. Complex impedance analysis shows that resistance decreases with the addition of ZrO2. The electric field distortion of the glass-ceramics is simulated by COMSOL. A low interfacial polarization activation energy Ea of 0.821 eV is achieved by the addition of ZrO2. The maximum pulse power density reaches 90 MW/cc at 350 kV/cm for the sample with x = 10, and the pulse energy density attains 0.91 J/cm3 at 300 kV/cm for the sample with x = 1. Light transmittance is achieved because of the low crystallinity and the disappearance of cristobalite SiO2 in the Na2O–K2O–Nb2O5–SiO2 glass-ceramics.

INVESTIGATE THE APPROPRIATE MODEL FOR DESCRIBING THE CRYSTALLIZATION PROCESS OF Te65Sb25Ga10 THIN FILM

The sheet resistance, Rs , measurements versus temperature, T, for 1000 nm Te - Sb -Ga thin films were performed at different heating rates (   5, 10, 20, 30 and 40 K/min) in the temperature range from 300 to 673 K. The kinetic transformation parameters of Te65Sb25Ga10 thin film were examined via the theoretical method developed (TMD) and the Johnson–Mehl–Avrami model (JMA). The crystallization activation energy Ec with the transformed fraction is not constant but change with the conversion fraction. These results refer to the rate constant of the transformation is in fact determined through the nucleation and diffusion processes. The results of the impingement exponent γi dependence of the conversion fraction (χ) revealed that the mode of impingement is due to “anisotropic growth”. In addition to that the average values of kinetic exponent parameters, n and m obtained by (TMD) and JMA models. are accounted for two and three-dimensional crystal growth with heterogeneous nucleation. Moreover, comparing the experimental curve of the transformed fraction indicated that the crystallization process of Te65Sb25Ga10 thin film cannot be satisfactorily described by Johnson-Mehl-Avrami (JMA) model. On contrary, the theoretical curves of the developed model are more realistic for describing the crystallization process of the investigated chalcogenide bulk glass.

Influences of Molecular Structure on the Non-Isothermal Crystallization Behavior of β-Nucleated Isotactic Polypropylene

In order to explore the effect of molecular structure on the crystallization and polymorphic behavior of β-nucleated isotactic polypropylene (β-iPP), four commercial iPP samples with different average isotacticities, molecular weights and isotactic distributions were used. The relationship between the molecular structure characteristics and β-crystallization behavior were investigated by means of xylene solvent fractionation (XS), successive self-nucleation and annealing fractionation (SSA), carbon-13 nuclear magnetic resonance spectrometry (13C NMR), gel permeation chromatography (GPC), melt index (MI) and differential scanning calorimetry (DSC). Results of molecular structure characterization revealed that their isotacticity can be ranged as F401 > 5014L > F03G ≈ T38F, while the order of their isotactic distribution width is 5014L ≈ T38F > F401 ≈ F03G. Results of crystallization kinetics revealed that the molecular weight of the samples has little effect on their crystallization and polymorphic behavior. Meanwhile, crystallization activation energy Ec can be ranged as 5014L < F401 < F03G < T38F, indicating that when the molecular weight was above a certain degree, the isotacticity is the main factor affecting the crystallization ability of β-type iPP (β-iPP). The higher the isotacticity and the wider the distribution is, the stronger the β-crystallization ability is. Moreover, the β-crystallization ability of the samples is closely related to the isotacticity of the sample, which can be effectively controlled by tuning the fraction of high isotacticity with high molecular weight components.

Structure, crystallization mechanism, and properties of glass ceramics from molten blast furnace slag with different B2O3/Al2O3

Glass ceramics with different B2O3/Al2O3 from molten blast furnace slag (BF slag) were prepared using traditional melting, annealing, and heat treatment method. According to DSC analysis, the parent glass samples were nucleated at 760 °C for 1 h, and then respectively crystallized at 900 °C, 920 °C, and 940 °C for 1 h. The structure of parent glass was characterized using XRD, Raman spectra, 27Al MAS NMR spectra. The results indicated that with an increasing B2O3/Al2O3, Q2 remained dominant in the glass network, Q0 disappeared and Q4 existed when B2O3/Al2O3 was 0.21. [BO3] and [BO4] were both characterized when B2O3/Al2O3 exceeded 0.09, but the further addition of B2O3 was prior to form [BO3] in glass network. The investigation of crystallization mechanism revealed that the crystallization activation energy Ec strikingly decreased from 403.8 kJ/mol to 277.8 kJ/mol with increasing B2O3, and surface crystallization was determined due to that the crystallization index n was below 3. The results of XRD and SEM-EDS analysis both confirmed the main crystalline in glass ceramics was gehlenite. The flexural strength of glass ceramics reached the minimum when B2O3/Al2O3 was 0.21. Glass ceramics nucleated at 760 °C for 1 h and crystallized at 940 °C for 1 h exhibited the highest flexural strength of 57.61 MPa.

Effect of CaO/Fe2O3 ratio on slag viscosity behavior under entrained flow gasification conditions

The key factor for smooth slag tapping of entrained flow gasifiers was slag viscosity behavior. Shanxi coals can’t meet the requirement for discharging slag due to its high SiO2 + Al2O3 contents. The single fluxing agent (CaO or Fe2O3) was also inoperative for Shanxi coals. Hence, the development of binary composite flux was urgent and necessary. The effect of CaO-Fe2O3 binary composite flux on slag viscosity temperature behavior was investigated in this work. As the CaO/Fe2O3 ratio decreased, the slag viscosity at same temperatures decreased. Furthermore, a linear relationship between the slag viscosity and CaO/Fe2O3 ratio was established at high temperatures. Characterization of slag structure showed that the polymerization degree decreased with the decreasing CaO/Fe2O3 ratio. The calculated BO/(BO + NBO) (fraction of bridging oxygen) also presented an excellent linear relationship with CaO/Fe2O3 ratio. This indicated that CaO/Fe2O3 ratio affected the slag structure, leading to the variation of slag viscosity. During the cooling step, the crystallization activation energy Ec was used to describe the effect of CaO/Fe2O3 ratio on slag crystallization behavior quantitatively. Besides, the growth pattern of crystal phases transformed from the surface crystallization to the bulk crystallization with the decreasing CaO/Fe2O3 ratio, and the bulk crystallization was more easily to promote the crystallization behavior. In brief, slag viscosity and crystallization behavior could be modified via adjusting CaO/Fe2O3 ratio. These results can provide a guide for using CaO-Fe2O3 binary composite flux to improve the slag viscosity behavior in entrained flow gasification.

Study of crystallization behavior and kinetics of magnetic FeCoCrNiZr high entropy amorphous alloy

A new magnetic Fe36Co22Cr17Ni15Zr10 high entropy amorphous alloy has been prepared and its crystallization behavior and kinetics been studied. The results show that, under non-isothermal conditions, the crystallization activation energy Ex was calculated by the Kissinger equation, which yield 373 kJmol−1. Relation plot of Ex vs crystallization volume fraction(x) manifests the non-isothermal crystallization process is from difficult to easy. On the other hand, base on Arrhenius relation, the crystallization activation energy Ec under isothermal conditions was calculated to be 370 kJmol−1. Relation plot of Ec vs x manifests the isothermal crystallization process is from easy to difficult. The isothermal kinetics was modeled by Johnson-Mehl-Avrami(JMA) equation, as the isothermal annealing temperature increases, the nucleus growth mechanism from diffusion-controlled 3-D growth convert into interface-controlled 3-D growth. Though proper heat treatment, the saturation magnetization Ms of this alloy can reach up to 106.8A∙m2∙kg−1, it will become promising functional materials in the future.

Exploring the Effects of Stereo-Defect Distribution on Nonisothermal Crystallization and Melting Behavior of β-Nucleated Isotactic Polypropylene/Graphene Oxide Composites.

In this work, using two isotactic polypropylene (iPP) resins with similar average isotacticity and molecular weight but different uniformities of stereo-defect distribution, the β-nucleated iPP/graphene oxide (β-iPP/GO) composites (NPP-A and NPP-B) were prepared to investigate the effect of stereo-defect distribution on the nonisothermal crystallization kinetics and polymorphic melting behavior of the composites by means of scanning electron microscopy, wide-angle X-ray diffraction, and differential scanning calorimetry. The results showed that more uniform stereo-defect distribution led to a slight increase of the crystallization rate and decrease of the crystallization activation energy Ec. NPP-B with more uniform stereo-defect was more favorable for the formation of a large amount of β-phase. Moreover, the role of the cooling rate was also discussed and it was found that the higher the cooling rate, the higher the β-phase content and the smaller the crystalline sizes, meanwhile, the higher the amount of β-phase with relatively lower thermal stability that will take part in β–α recrystallization during the subsequent melting process. For β-iPP/GO composites, although the cooling rate greatly influences the polymorphic behavior and crystalline structures of the composites, the uniformity of stereo-defect distribution was found to be the first factor determining the formation of the β-phase.

Phase separation and crystallization of La2O3 doped ZnO-B2O3-SiO2 glass

In order to investigate the effect of the La2O3 on the phase separation and crystallization of ZnO-B2O3-SiO2 glass, after the occurence of the phase separation and crystallization of glasses by heat treatment, the microstructure morphology and distribution of elements in different sample areas were characterized by the scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS); the non-isothermal crystallization kinetics of the glass samples was studied by using a differential scanning calorimeter (DSC) and the precipitated crystals of crystallized glass were determined by the X-ray diffraction (XRD). The results suggest that the phase separation and crystallization of 60ZnO-30B2O3-10SiO2 glass occur at glass surface, and the incorporation of small amount (<4 mol%) of La2O3 significantly inhibits the glass phase separation and consequently improves the thermal stability of glass. Doping of La2O3 accelerates the glass crystallization at the elevated temperature (660 °C), making the depth of crystal layer thicker and diffraction intensity in XRD patterns stronger. However, due to the precipitation of several crystals that occur simultaneously when La2O3 doping amount is 4 mol%, crystallization of the 60ZnO-30B2O3-10SiO2 glass is obviously depressed, the crystallization activation energy Ec and the relative crystallinity Xc of the glass reach the maximum and the minimum values, respectively. Although transition from one-dimensional growth of crystals to two-dimensional growth of crystals results from La2O3 addition, the one-dimensional growth of crystals remains dominant in crystallization process. This work can provide some useful information for preparing glass ceramics with nano-crystals precipitated in the glass surface.

Glass transition and crystallization of ZnO-B2O3-SiO2 glass doped with Y2O3

The effect of Y2O3 on the glass transition kinetics, crystallization kinetics, phase separation and crystallization behavior of 60ZnO–30B2O3–10SiO2 glass has been investigated by non-isothermal differential thermal analysis, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The glass transition activation energies Eg calculated by using both Kissinger and Moynihan model decrease from 668 kJ/mol to 573 kJ/mol for Kissinger model, and 682 kJ/mol to 587 kJ/mol for Moynihan model with the increase of yttrium oxide doping content from 0 to 6 mol%. And the glass crystallization kinetics parameters, crystallization activation energy Ec and Avrami exponent n stands for crystal growth, are also obtained on the basis of several well developed equations. Increase of about 58 kJ/mol in Ec values obtained by different theoretical equations is caused by addition of 6 mol% yttrium oxide into 60ZnO–30B2O3–10SiO2 glass, and the Avrami exponent (n close to 2) suggests that crystal growth in 60ZnO–30B2O3–10SiO2 glass doped with or without yttrium is mainly one-dimensional growth of crystals. The results on the phase separation and crystallization behavior occurred at 893 K and 993 K respectively for base and doped glass, are well consistent with the glass transition and crystallization kinetics results. Hence, addition of yttrium oxide into 60ZnO–30B2O3–10SiO2 glass decrease the glass transition activation energy while increase the crystallization activation energy of glass, thereby the stability of glass structure is improved. Phase separation phenomenon and crystallization behavior occurred at glass surface provide some useful information for preparing glass ceramics with micro- or nano-crystals in surface.

Thermal analysis of directional pressure annealed Fe78Si9B13 amorphous ribbons

The structure, magnetic properties and non-isothermal crystallization behavior of widthwise/lengthwise pressed and annealed (WPA and LPA), solely annealed (ANN) and as-quenched (AQ) Fe78Si9B13 amorphous ribbons were investigated. The first crystallization process of samples fits Johnson-Mehl-Avrami (JMA) model and then follows the Normal-Grain-Growth (NGG) model. Annealing treatment decreases the crystallization activation energy Ec; while WPA and LPA samples have a lower magnetic lose, larger nucleation and growth activation energies En and Eg than ANN sample, indicating that the pressure suppresses the crystallization and reduces free volume and forms the ordered clusters with a different structure of α-Fe(Si) during annealing process. In addition, the widthwise pressed treatment reduces free volume and suppresses crystallization in a larger degree than the lengthwise pressed treatment.

Crystallization behavior and properties of CaO-MgO-Al2O3-SiO2 glass-ceramics synthesized from granite wastes

Granite wastes were used as the raw materials for the preparation of CaO-MgO-Al2O3-SiO2 glass-ceramics. The waste loading was about 50.24–68.34wt% in the batch depending on the chemical compositions of glasses. Effects of SiO2/(CaO+MgO) ratio on the crystallization behavior, microstructure and properties of glass-ceramics were investigated. The results showed that the crystallization activation energy Ec increased from 322.68 to 477.10kJ/mol, and Avrami parameter n decreased from 3.78 to 2.89 as the SiO2/(CaO+MgO) ratio increase from 1.72 to 4.99, while, the crystallinity of diopside decreased gradually, and the main crystalline phase changed into armalcolite with SiO2/(CaO+MgO) ratio increase to 4.99. The increase in SiO2/(CaO+MgO) ratio lead to the decreasing in Vicker's hardness, bending strength and alkali resistance of the glass-ceramics, but improved the acid resistance.

Crystallization behavior and kinetics mechanism of 20GeS2·80Sb2S3 chalcogenide glass

Knowledge of crystallization behavior and kinetics mechanism is essential to achieve the controllable crystallization. Surface crystallization of 20GeS2·80Sb2S3 chalcogenide glass is realized using differential scanning calorimeter technique and heat treatment method. An about 40 μm thick Sb2S3 crystal layer is precipitated after heat treatment at 268℃ (Tg+30℃) for 60 h. Then, non-isothermal method is employed to theoretically analyze the crystallization kinetics of this glass sample. Crystallization activation energy Ec is calculated to be (223.6±24.1) kJ·mol-1, and crystallization rate constant K at 268℃ was obtained to be 1.23×10-4 s-1, indicating that the crystallization of 20GeS2·80Sb2S3 glass is more difficult than that of other chalcogenide glass system, such as GeS2-Ga2S3. The crystal growth index, m and crystal growth dimensionality, n both are equal to 2, which suggests that the crystallization of Sb2S3 glass phase is of 2D growth process. This work would contribute to the fabrication of Sb2S3 crystallites embedded chalcogenide glass-ceramics.

A study of non-isothermal primary crystallization kinetics and soft magnetic property of Co65Fe4Ni2Si15B14 amorphous alloy

The non-isothermal primary crystallization kinetics and soft magnetic properties of Co65Fe4Ni2Si15B14 amorphous alloy have been investigated using differential scanning calorimeter (DSC), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). It is found that the apparent crystallization activation energy Ec is not the same as the calculation methods of Kissinger and Doyle–Ozawa, and is 471.68 and 461.50kJ/mol, respectively. At the steady crystallization stage, the local crystallization energy decreases gradually, and the thermal stability of the residual amorphous matrix becomes weak finally. This is ascribed to the diffusion of boron atoms at elevated temperatures. As a result, this primary crystallization mechanism can be explained by JMA nucleation-and-growth model and normal grain growth kinetic mode. During crystallization, some of nanocrystals such as Co–B intermetallics, Co2Si, Fe23B6 and NiB precipitate from amorphous matrix after annealing at 773K. This leads to soft magnetic properties being improved finally.

Thermal Properties of Se&amp;lt;sub&amp;gt;100–x&amp;lt;/sub&amp;gt;Zn&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; Glassy System

The crystallization process in Se100–xZnx glassy system is investigated using differential scanning calorimeters (DSC). The samples are prepared by conventional melt-quenching technique in the composition range 2 ≤ x ≤ 20 (at%). Non-isothermal measurements are carried out for different heating rates .The value of the glass transition temperature Tg the crystallization temperature Tc and the crystallization peak temperature Tp, are found to be depending upon both heating rate as well as the composition from thermal analytical data. The investigation of crystallization kinetics indicates a single stage crystallization process. The glass transition energy Eg and the crystallization activation energy Ec are also evaluated from thermal analytical data. The analyzer has been used the most reliable non-isothermal kinetic methods. The value of kinetics parameters Eg, Ec and ‘n’ are calculated using non-isothermal kinetics methods. The analysis shows that the incorporation of Zinc content has a strong influence on the crystallization mechanism for the Se100–xZnx glassy system.

Effect of Nb addition on the glass transition and crystallization kinetics of bulk Cu-Zr metallic glasses

In the present work, bulk Cu50.3Zr49.7-xNbx(x=0,2) amorphous alloys 2 mm in diameter were produced by copper mold suction casting. The effect of Nb addition on the glass transition as well as crystallization kinetics of the binary Cu based amorphous alloy has been investigated by using differential scanning calorimetry (DSC). It is found that the alloy containing 2%Nb has a lower fragility parameter m and higher crystallization activation energy Ec, which suggests that the thermal stability and hence the glass forming ability of the surpercooled metallic liquid for the Cu based alloy are enhanced by the addition of very small amounts of Nb element.