Crystallization kinetics of gehlenite glass

Isothermal and non-isothermal kinetics of gehlenite glass devitrification have been studied. A Johnson—Mehl—Avrami rate equation was assumed. The values of kinetic parameters obtained from XRD patterns and DTA curves are in a good agreement. The crystallization process is thought to proceed by a rod-like growth controlled by diffusion from a fixed number of nuclei.     

Crystallization kinetics of SAPO-37

The crystallization kinetics of SAPO-37 have been studied for a wide range of silicon contents of the gel both in static and agitated systems. The products have been characterized by XRD, chemical and thermal analysis, scanning electron microscopy, and MAS n.m.r.A liquid-phase transportation mechanism operates during crystallization. An upper limit value of ≈ 38 Si atoms per unit cell has been found. Agitation does not modify the crystallization pattern or the chemical composition of the products, but slightly favors the substitution mechanism 3. Agitation also decreases appreciably the crystallization time.     

Crystallization kinetics of selenium-tellerium glasses

Bulk glasses of the compositions Se₇₀Te₃₀ and Se₈₀Te₂₀ were prepared by the melt quenching technique. Differential thermal analyses were performed at different heating rates. The values of the glass transition temperature,T _g, the crystallization temperature,T _c, and the peak temperature of crystallization,T _p, were found to depend on the composition and the heating rate. The activation energy for the glass transition,E _i, as well as the activation energy for crystallization,E _c, were evaluated from the heating rate dependence ofT _g andT _p. The crystallization mechanism was examined through analysis of the data under non-isothermal conditions. The results indicated that surface crystallization is dominant for both compositions.     

Crystallization kinetics of zeolite ZSM-5

Zeolite ZSM-5 was synthesized from aluminosilicate gels in the presence of organic templates — tetrapropylammonium bromide (TPABr) and pyrrolidine (Py) — at temperatures of 423, 438 and 453 K. Nucleation and crystallization processes were subjected to a detailed kinetic analysis. The nucleation region is subdivided into two periods: induction and transition ones. Values of nucleation energy and crystallization energy, preexponential factor, rate of crystallization, and geometric factor have been calculated. Correlations between the estimated kinetic characteristics were found. The activation energy and the preexponential factor for the transitional and crystal-growth periods have the character of a kinetic compensation effect. The mechanism of the crystallization process is discussed on the basis of the kinetic features and correlations.     

Crystallization kinetics of Si-TCP bioceramic films

The crystallization kinetics leading to the formation of a characteristic globular, interconnected morphology in the transformation of an unfired hydroxyapatite precipitate (HA) to silicon stabilized tri-calcium phosphate (Si-TCP) are examined by rapid thermal processing of thin films prepared on silica substrates. The results are interpreted using an Avrami model in which nucleation of Si-TCP is induced by diffusion of a silicon front from the substrate. The model is supported through SEM inspection of the morphological development. The transformation is characterized as an interfacial reaction with Avrami exponent m = 1.3 ± 0.2, activation energy for the reaction E _c = 2.5 ± 0.3 eV and time constant _c = 20 ± 1 s at 950°C. Silicon in the films acts to nucleate Si-TCP, while also causing impurity pinning of grains, resulting in a fine microstructure when excess Si is present in the film.     

非化学计量比SbOx薄膜的结晶动力学研究

利用直流磁控反应溅射法在不同氧分压下制备了SbOx薄膜,对退火前后薄膜的X射线衍射(XRD)分析表明,退火后薄膜结构发生了从非晶态向晶态的转变.利用示差扫描量热法(DSC)测出不同升温速度条件下非晶态薄膜粉末的晶化峰温度,用Kissinger公式计算了材料的结晶活化能计算结果表明,随着溅射时氧分压的增加,薄膜的结晶活化能增加,而相应的非晶态与晶态之间的焓差则呈现出相反的变化趋势.     

Crystallization kinetics of some iron-based metallic glasses

The crystallization behaviour of a range of iron-based metallic glasses has been examined by isothermal differential scanning calorimetry, optical and transmission electron microscopy. It was found that the conventional procedure of applying the Johnson-Mehl-Avrami equation to determine reaction mechanisms, i.e. calculating a mean value of the Avrami exponent over a range of volume fraction transformed, can be misleading. The technique suggested by Calka and Radlinski, when used in conjunction with detailed metallography, is shown to be a more sensitive and reliable indicator of reaction mechanisms.     

Crystallization kinetics of bulk amorphous Se-Te-Sn system

In the present work crystallization kinetics of the amorphous Se_80–xTe₂₀Sn_x (0 x 9) system have been investigated using Differential Scanning Calorimetry. From the heating rate dependence of the glass transition temperature and the crystallization temperature the activation energy for the glass transition and that for crystallization have been determined using the Kissingers equation and Matusitas equation for non-isothermal crystallization of materials. The effect of addition of Sn to the Se-Te system on the dimentionality of crystal growth has been investigated. An increase in the glass transition temperature with increase in Sn content suggests that Sn plays a role in cross-linking the already existing Se-Te chains which causes an increase in the thermal stability of the material.     

Crystallization kinetics of magnetron-sputtered amorphous CoNbZr thin films

For non-isothermal and isothermal annealing, the crystallization kinetics of magnetron sputtered Co_85.5Nb_8.9Zr_5.6 amorphous alloy thin films have been investigated by differential scanning calorimetry measurements. As a result, in the case of non-isothermal crystallization, one distinct exothermic peak is observed at 470 °C, which is due to the crystallization of hcp α-Co. With the Kissinger method, the apparent activation energy was obtained to be 99.82 kJ/mol. By using the Deloy-Ozawa method, the local activation energy of non-isothermal crystallization was calculated. For isothermal crystallization, the Avrami exponents were determined by means of the Johson-Mehl-Avrami equation, which is in the range of 1.19-1.37. Based on an Arrhenius relationship, the local activation energy was analyzed, which yields an average value E_c=88.51 kJ/mol. Finally, the local Avrami exponent was used for discussing the details of the nucleation and growth behaviour during the isothermal crystallization.     

Crystallization kinetics of V2AlC

X-ray amorphous V₂AlC and hexagonal (V,Al)₂C_x thin films were synthesized by magnetron sputtering from a compound target with the composition of V₂AlC. The crystallization kinetics was investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). During continuous heating up to 1200 °C, one exothermal peak is observed between 565 and 675 °C. XRD data suggest that the DSC peak is associated with the formation of V₂AlC. The activation energy of crystallization of V₂AlC is ~ 308 kJ/mol based on the Kissinger approach. This value is close to the 287 kJ/mol activation energy obtained here for the transformation of magnetron sputtered (V,Al)₂C_x thin films to V₂AlC. The here reported phase formation temperature of V₂AlC is about 800 °C lower than during hot pressing of elemental powders.     

Crystallization kinetics of an Fe-Co based metallic glass

Crystallization kinetics of the Fe₆₇Co₁₈Si₁B₁₄ metallic glass has been studied from electrical conductivity measurements. Results are interpreted on the basis of a modification of the Germainet al. model (J. Non-Cryst. Solids 23 (1977) 93). The characteristics of kinetics for different annealing temperatures are analysed and the activation energy is evaluated     

Crystallization kinetics of sol-gel derived hydroxyapatite thin films

The crystallization kinetics of sol-gel derived hydroxyapatite (HA) and tricalcium phosphate (TCP) thin films were studied to determine whether viscous sintering could be used for densification. The films were approximately 900 nm thick, and were synthesized and processed on silicon substrates. The films were fired in air in a rapid thermal annealer (RTA) for various times and the degree of crystallinity was determined by measuring the intensity of characteristic X-ray diffraction lines. The growth kinetics of HA and TCP were measured between 420 and 550 °C, and between 840 and 920 °C, respectively. Films that were subjected to an accelerated aging step before firing, exhibited a significantly lower crystallization growth rate when compared to unaged films. The aged films also became harder, as measured by nanoindentation. At temperatures above 840 °C, HA transformed into both -and -TCP, with the form being dominant at lower temperatures. The activation energies for both transformations (amorphous film to HA, and HA to TCP) were determined, as were the constants for the Avrami equation. Based on the rapid crystallization kinetics observed for the amorphous film to HA transformation, densification through viscous sintering is essentially precluded in this system. © 2001 Kluwer Academic Publishers     

Diffusion barrier performances of thin Mo, Mo-N and Mo/Mo-N films between Cu and Si

In this work, we have studied the diffusion barrier performances of Mo, Mo-N and Mo/Mo-N metallization layers deposited by sputtering Mo in Ar/N₂ atmospheres, respectively. Samples were subsequently annealed at different temperatures ranging from 400 to 800 °C in vacuum condition. The film properties and their suitability as diffusion barriers and protective coatings in silicon devices were characterized using four-point probe measurement, X-ray diffractometry, scanning electron microscopy, Auger electron spectroscopy and transmission electron microscopy analyses. Experimental results revealed that the Mo (20 nm)/Mo-N (30 nm) layer was able to prevent the diffusion reaction between Cu and Si substrate after being annealed at 600 °C for 30 min. The adhesion between layers and the content of N atoms are the key parameters to improve the properties of Mo-based barrier materials. The Mo layer interposed between Cu and Mo-N diluted the high nitrogen concentration of the barrier and so enhanced the barrier performances.     

不同形态石英玻璃的析晶动力学研究

应用XRD技术对三种形态（块状,粉末和纤维）石英玻璃在1200－1500℃范围内内的等温析动力学过程进行了实验研究,实验结果表明,不同形态石英玻璃的析晶产物都是低温方石英,但形态不同的石英玻璃的析昌开始温度,同一温度下的析昌量及析晶量随温度的变化关系是不同的,三种形态石英玻璃析晶动力学可较好地用Avrami方程表示,其中块状,粉末和纤维的平均n值分别为1.65,1.68和1.92,活化能分klj o 495,445和430kJ/mol,析晶中的成核为表面成核机制,晶体生长受扩散和重排双重控制,随比表面和杂质含量的增大（块状→粉末→纤维）,控制因素中扩散的比例降代,而重排的比例上升,因而n值上升而活化能下降,析晶倾向增大。     

Crystallization kinetics of neodymium disilicate obtained by polymeric xerogels

The kinetics of tetragonal Nd₂Si₂O₇ crystallization from polymeric xerogels was investigated under non-isothermal conditions via differential thermal analysis (DTA). The polymeric xerogels were prepared by the Pechini sol–gel method from tetraethoxysilane and neodymium nitrate. The crystallization fraction and rate of tetragonal Nd₂Si₂O₇ were determined based on the exothermic DTA data. The activation energy of tetragonal Nd₂Si₂O₇ crystallization, which is calculated by the Kissinger equation, is 673 kJ/mol. The crystallization process of tetragonal Nd₂Si₂O₇ could involve the nucleation and three-dimensional growth that follows the diffusion-controlled mechanism when the nucleation rate increased.     

Crystallization kinetics of Ga-Sb-Te films for phase change memory

Ga-Sb-Te ternary thin films were prepared by co-sputtering using targets GaSb and Sb₈Te₂. Crystallization processes of these films were studied by measuring the temperature-dependent electrical resistance during non-isothermal heating. The activation energy (E_a), rate factor (K_o), and kinetics exponent (n) were deduced from Kissinger and Ozawa's plots, respectively. The crystallization temperatures (T_x = 108∼319°C) increase with increasing GaSb contents. The activation energy (1.82∼7.52 eV) increases with increasing Ga content until 31.6 at.% then it decreases. The crystallization mechanisms of compositions A∼D (Ga_17∼32Sb_71∼62Te_12∼6), as evidenced from n values, are nuclei formation and subsequent crystal growth; the nucleation rate decreases with grain growth. While composition E (Ga_38.2Sb_57.7Te_4.1) reveals an n value lower than 1.5, it implies the one-dimensional crystal growth from the nuclei. The crystallization time of each composition was evaluated using JMA equation using all derived kinetics parameters. Composition C (Ga_26.4Sb_65.2Te_8.4), showing the shortest crystallization time, is suggested for phase change RAM applications.     

钼氮共掺杂TiO2的制备及其光催化活性

采用简单的溶胶-凝胶法制备了一系列不同钼掺杂比例的钼氮共掺杂TiO2光催化剂,并通过X射线衍射(XRD)、X射线光电子能谱(XPS)、紫外-可见吸收光谱(UV-Vis DRSs)及光致发光光谱(PL)等手段对催化剂进行了表征,并通过降解亚甲基蓝(MB)对催化剂光催化活性进行了评价.结果发现,掺杂后TiO2在可见光区吸收...     

Crystallization kinetics of amorphous Ga-Sb films extended for phase-change memory

Performance of phase-change materials based on Ga-Te-Sb was found getting better with decreasing Te content in our earlier studies. We concerned much properties of Te-free, Sb-rich binary Ga-Sb, which has been known to possess extremely fast crystallization behavior. Non-isothermal and isothermal crystallization kinetics of amorphous Sb-rich Ga-Sb films were explored by temperature dependent electrical resistance measurements. The crystallization temperature (183 to 261 degrees C) increases with decreasing Sb content (91 to 77 at%). The activation energy and rate-factor vary with Sb contents and reach the maximum at Ga19Sb81. The kinetic exponent is smaller than 1.5 at Sb < 85 at% denoting that the mechanism is one-dimensional crystal-growth from nuclei. The temperature corresponding to 10-year data-retention, evaluated from films, is 180 degrees C (Ga19Sb81) and 137 degrees C (Ga13Sb87), respectively. We verified memory performance using test-devices made of Ga16Sb84 working at voltages with 100 ns pulse-width.     

Crystallization kinetics of mechanically alloyed amorphous Fe-Ti alloys during annealing

The crystallization behaviors of mechanically alloyed amorphous Fe-Ti alloys were studied. The α-Fe phase formed during annealing as a result of the devitrification of the amorphous phase. According to the Kissinger plot, the crystallization activation energy (E) was obtained as 171 kJ/mol, which is close to the activation energy for the diffusion of Fe in α-Ti. According to the non-isothermal Johnson–Mehl–Avrami (JMA) analysis and obtaining the volume fraction of the crystalline phase from the differential scanning calorimetry (DSC) plots, the average Avrami exponent (n) was determined as 1.61 and 5.67 for low and high heating rates, respectively. Moreover, a method for obtaining the value of E based on the non-isothermal JMA analysis was proposed. The value of E was determined as ~185 and 191 kJ/mol respectively for low and high heating rates, which are consistent with the value determined from the Kissinger plot for all heating rates.     

Crystallization kinetics of Zr-33 at % Ni amorphous alloy

The amorphous to crystalline transition in Zr-33 at% Ni amorphous alloy has been found to occur by polymorphic crystallization. The product of the cyrstallization process has been identified as the equilibrium Zr₂Ni intermetallic phase. The kinetics of crystallization have been studied independently using differential scanning calorimetry (DSC) and transmission electron microscopy. The activation energy of crystallization has been evaluated by isothermal and continuous heating in DSC. The isothermal anneals have revealed that the crystallization follows the Johnson-Mehl-Avrami kinetics with an Avrami exponent close to 4. The microstructural changes accompanying crystallization have been studied for an interpretation of the Avrami exponent. The nucleation and growth rates of crystals have been estimated at different temperatures in order to determine the activation energies of the two processes. It has been found that nucleation is thermally activated and growth is interface controlled.