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Effect of Different Concentrations of Titanium Oxide (TiO2) on the Crystallization Behavior of Li2O-Al2O3-SiO2 Glasses Prepared from Local Raw Materials  [PDF]
Omar A. Al-Harbi,Esmat M.A. Hamzawy,M. Mujtaba Khan
Journal of Applied Sciences , 2009,
Abstract: Lithium Aluminum Silicate (LAS) glasses produced from local raw materials (white silica sand and clay) and Li2CO3 were nucleated by different concentrations of TiO2 to transform into glass-ceramics. Studies were performed using Differential Thermal Analysis (DTA), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Dilatometer. Addition of TiO2 affected phase evolution, morphology and formation of β-spodumene along with brookite and Al2TiO5 phases. The SEM micrographs of the heat-treated glass samples also reflected bulk crystallization. However, softness of crystal edges took place on samples subjected to muliti-stage heat-treatment. This may attributed to partial melting of the pre-developed phases. The CTE values were low to medium with the formation of β-spodumene and brookite, but were high with the formation of Al2TiO5 and amorphous phasesin addition to both the β-spodumene and brookite phases. The values of low, medium and high Coefficient of Thermal Expansion (CTE) ranged between 3.02-49.672x10-7 °C-1 in the double and -2.171-31.737x10-7 °C-1 in the multi-stage heat treatments with in a temperature range of 25-300°C.
Effect of Fluorine on the Crystallization of Li2O-Al2O3-SiO2 Glasses

HU An-Min,LIANG Xai-Ming,GU Shou-Ren,

无机材料学报 , 2003,
Abstract: 采用差热分析(DTA),X射线衍射分析(XRD),扫描电镜(SEM)等分析手段研究了F^-离子对Li2O—A12O3-SiO2系微晶玻璃形核和晶化的影响。结果发现,引入F^-离子使得玻璃的析晶峰值温度降低,玻璃的析晶活化能E降低,晶化指数n加大。引入F^-离子后,一方面促进了玻璃析晶和晶化,LixAlxSi1-xO2固溶体析出以及LixAlxSi1-xO2固溶体向β-锂辉石固溶体转变加快,晶化后的晶粒尺寸加大,析晶活化能E,晶化指数n与扫描电镜(SEM)分析一致。表明F^-离子促进了玻璃晶化和离子扩散。
Effect of ZrO2 on Crystallization and Phase Transformation in Low-temperature Processed BaO-Al2O3-SiO2 Glass-ceramics
ZrO2对低温烧结 BaO-Al2O3-SiO2系微晶玻璃析晶和晶型转变的影响

LU Yu-Feng,DU Yong-Guo,XIAO Jia-Yu,ZHANG Wei-Jun,WU Jian-Feng,YANG Guang,WANG Yue-Ran,

无机材料学报 , 2008,
Abstract: 用烧结法制备了化学计量比和高Ba含量的两组BaO-Al2O3-SiO2(BAS)系微晶玻璃,采用差示扫描量热法(DSC)和X射线衍射分析(XRD)等手段研究了ZrO2对BAS系微晶玻璃中六方钡长石析晶和六方钡长石向单斜钡长石晶型转变的影响.研究表明,两组BAS系玻璃的烧结温度低于850℃,晶化温度低于900℃.六方钡长石的析出为整体析晶.不加形核剂晶型转变为整体析晶;添加ZrO2晶型转变为表面析晶.提高Ba含量或添加ZrO2促进六方钡长石的析出和晶粒细化.化学计量比的BAS系微晶玻璃中添加ZrO2明显促进晶型转变.高Ba含量的BAS系微晶玻璃中添加ZrO2表现为抑制晶型转变,850℃保温100h不发生转变.

YANG Jueming,ZHANG Litong,ZHOU Wangcheng,

材料研究学报 , 1995,
Abstract: In this paper, the kinetics of nonisothermal crystallization of two BAS gel glasses were studied and the volume fraction of crystallization was calculated by a modified JMA equation, according to nonisothermal DTA measurements and the methods for calculating kinetic parameters by Bansal et al. The results show that the BAS gel glasses nucleate easily and appears the characterestic of bulk crystallization without a nucleating agent and the crystallization process of BAS gel glass is fast due to the large interior surface area and the presence of OH groups.When BaO content is low and SiO2 content is high comparatively, the rate of crystallization of BAS gel glass is slower.
The devitrification of PbO-B2O3-ZnO glass doped with Li2O
Journal of the Serbian Chemical Society , 2000,
Abstract: In this paper the effect of the addition of Li2O on the crystallization behavior of PbO-B2O3-ZnO glass was investigated by the differential thermal analysis (DTA) and X-ray powder diffraction (XRPD) methods. The crystallization ability, as well as the crystalline phases which develop during devitrification of the glass were examined. The results of DTA and XRPD analysis showed that the addition of Li2O varies the sequence of the crystallization as well as the phase composition of the crystalline phase. The glasses with Li2O crystallize at a lower temperature (360°C) with 4Li2O.4ZnO.3B2O3 as the major crystalline phase. The base PbO-B2O3-ZnO glass crystallizes at 480°C with PbO.2ZnO.B2O2 as the major crystalline phase.
Crystallization Mechanism of Hard Sphere Glasses  [PDF]
Eduardo Sanz,Chantal Valeriani,Emanuela Zaccarelli,Wilson C. K. Poon,Peter N. Pusey,Mike E. Cates
Physics , 2011, DOI: 10.1103/PhysRevLett.106.215701
Abstract: In supercooled liquids, vitrification generally suppresses crystallization. Yet some glasses can still crystallize despite the arrest of diffusive motion. This ill-understood process may limit the stability of glasses, but its microscopic mechanism is not yet known. Here we present extensive computer simulations addressing the crystallization of monodisperse hard-sphere glasses at constant volume (as in a colloid experiment). Multiple crystalline patches appear without particles having to diffuse more than one diameter. As these patches grow, the mobility in neighbouring areas is enhanced, creating dynamic heterogeneity with positive feedback. The future crystallization pattern cannot be predicted from the coordinates alone: crystallization proceeds by a sequence of stochastic micro-nucleation events, correlated in space by emergent dynamic heterogeneity.
Ceramics-Silikáty , 2011,
Abstract: The crystallization behavior of fluorphlogopite, a glass-ceramic in the MgO–SiO2–Al2O3–K2O–B2O3–F system, was studied by substitution of Li2O for K2O in the glass composition. DTA, XRD and SEM were used for the study of crystallization behavior, formed phases and microstructure of the resulting glass-ceramics. Crystallization kinetics of the glass was investigated under non-isothermal conditions, using the formal theory of transformations for heterogeneous nucleation. The crystallization results were analyzed, and both the activation energy of crystallization process as well as the crystallization mechanism were characterized. Calculated kinetic parameters indicated that the appropriate crystallization mechanism was bulk crystallization for base glass and the sample with addition of Li2O. Non-isothermal DTA experiments showed that the crystallization activation energies of base glasses was in the range of 234-246 KJ/mol and in the samples with addition of Li2O was changed to the range of 317-322 KJ/mol.
Dielectric properties of Li2O-3B2O3 glasses  [PDF]
Rahul Vaish,K. B. R. Varma
Physics , 2010, DOI: 10.1063/1.3225583
Abstract: The frequency and temperature dependence of the dielectric constant and the electrical conductivity of the transparent glasses in the composition Li2O-3B2O3 (LBO) were investigated in the 100 Hz- 10 MHz frequency range. The dielectric constant and the loss in the low frequency regime were electrode material dependent. Dielectric and electrical relaxations were respectively analyzed using the Cole-Cole and electric modulus formalisms. The dielectric relaxation mechanism was discussed in the framework of electrode and charge carrier (hopping of the ions) related polarization using generalized Cole-Cole expression. The frequency dependent electrical conductivity was rationalized using Jonscher's power law. The activation energy associated with the dc conductivity was 0.80 \pm 0.02 eV, which was ascribed to the motion of Li+ ions in the glass matrix. The activation energy associated with dielectric relaxation was almost equal to that of the dc conductivity, indicating that the same species took part in both the processes. Temperature dependent behavior of the frequency exponent (n) suggested that the correlated barrier hopping model was the most apposite to rationalize the electrical transport phenomenon in Li2O-3B2O3 glasses. These glasses on heating at 933 K/10h resulted in the known non-linear optical phase LiB3O5.
Crystallization process of Ni-base metallic glasses  [PDF]
T. Poloczek,S. Griner,R. Nowosielski
Journal of Achievements in Materials and Manufacturing Engineering , 2006,
Abstract: Purpose: The paper presents a crystallization process of Ni68,7Cr6,6Fe2,65Si7,8B14C0,25 metallic glasses. The Ni68,7Cr6,6Fe2,65Si7,8B14C0,25 metallic glasses were produced by the CBMS method for two different conditions of the casting, with different cooling rate.Design/methodology/approach: The crystallization of Ni68,7Cr6,6Fe2,65Si7,8B14C0,25 metallic glasses by method differential thermal analysis (DTA), internal friction (IF), X-ray diffraction and transmission electron microscopy (TEM) were studied. For calculation of activation energy of crystallization processes was used modified Kissingers formula.Findings: The investigation showed, that the conditions of vitrification (different, but higher than critical cooling rate) influence for different course elementary crystallization processes during thermal activation.Research limitations/implications: The differences in temperature of beginning of elementary crystallization processes of alloy, the activation energy of crystallization process as a function of thickness of strip were disclosed.Practical implications: The calculation values of activation energy of crystallization processes can used for analysis of thermal stability of metallic glasses.Originality/value: The paper presents, that the conditions of vitrification influence for different course elementary crystallization processes during thermal activation.
Crystallization of hard-sphere glasses  [PDF]
E. Zaccarelli,C. Valeriani,E. Sanz,W. C. K. Poon,M. E. Cates,P. N. Pusey
Physics , 2009, DOI: 10.1103/PhysRevLett.103.135704
Abstract: We study by molecular dynamics the interplay between arrest and crystallization in hard spheres. For state points in the plane of volume fraction ($0.54 \leq phi \leq 0.63$) and polydispersity ($0 \leq s \leq 0.085$), we delineate states that spontaneously crystallize from those that do not. For noncrystallizing (or precrystallization) samples we find isodiffusivity lines consistent with an ideal glass transition at $\phi_g \approx 0.585$, independent of $s$. Despite this, for $s<0.05$, crystallization occurs at $\phi > \phi_g$. This happens on time scales for which the system is aging, and a diffusive regime in the mean square displacement is not reached; by those criteria, the system is a glass. Hence, contrary to a widespread assumption in the colloid literature, the occurrence of spontaneous crystallization within a bulk amorphous state does not prove that this state was an ergodic fluid rather than a glass.
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