Kinetic study of surface nucleated MgO-CaO-Al2O3-SiO2 glasses

Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; Paganelli, Mariano; Pellacani, Gian Carlo

doi:10.1007/bf01979740

Cited by 12 publications

(5 citation statements)

References 8 publications

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“…As far as the activation energies are concerned, it can be said that they are fairly homogeneous, ranging from 166 to 190 and from 209 to 234kcalmo1-1 (1 kcal = 4.187 kJ) depending on the method, and the values differ slightly from the literature data. These energies, evaluated at 760-900 °C, are higher than those found at about 950-1000 °C for crystallization [15]. It can be assumed that, at the crystallization temperature, the activation energy for viscous flow is reduced in accordance with the fact that the plot of log r/versus 104/T is not a straight line The presence of crystallinity was checked by X-ray powder diffraction and a line drawn among amorphous and crystallized samples, according to Uhlmann and Kreidl [16].…”

Section: A = a E B = C B E T 2 T O = Tcontrasting

confidence: 50%

Influence of viscosity on the crystallization of some anorthite-diopside glass precursors

et al. 1993

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It is known that viscosity represents one of the most important properties for a quantitative interpretation of the processes that convert a glass into a glass-ceramic, giving information about the possible physicochemical behaviour of the material during heat treatment, so that the optimum heat treatment cycles can be determined.Many data are available on the viscosity and heat capacity of the MgO-CaO-A1203-SiO2 system, which forms diopside and anorthite glasses, since these components, being some of the major components in magmas, have been of great interest for the understanding of igneous petrological processes [1][2][3][4].Being particularly interested in the glass-ceramic field, in a previous paper we investigated the natural trend towards nucleation of three compositions belonging to the region in the glass formation in the quaternary MgO-CaO-A1203-SiO2 system where anorthite and diopside in 3/1, 1/1 and 1/3 ratios are stable [5]. In this letter we report an investigation on the flow behaviour of the previously investigated anorthite-diopside glasses over a temperature range (700-900 °C) higher than the glass transition temperature (Tg) with two different techniques: beambending and fibre elongation in isothermal conditions, in order to determine the activation energies for viscous flow to compare with that for crystallization, since viscous flow is the most important mass transportation phenomenon in glass devetrification. The time-temperature-transformationcurves for the different glasses are also presented (and discussed in relation to the viscosity data).The results are compared with lowwiscosity data obtained for systems with similar compositions [1,4] and with those from other researchers on the same compositions using different viscometers [6].Two different compositions in the system MgO-CaO-A1203-SiO 2 with the molar fractions 0.25CaO-0.20MgO-0.05A1203-0.50SiO2 and 0.25CaO-0.14MgO-0.11A1203-0.50SiO2 (hereafter abbreviated as A and B, respectively) and considered in a previous work [5], separate glass-ceramics containing calcium(II) feldspar (anorthite) and a pyroxene (diopside) in 1/3 and 1/1 ratios, respectively. The specimens were prepared from reagent grade powders of silica, alumina, magnesium carbonate and calcite. The samples were melted in alumina crucibles at 1450 °C for 1 h. Fibres for the elongation viscosimeter were drawn from the hot melt and not annealed, whereas samples for the beam bending were obtained in graphite moulds 294 with an approximate form of slabs and annealed for 30 min at 750 °C and naturally cooled overnight. The specimens were then cut to a tolerance of 0.01 cm in slabs of shape 2.0 cm x 0.35 c m x 0.15 cm.The property measured was the absolute viscosity (poise) with both viscometers, since the glassy samples were homogeneous and did not show nucleation or crystallization during the testing time.This experimental beam bending method for determining glass viscosities in the range 108-1015 P was experimentally developed by Jones [7] and revised by Hagy [8], who used the...

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Section: A = a E B = C B E T 2 T O = Tcontrasting

confidence: 50%

Influence of viscosity on the crystallization of some anorthite-diopside glass precursors

et al. 1993

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“…This was also confirmed by previous studies, which noted a value of 773 kJ/mol for the free iron oxide base composition. 11,12 In this case, iron oxide lowers glass viscosity (evident in DTA as a decrease in the glass transition temperature), and consequently increases the crystal growth rate, which is also at lower crystallization temperatures. 7 In fact, according to previous work, 10 the base glass presents an activation energy for viscous flow (794 kJ/mol), similar to the crystallization one, that is almost comparable to that of pyroxene crystals (752 kJ/mol).…”

Section: Resultsmentioning

confidence: 99%

Nucleation and Crystal Growth of a MgO–CaO–Al₂O₃–SiO₂Glass with Added Steel Fly Ash

Barbieri

Corradi

Lancellotti

et al. 2002

Journal of the American Ceramic Society

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The nucleation and growth of diopside Ca(Mg,Al)(Si,Al) 2 O 6 crystals on the free surface of a 24 wt% MgO, 14 wt% CaO, 9 wt% Al 2 O 3 , and 53 wt% SiO 2 glass, with a 2 wt% addition of steel fly ash, were investigated through DTA, XRD, SEM, and optical microscopy. Crystallization was complete at ϳ920°C with an activation energy of 589 kJ/mol. Samples with polished free surfaces were nucleated at selected temperatures in the range of 730°to 820°C, and then heat-treated at 870°C for 15 min for crystal growth. Nucleation was predominantly observed at the surface, and the number of diopside crystals per unit of area and the mechanism of crystallization were determined. It was concluded that nucleation reaches a maximum at 750°C, corresponding to an average density of diopside crystals of 8.4 ؋ 10 6 nuclei/cm 2 , and that between 900°and 1100°C, a uniformly crystallized layer is formed at an exponential rate. The crystallized volume fraction increased significantly in the 880°-890°C growth range, and remained almost constant at higher temperatures. In the 860°-910°C range, the size of the diopside crystals formed in the samples nucleated at the temperature of the maximum nucleation rate, and linearly increased, reaching values between 1.0 and 3.0 m at 870°and at 910°C, respectively.

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“…From the DTA data, a T g (glass transition temperature)/T m (melting temperature) ratio Ͼ 0.6 was calculated (namely, a range of ϳ0.62-0.66) indicating a heterogeneous nucleation and surface mechanism of crystallization. 22 23 and Barbieri et al, 24 the activation energy for the crystallization of the glasses was evaluated by applying the derivative method (Fig. 2(c)) to the single nonisothermal DTA run at the heating rate of 10°C/min.…”

Section: Resultsmentioning

confidence: 99%

Crystallization of (Na₂O–MgO)–CaO–Al₂O₃–SiO₂ Glassy Systems Formulated from Waste Products

Barbieri

Ferrari

Lancellotti

et al. 2000

Journal of the American Ceramic Society

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Aluminosilicate and silicate glass-ceramics were obtained from controlled devitrification of CaO-Al 2 O 3 -SiO 2 glassy systems starting from Spanish and Italian coal fly ash or Italian municipal incinerator slag mixed with other byproducts, such as glass cullet and dolomite. The nucleation mechanism and the crystallization kinetics were investigated by thermal, diffractometric, and microstructural measurements. Moreover, the experimentally observed devitrification and the identification of the crystalline phases formed were compared with the indications derived from Ginsberg, Raschin-Tschetveritkov, and Lebedeva diagrams used for petrological glass-ceramics. All the glasses showed a good crystallization tendency with the formation of dendritic pyroxene and acicular wollastonite together with feldspar and iron spinels starting from the surface. The activation energy values for crystallization ranging from 472 to 832 kJ⅐mol ؊1 were found to be close to those typical for aluminosilicate glasses; moreover, the possibility to vitrify and devitrify up to 100 wt% of slag and up to 40 -50 wt% of ash mixed with glass cullet and dolomite makes the vitrification treatment a suitable disposal procedure.

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Kinetic study of surface nucleated MgO-CaO-Al2O3-SiO2 glasses

Cited by 12 publications

References 8 publications

Influence of viscosity on the crystallization of some anorthite-diopside glass precursors

Influence of viscosity on the crystallization of some anorthite-diopside glass precursors

Nucleation and Crystal Growth of a MgO–CaO–Al₂O₃–SiO₂Glass with Added Steel Fly Ash

Crystallization of (Na₂O–MgO)–CaO–Al₂O₃–SiO₂ Glassy Systems Formulated from Waste Products

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Kinetic study of surface nucleated MgO-CaO-Al2O3-SiO2 glasses

Cited by 12 publications

References 8 publications

Influence of viscosity on the crystallization of some anorthite-diopside glass precursors

Influence of viscosity on the crystallization of some anorthite-diopside glass precursors

Nucleation and Crystal Growth of a MgO–CaO–Al2O3–SiO2Glass with Added Steel Fly Ash

Crystallization of (Na2O–MgO)–CaO–Al2O3–SiO2 Glassy Systems Formulated from Waste Products

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Nucleation and Crystal Growth of a MgO–CaO–Al₂O₃–SiO₂Glass with Added Steel Fly Ash

Crystallization of (Na₂O–MgO)–CaO–Al₂O₃–SiO₂ Glassy Systems Formulated from Waste Products