Densification kinetics of binary borosilicate glass composite

1994 ◽  
Vol 9 (2) ◽  
pp. 486-492 ◽  
Author(s):  
Jau-Ho Jean ◽  
Tapan K. Gupta
Keyword(s):  
Activation Energy ◽  
Viscous Flow ◽  
Borosilicate Glass ◽  
Critical Value ◽  
Energy Estimates ◽  
Glass Composite ◽  
Densification Mechanism ◽  
Microstructural Observation ◽  
High Silica ◽  
Kinetics Of

Densification kinetics and mechanism of a binary borosilicate glass composite, containing low-softening borosilicate (BSG) and high-softening high silica (HSG) glasses, have been studied. Apparent activation energy of densification varies from 200 to 400 kJ/mol, and decreases with increasing BSG content at a given densification factor. At a given BSG content, the activation energy of densification initially remains relatively unchanged with increasing densification factor (DF), but increases with densification when DF reaches a critical value (DF∗). Moreover, the value of DF∗ increases with increasing BSG content. From the activation energy estimates of densification, it is concluded that the predominant densification mechanism for BSG ≥ 30 vol. % with DF < DF∗ is viscous flow of low-softening BSG. For BSG ≥ 30 vol. % with DF < DF∗ and BSG ⋚ 20 vol. % with all DF investigated, the activation energies are within the range governed by viscous flow of both BSG and HSG, indicating that the densification is controlled by viscous flow of a new glass with a composition between BSG and HSG. The latter evidence stems from the microstructural observation that as sintering proceeds, the HSG particle undergoes an extensive dissolution process.

Effect of alumina on densification of binary borosilicate glass composite

1994 ◽  
Vol 9 (8) ◽  
pp. 1990-1996 ◽  
Author(s):  
Jau-Ho Jean ◽  
Tapan K. Gupta
Keyword(s):  
Activation Energy ◽  
Reaction Layer ◽  
Borosilicate Glass ◽  
Densification Rate ◽  
Glass Composite ◽  
Alkali Ions ◽  
Slowing Down ◽  
Binary Glass ◽  
High Silica ◽  
Glass Mixture

The effect of alumina on densification of the binary borosilicate glass composite, containing low-softening borosilicate glass (BSG) and high-softening high silica (HSG) glass, has been investigated. It is found that with a small amount of alumina, 2-10 vol. %, present as a dopant in the binary glass mixture of BSG and HSG, both densification and densification rate are significantly reduced, but the activation energy of densification at a given densification is dramatically increased. However, no significant change in densification behavior with increasing alumina content from 2 to 10 vol. % is observed. These results are attributed to a chemical reaction taking place at the interface of alumina/BSG, forming a reaction layer adjacent to alumina. Since the composition of the reaction layer is known to be rich in aluminum and alkali ions and poor in silicon, the alkali ions content in BSG is continuously decreased during sintering. Accordingly, the resultant loss of alkali ions from BSG causes a rise in viscosity of BSG, thus slowing down the densification kinetics and increasing the activation energy of densification.

Devitrification inhibitors in borosilicate glass and binary borosilicate glass composite

1995 ◽  
Vol 10 (5) ◽  
pp. 1312-1320 ◽  
Author(s):  
Jau-Ho Jean ◽  
Tapan K. Gupta
Keyword(s):  
Borosilicate Glass ◽  
Silica Glass ◽  
Elevated Temperatures ◽  
Glass Composite ◽  
Binary Glass ◽  
High Silica ◽  
Glass Mixture

Cristobalite is known to precipitate out of borosilicate glass (Corning 7740) and a binary glass mixture of borosilicate glass and high silica glass when these glasses are heated to elevated temperatures. To prevent cristobalite from forming in these glass systems, a devitrification inhibitor needs to be found. Among oxides selected for testing, both Al2O3 and Ga2O3 are found to prevent cristobalite from forming in these glass systems.

A Flow Model for the Kinetics of Dissolution of Nuclear Waste Forms; A Comparison of Borosilicate Glass, Synroc and High-Silica Glass

1981 ◽  
Vol 11 ◽  
Author(s):  
Pedro B. Macedo ◽  
Aaron Barkatt ◽  
Joseoph H. Simmons
Keyword(s):  
Nuclear Waste ◽  
Borosilicate Glass ◽  
Flow Model ◽  
Release Rates ◽  
Waste Forms ◽  
High Silica ◽  
Kinetics Of Dissolution ◽  
Kinetics Of ◽  
Nuclear Waste Forms

A model has been developed to predict the long-term leach or release rates of various waste-form materials under repository conditions.

Sintering of a Crystallizable K2O–CaO–SrO–BaO–B2O3–SiO2 Glass with Titania Present

2002 ◽  
Vol 17 (7) ◽  
pp. 1772-1778 ◽  
Author(s):  
Jau-Ho Jean ◽  
Yu-Ching Fang ◽  
Steve X. Dai ◽  
David L. Wilcox
Keyword(s):  
Activation Energy ◽  
Reaction Kinetics ◽  
Crystalline Phase ◽  
Glass Powder ◽  
Energy Analysis ◽  
Dissolution Kinetics ◽  
Critical Value ◽  
Sio2 Glass ◽  
Kinetics Of Formation ◽  
Kinetics Of

Crystallization and reaction kinetics of a crystallizable K2O–CaO–SrO–BaO–B2O3–SiO2 glass powder with 17–40 vol% titania powder were investigated. The initially amorphous K2O–CaO–SrO–BaO–B2O3–SiO2 glass powder formed cristobalite (SiO2) and pseudowollastonite [(Ca, Ba, Sr)SiO3] during firing. The above crystalline phases were completely replaced by a crystalline phase of titanite [(Ca, Sr, Ba)TiSiO5] when the amount of added titania was greater than a critical value, e.g., 10 vol%, at 99–1100 °C. A chemical reaction taking place at the interface between titania and the glass was attributed to the above observation. The dissolved titania changed the composition of the glass, and the dissolution kinetics was much faster than the formation of cristobalite and pseudowollastonite. Activation energy analysis showed that the crystallization of titanite [(Ca,Sr,Ba)TiSiO5] was controlled by a reaction-limiting kinetics of formation for the Ti–O bond.

Kinetics of interfacial reaction between borosilicate glass and sapphire substrate

1992 ◽  
Vol 7 (9) ◽  
pp. 2514-2520 ◽  
Author(s):  
Jau-Ho Jean ◽  
Tapan K. Gupta
Keyword(s):  
Activation Energy ◽  
Growth Rate ◽  
Diffusion Coefficient ◽  
Growth Kinetics ◽  
Sapphire Substrate ◽  
Reaction Layer ◽  
Borosilicate Glass ◽  
Chemical Analyses ◽  
Aluminum Ion ◽  
Kinetics Of

Reaction kinetics between borosilicate glass (BSG) and sapphire has been studied at temperatures from 850 °C to 950 °C. Microstructural and chemical analyses show that the nonporous interdiffusion layer is formed with Al+3 ion dissolving from sapphire and K+ diffusing from BSG onto the interface of sapphire/BSG, and that both ions are always coupled together in the reaction layer. The interdiffusion layer moves toward BSG with time and the reaction starts immediately at temperatures investigated without incubation period. The growth kinetics for the interdiffusion layer follows a parabolic rate law in the temperature range investigated, and shows an apparent activation energy in the range of 176 k–/mol. The diffusion coefficient of aluminum ion is determined from EDX analysis, and the values range from 0.7–1.4 × 10−12 at 850 °C to 3.0–6.0 × 10−12 cm2/s at 950 °C. The above results also show an activation energy close to that determined from the parabolic growth rate constants, suggesting that the mass-transport kinetics of aluminum ion from sapphire into the interdiffusion layer controls the formation process.

High-temperature creep of low-dielectric-constant glass composites

1996 ◽  
Vol 11 (8) ◽  
pp. 2098-2103 ◽  
Author(s):  
Jau-Ho Jean
Keyword(s):  
Dielectric Constant ◽  
Creep Behavior ◽  
Borosilicate Glass ◽  
Softening Point ◽  
Low Dielectric Constant ◽  
Glass Composite ◽  
Glass Composites ◽  
Low Dielectric ◽  
High Silica ◽  
Good Agreement

The constant-stress compressive creep behavior of a low-dielectric constant (low-k) glass composite, containing a low-softening-point borosilicate glass (BSG) and a high-softening-point high silica glass (HSG), has been investigated at 800–950 °C. For all stages of creep, the deformation behavior exhibits linear viscoelasticity, and is controlled by viscous flow of the low-softening-point borosilicate glass. An analytical expression is proposed to describe mathematically the creep behavior of the glass composite, and the results show a fairly good agreement with experimental observations.

Effect of gallium oxide in preventing cristobalite formation in binary borosilicate glass composite

1993 ◽  
Vol 8 (9) ◽  
pp. 2393-2399 ◽  
Author(s):  
Jau-Ho Jean ◽  
Tapan K. Gupta
Keyword(s):  
Binary Mixture ◽  
Reaction Layer ◽  
Borosilicate Glass ◽  
Crystalline Phase ◽  
Gallium Oxide ◽  
Oxide Particle ◽  
Glass Composite ◽  
Alkali Ions ◽  
High Silica ◽  
Oxide Particles

When an appropriate mixture of low-softening borosilicate (BSG) and high-softening high silica (HSG) glasses is sintered at temperatures ranging from 800 to 1000 °C, a crystalline phase, identified as cristobalite by XRD, is known to precipitate out of the initial amorphous binary mixture of glasses as the sintering continues. The precipitation of cristobalite is found to originate in HSG and is controlled by the transport of alkali ions (e.g., K, Na, and Li) from BSG to HSG.1 In this paper we report that when a small amount of gallium oxide is present as a dopant in the above binary mixture of BSG and HSG, the cristobalite formation is completely prevented at the sintering temperatures investigated. The above result is attributed to a strong affinity between Ga+3 from gallium oxide particle and alkali ions from BSG, which diverts the diffusion of alkali ions from HSG to gallium oxide, thus forming a K+ and Ga+3-rich reaction layer adjacent to gallium oxide particles far too rapidly compared with that of cristobalite formation.

Devitrification inhibitor in binary borosilicate glass composite

1993 ◽  
Vol 8 (2) ◽  
pp. 356-363 ◽  
Author(s):  
Jau-Ho Jean ◽  
Tapan K. Gupta
Keyword(s):  
Binary Mixture ◽  
Reaction Layer ◽  
Borosilicate Glass ◽  
Crystalline Phase ◽  
Silica Glass ◽  
Glass Composite ◽  
Alkali Ions ◽  
Strong Affinity ◽  
Alumina Particles ◽  
High Silica

When an appropriate mixture of a low-softening borosilicate glass (BSG) and a high-softening high silica glass (HSG) is sintered at temperatures ranging from 800 to 1000 °C, a crystalline phase, identified as cristobalite by XRD, is known to precipitate out of the initial amorphous binary mixture of glasses as the sintering continues. The precipitation of cristobalite is found to originate in HSG, and is controlled by the transport of alkali ions (e.g., K+, Na+, and Li+) from BSG to HSG.1 In this paper, we report that when a small amount of alumina is present as a dopant in the above binary mixture of BSG and HSG, the cristobalite formation is completely prevented at the sintering temperatures investigated. The above result is attributed to a strong affinity between Al+3 from alumina and alkali ions from BSG, which diverts the diffusion of alkali ions from HSG to alumina, thus forming a K+ and Al+3-rich reaction layer adjacent to the alumina particles far too rapidly compared to that of cristobalite formation.

Effect of ionizing radiation on the kinetics of hydrogenation on the Ni-MgO mixed catalyst

1982 ◽  
Vol 47 (7) ◽  
pp. 1780-1786 ◽  
Author(s):  
Rostislav Kudláček ◽  
Jan Lokoč
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Liquid Phase ◽  
Ionizing Radiation ◽  
Oxide Catalyst ◽  
Absorbed Dose ◽  
Hydrogenation Rate ◽  
Solution Composition ◽  
Mixed Catalyst ◽  
Kinetics Of

The effect of gamma pre-irradiation of the mixed nickel-magnesium oxide catalyst on the kinetics of hydrogenation of maleic acid in the liquid phase has been studied. The changes of the hydrogenation rate are compared with the changes of the adsorbed amount of the acid and with the changes of the solution composition, activation energy, and absorbed dose of the ionizing radiation. From this comparison and from the interpretation of the experimental data it can be deduced that two types of centers can be distinguished on the surface of the catalyst under study, namely the sorption centres for the acid and hydrogen and the reaction centres.

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