Title

The Effects of Composition on Aqueous Dissolution of Phosphate Glasses

Presenter Information

Melissa Malone

Department

Materials Science and Engineering

Major

Ceramic Engineering

Research Advisor

Brow, Richard K.

Advisor's Department

Materials Science and Engineering

Funding Source

US Department of Energy under Lawrence Livermore National Laboratory

Abstract

Phosphate glasses have useful optical and physical properties but are often less durable in aqueous environments than silicate glasses. Phosphate glasses react in different ways than silicate glasses. The dominant reaction step for the former glasses involves the hydration of modifying metal ions and the dissolution of intact phosphate anions, whereas the dominant reaction involving silicate glasses involves the selective leaching of metal ions and the formation of a hydrated silicate gel.

The effects of solution pH, temperature, and composition on the aqueous durability of a series of phosphate glasses were studied. Glasses were prepared from the K20-MgO- AL2O3-P2O5 system, with molar compositions that range from a metaphosphate stoichiometry (15K2O-15MgO-10AL2O3-60P2O5) to a pyrophosphate stoichiometry (25K2O-25MgO-10AL2O3-40P2O5). Bulk dissolution rates were determined by measuring weight losses and solution pH changes, in the pH range 3-10. Corrosion solutions were analyzed by High Pressure Liquid Chromatography (HPLC) to determine the kinetics of phosphate chain hydrolysis once the species are removed into solution. Other samples were analyzed under pH stat conditions, using an auto-titration system. The addition of high field strength cations, such as Al3+ or Mg2+ slows the reaction rates of these glasses in all pH ranges, particularly in acidic solutions. The addition of soluble species, such as K+, increases the reactivity of these glasses, as is shown by both bulk dissolution kinetics and the titration results.

Biography

Melissa Malone is a Senior in Ceramic Engineering from Columbia, MO. After graduation, Melissa is planning on pursuing a PhD at the University of Missouri--Rolla.

Research Category

Engineering

Presentation Type

Poster Presentation

Document Type

Poster

Presentation Date

12 Apr 2006, 1:00 pm

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Apr 12th, 1:00 PM

The Effects of Composition on Aqueous Dissolution of Phosphate Glasses

Phosphate glasses have useful optical and physical properties but are often less durable in aqueous environments than silicate glasses. Phosphate glasses react in different ways than silicate glasses. The dominant reaction step for the former glasses involves the hydration of modifying metal ions and the dissolution of intact phosphate anions, whereas the dominant reaction involving silicate glasses involves the selective leaching of metal ions and the formation of a hydrated silicate gel.

The effects of solution pH, temperature, and composition on the aqueous durability of a series of phosphate glasses were studied. Glasses were prepared from the K20-MgO- AL2O3-P2O5 system, with molar compositions that range from a metaphosphate stoichiometry (15K2O-15MgO-10AL2O3-60P2O5) to a pyrophosphate stoichiometry (25K2O-25MgO-10AL2O3-40P2O5). Bulk dissolution rates were determined by measuring weight losses and solution pH changes, in the pH range 3-10. Corrosion solutions were analyzed by High Pressure Liquid Chromatography (HPLC) to determine the kinetics of phosphate chain hydrolysis once the species are removed into solution. Other samples were analyzed under pH stat conditions, using an auto-titration system. The addition of high field strength cations, such as Al3+ or Mg2+ slows the reaction rates of these glasses in all pH ranges, particularly in acidic solutions. The addition of soluble species, such as K+, increases the reactivity of these glasses, as is shown by both bulk dissolution kinetics and the titration results.