The Formation of Pitted Features on the International Simple Glass during Dynamic Experiments at Alkaline pH
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.9
The Formation of Pitted Features on the International Simple Glass during Dynamic Experiments at Alkaline pH Adam J. Fisher1, Neil C. Hyatt1, Russell J. Hand1 and Claire L. Corkhill1
1 NucleUS Immobilisation Science Laboratory, Department of Materials Science and Engineering, The University of Sheffield, S1 3JD, UK.
ABSTRACT
The forward rate of dissolution of the International Simple Glass (ISG) was determined under alkaline conditions at 40 oC using the Single Pass Flow Through (SPFT) method. Forward rates were consistent with those obtained in the literature for this glass composition. The formation of altered gel layers and surface pits was observed on the surface of glass particles, especially at the very highest pH values, despite the application of high flow rates to prevent the build-up of solubility limiting phases. These features could be attributed to preferential localized dissolution at sites with a higher alkali concentration or from a separate, less durable, vitreous phase. These results may indicate that surface pit and altered gel formation occurs under the forward rate of dissolution as imposed by the SPFT method, particularly for simplified borosilicate glass materials.
INTRODUCTION The International Simple Glass (ISG) was developed as a standard material for international researchers to use to advance glass corrosion understanding in a coordinated approach [1]. The ISG is a six-component, non-radioactive alumino-borosilicate reference glass, with a composition simplified from the French inactive surrogate of the R7T7 nuclear waste, SON68. The ISG has been studied extensively, with the objective to understand glass corrosion mechanisms at a fundamental level and to underpin predictions of the long-term durability of nuclear waste glass over geological timescales in an underground repository.
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Here, the surface morphology of ISG particles were examined after being subjected to dissolution at pH(RT) 7, 9 and 11, at 40°C, using the Single Pass Flow Through method [2], which is commonly used to determine the forward rate of glass dissolution for input to glass dissolution models.
EXPERIMENTAL DETAILS The ISG was fabricated in 2012 by the MoSci Corporation in several batches (Rolla, MO, USA) [3]. The lot number of the batch used in this investigation was L1201 2601-M1205 0803, which was shown to be x-ray amorphous and single phase [4]. The nominal composition is reported as: 56.2 SiO2, 17.3 B2O3, 12.2 Na2O, 6.1 Al2O3, 5 CaO & 3.3 ZrO2 wt.% [5]. Crushed glass particles (75 – 150 μm diameter) were produced and washed according to the Single Pass Flow Through (SPFT) ASTM C1662-10 standard [2]. The SPFT method is a standard dynamic dissolution test where fresh solution constantly flows
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