Crystallization of an Yttrium Aluminosilicate Glass for Nuclear Waste Immobilization
- PDF / 372,190 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 9 Downloads / 218 Views
Crystallization of an Yttrium Aluminosilicate Glass for Nuclear Waste Immobilization Diana Carolina Lago1, 2, 3, Diana Garcés3, Miguel Oscar Prado1, 2, 3 1
Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Atómico Bariloche - Comisión Nacional de Energía Atómica. 3 Instituto Balseiro. Universidad Nacional de Cuyo. Av. Ezequiel Bustillo Km. 9.5, (8400) San Carlos de Bariloche, Pcia. Río Negro – Argentina. 2
ABSTRACT SiO2-Al2O3-Y2O3 glasses exhibit high glass transition temperatures, water corrosion resistance and good mechanical properties. These properties suggest that yttrium aluminosilicate glasses could potentially replace the borosilicate glasses usually used for immobilization of nuclear wastes. At the same time, yttrium can be used to simulate actinides. During waste immobilization, crystallization of the glassy matrix must be avoided or at least controlled, thus, the understanding of glass crystallization kinetics is essential. We found by XRD that the crystalline phases present on heat treatments are yttrium disilicate and sillimanite/mullite. By optical microscopy on polished cross-sections we could only identify highly yttrium enriched crystals which we associate with yttrium disilicate crystals. In this paper we measure the surface density of nucleation sites Ns in as obtained splat cooled pieces obtaining values of about 1.5 · 1011 nucleus · m-2. Crystal growth rate U in the temperature range 1000-1040 oC varies in the range 8-13 Pm · h-1. These data are useful for designing sintering or melting thermal paths of YAS glasses in order to control their microstructure. We show the effect of glass particle size on DTA results: crystallization peaks moves towards lower temperatures for smaller particle size, which confirms that mainly surface nucleation is taking place on heating. INTRODUCTION Yttrium aluminosilicate glasses can be formed over a wide compositional range and exhibit interesting chemical and physical properties such as high glass transition temperature [13], hardness, elastic modulus [4] and excellent chemical durability [5-7]. These glasses have a wide range of technological applications as a host material in laser applications, for bonding of silicon nitride ceramics, as microspheres for radiotherapy of hepatic cancer and for matrices to storage long-lived actinides. In particular, our work is concerned with the application of these glasses as a matrix for nuclear wastes immobilization. Although the inclusion of wastes in a proportion of the order of 20 % wt, most probably gives place to new phases to appear, in this work we are interested in the knowledge of the matrix behavior by itself, as a first step towards a possible use of this glass as a host of nuclear wastes. The determination of nucleation and crystal growth rates as a function of the temperature is important to understand the stability of glasses on heating or cooling from high temperatures. A clear example is the case of waste immobilization where the formation of the nuclei and subsequent crystal growth must b
Data Loading...
