ISSN:
1662-8985
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
The structure of a seven oxide aluminoborosilicate simplified nuclear glass, bearing ahigh amount of neodymium or lanthanum oxide (16 wt%), alkali and alkaline earth cations isstudied. Nd3+ or La3+ are supposed to simulate the trivalent lanthanides and minor actinides presentin nuclear wastes. In the studied glass composition, lanthanide ions have a modifying role and arelocated in highly depolymerized regions of the structure as shown by neodymium optical absorptionand EXAFS spectroscopies. Both alkali and alkaline earth cations are present around Nd3+ ionsenabling their stabilization in glass structure near non-bridging oxygen atoms (NBOs). We showthat both the nature of alkali R+ and alkaline earth R'2+ cations and the K = [R'O]/([R2O]+[R'O])ratio can greatly influence the structure of the aluminoborosilicate glass network. Three glass serieswere prepared for which: (i) K ratio was varied from 0 to 0.5 (Na+ and Ca2+ being respectively theonly alkali and alkaline-earth cations), (ii) the nature of R+ cation was varied from Li+ to Cs+ (Ca2+being the only alkaline earth cation and K = 0.3), (iii) the nature of R'2+ cation was varied fromMg2+ to Ba2+ (Na+ being the only alkali cation and K = 0.3). 27Al MAS NMR spectroscopy resultsshow that (AlO4)- units are preferentially charge compensated by alkali cations rather than byalkaline-earth cations. Both R+ and R’2+ cations can compensate (BO4)- units. Nevertheless, whereasthe proportion N4 of (BO4)- units increases with the size of R'2+ cations, the evolution of N4 with R+cation size for glasses of the R series is not monotonous. The evolution of sodium ions distributiontrough glass structure is followed by 23Na MAS NMR spectroscopy
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/01/40/transtech_doi~10.4028%252Fwww.scientific.net%252FAMR.39-40.19.pdf
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