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In order to encapsulate nuclear wastes (NW) enriched in Uranium, they have been designed and obtained vitrified matrices of iron aluminum phosphates including substitution of U by Bi. These glasses have been designed and obtained formulating all from the starting binary composition: 60P 2 O 5 ·40Fe 2 O 3 where the Fe/P ratio was 0.67. The thermal behavior has been investigated by DTA/TG analysis and thermal expansion, as well as identification of some phases by TEM/EDS. The vitrified structures are difficult to crystallize as is the case of the (Fe + U) contents in the range of 0.50 per P atom. Glasses with Bi-oxide are less resistant to crystallization than those containing U. The glasses here investigated depict a reasonable water chemical stability due to the high percentage of P O Fe O bonds and the presence of U (4+ to 6+). Lately, it has been also investigated the calcination of simulated miniplates of Si 2 U 3 /Al having additions of these glasses and U 3 O 8 to dilute this Uranium enriched in MTR combustible (Material Testing Reactor). [ABSTRACT FROM AUTHOR]

The thermal behaviour (viscosity variation, dilatometric and crystallization trends) of several iron aluminium magnesium phosphate glasses that contain significant amounts (6--19 wt%) of uranium oxide (UO2·67) is presented as well as new data related to the densification of powder compacts prepared from such compositions. The sintering study of such vitreous powders can help to assess the relative capability for the immobilization and stability of the uranium oxide in these glassy or glass-ceramic matrices. [ABSTRACT FROM AUTHOR]

The effect of iron oxide content on the crystallisation of a zirconium-based glass-ceramic glaze was investigated using a glass-ceramic “white of zirconium” frit and a granite waste glass. Measurements by X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and EDX microanalysis showed that Fe2O3 gives rise to the crystallisation of an iron-zinc ferrite, which is acting as nucleating agent of feather-like crystals of pyroxene while granite frit enhances the partial dissolution of zircon into the glassy phase, which is sharply increased for granite frit additions greater than 50%. [Copyright &y& Elsevier]

The effect of iron oxide content on the crystallisation of a diopside glass–ceramic glaze was investigated using a glass–ceramic frit in the K2O–ZnO–MgO–CaO–Al2O3–SiO2 system and a granite waste glass. Measurements by X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and EDX microanalysis showed that the distribution of Fe3+ ions among different crystalline phases such as franklinite (ZnFe2O4) and hematite Fe2O3 depends on the iron content in the original diopside mixture. Thus, the original glaze crystallises to franklinite or hematatite when iron content is greater than 2 and 15%, respectively. [Copyright &y& Elsevier]

The effect of chromium oxide additions (0.05–1.00 mol% interval) on the crystallization of an original 26Li 2 O·74SiO 2 glass (mol%) formulated in the liquid metastable immiscibility dome of the binary system has been investigated by XRD and TEM-replica electron microscopy. Results were discussed by considering the phases that can be formed in the Li 2 O-Cr 2 O 3 -SiO 2 partial equilibrium ternary diagram. From these glasses, lithium disilicate is the main crystalline phase after thermal treatments at 550–650 °C. Maximum crystallization is obtained with the lowest content addition of Cr 2 O 3 (0.05 mol%). Glass-in-glass phase separation was observed in these glasses coexisting with the crystallization areas. [ABSTRACT FROM AUTHOR]

Abstract: Six new glasses having 45–65wt.% P2O5, 18–42% Fe2O3, 6.2–18.7%UO2.67 and about 6% (Na2O+Al2O3 +MgO) were finally obtained after melting the batches in Al2O3/MgO crucibles. The higher Tg–TSOFT values were obtained for glasses AR6 (main components: 57.3%P2O5. 18.4%Fe2O3. 18.9%UO2.67) and AR7 (mc: 65%P2O5, 19%Fe2O3, 9.5%UO2.67) and were the most stable glasses against crystallization. The lowest thermal expansion α was measured for AR1 (mc: 54%P2O5, 27%Fe2O3, 13.5%UO2.67). AR7 was the least chemically durable composition, whereas the most durable glasses were those containing the highest percentages of UO2.67 (AR6, AR1 and AR5). The least stable glasses against crystallization were AR4 (mc: 45.8% P2O5, 42.2%Fe2O3, 6.4%UO2.67), AR5 (mc: 46.2%P2O5. 35.4%Fe2O3. 13.0%UO2.67) and AR2 (mc: 54.2% P2O5, 33.1%Fe2O3, 6.4%UO2.67); their DTA crystallization (Tc) peaks were met at 560°C (AR4), 600°C (AR5) and 620°C (AR2). For these glasses Tc increased with UO2.67 increasing. The highest internal crystallizations were met for AR2 and AR5. Dendritic crystal growth mode was detected for slowly heat treated (up to 650°C) AR5 glass. The dendrite arms were clearly seen by SEM and the EBSD (electron back scattered diffraction) patterns (fitted to phase FePO4) remained unaltered upon moving slightly the detection position throughout those arms. [ABSTRACT FROM AUTHOR]