Thermal properties and crystallization of iron phosphate glasses containing up to 25wt% additions of Si-, Al-, Na- and U-oxides

Abstract

The thermal properties (expansion, T g and T SOFT. ) of glasses, having 56-66% P 2 O 5 , 14.8-34.2% Fe 2 O 3 and 2-25 wt% additions of SiO 2 , Al 2 O 3 , Na 2 O and UO 2 , were comparatively estimated from dilatometric measurements in similar conditions. The T g reversibility was clearly verified by varying the heating rates between 1 and 5°C min À1 . From linear equations fits of the various glass properties as functions of the six components it is suggested the iron, sodium and uranium oxides decrease the thermal expansion (for 50 < T 6 300°C), T g and T SOFT. From DTA/XRD analysis of three glasses it was confirmed the crystallization tendency decreased with increasing the UO 2 level in the glasses. Leaching test data for two compositions containing Na 2 O suggest addition of UO 2 increases the chemical durability of the related glass. The roles of UO 2 , Na 2 O and Fe-oxide species as structural components of the glass network are discussed.

A review on immobilization of phosphate containing high level nuclear wastes within glass matrix – Present status and future challenges

“…Dependence of chemical durability on O/P molar ratio shows that maximum durable Fe-phosphate glasses can be obtained when O/P ratio is ∼3.6-3.7 (pyrophosphate glasses); on either side of this range chemical durability tends to decrease. Further, Fe 3 (P 2 O 7 ) 2 type structure shows that it contains interstitial voids large enough to accommodate ions as large as U 4+ and Cs + [119]. The ionic crystal radii (for coordination number 6; in Å) of some important HLW constituents within Fe-phosphate glasses are P 5+ : 0.35, O 2− : 1.40, Si 4+ : 0.40, Fe 2+ : 0.77, Fe 3+ : 0.65, U 4+ : 0.89-0.97, U 5+ : 0.79, Al 3+ : 0.53 and Na + : 1.02.…”

“…The ionic crystal radii (for coordination number 6; in Å) of some important HLW constituents within Fe-phosphate glasses are P 5+ : 0.35, O 2− : 1.40, Si 4+ : 0.40, Fe 2+ : 0.77, Fe 3+ : 0.65, U 4+ : 0.89-0.97, U 5+ : 0.79, Al 3+ : 0.53 and Na + : 1.02. This is why the Fe-phosphate glass networks remain largely insensitive to the additions of P 2 O 5 -HLW cations and can solubilize them in high quantity without sacrificing much on its chemical durability aspects [119]. Previously, Day et al [110] could load simulated waste of ∼32 wt% (against ∼10 wt% in borosilicate glass) for the high sulfate LAW (Hanford), to ∼40 wt% (against ∼20 wt% in borosilicate glass) for the SBW (INEEL), to ∼75 wt% (against ∼15 wt% in borosilicate glass) for the high chrome HLW (Hanford).…”

“…Bingham and Hand [114] noted 4 2− than it usually retains (<0.5 mol%). In continuation to these studies, Kim and Day [130] and Kim et al [131] could successfully load 30 wt% of simulated LAW and 40 wt% of simulated SBW within Fe-phosphate glass respectively, and satisfied all necessary product consistency and vapor hydration test requirements [132,133] even when deliberately crystallized (containing Fe 3 (P 2 O 7 ) 2 , Fe 4 (P 2 O 7 ) 3 , BiPO 4 , Na 3 Fe 2 (PO 4 ) 3 , Ca 5 F(PO 4 ) 3 , Al(PO) 4 and Al 2 O 3 ) [110,119]. Surficial layers developed on the waste glasses were found to consist of NaFe 3 P 2 O 7 (OH) 3 ·H 2 O, Na 3 Fe(PO 4 ) 2 ·H 2 O, NaFeH 2 (PO 4 ) 2 and Na 3 Al(PO 4 ) 2 ·1.5H 2 O, which according to Ewing and Wang [21] depends on the metal (M)-tophosphorous (P) ratio of the glass.…”

Crystallization of iron phosphate glasses containing up to 19wt.% UO2.67

“…Melting of industrial wastes has been considered recently for the immobilization and recycling of a wide range of wastes as well as isotopes of high and medium activity resulting from nuclear power [1][2][3][4][5][6][7][8][9][10]. Iron phosphate glasses are promising matrices for the immobilization of a wide range of substances including oxides of uranium [3][4][5].…”

“…Iron phosphate glasses are promising matrices for the immobilization of a wide range of substances including oxides of uranium [3][4][5]. The dilatometric characterization of glasses with composition 56-66 wt.% P 2 O 5 , 14.8-34.2% Fe 2 O 3 and 2-25% additions of SiO 2 , Al 2 O 3 , Na 2 O and UO 2 was performed elsewhere [5]. The Tg (glass transition temperature) reversibility was clearly verified by varying the heating/cooling rates between 1 and 5°C min −1 .…”