Some Microstructural Properties of Zinc Borosilicate Glass as a Possible Matrix in the Immobilization of Various Wastes

Zinc borosilicate glass with optimized chemical composition was synthesized and doped with 5 wt % α-Fe2O3. XRD, 57Fe Mössbauer, FT-IR, UV/Vis/NIR and FE SEM were used as the characterization methods. XRD showed the amorphous nature of the samples synthesized. 57Fe Mössbauer spectra confirmed the superposition of Fe3+ in tetrahedral and Fe2+ in octahedral positions. FT-IR spectra showed general features characteristic of different borosilicate glasses. The NIR band at 1116 nm in the UV/Vis/NIR spectrum was assigned to the Fe2+ transition, whereas the Fe3+ transition bands could not be assigned due to the overlapping of several spectral bands of different origin in the UV region centered at 282 nm and the Vis region between 415 to 496 nm. Zinc borosilicate glass as synthesized can be considered as a possible matrix in the immobilization of nonradioactive as well as radioactive wastes.

Barium (Zinc) Borosilicate Sealing Glass and Joining Interface with YSZ Electrolyte and Crofer22APU Interconnect in SOFCs

This work describes the performance of two glass-ceramic compositions, BaO-SiO2-B2O3 (Barium borosilicate glass: BaBS) and BaO-ZnO-SiO2-B2O3 (Barium zinc borosilicate glass: BaBS−Zn), used for joining YSZ ceramic electrolytes and Crofer22APU metallic interconnects in solid oxide fuel cells (SOFCs) working at 800°C for 50 h. ZnO had a negative effect on the thermal expansion coefficient (TEC) value of the BaBS-Zn glass-ceramic. XRD and SEM results revealed the formation of rod-shaped barium zinc silicate crystalline phases in the BaBS-Zn glass, which was accompanied by cracks and poor adherence at the YSZ/BaBS-Zn joint interface after working at 800°C for 50 h. The formation of cracks parallel to the interface between the Crofer22APU interconnect and the BaBS-Zn glass-ceramic sealant was observed due to the severe TEC mismatch. The BaBS glass–ceramic adhered well to the YSZ electrolyte as well as the pre-oxidized Crofer22APU without cracks. Chromium oxide scale developed between the pre-oxidized Crofer22APU/BaBS glass-ceramic joint interface with increasing the pre-oxidation temperature. This study shows that BaBS glass-ceramic is more effective than BaBS-Zn as a sealant for joining YSZ electrolytes and Crofer22APU metallic interconnects in SOFCs working at 800°C for 50 h.