Tatsumi Naganuma1,Toshihiro Kuzuya1,Hisayoshi Matsushima2,Ken Sawada1,Naoya Sawaguchi1,Akira Sato3
Muroran Institute of Technology1,Hokkaido University2,MATEC Inc3
Tatsumi Naganuma1,Toshihiro Kuzuya1,Hisayoshi Matsushima2,Ken Sawada1,Naoya Sawaguchi1,Akira Sato3
Muroran Institute of Technology1,Hokkaido University2,MATEC Inc3
We have investigated upcycling of waste glass from end-of-life vehicles. The waste glass contains various additives such as Ce, Ti, and other transition metals for UV-cut and coloring. Furthermore, alkaline earth metals were added to adjust the mechanical and chemical properties of the glass. These additives would better be used to fabricate upcycling glasses with novel functions. Therefore, we investigated the facile alkaline leaching to fabricate the nanostructure of these additives' oxides.<br/>Front and front door glass were recovered from end-of-life vehicles and pulverized into glass cullets. XRF analysis indicated that the glass cullet contained Ce, Fe, and alkaline earth metals. Glass cullets were heated at 1673K for 3 h. The glass melt was quenched on the steel plate and formed into a plate shape. Then, the as-quenched glass was annealed at 873 K for 2 h and cooled for 24 h to ambient temperature. Glass samples were cut to 7.5× 7.5mm<sup>2</sup> with a diamond cutter and mechanically polished to obtain a mirror finish. And then, the polished glass was annealed at 873K near the glass softening point for 24h. After annealing, the glass surface was polished again with 3 to 4 μm diamond paste. The glass samples were immersed in 1.0 mol/L NaOH solution for 1 or 8 days to etch Si atoms on the surface selectively. The morphology of the nanostructure formed on the surface was observed using an atomic force microscope (AFM) and a scanning electron microscope (SEM). A treated glass sample was thinned by a focused ion beam (FIB) to observe the distribution of elements near the glass surface using a STEM-EDX. The chemical state of the element on the glass surface was analyzed by XPS.<br/>AFM images indicated a significant surface morphological change between before and after etching. In the 1-day-etched glass, nano-sized precipitates were observed. After 8 days, the micrometer-order precipitates were also observed. XPS wide spectra indicated that the peak intensities of the Fe-2p, Ca-2p, Mg-2p, and Ce-3d relatively increased. The Ce-3d peak structure suggests that the Ce ion took the tetravalent state. STEM-EDX images revealed a thin film of approximately 25 nm thickness containing Fe, Ca, and Ce on the sample surface. This result is consistent with the XPS results. Furthermore, STEM and TEM images revealed nanosized cavities under the thin film of additives.<br/>NaOH reacts with SiO<sub>2</sub> to form soluble Na<sub>2</sub>O(SiO<sub>2</sub>)<sub>x</sub>. On the other hand, cerium hydroxide, calcium hydroxide, magnesium hydroxide, and iron hydroxide are deposited on the surface due to their low solubility products of 2.0×10<sup>－48</sup>(Ce(OH)<sub>4</sub>), 5.02×10<sup>-6</sup>(Ca(OH)<sub>2</sub>), 5.61×10<sup>-12</sup>(Mg(OH)<sub>2</sub>), 2.79×10<sup>-39</sup>(Fe(OH)<sub>3</sub>), respectively. As the leaching reaction proceeded, an insoluble hydroxide film formed and grew on the glass surface. Then, the leaching reaction proceeded through this thin film. As a result of this reaction process, the cavities were considered to be formed under this thin film. Because alkali earth metals and cerium exhibit strong interactions with phosphoric acid, a glass surface enriched with these elements is expected to be a strong candidate for antimicrobial and phosphoric acid recovery materials.