Metallic Cluster Formation in Glasses
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Hydrogen reactions with glasses containing different metallic ions were investigated. Hydrogen successfully reduced Ni, Co, Cu and Pb in soda-lime-silica glasses at a range of different temperatures (500°C, 550°C, 600°C, and Tg). The tarnishing model was successfully applied to account for the increase in the “free hydroxyl” absorption band at high reaction temperatures. At lower temperatures, it was shown that nickel and cobalt absorbance data did not follow the tarnishing model, most likely due to the slow reaction rates involved with reducing these ions and a dehydroxylation mechanism. The permeability of hydrogen molecules was calculated from the absorbance data and found to be ~30 times lower than that reported in the literature. This was again explained by a dehydroxylation mechanism. A possible interaction between the metallic clusters and the glass matrix was identified for the lead containing glass. This interaction is most likely an interfacial bond between the cluster and the glass which results in a stretching of the lead lattice upon cooling. Hydrogen also reduced indium in a series of sodium-indium-silicate glasses over a range of temperatures (500°C, 550°C, 600°C, and Tg). The indium containing glasses all exhibited an increase in the absorbance of the “free hydroxyl” band with the square root of reduction time, but the trends with temperature were inconsistent. This was explained through an enhanced dehydroxylation mechanism due to the high concentrations of hydroxyl being formed in the glass. These glasses also exhibited a clear property change (viscosity, Tg, durability, thermal expansion) at the surface due to the removal of indium leaving residual soda-silicate glass in the composition region of immiscibility. Hydrogen induced formation of alloys of nickel and copper was also demonstrated. The reaction rate had little effect on alloy formation and as long as the metals in question will form an alloy and diffuse at the treatment temperatures, an alloy composition is possible. This opens up the door for a variety of new, unexplored, bulk properties for glasses ranging from magnetism to catalysis.