Reduction Mechanisms of Cu²⁺-Doped Na₂O–Al₂O₃–SiO₂ Glasses during Heating in H₂ Gas

Abstract

Controlling valence state of metal ions that are doped in materials has been widely applied for turning optical properties. Even though hydrogen has been proven effective to reduce metal ions because of its strong reducing capability, few comprehensive studies focus on practical applications because of the low diffusion rate of hydrogen in solids and the limited reaction near sample surfaces. Here, we investigated the reactions of hydrogen with Cu-doped NaO-AlO-SiO glass and found that a completely different reduction from results reported so far occurs, which is dominated by the Al/Na concentration ratio. For Al/Na < 1, Cu ions were reduced via hydrogen to metallic Cu, distributing in glass body. For Al/Na > 1, on the other hand, the reduction of Cu ions occurred simultaneously with the formation of OH bonds, whereas the reduced Cu metal moved outward and formed a metallic film on glass surface. The NMR and Fourier transform infrared results indicated that the Cu ions were surrounded by Al ions that formed AlO, distorted AlO, and AlO units. The diffused H gas reacted with the Al-O···Cu units, forming Al-OH and metallic Cu, the latter of which moved freely toward glass surface and in return enhanced H diffusion.

Hydrogen transport property of polymer-derived cobalt cation-doped amorphous silica

“…Recently, Nogami et al reported the hydrogen diffusion coefficient through sodium aluminosilicate glasses (Na2O-Al2O3-SiO2) prepared by the melt-quenching technique. 34 The diffusion coefficients of hydrogen at 400-600 °C estimated for this glass with an Al/Na atomic ratio <1 were 10 −16 -10 −15 m 2 s −1 order; as a typical example, the diffusion coefficient at 500 °C estimated for 20Na2O•10Al2O3•70SiO2 glass was 1.8 × 10 −15 m 2 s −1 . 29 In this study, as listed in Table 4, the D(Free) at 500 °C estimated for non-doped amorphous silica was 6.1 × 10 −15 m 2 s −1 .…”

Study on surface modification and optical properties of Nd-doped phosphate glass

“…According to the model, the layer thickness, X, can be obtained as a function of heating time, t, as shown in the following Equation 1: X=(2pKt/Cx) 1/2 =(4D*t) 1/2 (1) where K is the permeation of the H 2 gas, D* is the apparent diffusion coefficients of the H 2 gas, p is the H 2 pressure, and Cx is the Cu ions concentration of reaction sites [18][19][20][21].…”

Post-Synthesis Boron Doping of Silicon Quantum Dots via Hydrosilsesquioxane-Capped Thermal Diffusion

“…79,80 Additionally, the presence of hydrogen in annealing gas has been found to promote the reduction of dopants in silica glasses. [81][82][83][84] An alternative source of B is found in the reaction we propose could occur in the presence of hydrogen (Equation 2) that produces water which would readily evaporate under the presented reaction conditions. This reaction provides B while providing an explanation for the observed weight-loss.…”