Noble metals and their oxide nano-clusters are considered to be the most promising candidates for fabricating advanced H₂ gas sensors. Through this work, we propose a novel strategy to grow and modulate the density of PdO/PdO₂ nanoparticles uniformly on nanostructured Pd-doped ZnO (ZnO : Pd) films by a one-step solution approach followed by thermal annealing at 650 °C, and thus to detect ppm-level H₂ gas in a selective manner. The gas sensing properties of such hybridized materials showed that the PdO-functionalized ZnO samples offer significantly improved H₂ gas sensing properties in an operating temperature range of 25–200 °C. The deposition of ZnO : Pd films via a simple synthesis from chemical solutions (SCS) approach with an aqueous bath (at relatively low temperatures, <95 °C) is reported. Furthermore, the functionalization of palladium oxide nanoclusters by a simple but highly effective approach on ZnO : Pd film surfaces was performed and is reported here for the first time. The morphological, structural, vibrational, optical, chemical, and electronic properties were studied in detail and the mixed phases of palladium oxide nanoclusters on the ZnO surface were found. Sensor studies of the ZnO : Pd samples (in the range of 25–350 °C operating temperature) showed good selectivity to H₂ gas, especially in the range of higher temperatures (>150 °C, up to 350 °C); however, the PdO/PdO₂ mixed phases of the nanocluster-modified surface ZnO : Pd films showed a much better selectivity to H₂ gas, even at a lower operating temperature, in the range of 25–150 °C. For such PdO-functionalized ZnO : Pd films, even at room temperature, a gas response of ∼12.7 to 1000 ppm of H₂ gas was obtained, without response to any other reducing gases or tested vapors. The large recovery time of the samples at room temperatures (>500 s) can be drastically reduced by applying higher bias voltages. Furthermore, we propose and discuss the gas sensing mechanism for these structures in detail. Our study demonstrates that surface functionalization with PdO/PdO₂ mixed phase nanoclusters–nanoparticles (NPs) is much more effective than only the Pd doping of nanostructured ZnO films for selective sensing applications. This approach will pave a new way for the controlled functionalization of PdO/PdO₂ nanoclusters on ZnO : Pd surfaces to the exact detection of highly explosive H₂ gas under various atmospheres by using solid state gas sensors.

Neutron diffraction experiments have been performed on alkali diborate glasses and melts, $M_2\mathrm{O}-2{\mathrm{B}}_2{\mathrm{O}}_3$ with $M=\mathrm{Li},$ Na, K, in order to investigate the structural changes above the glass transition. In the glassy state, the contributions of fourfold- and threefold-coordinated boron could be clearly distinguished on the first peak of the correlation functions, which has been fitted with two Gaussian components. The fraction of boron in fourfold coordination ${(N}_4)$ is 0.46, 0.43, and 0.40 for the Li-, Na-, and K-bearing glasses, respectively, in agreement with previous NMR studies. In the liquid state at $\sim 1200\mathrm{K},$ a one-component fit of the peak yields an $N_4$ value of about 0.30, which means that one-third of the ${\mathrm{BO}}_4$ tetrahedra in the glass converts to ${\mathrm{BO}}_3$ triangles in the melt. The estimated change of the mean heat capacity for this conversion is in the range $27–73{\mathrm{J}\mathrm{}\mathrm{mol}}^{-1}{\mathrm{K}}^{-1}.$ This value accounts for the major part of the total heat capacity change at $T_g,$ suggesting that the ${\mathrm{BO}}_4$ to ${\mathrm{BO}}_3$ conversion is mainly responsible for the fragile behavior of the viscosity of alkali borate melts. Indeed it is closely related to the dynamic processes of the viscous flow, which involve both the akali migration and B-O bond breakening and reforming.

While glass alteration in liquid water has been widely studied for decades, glass alteration in unsaturated atmosphere (relative humidity, RH < 100%) has been far less examined. However, the understanding of the mechanisms involved in the reactions between glass and water in vapor state is fundamental to several fields such as glass industry, conservation of glasses of the cultural heritage and long-term assessment of nuclear waste glasses. This paper outlines the issues raised by the atmospheric alteration of glass in these fields and attempts to summarize the scientific approaches and findings of the three communities. This short review reveals that atmospheric alteration should not be confused with liquid alteration at high S/V (S = exposed surface of glass and V = volume of solution), because the kinetics and the nature of the alteration products are distinct. Notably, alkalies and non-bridging oxygens may be significantly retained in glass hydrated in unsaturated atmosphere, depending on the glass composition. Future lines of research are drawn to progress in the understanding of the specificities of atmospheric glass alteration.