Role of Interfacial Energy and Crystallographic Orientation on the Mechanism of the ZnO + Al₂O₃ → ZnAl₂O₄ Solid-State Reaction: II. Reactivity of Films Deposited onto the Sapphire (001) Face

Abstract

The initial steps of the reaction between ZnO and (001)-oriented Al 2 O 3 single crystals have been investigated with X-ray diffraction, atomic force microscopy, and Xray absorption spectroscopy at the Zn−K edge starting from 45 nm thick zincite films. The reaction eventually yields the ZnAl 2 O 4 spinel on this interface but via a complex mechanism involving side and intermediate nonequilibrium compounds, the spinel initially forming with a distribution of lattice parameters. Evidence is given of the fact that one of the side compounds has a crystal structure close to that of the Zn 3 In 2 O 6 compound. The results are discussed in the general context of the same reaction on different single-crystal substrates and different film thicknesses.

Studying the surface reaction between NiO and Al2O3viatotal reflection EXAFS (ReflEXAFS)

“…This is in a sense the true chemical reaction and has been much less investigated with respect to the other reaction regimes (Kotula & Carter, 1995). Concerning the last topic, we have recently shown (Ghigna et al, 2003(Ghigna et al, , 2010d'Acapito et al, 2003a,b;Pin et al, 2009Pin et al, , 2011Pin et al, , 2013a the effectiveness of an approach to the chemical reactivity in the solid state based on the use of model reacting systems (NiO + Al 2 O 3 and particularly ZnO + Al 2 O 3 ) made of a thin layer of one reagent deposited onto a singlecrystal slab of the other reagent. The system is investigated by combining several experimental techniques and comparing the results obtained starting from different film-to-crystal orientations and different film thicknesses.…”

Unveiling the Anti-Trap Effect for Bridging Intermediates on ZnAlOx/AlPO-18 Bifunctional Catalysts to Boost Syngas to Olefin Conversion

“…However, compared with the result of the ZnO crystal, the white line peaks of Zn 0.5 AlOx (ZnAl 2 O 4 spinel) are separated into three subpeaks at about 9665, 9668, and 9672 eV, implying that there are obvious differences in the coordination structure of the Zn 2+ ion between ZnO and ZnAl 2 O 4 spinel samples. 34,35 Thanks to the different characteristic peaks of the two species, it is easily found that the XANES curve of Zn 1 AlOx exhibits typical characteristics of both ZnO and ZnAl 2 O 4 phases. To quantify the composition of Zn 1 AlOx oxide, we performed linear combination fitting of the XANES result (Figure 2c) and found that the concentrations of ZnO (56 mol %) and the ZnAl 2 O 4 spinel (44 mol %) are close to the theoretical value (50:50 in mol ratio) of the actual feeding.…”

Preparation of mesoporous ZnAl2O4 nanoflakes by ion exchange from a Na-dawsonite parent material in the presence of an ionic liquid

“…Zinc aluminate (ZnAl 2 O 4 ) spinel is a well-known wide band gap semiconductor (E g ¼ 3.8 eV) 1 ceramic material with optomechanical property, which has been extensively studied as a catalyst and catalyst support, [2][3][4] transparent conductor, 5 dielectric material, 6 optical material 7 and sensor 8 due to its high thermal stability, low surface acidity and high mechanical resistance. 9 Several methods, for example, the solid statereaction or ceramic method, 10 wet chemical routes, 11,12 the sol-gel method, 13,14 the hydrothermal method, 15 the solvothermal method, 16 the plasma method, 17 combustion in an aqueous solution 18 and molten salt synthesis 19 etc., have been applied for the preparation of ZnAl 2 O 4 spinel. However, to date, it is still a challenge to synthesize 2D or 3D ZnAl 2 O 4 spinel nanostructures via a solution route.…”