Types Of Oxygen Ions Research Articles

Unveiling the Surface Structure of ZnO Nanorods and H2 Activation Mechanisms with 17O NMR Spectroscopy.

ZnO plays a very important role in many catalytic processes involving H2, yet the details on their interactions and H2 activation mechanism are still missing, owing to the lack of a characterization method that provides resolution at the atomic scale and follows the fate of oxide surface species. Here, we apply 17O solid-state NMR spectroscopy in combination with DFT calculations to unravel the surface structure of ZnO nanorods and explore the H2 activation process. We show that six different types of oxygen ions in the surface and subsurface of ZnO can be distinguished. H2 undergoes heterolytic dissociation on three-coordinated surface zinc and oxygen ions, while the formed hydride species migrate to nearby oxygen species, generating a second hydroxyl site. When oxygen vacancies are present, homolytic dissociation of H2 occurs and zinc hydride species form from the vacancies. Reaction mechanisms on oxide surfaces can be explored in a similar manner.

Influence of CaF2 on viscosity of aluminosilicate melts

A model is developed to estimate the viscosity of aluminosilicate melts containing CaF2, in which the influence of chemical composition is expressed by different types of oxygen ions and CaF2 clusters. In this study, CaF2 is assumed to have no effect on the relative amounts of different structures Qi (i = 0–4) (where the superscript refers to the number of bridging oxygen in a given structural unit), but only acts as a diluter. The viscosity model can be well applied to CaO–FeO–CaF2–SiO2, CaO–Al2O3–CaF2–SiO2, CaO–Na2O–CaF2–SiO2 and CaO–FeO–CaF2–Al2O3–SiO2 melts. From the isoviscosity curves of the CaO–CaF2–SiO2 system plotted by the present model, it can be concluded that the substitution of CaF2 for CaO makes the viscosity decrease in an acidic composition area but almost keeps constant in the basic composition area.

Modeling Viscosities of CaO-MgO-FeO-MnO-SiO2 Molten Slags

A model for estimating the viscosity of silicate melts is proposed in this article. The structural characteristics of a silicate slag can be described by the numbers of the bridging oxygen, nonbridging oxygen, and free oxygen present in the slag. A method of calculating the numbers of the different types of oxygen ions is presented in this article, which involves a simple approximation of “complete bridge breaking.” With just a few parameters, the model provides both the temperature and composition dependencies of viscosity for the pure component: SiO2; the binary systems: MgO-SiO2, CaO-SiO2, FeO-SiO2, and MnO-SiO2; the ternary systems: CaO-MgO-SiO2, CaO-FeO-SiO2, MgO-FeO-SiO2, and CaO-MnO-SiO2; and the quaternary systems: CaO-MgO-MnO-SiO2 and CaO-FeO-MnO-SiO2. It was found that the ability of different basic metal oxides to decrease viscosity varies and is in the following hierarchy: FeO > MnO > CaO > MgO. Two factors influence the viscosity: The first is related to the mutual interaction among different ions, and the stronger the interaction, the higher the viscosity. The second factor is the size (radius) of basic oxide cation, with viscous flow becoming increasingly more difficult (i.e., viscosity increases) as the cation size increases. However, there is a paradox in the effect of cation radius (of the basic oxide) on the two factors. Thus, varying cation size causes competitive effects; smaller cationic radii give stronger interactions among ions but less hindrance to viscous flow (and vice versa for large cation radii).

Substrate-induced structural modulation of a CoO(111) bilayer on Ir(100)

We report on an unusual structural modulation of a single CoO(111) bilayer grown on $\text{Ir}(100)\text{\ensuremath{-}}(1\ifmmode\times\else\texttimes\fi{}1)$ by oxidation of slightly less than one monolayer of Co deposited on the substrate. Quantitative low-energy electron diffraction and scanning tunneling microscopy in combination with standard x-ray photoelectron spectroscopy and thermal-desorption spectroscopy reveal a cobalt layer next to the substrate covered by an oxygen layer. Both layers' hexagonal atomic arrangements are, however, strongly distorted by the quadratic substrate and form a $c(10\ifmmode\times\else\texttimes\fi{}2)$ superstructure on that. The Co layer's buckling amplitudes and atomic bond lengths to Ir atoms are consistent with the hard-sphere radius of metallic Co. The oxide's binding to the substrate appears to be further characterized by two types of oxygen ions. One of them is close to the expected rocksalt-type stacking with respect to the cobalt layer while the other type resides nearly on top of Ir atoms. Its hard-sphere radius is only $0.77\text{ }\text{\AA{}}$ (in contrast to $1.25\text{ }\text{\AA{}}$ in the CoO bulk) and it is by about $1\text{ }\text{\AA{}}$ closer to the substrate than the other type. Being so almost coplanar with the Co layer, it locally forms a hexagonal boron-nitride-type oxide. The oxygen bond to Ir can be interpreted as local pinning of the oxide to the substrate so modulating the entire oxide bilayer.

A study on the interfacial tension between solid iron and CaO–SiO2–MO system

Interfacial tension is an important property that plays an essential role in understanding wetting behavior between refractories–molten slag–steel in the steelmaking process. Most work on interfacial tensions of molten slag system have been done to clarify the effect of surface active elements in molten metal and slag composition, but there has been little work done with respect to the slags ionic structure. In this study, the interfacial tension between molten slag and solid Fe was investigated to understand the effect of the ionic structure of molten slag on interfacial tension by using solid Fe instead of molten steel. Interfacial tension measurements in CaO–SiO2–FeO and CaO–SiO2–MnO slags were carried out at 1,773 K on interstitial free (IF)-steel substrates using the sessile drop method. The composition of the slag was varied with amphoteric oxides of either FeO or MnO at unit basicity (C/S = 1.0). Results indicated a decrease in the interfacial tension with increased amphoteric oxide additions. The ionic species of molten slags were analyzed by FT-IR and the various types of oxygen ions (O2−, O−, O0) in the slag was determined by X-ray photoelectron spectroscopy. The silicate bonding degree and the slags ionic behavior were semi-quantitatively analyzed with respect to the slag’s ionic structure model. By dissociating the slags networking structure with increased free oxygen ions, the interfacial tension decreased. Considering the ionic theory of molten slags, results indicate that the interfacial properties are directly affected by the ionic structure of the slag. This work hopes to clarify the relationship between the interfacial tension and the distribution of various oxygen ions.

Prediction of transport properties of new functional materials based on lanthanum-strontium cuprates: Molecular mechanics calculations

The method of molecular dynamics is used for prediction of properties of new functional materials based on lanthanum-strontium cuprates La2 − x Sr x CuO4 − δ as new materials of the solid state ionics. The most interesting phases are synthesized to test the obtained calculation data and their electrophysical and thermomechanical characteristics are studied. It is shown that the high values of the oxygen diffusion coefficients are obtained in the La2 − x Sr x CuO4 − δ solid solutions with a high replacement degree of Sr → La (up to x = 1). The calculated values of lattice cell parameters, thermal expansion coefficients and oxygen diffusion coefficients agree with the experimental data. The observed anisotropy of anionic transport for all the studied compositions corresponds to the regularities of crystal structure of complex oxides. Using the molecular dynamics method allows tracing the contribution of separate types of oxygen ions (equatorial and apical) into ionic transport at the microscopic level and also confirming directly that oxygen diffusion occurs according to the usual jump mechanism, mainly in (CuO2) layers.

The molecular dynamics study of oxygen mobility in La 2− xSr xCuO 4− δ

Oxygen diffusion in layered cuprates La 1.63Sr 0.37CuO 3.81 and LaSrCuO 3.5 was simulated by molecular dynamics (MD) procedure. Two types of oxygen ions in the crystal lattice are characterized by different mobility at elevated temperatures (750–1000 K). Mechanistic features of oxygen transport are discussed.

Assignment of the hydroxyl bands in the infrared spectra of zeolites X and Y. Part 1.—Na—H zeolites

The infrared spectra of zeolites X and Y were recorded in the hydroxyl stretching region under high resolution conditions. The samples varied in their Al and proton content. The spectra were broken down into six different components. The selection of this number of components was based on reproducible details appearing in the high resolution spectra. An assignment for the different components is proposed, which considers the four different types of oxygen ions as possible sites for proton location. The narrow band at 3650 cm–1 is assigned to O1—H hydroxyl groups, while the broad and asymmetric band at 3550 cm–1 contains components due to O2—H, O3—H and O4—H groups.