Chemical state

About: Chemical state is a research topic. Over the lifetime, 2378 publications have been published within this topic receiving 78183 citations.

Chapter 1 Surface Spectroscopic Techniques

Abstract: Publisher Summary This chapter discusses the surface spectroscopic techniques. Surface analysis of heterogeneous catalysts involves the measurement of three different quantities. The most important of these are the qualitative identification of surface species—that is, what atom-type is at the surface. The second concerns the chemical state of these atoms—that is, the oxidation state of surface species. It is necessary to determine the spatial location of the surface structures. Most of the surface spectroscopies require an ordered surface—that is, a single crystal. The electron spectroscopies fall in this category, although Auger spectroscopy is not so rectricted, and has been successfully applied to the study of promoter distribution in a commercial ammonia synthesis K2O-Al2O3-Fe catalyst. The small area samples, single crystal or polycrystal-line foils, but well suited to characterize surfaces in ultrahigh vacuum by low energy electron diffraction (LEED), Auger spectroscopy (AES) or other surface sensitive techniques, can be used as model catalysts, as a special configuration provides parallel kinetic studies under conditions that are virtually identical to those used in the chemical technology.

Chemical State and Properties of the New Layer Structure Compound PrRh4.8B2 Single Crystals Obtained by Molten Metal Flux Method Using Cu as Solvent

Abstract: A new layer structure compound PrRh4.8B2 was obtained by a molten metal flux growth method, using Cu as a flux. This compound belongs to the orthorhombic system with the space group Fmmm. Lattice parameters were a=0.9697(4)nm, b=0.5577(2)nm and c=2.564(3)nm. The structure of the compound is of a modified CeCo3B2-type, which is explained by a stacking model of Pr-B and rhodium layers. X-ray photoelectron spectra were taken under three conditions: (i) surface of fractured in the vacuum of the spectrometer; (ii) surface exposed to air after fracture in the spectrometer; and, (iii) surface fractured in air. The X-ray photoelectron spectroscopic study and electron probe micro-analysis results show that a few monolayers of Cu atoms exist between the crystals of PrRh4.8B2. The thermo-gravimetric curve shows that oxidation of the PrRh4.8B2 proceeds above 873K. Weight gain of the specimen heated up to 1473K in air is 13.44%. Sample forms PrBO3 and Rh as a result of the oxidation. The temperature dependence of the inverse static magnetic susceptibility χ-1 obeys the Curie-Weiss law at temperatures above 50K. The magnetic moment μeff is 4.2μB and the Curie-Weiss temperature Θp is-13K. The value of micro Vickers hardness for c-plane with the orthorhombic symmetry of PrRh4.8B2 is 6.7±0.6GPa.

Effects of implantation conditions on retention behavior of deuterrium in highly oriented pyrolytic graphite

Abstract: Implantation temperature dependence on chemical behavior of energetic deuterium (D) implanted into highly oriented pyrolytic graphite (HOPG) was investigated by thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS) in the temperature range 323–873 K. The experimental results showed that the D retention decreased with the increase of the implantation temperature. The π-π* transition peak of HOPG, which suggests the existence of sp 2 -π bonding of graphite structure, disappeared after D 2 + implantation at 323 K, while the peak recovered when isochronal heating above 773 K was performed, which corresponded to the beginning temperature of the D desorption in the TDS spectrum. Therefore, this suggests that the D desorption could correlate with the recovery of graphite structure disordered by the D 2 + implantation. In addition, the implanted D was found to be trapped in two different chemical states that desorbed at 900 K and 1050 K, namely Peak 1 and Peak 2, respectively: the former is a trapping state of D with forming sp 3 hybrid orbital type C–D bond and the latter with forming σ type C–D bond of sp 2 hybrid carbon.

Effect of K doping on Mo6+stability and ionic conductivity study in La2Mo2O9 as oxide-ion conductor

Abstract: The structural stability and ionic conductivity of K doped LAMOX have been extensively studied by many researchers. But the chemical state analysis and relaxation dispersion studies of La1.9K0.1Mo2O9-delta, La1.8K0.2Mo2O9-delta and pristine La2Mo2O9 are very scarcely reported. Here in the present study, the chemical state analysis, relaxation dispersion along with structural stability and ionic conductivity studies are done to investigate the effect of K doping in LAMOX. The room temperature XRD analysis of La1.9K0.1Mo2O9-delta, La1.8K0.2Mo2O9-delta compounds shows formation of beta-LAMOX phase along with K2O as an additional phase. The x-ray photoelectron spectroscopy (XPS) results are analysed for both K doped compositions sintered in air as well as in Ar 90%-H-2 10% atmosphere. Both the compositions show good amount of Mo6+ stabilisation in Ar-H-2 atmosphere. The Raman spectroscopy analysis of La1.9K0.1Mo2O9-delta and La2Mo2O9 shows the signature of oxygen vacancies at 866 cm(-1). The activation energy (E-a) is found to be 0.66 eV for La1.8K0.2Mo2O9-delta. The low value of d.c. conductivity of 12 mu S cm(-1) at 400 degrees C may be due to the hindrance imposed by large ionic radius of K+ ion as compared to La3+ ion in the structure which restricts its applications in IT-SOFCs.