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Chemical state
About: Chemical state is a research topic. Over the lifetime, 2378 publications have been published within this topic receiving 78183 citations.
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TL;DR: In this article, a time-of-flight secondary ion mass spectrometry (TOF-SIMS) was employed to characterize the surface physical and chemical state of aluminovanadate oxide catalyst precursors ('V-Al-O') precipitated at different pH values in the range of 5.5...10.
Abstract: Time-of-flight Secondary Ion Mass Spectrometry (TOF-SIMS) has been employed to characterize the surface physical and chemical state of aluminovanadate oxide catalyst precursors ('V-Al-O') precipitated at different pH values in the range of 5.5...10. The reference oxide V2O5 has also been studied for comparison purposes. It is shown that the analysis of molecular ion emission yields valuable information on the surface elemental and phase composition. Increasing pH values while precipitating from aqueous precursor solutions are found to result in a monotonic variation of the surface composition, in a progressive hydroxylation of aluminium and vanadium and in an increasing dispersion of vanadium oxide species. SIMS data evaluated on the basis of Plog's valence model of molecular ion emission reveal reduced V4+ states, the fraction of which is dependent on the pH value. The SIMS results are supported by XPS data. The enhancement of the catalytic activity in oxidative propane dehydrogenation over V-Al-O prepared at high precipitation pH is in good correlation with the measured surface characteristics. Copyright (c) 2007 John Wiley & Sons, Ltd.
3 citations
20 Feb 2014
TL;DR: In this article, the authors defined the corrosion process as the destruction of metallic materials after direct chemical action to occur without an environment changed by the electric charges, where the products resulting from the interaction between the metal and environment remain on the metal surface in formats of thin films.
Abstract: The corrosion process involves a sequence of reactions in which a metal or an alloy is attacked by an aggressive agent [4, 13]. Due to their particular electronic structure characterized by the presence of free electrons in the crystalline network, metals and alloys react chemically or electrochemically and thus may suffer corrosion processes [13, p.85]. The stabile chemical state of the metals is the combined one (oxides, hydroxides, other components) as they appear in the ore from which it was derived. In other words, the metals have a spontaneous tendency to return in a thermodynamically stable combined state through corrosion. Chemical Corro‐ sion is the destruction of metallic materials after direct chemical action to occur without an environment changed by the electric charges. The products resulting from the interaction between the metal and environment remain on the metal surface in formats of thin films. The initial oxide layer/film has a thickness of 10 to 20A0, and then corrosive attack depends on its physical properties such as adhesion, compactness, porosity and the volume of this layer in relation to the volume of metal. The nature of the parent metal is determining both the thermodynamic stability and the properties of the oxide film formed on its surface. Some alloys have a corrosion resistance higher than that of the technical metals through their alloying elements (Al, Cr, Ni, Si) which allow the formation of protective oxide coatings. Electrochem‐ ical corrosion represent destructive attack on metals or alloys exercised by the corrosive environment through electrochemical reactions, in which the metal releases electrons and its positive ions enter in solution. The formation of positive ions and electrons create an electrical potential (in volts) called electrode potential [28, 29].
3 citations
TL;DR: In this paper, the correlation of surface states and photoactivity of a Pt/TiO2 catalyst prepared by means of photoreduction of on anatase nano-TiO 2 powders was investigated.
Abstract: This paper deals with the correlation of surface states and photoactivity of a Pt/TiO2 catalyst prepared by means of photoreduction of on anatase nano-TiO2 powders. Conductivity measurements of pressed powders and XPS were applied in analysis of the surface states energy levels and chemical states of Pt at the nano-TiO2 surface, respectively. The results revealed a new surface state with the energy level of 0.35 eV, lower than the conduction band edge of TiO2. According to the XPS analysis, the new surface state can be attributed to the Pt0 clusters deposited on the surface of TiO2 particles. The photoactivity of the as-prepared Pt/TiO2 catalyst was characterized by photodecoloration of brilliant red X-3B in aqueous solution. The experimental results indicated that the photoactivity of the Pt/TiO2 catalyst is much higher than that of TiO2. The surface Pt0 clusters possibly function as trapping centers of generated electrons, resulting in the promotion of photocatalytic activity.
2 citations
TL;DR: In this paper, the physico-chemical state of silicon atoms present in the HfO 2/SiO 2 /Si system is studied by X-ray emission spectroscopy induced by electrons.
2 citations
2 citations