Sergiy Vasil´ović Merzlikin

Anomalous surface compositions of stoichiometric mixed oxide compounds.

Surface-oxide films are present in many types of oxidecontaining materials, such as grain boundaries in ceramics, interfaces in ceramic-ceramic and metal-oxide systems, and affect their materials and transport properties. In heterogeneous catalysis, the properties of the outermost surface layer are of prime importance because they control the catalytic performance. Although bulk mixed-metal oxide catalysts are widely used in industrial selective oxidation processes, not much is known about their outermost surface composition. Models based on surfaces derived from a truncation of the bulk structure have dominated discussion on catalytic reaction mechanisms and active sites (reviewed, for example, in Ref. [6]). This view has been questioned by several recent studies reporting the surface enrichment and depletion phenomena in solid-oxide solutions (e.g., CoxNi1 xO ), the identification of TiO2-rich overlayers on reconstructed SrTiO3(001) model surfaces, [8] and evidence for the formation of amorphous oxide overlayers in which there is surface enrichment of one of the components under selective oxidation reaction conditions. However, the development of realistic concepts on reactant activation, surface reaction mechanisms, and the design of advanced catalytic materials are still hampered by the lack of detailed knowledge of the surface composition and structure of bulk mixed-metal oxides. For such studies, X-ray photoelectron spectroscopy (XPS) with laboratory sources is of limited value because its average sampling depth of 1–3 nm results in a signal where the outermost surface layer only contributes on the order of 30%. Synchrotron radiation allows for increasing the surface sensitivity of XPS by decreasing excitation and, hence, photoelectron kinetic energies. Exclusive information on the outermost surface layer, however, is only given by low-energy ion scattering (LEIS) because ions penetrating below the surface become largely neutralized. The surfaces of stoichiometric bulk mixed-metal molybdates and vanadates have also been characterized through their interactions with probe molecules, for example, CH3OH, [12–15] which allows CH3O* and intact CH3OH* intermediates on different surface cations to be discriminated by IR spectroscopy. For such materials, combined methanol chemisorption and oxidation kinetic studies suggested a strong surface enrichment of MoOx or VOx. [12,14,15] In methanol oxidation studies, similar catalytic turnover frequencies were found over bulk mixed-metal oxides and related supported metal oxides (e.g., Fe2(MoO4)3 and MoO3/Fe2O3), which supports the idea of surface MoOx enrichment of the bulk phases. These observations, however, are qualitative as exposed metal oxide ions of low catalytic activity would not be detected by the test reaction. Thus, we have undertaken a study of the outermost surface compositions of such compounds by LEIS and excitation-energy resolved XPS (ERXPS). The LEIS was applied in sputter series taking advantage of its destructive character, the ERXPS is a version utilizing information from different sampling depths. LEIS sputter series from stoichiometric bulk mixed oxides and related supported metal oxides are given in Figure 1 and [*] Dr. S. V. Merzlikin, Prof. Dr. W. Gr nert Lehrstuhl f r Technische Chemie, Ruhr-Universit t Bochum Postfach 102148, 44780 Bochum (Germany) Fax: (+49)234-32-14115 E-mail: w.gruenert@techem.rub.de Homepage: http://www.techem.rub.de Dr. N. N. Tolkachev N. D. Zelinsky Institute of Organic Chemistry Russian Academy of Sciences, Moscow (Russia)

An electrochemical calibration unit for hydrogen analysers

Determination of hydrogen in solids such as high strength steels or other metals in the ppb or ppm range requires hot-extraction or melt-extraction. Calibration of commercially available hydrogen analysers is performed either by certified reference materials CRMs, often having limited availability and reliability or by gas dosing for which the determined value significantly depends on atmospheric pressure and the construction of the gas dosing valve. The sharp and sudden appearance of very high gas concentrations from gas dosing is very different from real effusion transients and is therefore another source of errors. To overcome these limitations, an electrochemical calibration method for hydrogen analysers was developed and employed in this work. Exactly quantifiable, faradaic amounts of hydrogen can be produced in an electrochemical reaction and detected by the hydrogen analyser. The amount of hydrogen is exactly known from the transferred charge in the reaction following Faradays law; and the current time program determines the apparent hydrogen effusion transient. Random effusion transient shaping becomes possible to fully comply with real samples. Evolution time and current were varied for determining a quantitative relationship. The device was used to produce either diprotium (H2) or dideuterium (D2) from the corresponding electrolytes. The functional principle is electrochemical in nature and thus an automation is straightforward, can be easily implemented at an affordable price of 1-5% of the hydrogen analysers price.

Ultra high vacuum high precision low background setup with temperature control for thermal desorption mass spectroscopy (TDA-MS) of hydrogen in metals

In this work, a newly developed UHV-based high precision low background setup for hydrogen thermal desorption analysis (TDA) of metallic samples is presented. Using an infrared heating with a low thermal capacity enables a precise control of the temperature and rapid cool down of the measurement chamber. This novel TDA-set up is superior in sensitivity to almost every standard hydrogen analyzer available commercially due to the special design of the measurement chamber, resulting in a very low hydrogen background. No effects of background drift characteristic as for carrier gas based TDA instruments were observed, ensuring linearity and reproducibility of the analysis. This setup will prove to be valuable for detailed investigations of hydrogen trapping sites in steels and other alloys. With a determined limit of detection of 5.9×10(-3)µg g(-1) hydrogen the developed instrument is able to determine extremely low hydrogen amounts even at very low hydrogen desorption rates. This work clearly demonstrates the great potential of ultra-high vacuum thermal desorption mass spectroscopy instrumentation.

An Investigation of the Different Methods of Removing Specimens for Hydrogen Analysis from Damaged Cold Finishing Rolls

Kurzfassung Beim Kaltwalzen ist seit langem eine typische Art von Ausschalungsbrüchen der Walzen bekannt. Es wird angenommen, dass eine Wasserstoffversprödung der gehärteten Walzen für die Schäden verantwortlich ist. Atomarer Wasserstoff kann beim Walzvorgang durch eine galvanische oder eine chemische Reaktion entstehen und in die Walze eindringen. Bei jedem Verdacht auf wasserstoffinduzierten Walzenbruch muss der gesamte Wasserstoffgehalt bestimmt werden, um die Ursache des Schadens genau festzustellen. In dieser Arbeit wurde die Abhängigkeit der Ergebnisse der Wasserstoffanalysen von den jeweiligen Probenentnahmeverfahren untersucht, um dadurch mögliche Verfälschungen auszuschließen und eine Richtlinie für diese Prozedur für die Zukunft zu erarbeiten.Kurzfassung Beim Kaltwalzen ist seit langem eine typische Art von Ausschalungsbruchen der Walzen bekannt. Es wird angenommen, dass eine Wasserstoffversprodung der geharteten Walzen fur die Schaden verantwortlich ist. Atomarer Wasserstoff kann beim Walzvorgang durch eine galvanische oder eine chemische Reaktion entstehen und in die Walze eindringen. Bei jedem Verdacht auf wasserstoffinduzierten Walzenbruch muss der gesamte Wasserstoffgehalt bestimmt werden, um die Ursache des Schadens genau festzustellen. In dieser Arbeit wurde die Abhangigkeit der Ergebnisse der Wasserstoffanalysen von den jeweiligen Probenentnahmeverfahren untersucht, um dadurch mogliche Verfalschungen auszuschliesen und eine Richtlinie fur diese Prozedur fur die Zukunft zu erarbeiten.