Comparison of Drying Procedures for the Preparation of Alumina Powders with the System Al-Alkoxide/Tertiary Butanol/Water

Two series of alumina gel precursors, obtained from Al sec-butylate, ASB, or Al tert-butylate, ATB, dissolved in tertiary butanol, TB, have been dried according to five procedures, in order to compare their efficiency and the consequences they may have on the structure of the final product. They consist of lyophilization (or freezedrying), evacuation at room temperature (with or without ageing of the gel), drying in an oven at atmospheric pressure, or under hypercritical conditions. Chemical analysis, X-Ray diffraction and spectroscopic characterizations (FTIR and laser Raman) allow the identification of the phases present. The temperature of the drying step, as well as the nature of the alkoxide percursor, considerably affect the final dried products.     

A Deterministic Filter for non-Gaussian State Estimation

The usual mathematical method to represent uncertain quantities, for example the state of a dynamical system with uncertain initial conditions, are random variables (RVs). In many problems the space of elementary events Ω, on which the RVs are defined as functions of these events, is not concretely accessible, so that the usual idea of a function (e.g. given as a formula) loses much of its meaning. The representation of RVs is therefore often strikingly different from what is used for “normal” functions. With the help of RVs one can formulate Bayesian estimators for the uncertain quantity when additional information (usually noisy, incomplete measurements) becomes available. A common way to derive such an estimator is to use an instance of the projection theorem for Hilbert spaces. In this work we present a linear Bayesian estimation method which results from using a recently popular representation of an RV, the polynomial chaos expansion (PCE), also known as “white noise analysis”. The resulting method is completely deterministic, as well as computationally efficient. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Surface analytical examinations of welded nickel alloys by XPS, SNMS and SEM/EDX

Tarnish layers are formed in the heat affected zone during the welding of steels and nickel based alloys. They commonly consist of oxides of the alloying elements. The corrosion behaviour of welded components is generally influenced by the thickness and composition of the oxide films. In the following the corrosion behaviour of annealed samples cut from NiMo28 and NiMo16Cr16Ti is investigated, correlating XPS, SNMS and SEM/EDX data to their pitting corrosion potentials.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Synthesis and Characterization of Hydrophobic Silica Aerogels Using Trimethylethoxysilane as a Co-Precursor

The hydrophobic property is one of the most important requirements for the long-term use of silica aerogels for transparent or translucent window insulation and opaque thermal insulating systems. Therefore, the present paper deals with the synthesis and characterization of hydrophobic silica aerogels using trimethylethoxysilane (TMES) as a co-precursor. Silica sol was prepared by keeping the molar ratio of tetramethoxysilane (TMOS) precursor, methanol (MeOH) solvent, water (H₂O) and ammonia (NH₄OH) catalyst constant at 1:12:4:3.7 × 10^–3 respectively throughout the experiments and the TMES/TMOS molar ratio (A) was varied from 0 to 2.35. The resulting silica alcogels were dried supercritically by high-temperature alcohol solvent extraction. Hydrophobicity of the aerogels was tested by measuring the percentage of water adsorbed by the aerogels after putting them directly on the surface of water under humid conditions. Alternately, the hydrophobicity was also tested by contact angle measurements. It was found that as the A value increased, the hydrophobicity of the aerogels increased but the optical transmission decreased from 93% to less than 5% in the visible range. The thermal stability of the aerogels was studied in the temperature range from 25 to 400°C. The hydrophobic nature of the aerogels was maintained up to a temperature of 300°C. The aerogels were characterized by infrared spectroscopy, optical transmittance, Scanning electron microscopy (SEM) and contact angle measurements. The results have been discussed by taking into account the hydrolysis and condensation mechanisms.     

Effect of thermal ageing in oxidizing or reducing atmosphere on the texture and structure of palladium, copper and palladium-copper on alumina catalysts

A series of palladium, copper and palladium-copper supported on alumina catalysts were aged at high temperature (100°C) in oxidizing (oxygen) or reducing (hydrogen) atmosphere. The effect of this treatment on the texture and structure of these samples was studied. Oxidizing atmosphere gives large particles of palladium oxide, whgereas reducing atmosphere gives large particles of copper or of palladium-copper on alumina catalysts when agend in reducing conditions while the hydrogenating activity is drastically decreased.     

Kinetics of the catalytic transformation of isobutene into methacrylonitrile with NO on supported nickel oxide aerogel

Kinetic studies of the nitroxidation of isobutene by NO show that the reaction follows a redox mechanism in the temperature range of 300–400°C. This mechanism implies an interaction between dehydrogenated isobutene -allyl radical and atomic nitrogen due to the decomposition of NO by the reduced catalyst, which is then reoxidized.

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NO , 300–400°C. - , NO , .

     

Activation of magnesia by hydrogen spillover

Magnesia aerogel activated by hydrogen spillover at 430 °C or at 200 °C becomes a catalyst for the hydrogenation of ethylene. This catalytic activity, observed already at 50 °C, is further enhanced by a treatment in oxygen at 430 °C.

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, 430 200°C, . 50°C 430°C.

     

Isomerization and hydrogenation of butene-1 on a zirconia aerogel catalyst

Zirconia is well known as a promising support for active metallic centers but it is also by itself an interesting catalyst for reactions involving hydrogen in particular. This paper describes the catalytic properties of ZrO₂-obtained in the form of an aerogel-, towards butene-1-isomerization and/or its hydrogenation at low temperature. Activation at 430°C in vacuum led to the best results in cis-trans isomerization in the temperature range of 80–200°C. It is shown that at temperatures 150°C a carbanion mechanism is operating while at higher temperatures the thermodynamic selectivity is attained. Selective poisoning experiments by NH₃ or CO₂ were carried out in order to identify the catalytic sites for the isomerization of n-butene.

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, , . ZrO₂, , / -1 . 430°C - 80–200°C. , 150°C , . NH₃ CO₂ -.

     

Numerical Evaluation of Functionals based on Variance Minimisation

Numerically evaluating the effect of a functional on a function is a very common task in scientific computing. The definite integral of a function over a domain is an example, differentiating a function in a certain point into a certain direction is another one. We developed a generic method to compute the effect of a functional using a linear approximation formula. The method is designed to generate the nodes and weights needed to approximate different functionals using a single set of tools: it regards the target function as a stochastic field and uses a user–defined covariance function for this field to minimise the error made by the approximation formula. The resulting formulas are optimal in an average case sense: all possible realisations of this stochastic field are taken into account while computing the solution. This results in nodes and weights that evaluate the target functional applied to any realisation with a minimised average error. The space of all realisations of such a stochastic field can be of infinite dimension whereas classical approaches often only consider a finite dimensional space of functions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)