Zwang und Zwangskräfte

Übersicht Es werden mechanische Systeme behandelt, die über begrenzte Zeit wirksamen Zwängen unterworfen sind. Dies sind typischerweise Haft-Gleit-Übergänge und Stöße. Die Verwendung der Lagrangeschen Gleichungen erster Art bedarf bei Aktivwerden der Bindungen der Ermittlung der Langrangeschen Multiplikatoren. In der vorliegenden Arbeit wird ein Verfahren vorgestellt und an Beispielen erläutert, das die möglichen Bindungen à priori erfaßt, ohne daß Zwangskräfte explizit in Erscheinung treten. Letztere lassen sich jedoch im Bedarfsfall durch eine einfache Beziehung angeben.

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Constraints and constraint forces

Summary Mechanical systems are considered which are subject to temporary constraints. This is the case in stick-slip processes and impacts. The use of the first Lagrangian method requires the calculation of Lagragian multipliers whenever one of the additional constraints becomes active. In this paper a method is presented and illustrated by examples which takes all possible constraints into account à priori, without calculating constraint forces explicitly. However, the latter are easily calculated by a simple equation, if necessary.

     

Herstellung und Eigenschaften von Aluminiumaquoxid. I. Böhmit aus Aluminiumnitrat und Ammoniakwasser

Preparation and Properties of Aluminium Hydroxide. I. Boehmite from Aluminium Nitrate and Ammonia The physical-chemical properties of mainly boehmite containing aluminium hydroxide are studied which were made by continuous precipitation from aluminium nitrate solution with ammonia liquor using technical raw materials and test conditions being very similar to those applied in production. The influence of the precipitation conditions (pH value, temperature, concentration and residence time in the precipitation solution) on the composition, structure and texture of the precipitation products is investigated and information about their effect on the filtration behaviour are given. In the case of a continuous precipitation it is possible to obtain phase-pure boehmite being relatively well crystallised. The crystallinity and dispersity of the precipitated hydroxide determine their filterability and the cavity structure.     

Untersuchungen an oxidischen Katalysatoren. XLI. Redoxverhalten des Nickels in NiNa–Y-Zeolithen 3. Reduzierbarkeit von Ni2+ -Ionen und Eigenschaften des reduzierten Nickels in aciden NiNa–Y-Zeolithen

Studies on Oxide Catalysts. XLI. Redox Behavior of Nickel in Zeolites NiNa? Y. 3. Reducibility of Ni²⁺ Ions and Properties of the Reduced Nickel in Acidic Zeolites NiNa? Y The reducibility of nickel ions in zeolites NiNa? Y and the properties of metallic nickel were evaluated by tpr measurements, oxygen chemisorption and conversion of cyclohexane. In NiNa? Y samples which contain NH₄⁺(H⁺) and/or Al³⁺(H⁺) ions the reducibility of Ni²⁺ ions is decreased caused by increasing acidity and the metal dispersion is improved. The electronic interaction between the acidic support and the metallic nickel leads to a decrease of both dehydrogenation and hydrogenolysis activity whereas the dehydrogenation selectivity increases.     

Herstellung und Eigenschaften von Aluminiumaquoxid. II. Böhmit aus Natriumaluminat und Salpetersäure

Preparation and Properties of Aluminium Hydroxide. II. Boehmite from Sodium Aluminate and Nitric Acid A report is given on the physical-chemical characteristics of aluminium hydroxide which contain mainly boehmite, having been obtained by continuous precipitation from sodium aluminate solution with nitric acid using technical raw materials and conditions being very similar to those applied in production. The influence of the reaction conditions (pH value, temperature, concentration and residence time in the precipitation suspension) on the chemical composition, structure and texture of the hydrogels is studied. With rising precipitation temperature the pH range extends, within which already after short residence times pure-phase, relatively well crystalline boehmite hydrogels are obtained in the precipitated solution.     

Untersuchungen an oxidischen Katalysatoren. XXXVII. Zum Einfluß der Herstellungsbedingungen auf die Eigenschaften röntgenamorpher Al2O3?SiO2-Festkörper

Studies on Oxide Catalysts. XXXVII. On the Influence of Preparation Conditions on the Properties of Silica-Alumina Silica-alumina samples of different composition were prepared by coprecipitation from aqueous solutions at pH = 6 and pH = 9, respectively. Structures and properties of the solids were characterized (i.r., DTA, X-ray, molybdato method, surface acidity, catalytic activity in the cracking reaction of cumene). Solid composition and pH value of the precipitation medium equally exhibit influence on the structure of the silica-alumina (kind of incorporation of the aluminium) and thereby on the acidic and catalytic properties of the solids. Silica-alumina of equal composition but precipitated at different pH values may widely differ in their properties including activity-composition dependency.     

Untersuchungen an oxidischen Katalysatoren. XXXII. Die Wirkung siliciumreicher Y-Zeolithe beim Spalten und Isomerisieren von Paraffinen

Studies on Oxide Catalysts. XXXII. Effect of High-Silica Y Zeolites in the Cracking and Isomerization Reaction of Paraffins The catalytic properties of high-silica Y zeolites were investigated in the cracking of gasoil and – after addition of platinum – in the isomerization of n-hexane. Number and strength of Brönsted acid centres are influenced by dealumination. Strength and concentration of acid centres control catalytic activity, selectivity, and rate of coking.     

Untersuchungen an oxidischen Katalysatoren. XLVI. Synthetische Boroalumosilicate mit Pentasilstruktur (SABO): Strukturelle,oberflächenchemische und katalytische Eigenschaften

Studies on Oxide Catalysts. XLVI. Synthetic Boroaluminosilicates with Pentasil Structure (SABO): Structural, Surface Chemical, and Catalytical Properties A remarkable modification of ZSM-5 type zeolites is possible by isomorphous substitution of silicon and/or aluminium by boron. In the H-forms of these SABO zeolites the boron atoms mainly exist in a trigonal lattice oxygen environment and hence they are not envolved in the formation of Broensted acid sites. Consequences of incorporated boron for catalytic reactions result from a decrease in the strength of existing Broensted sites as well as from a partial lattice contraction.     

Peculiarities of the isotopic exchange of the hydrogen of the hydroxyl groups of metal-zeolite catalysts

Conclusions The hydrogen of the hydroxyl groups of HY zeolite, existing in a mechanical mixture with the catalyst 0.5% Pt-NaY, is exchanged with deuterium at room temperature. The rate of the reaction of isotopic exchange is controlled by the migration of D₂, activated on platinum.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2670–2673, December, 1975.