DECHEMA

About: DECHEMA is a nonprofit organization based out in Frankfurt am Main, Germany. It is known for research contribution in the topics: Corrosion & Oxide. The organization has 756 authors who have published 1307 publications receiving 25693 citations.

Zur Oligomerenbildung bei der thermischen Styrolpolymerisation

Abstract: Bei der thermische Styrolpolymerisation entstehen als Nebenprodukte geringe Mengen an Dimeren und Trimeren. In reinem Styrol handelt es sich uberwiegend um cyclische, gesattigte Verbindungen. Kinetische Messungen zeigen, das zwei voneinander unabhangige Reaktionen ablaufen: In einer Cycloaddition werden 1.2- Diphenylcyclobutane gebildet, Wahrend vier gesattigte Trimere uber das von MAYO formulierte DIELS-ALDER-Addukt entstehen. The thermal polymerisation of styrene produces small amounts of dimeric and trimeric adducts as by-products. For pure styrene, these are mainly saturated, cyclic compounds. Kinetic investigations show that two independent reactions occur: in the first, 1.2 – diphenylcylobutanes are produced by cycloaddition, whilst in the second, four saturated trimers are formed from an intermediate DIELSALDER adduct, as postulated by MAYO.

Dynamic modelling of gas hold-up in different electrolyte systems

Abstract: In measurements of gas hold-up of oxygen and hydrogen as a function of the gas flow rate it was found that the gas hold-up epsiv(ug0) depends on the type of electrolyte and its concentrations as well as on the type of gas. Using an ultrasonic Doppler velocimeter, bubble rise velocities were investigated. It was observed that the single bubble rise velocity in electrolyte solutions depended strongly on the concentration. A model, developed to take into account the impediment to coalescence by electrolytes, was used to evaluate the dependence of gas hold-up on electrolyte concentration. An almost linear correlation between the system specific parameter, epsivmax, of this model and the ionic strength was found. However, this correlation is not too accurate and can only be seen as a rough approximation. Experimental results indicate that another mechanism is responsible for the dependence of the gas hold-up on electrolyte concentration. Thus, a new model was derived, which incorporated results of measurements of bubble rise velocities. This model was also applied to describe the gas hold-up in different electrolyte solutions as a function of gas flow rate. It also includes a system-specific parameter. The dependence of this parameter on the concentration of electrolytes was found to be in accordance with current theories on the bubble coalescence.

Mechanical behaviour of as sprayed and sintered air plasma sprayed partially stabilised zirconia

Abstract: The mechanical behaviour of free standing air plasma sprayed (APS) partially yttria stabilised zirconia (P-YSZ) thermal barrier coatings (TBC) at room temperature and at elevated temperatures up to 1050°C have been investigated. Creep tests under constant compressive load have been conducted as well as cyclic measurements of compressive stress – strain hysteresis loops with increasing maximum load, yielding Young's moduli of the porous partially yttria stabilised zirconia. Both mechanical parameters are needed for accurate modelling of the local stress fields of, for example, airfoils to identify critical regions where damage or even failure of the component may occur. Specimens in the as sprayed and sintered state were tested. The microstructural changes caused by sintering and mechanical loading at high temperature of the thermal barrier coatings have been characterised by porosity measurements made from metallographic cross-sections.

Improving the selectivity of photocatalytic NOx abatement through improved O2 reduction pathways using Ti0.909W0.091O2Nx semiconductor nanoparticles: from characterisation to photocatalytic performance

Abstract: In this paper, we provide detailed insight into the electronic–crystallographic–structural relationship for Ti0.909W0.091O2Nx semiconductor nanoparticles, explaining the mutual electronic and magnetic influence of the photoinduced stable N- and W-based paramagnetic centers, their involvement in the photoinduced charge-carrier trapping, and their role in improving the nitrate selectivity of the photocatalytic oxidation of NOx to nitrates. In particular, reduced tungsten species in various crystallographic environments within the anatase host lattice were observed as playing a fundamental role in the storage and stabilization of photogenerated electrons. Here, we show how these reduced centers can catalyze multielectron transfer events without the need for rare and expensive platinum-group metals (PGMs). This allows for the versatile and elegant configuration of redox potentials. As a result, electron-transfer processes that are kinetically inaccessible with metal oxides such as TiO2 can now be accessed, en...

Behavior of the scale on a 9.5Cr steel under cyclical deformation of the base metal

Abstract: Low cycle fatigue tests have been performed with a 9.5Cr steel at 650°C in air with ramp rates of 7.5 10−8−7.5 10−7 sec−1 and deformation amplitudes of ±1% (R=−1). LCF deformation enhances the uniform scale growth as well as nodule formation. This enhancement is caused by repeated scale cracking in the tensile periods of the LCF cycles. The crack-healing process is very rapid and occurs during the deformation process. These processes lead to the formation of a scale rich in iron, because the chromium content of the alloy is too low for protective scale healing.