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.

High-temperature oxidation behavior of polymer-derived SiHfBCN ceramic nanocomposites

Abstract: Within this study, the oxidation behavior of SiHfBCN ceramic powders and monoliths was studied at temperatures from 1200 to 1400 °C. Both powder and monolithic samples exhibited parabolic oxidation behavior characterized by very low rates (10−9–10−8 mg2 cm−4 h−1). The activation energy of 112.9 kJ mol−1, which was determined for the SiHfBCN powder, is comparable to that of other silica formers such as silicon or SiC and relates to the diffusion of molecular oxygen through silica scale. Whereas, the values determined for the SiHfBCN ceramic monoliths (174 and 140 kJ mol−1, depending on the Hf content) indicate the complex nature of their oxidation process, leading at temperatures below 1300 °C to a continuous oxide scale consisting of borosilicate, silica, m-and t-HfO2. At higher temperatures, the oxide scale consists of silica, HfSiO4 as well as m-and t-HfO2 and becomes discontinuous, probably due to the evaporation of boria.

Modelling oxide scale fracture

Abstract: In the present paper the approaches to modelling scale failure described in EPRI report FP 686 are compared to a more recent approach based on micromechanical considerations. The latter requires a ...

Electrochemical regeneration of oxidised nicotinamide cofactors in a scalable reactor

Abstract: An efficient and scalable NAD(P)+ regeneration system to promote alcohol dehydrogenase-catalysed oxidation reactions is reported. Indirect electrochemical oxidation of NADH was established with 2,2′-azino-bis-(3 ethyl-benzo-thiazoline-6-sulfonic acid) (ABTS), being the most efficient mediator amongst the candidates screened. ABTS exhibited very high catalytic performance of 1200 catalytic turnovers per hour. In a three-dimensional electrochemical cell with a high working electrode surface area of 24 m2 and optimised concentrations of substrate, enzyme, cofactor and mediator, TTNs of 1860 for the mediator and of 93 for the cofactor were measured. Besides, a maximum STY of 1.4 g l−1 h−1 was determined. Here we show the highest TTN ever reported for a mediated NAD+ regeneration in an electro-enzymatic process. The use of the three-dimensional electrochemical reactor led to an 8-fold improvement of the STY compared to a published system, based on a two-dimensional cell.

Energy Storage as Part of a Secure Energy Supply

Abstract: The current energy system is subject to a fundamental transformation: A system that is oriented towards a constant energy supply by means of fossil fuels is now expected to integrate increasing amounts of renewable energy to achieve overall a more sustainable energy supply. The challenges arising from this paradigm shift are currently most obvious in the area of electric power supply. However, it affects all areas of the energy system, albeit with different results. Within the energy system, various independent grids fulfill the function of transporting and spatially distributing energy or energy carriers, and the demand-oriented supply ensures that energy demands are met at all times. However, renewable energy sources generally supply their energy independently from any specific energy demand. Their contribution to the overall energy system is expected to increase significantly. Energy storage technologies are one option for temporal matching of energy supply and demand. Energy storage systems have the ability to take up a certain amount of energy, store it in a storage medium for a suitable period of time, and release it in a controlled manner after a certain time delay. Energy storage systems can also be constructed as process chains by combining unit operations, each of which cover different aspects of these functions. Large-scale mechanical storage of electric power is currently almost exclusively achieved by pumped-storage hydroelectric power stations. These systems may be supplemented in the future by compressed-air energy storage and possibly air separation plants. In the area of electrochemical storage, various technologies are currently in various stages of research, development, and demonstration of their suitability for large-scale electrical energy storage. Thermal energy storage technologies are based on the storage of sensible heat, exploitation of phase transitions, adsorption/desorption processes, and chemical reactions. The latter offer the possibility of permanent and loss-free storage of heat. The storage of energy in chemical bonds involves compounds that can act as energy carriers or as chemical feedstocks. Thus, they are in direct economic competition with established (fossil fuel) supply routes. The key technology here – now and for the foreseeable future – is the electrolysis of water to produce hydrogen and oxygen. Hydrogen can be transformed by various processes into other energy carriers, which can be exploited in different sectors of the energy system and/or as raw materials for energy-intensive industrial processes. Some functions of energy storage systems can be taken over by industrial processes. Within the overall energy system, chemical energy storage technologies open up opportunities to link and interweave the various energy streams and sectors. Chemical energy storage not only offers means for greater integration of renewable energy outside the electric power sector, it also creates new opportunities for increased flexibility, novel synergies, and additional optimization. Several examples of specific energy utilization are discussed and evaluated with respect to energy storage applications. The article describes various technologies for energy storage and their potential applications in the context of Germany’s Energiewende, i.e. the transition towards a more sustainable energy system. Therefore, the existing legal framework defines some of the discussions and findings within the article, specifically the compensation for renewable electricity providers defined by the German Renewable Energy Sources Act, which is under constant reformation. While the article is written from a German perspective, the authors hope this article will be of general interest for anyone working in the areas of energy systems or energy technology.