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.

Optimal design of packed bed cells for high conversion

Abstract: In connection with the electrochemical purification of metal containing waste waters, the realization of a high concentration decrease per pass is one of the goals of design optimization. For a packed bed cell with crossed current and electrolyte flow directions high conversion in conjunction with a large space time yield requires limiting current conditions for the whole electrode. For establishing the concentration profiles in the direction of flow a plug flow model is used. These considerations result in a new packed bed electrode geometry for which an analytical bed depth function is derived. The basic engineering equations of such packed bed electrodes are given, and design equations for different arrangements are developed. The reliability of this scaling-up method is shown by comparison of theoretically predicted and experimental performance data of two cells. Engineering aspects such as easy matching of cells to waste water properties and parametric sensitivity are discussed. Some technical applications are reported.

Possible overestimation of shallow-depth calcium carbonate dissolution in the ocean

Abstract: [1] We argue that diagnostics of excess dissolved calcium carbonate (TA*) above the saturation horizon cannot be unambiguously interpreted in terms of local in situ dissolution. We examine a three-dimensional numerical model of global ocean circulation and biogeochemistry with explicit representation of the formation and dissolution of calcium carbonate. In particular, dissolution is only allowed to occur below the saturation horizon. The model qualitatively captures the observed basin- and global-scale patterns of alkalinity and TA* as well as the relationship between TA* and chlorofluorocarbon age in the thermocline. The existence of TA* above the saturation horizon in the model can only be explained in terms of transport subsequent to dissolution. The model study does not rule out the possibility of shallow-depth calcium carbonate dissolution but suggests that dissolution rates derived from tracer observations have not adequately accounted for the influence of transport.

The conversion of chromium oxide to chromium carbide

Abstract: The thermodynamic equilibria between chromium oxide, chromium carbide, and a CO-CO2 mixture was calculated for various conditions. Experimental results on the rate of the Cr2O3 conversion to chromium carbide in CO-CO2 mixtures at 1200°C are reported. The conversion rate was low and was strongly dependent on the carbon activity.