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.

An Electrically Rechargeable Zinc/Air Cell with an Aqueous Choline Acetate Electrolyte

Abstract: Due to the feasibility of an electrically rechargeable zinc/air cell made of a zinc foil as active material, an aqueous choline acetate (ChAcO) mixture as an electrolyte and a spinel MnCo2O4 (MCO) and NiCo2O4 (NCO) as a bi-functional oxygen catalyst was investigated in this work The 30 wt% water-containing aqueous ChAcO solution showed high contact angles close to those of KOH favoring triple-phase boundary formation in the gas diffusion electrode Conductivity and pH value of 30 wt% H2O/ChAcO amounted to 59 mS cm−1 and 108, respectively Best results in terms of reversible capacity and longevity of zinc/air cell were yielded during 100 h charge/discharge with the MnCo2O4 (MCO) air electrode polarization procedure at 100 µA cm−2 (28 mA g−1zinc) The corresponding reversible capacity amounted to 254 mAh (28% depth of discharge (DOD)) and the energy efficiency ranged from 29–54% during the first and seventh cycle within a 1500 h polarization period Maximum active material utilization of zinc foil at 100 µA cm−2 was determined to 381 mAh (42% DOD) whereas a further charging step was not possible due to irreversible passivation of the zinc foil surface A special side-by-side optical cell was used to identify reaction products of the zinc/air system during a single discharge step in aqueous ChAcO that were identified as Zn(OH)2 and ZnO by Raman analysis while no carbonate was detected

Coefficients of thermal expansion of (Ni 0·5 Al 0·5 ) (1–x) Hf x alloys (x =0...0·2)

Abstract: The coefficients of thermal expansion (CTEs) of Ni–Al–Hf alloys have been investigated due to their potential as corrosion resistant coatings in aggressive environments at high temperature. The CTEs of (Ni0·5Al0·5)(1–x)Hfx alloys (x=0...0·2) were measured between 473 and 1073 K (200–800°C) and range between 8 and 15×10–6 K–1 depending on temperature and alloy composition. The temperature dependence of the CTE was found to be properly described by a simple expression: (19·982–0·24016X Hf)[0·15182+1·8287×10–3(T/K)–2·12378×10–6(T/K)2+8·87011×10–10(T/K)3]. It was shown that the CTE of (Ni0·5Al0·5)(1–x)Hfx alloys varies linearly with the amount of Hf in the alloy which allows the control of the CTE. Within the (Ni0·5Al0·5)(1–x)Hfx alloy composition range (x=0...0·2) it covers the CTE range of most of the austenitic and ferritic steels and the CTE of the coatings can be adjusted to those of the substrate to be protected without inducing additional strains at the coatings/substrate interface.

Influence of cycling parameter variation on thermal cyclic oxidation testing of high temperature materials (COTEST)

Abstract: The effect of cycling parameter variation (i.e. oxidation temperature, upper and lower dwell time, humidity in test gas) of the oxidation/spallation kinetics on four alloys was investigated within the framework of an EC funded research project (COTEST). For this purpose, specimens of AISI 441, Alloy 800H, CM 247 and P91 were subjected to thermocyclic testing in dry or humidified air. It was found that a minimum of 300 h accumulated hot dwell time is required for meaningful test results. Detailed characterisation of the corrosion products was performed using OM, SEM/EDX and XRD. The net weight change curves were evaluated with regards to the characteristic quantitative parameters describing oxide growth rate, time to onset of spallation/breakaway and weight of spalled oxide. Analysis of these values was made by the ANOVA method, which allows assessment of the significance of the roles of different test parameters and parameter variations on the oxidation/ spallation kinetics from a limited number of experiments.

Approaches for the evaluation of future-oriented technologies and concepts in the field of water reuse and desalination

Abstract: Against the background of drastically rising global water demand and increasing pollution and overexploitation of regional water resources, the demand-driven water supply of households and industry is of central importance. Water reuse and desalination are seen as key technologies to overcome potential regional and local water shortage. In the joint projects funded by the German Federal Ministry of Education and Research (BMBF) ‘Future-oriented Technologies and Concepts to Increase Water Availability by Water Reuse and Desalination (WavE)’, evaluation approaches for analysing innovative technologies and concepts are being developed and assessed. All evaluation methods and criteria used were selected based on the decision situation at hand and the decisionmakers preferences. Based on the analysis of six multi-criteria evaluation concepts used in selected WavE projects, this paper presents a general approach for comparative multi-criteria evaluation of water reuse systems consisting of prerequisites, minimum requirements, evaluation criteria (qualitative, semi-quantitative or quantitative) and a final aggregation of results. Exemplary sets of criteria for the application in a more industrial, municipal and/or international context are presented as an aid for the application of holistic evaluation approaches for (process) concept and technology selection in the context of water reuse and desalination.

Sulfate–Vanadate-Induced Corrosion of Different Alloys

Abstract: Corrosion of boilers and heat exchangers is accelerated in the presence of vanadium, sodium, and sulfur from low-grade fuels Several iron- and nickel-based alloys were immersed in 60 mol% V2O5–40Na2SO4 salt for 1000 h in order to investigate their degradation behavior at 600 °C in air Materials performance was analyzed by means of substrate recession rate and metallographic characterization Their corrosion mechanism is characterized by the formation of a sulfide/oxide layer adjacent to the metal, the dissolution of scale oxides in the molten deposit, and their precipitation near the outer surface of the deposit High Ni- and Cr-containing alloys show the lowest metal loss rates Al addition was detrimental due to low-melting eutectic AlVO4–V2O5 formation Fe–Cr-based alloys showed the highest metal loss rates In such alloys, high Cr additions (above 20%) did not improve the performance due to the negative synergetic effect by simultaneous dissolution of Fe2O3 and Cr2O3 The predominant salt composition at the corrosion front varied from vanadate rich to sulfate rich during the exposure This change in the attacking salt makes it difficult to find a protective material for mixed sulfate–vanadate-induced corrosion