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.

The Reaction of OH Radicals with 1,1‐di‐, tri‐ and tetrachloroethylene

Abstract: The kinetics and product formation of the homogeneous gas-phase reactions of the OH radical with 1,1-di-, tri- and tetrachloroethylene were investigated at temperatures between 298–459 K, in the pressure range of 0.5–5.6 mbar. Measurements were made in a discharge-flow apparatus, using helium as the carrier gas. The OH radical and the reaction products were detected by mass spectrometry. The rate constants were observed to be pressure independent in the case of 1,1-di- and tetrachloroethylene but slightly pressure dependent in the case of trichloroethylene. The temperature dependencies can be expressed by the Arrhenius equation (in units of 1012 cm3 mol−1 s−1). k(T) = (0.136 ± 0.016) exp[(9.5 ± 0.4) kJ mol−1/RT] for 1,1-dichloroethylene, k(T) = (0.470 ± 0.051) exp[(2.0 ± 0.5) kJ mol−1/RT] for trichloroethylene, and k(T) = (3.33 ± 0.19) exp[−(8.6 ± 0.1) kJ mol−1/RT] for tetrachloroethylene. The major products are: CH2OH — CCl2 for 1,1-dichloroethylene; 2,2-dichloroethenol and Cl for trichloroethylene; trichloroethenol, dichloroacetyl chloride, Cl, CHCl2 and phosgene for tetrachloroethylene.

Oxidation of the intermetallics Mosi2 and TiSi2 : A comparison

Abstract: The oxidation behavior of two MoSi2 variants, one Mo-rich and one Si-rich, and TiSi2 was investigated between 1000 and 1400°C in air, oxygen and an 80/20-Ar/O2 mixture. A protective SiO2 scale develops on MoSi2 in all atmospheres in the temperature range investigated. The SiO2 modification changes around 1300°C from tridymite to cristobalite. This change in SiO2 modification seems to cause an enhanced formation of SiO2 and evaporation of MoO3. The SiO2 grows at the MoSi2-scale interface. In air a two-layer scale grows on TiSi2 between about 1000 and 1200°C with an inner inwards growing fine-grain mixture of SiO2 + TiO2 and an outer outward-growing TiO2 partial layer. TiN formation in the transient oxidation is responsible for the formation of the inner mixed partial layer because in N -free atmospheres a scale of a SiO2 matrix with some Ti oxide precipitates inside is formed. A one-layer scale structure similar as that in N-free atmosphere is found on TiSi2 in air at T > 1200°C. In oxygen the TiO2 precipitates grow as needles mostly oriented perpendicular to the surface. Due to the faster oxygen transport in TiO2 compared with SiO2, these TiO2 needles act as “oxygen pipes,” causing an enhanced oxidation of TiSi2 in front of these needles. The SiO2 scale dissolves about 1–2% TiO2. This doping causes a mixed oxygenand Si transport with the consequence that the SiO2 scale on TiSi2 grows partly by oxygen transport inwards and Si transport outwards. The SiO2 modification is cristobalite over the entire temperature range investigated.

D-Mannitol formation from D-glucose in a whole-cell biotransformation with recombinant Escherichia coli

Abstract: Recently, we reported on the construction of a whole-cell biotransformation system in Escherichia coli for the production of D: -mannitol from D: -fructose. Supplementation of this strain with extracellular glucose isomerase resulted in the formation of 800 mM D: -mannitol from 1,000 mM D: -glucose. Co-expression of the xylA gene of E. coli in the biotransformation strain resulted in a D: -mannitol concentration of 420 mM from 1,000 mM D: -glucose. This is the first example of conversion of D: -glucose to D: -mannitol with direct coupling of a glucose isomerase to the biotransformation system.