Novel Mullite Synthesis Based on Alumina Nanoparticles and a Preceramic Polymer

Heating in air of a selected mixture of a silicone resin and alumina nanoparticles in the temperature range 1200°–1500°C yielded dense, crack-free mullite samples. Al₂O₃, due to its nanometric size, proved to be very reactive toward silica, deriving from the ceramization of the preceramic polymer, leading to the formation of a large volume fraction of mullite crystals even at low firing temperatures (1250°C). Because of the homogeneity of the distribution of alumina nanoparticles in the starting system, the ceramized samples exhibited a very fine microstructure consisting of crystals with an average dimension in the range of 50–300 nm.     

The Role of Biomass in a Future World without Fossil Fuels

The demand, production, supply and use of biomass in a future world after the depletion of fossil fuels is described. In a world without fossils, the limited biomass harvest is the only carbon source. Supply of food and feed has first priority. Demand, supply and use of biomass as the only carbon raw material for the production of a number of indispensable carbon products are analyzed. Bioenergy via combustion plays a significant, but not a decisive role, because the future energy mix is dominated by other renewables. Despite considerable uncertainties of the long‐term assessment, some clear hints for a reasonable further development of biomass technologies can be extracted.     

Acetale als neuartige Kraftstoffadditive aus Glycerin und Olefinen

Long chain olefins are converted into aldehydes by hydroformylation using synthesis gas CO/H₂ and further converted in an acid‐catalyzed conversion with glycerol in a one‐pot procedure. Yields are up to 95 %. The obtained mixtures of 5‐ and 6‐membered rings are potential fuel additives offering alternative use of glycerol from renewable resources. By optimization of reaction conditions such as catalyst precursor, ligand, pressure, temperature, solvent or catalyst/substrate ratio a highly selective hydroformylation towards linear acetals was achieved. For synthesis of larger amounts, glycerol was converted with alkenes on a 2‐L‐scale and with aldehydes on a 60‐L‐scale.     

Bestimmung des Wirkstoffes Fenoxycarb in Holz mittels Hochdruckflüssigchromatographie

Fenoxycarb is an insecticide that can be used at very low concentrations in wood preservatives because of its hormon-like activity. As a consequence relatively low concentrations of fenoxycarb have to be determined in extracts of treated timber containing a background of wood extractives. It was demonstrated in parallel analyses in different laboratories that fenoxycarb can efficiently be extracted from treated wood by methanol and can be determined in the extracts by high performance liquid chromatography coupled with UV detection. However, fenoxycarb concentrations at the lower level of required retentions can only be determined according to the tested procedure with further sample preparation. The deviation of the results between the laboratories is relatively large caused by difficulties in the interpretation of the chromatograms.     

On-line pyrolysis-GC-IRMS: isotope fractionation of thermally generated gases from coals

The isotopic composition of reservoir gases is frequently used for source rock to gas correlations. The prime control on the isotopic signature of gas results from kinetic isotope fractionation during thermal gas generation.

A new on-line pyrolysis-GC-IRMS system has been developed as an analytical tool to study the kinetic isotope fractionation during thermal gas generation from sedimentary organic matter. The method is based on open-system non-isothermal pyrolysis in the temperature range from 100 to 1100°C and allows simultaneous monitoring of the isotopic composition of seven individual pyrolysis product (methane, ethane, ethene, propane, propane, carbon monoxide and carbon dioxide) at a high sampling frequency. Due to the high data density achieved by this procedure a detailed reaction kinetic interpretation of the pyrolysis curves in terms not only of compositional but also isotope specific reaction kinetics is feasible. This method and the data presented encourage both the re-evaluation of existing concepts for source-rock to gas correlations and also offer new insights into controls on isotope fractionation during thermal gas generation.

Current results indicate a high variability of the isotopic composition of the seven pyrolysis products. Although a general trend of enrichment in the ¹³C species with increasing pyrolysis temperature is observed, characteristic reversals of this isotopic trend are commonly occurring for methane, CO, and CO₂. These variations reflect differences in the isotopic composition of the precursor structures, which are progressively decomposed during pyrolysis. The analytical data obtained from the approach presented here open up the perspective of developing new kinetic fractionation models taking into account both the isotopic variability of precursor structures and their thermal stability.     

Modellierung der Methanolsynthese auf Basis von Elementarreaktionen

Using the transition state theory, parameters like the pre‐exponential factor and activation energy can be related to the active centers. These parameters suggest how a technical process can be described, even if the predominating geometries between the adsorbed species and the substrate are not known exactly. The approach to modelling methanol synthesis presented here shows that elementary reactions can be combined with simple coupled differential equations to derive major conclusions with respect to surface reactions of the catalyst.     

Flux cored arc welding — the state of the art and current applications

Abstract

The advantages and potential applications of flux cored welding are reported, together with a review of process developments and the situation internationally.