The focus of the research projects executed at the department of materials of the OWI lies on questions related to material application at high-temperature. Availability and reliability of the materials used are essential in the realisation of progressive high temperature processes. The data regarding the corrosion behaviour under the specific conditions of the particular processes are usually not available and must be determined experimentally.
Figure 1: Testbed with laboratory furnace for experiment of the corrosion behaviour
The corrosion resistance of metallic materials and coatings is studied either in original devices, burners and reformers, or under simulated operating conditions in laboratory furnaces. A test rig with a laboratory furnace for these analyses is shown in figure 1. Several temperature levels from room temperature up to 1280 °C and various atmospheres are selectable. Furthermore it is possible to change the atmospheres continuously or in steps during the experiment. Different temporal temperature profiles with a high heat-up- and cool down rate are realisable e.g. to test thermal shock resistance and adhesion of natural oxide layers or of coatings. The following methods for the material analysis are executed in cooperation with other departments: light microscopy, scanning electron microscopy, electron microprobe microanalysis, X-ray diffraction and glow discharge optical emission spectrometry (GDOES). Extensive knowledge about the oxidation resistance of iron- and nickel based- high temperature alloys has been acquired in multiple research projects.
Figure 2: Furnace material eroded by Metal-Dusting
The corrosion of flame tubes of oil burners by metal-dusting was studied in several research projects at the OWI in recent years. Metal-dusting is a form of carburisation which causes a rapid destruction of the metallic material and is often detected by the appearance of catalytic deposited carbon fibres in the area of the corrosion attack. All metallic high temperature materials are at long-term prone to corrode by carburisation, particularly in the form of metal-dusting, during an operation in carburising atmospheres whose carbon activity is higher than 1. Thus a demand exists for coatings which can protect the materials from carburisation under the operating conditions. Since August 2007 the AIF promotes a cooperation project with the OWI and the department of materials IWT Bremen as cooperation partner. In the project the resistance against metal-dusting of high temperature alloys typically used in industrial furnaces is investigated under the conditions of case hardening. Coatings are tested in addition. The OWI executes the corrosion tests (s. figure 2). At the IWT the materials are coated with the Sol-Gel-method. Microstructure analyses follow the corrosion tests.
Figure 3: Emplacement facility
Biogenous fuels and combustibles are used in motor vehicles and increasingly in oil heating systems in households in the near future. To prove their reliability the effects of the biogenous fuels and fuel blends, on the materials used, have to be investigated. In cooperation with the centre for synthetic analysis and -examination at the IKV Aachen and funded by the IWO Owi runs immersion tests of different synthetics and elastomeres in blends of light fuel oil and fatty acid methyl ester or soya oil (s. figure 3). The material characteristics are examined via measurements of mass change by weigh, thermal gravimetry, differential scanning calorimetry, in a tensile test, by hardness testing, charpy impact test and microscopy.
Abbildung 4: Mass change of polyethylene in different compositions of heating oil after emplacement during 6 month