Corrosion of yttria-fully stabilized zirconias in molten fluorides

Yttria-fully stabilized zirconia ceramics were manufactured from home-made and commercially available powders and were sintered under different conditions. The ceramics were immersed in the corrosive environment of molten LiF, NaF, KF (FLINAK) eutectic for up to 360 h from 700–900 °C. The changes caused in the crystal structure were probed with laser Raman spectroscopy and X-ray diffraction. The degree of corrosion (phase transformation) depends on immersion period, FLINAK temperature, and ceramics microstructure. From the tested ceramics, ZrO₂-8 mol % Y₂O₃ with a grain size larger than 8 μm and having zero open porosity, exhibits the best resistance to the corrosive influence of FLINAK.     

Grenzen des Wachstums?

Limits of Growth? Discussions on the environmental politics are dominated by theories on the downfall of the earth, which were proclaimed in the Club of Rome and further elaborated by extremists like Gruhl and others. According to them, the human beings are moving towards calamity, if the highly developed industrial nations do not radically change their economical and living habits at the last moment. The expansion of industry accompanied by stress on the nature, excessive exploitation of unreplacable raw materials and energy sources, explosive increase of world population along with inadequate production of foods are, according to the Club of Rome and its interpreters, the causes of the approaching global catastrophy. Statistical estimates, which are supposed to support these theories, are no longer valid and partly contradicted by other developments. The basis of such estimates is also wrong because they consider the reserve of raw material and agricultural land as constant but represent the utilization in an exponential manner without taking into account the flow of new inventions and regular increase of agricultural production. The theories of the Club of Rome are spiritual armaments of radical environmental protection fanatics who wish to change the existing system. They oppose the principles of free economy and free society.     

Note on the ill-conditioned eigenvalue problem in elastic vibrations

Two cases which could cause ill-conditioning of the lower modes and frequencies of an undamped elastic structure are discussed. The first case is when rigid body motions are connected to a relatively small moment of inertia. The second case is when the stiffness matrix is ill-conditioned with respect to the solution of linear equations. It is shown that the first kind of ill-conditioning is not serious provided that an appropriate method of computation is used. The second kind, which is more common and more serious, is dealt with in more detail. It is shown how the results may be improved in various ways by applying the Natural Factor approach of Argyris and Brönlund and computing singular values and vectors.     

Widely tunable narrow linewidth erbium doped fibre ring laser

An erbium doped fibre ring laser enabling singlemode operation over a continuous wavelength tuning range of 44 nm (1528 nm-1572 nm) with laser linewidths of less than 10 kHz is reported.<>     

Oxidation effects during laser cladding of aluminium with SiC/Al powders

Aluminium substrates were covered with a layer of an Al-SiC powder mixture. The surface was scanned with a laser beam during which the surface was melted. The top layer of the laser tracks contained oxide plates apart from some large SiC particles. In the bottom layer a cellular network was found with aluminium cells and silicon-rich cell walls.     

Knowledge-Based configuration of image segmentation processes

The solution of an image interpretation problem using digital image analysis methods requires the configuration of an image analysis system to meet the requirements of this specific task the specific data material. This process includes the selection of the appropriate sequence of operators and the adaptation of the free parameters. A system has been developed and is described, which performs this configuration process automatically on the basis of a user-specified task definition, and general knowledge of an image analysis expert. The latter knowledge has been assessed, stored, and used by employing different paradigms of knowledge representation similar to expert systems.     

Korrosionsinspektion im Flugzeugbau

Corrosion inspection in aircraft construction The inspections required on an aircraft during its operational phase are determined largely by the materials and constructions used. Practical experience has shown that corrosion can generally not be prevented on metallic aircraft structures, even if the surface protection systems have been chosen with great care. Constructions and materials used on aircraft and the result types of corrosion are described and the inspection concept is explained on the basis of this. Finally, typical inspection tasks are presented and the measurement results obtained with different NDT methods are presented and discussed.