The most effective measure for improving the capacity to analyse fibrous particles by SEM/EDXA is to automate the analytical procedure. This requires an appropriate image analysing system with which software routines are to be developed for the fibre discrimination, the use of the given counting criteria, the automatic EDX-analysis and the interpretation of the results.
A powerful image analysing system has been acquired, flexible enough for the complex nature of the task. By means of this system software routines have been developed, which run the following actions automatically: Change of field of view, image acquisition by SEM and quick check for the suitability of the image; separation of coarse particles from the background; detection of fine fibrous particles by means of a filter developed especially for this task; morphological image processing; extraction of line elements and two-dimensional objects; reconstruction of fibres broken into pieces and breaking up intersecting fibres by combining line elements (two-stage hierarchical procedure); measurement of the thickness of the fibre; assessment of the detected fibres according to length, thickness, aspect ratio and position in the field of measurement taking account of attached particles in accordance with given rules; acquisition of the X-ray spectra along the whole length of each fibre detected; analysis of the spectra; calculation of the result; collecting substantial data in the course of the programme for visualisation for debugging and for validation of the method in a later stage; change of up to eight samples one after the other.
Straight as well as bent thick and thin fibres (down to approx. 0.2 µm) can be detected by the programme developed for the automatic fibre analysis. Fibres broken into pieces caused by variations of the grey-levels of the fibres and of the background are reconstructed. Crossed fibres are reckognized and analysed separately. The counting criteria laid down in BGI 505-46 (former ZH 1/120.46) are implemented. The validation of the method is still to be done. Further optimization of the time required for the evaluation of a sample would be possible, but will be postponed for the time being. The present stage of development permits the evaluation of 350 up to 400 samples per year, if one SEM/EDXA-system is used just overnight and over the weekends. The still needed validation of the method will be done in the course of these evaluations.
-cross sectoral-Type of hazard:
Krebserregende Stoffe, MessverfahrenDescription, key words:
fibres, analysis, automation, electronic image analysis, scanning electron microscope (SEM), microanalysis (EDXA)