Optics: measuring and testing – For size of particles – By particle light scattering
Patent
1996-04-16
1998-06-09
Font, Frank G.
Optics: measuring and testing
For size of particles
By particle light scattering
356338, 356343, G01N 2100
Patent
active
057643580
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention firstly relates to a method for detecting the shape characteristics of particles.
It is known to determine the particle size distribution by means of light scattering. With this procedure a laser beam is directed through a transparent cell containing particles flowing therein and the intensity of the light scattered by the particles is determined with the aid of a photodetector array comprising a number of concentric rings or parts of rings which are coupled to an energy meter. The photodetector is a disc made of semiconductor material and the rings are formed by etching dividing lines on the semiconductor material and thus isolating the rings from one another.
The light intensity fluctuations can be processed statistically and the results (for example graphical results) thereof are an indication of the size distribution of the particles. Reference is made to the article in the journal Applied Optics, vol. 30. pp. 4818-4823, 1991 entitled Deconvolution of Lights Scattering Patterns by Observing Intensity Fluctuations, the authors of which are A. Boxman, H. G. Merkus. P. J. T. Verheijen and B. Scarlett.
However, information on the shape of the particles can also be derived from the fluctuation in the light intensity of light scattered be particles. The particle size is used as a control parameter in a number of individual processes and in various of these processes the shape of the particles is equally as important as, and possibly more important than, the size of the particles alone. Examples are grinding processes and industrial crystallisation processes, in which agglomeration, mutual abrasion of the particles and the effect of additives are of importance for the crystal shape.
Because signal fluctuations originating from a detector element are dependent not only on the number of particles but also on the shape of the particles, particle shape will also have to be taken into account when determining the particle size distribution in the case of particles which can change in shape.
SUMMARY OF THE INVENTION
The aim of the invention is, now, to provide a method for determining the shape characteristics of particles using apparatus which is largely known for determination of the particle size distribution.
According to the invention, the method is, to this end, characterised in that a light beam is directed onto a transparent cell containing particles flowing therein and the intensity of the light scattered by the particles is measured with the aid of a photodetector array or a mask containing programmable light valves comprising one or more concentric rings or parts of rings, at least one of which is provided with one or more isolated segments, the rings and isolated segments being coupled to an energy meter, the signal amplitudes of which are statistically processed to give amplitude classes, and the shape characteristics are determined from graphical or numerical comparison of said amplitude classes.
The amplitude of the signals from one or more rings and the amplitude of the signals from one or more isolated segments can be processed to produce an amplitude frequency distribution plot, the shape characteristics being determined from the difference in amplitude frequency distribution of signals originating from the ring or rings and signals originating from the isolated segment or isolated segments.
Another option is that the amplitude of the signals from a number of isolated segments of one ring are processed to produce a correlation plot and the shape characteristics are determined from the shape of this plot. This option had the advantage that the shape characteristics can be expressed in a characteristic angle spectrum.
The invention also relates to an apparatus for determining the shape characteristics of particles. An apparatus which comprises a light source or laser source for generating a light beam or laser beam, a transparent cell through which particles can be passed, a photodetector array or mask containing programmable light valves comprising one
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Font Frank G.
Stichting Voor De Technische Wetenschappen
Technische Universiteit Delft
Vierra-Eisenberg Jason D.
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