Abstract:
A sample cell for use in measuring the particle size distribution of samples using diffraction-scattering measurement methods has a radiating surface which is beveled to increase the angle of incidence of scattered light which is scattered at a large scattering angle such that it is transmitted through the radiating surface of the sample cell and thereby allowed to impinge upon a detector.

Description:
This is a continuation of application Ser. No. 671,496, filed on Mar. 19, 1991 for a SAMPLE CELL FOR DIFFRACTION-SCATTERING MEASUREMENT OF PARTICLE SIZE DISTRIBUTIONS. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the diffraction-scattering measurements of samples and, more particularly, to a sample cell used in measuring the particle size distribution of samples in a diffraction-scattering measurement and testing apparatus. 
     BACKGROUND OF THE INVENTION 
     A conventional apparatus for making diffraction-scattering measurements of the particle size distribution of a sample is shown in FIG. 4. As shown therein, a laser beam 1 is projected into a square cylindrical sample cell 2&#39; which contains a sample to be measured. 
     The sample cell 2&#39; has a square external cross-section and an internal space 2a&#39;. The internal space 2a&#39; of the sample cell 2&#39; is continuously supplied with the sample liquid from an ultrasonic diffusion bath (not shown) by means of a circulating pump (not shown). 
     Laser beam 1 is transmitted into and through the sample cell 2&#39;, and scattered (diffracted) by particulates contained within the sample liquid in the sample cell&#39;s internal space 2a&#39;. The scattered light 5 radiating from the sample cell 2&#39; is transmitted through a condenser lens 3, which collects the scattered light 5 and focuses the scattered light 5 upon the detector 4. The detector 4 may be a silicon photodiode. 
     Thus, the incident laser light 1 is scattered (diffracted) by the particles within the sample liquid, and the scattering or diffraction pattern 5 is directed onto the detector 4 for measurement. In this way it is possible to determine the particle size distribution of the particles within the sample liquid by measuring the intensity of the pattern of the scattered light 5. 
     A further depiction of the conventional sample cell 2&#39; may be seen in FIGS. 5A and 5B. Therein, a particular light beam 1&#39; from the laser beam 1 is scattered by a particle 6 within sample liquid in the sample cell 2&#39;. The scattered light 5, 5&#39;, which is diffracted by the particle 6, is directed towards the rear surface of the sample cell 2b&#39;. 
     When the particle 6 scatters the light 5 at a small scattering angle Θ1, the scattered light 5 is refracted through the sample cell and is allowed to impinge upon the detector 4 by passing through the rear surface 2b&#39; of the sample cell 2&#39;. As an example, when the disbursion medium is water, light which is scattered at a scattering angle Θ1 less than approximately 50 degrees will be transmitted through a rear surface 2b&#39;, which is normal to the original angle of incidence. 
     On the other hand, when the particle 6 causes scattered light 5&#39; to have a larger scattering angle Θ2, the scattered light 5&#39;interacts with the rear surface of the sample cell 2b&#39; at a minimal angle of incidence φ2. Since the angle φ2 is minimal, the scattered light 5&#39; is not transmitted through the rear surface 2b&#39;, but is reflected from that surface, and is not allowed to reach the detector 4. 
     Thus, in conventional cells as depicted in FIGS. 4 and 5, when a particle 6 causes light to be scattered at large scattering angles Θ 2 , the scattered light 5&#39; is fully reflected by the surface 2b&#39; without any transmission. This causes the diffraction-scattering measurement to be an erroneous representation of the overall particle size distribution within the sample. In general, where the disbursion medium is water, any particle 6 producing a scattering angle Θ greater than or equal to approximately 50 degrees will produce reflected scattered light yielding an erroneous measurement. 
     The scattering angle is generally inversely proportional to the particle size; the smaller the particle, the larger the scattering angle. Thus, in a conventional apparatus for measuring the distribution of particle size, the particle sizes of particulates having reduced particle diameters have been difficult to measure, and the measurement of the particle size distribution over a wide range has proven to be impossible with a conventional sample cell. 
     OBJECTS OF THE INVENTION 
     It is therefore an object of the present invention to provide an apparatus for diffraction-scattering measuring the particle size distribution of particulates in a sample. 
     It is yet a further object of the present invention to provide an apparatus for measuring the particle size distribution of particles having a wide range of sizes. 
     It is yet a still further object of the present invention to provide a sample cell for use in diffraction-scattering measurements of particle size distribution which allows the scattered light component from larger particulates to be measured. 
     It is yet a still further object of the present invention to provide a sample cell for use in making diffraction-scattering measurements of particle size distributions of samples, which sample cell allows the measurement of particulates having reduced particle diameters with high accuracy, and allows the measurement of the distribution of particle sizes over a wide range by a relatively simple device. 
     SUMMARY OF THE INVENTION 
     These and other objects are provided in the present invention by a sample cell for use in a particle size distribution measurement apparatus using diffraction-scattering measurement methods. The sample cell allows a wide range of particle size distributions to be measured, by providing a beveled outer surface on the radiating or exit side of the sample cell, and thereby allowing scattered light from smaller particles to be transmitted to detectors. 
     By providing a beveled radiating or exit surface on the outer surface of the sample cell, the angle between the scattered light and the outer surface of the sample cell can be substantially increased so that scattered light having a large scattering angle is allowed to pass to the detector. By beveling the outer or exit surface, the angle of incidence between the scattered light and the outer surface of the sample cell is increased enough to allow transmission and eliminate reflection. This allows a more accurate measurement of the particle size distribution over a greater range of particle diameters. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and features of the present invention, together with further objects and advantages, may be understood by reference to the following drawings. 
     FIG. 1A is a block diagram showing an apparatus for measuring particle size distribution utilizing the preferred embodiment of the invention; 
     FIG. 1B is a perspective view of a sample cell constructed according to the preferred embodiment of the present invention; 
     FIG. 2 is a cross-sectional view of the sample cell shown in FIG. 1B; 
     FIG. 3 shows a cross-sectional view of a second preferred embodiment of the present invention and the operation of a sample cell; 
     FIG. 4 shows a conventional apparatus for making diffraction measurements of particle size distributions; 
     FIG. 5A shows the operation of the sample cell utilized in the apparatus depicted in FIG. 4; and 
     FIG. 5B shows the interaction of scattered light within the sample cell of FIG. 5A. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor[s]of carrying out the invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of the present invention have been defined herein. 
     FIGS. 1A, 1B, and 2 show a preferred embodiment of the present invention. As shown in FIG. 1A, a laser device 7 projects a laser beam 1 through a beam expander 8 for magnifying and conditioning the laser beam 1. The conditioned laser beam 1 is then directed to a sample cell 2. 
     The sample cell 2 is connected with an ultrasonic disbursion bath (not shown) through a piping 9, allowing the sample cell 2 to be continuously supplied with the sample liquid by a circulating pump (not shown). Detectors 4, 4&#39; are positioned at the rear, exit, or radiating surface of the sample cell 2 for detecting and measuring light which passes through the sample cell 2 and has been diffracted-scattered by the particulates contained within the sample. 
     As shown in FIG. 1B, the sample cell 2 used in the preferred embodiment of the present invention is provided with a beveled portion 10 formed into the rear exit, or radiating outer surface 2b. Since the light is directed into the first surface of the sample cell 2, the light is transmitted through, and radiates or emerges from, the rear outer surface 2b and is projected onto the detectors 4, 4&#39;. 
     In the preferred embodiment of the invention, the sample cell 2 is constructed of a material which is transmissive to light. This material may be glass such as quartz or BK-7 glass. The sample cell has a square external cross-section and an internal space 2a as shown in FIG. 2. The beveled portion 10 may be formed in one edge of the outer surface 2b on the radiating side of the sample cell 2 to substantially increase the angle. The scattered light 5&#39; is incident upon the radiating surface by providing the beveled portion 10. The beveled portion 10 allows the scattered light 5&#39; to be transmitted through the rear surface of the sample cell 2 at the beveled portion 10 and thereby impinge on detector 4&#39;. 
     Additionally, scattered light 5 having small scattering angles will pass directly through the outer surface 2b of the sample cell 2 at a point which is not beveled and will thereby be detected by detector 4. 
     A collecting lens may also be placed behind the sample cell 2 to collect both scattered light 5 emanating from the outer surface 2b of the sample cell 2 and scattered light 5&#39; emanating from the beveled portion 10, the collecting lens focusing both components of the scattered light upon a single detector. 
     FIG. 3 shows a sample cell 2 constructed according to an additional preferred embodiment of the present invention. A sample cell 2 is provided with a beveled portion 11 formed in an edge portion opposite to that used in the preferred embodiment shown in FIG. 2. A detector 4&#39; is used to detect the scattered light 5&#39;  emanating through the beveled portion 11. Detector 4 measures the scatted light 5 emanating through the outer surface 2b. 
     The angles of the beveled portions 10, 11 shown in the preferred embodiment illustrated in FIGS. 1, 2, and 3 are configured differently, depending upon the material and size of the sample cell and the other transmissive characteristics of the sample cell and the medium being measured. In addition, the beveled portions 10, 11 may have either a curve or other geometry to allow simplified light transmission, the straight beveled portion being illustrated merely for ease of operation and explanation. 
     Thus, according to the preferred embodiment of the present invention, the particle size distribution of particulates within a sample ranging from small particle diameters to large particle diameters may be more accurately measured by a simplified device wherein a beveled portion is formed into the outer surface of the sample cell. 
     Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.