Optics: measuring and testing – For size of particles – By particle light scattering
Reexamination Certificate
2002-12-11
2004-06-01
Nguyen, Tu T. (Department: 2877)
Optics: measuring and testing
For size of particles
By particle light scattering
Reexamination Certificate
active
06744507
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dry particle-size distribution measuring apparatus in which so-called powdery and particulate members such as powdery members, particulate members, or a mixture of the members are used as a sample, and which measures the particle-size distribution of the sample while flowing the sample by a carrier gas such as air, and more particularly, to an apparatus and method of dispersing the particulate members into a primary particle status prior to submission to a flow cell.
1. Description of Related Art
Dry particle-size distribution measuring apparatus are widely used for measuring the particle-size distribution of powdery and particulate members which are easily soluble in a liquid, such as granules of a medicine, dehydrated food such as seasoning packets for precooked noodles, dried coating compositions, or coating particles.
Such powdery and particulate members are sometimes aggregated by an electrostatic force, a Van der Waals force, a magnetic force, or the like which acts among the powdery and particulate members even in a dry state, so that the powdery and particulate members are not formed as so-called primary particles in which powdery and particulate members are completely separated from each other, but rather are formed as secondary particles (in each of which several primary particles are aggregated) or tertiary particles (in each of which several secondary particles are aggregated). When such powdery and particulate members including not only primary particles but also secondary and tertiary particles are supplied to a flow cell as a sample and measurement is then conducted while irradiating the sample with light, it is impossible to obtain a true particle-size distribution of the powdery and particulate members.
Therefore, conventional dry particle-size distribution measuring apparatuses have been configured in the following manner to address this problem. When powdery and particulate members to be used as a sample are downwardly supplied from a charging port into a flow cell, compressed air may be injected in the outer periphery of the sample charging port, whereby the sample is dispersed so that secondary and tertiary particles in the sample are dispersed to try and change them to primary particles as far as possible.
In a sample dispersion method in the conventional dry particle-size distribution measuring apparatus, however, it is difficult to completely disperse aggregated or bonded powdery and particulate members to primary particles because dispersion is performed only one time. When a sample of high density is charged, or when so-called submicron powdery and particulate members in which the particle size is smaller than 1 &mgr;m are charged as a sample, particularly, there arises a disadvantage that only dispersion up to 1 &mgr;m which corresponds to the secondary particle state is usually performed.
Thus, there is a need in the prior art to provide an efficient and economical fluidic dispersion unit to disperse particles into substantially their primary particle state.
SUMMARY OF THE INVENTION
The present invention has been designed to resolve the above-mentioned problems.
It is an object of the invention to provide a dry particle-size distribution measuring apparatus in which a powdery and particulate sample that is conventionally known in the field of aerial dispersion to have a dispersion limit of 1 &mgr;m can be dispersed to a state of fine primary particles of a submicron particle size, and which therefore can accurately perform a desired particle-size distribution measurement.
In order to attain this objective, in a dry particle-size distribution measuring apparatus in which a powdery and particulate sample is supplied to a flow cell in which air flows, the flow cell is irradiated with a laser beam, and a particle-size distribution of the sample is measured on the basis of a detection output of scattered light and/or diffracted light caused by the sample, the sample which has not yet been supplied to the flow cell is subjected to a primary dispersion by a primary dispersion flow that reaches a critical pressure and a subsonic speed, and the sample is then subjected to secondary dispersion by a secondary dispersion flow that is different in direction from the primary dispersion flow, and that also reaches a critical pressure and a subsonic speed.
In the dry particle-size distribution measuring apparatus, even when the powdery and particulate members are not completely changed into the primary particle state which is the goal of the dispersion by the primary dispersion performed by the primary dispersion flow, the members are also subjected to a secondary dispersion by the secondary dispersion flow that is different in direction from the primary dispersion flow, whereby the entire powdery and particulate members are changed into the primary particle state.
The secondary dispersion flow may be positioned to have a forward angle with respect to a flow axis along the dropping direction of the sample, or may be perpendicular to a dropping direction axis of the sample. Furthermore, a sheath flow may be formed with respect to a flow of the sample after it has been subjected to the secondary dispersion as it is introduced into a measurement sample cell.
The present invention provides a fluidic dispersion unit having a first conduit or flow path for introducing the particulate or powdery sample along a flow axis towards a sample cell. A second conduit or flow path introduces a first peripheral flowing gas to generate first converging force vectors at an angle to the sample flow axis wherein the contact of the first peripheral flowing gas with the particulate or powdery sample generates a first turbulent zone for dispersing the particulate sample to enable a primary particle status. A third conduit or flow path, positioned downstream of the second conduit or flow path, introduces a second flowing gas to generate second force vectors at an angle to the sample flow axis wherein the contact of the second flowing gas with the particulate or powdery sample generates a second turbulent zone for further dispersing the particulate or powdery sample to enhance the ability to provide a primary particle status.
Finally, a fourth conduit can aspirate air as a sheath flow about the sample as it enters the sample measurement cell to insure a repetitive and reproducible flow condition.
The method of the present invention comprises the steps of introducing a particulate or powdery sample along a flow axis towards a sample cell. A first peripheral flowing gas is directed at a first converging angle to the flow axis to contact the sample and create a first turbulent zone to disperse the sample. A second flowing gas is directed downstream of the first flowing gas to contact the sample and create a second turbulent zone for further dispersing the sample to enhance the creation of a primary particle status prior to entering a flow sample cell. A sheath gas flow can be created about the sample to stabilize the measurement condition of the sample in the sample cell.
REFERENCES:
patent: 4708485 (1987-11-01), Illy
patent: 5579107 (1996-11-01), Wright et al.
patent: 5682235 (1997-10-01), Igushi
patent: 6384128 (2002-05-01), Wadahara et al.
patent: 6511712 (2003-01-01), Poliniak et al.
patent: 6553849 (2003-04-01), Scofield et al.
“Feeder System for Particle-Size Analyzer” NTIS Tech Notes, U.S. Dept. of Commerce Sep. 1, 1990, p. 743.
Horiba Ltd.
Nguyen Tu T.
LandOfFree
Dry particle distribution measuring apparatus and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dry particle distribution measuring apparatus and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dry particle distribution measuring apparatus and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3297083