Electricity: measuring and testing – Electrostatic field
Patent
1989-02-27
1991-10-22
Harvey, Jack B.
Electricity: measuring and testing
Electrostatic field
324453, 324 711, 73587, G01R 2912, G01N 2902
Patent
active
050599097
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of and means for the determination of particle size and electric charge or zeta potential in a colloidal system.
A colloid is a suspension of small particles in a fluid medium (e.g. aerosols and the dispersions of solids in liquids). Colloids have great scientific and industrial importance. Examples include blood, paints, slurries and milk.
The most significant characteristics of many colloidal systems are the size and charge of the particles, since most other properties of the system are influenced to some extent by these factors.
There are many areas of industry in which it is necessary to be able to determine the size of particles suspended in a liquid or the electric charge on the particles. For example, in the mining industry, mineral ores must be ground down until the particles are the right size for floating, and in liquid purification processes it is important to be able to keep particle charge low in order to encourage the coagulation of the particles into clumps large enough to be filtered out.
In nearly every colloidal system the particle carries an electric charge. This charge is balanced by an excess of ions of opposite charge in the suspending liquid. These ions tend to cluster around the particle, forming a diffuse cloud which is known as the double-layer. The voltage difference between the particle surface and the liquid beyond the double-layer in equilibrium is referred to as the "zeta potential" denoted by .zeta.. The bigger the particle charge, the bigger the .zeta. potential.
BACKGROUND ART
Known methods for measuring particle size include the use of electron microscopes, Coulter counters, centrifuges and dynamic light-scattering devices. However, all of these known methods require the removal, and subsequent dilution of the sample prior to testing, making such methods unsuited to on-line monitoring of particle size.
Known methods for measuring particle charge all involve the measurement of the particle velocity in an electric field. In some methods, the velocity is determined by measuring the time required for the particle to pass between two points on a microscopic grid when a steady electric field is applied. In other methods, particle velocity is measured by a light-scattering technique with an alternating electric field of 10 or 20 Hz.
There is apparatus suitable for determining both particle size and charge. The "Zeta Sizer" (Malvern Instruments) measures the light scattered from a laser beam as it passes through the suspension. In the absence of an applied field, the fluctuations in the scattered light provide information about the particle size, and if a slowly varying electric field is applied the particle charge can be obtained from the fluctuating light signal.
All of the above methods suffer the disadvantage that they require sample dilutions and most require use of light-scattering instruments. Accordingly, opaque samples cannot be measured.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a method of and means for the determination of particle size and electric charge or zeta potential of particles in a colloidal system.
It is another object of the present invention to provide a method of and means for the determination of particle size and electric charge or zeta potential of particles in a colloidal system on-line and without sample dilution, even in opaque solutions.
It is a further object of the present invention to provide a method of and means for determination of the motion of colloidal particles in a high-frequency field, for it is by the use of high frequency measurements of particle motion that the particle size and charge can be determined.
These and other objects of the present invention will be apparent from the following non-limiting disclosure of the invention.
According to one aspect of the present invention there is provided means for determining the size and charge of particles dispersed in a fluid medium from the phase lag and amplitude of particle velocity in an alternating e
REFERENCES:
patent: 4497208 (1985-02-01), Oja et al.
patent: 4633714 (1987-01-01), Mazumder et al.
patent: 4679439 (1987-07-01), Culkin
Colloidal Dynamics Pty. Ltd.
Harvey Jack B.
LandOfFree
Determination of particle size and electrical charge does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Determination of particle size and electrical charge, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Determination of particle size and electrical charge will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-111088