TECHNOLOGY
Particle size determination simplified New instrument from Freeport Kaolin cuts analysis time from several hours to just minutes
Determining particle sizes of pigments, clays, and other colloidal particles is something most research and quality control chemists do, at best, with disinterest and, at worst, with impatience. Soon, however, these chemists may be able to shake the routine of spending so much time doing so little; of tying themselves up with such tedious analyses. Sometime in April, Micrometrics Instrument Corp., Norcross, Ga., will bring to market a new x-ray particle size analyzer, Model 5000, to be priced between $10,000 and $13,000. The company will be manufacturing the solid-state, table-top instrument under license from Freeport Kaolin Co., a division of Freeport Sulphur Co. With this instrument, chemists
Equivalent spherical diameters are defined as spheres of such diameters that they have equivalent sedimentation rates to the irregularly shaped particles being measured. The particle size range of the instrument is dependent on the density of the material being analyzed. Typically, for a material with a specific gravity of 2.5, the instrument's range is from 50 microns to 0.20 micron. Also, denser particles require proportionately less analysis time and less dense particles greater time. The time required to analyze for diameters from 50 to 2.0 microns is 10 minutes; to one micron, 20 minutes; and to 0.20 micron, 100 minutes. The new particle size analyzer is the second instrument to evolve as a commercial product from Freeport Kaolin's research activities at its Gordon, Ga., laboratories. The first instrument was an electrophoretic masstransport analyzer, which Numec Instruments and Controls Corp. began marketing in mid-1967. Freeport Kaolin vice president and research director, Tex Morris, says that the company has no plans to establish its own instrument department, as several chemical companies have recently done, but plans simply to contract or license any further instrument developments.
will be able to run particle size distribution curves in as little as 10 minutes instead of the eight hours now required to plot similar curves. Current techniques of measuring subsieve particle size distribution include direct microscopic counting and measuring, electronic counting and sizing, light and small-angle x-ray scattering, and sedimentation rate determinations. In addition to the fact that some of these methods entail lengthy procedures, others are limited to narrow size distributions and are applicable only to specific size ranges. Freeport Kaolin's research chemist, Dr. James P. Olivier, designed the new instrument on basic sedimentation principles and, in particular, on those expressed in Stokes' law. The instrument measures the sedimentation velocities of fine particles as they settle through a liquid suspension. This analysis involves using a finely collimated beam of x-rays to determine the concentration of particles in suspension at a known sedimentation depth as a function of time. The logarithm of the transmitted x-ray intensity is electronically generated, scaled, and presented linearly as "cumulative per cent finer" on one axis of an x-y recorder. These data are plotted against equivalent spherical diameters along the other axis.
Inventor Olivier's instrument measures sedimentation rates Outlet nm X-ray tube
—-H Slit
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J — — ——• Slit
Detector
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Sample cell
Converter (x-ray intensity to concentration) ι I
Inlet Cda
Power source
Detector and converter power source
Relative concentration signal
Cell drive
Recording mechanism
I Cell height signal
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Size indication signal
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