Measuring and testing – Particle size
Patent
1990-09-10
1991-11-19
Raevis, Robert
Measuring and testing
Particle size
G01N 1508
Patent
active
050656341
ABSTRACT:
A method for determining the surface area of a material by using the dynamic flow method, by continuously passing a stream of a gaseous mixture of known and constant composition consisting of an adsorbate such as nitrogen and an inert gaseous diluent such as helium in contact at a constant pressure with a measured sample of the material at a temperature at which neither the inert diluent nor the adsorbate is appreciably adsorbed by the sample. Then, while continuing said stream, the sample is cooled to a temperature at which adsorption of the adsorbate by the sample selectively takes place. Using a detector, one continuously measures the decrease in the concentration of the adsorbate in the stream, down stream of the sample, during the cooling and until equilibrium is re-established. By using a sensing circuit, one integrates the measured decrease in concentration of the adsorbate over the period of cooling until the equilibrium is re-established. A gate circuit is used to inhibit all signals emanating from the detector immediately after the sample is immersed in the gaseous mixture, to eliminate false or phantom signals generated in the detector by the chilling of the gas mixture. The inhibit gate is then deactivated to reconnect the detector to the sensing or readout circuit so that the completion of the adsorption signal can be detected. The liquid nitrogen bath is then lowered or removed from the sample of material in response to the absorption completion signal to cause the sample of material to warm to ambient temperature, and permit desorption of the adsorpted nitrogen in the sample of material. The desorbed nitrogen from the sample of material is detected by the detectors, so as to generate a signal proportional to the volume of nitrogen adsorbed by the sample of material, so as to provide a measure of the surface area of the sample of material.
REFERENCES:
patent: 2960870 (1960-11-01), Nelsen et al.
patent: 3555912 (1971-01-01), Lowell
patent: 3884083 (1975-05-01), Lowell
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