GB1164359A - Surface Area Measurement of Standard Length Sample of Finely Divided Solids. - Google Patents

Abstract

1,164,359. Measuring total surface area of particulate materials; measuring porosity by gamma-rays. FULLER CO. Nov. 22, 1967 [Nov.29, 1966], No.53211/67. Headings G1A and G1N. In the determination of the total surface area or particle size of a finely divided material, e.g. concrete, by measuring the resistance to gas flow of a sample of fixed shape, volume and porosity or density, which is indicative of the particle size or total surfaces area of the sample particles, the required sample is prepared by compacting a portion of the material while measuring its density the compacting being stopped when the portion reaches the required density. A preset volume of this portion is then used as the sample. The density of the compacted portion of the material may be measured capacitatively, the dielectric constant of the material being indicative of its density. Alternatively it may be measured by transmitting gamma radiation through the mass and measuring the amount of radiation transmitted e.g. by an ionization chamber. As shown, a portion of the material is fed into a tube 18, Fig.1, of dielectric material, provided at its lower end with a perforate plate, through which the material cannot flow but gas can, the tube being connected at this end to a gas inlet 32. The tube is vibrated by a pneumatic vibrator 42 to compact the material. Alternatively mechanical compression or pulses of compressed air may be used for this purpose. Capacitor plates 44, mounted round the tube, whose capacitance is indicative of the density of the material, are connected to the output of an oscillator (122, Fig.3 not shown), and via an amplifier (126) to a comparator, where the signal from the capacitor is compared with a reference signal. When the two signals are equal, indicating that the required density has been reached, a relay (128) is energized, and the vibrator is de-energized. A member 48 is then moved across the upper end of the tube to separate off a fixed volume of the compacted material and provide a connection at the upper end of the sample via vent 60 to the at atmosphere, a perforate plate 58 containing the sample within the tube during the subsequent test. A constant pressure of gas is then applied to the lower end of the column of compacted sample and its rate of flow, indicative of the surface area of the sample, is measured, e.g. by a heat transfer transducer (114, Fig.2 not shown), and indicated and/or recorded on meter (120). The recorded signal may also be used for controlling the process producing the material, e.g. the grinding of cement, to keep the surface area constant.