Patent GB-1243143-A (GB)
Title: A method of and apparatus for the measurement of surface area
IPC: G01N15/08
Filed: 1969-04-02
Abstract: 1, 243, 143. Measuring surface area of powdered material. MICROMERITICS INSTRUMENT CORP. April 2, 1969 [April 8, 1968], No. 17143/69. Heading G1M. The surface area of a granular or powdery material is determined by measuring the adsorption of a gas on the surface of the sample of material and relating this volume of adsorption directly to the surface area. The method comprises placing a sample of the material in an initial volume of nitrogen, fixing the temperature of the N gas at its adsorption temperature, adding an additional volume of the gas to the initial volume as the gas is adsorbed so as to maintain a predetermined pressure, and measuring this additional volume. The apparatus comprises sample container tubes 10a, 10b and 10c each of which are connected to two par valves 16 by ducts 19, 15. The left hand part of each valve 16 may be connected by a passage 21 in a core 20 to either a tube 22 and a supply of N, or to tubes 30, 31. The tube 31 is connected to a piston and cylinder variable volume device 42 operated by a motor 50 and gearing, and to sealed bellows operated pressure sensing valves PS1 and PS2 operate switches 40, 41. The right hand side of each valve 16 may be connected by a passage 26 to a restricted tube 28 and to atmosphere. In operation the pipe 31 and the device 42 are filled with N by connecting the passages 22, 20, 32, and the housing 63 keeps them at constant temperature A sample of powder is then placed in the container 10a and heated by a jacket 63a and whilst this is happening the passages 22, 20 and 19 are connected and also the passages 15, 26 and 28 so that N scours through the container to atmosphere. The jacket 63a is then removed and the tube 10a placed in communication with the manifold 31 and surrounded by ice and water in a container 66. A control switch 60 is then operated to select the device PS1 which senses the N piston 45 until the total volume of the tubes 10a, 31 and the space 43 and connected components is at a first determined pressure to which the device PS1 is responsive and also at a predetermined first temperature of 0‹C. The device PS1 is now re-set and the sample tube 10a isolated by the valve 16 from tube 31 and cooled (by liquid N) to a convenient adsorption temperature. Switches 60, 61 are then operated to make the device PS2 sense the gas-pressure in 31 and also operates a solenoid valve 54 for a short period. The low-pressure device PS2 now operates and adjusts the volume of the space 43 as before to a pressure which the gas in the tube 10a would have after the change from the first temperature to the second temperature in the absence of any adsorption of the gas. The tube 10a at the adsorption temperature is now connected to 31 and some gas is adsorbed by the sample so that the pressure in 10a is less than the predetermined second pressure. The device PS2 now changes the volume of the space 43 and returns to the second pressure, the energizing of the motor 50 being used to operate a counter 62 whose reading is directly proportional to the distance moved by the piston 45 and to the change in the volume of space 43. The counter 62 may be calibrated to indicate directly the sample surface area. Prior to reusing the apparatus for sample tubes 10b, 10c the N in the apparatus is replaced.