Patent GB-808995-A (GB)
Title: Measuring porosity and distribution of pore size
Inventor: WIGGS PETER KENNETH CLIFFORD
IPC: G01N15/08
Filed: 1956-11-05
Abstract: 808,995. Determining porosity of materials. MORGAN CRUCIBLE CO. Ltd. Nov. 5, 1956, No. 33739/56. Class 106 (2). [Also in Group XXXVIII] A method of determining the distribution of pores of a given diameter and the porosity of a sample of material comprises placing the sample in a vertical dilatometer tube, partly filling it with an electrically conductive liquid which does not wet the sample, e.g. mercury, and measuring the difference between the resistance of a wire extending along the bore of the dilatometer tube and that of a wire of identical resistance per unit length extending along the bore of a second vertical dilatometer tube filled with the liquid to the same initial level as the first tube, while both tubes are maintained under identical conditions of temperature and pressure. Dilatometer.-This is shown in Figs. 3, 4, 6 and 7, and comprises a vertical casing 1 having vents 2 to allow oil to flow freely between its interior and exterior and having upper and lower closure members 3, 4. An end portion 21 (Figs. 6 and 7), has a screwed retaining-ring 22 which screws into the member 4, and a sealing-ring 25 provides a fluid-tight connection between them. Inside the casing 1 are three capillary tubes 5, 6, 7, each communicating with a recess 9 in the member 3, and forming a triangle in crosssection. Tubes 5, 6 project at their lower ends into bushes 15, only one of which is shown, in a cavity 17 formed between the member 4 and the end portion 21. These bushes 15 are in axial alignment with chambers 27, 28 in the end portion, and sealing-rings 29 provide a fluid-tight joint when the end portion is screwed home. The tube 7 is located in a bush 18 which does not project into the cavity 17, and a vent 30 with a detachable plug 32 is provided in the end portion. Inside the capillary tubes 5, 6, are resistance wires, which are anchored at their upper ends to terminals 36, 37 (not shown), insulated from the body of the dilatometer, and at their lower ends to anchorages inside the bushes 15. Four contacts A, B, C, D, (see Figs. 4 and 14) project from the lower end of the casing 1 and are connected as follows. Contact A is connected to two balance resistances 39, 40, fixed within the casing 1 and these are in turn connected to contacts 36, 37, respectively. Contact B is earthed to the dilatometer body 1 and thus connected to the liquid in the tubes 5, 6, and contacts C, D, are connected to terminals 36, 37, respectively, and also to resistance wires 34, 35. Porosimeter.-This is shown in Fig. 12 and comprises an upright cylindrical pressure vessel (not shown), open at its lower end, which screws into a base 50 and is maintained in a vertical position by two stanchions 50a. The base 50 has a recess 56 containing two upright supports 58 which fit into sockets 41, 42, of the end portion 21 of the dilatometer, Fig. 7, whilst a spring (not shown) on the centre support holds the dilatometer against the top of the pressure vessel cavity. The base 50 also contains a bore 61 communicating, as shown in Fig. 12, by means of a passage 60 and non-return ball valves 62a, 63a, 64, with the recess 56, connections 62, 63, to a compressed air supply and an oil reservoir respectively, and with the bore 67 of a hand-worked pump. Spring contacts 59 rest against the contacts A, B, C, D, on the dilatometer body 1 and are connected electrically to a terminal block on the exterior of the base 50. A safety-valve and a pressure-gauge are also fitted to the bore 61. Operation.-A sample of predetermined dimensions is placed in chamber 27, which is larger than chamber 28 by the size of the sample, and the end portion 21 lightly replaced. As shown in Fig. 13, a filling tube 100 connected to a closed mercury container 102 is screwed into vent 30 and a hollow cap 103, connected by a pipe 104 to a source of vacuum, is placed on the member 3 and sealed by an 0-ring 105. A glass tube 106 is connected to the pipes 104, 100 and serves to show the height of mercury in the capillary tubes 5, 6 and 7, the apparatus is evacuated, and mercury then introduced by raising the container 102. The end portion 21 is then tightened up, thus sealing the capillary tubes 5, 6, and the chambers 27, 28 from the rest of the apparatus at their lower ends, the container 102 lowered, and the vacuum released. When the pressure on the upper surface of the mercury in the tubes 5, 6, is again atmospheric, slight absorption of mercury into the larger pores of the sample takes place, and this gives a measure of the size of these pores. The filling apparatus can then be disconnected from the dilatometer 1 and the plug 32 replaced. The dilatometer is then placed in the recess 56 of the porosimeter and the pressure vessel screwed down. Air under pressure is then admitted through connection 62 into the space surrounding the dilatometer to prevent oil getting in the capillary tubes and contaminating the mercury. Oil is then pumped in through connection 63 by the hand pump, to a desired pressure. The mercury in tube 5 then sinks owing to absorption in those pores whose diameter is greater than or equal to the diameter of the smallest pore into which mercury would penetrate at the pressure then obtaining, and the volume of such pores is measured by the increase in resistance in the connection between contacts C and B due to this fall in level of the mercury. The measurement is made by means of a potentiometer P, having a double-throw switch, which compares the potential difference between contacts C and D with that between the ends of a standard resistance R.