1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS 7591 : Part 4 : 1993 I
2、ncorporating Amendment No. 1 ICS 17.040.20 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Porosity and pore size distribution of materials Part 4. Method of evaluation by liquid expulsionBS 7591 : Part 4 : 1993 Issue 2, August 1997 This British Standard, having been prepared
3、under the direction of the General Mechanical Engineering Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 15 September 1993 BSI 1997 The following BSI references relate to the work on this standard: Committee reference GME/29 Draft for co
4、mment 92/76154 DC ISBN 0 580 21847 3 Amendments issued since publication Amd. No. Date Text affected 9604 August 1997 Indicated by a sideline in the margin Committees responsible for this British Standard The preparation of this British Standard was entrusted by the General Mechanical Engineering St
5、andards Policy Committee (GME/-) to Technical Committee GME/29, upon which the following bodies were represented: BLWA Ltd. (The Association of the Laboratory Supply Industry) British Cement Association British Coal Corporation Coated Abrasives Manufacturers Association Guild of Metal Perforators In
6、stitution of Chemical Engineers Institution of Mining and Metallurgy Mechanical Handling Engineers Association Ministry of Defence NABIM Society of Chemical Industry Society of Cosmetic Scientists Woven Wire Association The following bodies were also represented in the drafting of the standard, thro
7、ugh subcommittees and panels: AEA Technology Aluminium Federation Brunel University China Clay Association Department of Trade and Industry (National Physical Laboratory) Department of Trade and Industry (Warren Spring Laboratory) GAMBICA (BEAMA Ltd.) Royal Pharmaceutical Society of Great Britain Ro
8、yal Society of Chemistry University College London University of Bradford University of Technology, Loughborough UKAEA Co-opted members1 BS 7591 : Part 4 : 1993 Contents Page Committees responsible Inside front cover Foreword 2 Method Introduction 3 1 Scope 3 2 Informative references 3 3 Definitions
9、 4 4 Principle 5 5 Apparatus 5 6 Procedure 7 7 Calculation of results 7 8 T est report 9 Annex A (informative) Examples of the calculation of maximum, minimum and mean flow pore diameters 10 Figures 1 Types of pore space 4 2 Simple form of typical manually controlled apparatus 5 3 Typical sample hol
10、der 6 4 Typical plot of flow rate against applied pressure for wet and dry runs, performed on a single test sample 8 5 Example of plot of wet and dry runs from maximum to minimum pore sizes 8 6 Cumulative flow pore size distribution 9 7 Differential flow pore size distribution 9 List of references I
11、nside back cover2 BS 7591 : Part 4 : 1993 1) In preparation Foreword This Part of BS 7591 has been prepared under the direction of the General Mechanical Engineering Standards Policy Committee and is one of a series which describes recommended methods for the evaluation of porosity and pore size dis
12、tribution. This Part of BS 7591 describes the evaluation of porosity by liquid expulsion. Other Parts of BS 7591 are as follows: Part 1. Method of evaluation by mercury porosimetry Part 2. Method of evaluation by gas adsorption 1) Part 3. Method of evaluation by challenge test This British Standard
13、describes a method of evaluation only and should not be used or quoted as a specification defining limits of performance. Reference to this British Standard should indicate that the method of evaluation used is in accordance with BS 7591 : Part 4 : 1993. Compliance with a British Standard does not o
14、f itself confer immunity from legal obligations.3 BS 7591 : Part 4 : 1993 2) 1P a=1N/m 2 . Method Introduction In general, different types of pores can be pictured as either apertures, channels or cavities within a solid body or as the space (i.e. interstices or voids) between solid particles in a b
15、ed, compact or aggregate. Porosity is a term which is often used to indicate the porous nature of solid material and is more precisely defined as the ratio of the volume of accessible pores and voids to the total volume occupied by a given amount of the solid. In addition to the accessible pores, a
16、solid can contain closed pores which are isolated from the external surface and into which fluids are not able to penetrate. The characterization of closed or blind pores is not covered in this Part of this standard. Porous materials can take the form of fine or coarse powders, compacts, extrudates,
17、 sheets or monoliths. Their characterization usually involves the determination of the pore size distribution as well as the total pore volume or porosity. For some purposes it is also necessary to study the pore shape and interconnectivity and to determine the internal and external surface area. Po
18、rous materials have great technological importance, for example in the context of: controlled drug release; catalysis; gas separation; filtration including sterilization; materials technology; environmental protection and pollution control; natural reservoir rocks. It is well established that the pe
19、rformance of a porous solid (e.g. its strength, reactivity, permeability or adsorbent power) is dependent on its pore structure. Many different methods have been developed for the characterization of pore structure. In view of the complexity of most porous solids, it is not surprising to find that t
20、he results obtained are not always in agreement and that no single technique can be relied upon to provide a complete picture of the pore structure. The choice of the most appropriate method depends on the application of the material, its chemical and physical nature and the range of pore size. The
21、most commonly used methods are as follows. Mercury porosimetry , where the pores are filled with mercury under pressure. This method is suitable for many materials with pores in the approximate diameter range of 0.003mmt o 400mm, and especially in the range 0.1mmt o 100mm. Gas adsorption, where the
22、pores are characterized by adsorbing a gas, such as nitrogen, at liquid nitrogen temperature. This method is most appropriate for pores in the approximate diameter range of 0.0004mm to 0.04mm (0.4 nm to 40 nm) and is an extension of the surface area estimation technique (see BS 4359 : Part 1). Chall
23、enge test, where the effective size of the through-pores in a structure is estimated by the passage of test particles or molecules of different sizes. This method is often used for pores in the approximate diameter range of 0.005mmt o 100mm. Liquid expulsion, where the through-pores in a structure a
24、re characterized by the pressure required to empty them of a wetting fluid. This method is normally used for pores in the approximate diameter range of 0.05mmt o5 0m m. 1 Scope This Part of BS 7591 describes the evaluation of pore size characteristics (such as mean, maximum and the distribution of p
25、ore sizes) that allow the flow of liquid from one side of the wetted structure to the other . It is a comparative and usually non-destructive test. Pore size is commonly expressed as pore diameter. The pore diameter is calculated from the applied gas pressure, which causes the liquid filled pores to
26、 be emptied, resulting in a flow of gas through the sample. The method is suitable for the study of through-pore materials, such as filter paper , paper , polymer membrane filters and cloth. It enables pore sizes to be estimated within the general size range of about 50mm down to about 0.05mm. The t
27、est involves the application of pressures up to 1M P a 2) (150 psi). For most materials this pressure does not cause compaction or deformation of the material which would result in a change in the pore structure. The technique should be considered to be comparative, as for most porous media a theory
28、 is not available to allow an absolute calculation of pore size. It is the recommended method for the evaluation of filter papers (see BS 6410). 2 Informative references This Part of BS 7591 refers to other publications that provide information or guidance. Editions of these publications current at
29、the time of issue of this standard are listed on the inside back cover , but reference should be made to the latest editions.BS 7591 : Part 4 : 1993 4 a) V oids between particles b) Types of pores Figure 1. Types of pore space 3 Definitions (see also figure 1) For the purposes of this Part of BS 759
30、1, the following definitions 3.1 blind pore (dead end pore) An open pore having a single connection with an external surface. 3.2 bubble point The pressure at which the first flow of gas through a wetted sample occurs; it is a measure of the largest pore in the sample. 3.3 closed pore A cavity with
31、no access to an external surface. 3.4 ink bottle pore A narrow necked open pore. 3.5 interconnected pore A pore which communicates with one or more other pores. 3.6 mean flow pore size The average pore diameter corresponding to the point where 50 % of the dry curve crosses the wet curve in a plot of
32、 flow rate against applied pressure. 3.7 open pore A cavity or channel with access to an external surface. 3.8 pore diameter The diameter of a pore, assumed to be cylindrical, emptied of fluids at a given pressure, as calculated from a given equation (see clause 7). 3.9 pore size distribution The di
33、stribution of pore diameters in a porous body by the application of a given equation (see clause 7, which assumes a cylindrical pore model).5 BS 7591 : Part 4 : 1993 Figure 2. Simple form of typical manually controlled apparatus 3.10 right cylindrical pore A cylindrical open pore perpendicular to th
34、e surface of the porous body and which passes through the body from one side to the other . 3.11 through-pore An open pore which passes through the sample from one side to the other . 3.12 void The space between particles or fibres in a bed, i.e. inter-particle, or inter-fibre, pore. 4 Principle If
35、the through-pores within a material are filled with a liquid, i.e. wetted, the liquid can be expelled by applying a differential gas pressure across the wetted sample. Gas will flow through the wetted sample when the differential gas pressure exceeds the capillary attraction forces of the liquid con
36、tained in the largest pores. Progressively increasing the differential gas pressure across the wetted sample will result in the smaller through-pores being emptied of their liquid, producing an increased gas flow. From a knowledge of the applied gas pressure and the resulting gas flow through the sa
37、mple, once when wetted and once when dry, the pore distribution is calculated. The technique is based on the relationship between pore diameter and applied pressure as described by the capillary rise equation (see 7.1). There are several assumptions inherent in the calculations. 5 Apparatus 5.1 Pore
38、 size apparatus NOTE 1. A schematic diagram of a simple form of manually controlled apparatus is shown in figure 2. This apparatus can be used to estimate pore size distribution by the liquid expulsion method as well as to obtain a reading of bubble point. NOTE 2. The bubble point (or bubble pressur
39、e) test is used for instance to determine the equivalent pore size of fabrics (see BS 3321) or the largest pore size of filter papers (see BS 6410).BS 7591 : Part 4 : 1993 6 Key A base B locking ring C O ring seal D support disc E air inlet F test sample Figure 3. Typical sample holder 5.1.1 Gas pre
40、ssure source, for example compressed air , at up to about 0.6 MPa to 1.0 MPa (about 100 psi to 150 psi) available at a flow rate of up to about 100 l/min. NOTE. There should be a buffer capacity between the compressor and the apparatus to minimize pressure fluctuations. When using high pressures, th
41、e operator should ensure adequate personal protection. 5.1.2 Gas pressure gauge, calibrated to the accuracy necessary for the test to be performed. NOTE. An error of 1 % in pressure reading will calculate to a 1 % error in pore size. 5.1.3 Sample holder NOTE. This typically holds a thin disc of samp
42、le material, usually supported downstream by a large pore structure, or mesh, which is too coarse to interfere with the pore sizes to be measured (see figure 3). 5.1.4 Bubble point detector , an optional device used to identify the onset of gas flow through the sample. 5.1.5 Flowmeter , for measurin
43、g the flow rate of gas through the specimen, calibrated to an accuracy of within 3%. 5.1.6 Liquid trap, for collecting liquid expelled from the pores to prevent it interfering with the detection of the bubble point or gas flow. 5.1.7 Two-way valve, for diverting the gas flow to either: a) the bubble
44、 point detector; or b) the flowmeter . 5.2 Vacuum vessel and pump, comprising a glass beaker within a vacuum desiccator or bell jar and a pump capable of producing a vacuum of 0.7 kPa. NOTE. The vacuum vessel is sometimes used for sample preparation.7 BS 7591 : Part 4 : 1993 6 Procedure 6.1 Sampling
45、 T ake the sample intended for analysis (the test sample) representatively from the bulk material and ensure it is of an area appropriate to the range of the flowmeter . NOTE. If the sample area is too large the flow of gas through the sample may be too large for the meter to measure. Highly permeab
46、le samples will need a smaller area; 20 mm to 50 mm is a typical diameter range for a sample of porous material. 6.2 Preparation of test samples T est the sample either in the as received condition, or after pre-treatment. NOTE. Typical pre-treatments are given in a) and b). a) Pre-treatment for pap
47、ers Test samples may be conditioned at a relative humidity of 50 % 2 % and a temperature of 23 C 1 C, in accordance with BS 3431 : 1973. An alternative pre-treatment may be by oven drying. b) Pre-treatment for resin treated papers The resin should be cured before commencing the test. Curing may be c
48、arried out by exposure to a high temperature for a period (e.g. 150 C for 10 min), or to high humidity, or to ultraviolet light depending on the resin involved. 6.3 Choice of wetting liquid Ensure that the liquid fully wets the sample, i.e. has a contact angle close to 0, low surface tension and low
49、 volatility, and is not reactive with the sample. NOTE. Water is not recommended; preferred is a fully fluorinated hydrocarbon liquid (i.e. a perfluorocarbon) or a high boiling point alkane, as they can be obtained as pure liquids whose surface tension is known and is not variable. Reference should be made to the suppliers literature regarding any health and safety instructions appropriate to the liquid used. 6.4 Pre-wetting of test sample Fully immerse the test sample in the wetting liquid and degas in the vacuum vessel, if appropriate, for 2 min or until no more gas
