1、 g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58porosimetry and gas adsorption Part 3: Analysis of micropores by gas adsorptionICS 19.120Pore size
2、distribution and porosity of solid materials by mercury BRITISH STANDARDBS ISO 15901-3:2007BS ISO 15901-3:2007This British Standard was published under the authority of the Standards Policy and Strategy Committee on 28 September 2007 BSI 2007ISBN 978 0 580 55281 6Amendments issued since publicationA
3、md. No. Date CommentsThis publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations. National forewordThis British Standard is the UK implement
4、ation of ISO 15901-3:2007. Together with BS ISO 15901-2:2006, it supersedes BS 7591-2:1992 which is withdrawn.The UK participation in its preparation was entrusted to Technical Committee LBI/37, Sieves, screens and particle sizing.A list of organizations represented on this committee can be obtained
5、 on request to its secretary.Reference numberISO 15901-3:2007(E)INTERNATIONAL STANDARD ISO15901-3First edition2007-04-15Pore size distribution and porosity of solid materials by mercury porosimetry and gas adsorption Part 3: Analysis of micropores by gas adsorptionDistribution des dimensions des por
6、es et porosit des matriaux solides par porosimtrie au mercure et par adsorption de gaz Partie 3: Analyse des micropores par adsorption de gaz BS ISO 15901-3:2007ii iiiContents Page Foreword iv Introduction v 1 Scope . 1 2 Normative references . 1 3 Terms and definitions. 1 4 Symbols . 3 5 Principles
7、. 5 5.1 General. 5 5.2 Methods of measurement 6 6 Procedure of measurements . 6 6.1 Sampling 6 6.2 Sample pre-treatment. 6 6.3 Measurement. 7 7 Verification of apparatus performance. 7 8 Calibration . 7 9 Evaluation of the micropore volume. 7 9.1 General. 7 9.2 Determination of the micropore volume
8、according to Dubinin and Radushkevich 9 9.3 Micropore analysis by comparison of isotherms 10 9.4 Determination of micropore size distribution by the Horvath-Kawazoe (HK) and the Saito-Foley (SF) method. 14 9.5 Determination of micropore size distribution by non-local density functional theory . 15 1
9、0 Test report . 19 Annex A (informative) Horvath-Kawazoe and Saito-Foley methods. 20 Annex B (informative) NLDFT method . 23 Bibliography . 26 BS ISO 15901-3:2007iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bo
10、dies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental an
11、d non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives,
12、 Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies cas
13、ting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 15901-3 was prepared by Technical Committee ISO/TC 24, Sieves, sieving and other siz
14、ing methods, Subcommittee SC 4, Sizing by methods other than sieving. ISO 15901 consists of the following parts, under the general title Pore size distribution and porosity of solid materials by mercury porosimetry and gas adsorption: Part 1: Mercury porosimetry Part 2: Analysis of mesopores and mac
15、ropores by gas adsorption Part 3: Analysis of micropores by gas adsorption BS ISO 15901-3:2007vIntroduction According to the IUPAC Recommendations, 1984 42, micropores are defined as pores with internal widths of less than 2 nm. Different methods for the characterization of micropores are available,
16、 including spectroscopy, electron and tunnel microscopy and sorption methods. In view of the complexity of most porous solids, it is not surprising that the results obtained are not always in agreement and that no single technique can be relied upon to provide a complete picture of the pore structur
17、e. With regard to the application of microporous material as specific sorbents, molecular sieves and carriers for catalysts and biological active material, the field-proven methods of gas sorption are of special value. On account of the fractality of dispersed and porous materials, the results of ad
18、sorption measurements depend on the size of the gas molecules used (effective diameter and space required at the surface). Furthermore, micropores might not be accessible for larger molecules and, thus, exclusion effects can be observed. The measuring techniques of the methods described in the prese
19、nt standard are similar to those of ISO 15901-2 and ISO 9277 for the measurement of gas adsorption at low temperature. From the measured isotherm, however, the very first part (i.e. relative pressures 101) is evaluated and thus the evaluation method is different. BS ISO 15901-3:2007blank1Pore size d
20、istribution and porosity of solid materials by mercury porosimetry and gas adsorption Part 3: Analysis of micropores by gas adsorption 1 Scope This part of ISO 15901 describes methods for the evaluation of the volume of micropores (pores of internal width less than 2 nm) and the specific surface are
21、a of microporous material by low-temperature adsorption of gases1,2,3,4,5,6,7. These are comparative, non-destructive tests. The methods use physisorbing gases that can penetrate into the pores under investigation. The method is applicable to isotherms of type I, II, IV or VI of the IUPAC classifica
22、tion (see ISO 15901-2:, Figure 1, and ISO 9277). The methods in this part of ISO 15901 are not applicable when chemisorption or absorption takes place. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edi
23、tion cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 3165, Sampling of chemical products for industrial use Safety in sampling ISO 8213, Chemical products for industrial use Sampling techniques Solid chemical products in th
24、e form of particles varying from powders to coarse lumps ISO 9277:1995, Determination of the specific surface area of solids by gas adsorption using the BET method ISO 15901-2:, Pore size distribution and porosity of solid materials by mercury porosimetry and gas adsorption Part 2: Analysis of mesop
25、ores and macropores by gas adsorption 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 adsorbate adsorbed gas 3.2 adsorption enrichment of the adsorptive at the external and accessible internal surfaces of a solid 3.3 adsorptive gas or vapour
26、to be adsorbed BS ISO 15901-3:20072 3.4 adsorbent solid material on which adsorption occurs 3.5 adsorption isotherm relationship between the amount of gas adsorbed and the equilibrium pressure of the gas at constant temperature 3.6 adsorbed amount number of moles of gas adsorbed at a given pressure,
27、 p, and temperature, T 3.7 equilibrium adsorption pressure pressure of the adsorptive in equilibrium with the adsorbate 3.8 monolayer amount number of moles of the adsorbate that form a monomolecular layer over the surface of the adsorbent 3.9 monolayer capacity volumetric equivalent of monolayer am
28、ount expressed as gas at standard conditions of temperature and pressure (STP) 3.10 macropore pore with width greater than about 50 nm 3.11 mesopore pore with width between approximately 2 nm and 50 nm 3.12 micropore pore with width of about 2 nm or less 3.13 physisorption weak bonding of the adsorb
29、ate, reversible by small changes in pressure or temperature 3.14 pore size pore width, i.e. diameter of cylindrical pore or distance between opposite walls of slit 3.15 relative pressure ratio of the equilibrium adsorption pressure, p, to the saturation vapour pressure, p0, at analysis temperature 3
30、.16 saturation vapour pressure vapour pressure of the bulk liquefied adsorptive at the temperature of adsorption 3.17 volume absorbed volumetric equivalent of the amount adsorbed, expressed as gas at standard conditions of temperature and pressure (STP), or expressed as the adsorbed liquid volume of
31、 the adsorbate BS ISO 15901-3:200734 Symbols For the purposes of this document, the following symbols apply, together with their units. All specific dimensions are related to sample mass, in grams. Symbol Term Unit KAaKirkwood-Mueller constant of adsorptive Jcm6KAsKirkwood-Mueller constant of adsorb
32、ent Jcm6asspecific surface area m2g1as,refspecific surface area of reference sample m2g1apolarizability of adsorptive cm3ammolecular cross-sectional area nm2snormalized adsorption (see Note 1) 1 (s*)polarizability of adsorbent cm3 affinity coefficient 1 c speed of light ms1dadiameter of an adsorptiv
33、e molecule nm dHSdiameter of hard spheres nm dpeffective pore diameter (cylindrical pore) nm dsdiameter of an adsorbent molecule nm d0d0= (ds+ da)/2, distance between adsorptive and adsorbent molecules nm E adsorption potential Jmol1E0characteristic adsorption energy Jmol1ffwell depth parameter of t
34、he gas-gas Lennard Jones potential K sfwell depth parameter of the gas-solid Lennard Jones potential K kBBoltzmann constant (1,380 650 5 1023) J K1l nuclei-nuclei pore width nm mamass adsorbed g memass of an electron kg mssample mass g NAAvogadros constant (6,022 1415 1023) mol1Nanumber of atoms per
35、 unit area (square metre) of monolayer m2BS ISO 15901-3:20074 Symbol Term Unit Nsnumber of atoms per unit area (square metre) of adsorbent m2naspecific amount adsorbed molg1nmmonolayer capacity cm3g1p pressure of the adsorptive in equilibrium with the adsorbate Pa p0saturation vapour pressure of the
36、 adsorptive Pa p/p0relative pressure of the adsorptive 1 R ideal gas constant (8,314 472) Jmol1K1ggas density gcm3g,STPgas density at STP (273,15 K; 101 325,02 Pa) gcm3lliquid density gcm3distance between two molecules at zero interaction energy nm ffdistance parameter of the gas-gas Lennard Jones p
37、otential nm sfdistance parameter of the gas-solid Lennard Jones potential nm T temperature K Tcrcritical temperature K t statistical layer thickness (see Note 2) nm Vaspecific adsorbed liquid volume of the adsorbate cm3g1Vgspecific adsorbed gas volume at STP (273,15 K; 101 325,02 Pa) cm3g1Vmicromicr
38、opore volume cm3g1W pore width (slit pore) nm adiamagnetic susceptibility of adsorptive cm3sdiamagnetic susceptibility of adsorbent cm3NOTE 1 According to ISO 31-043, the coherent SI unit for any quantity of dimension one (at present commonly referred to as “dimensionless”) is the unit one, symbol 1
39、. NOTE 2 While the symbol, t, is generally used to represent time, in the normal practice of pore size distribution analysis by gas adsorption, t is traditionally used to represent the statistical thickness of the liquid-like adsorbate layer. Therefore, all uses of the symbol t in this standard will
40、 refer to the statistical thickness and not time. For gravimetric measurements, the mass adsorbed is measured directly (see ISO 9277:1995, Figure 6), but a pressure-dependent buoyancy correction is necessary. Equilibrium is observed by monitoring the mass indication. In the region between about 0,1
41、Pa to 100 Pa, thermal gas flow can seriously disturb the measurements. Because the sample is not in direct contact with the thermostat, it is necessary to ensure the correct temperature experimentally. BS ISO 15901-3:200755 Principles 5.1 General The methods described in this part of ISO 15901-3 are
42、 based on the measurement of the adsorption and desorption of gases at a constant low temperature and the evaluation of the initial part of the isotherm. Gases used are those which are bound by physisorption at the solid surface, in particular N2at 77,4 K, Ar at 77,4 K or 87,3 K, and CO2at 195 K or
43、273,15 K. Because of the different size of the gas molecules, and hence, different accessibility of the pores, and also because of the different measuring temperatures, different results can be obtained. In micropores, the potential of interactions of the opposite pore walls are overlapping and, hen
44、ce, physisorption is stronger than in wide pores or at the external surface 8(see Figure 1). As a consequence, micropores are filled at very low relative pressure ( 0,01). A significant portion of the micropores is indicated by a large and steep increase of the isotherm near its origin and subsequen
45、t bending to a plateau. Micropores are characterized by the micropore volume and the micropore distribution. Because the pore size is similar to the molecule diameter, the choice of the gas is decisive. Key X distance between pore walls Y potential energy Figure 1 Three examples of the enhancement o
46、f interaction potential between a fluid and the surface in infinitely long, slit-like micropores as a function of the pore width (after Everett and Powl 8)The pore size and volume analysis of microporous materials, such as zeolites, carbon molecular sieves, etc., is difficult, because the filling of
47、 pores of dimension 0,5 nm to 1 nm occurs at relative pressures of 107to 105where the rate of diffusion and adsorption equilibration is very slow. Argon at 87,3 K fills micropores of dimension 0,5 nm to 1 nm at appreciably higher relative pressures compared to nitrogen (at 77,4 K). Both the higher p
48、ore-filling pressure and higher temperature help to accelerate diffusion and equilibration processes compared to nitrogen adsorption. Hence, it is of advantage to analyse microporous materials by using argon as the adsorptive at liquid-argon temperature (87,3 K). However, as in the case of nitrogen
49、adsorption at 77,4 K, the absolute pressures required to fill the most narrow micropores with argon are still very low. Associated with the low pressures required, is (as indicated above) the well known problem of diffusion restrictions, which prevent nitrogen molecules and also argon molecules from entering the narrowest micropores (as present in activated-carbon fibres, carbon molecular sieves, etc.). This can lead to erroneous adsorption isotherm
