1、Designation: D 4284 07Standard Test Method forDetermining Pore Volume Distribution of Catalysts byMercury Intrusion Porosimetry1This standard is issued under the fixed designation D 4284; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the porevolume distributions of catalysts and catalyst
3、supports by themethod of mercury intrusion porosimetry. The range of appar-ent diameters of pores for which it is applicable is fixed by theoperant pressure range of the testing instrument. This range istypically between apparent pore entrance diameters of about100 and 0.003 m (3 nm).1.2 The values
4、stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safet
5、y and health practices and determine the applica-bility of regulatory limitations prior to use. Specific hazardinformation is given in Section 8.2. Referenced Documents2.1 ASTM Standards:2E 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 456 Terminology Relating to Quality
6、and StatisticsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 apparent pore diameterthe diameter of a pore,assumed to be cylindrical, that is intruded at a pressure, P, andis calcu
7、lated with Eq 1.3.1.2 interparticle poresthose pores that occur betweenparticles when they are packed together and that are intrudedduring the test.3.1.3 intraparticle poresthose pores lying within the en-velopes of the individual catalyst particles and that are intrudedduring the test.3.1.4 intrude
8、d pore volumethe volume of mercury that isintruding into the pores during the test after this volume hasbeen corrected, if necessary, per 13.3.2.4. Summary of Test Method4.1 When a liquid does not wet a porous solid it will notvoluntarily enter the pores in the solid by capillary attraction.The nonw
9、etting liquid (mercury in this test method) must beforced into the pores by the application of external pressure.The size of the pores that are intruded is inversely proportionalto the applied pressure. When a cylindrical pore model isassumed, the relationship between pressure and size is:d 524gcosu
10、!P(1)where:d = apparent diameter of the pore being intruded,g = surface tension of the mercury,u = contact angle between the mercury and the solid, andP = absolute pressure causing the intrusion.4.2 The volume of the intruded pores is determined bymeasuring the volume of mercury that is forced into
11、them atvarious pressures.Asingle-pore size distribution determinationinvolves increasing the pressure, either continuously or step-wise, and recording the measured intruded volume.5. Significance and Use5.1 This test method is intended to determine the volumedistribution of pores in catalysts with r
12、espect to the apparentdiameter of the entrances to the pores. In general, both the sizeand volume of pores in a catalyst affect its performance. Thus,the pore volume distribution is useful in understanding acatalysts performance and in specifying a catalyst that can beexpected to perform in a desire
13、d manner.1This test method is under the jurisdiction of ASTM Committee D32 onCatalysts and is the direct responsibility of Subcommittee D32.01 on Physical-Chemical Properties.Current edition approved April 1, 2007. Published April 2007. Originallyapproved in 1983. Last previous edition approved in 2
14、003 as D 428403.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbo
15、r Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6. Limitations6.1 Mercury intrusion porosimetry, in common with manyother test methods, is only capable of sensing pores that areopen to the outside of a catalyst particle, and will not determinethe volume of any pores that are co
16、mpletely enclosed bysurrounding solid. Also, the test method will only determinethe volume of intrudable pores that have an apparent diametercorresponding to a pressure within the pressuring range of thetesting instrument.6.2 The intrusion process proceeds from the outside of aparticle toward its ce
17、nter. Comparatively large, interior porescan exist that have smaller pores as the only means of access.The test method will incorrectly register the entire volume ofthese “ink-bottle” pores as having the apparent diameter of thesmaller access pores.6.3 In the penetrometer, interparticle pores can be
18、 created inaddition to the intraparticle pores. (See Section 3 for terminol-ogy.) These interparticle pores will vary in size and volumedepending on the size and shape of the catalyst particles and onthe manner in which the particles are packed together in the testchamber. It is possible that some o
19、f the interparticle pores willhave the same apparent diameter as some of the intraparticlepores. When this occurs, the test method cannot distinguishbetween them. Thus, the test method can yield an intruded porevolume distribution that is, in part, dependent upon the packingof multi-particle samples
20、. However, many catalysts have intra-particle pores that are much smaller than the interparticlepores. This situation leads to a bimodal pore size distributionand the distinction between the two classes of pores canfrequently be made.6.4 Mercury intrusion can involve the application of highpressures
21、 on the sample. This may result in a temporary, orpermanent, alteration in the pore geometry. Generally, catalystsare made from comparatively strong solids and are less subjectto these alterations than some other materials. However, thepossibility remains that the use of the test method may alter th
22、enatural pore volume distribution that it seeks to measure.7. Apparatus7.1 Mercury Intrusion Porosimeter, equipped with a sampleholder capable of containing one or several catalyst particles.This holder is frequently called a penetrometer. The porosim-eter shall have a means of surrounding the test
23、specimen withmercury at a low pressure, a pressure generator to causeintrusion, pressure transducers capable of measuring the in-truding pressure with an accuracy of at least 61 % throughoutthe range of pressures over which the pores of interest arebeing intruded, and a means of measuring the intrud
24、ed mercuryvolumes with an accuracy of at least 61mm3(6103cm3).7.2 Vacuum Pump, if not part of the porosimeter, to evacuatethe sample holder.7.3 Analytical Balance capable of measuring the samplesmass with an accuracy of at least 60.1 %. This usually meansthat the balance must be sensitive to 6107kg
25、(60.1 mg).7.4 Mercury, with a purity equal to, or better than, doubledistilled.8. Hazards8.1 Samples that have been exposed to mercury are danger-ous. Apply the precautions that follow:8.1.1 Mercury is a hazardous substance that can causeillness and death. Mercury can also be absorbed through theski
26、n; avoid direct contact.8.1.2 Always store in closed containers to control its evapo-ration, and use it only in well-ventilated rooms.8.1.3 Wash hands immediately after any operation involvingmercury.8.1.4 Exercise extreme care to avoid spilling mercury. Cleanup any spills immediately using procedur
27、es recommendedexplicitly for mercury.8.1.5 Recycling of waste mercury is recommended and to beconducted in accordance with local government hazardouswaste regulations. Disposal of waste mercury and mercurycontaminated materials should be performed as mandated bylocal government hazardous waste regul
28、ations.9. Sampling9.1 The sample from which test material will be drawn shallbe representative of the catalyst. The actual amount of catalystused in a test will depend on the sensitivity of the porosimeterand the porosity of the sample.10. Conditioning10.1 The ideal preconditioning for the test spec
29、imen is anoutgassing procedure that removes all foreign substances fromthe pores and pore walls of the catalyst, but does not alter thesolid catalyst in any way. If possible, the appropriate combi-nation of heat and vacuum and the required time of condition-ing shall be experimentally determined for
30、 the specific catalystunder test. This outgassing technique shall then be the onespecified and used.10.2 Where the procedure described in 10.1 is not practical,outgas the catalyst in a vacuum of at least 1.3 Pa (10 mHg) ata temperature of 150C for at least 8 h.NOTE 1The procedure in 10.2 is unlikely
31、 to alter the pore structure ofa catalyst but it can severely change the pore structure of many othermaterials.11. Procedure11.1 Outgas the test sample in accordance with 10.1 or 10.2.11.2 Weigh the outgassed specimen and record this weight.11.3 Place the outgassed catalyst in the penetrometer inacc
32、ordance with the manufacturers instructions.NOTE 2Since, when performing the operations described in 11.2 and11.3, the outgassed catalyst is exposed to the laboratory atmosphere andcan readsorb vapors, carry these operations out as rapidly as possible.11.4 Place the penetrometer containing the sampl
33、e in theappropriate chamber of the porosimeter, following the manu-facturers instructions, and evacuate to a pressure of at least1.3 Pa (10 m Hg).11.5 Fill the penetrometer with mercury, in accordance withthe manufacturers instructions, by pressuring to some suitablylow pressure.NOTE 3The pressure r
34、equired to fill the penetrometer with mercury isD4284072also capable of filling sufficiently large pores of both the inter- andintra-particle classes. Thus, the filling process can fill some pores withmercury and the volume distribution of these pores cannot subsequentlybe determined. This fact shou
35、ld be recognized and, where possible, selecta filling pressure that will not intrude pores in the diameter range ofsubsequent interest.11.6 Place the filled penetrometer in the pressure vessel ofthe porosimeter and prepare the instrument for pressurizationand intrusion readings in accordance with th
36、e manufacturersinstructions.11.7 Raise the pressure, either continuously or step-wise,and record both the absolute pressure and the volume ofintruded mercury until the maximum pressure of interest isreached.NOTE 4When raising the pressure incrementally, minimize the pres-sure drop during the pause.
37、Certain modern instruments allow for anautomatic repressurization to the target pressure when the pressuredecreases. When samples with relatively narrow pore size distribution areanalyzed, the extent of depressurization and repressurization may affecttest method precision and the measured pore volum
38、e.NOTE 5When testing some materials, the time required to achieveintrusion equilibrium will not be the same at all pressures. Often, theequilibrium time is appreciably longer at pressures that cause an abruptand large increase in intruded volume. Failure to record the equilibriumintrusion will resul
39、t in some of the pore volume being incorrectly ascribedto smaller pore diameters. Assess the extent to which this may be aproblem by conducting two tests, each at a different pressuring rate, andcompare the results. Measure recorded intrusion values at, essentially,equilibrium.NOTE 6Use of Eq 1 requ
40、ires the absolute pressure, P. With someinstruments, it may not be possible to read the absolute pressure directly.In this case, record the gage pressure and calculate the absolute pressuressubsequently.NOTE 7If incremental pressure steps are used, the choice of pressureintervals at which data are t
41、o be recorded will be specified by thosedirecting the test or, left to the judgement of the operator. A minimum of10 to 15 data points will be required to define the pore volumedistribution. Frequently, 25 or more points are found to be helpful. Inselecting these pressure points, a rough idea of the
42、 expected distribution ishelpful, since the pressure intervals can be larger in regions where little orno intrusion occurs. The intervals should be smaller in regions where alarge volume of intrusion occurs abruptly.NOTE 8It is not necessary to continue the process up to the maximumpressuring capabi
43、lity of the instrument if all of the pores of interest in aparticular test have been intruded at a lesser pressure.11.8 Upon completion of the pressuring cycle, reduce thepressure and disassemble and clean the instrument in accor-dance with the manufacturers instructions.12. Blank Test for Correctio
44、ns12.1 An intrusion test on a nonporous sample may berequired to obtain values to use in correcting intrusion data forcompressibilities and temperature changes.12.2 Select a nonporous material for this test that hasapproximately the same compressibility and bulk volume asthe catalyst sample that is
45、to be tested.12.3 Test the nonporous sample in exactly the same manneras outlined in Section 11. Raise the pressure in the samemanner as used for the catalyst tests to ensure that temperaturechanges due to pressuring are the same.12.4 The results of this blank test are a series of measuredvolume cha
46、nges that can also be expected to occur, along withactual pore intrusion, during a test on a catalyst. They are usedto correct the intruded volumes as discussed in 13.3.2.12.5 The compressibilities of the various components in thesystem augment the measured intrusion values while thepressure-induced
47、 heating and consequent expansion of thesystem reduces the measured volumes. In a particular instru-ment, either one of these effects may be dominant. Hence, theresults of the blank test may be either an apparent intrusion(compressibility dominant) or an expulsion of mercury (heat-ing dominant).12.5
48、.1 If the blank results show apparent intrusion, they areto be subtracted from the values measured in the test on thecatalyst.12.5.2 If the blank results show a mercury expulsion, theyare to be added to the volumes measured on the catalyst.13. Calculations13.1 Express the intruding pressures as abso
49、lute pressuresprior to computing the corresponding pore diameters. If therecorded values are gage pressures, they must be converted toabsolute pressures in accordance with the instrument manufac-turers instructions. If the instrument reads directly in absolutepressure, omit this step.13.2 The absolute pressures are next converted to apparentintruded pore diameters with the equation in 4.1. This steprequires that the surface tension and contact angle be known.13.2.1 When double-distilled mercury is used, the value ofthe surface tension can generally be relied
