1、Designation: E 128 99 (Reapproved 2005)Standard Test Method forMaximum Pore Diameter and Permeability of Rigid PorousFilters for Laboratory Use1This standard is issued under the fixed designation E 128; the number immediately following the designation indicates the year oforiginal adoption or, in th
2、e case of revision, 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 maximumpore diameter and permeability of
3、 rigid porous filters used inthe laboratory for filtration or diffusion. They are applicable tofilters made of sintered glass, ceramic, metal, or plastic. Thistest method establishes a uniform designation for maximumpore diameter and also provides a means of detecting andmeasuring changes which occu
4、r through continued use.1.2 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 safety and health practices and determine the applica-bility of regulatory limitations prio
5、r to use.2. Referenced Documents2.1 ASTM Standards:2D 845 Specifications for Five-Degree Xylene3. Terminology3.1 Definitions:3.1.1 maximum pore diameterthe diameter in microme-tres of a capillary of circular cross section that is equivalent(with respect to characteristics related to surface-tension
6、ef-fects) to the largest pore in the filter under consideration.NOTE 1It is recognized that the maximum pore diameter as definedherein does not necessarily indicate the physical dimensions of the largestpore in the filter, and furthermore, that the pores are highly irregular inshape. Because of this
7、 irregularity in shape and other phenomenacharacteristic of filtration, a filter may be expected to retain all particleslarger than the maximum pore diameter as defined and determined by thistest method, and will generally retain particles which are much smallerthan the determined diameter.3.1.2 per
8、meabilitythe flow of air, in millimetres perminute per square centimetre of filter area per 1 cm of waterpressure differential.4. Summary of Test Method4.1 Maximum Pore Diameter, is determined by immersingthe filter in a suitable test liquid and applying air pressure untilthe first bubble of air pas
9、ses through the filter. The maximumpore diameter is calculated from the surface tension of the testliquid and the applied pressure.4.2 Permeability is determined by measuring the flow ofair through the filter when subjected to a pressure differential.5. Apparatus5.1 Because of the variety of shapes
10、of apparatus in whichporous filters are incorporated, the apparatus for this testmethod is not specified in detail.Apparatus that has been foundsatisfactory is illustrated in Fig. 1 and Fig. 2.6. Procedure6.1 Maximum Pore DiameterThoroughly wet the cleanfilter to be tested by soaking it in the presc
11、ribed test liquid (seeTable 1). Connect the filter to a controllable source of clean,dry compressed air, and a manometer (Fig. 1). Immerse thefilter just below the surface of the test liquid (Note 2) andgradually increase the air pressure at a rate of about 5 mm/minin the area of the test until the
12、first dynamic bubble passesthrough the filter and rises through the liquid. The appearanceof the first true dynamic bubble is readily recognized since it isfollowed by a succession of additional bubbles. Read thepressure from the manometer. If the test is to be repeated,thoroughly re-wet the filter
13、by soaking it in the test liquid,before proceeding with the retest. Calculate the maximum porediameter from the following equation (see Appendix X1 forderivation):D 5 30g/p (1)where:D = maximum pore diameter as defined in 3.1.1,g = surface tension of test liquid in dynes/cm at thetemperature of the
14、test, andp = pressure, mm Hg (Note 3).The uniformity of distribution of pores approaching themaximum pore size may be observed by gradually increasingthe air pressure and noting the uniformity with which streams1This test method is under the jurisdiction of ASTM Committee E41 onLaboratory Apparatus
15、and is the direct responsibility of Subcommittee E41 E41.05on Filtration Materials.Current edition approved May 1, 2005. Published October 2005. Originallyapproved in 1957. Last previous edition approved in 1999 as E 128 99.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcont
16、act 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 Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.of bubbles are distrib
17、uted over the surface of the filter. Cracks,fissures, and clogged areas are easily discerned by this opera-tion (Note 4).NOTE 2If there is significant head of liquid above the surface of thefilter, the back pressure so produced shall be deducted from the observedpressure, as follows:NOTE 1For tests
18、on filter-type crucibles, use a standard rubber crucible adapter. For test sticks and candles a rubber stopper with a rubber tubingattached is suitable. Clean dry compressed air shall be used.FIG. 1 Apparatus for Determining Maximum Pore Diameter of Rigid Porous FiltersNOTE 1For tests on filter-type
19、 crucibles, use a standard rubber crucible adapter. For test sticks and candles a rubber stopper with a rubber tubingattached is suitable. Clean dry compressed air shall be used.FIG. 2 Apparatus for Determination of PermeabilityTABLE 1 Test Liquids Suitable for Use with Various Types of FiltersFilte
20、r Suitable Test LiquidsAMaterial of ConstructionMax Pore Diameter,m LiquidApproximate SurfaceTension, dynes/cm at20CGlass 4 water 723 water 723 alcohol 22Stainless steel all alcohol 22xyleneC29Tetrafluoro-polyethylene all alcohol 22Trifluoromonochloropolyethylene all alcohol 22AThe specified liquids
21、 wet the respective filters completely. Other liquids which meet this criterion may be used. Values for surface tension in Table 1 are for generalguidance only and are approximate; surface tension of the liquid used should be determined.BEthyl alcohol 95 %.CFive- xylene conforming to Specifications
22、D 845.E 128 99 (2005)2Back pressure 5head of test liquid 3 density of test liquiddensity of mercury(2)ExampleIf the filter is immersed 3 cm below the surface of water asthe test liquid, a correction of 2.2 mm must be subtracted from thepressure observed on a mercury manometer.NOTE 3With the coarser
23、grades of filters it is more convenient tomeasure the pressure in millimetres of water, in which case the relation-ship becomes:D 5 30g313.53!/p (3)NOTE 4It is recommended that porous filters, where practical, bepermanently marked by the manufacturer with the lettersASTM, followedby a hyphenated num
24、ber which is the range, in micrometres, within whichthe maximum pore diameter falls. When the maximum pore diameter of anew filter is tested by this test method, it may be expected to be within themarked range; greater deviation may be found after use.6.2 PermeabilityConnect the dry filter with the
25、control-lable source of clean, dry compressed air, and a suitableflowmeter and manometer (Fig. 2). Adjust the pressure differ-ential to 10 cm water and observe the rate of flow of air throughthe filter in millilitres per minute. Calculate the permeability asfollows:Permeability 5 R/Ap (4)where:R = r
26、ate of flow of air, mL/min,A = effective area (Note 5) of the filter, andp = observed pressure of water, cm water (Note 6).NOTE 5In determining the effective area of the filter, care should betaken to exclude that portion of the filter which was rendered ineffectiveby sealing the filter to the appar
27、atus.NOTE 6The procedure for determination of permeability may beemployed to provide an approximate indication of the filtering rate ofindividual filters. However, immediately after being put into use thepermeability will change and may be expected to change further withrepeated use. Consideration h
28、as been given to marking filters with adesignation of permeability. However, the factors governing permeabilityin use make this undesirable at the present time.7. Precision7.1 The precision of this test method is being determinedand will be published when the study has been completed.8. Keywords8.1
29、diameter; filters; permeability; porousAPPENDIX(Nonmandatory Information)X1. DERIVATION OF THE PORE DIAMETER EQUATIONX1.1 In the classical determination of surface tension bycapillary rise, a capillary tube is immersed vertically in a liquidwhich wets the tube. The surface tension of the liquid crea
30、tesa force which draws the liquid upward into the capillary untilthis force is in equilibrium with the downward force caused bythe action of gravity on the column of liquid. This equilibriumcondition is expressed by the equation.2prg cos u5pr2hdg (X1.1)where:r = radius of the capillary,h = height of
31、 the column of liquid,g = surface tension of the liquid,d = density,u = angle of contact between the surface of the liquid andthe wall of the capillary, andg = acceleration due to gravity.When g is in dynes per centimetre, h and r will be incentimetres. When the liquid wets the capillary with a zero
32、contact angle as is specified by the method, u = 0 and cos u =1,so that Eq X1.1 may be restated as:r 5 2g/hdg (X1.2)orD 5 4g/hdg (X1.3)where D = diameter of the capillary in centimetres. Butunder the conditions of the method it is more convenient tomeasure the diameter in micrometres and the pressur
33、e, p,inmillimetres of mercury. Making these substitutions, the expres-sion becomes:D 5 30g/p (X1.4)ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that deter
34、mination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or
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36、 your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).E 128 99 (2005)3
