1、Designation: E2864 13Standard Test Method forMeasurement of Airborne Metal and Metal OxideNanoparticle Surface Area Concentration in InhalationExposure Chambers using Krypton Gas Adsorption1This standard is issued under the fixed designation E2864; the number immediately following the designation in
2、dicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers determination of
3、 surface area ofairborne metal and metal oxide nanoparticles in inhalationexposure chambers for inhalation toxicology studies. Surfacearea may be measured by gas adsorption methods usingadsorbates such as nitrogen, krypton, and argon (Brunauer etal., 1938; Anderson, 1975; Gregg and Sing, 1982) (1, 2
4、, 3)2orby ion attachment and mobility-based methods (Ku andMaynard, 2005) (4). This test method is specific to themeasurement of surface area by gas adsorption by krypton gasadsorption. The test method permits the use of any moderncommercial krypton adsorption instruments but strictly definesthe sam
5、ple collection, outgassing, and analysis procedures formetal and metal oxide nanoparticles. Use of krypton is requireddue to the low overall surface area of particle-laden samplesand the need to accurately measure the background surfacearea of the filter used for sample collection. Instrument-report
6、ed values of surface area based on the multipointBrunauer, Emmett and Teller (BET) equation (Brunauer et al.,1938;Anderson, 1975; Gregg and Sing, 1982) (1, 2, 3) are usedto calculate surface area of airborne nanoparticles collected ona filter.1.2 The values stated in SI units are to be regarded asst
7、andard. No other units of measurement are included in thisstandard. State all numerical values in terms of SI units unlessspecific instrumentation software reports surface area usingalternate units.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its u
8、se. 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 prior to use.2. Referenced Documents2.1 ASTM Standards:3B922 Test Method for Metal Powder Specific Surface Areaby Physical Adsorpt
9、ionC1274 Test Method for Advanced Ceramic Specific SurfaceArea by Physical AdsorptionE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE2456 Terminology Relating to Nanotechnology2.2 ISO Standards:4ISO 9277 Determination of the Specific Surface Area ofSo
10、lids by Gas Adsorption using the BET MethodISO 18757 Fine Ceramics (Advanced Ceramics, AdvancedTechnical Ceramics)Determination of Specific surfaceArea of Ceramic Powders by Gas Adsorption using theBET Method3. Terminology3.1 DefinitionsFor additional definitions related tonanotechnology, see Termin
11、ology E2456.3.1.1 nanoparticles, nin nanotechnology, a sub-classification of ultrafine particle with lengths in two or threedimensions greater than 0.001 micrometre (1 nanometre) andsmaller than about 0.1 micrometre (100 nanometres) and whichmay or may not exhibit a size-related intensive property.E
12、24563.1.2 adsorbate, nmaterial that has been retained by theprocess of adsorption. B9223.1.3 adsorbent, nany solid having the ability to concen-trate or collect significant quantities of other substances on itssurface. B9223.1.4 adsorption, na process in which fluid molecules areconcentrated or coll
13、ected on a surface by chemical or physicalforces, or both. B9221This test method is under the jurisdiction of ASTM Committee E56 onNanotechnology and is the direct responsibility of Subcommittee E56.02 onPhysical and Chemical Characterization.Current edition approved Sept. 1, 2013. Published October
14、 2013. DOI: 10.1520/E2864-13.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information,
15、refer to the standards Document Summary page onthe ASTM website.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United St
16、ates13.1.5 BET-constant, nan indication of the magnitude ofthe adsorbent/adsorbate interactions in the first adsorbed layer.3.1.6 outgassing, nthe evolution of gas from a material ina vacuum or inert gas flow, at or above ambient temperature.B9223.1.7 physical adsorption (van der Waals adsorption),n
17、the binding of an adsorbate to the surface of a solid byforces whose energy levels approximate those of condensation.B9223.1.8 surface area, nthe total area of the surface of apowder or solid including both external and accessible internalsurfaces (from voids, cracks, open porosity, and fissures); t
18、hearea may be calculated by the BET equation from gas adsorp-tion data obtained under specific conditions; it is useful toexpress this value as the specific surface area, for example,surface area per unit mass of sample (m2/kg). B9223.1.9 surface area (BET), nthe total surface area of a solidcalcula
19、ted by the BET equation, from gas adsorption dataobtained under specific conditions.3.1.10 surface area, specific, nthe area, per unit mass of agranular or powdered or formed porous solid, of all externalplus internal surfaces that are accessible to a penetrating gas orliquid. B9224. Summary of Test
20、 Method4.1 An appropriate filter is pre-weighed to the nearest 1 10-8kg (0.01 mg), outgassed, and the background surface areameasured prior to nanoparticle collection in an inhalationexposure chamber. A sufficient amount of nanoparticles (toprovide at least the minimum surface area required for reli
21、ableresults for the instrument used) are collected on the filter, thefilter with particles is post-weighed, outgassed, and totalsurface area measured. The surface area concentration of theairborne nanoparticles in the exposure chamber is estimated bysubtracting the background filter surface area fro
22、m the totalsurface area of the filter with nanoparticles and normalized bythe volume of air sampled, with the final result expressed asm2/m3(LeBouf et al., 2011) (5).4.2 Multipoint BET AnalysesVolume of gas adsorbed at77 K (liquid nitrogen temperature) is determined as 10-6m3(cm3) corrected to stand
23、ard temperature and pressure for aminimum of five relative pressures within the linear BETtransformation range of the physical adsorption isothermcharacteristic of the filter and/or nanoparticle. The linear rangeis that which results in a least squares correlation coefficient of0.999 or greater for
24、the relationship between BET transforma-tion and relative pressure. Typically, the linear range includesrelative pressures between 0.05 and 0.30.4.3 It is important to use an analytical balance to determinethe sample mass. The physical adsorption instrument measuresthe total amount of gas adsorbed o
25、nto the sample underanalysis. The sample mass is then used to normalize themeasured adsorption results.Any error in the sample mass willaffect the final BET surface area.4.4 Calculations are based on the BET equation, as requiredby the instrument being used for the determination. Theinstrument press
26、ure tolerance (pressure range that must bemaintained within a sample cell to accept a valid data point) is6.6 Pa. In this standard, the cross-sectional area for the kryptonadsorbate is taken to be 2.02 10-19m2(ISO 9277); however,some instrument software may use a different default value.Assuch, the
27、cross-sectional area of the krypton adsorbate used incalculations should be reported with the BET surface arearesults.5. Significance and Use5.1 A tiered strategy for characterization of nanoparticleproperties is necessary to draw meaningful conclusions con-cerning dose-response relationships observ
28、ed during inhalationtoxicology experiments. This tiered strategy includes charac-terization of nanoparticles as produced (that is, measured as thebulk material sold by the supplier) and as administered (that is,measured at the point of delivery to a test subject) (Oberdorsteret al., 2005) (6).5.2 Te
29、st Methods B922 and C1274 and ISO Standards 9277and 18757 exist for determination of the as produced surfacearea of bulk metal and metal oxide powders. During thedelivery of metal and metal oxide nanoparticles in inhalationexposure chambers, the material properties may undergochange and therefore ha
30、ve properties that differ from thematerial as produced. This test method describes the determi-nation of the as administered surface area of airborne metaland metal oxide nanoparticles in inhalation exposure chambersfor inhalation toxicology studies.6. Interferences6.1 This test method can be used t
31、o determine the internaland external surface of nanoparticles only after the surfaceshave been cleaned of any physically adsorbed molecules (forexample, water or volatile organic compounds) which preventphysical adsorption of the gas probe molecules used to measuresurface area. Therefore, it is nece
32、ssary to remove theseadsorbed contaminants prior to surface area analysis(Anderson, 1975; Gregg and Sing, 1982) (2, 3). Outgassing isperformed by evacuating the sample (typically at 10-1Pa) andcan be accelerated by using elevated temperatures, provided noirreversible sample changes occur. Outgassing
33、 is completewhen duplicate surface area analyses produce results withinexpected instrument repeatability limits.7. Apparatus7.1 Commercial instruments employing low temperature(77 K) krypton adsorption are available from several manufac-turers for the measurement of specific surface area by physical
34、adsorption. Use of krypton is required due to the low overallsurface area of particle-laden samples and the need to accu-rately measure the background surface area of the filter usedfor sample collection. Some instruments are automated ver-sions of the classical vacuum apparatus. Others make use ofb
35、alanced adsorption technology. Additionally, commercial in-struments are available which measure physical adsorptionbased on the dynamic flow method.7.2 Analytical Balance, having a sensitivity of110-8kg.E2864 1327.3 Degassing Equipment, capable of maintaining a sampledegas temperature of 120 6 10C.
36、7.4 Sampling pump, calibrated and capable of maintainingconstant flow.7.5 Pellet style glass sample cell, minimum internal diam-eter 9 mm.7.6 Static charge neutralizer, properly operating.NOTE 1Use caution with static charge neutralizers as static dischargecould be an ignition source for certain typ
37、es of filters that containflammable constituents (for example, nitroscellulose).8. Reagents and Materials8.1 Liquid Nitrogen.8.2 Krypton, 99.999 mole percent, with the sum of N2,O2,Ar, CO2, hydrocarbons (as CH4), and H2O totaling less than 10ppm, dry and oil-free, cylinder, or other source of purifi
38、edkrypton.8.3 Helium, 99.99 mole percent, with the sum of N2,O2,Ar,CO2, hydrocarbons (as CH4), and H2O totaling less than 10ppm, dry and oil-free, cylinder, or other source of purifiedhelium, if needed for determination of void space abovesample.8.4 Track-etched polycarbonate (TEPC) filters, 0.037 m
39、 (37mm) diameter,410-7m (0.4 m) pore size.NOTE 2Other filter types and sizes of filters may be used provided thattheir background weight, surface area, pressure drop, collection efficiency,and physical integrity have been characterized (LeBouf et al., 2011) (5).NOTE 3The 0.037 m diameter,410-7m pore
40、 size TEPC filter willcollect 20 nm to 100 nm particles with 97 % efficiency at a flow rate of0.002 m3/min (LeBouf et al., 2011; Liu et al., 1983) (5, 7).8.5 Plastic filter cassette sampler, 0.037 m diameter.9. Hazards9.1 Precautions applying to the use of liquid nitrogen andcompressed gases and han
41、dling of powdered nanomaterialsshould be observed.10. Procedure10.1 Calibration and Standardization:10.1.1 Follow manufacturers instructions for instrumentcalibration. Verify proper operational performance of theinstrument using an acceptable reference material. Examples ofavailable reference materi
42、als are provided in Table 1. Instru-ment manufacturers may also produce reference materials.10.2 Background Filter Surface Area:NOTE 4As an alternative to determining the background surface areafor each TEPC filter sample, an average background surface area can bedetermined from a representative sam
43、ple of filters from each lot. Thebetween-lot filter surface area variability for TEPC filters (0.037 mdiameter,410-7m pore size) accounted for 65 % of the total variabilitywhereas the within lot-filter variability accounted for 35 % of the totalvariability in one laboratory. The within lot filter re
44、peatability standarddeviation has been determined to be 0.03 (pooled relative standarddeviation) in that same laboratory.10.2.1 The user must verify the background surface area forthe particular type and lot of filter used.10.2.2 Handle a filter on the edges only using metaltweezers, pass through a
45、static charge neutralizer, and recordthe mass reading on a calibrated analytical balance capable ofreading to110-8kg.NOTE 5If desired, a control filter can be weighed and handled inexactly the same manner as the experimental filter to verify that the filterhandling steps do not result in gravimetric
46、 errors.10.2.3 Equilibrate the filter in the same temperature- andhumidity-controlled environment as the balance prior to weigh-ing.10.2.4 Wearing clean nitrile gloves roll the filter into acylinder having a diameter narrow enough to insert it into theglass sample cell.NOTE 6The filter can be wrappe
47、d around a clean glass rod to obtaincylindrical shape. If helpful, pass the filter through a static chargeneutralizer before inserting it into the glass sample cell.10.2.5 Attach the prepared sample cell to the outgassingport of the instrument. Secure heating mantle or oven aroundthe sample cell.10.
48、2.6 Outgas the sample for 18 to 24 hours at 393 K(120C) under light vacuum (1 to 2 Pa).10.2.7 Remove sample cell from heating mantle or oven andcool to ambient temperature. Remove and seal the sample cellaccording to the manufacturers instructions.10.2.8 Attach the appropriately prepared sample hold
49、er tosurface area analyzer instrument analysis port according tomanufacturers instructions. Include any required hardware.10.2.9 Use at least five adsorption points in the linear BETtransformation range of the isotherm, that is, relative pressure(p/p0) from 0.05 to 0.30). If necessary, input the blank filterweight determined in 10.2.2.10.2.10 Perform an analysis using the following instrumentsettings: pressure tolerance of 6.6 Pa and cross-sectional areaof a krypton adsorbate molecule of 2.02 10-19m2.10.2.11 When the analysis is completed and the
