ASTM D8325-20

Standard Guide for Evaluation of Nuclear Graphite Surface Area and Porosity by Gas Adsorption Measurements

SCOPE
1.1 The purpose of this Guide is to provide methodologic information specific to highly graphitized, low surface area materials used in the nuclear industry. It applies to nitrogen adsorption measurements at 77 K for the characterization of graphite pore structure, such as: (1) specific surface area; (2) cumulative volume of open pores (for pore sizes less than about 300 nm); and (3) distribution of pore volumes as a function of pore sizes (for pore sizes less than about 30 nm). These properties are related to graphite’s reactivity in oxidative environments, graphite’s ability to retain fission products, and gas transport through graphite’s pore system.  
1.2 Characterization of surface area (also known as the Brunauer-Emmett-Teller “BET” method) and porosity in nuclear graphite by gas adsorption is challenged by nuclear graphite’s low specific surface area, weak adsorption interactions, and energetic and structural heterogeneity of surface sites in gas-accessible pores. This guide provides recommendations and practical information related to the nitrogen adsorption method, including guidance on specimen preparation, selection of experimental conditions, data processing, and interpretation of results.  
1.3 Other porosity characterization methods used for nuclear graphite, such as krypton adsorption at 77 K, argon adsorption at either 77 K or 87 K, helium pycnometry (Test Method B923), and mercury intrusion porosimetry, are not in the scope of this guide.  
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-May-2020
• ICS: 27.120.30 - Fissile materials and nuclear fuel technology
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.F0 - Manufactured Carbon and Graphite Products

Relations

• Refers: ASTM B923-23 - Standard Test Method for Metal Powder Skeletal Density by Helium or Nitrogen Pycnometry
• Effective Date: 15-Nov-2023
• Refers: ASTM C1274-12(2020) - Standard Test Method for Advanced Ceramic Specific Surface Area by Physical Adsorption
• Effective Date: 01-Apr-2020
• Refers: ASTM D6556-19 - Standard Test Method for Carbon Black—Total and External Surface Area by Nitrogen Adsorption
• Effective Date: 01-Jan-2019
• Refers: ASTM D6556-17 - Standard Test Method for Carbon Black—Total and External Surface Area by Nitrogen Adsorption
• Effective Date: 01-Oct-2017
• Refers: ASTM D4641-17 - Standard Practice for Calculation of Pore Size Distributions of Catalysts and Catalyst Carriers from Nitrogen Desorption Isotherms
• Effective Date: 01-Feb-2017
• Refers: ASTM B923-16 - Standard Test Method for Metal Powder Skeletal Density by Helium or Nitrogen Pycnometry
• Effective Date: 01-Oct-2016
• Refers: ASTM D6556-14 - Standard Test Method for Carbon Black—Total and External Surface Area by Nitrogen Adsorption
• Effective Date: 01-Jun-2014
• Refers: ASTM C1274-12 - Standard Test Method for Advanced Ceramic Specific Surface Area by Physical Adsorption
• Effective Date: 01-Aug-2012
• Refers: ASTM D6761-07(2012) - Standard Test Method for Determination of the Total Pore Volume of Catalysts and Catalyst Carriers
• Effective Date: 01-May-2012
• Refers: ASTM C1274-10 - Standard Test Method for Advanced Ceramic Specific Surface Area by Physical Adsorption
• Effective Date: 01-Dec-2010
• Refers: ASTM D6556-10 - Standard Test Method for Carbon Black-Total and External Surface Area by Nitrogen Adsorption
• Effective Date: 01-Aug-2010
• Refers: ASTM B923-10 - Standard Test Method for Metal Powder Skeletal Density by Helium or Nitrogen Pycnometry
• Effective Date: 01-May-2010
• Refers: ASTM D6556-09 - Standard Test Method for Carbon Black-Total and External Surface Area by Nitrogen Adsorption
• Effective Date: 15-Feb-2009
• Refers: ASTM B923-02(2008) - Standard Test Method for Metal Powder Skeletal Density by Helium or Nitrogen Pycnometry
• Effective Date: 01-Apr-2008
• Refers: ASTM D4222-03(2008) - Standard Test Method for Determination of Nitrogen Adsorption and Desorption Isotherms of Catalysts and Catalyst Carriers by Static Volumetric Measurements
• Effective Date: 01-Apr-2008

Overview

ASTM D8325-20, published by ASTM International, is titled Standard Guide for Evaluation of Nuclear Graphite Surface Area and Porosity by Gas Adsorption Measurements. This guide provides methodology for characterizing the surface area and pore structure of highly graphitized, low surface area materials used in the nuclear industry, specifically through nitrogen adsorption measurements at 77 K. The standard is applicable to the measurement of specific surface area, total pore volume (for pore sizes under approximately 300 nm), and pore volume distribution (for pores under 30 nm). These properties are essential for assessing nuclear graphite’s reactivity, its capacity to retain fission products, and the efficiency of gas transport through its pore network. ASTM D8325-20 delivers practical recommendations on specimen preparation, experimental setup, data analysis, and interpretation, tailored to common challenges with nuclear graphite such as low surface area and heterogeneity.

Key Topics

• Surface Area Measurement (BET Method):

  • Use of the Brunauer-Emmett-Teller (BET) theory to determine mass-normalized surface area
  • Adaptation of data collection and processing due to the unique structure of nuclear graphite
  • Guidance on selecting an appropriate measurement range and ensuring accurate results

• Porosity Analysis:

  • Quantification of total open pore volume accessible to nitrogen gas at 77 K
  • Detailed assessment of pore size distributions for pores up to approximately 30 nm
  • Consideration of factors such as dead volume and the impact of sample size

• Sample Preparation and Measurement Procedures:

  • Recommendations for specimen outgassing to remove contaminants
  • Best practices for choosing sample size and equilibration time to enhance measurement consistency
  • Use of commercial volumetric adsorption analyzers with proper calibration and software

• Data Interpretation Guidelines:

  • Linearization criteria for the BET equation
  • Methods for reporting result details including BET range, sample mass, and correlation coefficients
  • Discussion of limitations and recommended alternative analysis methods when needed

Applications

ASTM D8325-20 is highly relevant to the nuclear energy sector and research facilities focused on nuclear graphite materials. Practical applications include:

• Nuclear Reactor Design and Safety:
  The standard supports quality control and reliability for graphite components by characterizing surface properties that influence oxidation behavior and fission product retention.

• Material Development and Lifespan Assessment:
  Researchers and manufacturers can use this guide to evaluate the microstructure of graphite before and after irradiation or environmental exposure, supporting both innovation and post-service analysis.

• Gas Transport and Containment Studies:
  Gas adsorption data is essential for understanding how gases move through graphite’s pore network, directly impacting operational safety and performance.

• Quality Assurance in Manufacturing:
  The standard provides repeatable protocols for manufacturers seeking to validate the consistency and specification compliance of graphite products.

Related Standards

For comprehensive evaluation of surface area and porosity, consider these related documents:

• ASTM C1274: Test Method for Advanced Ceramic Specific Surface Area by Physical Adsorption
• ASTM D3663: Test Method for Surface Area of Catalysts and Catalyst Carriers
• ASTM D6556: Test Method for Carbon Black-Total and External Surface Area by Nitrogen Adsorption
• ASTM D6761: Test Method for Determination of the Total Pore Volume of Catalysts and Catalyst Carriers
• ISO 9227: Determination of the specific surface area of solids by gas adsorption-BET method
• ASTM D4641: Practice for Calculation of Pore Size Distributions from Nitrogen Desorption Isotherms
• ASTM B923: Test Method for Metal Powder Skeletal Density by Helium or Nitrogen Pycnometry

Note: ASTM D8325-20 focuses exclusively on nitrogen adsorption at 77 K and does not cover alternative porosity characterization methods such as mercury intrusion or krypton/argon adsorption.

By following ASTM D8325-20, professionals in the nuclear and materials science sectors ensure reliable, standardized characterization of graphite’s surface area and porosity, supporting both safety and innovation.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D8325 − 20
Standard Guide for
Evaluation of Nuclear Graphite Surface Area and Porosity
by Gas Adsorption Measurements
This standard is issued under the fixed designation D8325; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.6 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.1 The purpose of this Guide is to provide methodologic
ization established in the Decision on Principles for the
information specific to highly graphitized, low surface area
Development of International Standards, Guides and Recom-
materials used in the nuclear industry. It applies to nitrogen
mendations issued by the World Trade Organization Technical
adsorption measurements at 77K for the characterization of
Barriers to Trade (TBT) Committee.
graphite pore structure, such as: (1) specific surface area; (2)
cumulative volume of open pores (for pore sizes less than
2. Referenced Documents
about 300nm); and (3) distribution of pore volumes as a
2.1 ASTM Standards:
function of pore sizes (for pore sizes less than about 30nm).
C1274Test Method forAdvanced Ceramic Specific Surface
Thesepropertiesarerelatedtographite’sreactivityinoxidative
Area by Physical Adsorption
environments, graphite’s ability to retain fission products, and
D3663Test Method for Surface Area of Catalysts and
gas transport through graphite’s pore system.
Catalyst Carriers
1.2 Characterization of surface area (also known as the
D4641Practice for Calculation of Pore Size Distributions of
Brunauer-Emmett-Teller “BET” method) and porosity in
Catalysts and Catalyst Carriers from Nitrogen Desorption
nuclear graphite by gas adsorption is challenged by nuclear
Isotherms
graphite’s low specific surface area, weak adsorption
D4222Test Method for Determination of Nitrogen Adsorp-
interactions, and energetic and structural heterogeneity of
tion and Desorption Isotherms of Catalysts and Catalyst
surface sites in gas-accessible pores. This guide provides
Carriers by Static Volumetric Measurements
recommendations and practical information related to the
D6556Test Method for Carbon Black—Total and External
nitrogen adsorption method, including guidance on specimen
Surface Area by Nitrogen Adsorption
preparation, selection of experimental conditions, data
D6761Test Method for Determination of the Total Pore
processing, and interpretation of results.
Volume of Catalysts and Catalyst Carriers
B923Test Method for Metal Powder Skeletal Density by
1.3 Other porosity characterization methods used for
Helium or Nitrogen Pycnometry
nuclear graphite, such as krypton adsorption at 77K, argon
2.2 ISO Standards:
adsorption at either 77K or 87K, helium pycnometry (Test
ISO9227Determinationofthespecificsurfaceareaofsolids
Method B923), and mercury intrusion porosimetry, are not in
by gas adsorption–BET method (Second edition)
the scope of this guide.
1.4 The values stated in SI units are to be regarded as
3. Terminology
standard. No other units of measurement are included in this
3.1 Definitions of Terms Specific to This Standard:
standard.
3.1.1 adsorbate, n—the material retained by adsorption at
1.5 This standard does not purport to address all of the
the interface between a solid and a gas or liquid.
safety concerns, if any, associated with its use. It is the
3.1.2 adsorbent, n—a solid material able to concentrate
responsibility of the user of this standard to establish appro-
measurable quantities of other substances on its accessible
priate safety, health, and environmental practices and deter-
surface, either external or in pores.
mine the applicability of regulatory limitations prior to use.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
This guide is under the jurisdiction of ASTM Committee D02 on Petroleum Standards volume information, refer to the standard’s Document Summary page on
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom- the ASTM website.
mittee D02.F0 on Manufactured Carbon and Graphite Products. Available from International Organization for Standardization (ISO), ISO
Current edition approved June 1, 2020. Published July 2020. DOI: 10.1520/ Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
D8325-20. Geneva, Switzerland, http://www.iso.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8325 − 20
3.1.3 adsorption, n—the process by which molecules are 3.1.11 micropores, n—according to IUPAC nomenclature,
concentrated on a solid surface by physical or chemical forces, pores with characteristic size (width for slit-shaped pores in
or both.
graphite) less than 2nm. Micropores are not usually present in
nuclear graphite.
3.1.4 adsorption isotherm, n—a collection of numerical
values showing the relationship between mass-normalized 3.1.12 molecular cross-sectional area—the area occupied
adsorbedamountsandthecorrespondingequilibriumpressures
by one single adsorbed molecule at the calculated completion
(or relative pressures) of the adsorptive at constant tempera- of the first monolayer uptake.
ture. It is the primary experimental result of adsorption
3.1.13 monolayer capacity (V ), n—the calculated amount
m
measurements and can be provided either in tabular form or
of adsorbate, expressed as the number of moles, weight, or
graphical representation. Adsorption and desorption isotherms
volumeatstandardtemperatureandpressure(STP),thatwould
are collected sequentially by gradually increasing and
be needed to form a monomolecular adsorbed layer extending
decreasing, respectively, the target pressures at which data
over the entire gas-accessible surface of the adsorbent.
points are collected.
3.1.14 nitrogen surface area (NSA), n—another name for
3.1.5 adsorptive, n—any substance available for adsorption.
SSA values measured using nitrogen as the adsorptive gas.
3.1.6 BET surface area (S )—the common name for SSA
BET
3.1.15 relative pressure (P/P )—the ratio between equilib-
values calculated using the Brunauer–Emmett– Teller (BET)
rium pressure (P) and saturation vapor pressure (P)ofthe
equation.
adsorptiveattheambientpressureandcoldbathtemperatureof
3.1.7 dead volume, n—the void volume around the adsor-
the measurement.
bent in the measurement cell and in the connecting tubes. The
3.1.16 saturation vapor pressure—vapor pressure (P)of
precision of dead space calibration is limited by the equip-
bulk adsorptive liquefied at the conditions of the measure-
ment’s performance and does not depend on the sample’s
ments.Itsvaluedependsonthelocalatmosphericpressureand
surface area. Errors in calculation of the dead space volume
the temperature of the cold bath used for temperature control.
affect the accuracy of gas adsorption results, especially for
samples with low surface area.
3.1.17 specific surface area (SSA), n—the total mass-
normalized area of a solid, including both external and acces-
3.1.8 distribution of pore volumes as a function of pore sizes
sibleinternalsurfaces(frompores,cracks,fissures,voids,etc.).
(or pore size distribution, PSD), n—a collection of numerical
values of mass-normalized pore volumes accessible to gas and
3.1.18 specific total volume of open pores (total pore
their corresponding pore sizes. It is calculated from adsorption
volume), n—the total mass-normalized volume of gas-
isotherms through model-dependent algorithms and can be
accessible pores in porous graphite. It is calculated from the
provided either in tabular form or graphical representation.
maximum amount of adsorbate condensed in open pores just
below the saturation pressure at measurement conditions. Pore
3.1.9 macropores, n—according to IUPAC nomenclature,
openings larger than about 300nm are generally too large for
pores with characteristic size larger than 50nm. In nuclear
nitrogen condensation to occur with enough measurable reso-
graphite, the class of macropores includes large pores and
lution at 77K.
cracks, gas evolution pores, fissures, etc. Gas adsorption
methods are limited to pores less than about 300nm, where
3.1.19 volume adsorbed (V ), n—the amount adsorbed,
a
condensation of nitrogen at 77K leads to measurable pore
calculated at standard temperature and pressure (STP), at each
filling. The volume of mesopores larger than about 300nm
equilibrium relative pressure (P/P ) value during adsorption or
cannot be measured with adequate precision by gas adsorption
desorption.
but can still be analyzed by mercury intrusion porosimetry.
4. Summary of Guide
3.1.10 mesopores, n—according to IUPAC nomenclature,
pores with characteristic size (width for slit-shaped pores in
4.1 In volumetric (manometric) adsorption methods a pre-
graphite, diameter for cylindrical pores) between 2nm and
viously outgassed specimen weighed with 0.1mg precision is
50nm.Innucleargraphite,theclassofmesoporesincludesthe
introduced in the measurement cell and evacuated. As part of
smallest cracks, thermal shrinkage pores, and Mrozowski
the initial routine of commercial instruments, the dead volume
cracks.
is measured by helium expansion.
4.2 After immersion of the specimen in a cold temperature
bath and evacuation, a known amount of the adsorptive gas is
Brunauer, S., Emmett, P. H.,Teller, E., “Adsorption of gases in multimolecular
introduced in the measurement cell. As adsorption proceeds,
layers,” Journal of the American Chemical Society, Vol 60, 1938, pp. 309–319.
the pressure in the cell drops until a constant (equilibrium)
Do, D. D., Do, H. D., Nicholson, D., “A computer appraisal of BET theory,
BET surface area and the calculation of surface excess for gas adsorption on a
pressure is achieved. The amount adsorbed is calculated from
graphite surface,” Chemical Engineering Science, Vol 65, 2010, pp. 3331–3340.
the difference between the amount of gas introduced and the
Thommes, M., Kaneko, K., Neimark, A. V., Olivier, J. P., Rodriguez-Reinoso,
amount remaining in the dead space volume.
F., Rouquerol, J., Sing, K. S. W., “Physisorption of gases, with special reference to
theevaluationofsurfaceareaandporesizedistribution(IUPACTechnicalReport),”
4.3 All pressure readings should be made at equilibrium
Pure and Applied Chemistry,Vol87,2015,pp.1051–1069;DOI10.1515/pac-2014-
1117. conditions and constant temperature.
D8325 − 20
4.4 The amounts adsorbed must be normalized by the mass PAC)classification. TypeIIisothermscharacterizeadsorbents
of the adsorbent in its outgassed condition. Any error in the which allow continuous monolayer - multilayer transitions and
sample weight is propagated in the final BET surface area unrestricted development of multilayers.
results.
4.8 In the example shown in Fig. 1, the desorption curve
4.5 BET surface area measurements can use just a few data
does not overlap the adsorption curve. This effect (hysteresis)
points equally spaced between 0.05 < P/P < 0.30 (Test
0 is observed with most nuclear graphites and is ascribed to the
Methods C1274, D6556, D3663, and ISO 9227). However,
presence of large pores (mesopores) where condensation and
usingalimitednumberofdatapointsmayleadtoanerroneous
evaporation of the adsorbate occur at different pressures.
selection of the linear range of the BETequation, and hence to
4.9 Nuclear graphite is usually free of micropores (width
inaccurate SSA values for weakly adsorbing nuclear graphite
<2nm), which would cause a strong initial rise of isotherms at
materials. For accurate SSA results it is always recommended
very low pressures (P/P < 0.001). High resolution adsorption
to collect a larger number of data points over a broader P/P
isotherms on well outgassed nuclear graphites may show an
range. See practical and methodological considerations in
initial isotherm rise starting from very low pressures. This
Section 7.
feature is attributed to strong 2D adsorption on atomically
4.6 If full adsorption (and desorption) isotherms over the
orderedbasalplanesofgraphiticcrystallitesduetotheirhigher
entire range of relative pressures (0 < P/P < 1) are available
adsorption energy and accessibility. A subtle change of slope
(Test Method D4222), they can be used to obtain more
nearP/P =0.01indicatesastructuralreorganizationinthefirst
information on graphite porosity (total pore volume and pore
monolayeronbasalplanesites(seeinsetinFig.1).Adsorption
size distribution). See discussion in Section 8.
continues at higher pressures on the remaining, energetically
4.7 Fig. 1 shows a representative nitrogen adsorption- non-uniform and atomically disordered graphite prismatic
desorption isotherm for a medium grained nuclear graphite. surfaces, and on other types of defective sites. On these
Based on shape, the isotherm belongs to type II according to surfaces statistical multilayer growth may commence long
the International Union of Pure and Applied Chemistry (IU- before the first monolayer is complete. This complicates the
FIG. 1 Nitrogen Adsorption – Desorption Isotherm at 77 K on a Typical Medium Grained Nuclear Graphite
D8325 − 20
correct determination of (P/P ) , the relative pressure corre- adsorbing surface in the cell, but not less than 20mg. With
0 m
sponding to the completion of a monolayer. rigidshapesoflowsurfaceareanucleargraphite,thiscondition
may be difficult to meet because of the limited capacity of
4.10 Adsorption through statistical growth of multilayers
typical sample cells. Breaking graphite specimens into smaller
continuesasdescribedbytheBETtheoryuptoabout0.35P/P
piecesmayhelpinfittingmorelowsurfaceareamaterialinthe
or higher (a deviation from the classical BETrange). Capillary
sample cell. However, crushing graphite into fine powder or
condensation in mesopores (2nm to 50nm in width), if
small chunks should be avoided because mechanical actions
present,maycausedifferencesbetweenadsorptionanddesorp-
maydistortthestructureandcreatelargerinternalsurfacesthan
tion branches, as noted before (see Fig. 1). Finally, a sudden
those present in the original graphite.
rise in the isotherm curve as P/P approaches 1 is generally
5.1.4 Outgas graphite prior to its analysis to remove from it
associated with the condensation of nitrogen in macropores
any moisture and pre-adsorbed organic vapors. Either inert gas
(large cracks, voids, fissures, etc., with sizes > 50nm).
flow or vacuum outgassing at 300°C to 350°C can be used.A
4.11 Apparatus:
lower temperature must be used if graphite properties may
4.11.1 Automatedvolumetricadsorptionanalyzersavailable
change at the recommended degassing temperature (for
commercially are preferred, as they ensure repeatability and
example, for graphite irradiated at a lower temperature).
reproducibility of measurements and unassisted operation over
Outgassed samples should be able to reach and hold a pressure
long periods of time. They also come equipped with data
of about 1.4Pa (10µmHg). Some commercial adsorption
analysis software.
analyzersoffertheoptionofdefiningacceptanceconditionsfor
4.11.2 The user should check the operation manual and
the outgassing step, based on rates of rise in background
other specific instructions for the specific gas adsorption
pressure.
analyzertobeusedandshouldunderstandandbecomefamiliar
5.2 Reagents:
with its recommended sample preparation and data collection
5.2.1 Ultra-highpurity,oil-freeadsorbategases(N,Heand
procedures.
optionally Kr or Ar) with less than 10ppmv total sum of
4.11.3 Each commercial adsorption analyzer may come
impurities supplied from a cylinder.
with its own series of options regarding the size of the coolant
5.2.2 Liquid nitrogen bath, preferably fresh. Impurities in
Dewarvessel,measurementmethodstoassesssaturationvapor
liquid nitrogen (water, dissolved oxygen) raise the bath tem-
pressure (P ), sample outgassing protocols, and data collection
perature and can thus lead to slow rises in saturation pressure
conditions.Followthemanufacturers’recommendationsunless
Po which may affect the isotherm data unless continuous P
indicated otherwise below
measurements are made during the analyses.
4.11.4 The time needed for collecting only multiple data
pointsforBETsurfaceareameasurementsmaybeabout2hto
6. Measurement Procedure
3h.
6.1 Theoperatorshouldselectthetableofrelativepressures
4.11.5 The time needed for collecting full adsorption-
(P/P ) according to the particular purpose of the intended
desorption isotherms may be 24h or longer. Using a large size
analysis. The following recommendations are provided as a
Dewar bath (2L or larger) is recommended in this case.
guidance but are not mandatory.
4.11.6 Among the various options for P measurement,
6.1.1 Although a minimum of five P/P points might be
continuous measurement (at each new relative pressure condi-
enough for BET surface area measurements of most materials,
tion) is the best practice. Other options, such as single P per
for accurate surface characterization of nuclear graphite it is
analysis, daily P measurements, or user entered P values
0 0
recommended to collect more data points. The linearization
should be avoided unless there is a distinct need for using
range of the BET equation is often found to be 0.05 < P/P <
them.
0.30, but practice has shown that this range often needs to be
extended up to 0.35 (or even beyond) for some weakly
5. Practical Recommendations on Procedure
adsorbing materials, such as nuclear graphite. See practical
5.1 Sample Preparation:
recommendations for the consistent selection of P/P linear-
5.1.1 The weight of the dry sample, free of adsorbed
ization range in 7.1.9.
contaminants,mustbeknownwitha0.1mgprecision.Theuse
...