ASTM C1274-12(2020)

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:C1274 −12 (Reapproved 2020)
Standard Test Method for
Advanced Ceramic Specific Surface Area by Physical
Adsorption
This standard is issued under the fixed designation C1274; 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 convention, many instruments (as well as certificates of refer-
2 –1
ence materials) report surface area as m g , instead of using
1.1 Thistestmethodcoversthedeterminationofthesurface
2 –1
SI units (m kg ).
area of advanced ceramic materials (in a solid form) based on
1.4 This standard does not purport to address all of the
multilayer physisorption of gas in accordance with the method
safety concerns, if any, associated with its use. It is the
of Brunauer, Emmett, and Teller (BET) (1) and based on
responsibility of the user of this standard to establish appro-
IUPAC Recommendations (1984 and 1994) (2, 3). This test
priate safety, health, and environmental practices and deter-
method specifies general procedures that are applicable to
mine the applicability of regulatory limitations prior to use.
many commercial physical adsorption instruments. This test
1.5 This international standard was developed in accor-
method provides specific sample outgassing procedures for
dance with internationally recognized principles on standard-
selectedcommonceramicmaterials,including:amorphousand
ization established in the Decision on Principles for the
crystalline silicas, TiO , kaolin, silicon nitride, silicon carbide,
Development of International Standards, Guides and Recom-
zirconium oxide, etc. The multipoint BET (1) equation along
mendations issued by the World Trade Organization Technical
with the single-point approximation of the BET equation are
Barriers to Trade (TBT) Committee.
thebasisforallcalculations.Thistestmethodisappropriatefor
measuringsurfaceareasofadvancedceramicpowdersdownto
2. Referenced Documents
at least 0.05 m (if in addition to nitrogen, krypton at 77.35 K
is utilized as an adsorptive). 2.1 ASTM Standards:
D1993Test Method for Precipitated Silica-Surface Area by
1.2 This test method does not include all existing proce-
Multipoint BET Nitrogen Adsorption
dures appropriate for outgassing of advanced ceramic materi-
E177Practice for Use of the Terms Precision and Bias in
als. However, it provides a comprehensive summary of proce-
ASTM Test Methods
dures recommended in the literature for selected types of
2.2 ISO Standards:
ceramic materials. The investigator shall determine the appro-
ISO 9277Determination of Specific Surface Area of Solids
priateness of listed procedures.
by Gas Adsorption Using the BET Method
1.3 The values stated in SI units are to be regarded as
ISO 15901-2:2006Pore Size Distribution and Porosity of
standard. State all numerical values in terms of SI units unless
Solid Materials by Mercury Porosimetry and Gas
specific instrumentation software reports surface area using
Adsorption,Part2—AnalysisofMesoporesandMacropo-
alternate units. In this case, provide both reported and equiva-
res by Gas Adsorption
lentSIunitsinthefinalwrittenreport.Itiscommonlyaccepted
ISO 8213:1986Chemical Products for Industrial Use—
and customary (in physical adsorption and related fields) to
Sampling Techniques—Solid Chemical Products in the
report the (specific) surface area of solids as m /g and, as a
FormofParticlesVaryingfromPowderstoCoarseLumps
This test method is under the jurisdiction of ASTM Committee C28 on
Advanced Ceramics and is the direct responsibility of Subcommittee C28.03 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Physical Properties and Non-Destructive Evaluation. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved April 1, 2020. Published April 2020. Originally Standards volume information, refer to the standard’s Document Summary page on
approved in 1994. Last previous edition approved in 2012 as C1274–12. DOI: the ASTM website.
10.1520/C1274-12R20. Available from International Organization for Standardization (ISO), 1, ch. de
The boldface numbers in parenthesis refer to the list of references at the end of la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http://
this standard. www.iso.ch.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1274−12 (2020)
ISO 18757Fine Ceramics (Advanced Ceramics, Advanced 3.1.15 surface area, specific (SSA), n—areaperunitmassof
Technical Ceramics)—Determination of Specific Surface a granular or powdered or formed porous solid of all external
Area of Ceramic Powders by Gas Adsorption Using the and internal surfaces that are accessible to a penetrating gas or
BET Method liquid.
3. Terminology 4. Summary of Test Method
3.1 Definitions:
4.1 An appropriately sized (to provide at least the minimum
3.1.1 adsorbate, n—material that has been retained by the surface area required for reliable results, refer to requirements
process of adsorption. provided by the manufacturer of the instrument or apparatus
being used) aliquot of sample is outgassed under appropriate
3.1.2 adsorbent, n—any solid having the ability to concen-
conditions prior to analysis. For details on outgassing methods
trate significant quantities of other substances on its surface.
and examples of specific outgassing conditions recommended
3.1.3 adsorption, n—process in which molecules are con-
for selected ceramic materials, see Section 11.
centrated on a surface by chemical or physical forces, or both.
4.2 The adsorptive gas is admitted to a sample container
3.1.4 adsorption isotherm, n—relation between the quantity
held at a constant temperature. The amounts adsorbed are
of adsorbate and the equilibrium (relative) pressure of the
measured in equilibrium with the adsorptive gas pressure, p,
adsorptive, at constant temperature.
and plotted against the relative pressure, p/p (where p is the
0 0
3.1.4.1 Discussion—Typically, the amount adsorbed is pre-
saturation vapor pressure), to give an adsorption isotherm.
sented on an isotherm as volume in cm STP (standard
Adsorption isotherms may be obtained by volumetric (mano-
temperature and pressure, that is, 273.15 K and 101325.02 Pa)
metric) measurements or by the carrier gas flow measurements
normalized per mass of sample.
(flowvolumetricmethod)andgravimetrictechniques.Thistest
method employs volumetric and flow volumetric methods.
3.1.5 adsorptive, n—any substance available for adsorption.
4.3 (Multipoint BET Analyses Only)—The volume of gas
3.1.6 aliquot, n—a representative portion of a whole that
adsorbed, or desorbed, is determined for a minimum of four
divides the whole, leaving a remainder.
relative pressures within the linear BET transformation range
3.1.7 molecular cross-sectional area, n—molecular area of
of the physical adsorption, or desorption, isotherm character-
the adsorbate, that is, the area occupied by an adsorbate
istic of the advanced ceramic. The linear range is that which
molecule in the completed closed-packed monolayer.
results in a least-square correlation coefficient of 0.995 (pref-
3.1.8 monolayer capacity, n—amount of the adsorbate (ex-
erably 0.999) or greater for the linear relationship (see linear
pressed as number of moles, volume at STP, or weight) that
form of BET equation, in Annex A1). Typically, the linear
forms a closed-packed (complete) monomolecular layer over
range includes relative pressures between 0.05 and 0.30 (4, 5).
the surface of the adsorbent.
However,microporousmaterialsusuallyrequireuseofarange
of lower relative pressures (often a linear BET range can be
3.1.9 outgassing, n—evolution of gas from a material under
foundintherelativepressurerangefrom0.01to0.1 (5, 6)).For
a vacuum or inert gas flow at or above ambient temperature.
details, see Annex A2.
3.1.10 physical adsorption (van der Waals adsorption),
4.4 (Single-Point BET Analyses Only)—The volume of gas
n—the binding of an adsorbate to the surface of a solid by
adsorbed, or desorbed, is determined at the highest known
forceswhoseenergylevelsapproximatethoseofcondensation.
relativepressurewithinthelinearBETtransformationrangeof
3.1.11 relative pressure, n—ratiooftheequilibriumadsorp-
the physical adsorption, or desorption, isotherm. Typically, a
tion pressure, p, to the saturation vapor pressure, p .
relativepressureof0.30isused.However,itmaybenecessary
3.1.12 saturation vapor pressure, n—vapor pressure of the
to perform a multipoint analysis of the material first to
bulk liquefied adsorbate at the temperature of adsorption.
determine the optimum single-point relative pressure.
3.1.13 surface area, n—total surface area of the surface of a
4.5 The physical adsorption instrument or apparatus mea-
powderorsolid,includingbothexternalandaccessibleinternal
sures the total amount of gas adsorbed onto, or desorbed from,
surfaces (from voids, cracks, open porosity, and fissures).
the sample under analysis. The sample mass is then used to
3.1.13.1 Discussion—Thesurfaceareamaybecalculatedby
normalize the measured results. Therefore, it is important to
the BET equation (1) from gas adsorption data obtained under
use an analytical balance to determine the sample weight. The
specific conditions. It is useful to express this value as the
mass of dry and outgassed sample, recorded to the nearest
specific surface area (see 3.1.13), that is, surface area per unit
0.1mg, shall be used. Any error in the sample weight will be
2 –1
mass of sample (m g ).
propagated into the final BET surface area result.
3.1.14 surface area (BET), n—total surface area of a solid
4.6 Typical steps involved in the evaluation of the BET
calculated by the BET equation (1) from gas adsorption or
surface area (see Annex A1 for calculation details):
desorption data obtained under specific conditions.
4.6.1 Transformation of a physisorption isotherm into the
BET plot;
4.6.2 An assessment of the monolayer capacity (multipoint
Compilation of ASTM Standard Terminology, 8th ed, 1994. orsingle-pointmethod).(SeeEqA1.1-A1.6inAnnexA1.);and
C1274−12 (2020)
NOTE1—Monolayercapacitycanbeexpressedalternativelyintermsof
6. Interferences
STP volume (V ), weight (w ), or number of moles (n ) of adsorbate in
m m m
6.1 This test method can be used to determine the internal
a complete monolayer per1gof sample.
and external surface of a powder or solid only after these
4.6.3 Calculation of the specific surface area (SSA), a (see
s
surfaces have been cleaned of any physically adsorbed mol-
Eq A1.7 in Annex A1), which requires knowledge of the
ecules. Such adsorbed species, for example water or volatile
monolayer capacity as well as the effective molecular cross-
organiccompounds,affectphysicaladsorptionofthegasprobe
sectional area of the adsorbate. Recommended customary
molecules used to measure surface area. Therefore, it is
values for molecules of N at 77.35 K, Ar at 87.27 K, and Kr
necessary to remove these adsorbed contaminants prior to
at 77.35 K, are provided in Table 1.
surfaceareaanalysis.Generally,suchaprocedureisperformed
byevacuatingorpurgingthesamplewithinertgas.Outgassing
5. Significance and Use
canbeacceleratedbyusingelevatedtemperatures,providedno
5.1 Advanced ceramic powders and porous ceramic bodies
irreversible sample changes occur. Typical minimum vacuum
–1
oftenhaveaveryfineparticulatemorphologyandstructurethat
levels attained are 10 Pa. Commonly used purging gases are
are marked by high surface-to-volume (S-V) ratios. These
helium, nitrogen, or a mixture of the two. The outgassing
ceramics with high S-V ratios commonly exhibit enhanced
procedure is optimal or complete, or both when: (1) duplicate
chemical reactivity and lower sintering temperatures. Results
surface area analyses produce results within expected instru-
of many intermediate and final ceramic processing steps are
ment repeatability limits, (2) constant residual vapor pressure
controlled by, or related to, the specific surface area of the
is maintained upon isolation from the vacuum source, or (3)
advanced ceramic. The functionality of ceramic adsorbents,
purging gas composition is unaffected while passing over the
separation filters and membranes, catalysts, chromatographic
sample.
carriers, coatings, and pigments often depends on the amount
6.2 The outgassing procedures and temperatures shall not
and distribution of the porosity and its resulting effect on the
produce any changes in composition, phase, or surface mor-
specific surface area.
phology of the powder specimens. The outgas temperature
5.2 This test method determines the specific surface area of
limits are determined by the stability limits of the powder
advanced ceramic powders and porous bodies. Both suppliers
samples.
and users of advanced ceramics can use knowledge of the
surface area of these ceramics for material development and
7. Apparatus
comparison, product characterization, design data, quality
7.1 Manometric (Volumetric) Apparatus—See Test Method
control, and engineering/ production specifications.
D1993 and ISO 15901-2 for description of technology.
7.2 Automated and Dynamic Flow Instruments—
Commercial instruments are available from several manufac-
turers for the measurement of specific surface area by physical
TABLE 1 Cross-Sectional Areas of Selected Commonly Used
Adsorptives adsorption. Some are automated versions of the classical
vacuum apparatus. Others may use a gravimetric technique to
Recommended Value
Adsorptive Temperature, K
of Cross-Sectional Area, nm
determine the amount of adsorbed gas on the sample surface.
A
Nitrogen 77.35 0.162
Additionally, commercial instruments are available that mea-
B
Argon 77.35 0.138
sure physical adsorption based on the dynamic flow method.
Argon 87.27 0.142
C
Krypton 77.35 0.202
7.3 Sample Cells, that when attached to the adsorption
A
Very often the orientation of the adsorbed N molecules (having quadruple
apparatus will maintain isolation from the atmosphere equiva-
moment) can be affected by specific interactions with polar groups on the surface
lent to a specified (helium) leak rate determined by the
ofadsorbent(i.e.incaseofhighlypolarsurfaces,suchaswithhydroxylatedoxide
surface groups (7-9)). This can lead to a significant reduction in the effective
manufacturer of the instrument.
cross-sectionalarea.Ifthestandardvaluefor N molecule(0.162nm at77.35K)
isused,theBETsurfaceareaofhydroxylatedsilicasurfacescanbeoverestimated
7.4 Heating Mantle or Equivalent, capable of maintaining a
by20 %.Therefore,incaseofceramicswithsurfacesofhighpolarity,argon(which
temperature in range from 100 to 300 6 10 °C.
is a chemically inert monoatomic gas) adsorption at 87.3 K is an alternative
adsorptiverecommendedforsurfaceareadetermination,sincethecross-sectional
7.5 Analytical Balance, with 0.1 mg sensitivity.
areaofargon(0.142nm at87.27K)islesssensitivetodifferencesinstructureof
the adsorbent surface. 7.6 Oven (Optional), gravity convection, capable of main-
B
The use of argon at 77.35 K (which is approximately 6.5 K below the triple point
taining a temperature of 115 6 10 °C.
of bulk argon) is considered to be less reliable than nitrogen, because at 77.35 K
the structure of the argon monolayer may be highly dependent on the surface
chemistry of the adsorbent. The cross-sectional area for argon at 77.35 K is not
8. Reagents and Materials
well defined. The value of 0.138 nm , as given in the table, is based on the
8.1 Liquid Nitrogen.
assumptionofaclosed-packedliquidmonolayerandcanalsobeconsideredtobe
the customary value.
C
8.2 Ultra-High Purity Nitrogen, 99.99 mol %, with the sum
The use of krypton at 77.35 K allows to manometrically measure very low
uptakeswithacceptableaccuracy.However,similartoargonat77.35K,kryptonat
of O,Ar,CO , hydrocarbons (as CH ), and H O totaling less
2 2 4 2
77.35 K is significantly below the triple point temperature of bulk krypton
than 10 ppm, dry and oil-free, from a cylinder or other source
(approximately 38.5 K), and the structure of the krypton monolayer may be
of purified nitrogen.
strongly affected by the surface chemistry of the adsorbent. This will directly
influence the effective krypton cross-sectional area. The value given in the table
8.3 Ultra-High Purity Helium, 99.99 mol %, with the sum
can be considered to be a customary value.
of N,O,Ar,CO , hydrocarbons (as CH ), and H O totaling
2 2 2 4 2
C1274−12 (2020)
less than 10 ppm, dry and oil-free, from a cylinder or other several small aliquots and combining them improves the
source of purified helium, if needed for determination of void reliability of the sampling process. Rotating rifflers that satisfy
space above sample. these requirements are commercially available.
8.4 Ultra-High Purity Blended Nitrogen and Helium, dry 10.2 Obtain enough powder samples to run one or more
and oil-free, from a cylinder or other source of blended gases. analyses in accordance with the equipment sample size recom-
The actual composition of the blend shall be known. For use mendations.
with dynamic flow instruments only.
11. Sample Preparation Procedure
8.5 Liquid Argon.
11.1 Remove physically adsorbed impurities from the
8.6 Ultra-High Purity Argon, 99.99 mol %, with the sum of
sample surface prior to the determination of an adsorption
O,Ar,CO , hydrocarbons (as CH ), and H O totaling less
2 2 4 2
isotherm. This can be achieved at elevated temperatures under
than 10 ppm, dry and oil-free, from a cylinder or other source
vacuum or by inert gas flow. It is crucial to outgas the sample
of purified argon.
under conditions (that is, time and temperature) which provide
8.7 Ultra-High Purity Krypton, 99.99 mol %, with the sum a clean sample surface at the beginning of the analysis while
of O,Ar,CO , hydrocarbons (as CH ), and H O totaling less
avoidingirreversiblechangestothesurface(solidsampleshall
2 2 4 2
than 10 ppm, dry and oil-free, from a cylinder or other source notbealtered).Mostceramicmaterialscanbesafelyoutgassed
of purified argon.
at relatively high temperatures (200 to 300°C) in a few hours;
however, outgassing overnight at temperatures around 150°C
8.8 Comments on Proper Selection of Adsorbate:
is generally a safe way to achieve a clean sample surface and
8.8.1 Nitrogen at its boiling point (about 77.35 K) is the
is commonly practiced (specific outgassing conditions recom-
most commonly used adsorptive for customary ceramic mate-
2 mended for selected ceramic materials are summarized in
rials (customary cross-sectional area of 0.162 nm ). (See Table
Table 2). Outgassing is complete when a steady value of the
1.)
residual gas pressure, p (recommended 1 Pa or lower ) of its
out
8.8.2 In case of ceramic materials with very low specific
composition, or when a steady sample mass, m, is reached.
surface, the sensitivity of the instrument when using nitrogen
adsorption may be insufficient. Therefore, for the BET surface 11.2 If the ceramic material is wet (that is, when any
area analysis of ceramics with specific surface areas below moisture condensation is observed on the walls of the sample
2 –1
1m g ,itisrecommendedtousekryptonadsorptionatliquid cell during sample outgassing), the sample requires pretreat-
nitrogen temperature.Application of Kr at 77.35 K as adsorp- ment to remove excess moisture. Dry an aliquot of a ceramic
tive allows for volumetric measurement of very low uptakes sample at 90 to 110°C for 1 to 2 h. If the ceramic material is
with acceptable accuracy (as a consequence of the low p of known to be substantially free of moisture, or subsequent
about 2.63 torr (360.63 Pa)) and for assessing specific surface preparation steps are known to be adequate for moisture
areas down to at least 0.05 m . For krypton at 77.35 K, the removal, then this step may be omitted.
number of molecules trapped in the void volume of the sample
11.3 The following examples and conditions shall be care-
cell is significantly reduced (to 1/300th) compared to the
fully considered for any unknown ceramic material:
conditions of nitrogen adsorption at the same temperature.
11.3.1 In most cases, physisorbed water has to be removed
8.8.3 Theresultsofmeasurementswithdifferentadsorptives
fromtheadsorbentsurfacespriortotheadsorptionexperiment.
may deviate from each other because of different molecular
If the sample contains a large amount of water, either phy-
areas, different accessibilities to pores, different measuring
sisorbed on the surface, condensed in pores, or within its
temperatures, and so forth.
crystalstructure,aspecialheatingprogramisoftenneededthat
allowsforaslowremovalofmostofthepre-adsorbedwaterat
9. Hazards
temperatures below 100°C, accompanied by a stepwise in-
9.1 Precautions applying to the use of LN , LAr, com-
crease in temperature until the final outgassing temperature is
pressed gases, and specific properties of powder samples shall
reached. This is done to avoid potential structural damage of
be observed.
the sample due to surface tension effects and hydrothermal
10. Sampling, Test Specimens, and Test Units
TABLE 2 Specific Examples of Outgassing Conditions (Under
10.1 The goal of powder sampling is to collect a small
Vacuum) for Various Ceramic Materials
amountofpowderfromthebulkquantitysuchthatthissmaller
Outgassing Outgassing
Ceramic Material
fraction is representative of the characteristics of the entire Temperature T,°C Time t, Minimum, h
Silica 200 (or 150) 3 (or 12)
bulk. No mandatory instructions are given. However, it is
Quartz 200 3
advisable to perform statistical sampling in accordance with
Boehmite 105 1
ISO 8213:1986 since it is important that the aliquot being Silica/alumina 300 3
Alumina 300 3
analyzed represent the larger bulk sample from which it is
Silicon carbide 200 3
taken. Homogenize the bulk sample before any sampling takes
Silicon nitride 200 3
place.Bestresultsareobtainedwhenaflowingbulkmaterialis Kaolin (Kaolinite) 200 3
Titania 140 12
temporarily diverted into a collector for an appropriate time. It
Glass fibers 120 24
is better to sample the entire flow for a short time than to
Zirconium oxide 140 12
sample a portion of the flow for a longer time. Collecting
C1274−12 (2020)
NOTE 2—After outgassing, the sample container is cooled to the
alteration. For outgassing of extremely sensitive samples and
measuring temperature. It should be noted that, at low gas pressures, the
fine powders, so-called pressure-controlled heating under
temperature of the sample needs some time to equilibrate due to the
vacuum is recommended. This outgassing procedure consists
reduced thermal conduction of the cooling bath.
of heating steps achieved by controlling the temperature rise
11.4.3.5 After outgassing, the sample cell may be moved
basedonthegaspressureevolvedfromaporousmaterialunder
directly to the analyzer. Otherwise, remove the sample cell
vacuum.When,duringevacuationandheating,afixedpressure
from the heat source and continue evacuation until it is ready
limit (usually approximately 7 to 10 Pa) is overtaken due to
for analysis.
species/moisture evolved from the sample surface, the tem-
perature ramp is stopped (the temperature is kept constant
11.4.3.6 Go directly to 11.4.5 and continue the remaining
while evacuation is continued). When the pressure falls back
steps of the procedure.
below the limit, the temperature ramp is continued, etc., until
11.4.4 Flow Outgassing:
a desired dwell temperature is achieved.
11.4.4.1 Open the gas control valve and insert the delivery
11.3.2 Take particular care during outgassing of certain
tube into the sample cell, and allow purging with either helium
ceramic materials (such as green-bodies) that may contain
or nitrogen for a minimum of 1 min.
organicbindersorotheradditives(seealsoISO18757).Insuch
11.4.4.2 Place a heating mantle or other source of heat
cases, any decomposition during outgassing at el
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