ASTM D3849-07(2011)
(Test Method)Standard Test Method for Carbon Black—Morphological Characterization of Carbon Black Using Electron Microscopy
Standard Test Method for Carbon Black—Morphological Characterization of Carbon Black Using Electron Microscopy
SIGNIFICANCE AND USE
Carbon black morphology significantly affects the transient and end-use properties of carbon black loaded polymer systems. A carbon black's particle size distribution is its single most important property, and it relates to degree of blackness and rubber reinforcement. For a given loading of carbon black, blackness and reinforcement increase with smaller particle size. Aggregate size and shape (structure) also affect a carbon black's end-use performance, as higher carbon black structure increases viscosity and improves dispersion. The stiffness (modulus) of elastomer systems becomes significantly higher with increasing structure. The preferred method for measuring these properties is transmission electron microscopy.
Carbon black aggregate dimensional and shape properties are dependent upon the nature of the system in which the sample is dispersed, as well as the mixing procedure.
SCOPE
1.1 This test method covers the morphological characterization of carbon black primary aggregates from transmission electron microscope images. These measurements are used to derive the mean particle and aggregate size of carbon black in the dry (as manufactured) state, from CAB chip dispersion or removed from a rubber compound.
1.2 The values stated in SI units are to be regarded as the standard. The values in parentheses are for information only.
1.3 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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Designation: D3849 − 07(Reapproved 2011)
Standard Test Method for
Carbon Black—Morphological Characterization of Carbon
Black Using Electron Microscopy
This standard is issued under the fixed designation D3849; 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 black particle size is a distributional property; therefore, the
term particle size implies the mean value from multiple
1.1 Thistestmethodcoversthemorphologicalcharacteriza-
measurements.
tion of carbon black primary aggregates from transmission
electron microscope images. These measurements are used to 3.1.1.3 glow discharge—a plasma of ionized gas that is
derive the mean particle and aggregate size of carbon black in formed in a high-voltage field at pressures of about 3 to 20 Pa
-3
the dry (as manufactured) state, from CAB chip dispersion or (25 to 150 × 10 torr). An alternating current (a-c) glow
discharge using air is effective in cleaning and oxidizing the
removed from a rubber compound.
surface of carbon substrates to improve the wetting character-
1.2 The values stated in SI units are to be regarded as the
istics of polar vehicles containing pigment dispersions.
standard. The values in parentheses are for information only.
3.1.1.4 substrate—athinfilmthatisusedtosupportelectron
1.3 This standard does not purport to address all of the
microscopespecimens.Evaporatedcarbonfilmsarecommonly
safety concerns, if any, associated with its use. It is the
used because of relatively good mechanical strength, stability,
responsibility of the user of this standard to establish appro-
and conductivity.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. 3.1.2 Aggregate Dimensional Properties from Image Analy-
sis:
2. Referenced Documents
3.1.2.1 area (A)—the two-dimensional projected area of the
carbon black aggregate image.
2.1 ASTM Standards:
D6556Test Method for Carbon Black—Total and External
3.1.2.2 perimeter (P)—the total boundary length of an
Surface Area by Nitrogen Adsorption
aggregate.
3.1.2.3 volume (V)—anestimateofthevolumeofthecarbon
3. Terminology
black aggregate using stereological principles.
3.1 Definitions:
3.1.3 Image Analysis:
3.1.1 General:
3.1.3.1 dilation—the converse of erosion. This process is
3.1.1.1 carbon black aggregate—a discrete, rigid colloidal
accomplished by changing any OFF pixel to ON if it has
entity that is the smallest dispersible unit; it is composed of
greater than a preset minimum of ON neighbors. This process
extensively coalesced particles. Carbon black aggregate size is
causes image features to grow in size, which fills in small
a distributional property; therefore, the term aggregate size
breaks in features, internal voids, or small indentations along
implies the mean value from multiple measurements.
the feature surface.
3.1.1.2 carbon black particle—a small spheroidally shaped,
3.1.3.2 erosion—the process by which image features are
paracrystalline,non-discretecomponentofanaggregate;itcan
reduced in size by selectively removing pixels from their
only be separated from the aggregate by fracturing. Carbon
periphery. It consists of examining each binary pixel and
changing it from ON to OFF if it has greater than a preset
minimum of neighbors that are OFF. It serves a number of
This test method is under the jurisdiction ofASTM Committee D24 on Carbon
useful functions, such as smoothing feature outlines and
Black and is the direct responsibility of Subcommittee D24.81 on Carbon Black
separating features touching each other.
Microscopy and Morphology.
Current edition approved Nov. 1, 2011. Published January 2012. Originally
3.1.3.3 feature—areas within a single continuous boundary
approved in 1980. Last previous edition approved in 2007 as D3849–07. DOI:
that have gray-level ranges that allow them to be distinguished
10.1520/D3849-07R11.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or from the background area outside the feature via thresholding.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3.1.3.4 thresholding—selecting a range of brightness such
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. that discrimination is possible between the feature and the
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3849 − 07 (2011)
background. The gray levels within carbon black images ability to introduce and remove the sample boat to the heated
become lower with decreasing particle size. zone without allowing oxygen intrusion.
5.9 Pyroprobe,capableofbeingheatedfrom150to1000°C
4. Significance and Use
in an inert environment.
4.1 Carbon black morphology significantly affects the tran-
5.10 Carbon Rods, approximately 3.1 mm in diameter.
sient and end-use properties of carbon black loaded polymer
5.11 Carbon Rod Sharpener.
systems.Acarbon black’s particle size distribution is its single
most important property, and it relates to degree of blackness
5.12 Glass Microscope Slides, 25 by 75-mm.
andrubberreinforcement.Foragivenloadingofcarbonblack, 3
5.13 Test Tubes,75by10-mm,4-cm capacity,0.5-mmwall
blackness and reinforcement increase with smaller particle
thickness, with corks.
size. Aggregate size and shape (structure) also affect a carbon
5.14 TransferPipets,disposablePasteur-type,225mmlong,
black’s end-use performance, as higher carbon black structure
1-mm inside diameter at tip.
increases viscosity and improves dispersion. The stiffness
(modulus) of elastomer systems becomes significantly higher
5.15 Rubber Bulbs, for pipets.
with increasing structure. The preferred method for measuring
5.16 Glass Vials, 40-cm capacity, with solvent-resistant
these properties is transmission electron microscopy.
tops.
4.2 Carbon black aggregate dimensional and shape proper-
5.17 Büchner Funnel, No. 3, 111-mm inside diameter.
ties are dependent upon the nature of the system in which the
5.18 Filter Paper, general purpose.
sample is dispersed, as well as the mixing procedure.
5.19 Carbon Coated Electron Microscope Specimen Grids,
5. Apparatus
3-mm diameter, 200 to 300 mesh. Commercially available or
can be prepared as described in Annex A1.
5.1 Electron Microscope, transmission-type, with a point-
to-point resolution of 1.0 nm or better. Operating voltages
5.20 Wire Screening, with openings approximately 1 mm .
should be high enough to provide the desired resolution and
5.21 Tweezers, fine-tipped.
low enough to produce images of sufficient contrast. Recom-
5.22 Spatulas, micro-type with V-shaped spoon that is
mended voltages can be in the 60 to 120 kV range. The
approximately 2 mm wide at top and 12.5 mm long.
microscope column should contain a liquid nitrogen-cooled
anti-contamination device or a “cold finger” to reduce sample
5.23 Fluorocarbon Duster.
contamination and to maintain column cleanliness. For image
5.24 Lens Tissue, lint-free.
acquisition, the microscope should include a charge-coupled
device (CCD) camera mounted either above or below the
5.25 Porcelain Boats, for pyrolysis, 98 mm long, 15 mm
instrument’s viewing chamber. wide at top.
5.2 Image Analysis System, consisting at minimum of a 5.26 Centrifuge, high speed (15000 to 20000 r/min) with
TEM-interfaced camera capable of 640 × 480 pixel or better head for 75 by 10 mm test tubes.
resolution,acomputerequippedwithframegrabbinghardware 3
5.27 Beakers, 2000-cm capacity.
to capture TEM images digitally, and software to perform
morphologicaloperationsandmeasurementsonimagefeatures
6. Reagents and Materials
and store resulting data. Operations must include background/
6.1 Chloroform, reagent grade.
noise elimination, thresholding, and edge smoothing.Area and
perimeter are then measured on features in the processed
6.2 Tetrahydrofuran (THF), reagent grade.
images.
6.3 1,2-Dichloroethane, reagent grade.
5.3 Two-Roll Mill.
6.4 Ethyl Acetate, reagent grade.
5.4 Vacuum Evaporator,standard-type,forpreparingcarbon
6.5 Poly (Vinyl Formal) Resin, Grade 15/95.
films to be used as substrates for electron microscopy. The
6.6 Cellulose Acetate Butyrate Resin (CAB).
evaporatorshouldbecapableofreducingtheabsolutepressure
-5
to1.3mPa(1×10 torr)andshouldalsocontainthenecessary
6.7 Phthalate-Type Plasticizer (such as santicizer).
apparatus for a-c glow discharge.
7. Sample Preparation—Dispersion Procedures
5.5 Ultrasonic Generator, variable power tank-type or
probe that provides sufficient energy to give acceptable disper-
7.1 Dry Carbon Black (Sonic Bath):
sion.
7.1.1 Weigh 8 to 10 mg of carbon black into a test tube
5.6 Dry Box, capable of maintaining a relative humidity containing 1 cm of solvent (typically chloroform or THF).
level of no greater than 30%.
NOTE 1—With experience, it may not be necessary to weigh each
carbon black sample, as an estimated amount from the microspatula may
5.7 Analytical Balance, with an accuracy of about 0.5 mg.
be sufficient. There is considerable latitude in the amount of carbon black
5.8 Electrically Heated Tube Furnace, capable of being
used.The finer N100 and N200 blacks may require somewhat less carbon
heated to 800 to 900°C under an inert environment, with the black than the coarser semi-reinforcing types.
D3849 − 07 (2011)
FIG. 1 Ultrasonic Dispersions of N-220 Carbon Black
NOTE2—Areasonabledegreeoflatitudeexistsforachievingtheproper
7.1.2 Adjust the power of the ultrasonic bath for maximum
concentration levels in the final dispersions for different grades of carbon
agitation; this may require that the water level be adjusted.As
black.Concentrationandoveralldispersionqualityarebestdeterminedby
the ultrasonic energy heats the water in the bath, ice should be
screening the actual specimens in the electron microscope and then
addedtocontrolthetemperatureinordertomaintainmaximum
making the necessary adjustments.
dispersive capability.
7.1.6 Place a specimen grid with carbon substrate (film side
7.1.3 Place the stoppered test tube containing the carbon
up) on a piece of filter paper. Remove a small amount of the
black and solvent mixture into the most intense part of the
final diluted dispersion using a fresh pipet and place one drop
ultrasonic field and allow the mixture to agitate for 3 to 5 min.
on the grid as close to the center as possible, from a height of
Thetesttubeshouldbeheldwithtongsormountedinasimple
about 12 mm.Allow the specimen to dry for about 1 min on a
wire holder.
piece of filter paper. This specimen preparation procedure
7.1.4 Transfer a small portion of the concentrated carbon
shouldbeperformedinadryboxiftherelativehumidityinthe
black-solvent mixture into another test tube containing 1 cm
room exceeds 30%.
of fresh solvent. The amount of concentrate required increases
7.1.7 For TEM grids that contain formvar or residual CAB
with particle size. Blend the mixture by repeatedly transferring
(CAB chip dispersions), place the TEM grid in an appropriate
the sample between the transfer pipet and the test tube, then
sample holder, place in the pyrolysis chamber and allow
cork the test tube and repeat the ultrasonic dispersion proce-
adequate time for the chamber to be purged by an inert gas to
dure.
prevent oxidation of the sample. Pyrolize the specimen grid at
7.1.5 Check the concentration of the diluted dispersion by
a sufficient temperature (typically greater than 550°C) to
extracting a small amount into the tip of the pipet and viewing
remove the poly (vinyl formal) film or CAB, or both.
against a white background. For tread grade carbon blacks, the
7.1.8 Acceptable dispersions of a carbon black in the dry
dispersions should be relatively transparent, becoming some-
state and removed from a rubber compound (SBR) are illus-
what darker with increasing particle size. The diluted disper-
trated for N-220 and N-774 carbon blacks in Figs. 1 and 2.
sions for very coarse carbon blacks such as N700 to N900
7.2 Dry Carbon Black (Ultrasonic Probe):
series will be on the threshold of complete opacity. If
7.2.1 Weigh 5 to 10 mg of carbon black into a 30-cm glass
necessary,adjusttheconcentrationbyaddingmoreconcentrate
vial and add approximately 20 cm of solvent (typically
or solvent as required, then repeat the ultrasonic agitation.The
chloroform).
volume of the carbon black-solvent mixture should be main-
tained at approximately 1 cm . If considerable dilution is
NOTE 3—With experience, it may not be necessary to weigh each
required, the excess volume above 1 cm should be discarded. carbon black sample, as an estimated amount from the microspatula may
D3849 − 07 (2011)
FIG. 2 Ultrasonic Dispersions of N-774 Carbon Black
be sufficient. There is considerable latitude in the amount of carbon black
carbon substrate (film side up) on a piece of filter paper. Using
used.The finer N100 and N200 blacks may require somewhat less carbon
afreshpipet,removeasmallamountofthefinaldispersionand
black than the coarser semi-reinforcing types.
place one drop on the grid as close to the center as possible,
7.2.2 Place the vial containing the carbon black and solvent
from a height of about 12 mm.Allow the specimen grid to dry
into an ice-water bath.
for approximately 1 min on the filter paper. (If the relative
7.2.3 Insert the probe to a depth of approximately 2.5 cm
humidity is greater than 35%, purge ultra-high purity nitrogen
into the vial and ultrasonicate at 40 to 50 watts for 10 min.
over the specimen grid retaining the sample.)
NOTE4—Theultrasonicprobeandice-waterbathcontainingthesample 7.2.8 Place the grid into the microscope and examine the
vial should be housed in an acoustic enclosure to reduce cavitation noise.
dispersion for visual separation of discrete aggregates. If the
dispersion shows a high concentration (overlap of aggregates,
7.2.4 Transferasmallportion(approximately2to4cm)of
agglomeration, and so forth), adjust the concentration of the
theconcentratedcarbonblack/solventmixtureintoanothervial
dispersionbyfollowing7.2.6andprepareanewspecimengrid
and add 20 cm of fresh solvent. An additional three-minute
by following 7.2.7.
sonication is recommended.
7.2.5 Check the concentration of the diluted dispersion by
7.3 Carbon Blacks Removed from Vulcanized Rubber Com-
extracting a small amount into a pipet and then placing 1 drop
pounds:
on a white filter paper. For tread grade carbon blacks, the
7.3.1 Cut thin sections (about approximately 1 mm)ofthe
dispersi
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