ASTM D6556-00a

Standard Test Method for Carbon Black—Total and External Surface Area by Nitrogen Adsorption

SCOPE
1.1 This test method covers the determination of the total surface area by the Brunauer, Emmett, and Teller (B.E.T. NSA) theory of multilayer gas adsorption behavior using multipoint determinations and the external surface area based on the statistical thickness surface area method.
1.2 The values stated in SI units are to be regarded as the standard. The values given 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. (The minimum safety equipment should include protective gloves, sturdy eye and face protection).

General Information

• Status: Historical
• Publication Date: 09-Dec-2001
• ICS: 83.040.30 - Auxiliary materials and additives for plastics
• Technical Committee: D24 - Carbon Black
• Drafting Committee: D24.21 - Carbon Black Surface Area and Related Properties

Relations

• Replaced By: ASTM D6556-01 - Standard Test Method for Carbon Black—Total and External Surface Area by Nitrogen Adsorption
• Effective Date: 10-Dec-2001
• Referred By: ASTM D4122-17(2023) - Standard Practice for Carbon Black—Evaluation of an Industry Reference Black
• Effective Date: 10-Dec-2001
• Referred By: ASTM D3849-22 - Standard Test Method for Carbon Black—Morphological Characterization of Carbon Black Using Electron Microscopy
• Effective Date: 10-Dec-2001
• Referred By: ASTM D4821-20 - Standard Guide for Carbon Black—Validation of Test Method Precision and Bias
• Effective Date: 10-Dec-2001
• Referred By: ASTM D7849-23 - Standard Classification for Nomenclature of Reference Materials of Committee D24
• Effective Date: 10-Dec-2001
• Referred By: ASTM D5817-20 - Standard Practice for Carbon Black, Pelleted—Reduction, Blending, and Drying of Gross Samples for Testing
• Effective Date: 10-Dec-2001
• Referred By: ASTM D1765-23a - Standard Classification System for Carbon Blacks Used in Rubber Products
• Effective Date: 10-Dec-2001
• Referred By: ASTM D8325-20 - Standard Guide for Evaluation of Nuclear Graphite Surface Area and Porosity by Gas Adsorption Measurements
• Effective Date: 10-Dec-2001
• Referred By: ASTM D3053-23 - Standard Terminology Relating to Carbon Black
• Effective Date: 10-Dec-2001
• Referred By: ASTM D6915-23 - Standard Practice for Carbon Black—Evaluation of Standard Reference Blacks
• Effective Date: 10-Dec-2001

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 6556 – 00a
Standard Test Method for
Carbon Black—Total and External Surface Area by Nitrogen
Adsorption
This standard is issued under the fixed designation D 6556; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope nitrogen adsorption. The NSA measurement is based on the
B.E.T. theory and it includes the total surface area, inclusive of
1.1 This test method covers the determination of the total
micropores, pore diameters less than 20 Å. The external
surface area by the Brunauer, Emmett, and Teller (B.E.T. NSA)
surface area, based on the statistical thickness method (STSA),
theory of multilayer gas adsorption behavior using multipoint
is defined as the specific surface area that is accessible to
determinations and the external surface area based on the
rubber.
statistical thickness surface area method.
1.2 The values stated in SI units are to be regarded as the
5. Apparatus
standard. The values given in parentheses are for information
5.1 Multipoint Static-Volumetric Gas Adsorption Apparatus,
only.
with Dewar flasks and all other accessories required for
1.3 This standard does not purport to address all of the
operation.
safety concerns, if any, associated with its use. It is the
5.2 Sample Cells that, when attached to the adsorption
responsibility of the user of this standard to establish appro-
apparatus, will maintain isolation of the sample from the
priate safety and health practices and determine the applica-
–5 3
atmosphere equivalent to a helium leak rate of <10 cm /min,
bility of regulatory limitations prior to use. (The minimum
per atmosphere of pressure difference.
safety equipment should include protective gloves, sturdy eye
5.3 Balance, Analytical, with 0.1 mg sensitivity.
and face protection).
5.4 Heating Mantle or Equivalent, capable of maintaining a
2. Referenced Documents temperature of 300 6 10°C.
5.5 Oven, Gravity Convection, capable of maintaining a
2.1 ASTM Standards:
temperature of 125 6 10°C.
D 1799 Practice for Carbon Black—Sampling Packaged
Shipments
6. Reagents
D 1900 Practice for Carbon Black—Sampling Bulk Ship-
2 6.1 Liquid nitrogen, 98 % or higher purity.
ments
6.2 Ultra-high purity nitrogen gas, cylinder or other source
D 3324 Practice for Carbon Black—Improving Test Repro-
2 of prepurified nitrogen gas.
ducibility Using ASTM Reference Blacks
6.3 Ultra-high purity helium gas, cylinder or other source of
D 4483 Practice for Determining Precision for Test Method
2 prepurified helium gas.
Standards in the Rubber and Carbon Black Industries
7. Sampling
3. Summary of Test Method
7.1 Samples may be taken in accordance with Practice
3.1 The total and external surface areas are measured by
D 1799 and Practice D 1900.
evaluating the amount of nitrogen adsorbed, at liquid nitrogen
temperature, by a carbon black at several partial pressures of
8. Sample Preparation Procedure
nitrogen. The adsorption data is used to calculate the NSA and
8.1 Dry a portion of carbon black at 125°C for 1 h. If the
STSA values.
carbon black is known to be substantially free of moisture, or
4. Significance and Use subsequent preparation steps are known to be adequate for
moisture removal, then this step may be omitted.
4.1 This test method is used to measure the total and
8.2 Condition an empty sample cell for a minimum of 10
external surface area of carbon blacks based on multipoint
minutes at the same conditions intended for degassing the
sample. Weigh the empty sample cell to the nearest 0.1 mg and
This test method is under the jurisdiction of ASTM Committee D24 on Carbon
record the mass.
Black and is the direct responsibility of Subcommittee D24.21 on Adsorptive
8.3 Weigh approximately 0.4 g of the carbon black into the
Properties of Carbon Black.
sample cell.
Current edition approved Nov. 10, 2000. Published January 2001. Originally
published as D 6556-00. Last previous edition D 6556-00
NOTE 1—For carbon black powder samples, add enough carbon black
Annual Book of ASTM Standards, Vol 09.01.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 6556
to give a depth of approximately 2 in. in straight wall sample tubes, or
the 0.1 to 0.5 relative pressure (P/P ) range. For some tread
o
approximately 0.4 g for bulb-type sample cells.
carbon blacks, particularly N100 and N200 series, it is neces-
sary to measure two additional data points, 0.05 and 0.075, in
8.4 Flow Degassing:
order to increase the accuracy of the NSA measurement. A data
8.4.1 Open the gas control valve and insert the delivery tube
point consists of the relative pressure of equilibrium and the
into the sample tube, and allow purging with either helium or
total amount of nitrogen gas adsorbed by the sample at that
nitrogen for a minimum of 1 minute.
relative pressure.
8.4.2 Place a heating mantle or other source of heat around
9.6 Determine the mass of the cell with dry sample to the
the sample cell and degas the sample at 300 6 10°C for ⁄2 h
nearest 0.1 mg. This may be done before or after measuring
or longer to ensure that all traces of moisture condensing in the
nitrogen adsorption. Avoid inconsistent use of helium, as a
top of the tube are absent. The minimum degassing time that
buoyancy error of 1 mg/cm of cell volume can occur. As an
gives a stable surface area (that is, a surface area that does not
alternative, the carbon black mass may be determined directly
increase with additional degassing) may be used for degassing.
by pouring it from the sample cell into a tared weighing pan,
8.4.3 Once the typical degassing times have been deter-
taking care to remove all of the carbon black.
mined, future samples can be degassed on the basis of time
alone, if desired, allowing a reasonable margin of excess time.
10. Calculation
Some samples will be found to require less than ⁄2 h, especially
10.1 Most automated instruments will perform the follow-
if moisture exposure has been minimal. In these cases, the
ing computations at the completion of the analysis. The user
minimum time that gives a stable surface area may be used for
must verify that the internal computations conform to the
degassing.
following method.
8.4.4 After degassing, the sample tube may be moved
10.2 Sample Mass:
directly to the analyzer. Otherwise, remove the sample tube
from the heat source and continue the flow of purging gas until
sample mass ~dried!5~mass of cell 1 sample! – ~mass of cell!
(1)
it is ready for analysis.
8.4.5 Go directly to Section 9 and continue the remaining
Record masses to nearest 0.1 mg.
steps of the procedure.
10.3 Volume of Nitrogen Adsorbed
8.5 Vacuum Degassing:
10.3.1 Calculate total volume of nitrogen adsorbed per gram
8.5.1 With the apparatus at atmospheric pressure, place the
of sample to the nearest 0.0001 cm /g as follows:
sample cell containing the carbon black onto the degassing
Volume of Nitrogen for each dosing in cm
apparatus.
V 5 (2)
a
sample mass in g
8.5.2 Begin the degassing procedure as appropriate for the
10.4 Nitrogen Surface Area:
apparatus.
10.4.1 Determine the nitrogen surface area (NSA) using a
8.5.3 Place a heating mantle or other source of heat around
B.E.T. plot from the Brunauer, Emmett, and Teller equation as
the sample cell and degas the sample at 300 6 10°C for ⁄2 h
follows:
or longer as required to obtain and hold a pressure less than 1.4
Pa (10 μm Hg).
P 1 C–1 P
5 1 3 (3)
8.5.4 Once the typical degassing times have been deter- V ~P –P! V C V C P
a o m m o
mined, future samples can be degassed on the basis of time
where:
alone, if desired, allowing a reasonable margin of excess time.
P = manometer pressure in kPa,
Some samples will be found to require less than ⁄2 h, especially
Po = saturation vapor pressure of nitrogen in kPa,
if moisture exposure has been minimal. In these cases, the
Vm = volume of nitrogen per gram that covers one mono-
minimum time that gives a stable surface area may be used for
molecular layer in standard cm /g, and
degassing.
C = a constant that is a function of average heat of
8.5.5 Go directly to Section 9 and continue the remaining
adsorption of the monomolecular layer,
steps of the procedure.
P
10.4.2 Plot P/P on the X-axis versus on the
o
V ~P –P!
9. Measurement Procedure
a o
Y-axis, for data sets having P/P in the range of 0.05 to 0.30
o
9.1 Refer to the user’s manual or specific instructions for the
(linear region of B.E.T. equation).
multipoint gas adsorption analyzer to be used, and become
10.4.3 The data points (three or more) that give the best
thoroughly familiar with the procedures.
straight line are used to calculate the slope and y-intercept. The
9.2 Fill the Dewar with liquid nitrogen and allow it to reach
slope and y-intercept are used to calculate the surface area. For
temperature equilibrium, preferably 0.5 to 1 h.
examples of how to select the proper relative pressure range,
9.3 Accurately determine the saturation pressure of the
see Table 1.
liquid nitrogen bath by running replicate determinations until
10.4.4 As an alternative, the interpretation of the proper
two consecutive saturation pressure values agree within 0.13
relative pressure can generally be simplified by specifying the
kPa (1 mm Hg).
following pressure ranges for the various carbon black types:
9.4 Determine the free space of the sample cell by measure-
ment with helium or by calculation using an assumed carbon
black density of 1.9 g/cm . 3
Brunuaer, Emmett and Teller, Journal of the American Chemical Society,
9.5 Obtain a minimum of five data points evenly spaced in Volume 60, 1938, p. 309.
D 6556
TABLE 1 Example of NSA Data Analysis 3
22400 = number of cm occupied by one mole of
A
N121
gas at STP.
Raw Data Calculation
10.5 Statistical Thickness Surface Area:
10.5.1 Determine the STSA of the black using a plot of the
Vol. Ads., Rel. Press. Correlation NSA,
3 2
P/Po cm /g Range Coefficient m /g
volume of nitrogen gas adsorbed per gram of sample at STP
0.0500 26.716 . . . . . . . . .
(V ) versus the statistical layer thickness (t).
a
0.1000 29.753 . . . . . . . . .
10.5.2 Prepare the V -t plot by plotting t (Å) on the X axis
a
0.1500 32.313 0.05–0.15
...