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Nanomaterial specific surface area

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Administrative data

Endpoint:
nanomaterial specific surface area
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2010
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study, no GLP-compliance

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2011
Report date:
2011

Materials and methods

Test guideline
Qualifier:
according to guideline
Guideline:
other: Internal method CA.MDA.050 " Specific surface area determination by BET method"
Principles of method if other than guideline:
The principle consists in the physical adsorption of a gas (adsorbate) at low temperature (78 K for liquid Nitrogen). The following adsorbates could be used: Argon for the microporous solids whose specific area is very large, Nitrogen for the mesoporous solids whose specific area is comprised between 10 and a few hundreds of m²/g, and Krypton for the weak specific areas (lower than 1 m²/g).
The method of BRUNAUER, EMMETT and TELLER (BET) allows to know the volume of an adsorbate monolayer from the quantity of adsorbed gas.
Knowing this volume as well as the hindrance of an adsorbate molecule, the specific area can be calculated.
GLP compliance:
no
Type of method:
BET
Details on methods and data evaluation:
Procedure:
The sample is placed in a pre-weighed cell. After degassing, the cell is weighed and is installed on the station of analysis. After having entered data (samples, mass of the sample, wished analysis), the analysis can start.

Successive introductions of Nitrogen in the Po tube and of Helium in the manifold and in the cell containing the sample permit to know all dead volumes thanks to Mariotte’s law. Then, the device conducts a leak test. Once vacuum is established the pressure must not pass 0,2 mm Hg. Then the Dewar filled of Nitrogen or liquid Argon rises in order to plunge the cell almost completely: pressure decreases and stabilizes. Once again dead volume of the manifold is determined with Helium, this time the sample being at equilibrium with he temperature of the liquid adsorbate used. The sample is then degassed in order to insure that it doesn’t desorbe longer impurities. Then, it measures Po while incrementing quantities of Nitrogen until saturation in the Po tube.

After all these stages, the five measurements process can begin. In a first time, one injects a certain pressure of Nitrogen in the manifold, it waits for the equilibrium (that means that the pressure stabilizes), then it opens the valve N° 9, the sample adsorbs a certain volume according to its surface. This operation is renewed five times (for a B.E.T. of five points) while increasing the pressure of the adsorbate to every point while remaining in the 0.05 P/Po 0.35 domain. At the end of manipulation, the Dewar descends and the pressure goes back until it reaches the air pressure.

The pressures are measured by two sensors: one of 1000 mm Hg and the other of 10 mm Hg. In fact, the apparatus only measures pressures, therefore it uses the PV/T = P1V1/T1 relation and of the corrective factors to calculate the adsorbed volumes.

The specific surfaces below 1 m²/g are determined by adsorption of krypton because the absorbed volumes being by definition very weak, the precision of the relative measures will be better while decreasing the value of Po (it is close to 2 mm Hg in the case of the Krypton condensed in the liquid Nitrogen). In the same way, when Krypton gas is used, the apparatus performs two leakage tests.

Expression of results:
The ASAP2000 equipment being computerized, the results are printed directly after exploitation by the software. Results include:
- The table of the absorbed volumes corresponding to the relative pressures (0.05 P/Po 0.35) for the different measuring points (in general 5).
- The curve of adsorption (its trend indicates if the analysis is valid or not).
- The linear transformed isotherm according to Brunauer, Emmett and Teller.
- The specific surface measured with its standard deviation.

The different files are classified by chronological order in a folder dedicated to the equipment ASAP 2000. Besides, they are kept in memory on the computing system or on archived disks in the laboratory.
Sampling:
In the case of a regular BET measurement with nitrogen, the mass of sample should be chosen in order to have to the minimum 10 m² in absolute. Exemple : For a sample whose surface is in the order of 100 m²/g, one will use 100 mg of sample. In the case of a BET measurement with Krypton, one weighs in any case 1 to 2 g of sample. A big attention will be brought to the representativeness of this sample. The samples are generally degassed during at least 3 ~ 4 hours to a temperature of about 300°C. The limit vacuum should be in the order o f 10 µm of Hg. This degassing permits the desorption of water or all other impurity and to free the totality of the specific surface. In the case of fragile materials (case of polymers), a lower degassing temperature is used.

Test material

Constituent 1
Chemical structure
Reference substance name:
Tangled Multi-Walled Carbon Nanotubes
EC Number:
701-160-0
Cas Number:
7782-42-5
Molecular formula:
Hollow tubular carbon, 1-dimensional nano structures with hexagonal arrangement of carbon atoms
IUPAC Name:
Tangled Multi-Walled Carbon Nanotubes
Constituent 2
Reference substance name:
GRAPHISTRENGTH C100
IUPAC Name:
GRAPHISTRENGTH C100
Test material form:
solid: nanoform

Data gathering

Instruments:
Equipment:
- ASAP 2000 from MICROMERITICS Company (cf. in appendix) with two degassing stations.
- A precision balance (METTLER AE200) for weighing the degassed samples before the analysis.

Results and discussion

Specific surface areaopen allclose all
Key result
Remarks on result:
other: trial 1
Key result
Remarks on result:
other: trial 2
Key result
Remarks on result:
other: trial 3
Key result
Remarks on result:
other: trial 4
Key result
Remarks on result:
other: trial 5
Key result
Remarks on result:
other: trial 6

Any other information on results incl. tables

Six experiments have been carried out, resulting in a mean value of 240.5 m²/g and a relative standard deviation of 3% (this value specifically applies to the tested sample).

Applicant's summary and conclusion

Conclusions:
The specific surface area (according to BET method) of test item is 240 m2/g with a relative standard deviation of 3% (this value specifically applies to the tested sample).
Executive summary:

Specific surface area of the test item was determined using the BET method. The measurements carried out show a specific surface area of 240 m2/g (this value specifically applies to the tested sample).