GB/T 24490-2009 (GB/T24490-2009, GBT 24490-2009, GBT24490-2009)
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Test method for purity of multi-walled carbon nanotubes
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GB/T 24490-2009
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| Standard ID | GB/T 24490-2009 (GB/T24490-2009) | | Description (Translated English) | Test method for purity of multi-walled carbon nanotubes | | Sector / Industry | National Standard (Recommended) | | Classification of Chinese Standard | G13 | | Classification of International Standard | 59.100.20 | | Word Count Estimation | 10,170 | | Date of Issue | 2009-10-30 | | Date of Implementation | 2010-06-01 | | Quoted Standard | GB/T 14837; GB/T 24491 | | Drafting Organization | Tsinghua University | | Administrative Organization | Nanotechnology Standardization Committee of the National Technical Committee of nanomaterials | | Regulation (derived from) | National Standard Approval Announcement 2009 No.12 (Total No.152) | | Proposing organization | National Technical Committee for Standardization of nanomaterials Nano Technical Committee (SAC/TC 279/SC 1) | | Issuing agency(ies) | Administration of Quality Supervision, Inspection and Quarantine of People's Republic of China; Standardization Administration of China | | Summary | This standard specifies the purity MWCNTs measurement methods, instrument, analysis procedures and results of representation. This standard does not apply to poor uniformity or chunk of carbon phase containing impurities in the sample. |
GB/T 24490-2009
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 59.100.20
G 13
Test method for purity of multi-walled carbon nanotubes
ISSUED ON: OCTOBER 30, 2009
IMPLEMENTED ON: JUNE 01, 2010
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine of PRC.
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Methods ... 4
4 Charcoal analysis ... 6
5 Thermogravimetric analysis (TGA) ... 8
6 Transmission electron microscope analysis (TEM) ... 10
Appendix A (Normative) Quantitative analysis method of transmission electron
microscopy (TEM) image ... 13
Test method for purity of multi-walled carbon nanotubes
1 Scope
This standard specifies the method, instrument, analysis procedure, result presentation
method for measuring the purity of multi-walled carbon nanotubes.
This standard provides a method for measuring the purity of multi-walled carbon
nanotubes (MWCNTs) samples, using a combination of charcoal burning,
thermogravimetric analysis (TGA), transmission electron microscopy (TEM), image
analysis. The purity is represented by the content (mass fraction) of multi-walled carbon
nanotubes in the sample.
This standard is not applicable to samples, which have poor uniformity OR contain
large carbon phase impurities.
2 Normative references
The provisions in following documents become the provisions of this Standard through
reference in this Standard. For the dated references, the subsequent amendments
(excluding corrections) or revisions do not apply to this Standard; however, parties who
reach an agreement based on this Standard are encouraged to study if the latest versions
of these documents are applicable. For undated references, the latest edition of the
referenced document applies.
GB/T 14837 Rubber and rubber products - Determination of composition by
thermogravimetry (GB/T 14837-1993, neq ISO/DIS 9924:1992)
GB/T 24491 Multi-walled carbon nanotubes
3 Methods
This standard provides a method for measuring the purity of multi-walled carbon
nanotubes. The flow chart is as shown in Figure 1.
and the results obtained by charcoal analysis -- is not greater than 1%, then the
carbon phase content (mass fraction) of the sample is given by TGA.
Using TEM observation and image analysis, to determine the type of carbon phase and
the proportion of multi-walled carbon nanotubes in the carbon phase. The method is as
follows:
a) If the TEM observation proves that the carbon phase in the sample is only multi-
walled carbon nanotubes, it can be known that the proportion of multi-walled
carbon nanotubes in the carbon phase is 100%;
b) If the sample contains large pieces of carbon phase impurities (such as: large
pieces of graphite, etc.), meanwhile the carbon phase impurities and multi-walled
carbon nanotubes cannot be clearly identified in the same field of view, then it is
determined that the sample is not suitable for the measurement of the purity of
multi-walled carbon nanotubes by this method;
c) If the multi-walled carbon nanotubes and carbon phase impurities can be
identified in the same field of view, it is necessary to increase the number of TEM
sample preparation and images, meanwhile obtain the proportion of multi-walled
carbon nanotubes in the carbon phase, through image analysis statistics;
d) If the absolute deviation of the proportion of multi-walled carbon nanotubes, in
the carbon phase obtained by two TEM sample preparation statistics, is higher
than 5%, it is judged that the sample uniformity is poor, so this method is not
suitable for measuring the purity of multi-walled carbon nanotubes;
e) The proportion of multi-walled carbon nanotubes in the carbon phase is obtained
statistically from the analysis of all TEM images of a sample.
Finally, the purity of the multi-walled carbon nanotubes is obtained, from the product
of the carbon phase content and the ratio of the multi-walled carbon nanotubes in the
carbon phase.
4 Charcoal analysis
4.1 General
This method is applicable to the determination of the ash content (mass fraction) of
multi-walled carbon nanotube samples. Fully oxidize a certain amount of sample, in a
high-temperature air atmosphere at 900 °C, until the carbon in the sample overflows in
the form of gaseous oxides. Measure the mass of ash. Then calculate the ash content
(mass fraction).
4.2 Instruments
a) Crucible with a cover: It is made of platinum, quartz or other materials, that do
not change under the measurement conditions, with a capacity of 50 mL ~ 100
mL;
b) Desiccator: It is equipped with an effective and sufficient desiccant and a porous
metal plate or porcelain plate;
c) Muffle furnace: There is a device for controlling and adjusting the temperature,
which can provide an incineration temperature of 900 °C;
d) Analytical balance: The accuracy is 0.1 mg.
4.3 Analytical procedures
a) Sample pretreatment: Mix the sample thoroughly. Place it in a muffle furnace.
Keep it warm at 120 °C for 5 hours. Then transfer it to a desiccator. Cool it to
room temperature for storage.
b) Pretreatment of the crucible: First use diluted hydrochloric acid to wash the
crucible. Then use tap water to wash it. Use deionized water to rinse it. Place the
cleaned crucible in a muffle furnace. Heat it at 900 °C for 30 min. Take it out and
put it in a desiccator, to cool to room temperature. Then weigh it, accurate to 0.1
mg.
c) Weighing of the sample: Weigh 1 g ~ 2 g of the sample, accurate to 0.1 mg. Place
the sample evenly in the crucible, without compacting it.
d) Charcoal burning: Cover the crucible and put it into the muffle furnace. Keep the
air atmosphere of natural convection in the furnace. Raise the temperature to
900 °C. Keep this temperature, until all the remaining carbon is oxidized and
overflows, which generally takes 3 h ~ 5 h. Place the crucible and the residue in
it in a desiccator, to cool to room temperature. Weigh it, accurate it to 0.1 mg.
4.4 Results presentation method
The ash content wh can be obtained from formula (1):
Where:
wh - Ash content (mass fraction);
n1 - The mass of the crucible with a lid, in grams (g);
n2 - The mass of the crucible and the sample before ashing, in grams (g);
Where:
wh - Ash content (mass fraction);
wC - Carbon phase content (mass fraction);
m0 - The initial mass of the sample, in milligrams (mg);
m300 - The mass of the sample at 300 °C, in milligrams (mg);
m850 - The mass of the sample at 850 °C, in milligrams (mg);
m900 - The mass of the sample at 900 °C, in milligrams (mg).
For one sample, a set of TGA measurements are performed three times independently.
Ash content (wh1, wh2, wh3) and carbon phase content (wC1, wC2, wC3) are calculated
according to formula (4) and formula (5), respectively.
Calculate the average value and average variance of the ash content, which is measured
by three TGAs; the calculation method is as shown in formula (2) and formula (3). In
the ash content measured three times, if there is a result with a variance greater than 2
times the average variance, it shall be considered as an abnormal result, which is caused
by sample inhomogeneity or measurement problems AND shall be eliminated and re-
measured; then recalculate the average value and average variance.
The average ash content, which is obtained by TGA, is compared with the average ash
content, which is obtained by burning charcoal. If the absolute deviation is greater than
1%, an additional set of TGA measurements (three times) is required.
After judging that the absolute deviation of the ash content, which is measured by TGA
and charcoal, meets the requirements, take one or two sets (if there are two sets for TGA
detection, two sets shall be selected) of TGA results, to calculate the average value of
carbon phase content and the average variance σC2. Taking a set of TGA as an
example, the calculation method is as shown in formula (6) and formula (7):
6 Transmission electron microscope analysis (TEM)
6.1 General
Through the observation and image analysis of the transmission electron microscope,
the type and proportion of the carbon phase in the sample are determined.
In TEM observation, the carbon phases other than multi-walled carbon nanotubes are
regarded as carbon phase impurities. According to the provisions of GB/T 24491:
"When the transmission electron microscope is magnified more than 100000 times, it
is observed as fibrous, meanwhile the ratio of length to diameter is greater than 20."
Therefore, if the ratio of length to diameter is less than 20, it is deemed as carbon phase
impurities. When the carbon phase impurities (such as graphite flakes, etc.) are large in
size and cannot be clearly identified in the same field of view, as the multi-walled
carbon nanotubes, the measurement method of this standard is not applicable.
If any 10 fields of view on a microgrid contain only multi-walled carbon nanotubes and
no other carbon phase impurities (as shown in Figure 3a), it can be determined that the
carbon phase content, which is obtained by TGA measurement, is all corresponding to
the multi-walled carbon nanotubes. At this time, the measured by TGA is the
content (mass fraction) of multi-walled carbon nanotubes.
If obvious carbon phase impurities are observed by TEM (as shown in Figure 3b), it
shall increase the number of TEM sample preparation and acquired TEM images;
meanwhile carry out quantitative analysis of TEM images. For a multi-walled carbon
nanotube product, it shall carry out at least two independent sampling, dispersion,
sample preparation (at least two micro-grids), take at least 15 TEM images, that meet
the quantitative analysis requirements, for each micro-grid.
All TEM images of a microgrid are calculated and accumulated, according to Appendix
A, to obtain the total volume V1 of multi-walled carbon nanotubes and the total volume
V2 of carbon phase impurities. Neglecting the density difference of different carbon
phases, the proportion of multi-walled carbon nanotubes in the carbon phase YC can be
obtained, by formula (8):
If the absolute deviation of the YC results, which are obtained by two microgrids, is
greater than 5%, then, it is required to add at least 15 TEM images, that meet the
quantitative analysis requirements for each microgrid, to perform quantitative statistics
again. If the absolute deviation of the YC results, which are obtained by the two micro-
grids, is still greater than 5%, then, it is judged that the uniformity of the sample is poor,
so this measurement method is not applicable.
All the TEM images of each microgrid of a sample are accumulated, to obtain the total
volume V1 of multi-walled carbon nanotubes and the total volume V2 of carbon phase
impurities. Use the formula (8), to calculate the proportion YC of the multi-walled
carbon nanotubes in carbon phase. The content (mass fraction) of multi-walled carbon
nanotubes in the sample can be obtained, by formula (9):
Appendix A
(Normative)
Quantitative analysis method of transmission electron microscopy (TEM) image
Randomly take TEM images, to ensure that the images are representative, that is,
sample areas with different morphology characteristics shall be included. The carbon
phase components (multi-walled carbon nanotubes, carbon fibers, carbon spheres,
carbon shells, graphite flakes, etc.) of different morphology are identified, using the
manual method or computer aid software, to obtain the characteristic parameters of
multi-walled carbon nanotubes and impurities. According to the corresponding
geometrical model, use statistical calculation to obtain the volume V1 of multi-walled
carbon nanotubes and the volume V2 of carbon phase impurities. For the carbon phase
impurity components with different geometric shapes, such as: carbon spheres, carbon
shells, carbon fibers, short tubes with an aspect ratio lower than 20, graphite flakes,
their corresponding volumes can be expressed as V21, V22, V23, V24, V25, respectively.
A.1 Geometric model and characteristic parameters of multi-walled carbon
nanotubes
Geometric model: Cylindrical tube model.
The volume V1 of multi-walled carbon nanotubes is calculated according to formula
(A.1):
Where:
V1 - The volume of multi-walled carbon nanotubes, in cubic nanometers (nm3);
D1 - The outer diameter of multi-walled carbon nanotubes, in nanometers (nm);
D2 - The inner diameter of multi-walled carbon nanotubes, in nanometers (nm);
L - The length of multi-walled carbon nanotubes, in nanometers (nm);
i - Any one multi-walled carbon nanotube.
Note: The sum means to accumulate all the multi-walled carbon nanotubes in one image. The
same goes for the following.
A.2. Geometric model and characteristic parameters of carbon phase impurities
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