Standards related to:

GB/T 24490-2009GB/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

...