Structural changes in four different precursors with heattreatment at high temperature and resin carbon structural model

Jincai Zhang • Jingli Shi • Yun Zhao •

Quangui Guo • Lang Liu • Zhihai Feng •

Zhen Fan

Received: 29 February 2012 / Accepted: 10 April 2012 / Published online: 28 April 2012

� Springer Science+Business Media, LLC 2012

Abstract Four precursors (mesophase pitch, condensed

polynuclear aromatic resin, polyimide resin, and thermo-

setting phenolic resin) were heat treated at temperatures

from 900 to 3000 �C. These products were characterized by

X-ray diffraction, transmission electron microscopy, and

helium adsorption density instruments. Heterogeneous

graphitization was observed above 2200 �C in the resin

carbons. Various constituents (amorphous, turbostratic, and

graphitic) coexisted and transformed from being disordered

to ordered with increasing treatment temperature. The

molecular structures of the starting materials played

important roles in the proportions of various constituents,

crystallite sizes, and preferred orientation of the graphitic

constituent of the different carbons during high temperature

treatment. High-resolution transmission electron micros-

copy images showed that the structural features of Jenkins’

and Shiraishi’s model all existed in three resin carbons.

Based on these results, we think that their structures are not

belong to Jenkins’ model, also do not belong to Shiraishi’s

model, are a complex of above two models.

Introduction

Carbon is a unique solid substance that can be manipulated

to exhibit broadly different, even controversial, structures

and properties. Some carbons can be extremely strong,

hard, and stiff; other forms can be soft and ductile. These

variations result from structural effects, such as the number

of defects, geomorphology, and amount of carbon phases

with modified extents of crystalline order [1]. Corre-

sponding to the degree of crystallinity, porosity, and

apparent density, Franklin [2] categorized carbon into

graphitizing and non-graphitizing. The structures, proper-

ties, and applications of graphitizing carbons, such as

mesophase pitch (MP) [3, 4], petroleum coke [5–7], coal

pitch coke [8–10], etc., have been extensively studied. The

apparent densities and pores of typical non-graphitizing

carbons (e.g., some carbons derived from thermosetting

resin, named as glassy carbons) have also been investi-

gated. The common feature of non-graphitizing carbons is

the decrease in the apparent density with increasing treat-

ment temperature [11–13]. Some theories involving vol-

ume expansion [14] and thermal strain [15] provide

relatively reasonable explanation. A well-known hetero-

geneous graphitization phenomenon in the high tempera-

ture treatment of some resin carbons [16–19] has been

reported by several studies. However, limited studies exist

on structural changes in these different constituent carbons

as well as the effects of these changes on the microstruc-

ture, apparent density, and porosity of non-graphitization

carbons. This change is very important for further studies

on non-graphitizing carbons.

J. Zhang � J. Shi (&) � Y. Zhao � Q. Guo � L. Liu

Key Laboratory of Carbon Materials, Institute of Coal

Chemistry, Chinese Academy of Sciences,

Taiyuan 030001, China

e-mail: shijingli1963@163.com

J. Zhang (&)

Graduate University of the Chinese Academy of Sciences,

Beijing 100039, China

e-mail: chaner9944@126.com

J. Shi

School of Materials Science and Engineering,

Tianjin Polytechnic University, Tianjin 300387, China

Z. Feng � Z. Fan

National Key Laboratory of Advanced Functional Composites

Materials, Aerospace Research Institute of Material and

Processing Technology, Beijing 10076, China

123

J Mater Sci (2012) 47:5891–5899

DOI 10.1007/s10853-012-6492-1

In the present study, the structural changes among multi-

phase carbons produced during the heterogeneous graphi-

tization of three resin carbons were investigated in detail.

Their microstructure features were also discussed. Based

on the discussions and a previous report [11, 16–20], a new

structural model of resin carbons that can demonstrate

the structural and property changes in resin carbons is

proposed.

Experimental

Starting materials

The four carbons investigated were obtained from the

carbonization of three resins, condensed polynuclear aro-

matic (COPNA), polyimide (PI), thermosetting phenolic

(PH), and also MP. Their detailed informations and mol-

ecules are listed in Table 1 and Fig. 1, respectively. The

synthesis of COPNA resin is given in the literature [21].

The synthesis condition was (120–135) �C for 4 h. COP-

NA, PI, and PH were first cured at 220 �C for 6 h, and then

carbonized at 900 �C for 2 h at a rate of 1 �C/min under a

N2 atmosphere.

MP was carbonized at the same condition as above for

comparison with graphitizing carbon.

The as-obtained carbons were COPNA carbon, PI car-

bon, PH carbon, and MP carbon, hereinafter denoted as

COC, PIC, PHC, and MPC, respectively.

Preparation of samples

The four carbons were treated at (1500, 2200, 2600, and

3000) �C for 0.5 h. The temperature for each sample was

increased from room temperature to the given temperature

point at a rate of 15 �C/min under an Ar atmosphere. After

natural cooling, the samples were removed from the

graphitization furnace and stored for analysis. Each sample

was named according to the starting material and treatment

temperature. For example, COC-30 was COPNA carbon

derived from the heat treatment of COC at 3000 �C; PHC-

15, PIC-22, and MPC-26 denoted PHC, PIC, and MPC

treated at (1500, 2200, and 2600) �C, respectively.

Characterization

Every sample treated at the various temperatures was

ground into particulates with diameters of \150 lm to

obtain their (002) diffraction profiles on a Rigaku-D/max-

Va rotate anode X-ray diffractometer with a silicon stan-

dard. The aim is to avoid the shift of diffraction peak to the

lower angle aside and also a broadening of the observed

profile. CuKaX-ray is used, where CuKbis removed by a

graphite counter monochromator. The accelerating voltage

and current applied to the X-ray tube are 30 kV and

100 mA, respectively. High-resolution transmission elec-

tron microscopy (HR-TEM) images of the samples were

obtained on an FEI Tecnai C2F20 field emission TEM. The

apparent densities were measured using an AccuPycII1340

helium adsorption density instrument. The porosities of the

various carbons treated at 3000 �C were calculated as

follows: porosity (%) = (qt - qa)/qt 9 100, where qt and

qa are the true and apparent densities, respectively. qt is

(2.15 and 2.26) g/cm3 for resin and pitch carbon,

Table 1 Manufacturers and product model of starting materials

Starting

materials

Manufacturer Product model

COPNA Experiment synthesis –

PI Qinyang tianyi chemical

Co, Ltd, China

TY005-1

PH Tianjin daying resin

and plastic Co, Ltd, China

413

MP Mitsubishi gas chemical

company Inc, Japan

Ar mesophase

pitch

* CH2 CH2 *

n

C

C

C

C

O

O O

O

N O *N*

n

OH

CH2

OH

*

n

H3C

COPNA PI

PH MP

Fig. 1 Molecules of starting materials

5892 J Mater Sci (2012) 47:5891–5899

123

respectively, according to the literature [2]. The interlayer

spacings were calculated using the Bragg equation.

Results and discussion

Structural changes of resin carbons

during heterogeneous graphitization

Figure 2 shows the X-ray diffraction (XRD) profiles of the

four carbons heat-treated at high temperatures. According

to the discussions in the literature [22], when the full width

at half maximum (FWHM) intensity of the observed 002

reflection is more than 0.5�, each diffraction profile of

carbon is necessary to correct for Lorentz factor (L),

polarization factor (P), absorption factor (A) and atomic

scattering factor of carbon (fc). These corrections of dif-

fraction profiles have been made according to the methods

[22]. The profile of the 002 peak was divided into two or

three smaller peaks through multiple peak fit using Voigt

function. The credibility of profile fitting can be examined

with an R factor defined as

R ¼ R2h Ið2hÞ � Prð2hÞj jR2h

� 100½22�

Here, I(2h) is the experimentally observed intensity and

Pr(2h) is the profile fitted by calculation profiles. The three

smaller fitting peaks in the diffraction peak of each sample

in Fig. 2 represent three constituents for PIC and COC,

namely, the amorphous (A-), turbostratic (T-), and

graphitic (G-) constituents [18, 19].However, in the case

of PHC, there were two peaks in the profile of the 002

peak. For MPC, only one peak denoting the G-constituent

was observed in the profile of the 002 peak, which implied

the graphitizable characteristic of MP as reported in the

literature [23]. A remarkable feature observed in the XRD

profiles of the resin carbons was the structural changes that

occurred in the various constituents, i.e., the changes of A

to T and T to G with increasing treatment temperature. This

result indicates that the carbonization process enables the

conversion of the carbon materials from a disordered

structure to an ordered graphitic structure within (2200 to

3000) �C. To understand the change in the amount of

various constituents in resin carbon, the mol% of each

constituent was calculated as follows: mol% = (Ssp /

Sto) 9 100, where Ssp and Sto denote the areas of the

single and total peaks, respectively.

Figure 3 shows that the A-constituent in COC dramati-

cally decreased from 50.26 % at 2200 �C to 39.08 % at

3000 �C with increasing treatment temperature. The

T-constituent slightly decreased and the G-constituent

visibly increased to 23.10 % at 3000 �C from 7.63 % at

2200 �C. An obviously distinct change compared with

COC was observed in PIC. The A-constituent slightly

decreased and the T-constituent sharply decreased from

60 % at 2200 �C to 39.99 % at 3000 �C. PIC exhibited a

tendency similar to COC in that the G-constituent also

significantly increased. These phenomena indicated that the

amount of the shift from A to T was more, and the one of T

to G was less for COC than PIC. However, in the case of

PIC-22

R=9.66

A

T

G

R=7.15

PIC-26

A

T

G

16 18 20 22 24 26 28 30 32 34

PIC-30

R=2.85

A

T

G

16 18 20 22 24 26 28 30 32 34

COC-30

R=6.12

A

T

G

COC-26

R=8.02

A

T

G

COC-22

R=7.36

A

T

G

MPC-22

MPC-26

16 18 20 22 24 26 28 30 32 34

MPC-30

PHC-22R=11.28

T

A

16 18 20 22 24 26 28 30 32 34

PHC-30

R=8.26

T

G

PHC-26R=10.58

A

G

Fig. 2 Profiles of XRD for various carbons (black and red solid lines are origin and fitting peaks, respectively)

J Mater Sci (2012) 47:5891–5899 5893

123

PIC, the increase in the G-constituent was primarily

dependent on the changes observed from the decrease in

T-constituent. A different feature observed during the

graphitization process of PHC was that its main compo-

nent, A-constituent, gradually converted to T-constituent,

and that PHC did not contain any G-constituent within

2200 to 2600 �C. With further increase in treatment tem-

perature, the A-constituent disappeared, the G-constituent

appeared and increased, and the T-constituent also

increased. These findings indicate that the changes of dif-

ferent structural carbons in PHC was drastic at the high

temperature of 3000 �C, at which all A-constituents were

converted into T-constituents, and part of the T-constitu-

ents also transformed into G-constituents.

The major factors affecting the above phenomena are

the precursor materials and the heat treatment conditions

(i.e., temperature, time, and heating rate). In the present

study, four carbons were treated under the same conditions;

thus, the precursor materials mainly accounted for the

differences in the four carbons. MP has good graphitization

ability due to its larger plane layer structure that can form a

liquid crystal state. Thus, only the G-constituent was

observed even at the relatively low graphitization temper-

ature of 2200 �C. The molecules of resin carbons play

important roles in the process of forming the graphitization

structure. In the present study, the three resins were poly-

mers consisting of long-chain molecules with many struc-

tural units linked with one another through C–C bonds

(Fig. 1). These molecular structures did not easily form

larger planes during post-high temperature treatments in

larger region due to the differences in the effect of thermal

stress on each structural unit, although every structural unit

also contained many benzene rings. However, under the

graphitization process, once the graphitic structure is

formed in a certain region, nearby chain molecules easily

crystallizes close to it, thereby producing entangled carbon

ribbons. Some carbons far from the graphitic region cannot

orient in the same direction at relatively low temperatures,

thus producing various constituents such as A-, T-, and

G-constituents, which shift according to the rules from a

disordered to a good ordered structure during high tem-

perature treatments.

Microstructure

Table 2 shows that the 2h positions of various constituents

in three resin carbons all shift to a larger angle side, the

interlayer spacings of every constituent gradually decrease

during high temperature heat treatment. These changes

obviously explain the microstructure conversion from dis-

ordered to ordered in three resin carbons. To know the

whole change in structure of every resin carbons, their

mean interlayer spacings were calculated by the equation:

d002 = k/(2Sinh), here d002, k and h are the mean interlayer

spacings, wavelength of X-ray (0.1540562 nm) and the

center position of total peak of each resin carbon, respec-

tively. Figure 4 exhibits that interlayer spacing of each

sample all decrease with increasing temperature. The range

2000 2200 2400 2600 2800 3000 32000

10

20

30

40

50

60

70

80

90

100V

ario

us c

onst

ituen

t con

tent

/ m

ol

Temperature /

A

T

G

COC

50.26%

42.11%

7.63%

44.59%39.66%

15.75%

39.08%37.82%

23.10%

2000 2200 2400 2600 2800 3000 32000

20

40

60

80

100

Var

ious

con

stitu

ent c

onte

nt /

mol A

T

G

PHC84.42%

15.58%

73.87%

26.13%

78.90%

21.10%

2000 2200 2400 2600 2800 3000 32000

10

20

30

40

50

60

70

80

90

100

Var

i ous

con

stitu

ent c

onte

nt /

mol

Temperature /

Temperature /

A

T

G

PIC

35.8%

60.0%

4.2%

35.62%

49.89%

14.49%

30.59%

39.99%

29.42%

Fig. 3 Relationship between various constituent carbons and

treatment temperatures

5894 J Mater Sci (2012) 47:5891–5899

123

of the fall is largest for PHC, followed by PIC, COC, and

MPC. The falling process of the interlayer spacing was a

graphitization process during which all disordered struc-

tures of carbon attempted all efforts to render themselves as

ordered as graphite as possible. However, molecules with

lesser aromatic ring (such as benzene) in its structural units

such as PHC apparently exhibited large scopes of change in

the interlayer spacing from 2200 to 3000 �C. For PIC,

impurity atoms such as O and N were released at below the

temperature of 1800 �C [24, 25] and produced a large

majority of defects in the carbon layers. This condition

favored the conversion of PIC from a very turbostratic to a

relatively higher ordered structure. Notably, the proportion

of the G-constituent was highest among the three resin

carbons. The interlayer spacing of COC has a largest

falling range in relatively low temperature of 2200 to

2600 �C, which shows that it is a relatively easy graphiti-

zation carbon. Figure 5 shows the HR-TEM images of the

four carbons treated at 3000 �C. The three resin carbons all

consisted of carbon ribbons entangled to different extents.

As reported in the literature [18], these are the typical and

characteristic structures of non-graphitizing carbons treated

at high temperatures. The homogeneous and heterogeneous

graphitization phenomena for MPC and the three resin

carbons COC, PIC, and PHC were clearly observed in these

images. These findings are consistent with the XRD results

previous. It can be found that the ‘‘retrogression points’’

exist in three resin carbons [24], i.e., defects of mutual

arrangement of layers in a carbon ribbon (G-constituent)

resulting in its stratification in two separate ones (Fig 5). In

images of COC and PIC, the A- and T-constituents mainly

existed in the region between two graphitic carbon ribbons

or the side of graphitic layers. In the case of PHC,

T-constituent has a similar existed form as in PIC and

COC.

Figure 6 shows the HR-TEM images of the G-constit-

uents in the three resin carbons treated at 3000 �C in some

minute area in nanometer. COC exhibited larger crystallite

sizes (La = 48 nm, Lc = 18 nm) than PIC and PHC, which

indicates that some the G-constituent in COC may have a

good preferred orientation and graphitization ability. PIC

exhibited the next larger crystallite sizes (La = 40 nm,

Lc = 8.3 nm), followed by PHC (La = 39 nm, Lc =

5.5 nm). This change tendency is similar to the theoretical

calculating result using the equation: Lc = k/(b Cosh002),

here k, b, and h are the wavelength of X-ray, FWHM, and

the center position of 002 peak of G-constituent in each

resin carbon. Lc is 22, 20, and 16 nm for COC, PIC, and

PHC treated at 3000 �C, respectively. The experiment

values are less than the theoretical results due to only a part

of the whole microstructure of G-constituent in three resin

carbons are observed because of the stacking among the

carbon ribbons and various constituents. Owing to these

Table 2 Interlayer spacing changes of every constituent in various resin carbons varying with increasing treatment temperature

Samples Temperature A-constituent T-constituent G-constituent

/�C 2h d/nm 2h d/nm 2h d/nm

COC 2200 22.03 0.4032 25.58 0.3480 26.49 0.3362

2600 24.04 0.3699 25.74 0.3458 26.49 0.3362

3000 24.61 0.3615 26.03 0.3420 26.50 0.3361

PIC 2200 20.34 0.4363 25.31 0.3516 26.46 0.3366

2600 22.17 0.4007 25.58 0.3480 26.50 0.3361

3000 24.25 0.3667 25.86 0.3443 26.51 0.3360

PHC 2200 24.33 0.3655 25.88 0.3440 – –

2600 24.47 0.3635 26.02 0.3422 – –

3000 – – 25.77 0.3454 26.43 0.3369

MPC 2200 – – – – 26.48 0.3363

2600 – – – – 26.52 0.3358

3000 – – – – 26.54 0.3356

2200 2400 2600 2800 3000

0.336

0.338

0.340

0.342

0.344

0.346

0.348

0.350

0.352

Inte

rlay

er s

paci

ng /

nm

Temperature /

COC

PIC

PHC

MPC

Fig. 4 Curve of interlayer spacing and treatment temperature

J Mater Sci (2012) 47:5891–5899 5895

123

reasons, in more area, the crystallite parameters of these

resins are smaller. The images of these resin carbon

(Fig. 7) show that there are a majority of carbon ribbons

that are long and stiff or flexible carbon ribbon that tangled

each other in a very quaint manner, or the two type forms

carbon ribbon coexisted in a sample. A typical feature in

PIC is that almost all carbon ribbons are entangled, trans-

form into each other, are stratified in some separate ones,

and merge in one ribbon with others, forming a complex

polymer-like structure. The spaces between the stacks form

micropores of various configuration and sizes [26]. How-

ever, for COC and PHC, they are a combination of carbon

ribbons with or without entangling each other. Observed all

images in Figs. 6, 7, and 8, in nature, three resin carbons all

are the combination carbons inside of which existing two

graphitic carbon layers such as no-entangling or entangling

each other, T-constituent, or A-constituent lie in the side of

these carbon ribbons or the separate region between carbon

ribbons. Only difference among three resin carbons is the

amount of these various form (G-,A- and T) constituents is

different for different resin carbons.

The molecules of the starting materials may explain the

above results, including the change in the interlayer spac-

ing during high temperature treatments and the properties

of the G-constituent. As shown in Fig. 3, the large plane

molecule of MP is made of many benzene rings, which is

considered as a graphitizing material [23]. For resin car-

bon, more benzene rings and heterocycles contained in the

structural unit of molecules corresponded to less impurity

elements (N, O, S, and so on) and to the easier graphiti-

zation of the resin. PIC-30 contained more G-constituents

than the other resin carbons due to the presence of more

benzene and heterocycle rings in the PI molecules. How-

ever, the release of more impurity atoms (5O and 2 N in a

structure unit) at below 1800 �C resulted in many plane

defects inside the carbon layers. These defects were kept

partly during the graphitization process due to the struc-

tural rearrangement of lattice defects [27], which is the

reason why the crystallite parameters are not the largest

among the three resin carbons, as shown in Fig. 6. COPNA

resin has relatively more benzene rings and no impurity

atom in its structural unit, the two advantages that enabled

Fig. 5 HR-TEM images of four precursor carbons treated at 3000 �C

5896 J Mater Sci (2012) 47:5891–5899

123

COC to possess the largest crystallite sizes. In the case of

PHC, only a benzene ring in conjunction with an oxygen

atom lying in the structural unit is the reason why PHC did

not have both a large layer size (La) and stack height (Lc) in

spite of these crystallite parameters are in local area.

Structural model of resin carbon

Figure 8 shows the structural models of graphitizing and

non-graphitizing carbons. MPC is ascribed to A (Flanklin’s

model of graphitizing carbon [2] B, C, and D are non-

graphitizing models proposed by Flanklin [2], Jenkins [28],

and Shiraishi [29], respectively). C consists of entangled

carbon ribbons and has little closed-pores, consequently

showing the highest apparent density. All three resin car-

bons in the present study had small apparent densities;

1.64, 1.49, and 1.57 g/cm3 for COC-30, PIC-30, and

PHC-30, respectively. The true density of non-graphitizing

carbon is 2.1–2.2 g/cm3 [2], which means three resin

carbons.

All have many closed-pores. The closed-pore volume

fractions are 23.72, 30.7, and 26.98 % for COC-30, PIC-

30, and PHC-30, respectively, if selecting true density is

2.15 g/cm3. B and D models in Fig. 8 can well explain the

low apparent density of the three resin carbons, although a

better approach would be to consider the various constit-

uents A, T, and G. The amount and shape of the closed

pores were also different for the various resin carbons.

Analysis from the microstructure feature, Jenkins’ model

contains ‘‘retrogression points’’ and ‘‘crisscross point’’ of

carbon ribbons, while Shiraishi’s model contains ‘‘retro-

gression points’’ and ‘‘connection point’’ of carbon ribbons

(Fig. 8). Figures 5 and 7 both show the three resin carbons

all have these features, which indicates they are practically

Fig. 6 HR-TEM images of G-constituents in various resin carbons treated at 3000 �C (in some minute area in nanometer)

J Mater Sci (2012) 47:5891–5899 5897

123

complex composed of two structural models. Only the

ratios of two models are different for various resin carbons,

which result to the difference in properties such as apparent

density and closed-pore content. In fact, the specific

amount ratios are very difficult to be calculated. However,

the images in Fig. 7 also indicate that difference in three

resin carbons: PIC contain many closed-pores that con-

tributed to the low apparent density and high closed-pore

content. PHC and COC both have lesser closed-pores than

the former, so exhibit slightly higher apparent density.

Based on the above discussion and those in the literature

[20], a new structural model of resin carbons is proposed.

In this model, Jenkins’ and Shiraishi’s models coexisted

and only the contents are different for various resin car-

bons. So, the closed-pore content and shape are different,

which account for the difference in properties. The A-, T-,

and G-constituents coexisted in these carbons, G-constitu-

ent appear in carbon ribbons form while A- and T-con-

stituent locate in the separate region between carbon

ribbons or aside zone.

Conclusions

The microstructures and properties of a graphitizing carbon

(MPC) and three non-graphitizing carbons (COC, PIC, and

PHC) were investigated within 900–3000 �C. Above

2200 �C, non-graphitizable resin carbons exhibited heter-

ogeneous graphitization; COC and PIC had three constit-

uents, and PHC had two constituents. These constituents

Fig. 7 HR-TEM images of various resin carbons treated at 3000 �C (in other area in nanometer)

5898 J Mater Sci (2012) 47:5891–5899

123

transformed their microstructures from a disordered (such

as A- or T-constituent) to an ordered (G-constituent)

structure. The HR-TEM images showed that COC could

form the largest crystallite sizes and the best preferred

orientation in some zone due to the relatively more ben-

zene rings and less impurity atoms in its molecule structure

unit, followed by PIC and PHC. The XRD profiles showed

that PHC had a drastic structural change compared with the

other two resin carbons. The observations of the HR-TEM

images indicate the microstructure features of Jenkins’ and

Shiraishi’s models all located in three resin carbons in the

present study. Based on these observations and analyses, a

new structural model is proposed and it explain the resin

carbons are a complex of above two models, the A-, T-,

and G-constituents coexist in these carbons.

Acknowledgements This study is supported by the National Basic

Research Program of China (973 Program) No.2011CB605802. All

authors are very grateful to them.

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Connection point

Retrogression point

Voids

(a) (b)

(c)(d)

Crisscross pointRetrogression point

Closed pore

Fig. 8 Structural models of

various carbons (A, B for

graphitizing and non-

graphitizing carbon,

respectively, C and D for non-

graphitizing carbon structure

model of Jenkins’ and Shiraishi’s

model, respectively.)

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