**5.2 Carbonaceous mesophase-based mesocarbon microbeads**

As a special type of carbon material, MCMB has some outstanding physical and chemical properties that other carbon materials do not have due to its unique spherical morphology and lamellar structure. Therefore, MCMB can be widely applied to various fields, such as high-performance liquid chromatography column materials, high-specific surface area activated carbon materials, high-efficiency lithium ion battery anodes, high-density and high-strength graphite materials, etc. [5, 21].

Under suitable thermal reaction conditions, homogeneous liquid-crystalline spheres with an identical diameter of ~10 μm which appeared in the optically isotropic pitch matrix can be achieved as shown in **Figure 14(a)**, which is closely related to the effective control of the polymerization degree of naphthalene molecules. Through subsequent separation, infusibilization, and carbonization treatments, uniform-sized MCMBs as shown in **Figure 14(b)** can be easily obtained by starting with a simple naphthalene molecule.

### **5.3 Carbonaceous mesophase-based porous carbon and carbon foam**

Recently, many researchers have used mesophase pitch as a raw material to prepare porous carbon materials (e.g., ultrahigh surface area activated carbon, mesoporous carbon, and hierarchical porous carbon) with controlled microstructure and morphology [22, 23]. The large specific surface area, rich pore structure and excellent adsorption performance of porous carbon materials provide excellent supporting characteristics for various transition metal and precious metal catalysts. Porous carbon support can resist the severe corrosion in harsh environments such as acid, alkali and salts, and greatly improve the adsorption performance and catalytic efficiency, and thus has broad applications [24].

Mesophase pitch-based carbon foam is a new type of porous carbon material prepared by foaming mesophase pitch as shown in **Figure 15**. Owing to its low density, high thermal and electrical conductivity, fire resistance, microwave absorption, noise reduction, low thermal expansion coefficient, chemical resistance, etc., carbon foam is extremely suitable for heat transfer systems, such as aerospace vehicles and satellites, rocket launching platforms, large heat exchangers, and computers in chemical plants [25–27]; therefore, such carbon foam sees promising application prospects.

#### **Figure 14.**

*(a) PLM micrograph of anisotropic liquid-crystalline carbonaceous spheres generated from naphthalene-based synthetic pitch and (b) SEM image of homogeneous MCMBs derived from the spherical liquid crystals.*

*Liquid Crystals and Display Technology*

**5. Applications of carbonaceous mesophase**

**5.1 Carbonaceous mesophase-derived coke**

during the liquid-phase carbonization process.

exhibits good wire-drawing performance and ideal viscoelastic property and the unwittingly drawn wires (i.e., large-diameter pitch fibers) possess an orderly liquid-crystalline texture as shown in **Figure 11**, which is closely related to its plastic flowing behavior and low apparent viscosity upon melting as shown in **Figure 12**. This is favorable for pitch melt spinning and other rheology applications [5].

It is well known that pitch-derived coke is mainly used to make carbon and graphite electrodes equipped within electric arc furnaces for steelmaking, and mesophase pitch-derived coke (or needle coke) has an overwhelming advantage to

It can be clearly seen that mesophase pitch-derived coke exhibits a well-oriented texture as shown in **Figure 13(a, b)**, which is closely related to the formation and development of flow-type liquid crystalline in carbonaceous mesophase products during the process of delayed coking [5]. In contrast, coarse-grained mosaic texture is presented in the coke derived from commercial coal-tar pitch as shown in **Figure 13(c, d)** [16, 20]. Thus it can be concluded that the carbonaceous feedstocks have a significant influence on the optical texture and microstructure of resulting coke, which depends on the development and evolution of carbonaceous mesophase

produce graphite electrodes with high and ultrahigh power [5, 20].

**108**

**Figure 13.**

*pitch-derived coke (c, d).*

*(a, c) Optical photographs and (b, d) PLM micrographs of mesophase pitch-derived coke (a, b) and coal-tar* 

**Figure 15.**

*(a) Optical photograph and (b) PLM micrograph of carbon foam derived from naphthalene-based mesophase pitch.*

#### **5.4 Carbonaceous mesophase-based carbon fibers**

Mesophase pitch-based carbon fibers firstly reported by Singer in 1978 are the most successful high-end product for the development and application of carbonaceous mesophase, which are derived from spinnable mesophase pitch by melt spinning, oxidative stabilization, and carbonization and graphitization treatments [28]. The inherent alignment structure of liquid crystal molecules is preserved within the as-spun pitch fibers. Upon high-temperature graphitization, the graphite crystals are preferentially oriented along the fiber axis, so the final fibers have super high Young's modulus (up to a theoretical value of graphite, 1000 GPa) and excellent axial electrical (as low as 1.0 μΩ m in electrical resistivity) and thermal conductivity (exceeding 1000 W/m K). Thus they are now being widely used in aviation, aerospace, nuclear, and other high-tech fields, in which polyacrylonitrile-based carbon fibers have a certain limitation [3, 5, 29–33]. At present, only the United States (Cytec Industries Incorporated) and Japan (Mitsubishi Chemical Corporation and Nippon Graphite Fiber Corporation) have mature manufacturing technology ranging from the precursor materials to the final products (i.e., mesophase pitch, high-performance carbon fiber continuous filaments, and carbon fiber composites). The morphology of commercial carbon fibers usually includes three types of forms, i.e., continuous filament, chopped fiber, and ground fiber powder.

The round-shaped carbon fibers with different diameters and large-sized ribbon-shaped carbon fibers (sectional width ~2 mm, thickness ~10 μm) as shown in **Figure 16** can been successfully prepared from the AR mesophase pitch owing to its good spinnability. It is worthy to point out that most large-diameter carbon fibers with a radial transverse texture are inclined to spit in the subsequent high-temperature heat treatment. The ribbon-shaped carbon fibers can efficiently solve the crack problem and maintain their shape and structure without any damage. The carbon crystalline structure and layered orientation parallel to the ribbon main surface are obviously better than those of round fibers. The axial electrical resistivity and thermal conductivity of the round and ribbon fibers graphitized at 3000°C are measured to be as low as 1.1–1.30 μΩ m and about 900–1000 W/m K at room temperature [19, 34–36].

#### **5.5 Carbonaceous mesophase-based carbon composites**

Mesophase pitch-based carbon (graphite) fibers are often used as ideal functional fillers for preparing various carbon-based composites with high thermal conductivity [5, 37–41], which can be widely utilized in the field of thermal management [32, 33]. The thermal conductivity of these carbon-based composites depends not only on the

**111**

**Figure 16.**

C/C composites [41].

*Preparation, Characterization, and Applications of Carbonaceous Mesophase: A Review*

conduction performance of carbon fibers themselves and their loading amount, as well as laying or weaving architecture in the composites, but also on the physical properties of matrix materials involved (i.e., the resin, mesophase pitch, or pyrolytic carbon). In the previous work, the mesophase pitch-based graphite fiber (long filament) reinforced one-dimensional (as shown in **Figure 17(a)**–(**c)**) and two-dimensional ABS resin composites with a large size of 10 cm × 10 cm x 0.3–2 cm can reach a high thermal conductivity of ~500 W/m K [37, 38]. However, the thermal conductivity of composites reinforced by shortcut carbon fibers and milled fiber powders as shown in **Figure 17(d, e)** is only 10–20 W/m K, which can be used as heat paste or thermal grease for interfacial heat dissipation. Using various mesophase pitchbased graphite fibers (i.e., round-shaped and ribbon-shaped fibers) as a reinforcing filler and the same mesophase pitch as a binder, ultrahigh thermal conductivity (700–900 W/m K) of the one-dimensional C/C composites as shown in **Figures 18** and **19** could be realized [39, 40]. However, it is disadvantage to use phenolic resin as a binder to prepare high-thermal-conductivity materials owing to its non-graphitizable nature (i.e., a typical hard carbon) as shown in **Figure 20**. By comparison, the mesophase pitch-derived carbon after high-temperature treatment exhibits good crystallinity, high graphitization degree, and orderly stacked graphene sheets as shown in **Figure 18(d)**, which is very important to improve the directional thermal conductivity performance. It is worth noting that the pyrolytic carbon with a highly oriented texture deposited on the mesophase pitch-based graphite fibers as shown in **Figure 21** is also found to markedly increase the thermal conductivity of

*(a, c) Optical photographs and (b, d) SEM micrographs of round- (a, b) and ribbon-shaped carbon fibers* 

It is interesting to note that mesophase pitch is a promising binder (due to its good flow orientation performance in the molten state, easily graphitizable

*DOI: http://dx.doi.org/10.5772/intechopen.88860*

*(c, d) derived from naphthalene-based AR mesophase pitch.*

*Preparation, Characterization, and Applications of Carbonaceous Mesophase: A Review DOI: http://dx.doi.org/10.5772/intechopen.88860*

**Figure 16.**

*Liquid Crystals and Display Technology*

**Figure 15.**

*pitch.*

**5.4 Carbonaceous mesophase-based carbon fibers**

Mesophase pitch-based carbon fibers firstly reported by Singer in 1978 are the most successful high-end product for the development and application of carbonaceous mesophase, which are derived from spinnable mesophase pitch by melt spinning, oxidative stabilization, and carbonization and graphitization treatments [28]. The inherent alignment structure of liquid crystal molecules is preserved within the as-spun pitch fibers. Upon high-temperature graphitization, the graphite crystals are preferentially oriented along the fiber axis, so the final fibers have super high Young's modulus (up to a theoretical value of graphite, 1000 GPa) and excellent axial electrical (as low as 1.0 μΩ m in electrical resistivity) and thermal conductivity (exceeding 1000 W/m K). Thus they are now being widely used in aviation, aerospace, nuclear, and other high-tech fields, in which polyacrylonitrile-based carbon fibers have a certain limitation [3, 5, 29–33]. At present, only the United States (Cytec Industries Incorporated) and Japan (Mitsubishi Chemical Corporation and Nippon Graphite Fiber Corporation) have mature manufacturing technology ranging from the precursor materials to the final products (i.e., mesophase pitch, high-performance carbon fiber continuous filaments, and carbon fiber composites). The morphology of commercial carbon fibers usually includes three types of

*(a) Optical photograph and (b) PLM micrograph of carbon foam derived from naphthalene-based mesophase* 

forms, i.e., continuous filament, chopped fiber, and ground fiber powder. The round-shaped carbon fibers with different diameters and large-sized ribbon-shaped carbon fibers (sectional width ~2 mm, thickness ~10 μm) as shown in **Figure 16** can been successfully prepared from the AR mesophase pitch owing to its good spinnability. It is worthy to point out that most large-diameter carbon fibers with a radial transverse texture are inclined to spit in the subsequent high-temperature heat treatment. The ribbon-shaped carbon fibers can efficiently solve the crack problem and maintain their shape and structure without any damage. The carbon crystalline structure and layered orientation parallel to the ribbon main surface are obviously better than those of round fibers. The axial electrical resistivity and thermal conductivity of the round and ribbon fibers graphitized at 3000°C are measured to be as low as 1.1–1.30 μΩ m and about 900–1000 W/m K at room temperature [19, 34–36].

Mesophase pitch-based carbon (graphite) fibers are often used as ideal functional fillers for preparing various carbon-based composites with high thermal conductivity [5, 37–41], which can be widely utilized in the field of thermal management [32, 33]. The thermal conductivity of these carbon-based composites depends not only on the

**5.5 Carbonaceous mesophase-based carbon composites**

**110**

*(a, c) Optical photographs and (b, d) SEM micrographs of round- (a, b) and ribbon-shaped carbon fibers (c, d) derived from naphthalene-based AR mesophase pitch.*

conduction performance of carbon fibers themselves and their loading amount, as well as laying or weaving architecture in the composites, but also on the physical properties of matrix materials involved (i.e., the resin, mesophase pitch, or pyrolytic carbon).

In the previous work, the mesophase pitch-based graphite fiber (long filament) reinforced one-dimensional (as shown in **Figure 17(a)**–(**c)**) and two-dimensional ABS resin composites with a large size of 10 cm × 10 cm x 0.3–2 cm can reach a high thermal conductivity of ~500 W/m K [37, 38]. However, the thermal conductivity of composites reinforced by shortcut carbon fibers and milled fiber powders as shown in **Figure 17(d, e)** is only 10–20 W/m K, which can be used as heat paste or thermal grease for interfacial heat dissipation. Using various mesophase pitchbased graphite fibers (i.e., round-shaped and ribbon-shaped fibers) as a reinforcing filler and the same mesophase pitch as a binder, ultrahigh thermal conductivity (700–900 W/m K) of the one-dimensional C/C composites as shown in **Figures 18** and **19** could be realized [39, 40]. However, it is disadvantage to use phenolic resin as a binder to prepare high-thermal-conductivity materials owing to its non-graphitizable nature (i.e., a typical hard carbon) as shown in **Figure 20**. By comparison, the mesophase pitch-derived carbon after high-temperature treatment exhibits good crystallinity, high graphitization degree, and orderly stacked graphene sheets as shown in **Figure 18(d)**, which is very important to improve the directional thermal conductivity performance. It is worth noting that the pyrolytic carbon with a highly oriented texture deposited on the mesophase pitch-based graphite fibers as shown in **Figure 21** is also found to markedly increase the thermal conductivity of C/C composites [41].

It is interesting to note that mesophase pitch is a promising binder (due to its good flow orientation performance in the molten state, easily graphitizable

#### **Figure 17.**

*(a) Optical photograph, (b–d) PLM micrographs, and (e) SEM image of ABS resin composites reinforced by unidirectional (b, c) and disordered (d, e) mesophase pitch-based carbon fibers ((b, c) are, respectively, imaged perpendicular and parallel to the fiber axis).*

#### **Figure 18.**

*(a) Optical photograph, (b) PLM micrograph, and (c)–(e) SEM images of unidirectional carbon/carbon composites reinforced by mesophase pitch-based carbon fibers using mesophase pitch as a binder ((b)–(d) are imaged perpendicular to the fiber axis, and (e) is imaged parallel to the fiber axis).*

**113**

**Figure 20.**

**Figure 19.**

*Preparation, Characterization, and Applications of Carbonaceous Mesophase: A Review*

characteristic, etc.) for large-scale fabricating natural flake graphite-molded blocks by using the cheap and available natural graphite flakes as a raw material.

*(a) PLM micrograph and (b) SEM image of unidirectional carbon/carbon composites reinforced by mesophase* 

*(a) Optical photograph, (b, c) PLM orthogonal micrographs, and (d) SEM image of unidirectional carbon/ carbon composites reinforced by mesophase pitch-based ribbon fibers using mesophase pitch as a binder.*

preferred structural orientation perpendicular to the hot-pressing direction as shown in **Figure 22** and a high thermal conductivity of 500–600 W/m K in plane

possess a highly

The prepared graphite blocks with a high bulk density of 1.9 g/cm3

two-dimensional direction [42, 43].

*pitch-based carbon fibers using phenolic resin as a binder.*

*DOI: http://dx.doi.org/10.5772/intechopen.88860*

*Preparation, Characterization, and Applications of Carbonaceous Mesophase: A Review DOI: http://dx.doi.org/10.5772/intechopen.88860*

#### **Figure 19.**

*Liquid Crystals and Display Technology*

**112**

**Figure 18.**

**Figure 17.**

*imaged perpendicular and parallel to the fiber axis).*

*(a) Optical photograph, (b) PLM micrograph, and (c)–(e) SEM images of unidirectional carbon/carbon composites reinforced by mesophase pitch-based carbon fibers using mesophase pitch as a binder ((b)–(d) are* 

*(a) Optical photograph, (b–d) PLM micrographs, and (e) SEM image of ABS resin composites reinforced by unidirectional (b, c) and disordered (d, e) mesophase pitch-based carbon fibers ((b, c) are, respectively,* 

*imaged perpendicular to the fiber axis, and (e) is imaged parallel to the fiber axis).*

*(a) Optical photograph, (b, c) PLM orthogonal micrographs, and (d) SEM image of unidirectional carbon/ carbon composites reinforced by mesophase pitch-based ribbon fibers using mesophase pitch as a binder.*

**Figure 20.**

*(a) PLM micrograph and (b) SEM image of unidirectional carbon/carbon composites reinforced by mesophase pitch-based carbon fibers using phenolic resin as a binder.*

characteristic, etc.) for large-scale fabricating natural flake graphite-molded blocks by using the cheap and available natural graphite flakes as a raw material. The prepared graphite blocks with a high bulk density of 1.9 g/cm3 possess a highly preferred structural orientation perpendicular to the hot-pressing direction as shown in **Figure 22** and a high thermal conductivity of 500–600 W/m K in plane two-dimensional direction [42, 43].

#### **Figure 21.**

*(a) Optical photograph, (b) PLM micrograph, and (c) SEM image of unidirectional carbon/carbon composites reinforced by mesophase pitch-based carbon fibers using pyrolytic carbon as a "binder."*

#### **Figure 22.**

*(a) Optical photograph, (b) PLM micrograph, and (c) SEM image of natural flake graphite-molded blocks perpendicular to the hot-pressing direction using mesophase pitch as a binder.*
