**1. Introduction**

In recent years, hybrid nanostructures have achieved great technological interest, because of the ability of the nanostructures which intends to design and manufacture hybrid materials with enhanced physical properties [1, 2]. For a desired technological application, various excellent properties can be combined into a single hybrid nanostructure, this is an excellent feature of the hybrid nanostructures. Moreover, in hybrid nanostructures, the enhanced electronic interactions among various types of components are possible, which is the main reason to enhance the physical properties of hybrids [3, 4]. In ceramics-graphene hybrids, enhanced physical properties can be used in the high electrical, mechanical, and thermal applications, because of higher electrical conductivity, thermal conductivity, dielectric and better mechanical properties [5]. Due to the versatile physical and chemical properties [6, 7], graphene has opted in huge scientific activities in

progress of research and development for the field of science and technology. The combination of suitable electrical, mechanical, thermal, and physical properties can apply not only for a broad spectrum of applications but also as a basic essential unite for the fundamental and advanced technological research [8, 9]. In hybrids or composite, scientists worldwide have been impressed by the unique combination of individual physical properties of graphene [8], that makes graphene an ideal option, or as an advanced component in both the hybrids as well as composites. For monolithic ceramics, in particular, physical properties of graphene have been researched and investigated as an ideal component in the monolithic ceramicsgraphene hybrids or composite [10, 11]. Due to the higher strength, stiffness, and high-temperature stability, monolithic ceramics are used and known commonly as a very promising structural material for mechanical and high-temperature applications [12, 13]. But the field of application is still vacant due to mechanical unreliability, and very lower electrical conductivity, and limited physical properties of the monolithic ceramics.

Due to graphene's extraordinary physical properties [14, 15], incorporating graphene in the ceramics can have great potential for electro-conductive, and high mechanical applications. In graphene-ceramics hybrids, enhanced physical properties could be implemented in a wide range of the material related applications in the field of aerospace, processing industries, and military based applications. [16, 17] In view of the fabrication routes [17, 18], development of the graphene ceramic hybrids is still complicated due to reinforcement particle at a very nanometric scale. For fabrication methodology, practical issues can be classified into wide categories such as (1) in ceramic nanostructures, homogenous dispersion of the graphene is important for enhanced physical properties; (2) easy processing route of grapheneceramics hybrids or nanocomposites is necessary; (3) interfacial bonding and interaction between graphene and ceramic nanostructures are very important as it directly reduces the physical properties of the graphene-ceramics hybrids or nanocomposites. For ceramics-graphene hybrids, uniform dispersion of the graphene in the ceramic matrices is an important factor [12]. Due to the high surface area of graphene [8], proper graphene dispersion is a very important factor, which further ensures efficient load transfer between graphene and available ceramics nanostructures in the hybrids. This is major concerns during the incorporation of graphene in the ceramics, due to the higher surface area of graphene [6]. For this purpose, scientists have used various dispersing agents [19, 20]. The use of dispersing agent gives rise to higher surface potential, double layer formation, as well possibility of strong electrostatic repulsion, which helps to uniform dispersion of graphene in graphene-ceramics hybrids. Mechanical dispersion of graphene is possible through many routes such as ultra-sonication, ball milling, and stirring [7, 21].

The enhanced physical properties of graphene-ceramic materials depend upon many factors such as thin layers of graphene, fine particles size and phase homogeneity [22]. For graphene-ceramics hybrids, well aligned and controlled nanostructures are important in toughening of hybrids. In literature, there are available many fabrication ways of graphene-ceramics hybrids such as powder processing, colloidal processing and sol-gel fabrication. In most of the work on graphene-ceramics by conventional powder routes, physical properties are not as good as expected because graphene is prone to agglomeration due to van der Waals forces. Therefore, in this chapter, our focus is on new solvothermal-hot press method, which is used to fabricate alumina-rGO, and silica-rGO hybrids, with a systematic study on enhanced physical properties of the hybrids for efficient application. In hybrids, the physical properties are enhanced by a great degree, because of use of calcination conditions, as well as the hot-pressing conditions. The two structural ceramics, which we will discuss in this chapter, are alumina and silica, respectively.

**161**

*Ceramics (Si- and Al-Based Oxides)-Graphene Hybrids and Advanced Applications*

Ceramics usually have a brittle attribute with low strength [11]. Among many ceramics, alumina is one of the widely used structural ceramic due to the shaping capability, and the good thermal conductivity [12]. Alumina has applications in the field of high-speed cutting tools, dental implants and insulators [13, 14]. To improve the mechanical properties, carbon nanotubes have been used to enhance the fracture toughness (by a degree of 94%), hardness (by a degree of 13%), and flexural strength (by a degree of 6.4%) of the alumina [15]. Ball-milled alumina/ zirconia/graphene composite has been investigated with 40% enhanced fracture toughness by adding the graphene platelets [16]. In another work, alumina-rGO nanocomposites have been fabricated by the dry sol-gel method, from which it was indicated that BET surface area of rGO is essential to enhance the surface charge properties of hybrids [17]. In another work, alumina-graphene composite films have been reported with low optical gap (1.53 eV) [18]. Alumina-rGO nanocomposite by in-situ deposition have shown morphologies of nanoparticles of alumina

Alumina/rGO/poly(ethylenimine) composite has been used to capture carbon dioxide from the flue gas [20]. In a microwave preparation of alumina-rGO composites, the grain size of alumina matrix was reduced to 180 nm compared to 475 nm of the conventional sintering process, leading to an increase in Young's modulus of 180 from 148 GPa under the same measurement condition [21]. In this chapter, we will discuss the preparation of hybrids consisting of γ-Al2O3 nanorods and rGO by a solvothermal method. This solvothermal method is used to form hybrids composed of cross-linked γ-Al2O3 nanorods and reduced graphite oxide (rGO) platelets. With further hot pressing, a hybrid monolith has been made for the systematic study on

The second structural ceramics, which we will discuss in this chapter, is silica. Among various kinds of the ceramics, silica particles are one of the widely used additive ceramic due to its functionalized ability and stability with a range of materials [23, 24]. Silica has various applications in the domain of polymer, biomedical, and composite engineering [25]. To improve the physical properties, rGO has been

and dielectric constant (77.23) of epoxy/SiO2/rGO hybrid [26]. In another work, in-situ sol-gel processed silica nanoparticles decorated with graphene oxide sheets are obtained, from which it was found that presence of rGO is essential to improve the corrosion resistance, dispersion, and the barrier properties of hybrid [27]. In another work, SiO2-graphene hybrids have shown superior gas sensing response (31.5%) towards 50 ppm NH3 for 850 s, in comparison to rGO based sensor (1.5%) [28]. Using one-step hydrothermal method, SiO2-rGO nanohybrid has shown

efficiency [29]. SiO2 supported polyvinylidene fluoride has shown high dielectric constant (72.94) and low dielectric loss (0.059), which is due to the addition of ultrathin graphene [30]. Among the field of diverse inorganic particles, still, there is need to do much of scientific research for enhanced physical properties of silica-

**2. Experimental setup/fabrication route for ceramics-graphene hybrids**

There are many fabrication methods for graphene-ceramics materials. Here in this chapter, In brief, the preparation of ceramics-graphene hybrids was done by mixing GO with cyclohexane and corresponding metal alkoxide followed by a solvothermal reaction. For the preparation, 0.1 g of GO was firstly dispersed in 35 ml cyclohexane, after which desired amount of corresponding metal alkoxide was

g<sup>−</sup><sup>1</sup>

K<sup>−</sup><sup>1</sup>

g<sup>−</sup><sup>1</sup>

and the low porosity [19].

), storage modulus (3.56)

) and 98.8% Cr(VI) adsorption

*DOI: http://dx.doi.org/10.5772/intechopen.85575*

structures on rGO with BET surface area of 242.4 m2

enhanced physical properties of the hybrids.

used to enhance thermal conductivity (0.452 Wm<sup>−</sup><sup>1</sup>

comparatively better BET surface area (676 m2

carbon based hybrids.

### *Ceramics (Si- and Al-Based Oxides)-Graphene Hybrids and Advanced Applications DOI: http://dx.doi.org/10.5772/intechopen.85575*

Ceramics usually have a brittle attribute with low strength [11]. Among many ceramics, alumina is one of the widely used structural ceramic due to the shaping capability, and the good thermal conductivity [12]. Alumina has applications in the field of high-speed cutting tools, dental implants and insulators [13, 14]. To improve the mechanical properties, carbon nanotubes have been used to enhance the fracture toughness (by a degree of 94%), hardness (by a degree of 13%), and flexural strength (by a degree of 6.4%) of the alumina [15]. Ball-milled alumina/ zirconia/graphene composite has been investigated with 40% enhanced fracture toughness by adding the graphene platelets [16]. In another work, alumina-rGO nanocomposites have been fabricated by the dry sol-gel method, from which it was indicated that BET surface area of rGO is essential to enhance the surface charge properties of hybrids [17]. In another work, alumina-graphene composite films have been reported with low optical gap (1.53 eV) [18]. Alumina-rGO nanocomposite by in-situ deposition have shown morphologies of nanoparticles of alumina structures on rGO with BET surface area of 242.4 m2 g<sup>−</sup><sup>1</sup> and the low porosity [19]. Alumina/rGO/poly(ethylenimine) composite has been used to capture carbon dioxide from the flue gas [20]. In a microwave preparation of alumina-rGO composites, the grain size of alumina matrix was reduced to 180 nm compared to 475 nm of the conventional sintering process, leading to an increase in Young's modulus of 180 from 148 GPa under the same measurement condition [21]. In this chapter, we will discuss the preparation of hybrids consisting of γ-Al2O3 nanorods and rGO by a solvothermal method. This solvothermal method is used to form hybrids composed of cross-linked γ-Al2O3 nanorods and reduced graphite oxide (rGO) platelets. With further hot pressing, a hybrid monolith has been made for the systematic study on enhanced physical properties of the hybrids.

The second structural ceramics, which we will discuss in this chapter, is silica. Among various kinds of the ceramics, silica particles are one of the widely used additive ceramic due to its functionalized ability and stability with a range of materials [23, 24]. Silica has various applications in the domain of polymer, biomedical, and composite engineering [25]. To improve the physical properties, rGO has been used to enhance thermal conductivity (0.452 Wm<sup>−</sup><sup>1</sup> K<sup>−</sup><sup>1</sup> ), storage modulus (3.56) and dielectric constant (77.23) of epoxy/SiO2/rGO hybrid [26]. In another work, in-situ sol-gel processed silica nanoparticles decorated with graphene oxide sheets are obtained, from which it was found that presence of rGO is essential to improve the corrosion resistance, dispersion, and the barrier properties of hybrid [27]. In another work, SiO2-graphene hybrids have shown superior gas sensing response (31.5%) towards 50 ppm NH3 for 850 s, in comparison to rGO based sensor (1.5%) [28]. Using one-step hydrothermal method, SiO2-rGO nanohybrid has shown comparatively better BET surface area (676 m2 g<sup>−</sup><sup>1</sup> ) and 98.8% Cr(VI) adsorption efficiency [29]. SiO2 supported polyvinylidene fluoride has shown high dielectric constant (72.94) and low dielectric loss (0.059), which is due to the addition of ultrathin graphene [30]. Among the field of diverse inorganic particles, still, there is need to do much of scientific research for enhanced physical properties of silicacarbon based hybrids.
