**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

*Silicon Materials*

monolithic ceramics.

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

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.

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added drop by drop to the GO suspension above. Centrifugation was used to separate the products which were then washed out several times with cyclohexane. The solid samples thus obtained are denoted as (Ceramics Oxide)x/GO. (Ceramic Oxide) x/GO was dispersed again in 50 ml cyclohexane and then transferred to a 100 ml Teflon-lined stainless-steel autoclave for hydrothermal reaction. After the reaction was carried out, samples denoted as (Ceramic Oxide)x/rGO. (Ceramic Oxide)x/ rGO was then calcinated at a temperature above 700 K for a specific interval of time to form Ceramics Oxide/rGO hybrids. Graphene-ceramics hybrid powder containing different wt.% of rGO were obtained using the same method. Hot pressing of ceramics-graphene hybrid powder was performed in a vacuum furnace (model number OTF-1200X-VHP4). The flowchart fabrication scheme of gamma aluminarGO hybrid with detailed experimental conditions is represented in **Figure 1**.

### **Figure 1.**

*Flow chart fabrication scheme for γ-Al2O3-rGO hybrids.*

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**Figure 3.**

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

obtained using specific temperature and hot pressing conditions.

**Figure 2** shows the fabrication flowchart of silica-rGO hybrids, which are

**3. Physical properties of alumina-graphene hybrids for technological** 

TGA (shown in **Figure 3**) of γ-Al2O3-rGO powder samples show that different calcination times has led to different concentrations of rGO in the hybrids. The TGA curves of all hybrids show a stable weight loss between 400 and 600°C, as a result of the removal of all carbon-related materials, and other impurities (if any) after heating these hybrids to 800°C in an air atmosphere. For the samples with 3-, 2- and 1-h calcination time, the 7.705, 12.830 and 16.707 wt.% loss were calculated.

SEM image in (**Figure 4a**) for bare Al2O3 shows particles like morphology. The size of particles has ranged from 500 nm to few micrometers. TEM image in (**Figure 4b**) shows elongated nanocrystals or nanorods of bare Al2O3. Sample before calcination but after autoclave heating has been referred as Al(O)x/rGO. SEM image of Al(O)x/rGO after heating in an autoclave at a temperature of 453 K for 6 h but before calcination is shown in the **Figure 4c**. Even after calcination at 723 K for 2 h, the SEM image in **Figure 4d** shows the same particle like morphology but size of particles has ranged from 1 micrometers to few micrometers. TEM image of γ-Al2O3-rGO hybrids after calcination at 723 K for 2 h is shown in the **Figure 4e**. It shows elongated and fine nanorods of γ-Al2O3 with rGO layer in hybrids. The TEM image in **Figure 4e** indicates the presence of a very thin rGO layer, which acts as a

The presence of rGO can also be confirmed by closely observing **Figure 4e**. In this figure, low-contrast features are actually edges or small portions of the graphene sheet (**Figure 4e**) on which γ-Al2O3 is uniformly distributed in dense concentrations. Further, the selected area electron diffraction pattern presented in **Figure 4f** shows the inter-planar spacing's of D = 0.175 nm and D = 0.151 nm, corresponding to the (200) and (111) planes of γ-Al2O3. The fabrication of the γ-Al2O3 phase was

*TGA curves of γ-Al2O3-rGO hybrids using calcination time of 1, 2 and 3 h in air atmosphere up to 800°C.*

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

**and applied applications**

continuum matrix in these hybrids.

For 1-h sample, the unique weight loss is observed.

*Flow chart fabrication scheme for SiO2-rGO hybrids.*

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

**Figure 2** shows the fabrication flowchart of silica-rGO hybrids, which are obtained using specific temperature and hot pressing conditions.
