Systematic Studies Of Enhanced Physical Properties Of Ceramics Graphene Nanostructures Assembly Prepared By Solvothermal/Hydrothermal And Hot-Pressing Process

This Ph.D.dissertation deals with the fabrication of ceramics-graphene nanostructures assembly and systematic studies on enhanced physical properties of hybrids.This Ph.D.dissertation contains two main parts.In the first part,a solvothermal method is employed first time to fabricate hybrids composed of cross-linked ?-Al2O3nanorods and reduced graphite oxide?rGO?platelets.After calcination and hot-press processing,monoliths of Al2O3-rGO hybrids are obtained with improved physical properties.It is found that the oxygen-containing groups on graphene oxide benefit to the adsorption of Al-?OC3H7?3?aluminum Isopropoxide?,leading to the uniform dispersion of rGO with Al2O3 which is hydrolyzed from aluminum Isopropoxide in solvothermal reactions.The hybrid processed at 3-h calcination time shows an electrical conductivity of 6.7 ×101 S ·m-1,simultaneously with 90%higher mechanical tensile strength and 80%higher thermal conductivity,compared to the porous Al2O3.The dielectric constant of the hybrid is 12 times higher than that of the porous Al2O3.In this work,highest values of electrical conductivity?8.2 ×101 S·m-1?,thermal conductivity?2.53 Wm-1 k-1?,dielectric constant?104?and young modulus?3.7 GPa?are determined for alumina-rGO hybrid which is processed at 1-h calcination time.The physical properties are best,which we are reporting in this work,compared to the previous reports and studies of alumina-rGO hybrids.Further,XRD characterizations show that the increase in calcination temperature and further hot-press processing at 900? leads to the enhanced crystallinity of ?-Al2O3 nanorods in the hybrid,resulting in enhanced physical properties of the hybrids.Moreover,the detailed effect of calcination and hot pressing conditions have been discussed on the alumina nanostructures,and on the crystallinity of the hybrids.In the second part of Ph.D.research work,we have extended our research methodology to another ceramics-graphene nanostructure assembly i.e.silica-rGO hybrids,by optimizing experimental conditions for the hydrothermal and hot pressing process.Hydrothermal-hot press processed monolithic SiO2 spheres and reduced graphite oxide?rGO?platelets are obtained with enhanced physical properties.After calcination and hot-press treatments,monolithic spheres of SiO2 and rGO platelets hybrids are achieved with improved physical properties.In this case,it is found that the oxygen-containing groups on graphene oxide benefit to the adsorption of ethyl silicate?C8H20O4Si?,leading to the uniform dispersion of rGO platelets with SiO2 spheres which is hydrolyzed from ethyl silicate during hydrothermal reactions.In this work,best physical properties such as high electrical conductivity?0.143 S·m-1?,thermal conductivity?1.612 Wm-1k-1?,dielectric constant?107?,BET surface area?712.01 m2g-1?,and tensile strength?225.74 MPa?are measured for SiO2-rGO hybrid which processed at 1-h calcination time.With 1.55 wt.%rGO,the SiO2-rGO hybrid shows a significant enhancement in electrical conductivity?0.02 S·m-1?,simultaneously with thermal conductivity?1.439 Wm-1k-1?,dielectric constant?500?,tensile strength?98.02 MPa?,and BET surface area?611.21 m2g-1?,compared to the electrical conductivity?1.9×10-6 S·m-1?,thermal conductivity?1.34 Wm-1k-1?,dielectric constant?3.79?,tensile strength?75.79 MPa?,and BET surface area?333.07 m2g-1?of the bare SiO2.XRD characterizations show that the increase in calcination temperature and further hot-press processing at 750? leads to the enhanced crystallinity of SiO2 spheres and rGO platelets in the hybrid,which is a significant factor for the improved physical properties of the SiO2-rGO hybrids.Further,the effect of calcination and hot pressing conditions are discussed on the crystallinity of the hybrids.This research work has introduced a method of hybrids preparation?which is not reported before for ceramics-graphene assembly nanomaterials i.e.?-Al₂O₃-rGO,SiO2-rGO hybrids?by the use of solvothermal/hydrothermal-hot pressing methods.Further,we have made complete systematic studies on enhanced physical properties of the hybrids.This research has a significant contribution for the applications of ceramics-graphene assembly nanomaterials which can be further applied as electrolytes,catalysts,conductive,electrochemically active,and as dielectric materials for the high-temperature applications due to enhanced physical properties.