Stablization of Zirconia Using Different Experimental Methods and their Applications

Abstract

Zirconia ceramics have received much attention due to its good mechanical strength, good thermal properties, biocompatibility and white color. These properties make zirconia more suitable for orthopedic and maxillofacial implants. Among three phases of zirconia (monoclinic, tetragonal and cubic), tetragonal zirconia is more suitable for implants and coatings, but tetragonal zirconia is stable at higher temperatures and transforms to monoclinic phase upon cooling. This research includes preparation and characterizations of zirconia coatings and nanostructures. Different routes of sol-gel preparation were used. Detailed study was carried out to optimize gelation agent, pH and molarity of the sol. Samples were prepared at different molarities (0.025, 0.050, 0.075, 0.10 and 0.125M) in acidic (pH 2) and basic mediums (pH 9) using three different gelation agents (NaOH, NH3 and NH4OH). Un-doped and doped zirconia nanostructures and coatings were studied in this research work with water as solvent. Molarity of the sol had a significant effect on the volume fraction of tetragonal zirconia content with a relatively small crystallite size <30nm. pH of the sol also played an important role for tetragonal zirconia formation; pH of zirconia sol was varied from 1 to 11. Optimization of stabilized tetragonal zirconia under as-synthesized conditions was obtained for samples prepared at molarity 0.1M in basic medium (pH 9) using NH3 as gelation agent. Fourier transform infrared spectroscopy (FTIR) results were consistent with XRD data that confirmed the formation of phase pure tetragonal zirconia under as-synthesized conditions. SEM micrographs revealed the formation of well-separated and well-defined nanoparticles of size range 30-50 nm that is compatible for implants. Along with thermal stability problem another drawback of zirconia is lack of bonding with body fluid. In order to increase its bonding strength some organic additives (Glucose and Fructose) have been added in zirconia. Nanowires of zirconia with diameter of 8nm were observed in case of organic additive zirconia with hardness ~1500HV. Effect of biocompatible dopant Fe3O4 in zirconia sol for stabilization of tetragonal content has also been studied to increase its application area. Fe3O4 was used as a dopant with acidic (pH 4) and basic (pH 10) nature with 2-10wt%. Pure tetragonal zirconia content has been observed under XRD study at 8-10wt% of basic (pH 10) nature. It is worth mentioning that biocompatible Fe3O4 has been used for the first time for stabilization of tetragonal zirconia. This optimized zirconia was coated on teeth that were soaked in several foods and beverages. Results reveal that after coatings teeth show no loss to enamel and weight even in strong acidic and basic mediums.