SYNTHESIS OF ALUMINA FROM ALUMINIUM TRIHYDRATE AS PRECURSOR OF YTTRIA-DOPED ALUMINA

• Main Author: CHRISTIO (NIM : 12514042), CLARISSA
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/26303
• Institution: Institut Teknologi Bandung

One of the characteristics of the Bayer process is the production of alumina trihydrate (ATH) during the precipitation stage as a precursor for the alumina production. In Indonesia, ATH is produced by PT Indonesia Chemical Alumina (PT ICA). ATH produced in PT ICA is expected to be utilized as engineered ceramic's raw materials. In recent years, the improvement of mechanical properties of alumina-based ceramic by doping with rare earth element has been realized by researchers. The doping of impurities or additive into structural ceramics has become one of the effective methods of tailoring various aspects such as grain size and shape, and grain-boundary structures and strengthening. The addition of yttria as a dopant that segregates to the Al2O3 grain boundaries can strongly affect the macroscopic properties of ceramics. In this study, the addition of yttria (Y2O3) to alumina that synthesized from ATH is performed. <br /> <br /> A series of yttria-doped alumina ceramic synthesis experiments have been performed to study calcination of ATH and the effect of dopant and sintering time on sintering characteristics, ceramics hardness, and fracture toughness. The effects of dopant and sintering time were studied on four different dopant concentrations of 0 ppm, 500 ppm, 1000 ppm, and 2000 ppm, sintering time of 2 hours, 3 hours, and 4 hours, at 1500°C. The experiment begins with the calcination of ATH into alumina that will be sintered with yttria into yttria-doped alumina. Samples that have been produced in this study were then characterized using XRD to determine the alumina phase formed after calcination, SEM-EDS to determine the morphology, sample grain size, and chemical composition of the sample. Vickers hardness tester to determine the hardness and fracture toughness of the samples. Optical microscope to observe and measure indentations and indentation cracks. <br /> <br /> The densification and hardness of the alumina ceramic samples increase with the increasing number of yttria dopants and sintering time. The highest densification and hardness values are obtained for 2000 ppm yttria doped sample, which was sintered for 4 hours with densification and hardness of 47,02% and 6,962 GPa, respectively. Thickness, diameter, mass, and volume shrinkages varied from 5,7%, 8,5%, 2,99%, and 22,7% to 11,6%, 12,4%, 6,86%, and 32,17%, respectively. There is an average increase in shrinkages with the increase in sintering time and this effect generally occurs in a normal sintering process. The dominant mass transfer mechanism in alumina ceramic sintering is the diffusion of the grain boundaries. The fracture toughness of alumina ceramic samples decreased with increasing number of yttria dopants and sintering time. The fracture toughness value (KIC) calculated using the Niihara equation is in the range 1,253 - 6,484 MPa.m1/2.