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contributor.authorSarkar, D-
contributor.authorAdak, S-
identifier.citationSynthesis and Thermo-Mechanical Properties of Sol-Gel Derived Zirconia Toughened Alumina Nanocomposite, Doctoral Thesis, submitted to NIT Rourkelaen
descriptionCopyright for the thesis belongs to NIT Rourkelaen
description.abstractAl2O3-ZrO2 composite precursor powder containing 5-15mol% ZrO2 is prepared by wet chemical route. The washed gel containing pseudoboehmite and amorphous zirconia are characterized with respect to DTA/TG, XRD and IR spectroscopy. In the calcined powder phase evolution of Al2O3 follows the sequence: pseudoboehmite → bayerite → boehmite → -Al2O3 → -Al2O3 → -Al2O3; while that of ZrO2 follows amorphous ZrO2 → t-ZrO2 → (t + m)-ZrO2. However, the crystallization behavior of aluminum-hydroxide is somewhat affected with addition of zirconia. FTIR study reveal the number of M-OH and M-O bond increases on increasing mol% of ZrO2 due to a change in the cationic charge of the composite powder. The formation of amorphous material before crystallization can also be predicted from TEM study, where particle exhibits different morphology; and show smooth, distinct and faceted surfaces at different temperature. A bimodal particle size distribution is observed because of both unagglomerated and partial agglomerated particles in the range from15 to 210nm for highest zirconia content, however, the specific surface area of powder decreases with increasing zirconia content. The addition of 5wt% uncalcined precursor enhances the consolidation process. The sintered zirconia toughened alumina nano-composite with 98% relative density has been achieved at 1550oC for 4h. The average grain size ratio dAl2O3/dZrO2 varies in between 4.35 for Al2O3-5ZrO2 and 2.29 for Al2O3-15ZrO2, whereas average grain size of alumina and zirconia in Al2O3-10ZrO2 composite are 360nm and 125nm respectively. EPMA confirms the near uniform distribution of zirconia particles in the alumina matrix. For homogenous dispersion of ZrO2 in Al2O3, the optimum amount of ZrO2 is found to be 10mol% and up to the critical amount of ZrO2 addition, flexural strength and fracture toughness increase and the size of the intergranular zirconia strongly influences these properties. The room temperature fracture strength of these composite varies within ~500 to 700MPa, but drastic decrease of high temperature strength for lowest zirconia containing specimen is observed above 6000C, where transformation toughening is no longer effective. The elastic modulus and hardness, both the properties decrease with ZrO2 content. Thermal shock study reveals the retained flexural strength varies with zirconia content. The hystersis effect in the dilatation curve due to t→m transformation is also influenced by the grain size of ZrO2en
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publisherNational Institute of Technology, Rourkelaen
titleSynthesis and Thermo-Mechanical Properties of Sol-Gel Derived Zirconia Toughened Alumina Nanocompositeen
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