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contributor.authorMohapatra, Deepak-
contributor.authorSarkar, D (Guide)-
identifier.citationProcessing of MgO-MgAl2O4 Ceramics and Study of its Microstructure, Strength and Thermal Shock resistance, Thesis submitted in partial fulfillment of the requirements for the degree of the Master of Technology by Research in Ceramic Engineering, to National Institute of Technology, Rourkelaen
descriptionCopyright for the thesis belongs to National Institute of Technology Rourkelaen
description.abstractMgO rich spinel precursor containing Al2O3 : MgO in weight proportions of 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4 is prepared by solid-state reaction route. The processed and calcined powders are characterized by Particle Size analysis, X-ray diffraction analysis and sintering behavior. The processed and calcined powder exhibits a bimodal distribution because of the presence of partially agglomerate and unagglomerated particle. However, the average particle size varies from 6.84μm to 3.48μm with increasing milling time. The optimized milling time and subsequent particle size are found 60h and 3.48μm respectively. In the calcined powder spinel phase evolution starts around 1000oC and follows an increasing trend in crystallinity and spinelization with increasing temperature. The crystallite size is 19nm for lowest calcination temperature and lowest content of MgO and gradually increases with increasing temperature and maximum 33nm has been detected for powder with highest MgO content at 1300oC for 2h. Initial calcination temperature and spinel seeds affect the densification as well as the extent of spinelization in the sintered bodies. The relative density after sintering at 1600oC for 4h varies between 96-98% for Al2O3 : MgO=1:1, whereas composition with highest MgO content exhibits this variation within the range of 95-97%. Low spinel seeding calcined batches show better densification. Microstructure reveals presence of non-uniform grains and inter-granular pores at lower calcination temperature and substantial grain growth is observed in higher calcination temperature. Random grain orientation and increased inter-granular porosity is responsible to deteriorate the density of high content of MgO powder when sintered after calcination at 1300oC. The mechanical properties of MgO rich spinel composites containing preformed spinel are more strongly influenced than the in-situ formed spinel composites by sintering temperature, volume fraction and particle size of spinel. The hardness of the MgO rich spinel composites is ~13.5GPa, which continuously decreases (13.7–12.1GPa) with the increase of spinel phase at sintered specimen. Higher amount of seed addition has an adverse affect on the hardness of the composites due to coarsening of the spinel grains and formation of subsequent porosity. The compressive strength (147-107MPa) is affected by the thermal expansion mismatch between spinel and x MgO and the partial bonding between MgO and spinel grains. The large amount of in-situ spinel seeding as a result of higher calcination temperature has a detrimental effect on strength values. The flexural strength of sintered specimens at room temperature as well as the retained strength of sintered specimens after 3cycles of thermal spalling has been measured. Both the tests have been carried out in 3-pt. loading system. The flexural strength is noted to be around ~137MPa for sintered specimen (with 70% spinel content) and has been found to decrease with increasing MgO content. The improved resistance (5-12% of original strength) to thermal shock in the ceramics is attributed to the the presence of higher amount of MgAl2O4 spinel at higher calcination temperature and microcrack network interlinking. The large thermal expansion coefficient difference between MgO and spinel, leads to extensive microcracking in ceramic materials with loss in strength values, when MgO content is higher.en
format.extent3904937 bytes-
publisherNational Institute of Technology, Rourkelaen
titleProcessing of MgO-MgAl2O4 Ceramics and Study of its Microstructure, Strength and Thermal Shock resistanceen
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