The effect of pressure and temperature on the microstructure and mechanical properties of polycrystalline graphites

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dc.contributor.advisorAllen, Colinen_ZA
dc.contributor.authorVan der Riet, Clement Daviden_ZA
dc.date.accessioned2016-09-06T14:40:57Z
dc.date.available2016-09-06T14:40:57Z
dc.date.issued1995en_ZA
dc.description.abstractA study has been made of the effects of combinations of pressure and temperature ori six polycrystalline, synthetic graphites, in the high pressure domain (> 1 GPa).The graphites were investigated in three different conditions: (1) the "as received" condition (AR condition),(2) after exposure to pressures of about 3 GPa at room temperature (in a piston-cylinder device – PC condition) and (3) after exposure to temperatures of about 1500°C at pressures of about 5.5 GP a (high temperature- high pressure, or HTHP, condition). Their microstructures have been compared on the basis of X-ray diffraction measurements to determine their crystallite sizes (L˳ and L˳), interplanar spacings (c and a) and textures. Optical and scanning electron microscopy were used to examine their fracture surfaces and macro porosity. Mercury porosimetry provided a means of establishing the pore size distribution of pores of less than 20 1-1m diameter. Bulk and skeletal densities were determined from mercury porosimetry and helium pycnometry respectively. The effects of PC and HTHP conditioning on their mechanical properties, were measured by both uniaxial compression fracture tests, and by electrical resistivity measurements. In addition, the triaxial behavioursof the six graphites in the AR condition were evaluated from piston-cylinder compression tests. All the isopressed graphites were found to have very similar crystallite sizes, interplanar spacings and textures in the AR condition. The extruded graphite had larger crystallite dimensions, and was slightly less isotropic, than the other grades. Fracture occurred due to cleavage of the basal planes of crystallites in the filler particles or binder. The size, shape and orientation of filler particles and porosity with respect to the applied stress field determined whether fracture was intergranular, or trans granular, in nature. Limited basal plane slip and sub-critical microcracking caused uniaxial compressive stress-strain curves typical of those of polycrystalline graphites,i.e. convex with respect to the strain axis. Fracture strengths and strains were related to the proportion of amorphous, intercrystallite bonding and, to a lesser extent, to porosity.en_ZA
dc.identifier.apacitationVan der Riet, C. D. (1995). <i>The effect of pressure and temperature on the microstructure and mechanical properties of polycrystalline graphites</i>. (Thesis). University of Cape Town ,Faculty of Engineering & the Built Environment ,Centre for Materials Engineering. Retrieved from http://hdl.handle.net/11427/21683en_ZA
dc.identifier.chicagocitationVan der Riet, Clement David. <i>"The effect of pressure and temperature on the microstructure and mechanical properties of polycrystalline graphites."</i> Thesis., University of Cape Town ,Faculty of Engineering & the Built Environment ,Centre for Materials Engineering, 1995. http://hdl.handle.net/11427/21683en_ZA
dc.identifier.citationVan der Riet, C. 1995. The effect of pressure and temperature on the microstructure and mechanical properties of polycrystalline graphites. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Van der Riet, Clement David AB - A study has been made of the effects of combinations of pressure and temperature ori six polycrystalline, synthetic graphites, in the high pressure domain (> 1 GPa).The graphites were investigated in three different conditions: (1) the "as received" condition (AR condition),(2) after exposure to pressures of about 3 GPa at room temperature (in a piston-cylinder device – PC condition) and (3) after exposure to temperatures of about 1500°C at pressures of about 5.5 GP a (high temperature- high pressure, or HTHP, condition). Their microstructures have been compared on the basis of X-ray diffraction measurements to determine their crystallite sizes (L˳ and L˳), interplanar spacings (c and a) and textures. Optical and scanning electron microscopy were used to examine their fracture surfaces and macro porosity. Mercury porosimetry provided a means of establishing the pore size distribution of pores of less than 20 1-1m diameter. Bulk and skeletal densities were determined from mercury porosimetry and helium pycnometry respectively. The effects of PC and HTHP conditioning on their mechanical properties, were measured by both uniaxial compression fracture tests, and by electrical resistivity measurements. In addition, the triaxial behavioursof the six graphites in the AR condition were evaluated from piston-cylinder compression tests. All the isopressed graphites were found to have very similar crystallite sizes, interplanar spacings and textures in the AR condition. The extruded graphite had larger crystallite dimensions, and was slightly less isotropic, than the other grades. Fracture occurred due to cleavage of the basal planes of crystallites in the filler particles or binder. The size, shape and orientation of filler particles and porosity with respect to the applied stress field determined whether fracture was intergranular, or trans granular, in nature. Limited basal plane slip and sub-critical microcracking caused uniaxial compressive stress-strain curves typical of those of polycrystalline graphites,i.e. convex with respect to the strain axis. Fracture strengths and strains were related to the proportion of amorphous, intercrystallite bonding and, to a lesser extent, to porosity. DA - 1995 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 1995 T1 - The effect of pressure and temperature on the microstructure and mechanical properties of polycrystalline graphites TI - The effect of pressure and temperature on the microstructure and mechanical properties of polycrystalline graphites UR - http://hdl.handle.net/11427/21683 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/21683
dc.identifier.vancouvercitationVan der Riet CD. The effect of pressure and temperature on the microstructure and mechanical properties of polycrystalline graphites. [Thesis]. University of Cape Town ,Faculty of Engineering & the Built Environment ,Centre for Materials Engineering, 1995 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/21683en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentCentre for Materials Engineeringen_ZA
dc.publisher.facultyFaculty of Engineering and the Built Environment
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherMaterials Engineeringen_ZA
dc.titleThe effect of pressure and temperature on the microstructure and mechanical properties of polycrystalline graphitesen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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