Processing, compatibility and oxidation of diboride-reinforced oxide matrix composites for ultrahigh-temperature applications

 
 
 
 

Processing, compatibility and oxidation of diboride-reinforced oxide matrix composites for ultrahigh-temperature applications

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dc.contributor.advisor Vedula, K. M. en_US
dc.contributor.author Abada, Ahmed en_US
dc.date.accessioned 2008-07-10T15:08:04Z
dc.date.available 2008-07-10T15:08:04Z
dc.date.created 1990 en_US
dc.date.issued 2008-07-10T15:08:04Z
dc.identifier.uri http://rave.ohiolink.edu/etdc/view?acc_num=case1055184368 en_US
dc.identifier.uri http://hdl.handle.net/2374.OX/17512
dc.description Promising results for the development of a ceramic/ceramic composite to be used for structural applications in the ultra high temperature range (1650-1850°C) have been obtained for alumina reinforced with titanium or zirconium diboribe coated with molybdenum disilicide. Prior to this achievement, several theoretical and experimental studies of particulate composites with (TiB2 or ZrB2) imbedded in (ZrO2, Y2O3 or Al2O3) were conducted. Calculations of the compatibility and stability of oxide matrices with the diborides in vacuum showed positive energies of formation, indicating suitability of reinforcement of alumina under vacuum conditions. Also, since the sublimation of vapor species at ultra high temperatures is very critical to the stability of substances still existing in their condensed states, a detailed thermodynamic analysis of the metal-oxygen systems, was carried out using elemental data of the TiB2, ZrB2, ZrO2, Y2O3, Al2O3, MoSi2 and their combinations (TiB2 or ZrB2)/(ZrO2, Y2O3 or Al2O3) for comparison, at 1650, 1850 and 2050°C. A comparison of the combination TiB2 and ZrB2 in Mo Si2/(Al2O3 or ZrO2) at 1650°C was also made. A stability analysis using equilibrium oxygen partial pressures for the TiB2 and ZrB2 decomposition at 1650, 1850 and 2050°C was carried out. A detailed characterization of the powders used for the oxide matrices, the diborides and the molybdenum disilicide are presented. The effects of the powder characteristics and the vacuum hot pressing parameters on the densification of the composites are discussed. Stability and chemical compatibility of the particulate and ternary composites in their as hot pressed states and following their vacuum and air oxidation treatments were characterized. Interdiffusion of elemental species across diboride/disilicide and oxide/disilicide interfaces was studies by EDS dot mapping. It is proposed that the growth of the Mo5Si3 is interface reaction controlled. It is proposed that diffusion of atmospheric gaseous oxygen through the porous texture left by the initial reaction of the oxide and diboride to form volatile B2O3 accounts for the continued erosion of the structure. (Abstract shortened with permission of author. en_US
dc.format application/pdf en_US
dc.format 254p. en_US
dc.rights unrestricted en_US
dc.rights Copyright and permissions information available at the source archive en_US
dc.subject Processing compatibility oxidation diboride reinforced oxide matrix composites ultrahigh temperature application en_US
dc.title Processing, compatibility and oxidation of diboride-reinforced oxide matrix composites for ultrahigh-temperature applications en_US
dc.type Electronic Thesis or Dissertation en_US
dc.degree.name PhD en_US
dc.degree.level doctoral en_US
dc.degree.discipline Materials Science & Engineering en_US
dc.degree.grantor Case Western Reserve University en_US
dc.contributor.publisher Case Western Reserve University / OhioLINK en_US

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