Zirconia Transport by Liquid Convection during Oxidation of Zirconium Diboride–Silicon Carbide

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65610/1/j.1551-2916.2007.02142.x.pd

Thermal properties of zirconium diboride ceramics

This presentation will focus on the thermal conductivity of zirconium diboride ceramics. Previous reports of thermal conductivity values for ZrB2 vary from as low as about 30 W/m•K to over 100 W/m•K without any direct evidence to identify the reasons for the variations. Our group systematically investigated the effects of transition metal impurities, which led to the discovery that the size of the dissolved impurity species was directly related to the decrease in thermal conductivity. Analysis of the electron contribution to thermal conductivity utilizing the Wiedemann-Franz methodology led to the conclusion that both the phonon and electron contributions were affected by dissolved metallic impurities. Further, the effects of some transition metals including Ti and Y were masked by other impurities in ceramics produced from commercial ZrB2 powders. Please click Additional Files below to see the full abstract

Mechanical properties of zirconium diboride ceramics

This presentation will focus on the mechanical properties of zirconium diboride ceramics. Diboride ceramics offer a combination of properties that include high elastic modulus, hardness, strength, and moderate fracture toughness to elevated temperatures. However, like all structural ceramics, their mechanical properties are controlled by microstructure wherein grain size, dispersion and size of second phases, and impurities limit their potential use at elevated temperatures, particularly for proposed extreme environment applications at temperatures exceeding 2000°C. As an example, the flexure strength of nearly phase pure ZrB2 ranges from 300 to \u3e600 MPa at room temperature but retains a strength of \u3e300 MPa at temperatures \u3e1500°C. Further, the fracture toughness of ZrB2 ceramics is generally low, typically in the range of 3 to 4 MPa-m1/2, at both room and elevated temperatures. Please click Additional Files below to see the full abstract