Young's Moduli of Compact Matrices for HTGR Fuel

Abstract

Young's moduli of matrices of compacted graphite samples were determined from measured values of ultrasonic-wave propagation through the sample at room temperature. The results were analyzed with particular interest directed to the effects of differences in matrix density and graphite orientation on the propagation velocity, from which the modulus was calculated. The characteristics of the matrices were observed by X-ray diffractometry on the crystallite sizes, and the shapes of the graphite powders constituting the main substance of the compact matrices were scrutinized by scanning electron microscope. The value of Young's modulus was found to increase with binder content in the matrices constituted uniquely of one kind of graphite material, while in the case of composite matrices embodying a mixture of petroleum coke graphite and natural graphite, the modulus decreased with increasing natural graphite content. The velocity of ultrasonic-wave propagation—from which the value of Young's modulus is derived—depends on the density alone in isotropic matrices prepared from milled isotropic coke graphite, whereas in anisotropic matrices embodying needle coke graphite it depends on graphite orientation as well as on density. The contributions of density (p) and of reflective intensity ratio (IR) to the propagation velocity (V) are expressed ΔV=a (Δo) n and ΔV=b (ΔIR), where the symbol Δ indicates increment, while a, b and n are constants depending upon the characteristics of the compact matrix.