| Popis: |
A series in this journal on high-temperature properties of “fracture-resistant ultralloys for space-power systems” preceded the present paper: the antecedent publications covered tungsten(W), rhenium(Re) alloys with and without thoria(ThO2) (W, 23Re; W, 27Re; W, 30Re and W, 30Re, 1ThO2). This paper reports radiative and thermionic effects of hafnium carbide(HfC) and Re variation in W alloys: normal spectral emissivity( ϵ λ ) is used in pyrometry to determine the true temperature of a surface. Effective work function ( φ e ) is an important consideration in the selection of the electrode materials for high-temperature thermionic energy converters in space-power applications. The e 0.535μ , ϵ 0.65μ and φ e trends of W, Re, 0.35HfC with 5–20% Re were measured in the range of 1700–2500K. The results indicate that ϵ λ decreases with increasing temperatures and Re contents. The presence of HfC produced higher ϵ λ values than those of sintered materials with comparable W,Re alloy contents. The results also indicate that φ e increases with rhenium contents. This can be explained as growth of the potential barrier at the metal, vacuum boundary associated with a volume effect—the decrease in the lattice constant of W. |
