Kinetics of the zirconium--carbon reaction at temperatures above 2000$sup 0$C

Abstract

The reaction between liquid zirconium and graphite at temperatures above 2000 C has been investigated. The reaction products were found to be carbon saturated zirconium metal and ZrC which formed between the graphite and the metal. Parabolic growth behavior was observed for the ZrC phase at all temperatures of this investigation. The parabolic growth constant at temperatures between 2000 and 2860 C was measured 2 to be 1.83 exp (-84,300/RT) cm /sec. The reaction mechanism was proposed to be the rapid carbon saturation of the liquid metal and the formation of ZrC at the metal-carbide interface with diffusion of carbon through the ZrC the "rate determining step" of the reaction. The concentration independent diffusion coefficient of carbon in ZrC, (D), was proposed to be 0. 95 exp (-78, 700/RT) cm /sec. This value was calculated using the temperature invariant ZrC phase fields proposed in the literature. The Zr(liq)l-Zr(liq) + ZrC I phase boundary over the temperature range 2000 to 2800 C was determined. The ZrC + C eutectic temperature was found to be 2890 + 50 C.

Reaction kinetics and ablation properties of C/C–ZrC composites fabricated by reactive melt infiltration

“…On the other hand, the carbon diffusion through ZrC layer at high temperatures is fast. As indicated by Adelsberg et al [21], the growth rate of ZrC layer by carbon diffusion at the temperature of 2000 8C is about 10 Â ffi ffi t p mm=min. The distribution of apertures in the porous C/C preform (Fig.…”

“…It is determined by the reaction between zirconium and carbon. According to Adelsberg's study [21], zirconium reacts with carbon to form a ZrC layer quickly and carbon will then diffuse through the layer to grow ZrC. The growth process is controlled by carbon diffusion.…”

Microstructural development of a Cf/ZrC composite manufactured by reactive melt infiltration

“…Zr-C binary phase diagram. 17 In an earlier work by Adelsberg et al, 16 the kinetics of the zirconium-carbon reaction at temperatures above 2000 • C were studied, the thickness of the continuous ZrC layer as a function of time and temperature was obtained, at each temperature investigated from 2000 • C to 2860 • C. The results showed that the ZrC phase grew parabolically into the carbon-saturated liquid, which is indicative of diffusion-controlled reaction. It was demonstrated that this was controlled by carbon diffusion through the ZrC.…”

“…15 In addition, the C solubility in Zr at the eutectic temperature (∼1.0 at.%) is much higher than that of C in Si (1.8 × 10 −4 at.%). 8,16 Only when the carbon concentration increases to ∼38.5 at.%, can ZrC form through the reaction between Zr and C, however, for the Si-C system, SiC forms through the reaction between C and Si only when the carbon concentration reaches 50 at.%. According to the lever law, the mass ratio of residual silicon to silicon carbide in the eutectic is much larger than that of residual zirconium to zirconium carbide in Zr-ZrC.…”

High temperature corrosion of carbon/carbon composites in Zr–Ti melts during liquid metal infiltration

“…In this work, the carbon matrix with a thickness in the range of 80-100 m would be consumed in the reaction. In fact, the corrosion depth is controlled by carbon diffusion in the carbide according to the study conducted by Adelsberg [28] and Zeng et al [25]. With increasing temperature and holding time, the carbon diffusion increases, which results in the increasing thickness of the carbide and the increasing corrosion depth of the carbon matrix.…”