DYNAMICS OF WETTING IN REACTIVE METAL CERAMIC SYSTEMS - LINEAR SPREADING/

The kinetics of wetting in the reactive pure aluminium/vitreous carbon (Cv) system was investigated by the sessile drop technique in high va cuum. It was found that the curve showing the radius of the metal drop base R as a function of time t consisted of a central part where the radial spreading of the drop is a linear function of time, and two ext remal parts where significant deviations from Linearity are observed. By characterising the Al/Cv interface at different stages of the proce ss, both far from and close to the Al/Cv/vapour triple line, it is sho wn that (i) in the linear spreading regime wetting kinetics is control led by a nearly 2D reaction between Al and Cv at the triple line, form ing aluminium carbide; and (ii) linearity is closely associated with s teady-state growth of the carbide at the triple line. At the beginning of the wetting process, deoxidation of the Al drop and, thereafter, t ransient-state growth of carbide, cause considerable deviations from l inearity in the R(t) curve. Moreover, at the end of spreading, when th e contact angle tends towards the steady contact angle of the system, a deviation from linearity is also observed and attributed to the roug hness of the reaction product. Finally, examples from the literature a re given suggesting that linear spreading may be effective in many rea ctive metal-on-metal and metal-on-ceramic systems. Copyright (C) 1996 Acta Metallurgica Inc.