LTPCM-INP Grenoble, UJF, URA 29, BP 75, 38402, Saint Martin d’He`res, Cedex, France(Received December 29, 1997)(Accepted January 14, 1998)IntroductionHigh-temperature capillary phenomena intervene in many material processing operations, includingbonding operations such as soldering and brazing, and infiltration processes used to produce metal orceramic matrix composites. Of particular importance in this class of processes is the issue of wettingof solids by molten inorganic materials: good wetting, as manifest by a low contact angle of the liquidon the solid in the processing environment, drives flow of the liquid over the solid and eases processingsignificantly. This issue has therefore motivated a large body of research aimed at developing methodsfor improving wetting in high-temperature systems of practical interest. Results from contact anglemeasurements, and also from process development work, indicate that chemical interaction between thesolid and the liquid tends to promote good wetting (1–5).Wetting is usually characterized by measurement of contact angles in sessile drop experiments,wherein a drop of the liquid is placed at fixed temperature on a smooth and flat substrate of the solid.When interfacial reactions drive wetting, these cause transitions with time in the contact angle while thetriple line advances at a rate determined by the rate of reaction product formation along the substratesurface (e.g., (6–9)): reactive wetting is thus generally a dynamic phenomenon. It is customarilyassumed in the interpretation of sessile drop data that the wetting process is isothermal, even in dynamicsituations typical of reactive wetting; however, interfacial reactions encountered in high-temperaturematerials processing can be highly exothermic. These could, therefore, cause a significant increase inthe local temperature at the triple line and, hence, influence both reaction kinetics and capillary forcesin reactive wetting.We examine here this influence using a simplified description of the problem, in which we take therate of heat evolution behind the triple line of solid/liquid/vapor contact to be constant and limited intime, and the wetting process to be fully steady-state. More specifically, we address two very basicsituations, encountered both in materials processes and in experimental measurements of wetting. Thefirst is that of a liquid spreading over a bulk solid substrate, typical in particular of sessile dropexperiments; the second is that of a liquid infiltrating a porous solid such as a preform of fibers orparticles, or a thin capillary. We seek, in the most simple and general terms possible, to assess whetherheat evolution at reacting interfaces could cause significant departures in the local temperature at thetriple line.