  A wealth of experimental data indicate that while capillarity controlled
infiltration gives an infiltration length that varies with the square root of
time, reactive infiltration is characterised by a linear relationship between
the two magnitudes. In addition the infiltration rate in the latter is at least
two orders of magnitude greater than in the former.
  This work is addressed to investigate imbibition of a non-wetting, albeit
reactive, liquid into a capillary, within the framework of a simple model that
includes capillarity effects, viscosity and gravity. The capillary radius is
allowed to vary, due to reaction, with both position and time, according to
either an interface or a diffusion law. The model allows for capillary closure
when reaction kinetics dominates imbibition. At short times, and depending on
whether infiltration is capillarity or gravity controlled, the infiltrated
length varies either as the square root or linearly with time. This suggest the
following track for reactive infiltration: i) In most cases, the contact angle
is initially larger than $90^\circ$, ii) after some time, reaction gradually
replaces the interface liquid/preform by the liquid/reaction product interface
and, concomitantly, the contact angle gets closer to $90^\circ$, iii) beyond
that time, gravity triggers infiltration (actually the contact angle does not
need to be smaller than $90^\circ$ for the initiation of infiltration due to
the metallostatic pressure exerted by the liquid metal on top of the porous
preform), iv) thereafter infiltration is controlled by viscosity and gravity,
provided that, due to reaction, the contact angle remains close to that at
which infiltration was initiated.

Soft Condensed Matter;Fluid Dynamics