PHYSICAL MATHEMATICS SEMINAR


TOPIC:		Microware-enhanced Chemical Vapor Infiltration Processing-
		A Sharp Interface Model


SPEAKER:	BURT TILLEY
		Department of Mathematics
		Olin College

ABSTRACT:

Chemical Vapor Infiltration (CVI) into a fibrous preform has been
used to fabricate ceramic composite materials that are mechanically strong
and can withstand large operating temperatures.  Conventional heating
strategies used in this process require large amounts of energy and long
processing times. Microwaves, on the other hand, efficiently heat the
preform volumetrically and produce an inverted temperature gradient; the
surface of the preform is cooler than the interior because of the
convective and radiative heat loss.  Thus, the reaction rate is higher in
the interior of the preform and this causes the composite to grow from the
inside out. This configuration results in a more uniform product after the
completion of the process.

A simple one-dimensional model for describing CVI into a fibrous perform
is presented and analyzed.  The derivation requires that the thermal and
electrical properties of the preform and substrate are disparate.
Mathematically the model takes the form of a moving boundary problem,
where the boundary is the interface between the preform and the substrate.
Effects of heat loss and radiation at the boundaries and the nonlinear
dependence of dielectric parameters on temperature are all taken into
account, in addition to the spatial dependence on gas concentration.
Processing times for different power levels and inlet concentrations for
different initial substrate thicknesses are obtained, and the implications
to processing strategies are discussed.

DATE:		TUESDAY, MARCH 19, 2002

TIME:		2:30 PM

LOCATION:	Building 2, Room 338


Refreshments will be served at 3:30 PM in Room 2-349


Massachusetts Institute of Technology
Department of Mathematics
Cambridge, MA  02139