Characterization and control of the fiber-matrix interface in ceramic ...

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furnace. The furnace is, therefore, loaded from the bottom and is
completely sealed using O-rings.
The furnace is resistively heated using a graphite element and
single-phase alternating current, Power is supplied by a 50 KVA
transformer, which is regulated by a silicon-controlled rectifier (SCR).
The SCR receives a corrt:rol signal from a number of sources that are
dependent on processing options. The temperature of the furnace can be
maintained utilizing either internal thermocouples or an ext;c?rnal
pyrometer, The device outputs are fed to a proportional controller.
Alternatively, the furnace can he operated in a manual model.
The critical components of the infiltration apparatus are the watercooled
injector and t-he graphite holder (Figure 9.2). The water-cooled
gas injector is composed of several concentrlc stainless steel tubes,
connected to form separate gas and water passages. The fibrous preform
is positioned atop the wat:er-cooled surface and is held in place hy an
outer perimeter lip and a cylindrical graphite chamber. The chamber also
acts to isolate the heating element from the reactant gases. The upper
section of the gas distibutor is protected by the graphite chamber and
the lower areas are insulated with graphite felt.
The injector i s
spring-loaded from the bottom such that the inner chamber is pressed
against the inner-surface water-cooled lid. Grafoil" gaskets at the
injector and holder surfaces seal the internal workings, forcing all
gases to flow through the preform.
The seals also hinder gas flow to the
heating element, and the element region is purged with argon to provide
*Union Carbide, Danbury , Connecticut.