Coating processes – Measuring – testing – or indicating
Reexamination Certificate
1999-07-29
2002-02-05
Barr, Michael (Department: 1762)
Coating processes
Measuring, testing, or indicating
C427S255240, C427S255280, C427S255500
Reexamination Certificate
active
06344232
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to fiber coating chemical vapor deposition systems and methods and more particularly to a system for controlling coating composition deposited by fiber coating chemical vapor deposition.
Most ceramic matrix composites (CMCs) require a fiber interface coating in order to exhibit the desirable properties that make them potentially useful high-temperature structural materials. Although interface coatings are widely recognized as a key to these properties, fiber-coating technology has received relatively little attention, hindering successful application of CMCs. In today's search for new high-temperature structural materials and oxidation-resistant interfaces, the inability to deposit coatings of controlled chemistry, thickness, and morphology is a significant problem.
Chemical vapor deposition (CVD) is a well-known process, used commercially to deposit coatings, thin films and bulk materials for a variety of industrial applications. CVD is herein considered to apply a thin-film interface coating to a ceramic fiber for the production of ceramic matrix composites. Traditionally, CVD fiber coating has been hampered by problems such as poor coating uniformity, thickness, and chemistry control. The present invention helps to solve these problems in the art by providing a method and device for computer control of the coating process.
A prior art hot wall CVD reactor system capable of coating fiber in a continuos manner is shown in FIG.
1
. The hot wall CVD system of
FIG. 1
consists of a hot-walled reactor
102
consisting of a 2.54 cm diameter quartz tube ~30 cm in length which can be heated to 1200° C. At the front of the reactor
102
a 4-way stainless steel cross
103
connects the reactor
102
to the vaporizer
104
, inlet seal
105
, and the process gas inlet
106
. The stainless steel cross
103
, inlet seal
105
, and process gases, inlet at
106
, are all heated to inhibit condensation of the vaporized precursor. At the exit of the reactor
107
, a 5-way heated cross
108
is used to connect the reactor
102
to the outlet seal
109
, mass spectrometer capillary tube
110
and reactor exhaust
111
. The 1 m long capillary tube
110
, which connects the reactor exhaust gas to the mass spectrometer, is also heated.
The CVD reactor system of
FIG. 1
is prepared to operate by flushing solvent and an inert gas, such as Argon, from the liquid delivery pump system, through the piping system
103
and through the hot wall reactor
102
and by using a flush pump to pump an alcohol, such as ethanol, through the vaporizer
104
. The solvent performs a combination of functions including purging the vaporizer capillary tube and purging the system of unwanted elements to prepare it for passage of the precursor material to be deposited. A slight pressure differential of approximately one torr is maintained by the venturi pump
113
between the liquid delivery pump system at
104
and the piping receiving the exhaust gas shown at
111
which produces flow through the hot wall reactor
102
. The metal-organic precursor material is then deposited on the fiber in the hot-wall reactor
102
. The effluent flows through a burn box
117
heated to >500° C. before exiting into the hood. This ensures that any residual hydrocarbons are fully oxidized. The effluent is diluted with compressed air in the venturi pump
113
; thus excess oxygen is always available.
The present invention helps solve problems in the chemical vapor deposition fiber coating art of poor coating uniformity, thickness, and chemistry control. The device and method of the invention allows an operator to employ a CVD system as shown in
FIG. 1
while measuring exhaust gas composition in real time during the coating deposition. The present invention provides the capability to (1) automate the CVD fiber coating process via computer control/logging of all measurable parameters; (2) implement in situ sensors so as to measure coating or gas phase properties in real time; and (3) implement close-loop process control based on the sensor data, to produce coatings with improved composition and desired thickness. The consistency and repeatability of fiber coating, made possible by the insitu control of CVD of the present invention, makes CVD a more viable option for industrial applications.
Fiber coating chemical vapor deposition is attractive from an industry standpoint because it produces a fiber interface coating for ceramic matrix composites. These interface coatings make possible the desirable properties that make them potentially useful high-temperature structural materials. The present invention advances the state of the art in CVD fiber coating by making it repeatable, consistent and cost effective. As a practical matter, the present invention minimizes operator error, provides a record of any deviations in coating runs, and integrates all automation components using one computer.
SUMMARY OF THE INVENTION
The present invention provides a computer controlled fiber coating chemical vapor deposition system and method for generating substantially uniform coated fibers by maintaining chemical vapor deposition reactor temperature in real time. Reactor temperature is monitored by in situ temperature sensors. Reactor temperature is sensitive to oxygen levels and oxygen levels within the reactor are varied in response to temperature sensor data. Closed loop process control software maintains reactor temperature at a preselected value resulting in predictable fiber coatings of a preselected thickness, crystallinity and chemistry.
It is therefore an object of the invention to provide a fiber coating chemical vapor deposition system capable of consistently producing fiber coatings of a predictable composition.
It is another object of the invention to provide a computer automated fiber coating chemical vapor deposition system and process.
It is another object of the invention to provide a fiber coating chemical vapor deposition system employing in situ temperature sensors to monitor and maintain reactor temperature in real time.
It is another object of the invention to provide a fiber coating chemical vapor deposition system capable of varying oxygen flow within the reactor based on in situ temperature measurements to in turn maintain reactor temperature at a preselected value.
These and other objects of the invention are described in the description, claims and accompanying drawings and are achieved by a computer control, fiber coating chemical vapor deposition method for generating substantially uniform coated fibers comprising the steps of:
threading a thin-film interface coating receiving fiber through a hot-walled reactor chemical vapor deposition system;
computer controlled setting up and heating of an inert gas containing precursor material liquid delivery system, precursor material vaporizer and said hot-walled reactor;
maintaining a computer controlled pressure differential between precursor material and reacting gas entering said hot-walled reactor and exhaust gas exiting said hot-walled reactor, reactor gas flowing through said hot-walled reactor dependent on said pressure differential;
providing a flow maintaining temperature sensor within said hot-walled reactor, said temperature sensor communicating with a process control computer;
exposing said thin-film interface coating receiving fiber to an oxygen containing reacting gas atmosphere within said hot-walled reactor, a chemical reaction therebetween resulting in ceramic compound deposition on said thin-film interface coating receiving fiber;
process control computer comparing of data from said temperature sensor with a preselected setpoint temperature;
varying oxygen flow into said oxygen containing reacting gas atmosphere within said hot-walled reactor proportionate to a variance between data from said temperature sensor and said preselected setpoint temperature in said process control computer whereby said temperature in said hot-walled reactor chemical vapor deposition system increases with increased
Jero Paul D.
Jones John G.
Barr Michael
Hollins Gerald B.
Kundert Thomas L.
The United States of America as represented by the Secretary of
Tollefson Gina S.
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