Patent Description:
A typical process to perform boron nitride (BN) interphase coatings on silicon carbide (SiC) fiber tows is through chemical vapor deposition (CVD) via either a continuous tow coating or batch process. <CIT> discloses the continuous atmospheric pressure CVD coating of fibers in which a single tow or multiple tows are pulled through a cylindrical BN CVD reactor, where reactants are fed into the reactor either via co-feed or counter-feed mode with respect to the tow travel direction, achieving the interphase coatings on the tows. This process is known as an open CVD process, wherein the tow entrance and exit are open to ambient atmosphere. Exhaust from the CVD process can exit to the hood where the tow coater is located. Therefore, this process may generate potential environmental risk and may not meet current environmental, health, and safety (EH&S) standards.

<CIT> discloses a reel to reel coating system for forming a superconducting wire on a tape substrate.

The use of probes to detect marker gas is known in the context of vapor deposition coating, e. g from <CIT> and <CIT>.

One potential solution to overcome this issue is to add an effluent outlet at the end of the tow coater and to pull a slightly low pressure inside the tow coater through the outlet by a vacuum pump to direct the effluent to a scrubber to neutralize the exhaust. Thus, with this approach, the pressure in the coater is less than the surrounding ambient pressure (Pcoater<Pamb). This creates a different problem, however, in that the slight difference in pressure between the inside of the tow coater and the ambient atmosphere can pull ambient air into the tow coater through the tow entrance and/or exit, thus leading to an unintended oxygen content in the BN coatings, which is undesirable.

The invention provides a system for chemical vapor deposition as defined in claim <NUM>. Particular embodiments of this system are defined in claims <NUM>-<NUM>.

The invention further provides a method for chemical vapor deposition coating of fiber tows as defined in claim <NUM>. Particular embodiments of this method are defined in claims <NUM>-<NUM>.

In one disclosed configuration, a system for chemical vapor deposition coating of fiber tows, comprises a coater comprising a housing having a tow entrance and a tow exit and defining an interior space, the coater further comprising a process gas inlet and a process gas outlet; at least one of an entrance side marker gas inlet at the tow entrance and an exit side marker gas inlet at the tow exit; at least one of an entrance side detection probe upstream of the entrance side marker gas inlet, and an exit side detection probe downstream of the exit side marker gas inlet, the at least one entrance side detection probe and exit side detection probe being configured to detect marker gas.

In one non-limiting configuration, the system further comprises a pump communicated with the interior space of the coater whereby operation of the pump can be adjusted to adjust pressure in the interior space.

In a further non-limiting configuration, the system further comprises a take-off spool for feeding fiber tow to the tow entrance, and a take-up spool for receiving coated fiber tow from the tow exit.

In a still further non-limiting configuration, the system further comprises a source of marker gas communicated with the at least one entrance side marker gas inlet and exit side marker gas inlet.

In another non-limiting configuration, the source of marker gas comprises a source of an inert carrier gas containing a detectable fraction of detectible gas.

In still another non-limiting configuration, the source of marker gas comprises a source of nitrogen gas dosed with helium.

In a further non-limiting configuration, the at least one detection probe comprises a probe configured to detect helium.

In a still further non-limiting configuration, the system further comprises a control unit configured to receive input from the at least one detection probe and, upon receiving input indicating no marker gas detected, configured to operate the coater at a higher pressure in the interior space.

In another non-limiting configuration, the system further comprises a control unit configured to receive input from the at least one detection probe and, upon receiving input indicating no marker gas detected, configured to change operation of the pump to operate the coater at a higher pressure in the interior space.

In still another non-limiting configuration, the system comprises both of the entrance side marker gas inlet and the exit side marker gas inlet, and both of the entrance side marker gas detection probe and the exit side marker gas detection probe.

In another disclosed configuration, a method for chemical vapor deposition coating of fiber tows, comprises feeding a fiber tow to a tow entrance of a coater comprising a housing defining an interior space; feeding a chemical vapor deposition process gas to the coater at a process gas inlet such that fiber tow in the coater is coated to produce coated fiber tow; removing coated fiber tow from a tow exit of the coater; feeding a marker gas to at least one of an entrance side marker gas inlet at the tow entrance and an exit side marker gas inlet at the tow exit; and monitoring at least one of upstream of the entrance side marker gas inlet, and downstream of the exit side marker gas inlet, for presence of marker gas.

In another non-limiting configuration, the method further comprises adjusting pressure in the coater when the monitoring step does not detect marker gas.

In still another non-limiting configuration, the monitoring step comprises positioning at least one marker gas detection probe in the at least one of upstream of the entrance side marker gas inlet and downstream of the exit side marker gas inlet; and further comprising feeding output from the at least one marker gas detection probe to a control unit configured to operate the coater at a higher pressure when the output indicates no detection of marker gas.

In a further non-limiting configuration, a pump is associated with the interior space of the coater, and the control unit is configured to change operation of the pump to operate the coater at a higher pressure.

In a still further non-limiting configuration, the marker gas comprises an inert carrier gas dosed with a detectable amount of marker gas.

In another non-limiting configuration, the carrier gas is nitrogen.

In still another non-limiting configuration, the marker gas is helium.

In a further non-limiting configuration, the method further comprises removing the process gas from the coater at a process gas outlet of the coater.

In a still further non-limiting configuration, the method further comprises feeding process gas from the process gas outlet to a scrubber.

In another non-limiting configuration, the step of feeding the chemical vapor deposition process gas to the coater is carried out such that pressure inside the coater (Pcoater) is less than ambient pressure (Pambient) outside the coater (Pcoater < Pambient).

The present disclosure relates to coating fiber tows and applies broadly to continuous and batch processes. As discussed below, the present disclosure is particularly well suited to processes wherein the ends or other areas of the coater are open to ambient conditions, and therefore is particularly well suited to continuous fiber tow coating processes.

<FIG> shows a chemical vapor deposition coater <NUM> having a tow entrance <NUM> and a tow exit <NUM>. Fiber tow can be fed from a take-off spool <NUM> to tow entrance <NUM>, and coated fiber tow leaving the tow exit <NUM> can be taken up on a take-up spool <NUM>. In <FIG>, fiber tow passes through the open end at tow entrance <NUM> of coater <NUM>, is coated within coater <NUM> to produce coated fiber tow, and coated fiber tow passes through the open end at tow exit <NUM>.

Process gas for conducting the chemical vapor deposition (CVD) coating is fed to a process gas inlet <NUM>, and can be removed from a process gas outlet <NUM>, for example under operation of a vacuum pump <NUM>.

An inlet side marker gas inlet <NUM> can be positioned at the tow entrance <NUM> of coater <NUM>. Further, an exit side marker gas inlet <NUM> can be positioned at the tow exit <NUM> of coater <NUM>.

An inlet side detection probe <NUM> (or entrance side detection probe) can be positioned upstream of inlet side marker gas inlet <NUM>, and an exit side detection probe <NUM> can be positioned downstream of exit side marker gas inlet <NUM>. Upstream and downstream as used with respect to the positioning of probes <NUM>, <NUM> is with respect to the intended direction of flow at tow entrance <NUM> and tow exit <NUM>. In the non-limiting configuration of <FIG>, the upstream positioning of inlet side detection probe <NUM> means that probe <NUM> is positioned away from coater <NUM> with respect to marker gas inlet <NUM>. In a further non-limiting configuration, probe <NUM> (See also <FIG>) can be positioned at an inlet <NUM> of tow entrance <NUM>. In this configuration, tow entrance <NUM> can be an elongated member sized sufficiently to accept incoming tow. Entrance <NUM> can be tubular, or have other cross-sectional shape to accept the entering tow to be coated. In this regard, while it is possible to coat a single tow as schematically illustrated, it should be appreciated that tow entrance <NUM> and reactor <NUM> can be configured to process numerous strands of tow in parallel as desired. Positioning of probe <NUM> at inlet <NUM> to tow entrance <NUM> helps to make sure that any marker gas detected at probe <NUM> is flowing sufficiently away from the reactor, rather than just being detected as part of a possible eddying of flow around marker gas inlet <NUM>.

Further, the downstream positioning of the exit side detection probe <NUM> means that probe <NUM> is positioned away from coater <NUM> with respect to marker gas inlet <NUM>. In this regard, and in similar manner to the inlet side, probe <NUM> can be positioned near an outlet <NUM> of tow exit <NUM>. In this configuration, tow exit <NUM> can be an elongated member sized sufficiently to accept exiting coated tow. Exit <NUM> can also be tubular, or can have other cross-sectional shape to accept the exiting coated tow. In this regard, while it is possible to coat a single tow as schematically illustrated, it should be appreciated that tow entrance <NUM> and reactor <NUM> can be configured to process numerous strands of tow in parallel as desired. Positioning of probe <NUM> at outlet <NUM> from tow exit <NUM> helps to make sure that any marker gas detected at probe <NUM> is flowing sufficiently away from the reactor, rather than just being detected as part of a possible eddying of flow around marker gas inlet <NUM>.

In the configuration described above, the marker gas detection probes <NUM>, <NUM> detect for marker gas, and when they do detect marker gas, this is a good indication that flow from marker gas inlets <NUM>, <NUM> is flowing away from the reactor as desired.

In an alternative configuration, probes <NUM>, <NUM> could be positioned between marker gas inlets <NUM>, <NUM> and the reactor <NUM>. In this configuration, detection by the probes <NUM>, <NUM> of no marker gas would be a favorable indication that no flow was traveling from the marker gas inlets <NUM>, <NUM> toward the reactor <NUM>. Thus, in this configuration, the marker gas would be used to allow confirmation that no air with accompanying marker gas is flowing from inlets <NUM>, <NUM> toward reactor <NUM>.

A control unit <NUM> can be provided and communicated with probes <NUM>, <NUM> as well as, in this non-limiting configuration, pump <NUM>. Control unit comprises or has access to storage to store control software configured to receive input from probes <NUM>, <NUM>. Further, control unit <NUM> is configured with this software to change operation of the coating process, for example by changing operation of pump <NUM>, when no marker gas is detected by either or both of probes <NUM>, <NUM> in which case it can be deduced that fluid or gas flow in the entrance <NUM> and/or exit <NUM> is flowing in the wrong direction and oxygen can be entering the coater <NUM>. In such an event, pump <NUM> can be operated to increase pressure in the coater sufficiently that flow changes to the intended direction, and marker gas is detected at probes <NUM>, <NUM>. In the non-illustrated embodiment wherein the sensors are positioned toward the coater from the marker gas inlets <NUM>, <NUM>, these steps can be taken when marker gas is detected.

Ideally, coater <NUM> is operated with a slight vacuum with respect to ambient conditions surrounding the coater. This helps to keep process gases from escaping into the surrounding area and creating hazardous conditions. Further ideally, and as mentioned above, it is desirable to not have ambient air enter the coater, as this creates undesirable oxygen levels in the coating.

The positioning of marker gas inlets <NUM>, <NUM> and probes <NUM>, <NUM> allows detection of the flow conditions at the tow entrance <NUM> and tow exit <NUM>. If probes <NUM>, <NUM> detect marker gas, this means that the marker gas flow from inlets <NUM>, <NUM> is at least partially moving away from the coater, and therefore that ambient air is not leaking into the coater. If, on the other hand, either or both probes <NUM>, <NUM> do not detect the presence of marker gas, this means that the marker gas is flowing entirely toward the coater, and therefore that it is likely that some ambient air is also flowing in this direction. When this is the case, an increase in the pressure within the coater can help to restore flow conditions as desired and keep ambient air from leaking into the coater. In such a case, the process parameters such as tow coater pressure or nitrogen purge flow needs to be adjusted to assure that some nitrogen purge gas or marker gas is coming out of the tow entrance or exit based on the He detection system. Thus, when either or both of probes <NUM>, <NUM> detects no marker gas, operation of vacuum pump <NUM> can be modified, or some other steps taken, to mildly increase pressure within the coater. Control unit <NUM> can be programmed and configured to operate in this manner.

The marker gas can be entirely a gas that can be detected by probes <NUM>, <NUM>, or can be a carrier gas doped with a marker gas fraction that can be detected by probes <NUM>, <NUM>. In one non-limiting configuration, marker gas can be a nitrogen carrier gas doped with helium. In this regard, a concentration of helium in the carrier gas can be between about <NUM> ppm and about <NUM> ppm, and these limits can be selected to be reliably detected while minimizing the use of potentially costly helium. In both cases, the gases used are inert with respect to the coating process to limit impact on the composition of the coating. In one non-limiting configuration, the marker gas can be any gas that would be specific to the gas fed to inlets <NUM>, <NUM>, and that can be detected by a sensor. In one non-limiting configuration, this marker gas is helium, and the sensors are sensors configured to detect small concentrations of helium. Other configurations are possible within the broad scope of the disclosure.

The marker gas is referred to herein in places as being a purge gas. This is so because the gas can be introduced to the marker gas inlets at a flow rate and pressure sufficient to help keep ambient air away from the open ends of the coater. In this regard, marker gas can suitably be fed to the marker gas inlets at a flow rate of between <NUM> standard liter per minute (SLM) and <NUM> SLM and at a pressure of between <NUM> psi and <NUM> psi (<NUM> kPa to <NUM> kPa) (or <NUM> to <NUM> per minute at a pressure of <NUM> kPa and a temperature of <NUM>).

Typical fiber tow to be coated in this process can be silicon carbide fiber tows, for example. Other suitable fiber tows include carbon (C), silicon oxycarbide (SiOC), silicon nitride (Si<NUM>N<NUM>), silicon carbonitride (SiCN), hafnium carbide (HfC), tantalum carbide (TaC), silicon borocarbonitride (SiBCN), and silicon aluminum carbon nitride (SiAlCN), and alumina (Al<NUM>O<NUM>).

Typical process gas for use in CVD coating of fiber tow as disclosed herein can be process gas selected to deposit boron nitride coatings on the fiber tow. These gasses include, without limitation, boron trichloride (BCl<NUM>) and ammonia (NH<NUM>) mixed with inert gas such as nitrogen(N<NUM>), hydrogen(H<NUM>), argon (Ar), or mixtures thereof.

The relative pressures with respect to ambient and the coater can be, for example, <NUM> psi (<NUM> kPa) at room temperature. Inside coater <NUM>, this pressure can be kept slightly lower, for example between <NUM> psi (<NUM> kPa) and <NUM> psi (<NUM> kPa), to prevent escape of process gas out of the coater. Temperature within the coater will be between <NUM> and <NUM>.

<FIG> is an enlarged portion of <FIG> and shows in greater scale one of the marker gas inlets <NUM>, <NUM> and the possible directions in which the marker gas can flow. As shown, marker gas (schematically illustrated at arrow <NUM>) can be introduced into marker gas inlet <NUM>, <NUM> and, when this gas flow reaches tow entrance <NUM> and/or tow exit <NUM>, it can flow in either or both directions shown, that is, in a direction <NUM> toward coater <NUM>, and/or in a direction <NUM> that is away from coater <NUM>. If flow is in direction <NUM> only, then no marker gas will reach probe <NUM>-<NUM>, which will then signal the possibility that air is leaking into coater <NUM>. If any flow of marker gas is detected in direction <NUM>, then this is conclusive evidence that marker gas is flowing out of the coater <NUM>, and therefore that ambient air is not leaking into coater <NUM>. The direction of flow of marker gas introduced into inlet <NUM>, <NUM>, can be determined by a combination of the relationship between pressure in the coater and surrounding ambient pressure. In this regard, this relationship can be adjusted by adjusting the pressure in the coater. In addition, the relationship can be determined by a volume of flow through inlets <NUM>, <NUM>.

It should be appreciated that in addition to the marker gas sensors as disclosed herein, one or more oxygen sensors can be added to the system to supplement the ability to monitor for oxygen in the reactor and in some instances be able to reduce the number of relatively more expensive helium sensors that are needed.

<FIG> schematically illustrates a process in accordance with the present disclosure which can be used to provide in situ monitoring of the inlet and outlet of a coater <NUM> as disclosed herein. As shown, the process can start with the feeding of process gas into a coater as shown at step <NUM>. Once the process gas is in place, the coating process can be started by feeding the fiber tow to coater <NUM> as shown in step <NUM>. Coater <NUM> can be kept at process conditions suitable to have the process gasses make a deposit of a process gas materials on the fiber tow, thereby coating such fiber tow materials with a coating derived from the process gasses.

While the coating is conducted, a marker gas can be fed to inlets <NUM>, <NUM> as shown in step <NUM>. As discussed above, this marker gas reaches entrance <NUM> and exit <NUM>, and can flow in either or both of away from coater <NUM>, and toward coater <NUM>. This step is schematically illustrated at <NUM>.

Next, in step <NUM>, probes <NUM>, <NUM> can be used to monitor upstream of the inlet <NUM> and downstream of the inlet <NUM>, for example at inlet <NUM> and outlet <NUM>, for the presence of marker gas. As long as marker gas is detected, the process can proceed in a normal and steady state condition. However, the absence of marker gas at the monitored areas of inlets <NUM> and <NUM>, for example at inlet <NUM> and outlet <NUM>, means that the marker gas is flowing entirely toward the coater, and therefore it is possible or likely that ambient air is also flowing toward the coater.

If this is the case, then in step <NUM>, steps can be taken to increase pressure within the coater. This can be done by increasing purge flow rate of the marker gas if desired, or by decreasing the pressure within the coater for example by increasing operation of vacuum pump <NUM>, or the like.

The system and method disclosed herein offer a continuous atmospheric pressure CVD tow coater process with in-situ air leak monitoring using a He detection system. The proposed process can improve the performance and lifetime of ceramic matrix composite (CMC) materials because it can reduce detrimental oxygen content in the interface coatings by avoiding ambient air leaking into the tow coater.

The use of the terms "a" and "an" and "the" and similar references in the context of description (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or specifically contradicted by context. The modifier "about" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. It should be appreciated that relative positional terms such as "forward," "aft," "upper," "lower," "above," "below," and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting.

It should be appreciated that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be appreciated that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit from the subject matter disclosed herein.

Claim 1:
A system for chemical vapor deposition coating of fiber tows, comprising:
a coater (<NUM>) comprising a housing having a tow entrance (<NUM>) and a tow exit (<NUM>) and defining an interior space, the coater (<NUM>) further comprising a process gas inlet (<NUM>) and a process gas outlet (<NUM>);
at least one of an entrance side marker gas inlet (<NUM>) at the tow entrance (<NUM>) and an exit side marker gas inlet (<NUM>) at the tow exit (<NUM>);
at least one of an entrance side detection probe (<NUM>) upstream of the entrance side marker gas inlet (<NUM>), and an exit side detection probe (<NUM>) downstream of the exit side marker gas inlet (<NUM>), the at least one entrance side detection probe (<NUM>) and exit side detection probe (<NUM>) being configured to detect marker gas.