US3365330A - Continuous vapor deposition - Google Patents

Description

Jan. 23, 1968 R. HOUGH 3,365,330

CONTINUOUS VAPOR DEPOSITION Filed May 28, 1964 ,2, v 2; Q7 k qp m I l5 l6 III INVENTOK fflLP/Y L 19006 United States Patent 3,365,330 CDNTHNUOUS VAPOR DEPOSITION Ralph L. Hough, Springfield, Ohio, assignor to the United States of America as represented by the Secretary of the Air Force Filed May 28, 1964, Ser. No. 371,140 Claims. (Cl. 117-201) ABSTRACT OF THE DKSCLOSURE Method and apparatus for continuously passing a tungsten strand substrate from a feed spool to within a vapor deposition chamber containing boron trichloride and hydrogen and a pair of mercury contact electrodes energized electrically to a deposition temperature of boron on the substrate, and passing the coated wire out of the chamber to a storage spool.

The invention described herein may be manufactured and used by or for the United State Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to a method and an apparatus for accomplishing vapor deposition on a substrate and particularly to the formation of long filaments by the continuous vapor deposition of a coating upon one or more filamentous substrates.

At least since the development of the incandescent electrio light bulb, the manufacture of filaments has been practiced by a variety of processes. With the steadily increasing prominence of the vacuum tube and, still more recently, with the advent of filament-Wound components such as ablative rocket engine casings and the like, the desires and demands for exotic modifications of filamentary materials and their properties have received steadily increasing attention. Particularly in the case of applications requiring long filaments as in almost all uses involving windings in one form or another, the art has resorted to a continuous process for the pyrolytic deposi tion of a coating upon a moving filamentary substrate which is sufficiently heated as it moves through the deposition chamber to cause the coating material with which the vapor is laden to undergo a gas phase reaction and plate out upon the substrate surfaces. A

The most advanced of these processes to date have relied for heating the substrate upon the passage of an electric current through it. This has, of course, requned the maintenance of electrical contact with the filament at a minimumof two spaced points along its length; and it follows that this method, particularly as practiced in the continuous formation of filaments of substantial lengths, has been limited to substrates and to coatings which are electrically conductive. As a result of these limitations to a disappointingly small number of materials, the filamentforming art has been substantially retarded. Moreover the efliciency, reliability and economy of the prior art vapor deposition processes, even when conductive substrates and coatings have been used, have left much to be desired.

It is accordingly an object of this invention to provide an improved method for continuous vapor deposition.

A more specific object of the invention is to provide 3,365,339 Patented Jan. 23, 1968 a universal method for continuous deposition upon a sub strate as it passes through a vapor laden with a coating material.

Yet another object of the invention is to provide such a. method which will be more economical than those heretofore practiced, particularly with regard to the more efiicient use of the heat energy utilized therein.

Yet another object of the invention is to provide a method for the pyrolytic vapor deposition of a coating upon a moving filamentary substrate wherein either or both of the substrate and the coating may be a wide vari ety of materials including electrical insulators.

Yet another object of the invention is the provision of an apparatus for practicing the method of this invention. These and other objects and advantages which will appear from a reading of the following disclosure are achieved by the juxtaposition of a plurality of substantially parallel substrates in the form of filaments, strips, strands, sheets or the like, at least a part of which are electrical conductors, within a vapor deposition chamber and electrically energizing at least some of such conductors for heat radiating temperature control. The temperature of these heat radiating conductors will be thereby elevated by electrical resistance or ohmic heating, and they in turn will radiate heat to the neighboring substrates which will thereupon and thereby be raised to a temperature at which a plating reaction may take place upon their surfaces, even though the filaments absorbing heat energy from the heat radiating filaments are not electrical condoctors and are not capable of being resistance heated.

In one modification of the invention, the maximum influence and most efiicient utilization of heat and electrical energy is achieved by the close spacing between the non-conductive substrates and the radiators and providing the interior of the deposition chamber, preferably near the substrates, with an inwardly or substrate-directed reflective or re-radiating surface such as a chromium plated surface or the like.

Depending upon a variety of circumstances including the particular substrates and coatings to be employed, the heat required for the gas-phase surface plating reaction, and the like, some or all of those substrates which are electrically conductive and supply the radiant heat may be held in a fixed position while those upon which the deposition of the coating is desired are moved continuously through the chamber. This procedure has been particularly desirable and is the only known method for the continuous pyrolytic deposition of a non-electrically conductive coating material. Since the electrically conductive radiating units are themselves within the chamber and are heated, they will of course be coated by the same electrically insulating coating which, if they were moved, would separate them from contact with the electrode upon which they depend for their electrical and heat energy. Where they are stationary, however, means can easily be provided to protect these radiators from the deposition of the insulative coating at least at the points where they are in contact with the electrodes.

- In other situations, particularly where an electrically conductive coating is being deposited upon a substrate which may be either an electrical conductor or an electrical insulator, the substrates being coated and the heatradiating substrates (whether or not they also are intended to be coated and so utilized thereafter) may move continuously through the deposition chamber in the same direction whether or not at different speeds of travel. In this siutation of course, the radiators will not lose their necessary contact with the electrical source since electricity will continue to pass through their conductive coatings.

By the addition of one more step in a further modification of the procedure according to this invention; viz, the preliminary passage of a leader of an electrically conductive material affixed to and trailed by the nonconductive material, the deposition of the electrically conductive coating upon the non-conductive substrate, though started by the resistance heating of the leader, may be continued on by the resistance heating of the coating even though the substrate itself carries no electricity. Even without a leader, however, comparable results can be achieved by a variant of this technique wherein electrically conductive substrates are introduced at one end of the deposition chamber and move in a direction opposed to that of the electrically non-conductive substrates introduced at the other end of the chamber.

When a electrically conductive coating is sought to be deposited upon all of the substrates in this modification of the method, the result will be that, as the conductive substrates pass through the chamber and acquire a greater thickness upon the buildup of the coating which is also electrically conductive, the increased flow of electricity in response to the same potential difference or voltage will provide more resistance heating thereby imparting greater radiating heat to influence the temperature of and the pyrolytic deposition upon the substrates that are electrical insulators.

The greater radiation from the electrically conductive substrates will of course take place just as the coated strands are leaving the vapor chamber, but this is the same point at which the non-conductive substrates are entering the chamber and are devoid of any deposited coating. The greatest amount of radiant heat is therefore available to heat the insulators and to cause the beginnings of a build-up of the electrically conductive coating upon them at the point at which they are totally incapable of heating themselves, so to speak, by resistance heating. As the coating builds up however, it is capable of carrying its own electric current and thereby resistance heating itself. The happy balance thus achieved is that, while the non-conductive strands require the greatest radiant heat influence; i.e. before they have received any electrically conductive coating, they are obtaining it by being at the point where the maximum thickness of the coated electrically conductive substrate allows their greatest radiation. On the other hand, by the time the non-conductive substrates reach the point at which the heat radiating from the conductive filaments is at least; i.e. immediately upon their entrance into the chamber, the non-conductors have themselves acquired sufficient conductive capacity under the influence of the coating they are carrying to be resistance heated.

The novel apparatus for establishing and maintaining the closely spaced parallelism of the various filamentary substrates within the vapor chamber according to the present invention comprises a guiding block through which extend a number of bores or passages aligned with the direction in which the strips or filaments are to pass through the chamber and spaced among themselves according to the manner in which the spacing of the moving substrates is ultimately desired.

Because the cross-sectional dimensions of the passages are necessarily large enough to accommodate the completely coated substrate without there being any contact between it and the passage walls, additional means must be provided to enable the guide blocks to act as the electrodes by which the substrates receive their electrical energy. According to this invention, such additional means comprise the provision within the guide block of a reservoir of an electrically conductive liquid such as a molten metal or a metal such as mercury which is liquid at room temperature.

The arrangement of the liquid-containing reservoir within the block is such that all of the bores or passages, and therefore all of the substrates passing therethrough, are in communication with the reservoir and the liquid it contains. Where this liquid is in contact with a source of electrical energy, it follows that all of the substrates passing through the block will thereby also be in such contact, even though they are not touching the block itself. It has been found that this desirable effect may be achieved in a manner which simultaneously contributes to the efficiency of the vapor deposition process and particularly to the purity and uniformity of the coating being thus deposited where the entire guide block or at least the portions thereof surrounding or defining the bores or passages therethrough are of a material which is not wetted by the conductive liquid employed. Thus, Where the mercury is used as the distributor of the electrical energy from the single source to all of the individual substrates, the guide block may be made of ferrous metals and alloys, steel, dielectrics, ceramics, mica, molded I plastics and the like. The non-wetting relationship between the liquid and the material defining the passages through the block is such that, where fine filamentous substrates are to be coated and the diameter of the passages may be reasonably small; i.e. on the order of from .010 to .125 inch, an outwardly curved or convex meniscus will be formed and act to prevent the escape of the mercury or other liquid from the openings, even when they are not partially occupied by the filament. Since the diameters of the full-coated filaments of the type normally to be manufactured according to this invention do not exceed .100 inch, this expedient is effective to accommodate almost all desired filament-forming or coating situations.

In one preferred embodiment of the apparatus according to this invention, the guide-block-electrode unit is composed of successive laminations of centrally bored plates, the broadside surfaces around the central opening of which are characterized by grooves extending from one end of said plates to the other and through said central openings so that, upon the superimposition of the plates, the grooves of one broadside surface will register with those on a continuous broadside surface of an adjoining plate to form closed cylindrical channels. At the same time, the central openings of the stacked plates will register to form an interiorly positioned reservoir for the electrically conductive liquid. Where the height of the liquid within the reservoir is such that its head or hydrostatic pressure will cause the liquid to tend to flow through the channels, notwithstanding the effects of the abovedescribed convex meniscuses, the primary reservoir may be divided into a series of segmented liquid pools by the positioning of solid sheets to act as reservoir separation lates between certain of the channel-forming plates.

The invention thus generally described may be more clearly understood by reference to the following detailed description of certain specific embodiments thereof in connection with which reference may be had to the appended drawings.

In the drawings:

FIGURE 1 is a fragmentary elevational view in partial cross-section and partially diagrammatic, of one preferred form of apparatus for practicing the method of the present invention;

FIGURE 2 is an enlarged, exploded perspective view of a five element filament-guiding electrode block that is a simplification of a seven element block in FIGURE 1;

FIGURE 3 is an elevational view of an end of the seven element filament-guiding electrode block in FIG- URE 1 showing one arrangement of filaments in travel therethrough; and

FIGURE 4 is a fragmentary sectional enlarged view of a segment of a filament-leader combination according to this invention at progressive stages of the deposition of a coating thereon.

Referring now to FIGURE 1, the principal features of one preferred embodiment of this invention are shown to involve the process of and the apparatus for the simultaneous passage of a plurality of filaments through a vapor deposition unit which, for the purposes of schematic illustration and in many actual applications, may comprise the tubular member defining the cylindrical hollow chamber 11 therewithin and being preferably substantially closed at its ends by the tapering of the tubular wall to a smaller opening 12. In many instances, it is desirable to provide the inwardly disposed surface 13 of the chamber with a chromium plating or other heat reflective surface.

The interior 11 of the chamber is filled with and supplied by a vapor which is laden with the material to be deposited with or without a carrier gas, as preferred, between supply and removal pipes 41 and 42.

In the case of pyrolytic boron deposition for example, the chamber interior 11 may be supplied with a mixture of boron trichloride and hydrogen gases, as the filament temperature is raised to l7002100 F., thermal decomposition occurs with the plating out of elemental boron. If boron hydrides are used, the filament temperature may be as low as 600 F. The end product, a boron fiber, is highly desirable because of the high strength and modulus.

In the case of a pyrolytic graphite deposition for example, the chamber 11 may be supplied with a vapor rich in hydrocarbons such as a hydrocarbon gas; e.g., methane or a vapor formed by bubbling or similar passage of a carrier gas through a hydrocarbon liquid. Such a gas may be supplied at the opening 12 of the chamber or at other openings communicating therewith. To insure proper maintenance of the vapor or otherwise to control the plating reaction, the pressure within the deposition chamber 11 is controlled at optimum values. The chamber may be fitted with suitable end seals, not shown, that makes suitable vacuum or pressure pumps to maintain optimum pressures through the orifice 12 or at some other opening communicating with the chamber 11. In most cases, and particularly where the pressure differential between the interior and exterior of the chamber is to be maintained, it will be understood that conventional liquid trap or sealing means may be associated with the various openings to provide for the passage of the filaments 14 through the chamber without at the same time allowing any interchange of pressure or vapor between the chamber and the surrounding atmosphere.

In general, a filamentous substrate passes through the chamber 11 thus constructed and filled with vapor. An electric current is caused to flow through the electrically conductive substrate filaments by virtue of its mercury contacts with the longitudinally spaced electrodes 19 and 26 or the like. The substrate filaments are resistance heated to a sufiiciently high temperature such that a vapor-phase plating reaction between the vapor and the substrates takes place, and the filaments will thereby become coated with the material carried by the gas within the chamber 11.

It will be observed in the case of the present invention, that a plurality of filamentous substrates 14, associated respectively with the reels or spools 15, 16, 17 and 18, are simultaneously led through the vapor chamber 11 by the filament electrode and guiding blocks 19 and 20. These blocks 19 and 20 are supported respectively by the brackets 21 and 22 afiixed to the interior wall of the chamber 11. Electrically conductive filaments are energized through the electrical circuit 23 associated with the power source 24. The completion of this circuit by the filaments between the electrodes establishes a potential difference which causes electricity to flow through such of the filaments as are or that deposition become electrical conductors. The brackets 21 and 22 also may, if preferred, house or support temperature-control means such as a circulating coolant or heating coils, not shown, for influencing the temperature of the electrode blocks 19 and 20, conductive fluids within or the substrates passing through them.

The present apparatus guides a desired number of electrically charged substrates simultaneously through the chamber 11 and establishes and preserves the close spacing and the parallel travel of the substrates for the purposes described herein.

A typical example of such an electrode guiding block is illustrated in exploded condition in FIGURE 2 of the drawinges, wherein the block is shown to be composed of superimposed larnine or plates 26, 31 and 35, that in FIG. 1 are secured together between end cover plates 25 and 39 as the filament guiding blocks 19 and 20 The uppermost filament guiding plate 26 is in the form of a fiat substantially rectangular frame surrounding the interior opening 27. Its lower broadside surface is provided with the longitudinally extending semi-circular grooves 28 and 28' which, though they are interrupted by the opening 27, extend from one edge of the plate to the other. The upper broadside surface 29 of this plate 26 however is free of any grooves or other channel-forming configurations. Projecting beyond the boundary of one corner of the general rectangle of the plate 26 is the funnel or receptacle 39 which is in communication with the inner opening 27 for the direction of a desired liquid electrical conductor, such as mercury, within the block to maintain electrical contact with the filaments from the spools 15 to 18 inclusive. Another form of plate to b used in the assembly is the plate 31 which, like the plate 26, is generally rectangular and defines a centrally spaced opening 32. On this plate however, the grooves 33, 33' and 34, 34' are provided on both the upper and lower surfaces, respectively. The plate 35 is also rectangular and has thecentral opening 36 in the manner of the plates heretofore described, but grooves 37, 37 are provided at the opposite ends of the plate in the upper broadside surface only, whereas the lower broadside surface is smooth or planar. Finally, in combination with one or more pairs of the filament guiding plates heretofore de scribed, a plain fiat solid rectangular cover plate 25 on the top and 351 on the bottom are employed to limit the depth of the reservoir within which are positioned the blocks 19 and 20 respectively.

As appears from the drawings, when the plates 25, 26, 31, 35 and 39 are superimposed and are secured together by bolts 49, or the like, they form a block-like assembly such as the filament electrode and guiding block 19 or 21 having a vertically disposed reservoir centrally thereof with filament guiding grooves extending from one vertical surface through and thereby in communication with the reservoir. Also communicating with the reservoir is the receptacle or mercury receiving spout30. This same sequence of plates may be repeated for a desired number of times in the same block 19 or 20.

The transversely extending channels provided by the registry of the grooves of semi-circular cross-section act as guides or passages through which a plurality of filaments 14 may pass and be held in closely spaced, parallel relationship. The diameter of the grooves and of the circular channels formed thereby should of course be controlled or pre-se'lected so that it will be at least as large are the maximum diameter of any coated filament to result from a particular vapor deposition operation.

Since the mercury or other electrically conductive liquid to be placed in the reservoir for the distribution of the electrical energy to all of the electrical conducting filaments passing therethrough will be of a relatively high specific gravity, any significant height of such reservoir will result in a hydrostatic pressure sufiicient to cause the liquid to fiow through the channels, notwithstanding their restricted diameter and the convex meniscus formed as a result of the non-wettable relationship between the channel surfaces and the liquid. This factor need not limit the height to which successive plates may be stacked to form a guide block according to this invention however, for the reason that the reservoir may be conveniently broken up into individual pools.

The receptacle 30 is in communication with the opening centrally of the plate to which it is affixed. The electrically conductive liquid is conveniently poured into the spout 30 until the individual reservoir segment is filled at least to the point at which the liquid therein covers all of the filament-guiding passages in communication therewith. A desired plurality of grooved blocks between a pair of sealing end blocks determines the depth of the mercury pool.

Where the diameter of the filament-guiding channels is particularly small, where the desired spacing between filaments is relatively small and thin plates may therefore be employed, or where the specific gravity of the electrically conductive liquid is not so great, it may well develop that the individual reservoir segments may be of a greater height and formed by a greater number of plates than is disclosed herein. In such instances, it can be appreciated that the height of the individual reservoir segments can be increased by the addition of more of the plates like the plate 31 having grooves upon both its upper and lower broadside surfaces. At the same time, each reservoir segment will require a pair of end cover plates. While for purposes of clarity of illustration, the blocks shown in FIGURE 3, secured together by bolts 40, 40' etc., contain only four rows of four filament-guiding channels, in actual practice it has been found convenient to employ a block having ten rows of ten channels each to form openings capable of simultaneously accommodating the guided movement and electrical energization of One hundred filaments.

While a hollow guiding block 19 or 20 having the filament-guiding passages properly arranged and aligned through the walls thereof, may be formed in different ways, as for example by the simple expedient of casting the hollow block and thereafter drilling the passages, the use of the laminated assembly as above-described is preferred in that the block may be loaded by simply laying the filaments in the grooves as the successive plates are stacked and bound, bolted or otherwise secured together, rather than threading the filaments through an integrated block that is included within the concept of this invention.

With means thus established for accommodating the simultaneous movement through a deposition chamber of a plurality of closely spaced filaments and for simultaneously passing an electric current through all of those filaments which are electrical conductors or which become electrical conductors in the process of such movement, the nature and characteristics of the respective filaments or substrates, as well as the rate and direction of their motion may be manipulated to achieve a variety of results which have been heretofore unobtainable.

One such manipulation is illustrated in FIGURE 3 showing the end of the guide block 1? upon which open the sixteen filament-guiding passages in vertically spaced parallel rows, each row containing four transversely spaced passages. Relating the block to a mechanism similar to that illustrated at 19 or 20 in FIGURE 1, the filaments passing through the channels in the top row are controlled by the reel 18, those in second row by the reel 17, those in the third row by the reel or spool 16 and those in the bottom row by the reel or spool 15.

To deposit an electrically conductive coating upon two or more different kinds of filamentous substrates, some of which are electrically conductive and some of which are non-conductive, in FIGURE 3 the conductive filaments are positioned to pass through the passages in the top and bottom rows, while the non-conductive filaments are placed in the two middle rows. The establishment of an electromotive force between the electrode blocks 19 and 20 will cause a flow of current only through such of those substrates as are bonductors such as tungsten wire conductors, for example; and, in the process, these conductors will become resistance heated to substantial temperatures on the order of 300 to 2,200 degrees centigrade at which the vapor plating reaction upon their surfaces can take place. At the same time, however, and particularly where the spacing between filaments both vertically and laterally is relatively close, for example on the order of from .015 to .150 of an inch in all directions, and where the vapor chamber is provided with appropriate heat reflective means, the electrically conductive filaments become radiators and give off heat energy which will elevate the temperature of the non-electrically conductive substrates adjacent the heat radiators to the point at which vapor deposition will take place also upon the surfaces of the non-conductor filaments.

In a further modification of the present invention, a non-electrically conductive substrate filament to be coated is heated to a deposition temperature by being positioned in close proximity to electrically conductive sacrificial filaments which are not used as a finished product but which are to act only as radiators for elevating the temperature of the non-conductive filaments as they pass through the vapor deposition chamber. In this modification, the reels, corresponding for example to the reels 15 and 18 in the apparatus of FIGURE 1, carry the sacrificial radiator filaments and are stopped so that the radiator filaments would not move while the non-conductive substrates carried by the reels 16 and 17 do move through the vapor deposition chamber 11 and are coated. Upon the energization of the electrodes 19 and 20, the necessary electric current passes through the conductive filament material whereby they undergo ohmic heating and become capable of radiating heat to raise the temperature of the non-conductive substrates to the degree at which the vapor deposition coating reaction takes place upon their surfaces.

It is to be noted that, where the coating is electrically non-conductive, the coating insulates the conductive radiator wire from electrical contact with the energized mercury or other metal, this insulation does not take place because the heat radiating filaments are not moving. There is therefore, no deposit upon the heat radiating filaments that are in contact with the mercury. After a time however, the portions of the non-moving radiator filaments that are exposed to the vapor deposition atmosphere may become excessively coated. At this point the apparatus may be temprorarily stopped and the heavily coated heat radiators are removed by rotating the reels 15 and '18 until filament of the length of the deposition chamber has been traversed and a set of new and uncoated electrically conductive filaments capable of acting as radiators are again presented within the deposition chamber 11. In this modification where the heat emitting filaments are electrical conductors; they cannot be resistance heated as they continue to move through the chamber for the reason that the building up of their coating will insulate them from electrical contact with the guide blocks.

Another modification of the apparatus and method of this invention is illustrated in FIGURE 4 of the drawings wherein an electrically conductive coating 43 is in process of being deposited upon a non-conductive substrate filament 44 that is butt welded at its end to an electrically conductive strand or leader substrate 45 first leading this leader strand substrate through the energized guide block 19 within the deposition chamber 11 so that the leader strand substrate 45 is resistance heated and the electrically conductive coating 43 will commence to build on the leader strand 45. The conductive coating 43 may then be resistance heated to encourage further deposition on the non-conductive filament 44 of the coating as the nonconductive substrate filament 44 passes into the chamber 11. Reasonable speed, economy and uniformity of coating in this situation require that the non-conductive filaments 44 once started with the leaders strand 45 is to continue to move in closely spaced parallel relationship with conductive heat-radiating filaments.

A particularly unique and advantageous arrangement in this situation involves manipulation of the reel 15, 16, 17 and 18 so that the non-conductive substrate filaments 44 move in one direction through the chamber While the adjacent conductor heat radiator strands move in the opposite direction. Thus for example, one set of the nonconductive filaments 44 with the con-ductive leader 45 initially attached thereto may be led forward from the passages such as those in middle pair of rows of FIGURE 3, while the conductive substrates in the top and bottom rows are simultaneously led in the opposite direction. The incoming filaments in the two middle rows, immediately upon their entrance into the vapor deposition chamber, will be in close proximity to the top and bottom rows of oppositely moving filament substrates which, by the time they have reached this point, have their maximum thickness and, for a given electromotive force, are capable thereby of being resistance heated to the highest temperature and of providing the greatest amount of radiant heat to elevate the temperature of the incoming substrates. Then as the second and third rows of filaments advance through the deposition chamber, they acquire sufficient coating (at first under the sole influence of the heat radiated by the conductive filaments) that the electrical current will pass through them (i.e. through their coating) and cause them to become resistance heated. As these strands are about to leave the vapor deposition chamber 11 they will have their maximum coating and resistance heating potential and be capable of providing the greatest amount of radiant heat to influence the oncoming strands in the first and fourth rows which, because they have just become clec trically energized, are in the same greater nee-d for radiant heating as were the strands in the two middle rows upon their entrance into the chamber. To utilize the electrical conductivity increases attending the build up of the coatings, it is necessary, particularly where a portion of the substrates within the chamber is a complete electrical insulator, to provide successive heating stages in the form of a plurality of a longitudinally spaced electrodes within the chamber, across successive pairs of which separate electromotive forces are applied.

Whereas the juxtaposition of the various radiating or non-radiating and conductive or non-conductive filaments is shown in FIGURE 3 to comprise an arrangement or pattern wherein non-conductors pass through the channels in the middle or interior rows and the conductors pass through channels in the first and fourth or exterior rows, similar alternation and even improved juxtaposition may be provided by successively alternating between conductors and non-conductors from one row to the next. Where preferred, the first and third rows might accommodate the electrically conductive filaments for example, and the second and fourth rows might guide the non-conductors. A still greater improvement in the even distribution of the various filaments and their heating effects and capabilities is achieved wherein the conductor and non-conductor filaments in each of the rows and columns, both vertically and laterally of the block, are alternately arranged so that each non-conductive filament is surrounded on all sides by the conductive filaments.

While the illustrated examples above have been described in connection with filamentous substrates of threadlike proportions, the teachings hereof are equally applicable to a broad range of filamentous or strip-like materials; e.g., thin strips or sheets of metal or fabric, foil or the like. The substrate passages through the electrodes in such cases are of course altered in configuration; and slits for example may replace the cylindrical passages. Where the strips are relatively wide, the slits may extend the length of the entire rows. In this situation, the substrates of differing electrical conductivities would be vertically alternated.

While the present invention has been described in considerable detail in connection with certain preferred embodiments thereof, it is to be understood that the foregoing particularization has been for the purposes of illustration only and does not limit the scope of the invention as it is defined in the subjoined claims.

I claim:

1. A- method for the continuous pyrolytic deposition of a coating material from its vapor phase upon a nonelectrically conductive substrate comprising the passage of such substrate through a pyrolytic vapor deposition chamber with and in close proximity to at least one electrically conductive strand, passing an electrical current through said strand while in proximity to said substrate whereby the strand will become a heat radiator to raise the temperature of the substrate to the point at which the coating material will plate out of its vapor phase and become deposited upon the substrate.

2. A method according to claim 1 wherein said strand is at least intermittently held in fixed position while the substrate travels through said chamber.

3. A method according to claim 1 wherein said strand moves in one direction through said chamber while the substrate moves in the opposite direction.

4. The method according to claim 1 wherein said coating material in its vapor phase assumes its solid phase on contacting said substrate within the temperature range from 300 C. to 220() C.

5. A method for the pyrolytic deposition of an electrically conductive coating upon a non-electrically conductive filament comprising passing the filament through a vapor deposition chamber in closely-spaced parallelism with an electrically conductive strand, establishing an electrical potential difference at spaced points along said strand and said filament within said chamber whereby the strand will become electrically heated, and allowing the strand and the filament to move in such parallelism for a sutlicient length of time radiantly to heat the filament to the point at which a plating reaction between the vapor and the surface thereof will take place and the coating of said filament will become electrically heated.

6. A method for the pyrolytic deposition of an electrically conductive coating upon a non-electrically conductive filament comprising attaching one end of the nonelectrically conductive filament to one end of an electrically conductive strand, passing the resultant end joined strand and filament through a vapor deposition chamber in closely-spaced parallelism with a plurality of electrically conductive strands moving through said chamber, establishing an electrical potential difference at spaced points along at least some of said electrically conductive strands within said chamber whereby the filament joined at its end to the electrically conductive strand will become electrically heated by reason of the electrically conductive coating acquired initially -by radiation heating from the moving filaments.

7. A method for the continuous pyrolytic deposition of an electrically non-conductive coating material from its vapor phase upon a filamentary substrate comprising the passage of such substrate through a pyrolytic vapor deposition chamber with and in close proximity to at least one electrically conductive strand, passing an electrical current through said conductive strand while in such proximity to said filamentary substrate whereby the conductive strand becomes a heat radiator and raises the temperature of the substrate to the point at which the precursor nonconductive coating material undergoes a gas-phase to solid-phase change in its physical state and plates out upon the surface of the filamentary substrate.

8. A method according to claim 7 wherein said strand 11 12 is held in fixed position while said electrical current is References Cited Passed thefethmugh- UNITED STATES PATENTS 9. A method according to claim 8 wherein said strand,

after it becomes heavily coated with the deposited coating if? T T T material, is removed from said chamber and replaced by 5 a new length of uncoated strand. F REIGN PATENTS 10. A method according to claim 9 wherein said new 264,814 12/1927 Great Britain.

length of uncoated strand is an adjoining segment of a continuous length of such strand which is intermittently ALFRED LEAVITT: Pmnmy Examine"- moved through said chamber. A. GOLIAN, Assistant Examiner.

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