US 3554782 A
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, Ja 12 19 71 VQAJh IIEBERLEIN I 3,554,782
METHOD FOR DEfOSITING CARBIDE COMPOUND Filed Au yzs. 1967 Vernon A. Nieberlein v INVENTOR.
3,554,78 METHOD FOR DEPOSITING CARBIDE COMPOUND Vernon A. Nieberlein, Huntsville, Ala., assignor. to the United States of America as represented by the Secretary of the Army 7 Filed Aug. 23, 1967, Ser. No. 662,830
Int. Cl. C23c 9/00 US. Cl. 117-46 7 "Claims ABSTRACT OF THE DISCLOSURE A method for depositing a carbide compound such as silicon carbide on a heated wire through the use of a filmboiling technique. The reinforced filament product is useful in reinforced filament-wound missile and aircraft structures.
BACKGROUND OF THE INVENTION The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to me of any royalty thereon.
This invention relates to an improved method for depositing a carbide compound such as silicon carbide on a wire.
Although most of the continuous ceramic filament research has been in the area of boron filaments, some work has been done with silicon carbide (and similar materials). However, in all cases vapor deposition has been used to make these filaments. Normally a very fine tungsten wire is drawn through a tube, or series of tubes, which contain vapors that will react at elevated temperatures. These vapors are typically SiCl +H i+RH, HSiCl -l-H -l-RH, or CH SiCl where R represents a monovalent organic radical.
The first two vapors give trouble by forming hot spots on the filament during the vapor deposition. These troubles are thought to be the result of the organic compound decomposing and preferentially forming WC or W C with the tungsten wire substrate, rather than uniformly depositing SiC. The hot spots, of course, soon cause the wire substrate to break before completion of deposition.
The third vapor, while being an improvement over the other two, still forms hot spots on the very finest tungsten wlre.
Accordingly, it is the principal object of this invention to provide an improved method for depositing a carbide compound such as silicon carbide on a wire.
It is a particular object of this invention to provide such a method that avoids the formation of hot spots.
SUMMARY OF THE INVENTION A film-boiling technique, rather than conventional vapor plating, is used in the method of this invention to deposit silicon carbide on a heated wire. The term filmboiling is defined herein to mean that stage of boiling wherein a submerged object does nob-directly contact the surrounding liquid, but is totally encased in a thin vapor sheath which is formed from the surrounding liquid being heated to boiling. In this invention, a fine tungsten or similar wire is submerged in a liquid whch includes the two elements silicon and carbon, preferably (CI-I SiCl, and is then heated to cause the liquid to boil. Other carbide compounds than silicon car-bide may also be deposited on the wire.
BRIEF DESCRIPTION OF THE DRAWING These and other objects and advantages of the method of this invention will become more readily understood by United States Patent O r6 CC reference to the following detailed description, of which the accompanying drawing forms an integral part.
In the drawing, the single figure is a cross-sectional view of an apparatus used in the method of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT Silicon carbide may be deposited on a fine tungsten (or other suitable metal) wire submerged in a liquid which chemically includes the elements silicon and carbon by heating the wire to cause the liquid to boil. The preferred liquid is (CH SiCl, trimethyl chlorosilane. Other satisfactory liquids include (CH SiCl CH SiCl or SiCh-i-RH.
Referring now to the figure, a water-jacketed cell 12 for use in accordance with this invention is shown. Cell 12 includes a water jacket 14 (containing water 13) in the outer portion thereof. Inside water-jacket 14 is a quartz reactor tube portion 16 having a wire 10 therein surrounded by plating fluid 8. Electrical contacts 11 are connected to wire 10. Plating liquid 8 in quartz reactor tube portion 16 is vented to surge tank 18. A conduit 7 is used for introducing or removing plating liquid into or from quartz reactor tube portion 16, while a conduit 9 is used to pass the gaseous 'byproducts into surge tank 18.
In operation, plating liquid 8 is introduced into quartz reactor tube portion 16 through conduit 7 to a level above wire 10. Conduit 7 is then closed by conventional valve means 6'. Any excess of plating liquid 10 is allowed to flow out conduit 7 before closing conduit 7 by valve means 6 Thus, a small space is left in the top of the quartz reactor tube portion 16. The submerged wire 10 is then heated electrically to incandescence (through electrical contacts .11). The plating liquid L1) is caused to be heated. At a sufficiently high temperature, nucleate boiling on the wire 10 surface stops and film boiling begins. In the stage of film boiling, the wire 10 is encased in a sheath of plating vapor which pyrolyzes to deposit silicon carbide on the hot wire 10 substrate. Water-jacket 14 merely causes vapors of the boiling liquid 8 to condense in the quartz reactor tube portion 16 of cell :12. rather than in a condenser. This feature is optional, however. The helium-filled surge tank 18 allows boiling to take place without a pressure buildup of the plating vapor and gaseous byproducts and without the danger of contaminating the plating liquid with humid air (Excess gas passes as exhaust out of the system.) After a specified length of time the electricity through contacts 11 is turned off and the coated tungsten wire is removed. X-ray diffraction analysis shows the coating to be alpha-Sic, type VI.
Typical conditions and deposit rates involve the use of (CH SiCl as a plating liquid, a wire diameter of 2 mils, a heating current of 1.2-2.4 amperes, a wire temperature of about 925 to about 1050 C., a plating time of 30 seconds (for undiluted liquid), and a finished wire diameter of 4l1 mils. The liquid used to plate a given carbide compound may, in general, be any organic liquid containing that particular compound. Although certain organic liquids containing the particular compound will not work, the choice of such a liquid is easily made by those skilled in the art.
Using a tungsten wire, (CH SiCl as the plating liquid and 30 seconds as the plating time, a heating cur-1 rent of 1.8 amperes AC produced a wire temperature of 925 C. and a finished wire diameter of 4 mils; a heating current of 2.2 amperes produced a wire temperature of 995 C. and a finished wire diameter of 7 mils; and a heating current of 2.4 amperes produced a wire temperature of 1050 C. and a finished wire diameter of 11 mils.
It has been found that the presence of iodine in the plating liquid improves the quality of the deposit somewhat. It has also been found that AC is superior to DC for resistive heating, provided the wire substrate is no finer than 2 mils (for tungsten). Smaller diameters are adversely affected by AC vibration. Furthermore, placing the system under positive pressures of 10, 20, 40, 80, and 160 mm. Hg has no eifect on the process or on the finished wire.
The wire 10 may also be graphite as well as other metals such as titanium, their carbides or alloys of the metal. In general, the wire 10 may be made up of any electrically conductive material that does not decompose except at relatively high temperatures.
It has been found experimentally that, for best results, the liquid should be diluted with an inert organic liquid, preferably cyclohexane. The inert organic liquid must be able to survive the extremely high temperatures encountered. The diluted solution normally contains about 80% by weight of the inert organic liquid. The use of such a diluted solution produces a filament product of greatly improved mechanical properties although, of course, slower deposit rates are obtained thereby.
The wire and carbide compound deposited thereon should have approximately matching coefficients of thermal expansion. This presents the occurrence of cracks upon cooling of the filament product.
The advantages of the method of this invention over previous methods are:
(1) very rapid plating rates are possible;
(2) no hot spots are formed;
(3) alternating current can be used for resistance heating (Vapor deposition requires D.C. because of the excess vibration caused by AC); and,
(4) the plating medium is conserved. (With vapor deposition, although only a small fraction of the vapor is consumed, all of the vapor must be replenished since the used vapor is lost to the exhaust or reclaimed.)
The method of this invention is not limited to the particular apparatus disclosed herein, which is merely illustrative of an apparatus used in the method of this invention. Some basic modifications and variations of the method of this invention are:
(a) wire need not be the only shaped article to be used in film-boiling deposition. Graphite, or other types of rocket nozzles, can be coated with silicon carbide to any desired thickness by the method of this invention;
(b) resistance heating is only one type of suitable heating. RF induction heating, radiant, nuclear, or any other heating process will also work;
(c) the method of this invention is not limited to atmospheric pressure;
(d) the film-boiling method of this invention will also work for depositing carbides other than silicon carbide (e.g., wc, BC, or TiC). Thus, 'rici, plus a suitable 5 organic compound will deposit TiC. Also, organic liquids 4 with one or more metal atoms in the molecule will deposit the metal carbide on a hot substrate; and,
(e) the batch process described herein lends itself very well to continuous operations, such as those used in the manufacture of other fibers, where wire is reeled off at one end of the equipment and the composite fiber is taken up at the other end.
Various other modifications and variations of this invention will become readily apparent to those skilled in the art in the light of the above teachings, which modifications and variations are within the spirit and scope of this invention.
1. A method of depositing silicon carbide on a wire comprising the steps of immersing a wire in an organic liquid chemically including silicon and carbon, heating said wire until said liquid boils vigorously and film boiling is achieved, and maintaining said film boiling for a period of time thereafter, said wire being an electrically conductive wire and having a melting point such that said film boiling can be maintained for a period of time sufficient to deposit a desired coating of said silicon carbide on said wire, said organic liquid containing a compound selected from the group consisting of methyl chlorosilane, dimethyl chlorosilane and trimethyl chlorosilane.
2. The method of claim 1 wherein said heating is effected by passing an electrical current through said wire.
3. The method of claim 2 wherein said wire is a metal, metal carbide, metal alloy or graphite.
4. The method of claim 3 wherein said wire is tungsten.
5. The method of claim 4 wherein said selected organic liquid is trimethyl chlorosilane.
6. The method of claim 5 wherein said organic liquid is diluted with an inert organic liquid.
7. The method of claim 6 wherein said inert organic liquid is cyclohexane.
References Cited UNITED STATES PATENTS 2,470,479 5/ 1949 Ferguson et a1. 117Organic Silicates 2,471,224 5/1949 Loughborough 117Organic Silicates 2,567,804 9/1951 Davies 117Organic Silicates 2,944,874 7/1960 Irvine, Jr. 117-1 13X 2,955,959 10/1960 DuRose 117-113 3,455,723 7/1969 Kern 117-113X 3,317,356 5/1967 Clendinning 1l7--106(C)UX ALFRED L. LEAVITT, Primary Examiner I. R. BATTEN, JR., Assistant Examiner US. Cl. X.R.
Notice of Adverse Decision in Interference In Interference No. 98,013 involving Patent No. 3,554,782, V. A. Nieberlein, METHOD FOR DEPOSITING CARBIDE COMPOUND, final judgment adverse to the patentee was rendered Jan. 18, 1974, as to claims 1, 2, 3
[Oflicial Gazette July 2, 1974.]