US3911194A

US3911194A - Method for forming pure metal or non-metal deposits

Info

Publication number: US3911194A
Authority: US
Inventors: Jacques Dejachy; Jacques Gillardeau
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1972-11-07
Filing date: 1973-11-01
Publication date: 1975-10-07
Anticipated expiration: 1992-10-07
Also published as: FR2205583A1; GB1406394A; DE2355531A1; JPS4995832A; FR2205583B1

Abstract

A method for forming pure metal or non-metal deposits, said method consisting in introducing, in the vapour state, at least one metal or non-metal fluoride of higher valence into an enclosure containing at least one substratum to be metal-coated and a source for providing the metal or non-metal to be deposited, heating said source in order that the higher-valence fluoride is transformed, when contacting said source, into at least one sub-fluoride which evaporates, is condensed on the substratum and is transformed into fluorine and into the metal, or the non-metal, which constitutes the desired deposit.

Description

ueu 5R lO--7-75 QR United States Patent [191 Dejachy et al.

[451 v Oct. 7, 1975 METHOD FOR FORMING PURE METAL OR NON-METAL DEPOSITS [75] Inventors: Jacques Dejachy, Saint-Cloud;

Jacques Gillardeau, Longjumeau, both of France [73] Assignee: Commissariat a IEnergie Atomique,

Paris, France 22 Filed: Nov. 1,1973

21 Appl.No.:4l2,0l6

[30] Foreign Application Priority Data Nov. 7, I972 France 72.39334 ['52] U.S. Cl. 428/408; 427/237; 427/253;

427/255; 428/450; 428/457; 428/472 [51] Int. Cl. C23C 11/02 [58] Field of Search 117/106 R, 107.2 R

[56] References Cited UNITED STATES PATENTS 2,887,407 5/1959 Koch 1 ll7/107 3,658,577 4/1972 Wakefield 117/106 R Primary Examiner-Harris A. Pitlick Attorney, Agent, or FirmCameron, Kerkam, Sutton, Stowell & Stowell 57 ABSTRACT 14 Claims, 2 Drawvin' g Figures US. Patent Oct. 7,1975

METHOD FOR FORMING PURE METAL OR NON-METAL DEPOSITS The present invention relates to a method for obtaining metal or metal-like coatings in the pure state from the high-valence corresponding fluorides.

It has already been possible to obtain metal coatings from metal fluorides by decomposing the latter in the vapour state, under a given pressure and at a given temperature, on a substratum to be metallized, said substratum being itself of metal or of a material likely to decompose fluorides.

According to the above method, whenever a metal M is brought into contact with its fluoride MFn (n being the valence of said metal) in the vapour state and at an appropriate temperature, there is formed on the surface thereof a deposit of the fluoride metal, according to the following reaction:

nF (adsorbed) Whenever a gaseous MF molecule impinges on the metal surface, the impact is efficient: the metal atom is deposited and two fluorine atoms are chemically adsorbed.

The positioning of the metal atom in the surface lattice of the receiver metal occurs very quickly. The adsorbed two fluorine atoms are capable of moving under the conditions of the experiment, and the desorption thereof, which proves to be one of the main factors governing the kinetics of the deposition, allows the metal surface to be permanently uncovered.

When a fluoride MF,,, in the vapour state and at an appropriate temperature is in contact with a substratum that provides volatile fluorides, the fluorides obtained are eliminated and leave the metal in the pure state.

When a fluoride MP in the vapour state and at an appropriate temperature is in contact with a metal that does not provide volatile fluorides and the pure metal obtained is soluble in the metal forming the substratum, alloys are obtained, which occurs, e.g., when the two metals involved are platinum and copper. When a fluoride MF,,, in the vapour state and at an appropriate temperature, happens to be in the presence of a substratum that does not provide volatile fluorides, and the substratum and the metal obtained are not miscible, it is possible to decompose the fluoride in contact with said substratum and then eliminate same with a view to obtaining pure metal.

The thus formed coatings are good, but they require a highly careful and uneasy preparation of the fluorides as used, which have to be thermally decomposable in a direct way. It happens that some fluorides are hygroscopic to such an extent that their previous preparation apart from the vapour-deposition enclosure could not be resorted to, since their handling is, in fact, rendered impossible in view of their considerable instability with respect to the traces of water which are always to be found on the sites of experiments.

Another method consists in reducing a fluoride by 1 means of hydrogen, and it also leads to good coatings,

while however showing major drawbacks.

In certain instances, e.g. when the geometry of the substratum to be coated prevents the easy renewal or 2 reagents, the excess hydrogen may alter the hydrogen/- gaseous fluoride ratio to the point of deteriorating the metal deposit, or even causing the vapour-deposition to stop.

The presence of hydrogen leads to the production of hydrofluoric gas, and steps, generally considered as dangerous, have to be taken for draining and storing said gas.

Too great a concentration of hydrofluoric gas in the vicinity of the substratum may, quite undesirably, lead to a reaction opposite to the desired one, viz. the recombination of the metal deposited in the fluoride state.

The reduction method has therefore to be rejected whenever the geometry of the objects to be coated is complicated, or whenever it is desired to form deposits inside parts comprising many branches or, e.g., inside long and narrow tubes.

A new method, free of the above drawbacks, has been discovered and it is based on the thermal decomposition of a metal or non-metal sub-fluoride, obtained in situ by the reaction of the corresponding higher valence fluoride on the metal or the non-metal substance.

The invention relates to a method for forming pure metal or non-metal deposits, said method consisting in introducing, in the vapour state, at least one metal or non-metal fluoride of higher valence into an enclosure containing at least one substratum to be coated and a source for providing the metal or non-metal to be deposited, heating said source in order that the higher valence fluoride is transformed, when contacting said source, into at least one sub-fluoride which evaporates, is condensed on the substratum and is transformed into fluorine and into the metal, or the non-metal, which constitutes the desired deposit.

It is well known that the fluorides of higher valence are fluoridizing and cannot be thermally decomposed until the metal is obtained. It is only by means of the reduction of these fluorides with hydrogen that a total chemical decomposition can be obtained. On the other hand, the sub-fluorides are not fluoridizing in general, and they can be thermally decomposed on a hot substratum in order to provide the metal directly.

According to the invention, the formation of subfluorides and the thermal decomposition of same occur simultaneously. The formation of a sub-fluoride, having the general formula MF froma higher fluoride, having the general formula MF,,, and the metal M is carried out as follows:

In MF,

gas

n and m being the valences of the elements and n being higher than m.

By way of non limitating. examples, the following compounds can be mentioned as fluorides of higher valence capable of providing a thermally decomposable sub-fluoride: wF6, MoF6, ReF6, PtF6, TaFS, NbFS, BFS, TiF4, CF4, SiF4 In order to obtain the useful sub-fluoride, the higher valence fluoride is caused to react on the corresponding metal or non-metal, heated to the appropriate temperature. It is to be noted that the generating metal or non-metal can be very easily located in the vicinity of the part to be coated, which permits to form the subfluoride in the vicinity of the surface on which the de- MFm MFm- M mF- M F adsorbed adsorbed adsorbed solid desorbed gas metal When a gaseous molecule of sub-fluoride MF,, inpinges on the substratum to be coated, heated to the appropriate temperature, the impact is efficient and the MF, molecule is activated to a sufficient extent to be quickly absorbed by the substratum. The chemical adsorption being of a dissociating nature, the sub-fluoride adsorbed decomposes into metal M and into fluorine atoms. The metal obtained is inserted into the surface cristalline lattice, and fluorine is desorbed, which permits further molecules of sub-fluorides to be introduced and the vapour deposition to proceed. The method according to the invention can be illustrated, for example, by the vapour deposition of tungsten (W). Hexafluoride WF reacts on tungsten metal W as follows:

SWF W--) 6 WF,,

gas metal gas When those two metals are different, reactions of the following types will take place:

It can be noted that the tungsten hexafluoride used at the beginning of the reaction is re-generated at the end of that reaction; it thus acts as a catalyst. It is therefore possible to introduce the gas into the enclosure and to carry out the reaction under constant pressure.

The above reaction can be written as follows:

The metal fluoride MF or MP thus formed is then decomposed on the suitably heated part to be coated, thus freeing the metal which is deposited:

MF MF M F---) M F gas adsorbed adsorbed adsorbed metal desorbed deposited or MF MF M 2F) M F gas adsorbed adsorbed adsorbed metal desorbed deposited and the tungsten pentafluoride thus formed is thermally decomposed as follows:

5 WF5 WF5 W 5F -)W F gas adsorbed adsorbed adsorbed metal desorbed The formation of sub-fluoride and the decomposition of said fluoride occur simultaneously provided the substratum to be coated and the sub-fluoride generating metal are heated to carefully chosen different temperatures.

A careful selection of these temperatures will permit not only to carry out the method but also to act favorably on the kinetics of vapour-deposition and on the properties of the metal deposits obtained.

It can be noted that, in the particular instance of tungsten, very good coatings are achieved by raising the generating source to a temperature of about 750F (400C) and the substratum to a slightly lower temperature. It can also be noted that similar results can be obtained by carrying out the reduction method, but, in the latter case, the temperature must reach about 1290F (700C), leaving aside the already mentioned drawbacks of the method itself.

Two different cases can be contemplated, according as the source metal and the metal of the gazeous fluoride introduced into the reaction enclosure are the same or not.

When those two metals are identical, reactions of the following types will take place:

The fluorine provided by the thermal decomposition of MP or MP recombines with Wlto give back fluoride WF i.e. the gaseous catalyst which is thus regenerated.

A great many metal deposits can be obtained in this way. By way of example can be mentioned the copper deposits from CuF and CuF, and the nickel deposits from NiF and NiF. The following metals are transfered and vapour-deposited according to that method: iron, cobalt, zinc, silver, gold, cadmium, and aluminum, to mention only the most frequently used metals.

The above reaction has the advantage of permitting the vapour-deposition of metals such as, e.g., nickel, copper, aluminum, zinc, cadmium, zirconium, the fluorides of which, which are not volatile enough, cannot be validly used in the other vapour-metallurgy methods.

The operating conditions and the results of several tests are summed up in the following table 1.

The method according to the invention has many others advantages.

It permits to obtain deposits of metals the fluorides of which are very poorly volatile, and therefore can hardly be used, and even cannot be used at all, in the ordinary vapour metallurgy methods, in particular in the reduction methods.

Since the gaseous phase contains no hydrogen, no hydrofluoric acid is formed, which might impair the formation of good deposits.

The method which consists in adsorbing the sub-fluorides molecules and desorbing the fluorine atoms formed which ensure a self-regulation of the deposition speed, necessarily leads to good deposits, even when operating at temperatures which would beconsidered as too low, for instance in a reduction method. It is thus possible to make metal deposits on substrata which could no sustain high temperatures. The deposits obtained by means of the method according to the invention are compact, even, adhesive and epitaxic,:whenever allowed by the nature of the substratum and of the deposit. a

A remarkable vapour-deposition technology. can be developed, taking account of the fact that the fluoride (MF or MP useful to thevapour-deposition, can be generated in the. vicinity of the surface to be coated, whatever be the shape of the latter; one has only to put the metal source near the substratum. This is of considerable advantage for carrying out depositions inside parts of various shapes such as tubes, valves and containers. The shape of the part to be coated by no means impairs .the very good penetration power associated to the method.

With a view to carrying out said method properly, it is necessary that the metal generating source be hot enough for causing the useful fluoride (MF or MF to vaporize and to be transferred to the substratum to be coated. I I

The metal generating member may be a wire or a bar, heated by Joule effect. The generatingsource may also be a rod, indirectly heated by means of a non-consumable thermal member, the shape of that rod being adapted to each particular instance.

That rod may either be coated with the metal obtained by sin'tering, or consist in a tank containing fragments of the metal to be vapour-deposited. I

In some devices for carrying out the above method, the part to be coated is preferably directly heated by the metal member which generates metal M, and in this case a heat insulating member must surround said part.

The shape of the devices for carrying out the method according to the invention varies according to the shape, the nature and the number of the articles to be coated.

The following description will provide two examples of the coating of tubes.

FIG. 1 is a section through a device for coating the inside of a tube, and

FIG. 2 is a section through a device for coating both the inner portion and the outer portion of a tube; as can be seen in FIG. 1, tube 1, made of any metal alloy, the inside portion of which is to be metal coated, is introduced into a heat insulated sleeve 2, with a view to avoiding as best as possible, heat-losses by radiation. A metal or non-metal rod 3 is held by the ends thereof inside the tube at the level of plugs 4 and 5. Plug 4 has an opening for conduct 6 through which a higher valence fluoride is introduced. For operating that device, the rod must be heated to a predetermined temperature before introducing, through conduct 6, the fluoride which, by contacting bar 3, generates a sub-fluoride that forms a deposit of the inner wall of tube 1.

In FIG. 2, the elements similar to those of FIG. 1 are given the same reference numerals. Tube 1 is held within an enclosure 7 by means of brackets (not shown). The arrangement as shown permits, as in the previous instance, to coat the innerportion of tube 1 with metal, and also permits to coat the outer portion of that tube, through the addition of bars 3 and 3" which are metal canon-metal generating sources like bar 3, and of conducts-5' and 5" for the introduction of fluorine. It is to be specified thatsthe inner wall of enclosure 7 is of a material which is not likely to retain a metal deposit. 1 Y v r In addition to the fact'that it is carried out as explained abovewith no. generation of hyrogen and hydrofluoric gas, the method according to the invention permits to. eliminate the fluorine generated during the dissociation of the sub-fluoride, by re-combining it with the source metal. The reaction interface, and more exactly the composition of the gaseous phase, are therefore perfectly constant for all the duration of the vapour-deposition, whatever be the shape of the part to be metal-coated. v

On account of the cristal growth whichfgoverns the deposition, viz. the adsorption of the sub-fluoride molecules and the desorption of the fluorine atoms generated through which .the deposition speed is selfregulated, the vapour-deposit is necessarily good. This is even the case with deposits carried out at temperatures which would prove much too low for the reduction method. It follows that the method according to the invention permits to coat materials likely to be definitively altered at higher temperatures,,. O ine can mention, for instance, the case of deposits made on metals subjected to allotropic transformations at high temperatures and for which there is a risk of deteriorating the deposit-substratum interface, at the moment of passing the allotropic transformation point, during the cooling step.

It must be pointed out that thedep osits obtained carrying out themethodaccording to,,th e invention are both adhesive, compact and even, and that their growth is carried out epitaxically, viz. the cristalline lattice 'develops atom per atom in agreement with the surface cristalline lattice, which permits to obtain as desired monocristals having agiven orientation.

Such deposits'can be made on many various substrata, all the more as, as already mentioned, the method accordingto the invention permits to obtain very good deposits at temperatures lower than those involved in known methods.

Excellent tungsten deposits were obtained, from WP on the following substrata, given merely as examples: tungsten, molybdenum copper, nickel, monel-metal, inconel, iron, graphite, silicon, alumina.

It is also to be noted that it is possible to make vapour-deposits with alloys. It is indeed possible to carry out the co-deposition of two metals, by taking advantage of the respective chemical natures of the generating metal and of the gaseous fluoride of higher valence. One can mention, by way of example, the excellent results acheived as regards the co-deposition of molybdenum and tungsten, starting with a generating source of tungsten and with molybdenum hexafluoride as the gas.

A remarkable vapour-deposition technology can be developed taking into account the fact that sub-fluoride useful for the vapour-deposition can be generated in the vicinity of the surface to be coated whatever be the shape of the latter. It is only sufficient to put the metal or non-metal source near the substratum. This is of considerable advantage for making deposits e.g. inside tubes, even very long and narrow tubes, inside valve bodies, complicated tubing, containers, etc The shape of the member to be coated by no means impairs the excellent penetrating power associated to the method.

The metal or non-metal source can be a wire or a bar, heated by Joule effect. That source can also be a rod directly heated by means of a non-consumable thermal member. The shape of that rod may be adapted to each particular instance. The rod either can be coated with the metal obtained by sintering or according to any vapour-deposition method, or consists in a tank containing metal fragments to be vapour-deposited.

In some devices for carrying out the method according to the invention, the part to be coated is preferably heated directly by the generating metal member, said part being surrounded by a heat-insulating member.

The invention may have quite a number of applications in the field of electronics, in particular for the manufacture of the transmitters of electronic-tungsten converters, and for the manufacture of X-ray tubes anticathodes and in particular, in the field of space research, for manufacturing titanium thermal shields. The following applications can also be mentioned:

- internal coating of tubular parts of small diameter;

- manufacture of metal tubes by making a deposit on the inner portion or on the outer portion of supporting tubes which are later on withdrawn either mechanically or chemically;

the deposition of reflecting or semi-reflecting metal layers of refractory metal, e.g. of tungsten, tantalum, molybdenum, on refractory substrata, such as ruby or corundum, permitting to use them at high temperatures; the deposition of refractory metals on various types of glass, in view of the possibility of making the deposition at a low temperature; the deposition of various metals on substrata sensitive to hydrogen; the production of catalysts, by depositing metals having a high specific area.

What is claimed is:

1. A method for forming pure metal deposits, said method consisting in introducing, in the vapour state, at least one metal or metalloid fluoride of higher valence selected from the group consisting of: WF MF ReF PtF TaF NbF BF TiF SiF CF, into an enclosure containing at least one substratum to be metal-coated and a source of the metal to be deposited selected from the group consisting of nickel, copper, aluminum, zinc, cadmium, molybdenum, tungsten and zirconium, heating said source in order that the higher valence fluoride is transformed, when contacting said source, into at least one sub-fluoride of the source metal which coats the substratum and is transformed into fluorine and into the metal, which constitutes the desired deposit.

2. A method according to claim 1, wherein the metal of the metal fluoride introduced in the vapour state is the same as the metal of the source.

3. A method according to claim 1, wherein the metal of the metal fluoride introduced in the vapour state is different from the metal of the source.

4. A method according to claim 2, wherein the fluoride introduced in the vapour state is molybdenum hexafluoride, and wherein the source is molybdenum.

5. A method according to claim 3, wherein the fluoride introduced in the vapour state is molybdenum hexafluoride and wherein the source is tungsten.

6. A method according to claim 1, wherein the substratum is a material selected from the group consisting of tungsten, molybdenum, copper, nickel, monel metal, inconel, iron, graphite, silicon and alumina.

7. A method according to claim 1, wherein the source is heated to a temperature above the substratum temperature.

8. A method according to claim 1, wherein the source of tungsten is heated to about 750F (400C).

9. A method according to claim 1, wherein the source is selected from the group consisting of an electrically heated wire or a hollow rod.

10. A method according to claim 9, wherein said rod is coated with a metal obtained by sintering or by vapour-deposition.

1 l. A method according to claim 9, wherein said hollow rod forms a tank containing fragments of the metal to be vapour-deposited.

12. A method according to claim 1, wherein said substratum is the inner wall of a tube, and the source and the fluorine inlet conduit are located within said tube.

13. A method according to claim 1, wherein said substratum is the outer wall of a tube, said source and fluorine inlet conduits being located, outside said tube, within an enclosure which does not retain the metal deposit.

14. A product coated with metal deposits by the method of claim 1.

Claims

1. A METHOD FOR FORMING PURE METAL DEPOSITS, SAID METHOD CONSISTING IN INTRODUCING, IN THE VAPOUR STATE, AT LEAST ONE METAL OR METALLOID FLUROIDE OF HIGHER VALENCE SELECTED FROM THE GROUP CONSISTING OF: WF6, MOF6, REF6, PTF6, TAF5, NBF5, BF5, TIF4, SIF4, CF4 INTO AN ENCLOSURE CONTAINING AT LEAST ONE SUBSTRATUM TO BE METAL-COATED AND A SOURCE OF THE METAL TO BE DEPOSITED SELECTED FROM THE GROUP CONSISTING OF NICKEL, COPPER, ALUMINUM, ZINC, CADMIUM, MOLYBDENUM, TUNGSTEN AND ZIRCONIUM, HEATING SAID SOURCE IN ORDER THAT THE HIGHER VALENCE FLUROIDE IS TRANSFORMED, WHEN CONTACTING SAID SOURCE, INTO AT LEAST ONE SUB-FLUORIDE OF THE SOURCE METAL WHICH COATS THE SUBSTRATUM AND IS TRANSFORMED INTO FLUORINE AND INTO THE METAL, WHICH CONSTITUTES THE DESIRED DEPOSIT.

8. A method according to claim 1, wherein the source of tungsten is heated to about 750*F (400*C).

11. A method according to claim 9, wherein said hollow rod forms a tank containing fragments of the metal to be vapour-deposited.

14. A product coated with metal deposits by the method of claim