US2450853A - Method of coating by evaporating metals - Google Patents

Description

1948. w. H. CQLBERT ETAL 2,450,853

METHOD OF COATING BY EVAPORATING METALS Filed Dec. 5, 1946 J4 ar 1-1 7.1T 1 1-1-111 ail. J:

19 mmiwizzd BY Mburl flint-12b,

M, 'Ml/ ATTOPNEKS Patented Oct. 5, 1948 METHOD F COATING BY EVAPORATING METALS William H. Colbert and Arthur R. Weinrich,

Brackenridgc, Pa, assignors toLibbey-Owens- 'Ford, Glass Company; Toledo, Ohio, a corporation of Ohio Application December 3, 1946, Serial No. 713,699

; =14. Claims.

TDurpresent invention relates to a novel method .of coating-byevaporating metals. 3 It has to do, more -particularly, with the coating or wet-ting,iby capillary attraction,- of a'filament which, for example, may be' formed from a coil of ordinary tungsten wire; tantalum, molybdenum or columbiumfiwirenbyvarious-metals in the form-of an alloy with. small amounts of titanium, which met- .als to be evaporated in pure form normally do hot wet theseimetalli-c' filaments, and the applicationbfrsaidmetals or cnetal alloys by deposition resulting r-from' thermal evaporation, to the face orasurfaceiofrean article,:such as a piece of glass, porcelain: rrplaster, ,aametal, plastic, Cellophane, rpapen-aorlthe like, toeprovide areflective or 'metalli-zed-surfacelcoating :for saidarticle. The in- :ventionralso has todowithsecuring wetting and withthermal-evaporation of. such metalsfifrom tungsten; tantalum,- molyb'denum, or columbium filamentsi-alloyed-"or coated with titaniumsbythe application :twthefilaments of the pure metals :desiredtobe' evaporated;

Thisrapplicati-on -:is a continuation-impart of ourc:co-:pending application, Serial-No. 552,290, filedfieptember? 1, 19.44,;nowPatent No. 2,413,606.

Methods -and-' apparatus have previously been employed :to apply coatings of metals by thermal evaporation to the faces or surfaces of' such articles to gr'produce-gmirrors reflectors or metallized materials forother purposes. In these methods it :is desirable to eff ect' the thermalevaporation rof themetal, such as silver, copper, golden-alumi- -num,--b applying'fthe. metal directly to an electrically energized" and thus heated tungsten" .or other metallic" filament which is' preferably '10- .cated :Within a vacuumizedchamber. 'Theunetals whichmay beused as filaments for suchtevaporations mustobviously be of high meltingipoint and ialsol oi 710W, vapor pressure at "the ,"elevated temperatures :at e which themetals applied. to the filaments evaporate. Thus, tungstemtantalum, molybdenumand colurnbium have represented the onlyepractical,lmaterials *for such use. TPlatinum lalso -has been:used-to a small degree but its :high cost ,is general-ly; prohibitive. "While iron and nickeleare. :ofrrelatively :low vapor pressure, 2 they areof lsuchrrelativelylcwmelting point thatfi1aments madeiirom'them-rapidly burnout.

lwithuthese :-.filaments many of the 'metals can be readilyrevaporated. Thus; for-example, aluminum; magnesium, yanadium, barium, strontium, irom-mickel, 'cobalt manganese; thorium, chromiumaand .-titanium when applied to filaments of tungsten, rtantalum molybdenum orqcolumbium, will lonmeatinein avacu m, melt -a.nd:spreadzover .2 the filament by capillary attraction'and satisfactorylevaporation of these metals then occurs from the large amount of'surface which the molten metal covers.

1 However, with alargeJnumber of;metals which it is desirable to beable to-thermally :evaporate and which-fromtheir vapor pressure at :elevated,

temperatures 'should readily evaporate, t-it has been found difliculhfiif not impossible, to carry out satisfactory deposition-of such coatings'by thermal evaporation. :f-lhus; for example-,silver and copper whileqreadily lending-themselves to thermal evaporation from a crucible, cannot-be evaporatedreadily from. a coil of tungsten,. tanta- .lum, molybdenumeorcolumbium when applied to a filament of these metals and heated by electrical resistance. The silver or copper on melting shows. no ,afllnity. for the metallic filaments :and almost immediately :after melting collects :into a drop. and falls off of l the filament. This :lack :of ability to wet tungsten, tantalum, molybdenum and columbium occurs also with themetals gold, zinc, tin, antimony,.,cadmium,bismuth, le'ad, thallium and indium. .Witheachofthese metals the use of the fourayailable coil-filamentsas ameans of evaporatingthese metals-has not beenpossible, and less desirable means of heating have'been necessary where it became necessary to evaporate these under practical conditions repeatedly infthe commercial production of mirrors and metallic coated articles. As each ofthese metals, after melting, pulls together into droplets and falls off the filaments, there has resulted a wastage of the metal Whenever it has been attempted to evaporate them 'fromthese filaments and there have been continuous failures of the apparatus to' function due to the'loss of the metals from the heated wires; and where any metal has been evaporated-the amounts so evaporated have alwaysbeen uncertain and without control,

We have found that we may use tungsten, tantalum, molybdenum *or columbium as 'filaments for the evaporation ofmetals which do not wet" these filaments by causing them to wet such filaments by the application to such filaments,

or*the -forming thereon, of alloys of thosemetals which we desire to evaporate with small amounts of titanium, such as amounts ranging-from 01% to"5%, which is characterized inthat it will also form an-'ialloywithtungsten, tantalum, molybdenum: and columbium in the 'presence of the metal we desire'to evaporate. 'Thus, for example, we may addlsmall amounts o'f'titanium to silver and when'such'alloys are melted ona tungsten filament, the :silver will be found to wet the tungsten filament and to spread itself by capillary attraction over the surface of the tungsten wires. In the absence of the titanium the silver melts, draws itself into a droplet and falls ofi 1e filament wire because it does not wet the same. Not all metal have been found to act in this manner. Alloying the normally nonwetting metals among themselves, such as adding lead to silver, does not seem to bring about any desirable improvement in the wetting characteristic. In each case, however, it is found that the titanium readily form alloys with tungsten, tantalum, molybdenum and colmbium and also forms alloys with copper, silver, gold, zinc, tin, antimony, cadmium, bismuth, lead, indium and thallium. It has also been found the titanium when heated reduces tungsten oxide, molybdenum oxide, tantalum oxide, and columbium oxide, to the metals, and that the removal of coatings of these oxides, normally present upon filaments composed of tungsten, molybdenum, tantalum, or columbium, aids in securing the desired wetting since silver, copper, gold, zinc, tin, antimony, cadmium, bismuth, lead, thallium, and indium do not wet the oxide-coated filament. Thus, the titanium readily brings about the desired wetting and it appears clearly that this is accomplished through the reduction of the oxide coating upon the filament and upon the mutual alloying tendency which these metals possess. The titanium may also be added to the filament either as an alloy with the tungsten, tantalum, molybdenum or columbium, or preferably it may be employed as a surface coating or surface alloy with such filaments. Filaments containing small amounts of titanium are found to wet readily when the pure otherwise nonwetting metals are fused thereon. Thus the wetting is brought about in the presence of the titanium, and it is immaterial as to whether the titanium is supplied in an alloy applied to the filament or exists in the filament surface.

One of the objects of our invention is to provide an improved and satisfactory method or process of evaporating metals which normally do not wet heater filament coils of tungsten, tantalum, molybdenum, or columbium, by alloying the metal so as to cause the metals to wet the coils of such filaments and to coat the coils by capillary attraction so that thermal evaporation can then be carried out.

Another object o our invention is to apply to a tungsten, tantalum, molybdenum or columbium filament a metal to be evaporated which does not wet such filament coils, alloyed with a suitable proportion of titanium which alloys with the filament and brings about a proper wetting or coating of the filament wires by capillary attraction under the influence of heat applied to the filament.

As another opject of our invention there is provided an improved method or process whereby a metal which is to be evaporated and which does not normally wet heater filaments of tungsten, tantalum, molybdenum and columbium is alloyed with titanium and applied to such a filament, and by securing a wetting and coating of the filament by capillary attraction of the metal desired to be evaporated may be deposited upon the face or surface of an article, by thermal evaporation, to provide such article with a reflective or metallized surface coating.

As a further object there are provided filaments which have been pre-alloyed with small amounts of titanium which may be used directly to evaporate the normally non-wetting metals since such alloyed filaments are found to be wetted readily by the molten pure metals desired to be evaporated.

A further object of our invention is to apply to a tungsten, tantalum, molybdenum or columbium filament, a metal such as copper, silver, gold, zinc, tin, antimony, cadmium, bismuth, lead, indium or thallium, alloyed with a suitable proportion of another metal which brings about a desirable wetting or coating of the filament metal by capillary attraction under the influence of heat applied to the filament and thus permits thermal evaporation of the metals.

Generally speaking, and in accordance with our present invention, the metal to be evaporated which normally does not wet the heater filament is applied alloyed with small amounts of titanium to the extent of 0.1% to 5% or more, providing wetting characteristics to the coils of a filament which may be formed from tungsten, tantalum, molybdenum or columbium. Thus in order to thermally evaporate copper, zinc, gallium or arsenic, which are metals of the chemical periodic table arrangement found in series 5 or the metals silver, cadmium, indium, tin and antimony, which include metals of series 7, or the metals gold, thallium, lead and bismuth which in the periodic arrangement include series 11, all of which metals do not wet filaments made of tungsten, tantalum, molybdenum or columbium, we first bring about a satisfactory wetting and adhesion of these metals to the filaments by applying the metals to the filaments as an alloy with small amounts of titanium and then by energizing the filament and thus heating it we cause a melting of the metals. When the applied metal alloys are thus melted they react with any oxide coatings upon the filaments and reduce such to the metals, tungsten, tantalum, molybdenum, or columbium and then they apparently alloy to some degree with the metal comprising the heater filament wire and by reason of such the molten metals wet the filament Wires and by capillary attraction are drawn out over the surface of the coils. The molten metal which has thus covered considerable surface of the heated coil and is held thereto by capillar adhesion is thereafter evaporated uniformly from the heater coils to apply a surface coating of a metallic or reflective nature to an article such as a piece of glass, porcelain, silica, mica, plastic, metal, Cellophane, resin, or other support material, by deposition resulting from the thermal evaporation of the metal from the filament. The operations of thermal evaporation may with some of the metals, be carried out at normal pressure but generally are preferably carried out in vacuum chambers known to the art and within a high vacuum, which may be of the order of one millimeter down to 10 to the minus 5 millimeters or 'better. It is very necessary that the metal to be evaporated wet and coat the coil surfaces in order that the metal will evaporate uniformly in all directions. By securing such wetting action the thermal deposition of these metals, in addition to being made possible, has been found by our process to give uniform coatings.

We may also proceed to secure the objects within the scope of this invention by supplying titanium in the filament either as an alloy with the tungsten-tantalum, molybdenum or columbium, or as a surface coating; or as a surface alloy on such filaments. When the pure metals such as silver, copper or gold which will not normally wet the ;;pure tungsten, tantalum, molybdenum or columbium filaments are applied .to these filaments containing some titanium they will ,on melting; readily wet the titanium-containing filaments. ,Thus, -in genera1, theiinvention comprises melting the metaldesired to be-evaporated upon a tungsten, tantalum,mol ybdenum or columbium filament in the presence of titanium whichbrings about the desired wetting.anduadherenceof the molten'metal .to the heated, filaments.

will ibezsho wnifully later, ;pieces of the metal to be .evaporatedand .whichiihave .been previously alloyed withithe metal which brings about the alloying'with'and wetting ofithe fi1ament,:may be hung-onto theloops or coilsof the filament.

.Thezforegoing and. other obj sets; and advantages of the present; inventionwillappear from the :following :description :and :appended claims when consideredinconnection with the accompanying drawings forming a part of this specification wherein similar characters of reference designate corresponding parts in the several views.

:In said drawings:

jiFigure l .is a perspective view, partly broken away, illustrating one suitable apparatus for c'arrying-outour improved method or process.

Figure? vis;a perspective view of a fragment of an electric filament showing the application of a suitablemetalalloy to several of the coils or convolutions thereof,.and illustrating one phase of the method or process of wetting or coating the filament :by'said alloy; and

"Figure'3 .is a view similarto Figure 2 showing the filament after the completion of the wetting process :by the alloy of Figure 2.

Figure 4 is an enlarged, cross-sectional view of artungsten, tantalum, molybdenum or columbium electric resistance filament precoated with a thin layer of titanium.

Figure '5 is another enlarged, cross-sectional view showing a filament of tungsten, tantalum, molybdenum or columbiumwhich is alloyed only in'the surface of the filament with titanium.

Figure 6 is also an enlarged, cross-sectional view 'of afilamentiformed from tungsten, tantalum, molybdenum or columlbiurn, which is alloyed throughout with a small amount of titanium and upon which thepure metals, on melting, will directlyshowsa good Wetting action.

Figure 7isa perspective view of 'afilament c'ontaining titanium such as shown in Figures 4, 5 and 6 and upon whichp-ieces of :the pure metal to be evaporated have been ihung.

:Figurefi is :a "perspective View after the 'fi.la. ment and pieces of the metal of Figure '7 have been heated to effect a wetting of the filament.

Before explaining in detail the present invention it is vto-ioe understood that the invention is not limited .in its application to the details of construction and arrangement-0f parts illustrated in the acoompanyingdrawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. It is to be:11nderstood also that the phraseology or terminologyemployed herein is for the purpose of descriptionand-not of limitation.

Referring now to the drawings, we have-shown a suitable apparatus for carrying out our improved-method or process, as weil'as one suitable metal alloy and the steps of applying the alloy ora filament by a wetting action resulting from capillary attraction. We have also shown suitable alloyed filaments and "the steps of applying the pure metal to be evaporatedto such filaments and the wetting actionupon the filament resultgroundingfiange or projection 92 which is adapted to rest upon the top face or surface of the supporting base it.

Within the chamber provided by the housing ,we-have shown a suitable Work-piecesupport I3 for supporting a work-piece, such as a plate or pieceof' glass, plastic, plaster, paper, porcelain, metal, or the like M, in upright position.

Located within the chamber and mounted upon the supporting base it is a pair of upright supporting posts IE-between which is carried orsupported, in substantially horizontal position, an electric filament H5. The filament, as shown, is in the form of a coiled wjre made of tungsten, tantalum, molybdenum or columbium, oran alloy of these'with titanium or'precoated with a layer of titanium whose opposite ends are attached to brackets ii mounted. upon the supporting posts i5 and adjustable thereon so as to vary the posi tionor location of the .filament it with relation to the supporting base it.

The chamber provided by the housing ii'may, if desired, be completely evacuated of air through outlet pipe or conduit iila and have a high vacuum created therein by means of suitable air evacuating and vacuum creating means, such as a pump (not shown).

In accordance-with one method embodying-our invention which is to be performed or carriedout within the chambered housing ii, we preferably provide a metal alloy which may consist of silver, copper or gold or other normally non-wetting metal'and approximately 0.1% to 5% or more or" titanium. Pieces of this preformed silver and titanium alloy,'for example, or copper and titanium alloy, for example, or gold and titanium alloy, for exampleseveral of which are shown at iii,

in Figures 1 and 2, arebent and hung on the loops or convolutions 56a of the filament i6 composed of pure tungsten, tantalum, molybdenum or columbium in the manner shown.

is known that silver, copper and gold lend themseives admirably to thermal 'evaporationbut they have no wetting affinity for tungsten, tantalurn, molybdenum or columbium surfaces and therefore silver, copper or gold alone is unsatisfactory for coating thefilament it formed from eitherof these metals by a wetting action effected by capillary attraction. Wetting of the filament wire is essential to secure a maximum of evaporating surfaces to provide evaporation uniformly in all directions, to the securing of uniform deposits and also to avoid the dropping of the molten metal off the heater wires. We have found that titanium readily alloys with silver, gold and copper and the alloys have a wetting affinity for the four above-mentioned metals, any one of or more, with the silver, copper or gold to form the alloy iii, the titanium will serve to bringabout wetting or coating of said filament by the-molten metal by capillary attraotionwhen' and have caused their deposition upon the face or surface of a workpiece to provide metallized or reflective surface therefor. It will also be seen that while we secure the desirable requisite of wetting of the filaments of tungsten, tantalum, molybdenum or columbium by metals which normally do not wet these, by the presence of titanium this may be accomplished in several ways. Thus,we may apply separate pieces by a preformed alloy of such metals with titanium and these will wet the pure metallic filaments, or we may apply the pure metals to be evaporated to a filament containing some titanium either in its surface or throughout.

While we have referred to the use of tungsten, tantalum, molybdenum, or columbium as suitable metals from which the coiled filament or element 16 may be formed, other suitable metals maybe used for this purpose. We have mentioned these metals particularly since their high melting points and low vapor pressures at the boiling temperatures of other metals make these the practically desirable metals for use as such filaments.

We have described our improved method or process as preferably being carried out in a vacuumized chamber in which the step of wetting the filament takes place, as does also the Step of thermal evaporation of the metal to effect its deposition upon the workpiece to provide arefiective coating thereupon.

Obviously also in the case of the most readily volatile metals, such as cadmium and zinc, the melting of the metals and the wetting of the filaments, as well as the evaporation of the readily volatile metals, such as cadmium or zinc, may be carried out under atmospheric conditions of pressure if desired, while employing a suitable inert atmosphere.

Having thus described our invention, what we claim is:

1. The method of making mirrors by the deposition of a metal on a polished support material, comprising evaporating a metal from a filament made of a metal selected from the group consisting of tungsten, tantalum, molybdenum and clumbium wherein the metal is heated on such filament as an alloy with titanium which causes the metal desired to be evaporated to wet, to adhere to, and to spread out over the filament surfaces and by the continued application of heat to evaporate, and depositing a coating thereof on said polished support material. I

2. The method of coating surfaces which comprises evaporating metals from a filament made of a metal selected from the group consisting of tungsten, tantalum, molybdenum and columbium wherein the metal is heated on such filament as an alloy with titanium which causes the metal desired to be evaporated to wet, to adhere to, and to spread out over the filament surfaces and by the continued application of heat, to evaporate and to deposit upon said surfaces.

3. The method of coating articles by evaporating silver from a filament selected from the group consisting of tungsten, tantalum, molybdenum and columbium wherein the silver is alloyed with titanium and is heated, on such filament and wherein said titanium causes the silver desired to be evaporated to wet, to adhere to, and to spread out over the filament surfaces and bythe continued application of heat, to evaporate and to coat the articles by deposition of the silver thereon.

4. The method of coating a support material by evaporating silver within a vacuum from a filament selected from the group consisting of tungsten, tantalum, molybdenum and columbium wherein the silver is heated on such filament in the presence of titanium and wherein said titanium causes the silver desired to be evaporated to wet, to adhere to, and to spread out over the filament surfaces and by the continued application of heat, to evaporate within the vacuum and to coat by deposition said support material.

5; The method of coating a support by evaporating copper from a filament selected from the group consisting of tungsten, tantalum, molybdenum and columbium wherein the copper is heated on such filament in the presence of titanium and wherein said titanium causes the.

copper desired to be evaporated to wet, to adhere to, and to spread out over the filament surfaces and by the continued application of heat, to evaporate and to coat by deposition thereof on a surface of the support.

6. The method of coating a support by evaporating copper within a vacuum from a filament selected from the group consisting of tungsten, tantalum, molybdenum and columbium wherein I the copper is alloyed with a relatively small amount of titanium and is heated on such filament and wherein said titanium causes the copper desired to be evaporated to wet, to adhere to, and to spread out over the filament surfaces and by the continued application of heat, to evaporate within the vacuum, and to coat the support by deposition.

'7. A method according to claim 4 wherein gold is substituted for silver. 7

8. A method according to claim 1, wherein the titanium is present in a relatively small amount.

9. A method according to claim 2, wherein the titanium is present in an amount less than 5%.

10. A method according to claim 3, wherein the titanium is present in an amount under 5%.

11. A method according to claim 4, wherein the titanium is present in a relatively small amount.

12. A method according to claim 4, wherein gold is substituted for silver and wherein the titanium is present in an amount less'than 5%.

13. The method of coating a support material by evaporating a metal within a vacuum from a filament selected from the group consisting of tungsten, tantalum, molybdenum and columbium wherein the metal is heated on said filament in the presence of titanium and wherein said titanium causes the metal desired to be evaporated to wet, to adhere to, and to spread out over the filament surfaces and by the continued application of heat, to evaporate within the-vacuum and to coat by deposition said support material.

14. A method according to claim 13, wherein the support material is a polished support material.

WILLIAM H. COLBERT. ARTHUR R. WEINRICH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Colbert Dec. 31, 1946 OTHER. REFERENCES

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