US2602033A - Carbonyl process - Google Patents

Description

*July 1, 1952 J. J. LANDER 2,602,033

CARBONYL PROCESS Original Filed April 6, 1946 3 Sheets-Sheet 1 20 '43 I zo@ 42 2/ /NVENTOR J J LANDE? July 1, 1952 J. J. LANDER 2,602,033

CARBONYL PROCESS OriginalA Filed April 6, 1946 3 Sheets-Sheet 2 METALL/c Hor ans cARoNn. www liv/.Er A INLET PLU.: co uw /Nl/ENTOR J. J ANDER A7' TORNEV july 1, 1952 .1.1. LANDER 2,602,033

CRBONYL PROCESS original Filed April e, 1946 3 sheetsheet 5 ATTORNEY atented .uly 1952 cARoNYL PROCESS Y James J. Lander, Millington, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Continuation of application Serial No. 660,140, filed April 6, 1946. This application January 18, 1950, Serial No. 139,301

W 10 Claims. 1

This invention relates to processes for coating metals such as iron, steel, nickel, copper or other metals and ceramics or vitreous materials, or any other materials capable of withstanding suiiiciently high temperatures to be plated with metals or carbides of chromium, tungsten, or molybdenum or compositions including a plurality of such metals or their carbides or mixtures of one or more of such metals or one or more oi their carbides.

This application is a continuation of my application Serial No. 660,140, filed April 6, 1946, now abandoned, which in turn is a continuation-inpart of my applications Serial No. 504,418, filed September 30, 1943, which issued on July 18, 1950 (U. S. Patent No. 2,516,058), and Serial No. 525,123, iiled March 4, 1944, now abandoned, and all rights, priorities, and benefits arising from such facts are claimed.

Others have previously suggested the plating of metals with certain other metals deposited from metallic carbonyls under conditions alleged to deposit pure or adhering layers but such suggestions have been defective and insufficient in setting forth the conditions necessary to deposit pure metals or adherent layers and also have failed to recognize that carbides may be so deposited. Y

There will herein be set forth conditions which must be observed and features of operation and procedure necessary to effect substantial improvements not disclosed by prior workers in the art.

The metals, tungsten, molybdenum or chromium, may apparently exist in different crystalline forms and they also may form several carbides. Inraccordance with features of the present invention, the processes described may be controlled to deposit platings of the metals in different crystalline forms and may also be controlled to plate carbides in different crystalline forms.

In particular, tungsten and molybdenum may exist in the form of carbides having a hexagonal crystalline structure and a cubic crystalline structure. Conditions may be controlled so that one or the other of these forms of the material may be deposited in the plating.

For certain purposes it may be desired to plate or cover the surfaces of metals or similar objects with coatings, especially tightly adhering coatings of oneA or another of such carbides or mixed carbides of these metals, or of the metals themselves. For example, an electrical contact may be plated with tungsten carbide to produce a durable and are resistant surface. Also, for example, an electrode or grid may be plated with a form of molybdenum carbide consisting essentially of MozC to make it heat resistant but poorly emissive of electrons or with tungsten carbide consisting vessentially of W2C to make it a good emitter of electrons when heated or M020 or W2C may be plated to form a hard facing on the object. Among such objects to be plated within the scope of the invention are included space discharge filaments, grids, anodes, electrical contacts, metal cutting tools having their working faces plated, metal working rolls having their working faces plated, metals to be subjected to corrosive gases at high pressures or high temperature, or both, either or not coincident with mechanical impact, wire drawing dies, bearings, such as clock, watch or compass bearings, mirrors for any purpose such as reiiectors of astronomical telescopic instruments.

A feature of the invention relates to the stabilizing effect of carbon monoxide under different conditions of vtemperature and pressure upon control of the production of definite carbides or relative portions of metals and carbides.

Another feature relates to the avoidance of the detrimental effect of impurities.

Another feature relates to preventing the existence of conditions inhibiting the formation of pure metals or conditions inhibiting the formation of carbides in general, or conditions inhibitving the production of particular carbides and promoting the production and deposition of the particular metal carbide or alloy which is to b deposited.

The invention may be applied to the plating of objects which have internal surfaces, under-cut surfaces, depressions or grooves or irregular surfaces with simple or mixed metals, carbides or alloys of the class mentioned, a matter of importance because it is often difficult to deposit material uniformly by plating upon internal surfaces, recesses, or in the bottoms of grooves of objects.

A feature of the disclosure relates to the removal of foreign bodies such as metallic oxides from the surface to be plated to such an extent that foreign bodies of natures and in such small quantities as one might think inconsequential are removed.

Other features of the invention relate to methods of promoting adherence of the plated metals, alloys or carbides to the surfaces to be plated, tothe eiects of varying one or more of the nature, pressure, temperature, purity, and kind of gas content supplied to the plating tank chamber. methods of and apparatus for causing plating to be applied on desired surfaces only, and control of the crystal structure or atomic arrangement of the applied plating by controlling pressure, temperature and influx of gases supplied coadjuvantly with the Agas or vapor.

A special feature of the invention relates to the use of a continuously maintained reduced pressure in the plating chamber. It is accomplished by sufficiently slow introduction of the metallic carbonyl and other gases coincident with a suiiiciently rapid and powerful pumping maintained at a very low degree of pressure in' the plating chamber. It is believed that this Ygives the molecules of metallic carbonyl a long, mean free path whereby the effects of thermal dissociation may be controlled and pure and more adherent coating produced.

Another feature of the invention relates to the control and rate of deposition by introducing 'ca-rbon monoxide or hydrogen or one of the other or both of these gases in controlled proportions to control the plated composition.

Another feature of the invention relates to the introduction also with the hydrogen of a limited and properly controlled amount of water vapor which, in the case of plating molybdenum or tungsten on certain kinds of objects, is found to be beneficial. In plating with chromium the use of water vapor is excluded and, furthermore, in plating base metals or materials containing substantial chromium contents the use of Water vapor is excluded. Thus, for example, in plating molybdenum or tungsten or their carbides upon a kind of steel known as Stellite which, in a typical form includes about 27.5 per cent chromium, the use of water vapor is excluded because the chromium becomes oxidized and results in a poorly adherent plate. However, in plating such objects with molybdenum or tungsten the plating may be initiated and carried through the preliminary stages with the exclusion of water vapor and thereafter water vapor may be introduced either for the purpose of controlling or varying the plated composition or for other reasons. In this case the initial deposit of molybdenum or tungsten or their carbides forms a protective layer over the Stellite or other material, which cannot be exposed to heated Water vapor in the plating chamber, so that thereafter the Water vapor may be introduced.

Carbonyls of tungsten, molybdenum and chromium are white solids which decompose at temperatures of around 150 C. and they have substantial vapor pressures ranging from 15 to '60 millimeters of mercury at 100 C. When Ythey decompose upon a hot metal or similar surface under properly controlled conditions a film of metal or carbide of the metal of the carbonyl or carbonyls is deposited uponthe hot surface.

A difficulty encountered in securing adherent deposits has been found to be due, in part at least, to foreign substances upon the surface. One of the most troublesome foreign substances upon the meta-l surfaces are undesired metal oxides.

A surface to be plated which is suitably free from oxides and other substances may be and has been produced by abrasion, electro-etching, or other chemical methods with prevention of subsequent contamination. Specifically, the metal object to be plated may be treated with acid and washed free of adherent acid in an organic solvent such as alcohol and thereafter placed .in the plating vessel hereinafter referred to and subiected to immediately applied vacuum. This serves to remove the residual alcohol by evapora tion.

The object to be plated may be treated preliminarily to the introduction of the carbonyl gas by heating to relatively high temperatures such as 600C. in a vacuum which is maintained by operating the kvacuum pump. This tends to clean the surface.

The object to be plated may thereafter be ,raised to the desired plating temperature, the carbonyl vapor admitted, and the plating accomplished.

However, hydrogen may be admitted to the plating lvessel prior to the plating operation with the result that the surface to be plated may be further or more effectively cleaned, with the result vof a more perfectly adhering plate. Hydrogen may be admitted to the plating vessel either immediately or after the object has been subjected to vacuum or heat or both for a period of time. The hydrogen is admitted from a suitable inlet and removed by a vacuum pump through suitable outlet and during the time-the object to be plated is exposed to the hydrogen the temperature of the object to be plated may be raised as high as 600 C., more or less, dependent upon the nature of the object and its surface impurities with the result that oxides and other substances upon the surface are more thoroughly removed. Thus, for example, oxides will be reduced and the oxygen will combinewith hydrogen to form water and carbides lose their carbon and the carbon thereof is combined with the hydrogen to form hydrocarbons such as -CI-I4. These hydrocarbons are carried out with the hydrogen and eliminated.

The admission of some hydrogen during the plating operation along with vthe carbonyl vapor and the carbon monoxide gas may be through either the same inlet which supplies the carbonyl vapor or through a separate inlet. In either case an effect of the hydrogen is to produce an effect analogous to that which in electrolytic plating is sometimes styled throwing power which signifies that plating in crevices, grooves or depressions is more effectively accomplished and the metal plate is applied more uniformly over the surface to be plated. The vinflux of hydrogen for the purpose of plating with carbides is subject to the limitations hereinafter set forth.

The deposition of adherent carbide coatingsA may be accomplished at relatively low tempera@ tures and moderately low vacua with little or Ano influx of carbon monoxide gas, as increasingly better vacua are employed the use of ,proportionately greater amounts of carbon monoxide is desirable. The nature of the carbide'deposit is also Variable with conditions, thus with 4little or no carbon monoxide gas, at pressures of a few millimeters of mercury, and at low temperatures molybdenum and tungsten carbonyls form chiefly face-centered MozC or W2C, whereas with higher pressures, higher temperatures, and kgreater'COv gas concentration, in the case of molybdenum carbonyl, MOC' is formed. One may introduce appreciable quantities of hydrocarbons of low molecular Weight such as methane CH4 into the plating vessel in the case of plating carbides, especially after the bond has been formed.

Under certain circumstances plating may be accomplished by the use of metallic carbonyl vapor alone in a ,pure form. For example, in order tov plate an iron surface 'the plating may be started at a sufficiently .high temperature to secure a satisfactory bond or adherence and deposit metal from molybdenum, tungsten or chromium carbonyl gas. In plating molybdenum, for example, at a relatively high plating temperature beginning at about 600 C. and continuing in the range of 400 C. to 500 C., metallic molybdenum is vdeposited provided the infiux of carbonyl gas is maintainedV suliciently low and the vacuum is maintained also suiiiciently low to hold the carbon monoxide gas, CO, to a low concentration. At a lower plating. temperature, for example, 200 C. to .400 C., a carbide plating is deposited which has a face-centered cubic arrangement. The tendency is to deposit the cubic carbide at low temperatures and athigh concentrations of carbon monoxide. As the temperature is raised and as the concentration of carbon monoxide is lowered, the tendency is to deposit the pure metal molybdenum. At a high temperature and at a relatively high carbon the case of plating from tungsten carbonyl vapor Y except that no plating occurs in the range around 200 C. to 300 C. and so far as has been determinable from X-ray analyses, the hexagonal carbide W2C has not been produced. However, a cubic carbide of tungsten may be produced. The boundary zone between pure metals and carbides is the combined function of temperature and carbon monoxide pressure. The pressures used may range from about 1/1000 to 10 or 12 millimeters of mercury. From X-ray analyses supplemented'by chemical analyses thecoatings or platings described as cubic molybdenum carbide occur roughly with the empirical formula MozC although the carbon content in atomic per cent varies over a range from around atomic per cent up to about atomic per cent.

Plating may also be accomplished by introducing purified hydrogen along with the gaseous carbonyl in amounts ranging from moderate to very considerable, for example, up to 1000 molecules of hydrogen per molecule of carbonyl vapor. Heating the surface to be plated in hydrogen is beneficial in reducing surface oxides, and, in some cases, it improves the bond between the plating and the surface to be plated and, in other cases,'itrappears to be fairly essential to producing a satisfactory bond. When the ratio of hydrogen to carbon monoxide gas in the plating chamber becomes large, the tendency is to remove carbon so that pure metals may be plated at somewhat lower temperatures and higher pressures. In general, in plating chromium there is a greater tendency to deposit both oxides and carbides than in the case of molybdenum and tungsten and in the caser of this metal an extremely puremetal free from carbides is not deposited but the plating may be made extremely hard. It appears that metallic tungsten can be plated at considerably higher pressures than in the case of molybdenum and therefore the plating rate in the case of tungsten may be higher.

Under many circumstances platings or coatings containing considerable carbon are more hard and brittle than may be desired for certain purposes and the hardness and brittleness may be reduced by introducinga certain percentage of water vapor along with the hydrogen. For

example, percentages of water vapor relative to the hydrogen ranging up to fteen molar and preferably no higher than ten molar per' cent may be utilized inthe case of plating certain' 6 metalsY as nickel, iron, copper and iiieriis forms of steel. Some steels, such as those con-V taining chromium, will be oxidized by water vapor and, consequently, water vapor or so-called wet hydrogen may not be used in plating them, al-

though the plating may be started without water vapor and after a suiicient layer to protect the plated object from the water is deposited, the

water vapor may be introduced and the plating continued. Subject to these limitations wet hydrogen may be utilized and is benecial when it may be desired to prevent the deposition of carbon in the plating. For example, in plating molybdenum at 625 C. in a plating gas containing 2 molar per cent of water, plating was found by analysis to contain 0.15 atomic per cent of carbon with a slow plating rate. However, vwith a considerable faster plating rate and by using 8 molar per cent of water, the plating contained 1.8 atomic per cent of carbon and withy a still higher plating rate and 25 molarper cent of water, the plating contained 7.0 atomic per cent of carbon. Therefore, while water vapor is useful v in reducing the carbon content, the carbon content can be kept extremely low only at a relatively low plating rate although these may be somewhat higher than may be used for depositing a similar composition without the useof water.

However, one should not conclude 'that the introduction of oxygen from the air is equivalent to a small added amount of water because the experimental evidence is to the contrary and the introduction of an amount of air equivalent to one per cent oxygen has been found to result in a very inferior plating.

As stated above the introduction of y/aterre-` resistant coating on dies, rolls, or machine tools,

hardness is highly desirable, but extreme brittleness is not desirable.

containing considerable carbon but no carbide:

-as such because the presence of the carbide makes.

the'coating more brittle without increase of hardness. Similar considerations apply to the production of tungsten plating. For example, platings of tungsten containing considerable carbon plated at 450 C. to 500 C. in dry hydrogen at a rather high pressure may have a hardness measured on the Vickers scale above 2000. `AIn plating chromium only relatively hard coatings ranging from Vickers 1200 to 1600 have been produced.

As previously stated, preliminary cleaning of a metallic specimen by abrasion in absolute alcohol is a satisfactory method of producing a surface to be plated. Also in plating some alloys such as Stellite electrochemical polishing can be employed. A preliminary step of introducing hydrogen before the metallic carbonyl vapor is introduced is often beneflcial in producing a surface to which the plating will form a good bond. At temperatures of 500 C'. to 800 C. wet hydrogen is a good cleaning agent for some sub-'- stances but at lower temperatures quite often only dry hydrogen may be' used.

For such purposes itv appears that the best type of plating will be one.v

loyed steel surfaces .can underlconditionsof .high punit-yV of hydrogen .and .good preliminary .abra sion be :satisfactorily .cleaned :at 590? '.CQzn hy-.- drogen containing from .two to .eight per .cent water vapor, .amore satisfactoryV technique isto use .only .dry v.hydrogen until .the `ternperature of the specimen `rises .above 500 C. whereupontne Wethydrogeri V.is introduced and vthe temperature rises continually. toBfl" C. 'In 'plating V copper Wet ihydrogenhas been foundto be satisfactory in heating the specimen .from-.room :temperature to .880?- C. .In the .case of ftellite all T vvatcr mustbe .vigorouslyexcluded and; a yeryhigh .temperature is required for adequatecleaning. Teinperaturesupto 100 C. upto il'lQWC. havebecn used. As a :general rule, bonding. of .the plating to the .metalto `be .plated is more satisfactory if..tl' ie..plating.is .started at relatively high tcmperatures. rihus inthe. case of .copper a teinperatureofaround 8.0.09 C. `issuitable Yand ape pearsto be beneficial. As `previously s et forth, a nigh plating rate is undesirable during .the bcndmg step as. colloidal particles 4oopsistiria largelyof :carbide .tend to beproducpd. Q onscquently. :goed bonds require `a low platine ratp and,A in practice, it has foftenbeen found desirable-tense a rateone-.tenth of that-v liislused at a later stage of the process.

substancescther than metals beplated within the limits that `the substances must be such as can withstand the requiredhigh teniperature. Within this liirlitation glass1 vitreous materialsfandother mat rials may te plated, ,it beine-understood,fhowwer. that the .Considerations for forming a good bond vary with the substance'which is to be plated.

Foreign materials such as Water, air and orearliomaterials mustbe guarded against Whether present in the 4carbonyl or Whether arising from supports or other elements in the platine ohamber Ol Whether introduced throughvleaks in the evacuatedsystein or from other causes. The in.- troduction of such substances is likely to lead to ,unsatisfactory or, at best, to unpredictable results.

The process may be employed for the formation c f plates .consisting oi allora Thus, for example, ari-alloy or" molybdenum and tungsten may be deposited-by utilizing carbonyls in a molecular ratio approximately equal lto their vapor pres sores. spccimensplated at 6oo C. with wet hydrogenzand'at a moderate plating rate were quite hard and brittle While molybdenumalcne plated under similar conditions is soft. By employing separate carbonyl chambers with separate controis alloys of various compositions may be similarly produced- Apparatus useful or convenientl for plating the variousbodies is illustrated in the accompanying drawings where:

Eig. 1 is a diagram or" essential parts of anapparatus Which may be employed for plating objetssuch assheetsJ plates, bars, contacts, electrodes, oto.;

Fig. lA is;a modification oi a fragmentary part oi Eig. 1-between the section lines X-X and YH-.YI-niodied to illustrate one method of securing @suitably thick layer of plating upon the innerA surface of an orice of ametal body;

Fig. `1B a further modification of a fragmentary part of Fig. 1 taken between section lines X-X and Y.-Y illustrating a method which may lberemployed for plating portions of metallic opjeotsapd .in platine other portions thereof to an appreciable extent:

Fig. 2; illustrates.the.modifled method ofmoll'l'lf' inge, relay armatureso as :to .platethe'working surfacesof its contacts;

Fig. 3 i1lust-rates a methodof mounting-metallic.discs.upon a vitreousfbody to prevent onesure face thereof from Lbeing plated .appreciably .While causingothersurfacesto be plated;

Fig. 4 villustrates apparatus suitable for plating one side of a discorsheet of material illustrated as a vitreous .material but which may be metal or othersubstances;

Fie. 5 is .a diagrammatic illustratiompartially in `cross section of an arrangement employing` a moving injector -for uniformly plating the interior surface of a body having acylindricalor approximately cylindrical opening therethrough;

and

Elsa, .7.;8fand 9 illustratedetails 'of the ape paratus ofFig. 5.

Beierripg to v iiig. .1 and its operation, acerarnic orelass vessel li! isi-providedwitha coolinewater iaolsat il having azwateriplet l.2- f,rom-asuitable Sourceoisupplyand awatercutlet I3. Theinlet. arid outlet ,rpay be loca-ted onany Suitabportions of. theeiass or ceramic vessel. The 4vessel I9 Which-is illustrated as tubular `in formis prof vided Wltha lareetielitlytiipe stopperl ld-.which marte made.easfiielitbyfmearlsor eroundgIass Suiiaoosor otherwise .and has connootpd-tozittwo other t 15 and liahichareU-shaped, Tube i5 isfprovided with Valras. aprilia and-a Sido inlet tube `|71; with avalve llc. Tube 1 6 is pro.- vided with a valve I8. A winding orooil i3v adapt ed-io botraversed by high froauanoypurrorltpupplied from a, Suitable bien, iraqaenoyfsource i9 hline, mounted orotilprwise disposed abaptithe tubell.

An Obiei. 20 .of metal ilo be plated ora group of Vobiola may be plaoedinside @estube I9 .by removing the Stopper li; the specimen-rimas' be placed on wedeefshaped Supports 2l Oriel-ass. mica or ceramic materialor otherwisegliilaefsppported or disposed-Within diei/osseil i0. I isomo instances it may be merely Sufficient-to larice obiectlpr group of Yobjects Within thevoSsel l0- Theobiect 20er objects -20 may oopsistfoflirop. nickel, any typeof steelor ferrousl cobaltou -or nickelous alloys known to lineart-as Well asimetals ,or alloys of the maialstunesteh. vanadium,

titanium, molybdenum. tantalum., copper. or

stainlesssteel, tccisreel, can metal., .ouilerystaet brass, bronze or any other metal of properties similar to these. I t may consist of a metallic obiect to be platedorcoated for-artistic reasons,

Vor durability, or toproduce a hard surfacerelsstant to abrasion or a surface resistance V-to chemicals ingaseousor liquidfom and may be of any shape whichniay be heated sufticintly uniformly upon the surface or surfacesto lice .z plated by means of high frequency induction. Carbonyl powder. for Yexample chromium. time sten or molybdenum-carbonyl powder, is placed in one of the Ufshapedtubeaior example, tube is, and the tube is mcmtaincd ccm by bengim mersedin brineI ice Water, solid CO2 or 'other suitable medium in a container 24. I'f valves I'1 and ila are closed, the tube l Bneednot be cooled. The tube I6 is connected to a vacuum pump and the 4valve I8 opened to thoroughly exhaust the vessel I U .0f air. n

An alternative object -2a consists of a grldfor a vacuum or Space discharge tube Whichliasa stem Zlib by which it may be mounted in the'tul for use forr` plating thestem 20h is :mounted inan opening in a block 2la of porcelain or glass; from 9 this diagrammatic indication one is not to infer that grids 20a and blocks 20 would be plated at one time or that the high frequency heating field suitable for a block 20 would be suitable for a grid 20a; in practice a number of grids might be mounted in a multiple block 2 Ia and plated at one operation. The grids could be of at mesh, cy- Y lindrical mesh or other desired shape and spacial- 1y positioned in the heating field as desired or as necessitated by their respective conformations.

'As a preliminary operation, after inserting the object 20 and closing the vessel I0, the carbonyl may be purified by placing it in either tube I5 orIB, exhausting the vessel I0, warming the tube in which the carbonyl is placed, chilling the other tube with solid CO2 mixture and passing tin pure hydrogen over the carbonyl to distill the metallic carbonyl from one tube to the other; gaseous impurities such as H2O Vapor may thus be reduced vor eliminated with the hydrogen. This'operation may be repeated one or more times or its equivalent may be performed in a separate vessel before placing the carbonyl powder in the apparatus illustrated. The advantage of doing it in thesame apparatus lies in the certainty with which recontamination of the material is prevented. We may assume that this step has been performed, if necessary, and the carbonyl is in the tube I at the beginning ofthe plating operation.

.After theexhaustion or during the exhaustion of the vessel`l hydrogen may be admitted through tube I or I6, preferably in a slow `stream through tube I5 until substantially the entire gas content of the tube consistsof hydrogen whereupon the switch 22 is closed and .the specimen 20 heated to redness by high frel,apparently approach near the melting point of the metal to be plated. The specimen has been cleaned and all oxides, or substantially all oxides, grease, film, etc. have been removed from its surface by the heating to redness in the presence of hydrogen gas. The Vessel 24 is now replaced with-another vessel containing warm water at a temperature of about 20 C. and the water in the water jacket II is meantime held at around 20 C. The operation of the vacuum pump at the outlet of tube I0 'is continued and at this stage or before, if desired, a vessel 25 filled with ice Water may be placed around the tube I6. The carbonyl powder in the tube I5 is now vaporized and passes through the tube I0 with the result that there is deposited upon the surface of the specimen 20 a coating of carbides of tungsten, molybdenum or chromium, as the case may be, 'of a thickness of about 2 mils in approximately 30' minutes. Rapid deposition of the coating is desirable and continuous pumping at the outlet of tube I6 is necessary to remove the carbon monoxide which is formed. The tube I5, being immersed in ice water or other low tem- .perature medium, such as solid CO2, serves as a trap to precipitate and recover any unreacted 10 reached the proper dimension as may be determined by observation or experiment, the interior of the vessel I0 may be restored to atmospheric pressure, the stopper I4 removed, and the'object 20 becomes accessible for removal from the vessel.

In a particular case 0.32 cubic centimeter per second of H2 was passed over `molybdenum carbonyl maintained at 16 C. for 60 minutes at a plating temperature of 370 C. to produce a plate thickness of 0.0022 inch which contained 25.0 atomic perv cent carbon and was estimated to consist of per cent molybdenum, or MozC, in gamma or face centeredfrom plus 5 per cent alpha molybdenum. By reducing the plating temperature to 330 C. the carbon was 25.5 atomic per cent andthe molybdenum per cent in gamma form. The structure was determined by X-ray examination, the carbon content by analysis.

As an alternative and for some purposes `preferred method, the ingress of carbon monoxide either with or without hydrogen along with the metal carbonyl may be continued during the entire plating process and'these gases may fbe caused to enter through the inlet tube containing the carbonyl powder or through another tube. The amount of carbon monoxide used may vary in accordance withv the principles elsewhere herein stated. Also when hydrogen or other gases is or are introduced, this may be through the same or a different'inlet and for this purpose the apparatus may be provided withl as many inlets like IIb as desired.

The apparatus of Fig. 1 thus may be employed to produce coatings, of tungsten carbide (W2C), molybdenum or chromiumcarbides on metallic objects, such as theobject 20 or similar objects such as contacts, filaments or other electrodes, edges of cutting tools or other objects. For example, a nickel grid 200. for a vacuum tube could be mounted inA a ceramic block Zia Vand coated with MozC or W2C bythis method, or a filament could be coated with W2C. Q

Fig. 1A represents almodification of Fig. 1 as applied to coat or plate the interior surface of a tubular object with little or no plating ofthe outer surface. 'I'he tubular object 20 to be plated is traversed by a passage 20c. It is mounted in a frame of mica which comprises two baffles 42 which substantially flll the cross section of tube I0 and cause all the carbonyl gas to pass through the passage 20c. The outer surface is covered with a mica layer 43; the ends of object 20 are in this case left exposed and are plated. Very little deposit occurs upon the surface of the mica and thatl only upon the part vwhich lies close to the object 20 and thus becomes heated.

In Fig. 1B which is a modification in part of Fig. 1 between the lines vX--X and Y-Y, two other objects are illustrated in. the plating chamber I0. Ordinarily, however, at most only one class of object would be placed in the plating chamber at a time. These would not necessarily be placed in the positions shown. The principal object of Fig. 1B is to illustrate methods of plating portions of the surface of an object to the exclusion of lother portions. A clock pinion mounted on axle 44 may be arranged to be plated on a conical end of the axle. Avplastic or vitreous body 45 is made in two or more halves into which the axle 44 and its associated wheel, for example, the balance wheel or pinion, is to be fitted. Thebody 45 isvmounted `on standards or conical supports 2|. When -thezhydlogengis spaanse appliedv then aXl'e 44 becomes.- heatedlbut'the 'Vitrleous.' body' 45.- doe's noti-become heated. therefrom' for a.- lor'1g"-tin:le-` especially' as.. the. constant now of' gas' including' hydrogen'.` carries away' the l'ieat. fairly' rapidly; The" plating' thus occurs solely upon the conical ends of the axlelsfor the purpose oifo'rming. hard bearing surfaces.V Platingslofi tungsten high. in interstitial carhideor tungsten'. carbide.` may be used. forztnis. .purpose and platings have been depositedwhich.. on test, were found to ber-harder thanl sapphire Thebody 46 may comprise a. cylindricalxelement. having asc'rew threaded portion such. as might be. utilizediforA an'. electrical relay or. switch contact-tube plated only-omits'end 41. A .plastic or' vitreousl body 48tmay be constructed: inY two halves and theobject: 4.1. placedbetween the' two halves so as izo-'expose only' the end 41 which is the onlyportion to beplated. Iii-the particular arrangement a series of openings49.' are provided tov permit they now oiA gases through. the plating chamber to the outletV t6; Ino'the'r. arrangements the body 48 mightv not fill the entirety of the cylindrical space inthe plating chamber. and the openings 49 would' beunnecessary.

Fig. 2 illustrates another. arrangement of plating the contact surface-50mi arelay armature L This armature may be placedbetween-'the twchalves of a vitreous-'body 52 so-tha-t only the con-tact surfaces 50 are exposed. 'I-'he assembly 5|-, 52 is then placed: in. the-plating chamber in -a manner to expose vthe-contact surfaces 5% symmetrically tothe stream-oi` carbonyl gas.

Fig. 3 illustrates anotherf arrangement in which a plastic or vitreous 'bod-y' 53 which may consist. of; glass or porcelain has-a-number ofcontactbuttons placed upon. itl so thatthe." upper surfaces and. the cylindrical surfaces.v of the buttons 54` may be. plated. 'Ehebottomsurface resting onthefbody 53 isv substantially `unplated. and couldbe welded, orsoldered vtoen armature or other metallic support .to serveas anY electrical contact.

Fig. 4 illustrates-another arrangementin which metallic carbonylsalong the. carbon monoxide and' hydrogen are introduced. .through pipes l5 and l'lb controlled by val-ves.` 11d and ITc -tothe interior of aplating chamber .55. Plating'chamber 55 has an outlet tube. I5' leading to a sunlcently powerful vacuum pump and controlled, if desired, by a valve 18.. A Water-jacket having an inlet tube 2 andan outlet tube L3 lsurrounds the chamber 5.5 whose walls 56' are kept cool. A sheet of material 51 to be plated is' placed 'against the end of the chamber 55 and sealed thereto by rubber or copper gaskets 58 and screws 53 which pass through the flanges of a ring Gland hold the sheet-51 in a, firm,l gas-tight man-ner against the arm of the plating chamber. A chamber 60A conventionally .illustrates -a ue'which may be supplied with hot gases from a furnace to heat' the sheet 51 to a desired'- considerably high temperature during" the plating' operation.. Any suitable 'source' of hot' gases' or appropriate heating means may be employed. The. inlet tubes l5 and' I'1b are connected to a plating head 6l which ispprovided onY the side towards' the sheet 51 with a considerable number of' uniform openings 62 through which the plating' gases pass to impinge upon the surface of the plate 51.` vSheet 51 may consist' of glass', vitreous material, any plastic which will withstand the'n'ecessai'y high temperature, andv possessesv a sufliciently low vapor pressure thereat, or metal sheetof any of the kinds previously enumerated.. Sheet. 51- 'n'e'ed not .necessarily be plane but may be* curved, bel

12 concave.v or convex orotherwise curved: or; shaped andztheadiacen't surface: ofthe plating head,- 62 may bei appropriately shapedin conformity therewith.

Figs'. 5- to 9, inclusive. illustrate .certain details of an arrangement for. plating.' or coating the interior:surface'` or hollow'bodes such as the body 63 .which may be longer-.short and whoseinterior surfaceY maybe straight or curved; grooved or slotted. The body 63 is:placed;in a. cylindrical plating. chamber: 64 mcuntedupox1a suitable support B5 which is placed in the plating. chamber to holdithe body 63 in; approprient-exposition; The bottom of theplating chamberisiclosed by means of a. bottom plate GEzheld. in position by screws 61 and. .sealedwitha copper orjothersuitable gasket. 68. The. top .of/the 4plating chamber is sealed. witha' plateI lill' held in place by'screws 19 also. sealed with an. appropriate gasket 1|. Through anopen'ing inthe-.topplately there extends a hollow' moving injector lz'forisupplyng plating. gas to the-interior'bore'of the objectlli. The moving injector passes through algas-tight seal. 13 which. is more or less .conventionally illustrated and may consist of severalsealsinseries. The top' andfbottom plates 66. and:Y 69 are provided with copper tubes- 14 forasupplying. cooling water. during the plating operation. These tubes 14 maybe soldered,A brazed, or: otherwise attached to the end plates'-tB-.andy 69 as well. as to the. upper and. lower .a'ngesof the:` main. body 5410i the plating. chamber so asA tofconductfhe'at away therefrom in an efcientmannen A. flexible-.bosch is firmly attached.' in anfiairtight manner to theupper end of the-movingilnjector. 12 for. supplying. carbonyli vapor alongi with hydrogen, carbonv monoxide'. and' waterr vapor.: if desired. from suitable sources? connected by'fappropriate piping systemsv and individually controlled by' valves. Themoving injector`12f has a'. bore 1G through. which the plating gases. .pass to they interior of the plating vessel 64; The moving injector'is also kept. coolv by means of. cooling, nuidisuppliedfrom inlet tube 11 which passes down a tube or passageway 18' on one side of the center Atubelil and back up through another tube 19to the'routlet 80. The. inlet and outlet tubes-11 and'- 80 may be' connected byh suitable hose connections to- .an appropriate .supply source and disposalsource of: cooling water orto a radiator. The bottom end of the moving injector 12 is. shown in horizontal. cross-section. in Eig. 7 andin vertical cross-section. innig.` 8. A septum el extendingacross' the tubes. 'separates the passageways 1.8 andl 19.v and: this septumtis discontinuous at. the bottom so that-the. passageways-1B and 19. are connected together by an annular opening 82` When the platingoperati'crr is started the moving injectorV 12 .is traversed upwardly and downwardly bymeans of a. reversing screw 83 which has its groove: engaged 'bya pin 84 (Iiig.v 9)f xedly engaged in anut 85. When the reversing screw isdrivenA by suitable gears, suchL as. the beveled. gears 86. the Vmoving injector isk caused to bev moved reciproca-Hy upward and downward so that the endmove's` from the-apprcximatetop to the'approximatebottom of theV element-53v to supply plating gas to causef a uniform plating along' the bore of the element 63.

The element 63 may conveniently be'h'eate'd by conduction.throughy and radiation from the-walls of chamber 64 during plating operation by'ahe'a'ting. winding 81. which may .be-insulated with asbestos: or other; heat-resistant material and packed in asbestos packing 88 which may largely or wholly ll the casing 39 which serves further to reduce lthe radiation and loss of heat to the surrounding atmosphere. The heating element 88 is conveniently supplied with heating current from any desired alternating current or direct current source.

Outlet tubes I2 are connected to a main outlet ltube l2a which in turn is connected to a suitable vacuum pump or vacuum pump system through valves as may be desired.

The operation of the arrangement of Figs. to 9, inclusive, will now be briefly outlined. An object 63 to be plated is placed in the plating chamber upon the support 65 by removing the bottom plate 66 and then sealing it back to forni a gas-tight connection. The heating winding Bl is then energized and as soon as the object 63 is appropriately hot, pure hydrogen gas may be introduced through the tube l5 and the traversing screw started into operation in order to clean the interior of the object 63 by removing foreign substancesA and reducing metallic oxides on the surface. After the cleaning has continued for suicient time, carbonyl vapor, with or without drogen, carbon monoxide, with or without other g gases, such as water vapor, which may be introduced. At the end of the operation the carbonyl gals is cut off, the object G3 is allowed to cool and it may then be removed from the plating chamber whereupon the apparatus is in con dition for repeating the operation to plate another object.

The arrangements described are exemplary for indicating various types of arrangements which may be employed for plating the whole or partsf of surfaces and the parts being of various sizes and shapes.

Tungsten carbide having the formula W2C, with a small variable. excess or one or the other of carbon or tungsten, may be plated; this plating is very hard. This hardness is considered to arise in part from the smallness of the crystals in the plate. Note is also made of the fact that the plating is free from iron, nickel, cobalt, or similar elements. Likewise, adherent plating of M040 and MozC or mixtures thereof which are hard can be produced. Y

Tests of carbides of composition MozC and M04C and upon platings consisting of various proportions of those carbides with molybdenum show that many of these platings have unexpected hardness. They are often composed of fine crystals and under some conditions which may be experimentally determined by X-ray analysis, the crystals have a strong orientation. As previously set forth, pure metals and alloys may also be deposited. In practice the last vestige of carbon cannot be eliminated from the plated metal although under appropriate conditions the carbon content may be made quite small or so small as to be insignicant in affecting the properties of the product.

The hardness combined with toughness in varying degrees together with resistance to corrosion make the process available for the production of various useful products. such 'as plated or coated working surfaces for wire drawing dies, cutting tools, machine drills, rolls, engine bearings, valves -of internal combustion engines, taps, reamers,

metal slitting saws, pinion bearings, nozzles, and rotors and stators of high temperature turbines, as well as the blades of combustion chambers of internal combustion turbines which .may be rendered less subject to corrosion by plating with suitable carbides of chromium, tungsten or molybdenum or by a mixture thereof with metals.

. Rolls of cylindrical or rolling pin form may 'be supported at the centers of their endsv by ceramic supporting frames including a ceramic holding screw in a manner similar to the method :of holding a work piece in a lathe. Similar or analogous methods may be employed to plate the whole or working surface of valves such as the valves of internal combustion engines. The whole or the working faces of precision tools, such as gauges and gauge blocks which are required to be hard and of exact dimensions, may also be plated by one or more carbides or by mixed carbides.

A metal coated with an adherent layer as defined herein signifies a condition of powerful adherence whereby the metallic body may be stretched or distorted or subjected to high temperatures or high pressures or both without separating the layer. In the case of tough layers of plated material, this stretching or distortion without cracking or breaking may be considerable; when the plated layer is hard and brittle the stretching or distortion may be slight before cracking or breaking, not because the adherence is less but because the plated metal will crack or break upon stretching or distortion but will nevertheless tend to adhere strongly even though cracked. A mere superficial attachment is not considered to be adherence in the sense of this specification.

What is claimed is: f

l. The method of plating an object which comprises heating the object tobe plated to a temperature sufficiently high to decompose carbonyl vapor of at least one metal selected from the group consisting of tungsten and molybdenum, passing said vapor along with hydrogen and water vapor to the extent of not over iifteen molecular per cent of the hydrogen over the object to be plated while it is maintained at said decomposition temperature, and while maintaining a pressure of up to 12 millimeters of mercury at the surface.

2. The method of plating an object with metal selected from the group consisting of tungsten and molybdenum which comprises heating the object to a temperature sufllciently high to decompose carbonyl vapor of metal selected from the group consisting of tungsten and molybdenum passed over the surface of the object and passing the vapor over the object while it is thus heated along with hydrogen and water vapor to the extent of not over 15 molecular per cent of the hydrogen while maintaining a vacuum of a small fraction of an atmosphere at the surface.

3. The method of plating an object of the class of steels which tend to oxidize in the presence of hot Water vapor which comprises exposing the object While heated to a gaseous metallic carbonyl of a metal selected from the group consisting of molybdenum and tungsten in the presence of hydrogen at a continuously maintained gas pressure low as compared to atmospheric pressure to form a bond of the plating with the object and thereatten continuing: theV plating-processwhile. maintaining the obiect heated by" causing the; inu-x o!V Water;y vapor withV the; hydrogen. to. the: extent of not over I5 molar per c'ent; ofk thee hydrogen.

4. 'Illieemethodoi'Y plating objectsY which comprises passing Ycarbonyl of metal: selected from theegroup' consistingof. molybdenum andA tungsten over the. surface of: the. object. to. be plated While it is maintained: free from foreign substances whileth'e surface. isalso'mantaned at a temperature suiiciently high; to decompose the metallic carbonyl, andv introduolng'with the metallic carbonyl. hydrogen plus Water vapor from a small amount'` up` toy 15 molar per centxwhile continuously" pumping the plating vessel to. maintain a pressure therein, which is a: small. fraction of. an atmosphere,v during the entirey platingv operation.

5; The-method oiplating-anobject which comprises heating. theA object to'` bev plated to atemperaturebetween 450' C; and;500 (Land passing tungsterrcarbonyl along with hydrogen-and water vapor to the extent of not over tenv molecular percent of the hydrogen over the object to be plated, While maintaining the object to beplated at said temperature and: while maintaining a pressure of from .00.1 to l2'millimeters ofmercury at the surface.

6. The method of plating an object which comprisesv heating the object. tobe plated to a temperature suflciently high to decompose a mixture of carbonyls. of molybdenum and tungsten, passing said carbonyls alongy with hydrogen and water' vapor to the extent of not over. iifteen molecular per cent of the hydrogen over the object. to be` plated, While it is maintained at said decomposition'. temperature and while maintaining ai pressure of upto 12A millimetersfof mercury atthe surface.

7. The method of plating an .objectwhic-h comprises heating the object -torbe plated to a temperature of about 600 C., passing a `mixture of carbonyls of molybdenum and tungsten along with hydrogen and water vapor to the extent of not over fifteen molecular per cent of the hydrogen over the object to loe-plated, while it is maintained at said temperature and while maintaining a pressure of upto 12 millimeters of mercury at thev surface.

8. The methcd'of plating anzobject which comprises. heating,A the object to be platedto atemperature of about 600 C. and. passing molybdenum carbonyl along Withhydrogen and Water Vapor tothe extent of not. over ten molecular per centv of the hydrogen over the objectto. be; plated while it is maintained at. said temperature. and while maintaining a pressure of from ;001 to 12 millimeters of mercury at the surface.

9. The method of plating an object with metal selected from the group consisting of tungsten and molybdenum which comprises heating the metal to a temperature suciently high to decompose. carbonyl vapor of a metal selected from thegroup consisting of tungsten and molybdenum passed over the surface of the object and passing the vapor over the metal while it i's thus' heated along with hydrogen and Water Vapor to the extent of not over ten moleculark per cent of the hydrogen while maintaining a yacuumof a small fraction of an atmosphere at the surface.

10. The method of plating anV object with metal selected from the group consisting of tungsten and molybdenum which comprises heating the metal to a temperature suiiiciently high to decompose carbonyl vapor of a metal selected from the group consisting of tungsten and molybdenum passed over the surface of the object and passing the vapor over the metal While it is thus heated along with hydrogen and Water Vapor to the extent of not over ten molecular per cent of the hydrogen While maintaining a pressure of from .001 to 12 millimeters of mercury at the surface.

JAMES J. LANDER.

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

UNITED STATES PATENTS Number Name Date 1,497,417 Weber June 10, 1924 2,063,596 Feiler Dec. 8, 1936 2,183,302 Brauer Dec. 12, 1939 2,344,138 Drummond Mar. 14, 1944 2,508,509- Germer et al May 23, 1950 FOREIGN PATENTS Number Country Date 491,948 Great Britain Dec. 9, 1936

Claims (1)

1. THE METHOD OF PLATING AN OBJECT WHICH COMPRISES HEATING THE OBJECT TO BE PLATED TO A TEMPERATURE SUFFICIENTLY HIGH TO DECOMPOSE CARBONYL VAPOR OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN AND MOLYBDENUM, PASSING SAID VAPOR ALONG WITH HYDROGEN AND WATER VAPOR TO THE EXTENT OF NOT OVER FIFTEEN MOLECULAR PER CENT OF THE HYDROGEN OVER THE OBJECT TO BE PLATED WHILE IT IS MAINTAINED AT SAID DECOMPOSITION TEMPERATURE, AND WHILE MAINTAINING A PRESSURE OF UP TO 12 MILLIMETERS OF MERCURY AT THE SURFACE.

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