US2698812A

US2698812A - Metal deposition process

Info

Publication number: US2698812A
Application number: US190306A
Authority: US
Inventors: Schladitz Hermann
Original assignee: Individual
Current assignee: Individual
Priority date: 1949-10-21
Filing date: 1950-10-16
Publication date: 1955-01-04
Anticipated expiration: 1972-01-04

Description

Jan. 4, 1955 H. SCHLADITZ METAL DEPOSITION PROCESS 2 Shee'ts-Sheet 1 Filed Oct. 16 1950 Jig,- Z

INVENTOR. fi e/"Mann Jc/Mad/fz 1955 H. SCHLADITZ 2,698,812

METAL DEPOSITION PROCESS Filed Oct. 16, 1950 2 Sheets-Sheet 2 1 1 .9. Try I0.

AN xxxyywm IN V EN TOR. Jz'ermann ,Sch lad/f2 United States Patent" Office 2,698,812 Patented Jan. 4, 1955 METAL DEPOSITION PROCESS Hermann Schladitz, Munich, Germany Application October 16, 1950, Serial No. 190,306 Claims priority, application Germany October 21, 1949 22 Claims. (Cl. 117-47) The invention relates to a process for the production of metal deposits, and has for its object to produce by thermal decomposition of metal compounds completely uniform fine-grained metal deposits of great adhering strength on substances of all kinds, that is to say, both on inorganic and on organic substances, regardless of the configuration of the surface of these substances. In contrast to known processes, this metal deposition is effected with great economy. A particular object is to produce metal deposits on heat-sensitive organic substances of very fine structure (for example textile fibres or fabrics).

In the process according to the invention, such metal deposition is elfected by separating the metal from the metal compound at such a short distance from the surface of the material to be metallized that the agglomeration (coarsening of the grain) of the metal particles before they are deposited is prevented, by maintaining the temperature of the surface to be metallized at an equal level during the separation process, and by limiting the maximum heating of the material to be metallized preferably to the surface layer.

In order that this process may achieve the desired result,

the conditions of dissociation of the metal compound must be maintained as uniform as possible on or above the deposition surface during the separation of the metal. The maintenance of constant dissociation conditions in the thermal decomposition of metal compounds is a necessary pre-condition for ensuring a uniform, fine-grained and firmly adhering deposit.

If it is desired to obtain a fine-grained deposit having excellent adhering strength on any desired materials, including more sensitive organic substances and on smooth, rough or porous surfaces, or surfaces of any other form, care must be taken to compensate for the heat losses occurring during the metallizing operation, by heating the surface of the substance to be metallized to the decomposition temperature from the outside and constantly supplying heat from the outside during the separating process. The temperature of the surface of the material must not in any circumstances be higher than the temperature of the decomposition of the metal compound. Experience has shown that this is of particularly great importance in the metallization of organic substances, since otherwise the organic substance is damaged and the adhering strength of the deposited layer is greatly reduced. In order to maintain constant decomposing conditions, it is proposed in accordance with the invention, in all the decompositions hereinafter described, to maintain a minimum path of movement of the metal atoms or fine metal particles from the point at which they are separated from the metal compound to the point at which they are deposited, that is to say, to ensure that the metal atoms or particles pass along the shortest path to the surface of deposition without having too great an opportunity of aggregating during their movement, since the finer the deposited particles remain the better are the molecular binding forces, by which they are bound to the surface of the article and by which they are incorporated in the growing metal film, able to take effect. It must be borne in mind that the length of the path of free movement is so small under normal pressure conditions that in the separation of metal from the compound the danger exists, even in the neighbourhood of the surface, of the metal particles agglomerating to form coarser particles before they reach the surface. It is therefore desirable either to cause the decomposition actually to take place only immediately on the surface of the articles to be metallized or to ensure, when the separation takes place at a distance from the surface, that the metal atoms or fine particles pass as rapidly as possible to this surface, by superimposing on their free movement a preferred direction towards the surface. This is done by directing a stream of the metal compound at great velocity towards the surface of the article, it being possible for the decomposition to take place at a more or less great distance from the surface.

The working conditions hereinbefore referred to which must be maintained in accordance with the invention in order to produce completely satisfactory metal deposits from metal compounds, namely constant, reproducible reaction conditions at the point of separation, heating at constant temperature preferably only at the surface of the article to be metallized, and prevention of agglomeration of the metal atoms or very line particles separated from the metal compound by adjusting the length of their path of free movement, constitute in combinauon new working directions.

If the decomposition takes place directly on the surface of the article to be metallized, or at a distance therefrom, it is in all circumstances important that only the surface itself, but not the mass of the entire article, be heated because heating of the mass of the article is completely unimportant to the metallizing process and involves a considerable loss of heat. More especially, if only the surface on which the metal compound is decomposed is heated, the conditions of dissociation can be much more readily maintained uniform and the metallizing process can proceed at great speed over the surface. Thus, only a fraction of the thermal energy otherwise necessary for heating the entire article to the decomposing temperature is required for the metallization. Similarly, the time taken by the metallization is only a fraction of that taken in the known processes.

The heating of the surface to the decomposition temperature does not preclude pre-heating of the article below the decomposition temperature from being expedient in special cases.

The manner in which the process according to the invention is carried into practice may vary greatly in accordance with circumstances. The performance of the process will hereinafter be described by way of example with reference to the embodiments illustrated in Figures 1 to '17 of the drawings.

According to Figure 1, a material or article 1 to be metallized is brought to decomposition temperature at the surface by contact heating, for example by means of the heating elements 2 sliding along the surface (or travelling heating rollers). The contact heating of the surface may also be effected by other means, namely by solid, fluid or pulverous heating elements. Arranged between these heating elements 2 are the feed ducts 3 for the metal compound, through which the metal compounds are blown in a jet 4 on to the surface. The

system

2, 3 is uniformly moved as a whole in the direction of the arrow A in relation to the fixed article 1, or vice versa, it being possible to carry out this movement at a very high speed of a few metres per second and nevertheless to obtain a cohesive metal coating of high electrical conductivity. In this movement according to Figure 1, each successive point of the surface is alternately heated and metallized, so that heat is continuously supplied from the outside to the point in question during the separation (deposition). According to the required thickness of the metal layer, a suitable number of heating elements 2 and metal feed ducts 3 are arranged one behind the other, or the

system

2, 3, is repeatedly passed over the article to be metallized.

In Figure 2, the heating of an element 1 to be metallized is indicated by jets of material (hot gases, vapours, powder), a hot jet of material 5 being blown through feed ducts 2a on to the surface. The metal compound is simultaneously blown in a uniform jet 4 on to the same point 6 of this surface through the feed duct 3. Alternatively, the heat and the metal compound can be alternately delivered for short intervals, for example with fifty alternations per second. By this continuous alternation, the temperature is maintained constant at the point 6 during the separation process. Here again, the mctallizing ar arrow througha thin foil in, for example of mica,

rangement 2a, 3 is moved in the direction of the arrow A over the surface, or vice versa.

As a modification of Figure 2, it is possible as shown in Figure l to heat the surface by replacing the contact heating elements 2 by feed ducts 2a for hot jets of material, so thatthe heating jet always precedes-a jet of metal compound by a short distance.

The stepwise heating of the surface according to the invention makes it possible, as indicated in-Figure 2, to house the

arrangement

2, 3 in a vessel 7, which projects thestill hot point just metallizedfrom the admission of air and consequently from oxidation;

Solids of revolution can be metallized on the surface by heating-the article, which-is rotated about its axis, from one side, for-exampleby ajet of gas, and blowing-on the metal compound fromthe opposite side.

In-the aforesaid surface heatingby means of jets of material, substances may be admixed with such jets of-material in order to effect an additional heating by chemical or physical. reactions on the surface, such admixed substances being, for example, hydrogen atoms, which recombine toform molecules while giving up heat on the surface tobe metallized; Moreover, substances such asfine metal powder may be admixed with the jet of material by which the surface is heated, in order to promote catalytically the thermal dccornpositionof the metal compound. The catalyst may be, for example, iron powder if iron carbonyl is employed as the metal compound. A jet of heated, finely distributed material, for example heated metal particles may also be employed to heat the surface, such material being deposited in solid form on the surface together with the metal deposition. Thus, for example, the known metal spraying process may be employed for this type of heat supply.

Thenew process may also be employed'to metallize the innersurface of porous articles, for example of wood or ceramics.

Such an article is shown at-fiinFigure 3. A hot gas (or vapour) is delivered at it from a vessel 9 and-penetrates through the article in the direction indicated-by the arrow, and heats the inner surface thereof. Thereafter, Orin continuous alternation withthe said gassupply, the metal compound is passed throughthe porous article at Inthe embodiment shown in Figure 4, a continuous heating of the inner surface of: anon-conductive porous element 8 isefiected bythe applicationof two lattice-like electrodes 12, between which an electric discharge (for example high-frequency) takes place.

Figure 5 shows by way of example the dielectric heating of the surface of a non-conductive article 1. This article has a. surface layer 13 having higher dielectric losses thanthe article 1, so that the heating of. the article 1- disposed between the electrodes 14 and l5islimited substantially to the surface layer 13.

If desired, the surface of an articlemay be inductively heated without-the aforesaid surface layer 13;

In the embodiment shown in Figure 6, the. surfaceof the article 1 isheated by electronic and/or ionic impact, the electrons emanating from a heating filament 16. This method of heating affords the advantage that the heating islimited to very small area 17 byv screening of the electron beam asshown in the drawing,,so that punctiform or lineated metallisation can be effectedwith this electronic impact heating.

A certain depth effect is obtained in the heating by electronic or ionic impact, so that metal compounds diffused into the surface are deposited in a certain surface layer. This iii-particularly advantageous for a good anchoring of a metaldeposit. The metal compoundis delivered-at 3.

While in Figure discharge, 7bya-discharge, in this case an are 18, an intensiveheatingtof the surface being effected both by the. heat of the arc and by the ions and electrons in the neighbourhood thereof. In thiscase, the arc is blown on to the surface by the: core of a blowing magnet energised by the magnetcoil 20.

Figure 8 shows a particular case of the application of the absorption of the energy of electrically charged and accelerated corpuscles which emanate from aheating filament land penetrate in the direction indicated by tlge t0 6 6 the surface is directly heated by a At the outlet point, the metal compound metallised.

it maybe indirectly'heated according to Figure fed thereto from the opposite side at 3 is decomposed by the impact energy of the corpuscles; In the first metal layer thus formed, the corpuscles are completely absorbed with temperature increase. This produces further thermal decomposition of the metal compound fed thereto.

In Figure 9 an embodiment is shown in which the surface is heated by electromagnetic radiation, for example infra-red or short-wave radiation. The metal compound is delivered at 3 tea bell-shaped container 21. The infrared radiation indicated by the arrows B penetrates through the closure plate 22, consisting of rock salt or the like, of this con'tainer to the surface of the article 1, so that this surface is continuously heated during the deposition of the metal.

Figure 10 shows diagrammatically a particularly economical method of metallizing an article 1 which already has a conductive surface 23 and which has been metallized, for example, by one of the aforesaid methods. Electrode rollers 24 are moved over the surface of this element at a distance apart, the said rollers being connected to a source of current 25, so that the surface layers 23" lying between these electrodes are brought by resistance heating to. the decomposition temperature. Resistance. heating may also be employed to metallize porous. articles already having a conductive inner surface as shown in Figure 4.

The surface heating may also be effected with supersonic oscillations, for example by transmitting oscillations by means of a quartz crystal 26 to anarticle 2S tapering to a point 2? or knife edge, as shown in Figure 11. The friction of the point 2'7 on the surface of theelement 1 produces a high local. heating which decomposes the metal compound delivered at 3..

In themetallization of materialsor articles by. heating and deposition directly on the surface, the metallization may be effected in vacuo inspecial cases, forexample. in the metallization of very smooth surfaces, one of. the methods already described. being. applied. Generally, however, the new metallizing process will be most: economically carried out.- at atmospheric pressure.

While the methods described. in: the foregoing examples effect. fundamentally a heating and deposition on the surface of the. article to be metallized,.the process according to, the invention. can also be carried out,. as illustrated by way. of example in Figures 12 to 14- by elfecting the decompositionof the. metal compound,.not on the surface, but at a distance. a therefrom. In order to prevent the agglomeration of the metal atoms or particles in the movement alongthe path a tothesurface, these metal particles must be blown onto the surface at great speed, for exampleat a few m. persecond. Theorder of magnitude of the distance a is in, this case of a few millimetres.

According to Figure 12, the metal compound is delivered, at. 3 at this high speed, thev issuing; metal compound-being guided in the vessel 29 through a heating ring 30 so that the metal compound is decomposed'by the heating action thereof.

According to Figure 13, the metal compound, for example nickel carbonyl, is under high pressure (about 100 atmospheres absolute pressure) in. a pressure-proof container 31 which is brought by means of an electric heating element 32 to a temperature (for example 240 C.) lying above the decomposition temperature of the metal compound at normal pressure. The metal compound is blown at high speed on to the surface of the article 1 through an outlet aperture 34 adapted to be. closed by a cone valve 33 or the like. Theexpansion occurring at the discharge of the metalcompound'brings the metal compound out' of the stable condition into. the unstable condition, so that it is decomposed.

Inthe example shown in Figure 14; the metal compound is introduced at 3. through a non-return valve 35 into a container 36 in which intensive spark discharges occur in rapid succession between the electrodes 37. The metal compound is decomposed by these spark: discharges and the products of decomposition are at the same time blown by the explosive effect at very high speed through the aperture 38 on to the surface of the article, th'isblowing-on .of the metal particles takingplace intermittently.

Again inFigure 15, such an intermittentdelivery. takes place, not of the metal particles, but. of the metal compound delivered at 3 into the container 39. This intermittent delivery to the surface of the article 1 is procompound is delivered to the surface during the metallization, it is possible in accordance with Figure 17 to apply the metal compound indicated at 42 previously to the cold surface of the'article 1. It adheres to the surface, and is diffused into or dissolved in the said surface, or rests thereon below a protective film which prevents it"from'rapi'dly evaporating. The heating is effected by the heating jet 5.

In carrying the process according to the invention into practice, all metal compounds may be employed which are dissociated into metal and residual substance under the action of heat. Such compounds are mainly metal carbonyls, metallic hydrides and metallic halogens. Examples of metal carbonyls are nickel tetracarbonyl, iron pentacarbonyl and the carbonyls of tungsten, molybdenum and cobalt. The hydrides which may be employed include, for example; copper hydride, germanium hydride, antimony hydride and others, while the chlorides include chromium'chloride and nickel chloride, and the other types of compounds which may be employed include particularly metallic acetyl acetonates such as copper acetyl acetonate. In addition to these compounds which can be directly separated under heat, metal compounds which liberate the metal on reduction or chemical reaction by thermal means may also be employed for the metallizing process according to the invention. As examples for the reduction method may be mentioned the oxides of the precious metals and of other heavy metals, and for the chemical reaction method the halogen compounds of the heavy metals, for example chromium chloride, are particularly suitable.

The process according to the invention may be employed inter alia to produce metal deposits on compact articles or on and in porous articles or materials. One of the characteristic features of this process resides in the fact that the quantity of metal deposited per unit time is substantially greater than in the metal vaporiza' tion process and is even greater than in the galvanic process. Moreover, metallic deposits can be applied by means of the process to bright, oxidized or otherwise coated metals, and especially to non-metals such as plastics, wood, fabrics, papers of all kinds, felts, fibres of organic and inorganic nature, glass, quartz, ceramics, salts and other compounds, that is to say, to all solid or plastic materials whose surface does not undergo any detrimental physical or chemical modification during the metallizing operation.

Extremely fine projections or pores can be filled by the metal deposit. Sensitive organic substances are also not damaged if the metallization process is correctly conducted. For example, papers, textiles and the like may be coated on their outer and inner surfaces with a metal film which embraces each individual fibre and which, if of suitable thickness, cannot be mechanically detached without partial destruction of the fibres.

The metallization is so clean and true to the surface and adheres so strongly that it can be used as a support for a further galvanic deposition of any desired metals. For this purpose, only an extremely thin layer deposited by the process described is required in the case of metallized non-conductors.

Naturally, the conductive layers deposited from the gas phase have, as compared with the layers hitherto produced by the deposition of silver or by the application of layers of graphite or silver sulphide coatings by the wet method, an immeasurably greater adhering strength which can only be compared to the ideal attachment of fine-grained deposits by the cathode atomization or vaporization process. Since the economy of the processes for the separation of metals from compounds according to the invention is nevertheless considerably greater and it must be taken into account that the adhesive strength of a conductive layer on a nonconductor is essential to the adherence of the metal film subsequently galvanically deposited, the process is also of particular nnportance in the electroplating field.

I claim:

1. Process of depositing a uniform firmly adherent coating of metallic particles of finely divided sub-crystalline size upon the surface of a base material which comprises heating the surface of said base material in successive small increments of surface area to a substantially constant temperature and not substantially above the decomposition temperature of a heat decomposable metallic compound and projecting jets containing such decomposable metalliccompound onto said heated surface to effect concomitant decomposition of said compound and coating of the surface, said heat and jets of metal compound being supplied to each small increment of surface area to' be metallized in constant alternation and in rapid succession whereby the temperature of the surface being metallized ismaintained evenly during the entire depositing process and the metal particles deposited on said surface are in sub-crystalline size.

2. The process as defined in claim 1, wherein the object to be coated is thin sheet material and the jets of decomposable metal compound are applied to one surface thereof while the heat is applied to an opposite surface thereof in rapidly alternating jets applied to small increments thereof.

3. Process of depositing a uniform firmly adherent coating of metallic particles of finely divided sub-crystalline size upon the surface of a non-metallic base material of relatively low heat conductivity which comprises heating the surface of said base material in successive small increments of surface area to a substantially constant temperature and not substantially above the decomposition temperature of the heat decomposable metallic compound and projecting jets containing said decomposable metallic compound onto said heated surface to effect concomitant decomposition of said compound and coating of the surface, said heat and jets of metal compound being supplied to each small increment of surface area to be metallized in constant alternation and in rapid succession whereby the temperature of the surface being metallized is maintained evenly during the entire depositing process and the metal particles deposited on said surface are in sub-crystalline size.

4. The process as defined in claim 1, wherein the base material to be coated is organic.

5. The process as defined in claim 1, wherein the base material to be coated is inorganic.

6. The process according to claim 1, wherein the metal compound is preheated to a temperature below the decomposition temperature.

7. The process according to claim 1, wherein the metal compound is applied by supersonic convection flow upon the surface to be coated.

8. Process as defined in claim 1, wherein the base material to be metallized is porous, the compound of a heat decomposable metal being supplied to the porous body together with an electric discharge, the heat decomposable metal compound being passed through the porous body and the electrical discharge serving to heat the inner porous surfaces thereof to effect metal deposition therein.

9. Process as defined in claim 1, wherein a jet of hot material containing a finely divided catalytic substance adapted to reduce the temperature of decomposition of a heat decomposable metallic compound is supplied to the surface to be coated together with the heat decomposable compound for metallizing thereof.

10. Process as defined in claim 1, wherein the surface to be metallized is first coated with material having higher dielectric losses than the material to be metallized and the material to be metallized is heated by induction heating while supplying thereto the heat decomposable metal compound, whereby the heating is limited substantially to the surface portion of the material to be metallized.

11. Process as defined in claim 1, wherein the article to be metallized is heated by electro-magnetic radiation.

12. Process as defined in claim 1, wherein the surface of the article to be metallized is coated with a conductive material and the surface is thereafter heated to the decomposition temperature of a heat decomposable metal compound to be coated thereon by heating said conductive material by electrical resistance heating.

13. Process as defined in claim 1, wherein the surface m tall zed, pos t t of the metal Particle b depositcd,,, the ar icle o be me a li edi eina 12p. ,..eab

to. the; e t'rvqn l x harged. Patt 's; a

:5... Pr ce s as, defined cl im Lwheteiw meta omtaoun s herma y; sl mpcsedi subst l I ita dist ncem th s rfa e pct l z d a p o compound are. blown onto, the. suriface 'to be metalliz'ed tiathigh spe e d ng about 9 met rs-Pe se on 16 Process as defined in claim 1, whereihthe heat decomposable metal compound is decomposed, explosively substantially at a distance from the surfiaee to berrietallized and the products of decompositionare simultaneously blown onto said surface' 17 Process as defined in claim 1, wherein the heat decomposable metal compound is sprayed onto the-surface to be metallized by contact with an elementoscillating at supersonic frequency.

18. Process as defined in claim 1, wherein ajet of hot finely divided metal particles is supplied, asa source oi heat alternately with the heat decomposable, metal cornpound, the finely divided hot metal particles being=deposited as a coating of metal upon the base being coated together with the extreme fine metal formed by decomposition of the heat decomposable metal compound.

cts of deco'mposit'on of the he it decomposable metal hot a '-i ui n+ e s ourc of, h tte st e l t .t i it s rfa e hea ed, a e substanti ll s it e i q mpe eli tsbein an s 'alte 1y ari'd in sequence progressively to each part otfthteisur ee a imof sma inqteme ts r ac T a ea and a p11 l Y- jets the met l ebh pqund one for ea h nously applied over successive small increments of is BefflfimesCited mhefi s. o t this ats ts UNITED: STATES :BATENTS 1, 8;, 9 QhQQR -v b- 9.,,19 2 1 3 7 .41 fi vl 'c a1 e t 9.; 19 2 233,304,. Blealgley eb, 2 1941 3 ,0 5,509 Germer et a .May. 23; 1950 2,576,289 rl. Q 1.19 1 26125433 Da s t a1- 1? New 2 .952 2 ;63l,'948. Belitz et a1. ,Mar. 17; 1253

Claims

1. PROCESS OF DEPOSITING A UNIFORM FIRMLY ADHERENT COATING OF METALLIC PARTICLES OF FINELY DIVIDED SUB-CRYSTALLINE SIZE UPON THE SURFACE OF A BASE MATERIAL WHICH COMPRISES HEATING THE SURFACE OF SAID BASE MATERIAL IN SUCCESSIVE SMALL INCREMENTS OF SURFACE AREA TO A SUBSTANTIALLY CONSTANT TEMPERATURE AND NOT SUBSTANTIALLY ABOVE THE DECOMPOSITION TEMPERATURE OF A HEAT DECOMPOSABLE METALLIC COMPOUND AND PROJECTING JETS CONTAINING SUCH DECOMPOSABLE METALLIC COMPOUND ONTO SAID HEATED SURFACE TO EFFECT CONCOMITANT DECOMPOSITION OF SAID COMPOUND AND COATING OF THE SURFACE. SAID HEAT AND JETS OF METAL COMPOUND BEING SUPPLIED TO EACH SMALL INCREMENT OF SURFACE AREA TO BE METALLIZED IN CONSTANT ALTERNATION AND IN RAPID SUCCESSION WHEREBY THE TEMPERATURE OF THE SURFACE BEING METALLIZED IS MAINTAINED EVENLY DURING THE ENTIRE DEPOSITING PROCESS AND THE METAL PARTICLES DEPOSITED ON SAID SURFACE ARE IN SUB-CRYSTALLINE SIZE.