US2650564A - Dynamic pyrolytic plating apparatus - Google Patents

Description

Sept. 1, 1953 o, F 2,650,564

DYNAMIC PYROLYTIC PLATING APPARATUS Original Filed Dec. 2, 1949 2 iL/ l INVENTOR ALBERT O. FINK av A W M150 ATTORNEYS Patented Sept. 1, 1953 DYNAMIC PYROLYTIC PLATIN G APPARATUS Albert 0. Fink, Dayton, Ohio, assignor to The Commonwealth Engineering Company of Ohio, Dayton, Ohio, a corporation of Ohio Original application December 2, 1949, Serial No. 130,671. Divided and this application October 27, 1950, Serial No. 192,421

4 Claims. (Cl. 118-48) This invention relates to the art of deposition of metals. More particularly, it relates to the plating of metals from the gaseous state and the apparatus for carrying out the process.

2 deposits adaptable to discontinuous or continuous plating.

It is also an object of the present invention to provide apparatus for carrying out the above This application is a division of Serial No. 5 pro e se 130,671, filed December 2, 1949, entitled Dynamic These and other more specific objects will be- Pyrolytic Plating, now Patent 2,576,289. come apparent from the following description:

Deposition of thin films of protective metal such The plating as carried out in accordance with as ic Cobalt, tungsten, molybdenum, their this invention is keeping the gas temperature bemetal alloys, and the like, has beenaccomplished low the intergaseous decomposition point and in the past by enclosing an object to be plated directing th metal-bearing gases in agitated in a chamber, charging the chamber with deturbulent flow against the surface to be plated. 0 1 8 1 metal-bearing g s, a t g the In this process, decomposable metal -bearing object to the decomposition temperature for said gases are heated to the decomposition temperaas ture by heat radiating from the object being In ordinary pyrolytic plating, the production of plated. The hot but undecomposed gases are redense metal deposits is made diflicult by two circulated through the system. Gas velocities phenomena, namely, intergaseous decomposition and volumes maintained within the plating chamand gas film resistance to true surface'contact. n ber quickly bring the hot gases into contact with Intergaseous decomposition is caused by the a cooler, whereby a gas temperature in the range plating gas becoming heated to an undesirably of 110 F. to 175 F., and preferably about 125 F., high temperature while not in contact with the is continuously maintained. object to be plated. This phenomenon causes To maintain the concentration of metal-bearparticles of the metal to be formed and which fall ing gases, fresh gases at a temperature of about on the plating surface, producing extreme rough- 100 F. are continuously or intermittently bled ness. Obviously, for sound plating this phenomeinto the gases being recirculated in the chamber. non must not be permitted to occur. The gaseous atmosphere may be formed by mix- The second phenomenon, gas film resistance, is ing an inert gas with the vapors of a volatile metal always present in gas to heated-solids systems compound, or by atomizing a liquid metal comand serves as a boundary between the solid and pound into a blast of warm inert gas or other the gas. It prevents the gaseous metal comequivalent method. pound from decomposing directly on the free sur- Carbon dioxide, helium, nitrogen, hydrogen, the face of the metal. gaseous product of controlled burning of hydro- The results of such phenomena show themcarbon gases free of oxygen and the like, have selves in the form of rough irregular plates, and been utilized as a carrier medium or inert gas thin porous coating. medium.

It is an object of the present invention to over- In some instances the use of hydrogen is precome the disadvantages and limitations of the ferred, as for example, in a cleaning anneal above described methods. chamber where its ability to act as a reducing It is another object of the present invention agent may be put to advantage to remove the to provide a method which increases the density oxide film or rust from iron. of th coating, Metals to be deposited may be introduced as It is a further object of the present invention gaseous metal carbonyls or vaporized solutions to provide a method which gives metal coatings of certain of the metal carbonyls in readily vaporindecreased porosity. izable solvents (for example, petroleum ether) It is a still further object of the present invenalso nitroxyl compounds, nitrosyl carbonyls, tion to provide a method which produces inmetal hydr es, metal y s, metal halides, and creased smoothness and brightnessof deposit. the like.

It is still another object of this invention to Illustrative compounds of the carbonyl type provide a method having increased efficiency due are nickel, iron, chromium, molybdenum, cobalt,

to elimination of intergaseous decompositions and the deposit of loose metal powder in the bottom of the plating chamber.

It is also an object of the present invention to provide a method for producing increased density and mixed carbonyls.

Illustrative compounds of other groups are the nitroxyls, such as copper nitroxyl; nitrosylcarbonyls, for example, cobalt nitrosyl carbonyl; hydrides, such as antimony hydride, tin hydride;

metal alkyls, such as chromyl chloride; and carbonyls halogens, for example, osmium carbonyl bromide, ruthenium carbonyl chloride, and the like.

Each material from which a metal may be plated has a temperature at which decomposition is complete. However, decomposition may take place slowly at a lower temperature or while vapors are being raised in temperature through some particular range. For example, nickel carbonyl completely decomposes at a temperature in the range of 375 F. to 400 F. However, nickel carbonyl starts to decompose slowly at about 175 F. and therefore decomposition continues during the time of heating from 200 F. to 380 F.

A large number of the metai 'c'arbony-ls and hydrides may be effectively and eflicien'tly decomposed at a temperature in the range of 350 F. to 450 F. When working with most metal carbonyls I prefer to operate in a temperature range of from 375 F. to 425 F.

Heating of objects to temperatures in the above range may be accomplished in man ways depending upon the type of object being plated. If the object is stationary, the object may be set on a resistance heater Or so-called hot plate. If the object is moving, it may be heated by passing over resistance heaters, or by infrared light, or by passage of electricity therethrough either of standard or high frequency or like means.

Preparatory to coating the material may be cleaned by employing conventional methods-used in the art, comprising electro-chernically cleaning by moving the same through a bath of alkali or acid electrolyte in which the object is made the cathode or anode. I I

Pickling with hydrochloric, sulfuric or nitric acid, or a combination of acids, may also be made a part of the cleaning process and the object thoroughl rinsed or washed prior to introduction into the plating apparatus. I

The invention will be more clearly understood from the following description of one embodiment of the apparatus and its mode of operation, taken in connection with the drawing wherein:

Figure l is a diagrammatic illustration of a complete plating unit; and

Figure 2 is a top view along the line -22 of Figure 1.

Referring to the drawing, there is shown a housing [0, which is provided with gas inlet and outlets H and I2, respectively. The internal arrangement is illustrated with respect to vertical gas flow within a single chamber, but other arrangernents are equally feasible.

Within housing I is a vertical panel l3 extending from the front to the back walls [4 and i5. Positioned adjacent the bottom of housing 10 is a heater I having a top plate I! capable of heating metal objects deposited thereon to temperatures in the range of 350 F. to 500 F., preferably 350 F. to 450 F. Heater 16 receives electric current through the lines LI and L2. Above the hot plate I! is suspended a fan 18 driven by an enclosed motor l9. This fan is adapted to maintain gas velocities of the order of 40 to 90 feet per second.

In the gas recirculation system, is a gas cooler 20 receiving coolant from an external system (not shown).

While this apparatus is shown as contained within a single housing, it will at once be apparent that the cooling of gas may be accomplished outside the plating zone and the gas recirculated by a fan taking suction on the plating chamber and forcing the gas back to the chamber through an outside duct.

The operation of this apparatus is illustrated by the following examples:

Example I Copper discs were wire brushed to clean the surface. The discs were positioned on the hot plate and heated to a temperature of approximately 400 F. Into the housing was fed a mixture of vaporous nickel carbonyl and carbon dioxide, the carbonyl being present in the proportions of approximately 5 ozs. of carbonyl per cubic foot of carbon dioxide.

The copper discs were plated in accordance with standard operating procedure of passing approximately 3 cubic feet of gas mixture per hour through the housing I0, for a period of 2 minutes, at the end of which time a plating of .0012 inch of nickel was obtained.

Example II New copper discs treated as in the previous operation were positioned on the hot plate and an identical gas mixture fed to the chamber. Inside the chamber the gas was maintained at a temperature of approximately F. by the coolant. However, the gas circulated in the housing III at a rate of about 60 feet per second due to the operation of fan I8. The plating time was 2 minutes, as in Example I, and the depth of deposit .0033 inch of nickel.

Upon comparison of the discs, it was found that the deposits obtained by the high gas velocity procedure were smoother. In addition, on the basis of the weight of metal deposited, the density of deposit on samples plated without mechanical agitation was 47 grams per cubic inch, whereas the density of the samples plated employing the fan to cause turbulent gas flow was 128 rams per cubic inch.

In salt tests the discs of Example II did not show signs of corrosion after 2 days, whereas the discs of Example I showed signs of corrosion after 4 hours.

It will be understood that while there have been given herein certain specific examples of the practice of this invention, it is not intended thereby to have this invention limited to or circumscribed by the specific details of materials, proportions, or conditions herein specified, in view of the fact that this invention may be modified according to individual preference or conditions without necessarily departing from the spirit of the disclosure and the scope of the appended claims.

I claim:

1. Apparatus for gaseous plating dense coatings comprising, a housing, a gaseous inlet and outlet for introducing and withdrawing a heatdecomposable gaseous metal to said housing, a vertical bafile extending from the front to the back wall of said housing and intermediate the top and bottom walls, means for supporting work to be plated adjacent the bottom of the chamber and on one side of said baflle, means for heating the work to be plated, a fan positioned in said housing and adapted to drive said heatdecomposable gaseous metal against said heated work, and cooling means arranged in the path of said gas for maintaining the circulating gas temperature at approximately 125 2. Apparatus for gaseous plating of work pieces at a high rate of deposition which comprises a chamber for containing the Work to be plated,

baffle means arranged in said chamber and dividing the same into compartments, means for admitting and discharging heat-decomposable gaseous metal to said chamber, means for causing forced circulation of said gaseous material introduced into said chamber, means for heating said work to a temperature to cause said heat-decomposable gaseous metal coming in direct contact therewith to be decomposed depositing the metal constituent thereof, and means for cooling said heat-decomposable gas and disposed in the path of the circulating gas and out of contact with said heated work to maintain said gas at a temperature substantially below that at which the same decomposes.

3. Apparatus for gaseous plating of work pieces at a high rate of deposition which comprises a chamber for containing the work to be plated, a bafile arranged in said chamber dividing the chamber into two parts, means for admitting and discharging heat-decomposable gaseous metal to said chamber, means disposed in said chamber for causing forced circulation of said gaseous material introduced into said chamber, means for heating said work to a temperature to cause said heat-decomposable gaseous metal coming in direct contact therewith to be decomposed depositing the metal constituent thereof, and means for cooling said heatdecomposable gaseous material, said cooling means being disposed in the path of the circulating gas and out of contact with said heated work to maintain said gaseous material at a temperature substantially below that at which the same decomposes.

4. Apparatus for gaseous plating of work pieces at a high rate of deposition which comprises a chamber for containing the work to be plated, means for admitting and discharging heatdecomposable gaseous metal to said chamber, means comprising a fan for causing forced circulation of said gaseous material introduced into said chamber, said fan being arranged to force the gaseous material directly upon said work to be plated, means for heating said work to a temperature to cause said heat-decomposable gaseous metal comin in direct contact therewith to be decomposed depositing the metal constituent thereof, and means for cooling said heat-decomposable gaseous material, said cooling means being arranged in the path of the circulating gas and out of contact with said heated work to maintain said decomposable gaseous material at a temperature substantially below that at which the same decomposes.

ALBERT O. FINK.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,965,059 seibt July 3, 1934 2,332,309 Drummond Oct. 19, 1943 2,508,509 Germer et a1 May 23, 1950 2,516,058 Lander July 18, 1950 2,587,036 Germer et al. Feb. 26, 1952 FOREIGN PATENTS Number Country Date 589,966 Great Britain July 4, 1947 OTHER REFERENCES Gaseous Plating (article), Metal Finishing Magazine, October 1949, pp. 79-82.

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