US 3549412 A
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Description (OCR text may contain errors)
Dec. 22, 1970 w, R JR" EI'AL 3,549,412
METAL PLATING PARTICULATED SUBSTRATES Filed April 29, 1968 United States Patent O 3,549,412 METAL PLATING PARTICULATED SUBSTRATES Frederick W. Frey, Jr., and David R. Carley, Baton Rouge, La., assignors to Ethyl Corporation, New York, N.Y., a corporation of Virginia Continuation-impart of application Ser. No. 378,145, June 26, 1964. This application Apr. 29, 1968, Ser. No. 725,119
Int. Cl. B44d 1/06; C23c 3/04 US. Cl. l17100 14 Claims ABSTRACT OF THE DISCLOSURE Process for metal plating a particulated substrate by preparing a heated solvent slurry of the substrate under inert conditions and introducing a heat-decomposable metal plating compound into the heated slurry while providing agitation of the slurry and refluxing of the solvent vapors.
CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 378,145, filed June 26, 1964, and now abandoned.
BACKGROUND OF THE INVENTION Solution plating as practiced in the art today generally comprises immersion of a hot substrate in a solution of a heat-decomposable metal compound. There are many advantages to solution plating employing heat-decomposable metal compounds to prepare high purity coatings. Among the attendant advantages of solution plating is that corrosion or oxidation of the substrate is greatly minimized both before and during the coating operation. Another chief advantage of solution plating is its simplicity and the economical attractiveness of the high utilization of the heat-decomposable metal compound which generally represents a significant portion of the cost of metal plating utilizing such materials. A serious limitation of solution plating, however, is its lack of suitability for plating substrates characterized by having a high heat trans'fer rate or low heat capacity, for example, see US. Pats. 2,523,461 and 3,041,197. The problem with such a substrate is that its contained heat as well as heat continually imparted to it is so rapidly conducted away and absorbed by the solution that little or no plating of the substrate occurs. In other words, the substrate is rapidly cooled below the temperature of decomposition of the heat-decomposable metal compound contained within the plating solution so that the process is generally restricted to the deposition of relatively thin coatings. The problem is not solved by simply increasing the heat input to the substrate because this leads to unfavorable side effects, such as decomposition of the compound away from the surface of the substrate and/or the formation of a loose nodular deposit. Moreover, there are many substrates having certain properties either inherent or imparted thereto which are altered or destroyed upon heating to an elevated temperature, e.g. metal powders having magnetic properties which are destroyed upon heating to elevated temperatures. The problems discussed above naturally result in a less efficient utilization of the heat-decomposable metal compound and impose a subsequent separation step to remove any decomposed free metal existing in the final product. The above disadvantages associated with solution plating as practiced in the art today makes coating of particulated substrates having a high surface area to mass ratio especially impracticable. Therefore, a low temperature process for the solution plating of particulated substrates, especially with more efficient utilization of the heat-decomposable metal compound, would represent a welcome contribution to the art.
An object of this invention is to provide a low temperature solution plating process whereby substrates having a high coeflicient of heat transfer can be readily plated.
Another object of this invention is to provide a low temperature solution plating process for plating substrates having special physical properties which would be impaired at high temperatures.
Yet another object of this invention is to provide a solution plating process utilizing a heat-decomposable metal compound whereby more efficient utilization of the compound is realized.
These and further objects will come to light as the discussion proceeds.
SUMMARY OF THE INVENTION The present invention provides a process for metal plating a particulated substrate, said process comprising in combination preparing a slurry of said particulated sub strate in a thermally stable organic solvent essentially inert under process conditions and capable of dissolving a heatdecomposable metal compound selected from the group consisting o'f triisobutylaluminum, diisobutylaluminum hydride, trimethylamine alane, bis(trimethylamine) alane, triethylamine alane, diethylaluminum hydride, and triethylaluminum, heating the prepared slurry in a system under substantially inert conditions to at least the decomposition temperature of said heat-decomposable metal compound, and introducing said heat-decomposable metal compound into the heated prepared slurry.
DESCRIPTION OF THE DRAWING The drawing depicts a schematic apparatus arrangement wherein a preferred embodiment of the present process can be conducted.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a process for metal plating a particulated substrate comprising preparing a slurry of the particulated substrate in a solvent capable of dissolving a heat-decomposable metal compound, heating the substrate-solvent slurry in a system under inert conditions to at least the decomposition temperature of the heat-decomposable metal compound, and incrementally introducing the heat-decomposable metal compound into the heated substrate-solvent slurry while continuously agitating the slurry. In this manner, the particulated substrate is expeditiously coated at a high degree of efficiency.
By incremental addition of the plating compound to the substrate-solvent slurry is meant addition at a rate sulficient to avoid excessive build up in concentration in the slurry, that is, opposed to a system where all of the plating compound is added initially. The heat-decomposable metal plating compound is preferably added to the particulated powder-substrate slurry at a rate sufficient to decompose the compound almost essentially instantaneously upon contact with the slurry. Generally, for most operations it can best be described as dripping the plating compound into the slurry. However, it is to be understood especially in the case of a large slurry mass, that the compound can be added in large volumes and on a continuous basis.
Addition of the plating compound to the slurry is regulated depending upon the ratio of substrate to solvent present, the mixing speed (that is, the rapidity at which each individual substrate member is brought into position and exposed to the plating compound), and the selected temperature for decomposing the plating compound.
Among the outstanding features and advantages of the instant invention is the fact that the thermal decomposition of heat-decomposable metal compounds in the above manner is primarily a surface catalyzed reaction such that decomposition proceeds at a temperature reduced below that normally required for decomposition of the specific heat-decomposable compound at the particulated substrate surface whereby a continuous, adherent, coherent coating is realized thereon. By controlling the process to effect a surface catalyzed reaction, deposition on non-substrate surfaces, such as the walls of a container, or in the solvent to produce free aluminum particles, is avoided. Moreover, it will be seen as the discussion proceeds that it is not necessary nor desirable to directly heat the substrate in order to decompose the heat-decomposable metal compound, but rather, the necessary heat can be supplied simply by heating the solvent to the preferred process temperature.
It is preferred to conduct the present process in a system under reflux conditions utilizing a solvent having a boiling point less than the temperature at which the heatdecomposable metal compound is normally decomposed but at least as great as the reduced temperature at which decomposition of the compound proceeds by a surface catalyzed reaction. Solvents having a boiling point greater than the normal decomposition temperature of the heatdecomposable metal compound can be used in an appplication where some solvent decomposition of the metal compound can be tolerated, for example in the coating of magnetic powders which are subsequently compactedinto a specific geometry, the main function of the coating being to serve as a binder so that some free metal can be tolerated. Reflux conditions are preferred since by continually cooling the solvent vapors and returning them to the slurry, the temperature of the substrate-solvent slurry is conveniently regulated.
Referring now to the drawing, the particulated substrate-solvent slurry contained in the vessel 11 is heated by heating means 12 and continually stirred or agitated by suitable means, such as the mixing means 13. When the substrate-solvent slurry 10 reaches the temperature at which the heat-decomposable metal compound is to be decomposed as indicated by the temperature indicating means 14, the plating compound 15 is then incrementally added via the conduit means 16 to the substrate-solvent slurry by regulation of the valve means 17. The plating compound is preferably brought into contact with the substrate-solvent slurry 10 in the close vicinity of the mixing means 13, e.g. in the vortex created thereby. This procedure insures rapid and efficient contact between the substrate and the plating compound. It is to be understood of course, that under refluxing conditions it is not mandatory to employ the mixing means 13 since sufiicient agitation can be achieved by ebullition of the solvent. As the substrate-solvent slurry 10 is heated, vapors 18 of the solvent are generated together with any volatile by-products of decomposition. The vapors 18 flow toward and upon contact with the condensing means 19 are condensed and returned to the slurry. Any by-product gases produced are allowed to pass out of or are swept out of the system by thermal ditfusion or with an inert carrier gas through the liquid bubbler means 20 via the line 22 wherein the valve means 23 is positioned. In this manner, the system is operated at essentially atmospheric pressure as would be indicated by the pressure gauge 21. The conduit 24 and valve means 25 are provided for purging and/ or filling the vessel 11.
It can be appreciated that considerable variations can be made in the apparatus arrangement depicted in the drawing without departing from the true spirit and scope of the present invention. For example, the plating compound 15 can be introduced directly within the substratesolvent slurry itself by immersing the conduit means 16 therein. Moreover, the substrate-solvent slurry 10 can be agitated by an inert gas introduced beneath the surface thereof and which gas can include vapors of the selected heat-decomposable metal compound. Additionally, automated components can be employed in the system and the operation conducted on a continuous basis.
The instant process is not limited by any particular size or geometry of substrate as long as it is capable of being mixed with a solvent to form a slurry. Moreover, the substrate must be capable of withstanding the requisite temperature to decompose the heat-decomposable metal compound, the only restriction being that it must be compatible with the solvent. Substrates employed herein can best be described as particulated materials, e.g. powders, pellets, small fasteners, and the like. Such finely comminuted materials are generally characterized as having a high heat transfer rate to the extent that they cannot be readily plated, if at all, by conventional solution plating techniques. Particulated metals, metal alloys, oxides, and carbides are especially preferred since these materials, heretofore difiicult to plate by conventional solution plating, are characterized by their excellent heat stability, plus the fact that unique articles of manufacture as hereinafter described are readily produced by way of the present process. However, other particulated materials, such as glass, ceramics, refractories, graphite, etc., can likewise be employed. The present process provides efficient plating of such substrates at low temperatures regardless of their particular size or configuration as long as they can be slurried. The instant process is, however, particularly attractive for coating particulated substrates having an average particle size less than about mils, especially less than about 30 mils. A preferred embodiment of the instant invention comprises utilizing as a particulated substrate a magnetic metal powder having an average particle size less than about 1 micron, e.g. fine particle magnets comprising an iron-cobalt alloy which materials cannot be heated above 200 C. for extended periods of time without losing their special magnetic properties. Such materials when coated by the instant process utilizing a heat-decomposable aluminum compound and dispersed in a non-magnetic matrix (e.g. aluminum) can be formed into a high coercive force permanent magnet.
Preferred heat-decomposable plating compounds are (A) metal hydrides and their complexes having the fol lowing formulas:
(I) MH or MH -Ligand and ( R MH wherein M is a metal atom, R is an alkyl or aryl group, H is hydrogen, and m and n are small whole integers ranging from 1 to 4, and (B) organometallic compounds having the following formulas:
(III) R M wherein is an alkyl, aryl, arene, cyclopentadienyl, cyclopentadrene, alkaryl, or aralkyl radical, M is a metal astom, and m is a small whole integer ranging from 1 to and (Iv) R MX wherein R and M are defined as above and X is selected from the group consisting of carbonyls, nitrosyls, phosphines, and mixtures thereof, and m and y are small whole integers ranging from 1 to 4, and
( )m 0r X( )n and (VI) M(CNR) wherein M is a metal atom, R is hydrogen, an alkyl, or aryl radical, in is a small whole integer ranging from 4 to 6, x is a small whole integer ranging from 2 to 4, and the ratio n/x ranges from 3 to 5 and (VII) )m( )n wherein M is a metal atom and m and n are small whole mtegers ranging from 1 to 3.
Exemplary of suitable compounds are: silane, stannane, diethylaluminum hydride, diisobutylaluminum hydride, trimethylaminegallane, tertiary amine alanes including trimethylaminealane, bis(trimethylamine)alane, triethylaminealane, triisopropylaminealane, tri-n-butylaminealane, and tri-sec-butylaminealane, diisobutylberyllium, di-tert-butylberyllium, diethylmagnesium, di-tertbutylmagnesium, diethylzinc, diethylcadmium, triethylborane, triethylaluminum, triisobutylaluminum, diethyltin, tetraethyltin, tetraethyllead, dibenzene chromium, dimesitylene chromium, dibenzene molybdenum, dimesitylene molybdenum, dicumene tungsten, bis-cyclopentadienyltitanium, bis-cyclopentadienylmanganese, bis-cyclopentadienyliron, bis-cyclopentadienylnickel, cumene chromium dinitrosyl, benzene molybdenum tricarbonyl, cyclopentadienyltitanium dicarbonyl, cyclopentadienylchromium tricarbonyl, cyclopentadienylmanganese tricarbonyl, methylcyclopentadienylmanganese tricarbonyl, cyclopentadienylcobalt dicarbonyl, bis(cyclopentadienylnickel carbonyl), methylcyclopentadienylnickel nitrosyl, vanadium hexacarbonyl, niobium hexacarbonyl, tantalum hexacarbonyl, chromium hexacarbonyl, molybdenum hexacarbonyl, tungsten hexacarbonyl, iron pentacarbonyl, cobalt tetracarbonyl, nickel tetracarbonyl, iron tricarbonyl nitrosyl, iron dicarbonyl dinitrosyl, cobalt tricarbonyl nitrosyl, chromium hexaphenylisonitrile, nickel tetra-phenylisonitrile, and the like.
Metals which can comprise the metal constituent of the metal compounds to be employed in this invention are, in general, any metals of Groups II-A through V-A of the Periodic Chart of the Elements (Fisher Scientific Company, 1955). However, heat-decomposable metal compounds containing the following metals are preferred: Beryllium, titanium, zirconium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, zinc, cadmium, aluminum, tin, and lead. Aluminum is an especially preferred metal for coating the preferred particulated substrates because it can be readily deposited, it is very soft and ductile and thereby amenable to powder metallurgical techniques, and exhibits good corrosion and high temperature oxidation resistance. Of the heat-decomposable aluminum compounds the most preferred are triisobutylaluminum, diisobutylaluminum hydride, and trimethylamine alane.
The organometallic compounds employed herein are generally decomposed at a temperature within the range of from about 100 C. to about 500 C., quite often even below 300 C. The preferred organoaluminum compounds triisobutylaluminum and diisobutylaluminum hydride are preferably decomposed at a temperature within the range of from about 175 C. to about 220 C. Trimethylamine alane is generally decomposed at a temperature of from about 100 C. to about 200 0., especially within about 120 C. to about 160 C.
The solvents which can be employed in the novel process of this invention are those thermally stable solvents which are essentially inert under the process conditions. Generally, organic solvents having up to about 18 carbon atoms are preferred since they are more economical, being readily available while offering many desirable features such as enumerated below. By thermal stability it is meant that the solvent must not decompose to carbon containing solid residues at the temperature required for the plating operation. The solvent should also be essentially inert and compatible with the plating compound so as to avoid any reaction leading to a loss of plating compound. Additionally the solvent should also be compatible with the coating effected and the particulated substrate being coated. Typical types of solvents that can be employed in the present process are hydrocarbon sol- Vents, such as: Alkanes, aromatics, cycloalkanes, fused ring aromatics, and the like. Ethers such as the alkyl ethers, glycol ethers, polyaromatic ethers, and such, can also be used. Typical of other solvents which can be employed in certain specific instances are the fluorocarbons, silicone oils, alcohols, ketones, and the like. From a cost-effectiveness standpoint, aromatic hydrocarbon solvents are preferred for use in this invention, such as: toluene, xylene, mesitylene, decalene, and the like.
Exemplary of suitable solvents are kerosene, Primol- D (an essentially aliphatic hydrocarbon solvent), hexane, benzene, toluene, xylene, alpha-methylnaphthalene, betamethylnaphthalene, 1,4-dimethylnaphthalene, decahydronaphthalene, 1-ethyl-3-methylbenzene, 1-ethyl-4-methylbenzene, isopropylbenzene, alpha-methoxy toluene, 1- methyl-2-propylbenzene, l-methyl 3 propylbenzene, lmethyl-4-propylbenzene, 1,2,3,4 tetrahydronaphthalene, pentane, heptane, decane, nonane, octane, cyclopentane, cyclohexane, methylcyclohexane, polymethylsiloxane, methylethylketone, dibutyl ketone, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol dimethyl ether, diphenyl ether, anisole, propyl ether, tetrahydrofuran, diethyl glycol dimethyl ether, and mixtures thereof, such as might be found in petroleum distillates.
In order that those skilled in the art can thus appreciate the process of this invention, the following examples are given by way of description and not by way of limitation. In the examples, the apparatus arrangement shown in the drawing was employed. The heating means 12 consisted of an electric resistance heater. A conventional electrically driven mixer was employed as the mixing means 13. The slurry 10 consisting of the particulated substrate and solvent was charged into the vessel 11 which had been previously purged with nitrogen through line 24 to rid the system of air and moisture. In those instances where the slurry 10 was thought to contain traces of moisture, the startup procedure comprised first heating the slurry 10 so as to distill off a small amount of solvent and co-distill any traces of moisture which was allowed to escape from the vessel 11 through the line 22 to the bubbler means 20. Thereafter the condenser means 19 was set into operation by opening the valve means 26 which allowed cooling fluid to move through the means 19. Concurrently, the mixing means 13 was set into operation and the heater means 12 adjusted so as to heat the slurry 10 to the temperature employed for decomposing the particular heat-decomposable metal compound employed in each specific instance enumerated below. By virtue of the temperature indicating means 14 the operator could observe and regulate the temperature during the plating operation. When the system reached equilibrium, that is, the flow rate of the solvent vapors 18 was equal to that of the solvent 27 refluxed back to the slurry 10 by controlling the extent of cooling via the cooling means 19 (for the preferred method of operation), the system was then ready to commence plating. Under these conditions the pressure gauge 21 read essentially atmospheric pressure.
The plating compound was incrementally added through the conduit means 16 as controlled by the valve means 17 to the agitated slurry 10 by dripping it into the vortex created by the impeller of the mixing means 13. In the following runs, where a solid plating compound was used the compound was initially dissolved in the same solvent as that employed to prepare the particulated powder-substrate slurry. Where liquid compounds were used, a sim ilar solvent system was employed. However, it is to be understood that the pure plating compound itself can be utilized.
EXAMPLE I Substrate-Magnetic Alloy Powder Plating compoundTriisobutylaluminum-(C H A1 SolventDodecane Temperature of slurry195 C.
ResultsGray metallic coating encapsulating individual agglomerates of alloy powder.
7 EXAMPLE II Substrate-Magnetic Powder Plating compoundTrimethylamine alaneAiH -Me N SolventXylene Temperature of slurryl40 C.
ResultsGray metallic coating encapsulating individual agglomerates of alloy powder.
EXAMPLE III SubstrateGlass fibers Plating compound-Trimethylamine a1aneAlH -Me N SolventXylene Temperature of slurryl40 C.
Results-Dull gray aluminum deposit coating individual particles of glass fibers.
EXAMPLE IV Substrate-Magnesium oxide-MgO Plating compoundChromium hexacarbonylCr(CO) SolventOctadecane Temperature of slurry3 C.
Results-Chromium coated MgO for compaction into massive metal with improved ductility.
EXAMPLE V SubstrateSubmicron thorium oxideThO Plating compound-Nickel tetracarbonylNi(CO) SolventXylene Temperature of slurry120" C.
ResultsThori-a dispersed nickel powder for conversion to dispersion strengthened nickel parts.
EXAMPLE VI EXAMPLE VI'I SubstrateBeryllium powder Plating compound-Diisobutylaluminum hydride SolventDodecane Temperature of slurry210 C.
ResultsAluminum-coated beryllium powder for compaction into light, ductile metal with high strength-toweight rates.
EXAMPLE VIII SubstrateMagnetic powder Plating compound-Cyclopentadienylcopper triethylphosphineCyCu (Et P) SolventDecalin Temperature of slurry-195 C.
ResultsCopper-coated magnetic powder for fabrication into corrosion-resistant magnetic parts with high coercive force.
EXAMPLE IX Substrate-Lead oxide Plating compound-Tetraethyllead-EQPb SolventDodecane Temperature of slurry126 C. ResultsDispersion-hardened Pb alloy.
EXAMPLE X SubstrateGraphite Plating compoundcyclopentadienyltitanium dicarbonylCyTi(CO) Solvent-Octfidecane Temperature of slurry-300 C. ResultsTitanium-coated graphite for fabrication into electrodes of improved oxidation resistance.
The amount of coating to be deposited pursuant to the present process will vary with the type of substrate and its subsequent application. In general, for most applications the coating is a minor constituent of the finished product, that is, thin coatings are generally suitable. Preferably, coating-buildup ranges upwards to 50 volume percent based upon the finished coated product. It is to be understood that the finished product can contain or include any free metal (constituting the metal constituent of the plating compound) that is formed during the coating operation. In fact, there are instances where free metal can be present in the end product in considerable amounts without detrimental effect. For example, in the case of coated magnetic powders utilized in the preparation of permanent magnets. The free metal (plating metal) together with the coated particulated substrate can be fabricated by conventional metallurgical techniques into the desired magnet whereby the free metal serves as a matrix wherein the particulated substrate is suspended.
A preliminary step prior to employing the technique of this invention may desirably require surface preparation of the substrate to be plated. However, a feature of the present invention is that preliminary surface preparation is not mandatory in the case of many substrates as they are commercially supplied since they are continually contacted and mixed with the solvent during the plating operation. Where it is desired to implement the present technique with a surface preparation step many well known methods of surface preparation can be employed. For example, degreasing followed by acid pickling and washing is one suitable approach.
Particulated materials coated pursuant to the present invention find diversified uses both as individual components as well as intermediate components that can be further fabricated into unique articles of manufacture. For example, appropriate base materials can be coated with materials such as nickel or the like to form catalysts. Pursuant to the preferred embodiment of the instant invention, appropriate metal powders can be initially coated with aluminum which when subjected to conventional metallurgical techniques will serve as an appropriate binder. Of special interest is the use of an aluminum coating deposited by the instant invention on particles of iron-cobalt alloy, the aluminum serving as a binder for the particles in the preparation of permanent magnetic materials and also for the protection of the parts against oxidation, and corrosion conditions. The instant invention is also attractive for the coating of glass fibers, the coating serving to minimize deterioration of the glass fibers against subsequent loss in strength due to aging. Moreover, the present invention represents excellent means for preparing special alloys by depositing special coatings on ultra-fine metal powders.
It is to be understood that the present invention is not limited by the specific embodiments described hereinabove, but includes such changes and modifications as may be apparent to one skilled in the art upon reading the appended claims.
1. A process for metal plating a particulated substrate, said process comprising in combination:
( 1) preparing a slurry of said particulated substrate in a thermally stable organic solvent essentially inert under process conditions and capable of dissolving a heat-decomposable metal compound selected from the group consisting of triisobutylaluminum, diisobutylaluminum hydride, and trimethylamine alane,
(2) heating the prepared slurry in a system under substantially inert conditions to at least the decomposition temperature of said heat-decomposable metal compound, and
(3) introducing said heat-decomposable metal compound incrementally into the heated prepared slurry while continuously agitating the slurry.
Z. The process of claim 1 wherein the heating step produces solvent vapors which are refluxed as a means of controlling the temperature of the substrate-solvent slurry.
3. The process of claim 1 wherein the substrate comprises small fasteners.
4. The process of claim 1 wherein the substrate comprises a powder.
5. The process of claim 1 wherein the substrate comprises pellets.
6. The process of claim 1 wherein the substrate comprises fibers.
7. A process for metal plating a particulated substrate, which process comprises, in combination:
(1) agitating a slurry of said particulated substrate in an organic solvent for a heat-decomposable metaldepositing compound selected from the group consisting of metal hydrides, complexes of metal hydrides, and organometallics, said solvent being essentially inert under metal-depositing conditions,
(2) heating the slurry to a temperature high enough to cause the metal-depositing compound to deposit a metal plating when' in contact with the substrate but below the normal decomposition temperature of the compound when not in such contact, and
(3) introducing said compound into the agitated heated slurry.
8. The process of claim 7 wherein said slurry is heated under substantially inert conditions.
9. The process of claim 7 wherein said compound is introduced incrementally.
10. The process of claim 7 wherein the heating step produces solvent vapors which are refluxed as a means of controlling the temperature of the substrate-solvent slurry.
11. The process of claim 7 wherein the substrate comprises small fasteners.
12. The process of claim 7 wherein the substrate comprises a powder.
13. The process of claim 7 wherein the substrate comprises pellets.
14. The process of claim 7 wherein the substrate comprises fibers.
References Cited UNITED STATES PATENTS 3,155,532 11/1964 Basile 1'17--130X 3,251,712 5/1966 Berger 117130X 3,300,329 1/1967 Orsino et al. 117--100X 2,523,461 9/1950 Young et a1. 117-47 2,918,392 12/1959 Beller 117160X 3,041,197 6/1962 Berger 1177-47 3,075,858 1/1963 Breining et al. 117-160X 3,138,479 6/1964 Foley 1177X 3,202,537 8/1965 Norman et a1. 117100 3,214,288 10/1965 McGraw 117l60X 3,216,845 11/1965 Brown 117-160X 3,237,066 2/1966 Martin et a1. 117-100 3,342,587 9/1967 Goodrich et a1 117100 WILLIAM D. MARTIN, Primary Examiner US. Cl. X.R.