US3061464A - Method of metal plating with a group iv-b organometallic compound - Google Patents

Description

United States Patent 3,061,464 METHOD OF METAL PLATING WITH A GROUP IV-B ORGANOMETALLIC COMPQUND Vello Norman and Thomas P. Whaley, Baton Rouge, La.,

assignors to Ethyl Corporation, New York, N.Y., a corporation of Delaware N0 Drawing. Filed Oct. 9, 1959, Ser. No. 845,306

9 Claims. (Cl. 117-1t)7) This invention relates to a process for plating group IV-B metals of the periodic chart of the elements on appropriate substrates by decomposition of organometallic compounds of such metals.

A simplified flow diagram of the process of this invention is as follows:

Substrate Heat to decomposition temperature of a monocyclopentadienyl group IV-B transition metal coordination compound Contact heated substrate with vapors of the above compound Cool In the past, processes for the preparation of a group IV-B metal plateparticularly titanium and zirconium plates-have been limited to impractical high temperature processes. Illustrative of these high temperature prior art processes are thermal decomposition of titanium or zirconium iodides at 1200 to 1500 C. and hydrogen reduction of titanium tetrachloride and titanium tetrabromide at 1100 to 1400 C.

Plates produced by prior art reduction methods are unsatisfactory for two major reasons. The first of these is that the resultant metal plate is of poor quality due to hydrogen embrittlement. It is well known that titanium and zirconium are particularly susceptible to hydrogen adsorption and this results in the preparation of poor quality hydrogen embrittled metal plates. The second deficiency is that metal plates produced by these prior art methods have poor adherence to the surface on which the metal is plated.

A further problem accompanying prior art processes is the necessity for excessively high temperatures. Furthermore, the plating agents utilized in these prior art processes (e.g. iodides or bromides of titanium or zirconium) are very reactive and also very difficult to purify. Because of their reactivity these plating agents are likely to react with the constituents of the atmosphere. When the plating agent, containing these constituents as an impurity, is subsequently introduced into the plating atmosphere, undesirable embrittlement of the plate results.

In addition to the above methods, electroplating from fused salt baths has been employed as a technique for producing group IV-B metal plates, particularly titanium plates. However, one of the foremost problems relative to this technique is that the plate is deposited thinly and unevenly, or dendritically. Thus, in short, there is no known satisfactory process for producing group -IVB metal plates.

Titanium and zirconium metal plates are highly desirable because of their high corrosion resistance and good temperature stability characteristics. Carbides of these metals are also highly desirable, since these materials are "ice extremely hard, high temperature resistant compounds. Heretofore, in producing coatings of hard carbides, ithas been necessary to employ temperatures of about 1200f C. in a reduction process utilizing a mixture of the metal halide, hydrogen and hydrocarbons.

In view of the foregoing, the novelty and great importance of the instant invention becomes clear. For the first time, employing the process of this invention, it is possible to produce-at temperatures significantly below those described above-a well-adhering, pure group IV-B metal plate. Furthermore, by a simple variation in the process, it is possible to produce the carbide of the corresponding metalssaid carbide being of excellent characteristics and well-adhering to the substrate upon which it is coated. To the best of our knowledge, this is the first time that such plating processes have been employed in providing group IV-B metal plates.

It is, therefore, an object of this invention to provide a process for the preparation of group IV-B metal plates. It is a further object of this invention to produce a welladhering, excellent group IV-B metal plate. A still further object of this invention is to produce a group IV-B carbide coating which has good adherence to the substrate upon which deposited.

These and other objects are accomplished in accordance with this invention by providing a process for plating a substrate with a group IV-B transition metal by the decomposition of a monocyclopentadienyl group IV-B transition metal coordination compound in contact with said substrate. (The group IV-B transition metals are titanium, zirconium and hafnium, e.g. see the periodic chart of the elements, Fisher Scientific Company, 1955.)

By the term cyclopentadienyl, which is a substituent in the aforementioned coordination compound, is included substituted cyclopentadienyl groups. The cyclopentadienyl moiety, therefore, includes alkyl and aryl substituted cyclopentadienyl groups as well as indenyl and fiuorenyl derivatives including substituted indenyl and fluorenyl derivatives. The term cyclopentadienyl preferably includes hydrocarbon cyclopentadienyl groups containing S to about 17 carbon atoms.

Alternatively the monocyclopentadienyl group IV-B coordination compounds of this invention can be defined as mono-(hydrocarbon cyclomatic) group IV-B coordination compounds. The term cyclomatic hydrocarbon includes cyclomatic hydrocarbon radicals having from about 5 to about 17, or more, carbon atoms and embodying a group of 5 carbons having the configuration found in cyclopentadiene. Such cyclomatic hydrocarbon group lV-B coordination compounds are further characterized in that the cyclomatic hydrocarbon radical is bonded to the group IV-B metal, by carbon to metal bonds, through the carbons of the cyclopentadienyl group contained therein.

The mono-cyclopentadienyl group IV-B transition metal coordination compound can be represented by the illustrative formula RMQ wherein R represents a cyclepentadienyl moiety containing a S-carbon n'ng, similar to that contained in cyclopentadiene itself, coordinated to the group IV-B transition metal, M, through the carbon atoms of the cyclopentadienyl ring; Q represents an electron donor group or a combination of separate electron donor groups, which can be the same or diflerent from each other, involved in covalent or coordinate-covalent bonding with the metal atom, x has a value of 0 to 4--'and usually 0 to 2. These group IV-B coordination compounds will bemore fully defined hereinafter.

By decomposition, as used herein, is meant any method feasible for decomposing a monocyclopentadienyl IV-B transition metal coordination compound. Thus, the

term includes decomposition by ultrasonic frequency and decomposition by ultraviolet irradiation, as well as thermal decomposition. Thermal decomposition is a preferred mode of carrying out the invention.

Therefore, within the scope of this invention, is a process for plating a substrate with a group IV-B transition metal comprising heating the substrate to be plated to a temperature above the decomposition temperature of a monocyclopentadienyl group IV-B transition metal coordination compound, and thereafter contacting said coordination compound with said heated substrate.

Examples of the monocyclopentadienyl group IV-B transition metal coordination compounds employed in this invention are: cyclopentadienyl titanium trichloride, cyclopentadienyl zirconium trichloride, cyclopentadienyl titanium dibutoxy chloride, cyclopentadienyl titanium diethoxy bromide, cyclopentadienyl zirconium di-methoxy chloride, cyclopentadienyl titanium butoxy dichloride, methyl cyclopentadienyl titanium trichloride, indenyl titanium trichloride, fiuorenyl zirconium trichloride, cyclopentadienyl hafnium trichloride, cyclopentadienyl hafnium di-butoxy chloride, cyclopentadienyl hafnium tribromide, methyl cyclopentadienyl hafnium triastatine, octylcyclopentadienyl titanium triiodide and the like.

In general, any prior art technique for metal plating an object by thermal decomposition of a metal-containing compound can be employed in the present plating process as long as a monocyclopentadienyl group IV-B coordination compound is employed as the plating agent (i.e., the metallic source for the metal plate). For example, any technique heretofore known for the thermal decomposition and subsequent plating of metals from the corresponding metal carbonyl can be employed. Illustrative are those techniques described by Lander and Germer, American Institute of Mining and Metallurgical Engineers, Technical Publication No. 2259 (1947). Usually, the technique to be employed comprises heating the object to be plated to a temperature above the decomposition temperature of a metal-containing compound and thereafter contacting the metal-containing compound with the heated object. The following examples are more fully illustrative of the process of this invention.

In Examples I-IV the following technique is used:

Into a conventional heating chamber housed in a resistance furnace and provided with means for gas inlet and outlet, is placed the object to be plated. The organometallic plating agent is placed in a standard vaporization chamber provided with heating means, said vaporization chamber being connected through an outlet port to the aforesaid combustion chamber inlet means.

For the plating operation, the object to be plated is heated to a temperature above the decomposition temperature of the organometallic plating agent, the system is evacuated and the organometallic compound is heated to an appropriate temperature where it possesses vapor pressure of up to about millimeters. In most instances, the process is conducted at no lower than 0.01 mm. pressure. The organometallic vapors are pulled through the system as the vacuum pump operates, and they impinge on the heated object, decomposing and forming the metallic coating. In most instances, no carrier gas was employed; however, in certain cases, a carrier gas can be employed to increase the efliciency of the above disclosed plating system. In those cases where a carrier gas is employed, a system such as described by Lander and Germer, page 7, is utilized.

Example I Compound C H TiCl Substrate Temp 400 C. Substrate Pyrex. Pressure 1mm. Compound Temp 200 C. Time (Hours) 2. Result Shiny, metallic coating.

4 Example II Compound C H ZrCl Substrate Temp 400 C. Substrate Pyrex fibers. Pressure 0.1 mm. Compound Temp 120 C. Time (Hours) 2. Result Shiny, metallic coating Example Ill Compound C5H5(C4HQO)ZTIBI'. Substrate Temp 300 C. Substrate Graphite. Pressure 0.5 mm. Compound Temp C. Time (Hours) 1. Result Grey coating.

Example IV Compound Indenyl(butoxy) '1"iBr. Substrate Temp 300 C. Substrate Copper mesh. Pressure 0.2 mm. Compound Temp C. Time (Hours) 2. Result Dull, grey coating.

In the above examples, the temperatures utilized (i.e., in the vicinity of 250-400 C.) gave excellent metal plates. The process employed resistance heating. In the following working examples an induction heating method, using higher temperatures (i.e., greater than 650 C.) was employed. In the latter process, titanium and zirconium carbide coatings of excellent characteristics were obtained as opposed to the metallic coatings obtained in the foregoing examples.

The process employed in these examples is essentially the same as that employed in Examples I through IV with the exception that the object to be plated was placed into a conventional heating chamber provided with means for high frequency induction heating as opposed to the former process where the heating chamber was housed in a resistance furnace.

Example V Compound C H TiBr Substrate Temp 650700 C. Substrate Ni-coated mild steel. Pressure 0.2 mm. Compound Temp 125 C. Time (Hours) 1%. Result Dark, shiny, hard, welladherent coating.

Example VI Compound C H ZrBr Substrate Temp 650700 C. Substrate Ni-coated mild steel. Pressure 0.5 mm. Compound Temp C. Time (Hours) 1%. Result Dark, shiny, hard, welladherent coating.

In addition to the thermal techniques disclosed hereinabove for decomposing the group IV-B plating agents of this invention, other methods for decomposition of these materials can be employed. Thus, the following working example is illustrative of the decomposition of a titanium compound by ultrasonic frequency.

The process employed in Examples V and VI is followed with the exception that an ultrasonic generator is proximately positioned to the plating apparatus. In this example the compound was heated to its decomposition threshold, i.e. in the vicinity of 200 C. and thereafter the ultrasonic generator was utilized to effect final decomposition.

Example VII Method Thermal and ultrasonic decomp.

Compound C H TiF Compound Temp 150 C.

Substrate Pyrex fibers.

Substrate Temp 200 C.

Pressure 0.1 mm.

Result Metallic coating.

Another method for decomposing the plating agent of this invention is by decomposition with ultraviolet irradiation. The following example is illustrative of this technique.

The method of Example I was employed, with the exception that, in place of the resistance furnace, there was utilized for heating a battery of ultraviolet and infrared lamps placed circumferentially around the outside of the heating chamber. The substrate to be heated was brought to a temperature just below the decomposition temperature of the plating agent with the infrared heating and, thereafter, decomposition was elfected with ultraviolet rays.

Example VIII Method Thermal and ultraviolet de'comp.

Compound CH C H ZrBr Compound Temp 90 C.

Substrate Aluminum.

Substrate Temp 200 C.

Pressure 1 mm.

Result Grey metallic coating.

The term substrate, as employed hereinbefore, can be defined further as the object to be plated and includes any material stable at the temperatures necessary for decomposition of the group IV-B transition metal coordination plating agent employed. Illustrative of various substrates are Pyrex glass and spun glass; various synthetic fibers and plastics such as polytetrafluoroethylene, polychlorotrifluoroethylene, rayon, nylon, Delrin (polyformaldehyde resin) and the like; steelsuch as nickel plated steel, mild steel, nickel plated mild steel; metallic turnings such as copper, zinc, and the like, cellulose materials such as cotton, paper, and the likein short, any materials stable under the plating conditions employed.

It should be noted that when employing the novel organometallic plating agents of this invention, it is necessary to maintain enough vapor pressure, below the decomposition temperature of the organometallic, to enable the process to be conducted at an appreciable rate of plating. Too high vapor pressure results in somewhat inferior substrate adherence. Thus, it is preferred to employ up to about mm. pressure during the plating operation-preferably 0.01 to 10 mm. pressure.

As has already been pointed out, temperatures are very important in obtaining the desired plated product. Thus, although temperatures above the decomposition temperature of the monocyclopentadienyl metal coordination compound can, in general, be employed in the plating process of this invention, best results have been attained within certain preferred temperature ranges. For example, temperatures ranging from about 280 C. to about 450 C. produce relatively pure metal plated products and temperatures in the range of about 650 C., or above, produce carbide-containing products when the chlorides of the monocyclopentadienyl titanium compounds are employed. The plating compounds of the present invention vary insofar as their thermal stability is concerned, but all of. them can be decomposed at a temperature above 400 C., and some as low as 100 C. Generally, decomposition occurs above 400 C. when employing chloride derivatives of the group IV-B cyclopentadienyl transition metal composition. Other materials, such as the bromides, decompose at lower temperatures (e.g. about 300 (3.). The maximum temperatures which are employed are around 700 to 750 C.

In one embodiment of the instant invention, mixtures of monocyclopentadienyl group IV-B coordination compounds containing different metals are employed in the plating process to produce alloys of the respective metals upon appropriate substrates. An example of this embodiment is the utilization of cyclopentadienyl titanium trichloride and cyclopentadienyl zirconium t'richloride as plating agents in a process similar to that used in Examples IIV. The following example more fully demonstrates this embodiment.

Example IX Method Thermal decomposition as in Ex. I.

Composition An equimolar mixture of cyclopentadienyl titanium trichlori'de and cyclopentadienyl zirconium trichloride.

Composition Temp.-. C.

Substrate Aluminum.

Time (Hours) 1.

Substrate Temp 450 C.

Pressure 0,7 mm.

Result Metallic coating.

The cyclopentadienyl substituents of the group IV-B transition coordination compounds, employed as plating agents in this invention, have previously been defined as substituted or unsubstituted cyclopentadienyl moieties. More specifically, these moieties have been defined as cyclopentadienyl moieties containing a five carbon ring similar to that contained in cyclopentadienyl itself. In most cases the cyclopentadienyl moiety contains from 5 to about 15 carbon atoms. Illustrative of these cyclopentadienyl moieties are cyclopentadienyl, l-methyl cyclopentadienyl, 2-(o-tolyl)-cyclopentadienyl, indenyl, 2- methylindenyl, 3-phenyl-inde'nyl, fiuorenyl, 3-'e'thyl-fluorenyl, 2-m-tolyl-tfluorenyl, and the like cyclopentadienyl containing moieties. The cyclopentadienyl radical can alternatively be considered as a cyclomatic radical such as 4,5,6,7-tetrahydroindenyl, 1,2,3,4,5,6,7,8-octahydrofluorenyl, 3-methyl-4,5,6,7-tetrahydroindenyl, and 2-ethyl- 3-phenyl-3,4,5,6,7-tetrahydroindenyl.

The con'stitutents represented by Q in the above formula are electron donating groups capable of coordinating with the group IV-B metal atom in the compounds which are employed as plating agents in the process of this invention. Thus the groups represented by Q in the above formula are capable of sharing electrons with the metal atom so that the metal achieves a more stable structure by virtue of such added electrons. These electron donating groups in coordination with the metal are, generally, either organic radicals or molecular species which contain labile electrons. These electrons assume a more stable configuration in the molecule when associated with the metal. The electron donating group represented by Q may also be inorganic entities which are capable or existing as ions, such as 'hydro'gen, the cyanide group, and the various halogens. In general, the electron donating groups represented by Q are capable of donating from 1 to 4 electrons. The halogens are representative of electron donating groups donating one electron and carbonyl illustrative of an entity donating two electrons. An entity donating three electrons is represented by the nit'rosyl group and aliphatic diolefins are illustrative of entities capable of donating four electrons. In those compounds which are preferred plating agents in the process of this invention, Q represents electron donating entities capable of donating one electron. Such entities are the halides such as chlorine, bromine, fluorine, iodine, and the like, and alkoxy and aryloxy groups. Of these it is most preferred that Q be chlorine, bromine, butoxy, propoxy, ethoxy, and methoxy groups.

The group IV-B metals which form the metallic constituent of a coordination compound of this invention include the metals titanium, zirconium and hafnium. Of these, titanium and zirconium are preferred because of their greater availability and excellent chemical and refractory properties. The most preferred metal is titanium because of its wide adaptability to a multitude of uses.

The following compounds more fully illustrate the types of group IV-B transition metal coordination compound which can be employed as plating agents in this invention. These compounds are methyl cyclopentadienyl titanium trichloride, methyl cyclopentadienyl titanium tribromide, methyl cyclopentadienyl titanium trifluoride, methyl cyclopentadienyl titanium triiodide, methyl cyclopentadienyl titanium triastatide, and the corresponding metal halide compounds containing ethyl cyclopentadienyl, butyl cyclopentadienyl, octyl cyclopentadienyl, dimethyl cyclopentadienyl, dihexyl cyclopentadienyl, vinyl cyclopentadienyl, ethynyl cyclopentadienyl, phenyl cyclopentadienyl, methylphenyl cyclopentadienyl, acetyl cyclopentadienyl, allyl cyclopentadienyl, benzyl cyclopentadienyl, tolyl cyclopentadienyl, and other like radicals. In addition to the aforementioned titanium compounds, the corresponding zirconium and hafnium compounds can also be employed. Thus, other monocyclopentadienyl compounds are methyl cyclopentadienyl zirconium trichloride, methyl cyclopentadienyl zirconium tribromide, cyclopentadienyl hafnium trichloride, cyclopentadienyl hafnium tribromide and the like. Other compounds are methyl cyclopentadienyl titanium dibutoXy chloride, cyclopentadienyl zirconium methoxy dibromide, cyclopentadienyl tributoxy hafnium, dimethyl cyclopentadienyl titanium trichloride, phenyl cyclopentadienyl zirconium trichloride, and the corresponding compounds of titanium, zirconium and hafnium containing butyl cyclopentadienyl, octyl cyclopentadienyl, dimethyl cyclopentadienyl, dihexyl cyclopentadienyl, vinyl cyclopentadienyl, allyl cyclopentadienyl and other like radicals. Other compounds are indenyl titanium trifluoride, indenyl zirconium trichloride, fluorenyl titanium tribromide, fluorenyl zirconium trifluoride, 2-methyl-indenyl titanium trichloride, and the like. Any of the above compounds can be employed to plate their respective metallic substituent upon a multitude of substrates-employing any of the techniques described hereinbeforeby controlling the temperature of the plating operation so that temperatures above the decomposition temperature of the particular monocyclopentadienyl group IV-B coordination compound are employed.

The group IV-B metal platesparticularly titanium and zirconium platesfind a multitude of uses in the aircraft, missile and chemical processing industries. Thus, aircraft and missile components which require ultra high quality performance characteristics, such as resistance to high temperatures and to chemical attack, can satisfac torily meet these requirements when coated with a group IV-B refractory, according to the process of the instant invention. In the chemical processing industry, the group IV-B metal plates produced by the process of this invention find use in equipment subjected to high temperatures and chemical attack--as, for example, heat exchangers employed in such an environment. A very thin film of the metal plated on various substrates is sufficient for most applications. In some instances this film has a thickness on the order of only a few microns. By employing the process described herein, thicker plates can easily and economically be obtained-should such thickness be necessary for a particular application.

Another important use of the titanium plates produced herein is in the coating of cooking utensils-particularly aluminum cooking utensils. By virtue of such coating food does not stick to the utensil, thereby eliminating the necessity for cooking lubricant and the like.

Another use of the metal plates produced according to the process of this invention is in the plating of plastics. An example of such a use is the titanium plating of automotive interior plastic trim. By virtue of such plating the serious problem encountered in automobile bodies stored for long periods of time, whereby vapor loss from the plastic deposits on car windows and Windshields, is simply and economically overcome.

We claim:

1. A process for plating a substrate with a group IV-B transition metal comprising decomposing the vapors of a monocyclopentadienyl group IV-B transition metal coordination compound while in contact with said substrate; said compound containing, in addition to the cyclopentadienyl group, at least one electron donor group capable of donating 1 to 4 electrons.

2. A process for plating a substrate with a group IV-B transition metal comprising heating the substrate to be plated to a temperature above the decomposition temperature of a monocyclopentadienyl group IV-B transition metal coordination compound, having, in addition to the cyclopentadienyl group, at least one electron donor group capable of donating 1 to 4 electrons, and contacting the vapors of said coordination compound with said heated substrate.

3. The process of claim 2 wherein said coordination compound is cyclopentadienyl titanium trichloride.

4. The process of claim 2 wherein the said coordination compound is cyclopentadienyl zirconium trichloride.

5. A process for plating a substrate with titanium which comprises decomposing the vapors of a monocyclopentadienyl titanium trihalide while in contact with said substrate.

6. A process for plating a steel substrate with titanium which comprises decomposing the vapors of a monocyclopentadienyl titanium trihalide while in contact with said substrate.

7. A process for plating an aluminum substrate with titanium which comprises decomposing the vapors of a monocyclopentadienyl titanium trihalide while in contact with said substrate.

8. A process for plating a carbonaceous substrate with a group IV-B transition metal which comprises decomposing the vapors of a monocyclopentadienyl group IV-B transition metal trihalide while in contact with said substrate.

9. A process for plating a substrate which comprises decomposing the vapors of a monocyclopentadienyl group IV-B transition metal coordination compound while in contact with said substrate; said compound containing, in addition to the cyclopentadienyl group, at least one electron donor group selected from the group consisting of chlorine, bromine, butoxy, propoxy, ethoxy, and methoxy groups.

References Cited in the file of this patent UNITED STATES PATENTS 2,508,509 Germer et al May 23, 1950 2,638,423 Davis et a1. May 12, 1953 2,690,980 Lander Oct. 5, 1954 2,898,235 Bullotf Aug. 4, 1959 2,955,958 Brown Oct. 11, 1960

Claims (1)

1. A PROCESS FOR PLATING A SUBSTRATE WITH A GROUP IV-B TRANSITION METAL COMPRISING DECOMPOSING THE VAPORS OF A MONOCYCLOPENTADIENYL GROUP IV-B TRANSITION METAL COORDINATION COMPOUND WHILE IN CONTACT WITH SAID SUBSTRATE; SAID COMPOUND CONTAINING, IN ADDITION TO THE CYCLOPENTADIENYL GROUPS, AT LEAST ONE ELECTRON GROUP CAPABLE OF DONATING 1 TO 4 ELECTRONS.