US3053654A - Producing lead shapes - Google Patents

Description

Patented Sept. 11 1962 3,053,654 PRODUCING LEAD SHAPES Paul A. McKim, Baton Rouge, La., assignor to Ethyl Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Mar. 28, 1960, Ser. No. 17,802 5 Claims. (Cl. 75-211) This invention relates to the manufacture of lead shapes. More particularly, the invention relates to the preparation of solid lead shapes or articles from finely divided lead, or essentially lead systems, and especially lead systems derived from the preparation of organometallic compounds.

Although the general technique of forming solid shapes of metals from finely divided metals has been known for quite some time, it has been, for all practical purposes, not utilized for lead metal, probably because of the relatively low physical strength of the resultant product. It has recently been discovered that certain finely subdivided, essentially lead powders are highly suitable for making solid articles. These lead powders are derived from a reaction of an alkylating agent and an alloy of an alkali metal with lead, resulting in formation of a lead tetraalkyl compound plus unreacted subdivided lead powder. Such powders are highly effective sources of subdivided lead metal for forming purposes. It has been found that by mechanically forming such subdivided lead, that solid shapes having surprising rigidity, tensile strength, and other properties, can be readily made. Such forming operations necessarily must be preceded or followed by treatment to eliminate minor quantities of the lead tetraalkyl component present, such component being a residual quantity which is not normally removed from the reaction product mixture. The removal of such minor impurities, prior to a mechanical forming operation, is an inconvenient and relatively expensive operation. By this is meant that, although the tetraalkyl lead compound can be readily removed to a concentration low enough to satisfy the economics of production of the tetraal'kyllead as a single product, considerable further treatment or effort is necessary to remove and recover the tetraalkyllead to the point that the ultimate lead shape is perfectly innocuous. Further, it has been discovered that the presence, of even minor quantities of liquid tetraalkyl compounds during a forming operation provides a beneficial effect in that such components appear to assist and facilitate the actual forming operation as such. The reasons for this are not fully understood, but the tetraalkyllead liquid components appear to have an oiliness and a lubricating eifect which apparently minimizes the mechanical effort required to form solid shapes from such subdivided systems. Hence, the total elimination of tetraalkyllead compounds, before forming, is not a particularly satisfactory type of operation.

A general object of the present invention is to provide a new and improved process for the formation of solid lead shapes. More particularly, an object is to provide an improved process for forming lead shapes from finely divided lead residues from a process for making a tetraalkyllead compound, said process being characterized by the reaction of an alkylating agent with a lead alloy and an alkali metal. A more specific object is to provide a process producing lead solid shapes, employing the above mentioned feed solids wherein the benefits of minor quantities of copresent tetraalkyllead components, upon the forming operation, are fully preserved, yet the ultimate solid lead shape is entirely freed of such materials. An additional object, of certain embodiments, is to provide a process wherein a portion only of a tetraalkyl component is removed and recovered and the solids, upon further processing are formed into desired solid shapes, and the remainder of the tetraalkyl is entirely eliminated. A more particular object is to provide in combination the synthesis of a finely divided lead solids system or mixture, and a forming operation for producing solid shapes therefrom. Other objects will appear hereinafter.

The process of the present invention comprises subjecting a finely divided lead powder, consisting essentially of finely divided lead metal and accompanying minor quantities of tetraalkyllead compounds, to forming pressure operations at sufiiciently elevated pressures to form the lead particles into an essentially homogeneous solid shape, and concurrently with said operation heating the lead particles and accompanying components to a temperature of from about C. to about 300 C., for a time sufficient to essentially entirely thermally decompose the tetraalkyllead components. When moving pressures are utilized, the degree of movement can be varied and minimized by an appropriate increase in the forming pressure. In certain instances, entirely static pressures, i.e., with no movement of the lead powders other than that accompanying bulk volume reduction are employed. In virtually all cases, pressures of about 5000 pounds per square inch and above are employed. The duration of the temperature application will vary with the particular identity of the tetraalkyllead impurity or component, the concentration, and the intensity of temperature applied to the system during the processing. When lower temperatures, in the neigh' borhood of l00 or are applied, and in the case of, for example, tetraethyllead, temperature applications of as high as an hour may sometimes be required, although usually 30 minutes is quite ample for most concentrations. On the other hand, when temperature levels of 200 to 300 C. are applied, the duration of such application can be as low as several seconds to about 10 minutes.

The general mode of operation, and the best manner of carrying out the invention, will be fully understood from the working examples and detailed description hereinafter.

Example I This example illustrates preparation of the charge stock for the present process by chemical means. 100 parts of monosodium lead alloy, NaPb, were charged to an autoclave along with about 50 parts of ethyl chloride, this amounting to approximately 75 percent excess ethyl chloride. The mixture was reacted at an autogeneous pressure at elevated temperature until the action was terminated, as shown by a decrease in temperature and pressure. The product of this reaction was an apparently dry reaction mixture containing about 55 weight percent lead, 24 percent tetraethyllead, and 20 percent sodium chloride. Excess ethyl chloride was vented during the reaction and upon completion of the reaction. The resultant dry granular material was then discharged from to steam distillation for a suificient period of time to re- 'move a large proportion of the tetraethyllead component. The resultant material is a multiphase mixture of the subdivided lead particles, sodium chloride (largely dissolved in the aqueous phase) and minor quantities of tetraethyllead, in a concentration usually, of the order of several percent, based upon the lead.

Screening a portion of this material, in US. standard screens, gives the following size distribution:

about 5 minutes. A finely grained lead solid, virtually free of tetraethyllead, is produced. In preferred embodiments of this example, the temperature gradient is applied so that a higher temperature is provided at the exggg gg Screen N trusion end of the chamber and lower temperatures are Retained of Screen applied in the chamber proper. This technique provides Openings the benefit of retaining the alkyl lead or tetraethyllead component unchanged during a large portion of the procg 52 8-8233 essing, and thus assures a lubricating effect derived from 25 35 010197 10 the tetraethyllead component. The accompanying Water 2; 3 8- with the change stock is concurrently vaporized from the 73 120 010049 system and is removed by blowby past the ram, and to a 3% 332 888%? certain extent by vaporizing through the die apertures. In addition to rolling and extrusion as exhibited in the above examples, the forming operations employed in- The lead powder, prepared as above described, is then elude dlTeCt pr ssing of the lead powder charged rn a fed to a rolling mill operation, being fed on a steel con- Press 1119M or (he havmg desn'ed final part configura' veyor belt threaded through a pair of pressing Tons tron, wh1ch can be, for example, forms for rad ator orna- Heating means, which are typically gas burners positioned ments, name Parts for Tallroad and ,Shlp models below the steel belt, are provided slightly before the en- 0 and Q artlcles- T e followrng example illustrates the trance to the rolling operation and provide sufiicient heat techmque employed m such mstancesto raise the temperature of the subdivided solids to about Example Ill 250 C. In assing through the rolls, a ressure a roximating 5000 gounds per square inch is agplied, the ctual g Powder employed. Is as i Exanjlp 16 I a time of contact between the rolls being about minute. Specimens of i Powder mserted m a dle or.mol The duration of the temperature indicated, of the order prfmdmg cyhndncal .bushmg pattern Pressure 15 apof about C is about 3 minutes. A Subsequent plied thereto by a matrngram, at a pressure of about longer period is provided as the charge material is lowpounds per Square Inch E the mold ered in temperature to about 100, this period requiring 1s heated to a tempefratire of 115 i i g usually about 7 to 10 minutes. The indicated processing temperature are mall/tamed i P g y g results in the formation of a thin lead strip, essentially i i t the termmatw? of i t e angled free of tetraalkyl lead, and having very good surface gloss mg 15 discharged fr he 2 E asfsmoot 1: or finish, as well as being a stiff, sturdy material, having and sharp configuratlons. na ysls of ragment to en tensile strength of the order of 4000 to 6000 pounds per from the shape shows virtually no detectable onganolead square inch. The degree of reduction of cross sectional component E I IV thickness accomplished during the actual rolling is subxamp e ject to easy adjustment. In typical operations, the aver- In this operation, the lead powder was derived genage thickness of the lead powder feed stream is from erally as obtained in the preceding examples, but the about /a to about A inch, and the pressing operation recomposition thereof differed in that it contained approxisults in a thickness reduction of from 50 to 90 percent, a 40 mately 6 weight percent tetraethyllead and about 11 typical sheet having a thickness of about 0.04 inch. percent water. The material was charged to an extrusion Example H chamber, and a pressure of about 15,000 pounds per square inch is applied, employing an extrusion ratio of In this example, the same feed supply is used, as in about 35. The extrusion chamber and contents are Example I, but instead of rolling the lead powder, it is heated to a temperature of about 190 C., resulting in charged to an elongated cylindrical extrusion chamber, rapid decomposition of the tetraethyllead component and having a die at one boundary thereof, the chamber and vaporizing of the water phase, which was discharged in die providing an extrusion ratio of the order of 42. The part as a vapor discharged backwards past the extrusion die is in the shape of a cylindrical or circular aperture of ram and to a minor extent, by concurrent discharge about 0.4 inch in diameter. Pressure of about 25,000 through the die orifice. The residence time of the mapounds per square inch is applied. Concurrently with apterial in process, in the extrusion chamber, is about 3 plying the pressure, the extrusion chamber is heated by minutes, and approximately 5 to 10 minutes additional external means, typically a resistance wire winding, or in time is required for the solid lead product to cool to a some cases, an induction heating coil, to heat the chamber temperature of below 100 C. The product is a dry, and the contents to. about 175 C. Upon application of substantially homogeneous bar, having virtually no tetrapressure to the charge, by a ram in the extrusion cham ethyllead as such therein. her, a substantially homogeneous, cylindrical shape is In addition to the foregoing operations, additional forced through the die, at a temperature approximating working examples are summarized in the following table:

Composition of Feed Forming and Treating Example Alkyllead Wt. Size of Solids Technique Pressure Temper- Dura- Percent (p.s.i.) ature, O. tion Min.

Tetra-n-butyl lead.... 5 Through on 200. Rolling... 4, 000 140 2 Tetra-1 Propyl lead. 5 Through 100- on 325. Extrusion- 10,000 130 4 Tetra-isoamyllead..-. 7 Through 35, on 100-. Pressing... 28,000 7 Methyl triethylleadn 2 Through 18.. .do..... 17,000 8 D1rnethyl-diethyl.--- 1.5 Through 18.- Rolling... 15,000 130 3 Methyl-triethyl lead-- 0.5 Through 18.. Extrusion- 20,000 5 1 Screen numbers refer to U.S. Sieve Series. 2 Refers to time under pressure or in processing; additional time also required in cooling to below 100 0.

As heretofore mentioned, the present forming operations can be carried out in conjunction with preceding C. The duration of residence time in the extrusion chamber and the die is up to about several minutes, and the formed lead shape retains the temperature, or a temperature of about 100 C. for an additional period of recovery operations of similar character.

In other Words,

an intermediate forming operation is directed to a partial removal of a co-present tetraethyllead, providing an intermediate solid shape having appreciable quantities of alkyl lead therein, and such shape is then further mechanically shaped by pressure application concurrently with thermal decomposition as in the preceding examples. An illustration of such embodiment follows.

Example XII A reaction mixture is prepared by reacting sodium lead alloy and ethyl chloride, as in Example I. Only a portion of the tetraethyllead is removed by steam distillation, however, reducing the concentration thereof to about 15 percent of the lead.

The solids containing residue is (free drained leaving a wet powder containing mixture with the indicated proportions of tetraethyllead and comparable amounts of aqueous phase. Portions of the mixture are pressed at ambient temperature. This initial pressing is in a cylindrical chamber, by application of pressure by a ram. Suflicient clearances are provided to allow discharge of liquid phases past the ram or plunger. Upon application of pressure of about 5000 pounds per square inch, a solid appearing shape is formed, having roughly about 3 weight percent tetraethyllead and comparable proportions of water or aqueous phase.

The solid shapes, as above formed, are then charged to an extrusion chamber and processed as in Exhibit II, except that the extrusion orifice in this instance is in the form of a thin strip shape. As in preceding exmaples, this operation is accompanied by heating to a temperature of, typically 150 C., to provide complete decomposition of the tetraethyllead content.

It will be apparent from the foregoing examples that the principles of the present invention are applicable to a substantial number of particular systems, and that a variety of forming techniques can be employed.

As evident from the examples, in all instances a substantial temperature of above 100 C. and below about 300 C., is employed for the process. The decomposition of the alkyl lead compounds varies in rapidity according to the particular identity of the particular alkyl lead and according to certain other factors, e.g., concentration. In the case of tetraethyllead, measurable decomposition occurs in the neighborhood of 100 C., but the rate is quite low, particularly when minor quantities of thermal decomposition inhibitors are present in solution in a solution in a tetraethyllead. Ordinarily then, and particularly because of a supplemental stabilizing eifect of solids present, a temperature of above about 130 C. is preferred for this particular material. However, temperatures, as indicated, of the order of above 110 or 115 C. are quite suitable and if the temperature level is maintained for a sufficient period of time, full decomposition of the organolead material is accomplished. The tetraalkyllead compounds having alkyl groups of more than two carbon atoms are more easily decomposed than the tetraethyllead. Tetramethyllead, on the other hand, is quite refractory in its resistance to thermal decomposition, and when this is the component present, temperatures approaching the range of about 290 to 300 C. are ordinarily preferred to accomplish this result.

The alkyl lead compounds, under the conditions of the present process, do not decompose violently. It appears that the relatively large proportions of lead solids, plus the co-presence, usually, of an aqueous phase, results in a distinct moderation of the potential severity of decomposition. Although alkyl lead compounds with higher alkyl substituents are more readily decomposed, the compounds with lower alkyl substituents are more apt to exhibit violent decomposition. Hence, in the case of the latter, it is highly preferred that the alkyl lead concentration should not exceed about 5 percent.

The time necessary to process and maintain temperature during the processing at the desired level necessary for decomposition, will depend to some extent upon the proportions of the alkyl lead compound, upon its identity, and by the temperature level applied. Heating and cooling periods, to and from the highest temperature of a process, also contribute to the decomposition. The overall processing times, in which temperatures of over 100 C. prevail, are usually from 1 to 15 minutes. However, by increasing the temperatures during actual pressure forming operations, the necessary pressure period can be drastically reduced. Thus, by increasing the maximum temperature, during Example III, to about 200 C., the pressure application period can be reduced to several seconds. Similar reductions in time are attainable in the other examples.

The actual pressures employed in forming the lead shapes will depend upon the degree of compacting actually desired and the mode or technique employed in the forming. As clear from the above examples, suitable pressure ranges are from the range of several thousand to about 30,000 pounds per square inch, although these are not explicitly limiting. A preferred range is from about 10,000 to about 20,000 pounds pressure.

The particular weight concentration of the lead alkyls is not highly critical. It is preferred that the lead powder feed contain not over about 5 weight percent of the alkyl lead component, but the process is equally operable with higher concentrations of the order of 7 or even up to about 10 weight percent. In these instances, a portion of the alkyl lead component is actually dislodged from the feed material under the influence of the pressure alone, and may be recovered as such. When the concentration is of the order of about 1.5 or 1 percent or lower, virtually all the removal of the alkyl lead is by the mechanism of thermal decomposition as above described.

Having fully described the invention in the several modes of operation, what is claimed is:

1. The process for forming solid lead shapes comprising forming, by application of pressure of at least about 5,000 pounds to about 30,000 pounds per square inch, a solid shape from a finely divided predominantly lead powder, said powder consisting essentially of finely subdivided lead and from about 0.5 to 10 weight percent of a tertaalkyllead compound, and concurrently with said pressure forming operation, heating to a temperature of above about 100 to about 300 C. for a time sufiicient to thermally decompose the tetraalkyllead compound.

2. The process of claim 1 further defined in that the pressure is static pressure applied to the lead powder in a forming die.

3. The process of claim 1 further defined in that the pressure is applied to the lead powder by forming rolls.

4. The process of claim 1 further defined in that the lead powder is charged to an extrusion chamber and pressure is applied to force a solid shape through a forming die in the boundary of said chamber.

5 The process comprising, in combination, reacting an alkali metal lead alloy with ethyl chloride, forming thereby a reaction product including tetraethyllead, excess lead in finely divided form, and alkali metal chloride, separating substantially all the alkali metal chloride and the preponderance of the tetraethyllead therefrom, thereby forming finely subdivided lead powder accompanied by minor quantities of from about 0.5 to 5 percent of tetraethyllead, then subjecting said powder to a forming operation including application of pressure of at least 5,000 pounds per square inch and concurrently heating to a temperature of above about 100 to about 300 C. for a time suflicient to thermally decompose the ,tetraethyllead, whereby a solid shape substantially free of tetraethyllead is produced.

Claims (1)

1. THE PROCESS FOR FORMING SOLID LEAD SHAPES COMPRISING FORMING, BY APPLICATION OF PRESSURE OF AT LEAST ABOUT 5,000 POUNDS TO ABOUT 30,000 POUNDS PER SQUARE INCH, A SOLID SHAPE FROM A FINELY DIVIDED PREDOMINANTLY LEAD POWDER, SAID POWDER CONSISTING ESSENTIALLY OF FINELY SUBDIVIDED LEAD AND FROM ABOUT 0.5 TO 10 WEIGHT PERCENT OF A TERTAALKYLLEAD COMPOUND, AND CONCURRENTLY WITH SAID PRESSURE FORMING OPERATION, HEATING TO A TEMPERATURE OF ABOVE ABOUT 100 TO ABOUT 300* C. FOR A TIME SUFFICIENT TO THERMALLY DECOMPSOE THE TETRAALKYLLEAD COMPOUND.