US2728656A - Method of preparing lead alloys - Google Patents

Description

Dec. 27, 1955 NEHER METHOD OF PREPARING LEAD ALLOYS 2 Sheets-Sheet 1 Filed Feb. 29, 1952 m \Q k E mm mm mm vw km mm INVENTOR.

CLARE EM. IVE HER B WW Y TTOR/VEY Dec. 27, 1955 c. M. NEHER 7 2, 8,

METHOD OF PREPARING LEAD ALLOYS FiledFeb. 29, 1952 2 Sheets-Sheet 2 f I85 190 195 200 205 M/Luvou's IN VENTOR.

CLARE E .NE'HER A T TOR/V5 Y United States Patent METHOD OF PREPARING LEAD ALLUYS Clarence M. Neher, Baton Rouge, La., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware Application February 29, 1252, Serial No. 274,233

3 Claims. (Cl. 75-467) This invention relates to the manufacture of reactive alloys of lead. More particularly the invention relates to a new and improved process for combining lead with at least one additional alloy component such as, for example, an alkali metal or an alkaline earth metal.

The alloys of lead with other metals find usage for various purposes. As examples of the lead alloys finding wide commercial usage may be mentioned solder, type metal, pewter and alloys of lead with the alkali metals or alkaline earth metals. The latter alloys, including, for example the alloys of lead with sodium, potassium, magnesium, calcium, lithium, find extensive usage as chemical reactants, particularly in the manufacture of organic compounds of lead, such as tetraethyllead. The alloys used for such purposes may be binary alloys, or may contain more than one alkali or alkaline earth metal component, or an alkali metal and an alkaline earth metal. The preparation of such alloys has heretofore been quite awkward. It has been considered essential in preparing such alloys, to thoroughly mix large batches, then analyze, and then to make further appropriate additions to correct the composition as required, then to remix, and reanalyze. The drawbacks of such a procedure are obvious. Further, in mixing the lead and added components, appreciable amounts of heat are frequently generated. For example, in mixing sodium and lead in proportion to provide monosodium lead alloy, sufficient heat is generated to raise the temperature as much as 800 F. Accordingly, it has been necessary to mix the components of the alloy slowly so as to avoid breakage of the manufacturing pots because of the thermal effects accompanying the process. The prior methods, then, have been limited in efiiciency owing to the apparent necessity of blending large batches of alloy, and further by the fact that the characteristics of the system restrict the rapidity with which such batches can be prepared. Some of these difficulties in the prior art are illustrated by Fisher et al. U. S. Patent No. 2,276,031, which shows the complications involved in one type of prior art preparation, as well as the Amick et a1. Patent No. 2,043,224, which illustrates the complicated apparatus heretofore considered necessary. The preparation of reactive lead alloys has been further complicated by the necessity of keeping the metals being processed, and samples thereof, at all times under inert conditions.

Among the objects of the present invention is the provision of a process for preparing alloys of lead with other metals, which process avoids the above and related disadvantages. A further object is to provide a high capacity process wherein a highly uniform composition is attained but nevertheless only a minor quantity of material is processed or mixed at any one time. Another object is to provide a continuous process having an effective method of flow control and proportioning. The control and proportioning is responsive to the composition of the alloy concurrently produced, so that alteration or error allows immediate adjustment. Still another object is to provide a process particularly effective in preparing the reactive 2,728,656 Patented Dec. 27, 1,955

2 alloys of lead, in that alloying to a desired composition is effected without exposure of the metal components. Additional objects will appear hereafter.

The present process attains the above objects and provides as well additional advantages over prior methods. The process and the details of operation, and of suitable equipment will be more readily understood from the description below, and by reference to the accompanying figures. Figure 1 is a schematic showing of an apparatus suitable for a preferred embodiment of the process wherein automatic operation is provided. Figure 2 presents a curve of a typical voltage versus composition relationship such as is employed in the process.

It has been discovered that the alloys oflead can be readilymanufactured by feeding together molten streams of the lead, or if desired, a predominantly lead alloy, and then the alloying metal, then mixing, the relative proportions of the components being controlled in accordance With a potential or voltage difference existent between the so-formed molten alloy and a molten reference metal at the same temperature as the alloy. A feature of the process is that at all times the composition of the alloy produced is immediately ascertained thereby allowing control of the feed proportions to provide a uniform composition.

In most forms of the process, the formation of the alloy is accompanied by the liberation of heat of reaction, and a cooling step is incorporated to reduce the temperature of the mixed alloy to a uniform temperature, above the freezing point of the alloy. Such a uniform temperature assures obtaining the full benefits of the process. In the preferred embodiments of the invention, the mixing and cooling operations are carried out concurrently. 7

Process flows and arrangement of suitable apparatus are illustrated by Figure l, for a preferred embodiment of the process wherein automatic proportioning of the alloy components is achieved. For simplification, the following description is given for application to the manufacture of a lead-sodium alloy, although the process is also fully applicable to other lead alloys.

Referring to Figure l, the apparatus shown includes a sodium feed tank 10, fed or charged as desired through a valved sodium feed line 14. A lead feed pot 12 is similarly charged as necessary with molten lead fed through a valved feed line 13.

feeds to the mixing operation. The flows of the sodium and lead are controlled by appropriate control valves 28 in the sodium transfer line, and 30 in the lead transfer line.

The sodium-is fed to the jacket tube 24 of a concentric tube feeder to the heat exchanger-mixer 32. The lead transfer line 22 is continued, as the center tube of the concentric tube feeder, into a mixing tube 26 in the heat exchanger-mixer 32. The concentric tube feeder 24 prevents the sodium and lead from contacting each other until within the heat removal zone. The heat exchangermixer, in addition to controlling the discharge temperature of the mixed alloy by removal of the heat of mixing, also assures uniform mixing of the sodium and lead by the internal turbulence generated by the flow of the liquid metal and the mixing currents generated by the heat of reaction.

The temperature of the alloy discharged by the heat exchanger-mixer is ascertained by a thermocouple element 34 inserted in the alloy line 56. The temperature is maintained constant by appropriate control of the flow of a coolant liquid to the jacket of the heat exchanger-mixer 32. Immediately following the thermocouple 34 the alloy flows through a chamber or cell 36 wherein the voltage of the alloy as ascertained with respect to that of a reference metal. It has been found that this voltage or E. M. F. difference provides an accurate guide or a measurement of the composition of the alloy.

The voltage as ascertained in the cell 36 is transmitted to an instrument 60 by electrical leads 59. The instru ment 60 may suitably provide a continuous record of the voltage, expressed directly in terms of the alloy composition if desired. Incorporated in the instrument is an amplifier or convertor which is of conventional design. The amplifier translates the voltage impulses received from the cell 36 to control forces, either pneumatic or electrical, for example, which are transmitted by line 57 and provide control of the setting of the control valve 28 by motor 58.

In operation, the flow of lead from the lead supply pot 12 is usually set at a constant value by setting the lead control valve 30. The sodium flow is maintained at the desired rate by the control valve 28 which is actuated as above described. Any change in setting of valve 28 is then in response to variations in the voltage of the alloy as measured in cell 36.

Following passage through the cell 36 the alloy flows through a conduit 56 and is delivered to a holdup pot 38. A supply of several hours production is maintained in the holdup pot 38, and continuous agitation of the product therein is provided by an agitator 40. Alloy is transferred to subsequent consuming operations through transfer line 42 by means of centrifugal pump and drive 55.

The heat exchanger 32 may be any of a variety of types, the most usual being to provide a jacket for a coolant around the mixing tube 26. A coolant is passed through the jacket, the coolant preferably being a material which is stable at the high operation temperatures required. A suitable coolant is the eutectic mixture of diphenyl and diphenyl-oxide. The coolant is fed countercurrently to the flow of the alloy in the heat exchanger-mixer, being introduced through a supply line and discharged by an outflow line 74. A coil 76 forms part of the coolant outflow line 74. A water spray, fed through a line 78, is sprayed over the coil 76 by a spray head 75, and provides for maintaining a uniform temperature of the coolant supply in the coolant tank 70. Customarily and preferably, the coolant supply temperature is held constant at a temperature slightly above the freezing point of the alloy being manufactured. This assures that the alloy will not be frozen in the heat exchanger-mixer unit. Coolant is discharged by pump 77 through a line 72 to the heat exchanger-mixer, the rate of fiow being controlled by valve 80. The control valve 80 is set by the operating motor thereof, which is actuated by electrical or pneumatic impulses from the conventional transmitter 61. The transmitter 61 may also incorporate a recorder for providing a chart of the alloy temperatureas determined by thermocouple 34.

It is highly desirable that means as above described, or equivalent means known in the process industries, be provided for assuring a constant temperature of the alloy discharged from the heat exchanger-mixer. This condition is desired because in addition to varying with the composition of the alloy, the voltage difference ascertained by cell element 36 varies somewhat with temperature. However in some few instances, when only a minor quantity of alkali metal is to be incorporated in the alloy, for example, temperature adjustment is not essential.

The cell or voltage detector 36 may assume several forms. In every instance, however, provision must be made for measurement of voltage difference which is truly representative of that between the alloy being produced and the reference metal. To accomplish this result, provision is necessarily made for isolating the reference metal from the surface of the body of the alloy, but within the mass of the alloy product. A suitable apparatus providing this isolation comprises a glass capsule or tube, holding the reference metal within the mass of alloy. A second glass envelope surrounds and is spaced apart from this tube at the alloy surface and provides electrical insulation of the surface thereof from the main tube. A two wire lead line 59 includes a probe or wire from the reference metal plus a wire from the alloy itself, and relays the voltage difference to the instrument 60. The glass of this capsule or envelope is necessarily of a composition permissive of migration or permeation therethrough of ions of the alloy component being ascertained. Thus a low sodium boro-silicate glass, besides being resistant to thermal shock, is permeable to sodium ions. When determining the concentration of other alloy components, for example, magnesium, it is desirable that the glass or barrier material contain some magnesium present in its composition, in order to provide a spatial configuration facilitating or permitting permeation of magnesium ions so as to permit measurement of a voltage difference.

A typical voltage-composition relationship as employed in an embodiment of the process is illustrated by Figure 2. The figure is a plot of'the relationship of the voltage difference between a molten alloy consisting of sodium and lead, and pure sodium. The chart shows such voltage-composition relationships at temperatures of 440 C. and 450 C. It will be noted that with an increase in sodium content, the voltage difference decreases. Thus, at 440 C., at a sodium content of 9.75 weight percent, the voltage is 202.6 millivolts, and at exactly 10 weight percent sodium, the voltage is 197 millivolts. This relationship thus provides an almost instantaneous method of ascertaining the composition of the alloy produced.

If desired, the manufacturing operation may be manually controlled. Thus, referring to the flow diagram of Figure 1, the sodium control valve may be manually adjusted in response to any changes in the voltage differences as determined by cell 34. Manual control is, however, ordinarily preferred only for standby or emergency operation, because of the high degree of uniformity readily attained by automatic means.

The holdup pot 38, while primarily intended as a product reservoir, also serves an additional function in minimizing variation of alloy delivered to subsequent consuming operations. Thus, even if a temporary unbalance in the flow rate of one of the alloy components results in production of alloy deviating from the desired composition, this effect is minimized by the dilution effect of the alloy in the holdup pot. In addition, the holdup pot provides storage capacity when either the alloy consuming operation is interrupted, or when operation of the alloy manufacturing unit is temporarily suspended.

As a working example of the production of monosodium lead alloy, NaPb, liquid lead is fed through the lead transfer line at a rate of about 8100 pounds per hour and at a temperature of about 450 C. Liquid sodium is fed through the sodium transfer line 20 at a rate of about 900 pounds per hour, the flow rate being controlled by regulating valve 28. The two metal streams are fed, through the feed section 24 to the cooling-mixing tube 26 in the heat-exchanger-mixer. In passing therethrough, the temperature of the metals rises, owing to the heat of mixing, but is again reduced to 450 C. before discharge. The alloy then is passed through the voltage determination cell 36, wherein the voltage with reference to pure sodium is measured. The voltage difference signal is transmitted to the recording-transmitting instrument 60, which in turn controls the setting of the sodium control valve 28 in response to any voltage difference deviation, to maintain a constant value of 196 millivolts. The manwrrfi i ufactured alloy then passes to the holdup pot 38, which normally contains about four hours production, but has capacity for approximately twice that quantity.

The process is capable of valuable usage for numerous embodiments in addition to the above manufacture of monosodium lead alloy. Alloys of appreciably lower or higher sodium content can be made, and in addition, the method is easily utilized in making ternary alloys. Thus, for example, if the preparation of an alloy containing percent sodium, 1 percent potassium, and 89 percent lead is desired, the lead and sodium are first blended. Potassium is then alloyed with the liquid sodium-lead alloy, the voltage difference between the final alloy and pure sodium again being employed as a guide or control point.

As indicated above, it is not essential that the reference metal employed be identical in composition to the alloying metal or metals being incorporated into the lead. As mentioned above, for example, when alloying potassium metal, the reference metal can be pure sodium and accurate results will be obtained. Therefore, it is possible to utilize a reference metal consisting of a low melting mixture containing as a component the alloying metal being determined. Thus, for example, in determining the amount of calcium in an alloy of lead and calcium, sodium saturated with calcium may be used as the reference metal mixture.

For simplicity, the apparatus illustrated by Figure 1 omits features usually found in processing reactive metals, which Will be readily apparent to those expert in the field. Thus, provision is made for minimizing exposure of the feed metals, or the product alloy, to moisture or active atmospheres. For example, a blanket or atmosphere of any pure inert gas is maintained over the metal components in tanks or vessels. Another frequently used feature is means to supply heat to the storage tanks and to the holdup pot. Normally such pots will be provided with efiicient insulation, but even under such conditions, some heat will occasionally be required to prevent freezeup.

The embodiment described above with reference to Figure 1 involves the concurrent mixing of the alloy components and the removal of reaction heat accompanying the mixing. This concurrent operation is highly desirable as it utilizes the natural turbulence of flow, and the tur bulence generated by the heat effects of alloy formation, to secure intimate dispersion of the alloy components one within the other. Although advantageous, this concurrent operation is not essential to obtain the major benefits of the process. If desired, the mixing can be carried out separately. This is done, for example, by feeding the sodium and lead streams to a small agitated vessel. Here, these components could be intimately mixed by mechanical stirring resulting in appreciable heating of the alloy. The mixed alloy is then passed through a heat exchanger for cooling to the desired control temperature. The advantage of this mode of operation is that the efliciency of the mixing step is rendered independent of the production rate, which is sometimes a factor in the embodiment illustrated by Figure 1.

As many modifications of the process will be evident in addition to the specific description and examples given herein, it will be understood the process is not limited except as by the claims below.

What is claimed is:

1. A process for continuously manufacturing a molten alloy of lead and at least one alkali metal comprising providing a stream comprising molten lead, and a stream of molten alkali metal, the flow of one of said streams being controlled by means responsive to a voltage difference, combining the lead and alkali metal streams as an additional combined stream and mixing the lead and the alkali metals in the combined stream and concurrently with the mixing removing the heat generated and cooling to a constant temperature, above the melting point of the alloy desired, then passing said combined stream past a reference metal specimen, comprising an alkali metal corresponding to a component of the alloy, the specimen being isolated from the periphery of the combined stream, and separated from the combined stream by a membrane permeable to ions of the reference metal, whereby a voltage ditference is developed between the combined alloy stream and the reference metal, and transmitting the voltage dilference to the means for controlling the flow of one of said streams.

2. The continuous process for manufacturing a molten alloy of sodium and lead of substantially constant composition comprising providing a stream of molten lead at a substantially constant rate, providing a stream of molten sodium at a rate controlled by means responsive to a voltage difference developed as hereafter defined, feeding together the lead stream and the sodium stream and mixing said streams by flow. through an, extended flow channel and concurrently removing heat developed in the mixing and cooling to a constant temperature, above the melting point of the desired alloy, then passing the mixed stream past a sodium metal specimen, the specimen being isolated from any boundary of the mixed stream and being separated from the mixed stream by a membrane permeable to sodium ions at the said temperature, whereby a voltage difference is developed between the mixed stream and the sodium specimen, and transmitting the voltage difierence to the means for controlling the flow of the sodium stream.

3. The continuous process for manufacturing a molten alloy of sodium, potassium and lead comprising providing a stream of molten lead at a substantially constant rate, providing a stream of molten sodium at a rate controlled by a first means responsive to a voltage difference developed as hereafter defined, feeding together the lead stream and the sodium stream and mixing said streams by flow through an extended flow channel and concurrently with the mixing removing heat developed in the mixing and cooling to a constant temperature above the melting point of the mixed stream, then passing the mixed stream past a first sodium metal specimen, the specimen being isolated from any surface of the mixed stream and being separated from the mixed stream by a membrane permeable to sodium ions, whereby a first voltage difierence is developed between the mixed stream and the first sodium specimen, and transmitting the first voltage difference to the first means, for controlling the flow of the sodium stream, providing a stream of molten potassium at a rate controlled by a second means responsive to a voltage difference developed as hereafter defined, feeding together the mixed stream and the potassium stream and mixing said streams by flow through an extended flow channel, and concurrently with the mixing removing heat developed in the mixing and cooling to a constant temperature, above the melting point of the desired alloy, then passing the so mixed alloy stream past a second sodium metal speci men, the specimen being isolated from any surface of the alloy stream and separated from the alloy stream by a membrane permeable to sodium ions, whereby a second voltage difference is developed, between the alloy stream and the second sodium specimen, and transmitting the second voltage difference to the second means for controlling the flow of the potassium stream.

References Cited in the file of this patent UNITED STATES PATENTS 1,450,023 Edelman Mar. 27, 1923 2,091,801 Amick et al. Aug. 31, 1937 2,565,121 Clardy et a1 Aug. 21, 1951 2,621,671 Eckfeldt Dec. 16, 1952 FOREIGN PATENTS 741,982 Germany Nov, 19, 1943

Claims (1)

1. A PROCESS FOR CONTINUOUSLY MANUFACTURING A MOLTEN ALLOY OF LEAD AND AT LEAST ONE ALKALI METAL COMPRISING PROVIDING A STREAM COMPRISING MOLTEN LEAD, AND A STREAM OF MOLTEN ALKALI METAL, THE FLOW OF ONE OF SAID STREAMS BEING CONTROLLED BY MEANS RESPONSIVE TO A VOLTAGE DIFFERENCE, COMBINING THE LEAD AND ALKALI METAL STREAMS AS AN ADDITIONAL COMBINED STREAM AND MIXING THE LEAD AND THE ALKALI METALS IN THE COMBINED STREAM AND CONCURRENTLY WITH THE MIXING REMOVING THE HEAT GENERATED AND COOLING TO A CONSTANT TEMPERATURE, ABOVE THE MELTING POINT OF THE ALLOY DESIRED, THEN PASSING SAID COMBINED STREAM PAST A REFERENCE METAL SPECIMEN, COMPRISING AN ALKALI METAL CORRESPONDING TO A COMPONENT OF THE ALLOY, THE SPECIMEN BEING ISOLATED FROM THE PERIPHERY OF THE COMBINED STREAM, AND SEPARATED FROM THE COMBINED STREAM BY A MEMBRANE PERMEABLE TO IONS OF THE REFERENCE METAL, WHEREBY A VOLTAGE DIFFERENCE IS DEVELOPED BETWEEN THE COMBINED ALLOY STREAM AND THE REFERENCE METAL, AND TRANSMITTING THE VOLTAGE DIFFERENCE TO THE MEANS FOR CONTROLLING THE FLOW OF ONE OF SAID STREAMS.

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