US2826491A - Method of producing refractory metals - Google Patents

Description

March 11, 1958 G. R. FINDLAY METHOD OF PRODUCING REFRACTORY METALS Filed Sept. 10; 1951 3 Sheets-Sheet 1 IN VEN TOR.

I| I- I BY 'GORDON R. FINDLAY Ola/((1 FIG.

ATTORNEY March 11, 1958 G. R. FINDLAY 2,826,491

METHOD OF PRODUCING REFRACTORY METALS FiledSept. 10, 1951 3Sheets-Sheet 2 IN VEN TOR BY GORDON R FINDLAY ATTORNEY March 11, 1958 ca. R. FINDLAY 1 METHOD OF PRODUCING REFRACTORY METALS Filed Sept 10. 19.51 s Sheets-Sheet s 7 80 All)? A(.g. H62 (1) v V S'l'orcige Melering Pump or Valve Pressure 46 f lgl.

Relief Valve 48 Argon 1 B 7 j VaporizAalion Bur l4 l jB(g) B (1) Argon J (9 Argon -66 97] t 24 Vaporizer Condensalion l for B of B 98? B (9) Free Airpressure vacuum 0'50 Microns Argon Press I aim. Pump 69 /89 l Mel'ering L l an H Pump B m A Halide 26 .1- 2

( Ingol 68 p Filler tIOO (c.g.Ti) or (2) Ti (powder) V-alve Bun Eleclrolysis of RH B (e.g. No) B Halide Slorage g CO l 92 Halogen l l SCrude A Formalion of A (e.greacl'ion of Halogen will: C-l-TiOz) Fraclionalion I Au -S+ripper Crude A Purifying ofA l I Column Sl'orage Agenl' 95 l Impurities (e.g. sich) INVENTOR;

Fmid FIG. 3 BY GORDON R. FINDLAY ATTORNEY rvmrnon or rnopnonso nnrnncronv METAES Gordon R. Findlay, Bedford, Mass, assignor to National Research Corporation, Cambridge, Mass, at corporation of Massachusetts Application eptember 10, 1951, Serial No. 245,873

4 Claims. (Cl. 7584.4)

This invention relates to the production of metals and more particularly to the production of metals in a high state of purity. This invention is particularly concerned with improvements in the metal torch process of the type described in the application of Gordon R. Findlay, Serial No. 200,606, filed December 13, 1950.

A principal object of the present invention is to provide improved processes for the production of metals and alloys thereof, and particularly high-melting-point metals, such as titanium, zirconium, and the like, by the reduction of a halide of such metals.

Another object of the invention is to provide for improved heat dissipation in processes of the above type wherein a highly exothermic reduction of the metal halide is achieved by reaction between the metal halide and an alkali metal or alkali earth metal.

Still another object of the invention is to provide an improved apparatus for carrying out processes of the above type wherein an improved arrangement is provided for initially starting a reaction by providing a pool of molten titanium or the like against the surface of which the reaction products are directed.

Another object of the present invention is to provide an apparatus of the above type wherein an electrode is employed for initially melting the titanium and this electrode is so arranged that it has a long life despite the high heat of the reaction during operation of the apparatus.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and the order of one or more of such steps with respect to each of the others, and the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding 'of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

Fig. 1 is a diagrammatic, schematic, partially sectional view of one preferred embodiment of the invention;

Fig. 2 is an enlarged sectional view of a portion of Fig. l; and

Fig. 3 is a flow sheet illustrating one preferred use of the invention.

in general the present invention relates to the productionof metals by the reduction of a reducible compound thereof. This reducible compound is preferably one which can be vaporized at a temperature below its decomposition temperature and the invention will, for simplicity of illustration, be initially described in connection with the production of titanium by the reduction of a titanium tetrahalide by an alkali metal or alkali earth metal.

The present invention is primarily directed to improvements in the metal torch process and apparatus of the type described in the above mentioned Findlay applicstion. in this metal torch, titanium tetrachloride, for example, is introduced, preferably as a vapor, into a reaction zone within a reaction chamber which has an atmosphere inert to titanium. This inert atmosphere is preferably an atmosphere of a gas such as argon. The reducing agent, which is also preferably introduced into the reaction zone in vapor phase is, in a preferred embodiment, an alkali metal such as sodium. The two reactants (i. e., sodium and titanium tetrachloride) are mixed to gether as they enter the reaction zone they burn with a highly exothermic reaction to form molten titanium droplets and sodium chloride vapors as by-products of the reaction. The rate of introduction of the two reactants is preferably such that the heat of the reaction is sufficient to melt the product titanium and to maintain the by product sodium chloride in a vapor phase. The reacting gases or vapors are preferably directed towards the molten surface of a titanium ingot so that the product titanium, in liquid form, coalesces on the surface of the ingot. The: by-product sodium chloride is preferably separately con-- densed from the point of collection of the product tita-- nium.

In the above reaction the heat generated is extremely high. The adiabatic flame temperature has been calcu lated to be on the order of 2800 C. However, even when: the refractory metals molybdenum or tungsten are utilized for lining the walls of the reaction chamber, it is undesirable to maintain temperatures as high as 1900 C. at the inner surfaces of these walls, since it is possible for titanium to condense on these walls and to form a lower melting eutectic with the refractory metal of the walls. This is due to the fact that some of the product titanium, even though it is a very small percentage, may not be collected by impingement on the ingot and is free to collect on the walls of the reaction chamber. As a consequence it is desirable to maintain the inner wall of the reaction chamber at a temperature below the melting point of the eutectic formed between the product titanium and the refractory metal of the inner wall. This temperature should preferably be maintained close to, but below about, 1465 C. (the boiling point of sodium chloride). it is also undesirable to maintain too high a temperature drop through the walls of the reaction chamber due to the thermal stresses to which these walls would be subjected.

In the present invention the refractory metal inner wall in the reaction chamber is maintained at a high temperature on the order of 1465 C., and the temperature drop through this wall is maintained low by making this wall quite thin, on the order of inch thick. Thus, even though there is a large heat flux through this wall, the temperature drop and thermal stresses in the wall are maintained at a minimum. In order to remove this high heat of reaction the heat passing through the inner wall is transmitted to the outer wall substantially entirely by radiation. This radiation heat transfer thus permits the great majority of the temperature drop to take place in the space between the inner wall and the outer wall. Thus the outer Wall may be maintained at a considerably lower temperature, on the order of 800 1000" 0., this outer wall being cooled by having a liquid heat-exchange medium in contact with the outer surface thereof. To prevent destructive oxidation of the inner wall, the space between the inner wall and the outer wall is preferably filled with inert gas such as argon, the pressure of this gas being such as to equalize the pressure within the reaction chamber so that there is essentially no mechanical stress applied to this inner walL. In order to increase the radiant heat between the outer surface of the inner wall and the inner surface of the outer wall, these surfaces are treated to give them a high emissivity on the order of about .9. This may be achieved by first coating these surfaces wtih chromium and then oxidizing the chromium. Such chromium oxide surfaces are capable of transferring well above 100,000 B. t. u. per square foot per hour by radiation if operating between a temperature level of 1465 C., and 1090" C.

The above described double wall construction for the reaction vessel provides a gas-tight reaction vessel whose inner surface can be subjected to high temperature radiation, and which can be maintained at a relatively high temperature without being destroyed. This reaction vessel is also capable of removing extremely large quantities of heat from the reaction chamber without subjecting either of the Walls of the reaction chamber to undue thermal stresses.

The present invention also includes a provision for are melting the surface of an ingot of titanium positioned within the reaction chamber prior to starting of the reaction. This is of particular importance in permitting the reaction to achieve a steady state very shortly after being started, and provides for high collection efficiency of the product titanium from the beginning of the reaction. In the preferred embodiment of the illustrated construction, the electrode used for are melting the surface of the titanium ingot is so arranged that when the reaction is started this electrode is withdrawn to a position Where it is completely protected from the high temperature of the reaction flame, and is maintained at a relatively low temperature by the flow of one of the reactant gases therepast.

Referring now more specifically to Figs. 1 and 2 there is shown one schematic, diagrammatic illustration of a preferred metal torch embodying the present invention. The apparatus comprises a reaction vessel 16 defining therewithin a reaction chamber 12, this reaction chamber being generally of the type described in the above mentioned Findlay application. Surrounding reaction vessel there is preferably positioned a second vessel 14, the space 16 between these two vessels being arranged to hold a heat-exchange medium 18. Near the bottom of the reaction chamber 12 there is located an ingot-forming mold 20 in which a titanium ingot 21 is formed during the reaction.

For obtaining intimate mixture of the titanium tetrachloride and sodium vapors there is provided a torch 22 which separately feeds these two vapors into the reaction chamber and directs these two vapors together as they enter the chamber so as to form a flame 23 in which the reduction takes place. This flame 23 serves as the reaction Zone and achieves complete reduction of the titanium tetrachloride to metallic titanium. Since the flame 23 is directed towards the ingot mold 20, the resultant titanium droplets are caused to impinge on the molten surface of an ingot in the mold and to coalesce on this surface, the flame being suificiently hot to maintain at least the upper surface of the ingot in molten condition.

The reaction chamber 12 includes a vacuum pumping port 24 connected to a suitable vacuum pumping system (not shown) which can evacuate the reaction chamber 12 to a low free air pressure on the order of less than .001 mm. Hg abs. Located near the bottom of the reaction chamber, and spaced to one side of the ingot mold, is an outlet pipe 26 for removing Liquid sodium chloride 27.

The vapor pressure of the heat-exchange medium 18 is controlled by a pressure relief valve, generally indicated at 28, the setting of this pressure relief valve 28 controlling the temperature of the liquid heat-exchange medium 18 as a function of the vapor pressure of the space 16a thereabove.

The torch 22 comprises, in the preferred form shown, an outer nozzle 30, through which sodium vapors are adapted to be introduced, an inner nozzle 32, through which titanium tetrachloride vapors are introduced, and

an intermediate nozzle 34, through which an inert gas such as argon is introduced. The inner nozzle 32 may also include an electrode 36 which, when moved to the dotted line position shown in Fig. 1, may be employed for initially melting the surface of the ingot 21.

As shown in greater detail in Fig. 2, the torch nozzle is preferably formed of a first tube 38, a second tube 40, and a third tube 42, these tubes being arranged concentrically. The sodium vapors enter between tubes 38 and 4t titanium tetrachloride vapors pass through the inner tube 42, and the argon passes between tubes 40 and 42. The sodium vapors are introduced into the torch nozzle through a pipe 44- from a suitable vaporizer, while the titanium tetrachloride vapors are introduced from a pipe 46 connected to a suitable supply thereof. Pipe 48 is employed for introducing the argon into the torch nozzle. A suitable oil-cooling jacket 50 is provided near the top of the torch assembly, while a water-cooling jacket 52 is provided for cooling the electrode 36. The nozzle in the electrode assembly also includes suitable insulating support members 54 and appropriate electrical connections (not shown). A suitable power source, such as a welding generator, is preferably provided for furnishing power to the electrode 36. This generator is preferably connected to the electrode 36 so that the electrode is negative with respect to the titanium ingot to be melted.

The electrode assembly preferably includes a vacuum seal 56 which may comprise an 0 ring arranged to slide on the inner surface 58 of the oil jacket 50. By this arrangement the O ring 56 and insulating members 54 support the electrode as it is moved down to its operative position. They also maintain the electrode positioned concentrically with respect to the nozzle 32 so that the titanium tetrachloride vapors flowing out of the nozzle 32 are evenly distributed around the circumference of the electrode tip.

The wall 10 of the reaction chamber is preferably made with a double wall construction, the inner wall 60 comprising a thin refractory metal shell and the outer wall 62 comprising a stainless steel shell. The facing surfaces 60a and 62a (see Fig. 2) of these two walls are preferably treated so as to have a high thermal emissivity and the space 64 therebetween is filled with an inert gas such as argon or the like, the pressure of which may be controlled by means of a pipe 66. This inert gas pressure is preferably maintained equal to the total pressure within the reaction chamber so that there is no pressure drop across wall 6i).

In a preferred embodiment of the invention the liquid heat-exchange medium 18 is sodium which is introduced into the space 16 by means of a pipe 68. The sodium preferably enters through pipe 68 at a lower temperature than the remainder of the sodium 18 in the space 16 so that this entering sodium removes heat from the walls of the mold 20 at a very high rate, thus maintaining a solid titanium interface at the interior surface of the ingot mold. Liquid sodium may be withdrawn from the space 16 by means of a pipe 69. A pair of withdrawal rolls 70 is provided for removing ingot 21 from the reaction chamber. A reducing die seal '71 may be provided for creating a vacuum-tight seal with the ingot being withdrawn from the mold. if desired, seal 71 may be replaced by a sleeve-type seal and the mold 29 may be supported on a hydraulic piston as illustrated in the copending application of Findlay, Serial No. 235,535, filed July 5, 1951, now Patent No. 2,709,842 issued June 7, 1955. In this modification of the invention the mold 26 is made with a slight taper so that the hydraulic force generated in the mold support is a direct function of the amount of titanium in the mold. This hydraulic force can be used to control a variable speed motor so as to speed up or slow down the withdrawal rolls to maintain the level of the molten metal in the mold substantially constant.

The preferred operation of the device of Fig. 1, and the arrangement of the auxiliary equipment, is illustrated best in the flow diagram of Fig. 3 wherein like numbers refer to like elements in the other figures. In this Fig. 3 there is provided a storage chamber 80 for holding the reducible metal compound A (e. g., titanium tetrachloride). A supply tank for holding the molten metallic reducing agent B (e. g., sodium) is indicated at 82. A pump or valve 84 is included for feeding the titanium tetrachloride from the supply 80 to a vaporizer 86 therefor, while a pump or valve 88 is included for transferring molten sodium from supply 82 to the space 16 surrounding the reaction vessel 10. From space 16, sodium may be transferred, by means of a metering pump 89, to a sodium vaporizer 96, the sodium vapors then passing into pipe 44.

The sodium chloride reaction product in pipe 26 passes through a filter 100 to an electrolysis chamber 90. Any titanium particles which do not collect on the titanium ingot are recovered by the filter 100 and reprocessed to titanium tetrachloride or melted in an arc furnace. The sodium formed in electrolysis chamber 90 is piped to supply 82 through a filter 91 for removing impurities such as oxides. The chlorine generated in chamber 90 is piped to a reaction vessel 92 in which the titanium tetrachloride is formed by reaction with titanium dioxide and carbon. This manufacture of titanium tetrachloride is well described in chapter 17 of Titanium, Its Occurrence, Chemistry and Technology, by Barksdale, published (1949) by the Ronald Press Company, New York. The resultant crude titanium tetrachloride is then piped to a crude storage tank 93 at which point a purifying agent such as oleic acid may be added. From the crude storage tank the crude titanium tetrachloride goes to a stripper 4 where some impurities, such as silicon tetrachloride, are removed. It then passes through a fractionation column 95', and the thus purified titanium tetrachloride is then pumped to a storage chamber 80.

For initially heating the sodium in the space 16 to a high temperature on the order of 1000 C., there may be provided a separate heater (not shown), the vapors of the sodium condensing at the top of the space 16 and the condensed sodium being recirculated through the heater until the sodium in space 16 has been brought up to the desired temperature. The inner reactor wall may, if desired, be brought up to operating temperature by heat received from the are by radiation. A separate condenser 9'7 for unreacted sodium may be provided in the vacuum pumping line 24 leading to a vacuum pumping system schematically indicated at 98.

In the operation of the device shown in Figs. 1, 2 and 3, the supply chambers 80 and 82 are filled with titanium tetrachloride and sodium, respectively, some of the sodium being fed to the space 16 so as to fill this space to the level indicated. This sodium in space 16 may then be heated to a relatively high temperature on the order of about 1000 C. During this heatup time the reaction chamber 12 is preferably evacuated by means of vacuum pump 98 to a free air pressure on the order of less than about 1 micron Hg abs. In lieu of evacuating chamber 12 it may be purged of air by sweeping with argon introduced through pipes 78 and 48 at a pressure slightly in excess of atmospheric pressure. When most of the air has been removed from the reaction chamber the electrode 36 may be moved from the full line position of Fig. 1 to the dotted line position, and a suitable power supply may be energized so that the upper surface of the ingot 21 in the mold 20 is melted.

When the reaction chamber 12 has been brought up to a desired high temperature, the feed of argon through the pipe 48 is commenced and the electrode 36 is returned to the full line position. Sodium is then pumped into the vaporizer 96 and titanium tetrachloride is pumped into the vaporizer 86. The vapors from these two Vaporizers are fed through their respective nozzles into the reaction chamber. As explained previously, the so= diurn enters through the outer nozzle 30 while the titanium tetrachloride enters through the inner nozzle 32. A thin blanket of argon passes from the end of nozzle 34 between the titanium tetrachloride and sodium vapors to prevent interdiffusion of these two vapors until they have passed a short distance into the reaction chamber.

The reactant vapors passing from the torch into the reaction chamber ignite with a highly exothermic reaction to give an intensely hot flame 23 in which the sodium completely reduces the titanium tetrachloride to metallic titanium with sodium chloride as a lay-product. In order to assure this complete reduction it is preferred that a slight excess of sodium over the stoichiometric quantity be provided in the sodium vapor feed. The reaction flame is directed against the top of the titanium ingot and maintains the upper surface of this ingot in molten condition. The high velocity of the reactant gases, and the consequent high velocity of the liquid titanium droplets formed in the reaction flame, achieves high impingement separation of the titanium droplets by coalescing thereof upon the surface of the molten titanium ingot.

Since the temperature of the flame 23 is extremely high, the by-product sodium chloride remains in vapor phase in the reaction zone and is substantially completely separated from the metallic titanium formed in the flame. The sodium chloride 27 is preferably condensed on the walls of the reaction chamber, the sodium chloride running down these Walls and being withdrawn from the reaction chamher by means of pipe 26.

In the present invention, tne heat of condensation of the sodium chloride is removed by radiation heat transfer from the inner wall 6% to the outer wall 62. The facing surfaces of these two walls are preferably so treated as to have high emissivities on the order of .85 to .9. In the preferred construction, inner wall 60 is formed of molybdenum having a thickness on the order of inch while the outer wall 62 is formed of /8 inch stainless steel. The facing surfaces of these walls are then given a coating of chromium oxide, for example, so that they have emissivities of about .85 or more. When the inner wall 6%? is maintained at temperatures of about 1465 C. (the boiling point of sodium chloride) approximately 144,000 B. t. u. per square foot per hour can be transferred from the reaction chamber. Thus an inner wall area of 10 square feet is ample to transmit the approximately 1,100,000 B. t. u. per hour required for a titanium production rate of 120 pounds per hour.

With the preferred construction described above the temperature drop through each of the walls 60 and 62 is maintained very low, well less than 100 C., while the majority of the temperature drop (on the order of 400 C.) is maintained between the walls. This arrangement has the particular advantage, in addition to the advantage of high heat transfer with low thermal stress, of preventing the creation of hot spots on the inner wall. This is due to the fact that the amount of heat transferred by radiation increases as the fourth power of the temperature. Thus, any temporary increase in the temperature of a portion of the inner wall immediately and enormously increases the radiation heat transfer from this hotter portion, thereby rapidly cooling it to the design temperature. Since the outer wall 62 has essentially the same temperature as the liquid sodium in the space 16 (plus a few degrees for the temperature drop through wall 62), the amount of heat transferred by radiation from the inner wall can be maintained essentially constant by controlling the vapor pressure, and thus the temperature, of the liquid sodium. I

The withdrawn sodium chloride passes to the electrolysis chamber where it is electrolyzed, by usual techniques, to sodium and chlorine. The resultant sodium is recirculated to the sodium supply 82 while the chlorine is passed to the reaction chamber for forming titanium tetrachloride by reaction with carbon and titanium dioxide.

seesaw This titanium tetrachloride is then purified and fed to the titanium tetrachloride supply 80. Any unreacted sodium is condensed in condenser 97 and fed back to the sodium supply 82. The argon passing out of the reaction chamber with any unreacted sodium vapors may be separated in the condenser 97 and recycled through the system.

During the build-up of metallic titanium in the mold 20, by the impingement of freshly formed titanium droplets on the surface of the ingot therein, the mold walls are kept below the melting point of titanium by the feed of the heat-exchange medium in contact with the outer surface of these mold walls. The level of the molten titanium in the mold is preferably maintained essentially constant by withdrawing the ingot 21 by means of rolls 70 as titanium is added to the ingot. This rate of withdrawal may be controlled by thermocouples positioned in the mold wall or by other means, such as means for measuring the withdrawal force, for indicating the level of the molten titanium in the mold. When visual means are employed it is preferred to use a sniperscope which will be affected only by radiation in the infrared so as to eliminate, as far as possible, the scattering of light by condensed smoke particles of sodium chloride in the reaction chamber.

While one preferred embodiment of the invention has been described above, wherein substantially all of the sodium chloride by-product is condensed within the reaction chamber, it is equally feasible to condense only a small portion (or none) of this sodium chloride in the reaction chamber and to condense most of the sodium chloride vapors outside of the reaction chamber. Such condensation may be achieved by quenching with a cooler liquid, such as a fused salt mixture of sodium and calcium chlorides. This modification of the invention is fully described in the copending application of Benedict and Pindla Serial No. 244,138, filed August 29, 1951, now abandoned.

Additionally, the present invention is of wide utility for processes and apparatus useful in the manufacture of numerous materials other than titanium. One such alternate process is the reduction of zirconium tetrachloride by sodium or magnesium. These alternative processes are set forth fully in the above mentioned copending application of Findlay, Serial No. 200,606. As described fully in this copending Findlay application, the basic metal torch" process can be utilized for making a number of metals or alloys, particularly the group lVa and Va metals (i. e., titanium, zirconium, hafnium, vanadium, columbium, and tantalum).

When alloys are to be made with the apparatus described above, the alloying element can be added in solid form to the ingot being formed in the mold 2ft. This may be done very conveniently by replacing electrode 36 with a rod of the alloying metal. This is particularly desirable when most of the reducible compounds of such alloying metals have low vapor pressures. When a rod of the alloying element is fed into the reaction chamber in place of the electrode d6, the alloying element is melted in the flame of the reactor and drips into the molten titanium in the ingot mold. in this case, the alloying element is fed at a rate adiusted to the rate of titanium production. If desired, this rate of rod feed can be controlled by the rate of ingot Withdrawal or by the rate of titanium tetrachloride feed, for example.

Additionally, the present invention can make the product metal in the form of a powder or a partially sintered mass. Equally, while it is preferred that a single reducing agent used, it is possible, and sometimes desirable, to use a mixture of two reducing agents so that the by-product halide is a mixed halide which, for some purposes, may have a desirably low melting point. The present invention has great utility in of these modifications of the metal torch invention.

While the present invention has been described primarily in connection with the removal of heat from the reaction chamber, it may be equally applied to the condensation of the sodium vapors in condenser 97 (Fig. 3). In this case the sodium vapor condenser may comprise a helical coil (for example) whose outer surface is blackened to increase its emissivity. This coil is placed between two water-cooled shells (also blackened) so that heat radiates from the coil (at 400 C. to 1000 C.) to the two shells (at about 100 C.). The space surrounding the coil is filled with an inert gas such as argon so that there will be no danger of oxidation of the coil at its relatively high operating temperature. With such an arrangement sodium vapors (at about 1000 C.) are fed into the top of the coil and liquid sodium (at about 400 C.) is withdrawn from the bottom of the coil. Obviously, if desired, the liquid sodium may be withdrawn at a lower or higher temperature, depending upon its use thereafter. Equally, the water jackets can be operated at temperatures above 100 C. to generate steam for heat exchange or power use. If desired, such a water jacket, separated by a radiation-transmitting space, can be provided outside of outer wall 14 of the reaction chamber so that the heat of the reactor can be converted into hot water or steam. In this case, a relatively small amount of sodium vapors would be generated in the space 16.

In connection with all of the above embodiments of the invention, the radiation heat transfer from the hot surface to the cooler surface can be controlled by interposing radiation reflectors between these surfaces to cut down the transfer of radiant heat. Such shields are particularly useful when it is desired to operate the inner wall 60, for example, at a higher temperature. Such flexibility of operation is particularly desirable for producing a Wide range of diiferent alloys or different metals in a single reaction chamber and permits use of a wide choice of reducible metal compounds and reducing agents.

The flow of heat by radiation from the inner reactor wall 60, for example, to the outer wall 62 can be readily varied by changing the temperature of the outer wall when the temperature difference between these walls is at a relatively low amount, such as 150 C. This is due to the fact that the heat transferred by radiation is expressed by the following formula:

e =ernissivity of radiator e =emissivity of receiver T =temperature of the radiator R) T =temperature of the receiver R) Q heat transferred (B. t. u./hr./ft.

When the temperature difference is small a relatively small change in the temperature of the cooler surface can exert a great change in the amount of heat transferred thereto from the hotter surface. When the hotter surface is to be maintained at about 1465 C., for example, and careful control is desired, even though the heat generation in the reactor is widely changed from optimum design conditions this control can be achieved by utilizing a heat-exchange medium which has a relatively lower vapor pressure than sodium. Thus the temperature of this heat-exchange medium can be conveniently raised to a temperature not much below the temperature of the inner wall. Thus, if the relative areas and emissivities require the outer wall to be at a temperature of about 1300 C. this may be readily achieved by using magnesium as the heat-exchange medium 18 and maintaining its vapor pressure at about 42 pounds/in. absolute. With sodium as the heat-exchange medium a where:

pressure of about pounds/in. absolute would be required to maintain a temperature of 1300 C.

Numerous types of high-emissivity surfaces may be employed in the present invention. Among these are chromium oxide, blueing (for low temperature use), iron oxide, nickel oxide, and various complex mixtures of these and other oxides.

In connection with the above described modifications of the invention, where heat is transferred by radiation from sodium at about 1000 C. to water at about 100 C., it should be pointed out that the present invention has the additional, and extremely important, advantage that a leak in either the sodium-confining wall or the waterconfining wall will not permit any mixing of sodium and water. The leaks would have to develop simultaneously since it is relatively simple to detect the presence of either sodium or water in the space between these walls by optical, electrical or chemical means. Thus the present invention, when applied to the condensation of one material by heat exchange with a second material which is highly reactive with the first material, provides a factor of safety not found in usual condensers.

Since certain changes may be made in the above process and apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a process for producing a product metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, columbium, tantalum and mixtures thereof by reduction of a halide of the product metal with a metallic reducing agent selected from the group consisting of lithium, sodium, potassium, magnesium and calcium, the improvement which comprises mixing at least one halide and the reducing agent each in fluid phase in a reaction zone in a reaction chamber having an inner metallic wall and an outer wall, the introduced halide and reducing agent reacting with intense heat to form a highly heated reaction flame which is at a temperature above the melting point of the product metal and above the vaporization temperature of the by-product halide, directing said flame against a body of the product metal to maintain the surface of the product metal at an elevated temperature above the vaporization temperature of the by-product halide and to collect the product metal in the flame on the hot product metal surface, the elevated temperature being due substantially to the reaction heat and the superheat of the reactants,'separately withdrawing the product metal and the by-product halide from the reaction zone, maintaining the inner wall of the reaction chamber adjacent the reaction zone at a temperature between the melting point of the by-product halide and the melting point of any eutectic formed between the product metal and the metal of the inner wall, and transferring heat from the inner Wall to the outer wall primarily by radiation.

2. In a process for producing a group IV metal from the class consisting of titanium and zirconium by reduction of a group IV metal tetrahalide with a metallic re ducing agent from the group consisting of the alkali metals and the alkaline earth metals, the improvement which comprises mixing vapors of the tetrahalide and vapors of the reducing agent in a reaction zone in a reaction chamber having an inner metallic wall and an outer wall,

the introduced halide and reducing agent reacting with intense heat to form a highly heated reaction flame which is at a temperature above the melting point of the group IV metal and above the vaporization temperature of the by-product halide, directing said reaction flame against the surface of the group IV metal body to maintain said surface molten by transfer of heat from the flame to the surface and to collect on the molten group IV metal surface liquid group IV metal carried in the flame, simul taneously removing heat from the group IV metal body to solidify liquid group IV metal at the solid-liquid interface, separately withdrawing the product group IV metal and the by-product halide from the reaction zone, maintaining the inner wall of the reaction chamber adjacent the reaction zone at a temperature between the melting point of the by-product halide and the melting point of any eutectic formed between the product metal and the metal of the inner wall, and transferring heat from the inner wall to the outer wall primarily by radiation.

3. The process of claim 1 wherein the inner surface of the inner wall is maintained at a temperature such that it is substantially completely wet by condensing the byproduct halide as a liquid thereon.

4. The process of claim 1 wherein a protective atmosphere is maintained between the inner and outer walls, the total pressure of the protective atmosphere being essentially the same as the total pressure inside of the reaction chamber.

References Cited in the file of this patent UNITED STATES PATENTS 872,351 King Dec. 3, 1907 1,046,043 Weintraub Dec. 3, 1912 1,074,097 Stevens Sept. 23, 1913 1,193,783 Hillhouse Aug. 8, 1916 1,249,151 McKee Dec. 4, 1917 1,306,568 Weintraub June 10, 1919 1,847,527 Greene Mar. 1, 1932 2,091,087 Wernpe Aug. 24, 1937 2,177,681 Anderson Oct. 31, 1939 2,246,907 Webster June 24, 1941 2,541,764 Herres et a1 Feb. 13, 1951 2,548,876 De Jahn Apr. 17, 1951 2,551,341 Scheer et a1. May 1, 1951 2,556,763 Maddex June 12, 1951 2,564,337 Maddex Aug. 14, 1951 2,586,134 Winter Feb. 19, 1952 2,586,713 Ratclifle Feb. 19, 1952 2,607,674 Winter Aug. 19, 1952 2,621,121 Winter Dec. 9, 1952 2,638,646 Rubissow May 19, 1953 2,656,743 Leavenworth Oct. 27, 1953 2,708,158 Smith May 10, 1955 2,709,842 Findlay June 7, 1955 FOREIGN PATENTS 853 Great Britain of 1863 253,161 Great Britain June 7, 1926 296,867 Germany Mar. 13, 1917 OTHER REFERENCES Chemical Engineers Handbook, by Perry, 3rd ed., published 1950 by McGraw-Hill Book Co., Inc., New York, N. Y., pages 485, 486.

Claims (1)

1. IN A PROCESS FOR PRODUCING A PRODUCT METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM, HAFNIUM, VANADIUM, COLUMBIUM, TANTALUM AND MIXTURES THEREOF BY REDUCTION OF A HALIDE OF THE PRODUCT METAL WITH A METALLIC REDUCING AGENT SELECTED FROM THE GROUP CONSISTING OF LITHIUM, SODIUM, POTASSIUM, MAGNESIUM AND CALCIUM, THE IMPROVEMENT WHICH COMPRISES MIXING AT LEAST ONE HALIDE AND THE REDUCING AGENT EACH IN FLUID PHASE IN A REACTION ZONE IN A REACTION CHAMBER HAVING AN INNER METALLIC WALL AND AN OUTER WALL, THE INTRODUCED HALIDE AND REDUCING AGENT REACTING WITH INTENSE HEAT TO FORM A HIGHLY HEATED REACTION FLAME WHICH IS AT A TEMPERATURE ABOVE THE MELTING POINT OF THE PRODUCT METAL AND ABOVE THE VAPORIZATION TEMPERATURE OF THE BY-PRODUCT HALIDE, DIRECTING SAID FLAME AGAINST A BODY OF THE PRODUCT METAL TO MAINTAIN THE SURFACE OF THE PEODUCT METAL AT AN ELEVATD TEMPERATURE ABOVE THE VAPORIZATION TEMPERATURE OF THE BY-PRODUCT HALIDE AND TO COLLECT THE PRODUCT METAL IN THE FLAME ON THE HOT PRODUCT METAL SURFACE, THE ELEVATED TEM PERATURE BEING DUE SUBSTANTIALLY TO THE REACTION THE SUPERHEAT OF THE REACTANTS, SEPARATELY WITHDRAWING THE PRODUCT METAL AND THE BY-PRODUCT HALIDE AND ACTION ZONE, MAINTAINING THE INNER WALL OF THE REACTION CHAMBER ADJACENT THE REACTION ZONE AT A TEMPERATURE BETWEEN THE MELTING POINT OF ANY EUTECTIC FORMED BETWEEN THE THE MELTING POINT OF ANY EUTECTIC FORMED BETWEEN THE PRODUCT METAL AND THE METAL OF THE INNER WALL, AND TRANSFERRING HEAT FROM THE INNER WALL TO THE OUTER WALL PRIMARILY BY RADIATION.

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