US2732292A

US2732292A - Process of heating particulate metal

Info

Publication number: US2732292A
Authority: US
Publication date: 1956-01-24
Anticipated expiration: 1973-01-24

Description

Jan. 24, 1956 J. F. JORDAN 2,732,292

PROCESS OF HEATING PARTICULATE METAL Filed Sept. 22, 1952 III! 4 U INVENTOR United States Patent 2,732,292 PROCESS OF HEATING PARTICULATE METAL James Fernando Jordan, Huntington Park, Calif., assignor of one-third to the estate of James Jordan, deceased, and one-third to Abigail Jordan Application September 22, 1952, Serial No. 310,911

8 Claims, (Cl. 75-'--10) My invention relates to metallurgy wherein a metal is to be heated.

Circumstances occasionally arise wherein a metal must be inductively heated within a vessel that is lined with a refractory with which said metal is adversely reactive. An outstanding example of this situation involves melting titanium in a carbon-lined induction furnace wherein carbon dissolved by the metal has an adverse effect on the physical properties of the metal, especially when an alloy of titanium is being melted. Other examples wherein a metal that dissolves carbon must be heated within a carhon-lined induction furnace will occur to those skilled in the art, and it is clear that the solution of the carbon lining in the metal being heated is always a handicap, not only because of the attack on the lining, but also becausecontrol over the carbon content of the. metalsuggests the deliberate addition of carbon to the bath by means of an addition agent rather than by means of said lining.

I have discovered a method of heating a metal within a carbon-lined induction furnace without permitting any substantial contact between said metal and said lining. My new method has particular utility in connection with titanium metallurgy; however, its utility in other metallurgies will be apparent to those skilled in the art.

In my new method, I immerse the titanium in a pool of molten, inert salt contained within the inductively heated carbon lining, and I formulate said molten salt bath so that it contains, or consists of, a compound whose boiling point lies above the temperature to which I desire to'heat said immersed titanium. And then I inductively heat said carbon lining at a rate that results in said carbon lining being maintained above the boiling point of said compound, so that said compound boils at the surface of said lining, so as to form a substantially continuous layer of the gas of said compound between said molten salt bath and said carbon lining, so as to prevent any substantial contact between said molten salt bath and said carbon lining.

When, for example, it is desired to heat titanium powder to some temperature in the range between 700 and 1400 C., l disperse said titanium powder in a pool of molten magnesium chloride 11 within carbon-lined, inductiveheating vessel 16, and then I introduce heat into pool '11 by means of inductive coils '14 at such a rate that the boiling point of magnesium chloride is exceeded at the inner sur face of lining 16, so that the continuous evaporation of said magnesium chloride adjacent to said inner surface of lining 16 results in the formation of a substantially continuous layer 17 of the gas or vapor of said magnesium chloride, thus holding the magnesium chloride pool out of contact with said inner carbon surface, the temperature of pool 11 to be lifted to the desiredtemperature within the range between the melting and boiling point of magnesium chloride. .When the titanium particles have been thus heated to the desired temperature, I remove them from the heating arrangement by various methods.

If it is desired to maintain molten salt bath 11 at some temperature within the mentioned range, this may be ice done by regulating the high-frequency current being supplied to coils 14 by suitable generators (not shown) of such current, this in accordance with temperature readings obtained with the aid of a thermocouple (not shown) that is immersed in bath 11, all the while maintaining the rate of heat input high enough to maintain gas layer 17 betweenbath 11 and lining 16. Generally speaking, this last stipulation merely involves avoiding the full-on, fulloft type of control. Other methods of controlling the temperature of bath 11 are available. For example, the temperature of bath 11 may be controlled by controlling the cooling action of water-jackets, such as 8, in contact with which bath 11 lies. Or, the temperature of bath 11 may be controlled-by controlling the rate at which a titanium powder is fed into bath 11 by suitable feeding arrangements (not shown). Or, the temperature may be controlled by introducing cold magnesium chloride in the same manner.

When bath 11 is-to be held at some temperature in excess of about 1100? 0.; I prefer to control the temperature of bath 11 by continuously feeding a titanium iodide 10 into bath 11, so that the thermal dissociation of said iodide within bath 11 absorbs the excess heat being introduced via lining 16. This embodiment has the striking advantage of producing, within bath 11, the titanium powder that is being heated therein, thus eliminating, as shall be shown, a'number of the steps in the Van Arkel process wherein titanium precipitated by thermal dissociation of an iodide is to be converted into a commerciallyusable form such as an ingot.

The conventional Van Arkel process depends upon the fact that, while iodine "atta cks'titanium at temperatures somewhat below 1100 C., it is essentially non-reactive therewith at temperatures somewhat in excess of 1100 C., and that a titanium' iodide formed below 1100 C. will dissociate to yield titanium and iodine if it is raised above 1100 C. In the conventional Van Arkel procedure, these facts are taken advantage of by maintaining a cooled layer of crude titanium within an evacuated envelope in juxtaposition to, but out of contact with, a filament that is heated electrically to over 1100 C. Under this set of conditions, given time, iodine introduced into the system will react with the cooled, crude titanium, and the titanium iodide vapor produced thereby will diffuse into contact with the incandescent filament, thus producing a deposit of titanium on the filament and iodine gas, the iodine being thus freed to react with more crude titanium.- When a sulticiently thick titanium deposit has been built up on the filament, the process is stopped and the titanium filament removed "from the envelope.- Titaniumfilaments so produced have no commercial value, due to their small size and coarse structure, it being. therefore necessary to consolidate a number of these filaments by melting to yield the desired commercial shape, usually an ingot. This consolidation is normally carried out by melting the filaments within a water jacket furnace heated with an are or in a carbon-lined induction furnace, the ingot being formedby casting the titanium melt.

I carry out this process with fewer steps by introducing a titanium iodide 10 into molten salt bath 11, bath 11 being maintainedat a temperature that lies above the melting point of titanium by means of inductive heating means 16, the function and operation of which being previously described. The titanium set free in contact with bath 11 is wetted thereby and accumulates therein or forms larger titanium particles as the result of the coalescence'of smaller particles or as the result of iodide dissociation in contact with such smaller particles, or both. When such molten titanium particles have grown large enough to sink thru bath 11 in the face of the violent agitation arising from the maintenance of gas layer 17 on the inner surface of lining --16, said titanium particles sink thru bath 11 to consolidate with molten titanium pool 18 upon which bath 11 is floating. Titanium pool 18, being contained within an open-ended mold 15 of the waterjacket type, is continuously fed bysuch'large titanium particles as iodide 10 is continuously introduced into bath 11, resulting in the necessity for a continuous lowering of shape 20 within mold 15 if the surface of pool 18 is to be maintained at a substantially-fixed position within mold 15. This results in a continuous production of cast shape 20. The conversion of pool 18 to solidified, cast shape 20 arises from the cooling action of water 13 as it circulates through mold v15 to leave said mold 15 as heated water 4. The level of pool 18 within mold 15 may be maintained in a number of ways. One of the best ways involves placing a number of thermocouples (not shown) in contact with the inner wall of mold 15 but out of contact with the water circulating therein and the titanium metal passing therethru, said thermocouples being positioned adjacent to the level of pool 18 within mold 15. Such thermocouples, connected to suitable recorders, will accurately indicate the level of pool 18 within mold 15, for the highest mold wall temperature will always be located immediately adjacent to the position where pool 18 contacts mold 15.

The iodine set free from the dissociation of iodide 10 within bath 11 rises to surface 7 of bath 11, being thereupon removed from the vessel as gas via opening 6. In the modification shown, bath 11 is contained within a vessel of the water-jacket type, the cooling action of the water 13 circulating therethru causingthe formation of a solidified layer 9 of the compound(s) of bath 11 on the inner surface of vessel 8, thereby protecting the metal vessel 8 from attack by the freed iodine. The compound(s) available as constituents of bath 11 being all poor conductors of heat, solidified lining 9 acts to conserve heat in the system.

Suitable for use as the compound of bath 11 in this modification is molten calcium chloride. pounds and; compound mixtures will occur to those skilled in the art. In view of the fact that itis'to be'expected that gas 5 will be at once reacted with crude titanium to yield more iodide 10, and that such iodide 10 will be recycled back into bath 11, and due to the exothermic character of the reaction between gas 5 and crude titanium, the system .contains an excess of heat that must be removed somewhere if excessive temperatures are to be avoided within the process; that is, bath 11 must be maintained below the boiling point of the compound(s) of which it is composed-below about 2000 C. if bath 11 is calcium chloride, for example. This is why I prefer that vessel 8 be formed with a water-jacket. However, circumstances may arise wherein itis desired to: form vessel 8 of a nonmetallic refractory, such as carbon, magnesia, etc.

While I prefer the embodiment wherein the process produces a continuous ingot 20, the process may be operated ona batch basis, soas to produce one ingot 20 at a time. Such abatch operation may be arranged by attaching to the bottom of heating lining 16 a mold whose bottom is closed and whose top is open, so that the metal of my process. may pass thru lining 16 to enter the mold and thus slowly fill said mold up. When the operation has filled the closed-end'mold, the process may be stopped by draining the molten salt out of the vessel and then cooling the apparatus sufliciently to permit the removal of .the solidified ingot from the closed-end mold. Such a closed-end mold may be cooled in any convenient manner; that is, by air, water, etc.

Contacting particles of most metals, such as titanium, will coalesce to yield an essentially solid single particle at temperatures below their meltingpoint. Advantage may be taken ofthis to process an ingot without melting the metal out of which the ingot is formed. The temperature at which such a welding action between contact- Other com- I ing particles will take place depends upon the metal and its purity; that is, upon its composition, if it is an alloy. If the metal being produced is an essentially-pure titanium, bath 11 may be composed of sodium fluoride, and, with bath 11 being maintained at a temperature somewhat below 1675 C., an ingot 20 may be built up out of titanium particles at a temperature that lies below the melting point of titanium. Knowing the melting point of the metal being produced, those skilled in the art may form a-bath 11 of compounds which are essentially inert towards the metal being produced and which exhibit a boiling point that lies below the melting point of the metal being produced, and such a bath 11, operated below, but preferably close to, the boiling point ofsaid bath 11, may be employed to produce an ingot of said metal without the operating temperature exceeding the melting point of said metal.

Naturally, due to the high rate of heat input via lining 16, the temperature of that portion of bath 11 lying between the wall(s) constituting lining 16 will be somewhat-higher than the mean temperature of bath 11, with the result that, even tho bath 11 may exhibit an overall temperature just below the melting point of the metal being produced, said metal will be lifted to said melting point as it passes thru lining 16; furthermore, the rate of heat input may be so high that layer 7 will occupy essentially all of the space formed by lining 16that is, pool 11 will not extend down into arrangement 16. In such a case, while bath 11 is floating on the surface of ingot 20, it is doing so thru the instrumentality of a layer of gas that separates bath 11 from said surface. Actually, this does not seem to be a very desirable situation, and, accordingly, my preferred embodiment envisions the situation wherein the operation is large enough and the rate of heat input such that a pool of bath 11 lies within lining 16, as shown, for then the separation of the sinking metal particles from lining 16 is assured.

In the modification wherein a dissociatable compound 10 is being introduced into bath 11 for the purposes of cooling bath 11 and forming or setting free a'meta'l within bath 11, said dissociatable compound or compounds may be introduced into. bath 11 as solids, gases or liquids. I v

While I have. discussed the modifications wherein the metal particles of my process are accumulated to form a shape thereof, my process need not be operated in this manner, for, as has been pointed out, my process involves the basic scheme of heating a metal powder within a carbon-lined induction furnacev so that said powder does not contact said lining. Thus, the heated particles may be removed from my process dispersed within the inert media which comprises bath 11, and said metal particles may be separated from the media comprising bath 11 in a manner dilfering from that described. For example, the heating of titanium particles may be accomplished in a bath 11 consisting of magnesium chloride, the heated magnesium chloride/titanium particle mixture being continuously removed from the base of the process, the mag nesium chloride being separated from the dispersed titanium particles before or after said magnesium chloride is allowed to-cool below its melting point. With respect to the latter, the mixture may be cooled to room temperature and the magnesium chloride extracted from the mixture with cold, dilute HCl or the magnesium chloride may be distilled oii by vacuum distillation. Other methods of separating the compound(s) of bath 11 from the dispersed metal will occur to those skilled in the art. In addition, in'this modification, the dispersion of said metal particles within bath 11 may be achieved in a number of ways. Thus, titanium p'owder'may be directly fed into bath 11, or the titanium content of the mixture may beforrned by feeding a form ofititanium t'etraiodide. into the'magnes'ium chloride bath' 11'.'.at- 'a 'temperatureIthat lies above 1100 C. and below the boilingpoint of magnesium chloride. Obviously, if the heated metal particles are being removed with bath 11, the amount of bath 11 so removed must be replaced ifa continuation of the process is desired. This replacement may bearranged in any convenient manner; thus, the compound( s) of bath 11 may be introduced in the solid, gaseous and/or liquid form with dissociatable' compound or by means of a special entry port adapted for the purpose (not shown). This modification of my process has very practical application; for example, if it is desired to recover the titanium content of titanium scrap in an operation that ties in with the production of primary sponge titanium, the magnesium chloride/titanium mixture from my process may be directly fed into that phase of the Kroll procedure wherein magnesium chloride is separated from titanium, thus making it possible to recover titanium scrap with the minimum inconvenience to the Kroll process setup.

If, instead of pure titanium, it is desired to produce an alloy thereof, this may be easily arranged. If the metal of shape 20 is not being melted within the process, the simplest way to form the alloy is by introducing the alloying element(s) in the form of dissociatable compound(s) or in the form of compound(s) that are reductible by titanium to yield the required alloying element' (s). Thus, if the alloying element exhibits a halide that'fdissociates at the temperature of bath 11 to yield said alloy element, or if said alloy element exhibits a halide that is reductible by titanium, then the required alloy may be produced by introducing said halide into bath 11 with, or separate from, the titanium being dispersed therein. If the operating temperature is above the melting point of the alloy being produced and below the melting point of titanium, or if the operating temperature is above the melting point of titanium and the alloy being produced, the required alloying element(s) may be introduced into bath 11 in the mentioned manner, or said alloy element(s) may be directly fed into bath 11 in the form of the powdered element(s). If desired, such alloy additions may be made with relatively-coarse particles, so that said alloy(s) immediately sink thru bath 11 to join pool 18.

While I have discussed my process in connection with the thermal dissociation of titanium iodide, other titanium halides are thermally dissociatablethe dichloride, for example. Accordingly, I do not restrict my process to the use of such iodides, and specifically include all halides which dissociate thermally to yield titanium or zirconium. In general, the iodides, chlorides and bromides are the most suitable for my process. Furthermore, it is' anticipated that operating conditions, such as catalytic agents, will be found which will greatly lower the cracking temperature of compounds which do not normally crack within the temperature range herein discussed. While I do not of course lay claim to such special conditions, I do lay claim in the broadest sense to the use of dissociatable compounds to cool my bath 11 while precipitating a metal therein.

While my process is applicable in a number of metallurgies, I am specifically interested only in titanium and zirconium. With respect to zirconium; the same inert compounds may be used for heating zirconium as were mentioned in connection with titanium. Zirconium, having a lower melting point than titanium, has a larger group of inert compounds from which to select an inert bath 11. In general, as with titanium, suitable inert compounds will be found by comparing the desired operating temperature with the melting and boiling points of the alkali and alkaline-earth chlorides and/or fluorides; specifically, as with titanium, with the chlorides and fiourides of sodium, potassium, calcium and magnesium. Within this group of inert salts, practically any desired operating temperature may be obatined. Other of the rarer alkalies and alkaline-earth metal halides may of course be used, and the desired ends may be attained by employing a bath 11 consisting of one or more salts. For example, bath 11 may be composed of calcium chloride containing about 20% magnesium chloride, the magnesium chloride formavera e 6 ing layer 17. Other modifications will occur to those skilled in the art.

By inert, Imean that hath 11 must be inert towards the process herein contemplated; that is, towards the metal being heated, lining 16 and/or compound(s) 10. This means substantially inert; for, at the contemplated temperatu'res, a certain measure of interaction between all factors is inevitable; however, so long as such interaction does not prevent my process from operating substantially as herein disclosed, a given molten salt bath is inert within my meaning. For example, if a measure of the titanium being dispersed within bath 11 reacts therewith, po sibly with the formation of some subhalide, bath 11 is inert within my meaning if the solution of the added titanium metal in bath 11 does not proceed to the point wherein a major part of the titanium is so dissolved in bath 11, it being realized that a bath 11 may be rendered inert by reason of its saturation with a titanium halide.

As has been pointed out, layer 17 consists of a layer of gas of a compound of bath 11. In view of the fact that bath 11 itself is maintained below the boiling point of said compound, layer 17 continuously gives rise to a gas that passes into and is condensed by said bath 11, as shown.

While the simplest lining 16 is formed of carbon, it may also be formed of one of the metallic carbides, such as silicon carbide. Metallic carbides being reactive with hot titanium and zirconium, it follows that my process may be applied to operations wherein it is desired to keep such carbide lining 16 out of contact therewith. Accordingly, in my claims, I refer to the subject lining 16 as a carbon-bearing refractory.

Having now described and shown several forms of my invention, I wish it to be understood that my invention is not to be limited to the specific form or arrangement of steps hereinbefore shown and disclosed, except insofar as such limitations are specified in the appended claims.

I claim as my invention:

1. The process of heating a sub-divided metal selected from the group consisting of titanium and zirconium, which comprises: dispersing said metal within a molten salt bath that is essentially inert towards said metal, said molten salt bath containing a compound whose boiling point lies above the temperature to which said dispersed metal is to be heated within said molten salt bath, said temperature being in the range between above the melting point and below the boiling point of said molten salt bath; and heating said molten salt bath containing said dispersed metal to said temperature by contacting and retaining at least a portion of said molten salt bath with a layer of gas containing said compound in vapor phase, said layer of gas being formed by inductively-heating a carbon-bearing refractory body that is positioned beneath the upper surface and at the lateral side of said molten salt bath, said heating being conducted at a sufficiently fast rate to evaporate said compound out of said molten salt bath adjacent to said refractory body to form said layer of gas between said molten salt bath and said refractory body.

2. The process according to claim 1 in which said metal is removed from said furnace while still dispersed within said molten salt.

3. The process according to claim 1 in which said metal is allowed to settle in said molten salt bath before being removed from said furnace.

4. The process according to claim 1 in which said metal is heated to a temperature at which contacting particles of said metal coalesce, and in which said metal is allowed to settle in said molten salt bath to form a shape consisting of coalesced particles of said metal.

5. The process according to claim 4 in which said temperature lies below the melting point of said metal.

6. The process according to claim 4 in which said temperature lies above the melting point of said metal.

7. The process according to claim 6 in which said shape consists of an alloy of said metal with at least one other element, and in which said alloy is formed by introducing said other element into said molten salt bath.

8. The process according to claim 7 in which said other element is formed within said molten salt bath by reacting a compound of said other element that is reducible by said metal within said molten salt bath with a portion of said metal dispersed within said molten salt bath.

References Cited in the file of this patent UNITED STATES PATENTS 1,671,213 Van Arkel et a1 May 29, 1928 8 Wempe Aug. 24, 1937 Freudenberg -L--- Feb. 21, 1939 Kroll June 25, 1940 Maddex Aug. 14, 1951 Winter Aug. 19, 1952 Jordan Jan. 26, 1954