US3857695A - Production of vanadium composition - Google Patents

Abstract

Vanadium values in the form of vanadium pentoxide in metal complexes are reduced to a metallic vanadium-based alloy suitable for use as a steel additive at a temperature of about 1300*C. in an atmosphere comprising nitrogen and hydrogen or ammonia at ambient pressures. Carbon is employed as a reducing agent and the product typically will be a vanadium nitride containing minor quantities of iron.

Description

United States Patent 1191 Vojkovic Dec. 31, 1974 1 PRODUCTION OF VANADIUM 3,389,957 6/1968 Olds 423/62 COMPOSITION 3,745,209 7/ i973 Middelhoek 423/409 X e [75] Inventor: Milos Yojkovic, Libertyville, Ill. Primary Examiner L Dewayne Rutledge [73] Assignee: International Minerals & Chemical Assistant EXaminerAfthuF Steiner Corporation, N w Yo k, N Y, Attorney, Agent, or Firm,James E. Wolber; Peter 22 Filed: June 21, 1973 Andre 21 Appl. No.: 372,154 57 ABSTRACT Vanadium values in the form of vanadium pentoxide [52] US. Cl. 75/.5 BB, 75/ 134 V in metal complexes are reduced to a metallic Vanadi- 51 Int. Cl. C22c 27/00, C22C 35/00 urn-based alloy Suitable for use as a Steel additive at a 58 Field of Search....; 75/151313, 134 v, 84; temperature of about in an atmosphere 423 2 409 5 prising nitrogen and hydrogen or ammonia at ambient pressures. Carbon is employed as a reducing agent and 5 References Cited the product typically will be a vanadium nitride containing minor quantities of iron.

9 Claims, N0 Drawings BACKGROUND OF THE INVENTION The reduction of vanadium oxide with carbon to produce a vanadium-containing alloying agent for the steel industry has provideda difficult technical challenge. Such an additive must contain under 2% oxygen, should contain under l% oxygen, and preferably will contain only about 0.2% oxygen.

Various techniques have been proposed for the reduction of vanadium pentoxide to producea substantially oxygen-free product. Typically, the reduction is carried out in the presence of finely divided, particulate carbon under vacuum or in the presence .of an inert or reducing gaseous atmosphere; Noble gases have been employed as an inert atmosphere and hydrogen has been'employed as a reducingatmosphere. It has been proposed to maintain the oxygen content of the atmosphere at a very low level either by continuous evacuation or by continuous sweep of a flowing atmosphere over the admixture to be reduced. The reduction is typically carried out at an-elevated temperature in the range of l200 to l700C., often in the presence of carbon, and the reduced vanadium product is cooled in the presence of an-inert atmosphere (or in the presence of nitrogen when a nitrided product isdesired), until its temperature falls below the temperature-at which spontaneous oxidation in the presence of air will occur.

Feedstocks for such processes typically are admixtures of a vanadium containing complex with finely divided particulate carbon. Such vanadium-containing complexes comprise vanadium as the pentoxide, together with other metal values, typicallywith'iron as the hydroxide.

It had been thought, heretofore, that reduction of vanadium to an essentially oxygen-free product would not occur in the presence of nitrogen. See, for example, U.S. Pat. No. 3,389,957, where the formation of an oxycarbide is disclosed. Nevertheless, applicant has found that in accordance with thisinvention a nitrogencontaining reducing atmosphere can be employed to produce an essentially oxygen-free product, with the advantage of forming a nitride in the same process.

Especially preferred carbon-vanadium complex admixtures useful in the method of this invention, and their preparation, are described in U.S. Pat. application Ser. No. 154,686, entitled Recovery of Refractory Metal Values", filed June 18, 1971 naming Milos Vojkovic as inventor. Since such starting materials are known in the art and per se comprise no part of the instant invention, these materials and their method of preparation will not be described in detail.

DESCRIPTION OF THE INVENTION Briefly, the method of .the instantinvention is one for producing nitrided alloys containing about 50 to 82% by weight vanadium, together with minor amounts of iron, carbon and nitrogen, and at most about 1% by 135( )C. for a period of 20 to 120 minutes in the presence of a reducing atmosphere of'the group consisting ofammonia and mixtures of hydrogen and nitrogen having mole ratios in the range of about 2:1 to about 4:1, while continuously removing oxygen-containing gases from said reaction zone, whereby said vanadium pentoxide and iron salt are reducedand a nitrided alloy is formed, cooling said alloy to a temperature below that at which spontaneous ignition of the alloy occurs on exposure to atmospheric air and recovering the nitrided alloy.

As aforementioned, the nitrided alloys produced in accordance with this invention will contain an amount of vanadium which is essentially dependent upon the vanadium content of the initial admixture reduced. Products having a vanadium content in the range of about 50 to 82% are suitable and preferred. Slightly higher'vanadium contents are achievable and lower vanadium contents are of course possible, but not preferred.

The admixture reduced in accordance with this invention is preferably prepared in accordance with the teachings of the aforementioned U.S. Pat. application Ser. No. 154,686, and will ordinarily contain about 35 to about vanadium calculated as V 0 The admixture will generally also contain a minor amount of iron, generally as the hydroxide, which may be as little as 0.2% or as much as about 21%, depending upon the process by which the admixture was produced. The admixture will further contain an amount of finely divided carbon in the range of to about 12.0% of the carbon stoichiometric to reduce the reducible metal values in the admixture assuming the production of carbon monoxide. The amount of carbonwill thus generally be about 12 to about 26% by weight of the admixture. The amount of residual carbon (carbide) in the nitrided alloy after reduction will be in the range of 0.1 to l3% by weight of the alloy, and more generally in the range of about 1 to 5% by weight of the nitrided alloy. Nitrogen in the alloy may range from l to 20%.

The process of this invention may be carried out in a number of different vessels. A tunnel-type furnace is preferred because it permits continuous operation. A batch operation in a closed vessel is possible, as is reduction of the particulate admixture in a fluidized bed or a gravitating compact bed through which the reducing atmosphere is passed. In any event, an appropriate reaction zone is maintained and the feed admixture is reduced at a temperature in the range of 1250C. to 1350C. in the presence ofa reducing atmosphere. The reduction is carried out at the aforestated temperature for a period of about 20 to about minutes exclusive of the time required to reach temperature and to cool the product to a lower temperature at which it may be recovered. In a typical operation employing a tunneltype furnace in which the feed material is in a bed about 3 inches high, a time of 50 minutes at a temperature of l300C. is satisfactory to provide essentially complete reduction of the vanadium values. With thicker beds, longer times are required, and, conversely, with thinner beds providing better access of the atmosphere to the admixture to be reduced, shorter times are required. If a fluidized bed or a gravitating compact bed through which the atmosphere is passed upwardly is employed, shorter reduction times are acceptable. The reducing atmosphere may be either ammonia or mixtures of nitrogen and hydrogen having mole ratios in the range of about 2:1 to about 4:1. Ammonia or dissociated ammonia may be employed, and when ammonia is used it mainly dissociates to form hydrogen and nitrogen in the moleratio of 3:1 at the elevated temperature and in the presence of .the feed admixture. 1

The presence of nitrogen, notwithstanding the suggestions of the priorart, forms a nitrided and essentially fully reduced vanadium alloy, as distinct from the oxycarbide heretofore thought to result when the condi- EXAMPLE I.

Reduction of vanadium complex, prepared according to the process of US. Pat. application Ser. No. 154,686, was carried out under different conditions of temperature and reducing atmosphere. This work was done utilizing a small electric tube furnace where reduction was done as a batch operation and also in a tunnel-type furnace'in which reduction was carried out continuously.

The extent of carbon impregnation during precipitation of the complex-and its effect on the composition of product obtained after reduction were investigated to give the results listed below:

' Furnace employed: tunnel-type, continuous Charge composition: varied, but with each constituent within 3 percentage points of Charge Composition 3, which analyzed as follows:

36.2%-V; 2.5% Fe; 21.7% C; 26.7% 11.0% Nl-l Reducing temperature: 2200F.

Reducing time: 72 minutes total; 48 minutes at temperature Reducing atmosphere: Mixture (N 3H Reducing pressure: ambient Results:

Vanadium Carbon:

Charge 1n Ratio Analysis of Product Composition Feed In Product Carbon, 71 Oxygen. 7:

No. l 0.47 0.14 11.8 8.4 No. 2 0.49 0.15 12.2 8.5 No.3 0.60 1' 4.4

Charge layerthickness: 2in. Reducing temperature: 2450F.

Reducing time: 72 minutes Reducing atmosphere: Mixture (N 3H Charge composition: 36.2% V; 2.5% Fe: 21.7% C 26,771 0. 110% NH.

It will be noted that, with the exception of Charge No. 1, the results for which are not explainable, a satisfactory product having very little low residual oxygen was obtained. 7

EXAMPLE 111.

In a larger scale test, l6,709.4 lbs. of complex were reduced'in the tunnel-type furnace purged with (N 3H )to obtain 6,516.7 lbs. of metallic, softly sintered product. This product was compressed mechanically into briquettes and annealed by passing through the furnace purged with nitrogen and hydrogen. The resulting final product weighed 6,451.51bs. and analyzed as follows:

v 75.95 47.86% A1 0.01 004% N 8.86 9.07 Cr 0.02 -0.03- c 9.07 9.68 Mg 0.01 0.07 Fe 4.91 5.01 Ni 0008-0015 0 0.15 0.34 Ba 0.01 -0.02

s 0.05 0.08 Mn 0.01 P 0053- 0.057 Zr 0.01 S1 0039- 0.057 Ca 0.006-002 Na 0010- 0.012 Cu 0002-0004 Mo 0.02 0.07 Co 0.001

The details of this work were as follows:

The dry complex, a mixture of lumpyand fine material, was placed in metallic trays 10 X 5 X 3 inches as to fill trays to two-thirds of their capacity. These trays were inserted into the tunnel .furnace to form a train, and trays were continuously moved along from feed inlet to discharge outlet by a mechanical device set to move trays at 0.67 inch per minute.

' The furnace tunnel was purged with dissociated ammonia'gas at 120-200 cu. ft./hr., the volume measure-v ments being recorded at ambient temperature and pressure. The extremities of tunnel were closed by I gates and these gates are opened alternatively, i.e., to

insert feed and to remove product. To guard the atmosphere inside the furnace, each gate wasguarded by a protective gas flame which came on automatically whenever the gate was opened.

The furnace tunnel was heated indirectly by wound electrical elements. The charge, after passing through the furnace hot zone, traveled through a water-cooled zone before being discharged.

The exhaust gases from the tunnel were burned at the feed end of the furnace. Under prevailing furnace conditions the oxygen removedfrom the charge, and com- 3 bined with carbon and hydrogen, exerted a minimum partial pressure of 0.0865 atm.

The typical reducing conditions were as follows:

Charge feed rate 0.67 in/min. v Charge layer thickness 2.0 inches Loss in weight on reduction 60.84% Temperature of hot zone for reduction 2400i50F. Maximum hot residence time 72 minutes Annealing temperature 2400i50F.

Hot annealing time (maximum) 65 minutes EXAMPLE 1v.

Laboratory tests were carried out reducing vanadium complex in ammonia gas and in dissociated ammonia The complex feed analyzed: 32.7% V; 2.20% Fe; 18.-

65% C; 24.89% 0, 7.31% N11 the temperature employed was 2400:50F. with a residence time attemperature of 30 minutes for ammonia and 72 minutes for dissociated ammonia.

Work with ammonia was carried out in an electric tube furnace (batch operation) and using 1 inch layer thickness of the charge, while work with dissociated ammonia, i.e., (N 3H was done in a tunnel-type furnace using 2 inch layer thickness of the charge and conducting operation continuously. The results obtained and analysis of theproducts are given below:

The ammonia gas was fed to the tube furnace from a gas cylinder with pressure suitably adjusted. At the exhaust end of thetube, the gas was set alight.

Under condition of experiment, ammonia gas became dissociated when passing through the hot zone.

It has further been found that it is possible to control the relative amounts of carbon and nitrogen in the reduced alloy. Generally, as the amount of carbon in the feed material is increased the carbon content of the product alloy will also increase. it has been found, most unexpectedly, that as the carbon content of the reduced alloy increases, the nitrogen content decreases and, conversely, as the carbon content decreases the nitrogen content increases. By controlling the amount of carbon in the admixture employed as raw material in the reduction step, the nitrogen content of the reduced alloy produced can be controlled. This phenomenon is illustrated by the following data which represents the results of reduction tests carried out at varying carbon levels. it will be understood that failure of the totals in each column to add to 100% results from cumulative errors in the analyses.

Product Analysis v,% 65.8 65.5 67.4 68.0 00.7 FE.% 16.7 16.6 17.1 17.3 16.9 C,% 0.4 1.0 5.7 9.2 11.21 o.% 0.9 0.2 0.2 0.2 v 0.2 N.% 20.8 19.8 11.0 7.8 0

I claim:

1. The method of producing a nitrided alloy containing about 50 to 82% by weight vanadium, together with minor amounts of iron, carbon, and nitrogen, and at most 1% by weight oxygen, comprising establishing an intimate admixture ofa complexcomprising vanadium pentoxideand an iron salt, together with finely divided carbon in an amount in the range of about to of the carbon stoichiometric to reduce the reducible metal values in said complex with the production of carbon monoxide, maintaining said admixture in an enclosed reaction zone for a period of about 20 to 120 minutes, at a temperature in the range of about 1250C. to about 1350C. in the presence of a reducing atmosphere of the group consisting of ammonia and mixtures of hydrogen and nitrogen having mole ratios in the range. of 2:1 to 421, while continuously removing said atmosphere consists essentially of dissociated ammonia.

4. The method in accordance with claim 2 in whic said alloy is cooled to a temperature below 200C. in

the presence of said atmosphere and prior to recovery. 5. The method in accordance with claim 4 in which said admixture contains about 35 to 70% V 0 by weight.

6. The method in accordance with claim 5 in which said admixture contains about 0.2% to 21.0% iron by 7 weight.

7. The method in accordance with claim 6 in which said admixture contains carbon in an amount sufficient to provide an alloy having a residual carbon content in the range of about 0.1 to 13.0% by weight of the alloy. 8. The method in accordance with claim 7 in which the nitrogen content of the alloy is in the range of about 1 to 20% by weight. Y

9. The method in accordance with claim 8 in which the reduction is carried out at a temperature of about 1300C. for a time of about 50 minutes.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3 3,857,695

DATED 2 December 31, 1974 INVENTOR(S) Milos Vojkovic It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Table in Example 11, colurm 4 should read as follows:

Charge Carbon: Vanadium Ratio Y Analysis of Product Composition In Feed 'ln' roducr: Carbon; 'owg'en;

*Charge odrposition: 36.2% V; 2.5% Fe; 21.7% C; 26.7% 0; 11.0% NH Column 6, line 2 of table entitled fProcituct: Analysis", "FE" should be -Fe.

Signed and Scaled this [SE Tenth f August 1976 A ttes t:

c. mnsmu. DANN Commissioner ofPatenn and Trademarks

Claims (9)

1. THE METHOD OF PRODUCING A NITRIDE ALLOY CONTAINING ABOUT 50 TO 82% BY WEIGHT VANADIUM, TOGETHER WITH MINOR AMOUNTS OF IRON, CARBON, AND NITROGEN, AND AT MOST 1% BY WEIGHT OXYGEN, COMPRISING ESTABLISHING AN INTIMATE ADMIXTURE OF A COMPLEX COMPRISING VANADIUM PENTOXIDE AND AN IRON SALT, TOGETHER WITH FINELY DIVIDED CARBON IN AN AMOUNT IN THE RANGE OF ABOUT 90 TO 120% OF THE CARBON STOICHIOMETRIC TO REDUCE TOGETHER WITH FINELY DIVIDED CARBON IN AN AMOUNT IN THE RANGE TION OF CARBON MONOXIDE, MAINTAINING SAID ADMIXTURE IN AN ENCLOSED REACTION ZONE FOR A PERIOD OF ABOUT 20 TO 120 MINUTES, AT A TEMPERATURE IN THE RANGE OF ABOUT 1250*C. TO ABOUT 1350*C. IN THE PRESENCE OF A REDUCING ATMOSPHERE OF THE GROUP CONSISTING OF AMMONIA AND MIXTURES OF HYDROGEN AND NITROGEN HAVING MOLE RATIOS IN THE RANGE OF 2:1 TO 4:1, WHILE CONTINUOSULY REMOVING OXYGEN-CONTAINING GASES FROM SAID REACTION ZONE, WHEREBY SAID VANADIUM PENTOXIDE AND IRON SALT ARE REDUCED AND A NITRIDED ALLOY IS FORMED, COOLING THE REDUCED ADMIXTURE IN THE PRESENCE OF SAID ATMOSPHERE TO A TEMPERATURE BELOW THE TEMPERATURE AT WHICH SPONTANEOUS IGNITRION OF SAID ALLOY OCCURS ON EXPOSURE TO AIR, AND RECOVERING SAID NITRIDED ALLOY.

2. The method in accordance with claim 1 in which said atmosphere consists essentially of ammonia and dissociated ammonia.

3. The method in accordance with claim 1 in which said atmosphere consists essentially of dissociated ammonia.

4. The method in accordance with claim 2 in which said alloy is cooled to a temperature below 200*C. in the presence of said atmosphere and prior to recovery.

5. The method in accordance with claim 4 in which said admixture contains about 35 to 70% V2O5 by weight.

6. The method in accordance with claim 5 in which said admixture contains about 0.2% to 21.0% iron by weight.

7. The method in accordance with claim 6 in which said admixture contains carbon in an amount sufficient to provide an alloy having a residual carbon content in the range of about 0.1 to 13.0% by weight of the alloy.

8. The method in accordance with claim 7 in which the nitrogen content of the alloy is in the range of about 1 to 20% by weight.

9. The method in accordance with claim 8 in which the reduction is carried out at a temperature of about 1300*C. for a time of about 50 minutes.