Claims:I/WE CLAIM:
1. A process for preparing ferrovanadium nitride alloy, comprising:
preparing briquette comprising a vanadium source, an iron source and a carbon source, and
subjecting the briquette to reduction and nitridation to obtain the ferrovanadium nitride alloy;
wherein the reduction is carried out in presence of a gaseous reducing agent, and the nitridation is carried out in presence of a nitrogen source and a reducing atmosphere.

2. The process of claim 1, wherein the reduction is in-situ reduction; wherein the gaseous reducing agent is selected from a group comprising carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H2), a mixture of carbon monoxide (CO) and carbon dioxide (CO2), a mixture of carbon monoxide (CO) and hydrogen (H2), flue gases from metallurgical furnaces, and combinations thereof; and wherein the flue gas is selected from a group comprising blast furnace gas, steelmaking gas, electric furnace gas and combinations thereof.

3. The process of any of the preceding claims, wherein the gaseous reducing agent is CO.

4. The process of any of the preceding claims, wherein the gaseous reducing agent is a mixture of CO and CO2 at a ratio of 1:1 or a mixture of CO and H2 at a ratio of 4:1.

5. The process of claim 1, wherein the nitrogen source is ammonia.

6. The process of claim 1, wherein the nitrogen source is gaseous nitrogen (N2).

7. The process of claim 1, wherein the nitridation is carried out in presence of nitrogen, ammonia or a combination of nitrogen and ammonia.

8. The process of claim 1, wherein the vanadium source is selected from a group comprising vanadium pentoxide, ammonium metavanadate, vanadium trioxide, poly vanadate salts or oxides, and combinations thereof.

9. The process of claim 1, wherein the iron source is iron oxide selected from a group comprising mill scale, iron oxide comprising less than 2% alumina or silica, iron dust obtained from pickling liquor, dust obtained from galvanization, iron oxide from acid regeneration plant, and combinations thereof.

10. The process of claim 1, wherein the carbon source is a solid carbonaceous reducing agent selected from a group comprising graphite, coke powder, graphite electrode powder, carbon black, and combinations thereof.

11. The process of any of the preceding claims, wherein a carbon to oxygen (C/O) ratio ranging from about 0.9 to 1.1 is maintained in the briquette comprising the vanadium source, the iron source and the carbon source.

12. The process of any of the preceding claims, wherein preparing the briquette comprises:
mixing a vanadium source, an iron source and a carbon source in presence of a binder composition to prepare a mixture,
casting said mixture into compacts under pressure of about 5 to 50 MPa, and drying the compact.

13. The process of claim 12, wherein the binder composition comprises a binder, solvent and water; wherein the binder is selected from a group comprising starch, sugar, polyacrylamide, molasses, cellulose based binder, and combinations thereof; and wherein the solvent is selected from a group comprising isopropyl alcohol (IPA), methanol, ethanol, formic acid, and combinations thereof.

14. The process of claim 12, wherein the vanadium source is added at a concentration of about 50 wt% to 70 wt% of the total mixture, the iron source is added at a concentration of about 10 wt% to 20 wt% of the total mixture, the carbon source is added at a concentration of about 3 wt% to 8 wt% of the total mixture, and the binder composition is added at a concentration of about 6 wt% to 20 wt% of the total mixture.

15. The process of claim 12, wherein the vanadium source, the iron source and the carbon source possess a particle size ranging from about 37 µm to 100 µm.

16. The process of any of the preceding claims, wherein the reduction and the nitridation comprises:
a) heating the briquette from ambient temperature to about 200? and holding the temperature at about 200? for about 1 to 10 minutes,
b) reduction of the briquette in presence of the gaseous reducing agent by increasing the temperature from about 200? to 600?, and holding the temperature at about 600? for about 4 to 6 hours,
c) further reduction and nitriding of the briquette in presence of the gaseous reducing agent and the nitrogen source by increasing the temperature from about 600? to 1400?, and holding the temperature at about 1400? for about 2 hours to 12 hours, and
d) cooling the briquette from the temperature of about 1400? to ambient temperature in presence of the nitrogen source.

17. The process of claim 16, wherein the step c) comprises heating a partially reduced briquette obtained in step b) at temperature from about 600? to 1400? under CO and N2 atmosphere to complete the reduction, followed by holding the temperature at about 1400? for about 2 hours to 12 hours under N2 atmosphere to complete the nitridation.

18. The process of any of the preceding claims, wherein an oxygen partial pressure (PO2) ranging from about 10-8 atm to 10-20 atm is maintained during the reduction and the nitridation.

19. The process of any of the preceding claims, wherein the ferrovanadium nitride alloy comprises vanadium (V) at a wt% of about 72 to 82, nitrogen (N) at a wt% of about 7 to 16, iron (Fe) at a wt% of about 0.4 to 4, carbon (C) at a wt% of about 6 to 12, silicon (Si) at a wt% of less than about 1%, aluminium (Al) at a wt% of less than about 0.01, manganese (Mn) at a wt% of less than about 0.05, sulphur (S) at a wt% of less than about 0.05 and phosphorous (P) at a wt% of less than about 0.05.

20. The process of any of the preceding claims, wherein the process comprises:
a) preparing the mixture comprising vanadium source, iron source and carbon source,
b) casting the mixture into compacts under pressure of about 5 to 50 MPa to form the briquette,
c) heating the briquette from ambient temperature to about 200? and holding the temperature at about 200? for about 1 to 10 minutes,
d) reduction of the briquette in presence of the gaseous reducing agent by increasing the temperature from about 200? to 600?, and holding the temperature at about 600? for about 4 to 6 hours, and
e) further reduction and nitriding of the briquette in presence of the gaseous reducing agent and the nitrogen source by increasing the temperature from about 600? to 1400?, and holding the temperature at about 1400? for about 2 hours to 12 hours, and
f) cooling the briquette from the temperature of about 1400? to ambient temperature in presence of the nitrogen source, to obtain the ferrovanadium nitride alloy.

21. The process of any of the preceding claims, wherein the process comprises:
a) preparing a mixture comprising vanadium pentoxide, iron oxide and graphite,
b) casting the mixture into compacts under a pressure of about 50 MPa to form briquette,
c) heating the briquette from ambient temperature to about 200? and holding the temperature at about 200? for about 10 minutes,
d) reduction of the briquette in presence of gaseous reducing agent by increasing the temperature from about 200? to 600?, and holding the temperature at about 600? for about 6 hours, wherein the gaseous reducing agent is selected from a group comprising CO, CO2, H2, a mixture of CO and CO2, a mixture of CO and H2, flue gases from metallurgical furnaces, and combinations thereof,
e) further reduction and nitriding of the briquette in presence of gaseous reducing agent and nitrogen (N2) atmosphere by increasing the temperature from about 600? to 1400?, and holding the temperature at about 1400? for about 6 hours, wherein the gaseous reducing agent is selected from a group comprising CO, CO2, H2, a mixture of CO and CO2, a mixture of CO and H2, flue gases from metallurgical furnaces, and combinations thereof, and
f) cooling the briquette from the temperature of about 1400? to ambient temperature in presence of N2 atmosphere, to obtain the ferrovanadium nitride alloy.

22. The process of any of the preceding claims, wherein the process comprises:
a) preparing a mixture comprising vanadium pentoxide, iron oxide and graphite in presence of starch, isopropyl alcohol (IPA) and water at a ratio of 78:2:20,
b) casting the mixture into compacts under a pressure of about 50 MPa to form briquette,
c) heating the briquette from ambient temperature to about 200? and holding the temperature at about 200? for about 10 minutes,
d) reduction of the briquette in presence of CO or a mixture of CO and CO2 at 1:1 ratio by increasing the temperature from about 200? to 600?, and holding the temperature at about 600? for about 6 hours,
e) reduction and nitriding the briquette in presence of CO or a mixture of CO and CO2 at 1:1 ratio, and N2 atmosphere by increasing the temperature from about 600? to 1400?, and holding the temperature at about 1400? for about 6 hours, and
f) cooling the briquette from the temperature of about 1400? to ambient temperature in presence of N2 atmosphere, to obtain the ferrovanadium nitride alloy.

23. A process of alloying steel, the process comprising adding the ferrovanadium nitride alloy obtained by the process according to any of the preceding claims to the steel or during the production of steel.

24. The process of claim 23, wherein the process incorporates vanadium and nitrogen into the steel.

25. The process of claim 23 or claim 24, wherein obtained steel is high-strength low-alloy (HSLA) steel or tool steel.

26. Use of the ferrovanadium nitride alloy obtained by the process according to any of the preceding claims as an alloying agent during production of steel.
, Description:TECHNICAL FIELD
The present disclosure is in the field of metallurgy. The present disclosure provides a simple and efficient process of producing nitrogen rich ferrovanadium alloy.

BACKGROUND OF THE DISCLOSURE
Vanadium is an important alloying element in steels as such in High Strength Low-Alloy (HSLA) steels and tool steels. Addition of vanadium in steel promotes improvement of the yield strength, wear resistance and hardness. Incorporating nitrogen along with vanadium in the steel promotes enhancement in yield strength. Hence, the usage of vanadium-nitrogen based alloys are more beneficial.

The methods of increasing nitrogen in steel are carried out usually by: (1) addition of vanadium nitride, (2) adding calcium cyanamide, (3) by nitrogen blowing, or (4) addition of conventional iron vanadium nitride alloys. However, operational difficulties are associated with above mentioned processes such as low yield of the nitrogen dissolution due to low density of the alloy than steel. Further, with these processes, the yield of nitrogen in steel is less.

Further, some of the limitations of the existing routes for preparing vanadium-nitrogen based alloys are as follows:
- lower yields due to formation of fines while processing the agglomerates to alloy,
- employing carbothermic reduction route with carbon as primary reductant (although solid-state reduction is relatively slow),
- employing nitrogen at higher flowrate or at higher pressure,
- higher production time of the alloy,
- low nitrogen content in the final alloy,
- obtaining the final alloy via. V-N formation thereby leading to low density of the final alloy etc.

Thus, the existing state of the art techniques related to vanadium-nitrogen based alloys or their production have limitations as discussed above. Hence, there is a need for a simple, economical and efficient method for production of vanadium-nitrogen based alloys. The present disclosure tries to address said need.

STATEMENT OF THE DISCLOSURE
The present disclosure relates to a process for preparing ferrovanadium nitride alloy, comprising:
preparing briquette comprising a vanadium source, an iron source and a carbon source, and
subjecting the briquette to reduction and nitridation to obtain the ferrovanadium nitride alloy;
wherein the reduction is carried out in presence of a gaseous reducing agent, and the nitridation is carried out in presence of a nitrogen source and a reducing atmosphere.

The present disclosure further relates to a process of alloying steel, said process comprising adding the ferrovanadium nitride alloy obtained by the process described above to the steel or during the production of steel.

The present disclosure also relates to the use of the ferrovanadium nitride alloy obtained by the process described above as an alloying agent during production of steel.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1 depicts a block flow diagram representing an exemplary embodiment of ferrovanadium nitride alloy production according to the present disclosure.

Figure 2 depicts TGA-DSC data for non-isothermal nitriding of sample having C/O molar ratio of 0.9 and up to 1400?.

Figure 3 depicts XRD superimposed plots for samples with different C/O ratio nitrided under mixture of N2 and CO atmosphere till about 1400? for about 15 minutes, after reduction at 600? for about 4 hours under CO atmosphere.

Figure 4 depicts heat treatment cycle for nitriding followed by reduction.

Figure 5 depicts microstructure of ferrovanadium nitride alloy.

DETAILED DESCRIPTION OF THE DISCLOSURE
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results. Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” or “containing” or “has” or “having” wherever used, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

As used herein, the phrase ‘reducing atmosphere’ refers to an atmospheric condition in which oxidation is prevented by removal of oxygen and other oxidizing gases or vapours, and which may contain actively reducing gases that would be oxidized by any present oxygen. In an embodiment, the nitridation step of the present process is carried out under a nitrogen source and reducing atmosphere.

As used herein, the phrase ‘in-situ reduction’ or ‘in-situ chemical reduction’ refers to chemical reduction (removal of oxygens) occurring in place or at the site.

As used herein, the phrase ‘ambient temperature’ refers to standard or normal air temperature of an environment. In an embodiment, the ambient temperature refers to a temperature range of 15? to 25?.

The present disclosure is in relation to ferrovanadium nitride alloy production.

An objective of the present disclosure is to develop a simple, less time consuming, economical and efficient process of producing ferrovanadium nitride alloy.

Another objective of the present disclosure is to employ a gaseous reductant for producing ferrovanadium nitride alloy.

Yet another objective of the present disclosure is to provide a process for preparing ferrovanadium nitride alloy by employing a vanadium source, a carbon source, and an iron source to prepare compacts/briquettes, and carbonizing said compacts under a gaseous reductant in a metallurgical furnace to prepare the final alloy.

Still another objective of the present disclosure is to maintain appropriate oxygen partial pressure (PO2) by employing gaseous reductant during production of ferrovanadium nitride alloy.

Still another objective of the present disclosure is to develop a ferrovanadium nitride alloy production process wherein heat treatment cycle during reduction is designed such that sublimation loss of vanadium source is avoided and nitrogen absorption capacity of the alloy is maximized.

Accordingly, the present disclosure provides a process for preparing ferrovanadium nitride alloy, comprising:
preparing briquette comprising a vanadium source, an iron source and a carbon source, and
subjecting the briquette to reduction and nitridation to obtain the ferrovanadium nitride alloy;
wherein the reduction is carried out in presence of a gaseous reducing agent, and the nitridation is carried out in presence of a nitrogen source and a reducing atmosphere.

In an embodiment of the present process, the reduction is in-situ reduction.

In another embodiment of the present process, the gaseous reducing agent is selected from a group comprising carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H2), a mixture of carbon monoxide (CO) and carbon dioxide (CO2), a mixture of carbon monoxide (CO) and hydrogen (H2), flue gases from metallurgical furnaces, and combinations thereof.

In an embodiment of the present process, the flue gas is selected from a group comprising blast furnace gas, steelmaking gas, electric furnace gas and combinations thereof.

In a preferred embodiment of the present process, the gaseous reducing agent is CO.

In another preferred embodiment of the present process, the gaseous reducing agent is a mixture of CO and CO2.

In an exemplary embodiment of the present process, the gaseous reducing agent is a mixture of CO and CO2 at a ratio of 1:1.

In another embodiment of the present process, the gaseous reducing agent is a mixture of CO and H2.

In an exemplary embodiment of the present process, the gaseous reducing agent is a mixture of CO and H2 at a ratio of 4:1.

In an embodiment of the present process, the nitridation is carried out in presence of a nitrogen source selected from ammonia and gaseous nitrogen (N2).

In an exemplary embodiment of the present process, the nitrogen source is ammonia (NH3).

In an exemplary embodiment of the present process, the nitrogen source is N2.

In a preferred embodiment of the present process, the nitridation is carried out in presence of N2 or NH3 under reducing atmosphere.

In an embodiment of the present process, the vanadium source is selected from a group comprising vanadium pentoxide, ammonium metavanadate, vanadium trioxide, poly vanadate salts or oxides, and combinations thereof.

In a preferred embodiment of the present process, the vanadium source is vanadium pentoxide.

In another embodiment of the present process, the iron source is an iron oxide.

In yet another embodiment of the present process, the iron oxide is selected from a group comprising mill scale, iron oxide comprising less than 2% alumina or silica, iron dust obtained from pickling liquor, dust obtained from galvanization, iron oxide from acid regeneration plant, and combinations thereof.

In still another embodiment of the present process, the carbon source is a solid carbonaceous reducing agent.

In another embodiment of the present process, the carbonaceous reducing agent is selected from a group comprising graphite, coke powder, graphite electrode powder, carbon black, and combinations thereof.

In an exemplary embodiment of the present process, the carbonaceous reducing agent is graphite.

In another embodiment of the present process, the carbonaceous reducing agent possesses an average particle size distribution of below 100µm.

In an embodiment of the present process, a carbon to oxygen (C/O) ratio ranging from about 0.9 to 1.1 is maintained in the briquette comprising vanadium source, iron source and carbon source.

In another embodiment of the present process, the preparation of briquette comprises:
mixing the vanadium source, the iron source and the carbon source in presence of a binder composition to prepare a mixture,
casting said mixture into compacts under pressure of about 5 to 50 MPa, and drying the compact.

In yet another embodiment of the present process, the binder composition comprises a binder, solvent and water. In an embodiment, the binder is selected from a group comprising starch, sugar, polyacrylamide, molasses, cellulose based binder, and combinations thereof. In an exemplary embodiment of the present process, the binder is starch. In another embodiment, the solvent is selected from a group comprising isopropyl alcohol (IPA), methanol, ethanol, formic acid, and combinations thereof. In an exemplary embodiment of the present process, the solvent is isopropyl alcohol (IPA).

In an embodiment of the present process, the vanadium source is added at a concentration of about 50 wt% to 70 wt% of the total mixture, the iron source is added at a concentration of about 10 wt% to 20 wt% of the total mixture, the carbon source is added at a concentration of about 3 wt% to 8 wt% of the total mixture, and the binder composition is added at a concentration of about 6 wt% to 20 wt% of the total mixture.

In another embodiment of the present process, the vanadium source, the iron source and the carbon source possess a particle size ranging from about 37 µm to 100 µm.

In a preferred embodiment of the present process, the reduction and the nitridation steps comprise:
a) heating the briquette from ambient temperature to about 200? and holding the temperature at about 200? for about 1 to 10 minutes,
b) reduction of the briquette in presence of the gaseous reducing agent by increasing the temperature from about 200? to 600?, and holding the temperature at about 600? for about 4 to 6 hours,
c) further reduction and nitriding of the briquette in presence of the gaseous reducing agent and the nitrogen source by increasing the temperature from about 600? to 1400?, and holding the temperature at about 1400? for about 2 hours to 12 hours, and
d) cooling the briquette from the temperature of about 1400? to ambient temperature in presence of the nitrogen source.

In another embodiment of the above described reduction and nitridation steps of the present process, the step c) comprises heating a partially reduced briquette obtained in step b) at a temperature from about 600? to 1400? under CO and N2 atmosphere to complete the reduction, followed by holding the temperature at about 1400? for about 2 hours to 12 hours under N2 atmosphere to complete the nitridation.

In an embodiment of the present process, an oxygen partial pressure (PO2) ranging from about 10-8 atm to 10-20 atm is maintained during reduction and nitridation.

In another embodiment of the present process, the prepared ferrovanadium nitride alloy comprises vanadium (V) at a wt% of about 72 to 82, nitrogen (N) at a wt% of about 7 to 12, iron (Fe) at a wt% of about 0.4 to 4, carbon (C) at a wt% of about 6 to 12, silicon (Si) at a wt% of less than about 1%, aluminium (Al) at a wt% of less than about 0.01, manganese (Mn) at a wt% of less than about 0.05, sulphur (S) at a wt% of less than about 0.05 and phosphorous (P) at a wt% of less than about 0.05.

In an exemplary embodiment of the present disclosure, the process for preparing ferrovanadium nitride alloy comprises steps of:
a) preparing the mixture comprising vanadium source, iron source and carbon source,
b) casting the mixture into compacts under pressure of about 5 to 50 MPa to form the briquette,
c) heating the briquette from ambient temperature to about 200? and holding the temperature at about 200? for about 1 to 10 minutes,
d) reduction of the briquette in presence of the gaseous reducing agent by increasing the temperature from about 200? to 600?, and holding the temperature at about 600? for about 4 to 6 hours, and
e) further reduction and nitriding of the briquette in presence of the gaseous reducing agent and the nitrogen source by increasing the temperature from about 600? to 1400?, and holding the temperature at about 1400? for about 2 hours to 12 hours, and
f) cooling the briquette from the temperature of about 1400? to ambient temperature in presence of the nitrogen source, to obtain the ferrovanadium nitride alloy.

In another exemplary embodiment of the present disclosure, the process for preparing ferrovanadium nitride alloy comprises steps of:
a) preparing a mixture comprising vanadium pentoxide, iron oxide and graphite,
b) casting the mixture into compacts under a pressure of about 50 MPa to form briquette,
c) heating the briquette from ambient temperature to about 200? and holding the temperature at about 200? for about 10 minutes,
d) reduction of the briquette in presence of gaseous reducing agent by increasing the temperature from about 200? to 600?, and holding the temperature at about 600? for about 6 hours, wherein the gaseous reducing agent is selected from a group comprising CO, CO2, H2, a mixture of CO and CO2, a mixture of CO and H2, flue gases from metallurgical furnaces, and combinations thereof,
e) further reduction and nitriding of the briquette in presence of gaseous reducing agent and nitrogen (N2) atmosphere by increasing the temperature from about 600? to 1400?, and holding the temperature at about 1400? for about 6 hours, wherein the gaseous reducing agent is selected from a group comprising CO, CO2, H2, a mixture of CO and CO2, a mixture of CO and H2, flue gases from metallurgical furnaces, and combinations thereof, and
f) cooling the briquette from the temperature of about 1400? to ambient temperature in presence of N2 atmosphere, to obtain the ferrovanadium nitride alloy.

In yet another exemplary embodiment of the present disclosure, the process for preparing ferrovanadium nitride alloy comprises steps of:
a) preparing a mixture comprising vanadium pentoxide, iron oxide and graphite in presence of starch, isopropyl alcohol (IPA) and water at a ratio of 78:2:20,
b) casting the mixture into compacts under a pressure of about 50 MPa to form briquette,
c) heating the briquette from ambient temperature to about 200? and holding the temperature at about 200? for about 10 minutes,
d) reduction of the briquette in presence of CO or a mixture of CO and CO2 at 1:1 ratio by increasing the temperature from about 200? to 600?, and holding the temperature at about 600? for about 6 hours,
e) reduction and nitriding the briquette in presence of CO or a mixture of CO and CO2 at 1:1 ratio, and N2 atmosphere by increasing the temperature from about 600? to 1400?, and holding the temperature at about 1400? for about 6 hours, and
f) cooling the briquette from the temperature of about 1400? to ambient temperature in presence of N2 atmosphere, to obtain the ferrovanadium nitride alloy.

The present disclosure further describes a ferrovanadium nitride alloy obtained by the above described process, wherein the alloy comprises vanadium (V) at a wt% of about 72 to 82, nitrogen (N) at a wt% of about 7 to 16, iron (Fe) at a wt% of about 0.4 to 4, carbon (C) at a wt% of about 6 to 12, silicon (Si) at a wt% of less than about 1%, aluminium (Al) at a wt% of less than about 0.01, manganese (Mn) at a wt% of less than about 0.05, sulphur (S) at a wt% of less than about 0.05 and phosphorous (P) at a wt% of less than about 0.05.

In an embodiment of the present disclosure, the nitrogen rich ferrovanadium nitride alloy possesses a maximum carbon content of about 12%.

In another embodiment of the present disclosure, the ferrovanadium nitride alloy possesses a density of about 3.6 g/cm3 to 4.2 g/cm3.

The present disclosure further relates to a process of alloying steel, said process comprising adding the ferrovanadium nitride alloy described above to the steel or during the production of steel.

In an embodiment, the present process of alloying steel incorporates vanadium and nitrogen into the steel.

In another embodiment, the present process of alloying steel results in a high-strength low-alloy (HSLA) steel or tool steel.

The present disclosure also relates to the use of the presently prepared ferrovanadium nitride alloy described above as an alloying agent during production of steel.

Thus, the present disclosure relates to a simple, unique, less time consuming and cost-effective process of preparing ferrovanadium nitride alloy wherein the prepared alloy can be further employed as an alloying agent during production of steel. In particular, the employment of gaseous reducing agent leads to higher reduction potential and thereby the nitriding kinetics is also improved, resulting in an overall enhancement in the efficiency of the process. The present process also envisages in-situ reduction by said gaseous reductants such as CO and/or CO2. Additionally, the present process employs a unique temperature cycle and reduction profile to obtain the ferrovanadium nitride alloy.

In an exemplary embodiment, the present disclosure provides a process for processing high pressure compact briquettes of vanadium source (such as vanadium pentoxide), iron/iron oxide source and carbon in a reducing gas environment followed by nitriding to form ferrovanadium nitride alloy. The process controls the reduction temperature cycle to avoid the sublimation loss of the vanadium source (such as vanadium pentoxide), resulting in higher productivity. In this process, oxygen potential during reduction is controlled by addition of gaseous reducing agent(s) (such as CO, CO2 or a mixture thereof) which results in in-situ reduction of vanadium and iron oxides.

In an embodiment of the present disclosure, reduction of the compacts/briquettes is carried out in ordinary furnaces such as pusher furnaces where the gas flow rate is counter current to sample movement with protective nitrogen atmosphere or cracked ammonia or mixture of both to maximize the nitrogen partial pressure during nitriding.

In another exemplary embodiment, the process route for preparation of ferrovanadium nitride alloy comprises:
(a) mixing vanadium oxides of particle size distribution below 100µm (d50=60µm) with iron oxide, solid carbonaceous reducing agent. The mixture is well mixed in presence of a binder composition (organic binder, solvent and moisture) for homogenization in ribbon blender;
(b) the above material is casted into flat compacts under the pressure of 500Pa;
(c) the obtained compacts/ briquettes are dried at a temperature of about 120-150oC for about 2-4 hours to remove inherent moisture and the briquettes are allowed for curing;
(d) after drying/curing, these compacts/briquettes are fed into the tunnel kiln in cylinders called as sager made out of silicon carbide and gas flow direction is kept opposite to the direction to provide a counter current contacting with pressure maintained between about 2-4 bar inside the furnace;
(e) briquettes are heated such that temperature is increased from ambient temperature to about 200oC for removing any associated moisture followed by reduction using reducing gas such as CO or a mixture of CO and CO2 at about 200oC to 600oC non-isothermally and holding at about 600oC for about 4-6 hours allowing for reduction of vanadium pentoxide to be complete to lower vanadium oxides;
(f) the partially reduced briquettes were again non-isothermally heated from about 600oC to 1400oC under CO and N2 atmosphere maintaining an oxygen partial pressure of about -8 atm, followed by isothermal holding at about 1400oC for about 2-12 hours under N2 atmosphere to complete the nitridation;
(g) after completion of the reaction, the briquettes are cooled to ambient temperature under N2 atmosphere inside the furnace to obtain the ferrovanadium nitride alloy with composition: V:-72-82%, N:7-16%, Fe: 0.4-4%, C: 6-12% and impurity profiles with Si= 1%, Al<0.01%, Mn<0.05%, S<0.05% and P<0.05%.

In an embodiment of the present disclosure, a flow diagram indicative of the present process is shown in Figure 1. The overall reduction and nitriding cycle for preparing the ferrovanadium nitride alloy can be written as:

V2O5+Fe2O3+8C+N2 ? 2VN+2Fe+8CO

In another embodiment of the present disclosure, to understand the mechanism of reduction in reducing atmosphere, thermogravimetric analysis - differential thermal analysis (TGA-DTA) of the briquettes were performed. TGA-DTA curves for the samples heated non-isothermally up to about 1400oC is represented in Figure 2. As seen in said figure, exothermic peak at 655.5oC indicates the volatilization loss of vanadium pentoxide (V2O5). Endothermic and exothermic differential scanning calorimetry (DSC) peaks represent intermediate reduction reactions that occur during non-isothermal nitriding up to about 1400oC. TG curve indicates mass loss of 43.04 % during non-isothermal treatment. Hence, a proper heating cycle should be devised to control V2O5 loss and achieve efficient reduction of starting oxides along with nitriding of the reduced products. Temperature cycle for reduction and nitriding is designed such that sublimation loss of V2O5 has been minimized by carrying out the reduction completely to lower vanadium oxides. In particular, reduction needs to be carried out at constant temperature before the melting of vanadium oxide compound (such as V2O5) occurs and reduction can also be maximized. Few isothermal reductions of the compacts have been performed to estimate its mass loss saturation with time and the hypothesis has been supported even by X-ray diffraction (XRD) data at these subsequent conditions, showing the presence of vanadium pentoxide. To estimate the effect of oxygen partial pressure during reduction, reduction was performed with 100% carbon monoxide from time horizon of 2-18 hours at a temperature where melting and volatilization loss of vanadium pentoxide can be minimized with subsequent near to completion of reduction of higher oxides of vanadium to lower valences. Further, to promote in-situ reduction, carbon dioxide or mixture of carbon monoxide and carbon dioxide was used to reduce the compacts while maintaining an oxygen partial pressure during reduction, which subsequently supports in promoting reduction such that volatilization loss of vanadium can be minimized. XRD analysis of this isothermal samples of compacts are shown in Figure 3 for different experimental conditions. To carry out further reduction and nitriding, an overall cycle of reduction and nitriding was performed. A typical reduction and nitriding cycle is shown in Figure 4. To perform the nitriding, the reduction of iron and vanadium oxides are performed which leads to formation of vacancy in the crystal structure and eventually macroscopically leads to higher porosity in the briquettes, which promotes diffusion of nitrogen. The nitrogen molecule gets adsorbed on the surface of reduced vanadium and iron oxides, which eventually leads to form a solid solution of vanadium and iron nitride along with vanadium and iron carbide respectively. Evidence of nitridation can be obtained from the microstructures of the final product samples obtained after reduction and nitriding as shown in Figure 5. Solubility of nitrogen is highest in vanadium rich phase, which is evident from point analysis of the microstructure.

The present process for preparation of ferrovanadium nitride alloy simplifies the traditional/conventional process and hence leads to lowering of the preparation time, lowering equipment investment and production costs. The process focuses on reduction of composite briquettes of vanadium source and iron/iron oxide source using a carbon source with primary focus on gas-based reduction followed by nitriding involving a unique heat treatment cycle to produce an alloy of vanadium-iron-nitrogen as primary elements. The present process also helps in higher yield of vanadium in the final alloy, and a zero-waste process with high density and lower melting point of the alloy.

The present invention primarily comprising the process of preparing ferrovanadium nitride alloy possesses at least the following advantages:
a) the process employs a well-designed and unique heat treatment cycle for reduction and nitridation steps,
b) the process also employs gaseous reducing agent(s) for reduction,
c) the process employs iron oxide as one of the raw materials which leads to the formation of the final ferrovanadium nitride alloy via. iron-vanadium (Fe-V) route rather than vanadium-nitride (V-N) route, thereby leading to an increase in density of the final alloy,
d) the present process is simple and efficient with reduced reduction and nitridation time,
e) the overall time taken for processing of briquettes to obtain the final alloy is about 10 to 18 hours.

In an embodiment, the foregoing descriptive matter is illustrative of the disclosure and not a limitation. While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

EXAMPLES

EXAMPLE 1: Preparation of ferrovanadium nitride alloy
The present example provides processing of a mixture comprising vanadium pentoxide (V2O5), iron oxide and carbon powder to form an alloy of vanadium-iron-nitrogen (ferrovanadium nitride). The process was carried out as follows:

Vanadium pentoxide either as lumps or powder were pulverized such that the particle size distribution of d80= 150µm was obtained. Iron oxide and graphite powder were pulverized to get a particle distribution with similar size fraction as of vanadium pentoxide. The oversized particles were screened and recycled back to feed section. As per the required chemistry of maintaining a carbon to oxygen ratio of 0.9 (C/O:0.9), raw materials were dry mixed as per the required chemistry of alloy requirement. A mixture of isopropyl alcohol and starch along with water in proportion of 78:2:20 was added to the dry mixture and mixing was carried out for about 60 minutes followed by briquetting (i.e. preparing solid compacts). During briquetting, a wet mixture obtained above was added and pressed under a pressure of about 50 MPa. The obtained compact was dried in oven for about 6 hours at a temperature of about 70°C.

The briquettes were arranged in crucibles in the shape of cylinder and pushed inside the tube furnace with curtain of N2 followed by carbon monoxide (CO) which was flowing in counter current mode. The samples were heat treated as per the temperature cycle for reduction-nitriding reactions. In particular, the compacts were heated from ambient temperature to about 200°C to remove bound moisture with a hold of about 10 minutes. Reduction of briquettes were carried out from about 200oC to about 600°C with a hold for about 6 hours under carbon monoxide (CO) environment maintaining an oxygen partial pressure below PO2= 10-20 atm. Eventually, the samples were again ramped up from about 600°C to 1100°C under a mixture of nitrogen (N2) and carbon monoxide (CO) environment such that an oxygen partial pressure PO2= 10-10 atm was maintained during reduction. Finally, the reduced compacts were heated non-isothermally from about 1100°C to about 1400°C and were allowed to be isothermally heated for about 6 hours to perform the nitriding reaction. The off-gas obtained after reduction was sent for analysis to estimate the degree of reduction and part of the gas was recycled back for further reduction along with fresh gas. Figure 2 depicts the TGA-DSC data/analysis for non-isothermal nitriding of sample having C/O molar ratio of 0.9 and up to 1400?. Figure 4 depicts heat treatment cycle for nitriding followed by reduction.

The reduced compacts were now cooled from about 1400°C to ambient temperature under nitrogen environment and the nitride briquettes obtained were tested for generation of fines by tumbling them in a cylindrical drum for about 30 minutes at about 45 RPM. Details of the chemical analysis of the raw materials and the obtained alloy is provided below.

Table 1: Chemical analysis (wt%) of the raw materials employed for preparing briquettes
Species V2O5 (%) Fe2O3
(%) C
(%) SiO2
(%) Al2O3
(%) CaO
(%) MgO (%) TiO2
(%)
Vanadium oxide 98 0.5 <0.1 <0.1 <0.1 0.02 <0.05 <0.01
Iron oxide - 98.5 0.05 0.01 0.05 <0.01 <0.01 -

Table 2: Chemical analysis (wt%) of the obtained ferrovanadium nitride alloy
V (%) C (%) N (%) Fe (%) Ti (%) Si (%) Ca (%) Al
(%) Mn
(%) S
(%) P
(%) Density (g/cm3)
78.66 8.86 9.95 0.48 0.02 0.004 0.03 0.01 0.05 0.05 0.05 3.6

EXAMPLE 2: Preparation of ferrovanadium nitride alloy with varying C/O ratio
This example provides a process for preparation of vanadium nitride alloy as described in Example 1 except for varying C/O ratios.

To estimate the variation of carbon on the nitrogen pickup in the alloy, a briquette with variation of C/O was carried out. Two samples of C/O: 1.0 and 1.1, respectively were prepared and firing of the briquettes were carried out under similar temperature cycle as described in Example 1. Detailed analysis of the briquette and alloy is provided below for both briquette compositions. Figure 4 depicts heat treatment cycle for nitriding followed by reduction.

Table 3: Chemical analysis of the briquettes used for nitriding
Sample C/O V2O5
(wt %) Fe2O3
(wt %) C
(wt %)
1 1.0 69.99 5.71 24.29
2 1.1 68.2 5.71 26.08

Table 4: Chemical Analysis (wt%) of ferrovanadium nitride alloy
Sample V C N Fe Ti Si Ca Density (g/cm3)
1 81.06 7.09 10.95 0.43 0.02 0.004 0.03 3.65
2 76.45 6.36 15.43 0.78 0.01 0.002 0.03 3.87

The above results indicate that varying C/O of the briquette samples do not decrease the nitrogen content of the final alloy and has a positive effect. Also, it is observed that increasing the C/O ratio enhances the nitrogen content of the alloy.

EXAMPLE 3: Preparation of ferrovanadium nitride alloy by employing a mixture of gaseous reductants
To estimate the effect of reduction potential on nitriding of vanadium-iron compacts, partial pressure of reduction gas was varied and its effect on nitrogen content in the alloy was studied. The experiment was conducted as described in Example 1. Sample with C/O of 0.9 was studied by employing reducing gas of 50:50 % CO and CO2, respectively. Chemical analysis of the final alloy is provided below. Further, Figure 2 depicts TGA-DSC data for non-isothermal nitriding of sample having C/O molar ratio of 0.9 and up to 1400?, and Figure 4 depicts heat treatment cycle for nitriding followed by reduction.

Table 4: Chemical Analysis (wt%) of ferrovanadium nitride alloy
V C N Fe Ti Si Ca
76.13 8.75 12.90 1.8 0.03 0.005 0.04

The above results indicate that varying partial pressure by employing mixture of gaseous reductants (such as CO and CO2) can be successfully used for preparing ferrovanadium nitride alloy.

Additionally, various experiments were conducted according to the flow chart indicated in Figure 1. Different ferrovanadium nitride alloy samples were accordingly obtained which had the composition as per Table 5 below.

Table 5: Chemical Analysis (wt%) of different ferrovanadium nitride alloy samples
Sr. No V C N Fe Ti Si Ca Total
1 80.79 9.05 9.35 0.48 0.04 0.02 0.03 99.76
2 80.72 8.96 9.17 0.50 0.01 0 0.03 99.39
3 80.62 8.43 10.29 0.45 0.01 0 0.04 99.84
4 80.45 8.81 9.92 0.57 0.01 0 0.05 99.81
5 80.73 8.60 10.03 0.37 0.01 0 0.03 99.77

The present disclosure is thus successful in providing a simple, economical and efficient process of ferrovanadium nitride alloy production. The produced ferrovanadium nitride alloy is immensely advantageous, especially in applications related to steel making.