Electrolytic reduction and deoxygenation of titanium and titanium alloys

Abstract

A method (100) of producing a deoxygenated titanium product can include electrolytic reduction of a titaniferous material followed by deoxygenation. The method can include reducing (110) a titanium oxide material to form a reduced titanium product using an electrolytic reduction process. The reduced titanium product has an oxygen content greater than about 0.25 wt% prior to deoxygenation. The method can further include deoxygenating (120) the reduced titanium product by heating the reduced titanium product to a deoxygenation temperature with a deoxygenation agent in a molten salt for a period of time under a hydrogen-containing atmosphere to form the deoxygenated titanium product having a reduced residual oxygen content.

Description

[0001] ELECTROLYTIC REDUCTION ND DEOXYGENATION OF TITANIUM AND TITANIUM ALLOYS

[0002] CROSS REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Provisional Patent Application No. 63 / 671,881, filed on July 16, 2024, which is hereby incorporated herein by reference.

[0004] BACKGROUND

[0005] Current electrochemical reduction processes for producing titanium can include the FFC Cambridge process, Ono & Suzuki process, QIT processes, and the like. Although such processes can offer desirable advantages, electrochemical reduction of titanium oxide is not currently capable of directly producing very low dissolved oxygen content, e.g. < 0.2%, or they cannot do so at reasonable efficiency or cost effectively. Residual dissolved oxygen in titanium and titanium alloy powders is considered unacceptable for both conventional manufacturing and additive manufacturing processes due to the adverse effect of oxygen on mechanical properties. This is especially true for aerospace and similar industries where mechanical strength of the sintered titanium products is particularly relevant. Therefore, high-purity titanium and its alloy powders have high demand in the market. The residual dissolved oxygen in the titanium and titanium alloy powder can be largely removed by a process generally referred to as deoxygenation. However, current deoxygenation processes suffer from diminishing returns at extra-low oxygen levels, and can tend to be energy intensive. Although some more exotic deoxygenation processes are known, currently favored processes use a highly reactive metal (Ca, Na, etc.) which reacts with the residual oxygen and makes the titanium powder pure. However, achieving extra-low interstitial oxygen (<0.13wt%) in coarser (>20pm) powder and low interstitial oxygen (<0.20wt%) in fine powders (<20pm) with high BET (>0.15m2 / g) by these deoxygenation processes has proven challenging.

[0006] SUMMARY

[0007] This invention relates to methods of producing titanium products and to deoxygenation of titanium materials. In one aspect, a method of producing a deoxygenated titanium product can include electrolytic reduction of a titaniferous material followed by deoxygenation. More specifically, a method of producing a deoxygenated titanium product can include reducing a titanium oxide material to form a reduced titanium product using an electrolytic reduction process. The reduced titanium product has an oxygen content greater than about 0.25 wt% prior to deoxygenation. The method can further include deoxygenating the reduced titanium product by heating the reduced titanium product to a deoxygenation temperature with a deoxygenation agent in a molten salt for a period of time under a hydrogen-containing atmosphere to form the deoxygenated titanium product having a reduced residual oxygen content. In some cases, the reduced residual oxygen content can be less than 0.2 wt%.

[0008] There has thus been outlined, rather broadly, the more important features of the invention so that the detailed description thereof that follows may be better understood, and so that the present contribution to the art may be better appreciated. Other features of the present invention will become clearer from the following detailed description of the invention, taken with the accompanying drawings and claims, or may be learned by the practice of the invention.

[0009] BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. l is a flow chart of a method of producing titanium product having low oxygen content in accordance with one example.

[0011] FIG. 2 is a schematic illustration of an example system for performing a method of producing a deoxygenated titanium product in accordance with one example.

[0012] FIG. 3 is a graph of oxygen potential vs. reductant cost and electricity cost at various current efficiency levels for electrolytic reduction, in accordance with one example.

[0013] FIG. 4 is a magnesium-calcium phase diagram as published in the ASM phase diagram database.

[0014] FIG. 5 is a flow chart of a method of deoxygenating a titanium product using a Mg- Ca alloy as a deoxygenation agent in accordance with one example.

[0015] These drawings are provided to illustrate various aspects of the invention and are not intended to be limiting of the scope in terms of dimensions, materials, configurations, arrangements or proportions unless otherwise limited by the claims. DETAILED DESCRIPTION

[0016] While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that various changes to the invention may be made without departing from the spirit and scope of the present invention. Thus, the following more detailed description of the embodiments of the present invention is not intended to limit the scope of the invention, as claimed, but is presented for purposes of illustration only and not limitation to describe the features and characteristics of the present invention, to set forth the best mode of operation of the invention, and to sufficiently enable one skilled in the art to practice the invention. Accordingly, the scope of the present invention is to be defined solely by the appended claims.

[0017] Definitions

[0018] In describing and claiming the present invention, the following terminology will be used.

[0019] The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a salt” includes reference to one or more of such materials and reference to “heating” refers to one or more of such steps.

[0020] As used herein with respect to an identified property or circumstance, “substantially” refers to a degree of deviation that is sufficiently small so as to not measurably detract from the identified property or circumstance. The exact degree of deviation allowable may in some cases depend on the specific context.

[0021] As used herein, “adjacent” refers to the proximity of two structures or elements. Particularly, elements that are identified as being “adjacent” may be either abutting or connected. Such elements may also be near or close to each other without necessarily contacting each other. The exact degree of proximity may in some cases depend on the specific context.

[0022] As used herein, the term “about” is used to provide flexibility and imprecision associated with a given term, metric or value. The degree of flexibility for a particular variable can be readily determined by one skilled in the art. However, unless otherwise enunciated, the term “about” generally connotes flexibility of less than 2%, and most often less than 1%, and in some cases less than 0.01%.

[0023] As used herein, the term “solid solution” is used to denote a solid-state solution of one or more solutes in a solvent, particularly a solid metal. In a solid solution, the crystal structure of the solvent remains substantially unchanged by the solute atoms. For example, in a solid solution of oxygen in titanium, oxygen atoms are dissolved in elemental titanium metal without substantially changing the crystal structure of the titanium metal. Thus, a solid solution of oxygen in titanium metal is substantially different from a titanium oxide, which has a different structure from elemental titanium metal.

[0024] As used herein, “deoxygenation” refers to the process of removing oxygen from a solid solution. As such, deoxygenation as a mechanism is distinct from reduction. For example, a Ti(O) solid solution can be deoxygenated to remove dissolved oxygen, while a TiCh oxide can be reduced to convert the oxide to metallic Ti. Thus, reduction involves a change in oxidation state of Ti, while removing dissolved oxygen does not involve a change in oxidation state of Ti.

[0025] As used herein, the term “eutectic” is used to describe a homogenous mixture of two or more components that has a lower melting point than either component alone. More specifically, a eutectic composition only occurs at a local minimum in melting point (i.e. certain systems may have more than one eutectic point. Thus, a “eutectic salt” has a lower melting point than the individual salts making up the eutectic salt mixture. As used herein, “eutectic” requires that the composition of the mixture is at precisely the “eutectic point,” which is a singular composition that produces a local minimum melting point. In other words, the eutectic point is the three-phase equilibrium point where the liquid phase is in equilibrium with two solid phases. The temperature and the composition of this point are fixed. The liquid phase transforms into the two solid phases. The composition of the liquid is the eutectic composition. The composition of the two solid phases are different as depicted in the phase diagram.

[0026] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

[0027] As used herein, the term “at least one of’ is intended to be synonymous with “one or more of.” For example, “at least one of A, B and C” explicitly includes only A, only B, only C, or combinations of each.

[0028] Numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a numerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly recited limits of 1 to about 4.5, but also to include individual numerals such as 2, 3, 4, and subranges such as 1 to 3, 2 to 4, etc. The same principle applies to ranges reciting only one numerical value, such as “less than about 4.5,” which should be interpreted to include all of the above-recited values and ranges. Further, such an interpretation should apply regardless of the breadth of the range or the characteristic being described.

[0029] Any steps recited in any method or process claims may be executed in any order and are not limited to the order presented in the claims. Means-plus-function or step-plus- function limitations will only be employed where for a specific claim limitation all of the following conditions are present in that limitation: a) “means for” or “step for” is expressly recited; and b) a corresponding function is expressly recited. The structure, material or acts that support the means-plus function are expressly recited in the description herein. Accordingly, the scope of the invention should be determined solely by the appended claims and their legal equivalents, rather than by the descriptions and examples given herein. Example Embodiments

[0030] This invention relates to methods of producing deoxygenated titanium products from a titaniferous material containing titanium oxides using electrolytic reduction followed by deoxygenation of the reduced titanium materials. Referring to FIG. 1, a method 100 of producing a deoxygenated titanium product can include reducing 110 a titanium oxide material to form a reduced titanium product using an electrolytic reduction process. The reduced titanium product has an oxygen content greater than about 0.25 wt% prior to deoxygenation, in some cases 0.5 to 10%, and in other cases 1 to 3%. The method can further include deoxygenating 120 the reduced titanium product by heating the reduced titanium product to a deoxygenation temperature with a deoxygenation agent in a molten salt for a period of time under a hydrogen-containing atmosphere to form the particulate titanium product having a reduced residual oxygen content. The reduced residual oxygen content can be less than 0.2 wt%, and in some cases down to about 0.1 wt%, and in other cases down to about 0.03%. Each of these steps will be explained in further detail in the following passages.

[0031] Generally, the titanium oxide material can include any titanium oxide containing materials. As non-limiting examples, the titanium oxide material can comprise one or more of titanium dioxides (e.g. titanium dioxide pigments, titanium dioxide slags such as UGS, chloride slag, sulfate slag), titanium suboxides, titanium-bearing minerals, rutile (natural or synthetic), and ilmenite.

[0032] The titanium oxide material can also be provided as a particulate starting material. As a general guideline, the particulate material can have an average size range of 1 pm to 5mm, and in some cases 5 pm to 50 pm, and in some cases less than 20 pm.

[0033] The electrolytic reduction process can be any process which uses electrolytic reactions to reduce titanium oxides (e.g. including dioxides and suboxides) to elemental titanium. Non-limiting examples of electrolytic reduction processes can include the FCC Cambridge process, Ono & Suzuki process, QIT, or the like. In one example, the reduced titanium product is a hydrogenated titanium product. In another example, the reduced titanium product has a fine powder size of less than about 20 pm, and in some cases, less than about 16 pm.

[0034] Regardless of the chosen electrolytic reduction route, in some examples, the reduced titanium product can be deoxygenated in a molten salt under a hydrogen-containing atmosphere to achieve a residual oxygen content of less than 0.2 wt%, in some cases less than 0.13%.

[0035] In one example, the deoxygenation agent can be one or more of a metallic deoxygenation agent and a hydride. For example, suitable metallic deoxygenation agent can include at least one of magnesium and calcium. In another example, the deoxygenation agent can be one or both of magnesium hydride and metallic magnesium. Similarly, in another example, the deoxygenation agent can be one or both of calcium hydride and metallic calcium. The deoxygenation agent can be chosen so as to be in a molten state at a desired deoxygenation temperature.

[0036] Further, during deoxygenation the molten salt can be chosen to provide a suitable medium in which the deoxygenation agent can be distributed. As such, the molten salt can be chosen to have a melting point which is below the desired deoxygenation temperature. In one example, the molten salt can include a primary salt which is a magnesium salt or a calcium salt. Non-limiting examples of suitable magnesium salt includes magnesium halides such as one or more of MgCh, MgBn, and MgF2. Non-limiting examples of suitable calcium salts can include one or more of CaCh, CaBr2, and CaF2. In some cases, a secondary salt which is different from the primary salt can be included as part of the molten salt. In some cases, the deoxygenation step using this approach can provide a reduced residual oxygen content which is less than 0.2 wt%, in some cases less than 0.13 wt%, and in other cases less than 0.06 wt%.

[0037] As a specific example, magnesium can be used as the deoxygenation agent (e.g. without a corresponding secondary salt such as a calcium salt). Although magnesium tends to be weaker deoxygenation agent than Ca for titanium at modest temperatures, the presence of hydrogen in the hydrogen-containing atmosphere shifts the oxygen potential curves of Ti(O) solid solutions such that MgO becomes more stable than Ti(O) at those corresponding temperatures. This can be particularly true when solid oxygen content is less than about 2.0 wt% and in some cases less than 0.2 wt%. Deoxygenation temperatures of less than about 900 °C such as about 500 °C to about 900 °C, in some cases 600 °C to 800 °C.

[0038] As an additional example deoxygenation approach, the deoxygenation agent can include a Mg-Ca alloy and a molten salt in a deep deoxygenation step. The Mg-Ca alloy can have an alloy melting point which is below that of either magnesium or calcium. Further, this deep deoxygenation can be performed either subsequent to a first deoxygenation stage (e.g. such as those described previously) or as a sole deoxygenation step.

[0039] The Mg-Ca alloy can be chosen having varied concentration of magnesium and calcium. In one example, the alloy melting point is 448 °C to less than 842 °C. In another example, the alloy melting point is 448 °C to less than 650 °C. In some cases, the alloy melting point is 440 °C to 600 °C, and in other cases 440 °C to 550 °C. As one example, the Mg-Ca alloy can have a magnesium atomic percentage of 80% to 99% (72-99 wt%), and in some cases 85% to 92% (78-88 wt%). In another example, the Mg-Ca alloy can have a calcium atomic percentage of 60% to 85% (71-90 wt%), and in some cases 67% to 77% (77.0-85 wt%). In one specific, example, the Mg-Ca alloy is a eutectic alloy. Mg-Ca alloys have two eutectic points. One example eutectic alloy is 89 at% (83 wt%) Mg and 11 at% (17 wt%) Ca. However, in some cases suitable alloys can be within 10 at% of the first eutectic point, and in other cases within 5 at%. In another example, the eutectic alloy is 26 at% (18 wt%) Mg and 74 at% (82 wt%) Ca. However, in some cases the Mg-Ca alloy can be within 10 at% of the second eutectic point, and in other cases within 5 at%.

[0040] As part of the deep deoxygenation process, the molten salt can also be carefully chosen to have a melting point below a desired deoxygenation temperature. Generally, the molten salt can have a salt melting point which is also less than or equal to the alloy melting point; however, the salt melting point may be above the alloy melting point as long as both are below the desired deoxygenation temperature. In one example, the molten salt is free of magnesium. In another example, the molten salt comprises a salt mixture of multiple salts. As one specific example, the salt mixture comprises a calcium halide and a secondary salt as a eutectic salt mixture. Providing a mixture of salts can also allow additional flexibility in achieving a lower salt melting point. As an example, the salt mixtures can often have a salt melting point which is 300 °C to less than 650 °C, and in some cases 400 °C to 600 °C.

[0041] As mentioned above, the deoxygenation temperature can be above the alloy melting temperature. As a general guideline, the deoxygenation temperature can be 448 °C to 680 °C, and in some cases to about 650 °C, and in other cases up to about 600 °C. The deoxygenation can be maintained for a period of time which can vary depending on the chosen temperatures, titanium particle sizes, and other factors. However, as a general guideline, the deoxygenation time can vary from about 10 minutes to about 24 hours, and in some cases 15 minutes to 6 hours. Regardless, the reduced residual oxygen content can be less than 0.2 wt%, and in some cases less than 0.13 wt%, down to about 0.01 wt% depending on conditions.

[0042] The deep deoxygenation can also be maintained at least partially under a hydrogencontaining atmosphere. The hydrogen-containing atmosphere can generally comprise from 5% by volume up to 100% by volume, and in some cases 50% to 100%. Additional gases can be included such as, but not limited to, inert diluents such as argon and the like. The hydrogen-containing atmosphere can also be substantially free or entirely free of oxygen or oxygen-containing compounds upon initiation of the deoxygenation process. Further, oxygen gas is generally not produced.

[0043] In certain examples, a method of deoxygenating a titanium product can comprise forming a molten mixture including the titanium product, a molten salt, and a deoxygenation agent, wherein the molten salt having a salt melting point and the deoxygenation agent is a Mg-Ca alloy having an alloy melting point. The deoxygenation can also involve heating the molten mixture at a deoxygenation temperature under a hydrogen-containing atmosphere for a deoxygenation time sufficient to form a deoxygenated titanium product, wherein the deoxygenation temperature is above the salt melting point and the alloy melting point. The same conditions, variations, materials, and options outlined above can also be applied here.

[0044] This deoxygenation method can also lower the oxygen further in coarser (>20pm) powder and help meet the requirement of grade 23. Similarly, these approaches can reduce the oxygen from finer (>45pm) powder with high BET and make them more attractive for sinter-based PM technology like Metal Injection Molding (MIM).

[0045] In more detail regarding the starting materials, a variety of titaniferous materials can be used as a starting material in the methods described herein. Generally, the titaniferous material can be a titanium oxide-containing material such as raw ores, intermediate titanium products, or synthetic titanium materials. As non-limiting examples, the titanium oxide material can comprise one or more of titanium dioxides (e g. titanium dioxide pigments, titanium dioxide slags such as UGS, chloride slag, sulfate slag), titanium suboxides, titanium- bearing minerals, rutile (natural or synthetic TiCh), ilmenite (FeTiCh), and leucoxene (an alteration product of titanium containing minerals). Such materials may be composed of varying degrees of titania. A raw titanium ore starting material can be treated to increase titanium percentage. Synthetic rutile tends to have a titanium oxide content of 80% to 98% by weight, ilmenite generally has an oxide content of 45% to 60%, natural rutile can often have a titanium oxide content of about 92% to 98%, titanium dioxide slags can often have an oxide content of 60% to 85%, upgraded slag (UGS) tends to have an oxide content of about 92% to about 95 wt%, and titanium dioxide pigments tend to have oxide content of 95% to 99.9% by weight. Typically, raw ore can have a titanium oxide content from about 50 wt% to about 65 wt%. Although other methods can be used, raw titanium ore can be carbothermally reduced to form TiCh-slag. Such low grade TiCh-slag can often contain about 80 wt% titanium oxide, although from about 70 wt% to 90 wt% may be achieved under varying feed and processing conditions. Other known hydrometallurgical or chemical metallurgical processes may be involved to produce highly concentrated raw material with TiO2 content more than 80 wt%, and in some cases up to 99.5 wt%.

[0046] Consistent with these principles, one or more secondary particulate materials which are not titanium-based can also be included so as to reduce both titanium and secondary alloying metals contemporaneously. Such secondary particulate materials can include one or more of elemental metals, metal oxides, and metal hydrides which can be included so as to form titanium alloys upon further processing. Non-limiting examples of suitable secondary particulate materials can include metal oxides such as AI2O3, V2O5, CuO, MnO, V2O3, Fe2O3, Nb20s, ZrCh, MoOs, MoO2, Cr2C>3, SnCh, SiCh, Ta20s, CoO, WO3, and NiO; elemental metals such as Al, Mo, V, Nb, Ta, Fe, Cr, Mn, Co, Cu, W, Zr, Sn, Ni, and Si; and metal hydrides such as aluminum hydride, vanadium hydride, niobium hydride, tantalum hydride, zirconium hydride, and silicon hydride. Appropriate molar ratios of metals in a feed powder can be chosen in order to produce a desired alloy. Non-limiting examples of titanium alloys which can be produced include Ti-6A1-4V, Ti-2.5Cu, Ti-8Mn, Ti-3A1-2.5V, Ti-5Al-2.5Fe, Ti-6Al-7Nb, Ti-13Nb-13Zr, Ti-15Mo-5Zr, Ti-10V-2Fe-3Al, Ti-8V-3Al-6Cr-4Mo-4Zr, Ti- 6Al-2Sn-4Zr-2Mo-0.1Si, Ti-15Mo-3Al-2.7Nb-0.25Si, Ti-15Mo-2Sn-4Zr-4Mo-2Cr-lFe, and the like. Such alloys can be formed by premixing precursor powders prior to reduction, or can be mixed after reduction. Further, excessive impurities can reduce product quality and may interfere with reduction and deoxygenation steps. Accordingly, in some cases it can be desirable to subject feed powders to purification steps such as leaching, electrolysis, precipitation, washing, etc. prior to reduction and / or deoxygenation in order to reduce impurities to below a target level.

[0047] Regardless, the titanium oxide material can also be provided as a particulate starting material. As a general guideline, the particulate material can have an average size range of 0.1 pm to 5mm, and in some cases 1 pm to 500 pm, in other cases 5 pm to 200 pm, in some cases 5 pm to 50 pm, and in some cases less than 20 pm. In some cases, the titanium oxide material can be comminuted to reduce particle size to a desired size. For example, relatively larger pieces (e.g. greater than about 5 mm) can be milled, crushed or otherwise subjected to a particle size reduction process. The particles can be spherical, asymmetrical, or other shape. In one example, the particles can have an average particle aspect ratio less than 2.0. Smaller particle sizes result in higher exposed surface areas per volume of material and also reduce diffusion depths through each particle. Larger particle sizes will generally be associated with higher processing times and / or temperatures, while smaller particles sizes allow for reduced processing times.

[0048] The particulate starting material can be sintered in some examples to form a sintered cathode before the electrolytic reduction step is performed. This sintering can refer to partial sintering, in which the sintered cathode retains a high porosity with void spaces between the particles of titanium oxide material. In some examples, a particulate titanium oxide material, such those described above, can be compacted and heated to a sintering temperature to partially fuse the particles together. The sintering temperature used to make the cathode can be from about 900 °C to about 1200 °C in some examples, or from about 900 °C to about 1100 °C, or from about 1000 °C to about 1100 °C in further examples. Using higher sintering temperatures can ten to produce a cathode with lower porosity because more necking can occur between titanium oxide particles, while lower temperatures can produce a cathode with higher porosity. In some cases, the porosity can be maximized by using lower temperatures. In various examples, the porosity of the sintered cathode can be from about 20% to about 90%, or from about 20% to about 80%, or from about 20% to about 70%. Additionally, the sintered cathode can have a specific surface area from about 0.1 m2 / cm3to about 10 m2 / cm3, or from about 1 m2 / cm3to about 10 m2 / cm3, or from about 1 m2 / cm3to about 5 m2 / cm3.

[0049] Sintered cathodes can also be made with a controlled pore size distribution in some examples. In certain examples, the sintered cathode can have a bimodal pore size distribution, with a set of smaller micropores and a set of larger macropores. The macropores can be formed by mixing a space holder particulate material with the titanium oxide material. The space holder particulate material can have a larger particle size than the titanium oxide material. For example, the average particle size of the space holder can be from 5 times to 50 times larger than the average particle size of the titanium oxide material. The space holder material can be removed either during sintering or after sintering to leave larger macropores in the sintered cathode. The smaller micropores can be derived from the spaces between the smaller individual particles of titanium oxide material. In certain examples, ammonium carbonate can be used as the space holder material. A mixture of a particulate titanium oxide material with larger particles of ammonium carbonate can be sintered and the ammonium carbonate can be removed to make a sintered cathode with a bimodal pore size distribution. In some examples, the pore size distribution can include a larger peak that may be from about 0.5 pm to about 5 mm, and a smaller peak that may be from about 0.1 pm to about 1 mm. In other examples, the cathode can be made without using spacer materials and the pore size distribution can have a single peak average pore size from about 0.1 pm to about 1 mm.

[0050] The electrolytic reduction process can be any process which uses electrolytic reactions to reduce titanium oxides (e.g. including dioxides and suboxides) to elemental titanium. Non-limiting examples of electrolytic reduction processes can include the FCC Cambridge process, Ono & Suzuki process, QIT, or the like.

[0051] Regardless of the reduction process, in some cases, the reduced titanium product can be a hydrogenated titanium product. Hydrogenated titanium product can be desirable when storage or transport is needed prior to producing a final titanium product. This is at least partially due to the high oxidation potential of elemental titanium such that hydrogenated titanium is more stable than elemental titanium, especially at smaller particle sizes. In another example, the reduced titanium product has a fine powder size of less than about 20 pm, and in some cases, less than about 16 pm. In some cases, the reduced titanium product has a powder size of 1 pm to 200 pm, 10 pm to 100 pm, or 20 pm to 50 pm. Notably, the oxygen content in the reduced titanium product can generally be in the form of oxygen dissolved in a solid solution, as opposed to titanium oxide.

[0052] In one specific example, the electrolytic reduction process is the FCC Cambridge process which includes carbothermally reducing ilmenite ore to titanium-slag and pig iron, chemically extracting titanium oxide from the titanium slag to produce an upgraded synthetic rutile, and electrolysis of the upgraded synthetic rutile which functions as a sintered cathode in a molten calcium chloride salt to form the reduced titanium product. Additional details for this process can be found in the literature, e.g. WO 99 / 64638 and Chen, G.Z., Fray, D.J., and Farthing, T.W., Direct Electrochemical Reduction of Titanium Dioxide to Titanium in Molten Calcium Chloride, Nature, vol. 407, 2000, pp. 361-4.

[0053] In another example, the electrolytic reduction process includes calciothermic reducing the titanium oxide material and electrolysis of CaO in a molten calcium chloride to form the reduced titanium product. One example of this process is known as the Ono & Suzuki process and additional details can be found in the literature, e.g. U.S. Patent No. 7,264,765.

[0054] In still another example, the electrolytic process includes electrolysis and electrowinning of the titanium oxide material in molten calcium fluoride, e.g. QIT process as described in WO 01 / 62994 Al and U.S. Patent No. 7,504,017.

[0055] Regardless of the chosen electrolytic reduction route, the reduced titanium product can be deoxygenated in a molten salt under a hydrogen-containing atmosphere to achieve a residual oxygen content of less than 0.2 wt%.

[0056] FIG. 2 shows a schematic representation of a more specific example of a system for performing a method of producing a deoxygenated titanium product. An electrolytic cell 210 includes a cathode 212 made of a sintered titanium oxide material. In some examples, this cathode can include a sintered particulate titanium oxide material held inside a basket or cage, such as a steel basket. The cathode is attached to a cathode current collector 214 which can be connected to an electric power source outside the cell. The electrolytic cell also includes an anode 216. In some examples, the anode can be made of graphite or another material. The cathode and anode are both in contact with an electrolyte 218, which can be a molten salt electrolyte, such as CaO and CaCh or others, in some examples. An electric current can be applied between the anode and the cathode to electrolytically reduce the titanium oxide material in the cathode. This electrolytic reduction step converts the titanium oxide material to a reduced titanium product 220, which is shown schematically as a particulate material produced from the electrolytic cell. The reduced titanium product can include oxygen in a greater than desired concentration. For example, the oxygen content in the reduced titanium product can be greater than 0.25 wt% in some cases, and in some cases from 1 wt% to 5 wt% (e.g. especially in the case of using the FFC process). This reduced titanium product can then be deoxygenated in a deoxygenation step. The figure shows that the reduced titanium product can be placed into a deoxygenation reactor 230 with a deoxygenation agent in a molten salt 232 under a hydrogen-containing atmosphere 234. The combination of the deoxygenation agent, molten salt, and hydrogen-containing atmosphere can reduce the oxygen content when this combination is heated to a deoxygenation temperature for a sufficient time. During the electrolytic reduction step, electrons can be added to the titanium oxide material to reduce the titanium oxide and convert the titanium oxide to titanium metal. In some examples, multiple chemical reactions can occur during this reduction process. Initially, the titanium oxide material (which can be in the form of TiCh) can be converted to Magneli phases by the addition of electrons. Magneli phases refer to a group of substoichiometric titanium oxide phases having the formula TinChn-i, where n is from 4 to 10. The further addition of electrons to the Magneli phases can result in the formation of TiO and CaTiCh through reaction with calcium in the molten salt electrolyte. Another reaction can occur between TiO and CaTiOs to form CaTi2O4. The CaTi2O4 can also be reduced by the addition of electrons, forming TiO and Ca2+. Finally, TiO can also be reduced to form metallic titanium, which can contain dissolved oxygen in a solid solution.

[0057] During the electrolytic reduction process, the titanium oxide material and the molten salt electrolyte can be heated at a temperature from about 800 °C to about 1000 °C, or from about 850 °C to about 950 °C. The time utilized for the electrolytic reduction process can be sufficient to substantially convert the titanium oxide material to titanium metal. The amount of time to accomplish this may depend on various factors, including the temperature, voltage, electrolyte, amount of titanium oxide material to be reduced, surface area of the titanium oxide material, and others. In some examples, the reduction time can be from about 1 hour to about 24 hours, or from about 4 hours to about 20 hours, or from about 8 hours to about 20 hours, or from about 12 hours to about 20 hours.

[0058] Electrolytic reduction can be a more attractive approach for producing titanium metal compared to metallothermic reduction because of the elimination of the cost of a reducing agent. In metallothermic reduction, a stoichiometric amount of a metallic reducing agent is consumed by the reduction reaction in order to acquire metallic titanium. The cost of the reducing agent can be the largest cost of metallothermic reduction processes. In contrast, electrolytic reduction does not involve consuming a reducing agent. Instead, the reduction is provided by electric current. Accordingly, the main cost in electrolytic reduction can be the cost of electricity. In electrolytic reduction processes, the current efficiency (CE) is defined as the fraction of the total electric current used in the process that directly results in the desired reduction reaction (in this case, TiCh being reduced to Ti metal). In some examples, the current efficiency of the electrolytic reduction step can be from about 10% to about 50%. The higher the current efficiency, the more cost-effective the electrolytic reduction process can be.

[0059] FIG. 3 shows a graph representing the cost vs. oxygen potential. In particular, the x- axis shows cost of reducing agents that can be used in metallothermic reduction processes. The y-axis shows the oxygen potential of the various reducing agents. Individual reducing agents are plotted on the graph. Calcium is the reducing agent with the lowest (most negative) oxygen potential out of these, which is why calcium has been used in calciothermic reduction processes. However, calcium is also more expensive than the other reducing agents. As shown on the graph, a combination of magnesium and hydrogen can have almost the same oxygen potential as calcium at a much lower cost. This graph also includes slanting lines that represent the cost of electrolytic reduction at various levels of current efficiency. Logically, the highest cost is found when the current efficiency is low, at 10%. This is represented by the right-most slanted line. Proceeding the left, the slanting lines represent current efficiencies of 20%, 30%, and so on up to 100%. This graph demonstrates that even with a current efficiency of only 10%, the electrolytic reduction process can be cheaper than using calcium as a reducing agent. Additionally, any current efficiency of 20% or greater can be cheaper than using the combination of Mg and H2 as a reducing agent.

[0060] Despite this potential for cost savings over metallothermic reduction processes, it has been difficult to achieve sufficiently low oxygen content in the titanium produced by electrolytic reduction. For this reason, the methods described herein utilize electrolytic reduction together with a deoxygenation step that can include a reducing agent such as Mg or Ca with a hydrogen-containing atmosphere. Thus, the methods can take advantage of the low cost of electrolytic reduction and the low cost and ability to further reduce the oxygen content provided by a magnesium or calcium reducing agent and hydrogen gas.

[0061] It is noted that relatively low current efficiency is often achieved in the electrolytic reduction step, such as from 10% to 40%. Without being bound to a particular mechanism, it is believed that the low current efficiency can be a result of current leakage, parasitic reactions, and long process run time. In some examples, the electrolyte used in the electrolytic reduction can include CaCL and CaO. Unfortunately, at the temperatures used to melt the molten salt electrolyte, the electrochemical potential needed to reach low oxygen content (such as about 300 ppm or less) is also sufficient to reduce CaO to form Ca metal. Thus, a significant portion of the electric current can be consumed by this side reaction, and the electrolyte can break down. The presence of Ca in the electrolyte can also lead to background conductivity between the cathode and anode, which can also waste a portion of the electric current. Additionally, carbon can be present in the electrolyte as carbon may be removed from the graphite anode. This carbon can also increase the background conductivity of the electrolyte. These factors can lead to low current efficiency.

[0062] In some examples, the electrolytic reduction step can be performed with a lower potential to reduce the occurrence of electrolyte breakdown. This can help to increase the current efficiency. However, this can also result in a tradeoff of a higher oxygen content in the reduced titanium product. Therefore, the combination of the electrolytic reduction step and the deoxygenation step in the methods described herein can be useful to reduce the overall cost of the method while still achieving low oxygen content in the final deoxygenated product.

[0063] Other issues that can occur during the electrolytic reduction step can include in-situ perovskitization that can occur when DO2 reacts with CaO to form CaTiCf and CaTi2O4. This also consumes the electrolyte, and can cause the cathode to expand in volume. In some examples, forming the cathode with a high porosity and / or a bi-modal porosity as described above can help to prevent problems cause by in-situ perovskitization. In further examples, ex-situ perovskitization can be used, in which the titanium oxide starting material is converted to CaTiCf or CaTi2O4 before the electrolytic reduction. These perovskite materials can then be directly reduced to form the reduced titanium product.

[0064] In some examples, the electrolytic cell can include an anode made of graphite. During the electrolytic reduction process, a portion of the graphite anode can be consumed by reaction of O2' with carbon to form CO2. In some cases, this can form cracks in the graphite anode, and cracks can be expanded further by gas pressure of CO2 inside the cracks. This can lead to erosion of the anode and graphite debris may detach from the anode. In some examples, such erosion of the anode can be reduced by including a thin layer of AI2O3 as a barrier on the surface of the graphite anode. In other examples, a different material can be used for the anode. Some alternative materials can include ceramics, such as CaRuCh-doped CaTiCh. After the electrolytic reduction step has been performed to obtain a reduced titanium product, the reduced titanium product can be deoxygenated by heating the reduced titanium product to a deoxygenation temperature with a deoxygenation agent in a molten salt under a hydrogen-containing atmosphere. The deoxygenation agent can vary but is generally chosen to react with interstitial oxygen in solid solution of a titanium mass. In some examples, an oxide of the deoxygenation agent can be formed. In one example, the deoxygenation agent can be one or more of a metallic deoxygenation agent and a hydride. For example, suitable metallic deoxygenation agent can include at least one of magnesium and calcium. In such case, oxygen trapped in the reduced titanium product can react to form MgO or CaO. These oxides can then be recycled or discarded. In another example, the deoxygenation agent can be one or both of magnesium hydride and metallic magnesium. Similarly, in another example, the deoxygenation agent can be one or both of calcium hydride and metallic calcium. The deoxygenation agent can be chosen so as to be in a molten state at a desired deoxygenation temperature. As a general rule, the melting point of these deoxygenation agents can be 325 °C to 845 °C (e.g. 327 °C for Mg, 650 °C for Mg hydride, 816 °C for calcium, and 842 °C for Ca hydride).

[0065] During deoxygenation, the molten salt can be chosen to provide a suitable matrix in which the deoxygenation agent can be distributed. As such, the molten salt can be chosen to have a melting point which is below the desired deoxygenation temperature. In one example, the molten salt can include a primary salt which is a magnesium salt or a calcium salt. Nonlimiting examples of suitable magnesium salt includes magnesium halides such as one or more of MgCh, MgBr2, and MgF2. Non-limiting examples of suitable calcium salts can include one or more of CaCh, CaBn, and CaF2. In some cases, a secondary salt which is different from the primary salt can be included as part of the molten salt. Non-limiting examples of suitable secondary salts can include KC1, NaCl, LiCl, RbCl, CsCl, CaCh (if the primary salt is MgCh), MgCh (if the primary salt is CaCh), and the like. In some examples, the melting point of the individual molten salts can range from 700 °C to 820 °C. However, mixtures of two or more salts can have lower melting points. Deoxygenation times for these deoxygenation agents will vary based on various factors such as oxygen content in the reduced titanium material, specific salts, and deoxygenation temperature above the melting point. In some cases, the deoxygenation step using this approach can provide a reduced residual oxygen content which is less than 0.2 wt%, in some cases less than 0.13 wt%, down to about 0.01 wt%.

[0066] As an additional example deoxygenation approach, the deoxygenation agent can include a Mg-Ca alloy and a molten salt in a deep deoxygenation step. The Mg-Ca alloy can have an alloy melting point which is below that of either magnesium or calcium individually. Further, the deep deoxygenation can be performed either subsequent to a first deoxygenation stage (e.g. such as those described previously or other alternatives), or as a sole deoxygenation step. Mg can deoxygenate titanium and its alloys in hydride forms. This process uses hydrogen-induced destabilization to increase the oxygen potential, enabling the enhanced removal of residual oxygen. This deep deoxygenation process utilizes the principles of hydrogen-assisted magnesiothermic reduction to perform deoxygenation with a Mg-Ca alloy mixture (e g. especially eutectics) instead of using Mg metal alone. Using Mg-Ca alloy compositions offers a more reactive deoxidizing agent and the option of deoxygenation at lower temperatures. Lowering or minimizing the deoxygenation temperature has benefits such as reduced energy use, reduced corrosive and thermal damage to reaction vessels, reduced evaporation of the deoxygenation agent, and reduced sintering of metal powder particles during deoxygenation. Lower temperatures can also allow for a purer metal product, since some impurities are more likely to enter the metal at higher temperatures. For example, the diffusion coefficient of iron in titanium at 1000 °C is 100 times higher than that at 650 °C (5x 10'11m2 / sec vs. 5xl0'13m2 / sec). Accordingly, when deoxygenation is carried out at lower temperatures, the likelihood of impurities contaminating the metal product can be greatly reduced. This can expand the range of options for reaction vessel materials available to be used for the deoxygenation. For example, materials such as steel, which can contaminate titanium or other metal at higher temperatures, can be used at the lower temperatures of the present methods with little contamination of the deoxygenated titanium materials. Additionally, in some cases, lower temperatures can allow for a lower thermodynamic limit on the final oxygen content achievable in the deoxygenated metal especially when additional secondary metals are added since these metals can also react less strongly with oxygen at lower temperatures.

[0067] The Mg-Ca alloy can be chosen having varied concentration of magnesium and calcium. In one example, the alloy melting point is 448 °C to less than 842 °C. In another example, the alloy melting point is 448 °C to less than 650 °C. In some cases, the alloy melting point is 440 °C to 600 °C, and in other cases 440 °C to 550 °C, and in one example 575 °C. In certain examples, the Mg-Ca alloy can have a melting point of about 521 °C, and in other examples, the Mg-Ca alloy can have a melting point of about 448 °C. As one example, the Mg-Ca alloy can have a magnesium atomic percentage of 80% to 99%, and in some cases 85% to 92%. In another example, the Mg-Ca alloy can have a calcium atomic percentage of 60% to 85%, and in some cases 67% to 77%. In terms of weight percent, the Mg-Ca alloy can include magnesium in an amount of 70 wt% to 90 wt%, or 75 wt% to 85 wt%, or 80 wt% to 85 wt% in some examples. In other examples, the Mg-Ca alloy can include calcium in an amount from about 60 wt% to about 90 wt%, or from about 60 wt% to about 80 wt%, or from about 60 wt% to about 70 wt%, or from about 70 wt% to about 80 wt%, or from about 75 wt% to about 80 wt%. In one specific, example, the Mg-Ca alloy is a eutectic alloy. Referring to FIG. 4, the Ca-Mg phase diagram shows two eutectic points. Accordingly, one example eutectic alloy is 89 at% (82 wt%) Mg and 11 at% (18 wt%) Ca. However, in some cases suitable alloys can be within 10 at% of the first eutectic point, and in other cases within 5 at%. In another example, the eutectic alloy is 26 at% (35 wt%) Mg and 74 at% (65 wt%) Ca. However, in some cases the Mg-Ca alloy can be within 10 at% of the second eutectic point, and in other cases within 5 at%.

[0068] Notably, the use of eutectic Mg-Ca alloy effectively provides the opportunity to use Mg2Ca intermetallic as the deoxidizing agent which can reduce the deoxygenation temperature by 100°C or more. Such lower deoxygenation temperatures help obtain low oxygen in the powder while reducing and controlling particle sintering during deoxygenation, improving the quality of the deoxygenated powder. Further, low deoxygenation temperature reduces electrical costs, energy consumption, and overall process complexity. Further, calcium tends to be a stronger oxygen scavenger, while magnesium is less expensive. However, it has been found that the presence of at least some magnesium tends to not only reduce deoxygenation temperatures but also increase oxygen scavenging performance of the deoxygenation agent.

[0069] The deoxygenation agent can generally be present in excess (i.e. compared to residual oxygen). As an example, the deoxygenation agent can be present at a mole ratio of residual oxygen to deoxygenation agent from 1 : 1 to 1 :5, and in some cases about 1 :1 to 1 :2. Regardless, the deoxygenation agent can be introduced in at least stoichiometric amounts, and in some cases up to about 6 times the mole amount of oxygen.

[0070] It has also been found that this deep deoxygenation process can allow for reduction of residual oxygen content to less than 0.2 wt%, less than 0.13 wt% and in some cases less than 0.10 wt%, even for particle sizes less than about 20 pm, and in some cases less than 15 pm. In some examples, the reduced titanium product can have an oxygen content greater than about 0.2 wt% before the deoxygenation step, and this deep deoxygenation process can be used to reduce the oxygen content below 0.2 wt%. Additionally, the reduced titanium product can be a particulate with an average particle size from about 1 pm to about 200 pm. The particle size can affect the final oxygen content, as smaller particle size can typically be more difficult to deoxygenate. Therefore, with smaller particle size the deep deoxygenation process may not reduce the oxygen content below 0.2 wt%. However, the deep deoxygenation process can reduce the oxygen content compared to the initial oxygen content of the reduce titanium product prior to performing the deep deoxygenation step.

[0071] As part of the deep deoxygenation process, the molten salt can also be carefully chosen to have a melting point below a desired deoxygenation temperature. Generally, the molten salt can have a salt melting point which is also less than or equal to the alloy melting point; however, the salt melting point may be above the alloy melting point as long as both are below the desired deoxygenation temperature. The molten salt can kinetically enhance the deoxygenation rate, but does not change the thermodynamic limits involved (i.e. reaction of oxygen with deoxygenation agent). In another example, the molten salt comprises a salt mixture of multiple salts including binary salts, ternary salts, etc. As one specific example, the salt mixture comprises a calcium halide and a secondary salt as a eutectic salt mixture. In one specific example, the secondary salt is a sodium salt. Providing a mixture of salts can also allow additional flexibility in achieving a lower salt melting point. As an example, the salt mixtures can often have a salt melting point which is 300 °C to less than 650 °C, and in some cases 400 °C to 600 °C. In some cases, the salt melting point can be at least 30 °C below the deoxygenation temperature. Non-limiting examples of suitable calcium halide salts can include one or more of CaCh, CaBr2, CaF2, and Cah. Non-limiting examples of suitable secondary salts can include KC1, KF, KBr, KI, NaCl, NaF, NaBr, Nal, LiCl, LiBr, LiF, Lil, RbCl, CsCl, CsBr, CsI, calcium halides different from the primary salt, and the like. In one example, the molten salt is free of magnesium.

[0072] As mentioned above, the deoxygenation temperature can be above the alloy melting temperature. As a general guideline, the deoxygenation temperature can be 448 °C to 680 °C, and in some cases to about 650 °C, and in other cases up to about 600 °C. The deoxygenation can be maintained for a period of time which can vary depending on the chosen temperatures, titanium particle sizes, target residual oxygen content, and other factors. However, as a general guideline, the deoxygenation time can vary from about 10 minutes to about 24 hours, and in some cases 30 minutes to 6 hours. Regardless, the reduced residual oxygen content can be less than 0.2 wt%, and in some cases less than 0.13 wt% down to about 0.01 wt%.

[0073] The deep deoxygenation can also be maintained at least partially under a hydrogencontaining atmosphere. The hydrogen-containing atmosphere can generally comprise from 5% by volume up to 100% by volume of hydrogen, and in some cases 50% to 100%. Additional gases can be included such as, but not limited to, inert diluents such as argon and the like. The hydrogen-containing atmosphere can also be substantially free or entirely free of oxygen or oxygen-containing compounds upon initiation of the deoxygenation process. The hydrogen-containing atmosphere can be introduced in a single step, introduced in stages, or can be introduced gradually by ramping up hydrogen content relative to one or more other gases such as argon. For example, initial heating can be performed under an inert gas while hydrogen can be introduced as temperatures are ramped up to the deoxygenation temperature. The deoxygenation temperature (e.g. static isothermal conditions or varied temperatures above the melting points of the alloy and salt) can be maintained for the deoxygenation time which is sufficient to achieve the target residual oxygen content. For example, the deoxygenation temperature may vary within a range of 10 °C to about 30 °C above the salt melting point and the alloy melting point.

[0074] In various examples, the methods described herein can include any of the deoxygenation and / or deep deoxygenation steps described above. In a certain example, a method of producing a deoxygenated titanium product can include deoxygenating the reduced titanium product using a single deoxygenation step that utilizes a magnesium reducing agent, such as Mg and / or MgJL. In another example, the method can include a multi-stage deoxygenation that includes a first stage with a magnesium reducing agent, and the second stage comprising a deep deoxygenation process as described above, which can utilize a Mg-Ca alloy. In yet another example, the method can include a direct deep deoxygenation step, in which the reduced titanium product is subjected to the deep deoxygenation process with a Mg-Ca alloy straightaway without performing any prior deoxygenation stage with a magnesium reducing agent.

[0075] Once deoxygenation is completed the particulate titanium product can be cooled to room temperature. The cooling stage can include a hydrogen atmosphere where inert gas is optionally included. The concentration of optional inert gas can be varied in order to carefully maintain hydrogenation and formation of TiFh. In this case, after deoxygenation, equilibrium hydrogen content in the titanium material will increase with the decreasing temperature, under the same pressure (e g. 1 atm and flowing hydrogen gas). After the product is completely cooled down to room temperature, titanium is largely in a hydride condition. In some cases, hydrogen content in the atmosphere can be reduced or tapered just before or during cooling in order to dehydrogenate the product, rather than performing dehydrogenation in a separate subsequent step.

[0076] The final cooled product can then be stored, shipped, sold, post-processing, or immediately used in sintering processes to produce a final product. In one alternative, after deoxygenation, the deoxygenated titanium product can be maintained in a hydride form since the hydride minimizes oxygen pick up during storage over non-hydride forms. When the titanium product is ready to be used, the hydrogenated product can be dehydrided to remove hydrogen (i.e. including hydride and residual dissolved hydrogen), typically to less than about 60 ppm. Dehydrogenating can include heating the deoxygenated titanium product in a hydrogen deficient atmosphere sufficient to drive hydrogen out from the deoxygenated titanium product to form the titanium product having a hydrogen content less than about 100 ppm. The dehydrogenating can typically be performed at temperatures from 400 °C to 800 °C. Most often, the dehydrogenating can maintain both pore size and specific surface area.

[0077] Further, deoxygenation by-products such as MgO and CaO can be removed from the titanium product. By-product removal can include one or more of leaching, washing, and all particle separation techniques including, but not limited to, gravitational, magnetic, centrifugal, aqueous, flotation, and other hydrometallurgical techniques. For example, after deoxygenation particulate titanium product can be mixed with MgO, CaO, residual salt, and residual Mg-Ca alloy powders. This powder mixture can be soaked in water and then subjected to acid leaching in order to remove oxides, salt, and alloy while leaving the leached particulate titanium product. This leached product can then be dried in the absence of oxygen. Leachate can then be recycled or discarded.

[0078] Notably, this deep deoxygenation process can also be performed after any titanium oxide reduction process and not only after electrolytic based reduction. Accordingly, as shown generally in FIG. 5, a method 500 of deoxygenating a titanium product can comprise forming a molten mixture 510 including the titanium product, a molten salt, and a deoxygenation agent, wherein the molten salt having a salt melting point and the deoxygenation agent is a Mg-Ca alloy having an alloy melting point. The deoxygenation can also involve heating the molten mixture 520 at a deoxygenation temperature under a hydrogen-containing atmosphere for a deoxygenation time sufficient to form a deoxygenated titanium product, wherein the deoxygenation temperature is above the salt melting point and the alloy melting point. The same conditions, variations, materials, and options outlined above can also be applied here.

[0079] Further, the deep deoxygenation process can be applied to any titanium or titanium- containing material. Non-limiting examples include commercially pure titanium, titanium alloys (e.g. Ti-6A1-4V, Ti6Al, Ti3A12.5, Ti5Al-2.5Sn, Ti-6Al-2Sn-4Zr-2Mo, Ti-5Al-5Sn- 2Zr-2Mo, IMI 685, Ti 1100, Ti-6Al-6V-2Sn, Ti-6Al-7Nb, Ti62A, Ti-10V-2Fe-3Al, Ti- 29Nb-13Ta-4.6Zr, Ti-13V-l lCr-3Al, Ti-8Mo-8V-2Fe-3Al, Beta C, Ti-15-3, Ti-4A1 -2.5V -1.5Fe -0.250, Ti-6Al-l.7Fe-0. lSi, Ti-0.3Mo-0.8Ni, Ti-4.5Fe-6.8Mo-l.5Al, Ti-0.05Pd- 0.3Co, and the like).

[0080] In context of deep deoxygenation, hydrogen acts as a temporary destabilizing aid (e g. alloying element) to ensure the removal of oxygen by Mg or Ca until the oxygen content is sufficiently low (i.e. <0.2 wt%). However, the hydrogen content in Ti is a function of temperature. For example, at relatively higher temperatures (>400 °C), Ti contains hydrogen, but it is not uniformly present as a hydride. Rather, hydrogen can dissolve in Ti to some extent without forming hydride, i.e. TiH2 or TiHz-x. Although pressures can be varied, the pressure is typically within about 100% of atmospheric pressure, and in some cases is atmospheric. Examples

[0081] Example: Deoxygenation Step

[0082] An example of the deoxygenation step of the methods described herein is illustrated below. The starting materials in this example can be prepared by electrolytically reducing a titanium oxide material according to the methods described above. In one example, the electrolytic reduction step can produce reduced titanium metal, and the titanium metal can be hydrogenated to form titanium hydride (TiTh) that is then deoxygenated. In another example, the reduced titanium metal can be a Ti-6A1-4V alloy, or reduced titanium can be mixed with aluminum and vanadium in particulate form in appropriate amounts to make a Ti-6A1-4V alloy.

[0083] An amount of 20g TiH2 of particle size 75-109pm was mixed with 4g Mg-Ca alloy powder (82% Mg and 18% Ca), and 5g of a CaCh and NaCl mixture. CaCh and NaCh were mixed with a 3.4: 1.6 weight ratio to make a 5g CaCh-NaCl mixture. The mixture was then taken into a steel crucible and loaded into a tube furnace for deoxygenation. Deoxygenation was carried out at 575°C temperature for 6 hrs. The hydrogen atmosphere was used for the whole deoxygenation process.

[0084] Using the same procedure, a second batch was made with 20g Ti-6A1-4V alloy powder of particle size 109-150pm and deoxygenated under the same conditions.

[0085] After deoxygenation, steel crucibles containing Ti and Ti-6A1-4V powders were removed and soaked in water. The soaked powders were leached separately into two beakers with dilute hydrochloric acid. After leaching, the powders were washed and dried in air.

[0086] After complete drying, the powders were characterized with a Leco ONH analyzer by the Inert gas fusion method (IGF) to determine the oxygen content. The Ti I U powder contains 384±50ppm oxygen, and the (Ti-6A1-4V) H2 contains 295±50ppm oxygen.

[0087] Additional Examples

[0088] The present technology can also include the following enumerated examples:

[0089] 1. A method of producing a deoxygenated titanium product, comprising: reducing a titanium oxide material to form a reduced titanium product using an electrolytic reduction process, wherein the reduced titanium product has an oxygen content greater than about 0.25 wt%; and deoxygenating the reduced titanium product by heating the reduced titanium product to a deoxygenation temperature with a deoxygenation agent in a molten salt under a hydrogen-containing atmosphere to form the deoxygenated titanium product having a reduced residual oxygen content.

[0090] 2. The method of any of examples 1-37, wherein the titanium oxide material comprises titanium dioxide, a titanium dioxide pigment, a titanium dioxide slag, upgraded slag (UGS), chloride slag, sulfate slag, a titanium suboxide, a titanium-bearing mineral, natural rutile, synthetic rutile, ilmenite, or a combination thereof.

[0091] 3. The method of any of examples 1-37, wherein the titanium oxide material has a porosity from about 20% to about 90%.

[0092] 4. The method of any of examples 1-37, wherein the titanium oxide material is porous and has a bimodal pore size distribution.

[0093] 5. The method of any of examples 1-37, wherein the reduced titanium product is a hydrogenated titanium product.

[0094] 6. The method of any of examples 1-37, wherein the reduced titanium product is a particulate.

[0095] 7. The method of any of examples 1-37, wherein the reduced titanium product has a fine powder size of less than about 20 pm.

[0096] 8. The method of any of examples 1-37, wherein the oxygen content in the reduced titanium product is in the form of oxygen dissolved in a solid solution. 9. The method of any of examples 1 -37, wherein the electrolytic reduction process comprises electrolysis of the titanium oxide material as a cathode in a molten salt.

[0097] 10. The method of any of examples 1-37, wherein the titanium oxide material is upgraded synthetic rutile, wherein the electrolytic reduction process comprises carbothermally reducing ilmenite ore to a titanium slag and pig iron, chemically extracting titanium oxide from the titanium slag to produce the upgraded synthetic rutile, wherein the upgraded synthetic rutile is sintered to form the cathode, and wherein the molten salt comprises calcium chloride.

[0098] 11. The method of any of examples 1-37, wherein the electrolytic reduction process comprises applying a voltage between the cathode and a graphite anode in the molten salt.

[0099] 12. The method of any of examples 1-37, wherein the graphite anode comprises an AI2O3 barrier.

[0100] 13. The method of any of examples 1-37, wherein the electrolytic reduction process comprises calciothermic reduction of the titanium oxide material and electrolysis of CaO in a molten calcium chloride to form the reduced titanium product.

[0101] 14. The method of any of examples 1-37, wherein the electrolytic process comprises electrolysis and electrowinning of the titanium oxide material in molten calcium fluoride.

[0102] 15. The method of any of examples 1-37, wherein the deoxygenation agent is a metallic deoxygenation agent comprising at least one of magnesium and calcium.

[0103] 16. The method of any of examples 1 -37, wherein the deoxygenation agent comprises magnesium hydride, metallic magnesium, or a combination thereof.

[0104] 17. The method of any of examples 1-37, wherein the deoxygenation agent comprises calcium hydride, metallic calcium, or a combination thereof. 18. The method of any of examples 1 -37, wherein the molten salt includes a primary salt comprising a magnesium salt or a calcium salt.

[0105] 19. The method of any of examples 1-37, wherein the primary salt comprises MgCh, MgBr2, MgF2, or a combination thereof.

[0106] 20. The method of any of examples 1-37, wherein the primary salt comprises CaCh, CaBr2, CaF2, or a combination thereof.

[0107] 21. The method of any of examples 1-37, wherein the molten salt further includes a secondary salt which is different from the primary salt.

[0108] 22. The method of any of examples 1-37, wherein the reduced residual oxygen content is less than 0.2 wt%.

[0109] 23. The method of any of examples 1-37, wherein the deoxygenation agent is a Mg- Ca alloy having an alloy melting point.

[0110] 24. The method of any of examples 1-37, wherein the alloy melting point is from 448 °C to less than 842 °C.

[0111] 25. The method of any of examples 1-37, wherein the Mg-Ca alloy has a magnesium atomic percentage of 80% to 99%.

[0112] 26. The method of any of examples 1-37, wherein the Mg-Ca alloy has a calcium atomic percentage of 60% to 85%.

[0113] 27. The method of any of examples 1-37, wherein the Mg-Ca alloy is a eutectic alloy.

[0114] 28. The method of any of examples 1-37, wherein the eutectic alloy comprises about 89 at% (83 wt%) Mg and about 11 at% (17 wt%) Ca. 29. The method of any of examples 1-37, wherein the eutectic alloy comprises about 26 at% (18 wt%) Mg and about 74 at% (82 wt%) Ca.

[0115] 30. The method of any of examples 1-37, wherein the molten salt is free of magnesium.

[0116] 31. The method of any of examples 1-37, wherein the molten salt comprises a salt mixture of multiple salts having a salt melting point.

[0117] 32. The method of any of examples 1-37, wherein the salt mixture comprises a calcium halide and a secondary salt as a eutectic salt mixture.

[0118] 33. The method of any of examples 1-37, wherein the salt melting point is from 300 °C to less than 650 °C.

[0119] 34. The method of any of examples 1-37, wherein the salt melting point is less than or equal to the alloy melting point.

[0120] 35. The method of any of examples 1-37, wherein the deoxygenation temperature is above the alloy melting point.

[0121] 36. The method of any of examples 1-37, wherein the deoxygenation temperature is 448 °C to 680 °C.

[0122] 37. The method of any of examples 1-37, wherein the reduced titanium product is heated at the deoxygenation temperature for a deoxygenation time from about 10 minutes to about 24 hours.

[0123] While the flowcharts presented for this technology may imply a specific order of execution, the order of execution may differ from what is illustrated. For example, the order of two more blocks may be rearranged relative to the order shown. Further, two or more blocks shown in succession may be executed in parallel or with partial parallelization. In some configurations, one or more blocks shown in the flow chart may be omitted or skipped.

[0124] Reference was made to the examples illustrated in the drawings and specific language was used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the technology is thereby intended. Alterations and further modifications of the features illustrated herein and additional applications of the examples as illustrated herein are to be considered within the scope of the description.

[0125] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more examples. In the preceding description, numerous specific details were provided, such as examples of various configurations to provide a thorough understanding of examples of the described technology. It will be recognized, however, that the technology may be practiced without one or more of the specific details, or with other methods, components, devices, etc. In other instances, well-known structures or operations are not shown or described in detail to avoid obscuring aspects of the technology.

[0126] Although the subject matter has been described in language specific to structural features and / or operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features and operations described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. Numerous modifications and alternative arrangements may be devised without departing from the spirit and scope of the described technology.

Claims

CL IMSWhat is claimed is:

1. A method of producing a deoxygenated titanium product, comprising: reducing a titanium oxide material to form a reduced titanium product using an electrolytic reduction process, wherein the reduced titanium product has an oxygen content greater than about 0.25 wt%; and deoxygenating the reduced titanium product by heating the reduced titanium product to a deoxygenation temperature with a deoxygenation agent in a molten salt under a hydrogen-containing atmosphere to form the deoxygenated titanium product having a reduced residual oxygen content.

2. The method of claim 1, wherein the titanium oxide material comprises titanium dioxide, a titanium dioxide slag, upgraded slag (UGS), chloride slag, sulfate slag, a titanium suboxide, a titanium-bearing mineral, natural rutile, synthetic rutile, ilmenite, or a combination thereof.

3. The method of claim 1, wherein the titanium oxide material is porous.

4. The method of claim 1, wherein the reduced titanium product is a hydrogenated titanium product.

5. The method of claim 1, wherein the reduced titanium product is a particulate.

6. The method of claim 5, wherein the reduced titanium product has a sponge morphology.

7. The method of claim 1, wherein the oxygen content in the reduced titanium product is in the form of oxygen dissolved in a solid solution.

8. The method of claim 1, wherein the oxygen content in the reduced titanium product is 0.5 wt% to 10 wt%.

9. The method of claim 1, wherein the electrolytic reduction process comprises electrolysis of the titanium oxide material as a cathode in a molten salt.

10. The method of claim 9, wherein the titanium oxide material is upgraded synthetic rutile, wherein the electrolytic reduction process comprises carbothermally reducing ilmenite ore to a titanium slag and pig iron, chemically extracting titanium oxide from the titanium slag to produce the upgraded synthetic rutile, wherein the upgraded synthetic rutile is sintered to form the cathode, and wherein the molten salt comprises calcium chloride.

11. The method of claim 9, wherein the electrolytic reduction process comprises applying a voltage between the cathode and a graphite anode in the molten salt.

12. The method of claim 11, wherein the anode is made of graphite.

13. The method of claim 1, wherein the deoxygenation agent is a metallic deoxygenation agent comprising at least one of magnesium and calcium.

14. The method of claim 13, wherein the deoxygenation agent comprises magnesium hydride, metallic magnesium, or a combination thereof.

15. The method of claim 13, wherein the deoxygenation agent comprises calcium hydride, metallic calcium, or a combination thereof.

16. The method of claim 13, wherein the molten salt includes a primary salt comprising a magnesium salt or a calcium salt.

17. The method of claim 16, wherein the primary salt comprises MgCh, MgBr2, MgF2, or a combination thereof.

18. The method of claim 16, wherein the primary salt comprises CaCh, CaBr2, CaF2, or a combination thereof.

19. The method of claim 16, wherein the molten salt further includes a secondary salt which is different from the primary salt.

20. The method of claim 13, wherein the reduced residual oxygen content is less than 0.2 wt%.

21. The method of claim 13, wherein the reduced residual oxygen content is less than 0.13 wt%.

22. The method of claim 13, wherein the molten salt is free of calcium.

23. The method of claim 22, wherein the molten salt is a magnesium salt and the deoxygenation temperature is 500 °C to 900 °C.

24. The method of claim 1, wherein the deoxygenation agent is a Mg-Ca alloy having an alloy melting point.

25. The method of claim 23, wherein the alloy melting point is from 448 °C to less than 842 °C.

26. The method of claim 23, wherein the Mg-Ca alloy has a magnesium atomic percentage of 80% to 99%.

27. The method of claim 23, wherein the Mg-Ca alloy has a calcium atomic percentage of 60% to 85%.

28. The method of claim 23, wherein the Mg-Ca alloy is a eutectic alloy.

29. The method of claim 27, wherein the eutectic alloy comprises about 89 at% (83 wt%) Mg and about 11 at% (17 wt%) Ca.

30. The method of claim 27, wherein the eutectic alloy comprises about 26 at% (18 wt%) Mg and about 74 at% (82 wt%) Ca.

31. The method of claim 23, wherein the molten salt comprises a salt mixture of multiple salts having a salt melting point.

32. The method of claim 31, wherein the salt mixture comprises a calcium halide and a secondary salt as a eutectic salt mixture.

33. The method of claim 32, wherein the salt melting point is from 300 °C to less than 650 °C.

34. The method of claim 31, wherein the salt melting point is less than or equal to the alloy melting point.

35. The method of claim 23, wherein the deoxygenation temperature is above the alloy melting point.

36. The method of claim 1, wherein the deoxygenation temperature is 448 °C to 680 °C.

37. The method of claim 1, wherein the reduced titanium product is heated at the deoxygenation temperature for a deoxygenation time from about 10 minutes to about 24 hours.

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