Method for producing doped aluminous materials - Patents.com

Abstract

The present invention relates to a method for producing doped aluminous materials, and in particular to a method for producing doped aluminum oxyhydroxide chloride and doped alpha-alumina.

Description

[Technical Field]

[0001] The present disclosure relates to methods for producing doped metal oxides or doped metal oxyhydroxide chlorides, for example, doped alumina or doped aluminum oxyhydroxide chloride. [Background technology]

[0002] Doping a metal oxide involves introducing impurities into the material to change its properties (such as its electrical conductivity or optical properties). Doped metal oxides (including aluminum-based oxides) are widely used as phosphors, pigments, catalysts, and lasing materials.

[0003] Methods for preparing such doped metal oxides are difficult to implement because ensuring uniform, atomic-scale dispersion of the dopant atoms within the metal oxide matrix is ​​a significant challenge. Traditional doping approaches involve physically mixing a slurry containing metal oxide particles (e.g., alumina) with the dopant particles, followed by extensive milling, drying, and calcination of the slurry, or mixing a dopant solution with the metal oxide powder in a series of steps including multiple calcinations. As a result, traditional doping approaches involve multiple process steps that increase the process complexity and energy requirements. Other examples of approaches to doping metal oxides in the literature include the sol-gel process using boehmite (AlOOH) as an alumina source and the precipitation of doped aluminum hydroxide from a solution of nitrates. However, the sol-gel and aluminum hydroxide approaches are costly due to the use of expensive raw materials and the need for significant post-processing operations.

[0004] There is a need for improved methods for forming doped metal oxides (or intermediate materials) that ameliorate or at least overcome some of the problems of the prior art, or at least provide a useful alternative. [Brief explanation of the drawings]

[0005] [Figure 1] 1 illustrates a method for producing a doped alumina-based material according to one embodiment of the present invention. [Figure 2] FIG. 2 illustrates a method for producing a doped alumina-based material according to another embodiment of the present invention. [Figure 3] FIG. 10 illustrates a method for producing a doped alumina-based material according to yet another embodiment of the present invention. [Figure 4] 4A-4C illustrate a method of producing a doped alumina-based material according to a further embodiment of the present invention. [Figure 5] Graph showing Cr-induced luminescence (excitation 525 nm) in doped alumina. [Figure 6] Graph showing Mn-induced luminescence (excitation 525 nm) in doped alumina. DETAILED DESCRIPTION OF THE INVENTION

[0006] According to one embodiment of the present disclosure, there is provided a method for producing a doped material, the method comprising: providing a pregnant liquor comprising a soluble metal or a soluble metal salt; adding one or more dopants to the pregnant liquor to form a doped liquor; A crystallization step of subjecting the dope solution to a crystallization process, the crystallization process comprising: a temperature adjusting step of adjusting the temperature of the dope solution; a crystallization step, comprising sparging gaseous hydrochloric acid into the dope solution to form a slurry of doped metal chloride / hydrated metal chloride / hydrated metal chloride (doped metal chloride / hydrated metal chloride / hydrated metal chloride) crystals; isolating the doped metal chloride / hydrated metal chloride crystals for heating; and a heating step of heating the doped metal chloride / hydrated metal chloride crystals to obtain the doped material.

[0007] In one or all embodiments, the pregnant liquor is pre-prepared and provided to the process. Alternatively, the method may include steps involved in the formation of the pregnant liquor.

[0008] Depending on the temperature in the heating step, the resulting doped material may be dried, heated, decomposed, and / or calcined. If the doped material is dried without calcination, the doped material may be an oxyhydroxide chloride. If the doped material is also calcined, the product may be a doped metal oxide.

[0009] In one or all embodiments, the metal in the feedstock material is aluminum. Thus, if the doped material is dried without being calcined, the doped material can be aluminum oxyhydroxide chloride. If the doped material is also calcined, the product can be doped alumina.

[0010] The present doping method is made possible by the manner in which the present alumina (or oxyhydroxide chloride intermediate) is formed. Its significance lies in the doping via a different chemical process, which avoids traditional doping routes that involve costly post-processing steps. This method involves incorporating the dopant directly during the crystallization of the material and before conversion to alumina. This is believed to avoid the high-energy mixing and calcination steps of traditional doping processes. In situ doping also has the advantage of providing greater control over the wettability, particle size, chemical stability, porosity, and surface charge of the doped alumina. In embodiments, this results in safer, higher-performance materials. In one or all embodiments, the doped material can be used as a separator for batteries. The doped material formed by the present process can also find use in phosphors, pigments, catalysts, thermochromic sensors, and lasing materials. There may be other, as yet unknown, applications to which the doped material can be applied. It can be understood that the uses of doped alumina can vary depending on the type and concentration of dopant in the alumina lattice.

[0011] Advantageously, doped materials may have improved material properties such as porosity (e.g., due to improved ion transport, wettability), and improved process economics (e.g., reduced energy requirements for material phase transformation). With respect to aluminum as an example, without wishing to be bound by theory, it is believed that dopants may distort the α-alumina lattice, and this distortion may result in the above properties compared to undoped alumina.

[0012] In one or all embodiments, the process can begin by dissolving a feed material, which can be one or more metals (optionally in salt form), in a solvent to form a pregnant liquor.

[0013] In one embodiment, the pregnant liquor is provided to the process with the feedstock material already solubilized therein. The pregnant liquor may be formed by a third party, and then a different party may perform the doping process described herein. Notably, the method for forming the pregnant liquor is not limited, and any means for obtaining the pregnant liquor is within scope. For illustrative purposes only, the following provide some examples of how the pregnant liquor may be formed.

[0014] Suitable feedstock materials are those that contain the metal of interest (such as aluminum) and exist as a compound that is soluble in the solvent used (such as HCl). When metal salts are used as feedstock materials, the soluble metal salts may be industrial reagent grade, laboratory reagent grade, guaranteed reagent grade, or analytical reagent grade, or may be produced from various feedstocks. The soluble metal salts may be in any suitable form. For example, the soluble metal salts may be in granular or solid form. For example, the soluble metal salts may include crystals or crystalline powders. There may be one salt, or more than one soluble metal salt. One or more of the metal salts may be metal chlorides. In one embodiment, the soluble metal salt is a metal chloride. The metal chloride may be aluminum chloride hexahydrate (ACH).

[0015] The feedstock material may be an aluminum-containing feedstock. In some embodiments, the aluminum-containing feedstock may be a source of alumina, aluminum hydroxide, metallic aluminum, aluminum chloride hexahydrate, red mud, fly ash, aluminosilicates, kaolin, zeolites, feldspar, etc. The metallic aluminum may be in the form of aluminum foil.

[0016] In one or all embodiments, the aluminium-containing feedstock may be roasted if the feedstock requires it, in which case it will be understood that the aluminium-containing feedstock may have been subjected to a heating process to reduce impurities or to thermally dehydroxylate the aluminium-containing feedstock prior to dissolution in the solvent to form the pregnant liquor.

[0017] Any suitable solvent may be used to solubilize the feedstock and prepare the pregnant liquor. The solvent is sufficient to solubilize the selected feedstock material in solution. For example, the solvent may be an aqueous solution (e.g., water or an acidic solution), an alcohol (e.g., ethanol), or an organic solvent (e.g., glycerol (reactive), chloroform, carbon tetrachloride, ether, benzene, or other hydrocarbon solvents). In some embodiments, the solvent may be ultrapure water, demineralized water, or the like.

[0018] In one or all embodiments, the solvent may be sufficient to leach metals, such as aluminum, from the feedstock. For example, the solvent may be a strong acid, such as hydrochloric acid, sulfuric acid, or nitric acid. The acid solvent may be of any suitable concentration. Generally, the concentration of the acid solvent may be sufficient to solubilize the feedstock material.

[0019] In addition to the requirement that the solvent be sufficient to solubilize the feedstock material, the solvent must also be one in which HCl is soluble. As may be apparent from the teachings herein, one of the process steps includes a sparging step with HCl. Therefore, the solvent must be one in which HCl is soluble so that the sparging is successful. Furthermore, the metals / dopants used in the process must also be soluble in the selected solvent. Those skilled in the art may use their background knowledge or by trial and error to determine an appropriate solvent to arrive at a pregnant liquor as described herein.

[0020] The feedstock may be added to the solvent in a stirred reaction vessel, hi some embodiments, the reaction vessel is heated when the feedstock is added to the solvent. In one or all embodiments, the aluminum-containing feedstock may be kaolin, in which case the kaolin may be roasted to form metakaolin and then leached with hydrochloric acid. In one or all embodiments, the aluminum-containing feedstock may be mining tailings or aluminum-containing waste material, which may be leached using hydrochloric acid to extract the aluminum.

[0021] In one or all embodiments, the aluminum-containing feedstock is aluminum chloride hexahydrate (ACH) dissolved in the solvent hydrochloric acid. The pregnant liquor comprises the feedstock material in a solvent. The pregnant liquor can have a cation concentration that is near saturation. The solution can be at or just below the saturation level. In one embodiment, the solution is between about 60% and about 100% saturated. A near-saturated metal / dopant solution means that successful crystallization is more likely when HCl gas is added during sparging.

[0022] As the solution approaches saturation, the pregnant liquor should be free of any undissolved matter. In one or all embodiments, if undissolved matter is present, the pregnant liquor can be treated to remove it. Treatment to remove undissolved matter can be referred to as "polishing." Any suitable technique known in the art may be used to polish or clarify the pregnant liquor. For example, a polishing step may be sufficient to remove or reduce suspended solids, such as fine precipitates, insoluble matter, etc. In some embodiments, the pregnant liquor may be polished or clarified using a filtration process and / or a flocculant.

[0023] When the feedstock material is aluminum in the form of aluminum chloride hexahydrate (ACH), a solution of any suitable aluminum concentration may be formed by dissolving the metal chloride hexahydrate in a solvent. For example, the solution may have a cation concentration of between about 30 g / L and about 80 g / L, between about 35 g / L and about 75 g / L, between about 40 g / L and about 70 g / L, or between about 45 g / L and about 65 g / L. The solution may have a cation concentration of about 60 g / L. 60 g / L is an example for aluminum, where saturation may be about 90 g / L. It should be understood that g / L values ​​may vary for other metal starting materials. The g / L values ​​may also vary depending on the solvent.

[0024] If the solution is not sufficiently concentrated, a concentration step can be carried out. The pregnant liquor may be concentrated using any suitable technique known in the art. When ACH is the starting material, the concentration technique will generally be sufficient to increase the aluminum in the pregnant liquor to its saturation point without precipitating the aluminum as aluminum chloride hexahydrate crystals. For example, the pregnant liquor may be concentrated by heating it to its boiling point, or by evaporation by heating the pregnant liquor below its boiling point. The concentrated pregnant liquor may be subjected to a polishing step to remove insoluble contaminants such as silica or other precipitates.

[0025] According to one or all embodiments, the pregnant liquor containing ACH and HCl may be concentrated to its saturation point by evaporation. The pregnant liquor containing ACH and HCl may be concentrated by boiling the pregnant liquor at a temperature between about 75°C and about 130°C, between about 85°C and about 120°C, for example, between about 95°C and about 110°C. In one or all embodiments, the pregnant liquor may be concentrated by boiling the pregnant liquor at a temperature between about 95°C and about 110°C. In some embodiments, the pregnant liquor may be concentrated to an aluminum concentration of about 60,000 ppm. These temperature ranges may vary if other metal feedstocks are dissolved in other solvents. However, based on this teaching, one skilled in the art may be able to generalize the method to form a pregnant liquor of a desired concentration.

[0026] Advantageously, by concentrating the pregnant liquor, the consumption of hydrogen chloride gas per unit mass of crystals precipitated during crystallization can be reduced. Furthermore, for the same given gas flow rate, the seed nucleation stage may be reduced relative to the growth stage, thereby reducing the overall uptake of impurities from the liquor that may be more easily captured during nucleation.

[0027] It should also be noted here that the cation concentration of the pregnant liquor relative to the metal may vary depending on the concentration of dopant added, as outlined below. If a high concentration of dopant is added, it may be necessary to reduce the concentration of the metal to keep everything in solution. The way to find the limit is whether there is any undissolved material after mixing all the components together.

[0028] One or more dopants may be added to the pregnant liquor to provide a doped liquor. The step of adding one or more dopants may occur before, simultaneously with, or consecutively after the step of dissolving a soluble metal / metal salt in a solvent to provide the desired liquor composition before crystallization.

[0029] In one or all embodiments, the dopant is provided with the feed material. In one or all embodiments, the dopant is provided in the pregnant liquor. The dopant may be added to the solubilized feed material in a stirred reaction vessel. The dopant can be added gradually. The reaction vessel may be heated when the dopant is added to aid in solubilizing the dopant metal salt.

[0030] When a material is doped, dopant atoms are intentionally introduced into the crystal lattice of the original compound. A crystal lattice is a regular and repeating three-dimensional arrangement of atoms in a solid material. In semiconductor doping, dopant atoms replace some of the host atoms in the lattice structure. The dopant atoms may have a different number of valence electrons compared to the host atoms, and this mismatch results in a change in the electrical properties of the material.

[0031] Typically, one or more dopants may comprise a metal compound soluble in a given solvent. For example, the dopants may comprise an alkali metal compound, an alkaline earth metal compound, a transition metal compound, or a rare earth metal compound. In some embodiments, the one or more dopants may comprise a transition metal compound or a rare earth metal, such as a lanthanide compound.

[0032] For the process to work, the dopant must be soluble in the dopant / metal mixture solution. Furthermore, the dopant must remain in the doped metal oxide material after heat treatment. Dopants that are volatile under the selected heating conditions may not be suitable. Suitable dopants can be incorporated into the host metal material. The dopant must not form a secondary crystalline phase in the resulting material that is detectable by techniques such as XRD. Regarding the last point, it is possible that small regions of concentrated dopant can be detected by certain techniques, which may be interpreted as a secondary phase at the micro / nanoscale. However, as long as there is a substantially uniform doped metal oxide material detected by techniques such as XRD, the doping is considered successful.

[0033] The dopant may be provided as a metal salt. In embodiments in which the dopant is a metal salt, the metal salt may be a soluble metal salt. For example, the dopant is soluble in the solvent used to dissolve the feedstock material. One or more dopants may be a metal chloride. By way of example only, the metal chloride may be one or more of the following salts: La, Mg, Ce, Co, Cr, Ni, Fe, or Cu.

[0034] Advantageously, metal chloride dopants are compatible with processes for preparing mixed metal oxide materials, such as dissolving aluminum chloride hexahydrate in aqueous solution and crystallizing by sparging with gaseous hydrochloric acid. Furthermore, it is believed that the use of metal chloride salts as dopants provides improved control over dopant incorporation into the final doped metal chloride intermediate product by preventing speciation in solution, which can occur with other metal salts, thereby minimizing impurities remaining after calcination. Furthermore, metal chlorides release hydrochloric acid gas during processing of the oxide material, which can be captured and reused.

[0035] The concentration of the doping solution can vary depending on many factors, including the concentration of the feedstock materials and the solvent system. Depending on the dopant selected, the dopant concentration per volume of solution can be between about 10 mg / L and about 40,000 mg / L, between about 25 mg / L and about 7,500 mg / L, between about 50 mg / L and about 5,000 mg / L, between about 75 mg / L and about 2,500 mg / L, or between about 100 mg / L and about 2,000 mg / L, e.g., between about 100 mg / L and about 1,000 mg / L. In one or all embodiments, the dopant concentration can be outside these ranges if needed to obtain a suitable end product.

[0036] Once doped, the dope solution is subjected to a crystallization process. Generally, any suitable crystallization process sufficient to precipitate the doped crystals while minimizing the precipitation of impurities may be used. Typically, the crystallization process may include adjusting the temperature of the dope solution and sparging gaseous hydrochloric acid through the dope solution to form a slurry of doped metal chloride / hydrated metal chloride crystals, as described below.

[0037] The crystallization process involves adjusting the temperature of the dope (up or down) and sparging gaseous hydrochloric acid into the saturated dope to induce crystallization and form a crystalline slurry.

[0038] The dope may be adjusted to any suitable temperature during crystallization, typically in a heated or cooled reaction vessel, for example, the dope may be cooled to control the rate of dopant incorporation into the crystallized product.

[0039] Higher temperatures are believed to suppress nucleation and maximize the crystal growth phase. However, if a dopant is intended to be included, the aim is to promote nucleation and shorten the crystal growth phase. This can be done by lowering the temperature of the dopant solution. When aluminum is the metal chosen as the doped host material, this cooling method works well because the solubility of aluminum chloride remains reasonably stable with temperature. The solution can be cooled before aeration without risk of crystallization. However, this may not be universally true, so temperature adjustments must be made carefully to avoid precipitation before aeration begins.

[0040] For ACH, the adjusted temperature range can be from about −10° C. to about 40° C. or less. However, the temperature range is actually determined by the following factors: (i) the solution must remain liquid before aeration, and (ii) the metal and dopant must remain soluble and not crystallize due to the low temperature.

[0041] The doped solution may be cooled using any suitable technique. For example, the solution may be actively cooled, such as by refrigeration. Alternatively, the solution may be cooled by removing the heat source and allowing the solution to cool to ambient temperature over a period of time. Advantageously, cooling the solution also improves hydrogen chloride recovery.

[0042] The solution may be stirred during cooling. It is envisaged that, in use, stirring the solution during cooling helps to avoid the formation of agglomerates and aids in the formation of smaller particles.

[0043] The cooled dope solution is sparged with gaseous hydrochloric acid. Generally, sparging the dope solution may be sufficient to form a slurry of doped metal crystals. Any suitable type of gaseous hydrochloric acid may be used for sparging. For example, the gaseous hydrochloric acid may be purified.

[0044] Gaseous hydrochloric acid may be sparged into the doped solution until the saturated solution reaches a suitable hydrochloric acid concentration for crystallization of the doped metal chloride product. The endpoint may be flexible depending on the desired results. Generally, sparging is carried out until HCl approaches saturation in the solution. However, in some cases, there may be some benefit in stopping crystallization prematurely, as this may favor the nucleation stage versus the crystal growth stage. Sparging can be stopped any time after visible crystals form.

[0045] The precipitated crystal slurry may be separated using any suitable technique known in the art. For example, the separation technique may be sufficient to separate the precipitate from the waste liquid. For example, separation techniques may include gravity settling clarifiers, sedimentation, decantation, centrifugation, filtration, etc.

[0046] The precipitate may be washed to separate the doped crystals from impurities in the precipitate. The precipitate may be washed with any suitable washing solution. Generally, the washing solution may be sufficient to redissolve soluble contaminants from the doped crystals, etc. The washing solution may be sufficient to displace entrained contaminated supernatant and replace it with less contaminated washing solution.

[0047] In some embodiments, the cleaning solution may be hydrochloric acid, aluminum chloride hexahydrate in hydrochloric acid solution, or waste liquid. In one or all embodiments, the method comprises: (a) drying the doped metal chloride / hydrated metal chloride crystals, optionally under at least partial vacuum; (b) heating the dried doped metal chloride / hydrated metal chloride crystals, optionally under controlled air flow; (c) decomposing the heated doped metal chloride / hydrated metal chloride crystals; In that case, the one or more pyrolysis steps are carried out after the step of separating the doped metal chloride / hydrated metal chloride crystals from the waste liquor and before the step of calcining the doped metal chloride / hydrated metal chloride crystals.

[0048] In the method, the following steps may be present: drying the doped metal chloride / hydrated metal chloride crystals, optionally under at least partial vacuum; Heating the doped metal chloride hexahydrate crystals, optionally under controlled air flow, and then calcining the doped metal chloride / hydrated metal chloride crystals to obtain the doped metal oxide.

[0049] The step of drying the doped metal chloride / hydrated metal chloride crystals can, in one or all embodiments, be carried out under at least a partial vacuum after separating the doped metal chloride / hydrated metal chloride crystals from the waste liquid and before heating the doped metal chloride / hydrated metal chloride crystals under a controlled air flow.

[0050] Typically, the doped metal chloride / hydrated metal chloride crystals may be dried under partial vacuum to facilitate evaporation of the liquid by lowering the boiling point of the liquid. The doped metal chloride / hydrated metal chloride crystals may be dried at any temperature that removes the solvent, in one or all embodiments, the temperature ranges from about 50° C. and about 150° C., or between about 60° C. and about 140° C., for example, between about 80° C. and about 130° C.

[0051] In one or all embodiments, the doped metal chloride / hydrated metal chloride crystals contain residual chloride at a level of about 30% to about 45% by weight of the doped metal chloride / hydrated metal chloride crystals after the drying step.

[0052] In one or all embodiments, the doped metal chloride / hydrated metal chloride crystals are substantially free of residual moisture. It is envisioned that in use, a low temperature heating step of the doped metal chloride / hydrated metal chloride crystals under at least a partial vacuum may serve to reduce entrained liquid (including water) within the crystals to produce stabilized, dehydrated doped metal chloride / hydrated metal chloride crystals.

[0053] Advantageously, a low temperature drying step under partial vacuum to reduce entrained liquid before the crystals are dried at higher temperatures can improve the energy efficiency of the drying stage compared to drying at higher temperatures alone.

[0054] The doped metal chloride / hydrated metal chloride crystals may be dried using any suitable technique known in the art. The drying step may be carried out with or without a vacuum. For example, a microwave dryer, a vacuum dryer, a microwave-assisted vacuum dryer, or any other suitable indirect drying technique under vacuum may be used.

[0055] The method comprises: The method may further comprise the step of heating the doped metal chloride / hydrated metal chloride crystals under a controlled air flow and then calcining the doped metal chloride / hydrated metal chloride crystals to obtain the doped metal oxide.

[0056] The step of heating the doped metal chloride / hydrated metal chloride crystals under a controlled air flow may be carried out after the step of separating the doped metal chloride / hydrated metal chloride crystals from the waste liquor and before the step of calcining the doped metal chloride hexahydrate crystals.

[0057] Doped metal oxyhydroxide chlorides are produced by heating doped metal chloride hexahydrate crystals under a controlled air flow. The term "metal oxyhydroxide chloride" refers to an intermediate product in the formation of metal oxides formed by heating metal chloride / hydrated metal chloride crystals at low temperatures. Metal oxyhydroxide chlorides typically comprise a mixture of metal oxychloride species with low free chloride concentrations, which are generally dry, chemically stable, and have good flow properties.

[0058] When ACH is used as the starting material, the doped aluminum chloride crystals may be heated under controlled airflow conditions using any suitable technique to dry the doped aluminum chloride and produce doped aluminum oxyhydroxide chloride. For example, the dried doped metal chloride / hydrated metal chloride crystals may be heated in a forced air oven, a flash dryer, or a fluidized bed dryer. Suitably, air is directed toward the container under controlled airflow conditions to contact the doped metal chloride / hydrated metal chloride crystals and aid in the removal of water and hydrochloric acid vapor from the container.

[0059] The dried doped metal chloride / hydrated metal chloride crystals may be heated in a heated container under a flow of heated and / or dry air. Typically, the doped metal chloride / hydrated metal chloride crystals may be gradually heated to the hold temperature, typically using a heating rate (rate of temperature change over time) that reaches the hold temperature as quickly as possible. As used herein, the term "hold temperature" may refer to a substantially constant temperature or temperature range to which a material is heated and held during a process step. Any suitable hold temperature may be used. For example, for crystals, the hold temperature may be between about 150°C and about 300°C, between about 160°C and about 280°C, or between about 170°C and about 250°C, e.g., between about 180°C and about 230°C. Similarly, any suitable heating rate may be used to reach the hold temperature. For example, the heating rate may be about 10°C / min, about 20°C / min, about 30°C / min, about 40°C / min, about 50°C / min, about 75°C / min, about 100°C / min, or greater. The doped metal chloride / hydrated metal chloride crystals may be heated at the holding temperature for any suitable period of time. For example, the crystals may be heated at the holding temperature for about 30 minutes or more, 60 minutes or more, about 90 minutes or more, about 120 minutes or more, about 150 minutes or more, about 180 minutes or more, about 210 minutes or more, about 240 minutes or more, about 270 minutes or more, about 300 minutes or more, about 330 minutes or more, or in some cases, about 360 minutes or more. The doped metal chloride / hydrated metal chloride crystals may be stirred while heating under controlled airflow conditions.

[0060] It is contemplated that, in use, agitating the crystals while heating can help break up any agglomerates that have formed and reduce the particle size of the crystals. Additionally, heating the doped metal chloride / hydrated metal chloride crystals under controlled airflow conditions can help deagglomerate and / or reduce the particle size of the crystals through the introduction of high velocity air into the vessel. In other embodiments, the doped metal chloride / hydrated metal chloride crystals may undergo a particle size reduction process before, during, or after the heating step under controlled airflow conditions.

[0061] The method comprises: The method may further comprise the step of decomposing the doped metal chloride / hydrated metal chloride crystals before the crystals are calcined.

[0062] For example, if the doped material is alumina (such as doped γ-alumina and doped amorphous alumina before being calcined at high temperature to obtain primarily doped α-alumina), the doped metal chloride / hydrated metal chloride crystals may be decomposed at high temperature in a rotary kiln or fluidized bed to cause a phase transformation.

[0063] Typically, the decomposition temperature may be sufficient to remove most of the residual chlorides. For example, the decomposition temperature may be between about 600°C and about 1,800°C (such as between about 700°C and about 1,400°C, or between about 800°C and about 1,000°C).

[0064] When ACH is the starting material and doped alumina oxide is the desired product, the doped metal chloride / hydrated metal chloride crystals may be heated at a decomposition temperature of about 800° C. The crystals may be heated at a holding temperature for about 30 minutes or more, 60 minutes or more, about 90 minutes or more, about 120 minutes or more, about 150 minutes or more, about 180 minutes or more, about 210 minutes or more, about 240 minutes or more, about 270 minutes or more, about 300 minutes or more, about 330 minutes or more, about 360 minutes or more, or more. These times and temperatures may vary depending on the metal and dopant.

[0065] In some embodiments, the decomposition step may include controlling the humidity in the container, which is contemplated as helping to facilitate chloride removal prior to calcination.

[0066] In some embodiments, the doped metal oxide formed by the decomposition process contains a residual chloride level of less than about 1.5% by weight of the doped metal oxide, e.g., less than about 1.0% by weight, e.g., less than about 0.4% by weight. Advantageously, reducing the residual chloride level of the doped metal oxide reduces a potential source of corrosion in the vessel during calcination. As a result, this allows for a wider selection of materials to be used in the construction of the vessel, kiln, calciner, etc., in which the pyrolysis occurs.

[0067] Furthermore, by dividing the decomposition process into a lower temperature heating step and a higher temperature decomposition stage, the process is effectively divided over two pieces of equipment that can each be designed for a narrower range of operating conditions, thereby reducing the stress on each piece of equipment and potential equipment failure.

[0068] The doped metal chloride / hydrated metal chloride crystals can be heated through several steps as described and then calcined at temperatures between about 800°C and about 1,750°C to obtain the doped metal oxide material.

[0069] After calcination, the doped metal oxide may contain about 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, 95% or more, 99% or more of the metal from the feedstock material, with the remainder being doped metal atoms.

[0070] The doped metal chloride / hydrated metal chloride crystals may be heated at any temperature and for any length of time that results in calcination of the material. The term "calcining" refers to a high-temperature heating process in which mineral inclusions are converted to their oxide form. This is also commonly referred to as ignition, heating, decomposition, pyrolysis, or hydro-pyrolysis. By way of example only, the calcination temperature may be between about 800°C and about 1,350°C, or between about 950°C and about 1,300°C (such as between about 1,100°C and about 1,250°C). Heating may be carried out for any suitable period of time. For example, the crystals may be heated for about 30 minutes or more, 60 minutes or more, 90 minutes or more, 120 minutes or more, 150 minutes or more, 180 minutes or more, 210 minutes or more, 240 minutes or more, or longer.

[0071] The calcined doped metal oxide comprises a final oxide phase of the metal and one or more dopants, which may comprise from about 1 mg / kg to about 1,000 mg / kg, 10,000 mg / kg, or 20,000 mg / kg of the metal oxide.

[0072] Any of the features described herein may be combined in any combination with any one or more of the other features described herein within the scope of the present invention.

[0073]

[0013] Exemplary features, embodiments, and variations of the present invention can be discerned from the following detailed description of the invention, which provides sufficient information for those skilled in the art to practice the invention. The detailed description of the invention should not be construed as limiting the scope of the foregoing summary of the invention in any way. The detailed description of the invention may refer to several drawings.

[0074] A method (100) for producing a doped alumina-based material is described in detail below, as shown in Figure 1. The doped alumina-based material comprises doped alumina. In step 10, aluminum chloride hexahydrate (ACH) is dissolved in a solvent to provide a liquor. In this embodiment, the solvent comprises a 10% hydrochloric acid solution. The resulting liquor has an aluminum concentration of approximately 60 g / L.

[0075] In step 20, one or more dopants are added to the solution to form a doped solution. The one or more dopants are transition metal chlorides. The doped solution contains between about 100 mg and about 1,000 mg of the one or more dopants per liter of solution.

[0076] In step 30, the dope solution is subjected to a crystallization process. The crystallization process includes adjusting the temperature of the dope solution. The temperature of the dope solution is adjusted to a range of about 0°C to about 20°C. Gaseous hydrochloric acid is sparged into the dope solution to form a slurry of doped aluminum chloride crystals. The sparging can be during or after the temperature change. Gaseous hydrochloric acid is sparged into the dope solution to reach a concentration of hydrochloric acid of between about 30% and about 35% to precipitate at least some, and preferably all, of the doped aluminum chloride crystals.

[0077] In step 40, the slurry of doped aluminum chloride crystals formed as a precipitate is separated to provide doped aluminum chloride crystals and waste liquor. In this embodiment, the doped aluminum chloride crystals are separated from the waste liquor using vacuum filtration. The crystals are washed with either a hydrochloric acid solution or an aluminum chloride hexahydrate-hydrochloric acid solution.

[0078] In step 50, the doped aluminum chloride hexahydrate crystals are calcined at a temperature between about 1100° C. and about 1250° C. to obtain a doped aluminous material, preferably primarily doped alpha-alumina.

[0079] Referring now to Figure 2, another method (200) for producing a doped alumina-based material will now be described in detail. In this embodiment, the doped alumina-based material comprises doped alumina. However, the method (200) shown in Figure 2 and described herein is the same as the method (100) shown in Figure 1 and described herein, except that the doped alumina-based material is subjected to an additional processing step 60.

[0080] Steps 10, 20, 30, 40, and 50 of the process shown in Figure 2 correspond to steps 10, 20, 30, 40, and 50 of the process shown in Figure 1. In step 60, the doped aluminum chloride crystals are decomposed at a temperature between about 800°C and about 1000°C, and then the doped aluminum chloride crystals are calcined at a temperature between about 1100°C and about 1250°C to obtain primarily doped α-alumina. The decomposition of the doped aluminum chloride crystals results in the formation of primarily amorphous alumina.

[0081] Referring now to Figure 3, another method (300) for producing a doped alumina-based material will now be described in detail. In this embodiment, the doped alumina-based material comprises doped α-alumina. The method (300) shown in Figure 3 and described herein is also the same as the method shown in Figure 2 and described herein, except that the doped alumina-based material is subjected to additional processing steps 70 and 80.

[0082] Steps 10, 20, 30, 40, 50, and 60 of the process shown in Figure 3 correspond to steps 10, 20, 30, 40, 50, and 60 of the process shown in Figure 2. After separation step 50, a drying step 70 is used, followed by a heating step 80. In step 70, the doped aluminum chloride crystals are dried under at least a partial vacuum. The doped aluminum chloride crystals are dried at a temperature between about 80°C and 130°C under at least a partial vacuum.

[0083] After the doped aluminum chloride crystals are dried under at least a partial vacuum, a heating step 80 is employed. In step 80, the doped aluminum chloride crystals are heated under a controlled air flow at a temperature between about 180°C and about 230°C. The doped aluminum chloride crystals are stirred while heating under controlled air flow conditions. It is believed that the low-temperature heating step of the doped aluminum chloride crystals, which may be performed under at least a partial vacuum, may help reduce entrained liquid (including water) within the crystals to produce stabilized, dehydrated doped aluminum chloride. The stabilized, dehydrated doped aluminum chloride is then dried to obtain an intermediate product in the form of doped aluminum oxyhydroxychlorides.

[0084] Referring now to Figure 4, another method (400) for producing a doped alumina-based material will now be described in detail. In this embodiment, the doped alumina-based material comprises doped aluminum oxyhydrochlorides. Also, the method (400) shown in Figure 4 and described herein is fully encompassed within the method (300) shown in Figure 3.

[0085] Steps 10, 20, 30, and 40 of the method (400) shown in Figure 4 correspond to steps 10, 20, 30, and 40 of the method shown in Figure 1. Steps 70 and 80 of the method (400) shown in Figure 4 correspond to steps 70 and 80 of the method (300) shown in Figure 3. The final product of Figure 4 is aluminum oxyhydroxide chloride, which is the intermediate product of Figure 3.

[0086] Example The following examples of embodiments of the present invention are illustrative only and are not intended to be limiting.

[0087] Cr-doped alumina: A noble solution containing 60 g / L Al and 0.5 g / L Cr was prepared from commercially available AlCl3·6H2O and CrCl3·6H2O. The doped aluminum chloride was crystallized by sparging with HCl gas at 0°C until saturated with HCl (30%-32% HCl). The doped aluminum chloride was decomposed in air at 800°C for 2 hours and then calcined at 1250°C.

[0088] The resulting alumina had a Cr concentration of 950 mg / kg and exhibited novel properties including narrowband red fluorescence at 693 nm and 694 nm, as well as expansion of the alumina crystal lattice. Fe-doped alumina: A pregnant solution containing 60 g / L Al and 0.35 g / L Fe was prepared from commercially available AlCl3·6H2O and FeCl3·6H2O. The doped aluminum chloride was crystallized by sparging with HCl gas at 0°C until saturated with HCl (30%-32% HCl). The doped aluminum chloride was decomposed in air at 800°C for 2 hours and then calcined at 1250°C.

[0089] The resulting alumina had an Fe concentration of 530 mg / kg and exhibited novel properties, including a reduction in the band gap to 4.4 eV compared to 8.8 eV for pure alumina. Mn-doped alumina: A pregnant solution containing 55 g / L Al and 0.7 g / L Mn was prepared from commercially available AlCl3·6H2O and MnCl2·4H2O. The doped aluminum chloride was crystallized by sparging with HCl gas at 0 °C until saturated with HCl (30%-32% HCl).

[0090] The doped aluminum chloride was decomposed in air at 800°C for 2 hours and then calcined at 1250°C. The resulting alumina had a Mn concentration of 240 mg / kg and exhibited novel properties, including emission at 678 nm.

[0091] Where any prior art publication is referred to herein, it should be understood that such reference does not constitute an acknowledgement that the publication forms part of the common general knowledge in the art in Australia or any other country.

[0092] Any promises made in this description are understood to relate to some embodiments of the invention and are not intended to be promises made about the invention as a whole. If there are promises that are believed to apply to all embodiments of the invention, the applicant / patentee reserves the right to subsequently remove them from the description and will not rely on these promises for the acceptance or subsequent grant of a patent in any country.

[0093] In this specification and claims (where present), the term "comprising" and its derivatives (including "comprises" and "comprise") includes each of the listed elements while not excluding the inclusion of one or more additional elements.

[0094] As used herein, the term "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with that embodiment is included in one or more embodiments. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

[0095] In accordance with the statute, the invention has been described in language specific to certain structural or methodological features. Since the means described herein include preferred modes of carrying out the invention, it is to be understood that the invention is not limited to the specific features shown or described. The invention is therefore claimed in any of its forms or modified forms within the proper scope of the appended claims (if any) as appropriately interpreted by those skilled in the art.

Claims

1. 1. A method for producing a doped material, comprising: providing a pregnant liquor comprising a soluble metal or a soluble metal salt; adding one or more dopants to the pregnant liquor to form a doped liquor; A crystallization step of subjecting the dope solution to a crystallization process, the crystallization process comprising: a temperature adjusting step of adjusting the temperature of the dope solution; a crystallization step comprising sparging gaseous hydrochloric acid into the dope solution to form a slurry of doped metal chloride / hydrated metal chloride / hydrated metal chloride crystals; a temperature increasing step of increasing the temperature of the doped metal chloride / hydrated metal chloride crystals to obtain the doped material.

2. 10. The method of claim 1, wherein the soluble metal or soluble metal salt is aluminum or an aluminum salt.

3. 3. The method of claim 2, wherein the soluble metal or soluble metal salt is aluminum chloride hexahydrate.

4. 4. The method of claim 1, wherein the step of preparing the pregnant liquor comprises dissolving a soluble metal or a soluble metal salt as a feedstock in a solvent.

5. The method according to any one of claims 1 to 4, wherein the dopant is selected from alkali metal compounds, alkaline earth metal compounds, transition metal compounds, or rare earth metal compounds such as lanthanide compounds.

6. The method of claim 5 wherein the dopant is chloride.

7. The method according to any one of claims 1 to 6, wherein the temperature adjustment step includes a step of cooling the dope solution.

8. The temperature increasing step includes: A method according to any one of claims 1 to 7, wherein the doped metal chloride / hydrated metal chloride crystals are dried under at least partial vacuum.

9. The temperature increasing step includes:

9. The method of claim 8, comprising heating the dried doped metal chloride / hydrated metal chloride crystals under a controlled air flow to form a doped metal oxyhydroxide chloride compound.

10. The temperature increasing step includes:

10. The method of claim 9, including the step of calcining the decomposed doped metal chloride / hydrated metal chloride crystals to form a doped metal oxide.

11. The method of claim 10, wherein the metal oxide is an alumina oxide.

12. 10. A doped metal oxyhydroxide chloride compound formed by the method of claim 9.

13. 10. A doped metal oxide compound formed by the method of claim 9.

14. 14. A product comprising a material made from or using the doped metal oxyhydroxide chloride or doped metal oxide of claim 12 or 13.

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