WO2015080780A2

WO2015080780A2 - Metal oxide nanopowders as alternate precursor source to nitrates

Info

Publication number: WO2015080780A2
Application number: PCT/US2014/055000
Authority: WO
Inventors: Kamal Hadidi; Makhlouf Redjdal
Original assignee: Amastan Technologies Llc
Priority date: 2013-09-10
Filing date: 2014-09-10
Publication date: 2015-06-04
Also published as: WO2015080780A3

Abstract

This invention applies to thermal spray coating and powder manufacturing of materials where non-nitrate precursors are required to obtain the desired coating and/or powder characteristics. In general, the most economical path in material synthesis involves the use of readily available metal sources consisting of nitrates or acetates. Some metallic sources exist only in nitrate form and do not have a liquid solvent soluble acetate form. Using this metal nitrate in a pyrolysis process produces fluffy powders that lead to porous and poor coatings, or fluffy powders that do not have the proper flowability. In this disclosure, the metal or metal oxide that offer only nitrate based precursor is replaced with a nanopowder of the metal or metal oxide as the feedstock source. The nanopowder is homogeneously dispersed as a suspension and mixed with the other solvent based solution precursors of the accompanying solutes to produce the desired composite metal oxide.

Description

METAL OXIDE NANOPOWDERS AS ALTERNATE

PRECURSOR SOURCE TO NITRATES

Related Applications

[0001] This application claims the benefit of and priority to U.S. Provisional Application No. 61/875,840, entitled "Metal or Metal Oxide Nanopowders as an Alternate Precursor Source to Nitrates or Acetates Sources of Metal or Metal Oxide for Thermal Spray Coating and Powder Synthesis" and having a filing date September 10, 2013, which is incorporated herein by reference in its entirety.

Statement Regarding Federally Sponsored Research & Development

[0002] The invention(s) contained in the present disclosure were made with government support under Grant No. W911-W6-13-C-0028, awarded by the Department of Defense Aviation Applied Technology Directorate, Fort Eustis VA 23604-5577. The government has certain rights in the invention(s).

Field of the Technology

[0003] The present disclosure relates to precursor compositions and methods of manufacturing nanopowders and/or coatings from precursors using a pyrolysis process. In a particular embodiment, dense coatings or powders can be manufactured utilizing microwave plasma technology and a non-nitrate precursor, such as, for example, a solution precursor formed from metal oxide nanopowder and an acetate based compound.

Background

[0004] It is customary that readily available metal sources of nitrate or acetate are the most relied upon sources for the production of metal oxides as coatings or as powders. In general, these sources are inexpensive and highly soluble in low-cost solvents such as water, which facilitates the mixing of constituent solutes to produce metal oxides or their composites with desired thermal, mechanical, optical, and magnetic properties. However, using nitrate or acetate metal sources in pyrolysis processes involving combustion or plasma leads to particle products that are drastically different in morphology, and density.

[0005] Pyrolysis of metal nitrates leads to fluffy and porous material particles that are difficult, if not impossible to deposit directly as a coating due to their poor flowability prior to injection and poor entrainment as melted particles prior to impact on a coating substrate. Melted particles from fluffy products tend to fly tangentially with respect to coating surfaces instead of depositing due to low entrainment velocity prior to impact. Direct deposition of metal oxides from nitrate based solution precursors leads to porous, non homogeneous, and low yield coatings with poor adhesion to the substrate.

[0006] Pyrolysis of metal acetates for the production of metal oxide powders or coatings has been found to be the most reliable route to dense and homogeneous coatings with good adhesion to the substrate. Acetate based solution precursor tend to yield more charring during pyrolysis and less explosiveness than with nitrate based precursor. The end product is a melted dense particle which, in combination with sufficient entrainment flow from the process, allows the deposition of dense and melted splats on a substrate. The charring is facilitated by the presence of carbon and hydrogen components in the acetate based solution. A typical example would be the deposition of 8 mass Yttria-Stabilized-Zirconia (8YSZ) solution precursor using Atmospheric Plasma Spray (APS) processes, High Velocity Oxygen Fuel (HVOF) processes, or microwave plasma processes. The coatings are dense and platelet-like due to splattering of melted and dense particles deposition on a substrate. Acetate based precursors are the cheapest and easiest route for the synthesis of dense metal oxide powders and substrate coatings.

[0007] There are situations where dense coatings or powders are sought but the acetate source of the metal does not exist, or is not favored chemically, or is not readily available, or for cost reason too prohibitive that some manufacturers stopped its production. As a result, for these metals without an acetate source, dense metal oxide coatings or nanopowders have yet to be achieved.

[0008] In US Patent No. 6,998,064, Gadow teaches a method on how to produce alumina oxide containing compounds for the purpose of coating or consolidation into dense parts. The method disclosed in US Patent No. 6,998,064 involves making a slurry of aluminum oxide with other metallic salts followed by spray drying to make granules (having an average diameter of over 1 micron) and then annealing to achieve the phase crystallinity desired for compounds such as LaMgAlnOig. The thermal material granules of Gadow are then sprayed using atmospheric plasma spray (APS) to produce coatings. Although, Gadow teaches the inclusion of alumina, his method utilizes a spray drying intermediate process followed by a thermal anneal to achieve the desired coatings. Without the mentioned two steps of spray drying and annealing, Gadow would not achieve the alumina based coatings. Further, Gadow reports that during the annealing process, pores within the coating grow into the micrometer range. As a result, these coatings are not dense.

[0009] In US Patent No. 8,679,246, Jordan teaches a method on how to produce composite metal oxide coatings using a mixture of amorphous metal oxide components as feedstock material. The primary purpose is to expand the range of feedstock chemical compositions and reduce energy consumption when compared to thermal spray coating methods using crystalline metal oxide feed stocks. The coatings are deposited using a suspension plasma spray process using atmospheric plasma spray. Alumina oxide powder particles with a wide size distribution ranging from 0.2 microns to 200 microns are dispersed in an aqueous solution containing other metal oxides. The suspension is then air atomized and sprayed on a substrate using arc plasma as the thermal process. This method does not produce uniform nanopowders with single phase nano structure due to the wide size distribution of the feedstock particles and the non uniformity of the thermal plasma process. As for coatings produced with the same type of feedstock using the same thermal process, they inherit the same phase non homogeneity with a mixture of amorphous and crystalline coatings.

Summary of the Invention

[0010] Exemplary embodiments of the present technology are directed to solution precursors, nanopowder materials, material coatings, and systems and methods for preparing such solutions, materials, and coatings. One aspect of the present disclosure provides an alternate route of precursor preparation to remedy the absence of the metal acetate. The nanopowder form of a metal or the metal oxide may be used to provide a precursor source for the metal or the metal oxide composite. This need rises especially when a specific metal with no acetate source is a major component of the sought composite oxide. The alternate nanopowder of the metal can also be used when it is a minority component of the composite oxide. The nanopowder may be dispersed in a solvent to form a homogenous suspension to which additional solutes, in the form of solvent dissolvable acetates or other forms of salts, are added in adequate concentrations to form the desired final composition of the composite metal oxide. This emulsion can then be used as a solution precursor for thermal spray coatings or powder production.

[0011] As used herein, the terms nanopowder or nanoparticle define a powder or particle that is sized within the nanoscale range (i.e. having dimensions of under 300 nm). Nanoscale powders and particles tend to exhibit different material properties than their larger scale counterparts due to their high grain boundary energies (i.e., a high amount of the atoms/molecules within the particle/powder reside at a boundary than within the particle/powder). In general, the metal or metal oxide nanoparticles have a diameter size (or a cross sectional length if the particle or powder is not spherical) of less than about 300 nanometers (nm). In some embodiments, the average diameter of the metal oxide nanoparticles used to for precursors is less than 300 nm. In other embodiments the average diameter of metal oxide nanoparticles is less than 200 nm, less than 150 nm, or less than 100 nm. That is, while a portion of the composite nanopowders or nanoparticles may be greater than 200 nm, the average size of the manufactured nanopowders is less than 200 nm, less than 150 nm, or less than 100 nm.

[0012] In accordance with an aspect of the present disclosure, a method of manufacturing a material coating is disclosed. The method includes mixing a solution precursor for a metal oxide composite material, injecting the solution precursor into a pyrolysis process to form the metal oxide composite material, and coating a substrate with a layer of the metal oxide composite material. The solution precursor includes a metal oxide nanopowder and an acetate based compound.

[0013] Embodiments of the above exemplary method can include one or more of the following features. In some embodiments, the metal oxide nanopowder is alumina nanopowder, and the acetate based compound includes magnesium acetate, lanthanum acetate, and/or yttrium acetate. In some embodiments, the metal oxide composite material includes lanthanum-magnesium-hexaaluminate (LaMgAlnO^, LMHA), yttrium-aluminum- garnet (Υ₃Αΐ₅θ₁₂, YAG), or magnesium-aluminum-spinel (MgAl₂0₄). In some embodiments, mixing a solution precursor includes mixing concentrations of alumina nanopowder and yttrium acetate to yield a stoichiometric composition of YAG. In some embodiments, mixing a solution precursor includes mixing concentrations of alumina nanopowder, lanthanum acetate, and magnesium acetate to yield a stoichiometric composition of LMHA. In some embodiments, mixing a solution precursor includes mixing concentrations of magnesium acetate and alumina nanopowder to yield a stoichiometric composition of MgAl₂0₄. In some embodiments, the method also includes ball milling the solution precursor prior to injecting the solution precursor into the pyrolysis process. In some embodiments, the method also includes dispersing the solution precursor via a high power ultrasonic dispersion process prior to injecting the solution precursor into the pyrolysis process. In some embodiments, the method also includes filtering the solution precursor prior to injecting the solution precursor into the pyrolysis process. In some embodiments, the pyrolysis process includes at least one of a microwave plasma spray process, arc discharge plasma spray process, inductively coupled plasma spray process, low-pressure plasma spray process, or HVOF process. In some embodiments, injecting the solution precursor into a pyrolysis process includes injecting droplets of the solution precursor into a microwave plasma torch. In some embodiments, injecting the solution precursor into a pyrolysis process results in formation of a metal oxide composite powder prior to coating the substrate with a layer of the metal oxide composite material. In some such embodiments, the metal oxide nanopowder is alumina nanopowder and the metal oxide composite powder includes at least one of LMHA, YAG, and MgAl₂0₄. In other such embodiments, coating a substrate with a layer of the metal oxide composite material includes injecting the metal oxide composite powder (formed by utilizing the methods of this disclosure) into a subsequent pyrolysis process.

[0014] In accordance with another aspect of the present disclosure, a method of manufacturing a material coating is disclosed. The method includes mixing a solution precursor, injecting the solution precursor into a pyrolysis process to form an aluminum oxide composite material, and coating a substrate with a layer of the aluminum oxide composite material. The solution precursor includes an alumina nanopowder, and a rare-earth oxide nanopowder. Embodiments of the above exemplary method can include one or more of the following features. In some embodiments, the rare-earth oxide nanopowder includes yttrium, gadolinium, or lanthanum.

[0015] In accordance with yet another aspect of the present disclosure, a method of manufacturing a metal oxide composite powder is disclosed. The method includes mixing a solution precursor and injecting the solution precursor into a pyrolysis process to form a metal oxide composite powder. The solution precursor includes a metal oxide nanopowder and an acetate based compound. Embodiments of the above exemplary method can include one or more of the following features. In some embodiments, the solution precursor also includes a surfactant, the metal oxide nanopowder is an alumina nanopowder, and the acetate based compound includes magnesium acetate, lanthanum acetate, or yttrium acetate.

[0016] In accordance with another aspect of the present disclosure, a solution precursor for a metal oxide material is disclosed. The solution precursor includes a mixture of between 0.10 Mol/liter to 2.0 mol/liter metal oxide nanopowder, between 0.05 Mol/liter to 2.80 Mol/liter an acetate based compound, and a solvent. Embodiments of the above exemplary method can include one or more of the following features. In some embodiments, the metal oxide nanopowder is alumina nanopowder, and the acetate based compound includes magnesium acetate, lanthanum acetate, and/or yttrium acetate. In some such embodiments, the alumina nanopowder loading is between 100 g - 200 g per liter. In some embodiments, the solution precursor further includes a surfactant.

[0017] In accordance with another aspect of the present disclosure, a metal or metal oxide composite coating is disclosed. The coating includes an aluminum oxide composite layer between 30 micrometers and 1.0 millimeter thick, having a hardness between 6.0 GigaPascal and 10.0 GigaPascal, and a porosity between 5% and 20%, wherein the aluminum oxide composite layer is deposited on a substrate via thermal spraying. Embodiments of the above exemplary method can include one or more of the following features. In some embodiments, the aluminum oxide composite material includes lanthanum-magnesium-hexaaluminate (LaMgAlnOig, LMHA), yttrium-aluminum-garnet (Υ₃Αΐ₅θ₁₂, YAG), or magnesium- aluminum spinel (MgAl₂0₄).

[0018] Embodiments of the above exemplary methods, coatings and precursors can include one or more of the following advantages. In some embodiments, mixing a metal oxide nanopowder with an acetate based compound to form a solution precursor is an efficient and economical technique for forming dense metal oxide composite powders and coatings. Such acetate based solution precursors may yield a more dense or homogeneous metal oxide composite powder or metal oxide composite coating than nitrate based precursors. In addition, for embodiments which feature forming a coating directly from a pyrolysis process, intermediate steps of heating/annealing are eliminated as compared to prior art processes. As a result, not only is a processing step eliminated, but also eliminated is the coating's exposure to further opportunities for impurities to be introduced. By eliminating processing steps, purity or the quality of the manufactured film is increased.

Brief Description of the Drawings

[0019] The features and advantages of the present disclosure will be more fully understood from the following description of exemplary embodiments when read together with the accompanying drawings, in which:

[0020] Figure 1 is a flow chart showing a method of making a metal oxide composite powder, according to one embodiment of the present disclosure. [0021] Figure 2 is a flow chart showing a method of making an aluminum oxide composite powder, according to one embodiment of the present disclosure.

[0022] Figure 3 is a flow chart showing a method of depositing a metal oxide composite coating on a substrate, according to one embodiment of the present disclosure.

[0023] Figure 4 is a flow chart showing a method of depositing a metal oxide composite coating on a substrate, according to another embodiment of the present disclosure.

[0024] Figure 5 is a flow chart showing a method of producing LMHA coatings or powders, according to one embodiment of the present disclosure.

[0025] Figure 6 is a flow chart showing a method of producing YAG coatings or powders, according to one embodiment of the present disclosure.

[0026] Figure 7 is a flow chart showing a method of producing MgAl₂0₄ spinel coatings or powders, according to one embodiment of the present disclosure.

[0027] Figure 8 is a flow chart showing a method of producing aluminum oxide composite coatings or powders, according to one embodiment of the present disclosure.

[0028] Figure 9 is a flow chart illustrating a method of producing aluminum oxide composite powders, according to another embodiment of the present disclosure.

[0029] Figure 10 illustrates an example system for depositing a metal oxide composite coating on a substrate, according to one embodiment of the present disclosure.

Detailed Description of the Invention

[0030] One aspect of the present invention involves utilizing an alternative precursor source to improve the properties of a metal or a metal oxide coating or powder. Such an alternative precursor source may be desirable when a coating or powder is found to be fluffy or porous and inadequate for application where hard and dense coatings or dense powders are required. This applies also to applications where dense and flowable powders are needed but only the fluffy or porous form of these powders can be produced using nitrate based precursors. In particular, such situations apply to coating or powder production using aluminum nitrate sources for composite materials such as LMHA, YAG, or MgAl₂0₄ spinel. This situation can be generalized to the production of any composite material that incorporates aluminum oxide, or composite materials that incorporate metals having an unstable or otherwise undesirable acetate compound. This disclosure introduces alumina nanopowder, or any metal and/or metal oxide nanopowder, as an alternative to aluminum nitrate, or any metal nitrate, as a source of aluminum or any metal of interest. As will be appreciated, the examples included herein are for illustrative purposes only and the present disclosure is not intended to be limited to the examples provided.

[0031] In general, this disclosure is directed toward advantageous methods of forming dense, pure metal oxide nanopowders and/or coatings. The methods employ a pyrolysis process (e.g., a microwave plasma torch) to form the dense and/or pure powders and/or coatings. In addition, the disclosure is directed toward solution precursors which do not utilize nitrates as the feedstock or source for the methods disclosed herein. The solution precursors may include a metal oxide nanopowder and an acetate based compound. In addition, the solution precursors can also include additional materials, such as constituents of the metal oxide composites, or surfactants to help with the mixing and/or homogenization of the solution. In one embodiment, a solution precursor for an aluminum oxide composite nanopowder and/or coating includes aluminum oxide nanopowder mixed with an acetate based compound. There are many embodiments of the solution precursor, and the following paragraphs provide some illustrative examples of these solutions.

Solution Precursor Examples

[0032] In one embodiment of the present disclosure, LMHA coatings or powders may be produced using a solution precursor in which an aluminum oxide nanopowder is used as an alternative to aluminum nitrate. In one particular example, the solution precursor may include a mixture of 25.000 grams of alumina nanopowder, 15.300 grams of lanthanum acetate sesquihydrate [La(CH₃COO)3* 1.5H₂0], and 9.564 g of magnesium acetate tetrahydrate [Mg(CH₃COO)₃ ^e4H₂0], in 600 milliliters (ml) of methanol and 350 ml of distilled water (H₂0). This corresponds to 0.245 moles of nano alumina, 0.048 moles of lanthanum acetate sesquihydrate, and 0.044 moles of magnesium acetate tetrahydrate in a total volume of liquid of 950 ml; or 0.258 Mol/L nano alumina, 0.050 Mol/L lanthanum acetate sesquihydrate, and 0.046 Mol/L magnesium acetate tetrahydrate. The solution is mixed to form a well dispersed suspension. In one embodiment, mixing is achieved by mechanical stirring for about 24 hours. The final LMHA product of such a solution precursor may correspond to 7.14 mol of lanthanum oxide (La₂0₃), 14.28 mol of magnesium oxide (MgO), and 78.57 mol of aluminum oxide (AI₂O₃). Other product compositions consisting of lanthanum oxide, magnesium oxide, and aluminum oxide can be produced by varying the concentration of each component from about 20-80 mol . For example, the final lanthanum magnesium aluminate may include about 20 mol lanthanum oxide, about 20 mol of magnesium oxide, and a balance of about 60 mol aluminum oxide.

[0033] In another embodiment of the present disclosure, YAG coatings or powders may be produced using a solution precursor in which an aluminum oxide nanopowder is used as an alternative to aluminum nitrate. In one particular example, the solution precursor may include a mixture of 25.00 grams of aluminum oxide nanopowder, and 99.40 grams of yttrium acetate tetrahydrate [Y(CH₃COO)₃ ^»4H₂0] in 600 ml of methanol and 1100 ml of distilled water (H₂0). In one embodiment, mixing is achieved by mechanical stirring for about 24 hours. The final YAG product of such a solution precursor may include about 37.5 mol of Y₂0₃, and about 62.5 mol of A1₂0₃. Other product compositions can be produced by varying the concentration of aluminum oxide nanopowder and yttrium acetate tetrahydrate. This corresponds to 0.245 moles of nano alumina, and 0.293 moles of yttrium acetate tetrahydrate in a total volume of liquid of 1700 ml; or 0.144 Mol/L nano alumina, and 0.172 Mol/L of yttrium acetate tetrahydrate.

[0034] In another embodiment of the present disclosure, MgAl₂0₄ spinel coatings or powders may be produced using a solution precursor in which an aluminum oxide nanopowder is used as an alternative to aluminum nitrate. In one particular example, the solution precursor may include a mixture of 25.00 grams of alumina nanopowder, and 52.54 grams of magnesium acetate tetrahydrate [Mg(CH₃COO)₃ ^»4H₂0] in 600 ml of methanol and 120 ml of distilled water (H₂0). This corresponds to 0.245 moles of nano alumina, and 0.245 moles of magnesium acetate tetrahydrate in a total volume of liquid of 820 ml; or 0.298 Mol/L nano alumina, and 0.299 Mol/L magnesium acetate tetrahydrate. In one embodiment, mixing is achieved by mechanical stirring for about 24 hours. The final MgAl₂0₄ product of such a solution precursor may include about 33.3 mol of MgO, and about 66.6 mol of A1₂0₃. Other product compositions of MgO and A1₂0₃ can be produced, for example, by varying the concentration of each component from between 20-80 mol . For instance, the final magnesium aluminate may include about 20 mol of magnesium oxide, with the balance of about 80 mol made out of A1₂0₃.

[0035] While the above examples are directed toward solution precursors that include an aluminum oxide nanopowder mixed with an acetate based compound, in other embodiments the solution precursor may include a mixture of a metal oxide nanopowder with a rare-earth oxide nanopowder, such as yttrium oxide (Y₂0₃) nanopowder. In one such example, the solution precursor includes a mixture of aluminum oxide nanopowder, yttrium oxide nanopowder, and a solvent, such as methanol. The mixture may be ball-milled for about 24 hours for optimum dispersion. Various yttrium aluminum composite materials (e.g., YAG) may be produced by varying the concentrations of the yttrium oxide nanopowder and aluminum oxide nanopowder from between 20-80 mol %. For instance, yttrium aluminum perovskite (YAP) may be formed including about 50 mol yttrium oxide and about 50 mol aluminum oxide, or yttrium aluminum monoclinic (YAM) may be formed including about 66.6 mol of yttrium oxide and about 33.3 mol aluminum oxide.

[0036] Once the solution precursor is prepared, it may be used in a pyrolysis process to make dense and/or pure nanopowders. The nanopowders manufactured by this process may have an average size, for example, of about 10-300 nm. In some embodiments, the manufactured nanopowders have an average size of about 50 to 150 nm. In general, the manufactured nanopowders are dense (i.e., the porosity is less than about 1%, 3%, 5%, or 10%)

[0037] Fig. 1 is a flow chart showing a method 100 of making a metal oxide composite powder, according to one embodiment of the present disclosure. The method may begin with making 110 a solution precursor by dispersing a metal oxide nanopowder, such as alumina nanopowder, in a solvent. Other metal salts may be added to the solution in order to achieve a desired composition. In general, the metal or metal oxide nanoparticles have a diameter size (or a cross sectional length) less than about 200 nanometers (nm). In some embodiments, the average diameter of the metal oxide nanoparticles in the suspension is less than 200 nm. In other embodiments the average diameter of metal oxide nanoparticles is less than 150 nm, less than 100 nm, or less than 75 nm. That is, while a portion of the composite nanopowders may be greater than 200 nm, the average size of the manufactured nanopowders is less than 200nm, less than 150 nm, or less than 100 nm. The solvent may be, for example, water, methanol, ethanol, isopropanol, acetic acid, tetrahydrofuran (THF), ethyl acetate, or acetone. In some embodiments, the solution precursor may include a surfactant, to allow increased dispersion of the metal oxide nanoparticles in the suspension. In some embodiments, the surfactant may be, for example, glycine, sucrose, triethanolamine, or polyoxyethylene glycol. The metals salts added may include anions of acetates, or any anion salts that would lead to good charring during pyrolysis, since the desired product ought to be solid and not porous. In some embodiments, the solution may be ball-milled for between 24- 72 hours at room temperature in order to increase dispersion of constituents, and subsequently filtered to remove any residual agglomeration of particles. Alternatively, high energy ultrasonic dispersion can also be used instead of ball-milling. The solution may then be atomized as droplets using air atomizing techniques or transducer-driven droplet making devices. These droplets may be injected 120 into a pyrolysis process, where solvents are evaporated and spherical solid particles are precipitated following pyrolysis, melted and cooled as they exit the plasma. In some embodiments, the pyrolysis process may be a microwave plasma process, and the droplets may be injected axially into a microwave plasma torch. In other embodiments, the pyrolysis process may include an arc discharge plasma spray process, inductively coupled plasma spray process, low-pressure plasma spray process, or HVOF process. The cooled metal oxide composite particles may then be collected 130 using a filter.

[0038] In general, one aspect of this disclosure is directed toward advantageous methods of forming dense, pure metal oxide nanopowders. The methods employ a pyrolysis process (e.g., a microwave plasma torch) to form the dense and/or pure powders. There are many embodiments of the metal oxide nanopowders, and the following paragraphs provide some illustrative examples of these powders.

Metal Oxide Composite Powder Examples

[0039] As discussed above, a solution precursor with an acetate based compound may be used to produce an aluminum oxide composite nanopowder, such as LMHA, YAG, YAP, YAM, or MgAl₂0₄ spinel. These aluminum oxide composite nanopowders may be of particular interest in the production of thermal insulating materials for thermal barrier coating (TBC) applications. In some embodiments, these nanopowders may be produced according to the method disclosed in Fig. 1 (discussed above), wherein an aluminum oxide nanopowder is mixed with an acetate based compound, such as magnesium acetate, lanthanum acetate, or yttrium acetate.

[0040] In another embodiment, methods feature forming a metal or metal oxide composite material utilizing a precursor formed from a mixture of two different nanoparticles. Fig. 2 is a flow chart showing a method 200 of making an aluminum oxide composite powder, according to this embodiment. In this particular example, the method may begin with making 210 a solution precursor by dispersing aluminum oxide (alumina) nanoparticles, in a solvent and mixing a rare-earth oxide (Y₂0₃) nanoparticle. In some embodiments, the rare-earth oxide nanoparticle/nanopowder is yttrium oxide nanopowder. The mixture of nanopowder is combined with a solvent and/or surfactant to make the solution precursor. Droplets are formed from the solution and these droplets are injected 220 into a pyrolysis process, where solvents are evaporated and spherical solid particles are precipitated following pyrolysis, melted and cooled as they exit the plasma. As discussed above, the pyrolysis process may be a microwave plasma process, arc discharge plasma spray process, inductively coupled plasma spray process, low-pressure plasma spray process, or high velocity oxygen fuel process. The cooled aluminum oxide composite particles/nanopowder is then be collected 230 using a filter.

[0041] In the methods featured in Figs. 1 and 2, solvents and/or surfactants are added to create a suspension prior to the pyrolysis process. Solvents used in these methods can include, for example: water, methanol, ethanol, isopropanol, acetic acid, tetrahydrofuran (THF), ethyl acetate, or acetone. The solution precursor may also include a surfactant, such as, for example one or more of: glycine, sucrose, triethanolamine, or polyoxyethylene glycol. In some embodiments, the solution precursor, after mixing together the constituent nanopowder components and solvents/surfactants, may be ball-milled for between 24-72 hours at room temperature in order to increase dispersion of constituents, and subsequently filtered to remove any residual agglomeration of particles. Alternatively, high energy ultrasonic dispersion can also be used instead of ball-milling to create a homogenous and well dispersed solution precursor. Filtering after high energy ultrasonic dispersion may also be performed. Once the solution precursor is mixed and dispersed, droplets of the solution are introduced into a pyrolysis process. Examples of pyrolysis processes include, microwave plasma processes, atmospheric plasma spray (APS) processes, low pressure plasma spray processes, HVOF processes, RF plasma processes, and flame combustion processes.

[0042] While the above examples have been directed to forming metal or metal oxide composite nanopowders directly from the solution precursor, in other aspects of this technology, composite coatings are formed directly from a pyrolysis process utilizing the same solution precursors. In some embodiments, a metal or metal oxide composite coating may be deposited via direct spray coating by feeding a metal oxide nanopowder-based solution precursor to a pyrolysis process. In other embodiments, the metal or metal oxide composite coating may be deposited by feeding a metal oxide composite powder into a pyrolysis process. The following paragraphs provide numerous examples of forming coatings either directly from the solution precursor (without an intermediate formation of nanopowder) or from the nanopowders formed from the methods disclosed herein. Metal Oxide Composite Coating Examples

[0043] In one embodiment, a metal or metal oxide composite coating is deposited on a substrate directly from the solution precursor. Fig. 3 is a flow chart showing a method 300 of depositing a metal oxide composite coating on a substrate, according to this embodiment. In this particular embodiment, the method begins with making 310 a solution precursor containing a metal oxide nanopowder, as discussed above. In one embodiment, the solution precursor may include an aluminum oxide nanopowder mixed with an acetate based compound such as lanthanum acetate, magnesium acetate, or yttrium acetate. In another embodiment, the solution precursor may include a mixture of two metal oxide nanopowders, such as aluminum oxide nanopowder and yttrium oxide nanopowder. As discussed above, solvents and/or surfactants may be added to create a suspension prior to the pyrolysis process. Other metal salts may be added to the solution in different concentrations, and may include anions of acetates, or any anion salts that would lead to good charring during pyrolysis, since the desired product ought to be solid and not porous. Once the solution precursor is formed, the solution may be injected 320 into a pyrolysis process to form a dense and/or pure metal oxide composite nanopowder. The solution precursor may be injected into the pyrolysis process in droplets, that may be formed using air atomizing techniques or by injecting the solution precursor into a transducer-driven droplet maker. The droplets may be injected axially into a microwave plasma torch, where solvents are evaporated and spherical solid particles are precipitated following pyrolysis and melted as they exit the plasma. Alternatively, the droplets could be injected laterally onto an atmospheric plasma spray (APS) device where the solvents are evaporated and spherical solid particles are precipitated following pyrolysis, and melted as they exit the plasma. Other pyrolysis processes may include, for example, low pressure plasma spray processes, HVOF processes, RF plasma processes, or flame combustion processes. The melted metal oxide composite material is then deposited 330 on a substrate. The substrate may be, for example, a stainless steel or bond-coated superalloy substrate.

[0044] In another embodiment, a metal or metal oxide composite coating may be deposited by first forming a metal oxide composite nanopowder using a first pyrolysis process, and subsequently feeding the metal oxide composite nanopowder into a second pyrolysis process. Fig. 4 is a flow chart showing a method 400 of depositing a metal oxide composite coating on a substrate, according to this embodiment. In this particular example, the method combines making a metal oxide composite nanopowder using a pyrolysis process, as a first step, with depositing a metal oxide composite coating on a substrate using a subsequent pyrolysis process, as a second step. The method begins with making 410 a solution precursor containing a metal oxide nanopowder, as discussed above in reference to Fig. 3. Once the solution precursor is formed, the solution may be injected 420 into a pyrolysis process to form a dense and/or pure metal oxide composite nanopowder. The solution precursor may be injected into the pyrolysis process in droplets, that may be formed using air atomizing techniques or by injecting the solution precursor into a transducer-driven droplet maker. The droplets may be injected axially into a microwave plasma torch, where solvents are evaporated and spherical solid particles are precipitated following pyrolysis, melted and cooled as they exit the plasma. Alternatively, the droplets could be injected laterally onto an atmospheric plasma spray (APS) device where the solvents are evaporated and spherical solid particles are precipitated following pyrolysis, and melted as they exit the plasma. The method continues with collecting 430 the cooled metal oxide composite nanopowders and injecting 440 the nanopowders into a subsequent pyrolysis process. In one embodiment, the metal oxide composite nanopowders are injected laterally into an atmospheric plasma spray (APS) device and melted as they exit the plasma. In other embodiments, the subsequent pyrolysis process may include a microwave plasma process, low pressure plasma spray process, HVOF process, RF plasma process, or flame combustion process. The melted metal oxide composite material is then deposited 450 on a substrate. The substrate may be, for example, a stainless steel or bond-coated superalloy substrate.

[0045] Fig. 5 is a flow chart showing a method of producing dense and/or pure LMHA coatings or powders, according to one embodiment of the present disclosure. The method begins with adding 510 lanthanum acetate and magnesium acetate, adding 520 an aluminum oxide (alumina) nanopowder, and adding 530 a surfactant to create a suspension. Surfactants used may include, for example one or more of: glycine, sucrose, triethanolamine, or polyoxyethylene glycol. Adequate concentrations of lanthanum acetate, magnesium acetate, and alumina nanopowder may selected, as discussed above, to yield a stoichiometric composition of LMHA materials. In this example, acetate loading is limited by the maximum loading of the lanthanum acetate in water, while the loading of aluminum oxide nanopowder can attain about 100 g to 200 g per liter. The method continues with stirring 540 the lanthanum acetate, magnesium acetate, aluminum oxide nanopowder, and surfactant in a solvent. Solvents used may include, for example: water, methanol, ethanol, isopropanol, acetic acid, tetrahydrofuran (THF), ethyl acetate, or acetone. After mixing together the constituent nanopowder components and solvents/surfactants, the solution precursor is ball- milled 550 using zirconia balls for between 24-72 hours at room temperature in order to increase dispersion of the aluminum oxide nanopowder. The solution is subsequently filtered 560 to remove any residual agglomeration of particles that survived the ball-milling. Once the solution precursor is formed, stirred, and filtered, it is injected 570 as droplets into a microwave plasma process. In the plasma torch, the droplets undergo size shrinkage due to solvent evaporation and solid solutes diffusion, precipitation, into the center of the droplet. These solutes include the lanthanum and magnesium acetates and the aluminum oxide nanopowder. The acetate melts at low temperature, however, the aluminum oxide nanopowder requires a much higher temperature to melt and thus remains solid during droplet shrinkage. By replacing aluminum nitrate with aluminum oxide nanopowder, exothermic exfoliation associated with the more energetic nitrates is eliminated. The aluminum oxide nanopowders will melt within the drying droplet and mix homogeneously with lanthanum and magnesium oxides. The method continues with producing 580 LMHA coatings or nanopowders by depositing the melted LMHA particles on a substrate, or by cooling and collecting the LMHA nanopowder as it exits the plasma torch. In some embodiments, dense LMHA coatings or powders may be used for TBC applications. LMHA coatings may be characterized by their thickness, porosity, and hardness; and in one particular embodiment, a LMHA coating produced according to the method disclosed in Fig. 5 has a thickness between about 30 micrometers to 1.0 millimeters (mm), a porosity between about 5% to 20%, and a Vickers micro-hardness from between about 6.0 GigaPascal (GPa) to 10.0 GPa.

[0046] One aspect of the present disclosure is aimed at producing coatings of YAG directly from suspension without the penalty of dealing with fluffy powders produced using nitrate sources of aluminum and yttrium. In one embodiment, yttrium acetate is used in the solution precursor instead of yttrium nitrate, as yttrium oxide accounts for about 40 mass% of the total mass of YAG. Fig. 6 is a flow chart showing a method of producing dense and/or pure YAG coatings or powders, according to this embodiment. The method begins with adding 610 yttrium acetate, adding 620 an aluminum oxide (alumina) nanopowder, and adding 630 a surfactant to create an homogeneous solution. Surfactants used may include, for example one or more of: glycine, sucrose, triethanolamine, or polyoxyethylene glycol. Adequate concentrations of yttrium acetate and alumina nanopowder may be selected, as discussed above, to yield a stoichiometric composition of YAG materials. In this example, the loading of aluminum oxide nanopowder can attain about 100 g to 200 g per liter. The method continues with stirring 640 the yttrium acetate, aluminum oxide nanopowder, and surfactant in a solvent. Solvents used may include, for example: water, methanol, ethanol, isopropanol, acetic acid, tetrahydrofuran (THF), ethyl acetate, or acetone. After mixing together the constituent nanopowder components and solvents/surfactants, the solution precursor is ball- milled 650 using zirconia balls for between 24-72 hours at room temperature in order to increase dispersion of the aluminum oxide nanopowder. The solution is subsequently filtered 660 to remove any residual agglomeration of particles that survived the ball-milling. Once the solution precursor is formed, stirred, and filtered, it is injected 670 as droplets into a microwave plasma process. In the plasma torch, the droplets undergo size shrinkage due to solvent evaporation and solid solutes diffusion, precipitation, into the center of the droplet. The aluminum oxide nanopowders will melt within the plasma and diffuse with the yttrium acetate to form molten YAG particles. The method continues with producing 680 YAG coatings or nanopowders by depositing the melted YAG particles on a substrate, or by cooling and collecting the YAG nanopowder as it exits the plasma torch. In some embodiments, dense YAG coatings or powders may be used for TBC applications. YAG coatings may be characterized by their thickness, porosity, and hardness; and in one particular embodiment, a YAG coating produced according to the method disclosed in Fig. 5 has a thickness between about 30 micrometers to 1.0 mm, a porosity between about 5% to 20%, and a Vickers micro-hardness from between about 6.0 GigaPascal (GPa) to 10.0 GPa

[0047] In an alternative embodiment similar to that described in Fig. 6, yttrium nitrate can be used instead of yttrium acetate where the yttrium oxide contributes a smaller composition to the final alumina containing composite. This case applies to all alumina containing composites in which the other oxide components account for less than 15 mol% of the composition in the final yttrium aluminum composite product.

[0048] Magnesium aluminum spinel is used as a transparent armor, and the general precursor source for aluminum is aluminum nitrate. The spinel is generally produced as powders which are consolidated into monoliths and then polished to yield strong, transparent, armor material. The presence of aluminum nitrates, however, does not allow consolidation through direct coating using thermal spray processes. One embodiment of the present disclosure alleviates this problem and allows direct coating by replacing aluminum nitrate as a precursor source with a suspension containing well dispersed alumina nanopowders along with magnesium acetate. The presence of magnesium acetate fosters charring during pyrolysis in order to obtain dense particles that can lead to dense coatings on a substrate. Fig. 7 is a flow chart showing a method of producing dense and/or pure MgAl₂0₄ spinel coatings or powders, according to this embodiment. The method begins with adding 710 magnesium acetate, adding 720 an aluminum oxide (alumina) nanopowder, and adding 730 a surfactant to create a solution suspension. Surfactants used may include, for example one or more of: glycine, sucrose, triethanolamine, or polyoxyethylene glycol. Adequate concentrations of magnesium acetate and alumina nanopowder may be selected, as discussed above, to yield a stoichiometric composition of MgAl₂0₄ spinel materials. In this example, acetate loading is limited by the maximum loading of the magnesium acetate in water, which is about 534 g/1, and the loading of aluminum oxide nanopowder can attain about 100 g to 200 g per liter. The method continues with stirring 740 the magnesium acetate, aluminum oxide nanopowder, and surfactant in a solvent. Solvents used may include, for example: water, methanol, ethanol, isopropanol, acetic acid, tetrahydrofuran (THF), ethyl acetate, or acetone. After mixing together the constituent nanopowder components and solvents/surfactants, the solution precursor is ball-milled 750 using zirconia balls for between 24-72 hours at room temperature in order to increase dispersion of the aluminum oxide nanopowder. The solution is subsequently filtered 760 to remove any residual agglomeration of particles that survived the ball-milling. Once the solution precursor is formed, stirred, and filtered, it is injected 770 as droplets into a microwave plasma process. In the plasma torch, the droplets undergo size shrinkage and the aluminum oxide nanopowder melts within the plasma and diffuses with the magnesium acetate to form molten MgAl₂0₄ spinel particles. The method continues with producing 780 MgAl₂0₄ spinel coatings or nanopowders by depositing the melted MgAl₂0₄ spinel particles on a substrate, or by cooling and collecting the MgAl₂0₄ spinel nanopowder as it exits the plasma torch. In some embodiments, dense MgAl₂0₄ spinel coatings or powders may be used for TBC applications. MgAl₂0₄ spinel coatings may be characterized by their thickness, porosity, and hardness; and in one particular embodiment, a MgAl₂0₄ spinel coating produced according to the method disclosed in Fig. 5 has a thickness between about 30 micrometers to 1.0 mm, a porosity between about 5% to 20%, and a Vickers micro- hardness from between about 6.0 GigaPascal (GPa) to 10.0 GPa.

[0049] In an alternative embodiment similar to the one described in Fig. 6, yttrium acetate may be replaced with a rare-earth oxide nanopowder (such as yttrium oxide nanopowder) and mixed with aluminum oxide nanopowder to produce an aluminum oxide composite material solution precursor. Fig. 8 is a flow chart showing a method of producing aluminum oxide composite coatings or powders, according to this embodiment. The method begins with adding 810 a rare-earth oxide nanopowder, adding 820 an aluminum oxide (alumina) nanopowder, and adding 830 a surfactant to create a solution suspension. Surfactants used may include, for example one or more of: glycine, sucrose, triethanolamine, or polyoxyethylene glycol. The method continues with stirring 840 the rare-earth oxide nanopowder, aluminum oxide nanopowder, and surfactant in a solvent. Solvents used may include, for example: water, methanol, ethanol, isopropanol, acetic acid, tetrahydrofuran (THF), ethyl acetate, or acetone. After mixing together the constituent nanopowder components and solvents/surfactants, the solution precursor is ball-milled 850 using zirconia balls for between 24-72 hours at room temperature in order to increase dispersion of the aluminum oxide nanopowder. The solution is subsequently filtered 860 to remove any residual agglomeration of particles that survived the ball-milling. Once the solution precursor is formed, stirred, and filtered, it is injected 870 as droplets into a microwave plasma process. In the plasma torch, the droplets undergo size shrinkage due to solvent evaporation and solid solutes diffusion, precipitation, into the center of the droplet. The aluminum oxide nanopowders will melt within the plasma and diffuse with the rare-earth oxide nanopowder to form molten aluminum oxide composite particles. The method continues with producing 880 aluminum oxide composite coatings or nanopowders by depositing the melted aluminum oxide composite particles on a substrate, or by cooling and collecting the nanoparticles as they exit the plasma torch. In some embodiments, the rare- earth oxide nanopowders is yttrium oxide nanopowder, in which case the method described in Fig. 8 may be used to produce dense and/or pure YAG coatings or powders.

Using Microwave Plasma Processing

[0050] Fig. 9 is a flow chart illustrating a method of producing aluminum oxide composite powders, according to another embodiment of the present disclosure. In particular, this embodiment is directed to method 900 using a microwave plasma torch to generate spherical metal oxide composite powders. The first step of method 900 is to form the solution precursor. (See above section entitled "Solution Precursor Examples" for illustrative embodiments of specific solution precursors.). To do so, a metal oxide nanopowder is mixed with an acetate based compound in step 910. The mixed nanopowder and acetate based compound are stirred together to disperse the constituents in step 920. Additional solvents and/or surfactants may be added to disperse the constituents. In addition, the mixture can be ball milled or high energy ultrasonic dispersion can be applied to further disperse the constituents to attain a homogenous mixture or suspension. The well dispersed solution precursor is then pumped into a droplet maker for injection into a microwave plasma torch in steps 930 and 940. The droplet maker is a device which forms uniformly sized droplets (i.e., each drop has substantially the same size within ±\% to 5%). Examples of droplet makers that form uniform droplets and can be used in this method are further described in US Patent Publication No. US 2014/0091155, hereby incorporated by reference in its entirety.

[0051] The uniform droplets are injected into a microwave plasma torch to react the constituents within the droplets of the solution precursor to form the metal oxide composite powder. To do so a uniform melt state process 960 is created by the energy and operation conditions of the plasma torch. To operate the plasma torch the following processes are conducted. First, microwave radiation is generated and transmitted to the torch through a waveguide in step 912. Fluid flowstreams are introduced into the torch to create the proper conditions for generating the plasma as well as creating a flow condition for the precursor materials. Specifically, entrainment and sheath gas flows are introduced into the dielectric torch in step 922. The plasma is ignited in step 932 and then to create the operating conditions for uniform melt of the precursor droplets, the impedance for minimum reflected power is tuned in step 942 and the flow conditions are updated to provide a laminar flow plasma in step 952. A description of generating laminar plasma flow conditions is provided in U.S. Patent Publication No. US 2013/0270261, hereby incorporated by reference in its entirety. Additional factors relating to droplet size, droplet uniformity, droplet injection frequency, etc., and the effect of these on the produced powders and/or coatings are discussed in this publication.

[0052] Once the proper operating conditions of the plasma torch are achieved, the droplets of injected solution precursor are melted to form a composite material. The composite material is in the form of nanoscale powders. The size of the produced nanoscale powder depends on the solution material loading, chemistry of the solution, and the feedstock droplet size, among other factors. The composite nanoscale powders are quickly cooled or quenched as they leave the torch in step 970. This is the results of the vast difference in temperature between the plasma in the torch and room conditions. In general, the nanopowders are collected with filters as shown in step 980. The resulting powder is both spherical and can be tuned to be single-crystalline, polycrystalline, nanocrystalline, amorphous or combinations thereof.

[0053] Fig. 10 is an illustration of a representative microwave plasma torch, such as the one used in the method presented in Fig. 9, and its operation to create a metal oxide composite coating on a substrate from a solution precursor. In this embodiment, precursor components 1010 are mixed together to form a solution precursor 1020, which may be mixed, dispersed, milled, etc. as discussed above. (See above section entitled "Solution Precursor Examples" for illustrative embodiments of specific solution precursors.). The mixed solution precursor is then injected into a droplet maker 1030, which forms uniformly sized droplets 1040 of the solution precursor 1020. These droplets 1040 are then injected into a microwave plasma torch 1050, which creates a microwave generated plasma 1070, as discussed above in reference to Fig. 9. Specifically, an entrainment laminar gas flow and a sheath laminar gas flow may be injected through inlets 1042 and 1044, respectively, to create laminar flow conditions in the plasma torch 1050 prior to ignition of the plasma 1070 via microwave radiation source 1060. The droplets 1040 may be injected axially into the microwave plasma torch 1050, where solvents are evaporated and spherical particles 1080 are precipitated following pyrolysis and melted as they exit the plasma 1070. The melted metal oxide composite particles 1080 are then deposited as a coating 1090 on a substrate 1200. The substrate 1200 may be, for example, a stainless steel or bond-coated superalloy substrate. In one particular embodiment, the droplet maker 1030 and plasma torch 1050 may be implemented to deposit a coating 1090 of LMHA having a thickness between about 30 micrometers to 1.0 millimeters (mm), a porosity between about 5% to 20%, and a Vickers micro-hardness from between about 6.0 GPa to 10.0 GPa. As will be appreciated, the plasma torch 1050, coating 1090, substrate 1200, and other elements shown in Fig. 10 are not drawn to scale and are not intended to represent the actual or relative sizes of those elements.

[0054] In describing exemplary embodiments, specific terminology is used for the sake of clarity and in some cases reference to a figure. For purposes of description, each specific term is intended to at least include all technical and functional equivalents that operate in a similar manner to accomplish a similar purpose. Additionally, in some instances where a particular exemplary embodiment includes a plurality of system elements, device components or method steps, those elements, components or steps may be replaced with a single element, component or step. Likewise, a single element, component or step may be replaced with a plurality of elements, components or steps that serve the same purpose. Moreover, while exemplary embodiments have been shown and described with references to particular embodiments thereof, those of ordinary skill in the art will understand that various substitutions and alterations in form and detail may be made therein without departing from the scope of the invention. Further still, other functions and advantages are also within the scope of the invention.

Claims

What is claimed is:

1. A method of manufacturing a material coating comprising:

mixing a solution precursor for a metal oxide composite material, the solution precursor including a metal oxide nanopowder and an acetate based compound;

injecting the solution precursor into a pyrolysis process to form the metal oxide composite material; and

coating a substrate with a layer of the metal oxide composite material.

2. The method of claim 1, wherein the metal oxide nanopowder is alumina nanopowder, and the acetate based compound comprises at least one material selected from the group consisting of: magnesium acetate, lanthanum acetate, or yttrium acetate.

3. The method of claim 2, wherein the metal oxide composite material comprises at least one of lanthanum-magnesium-hexaaluminate (LaMgAlnO^, LMHA), yttrium- aluminum- garnet (Y3Al50₁₂, YAG), and magnesium-aluminum-spinel (MgAl₂0₄).

4. The method of claim 1, wherein mixing a solution precursor further comprises mixing concentrations of alumina nanopowder and yttrium acetate to yield a stoichiometric composition of YAG.

5. The method of claim 1, wherein mixing a solution precursor further comprises mixing concentrations of alumina nanopowder, lanthanum acetate, and magnesium acetate to yield a stoichiometric composition of LMHA.

6. The method of claim 1, wherein mixing a solution precursor further comprises mixing concentrations of magnesium acetate and alumina nanopowder to yield a stoichiometric composition of MgAl₂0₄.

7. The method of claim 1, further comprising ball milling the solution precursor prior to injecting the solution precursor into the pyrolysis process.

8. The method of claim 1, further comprising dispersing the solution precursor via a high power ultrasonic dispersion process prior to injecting the solution precursor into the pyrolysis process.

9. The method of claim 1, further comprising filtering the solution precursor prior to injecting the solution precursor into the pyrolysis process.

10. The method of claim 1, wherein the pyrolysis process comprises at least one of a microwave plasma spray process, arc discharge plasma spray process, inductively coupled plasma spray process, low-pressure plasma spray process, and high velocity oxygen fuel process.

11. The method of claim 1, wherein injecting the solution precursor into a pyrolysis process comprises injecting droplets of the solution precursor into a microwave plasma torch.

12. The method of claim 1, wherein injecting the solution precursor into a pyrolysis process results in formation of a metal oxide composite powder prior to coating the substrate with a layer of the metal oxide composite material.

13. The method of claim 12, wherein the metal oxide nanopowder is alumina nanopowder and the metal oxide composite powder comprises at least one of LMHA, YAG, and MgAl₂0₄.

14. The method of claim 12, wherein coating a substrate with a layer of the metal oxide composite material comprises injecting the metal oxide composite powder into a subsequent pyrolysis process.

15. A method of manufacturing a material coating comprising:

mixing a solution precursor including an alumina nanopowder, a rare-earth oxide nanopowder, and a surfactant;

injecting the solution precursor into a pyrolysis process to form an aluminum oxide composite material; and

coating a substrate with a layer of the aluminum oxide composite material.

16. The method of claim 15, wherein the rare-earth oxide nanopowder comprises at least one material selected from the group consisting of: yttrium, gadolinium, or lanthanum.

17. A method of manufacturing a metal oxide composite powder comprising:

mixing a solution precursor including a metal oxide nanopowder and an acetate based compound; and

injecting the solution precursor into a pyrolysis process to form a metal oxide composite powder.

18. The method of claim 17, wherein the solution precursor further includes a surfactant, the metal oxide nanopowder is an alumina nanopowder, and the acetate based compound comprises at least one material selected from the group consisting of: magnesium acetate, lanthanum acetate, or yttrium acetate.

19. A solution precursor for a metal oxide material, the solution precursor comprising: a mixture of between 0.10 Mol/liter to 2.0 Mol/liter metal oxide nanopowder, between 0.04 Mol/liter to 2.80 Mol/liter an acetate based compound, and a solvent.

20. The solution precursor of claim 19, wherein the metal oxide nanopowder is alumina nanopowder, and the acetate based compound comprises at least one material selected from the group consisting of: magnesium acetate, lanthanum acetate, or yttrium acetate.

21. The solution precursor of claim 20, wherein the alumina nanopowder loading is between 25 g - 200 g per liter.