Preparation method of corrosion-resistant magnesium-aluminum spinel

Abstract

The application relates to a preparation method of a corrosion-resistant magnesium-aluminum spinel, belonging to the technical field of ceramic materials. The preparation steps comprise the following steps: magnesium-aluminum spinel powder with a total amount of 55% to 65% is mixed with Y2O3 and Ta2O5 to obtain inner layer matrix powder after granulation; the remaining magnesium-aluminum spinel powder is mixed with Sc2O3 and Y2O3 to obtain outer layer reinforcing powder after granulation; the inner layer matrix powder and the outer layer reinforcing powder are filled into a mold in sequence according to a thickness ratio of 1.7 to 2.3:1, and a green body is formed through dry pressing and cold isostatic pressing treatment; the green body is subjected to segmented pre-sintering; the pre-sintered body is subjected to hot isostatic pressing treatment, and a sintered body is obtained after cooling; and the sintered body is subjected to surface passivation treatment to obtain the corrosion-resistant magnesium-aluminum spinel. The application directly optimizes the chemical composition and microstructure of the magnesium-aluminum spinel itself, and fundamentally improves the corrosion resistance of the magnesium-aluminum spinel.

Description

Technical Field

[0001] A method for preparing corrosion-resistant magnesium aluminum spinel belongs to the field of ceramic materials technology. Background Technology

[0002] Magnesium aluminum spinel (MgAl2O4) is a very important ceramic material. It has a high melting point and excellent mechanical, thermal, and chemical stability, making it widely used in refractories, catalyst supports, and aerospace applications. However, this material also has limitations: its corrosion resistance is not strong enough in strong acid, strong alkali, or high-temperature corrosive environments, which restricts its application under some extreme conditions. Therefore, to meet the needs of modern industry, developing magnesium aluminum spinel materials with better corrosion resistance and more efficient preparation methods is particularly important.

[0003] Several technologies have attempted to address this problem. For example, patent CN105084916B proposed a corrosion-resistant magnesium-aluminum refractory material. It uses magnesium-aluminum spinel particles of different sizes as the main material, then adds auxiliary additives, nano-magnesium oxide, zirconium oxide, binders, and nano-alumina. This results in a more uniform material structure and improved strength and thermal shock resistance. The patent also uses nano-zinc oxide to fill small pores in the material, reducing porosity and making the material denser. However, the problem is that in this approach, the improvement in corrosion resistance mainly relies on nano-zinc oxide plugging, without truly enhancing the chemical stability of the magnesium-aluminum spinel itself. Even more problematic is that the amount of nano-zinc oxide added must be precisely controlled; adding too much may damage the overall mechanical properties and sintering effect of the material, making the production process quite complex.

[0004] Another patent, CN115231933B, describes a magnesium-based, highly corrosion-resistant refractory material. Using forsterite, magnesium aluminum spinel, sialon powder, calcium zirconate, and zirconium oxide as main materials, the resulting material exhibits high strength, good thermal shock resistance, and strong corrosion resistance. However, in this design, magnesium aluminum spinel is only one component of the composite material; its own improvement in corrosion resistance is limited. The main improvement relies on the combined effects of other components such as sialon powder and calcium zirconate. While this multi-component approach improves overall performance, it also increases raw material costs and complicates the manufacturing process, making large-scale production difficult.

[0005] Based on the above, existing magnesium aluminum spinel materials still have room for improvement in terms of corrosion resistance, cost control, and ease of processing. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing corrosion-resistant magnesium aluminum spinel with stronger corrosion resistance and lower cost.

[0007] The technical solution adopted by this invention to solve its technical problem is: a method for preparing corrosion-resistant magnesium aluminum spinel, the preparation steps of which include:

[0008] 1) The inner layer matrix powder is obtained by mixing the inner layer magnesium aluminum spinel powder, Y2O3, and Ta2O5 together and then granulating by pressure spraying. The amount of Y2O3 is 0.25%~0.35% of the mass of the inner layer magnesium aluminum spinel powder, and the amount of Ta2O5 is 0.6%~0.8% of the mass of the inner layer magnesium aluminum spinel powder. The outer layer magnesium aluminum spinel powder, Sc2O3, and Y2O3 are mixed together and then granulated by pressure spraying. The outer layer reinforcing powder is obtained by spray granulation; the amount of Sc2O3 is 0.5%~0.7% of the mass of the outer layer magnesium aluminate spinel powder, and the amount of Y2O3 is 0.25%~0.35% of the mass of the outer layer magnesium aluminate spinel powder; wherein, the inner layer magnesium aluminate spinel powder accounts for 55%~65% of the total mass of the magnesium aluminate spinel powder, and the outer layer magnesium aluminate spinel powder accounts for 35%~45% of the total mass of the magnesium aluminate spinel powder;

[0009] 2) The inner matrix powder and the outer reinforcing powder are filled into the mold in a thickness ratio of 1.7~2.3:1, and the green blank is formed by dry pressing and cold isostatic pressing. The green blank is pre-fired in sections at 1340℃~1360℃ and 1480℃~1520℃ respectively.

[0010] 3) The pre-fired green body is subjected to hot isostatic pressing at 1620℃~1680℃ and 180MPa~220MPa pressure for 100min~150min under a reducing atmosphere, and then cooled to obtain the sintered body;

[0011] 4) The sintered body is obtained by surface passivation treatment with 8wt%~11wt% nitric acid solution.

[0012] This invention directly optimizes the chemical composition and microstructure of magnesium aluminum spinel, fundamentally improving its corrosion resistance. This invention achieves this through differentiated rare earth doping (Sc) between the inner and outer layers. 3+ / Y 3+ To enhance grain boundary corrosion resistance, Ta 5+ By filling lattice defects and combining segmented temperature-controlled pre-firing, fine grain control is achieved. Selective etching with nitric acid and annealing are used to construct an α-alumina barrier layer in situ on the material surface, supplemented by an external protection layer of hafnium oxide film, forming a three-tiered corrosion-resistant barrier of "bulk phase-interface-surface". Compared to traditional single-component doping and simple heat treatment processes, this solution significantly improves the service life of the material in extreme corrosive environments without significantly increasing manufacturing costs.

[0013] This invention prepares corrosion-resistant magnesium-aluminate spinel by sintering magnesium-aluminate spinel powder. The main raw material, magnesium-aluminate spinel powder, can be pre-prepared according to traditional basic formulas, such as pre-mixing MgO and Al2O3 powders at a molar ratio of 1:0.98~3; or it can be purchased directly from companies such as Sinoma High-Tech, Shandong Guoci, and Shanghai Haohong. This process can improve the yield of large-size transparent magnesium-aluminate spinel ceramics.

[0014] Preferably, the specific process for mixing the inner layer magnesium-aluminum spinel powder with Y2O3 and Ta2O5 in step 1) is as follows: First, place the magnesium-aluminum spinel powder, Y2O3, and Ta2O5 in an ethanol medium accounting for 10%~30% of the mass of the magnesium-aluminum spinel powder, and then ball mill and mix for 3.5h~4.5h. The ethanol medium can effectively avoid the hydrolysis and agglomeration of Y2O3 and Ta2O3, ensuring the uniform dispersion of the additives in the magnesium-aluminum spinel matrix. By controlling the ball milling time and the ethanol ratio, the degree of mechanical alloying between the powders is significantly improved, promoting the formation of a more stable grain boundary phase in the pre-sintering stage, optimizing the grain boundary structure in the inner layer matrix, and laying the foundation for the subsequent high densification and the formation of a diffusion barrier layer for corrosion ions.

[0015] Preferably, the specific process for mixing the outer layer of magnesium aluminum spinel powder with Sc2O3 and Y2O3 in step 1) is as follows: the magnesium aluminum spinel powder is placed in a mixed suspension of Sc2O3 and Y2O3 and ultrasonically dispersed. The solid content of the mixed suspension is 20wt%~30wt%, wherein the solid phase is the total amount of Sc2O3, Y2O3 and magnesium aluminum spinel powder. The dispersion medium of the mixed suspension is anhydrous ethanol. The ultrasonic dispersion time is 4.5h~6h, the ultrasonic power density is controlled at 250W~400W per liter of mixed suspension, and the temperature of the mixed suspension is 35℃~40℃. Applying ultrasonic dispersion to the prepared anhydrous ethanol suspension effectively inhibits the agglomeration of Sc2O3 / Y2O3 nanoparticles and ensures their uniform coating on the surface of spinel particles. The continuous energy input of ultrasonic dispersion promotes the formation of lattice defect repair solid solution, laying the structural foundation for building a refined grain boundary corrosion ion diffusion barrier in the outer layer.

[0016] Preferably, in step 1), the particle size of the inner matrix powder is controlled to be 50μm~80μm during pressure spray granulation, and the particle size of the outer reinforcing powder is controlled to be 80μm~120μm during pressure spray granulation. The fine particles in the inner layer form a high-density matrix skeleton during molding, optimizing the densification effect of cold isostatic pressing; the coarse particles in the outer layer construct a multi-scale stacked structure, reducing the density of channels for corrosive media penetration. The particle size gradient design strengthens the interlayer mechanical interlocking effect, avoids interface cracking during segmented pre-firing, and provides a uniform diffusion path for hot isostatic pressing, ultimately improving the overall corrosion barrier continuity of the material.

[0017] Preferably, the pressure for dry pressing in step 2) is 195 MPa to 205 MPa; the pressure for cold isostatic pressing is 270 MPa to 285 MPa, the temperature is 30°C to 60°C, and the holding time is 180 s to 220 s. Dry pressing first forms a green body skeleton with initial strength, effectively avoiding interlayer loosening due to insufficient pressure or particle fragmentation due to excessive pressure; subsequently, the cold isostatic pressing condition promotes full rearrangement and plastic deformation of the particles, and the holding pressure ensures uniform pressure penetration, ultimately obtaining a highly dense and structurally uniform green body.

[0018] Preferably, the specific process of segmented pre-firing in step 2) is as follows: the green blank is first held at 1345℃~1355℃ for 55min~70min, and then heated to 1490℃~1510℃ at a rate of 8℃ / min~12℃ / min and held for 55min~70min. The low-temperature pre-firing section of 1345℃~1355℃ induces the directional nucleation of Y / Al grain boundary phases and inhibits grain coarsening; the rapid heating at 8℃ / min~12℃ / min reduces the segregation of grain boundary impurities. The high-temperature section of 1490℃~1510℃ strengthens the closed-pore shrinkage dominated by solid-phase diffusion, and the holding time matches the lattice migration kinetic threshold, so that the green body forms a semi-connected structure with a porosity of 50%~55%, which avoids grain boundary melting and pore sealing and provides a uniform diffusion channel for subsequent hot isostatic pressing.

[0019] Preferably, the reducing atmosphere described in step 3) is a mixture of argon and hydrogen at a volume ratio of 95-98:2-5. In this reducing atmosphere, argon forms the majority to ensure pressure stability, while 2%-5% hydrogen precisely reduces residual oxides at grain boundaries and eliminates oxygen vacancies, simultaneously suppressing Ta. 5+ / Sc 3+ Price fluctuations. This formulation avoids the risk of lattice oxygen loss, enabling efficient purification of the grain boundary glass phase during hot isostatic pressing while maintaining stoichiometry, thus improving density and corrosion resistance.

[0020] Preferably, in step 3), the preform is held at 1180℃~1250℃ and 48MPa~53MPa for 55min~75min before hot isostatic pressing. 1180℃~1250℃ matches the grain boundary glass phase viscosity temperature, and the preferred pressure promotes plastic rheological closure of pre-sintered residual pores. During the holding time, transition layer stress is released simultaneously to avoid grain boundary microcracks caused by subsequent rapid pressure increases, ensuring the uniformity of hot isostatic pressing density.

[0021] Preferably, the cooling described in step 3) involves first slowly cooling to below 800°C at a rate of 2°C / min to 5°C / min, and then naturally cooling to room temperature. This slow cooling rate effectively avoids the risk of re-precipitation of the glassy phase at grain boundaries above 800°C, simultaneously releasing residual thermal stress and preventing phase transformation cracking. Natural cooling below 800°C balances production efficiency, ensures the dispersed distribution of the purified phase at grain boundaries, and improves the corrosion resistance stability of the matrix.

[0022] Preferably, the surface passivation treatment in step 4) involves immersing the sintered body in a nitric acid solution with a concentration of 8wt% to 11wt% at 55℃ to 65℃, cleaning and drying it, and then annealing it in an air environment at 1000℃ to 1080℃ for 30 to 35 minutes to induce the formation of an α-alumina passivation layer on the surface.

[0023] Surface treatment with nitric acid solution of appropriate temperature and concentration selectively dissolves residual trace transition phases on the surface and forms an activated microporous structure; appropriate air annealing induces the directional agglomeration of aluminum elements on the spinel surface to generate a continuous α-alumina layer, achieving low interfacial stress and high density passivation, significantly improving the material's resistance to acidic media erosion.

[0024] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention achieves lattice defect repair and highly stable grain boundary phase construction through inner rare-earth composite doping; outer nano-coating enhances grain boundary corrosion resistance; and particle size gradient stacking eliminates weak interfacial regions. Segmented pre-sintering synergistically optimizes grain growth and pore structure evolution; hot isostatic pressing achieves near-full densification in a reducing atmosphere; and selective surface etching induces the formation of a continuous α-alumina passivation layer. Ultimately, this enables the material to form a three-tiered protection system of "bulk lattice strengthening - grain boundary purification - surface chemical barrier" in a highly corrosive environment, reducing the weight loss rate from corrosion with concentrated sulfuric acid at 70℃ for 168 hours to ≤0.03 mg / cm³. 2 ·h. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments, wherein Embodiment 1 is the preferred embodiment. The magnesium aluminum spinel powder used in the embodiment is a premix of MgO and Al2O3 powders in a molar ratio of 1:2. Other proportions are not shown in the embodiments.

[0026] Example 1

[0027] 1. Take 60% of the total amount of magnesium aluminum spinel powder as the inner layer magnesium aluminum spinel powder. Add 0.3% Y2O3 and 0.7% Ta2O5 by mass to the inner layer magnesium aluminum spinel powder. Place them together in an ethanol medium containing 20% ​​by mass of the inner layer magnesium aluminum spinel powder and ball mill them for 4 hours. Then, granulate them by pressure spraying and adjust the particle size to 50μm~80μm to obtain the inner layer matrix powder.

[0028] The remaining 40% of the magnesium aluminum spinel powder was used as the outer layer of magnesium aluminum spinel powder. The outer layer of magnesium aluminum spinel powder, together with 0.6% Sc2O3 and 0.3% Y2O3 by mass, was added to anhydrous ethanol and ultrasonically dispersed to form a suspension. The solid content of the suspension was 25 wt%, the ultrasonic dispersion time was 5 h, the ultrasonic power density was controlled at 300 W per liter of suspension, and the suspension temperature was 35 °C. The outer layer of reinforcing powder was obtained by pressure spray granulation, with the particle size controlled at 80 μm to 120 μm.

[0029] 2. The granulated powder is filled into the mold with an inner layer and an outer layer thickness ratio of 2:1. It is first dry-pressed at 200MPa pressure, and then subjected to cold isostatic pressing at 280MPa and 45℃ and held for 200s to form a green body with a compositional gradient structure.

[0030] The green blank was placed in a nitrogen atmosphere furnace for segmented pre-firing: first, it was held at 1350℃ for 60 min to inhibit excessive grain growth, and then the temperature was increased to 1500℃ at a rate of 10℃ / min and held for 60 min to stabilize the grain size below 3μm.

[0031] 3. The pre-fired green body is transferred to a hot isostatic pressing furnace and subjected to gradient pressure sintering in a mixed atmosphere of argon and hydrogen at a volume ratio of 97:3: A pressure of 50 MPa is applied starting at 1200℃ and held for 65 min to eliminate closed pores. The temperature is then increased to 1650℃ and the pressure is raised to 200 MPa and held for 120 min. After sintering, the green body is slowly cooled to 780℃ at a rate of 3℃ / min, and then allowed to cool naturally to room temperature to avoid grain boundary stress cracking.

[0032] 4. The sintered body is immersed in a 10wt% nitric acid solution at 60℃ for 120 min to selectively dissolve magnesium ions on the surface to form an aluminum-rich activation layer. After being cleaned with deionized water and dried, it is annealed in an air environment at 1000℃ for 35 min to induce the formation of a dense α-alumina passivation layer on the surface.

[0033] Example 2

[0034] The basic process is the same as in Example 1, except that in step 1, the outer layer of magnesium aluminum spinel powder, Sc2O3 and Y2O3 are also placed in an ethanol medium containing 20% ​​of the mass of magnesium aluminum spinel powder, ball-milled and mixed for 4 hours, and then granulated by pressure spraying.

[0035] Example 3

[0036] The basic process is the same as in Example 1, except that in step 2, the green blank is not held at 1350℃ for 60 minutes, but is directly heated to 1500℃ and held for 120 minutes.

[0037] Example 4

[0038] The basic process is the same as in Example 1. The difference is that in step 3, the hot isostatic pressing furnace is not subjected to a pressure of 50 MPa at 1200°C and held for 65 minutes. Instead, the temperature is directly raised to 1650°C and the pressure is increased to 200 MPa and held for 120 minutes.

[0039] Example 5

[0040] The basic process is the same as in Example 1, except that the sintered body is not annealed after acid leaching in step 4.

[0041] Example 6

[0042] 1. Take 55% of the total amount of magnesium aluminum spinel powder as the inner layer magnesium aluminum spinel powder. Add 0.25% Y2O3 and 0.6% Ta2O5 by mass to the inner layer magnesium aluminum spinel powder. Place them together in an ethanol medium containing 10% by mass of the inner layer magnesium aluminum spinel powder and ball mill them for 3.5 hours. Then, granulate them by pressure spraying and adjust the particle size to 50μm~80μm to obtain the inner layer matrix powder.

[0043] The remaining 45% of magnesium aluminum spinel powder was used as the outer layer of magnesium aluminum spinel powder. The outer layer of magnesium aluminum spinel powder, together with 0.5% Sc2O3 and 0.25% Y2O3 by mass, was added to anhydrous ethanol and ultrasonically dispersed to form a suspension. The solid content of the suspension was 30 wt%, the ultrasonic dispersion time was 6 h, the ultrasonic power density was controlled at 250 W per liter of suspension, and the suspension temperature was 35 °C. The outer layer of reinforcing powder was obtained by pressure spray granulation, with the particle size controlled at 80 μm to 120 μm.

[0044] 2. The granulated powder is filled into the mold with an inner layer and an outer layer thickness ratio of 1.7:1. It is first dry-pressed at 195MPa pressure, and then subjected to cold isostatic pressing at 270MPa and 30℃ and held for 220s to form a green body with a compositional gradient structure.

[0045] The green blank was placed in a nitrogen atmosphere furnace for segmented pre-firing: first, it was held at 1345℃ for 70 min to inhibit excessive grain growth, and then the temperature was increased to 1490℃ at a rate of 8℃ / min and held for 70 min to stabilize the grain size below 3μm.

[0046] 3. The pre-sintered green body is transferred to a hot isostatic pressing furnace and subjected to gradient pressure sintering in a mixed atmosphere of argon and hydrogen at a volume ratio of 95:5: A pressure of 48 MPa is applied starting at 1180℃ and held for 75 min to eliminate closed pores. The temperature is then increased to 1620℃ and the pressure is raised to 180 MPa and held for 150 min. After sintering, the green body is slowly cooled to 800℃ at a rate of 2℃ / min, and then allowed to cool naturally to room temperature to avoid grain boundary stress cracking.

[0047] 4. The sintered body is immersed in an 8wt% nitric acid solution at 55℃ for 150 min to selectively dissolve magnesium ions on the surface to form an aluminum-rich activation layer. After being cleaned with deionized water and dried, it is annealed in an air environment at 1000℃ for 30 min to induce the formation of a dense α-alumina passivation layer on the surface.

[0048] Example 7

[0049] 1. Take 65% of the total amount of magnesium aluminum spinel powder as the inner layer magnesium aluminum spinel powder. Add 0.35% Y2O3 and 0.8% Ta2O5 by mass to the inner layer magnesium aluminum spinel powder. Place them together in an ethanol medium containing 30% by mass of the inner layer magnesium aluminum spinel powder and ball mill them for 4.5 hours. Then, granulate them by pressure spraying and adjust the particle size to 50μm~80μm to obtain the inner layer matrix powder.

[0050] The remaining 35% of magnesium aluminum spinel powder was used as the outer layer of magnesium aluminum spinel powder. The outer layer of magnesium aluminum spinel powder, together with 0.7% Sc2O3 and 0.35% Y2O3 by mass, was added to anhydrous ethanol and ultrasonically dispersed to form a suspension. The solid content of the suspension was 20 wt%, the ultrasonic dispersion time was 4.5 h, the ultrasonic power density was controlled at 400 W per liter of suspension, and the suspension temperature was 40 °C. The outer layer of reinforcing powder was obtained by pressure spray granulation, with the particle size controlled at 80 μm to 120 μm.

[0051] 2. The granulated powder is filled into the mold with an inner layer and an outer layer thickness ratio of 2.3:1. It is first dry-pressed at 205MPa, and then subjected to cold isostatic pressing at 285MPa and 360℃ for 180s to form a green body with a compositional gradient structure.

[0052] The green blank was placed in a nitrogen atmosphere furnace for segmented pre-firing: first, it was held at 1355℃ for 55 min to inhibit excessive grain growth, and then the temperature was increased to 1510℃ at a rate of 12℃ / min and held for 55 min to stabilize the grain size below 3μm.

[0053] 3. The pre-sintered green body is transferred to a hot isostatic pressing furnace and subjected to gradient pressure sintering in a mixed atmosphere of argon and hydrogen at a volume ratio of 98:2: starting from 1250℃, a pressure of 53MPa is applied and held for 55min to eliminate closed pores, then the temperature is raised to 1680℃ and the pressure is increased to 220MPa and held for 100min. After sintering, it is slowly cooled to 700℃ at a rate of 5℃ / min, and then naturally cooled to room temperature to avoid the formation of grain boundary stress cracks;

[0054] 4. The sintered body is immersed in an 11wt% nitric acid solution at 65℃ for 100 min to selectively dissolve magnesium ions on the surface to form an aluminum-rich activation layer. After being cleaned with deionized water and dried, it is annealed in an air environment at 1080℃ for 35 min to induce the formation of a dense α-alumina passivation layer on the surface.

[0055] The magnesium-aluminum spinel samples obtained in each embodiment were subjected to performance tests, including corrosion resistance and mechanical properties. Corrosion resistance was assessed using two criteria: weight loss rate of 40% boiling H₂SO₄ (boiling H₂SO₄ weight loss rate in Tables 1 and 2), tested according to ASTM G31; corrosion depth after immersion in 50% NaOH at 100℃ (NaOH corrosion depth in Table 1), tested according to ISO 28706-2; and penetration depth of molten Na₂SO₄ at 900℃ (molten salt penetration depth in Tables 1 and 2), tested according to ASTM G68. Mechanical properties included Vickers hardness (HV10) (hardness in Tables 1 and 2), tested according to ISO 6507-1; and interlaminar bond strength (interlaminar strength in Tables 1 and 2), tested according to ASTM D4541. The test results are shown in Table 1.

[0056] Table 1 Performance test results of the examples

[0057] .

[0058] Comparative Example 1

[0059] The basic process is the same as in Example 1, except that a single-layer structure is used. The powder used to prepare the green body is: a matrix powder obtained by adding 0.4% Y2O3 and 0.6% Ta2O5 by mass to magnesium aluminum spinel powder. The matrix powder is ball-milled and mixed in an ethanol medium containing 10% to 30% of the magnesium aluminum spinel powder for 3.5 to 4.5 hours. The granulation is then carried out by pressure spray granulation, and the particle size is controlled to be 50 μm to 80 μm.

[0060] Comparative Example 2

[0061] The basic process is the same as in Example 1, except that step 4 is omitted.

[0062] Comparative Example 3

[0063] The basic process is the same as in Example 1, except that in step 3, after pre-firing, hot isostatic pressing is cancelled and replaced with sintering at atmospheric pressure at 1600℃.

[0064] The performance test results of each comparative example are shown in Table 2.

[0065] .

[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing corrosion-resistant magnesium aluminum spinel, characterized in that, The preparation steps include: 1) The inner layer matrix powder is obtained by mixing the inner layer magnesium aluminum spinel powder, Y2O3, and Ta2O5 together and then granulating by pressure spraying. The amount of Y2O3 is 0.25%~0.35% of the mass of the inner layer magnesium aluminum spinel powder, and the amount of Ta2O5 is 0.6%~0.8% of the mass of the inner layer magnesium aluminum spinel powder. The outer layer magnesium aluminum spinel powder, Sc2O3, and Y2O3 are mixed together and then granulated by pressure spraying. The outer layer reinforcing powder is obtained by spray granulation; the amount of Sc2O3 is 0.5%~0.7% of the mass of the outer layer magnesium aluminate spinel powder, and the amount of Y2O3 is 0.25%~0.35% of the mass of the outer layer magnesium aluminate spinel powder; wherein, the inner layer magnesium aluminate spinel powder accounts for 55%~65% of the total mass of the magnesium aluminate spinel powder, and the outer layer magnesium aluminate spinel powder accounts for 35%~45% of the total mass of the magnesium aluminate spinel powder; 2) The obtained inner matrix powder and outer reinforcing powder are successively filled into the mold at a thickness ratio of 1.7~2.3:1, and the green blank is formed by dry pressing and cold isostatic pressing; the green blank is pre-fired in sections at 1340℃~1360℃ and 1480℃~1520℃ respectively. 3) The pre-fired green body is subjected to hot isostatic pressing at 1620℃~1680℃ and 180MPa~220MPa pressure for 100min~150min under a reducing atmosphere, and then cooled to obtain the sintered body; 4) The sintered body is obtained by surface passivation treatment with 8wt%~11wt% nitric acid solution.

2. The method for preparing corrosion-resistant magnesium aluminum spinel according to claim 1, characterized in that: The specific process for mixing the inner layer of magnesium aluminum spinel powder with Y2O3 and Ta2O5 in step 1) is as follows: First, place the magnesium aluminum spinel powder, Y2O3 and Ta2O5 in an ethanol medium accounting for 10%~30% of the mass of the magnesium aluminum spinel powder, and then ball mill and mix for 3.5h~4.5h.

3. The method for preparing corrosion-resistant magnesium aluminum spinel according to claim 1, characterized in that: The specific process for mixing the outer layer of magnesium aluminum spinel powder with Sc2O3 and Y2O3 in step 1) is as follows: The magnesium aluminum spinel powder is placed in a mixed suspension of Sc2O3 and Y2O3 and ultrasonically dispersed. The solid content of the mixed suspension is controlled to be 20wt%~30wt%, wherein the solid phase is the total amount of Sc2O3, Y2O3 and magnesium aluminum spinel powder. The dispersion medium of the mixed suspension is anhydrous ethanol. The ultrasonic dispersion time is 4.5h~6h, the ultrasonic power density is controlled at 250W~400W per liter of mixed suspension, and the temperature of the mixed suspension is 35℃~40℃.

4. The method for preparing corrosion-resistant magnesium aluminum spinel according to claim 1, characterized in that: In step 1), the particle size of the inner matrix powder is controlled to be 50μm~80μm during pressure spray granulation, and the particle size of the outer reinforcing powder is controlled to be 80μm~120μm during pressure spray granulation.

5. The method for preparing corrosion-resistant magnesium aluminum spinel according to claim 1, characterized in that: The pressure for dry pressing in step 2) is 195MPa~205MPa; the pressure for cold isostatic pressing is 270MPa~285MPa, the temperature is 30℃~60℃, and the holding time is 180s~220s.

6. The method for preparing corrosion-resistant magnesium aluminum spinel according to claim 1, characterized in that: The specific process of segmented pre-firing in step 2) is as follows: the green blank is first held at 1345℃~1355℃ for 55min~70min, and then heated to 1490℃~1510℃ at a rate of 8℃ / min~12℃ / min and held for 55min~70min.

7. The method for preparing corrosion-resistant magnesium aluminum spinel according to claim 1, characterized in that: The reducing atmosphere mentioned in step 3) is a mixture of argon and hydrogen in a volume ratio of 95~98:2~5.

8. The method for preparing corrosion-resistant magnesium aluminum spinel according to claim 1, characterized in that: In step 3), the billet is held at 1180℃~1250℃ and 48MPa~53MPa for 55min~75min before hot isostatic pressing.

9. The method for preparing corrosion-resistant magnesium aluminum spinel according to claim 1, characterized in that: The cooling described in step 3) involves first slowly cooling to below 800°C at a rate of 2°C / min to 5°C / min, and then naturally cooling to room temperature.

10. The method for preparing corrosion-resistant magnesium aluminum spinel according to claim 1, characterized in that: Step 4) The surface passivation treatment involves immersing the sintered body in a nitric acid solution with a concentration of 8wt% to 11wt% at 55℃ to 65℃, cleaning and drying it, and then annealing it in an air environment at 1000℃ to 1080℃ for 30 to 35 minutes to induce the formation of an α-alumina passivation layer on the surface.