CN111807828A - Preparation method of low-cost magnesia-alumina spinel transparent ceramic product - Google Patents
Preparation method of low-cost magnesia-alumina spinel transparent ceramic product Download PDFInfo
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Abstract
The invention discloses a preparation method of low-cost magnesia-alumina spinel transparent ceramic, which is characterized by comprising the following steps of; preparing submicron-grade high-purity magnesia-alumina spinel into slurry; granulating powder with different ball diameters is obtained by a spray drying granulation method; preparing a high-density biscuit by a dry pressing, isostatic pressing or dry pressing and isostatic pressing method; sintering the high-density biscuit into a sintered body with the relative density of more than 99.9 percent by adopting an isothermal and isobaric double control technology in a vacuum hot-pressing furnace; and then the high-density magnesium aluminate spinel transparent ceramic product is obtained after heat treatment, double-sided coarse grinding, fine grinding and polishing. The invention does not adopt a high-temperature hot isostatic pressing process, so the method is more suitable for preparing the magnesia-alumina spinel transparent ceramic product with large size, large batch and low cost, and the prepared product has the characteristics of high density, transmittance of infrared to ultraviolet bands of more than 80 percent, good strength, corrosion resistance and the like, and can be widely applied to the fields of antenna covers, various window materials and the like.
Description
Technical Field
The invention relates to the technical field of transparent ceramic product preparation, in particular to a preparation method of a low-cost magnesium aluminate spinel transparent ceramic product, and especially relates to a low-cost and quantitative production process for a large-size magnesium aluminate spinel transparent ceramic product.
Background
The magnesia-alumina spinel transparent ceramic has the characteristics of high hardness, high strength, impact resistance, corrosion resistance, wear resistance, good electrical insulation performance and the like. Has good optical transmittance in ultraviolet, visible light and infrared light bands and has isotropic property. Therefore, the magnesium aluminate spinel transparent ceramic has wide application prospect in many fields. However, when the high-performance magnesia-alumina spinel transparent ceramic product is prepared by the prior art, the high-performance magnesia-alumina spinel transparent ceramic product is almost prepared by a nano powder sintering method, and small pores in a blank are difficult to remove, so that the transparency of the product is influenced. Therefore, the removal of small pores in the green body needs to be promoted by means of a high-temperature hot isostatic pressing process, but the matching equipment of the high-temperature hot isostatic pressing process is expensive, so that the manufacturing cost of the product is quite high, the batch production is not easy, the size of the product is limited, and the like, thereby severely limiting the application range of the magnesium aluminate spinel ceramic. Currently, the method is only focused on the military and aerospace field with higher performance requirements, and for example, the high-strength and large-size transparent ceramic products have a small number of applications in the aspects of transparent armors, windows, hoods and the like. In short, it cannot be widely used because of its high manufacturing cost.
At present, the related patent applications related to magnesium aluminate spinel transparent ceramics mainly focus on the preparation of magnesium aluminate spinel powder and a sintering densification method, wherein the preparation of the magnesium aluminate spinel powder comprises the following steps: mixing inorganic salt of magnesium with inorganic salt of aluminum, and adding aluminum2O3Dissolving MgO in water, mixing uniformly, drying and dehydrating to obtain high-purity magnesia-alumina spinel nano-powder, and calcining to obtain high-purity magnesia-alumina spinel nano-powder; adding magnesium oxide powder and alpha-aluminum oxide powder into the mixture, and performing mixed ball milling-high temperature solid phase reaction to obtain the magnesium oxide powder; synthesizing nano magnesia alumina spinel powder with high sintering activity by field fast synthesis-MgAlON ceramic powder and other methods; the sintering densification method comprises the following steps: the nano-particles with high sintering activityThe grade magnesium aluminate spinel powder is subjected to dry pressing, isostatic pressing and hot pressing sintering to form a blank with the relative density of more than 95%, and then the blank is further prepared into high-density magnesium aluminate spinel transparent ceramic with the relative density of more than 99.8% by a high-temperature hot isostatic pressing method, and rare earth element oxide is mixed with the magnesium aluminate spinel powder as a sintering aid before dry pressing in some schemes, so that the densification process and pore elimination are promoted.
From the existing patents and literature reports at home and abroad, the transparent ceramics are almost prepared by adopting nano-scale magnesia-alumina spinel powder at present. The nano-scale magnesia-alumina spinel powder has fine particles and high sintering activity, but is difficult to be pressed into a biscuit with high density, a large number of pores exist in the biscuit, and the small pores are difficult to remove in the middle sintering period of the nano particles, which seriously influences the subsequent densification, particularly, the residual pores are difficult to completely remove in the middle and later sintering periods, thereby influencing the transparency of products. Therefore, in the process of preparing high-transparency magnesia-alumina spinel transparent ceramic by using nano-scale magnesia-alumina spinel powder, residual small air holes have to be further removed by using a high-temperature hot isostatic pressing method, so that the relative density is increased to more than 99.9 percent. Therefore, the technical difficulty and the preparation cost of the high-transparency magnesia-alumina spinel transparent ceramic product are greatly improved, and the application range of the magnesia-alumina spinel transparent ceramic is seriously influenced.
Disclosure of Invention
Technical problem to be solved
In view of the above disadvantages and shortcomings of the prior art, the present invention provides a method for preparing a low-cost magnesium aluminate spinel transparent ceramic product, which is mainly used for realizing the mass production and low-cost manufacture of large-size, high-density and high-transparency magnesium aluminate spinel transparent ceramic.
(II) technical scheme
In order to achieve the purpose, the invention adopts the main technical scheme that:
in a first aspect, embodiments of the present invention provide a method for preparing a low-cost magnesium aluminate spinel transparent ceramic product, which includes the following steps:
s1: dispersing submicron-grade high-purity magnesia-alumina spinel powder into a solvent to prepare slurry;
s2: granulating powder with different spherical diameters is obtained from the slurry by a spray drying granulation method;
s3: sorting and grading the granulated powder according to different sphere diameters to obtain two or more granulated powders with different sphere diameter interval grades;
s4: grading the granulation powders of two or more different sphere diameter interval grades to find a grading proportion capable of obtaining the maximum bulk density, mixing the granulation powders of different sphere diameter interval grades according to the grading proportion, and pressing to form a high-density biscuit;
s5: putting the high-density biscuit into a vacuum hot-pressing furnace, and sintering the biscuit into a sintered body with the relative density of more than 99.9 percent by using an isothermal and isobaric double control technology;
s6: putting the sintered body into a heating furnace in an oxidizing atmosphere for heat treatment to eliminate open pores and infiltrated carbon;
s7: and (3) performing double-sided coarse grinding, fine grinding and polishing on the sintered body subjected to heat treatment to obtain the high-density magnesium aluminate spinel transparent ceramic product.
According to a preferred embodiment of the present invention, wherein: in step S1, the submicron-grade high-purity magnesia-alumina spinel powder is a high-purity magnesia-alumina spinel phase, the purity is more than 99.9%, the ratio of aluminum to magnesium is 0.95-1.6, and harmful impurities are controlled to ppm level; the content of large particles of 5 μm or more was 0. The submicron material has a median particle diameter D50 of 0.2-0.9 μm.
According to a preferred embodiment of the present invention, wherein: in step S1, the slurry contains: submicron-grade high-purity magnesia-alumina spinel powder, pure alumina balls, absolute alcohol or acetone, a sintering aid, a dispersing agent, a bonding agent and a defoaming agent.
According to a preferred embodiment of the present invention, wherein: in step S1, the preparation method of the slurry includes: adding 40-60 parts by mass of submicron-grade high-purity magnesia-alumina spinel powder and 15-25 parts by mass of pure alumina balls into absolute alcohol or acetone, adding a bonding agent, a sintering aid, a defoaming agent and a dispersing agent, and fully stirring or ultrasonically dispersing or stirring and assisting in ultrasonically dispersing in a container to obtain submicron-grade high-purity magnesia-alumina spinel slurry with good dispersibility and non-agglomeration solid content of 40-55%.
According to a preferred embodiment of the present invention, wherein: in step S1, the usage amounts of the sintering aid, the binder, the defoaming agent, and the dispersant in the slurry respectively account for 0-0.5 wt%, 0.1-0.5 wt%, 0.01-0.03 wt%, and 0.01-0.5 wt% of the mass of the slurry. Finally, the addition amount of each component controls the pH value of the prepared slurry to be 7.5-8 and the viscosity to be 50-100 Pa.s. When the amount of the sintering aid is 0, the slurry is not added with the sintering aid.
The dispersing agent is used for enhancing the dispersion degree, improving the uniformity of the slurry and reducing the agglomeration phenomenon. The defoaming agent is used for eliminating air bubbles in the slurry, so that granulation powder with uniform spherulite shape and spherical diameter can be obtained in spray drying granulation, and the generation of a large amount of fine powder particles is reduced. Absolute alcohol or acetone is used as a solvent for pulping. The sintering aid is used for promoting the green body pressed by the granulated powder to be more densified and eliminate air holes in the sintering and heat treatment processes, and the transmittance of the ceramic product is improved. The binder is mainly used for granulation and compression molding of biscuit, so that dispersed particles have proper viscosity, balls with different sizes can be formed during spray drying granulation, and the moldability of the pressed compact and the density of the biscuit are improved after grading.
According to a preferred embodiment of the present invention, wherein: in step S1, the pure alumina spheres are high-purity alumina spheres with a purity of 99.9%; the sintering aid is one or more of high-purity lithium, calcium and other rare earth oxides (the sintering aid can be not added); the binder is one or two of high-purity polyvinyl alcohol or high-purity polyvinyl butyral; the defoaming agent is octanol defoaming agent; the dispersant is a high-purity organic base dispersant.
According to a preferred embodiment of the present invention, wherein: in step S2, the method for obtaining granulated powders with different spherical diameters includes: spray-drying and granulating the slurry by adopting an explosion-proof pressure type or centrifugal spray-drying granulator with atmosphere protection; the inlet and outlet temperatures of the spray drying granulator are respectively controlled at 210 ℃ and 85-95 ℃, so that granulated powder with the sphere diameter of 20-150 microns is obtained.
According to a preferred embodiment of the present invention, wherein: in step S3, the granulated powder obtained in step S2 with different spherical diameters is sorted and classified by a sieving machine, or sorted and classified by an air suspension method, so that granulated powder with two or more different spherical diameter interval grades is obtained.
According to a preferred embodiment of the present invention, wherein: in step S4, the grading ratio of the granulated powder with the best bulk density can be found by using a sand-pack method or a tap grading machine. In step S3, the different sphere diameter interval grades include three different sphere diameter interval grades: a first stage with a sphere diameter of 120-; the mixing ratio for press-molding the high-density biscuit in step S4 is 3: 2: 5.
according to a preferred embodiment of the present invention, wherein: the method for pressing and molding the high-density biscuit in the step S4 comprises the following steps: putting the granulated powder of different ball diameter interval grades mixed according to the mixing proportion into a mould to prepare a high-density biscuit by a dry pressing, isostatic pressing or dry pressing and isostatic pressing forming method; wherein, when the dry pressing method is simply adopted, a high-density biscuit is prepared by adopting a 100-150MPa pressure bidirectional pressurization mode; when the dry pressing and isostatic pressing forming method is adopted, the biscuit with high density is prepared by firstly using dry pressing of more than 60MPa for preliminary forming and then using cold isostatic pressing under the pressure of 200 and 300 MPa. The relative density of the high-density biscuit prepared by the two methods can respectively reach more than 40 to 55 percent of theoretical density.
According to a preferred embodiment of the present invention, wherein: the process of step S5 is: putting the high-density biscuit into a graphite mold in a vacuum hot-pressing furnace, placing the graphite mold in a constant-temperature area of the vacuum hot-pressing furnace, and sintering the graphite mold into a sintered body with the relative density of more than 99.9 percent by using an isothermal and isobaric double control technology; the sintering temperature is 1550-- 3Pa。
The heating mode of the vacuum hot-pressing furnace is one of a tungsten wire, a graphite rod or an induction heating mode; vacuum degree of 10-3Pa is above; the pressure regulating interval is 0-700T, stepless regulation and control; the temperature regulating interval is from room temperature to 2000 ℃, and stepless regulation is realized. The effective area of the furnace cavity is 1200x800mm, the constant temperature area is more than 500mm, and the temperature uniformity of the constant temperature area of the furnace cavity is +/-5 ℃.
According to a preferred embodiment of the present invention, wherein: in step S6, the sintered body is put into a furnace with an oxidizing atmosphere for heat treatment at 1050 ℃ and 1250 ℃ for 10-15h in the furnace to eliminate open pores and infiltrated carbon. Wherein the temperature in the furnace body can be steplessly regulated and controlled from room temperature to 1400 ℃; the temperature uniformity of the furnace chamber is +/-5 ℃.
According to a preferred embodiment of the present invention, wherein: in step S7, a grinding wheel or a grinding disc is adopted to carry out double-sided coarse grinding, fine grinding and polishing; the grinding wheel or the grinding disc is made of silicon carbide particles or diamond abrasive particles; wherein, the grinding wheel or the grinding disc used for rough grinding has the mesh numbers of silicon carbide or diamond grinding material W10 and 120 meshes respectively, and the grinding wheel or the grinding disc used for fine grinding has the mesh numbers of silicon carbide or diamond grinding material W3 and 240 meshes respectively; polishing with diamond grinding glue with grain size of 0.1-0.5 micron; after double-sided coarse grinding, fine grinding and polishing, the surface of the high-density magnesia-alumina spinel transparent ceramic product has the smoothness of more than Ra0.1 mu m mirror surface level.
(III) advantageous effects
(1) Compared with the prior art which adopts nano high-purity magnesia-alumina spinel powder, the process of the invention is simpler, the raw materials are easy to obtain, the high-purity submicron magnesia-alumina spinel powder can be self-made or purchased in the market, and the manufacturing cost of the product can be reduced.
(2) The invention adopts the vacuum hot-pressing isothermal and isobaric double control technology to prepare the transparent ceramic in the process of sintering the biscuit, compared with the prior art which adopts the non-pressure or hot-pressing presintering and then the high-temperature hot isostatic pressing method, the invention can greatly reduce the manufacturing cost of the transparent ceramic, and the size of the transparent ceramic product is not limited by expensive 'high-temperature hot isostatic pressing matching equipment'.
(3) The invention uses submicron high-purity magnesia-alumina spinel powder as raw material to prepare slurry, adopts static methods such as spray drying granulation method granulation, dry pressing or dry pressing and cooling to prepare high biscuit, and then prepares transparent ceramic by hot pressing sintering.
(4) The size of the magnesium aluminate spinel transparent ceramic product can be designed and produced according to requirements, and sintering of multiple pieces in one furnace can be realized, so that batch production is realized.
Therefore, the process method is suitable for preparing the magnesia-alumina spinel transparent ceramic product in large batch at low cost, and the prepared transparent ceramic product has the characteristics of high density, infrared-ultraviolet band transmittance of more than 80%, good strength, corrosion resistance and the like, so the process method can be widely used for antenna covers and various window materials with strict requirements.
Drawings
Fig. 1 is a flow chart of a method for preparing a magnesium aluminate spinel transparent ceramic article according to the invention.
Detailed Description
For the purpose of better explaining the present invention and to facilitate understanding, the present invention will be described in detail by way of specific embodiments with reference to the accompanying drawings.
The invention provides a preparation method of a low-cost magnesia-alumina spinel transparent ceramic product, which mainly takes submicron-grade high-purity magnesia-alumina spinel powder as a raw material, firstly, the submicron-grade high-purity magnesia-alumina spinel powder is dispersed into a solvent, and hard agglomeration in the powder is eliminated to prepare slurry; then preparing the slurry into granulating powder with different sphere diameters by adopting a spray drying granulation method, and sorting and grading the granulating powder according to different sphere diameters to obtain the granulating powder with different sphere diameter interval grades; carrying out bulk density test on the granulated powder with different ball diameter interval grades to find a matching proportion capable of obtaining the maximum bulk density, and then mixing the granulated powder with different ball diameter interval grades according to the matching proportion; filling the mixed granulation powder into a die, molding a densified biscuit by dry pressing or isostatic pressing, sintering the high-density biscuit into a high-density magnesia-alumina spinel transparent ceramic material with the relative density of more than 99.9 percent by adopting a pressure-temperature double-control hot-pressing sintering branch, and performing heat treatment in an oxidizing atmosphere to eliminate open pores and infiltrated carbon; and performing double-sided coarse grinding, fine grinding and polishing to obtain the high-density magnesia-alumina spinel transparent ceramic product.
As shown in fig. 1, the process flow of the preparation method of the magnesium aluminate spinel transparent ceramic product of the present invention specifically includes the following steps:
s1: dispersing submicron-grade high-purity magnesia-alumina spinel powder into a solvent to prepare slurry;
s2: granulating powder with different spherical diameters is obtained from the slurry by a spray drying granulation method;
s3: sorting and grading the granulated powder according to different sphere diameters to obtain two or more granulated powders with different sphere diameter interval grades;
s4: grading the granulation powders of two or more different sphere diameter interval grades to find a grading proportion capable of obtaining the maximum bulk density, mixing the granulation powders of different sphere diameter interval grades according to the grading proportion, and pressing to form a high-density biscuit;
s5: putting the high-density biscuit into a vacuum hot-pressing furnace, and sintering the biscuit into a sintered body with the relative density of more than 99.9 percent by using an isothermal and isobaric double control technology;
s6: putting the sintered body into a heating furnace in an oxidizing atmosphere for heat treatment to eliminate open pores and infiltrated carbon;
s7: and (3) performing double-sided coarse grinding, fine grinding and polishing on the sintered body subjected to heat treatment to obtain the high-density magnesium aluminate spinel transparent ceramic product.
The technical solution and the technical effect of the present invention will be described below with reference to specific embodiments.
Example 1
The embodiment provides a preparation method of a low-cost magnesium aluminate spinel transparent ceramic product, which comprises the following steps:
(1) the preparation method comprises the following steps of preparing slurry from commercially available and completely synthesized magnesia-alumina spinel powder with the ratio of n to n of 1 submicron grade high purity:
stirring 50 parts by mass of submicron-grade high-purity magnesia-alumina spinel powder, 70 parts by mass of absolute alcohol solvent and 20 parts by mass of 99.9% high-purity alumina balls in a stirring mill for 10 hours to obtain submicron-grade high-purity magnesia-alumina spinel slurry with good dispersibility and non-agglomeration solid content of more than 50 wt%; wherein, 0.5 wt% of tetramethyl ammonium hydroxide dispersant, 0.5 wt% of high-purity polyvinyl alcohol adhesive and 0.01 wt% of octanol antifoaming agent are additionally added.
Wherein, the submicron-grade high-purity magnesia-alumina spinel powder is a high-purity magnesia-alumina spinel phase, the grain diameter is 0.20 to 0.60 mu m, the purity reaches more than 99.9 percent, and harmful impurities are controlled at the ppm level; median particle diameter D500.30 μm, and a large particle content of 2 μm or more is 0.
(2) And (3) carrying out spray granulation on the slurry of the submicron-grade high-purity magnesia-alumina spinel by using an explosion-proof pressure type spray drying granulator to obtain granulated powder with different sphere diameters, wherein the inlet temperature and the outlet temperature of the spray drying granulator are respectively controlled at 180 ℃ and 88 ℃. Thus, the granulated powder with different sphere diameters of 20-150 microns is obtained, and the granulated powder is classified by a sieving machine into three kinds of granulated powder with different sphere diameter grades of 120-150 microns, 60-90 microns and 20-40 microns.
(3) According to the following steps of 3: 2: 5, mixing the granulation powders with different sphere diameters, filling the mixture into a mold, and molding the mixture by using a 150MPa bidirectional pressurizing square to prepare a biscuit with the density reaching 45 percent of theoretical density.
(4) The biscuit is put into a vacuum hot pressing furnace and sintered for 5 hours at 1600 ℃ and 30MPa by using an isothermal and isobaric double control technology, and the biscuit is sintered into a sintered body with the relative density of more than 99.9 percent. Then, the sintered body was heat-treated at 1200 ℃ for 8 hours in a furnace of an oxidizing atmosphere to eliminate open pores and infiltrated carbon. Wherein the temperature in the furnace body can be steplessly regulated and controlled from room temperature to 1400 ℃; the temperature uniformity of the furnace chamber is +/-5 ℃.
(5) And performing double-sided coarse grinding, fine grinding and polishing on the heat-treated sintered body to obtain the high-density magnesium aluminate spinel transparent ceramic product. The mesh number of diamond grinding materials of the rough grinding disc is W10 and 120 meshes respectively, and the mesh number of diamond grinding materials of the fine grinding disc is W3 and 240 meshes respectively; polishing with diamond grinding glue with grain size of 0.1-0.5 micron, and final product with surface smoothness over Ra0.1 micron level.
The density of the magnesium aluminate spinel transparent ceramic product prepared by the method is 3.58g/cm3(ii) a The bending strength is 200 MPa; hardness: 1700HKnoop (Knoop)(ii) a Light transmittance: > 81% (2-7 μm), (lambda: 1900-6000 nm); the size of the magnesium aluminate spinel transparent ceramic product can be produced and prepared according to actual requirements, and one-furnace multi-chip sintering can be realized.
Example 2
The embodiment provides a preparation method of a low-cost magnesium aluminate spinel transparent ceramic product, which comprises the following steps:
(1) the totally synthesized aluminum-magnesium ratio n which is purchased from the market is 1.2 and D50The preparation method of the submicron-grade high-purity magnesia-alumina spinel powder with the particle size of 0.2 micron comprises the following steps:
stirring 50 parts by mass of submicron-grade high-purity magnesia-alumina spinel powder, 70 parts by mass of absolute alcohol solvent and 20 parts by mass of 99.9% high-purity alumina balls in a stirring mill for 10 hours to obtain submicron-grade high-purity magnesia-alumina spinel slurry with good dispersibility and non-agglomeration solid content of more than 50 wt%; wherein, 0.2 wt% of tetramethyl ammonium hydroxide dispersant, 0.5 wt% of high-purity polyvinyl alcohol adhesive and 0.01 wt% of octanol antifoaming agent are additionally added.
Wherein, the submicron-grade high-purity magnesia-alumina spinel powder is a high-purity magnesia-alumina spinel phase, the grain diameter is 0.3-1.0 mu m, the purity reaches more than 99.9 percent, and harmful impurities are controlled at the ppm level; the content of large particles of 5 μm or more was 0.
(2) The slurry of the submicron-grade high-purity magnesia-alumina spinel is subjected to spray granulation by an explosion-proof pressure type spray drying granulator to obtain granulated powder with different spherical diameters, and the inlet temperature and the outlet temperature of the spray drying granulator are respectively controlled at 160 ℃ and 170 ℃ and 90-92 ℃. Thus, the granulated powder with different sphere diameters of 20-150 microns is obtained, and the granulated powder is classified by a sieving machine into three kinds of granulated powder with different sphere diameter grades of 120-150 microns, 60-90 microns and 20-40 microns.
(3) According to the following steps of 3: 2: 5, mixing the granulation powders with different sphere diameters, filling the mixture into a mold, and molding the mixture by using a 150MPa bidirectional pressurizing square to prepare a biscuit with the density of 55 percent of theoretical density.
(4) The biscuit is put into a vacuum hot pressing furnace and sintered for 6 hours at 1650 ℃ and 30MPa by using an isothermal and isobaric double control technology, and the biscuit is sintered into a sintered body with the relative density of more than 99.9 percent. Then, the sintered body was heat-treated at 1200 ℃ for 6 hours in a furnace of an oxidizing atmosphere to eliminate open pores and infiltrated carbon. Wherein the temperature in the furnace body can be steplessly regulated and controlled from room temperature to 1300 ℃; the temperature uniformity of the furnace chamber is +/-5 ℃.
(5) And performing double-sided coarse grinding, fine grinding and polishing on the heat-treated sintered body to obtain the high-density magnesium aluminate spinel transparent ceramic product. The mesh number of diamond grinding materials of the rough grinding disc is W10 and 120 meshes respectively, and the mesh number of diamond grinding materials of the fine grinding disc is W3 and 240 meshes respectively; the polishing is carried out by diamond grinding glue with grain diameter of 0.1-0.5 μm, and the surface finish of the final product reaches more than Ra0.1 μm mirror surface level.
The density of the magnesia-alumina spinel transparent ceramic product prepared by the method is 3.59g/cm3(ii) a The bending strength is 210 MPa; hardness: 1700HKnoop (Knoop)(ii) a Light transmittance: > 80% (2-7 μm), (lambda: 1900-6000 nm); the size of the magnesium aluminate spinel transparent ceramic product can be prepared according to the requirement, and the sintering of multiple pieces in one furnace can be realized.
Example 3
The embodiment provides a preparation method of a low-cost magnesium aluminate spinel transparent ceramic product, which comprises the following steps:
(1) self-synthesis with magnesium sulfate and gamma-alumina at 1100 deg.C, Al-Mg ratio n is 1, D500.5 micron submicron grade high purity magnesia-alumina spinel powder.
(2) The submicron-grade high-purity magnesia-alumina spinel powder is prepared into slurry by the following preparation method:
50 parts by mass of submicron-grade high-purity magnesia-alumina spinel powder, 70 parts by mass of absolute alcohol solvent and 20 parts by mass of 99.9% high-purity alumina balls are added, and stirred in a stirring mill for 10 hours to obtain submicron-grade high-purity magnesia-alumina spinel slurry with good dispersibility and non-agglomeration solid content of more than 50 wt%; wherein, the external burning-assistant agent calcium oxide is 0.5 wt%, the tetramethyl ammonium hydroxide dispersant is 0.5 wt%, the high-purity polyvinyl alcohol adhesive is 0.5 wt%, and the octanol antifoaming agent is 0.02 wt%.
Wherein, the submicron-grade high-purity magnesia-alumina spinel powder is a high-purity magnesia-alumina spinel phase, the grain diameter is 0.2-1.0 mu m, the purity is more than 99.9 percent, and harmful impurities are controlled at the ppm level; the content of large particles of 5 μm or more was 0.
(2) The slurry of the submicron-grade high-purity magnesia-alumina spinel is subjected to spray granulation by adopting a centrifugal spray drying granulator to obtain granulated powder with different spherical diameters, and the inlet temperature and the outlet temperature of the spray drying granulator are respectively controlled at 155 ℃ and 85-88 ℃. Thus, the granulated powder with different sphere diameters of 20-150 microns is obtained, and the granulated powder is classified by a sieving machine into three kinds of granulated powder with different sphere diameter grades of 120-150 microns, 60-90 microns and 20-40 microns.
(3) According to the following steps of 3: 2: 5, mixing the granulation powders with different sphere diameters, filling the mixture into a mold, and molding the mixture by using a 150MPa bidirectional pressurizing square to prepare a biscuit with the density of 50 percent of theoretical density.
(4) The biscuit is put into a vacuum hot pressing furnace and sintered for 5 hours at 1650 ℃ and 30MPa by using an isothermal and isobaric double control technology, and the biscuit is sintered into a sintered body with the relative density of more than 99.9 percent. Then, the sintered body was heat-treated at 1200 ℃ for 5 hours in a furnace of an oxidizing atmosphere to eliminate open pores and infiltrated carbon. Wherein the temperature in the furnace body can be steplessly regulated and controlled from room temperature to 1300 ℃; the temperature uniformity of the furnace chamber is +/-5 ℃.
(5) And performing double-sided coarse grinding, fine grinding and polishing on the heat-treated sintered body to obtain the high-density magnesium aluminate spinel transparent ceramic product. The mesh number of diamond grinding materials of the rough grinding disc is W10 and 120 meshes respectively, and the mesh number of diamond grinding materials of the fine grinding disc is W3 and 240 meshes respectively; the polishing is carried out by diamond grinding glue with grain diameter of 0.1-0.5 μm, and the surface finish of the final product reaches more than Ra0.1 μm mirror surface level.
The density of the magnesia-alumina spinel transparent ceramic product prepared by the method is 3.59g/cm3(ii) a The bending strength is 210 MPa; hardness: 1700HKnoop (Knoop)(ii) a Light transmittance: > 83% (2-7 μm), (lambda: 1900-6000 nm); the size of the magnesium aluminate spinel transparent ceramic product can be prepared according to the requirement, and the sintering of multiple pieces in one furnace can be realized. The addition of sintering aid can promote the granulation powder pressureThe prepared biscuit is more compact and air holes are eliminated in the sintering and heat treatment processes, and the transmittance of the ceramic product is improved.
The method is suitable for preparing the magnesia-alumina spinel transparent ceramic product in large batch at low cost, and the product has the characteristics of high density, high transmittance in infrared to ultraviolet bands, good strength, corrosion resistance and the like; the material can be used for antenna covers and various window materials, and is expected to be widely applied to the fields of nuclear reactor wall materials, low-voltage high-frequency capacitance induction coil frameworks, optical fibers, optical fiber sensors, optical computer parts, high-grade watches, shells and mirror surfaces of precision instruments, various goggles and lenses and the like.
The invention can use submicron grade high-purity magnesia-alumina spinel without using nano-grade raw materials; the product with large size can be prepared by the conventional ceramic process; the isothermal and isobaric double control technology can be used in a vacuum hot-pressing furnace without expensive high-temperature hot static pressure equipment; preparing the high-density magnesia-alumina spinel transparent ceramic product, and the like. Therefore, the method is suitable for preparing the magnesia-alumina spinel transparent ceramic product in large batch at low cost.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. A preparation method of a low-cost magnesium aluminate spinel transparent ceramic product is characterized by comprising the following steps:
s1: dispersing submicron-grade high-purity magnesia-alumina spinel powder into a solvent to prepare slurry;
s2: granulating powder with different spherical diameters is obtained from the slurry by a spray drying granulation method;
s3: sorting and grading the granulated powder according to different sphere diameters to obtain two or more granulated powders with different sphere diameter interval grades;
s4: grading the granulation powders of two or more different sphere diameter interval grades, finding a grading proportion capable of obtaining the maximum stacking density, mixing the granulation powders of different sphere diameter interval grades according to the grading proportion, and pressing to form a high-density biscuit;
s5: putting the high-density biscuit into a vacuum hot-pressing furnace, and sintering the biscuit into a sintered body with the relative density of more than 99.9 percent by using an isothermal and isobaric double control technology;
s6: putting the sintered body into a heating furnace in an oxidizing atmosphere for heat treatment to eliminate open pores and infiltrated carbon;
s7: and (3) performing double-sided coarse grinding, fine grinding and polishing on the sintered body subjected to heat treatment to obtain the high-density magnesium aluminate spinel transparent ceramic product.
2. The preparation method of claim 1, wherein in step S1, the submicron-grade high-purity magnesia-alumina spinel powder is a high-purity magnesia-alumina spinel phase with a purity of 99.9% or more, an aluminum-magnesium ratio of 0.95 to 1.6, and harmful impurities in ppm level; median particle diameter D500.2-0.9 μm, and 0 content of large particles of 5 μm or more.
In step S1, the slurry contains: submicron-grade high-purity magnesia-alumina spinel powder, pure alumina balls, absolute alcohol or acetone, a sintering aid, a dispersing agent, a bonding agent and a defoaming agent.
3. The method according to claim 2, wherein in step S1, the slurry is prepared by: adding 40-60 parts by mass of submicron-grade high-purity magnesia-alumina spinel powder and 15-25 parts by mass of pure alumina balls into absolute alcohol or acetone, adding a dispersing agent, a sintering aid, a bonding agent and a defoaming agent, and fully stirring or ultrasonically dispersing or stirring and assisting in ultrasonically dispersing in a container to obtain submicron-grade high-purity magnesia-alumina spinel slurry with good dispersibility and non-agglomeration solid content of 40-55%.
4. The method according to claim 3, wherein in step S1, the sintering aid, the binder, the defoaming agent and the dispersant are respectively used in an amount of 0-0.5 wt%, 0.1-0.5 wt%, 0.01-0.03 wt% and 0.01-0.5 wt% based on the mass of the slurry.
In step S1, the pure alumina spheres are high-purity alumina spheres with a purity of 99.9%; the sintering aid is one or more of high-purity lithium, calcium and rare earth oxides; the binder is one or two of high-purity polyvinyl alcohol or high-purity polyvinyl butyral; the defoaming agent is octanol defoaming agent; the dispersant is a high-purity organic base dispersant.
5. The method for preparing granulated powder according to claim 1, wherein in step S2, the method for obtaining granulated powder with different spherical diameters comprises: spray-drying and granulating the slurry by adopting an explosion-proof pressure type or centrifugal spray-drying granulator with atmosphere protection; the inlet and outlet temperatures of the spray drying granulator are respectively controlled at 210 ℃ and 85-95 ℃, so that granulated powder with the sphere diameter of 20-150 microns is obtained.
In step S3, the granulated powder obtained in step S2 with different spherical diameters is sorted and classified by a sieving machine, or sorted and classified by an air suspension method, so that granulated powder with two or more different spherical diameter interval grades is obtained.
6. The method according to claim 1 or 5, wherein the step S4 for finding the gradation ratio for obtaining the maximum bulk density comprises mixing the granulated powders at different ratios by a sand-pack method, performing a density test, and finding the gradation ratio for obtaining the maximum bulk density, wherein the test method comprises: firstly, assuming a grading proportion, respectively measuring the density of a tamping state, continuously adjusting the grading proportion according to the variation trend of the density until the maximum bulk density in the tests is obtained, and taking the grading proportion corresponding to the bulk density as the mixing proportion of the biscuit with high density formed by compression; or a vibration grading instrument is adopted to find the optimal grading proportion.
7. The method according to claim 6, wherein in step S3, the different sphere diameter interval grades include three different sphere diameter interval grades: a first stage with a sphere diameter of 120-; the mixing ratio for press-molding the high-density biscuit in step S4 is 3: 2: 5.
8. the method of claim 1, wherein the step S4 of pressing the high-density biscuit is performed by: putting the granulated powder of different ball diameter interval grades mixed according to the mixing proportion into a mould to prepare a high-density biscuit by a dry pressing, isostatic pressing or dry pressing and isostatic pressing forming method; wherein, when the dry pressing method is simply adopted, a high-density biscuit is prepared by adopting a 100-150MPa pressure bidirectional pressurization mode; when the dry pressing and isostatic pressing method is adopted, the biscuit with high density is prepared by firstly using dry pressing of more than 60MPa for preliminary forming and then using cold isostatic pressing under the pressure of 200 and 300 MPa.
9. The method according to claim 1, wherein the step S5 is carried out by: putting the high-density biscuit into a graphite mold in a vacuum hot-pressing furnace, placing the graphite mold in a constant-temperature area of the vacuum hot-pressing furnace, and sintering the graphite mold into a sintered body with the relative density of more than 99.9 percent by using an isothermal and isobaric double control technology; the sintering temperature is 1500--3Pa。
In step S6, the sintered body is put into a furnace with an oxidizing atmosphere for heat treatment at 1050 ℃ and 1250 ℃ for 10-15h in the furnace to eliminate open pores and infiltrated carbon.
10. The method according to claim 1, wherein in step S7, a grinding wheel or a grinding disc is used to perform double-sided rough grinding, fine grinding, and polishing; the grinding wheel or the grinding disc is made of silicon carbide particles or diamond abrasive particles; wherein, the grinding wheel or the grinding disc used for rough grinding has the mesh numbers of silicon carbide or diamond grinding material W10 and 120 meshes respectively, and the grinding wheel or the grinding disc used for fine grinding has the mesh numbers of silicon carbide or diamond grinding material W3 and 240 meshes respectively; polishing with diamond grinding glue with grain size of 0.1-0.5 micron; after double-sided coarse grinding, fine grinding and polishing, the surface smoothness of the high-density magnesia-alumina spinel transparent ceramic product reaches more than Ra0.1 mu m mirror level.
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