A kind of magnesium aluminum spinel transparent ceramic and preparation method thereof

Abstract

The present invention relates to a magnesium aluminate spinel transparent ceramic and a preparation method thereof. The preparation method of the magnesium aluminate spinel transparent ceramic includes: mixing a phase-forming magnesium aluminate spinel powder and a sintering aid to obtain a ceramic slurry, drying, sieving and calcining the ceramic slurry to obtain a raw material powder; pressing the raw material powder into a shape to obtain a ceramic green body; sequentially calcining and pressureless pre-sintering the ceramic green body to obtain a pre-sintered body; after hot isostatic pressing sintering the pre-sintered body, obtaining the magnesium aluminate spinel transparent ceramic; the sintering aid is at least one of fluorides or fluorine oxides containing Y, La, Lu, and preferably at least one of YF3 or YOF.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramic material preparation, and in particular relates to a magnesium-aluminum spinel transparent ceramic and a preparation method thereof. Background Art

[0002] Magnesium aluminate spinel (MgAl 2 O 4 ) ceramics are an excellent transparent ceramic material with good light transmittance in the 0.19-5.5μm band. In addition, magnesium-aluminum spinel transparent ceramics also have good thermodynamic properties and chemical corrosion resistance. These excellent properties make magnesium-aluminum spinel transparent ceramics widely used in armor, infrared windows, lenses, chemical reactor windows, sensors and building materials.

[0003] Since 1961, General Electric Company of the United States has 2 O and SiO 2 After the semi-transparent magnesium-aluminum spinel ceramics were prepared by solid-phase reaction method using MgO as sintering aid, researchers from all over the world have shown great interest in magnesium-aluminum spinel transparent ceramics and have conducted extensive research on its preparation and sintering mechanism. 2- Diffusion rate, this characteristic makes it difficult to achieve densification during the sintering process. To solve this problem, researchers have proposed many methods, among which adding sintering aids as a simple and effective method has attracted widespread attention. At present, many scientific research institutions have explored the effects of different sintering aids on the properties of magnesium aluminum spinel transparent ceramics, such as halide sintering aids LiF, NaF, MgF 2 , AlF 3 ,KF,NaCl,KCl,LiCl,AlCl 3 MgCl 2 ; Oxide sintering aid La 2 O 3 , CaO, Y 2 O 3 , B 2 O 3 wait.

[0004] LiF is the most commonly used sintering aid for the preparation of high-quality magnesium-aluminum spinel transparent ceramics. However, the addition of LiF can easily cause grain coarsening and grain boundary microcracks, which seriously affects the mechanical properties and optical quality of ceramic samples. Therefore, it is urgent to explore a new sintering aid system that can replace LiF. This new sintering aid needs to be able to increase the densification rate of magnesium-aluminum spinel ceramics while ensuring its optical quality. Summary of the invention

[0005] In view of the above problems, the present invention aims to provide a method for preparing magnesium-aluminum spinel transparent ceramics. The method has a simple preparation process and strong repeatability, and the obtained magnesium-aluminum spinel transparent ceramics have excellent optical quality in the visible-near infrared band.

[0006] Specifically, in a first aspect, the present invention provides a method for preparing a magnesium-aluminum spinel transparent ceramic, comprising: mixing a phase-forming magnesium-aluminum spinel powder and a sintering aid to obtain a ceramic slurry, and drying, sieving and calcining the ceramic slurry to obtain a raw material powder;

[0007] Pressing the raw material powder into a shape to obtain a ceramic green body;

[0008] The ceramic green body is sequentially calcined and pressureless pre-sintered to obtain a pre-sintered body; the pre-sintered body is subjected to hot isostatic pressing to obtain the magnesium-aluminum spinel transparent ceramic;

[0009] The sintering aid is at least one of fluorides or fluoride oxides containing Y, La, and Lu, preferably YF 3 , or at least one of YOF.

[0010] Preferably, the total amount of the sintering aid added is 0.005wt.% to 0.08wt.%, preferably 0.005wt.% to 0.05wt.% of the mass of the phase-forming magnesium aluminum spinel powder; when the sintering aid is YF 3 When the sintering aid is YOF, the added amount is more preferably 0.005wt.% to 0.02wt.%; when the sintering aid is YOF, the added amount is more preferably 0.005wt.% to 0.02wt.%.

[0011] Preferably, the purity of the phase-forming magnesia alumina spinel powder is ≥99.9%, and the primary particle size is 20nm-200nm; the purity of the sintering aid powder is ≥99.9%, and the primary particle size is 20nm-3000nm.

[0012] Preferably, the pressing method is dry pressing and / or cold isostatic pressing, preferably dry pressing first and then cold isostatic pressing.

[0013] Preferably, the process conditions for dry pressing are: using a pressure of 5 to 30 MPa and maintaining the pressure for 1 to 3 minutes; the process conditions for cold isostatic pressing are: using a pressure of 150 to 250 MPa and maintaining the pressure for 3 to 20 minutes.

[0014] Preferably, the biscuit is calcined at a temperature of 600° C. to 900° C. and for a calcination time of 4 to 10 hours.

[0015] Preferably, the temperature of the pressureless pre-sintering is 1300° C. to 1600° C., the pressureless pre-sintering time is 1 to 10 hours, and the atmosphere used is air atmosphere or vacuum.

[0016] Preferably, the relative density of the calcined body obtained after pressureless calcination is 90-99%.

[0017] Preferably, the hot isostatic pressing sintering temperature is 1400° C. to 1900° C., the sintering time is 1 to 6 hours, and the sintering pressure is 100 to 250 MPa; the atmosphere used is an inert atmosphere, preferably a nitrogen and / or argon atmosphere.

[0018] In a second aspect, the present invention provides a magnesium-aluminum spinel transparent ceramic obtained by the above-mentioned preparation method, wherein the magnesium-aluminum spinel transparent ceramic has a linear transmittance of ≥78.9% in the wavelength range of 400nm to 2500nm when the thickness is ≥4mm.

[0019] Beneficial Effects

[0020] 1) Compared with the existing preparation technology of magnesium-aluminum spinel transparent ceramics, the sintering aid selected in the present invention can effectively promote the sintering densification of magnesium-aluminum spinel ceramics, and is enriched at the grain boundaries, plays a pinning role, inhibits grain growth, and accelerates the removal of pores; the obtained magnesium-aluminum spinel transparent ceramics have uniform grain size and no obvious pores, and the sample has high optical quality. When the thickness is ≥4mm and the linear transmittance in the wavelength range of 400nm to 2500nm is ≥78.9%, the transmittance is significantly improved compared with the sample without adding the sintering aid;

[0021] 2) The preparation method provided by the present invention adopts a process of pressureless sintering combined with hot isostatic pressing, which is simple and easy to operate, and the required pre-sintering temperature and hot isostatic pressing temperature are both low, and can be mass-produced at a low cost under existing technical conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a photo of the magnesium aluminum spinel transparent ceramic sample prepared in Example 1 after double-sided polishing;

[0023] Figure 2 This is a linear transmittance curve of the magnesium aluminum spinel transparent ceramic sample prepared in Example 1;

[0024] Figure 3 This is a linear transmittance curve of the magnesium aluminum spinel transparent ceramic sample prepared in Example 2;

[0025] Figure 4 The photos of the magnesium-aluminum spinel transparent ceramic samples prepared in Example 3 with different contents of YOF sintering aid added;

[0026] Figure 5 This is a comparison diagram of the linear transmittance curves of the magnesium-aluminum spinel transparent ceramic samples prepared in Example 3 and added with different contents of YOF sintering aid;

[0027] Figure 6 These are photos of the magnesium-aluminum spinel transparent ceramic samples prepared in Example 4 with different contents of YOF sintering aid added;

[0028] Figure 7 This is a comparison diagram of the linear transmittance curves of the magnesium-aluminum spinel transparent ceramic samples prepared in Example 4 and added with different contents of YOF sintering aid;

[0029] Figure 8 This is a photo of the magnesium aluminum spinel ceramic sample prepared in Comparative Example 1 after double-sided polishing;

[0030] Fig. 9 This is a photo of the magnesium aluminum spinel transparent ceramic sample prepared in Comparative Example 2 after double-sided polishing;

[0031] Fig.10 This is the backscattered image and surface scanning element distribution map of the magnesium aluminum spinel transparent ceramic sample prepared in Comparative Example 2. DETAILED DESCRIPTION

[0032] The present invention is further described below by way of embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, but not to limit the present invention.

[0033] The following is an exemplary description of the preparation method of the magnesium-aluminum spinel transparent ceramic provided by the present invention, wherein the preparation method mainly comprises three steps: raw material powder preparation, molding and sintering densification.

[0034] (1) Preparation of raw material powder. The phase-forming magnesium aluminum spinel powder and the sintering aid are ball-milled and mixed to obtain a ceramic slurry. The grinding balls can be alumina balls, and the dispersion medium can be anhydrous ethanol. The ball-to-material mass ratio can be 5:1. The ceramic slurry is dried, sieved and calcined to obtain a raw material powder.

[0035] In some embodiments, the sintering aid may be at least one of fluorides or oxyfluorides containing Y, La, and Lu, preferably YF 3 , or YOF. The total amount of the sintering aid added can be 0.005wt.% to 0.08wt.% of the mass of the phase-forming magnesium aluminum spinel powder, preferably 0.005wt.% to 0.05wt.%; when the sintering aid is YF 3When the sintering aid is YOF, the added amount is more preferably 0.005wt.% to 0.02wt.%. When the sintering aid is YOF, the added amount is more preferably 0.005wt.% to 0.02wt.%. If the added amount of the sintering aid is too low, the densification rate of the material will decrease during the subsequent sintering process, and it will be unfavorable for the removal of pores, resulting in a decrease in the transmittance of the prepared ceramic sample or even opacity; if the added amount of the sintering aid is too high, it is easy to precipitate a second phase during the sintering process, which will also affect the optical properties of the transparent ceramic sample.

[0036] The purity of the phase-forming magnesium aluminum spinel powder is ≥99.9%, and the primary particle size is 20nm-200nm; the purity of the sintering aid powder is ≥99.9%, and the primary particle size is 20nm-3000nm. The smaller the particle size of the powder, the higher the sintering activity, but too low a particle size is easy to agglomerate, which is not conducive to the removal of gas during the sintering process, and the residual pores will affect the transmittance of the ceramic material sample; if the particle size is too large, it will cause the sintering activity to decrease, and the preparation is more difficult.

[0037] The YOF and YF used in the present invention 3 The sintering aids such as fluoride and fluoride oxide can form a pinning effect at the grain boundary, inhibit grain growth, and accelerate the elimination of pores. Under sintering conditions, the fluoride or fluoride oxide sintering aid can promote sintering densification in a liquid phase sintering manner and accelerate the elimination of pores.

[0038] The ball milling process can be: ball milling at a speed of 250 rpm for 3 to 12 hours; the drying conditions can be: drying at 50 to 80° C. for 12 to 48 hours; the sieve used for sieving can be a sieve of 80 to 200 meshes. The organic impurities introduced during the ball milling and sieving process are removed by calcining, and the calcining process can be: keeping warm at 500 to 900° C. in a muffle furnace for 4 to 12 hours.

[0039] (2) Molding: The raw material powder prepared in step (1) is pressed into a shape to obtain a ceramic green body.

[0040] The molding method may be dry pressing or / and cold isostatic pressing, preferably dry pressing first and then cold isostatic pressing. Specifically, the calcined raw material powder is first loaded into the mold, and the process conditions for dry pressing may be: using a pressure of 5 to 30 MPa and maintaining the pressure for 1 to 3 minutes; the process conditions for cold isostatic pressing may be: using a pressure of 150 to 250 MPa and maintaining the pressure for 3 to 20 minutes.

[0041] (3) Sintering densification: The green blank formed in step (2) is sequentially calcined and pressureless pre-sintered to obtain a pre-sintered body, so that the open pores of the green blank are closed; the pre-sintered body is sintered by hot isostatic pressing and double-sided polishing to obtain the magnesium-aluminum spinel transparent ceramic.

[0042] Organic impurities introduced during the forming process can be removed by calcining the green billet. In some embodiments, the green billet calcination temperature can be 600°C to 900°C, and the calcination time can be 4 to 10 hours; the pressureless pre-sintering temperature can be 1300°C to 1600°C, and the pressureless pre-sintering time can be 1 to 10 hours, and the atmosphere used can be air atmosphere or vacuum.

[0043] After the biscuit calcination and pressureless pre-sintering treatment, a pre-sintered body with a relative density of 90-99% and closed open pores can be obtained. Subsequent hot isostatic pressing sintering generally cannot eliminate a large number of open pores, but the residual pores will seriously affect the transmittance of the transparent ceramic sample. Therefore, reasonable control of the pre-sintering conditions can ensure that a ceramic sample with good transmittance is obtained during the subsequent hot isostatic pressing sintering process.

[0044] Combined with the principle of removing residual pores by hot isostatic pressing, it can be known that for samples pre-fired at low temperature (low relative density), the pores inside the pre-fired body are mainly located at the grain boundaries and have a low content, which is easier to be eliminated during hot isostatic pressing. However, when the pre-fired temperature is relatively high (high relative density), some of the pores inside the pre-fired body will enter the interior of the grains to form intracrystalline pores and the pore content is relatively high. This type of pores often requires high temperature and high pressure hot isostatic pressing to provide sufficient energy to achieve the removal of pores, and the removal effect is poor. In addition, high temperature pre-fired (which will lead to high relative density) is likely to cause the pores inside the sample to grow, forming large pores with a high coordination number, thereby hindering the later densification process. Therefore, the transmittance of the ceramic material sample obtained after hot isostatic pressing of the high temperature pre-fired sample (high relative density) is usually relatively low. The technical solution provided by the present invention achieves the successful preparation of ceramic materials with higher optical quality by reasonably controlling the pre-fired system and selecting a suitable relative density.

[0045] In some embodiments, the hot isostatic pressing sintering temperature may be 1400°C to 1900°C, the sintering time may be 1 to 6 hours, the sintering pressure may be 100 to 250 MPa, and the atmosphere may be an inert gas, preferably nitrogen and / or argon. If the hot isostatic pressing sintering temperature is too low, it is not conducive to the removal of residual pores, which affects the transmittance of the sample and the ceramic sample cannot be transparent; if the hot isostatic pressing sintering temperature is too high, the sintering aid is easy to precipitate in the form of a second phase, which also affects the transmittance of the ceramic sample.

[0046] Hot isostatic pressing can eliminate residual pores inside the ceramic and heal defects, but it requires that the ceramic before treatment contains substantially no open pores, so the green body after the pressureless pre-sintering treatment needs to reach a relative density of 90 to 99%.

[0047] The invention uses high-purity commercial magnesium aluminum spinel nanopowder as raw material, adds sintering aids to promote densification and the elimination of pores, and adopts pressureless pre-sintering combined with hot isostatic pressing to prepare magnesium aluminum spinel transparent ceramics with high optical quality. The magnesium aluminum spinel transparent ceramics have good optical properties in the visible-near infrared wavelength range: when the thickness is ≥4mm, the linear transmittance in the wavelength range of 400nm to 2500nm is ≥78.9%.

[0048] The following examples are further cited to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention, and the specific process parameters of the following examples are only an example within the appropriate range.

[0049] Example 1

[0050] (1) Preparation of raw powder. Taking the total mass of the phased magnesium aluminum spinel powder (60g) as 100wt.%, add 0.01wt.% (0.006g) YOF additive, use anhydrous ethanol as the dispersion medium, use high-purity alumina balls as the ball milling medium, control the ball-to-material mass ratio to 5:1, use a planetary ball mill for ball milling, the speed is 250 rpm, and the ball milling time is 12 hours. The milled slurry is placed in a 65℃ oven to dry for 12 hours, and the dried powder is passed through a 100-mesh sieve. The sieved powder is placed in a muffle furnace and calcined at 800℃ for 6 hours to obtain the raw powder.

[0051] (2) Molding. The calcined raw material powder is molded by dry pressing combined with cold isostatic pressing to obtain a magnesium-aluminum spinel ceramic blank. The dry pressing pressure is 10 MPa and the pressure is maintained for 2 minutes; the cold isostatic pressing pressure is 200 MPa and the pressure is maintained for 3 minutes.

[0052] (3) Sintering densification. The formed green body was first calcined in a muffle furnace at 800°C for 6 hours; then, after being pre-pressurized at 1470°C in air atmosphere for 6 hours, a pre-burned body with a relative density of 94.70% and closed pores was obtained; the pre-burned body was hot isostatically pressed at 200 MPa and 1550°C for 3 hours to obtain a magnesium-aluminum spinel transparent ceramic sample.

[0053] Figure 1 This is a photo of the double-sided polished magnesium-aluminum spinel transparent ceramic sample prepared in Example 1. As can be seen from the figure, the magnesium-aluminum spinel transparent ceramic sample prepared in Example 1 has high transparency.

[0054] Figure 2The linear transmittance curve of the magnesium aluminum spinel transparent ceramic sample prepared in Example 1 is shown in FIG. The sample is 4 mm thick. Figure 2 It can be seen that the linear transmittance of the magnesium aluminum spinel transparent ceramic sample with 0.01wt.% YOF added is 82.60% at 400nm and 87.30% at 1100nm, and the sample has excellent optical quality.

[0055] Example 2

[0056] The preparation process of this example is similar to that of Example 1. The main difference is that in step (1), 0.03 wt.% YF 3 As a sintering aid; in step (3), the temperature of the pressureless pre-sintering of the green billet after forming is 1480°C.

[0057] Figure 3 The linear transmittance curve of the magnesium aluminum spinel transparent ceramic sample prepared in Example 2. The sample was double-sided polished to a thickness of 4 mm. Figure 3 It can be seen that the sample has a high transmittance, the transmittance at 1100nm is 86.1%, close to the theoretical transmittance; the transmittance at 400nm is 78.9%.

[0058] Example 3

[0059] The preparation process of this embodiment refers to that of Embodiment 1. The main differences are as follows: in step (1), 0.005wt.% and 0.01wt.% of YOF are added as sintering aids respectively; in step (3), the temperature of the pressureless pre-sintering of the green blank after forming is 1480°C, and the hot isostatic pressing temperature is 1600°C.

[0060] Figure 4 The photos are of the magnesium-aluminum spinel transparent ceramic samples with different contents of YOF sintering aid added, prepared in Example 3. All samples were double-sided polished to a thickness of 4 mm.

[0061] Figure 5 This is a comparison chart of the linear transmittance curves of the magnesium-aluminum spinel transparent ceramic samples prepared in Example 3 and added with different contents of YOF sintering aid. Figure 5 It can be seen that the samples all have high transmittance, and the transmittances at 400 nm are 82.0% and 80.8% respectively.

[0062] Example 4

[0063] The preparation process of this embodiment refers to that of Embodiment 1. The main differences are as follows: in step (1), 0.005wt.%, 0.01wt.% and 0.05wt.% of YOF are added as sintering aids respectively; in step (3), the temperature of the pressureless pre-sintering of the green blank after forming is 1480°C, and the hot isostatic pressing temperature is 1550°C.

[0064] Figure 6 The photos are of the magnesium-aluminum spinel transparent ceramic samples with different contents of YOF sintering aid added, prepared in Example 4. All samples were double-sided polished to a thickness of 4 mm.

[0065] Figure 7 This is a comparison of the linear transmittance curves of the magnesium-aluminum spinel transparent ceramic samples with different contents of YOF sintering aid added prepared in Example 4. All samples were double-sided polished to a thickness of 4 mm. Figure 7 It can be seen that the transmittances of the magnesium aluminum spinel transparent ceramic samples with 0.005wt.%, 0.01wt.% and 0.05wt.% YOF additive added at 400nm are 79.9%, 80.2% and 81.6%, respectively.

[0066] Comparative Example 1

[0067] The preparation process of this comparative example refers to Example 1. The main differences are: in step (1), no sintering aid is added; in step (3), the temperature of the pressureless pre-sintering of the green blank after forming is 1470°C and 1480°C, and the hot isostatic pressing temperature is 1550°C and 1600°C.

[0068] Figure 8 The photo is of the double-sided polished magnesium-aluminum spinel ceramic sample prepared in Comparative Example 1. It can be seen from the figure that the four samples are all opaque magnesium-aluminum spinel ceramics.

[0069] Comparative Example 2

[0070] The preparation process of this comparative example refers to Example 1. The main difference is that in step (1), 0.1 wt.% YOF is added as a sintering aid.

[0071] Fig. 9 This is a photo of the magnesium aluminum spinel transparent ceramic sample prepared in Comparative Example 2 after double-sided polishing. It can be seen from the figure that the optical quality of the ceramic sample is poor. In order to prove that the sintering aid with too high a content will precipitate a second phase and affect the optical quality of the ceramic sample, the sample in this comparative example was analyzed using a scanning electron microscope (SEM) and an energy dispersive spectrometer (EDS). Fig.10 The backscattered image and surface scanning element distribution map of the magnesium aluminum spinel transparent ceramic sample prepared in Comparative Example 2. From the SEM image, it can be seen that there is obvious precipitation of the second phase at the grain boundary, and the grain size of the second phase is about 0.44μm; the EDS surface scanning element distribution shows that Al, Mg, and O are evenly distributed, and only the Y element is enriched at the second phase position, so the second phase is produced by the introduction of the additive.

[0072] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for preparing a magnesium aluminum spinel transparent ceramic, It is characterized in that include: The phase-forming magnesium aluminum spinel powder and the sintering aid are mixed to obtain a ceramic slurry, and the ceramic slurry is dried, sieved and calcined to obtain a raw material powder; Pressing the raw material powder into a shape to obtain a ceramic green body; The ceramic green body is sequentially calcined at 600°C to 900°C for 4 to 10 hours and pressurelessly pre-sintered at 1300°C to 1600°C for 1 to 10 hours to obtain a pre-sintered body; the pre-sintered body is hot isostatically pressed at 1400°C to 1900°C for 1 to 6 hours to obtain the magnesium-aluminum spinel transparent ceramic; The sintering aid is YOF, and the addition amount of the YOF is 0.005 wt.% to 0.02 wt.% of the mass of the phase-forming magnesium aluminate spinel powder; the purity of the phase-forming magnesium aluminate spinel powder is ≥99.9%, and the primary particle size is 20 nm to 200 nm; the purity of the sintering aid powder is ≥99.9%, and the primary particle size is 20 nm to 3000 nm.

2. The preparation method according to claim 1, It is characterized in that The compression molding method is dry compression molding and / or cold isostatic compression molding.

3. The preparation method according to claim 2, It is characterized in that The compression molding method is dry compression molding first and then cold isostatic compression molding.

4. The preparation method according to claim 2 or 3, It is characterized in that The process conditions for dry pressing are: using a pressure of 5 to 30 MPa and maintaining the pressure for 1 to 3 minutes; the process conditions for cold isostatic pressing are: using a pressure of 150 to 250 MPa and maintaining the pressure for 3 to 20 minutes.

5. The preparation method according to claim 1, It is characterized in that The atmosphere used for the pressureless pre-firing is air atmosphere or vacuum.

6. The preparation method according to claim 1, It is characterized in that The relative density of the calcined body obtained after pressureless calcination is 90 to 99%.

7. The preparation method according to claim 1, It is characterized in that The sintering pressure of hot isostatic pressing is 100-250 MPa; the atmosphere used is an inert atmosphere.

8. The preparation method according to claim 7, It is characterized in that The atmosphere used was nitrogen and / or argon.

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