Preparation method of low-hydroxyl yttrium oxide and magnesium oxide composite ceramic

Abstract

The preparation method comprises the following steps: adding an ammonium bifluoride and absolute ethyl alcohol mixed solution in a ball-milling stage in a preparation process of yttrium oxide and magnesium oxide complex-phase powder, and designing gradient temperature control and hydroxyl removal in a pre-sintering process of a ceramic green body. According to the invention, hydroxyl removal of yttrium oxide and magnesium oxide composite ceramic is realized, and the difficulty that magnesium oxide easily absorbs moisture and is difficult to remove hydroxyl is solved. The method has the characteristics of simple experimental operation and high hydroxyl removal efficiency.

Description

Technical Field

[0001] The invention relates to a method for preparing low-hydroxyl yttrium oxide magnesium oxide nano-composite ceramics for mid-infrared windows, in particular to fluorination removal of hydroxyl groups in composite phase powders and gradient temperature-controlled removal of hydroxyl groups in ceramic blanks. Background Art

[0002] 3-5 micron infrared imaging and precision guidance have the advantages of high precision, strong concealment, and low susceptibility to interference. They are the key development direction of future wars and have been widely used in various supersonic fighters, air-to-air missiles, and defense interception systems. Among them, infrared window materials are important components and are required to have high optical transparency in the working band and high strength and hardness mechanical properties.

[0003] Yttrium oxide magnesium oxide composite ceramics have the advantages of wide band, high transmittance, high strength and low emission at 3-5 microns. They are good candidate materials for window materials in the mid-infrared band, especially for high Mach aircraft windows. Jiang et al. [JIANG DT, MUKHERJEE AK. Spark plasma sintering of an infrared-transparent Y2O3-MgO nanocomposite [J]. J Am Ceram Soc, 2010, 93 (3): 769-773.] first proposed the concept of Y2O3-MgO composite ceramics in 2008. Nanopowders were prepared by sol-gel method and then sintered by discharge plasma. Subsequent scholars prepared composite nanopowders by ammonium acetate combustion method, glycine combustion method, esterification sol-gel method and other methods. The sintering process includes hot pressing, heat, vacuum sintering, microwave sintering and other methods to prepare composite ceramics. However, the ceramics sintered by the above methods have hydroxyl absorption around 3 microns. The hydroxyl problem also needs to be solved when preparing glass. For example, when preparing quartz glass by chemical vapor deposition, high-temperature SiO2 loose bodies are dehydroxylated, and chlorine gas Cl2 or thionyl chloride (SOCl2) is introduced as a dehydrating agent; the dehydroxylation process of fluorine-indium glass is mainly based on the introduction of a small amount of NF3 reaction atmosphere during the reaction of ammonium bifluoride method. However, the above-mentioned glass dehydroxylation method is not suitable for yttrium oxide magnesium oxide composite ceramics. The hydroxyl groups of this ceramic mainly come from the easy moisture absorption of MgO, which leads to the disadvantage of reduced transmittance at 3 microns. Therefore, it is urgent to solve the problem of hydroxyl adsorption. Summary of the invention

[0004] The present invention aims at the existing 3-micron hydroxyl adsorption problem of yttria-magnesium oxide nanocomposite ceramics and provides a fluorination removal of hydroxyl in the preparation process of nanocomposite powder and a gradient temperature controlled hydroxyl removal method for pre-firing a ceramic body. The transmittance of the obtained low-hydroxyl nanocomposite ceramics is improved near 3 microns. The method has the advantages of simple operation and high efficiency.

[0005] The technical solution of the present invention is as follows:

[0006] Yttrium oxide and magnesium oxide nanocomposite powders are prepared by a glycine-nitrate combustion method. The required components include glycine, magnesium nitrate, yttrium nitrate and deionized water. After the nanocomposite powders are obtained by combustion reaction, ball milling is performed. The solution used for the ball milling is obtained by mixing ammonium bifluoride and anhydrous ethanol in a mass ratio of 1:100-1:200. The slurry after ball milling is dried, sieved, bisque-fired and ceramic body formed. The ceramic body is pre-fired by gradient temperature control sintering. The heating rate within 0-600°C is 1-3°C / min, and the heating rate within 600-1360°C is 3-10°C / min.

[0007] The specific preparation steps of the above scheme are as follows:

[0008] 1) preparing a mixed solution using yttrium nitrate, magnesium nitrate, glycine and deionized water, wherein the molar ratio of yttrium nitrate:magnesium nitrate:glycine is 1:4:3 to 1:4:10, and heating and stirring with deionized water until the mixture is uniformly mixed and in a transparent gel state;

[0009] 2) placing the mixed gel obtained in 1) in a muffle furnace for combustion reaction, wherein the mixture is kept at 200-300° C. for 3-5 hours to fully burn and evaporate the water, and kept at 700-900° C. for 3-5 hours to remove carbon;

[0010] 3) preparing a mixed solution of ammonium bifluoride and anhydrous ethanol in a mass ratio of 1:100-1:200, and mixing the mixture thoroughly on a magnetic stirrer;

[0011] 4) ball milling the mixed yttrium oxide magnesium oxide composite powder obtained in 2) and the anhydrous ammonium bifluoride ethanol solution in 3) at a mass ratio of 1:3-1:5, at a ball milling speed of 200-250 rpm / min, for 24-60 hours;

[0012] 5) The slurry after ball milling in 4) is repeatedly washed with anhydrous alcohol and filtered, and then dried at 70-100° C. to obtain a dry block powder, which is then sieved, and the obtained nanocomposite powder is then subjected to a high temperature treatment at 700-900° C.;

[0013] 6) isometrically pressing the yttrium oxide magnesium oxide nanocomposite powder obtained above at a pressure of 5-10 MPa to obtain an initial sample with a density of about 30%, and then cold isostatically pressing the powder at a pressure of 200-220 MPa for a holding time of 2-5 minutes to obtain a composite ceramic body with a density of about 50%;

[0014] 7) The ceramic green body is pre-fired in a muffle furnace at a sintering temperature of 1330 - 1360 °C for 1 - 2 h. The heating rate is 1 - 3 °C / min within 0 - 600 °C and 3 - 10 °C / min within 600 - 1360 °C, obtaining a composite ceramic with a relative density greater than 95%. Then, it is subjected to hot isostatic pressing treatment at 1250 - 1350 °C to obtain a composite ceramic with a relative density close to 100%.

[0015] 8) The composite ceramic in 7) is subjected to annealing treatment at high temperature and then double-sided polished to obtain a yttrium oxide - magnesium oxide composite ceramic.

[0016] Preferably, in step 1), the molar ratio of yttrium nitrate, magnesium nitrate, and glycine is 1:4:7.

[0017] Preferably, in step 2), the combustion reaction is specifically as follows: First, heat to 230 °C and hold for 3 h, then continue to heat to 800 °C and hold for 5 h.

[0018] Preferably, in step 3), the mass ratio of ammonium bifluoride to absolute ethanol is 1:100, and the magnetic stirring time is 24 h.

[0019] Preferably, in step 4), the mass ratio of the mixed yttrium oxide - magnesium oxide composite powder to the ammonium bifluoride - absolute ethanol solution is 1:4, the ball - milling speed is 250 rpm / min, and the ball - milling time is 48 h.

[0020] Preferably, in step 5), the drying temperature is 80 °C, and it is sieved through a 200 - mesh sieve. The obtained nano - composite powder is then subjected to high - temperature treatment at 700 °C.

[0021] Preferably, in step 6), the pressure of isostatic pressing is 8 MPa, and the relative density of the initial sample is about 30%. The pressure of cold isostatic pressing is 200 MPa, and the pressure is maintained for 5 minutes, obtaining a green body of the composite ceramic with a relative density of about 50%.

[0022] Furthermore, before pre - firing the ceramic green body in the muffle furnace in step 7), the muffle furnace is pre - fired at 400 °C without load.

[0023] Preferably, in step 7), the sintering temperature is 1350 °C, the holding time is 2 h, the heating rate is 1 °C / min within 0 - 600 °C, and 5 °C / min within 600 - 1350 °C. Then, it is subjected to hot isostatic pressing treatment at 1250 °C.

[0024] Furthermore, in step 8), the annealing treatment is specifically holding at 1000 °C for 10 h.

[0025] The beneficial technical effects of the present invention:

[0026] 1) The fluorination removal of hydroxyl and ceramic gradient temperature control removal of hydroxyl proposed in the present invention are used to prepare low-hydroxyl yttrium oxide magnesium oxide nanocomposite ceramics, achieving high transmittance of 2.5-5 microns, and the hydroxyl absorption peak near 3 microns is significantly reduced. This method has the characteristics of simple preparation process, convenient hydroxyl removal, and significant effect.

[0027] 2) When glycine is heated and reaches a certain temperature, it will spontaneously combust. Under its own high-temperature ignition state, it can dry out the moisture in the air around the powder and prevent the magnesium oxide from adsorbing water molecules during the nucleation stage.

[0028] 3) During the ball milling process of preparing the yttrium oxide-magnesium oxide composite powder, a trace amount of fluoride ions is introduced. The fluoride ions with lower binding energy can bind to magnesium ions preferentially over hydroxyl groups, isolating the hydroxyl adsorption; the mixed slurry after ball milling is strictly filtered, rinsed and dried to obtain a low-hydroxyl composite powder.

[0029] 4) During the high-temperature sintering process of yttrium oxide magnesium oxide composite ceramics, gradient temperature control can remove the air and impure water molecules introduced by powder tableting during the ceramic densification stage, further completing the physical adsorption isolation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The XRD spectrum of the low-hydroxyl yttrium oxide magnesium oxide nanocomposite ceramic prepared in Example 1 of the present invention;

[0031] Figure 2 (a) and (b) are cross-sectional SEM images of two scanning points of the low-hydroxyl yttrium magnesium oxide nanocomposite ceramic prepared in Example 1 of the present invention;

[0032] Figure 3 The mid-infrared transmittance curves of the low-hydroxy yttrium-magnesium oxide nanocomposite ceramics prepared in Examples 1, 2 and 3 of the present invention and the composite ceramic prepared in Comparative Example 1 are shown. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the embodiments and accompanying drawings. These examples are only used to illustrate the present invention but should not be used to limit the protection scope of the present invention.

[0034] Example 1

[0035] According to the molar ratio of yttrium nitrate: magnesium nitrate: glycine of 1:4:7, 39.53g of yttrium nitrate, 52.99g of magnesium nitrate and 87g of glycine were weighed, and heated and stirred with deionized water until they were transparent and uniform gel; the mixed gel was placed in a muffle furnace for combustion reaction at 800°C, kept at 230°C for 3h to fully burn and evaporate the water, and kept at 800°C for 5h to remove carbon; at the same time, ammonium bifluoride / anhydrous ethanol solution with a mass ratio of 1:100 was prepared and fully mixed on a magnetic stirrer; the yttrium oxide magnesium oxide composite powder obtained by the combustion reaction was ball-milled with the ammonium bifluoride anhydrous ethanol solution at a mass ratio of 1:4, the ball milling speed was 250rpm / min, and the ball milling was carried out for 48h; the ball-milled slurry was rinsed with anhydrous alcohol several times and filtered, and then dried at 80°C to obtain a dry block powder, and then passed through 20 0 mesh sieve, and the obtained nano-composite powder is further treated at 700°C; the yttrium oxide magnesium oxide nano-composite powder obtained above is isometrically pressed at a pressure of 8MPa, and then cold isostatically pressed at a pressure of 200Mpa, and the pressure is maintained for 5 minutes to obtain a composite ceramic body; the ceramic body is pre-fired in a muffle furnace, the muffle furnace is first fired at 400°C, and then the ceramic is sintered at a sintering time of 1350°C, and the temperature is maintained for 2h, wherein the heating rate within 0-600°C is 1°C / min, and the heating rate within 600-1350°C is 5°C / min, to obtain a composite ceramic with a density greater than 95%, and then hot isostatic pressing at 1250°C is performed to obtain a composite ceramic with a density close to 100%; and then annealing is performed at 1000°C for 10h, followed by double-sided polishing to obtain yttrium oxide magnesium oxide composite ceramics.

[0036] See attached Figure 1 The XRD spectrum of the low-hydroxy yttrium oxide magnesium oxide nanocomposite ceramic prepared in this embodiment shows that the X-ray diffraction peaks of the prepared nanocomposite ceramic are consistent with the standard cards of yttrium oxide (JCPDS#41-1105) and magnesium oxide (JCPDS#45-0946), and the physical phases are consistent.

[0037] See attached Figure 2 (a) and (b) are cross-sectional SEM images of two scanning points of the low-hydroxyl yttrium magnesium oxide nanocomposite ceramic prepared in this example. The internal structure of the ceramic has no obvious defects, is relatively dense as a whole, and has uniform grain distribution.

[0038] See attached Figure 3 The transmittance of the low-hydroxyl yttrium oxide magnesium oxide nanocomposite ceramics prepared in this example at 2.5-5 microns is significantly higher than that of the yttrium oxide magnesium oxide nanocomposite ceramics in control example 1 which has not undergone the hydroxyl removal process, and the hydroxyl absorption peak near 3 microns is significantly reduced.

[0039] Example 2

[0040] According to the molar ratio of yttrium nitrate: magnesium nitrate: glycine of 1:4:10, 39.53g of yttrium nitrate, 52.99g of magnesium nitrate and 109.59g of glycine were weighed, and heated and stirred with deionized water until they were transparent and uniform gel; the mixed gel was placed in a muffle furnace for combustion reaction at 700℃, kept at 200℃ for 4h to fully burn and evaporate the water, and kept at 700℃ for 3h to remove carbon; at the same time, ammonium bifluoride / anhydrous ethanol solution with a mass ratio of 1:150 was prepared and fully mixed on a magnetic stirrer; the yttrium oxide magnesium oxide composite powder obtained by the combustion reaction was ball-milled with ammonium bifluoride anhydrous ethanol solution at a mass ratio of 1:3, the ball milling speed was 200rpm / min, and the ball milling was carried out for 24h; the ball-milled slurry was rinsed with anhydrous alcohol several times and filtered, and then dried at 70℃ to obtain dry block powder, and then passed through 2 00 mesh sieve, and the obtained nano-composite powder is then treated at 800°C; the yttrium oxide magnesium oxide nano-composite powder obtained above is isometrically pressed at a pressure of 5MPa, and then cold isostatically pressed at a pressure of 220Mpa, and the pressure is maintained for 3 minutes to obtain a composite ceramic body; a muffle furnace is used to pre-sinter the ceramic body, the muffle furnace is first empty-fired at 400°C, and then the ceramic is sintered at a sintering time of 1340°C, and the heat preservation is 1.5h, wherein the heating rate within 0-600°C is 2°C / min, and the heating rate within 600-1340°C is 3°C / min, to obtain a composite ceramic with a density greater than 95%, and then hot isostatic pressing at 1300°C is performed to obtain a composite ceramic with a density close to 100%; and then annealing treatment is performed at 1000°C for 10h, followed by double-sided polishing to obtain yttrium oxide magnesium oxide composite ceramics.

[0041] See attached Figure 3 The transmittance of the low-hydroxyl yttrium oxide magnesium oxide nanocomposite ceramics prepared in this example at 2.5-5 microns is significantly higher than that of the yttrium oxide magnesium oxide nanocomposite ceramics in control example 1 which has not undergone the hydroxyl removal process, and the hydroxyl absorption peak near 3 microns is significantly reduced.

[0042] Example 3

[0043] According to the molar ratio of yttrium nitrate: magnesium nitrate: glycine of 1:4:3, 39.53g of yttrium nitrate, 52.99g of magnesium nitrate and 36.53g of glycine were weighed, and heated and stirred with deionized water until they were transparent and uniform gel; the mixed gel was placed in a muffle furnace for combustion reaction at 900℃, kept at 300℃ for 5h to fully burn and evaporate the water, and kept at 900℃ for 4h to remove carbon; at the same time, ammonium bifluoride / anhydrous ethanol solution with a mass ratio of 1:200 was prepared and fully mixed on a magnetic stirrer; the yttrium oxide magnesium oxide composite powder obtained by the combustion reaction was ball-milled with the ammonium bifluoride anhydrous ethanol solution at a mass ratio of 1:5, the ball milling speed was 230rpm / min, and the ball milling was carried out for 60h; the ball-milled slurry was rinsed with anhydrous alcohol several times and filtered, and then dried at 100℃ to obtain dry block powder, and then passed through 2 00 mesh sieve, and the obtained nano-composite powder is then treated at 900°C; the yttrium oxide magnesium oxide nano-composite powder obtained above is equiaxed static pressing at a pressure of 10MPa, and then cold isostatic pressing at a pressure of 210Mpa, and the pressure is maintained for 4 minutes to obtain a composite ceramic body; a muffle furnace is used to pre-sinter the ceramic body, the muffle furnace is first fired at 400°C, and then the ceramic is sintered at a sintering time of 1360°C, and the heat preservation is 1h, wherein the heating rate within 0-600°C is 3°C / min, and the heating rate within 600-1360°C is 10°C / min, to obtain a composite ceramic with a density greater than 95%, and then a hot isostatic pressing treatment at 1350°C is performed to obtain a composite ceramic with a density close to 100%; and then an annealing treatment is performed at 1000°C for 10h, followed by double-sided polishing to obtain yttrium oxide magnesium oxide composite ceramics.

[0044] See attached Figure 3 The transmittance of the low-hydroxyl yttrium oxide magnesium oxide nanocomposite ceramics prepared in this example at 2.5-5 microns is significantly higher than that of the yttrium oxide magnesium oxide nanocomposite ceramics in control example 1 which has not undergone the hydroxyl removal process, and the hydroxyl absorption peak near 3 microns is significantly reduced.

[0045] Comparative Example 1

[0046] According to the molar ratio of yttrium nitrate: magnesium nitrate: glycine of 1:4:7, 39.53g of yttrium nitrate, 52.99g of magnesium nitrate and 87g of glycine were weighed, and heated and stirred with deionized water until a transparent and uniform gel was formed; the mixed gel was placed in a muffle furnace for combustion reaction, kept at 230°C for 3h to fully burn and evaporate the water, and kept at 800°C for 5h to remove carbon; the yttrium oxide and magnesium oxide composite powder obtained by the combustion reaction were ball-milled with anhydrous ethanol solution at a mass ratio of 1:4, the ball milling speed was 250rpm / min, and the ball milling was carried out for 48h; then it was dried at 80°C to obtain a dry block powder, and passed through a 200 mesh. The obtained nano-composite powder is sieved and then treated at 700°C; the yttrium oxide magnesium oxide nano-composite powder obtained above is isometrically pressed at a pressure of 8MPa, and then cold isostatically pressed at a pressure of 200Mpa for 5 minutes to obtain a composite ceramic body; the ceramic body is pre-fired in a muffle furnace at a sintering time of 1350°C for 2h to obtain a composite ceramic with a density greater than 95%, and then hot isostatically pressed at 1250°C to obtain a composite ceramic with a density close to 100%; and then annealed at 1000°C for 10h, followed by double-sided polishing to obtain yttrium oxide magnesium oxide composite ceramics.

[0047] See attached Figure 3 The transmittance of the yttrium oxide magnesium oxide nanocomposite ceramic prepared in this comparative example at 2.5-5 microns is significantly lower than that of Examples 1, 2, and 3, and the hydroxyl absorption peak near 3 microns is obvious.

Claims

1. A preparation method of a low-hydroxyl yttrium oxide-magnesium oxide nanocomposite ceramic, characterized in that, The following steps are involved: 1) preparing a mixed solution using yttrium nitrate, magnesium nitrate, glycine and deionized water, wherein the deionized water is used as a solvent, and the molar ratio of yttrium nitrate, magnesium nitrate and glycine is 1:4:3 to 1:4:10, and heating and stirring to form a uniformly mixed transparent gel solution; 2) placing the transparent gel solution obtained in step 1) in a muffle furnace for combustion reaction, firstly keeping the temperature at 200-300° C. for 3-5 hours to fully burn until the water is completely evaporated, then continuing to increase the temperature, keeping the temperature at 700-900° C. for 3-5 hours to remove carbon residues, and obtaining yttrium oxide magnesium oxide composite powder; 3) preparing a mixed solution of ammonium bifluoride and anhydrous ethanol in a mass ratio of 1:100-1:200, and mixing the mixture thoroughly on a magnetic stirrer; 4) ball milling the yttrium oxide magnesium oxide composite powder obtained in step 2) and the ammonium bifluoride anhydrous ethanol solution obtained in step 3) at a mass ratio of 1:3-1:5, with a ball milling speed of 200-250 rpm / min and a ball milling time of 24-60 h; 5) The slurry after ball milling in step 4) is repeatedly washed with anhydrous alcohol and filtered, and then dried at 70-100° C. to obtain a dry block powder, which is then sieved to obtain yttrium oxide magnesium oxide nanocomposite powder and then subjected to high temperature treatment at 700-900° C.; 6) isometrically pressing the yttrium oxide magnesium oxide nanocomposite powder obtained by high temperature treatment in step 5) at a pressure of 5-10 MPa to obtain an initial sample, and then cold isostatically pressing the powder at a pressure of 200-220 MPa for a holding time of 2-5 minutes to obtain a composite ceramic body; 7) pre-firing the composite ceramic body obtained in step 6) in a muffle furnace at a sintering temperature of 1320-1360° C. for a holding time of 1-2 h, wherein the heating rate in the range of 0-600° C. is 1-3° C. / min, and the heating rate in the range of 600-1360° C. is 3-10° C. / min, to obtain a composite ceramic having a density greater than 95%, and then performing hot isostatic pressing at 1200-1350° C. to obtain a composite ceramic having a density close to 100%; 8) The composite ceramic obtained in step 7) is subjected to high temperature annealing treatment, and then double-sided polishing to finally obtain yttrium oxide magnesium oxide composite ceramics.

2. The preparation method of a low-hydroxyl yttrium oxide magnesium oxide nanocomposite ceramic according to claim 1, characterized in that, In step 1), the molar ratio of yttrium nitrate, magnesium nitrate and glycine is 1:4:

7.

3. The preparation method of a low-hydroxyl yttrium oxide-magnesium oxide nanocomposite ceramic according to claim 1, characterized in that, The combustion reaction in step 2) is specifically as follows: firstly, heating to 230°C and keeping the temperature for 3 hours, and then continuing to heat to 800°C and keeping the temperature for 5 hours.

4. The preparation method of a low-hydroxyl yttrium oxide magnesium oxide nanocomposite ceramic according to claim 1, characterized in that, In step 3), the mass ratio of ammonium bifluoride to anhydrous ethanol is 1:100, and the magnetic stirring time is 24 hours.

5. The preparation method of a low-hydroxyl yttrium oxide-magnesium oxide nanocomposite ceramic according to claim 1, characterized in that, In step 4), the mass ratio of the mixed yttrium oxide magnesium oxide composite powder and the anhydrous ethanol solution of ammonium bifluoride is 1:4, the ball milling speed is 250 rpm / min, and the ball milling time is 48 hours.

6. The preparation method of a low-hydroxyl yttrium oxide-magnesium oxide nanocomposite ceramic according to claim 1, characterized in that, In step 5), the drying temperature is 80°C, the powder is sieved through a 200-mesh sieve, and the obtained nanocomposite powder is then subjected to a high-temperature treatment at 700°C.

7. The preparation method of a low-hydroxyl yttrium oxide-magnesium oxide nanocomposite ceramic according to claim 1, characterized in that, In step 6), the pressure of isostatic pressing is 8 MPa, and the density of the initial sample is about 30%. The pressure of cold isostatic pressing is 200 Mpa, and the pressure is maintained for 5 minutes, and the density of the green body of the composite ceramic is about 50%.

8. The preparation method of a low-hydroxyl yttrium oxide-magnesium oxide nanocomposite ceramic according to claim 1, wherein Before pre-sintering the ceramic green body in the muffle furnace in step 7), the muffle furnace is pre-fired at 400 °C in air first.

9. The preparation method of a low-hydroxyl yttrium oxide-magnesium oxide nanocomposite ceramic according to claim 1 or 8, characterized in that, The sintering temperature in step 7) is 1350 °C, and the holding time is 2 h. The heating rate is 1 °C / min within 0-600 °C, and the heating rate is 5 °C / min within 600-1350 °C, and then hot isostatic pressing treatment is carried out at 1250 °C.

10. The preparation method of a low-hydroxyl yttrium oxide magnesium oxide nanocomposite ceramic according to claim 1, characterized in that, In step 8), the annealing treatment is specifically to hold at 1000 °C for 10 h.

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