Preparation method for magnesium niobate

Abstract

The present application provides a preparation method for magnesium niobate (MN), comprising: wet ball milling and uniformly mixing MgO and Nb2O5, and drying to obtain mixed powder; heating the mixed powder for 1-3 h until the temperature is 1,500-1,700°C, and then performing water quenching to obtain solid particles as core-shell structure inclusions; heating the solid particles to 1,000-1,200°C, and performing heat preservation to obtain MN. According to the present application, the solid particles as core-shell structure inclusions are formed by means of a water quenching process and are then quickly heated and sintered to obtain MN, the MN has high purity and stability, and components Mg2+ and Nb5+ in MN have high uniformity and high reaction activity, thus facilitating full mixing with PbO and TiO2 at a high temperature to form a liquid phase; and raw materials for PMNT crystal growth have better singularity and uniformity, such that a PMNT single crystal having a single perovskite structure, high purity, and excellent piezoelectric properties is obtained, thereby improving the yield.

Description

A preparation method of magnesium niobate

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on August 14, 2023, with application number CN202311019095.7 and invention name “A method for preparing magnesium niobate”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of piezoelectric materials, and in particular to a method for preparing magnesium niobate. Background Art

[0003] Lead magnesium niobate-lead titanate (PMNT) is a typical perovskite ferroelectric with excellent piezoelectric properties. 33 It is 4-5 times that of PZT ceramics, so it has broad application prospects in medical ultrasound imaging, sonar, underwater acoustic transducers, etc. However, in order to obtain high-quality PMNT single crystals, high-purity crystal growth raw materials are required.

[0004] Currently, the raw materials for PMNTs are primarily prepared using a two-step synthesis process: first, a magnesium niobate (MN) precursor is synthesized through a solid-phase reaction of niobium pentoxide (Nb2O5) and magnesium oxide (MgO); this is then reacted with titanium oxide (TiO2) and lead oxide (PbO) to obtain the raw material for PMNT growth. However, during the preparation of the MN precursor, the reaction between MgO and Nb2O5 is incomplete, resulting in the formation of free niobium in the MN. This causes the residual Nb2O5 to react with PbO to form a secondary phase (Pb2Nb2O7) (pyrochlore). The coexistence of the pyrochlore phase with the primary perovskite phase severely degrades the piezoelectric properties of PMNT single crystals, hindering the full utilization of the material's properties. Therefore, finding a method to synthesize high-purity magnesium niobate is key to improving the purity of the raw materials for crystal growth.

[0005] Summary of the Invention

[0006] The purpose of this application is to provide a method for preparing magnesium niobate, which can improve the purity and stability of the prepared magnesium niobate. The specific technical solution is as follows:

[0007] A first aspect of the present application provides a method for preparing magnesium niobate, comprising the following steps:

[0008] (1) Wet-milling MgO and Nb2O5 to mix uniformly, and drying to obtain a mixed powder;

[0009] (2) heating the mixed powder to 1500-1700° C. for 1-3 hours and then quenching with water to obtain solid particles with core-shell structure inclusions;

[0010] (3) Heating the solid particles to 1000-1200° C. and maintaining the temperature to obtain the magnesium niobate.

[0011] In some embodiments of the present application, the molar ratio of the MgO to the Nb2O5 is 1:1.

[0012] In some embodiments of the present application, the Dv50 particle size of the MgO is 50-100 nm.

[0013] In some embodiments of the present application, the Dv50 particle size of the Nb2O5 is 2-15 μm.

[0014] In some embodiments of the present application, the mass ratio of the grinding balls, materials, and ball milling media used in the wet ball milling is 1: (0.9-1.1): (1.2-1.8).

[0015] In some embodiments of the present application, the ball mill jar material used in the wet ball milling is polyurethane.

[0016] In some embodiments of the present application, the ball milling medium used in the wet ball milling is anhydrous ethanol.

[0017] In some embodiments of the present application, the grinding balls used in the wet ball milling are alumina balls.

[0018] In some embodiments of the present application, the rotation speed of the wet ball milling is 100-200 r / min, and the time of the wet ball milling is 20-30 h.

[0019] In some embodiments of the present application, the heating rate of heating to 1000-1200° C. is 5-10° C. / min.

[0020] In some embodiments of the present application, the insulation time is 25-35 minutes.

[0021] In some embodiments of the present application, the Dv50 particle size of the solid particles is 0.5-2 mm.

[0022] In some embodiments of the present application, the drying temperature is 90-110°C.

[0023] The second aspect of the present application provides a method for preparing raw materials for growing lead magnesium niobate-lead titanate (PMNT), which includes the method for preparing magnesium niobate described in the first aspect of the present application.

[0024] Beneficial effects of this application:

[0025] The present invention adopts wet ball milling to make the obtained slurry more uniform; the present invention forms a core-shell structure inclusion through water quenching process, that is, Nb2O5 is evenly wrapped around the outside of MgO, so that the contact area between the two is larger and the bonding force is stronger; in the subsequent rapid temperature rise sintering process, the solid phase reaction between the core and shell parts of the solid particles can be more complete, and the obtained magnesium niobate (MgNb2O6, MN) has high purity and high stability. The Mg in MN is 2+ 、Nb 5+ The two components have high uniformity and high reaction activity, which is conducive to the full mixing with PbO and TiO2 to form a liquid phase at high temperature. The raw materials for the growth of the formed lead magnesium niobate-lead titanate (PMNT) crystals are more uniform and uniform, which in turn helps to obtain PMNT single crystals with a single perovskite structure, high purity and excellent piezoelectric properties, thereby improving the yield.

[0026] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0028] FIG1 is a schematic diagram of the structure of solid particles of the core-shell structure inclusion prepared in this application;

[0029] FIG2 is an X-ray diffraction spectrum of the magnesium niobate product prepared in Example 1;

[0030] FIG3 is an X-ray diffraction spectrum of the magnesium niobate product prepared in Comparative Example 4. DETAILED DESCRIPTION

[0031] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0032] In a first aspect, the present application provides a method for preparing magnesium niobate, characterized in that it comprises the following steps:

[0033] (1) Wet-milling MgO and Nb2O5 to mix uniformly, and drying to obtain a mixed powder;

[0034] (2) heating the mixed powder to 1500-1700° C. for 1-3 hours and then quenching with water to obtain solid particles with core-shell structure inclusions;

[0035] (3) Heating the solid particles to 1000-1200° C. and maintaining the temperature to obtain the magnesium niobate.

[0036] The preparation method of magnesium niobate provided in the present application does not have the problem of incomplete reaction between MgO and Nb2O5, and no free niobium will appear in the prepared magnesium niobate, so that the Pb2Nb2O7 second phase (pyrochlore phase) will not be generated during the subsequent reaction between Nb2O5 and PbO.

[0037] The present invention adopts wet ball milling to make the obtained slurry more uniform; the present invention forms a core-shell structure inclusion through water quenching process, that is, niobium pentoxide is uniformly wrapped on the outside of magnesium oxide (the structural schematic diagram is shown in Figure 1), so that the contact area between the two is larger and the bonding force is stronger; in the subsequent rapid temperature rise sintering process, the solid phase reaction between the core and shell parts of the solid particles can be more complete, and the obtained magnesium niobate (MgNb2O6, MN) does not contain free niobium, has high purity and high stability, and the Mg in MN is 2+ 、Nb 5+ The two components have high uniformity and high reaction activity, which is conducive to the full mixing with PbO and TiO2 to form a liquid phase at high temperature. The raw materials for the growth of the formed lead magnesium niobate-lead titanate (PMNT) crystals are more uniform and uniform, which in turn helps to obtain PMNT single crystals with a single perovskite structure, high purity and excellent piezoelectric properties, thereby improving the yield.

[0038] In some embodiments of the present application, the initial raw materials MgO and Nb2O5 are high-purity reagents with a purity greater than 99.99%. When the purity of the initial raw materials MgO and Nb2O5 is within the above range, the influence of impurities on the purity of magnesium niobate can be avoided, thereby improving the quality of magnesium niobate.

[0039] The initial raw material MgO used in this application is preferably nano-scale high-activity MgO, and Nb2O5 is preferably micron-scale Nb2O5.

[0040] The present application has no particular restrictions on the specific operating method and the device used for heating the mixed powder to 1500-1700°C for 1-3 hours, as long as the purpose of the present application can be achieved. For example: the mixed powder is placed in a crucible, and then placed in a high-temperature melting furnace, and heated to 1500-1700°C for 1-3 hours.

[0041] In this application, the temperature is raised to 1500-1700°C over 1-3 hours at a constant heating rate, with the temperature before heating being room temperature. When the heating time and the temperature after heating of the mixed powder are controlled within the above ranges, MgO and Nb2O5 can fully form core-shell structure inclusions, and the magnesium niobate obtained after rapid heating and sintering has higher purity and greater reactivity.

[0042] The room temperature mentioned in this application refers to the indoor temperature, which is generally around 25°C.

[0043] The present application has no particular restrictions on the specific operation method of water quenching, as long as the purpose of the present application can be achieved. For example, the mixed powder is quickly released from the high-temperature melting device after high-temperature treatment, flows into room temperature water, and water quenched to obtain solid particles.

[0044] The present application has no particular restrictions on the specific operating method and device used to heat the solid particles to 1000-1200°C, as long as the purpose of the present application can be achieved. For example, the solid particles are placed in a high-temperature electric furnace and heated from room temperature to 1000-1200°C.

[0045] In some embodiments of the present application, the molar ratio of MgO to Nb2O5 is 1: 1. When the molar ratio of MgO to Nb2O5 is controlled within the above ratio, the problem of incomplete reaction of MgO and Nb2O5 can be better avoided.

[0046] In some embodiments of the present application, the Dv50 particle size of the MgO is 50-100 nm. When the Dv50 particle size of the MgO is controlled within the above range, the slurry obtained by grinding can be more uniform, so that the reaction in the subsequent process is more sufficient, and the resulting magnesium niobate has higher purity.

[0047] In some embodiments of the present application, the Dv50 particle size of the Nb2O5 is 2-15 μm. When the Dv50 particle size of the Nb2O5 is controlled within the above range, the ground mixed powder can be more uniform, allowing for a more complete reaction in subsequent processes and resulting in a higher purity of the magnesium niobate.

[0048] In some embodiments of the present application, the mass ratio of the grinding balls, material, and milling media used in the wet ball milling process is 1:(0.9-1.1):(1.2-1.8). When the mass ratio of the grinding balls, material, and milling media is controlled within the above range, MgO and Nb2O5 can be mixed more evenly, allowing for a more complete reaction in subsequent processes and resulting in a higher purity of the magnesium niobate.

[0049] In some embodiments of the present application, the ball mill jar material used in the wet ball milling is polyurethane. The present application selects polyurethane as the ball mill jar material, which can make the slurry obtained by grinding more uniform and can better avoid the introduction of new impurities.

[0050] In some embodiments of the present application, the wet ball milling medium used is anhydrous ethanol. The present application selects anhydrous ethanol as the ball milling medium to make the milled slurry more uniform, allowing for a more complete reaction in subsequent processes and resulting in a higher purity of the magnesium niobate.

[0051] In some embodiments of the present application, the wet ball milling process uses alumina balls. The use of alumina balls as grinding balls in the present application can make the slurry obtained by grinding more uniform, allowing for more complete reaction in subsequent processes and resulting in higher purity magnesium niobate.

[0052] In some embodiments of the present application, the wet ball milling speed is 100-200 r / min, and the wet ball milling time is 20-30 hours. When the wet ball milling speed and time are controlled within the above ranges, MgO and Nb2O5 can be mixed more evenly, allowing for a more complete reaction in subsequent processes, and the resulting magnesium niobate has a higher purity.

[0053] In some embodiments of the present application, the drying temperature is 90-110°C. When the drying temperature is controlled within this range, the slurry mixed and uniformly mixed by wet ball milling can be dried more thoroughly. The present application does not particularly limit the drying time, as long as it can achieve the purpose of the present application, for example, 20-30 hours.

[0054] In some embodiments of the present application, the heating rate to 1000-1200°C is 5-10°C / min. In the present application, the temperature of the solid particles before heating is room temperature. When the heating rate of the solid particles of the core-shell structure inclusion is controlled within the above range, rapid temperature sintering can be achieved, which can achieve a more complete solid-phase reaction between the core and shell portions of the solid particles, resulting in a higher purity of the magnesium niobate.

[0055] In some embodiments of the present application, the holding time is 25-35 minutes. When the holding time is controlled within the above range, the solid-phase reaction between the core and shell of the solid particles can be more complete, and the generated magnesium niobate has higher purity.

[0056] In some embodiments of the present application, the solid particles have a Dv50 particle size of 0.5-2 mm. When the solid particles have a Dv50 particle size within this range, they exhibit greater reactivity, enabling better reactions with titanium oxide and lead oxide, resulting in a more uniform and homogeneous raw material for PMNT growth.

[0057] The second aspect of the present application provides a method for preparing raw materials for PMNT growth, which includes the method for preparing magnesium niobate described in the first aspect of the present application.

[0058] By using the magnesium niobate obtained in the first aspect of the present application and reacting it with titanium oxide (TiO2) and lead oxide (PbO), a raw material for PMNT growth can be obtained.

[0059] Example

[0060] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0061] The MgO and Nb2O5 used in the following examples and comparative examples are both high-purity reagents with a purity of 99.99%, wherein the MgO is nano-scale high-activity MgO, and the Nb2O5 is micron-scale Nb2O5 with a Dv50 particle size of 10.5 μm.

[0062] X-ray diffraction spectrum test:

[0063] The prepared magnesium niobate was tested using an X-ray powder diffractometer (model: Bruker D8 Advance) (Cu Kα), wherein the scanning range 2θ was 10°-80°, the scanning rate was 6° / min, and the test temperature was 20±5°C.

[0064] Example 1

[0065] MgO (Dv50 particle size is 50nm) and Nb2O5 are weighed in a molar ratio of 1:1, and wet ball milled in a ball mill at a rotation speed of 150r / min for 24h to obtain a slurry; then the slurry is dried at 100℃ for 24h to obtain a mixed powder; wherein, the ball mill material used in the wet ball milling is polyurethane, the ball milling medium is anhydrous ethanol, and the grinding balls are alumina balls; the mass ratio of grinding balls, materials, and ball milling medium is 1:1:1.5.

[0066] The dried mixed powder was placed in a crucible, placed in a high-temperature melting furnace, and heated from room temperature to 1600°C over 120 minutes. The mixture was then quickly discharged from the bottom of the melting furnace and poured into room temperature water for quenching to obtain solid particles with a Dv50 particle size of 1.5 mm.

[0067] The solid particles were placed in a high-temperature electric furnace, heated from room temperature to 1100° C. at a heating rate of 8° C. / min, and kept at this temperature for 30 minutes to obtain the magnesium niobate.

[0068] Examples 2-4

[0069] Except for adjusting the preparation parameters as shown in Table 1, the rest is the same as Example 1.

[0070] Comparative Examples 1-3

[0071] Except for adjusting the preparation parameters as shown in Table 1, the rest is the same as Example 1.

[0072] Table 1 Preparation parameters and product conditions of Examples 1-4 and Comparative Examples 1-3

[0073] The X-ray diffraction spectrum of the magnesium niobate product obtained in Example 1 is shown in FIG2 . As can be seen from FIG2 , the magnesium niobate product prepared in Example 1 has a single crystal phase, indicating that the magnesium niobate obtained by the preparation method of the present application has a high crystal phase purity and does not contain impurities; this is conducive to further obtaining PMNT single crystals with high purity and excellent piezoelectric properties.

[0074] As can be seen from Table 1, in Examples 1-4, the mass ratios of the grinding balls, materials, and ball milling media, the rotation speed and time of the wet ball milling, the temperature rise process of the mixed powder, and the Dv50 particle size of the raw material MgO were all controlled within the range of this application. The crystalline phase of the prepared magnesium niobate products was a single phase, and no residual niobium pentoxide (Nb2O5) was present.

[0075] In Comparative Example 1, the mixed powder heating process and the Dv50 particle size of MgO were not controlled within the scope of the present application, resulting in a small amount of niobium pentoxide (Nb2O5) remaining in the prepared magnesium niobate product. When used as a raw material for subsequent reactions, the residual Nb2O5 may react with PbO to form a pyrochlore phase during the subsequent reaction process, thereby reducing the crystal phase purity of the raw material for growing PMNT single crystals, thereby affecting the performance of the obtained PMNT single crystals.

[0076] In Comparative Example 2, the mass ratio of the grinding balls, materials, and ball milling media, the mixed powder heating process, and the Dv50 particle size of MgO were not controlled within the scope of the present application. In Comparative Example 3, the rotation speed, heating process, and Dv50 particle size of MgO during the wet ball milling process were not controlled within the scope of the present application. As a result, a trace amount of niobium pentoxide (Nb2O5) remained in the prepared magnesium niobate product. When used as a raw material for subsequent reactions, the residual Nb2O5 may react with PbO to form a pyrochlore phase during the subsequent reaction process, resulting in low crystal phase purity of the raw material for growing PMNT single crystals, which in turn affects the performance of the obtained PMNT single crystals.

[0077] Comparative Example 4

[0078] MgO and Nb2O5 were weighed in a 1:1 molar ratio and wet-milled in a ball mill at 150 rpm for 24 hours to obtain a slurry. The wet milling process used a polyurethane jar, anhydrous ethanol as the milling medium, and alumina balls. The mass ratio of grinding balls, materials, and milling medium was 1:1:1.5. The slurry was dried, placed in a corundum crucible, sealed with a lid, and placed in a box-type electric furnace. The temperature was then raised from room temperature to 1000°C over 360 minutes, then to 1200°C over 120 minutes, and maintained at this temperature for 360 minutes. The temperature was then lowered to 300°C over 240 minutes, and then to room temperature over another 120 minutes to obtain magnesium niobate.

[0079] The X-ray diffraction spectrum of the obtained magnesium niobate product is shown in FIG3 . As can be seen from FIG3 , the magnesium niobate product prepared in Comparative Example 4 contains, in addition to magnesium niobate, residual niobium pentoxide (Nb2O5). This indicates that when the magnesium niobate product prepared by the conventional synthesis method provided in Comparative Example 4 is used as a raw material for subsequent reactions, some residual Nb2O5 may react with PbO to form a pyrochlore phase during the subsequent reaction process, resulting in low crystal phase purity of the raw material for growing PMNT single crystals, thereby affecting the performance of the obtained PMNT single crystals.

[0080] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing magnesium niobate, characterized in that: The following steps are involved: (1) mixing MgO and Nb2O5 by wet ball milling and drying to obtain a mixed powder; (2) heating the mixed powder to 1500-1700° C. for 1-3 hours and then quenching with water to obtain solid particles of core-shell structure inclusions; (3) Heating the solid particles to 1000-1200° C. and maintaining the temperature to obtain the magnesium niobate.

2. The preparation method according to claim 1, characterized in that: The Dv50 particle size of the MgO is 50-100 nm.

3. The preparation method according to claim 1, characterized in that: The Dv50 particle size of the Nb2O5 is 2-15 μm.

4. The preparation method according to claim 1, characterized in that: The mass ratio of the grinding balls, materials and ball milling media used in the wet ball milling is 1:(0.9-1.1):(1.2-1.8).

5. The preparation method according to claim 1, characterized in that: The rotation speed of the wet ball mill is 100-200 r / min, and the time of the wet ball mill is 20-30 h.

6. The preparation method according to claim 1, characterized in that: The heating rate to 1000-1200° C. is 5-10° C. / min.

7. The preparation method according to claim 1, characterized in that: The insulation time is 25-35 minutes.

8. The preparation method according to claim 1, characterized in that: The Dv50 particle size of the solid particles is 0.5-2 mm.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The drying temperature is 90-110°C.

10. A method for preparing a raw material for PMNT growth, characterized in that: A method for preparing the magnesium niobate according to any one of claims 1 to 9.

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