Preparation method of magnesium niobate

Abstract

The invention provides a preparation method of magnesium niobate, which comprises the following steps: carrying out wet ball milling on MgO and Nb2O5, uniformly mixing, and drying to obtain mixed powder; the mixed powder is heated to 1500-1700 DEG C for 1-3 h and then subjected to water quenching, and solid particles of a core-shell structure inclusion are obtained; and heating the solid particles to 1000-1200 DEG C, and carrying out heat preservation to obtain the magnesium niobate. Solid particles of a core-shell structure inclusion are formed through a water quenching process, then MN obtained through rapid heating sintering is high in purity and stability, Mg < 2 + > and Nb < 5 + > in the MN are high in uniformity and large in reaction activity, sufficient mixing with PbO and TiO2 at a high temperature is facilitated to form a liquid phase, the formed raw material for PMNT crystal growth is better in singleness and uniformity, and the preparation method is simple and easy to implement. Furthermore, the PMNT single crystal with a single perovskite structure, high purity and excellent piezoelectric property can be obtained, and the yield is improved.

Description

Technical Field

[0001] The present application relates to the technical field of piezoelectric materials, and in particular to a method for preparing magnesium niobate. Background Art

[0002] 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.

[0003] At present, the preparation of PMNT raw materials mainly adopts a two-step synthesis method: first, the magnesium niobate (MN) precursor is synthesized by solid-phase reaction of niobium pentoxide (Nb2O5) and magnesium oxide (MgO); then it is reacted with titanium oxide (TiO2) and lead oxide (PbO) to obtain the raw material for PMNT growth. However, in the preparation process of MN precursor, there is a problem of incomplete reaction between MgO and Nb2O5, which makes it easy for free niobium to appear in MN, resulting in the reaction of residual Nb2O5 and PbO to form the second phase (pyrochlore phase) of Pb2Nb2O7; the coexistence of pyrochlore phase and main crystal perovskite phase will seriously reduce the piezoelectric properties of PMNT single crystal and hinder the full utilization of material properties. Therefore, finding a method to synthesize high-purity magnesium niobate is the key to improving the purity of crystal growth raw materials. Summary of the invention

[0004] 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:

[0005] The first aspect of the present application provides a method for preparing magnesium niobate, comprising the following steps:

[0006] (1) mixing MgO and Nb2O5 by wet ball milling and drying to obtain a mixed powder;

[0007] (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;

[0008] (3) Heating the solid particles to 1000-1200° C. and maintaining the temperature to obtain the magnesium niobate.

[0009] In some embodiments of the present application, the molar ratio of the MgO to the Nb2O5 is 1:1.

[0010] In some embodiments of the present application, the Dv50 particle size of the MgO is 50-100 nm.

[0011] In some embodiments of the present application, the Dv50 particle size of the Nb2O5 is 2-15 μm.

[0012] 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).

[0013] In some embodiments of the present application, the ball mill jar material used in the wet ball milling is polyurethane.

[0014] In some embodiments of the present application, the ball milling medium used in the wet ball milling is anhydrous ethanol.

[0015] In some embodiments of the present application, the grinding balls used in the wet ball milling are alumina balls.

[0016] 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.

[0017] In some embodiments of the present application, the heating rate of heating to 1000-1200° C. is 5-10° C. / min.

[0018] In some embodiments of the present application, the insulation time is 25-35 minutes.

[0019] In some embodiments of the present application, the Dv50 particle size of the solid particles is 0.5-2 mm.

[0020] In some embodiments of the present application, the drying temperature is 90-110°C.

[0021] The second aspect of the present application provides a method for preparing raw materials for growing lead magnesium niobate-lead titanate (PMNT), including the method for preparing magnesium niobate described in the first aspect of the present application.

[0022] Beneficial effects of this application:

[0023] The present invention adopts wet ball milling to make the obtained slurry more uniform; the present invention forms a core-shell structure inclusion through a water quenching process, that is, Nb2O5 is uniformly 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, 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 rate.

[0024] Of course, implementing any product or method of the present application does not necessarily require achieving all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0026] Figure 1 This is a schematic diagram of the structure of solid particles of the core-shell structure inclusion prepared in this application;

[0027] Figure 2 is the X-ray diffraction spectrum of the magnesium niobate product prepared in Example 1;

[0028] Figure 3 This is the X-ray diffraction spectrum of the magnesium niobate product prepared in Comparative Example 4. DETAILED DESCRIPTION

[0029] The following will be combined with the 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 described embodiments 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 the present application belong to the scope of protection of the present application.

[0030] The first aspect of the present application provides a method for preparing magnesium niobate, characterized in that it comprises the following steps:

[0031] (1) mixing MgO and Nb2O5 by wet ball milling and drying to obtain a mixed powder;

[0032] (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;

[0033] (3) Heating the solid particles to 1000-1200° C. and maintaining the temperature to obtain the magnesium niobate.

[0034] The preparation method of magnesium niobate provided in the present application does not have the problem of incomplete reaction of MgO and Nb2O5, and no free niobium will appear in the prepared magnesium niobate, so that the second phase (pyrochlore phase) of Pb2Nb2O7 will not be generated in the subsequent reaction process of Nb2O5 and PbO.

[0035] The present application adopts wet ball milling to make the obtained slurry more uniform; the present application forms a core-shell structure inclusion body through water quenching process, that is, niobium pentoxide is uniformly wrapped around the outside of magnesium oxide (the structural schematic diagram is shown in FIG. Figure 1 As shown in the figure, 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 of the solid particles can be more complete, and the obtained magnesium niobate (MgNb2O6, MN) contains no 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 rate.

[0036] 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.

[0037] The initial raw material MgO used in the present application is preferably nano-scale high-activity MgO, and Nb2O5 is preferably micron-scale Nb2O5.

[0038] 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 the temperature is raised to 1500-1700°C for 1-3 hours.

[0039] In the present application, the temperature is raised to 1500-1700°C for 1-3h at a constant heating rate, and the temperature before heating is room temperature. When the heating time of the mixed powder and the temperature after heating are controlled within the above range, MgO and Nb2O5 can fully form a core-shell structure inclusion body, and the magnesium niobate obtained after rapid heating and sintering has higher purity and greater reaction activity.

[0040] The room temperature mentioned in this application refers to the indoor temperature, which is generally around 25°C.

[0041] 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.

[0042] The present application has no particular restrictions on the specific operation method and the 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: placing the solid particles in a high-temperature electric furnace and heating them from room temperature to 1000-1200°C.

[0043] 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.

[0044] 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 purity of the generated magnesium niobate is higher.

[0045] 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 mixed powder obtained by grinding can be more uniform, so that the reaction in the subsequent process is more sufficient, and the purity of the generated magnesium niobate is higher.

[0046] 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). When the mass ratio of the grinding balls, materials, and ball milling media is controlled within the above range, MgO and Nb2O5 can be mixed more evenly, so that the reaction in the subsequent process is more complete, and the purity of the generated magnesium niobate is higher.

[0047] In some embodiments of the present application, the ball mill material used in the wet ball milling is polyurethane. The present application selects polyurethane as the ball mill material, which can make the slurry obtained by grinding more uniform and can better avoid the introduction of new impurities.

[0048] In some embodiments of the present application, the wet ball milling medium is anhydrous ethanol. The present application selects anhydrous ethanol as the ball milling medium, which can make the slurry obtained by grinding more uniform, make the reaction more complete in the subsequent process, and generate magnesium niobate with higher purity.

[0049] In some embodiments of the present application, the grinding balls used in the wet ball milling are alumina balls. The present application selects alumina balls as grinding balls, which can make the slurry obtained by grinding more uniform, make the reaction more complete in the subsequent process, and generate magnesium niobate with higher purity.

[0050] In some embodiments of the present application, the speed of the wet ball milling is 100-200 r / min, and the time of the wet ball milling is 20-30 h. When the speed and time of the wet ball milling are controlled within the above range, MgO and Nb2O5 can be mixed more evenly, so that the reaction in the subsequent process is more sufficient, and the purity of the generated magnesium niobate is higher.

[0051] In some embodiments of the present application, the drying temperature is 90-110° C. When the drying temperature is controlled within the above range, the slurry after wet ball milling can be dried more fully. The present application has no particular limitation on the drying time, as long as the purpose of the present application can be achieved, for example, 20-30 hours.

[0052] In some embodiments of the present application, the heating rate to 1000-1200°C is 5-10°C / min. The temperature of the solid particles before heating in the present application 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 make the solid phase reaction between the core and shell parts of the solid particles more complete, and the generated magnesium niobate has a higher purity.

[0053] 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 a higher purity.

[0054] In some embodiments of the present application, the Dv50 particle size of the solid particles is 0.5-2 mm. When the Dv50 particle size of the generated solid particles is within the above range, the reaction activity is greater, and it can react better with titanium oxide and lead oxide to obtain a single and more uniform raw material for PMNT growth.

[0055] 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.

[0056] 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), the raw material for PMNT growth can be obtained.

[0057] Example

[0058] The following examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0059] The MgO and Nb2O5 used in the following examples and comparative examples are both high-purity reagents with a purity of 99.99%, wherein MgO is nano-scale high-activity MgO, and Nb2O5 is micron-scale Nb2O5 with a Dv50 particle size of 10.5 μm.

[0060] X-ray diffraction spectrum test:

[0061] The prepared magnesium niobate was tested by an X-ray powder diffractometer (model: Bruker D8 Advance) (Cu Kα), wherein the scanning range 2θ: 10°-80°, the scanning rate: 6° / min, and the testing temperature: 20±5°C.

[0062] Example 1

[0063] Weigh MgO (Dv50 particle size is 50nm) and Nb2O5 in a molar ratio of 1:1, and wet-mill them in a ball mill at a rotation speed of 150r / min for 24h to obtain a slurry; then dry the slurry 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.

[0064] The dried mixed powder was placed in a crucible, put into a high-temperature melting furnace, heated from room temperature to 1600°C over 120 minutes, then quickly released from the bottom of the melting furnace, flowed into room temperature water, and quenched to obtain solid particles with a Dv50 particle size of 1.5 mm.

[0065] The solid particles are placed in a high-temperature electric furnace, and the temperature is increased from room temperature to 1100° C. at a heating rate of 8° C. / min, and the temperature is kept for 30 minutes to obtain the magnesium niobate.

[0066] Embodiment 2-4

[0067] Except for adjusting the preparation parameters as shown in Table 1, the rest is the same as Example 1.

[0068] Comparative Examples 1-3

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

[0070] Table 1 Preparation parameters and product conditions of Examples 1-4 and Comparative Examples 1-3

[0071]

[0072] The X-ray diffraction spectrum of the magnesium niobate product obtained in Example 1 is as follows: Figure 2 As shown, from Figure 2 It can be seen that 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; it is conducive to further obtaining PMNT single crystals with high purity and excellent piezoelectric properties.

[0073] As can be seen from Table 1, in Examples 1-4, the mass ratio of the grinding balls, materials, and ball milling media, the rotation speed and time of the wet ball milling, the mixed powder heating process, and the Dv50 particle size of the raw material MgO are controlled within the scope of the present application, and the crystal phase of the prepared magnesium niobate products is a single phase without the presence of residual niobium pentoxide (Nb2O5).

[0074] The mixed powder heating process and the Dv50 particle size of MgO in Comparative Example 1 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 making the crystal phase purity of the raw material for growing the prepared PMNT single crystal low, thereby affecting the performance of the obtained PMNT single crystal.

[0075] The mass ratio of the grinding balls, materials, and ball-milling media, the mixed powder heating process, and the Dv50 particle size of MgO in Comparative Example 2 were not controlled within the scope of the present application. The rotation speed, heating process, and Dv50 particle size of the wet ball milling in Comparative Example 3 were not controlled within the scope of the present application, resulting in a trace 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 causing the crystalline phase purity of the raw material for the growth of the prepared PMNT single crystal to be low, thereby affecting the performance of the obtained PMNT single crystal.

[0076] Comparative Example 4

[0077] Weigh MgO and Nb2O5 in a molar ratio of 1:1, and wet-mill them in a ball mill at a speed of 150r / min for 24 hours to obtain a slurry; wherein, the ball mill material used in the wet milling is polyurethane, the ball milling medium is anhydrous ethanol, and the grinding ball is an alumina ball; the mass ratio of grinding ball, material, and ball milling medium is 1:1:1.5. After drying the above slurry, place it in a corundum crucible, cover it tightly, put it in a box-type electric furnace, and then heat it from room temperature to 1000℃ for 360min, then heat it to 1200℃ for 120min, and keep it warm for 360min; then cool it to 300℃ for 240min, and then cool it to room temperature for 120min to obtain a magnesium niobate product.

[0078] The X-ray diffraction spectrum of the obtained magnesium niobate product is as follows: Figure 3 As shown, from Figure 3 It can be seen that the magnesium niobate product prepared in Comparative Example 4 contains not only magnesium niobate but also residual niobium pentoxide (Nb2O5), which means 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 reactions, thereby causing the raw material for PMNT single crystal growth to have low crystal phase purity, thereby affecting the performance of the PMNT single crystal obtained.

[0079] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, 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.

Images