WO2020215535A1

WO2020215535A1 - Nano barium titanate powder and preparation method thereof, ceramic dielectric layer and manufacturing method thereof

Info

Publication number: WO2020215535A1
Application number: PCT/CN2019/100604
Authority: WO
Inventors: 瞿海锋
Original assignee: 苏州宝顺美科技有限公司; 瞿海锋
Priority date: 2019-04-25
Filing date: 2019-08-14
Publication date: 2020-10-29
Also published as: KR20210153704A; CN110028317A; JP2022530627A; KR102590441B1; CN110028317B; JP7382083B2

Abstract

Provided are a nano barium titanate powder and a preparation method thereof, a ceramic dielectric layer and a manufacturing method thereof. The preparation method of the nano barium titanate powder comprises: rapidly mixing a nano titanium dioxide aqueous dispersion at a lower temperature with a barium hydroxide aqueous solution at a higher temperature, so that the temperature of an obtained mixed system is at least 2℃ lower than that of the barium hydroxide aqueous solution due to rapid mixing of the nano titanium dioxide aqueous dispersion and the barium hydroxide aqueous solution; wherein the mass concentration of the nano titanium dioxide aqueous dispersion is not lower than 20%; carrying out a high-pressure hydrothermal synthesis reaction on the mixed system, and washing and drying an obtained reaction product to obtain the nano barium titanate powder. The nano barium titanate powder can be well used for manufacturing the ceramic dielectric layer.

Description

Nano barium titanate powder and preparation method thereof, ceramic dielectric layer and manufacturing method thereof

Technical field

The invention relates to nano material synthesis technology, in particular to a nano barium titanate powder and a preparation method thereof, a ceramic dielectric layer and a manufacturing method thereof, and in particular to an industrialized production method of nano barium titanate powder and the method thereof Ceramic dielectric layer made of raw materials.

Background technique

Nano-barium titanate (BaTiO ₃ ) is widely used in the electronic ceramic industry because of its high dielectric constant, low dielectric loss, high resistivity, excellent insulation performance and high compressive strength, and is the preparation of multilayer ceramics The basic materials of electronic components such as capacitors (MLCC), positive temperature coefficient thermistors (PTC), and dynamic random access memory (DRAM).

Improving the uniformity and compactness of the ceramic dielectric layer and reducing the porosity are effective means to improve the capacitance of electronic components. According to the Horsfield model, it is best to mix barium titanate particles of different particle sizes so that the barium titanate particles of smaller particle size are filled into the gaps formed between the barium titanate particles of relatively large particle size to increase the bulk density . At the same time, the use of barium titanate powder with a small particle size helps to form smaller crystal grains in the ceramic dielectric layer, form more grain boundaries, and help improve the performance of the ceramic dielectric layer. However, at present, the particle size of commercially available barium titanate powder particles is mostly above 100 nm, while small-particle nano-barium titanate powder is relatively rare.

At this stage, the mainstream process for preparing nano-barium titanate powder can be roughly divided into solid phase sintering method and liquid phase synthesis method. The solid-phase sintering method is to mix and grind the oxides of the metal elements (Ti and Ba) or their acid salts that make up barium titanate, and then calcinate at a high temperature of about 1100°C to form the required powder through solid-phase reaction . The process of solid phase method is relatively simple, but the particle size of the barium titanate powder produced is large, the particle size distribution is not concentrated, and there are also defects of low purity and unstable performance. It is difficult to satisfy the ceramic dielectric layer for nano titanic acid. Demand for barium powder.

The liquid phase synthesis method can be further divided into sol-gel method, hydrothermal method and so on. The hydrothermal method refers to the hydrothermal treatment of a Ba(OH) ₂ aqueous solution containing dispersed TiO ₂ fine particles in a closed system such as an autoclave to provide a normal pressure condition at a certain temperature and autogenous pressure of water Unattainable special physical and chemical environment to form powder with high crystallinity, high purity and small size. However, in the hydrothermal reaction system, it is often necessary to control the mass concentration of TiO ₂ in a very low range, generally not exceeding 15%, to avoid problems such as particle agglomeration caused by excessive TiO ₂ concentration. However, at low concentrations, the volume of the TiO ₂ dispersion is too large, resulting in longer reaction time, increased energy consumption, and very low equipment yield. Moreover, in actual industrial production, the large amount of solvent causes uneven temperature control and other factors, which will also adversely affect the uniformity of the barium titanate powder.

In view of the above situation, it is expected to develop an industrial production process for nano-barium titanate powder. In the case of a high concentration of titanium dioxide, it is still possible to obtain high-quality nano-barium titanate powder that meets the requirements of the ceramic dielectric layer. Higher yield.

Summary of the invention

In view of the above-mentioned defects, the present invention provides a method for preparing nano-barium titanate powder, which uses a high-concentration titanium dioxide aqueous dispersion as a raw material, which not only has a very high yield and meets the needs of industrial production, but also obtains nano-titanic acid Barium powder has the advantages of small particle size, narrow particle size distribution, high purity, and well-developed crystal grains, which can meet the quality requirements of ceramic dielectric layers.

The invention provides a nano barium titanate powder, which is prepared by the above preparation method. The nano barium titanate powder has the characteristics of small particle size, narrow particle size distribution, high purity and good crystal grain development, and can meet the requirements of ceramic dielectric layers.

The present invention provides a method for manufacturing a ceramic dielectric layer, which includes first preparing the above-mentioned nano barium titanate powder. The manufacturing method can improve the uniformity and compactness of the ceramic dielectric layer and reduce the porosity.

The present invention provides a ceramic dielectric layer, which is prepared by the above-mentioned manufacturing method. The ceramic dielectric layer has high uniformity, compactness and low porosity.

In order to achieve the above objective, the present invention provides a method for preparing nano-barium titanate powder, which includes: rapidly mixing the nano-titanium dioxide aqueous dispersion with the barium hydroxide aqueous solution, so that the temperature of the resulting mixed system is relatively higher due to the rapid mixing of the two. The temperature of the barium hydroxide aqueous solution is at least 2°C lower; wherein the mass concentration of the nano-titanium dioxide aqueous dispersion is not less than 20%;

The mixed system is subjected to a high-pressure hydrothermal synthesis reaction, and the resulting reaction product is washed and dried to obtain nano-barium titanate powder.

When using the hydrothermal method to synthesize nano-barium titanate powder, if the concentration of TiO ₂ as the titanium source is high, it will easily cause the agglomeration of nano-barium titanate particles to be very serious; while the concentration of TiO ₂ is too low, which will lead to production efficiency Many problems such as too low and large product particle size. In view of this situation, the present invention provides a solution, using high-concentration (mass concentration ≥20%) nano-titanium dioxide aqueous dispersion as a raw material. Firstly, the nano-titanium dioxide aqueous dispersion and barium hydroxide aqueous solution are quickly mixed, and then implemented High-pressure hydrothermal synthesis can not only reduce the amount of solvent (usually deionized water) in the process of high-pressure hydrothermal synthesis reaction, improve production efficiency, but also achieve controllable barium titanate nano-particle size, and can obtain narrower The particle size distribution can also ensure the high purity of the nano barium titanate powder and the good growth of crystal grains, and finally obtain the nano barium titanate powder product with excellent performance.

In the present invention, the rapid mixing between the nanometer titanium dioxide aqueous dispersion and the barium hydroxide aqueous solution, or the rapid mixing of the titanium source and the barium source, is reflected by the temperature reduction degree of the mixing system, that is, due to the rapid mixing of the two The obvious temperature drop caused directly, excluding the obvious temperature drop caused by external cooling during the mixing process. In the rapid mixing process of the two, even if heating equipment is being used to heat the system, due to the rapid mixing of the two temperature liquids, the heating equipment is insufficient to maintain the temperature in a timely manner to reach the temperature of the barium hydroxide aqueous solution before mixing, resulting in a mixed system The temperature is significantly lower than that of barium hydroxide aqueous solution.

It is obvious that the decrease of the system temperature is mainly affected by the amount and initial temperature of the nano-TiO2 aqueous dispersion, the addition speed and mixing speed of the nano-TiO2 aqueous dispersion, as well as the power and heat conduction of the system heating equipment; taking into account the conventional electric heating Or the heating power of the heat transfer mode of the heat medium is limited. When the initial temperature T1 of the nano-titanium dioxide aqueous dispersion is quickly added to the barium hydroxide aqueous solution at the initial temperature T2, it is not enough to compensate for the decrease in temperature, and the temperature of the mixed system T3 drops by 2℃ Above; only when the addition speed and mixing speed are slow, the heating power can compensate for the decrease in system temperature within 2°C. In addition, if the mixing speed is insufficient, it will not only cause uneven temperature everywhere in the system, but also cause uneven distribution of the nanometer titanium dioxide aqueous dispersion in the system, which will affect the consistency of the product. Therefore, this patent adopts the definition of system temperature reduction to judge the speed of addition and mixing.

Specifically, in order to achieve rapid mixing of the two, in industrial production, the aqueous solution of barium hydroxide can be placed in a heated stirred tank, and the amount of nanometer titanium dioxide aqueous dispersion can be injected into the heated stirred tank through a pump or other liquid feeding methods, and supplemented by High-speed stirring and dispersion; or two liquids can be continuously mixed online through a meterable liquid-liquid mixing device. In practice, all production methods that can achieve high-speed mixing of liquid and liquid at a certain temperature can be used in the implementation of the technical scheme of the present invention.

Of course, the feeding or mixing speed should ensure that the temperature of the overall mixed solution tends to balance as soon as possible, so as to avoid the uniformity of the subsequent growth of the barium titanate particles due to the uneven temperature of the mixing system. In actual industrial production, multiple representative monitoring points can generally be selected to test the temperature changes during the mixing process. It is advisable that the temperature of each monitoring point is reduced by more than 2°C and the reduction range is basically the same.

Furthermore, in order to ensure the consistency of the subsequent barium titanate particle growth size, the temperature difference between the temperature of the mixed system and the barium hydroxide aqueous solution before mixing should not be too large, generally controlled at 2-20 ℃, usually controlled at 2-10 ℃. This can also effectively avoid the precipitation of barium hydroxide caused by a jump in temperature.

It should be noted that, due to the very high concentration (≥20%) of nanometer titanium dioxide in the aqueous dispersion of nanometer titanium dioxide, in order to achieve high yield of nanometer barium titanate powder, the aqueous solution of barium hydroxide also needs to contain high concentration of barium. Ions to ensure the molar ratio between barium ions and titanium atoms and the rapid mixing between the barium source and the titanium source. Generally, in barium hydroxide aqueous solution, the concentration of barium hydroxide should be close to the saturation concentration. For example, the concentration of barium source is more than 20%, and even can reach more than 50%. Therefore, in order to ensure that barium hydroxide is fully dissolved in water, hydrogen is generally controlled The temperature of the barium oxide aqueous solution is not lower than 90°C, generally 90-110°C, which can ensure the ratio between the barium source and the titanium source.

It is not difficult to understand that the temperature of the nanometer titanium dioxide aqueous dispersion is lower than that of the barium hydroxide aqueous solution. In order to ensure the temperature drop during the rapid mixing process, the temperature of the nanometer titanium dioxide aqueous dispersion should not exceed 70℃, and it is generally stored at room temperature. The temperature reaches 70°C.

In the present invention, the preparation of the mixed system can be carried out in an atmospheric environment. Of course, in order to avoid the occurrence of side reactions, the preparation of the mixed system can also be carried out under an inert atmosphere, such as under the protection of nitrogen or argon, and the present invention is not particularly limited herein.

As mentioned above, the preparation of the above-mentioned mixed system can be realized by adding the aqueous dispersion of nanometer titanium dioxide to the aqueous solution of barium hydroxide, or adding the aqueous solution of barium hydroxide to the aqueous dispersion of nanometer titanium dioxide, or The nanometer titanium dioxide aqueous dispersion and the barium hydroxide aqueous solution are mixed in a co-current mixing manner.

In a preferred embodiment of the present invention, the nano-titanium dioxide aqueous dispersion is quickly added to the barium hydroxide aqueous solution, so that the temperature of the resulting mixed system is at least 2°C lower than that of the barium hydroxide aqueous solution. Using this method to prepare a mixed system does not involve the feeding and transportation of high-temperature barium hydroxide aqueous solution, and has lower requirements on the process and equipment, and is easier to implement.

The aqueous nano-titanium dioxide dispersion used in the present invention is formed by dispersing nano-titanium dioxide powder in water. Preferably, in the aqueous nano-titanium dioxide dispersion, the median diameter D50 of the nano-titanium dioxide by volume does not exceed 30 nm.

In the present invention, the source of the nano-titanium dioxide powder or the nano-titanium dioxide aqueous dispersion is not particularly limited, and it can be purchased commercially or prepared by itself. For example, the nano-titanium dioxide powder can be prepared according to the process described in the patent application 201610879270.3 or 201610879701.6, and then dispersed in water in proportion to obtain an aqueous nano-titanium dioxide dispersion.

Reasonable control of the concentration of the aqueous dispersion of titanium dioxide is also beneficial to avoid problems such as agglomeration of the nano-barium titanate powder during the synthesis process. Therefore, the mass concentration of the aqueous dispersion of nano-titanium dioxide is generally controlled to be 20-50%. The inventor found that by setting the mass concentration in this interval, not only can the nanometer barium titanate powder with good dispersibility be obtained, but also the mass concentration of the nanometer titanium dioxide aqueous dispersion is changed within this interval, and the average nanometer barium titanate powder The particle size changes little.

Ideally, when the molar ratio of Ba to Ti is 1, the two can fully react to form barium titanate and avoid raw material remaining. It can be understood that an excess of a titanium source or a barium source is more conducive to the positive progress of the reaction toward the synthesis of barium titanate, for example, excess Ba is conducive to reducing the content of titanium dioxide impurities in the reaction product. However, a large amount of barium surplus will not only cause a waste of barium source, but also may introduce barium carbonate impurities if the reaction product is in contact with air. Considering the hydrothermal reaction efficiency and economic factors, the molar ratio between Ba ions and Ti atoms is generally controlled to be 1 to 4: 1, so that the final nano barium titanate powder has a higher purity, and it can also ensure titanium dioxide The full response.

The high-pressure hydrothermal synthesis reaction conditions in the present invention can be carried out with reference to the current hydrothermal synthesis process of barium titanate. In the specific implementation of the present invention, the temperature of the high-pressure hydrothermal synthesis reaction is usually controlled to be 100-250°C, and the pressure is less than 7 MPa. Specifically, the prepared mixed system is transferred to an autoclave, sealed and heated, and reacted at 100-250°C.

The present invention uses high-concentration nano-titanium dioxide aqueous dispersion as the raw material. Compared with the traditional high-pressure hydrothermal synthesis process, the reaction time can be greatly shortened. Generally, it takes about 1 hour, such as 1-24 hours, to complete the high-pressure water. Thermal synthesis reaction.

In the specific implementation process of the present invention, the corresponding high-pressure hydrothermal synthesis reaction conditions can be set reasonably according to the actual demand for nano barium titanate powder, for example, by changing the reaction temperature, reaction time and other conditions to obtain different particle sizes and/ Or nano barium titanate powder with different tetragonal phase (or cubic phase) specific gravity.

After the high-pressure hydrothermal synthesis reaction is completed, the temperature is lowered and the reaction product is collected, and then washed and dried to obtain high-quality nano-barium titanate powder. In the specific implementation process of the present invention, deionized water or deionized water and ethanol are used to wash the reaction product one or more times, and then filtered and dried at 60-90°C to obtain nano-barium titanate powder .

The invention provides a nano barium titanate powder, which is prepared by the above preparation method.

The nano barium titanate powder provided by the present invention has a very small particle size, and its average particle size is below 100 nm, and can even reach 5-50 nm; the particle size of the nano barium titanate powder is basically normal distribution, and Calculated, the relative standard deviation is below 25%, so the particles of the barium titanate powder are very uniform and the particle size distribution is narrow; the XRD pattern of the nano-barium titanate powder shows that the 2θ angle is between 44° and 46° The diffraction peak appears as a single peak without obvious splitting, which indicates that the crystal grains are well developed and the crystal form is good; the Ba/Ti ratio is around 1, indicating that the nano barium titanate powder has very high purity. Therefore, the nano barium titanate powder provided by the present invention has very high quality, and can meet the production requirements of the ceramic dielectric layer.

The present invention provides a method for manufacturing a ceramic dielectric layer, which includes the following steps:

First, the nano barium titanate powder is prepared according to the aforementioned preparation method; then, the nano barium titanate powder is prepared and fired to obtain a ceramic dielectric layer.

Specifically, you can first prepare nano-barium titanate powders with different particle sizes according to requirements, and then mix the nano-barium titanate powders with different particle sizes in proportion, for example, two kinds of nano-titanium with an average particle size of 75nm and 29nm. Barium titanate powder; alternatively, nano barium titanate powder with a single (average) particle size can be used as a raw material; or alternatively, the nano barium titanate powder and particles obtained by the preparation process of the present invention Barium titanate powders with a diameter greater than 100nm are mixed to achieve close packing.

The above-mentioned mixing can use the conventional mixing process of ceramic dielectric layer, for example, wet ball milling nano-barium titanate powder of different particle sizes in a planetary ball mill at 450 rpm for 10 hours, and using water or ethanol as a dispersant , And finally the obtained slurry is dried at a temperature of about 80°C.

The above-mentioned tableting and firing can also adopt the conventional preparation process of ceramic dielectric layer, such as grinding and mixing the mixed barium titanate powder and polyvinyl alcohol aqueous solution, pressing the original tablet with a press and a mold, and debinding. Sintered into porcelain at a temperature above 1100°C to obtain a ceramic dielectric layer.

The invention also provides a ceramic dielectric layer, which is prepared by the above-mentioned manufacturing method. Because the above-mentioned high-quality nano barium titanate powder is used as the raw material, it can ensure the high density and low porosity of the ceramic dielectric layer, avoid holes or cracks in the ceramic dielectric layer, and better meet the requirements of MLCC and other devices The development needs of miniaturization, thinning, and high performance.

The method for preparing nano barium titanate powder provided by the present invention firstly quickly mixes a high-concentration nano titanium dioxide aqueous dispersion with a barium hydroxide aqueous solution, and then implements high-pressure hydrothermal synthesis, which solves the problem of the existing hydrothermal synthesis method. In the case of nano-barium titanate powder, the agglomeration of barium titanate particles caused by excessively high concentration of titanium dioxide, and the problem of low production efficiency and poor product quality caused by low concentration of titanium dioxide is solved. By adopting the preparation method of the present invention, due to the very high concentration of nano titanium dioxide, the industrial production efficiency is significantly improved; and the obtained nano barium titanate powder has the following advantages:

1) Small particle size: the average particle size is less than 100nm, and can even reach 5-50nm;

2) Uniform particle size and narrow particle size distribution: the relative standard deviation of the particle size distribution is within 25%;

3) The crystal grains are well developed and the crystal form is good: in the XRD pattern, the diffraction peak with a 2θ angle between 44° and 46° appears as a single peak without obvious split;

4) High purity: Ba/Ti ratios are all around 1, mostly between 0.990 and 0.999.

The nano barium titanate powder provided by the present invention is prepared by the above-mentioned preparation method. The nano barium titanate powder has the advantages of small particle size, narrow particle size distribution, good crystal form, and high purity, and thus can meet the use requirements of ceramic dielectric layers.

The method for manufacturing a ceramic dielectric layer provided by the present invention includes the method for preparing the aforementioned nano barium titanate powder. Since the above-mentioned high-quality nano barium titanate powder is prepared and fired, it can help to ensure the high density and low porosity of the ceramic dielectric layer thickness, and avoid holes or cracks in the ceramic dielectric layer.

Since the ceramic dielectric layer provided by the present invention uses the aforementioned nano-barium titanate powder as a raw material, it can ensure the high uniformity, high density and low porosity of the ceramic dielectric layer thickness.

Description of the drawings

Figure 1 is a particle size distribution curve measured when nano titanium dioxide used in Examples 1-10 of the present invention is dispersed in deionized water at a mass concentration of 1%;

Figure 2 is a particle size distribution curve measured when nano titanium dioxide used in Examples 1-10 of the present invention is dispersed in deionized water at a mass concentration of 10%;

Figure 3 is a particle size distribution curve measured when nano-titania used in Examples 1-10 of the present invention is dispersed in deionized water at a mass concentration of 50%;

4 is a transmission electron micrograph of the nano-barium titanate powder prepared in Example 1 of the present invention;

Figure 5 is a particle size distribution diagram of nano barium titanate powder prepared in Example 1 of the present invention;

Fig. 6 is an XRD pattern of nano barium titanate powder prepared in Example 1 of the present invention;

Figure 7 is a scanning electron micrograph of the nano barium titanate powder prepared in Example 2 of the present invention;

Figure 8 is a particle size distribution diagram of nano barium titanate powder prepared in Example 2 of the present invention;

Figure 9 is an XRD pattern of the nano barium titanate powder prepared in Example 2 of the present invention;

Figure 10 is a scanning electron micrograph of the nano barium titanate powder prepared in Example 3 of the present invention;

11 is a diagram of the particle size distribution of nano barium titanate powder prepared in Example 3 of the present invention;

Figure 12 is an XRD pattern of the nano barium titanate powder prepared in Example 3 of the present invention;

Figure 13 is a scanning electron micrograph of the nano barium titanate powder prepared in Comparative Example 1 of the present invention;

14 is the XRD pattern of the nano barium titanate powder prepared in Comparative Example 1 of the present invention;

Figure 15 is a scanning electron micrograph of the nano barium titanate powder prepared in Comparative Example 2 of the present invention;

16 is the XRD pattern of the nano barium titanate powder prepared in Comparative Example 2 of the present invention;

Figure 17 is a scanning electron micrograph of the nano barium titanate powder prepared in Comparative Example 3 of the present invention;

18 is the XRD pattern of the nano barium titanate powder prepared in Comparative Example 3 of the present invention;

Figure 19 shows the XRD spectra of barium titanate dielectric ceramic sheets obtained by mixing and sintering nano barium titanate powders of different particle sizes in different proportions;

Fig. 20 is a partial enlarged view of Fig. 19.

Detailed ways

In order to make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

In the following examples and comparative examples, the following detection techniques are used to test and determine the characteristics of nano-barium titanate powder or titanium dioxide powder:

1. Use a Malvern laser particle size analyzer (Zetasizer Nano ZS) to test the dispersion particle size of the sample to obtain the volume distribution and dispersion particle size distribution diagram of nanometer titanium dioxide in water, and from this, the volume median particle size D50 can be obtained.

2. Observe the surface morphology of the sample with a scanning electron microscope or a transmission electron microscope, and calculate the particle size of about 200 particles to obtain the average particle size of the primary particles of barium titanate.

3. The relative standard deviation is the ratio of the standard deviation to the measured average value, which is given by the origin software.

4. Use an X-ray diffractometer (D8Advance) to collect X-ray diffraction patterns in the range of 20-80° with a step length of 0.02° and an integration time of 2s, and use the Rietveld method to refine the structure to calculate the lattice constant ratio through Topas software (c/a), the closer the lattice constant ratio is to 1, the closer the crystal structure is to the cubic phase, and vice versa. The content of the tetragonal and cubic phases is calculated by quantitative analysis without standard samples.

5. Use the BET method to analyze the specific surface area of the material.

6. Determine the ratio of barium to titanium of barium titanate powder by ICP-MS analysis.

Example 1

Disperse the titanium dioxide nano powder in deionized water at room temperature to obtain 200 g of a 48% mass concentration of nano titanium dioxide aqueous dispersion;

Under the protection of nitrogen, add 710g of barium hydroxide and 700mL of deionized water to a three-necked flask, and stir at 90℃ to dissolve;

Under the condition that the barium hydroxide does not precipitate, quickly add the nano-titanium dioxide aqueous dispersion to the three-necked flask, measure the temperature of the mixed system to decrease by 2～5℃, and stir quickly during the rapid addition. After the addition is complete, continue to stir About half an hour, a uniformly dispersed mixed system is obtained;

Transfer the mixed system to the reaction kettle, seal, heat at 120°C for about 16 hours, take out the reaction product after cooling, wash the product with deionized water several times, and dry at 80°C for several hours to obtain nano-barium titanate powder .

The nano titanium dioxide powder used in this embodiment has a D50 by volume ≤ 10nm, and the particle size distribution curves measured by dispersing it in deionized water at a concentration of 1%, 10%, and 50% are shown in Figure 1, respectively. Shown in Figure 2 and Figure 3.

Example 2

The temperature of the high-pressure hydrothermal synthesis reaction was changed to 160°C, and the remaining conditions were the same as in Example 1, to obtain nano-barium titanate powder.

Example 3

The temperature of the high-pressure hydrothermal synthesis reaction was changed to 220°C, and the other conditions were the same as in Example 1, to obtain nano-barium titanate powder.

Example 4

The time of the high-pressure hydrothermal synthesis reaction was changed to 4 hours, and the remaining conditions were the same as in Example 1, to obtain nano-barium titanate powder.

Example 5

The time of the high-pressure hydrothermal synthesis reaction was changed to 24 hours, and the remaining conditions were the same as in Example 1, to obtain nano-barium titanate powder.

Example 6

Keep the volume of deionized water unchanged, reduce the mass of titanium dioxide to half of the original, thereby changing the molar ratio of titanium dioxide to barium hydroxide, and other operating steps and conditions are the same as in Example 1.

Example 7-8

The preparation process of Examples 7-8 is basically the same as that of Example 2, except that: the mass concentration of the nanometer titanium dioxide aqueous dispersion in Example 7 is 36%; the mass concentration of the nanometer titanium dioxide aqueous dispersion in Example 8 is 24% .

Examples 9-10

The preparation process of Examples 9-10 is basically the same as that of Example 2, except that: in Example 9, 710g of barium hydroxide and 1000mL of deionized water are added to a three-necked flask, and stirred at 70°C until dissolved; In Example 10, 710 g of barium hydroxide and 300 mL of deionized water were added to a three-necked flask and stirred at 110° C. to dissolve.

Examples 11-12

The preparation process of Examples 11-12 is basically the same as that of Example 2, except that: the median diameter D50 of nanometer titania by volume in Example 11 is about 18nm; the median diameter of nanometer titania by volume in Example 12 The particle size D50 is about 27nm.

The reaction conditions for synthesizing nano-barium titanate powder in the foregoing Examples 1-12 are shown in Table 1, and the performance test results of the obtained nano-barium titanate powder are shown in Table 2.

Table 1 High-pressure hydrothermal synthesis reaction conditions of nano-barium titanate powder

Table 2 Physical properties of nanometer barium titanate powder synthesized by high pressure hydrothermal

The transmission electron microscope (SEM) photographs, particle size distribution diagrams and XRD patterns of the nano-barium titanate powder obtained in Example 1 are shown in Figure 4, Figure 5 and Figure 6, respectively; the nano-titanium obtained in Example 2 The scanning electron micrographs, particle size distribution and XRD patterns of the barium oxide powder are shown in Figures 7, 8 and 9 respectively; the scanning electron micrographs and particle size distribution of the nano-barium titanate powder obtained in Example 3 The graph and the XRD pattern are shown in FIG. 10, FIG. 11, and FIG. 12 respectively; for the characterization results of other embodiments, refer to FIG. 4 to FIG. 12.

According to the specific surface area and particle size data in Table 2, combined with transmission electron microscopy photos or scanning electron microscopy photos, and particle size distribution diagrams, it can be seen that using the preparation method in Examples 1-12 of the present invention, the obtained nano barium titanate powder is The average particle size does not exceed 100nm, and can even reach 5-50nm, and the particle size distribution is uniform, the particle size is basically a normal distribution, the particles are well dispersed, and no particle agglomeration is seen. After further calculation, the relative standard deviation of the particle size does not exceed 23%. It can be seen that the preparation method provided by the present invention can obtain a small and uniform nano-barium titanate powder.

Further combining with the XRD diffraction pattern, it can be seen that the diffraction peak of the nano-barium titanate powder obtained in Examples 1-12 with a 2θ angle between 44° and 46° is a single peak without obvious splitting; the crystals are calculated separately. The lattice constant ratio (c/a) is all around 1.0000, mostly between 1.0000 and 1.0070, indicating that the nano-barium titanate powder has complete crystal grain development, good crystal form, and mainly cubic phase or all cubic phase .

According to the Ba/Ti ratio data in Table 2, it can be seen that the Ba/Ti ratio of the nano-barium titanate powder obtained in Examples 1-12 is around 1, mostly concentrated between 0.990 and 0.999. It can be seen that, The nano barium titanate powder has very high purity.

It can be seen that by adopting the preparation method provided by the present invention, high-quality nano-barium titanate powder with small particle size, uniform particle size distribution, complete crystal growth, and high purity can be obtained.

Furthermore, according to the test results of Examples 1-3, it can be known that increasing the temperature of the hydrothermal synthesis reaction increases the particle size of the nano-barium titanate powder, and the cubic phase content decreases while the tetragonal phase content increases.

According to the comparison of the test results of Examples 1 and 4, and Examples 3 and 5, it can be seen that extending the time of the hydrothermal synthesis reaction will increase the particle size of the nano-barium titanate powder, which may also increase the specific gravity of the square. , The cubic weight is reduced.

According to the test results of Examples 2, 7 and 8, it can be known that changing the mass concentration of nanometer titanium dioxide aqueous dispersion, or the mass concentration of titanium dioxide in the mixed system, has a significant effect on the particle size and tetragonal phase (or cubic phase) of nanometer barium titanate powder. Phase) will also have an impact. Generally speaking, the mass concentration of nanometer titanium dioxide aqueous dispersion is reduced, the particle size of nanometer barium titanate powder is slightly reduced, but the reduction is not obvious, and the relative weight of the square is also slightly reduced, but the reduction is also not large. For example, the mass concentration of nanometer titanium dioxide aqueous dispersion is reduced from 48% to 24%, the average particle size of nanometer barium titanate powder is reduced from 29nm to 25nm, and the tetragonal phase content is reduced from 37.9% to 37.5%.

According to the test results of Examples 1, 11 and 12, it can be seen that increasing the median diameter of titanium dioxide in the nanometer titanium dioxide aqueous dispersion will increase the particle diameter of nanometer barium titanate powder and increase the specific gravity of the square , The cubic specific weight is reduced.

It can be inferred that, using the preparation method provided by the present invention, a high-concentration (20%-50%) nano-titanium dioxide aqueous dispersion is used as a raw material, and the titanium source and the barium source are quickly mixed before the high-pressure hydrothermal synthesis reaction. , It can overcome the defects of large barium titanate particles caused by the low concentration of titanium dioxide in the existing hydrothermal synthesis process for preparing nano-barium titanate, and the particles caused by the high concentration of titanium dioxide cannot obtain small particles due to agglomeration. The defects of the particle size barium titanate can obtain high-quality nano-barium titanate powder with narrow particle size distribution range, complete crystal grain development and high purity.

Comparative example 1

The preparation process of Comparative Example 1 is basically the same as that of Example 2. The only difference is that the quality of the nano-TiO2 powder is kept unchanged (that is, the molar ratio of barium ion to titanium atom is unchanged) when the mixed system is prepared, but the nano-TiO2 The mass concentration is 8%.

The specific physical property test results of the nano barium titanate powder are shown in Table 3, and the SEM photo and XRD pattern are shown in Figure 13 and Figure 14 respectively. After calculation, the average particle size is 33 nm, which is greater than the result obtained in Example 2 (29 nm). It shows that when the concentration of the aqueous dispersion of titanium dioxide is reduced, the average particle size of the obtained nano barium titanate powder becomes larger. In addition, since the concentration of the nanometer titanium dioxide aqueous dispersion is only 8%, the production efficiency of nanometer barium titanate powder is low.

Comparative example 2

The preparation process of Comparative Example 2 is basically the same as that of Example 2. The only difference is that when preparing the mixed system, the nano-titanium dioxide aqueous dispersion is slowly injected into the three-necked flask containing the barium hydroxide aqueous solution, and the mixture is quickly stirred while adding. Evenly, and maintain the temperature of the mixed solution in the range of 90±2℃ during the addition.

The specific physical property test results of the nano barium titanate powder are shown in Table 3, and the SEM photo and XRD pattern are shown in Figure 15 and Figure 16 respectively.

The calculation shows that the average particle size is 37nm, which is significantly higher than that of Example 2 (29nm). It shows that when the titanium dioxide aqueous dispersion is slowly injected, the average particle size of the nano-barium titanate powder becomes larger.

Comparative example 3

Under the protection of nitrogen, add 710g of barium hydroxide and 700mL of deionized water to the three-necked flask, stir at 90℃ until dissolved; then, under the condition of no precipitation of barium hydroxide, add 96g of commercial 5-10nm titanium dioxide powder into the three-necked flask In the process, stir and mix quickly while adding to obtain a uniformly dispersed mixed system. Continue stirring for half an hour. Transfer the mixed system to the reactor, seal it, heat it at about 120°C for about 16 hours, and take out the reactor after cooling. The product was washed with deionized water and ethanol several times, and dried at about 80°C for several hours to obtain nano-barium titanate powder.

The specific physical property test results of the nano barium titanate powder are shown in Table 3, and the SEM pictures and XRD patterns are shown in Figure 17 to Figure 18 respectively.

Comparing the test results of Comparative Example 3 and Example 2, especially the SEM photos of Comparative Example 3, it is obvious that nano-titanium dioxide is directly used as the raw material (equivalent to using a 100% mass concentration of nano-titanium dioxide aqueous dispersion as the raw material ), even if the nanometer titanium dioxide powder has a very small particle size (5-10nm), the obtained nanometer barium titanate particle agglomeration is very serious and cannot be directly applied at all, especially because it cannot be used for close packing. As a raw material for ceramic dielectric layers.

Table 3 Physical properties of hydrothermally synthesized barium titanate powder in Comparative Examples 1～3

Examples 13-18

The nano barium titanate powders obtained in Example 2 and Example 3 are mixed, tableted and fired in different proportions to obtain a ceramic dielectric layer. The specific method is:

Weigh barium titanate powders of different particle sizes in proportion, ball mill them in a planetary ball mill at a speed of 450 revolutions per minute for 10 hours, and dry the obtained slurry at 80°C.

Ceramic chip production: Grind and mix the single powder and formula powder with 5% polyvinyl alcohol aqueous solution separately, press and mold at 8MPa to form a disc with a diameter of 12.7mm and a thickness of about 1mm, and then heat the disc Heat up to 550°C for 4 hours to discharge the glue, continue to heat up to 1150°C, heat for 2 hours to sinter into porcelain, and test the dielectric properties with gold-plated electrodes on the ceramic sheet surface.

An Agilent LCR measuring instrument (4294A) was used to detect the density and dielectric constant of the obtained ceramic dielectric layer. The density and dielectric properties of the ceramic dielectric layers obtained in different proportions are shown in Table 4.

Table 4 Density and dielectric properties of ceramic dielectric layers obtained in different compound ratios

It can be seen from the test results in Table 4 that the nano-barium titanate powders obtained in the examples of the present invention are mixed, sliced and fired in different proportions to obtain the ceramic dielectric layers, all of which have very high density and small pores. Degree, and has good dielectric properties. In particular, mixing nano-barium titanate powders with different (average) particle sizes in an appropriate ratio can make the ceramic dielectric layer have a higher density and better dielectric properties.

19 is the XRD patterns of the ceramic dielectric layers obtained in Examples 13, 15, 16 and 18. It can be clearly seen from FIG. 19 that the ceramic dielectric layers of Examples 13, 15, 16 and 18 all have good crystal structures. Enlarge the peak at about 45° in 2θ in Fig. 19, that is, Fig. 20. It can be seen that the mixed and fired examples 15 and 16 of the two particle diameters have higher results than those of the examples 13 and 18 fired by the individual particle diameters. The more obvious bimodal structure, with the obvious characteristics of tetragonal phase barium titanate. This shows that barium titanate particles of different particle diameters are mixed, tableted, and calcined in an appropriate ratio to obtain a better tetragonal barium titanate ceramic dielectric layer.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand: It is still possible to modify the technical solutions described in the foregoing embodiments, or equivalently replace some or all of the technical features; these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention range.

Claims

A method for preparing nano barium titanate powder, which is characterized in that it comprises:

The lower temperature nanometer titanium dioxide aqueous dispersion is quickly mixed with the higher temperature barium hydroxide aqueous solution, so that the temperature of the resulting mixed system is at least 2°C lower than the temperature of the barium hydroxide aqueous solution due to the rapid mixing of the two; , The mass concentration of the nanometer titanium dioxide aqueous dispersion is not less than 20%;

The mixed system is subjected to a high-pressure hydrothermal synthesis reaction, and the resulting reaction product is washed and dried to obtain nano barium titanate powder.
The preparation method according to claim 1, characterized in that the lower temperature nano titanium dioxide aqueous dispersion is added to the higher temperature barium hydroxide aqueous solution and mixed quickly to obtain the mixed system.
The preparation method according to claim 1 or 2, wherein the temperature of the aqueous dispersion of nanometer titanium dioxide is not higher than 70°C; before the rapid mixing, the temperature of the aqueous solution of barium hydroxide is controlled not to be lower than 90°C .
The preparation method according to any one of claims 1 to 3, characterized in that, in the aqueous nano-titanium dioxide dispersion, the volume-based median diameter of the nano-titanium dioxide is less than or equal to 30 nm.
The preparation method according to any one of claims 1 to 3, characterized in that, in the mixed system, the molar ratio between Ba ions and Ti atoms is 1 to 4:1.
The preparation method according to claim 1 or 5, wherein the mass concentration of the aqueous barium hydroxide solution is not less than 20%.
The preparation method according to claim 1, wherein the temperature of the high-pressure hydrothermal synthesis reaction is 100-250°C, the pressure is less than 7 MPa, and the time is not less than 1 hour.
A nano barium titanate powder, characterized in that it is prepared by the preparation method of any one of claims 1-7.
A method for manufacturing a ceramic dielectric layer is characterized in that it comprises the following steps:

Prepare nano barium titanate powder according to the preparation method of any one of claims 1-7;

The nano barium titanate powder is prepared and fired to obtain a ceramic dielectric layer.
A ceramic dielectric layer, characterized in that it is produced by the manufacturing method of claim 9.