CN111533553A

CN111533553A - Nanocrystalline barium titanate ceramic and preparation method thereof

Info

Publication number: CN111533553A
Application number: CN202010104781.4A
Authority: CN
Inventors: 张蕾; 于洪宇; 王宏兆; 庄后荣; 曾俊
Original assignee: Southwest University of Science and Technology
Current assignee: Southwest University of Science and Technology; Southern University of Science and Technology
Priority date: 2020-02-20
Filing date: 2020-02-20
Publication date: 2020-08-14

Abstract

The invention belongs to the technical field of capacitor dielectric materials, and particularly relates to nanocrystalline barium titanate ceramic and a preparation method thereof. The preparation method of the nanocrystalline barium titanate ceramic comprises the steps of mixing barium carbonate and titanium dioxide, and performing ball milling, sanding, drying, sieving and calcining to obtain the barium titanate ceramic. The preparation method of the nano-crystalline barium titanate ceramic comprises the steps of mixing barium carbonate and titanium dioxide, ball milling to increase the sintering activity of the barium carbonate and the titanium dioxide, then carrying out solid phase synthesis on the barium titanate nano-powder with small particle size and high tetragonality by a sanding method, and calcining the barium titanate nano-powder to obtain the nano-crystalline barium titanate ceramic with small grain size and high dielectric constant, wherein the nano-crystalline barium titanate ceramic can meet the requirement that a capacitor device contains 5-6 ceramic grains in each single dielectric medium.

Description

Nanocrystalline barium titanate ceramic and preparation method thereof

Technical Field

The invention belongs to the technical field of capacitor dielectric materials, and particularly relates to nanocrystalline barium titanate ceramic and a preparation method thereof.

Background

Ferroelectric materials have a wide range of applications in electronic and electro-optical devices, such as high dielectric constant multilayer ceramic capacitors (MLCC), thermistors, dielectricsMass, underwater sensors, pyroelectric sensors, medical diagnostic sensors, electro-optic light valves, etc. Perovskite-structured materials are the most important of ferroelectric materials and are therefore the most studied. Perovskites are commonly denoted ABO₃Among the perovskite materials, barium titanate (BaTiO)₃) Is the ferroelectric material which is most widely researched and is also widely used. Barium titanate is widely studied for its excellent dielectric, ferroelectric, piezoelectric properties and relatively low loss and good insulating properties.

With the miniaturization, high reliability, thinning and low cost of electronic devices and components thereof, ceramic capacitors continue to be developed in two directions in the field of chip capacitors: smaller size components and larger capacitance values. In order to be able to obtain a larger capacitance with a relatively smaller volume, the dielectric layer thickness must be reduced while increasing the total number of layers. The dielectric thickness of the capacitor device is reduced from 10 mu m to less than 1 mu m, and the number of layers is increased to hundreds, which not only requires the granularity of the ceramic powder to be in a nanometer level, but also more importantly controls the growth of ceramic grains in the calcining process. In the last decade, a number of synthetic methods for obtaining barium titanate nanostructures, in particular nanopowders, have been developed. The mass production of barium titanate is mainly based on the solid state reaction between barium and titanium oxides, and in order to manufacture miniaturized high capacitance MLCCs, it is necessary to prepare high quality barium titanate powder with a particle size of less than 200 nm. At the same time, the properties and performance of the electroceramic powder are significantly affected by its purity, particle size and morphology. From these aspects, it is of great significance to produce barium titanate nanopowder with no agglomeration, uniform composition and high purity.

The main preparation methods of barium titanate include a solid phase method, a liquid phase method and a gas phase method. The solid phase method is a traditional method and is a main method for industrially producing barium titanate at present, and a flow chart of the method is shown in figure 1. The traditional solid phase synthesis method has the advantages of lower requirements on production conditions, simple process and lower production cost, but the ball milling of barium titanate generated at high temperature in water can cause Ba²⁺Leaching of (a) results in an increase in pH, which is detrimental to further processing; meanwhile, barium titanate powder is easy to generate relatively broken pieces after ball millingThe small particles are easy to agglomerate, and thicker particles appear, so that the uniformity of the powder is poor, the particle size distribution is widened, and the performance of the product is obviously reduced.

Disclosure of Invention

The invention aims to provide a nanocrystalline barium titanate ceramic and a preparation method thereof, and aims to solve the technical problems of wider particle size distribution, poorer performance and the like in the existing solid-phase synthesis method for preparing barium titanate ceramic.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows:

the invention provides a preparation method of nanocrystalline barium titanate ceramic on one hand, which comprises the following steps:

mixing barium carbonate and titanium dioxide, and performing ball milling to obtain slurry A;

sanding the slurry A to obtain slurry B;

and drying, sieving and calcining the slurry B to obtain the nanocrystalline barium titanate ceramic.

As a preferable technical scheme of the invention, the particle size of the titanium dioxide is 60nm-200 nm.

As a preferable technical scheme of the invention, the sanding time is 1-4 h.

As a preferred technical scheme of the invention, the rotational speed of the sanding is 2000rpm-3500 rpm.

As a preferred technical scheme of the invention, the calcination comprises binder removal and sintering.

As a further preferable technical scheme of the invention, the temperature of the rubber discharge is 500-1000 ℃.

As a further preferable technical scheme of the invention, the heating rate of the rubber discharge is 1-5 ℃/min.

As a further preferable technical scheme of the invention, the time for discharging the glue is 1-10 h.

As a further preferable technical scheme of the invention, the sintering temperature is 900-1200 ℃.

As a further preferable technical scheme of the invention, the temperature rise rate of the sintering is 2-10 ℃/min.

As a further preferable technical scheme of the invention, the sintering time is 1-10 h.

In a preferred embodiment of the present invention, in the step of mixing barium carbonate and titanium dioxide and ball-milling, the molar ratio of barium carbonate to titanium dioxide is (0.5-1.6): 1.

As a preferred technical scheme of the invention, in the step of mixing and ball-milling the barium carbonate and the titanium dioxide, the mixing and ball-milling time is 1-10 h.

In a preferred embodiment of the present invention, in the step of mixing and ball-milling barium carbonate and titanium dioxide, a grinding medium and water are further added to the mixed ball-milling.

In a preferred embodiment of the present invention, in the step of mixing and ball-milling barium carbonate and titanium dioxide, a dispersant is further added to the mixed ball-milling.

In a preferred embodiment of the present invention, in the step of sanding the slurry a, a grinding medium and water are further added to the sanding.

In a preferred embodiment of the present invention, in the step of sanding the slurry a, a dispersant is further added to the sanding.

As a preferred technical scheme of the invention, the drying temperature is 50-150 ℃.

As a preferable technical scheme of the invention, the mesh number of the sieved screen is 60-400 meshes.

The invention also provides a nano-crystalline barium titanate ceramic prepared by the preparation method of the nano-crystalline barium titanate ceramic.

In order to obtain the nanocrystalline barium titanate ceramics with no agglomeration, uniform components and high purity, the invention firstly mixes barium carbonate and titanium dioxide for ball milling to increase the sintering activity of the nanocrystalline barium titanate ceramics, then adds the step of sand milling on raw material powder on the basis of the traditional solid phase synthesis method to obtain powder particles with uniform size and better mixing degree, and then obtains the nanocrystalline barium titanate nanoceramic with small particle size, uniform distribution and high tetragonality by calcining treatment.

The nano-crystalline barium titanate ceramic obtained by the invention has the average particle size of 196.64nm and the BET of 4.98g/m²And c/a is more than 1.0089, so that the capacitor device meets the requirement that each single dielectric contains 5-6 ceramic grains and has good electrical performance.

Drawings

FIG. 1 is a flow chart of a conventional solid-phase synthesis process for preparing barium titanate;

FIG. 2 is a schematic diagram of a reaction process for preparing barium titanate by a solid-phase synthesis method;

FIG. 3 is a SEM scan of barium carbonate and titanium dioxide used in each example, wherein (a) is KSBaCO₃(ii) a (b) Is TA60 TiO₂(ii) a (c) Is AR TiO₂(ii) a (d) Is TA200TiO₂；

In FIG. 4, (a), (b), (c), and (d) correspond to SEM scanned images and particle size distribution maps of the nano-crystalline barium titanate obtained in examples 1 to 4, respectively;

in FIG. 5, (a), (b), (c), and (d) correspond to SEM scanned images and particle size distribution maps of the nano-crystalline barium titanate obtained in examples 5 to 8, respectively;

in FIG. 6, (a), (b), (c), and (d) correspond to SEM scanned images and particle size distribution maps of the nano-crystalline barium titanate obtained in examples 9 to 12, respectively;

FIG. 7 is a graph showing the relationship between the sintering temperature and the average particle size of BT1 powder;

FIG. 8 is a graph showing the relationship between the sanding time and the average particle size of BT1 powder;

in FIG. 9, (a), (b), (c), and (d) correspond to SEM scanning images and particle size distribution maps of the nano-crystalline barium titanate obtained in examples 13 to 16, respectively;

in FIG. 10, (a), (b), (c), and (d) correspond to SEM scanning images and particle size distribution maps of the nano-crystalline barium titanate obtained in examples 17 to 20, respectively;

FIG. 11 is a graph showing the relationship between the sintering temperature and the average particle size of BT3 powder;

in FIG. 12, (a), (b), (c), (d), and (e) correspond to SEM scanned images and particle size distribution maps of the nano-crystalline barium titanate obtained in examples 21 to 25, respectively;

in FIG. 13, (a), (b), (c), (d) and (e) correspond to SEM scanned images and particle size distribution maps of the nano-crystalline barium titanate obtained in examples 26 to 30, respectively;

in FIG. 14, (a), (b), (c), (d) and (e) correspond to SEM scanning images and particle size distribution maps of the nano-crystalline barium titanate obtained in examples 31 to 35, respectively;

FIG. 15 is a graph showing the relationship between the sintering temperature and the average particle size of BT2 powder;

FIG. 16 is a graph showing the effect of sintering temperature on the tetragonality in examples 1 to 4;

FIG. 17 is a graph showing the effect of sintering temperature on tetragonality in examples 5 to 8;

FIG. 18 is a graph showing the results of the effects of sanding time on tetragonality in examples 13-16;

FIG. 19 is a graph showing the results of the effects of sanding time on tetragonality in examples 17 to 20;

FIG. 20 is a graph showing the effect of sanding time on the average particle size of BT1, BT2 and BT3 powders at a sintering temperature of 1100 ℃;

FIG. 21 is a graph showing the effect of sanding time on the tetragonality of BT1, BT2 and BT3 powders at a sintering temperature of 1100 ℃;

FIG. 22 is a graph showing the effect of different sanding times on particle size tetragonality at a sintering temperature of 1050 ℃.

Detailed Description

In order to make the objects, technical solutions and technical effects of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described, and the embodiments described below are a part of the embodiments of the present invention, but not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art without any inventive step in connection with the embodiments of the present invention shall fall within the scope of protection of the present invention. Those whose specific conditions are not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer; the reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

In the description of the present invention, it should be understood that the weight of the related components mentioned in the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, it is within the scope of the disclosure that the content of the related components is scaled up or down according to the embodiments of the present invention. Specifically, the weight described in the embodiments of the present invention may be a unit of mass known in the chemical field such as μ g, mg, g, kg, etc.

In the description of the invention, an expression of a word in the singular should be understood to include the plural of the word, unless the context clearly dictates otherwise. The terms "comprises" or "comprising" are intended to specify the presence of stated features, quantities, steps, operations, elements, portions, or combinations thereof, but are not intended to preclude the presence or addition of one or more other features, quantities, steps, operations, elements, portions, or combinations thereof.

In the description of the present invention, when an element such as a layer, film, region, or substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present.

In the description of the present invention, "lower" or "upper" is not an absolute concept, but may be a relative concept that can be explained by replacing "upper" or "lower", respectively, according to the viewpoint of the observer.

The embodiment of the invention provides a preparation method of nanocrystalline barium titanate ceramic, which comprises the following steps:

s1, mixing barium carbonate and titanium dioxide, and ball-milling to obtain slurry A;

s2, sanding the slurry A to obtain slurry B;

and S3, drying, sieving and calcining the slurry B to obtain the nanocrystalline barium titanate ceramic.

The raw materials for synthesizing barium titanate by the solid-phase synthesis method are barium carbonate and titanium dioxide, and the reaction process can be decomposed into the following three steps:

BaCO₃+TiO₂→BaTiO₃+CO₂↑

BaTiO₃+BaCO₃→Ba₂TiO₄+CO₂↑

Ba₂TiO₄+TiO₂→2BaTiO₃

firstly, reacting slender barium carbonate particles at a surface contact point of titanium dioxide to generate a layer of barium titanate on the surface of the titanium dioxide; then the barium titanate generated on the surface reacts with the barium carbonate outside to generate barium orthotitanate, and the barium orthotitanate continuously reacts with the titanium dioxide inside to generate barium titanate, so that barium titanate particles move inwards, and finally all the titanium dioxide is converted into barium titanate (as shown in fig. 2). According to the reaction process shown in fig. 2, it can be seen that the particle size of barium titanate and titanium dioxide is also directly related, the smaller the particle size of titanium dioxide is, the smaller the particle size of the finally obtained barium titanate is, and the titanium dioxide with smaller particle size can also effectively avoid the generation of miscellaneous item original barium titanate. Thus, in some embodiments, the titanium dioxide has a particle size of 60nm to 200 nm. Specifically, typical, but not limiting, particle sizes of titanium dioxide are 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200 nm.

In S1, in order to ensure the barium carbonate and titanium dioxide to react completely and reduce the generation of impurities when the barium carbonate and titanium dioxide are mixed and ball-milled, the molar ratio of barium carbonate to titanium dioxide is (0.5-1.6):1 in some embodiments. In particular, typical but not limiting molar ratios between barium carbonate and titanium dioxide are 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6: 1; preferably 1: 1.

In some embodiments, a grinding medium and water are added in the mixing and ball milling process, which is helpful for generating sufficient impact on materials, reducing the reaction activation energy of barium carbonate and titanium dioxide, refining the crystal grains of the subsequently obtained barium titanate, enhancing the activity of the powder and improving the sintering capacity of the powder. Moreover, the ball-to-feed ratio is an important parameter influencing the ball milling process, the quantity of grinding media is too small, and the times of impact and grinding are insufficient, so that the grinding efficiency is low; if the number of grinding media is too large, most of the impact between the grinding media cannot fully exert the crushing effect on the materials. Therefore, the mass ratio of the mixture formed by mixing barium carbonate and titanium dioxide, the grinding medium and the water is preferably 1:2: 3. Wherein, the grinding medium and the parameters thereof can be selected according to the actual situation.

Because of the electrostatic friction effect generated by the mutual high-speed collision among the materials, the grinding medium and the grinding container in the ball milling process, some powder is adhered to the container wall and the grinding medium to form larger particles, and further, a dispersing agent can be added in the ball milling process to avoid the formation of the large particles. The dispersing agent can be adsorbed on the surface of the powder to play a role in reducing the surface activity of the powder, and the agglomeration capability of the powder is weakened. The dispersant may be selected according to the actual conditions.

The length of the mixing and ball milling time directly affects the size of the obtained crystal grains. In the initial stage, the particle size reduction speed is high, but after a certain time, even if the ball milling is continued, the particle size reduction range of the obtained crystal grains is very small and even the particle size reduction is not reduced any more; meanwhile, the ball milling time is too long, so that pollution is easily caused, and the purity of the product is influenced, therefore, in some embodiments, the mixing and ball milling time is controlled to be 1h-10h, preferably 1h-4 h. Specifically, typical, but not limiting, mixing and ball milling times are 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10 h.

When the mixing ball milling is carried out by using the ball mill, the higher the rotating speed of the stirring shaft of the ball mill is, the more energy is transferred to the grinding material, but the higher the rotating speed is, the temperature of the ball milling system is increased too fast, the leaching of barium ions and the increase of pH are caused, and the subsequent processing is not favorable. Thus, in some embodiments, the rotational speed of the mixing ball mill is 280 rpm.

S2 is a sand grinding treatment of the slurry A obtained in S1. Sanding can significantly reduce the grain size of the grains while making the distribution of the grains more uniform. By optimizing the sanding time, the grain size of the obtained crystal grains can be smaller, and the grain size distribution is more uniform; an excessively long sanding time results in the formation of larger grains, and grains having a smaller grain size than normal are distributed around the grains to form agglomerates. Thus, in some embodiments, the sanding time is controlled to be between 1h and 4h, preferably between 1h and 2 h. Specifically, typical, but not limiting, sanding times are 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4 h.

In some embodiments, grinding media and water are added during the sanding process, wherein the grinding media and its parameters can be selected as appropriate. In order to make the powder obtained after sanding more uniform and have better dispersibility, the mass ratio of the mixture formed by mixing barium carbonate and titanium dioxide, the grinding medium and water is preferably 1:2:4 in the sanding process.

Similarly to ball milling, the sanding process also causes some of the powder to adhere to the walls of the container and to the grinding media and, therefore, in some embodiments, a dispersant is added to the sanding process to adsorb onto the surface of the powder to reduce its surface activity and reduce the ability of the powder to agglomerate. The dispersant may be selected according to the actual conditions.

In the sanding treatment with the sand mill, the rotational speed in the sanding treatment is set to 2000rpm to 3500rpm, preferably 2800rpm, in order to supply sufficient energy to destroy the primary particle diameter of the powder particles and to perform the function of refining the powder particles. Specifically, typical, but not limiting, rotational speeds are 2000rpm, 2100rpm, 2200rpm, 2300rpm, 2400rpm, 2500rpm, 2600rpm, 2700rpm, 2800rpm, 2900rpm, 3000rpm, 3100rpm, 3200rpm, 3300rpm, 3400rpm, 3500 rpm. The D50 of the barium titanate powder is rapidly reduced

And S3, drying, sieving and calcining the slurry B obtained in the step S2 to obtain the nanocrystalline barium titanate ceramic. Wherein, the slurry B is dried to form liquid slurry B into barium titanate powder, which is beneficial to the subsequent calcination treatment. In some embodiments, the temperature of drying is from 50 ℃ to 150 ℃, preferably 110 ℃. Specifically, typical but not limiting drying temperatures are 50 deg.C, 60 deg.C, 70 deg.C, 80 deg.C, 90 deg.C, 100 deg.C, 110 deg.C, 120 deg.C, 130 deg.C, 140 deg.C, 150 deg.C.

The particle size distribution difference of the barium titanate powder can be further reduced by sieving the dried barium titanate powder, so that the obtained nanocrystalline barium titanate ceramic has smaller particle size and more uniform distribution. In some embodiments, the mesh size of the screen is 60 mesh to 400 mesh, preferably 80 mesh. Specifically, typical, but non-limiting, screen mesh numbers are 60 mesh, 80 mesh, 100 mesh, 150 mesh, 200 mesh, 250 mesh, 300 mesh, 350 mesh, 400 mesh.

In some embodiments, the calcination is specifically a two-stage pressureless calcination, including debinding and sintering. Wherein, the binder removal is carried out before sintering, and is used for removing organic matters in the barium titanate powder so as to improve the quality of the obtained nanocrystalline barium titanate ceramic.

Since the d and a axes of the inter-plane distances of the crystal grains (111) gradually decrease with the increase of the temperature, the c axis gradually increases, and the tetragonality c/a of the crystal grains gradually increases with the increase of the temperature. Therefore, by optimizing the temperature, the heating rate and the time of binder removal and sintering, the grain size of the obtained nanocrystalline barium titanate is smaller, and the tetragonality is better; however, the colloid removal and sintering temperatures are too high, which leads to serious agglomeration of the nanocrystalline barium titanate grains, so that the calcination temperature and the sand milling time are required to be selected for obtaining powder with excellent performance, i.e. relatively small grain size and high tetragonality. In some embodiments, the temperature of the binder removal is set to 500 ℃ to 1000 ℃, preferably 800 ℃; the heating rate of the discharged glue is 1-5 ℃/min, preferably 2 ℃/min; the glue discharging time is 1h-10h, preferably 2 h; the sintering temperature is 900-1200 ℃; the temperature rise rate of sintering is 2-10 ℃/min, preferably 5 ℃/min; the sintering time is 1h-10h, preferably 3 h. Specifically, the typical, but not limiting, binder removal temperature is 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃, 950 ℃, 1000 ℃; typical but non-limiting glue-discharging heating rates are 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min and 5 ℃/min; typical but not limiting glue discharging time is 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h and 10 h; typical but non-limiting sintering temperatures are 900 deg.C, 950 deg.C, 1000 deg.C, 1050 deg.C, 1100 deg.C, 1150 deg.C, 1200 deg.C; typical but non-limiting sintering heating rates are 2 ℃/min, 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, 9 ℃/min, 10 ℃/min; typical but not limiting sintering times are 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10 h.

Correspondingly, the embodiment of the invention also provides the nanocrystalline barium titanate ceramic prepared by the preparation method of the nanocrystalline barium titanate ceramic.

In order to make the above implementation details and operations of the present invention clearly understood by those skilled in the art and to make the advanced performance of the nanocrystalline barium titanate ceramic and the preparation method thereof according to the embodiments of the present invention remarkably manifest, the above technical solutions are exemplified by a plurality of embodiments below.

Example 1

A preparation method of nanocrystalline barium titanate ceramic comprises the following steps:

(1) mixing KS BaCO₃(BET is 12 m)²/g) with TA60 TiO₂(D₅₀60nm, BET 83.8m²/g, the manufacturer is alatin) is weighed according to the proportion that Ba/Ti is 1, and then the materials are put into a nylon ball milling tank, and zirconium beads with the diameter of 5mm are added as ball milling materials, wherein the ratio of the materials to water is 1:2.5: 2.5; adding triethanolamine which accounts for 1 percent of the sum of the mass of the barium carbonate and the titanium dioxide as a dispersing agent, and carrying out ball milling for 4 hours at the rotating speed of 280rpm to obtain slurry A;

(2) pouring the slurry A into a horizontal sand mill for sanding, taking zirconium beads with the diameter of 0.1mm as a ball milling material, adding triethanolamine accounting for 2% of the total mass of the barium carbonate and the titanium dioxide as a dispersing agent for sanding for 2 hours, setting the rotating speed of the sand mill to be 2800rpm, and setting the pump speed to be 100L/h to obtain slurry B;

(3) and (3) putting the slurry B into a 110 ℃ oven for drying treatment, manually grinding, sieving by a 80-mesh sieve, then putting into a Nabo heat lifting furnace, heating to 800 ℃ at a heating rate of 2 ℃/min, preserving heat for 2h for removing glue, heating to 900 ℃ at a heating rate of 5 ℃/min, preserving heat for 3h, and sintering to obtain the nanocrystalline barium titanate ceramic.

Example 2

This example is substantially the same as example 1 except that the sintering temperature is 1000 ℃.

Example 3

This example is substantially the same as example 1 except that the sintering temperature was 1100 ℃.

Example 4

This example is substantially the same as example 1 except that the sintering temperature was 1200 ℃.

Example 5

This example is substantially the same as example 1 except that the sanding time was 3 hours.

Example 6

This example is essentially the same as example 1, except that the sanding time was 3 hours and the sintering temperature was 1000 ℃.

Example 7

This example is essentially the same as example 1, except that the sanding time was 3 hours and the sintering temperature was 1100 ℃.

Example 8

This example is essentially the same as example 1, except that the sanding time was 3 hours and the sintering temperature was 1200 ℃.

Example 9

This example is substantially the same as example 1 except that the sanding time was 4 hours.

Example 10

This example is essentially the same as example 1, except that the sanding time was 4 hours and the sintering temperature was 1000 ℃.

Example 11

This example is essentially the same as example 1, except that the sanding time was 4 hours and the sintering temperature was 1100 ℃.

Example 12

This example is essentially the same as example 1, except that the sanding time was 4 hours and the sintering temperature was 1200 ℃.

Example 13

(1) mixing KS BaCO₃(BET is 12 m)²/g) with TA200TiO₂(D₅₀200nm, BET of 11.6m²/g, the manufacturer is alatin) is weighed according to the proportion that Ba/Ti is 1, and then the materials are put into a nylon ball milling tank, and zirconium beads with the diameter of 5mm are added as ball milling materials, wherein the ratio of the materials to water is 1:2.5: 2.5; adding triethanolamine which accounts for 1 percent of the sum of the mass of the barium carbonate and the titanium dioxide as a dispersing agent, and carrying out ball milling for 4 hours at the rotating speed of 280rpm to obtain slurry A;

(2) pouring the slurry A into a horizontal sand mill for sanding, taking zirconium beads with the diameter of 0.1mm as a ball milling material, adding triethanolamine accounting for 2% of the mass sum of barium carbonate and titanium dioxide as a dispersing agent for sanding for 1h, setting the rotating speed of the sand mill to be 2800rpm, and setting the pump speed to be 100L/h to obtain slurry B;

(3) and (3) putting the slurry B into a 110 ℃ oven for drying treatment, manually grinding, sieving by a 80-mesh sieve, then putting into a Nabo heat lifting furnace, heating to 800 ℃ at a heating rate of 2 ℃/min, preserving heat for 2h for removing glue, heating to 1000 ℃ at a heating rate of 5 ℃/min, preserving heat for 2h, and sintering to obtain the nanocrystalline barium titanate ceramic.

Example 14

This example is substantially the same as example 13 except that the sanding time was 2 hours.

Example 15

This example is substantially the same as example 13 except that the sanding time was 3 hours.

Example 16

This example is substantially the same as example 13 except that the sanding time was 4 hours.

Example 17

This example is substantially the same as example 13 except that the sintering temperature was 1100 ℃.

Example 18

This example is essentially the same as example 13, except that the sanding time was 2 hours and the sintering temperature was 1100 ℃.

Example 19

This example is essentially the same as example 13, except that the sanding time was 3 hours and the sintering temperature was 1100 ℃.

Example 20

This example is essentially the same as example 13, except that the sanding time was 4 hours and the sintering temperature was 1100 ℃.

Example 21

(1) mixing KS BaCO₃(BET is 12 m)²/g) with AR TiO₂(D₅₀120nm and a BET of 10.93m²/g, the manufacturer is alatin) is weighed according to the proportion that Ba/Ti is 1, and then the materials are put into a nylon ball milling tank, and zirconium beads with the diameter of 5mm are added as ball milling materials, wherein the ratio of the materials to water is 1:2.5: 2.5; adding triethanolamine which accounts for 1 percent of the sum of the mass of the barium carbonate and the titanium dioxide as a dispersing agent, and carrying out ball milling for 4 hours at the rotating speed of 280rpm to obtain slurry A;

(3) and (3) putting the slurry B into a 110 ℃ oven for drying treatment, manually grinding, sieving by a 80-mesh sieve, then putting into a Nabo heat lifting furnace, heating to 800 ℃ at a heating rate of 2 ℃/min, preserving heat for 2h for removing glue, heating to 900 ℃ at a heating rate of 5 ℃/min, preserving heat for 4h, and sintering to obtain the nanocrystalline barium titanate ceramic.

Example 22

This example is essentially the same as example 21, except that the sanding time was 0h, i.e., only ball milled, not sanded.

Example 23

This example is substantially the same as example 21 except that the sanding time was 2 hours.

Example 24

This example is substantially the same as example 21 except that the sanding time was 3 hours.

Example 25

This example is substantially the same as example 21 except that the sanding time was 4 hours.

Example 26

This example is substantially the same as example 21 except that the sintering temperature was 1000 ℃.

Example 27

This example is essentially the same as example 21 except that the sintering temperature is 1000 ℃ and the sanding time is 0h, i.e. only ball milling, not sanding.

Example 28

This example is substantially the same as example 21 except that the sintering temperature was 1000 ℃ and the sanding time was 2 hours.

Example 29

This example is substantially the same as example 21 except that the sintering temperature was 1000 ℃ and the sanding time was 3 hours.

Example 30

This example is substantially the same as example 21 except that the sintering temperature was 1000 ℃ and the sanding time was 4 hours.

Example 31

This example is substantially the same as example 21 except that the sintering temperature was 1100 ℃.

Example 32

This example is essentially the same as example 21 except that the sintering temperature is 1100 ℃ and the sanding time is 0h, i.e. only ball milling, not sanding.

Example 33

This example is substantially the same as example 21 except that the sintering temperature was 1100 ℃ and the sanding time was 2 hours.

Example 34

This example is substantially the same as example 21 except that the sintering temperature was 1100 ℃ and the sanding time was 3 hours.

Example 35

This example is substantially the same as example 21 except that the sintering temperature was 1100 ℃ and the sanding time was 4 hours.

Example 36

This example is essentially the same as example 21 except that the sintering temperature is 1050 ℃ and the sanding time is 0h, i.e. only ball milling, not sanding.

Example 37

This example is essentially the same as example 21 except that the sintering temperature was 1050 ℃ and the sanding time was 0.5 h.

Example 38

This example is substantially the same as example 21 except that the sintering temperature was 1050 ℃.

Example 39

This example is essentially the same as example 21 except that the sintering temperature was 1050 ℃ and the sanding time was 1.5 hours.

Example 40

This example is substantially the same as example 21 except that the sintering temperature was 1050 ℃ and the sanding time was 2 hours.

EXAMPLE 41

This example is substantially the same as example 21 except that the sintering temperature was 1050 ℃ and the sanding time was 3 hours.

Example 42

This example is substantially the same as example 21 except that the sintering temperature was 1050 ℃ and the sanding time was 4 hours.

Performance testing and characterization method

1. Structural analysis

The powder to be subjected to structural analysis according to the present invention was subjected to structural analysis using a 9KW multifunction X-Ray diffractometer manufactured by Rigaku, japan. When preparing a sample to be detected by XRD, about 3g of powder to be detected is placed in the center of a glass slide. And applying pressure to the glass slide by using another glass slide to flatten the top layer of the stacked powder. And (5) placing the sample into an XRD testing device for measurement and analysis.

2. Topography analysis

For the calcined powder, a Gemini SEM300 model field emission scanning electron microscope from ZEISS, Germany was used for testing.

When preparing the powder sample, firstly, absolute ethyl alcohol is poured into the sample tube, and about 0.2g of the sample to be detected is taken out by tweezers and dissolved in the absolute ethyl alcohol. After the sample tube is shaken, the sample tube is subjected to ultrasonic dispersion for about 40 minutes, a dropper is used for taking out 5-6 drops of sample solution from the sample tube to be dropped on the surface of a glass slide, and then the glass slide is placed into a 100 ℃ oven to be dried, so that the absolute ethyl alcohol is evaporated. After about 2-3 min, the absolute ethyl alcohol dissolving the powder is completely evaporated. And taking out the glass slide, using conductive adhesive to pick the powder on the surface of the glass slide, selecting a place where the powder is uniform and smooth when sampling, and then fixing the conductive adhesive with the powder on a special sample table of the scanning electron microscope. Since the ceramic sample is not conductive, the surface of the sample needs to be treated by spraying gold by using a gold spraying instrument.

When the surface morphology of a sample is observed by using a scanning electron microscope, the voltage is 10kV, the 10000 times, 20000 times, 30000 times, 40000 times and 50000 times of the surface morphology are respectively subjected to screenshot analysis, and particle size statistics is performed by using particle size statistics software.

Performance test and characterization results

For convenience of explanation, KS BaCO₃(BET is 12 m)²/g) with TA60 TiO₂(D₅₀60nm, BET 83.8m²/g, alatin manufacturer) is BT 1; mixing KS BaCO₃(BET is 12 m)²/g) with AR TiO₂(D₅₀120nm and a BET of 10.93m²/g, aladine from the manufacturer) as BT 2; mixing KS BaCO₃(BET is 12 m)²/g) with TA200TiO₂(D₅₀200nm, BET of 11.6m²/g, avastin from the manufacturer) is denoted as BT 3.

SEM scan pictures of barium carbonate and titanium dioxide used in the above examples are shown in fig. 3. As can be seen from FIG. 3, the uniformity of the four raw material powders is good, and meets the requirements of preparing the nanocrystalline barium titanate on the raw material powders.

The SEM images and the particle size distribution diagrams of the nanocrystalline barium titanate ceramics obtained in examples 1 to 12 are shown in fig. 4 to 6, wherein the particle size distribution diagram at 1200 ℃ is not shown because the powder is agglomerated and the particles are sintered into blocks at 1200 ℃. Based on the results of examples 1 to 12, FIG. 7 was obtained with the sintering temperature as the abscissa and the average particle diameter as the ordinate. As can be seen from fig. 7, the barium titanate powder produced by sintering after sanding exhibited excellent uniformity. As the temperature increases, the particle size of the particles tends to increase slowly and changes greatly at 1200 ℃, resulting in coarser particles with some smaller size grains interspersed around the larger grains. The phenomenon can be explained by abnormal grain growth in thermodynamics, the movement speed of grain boundaries is obviously accelerated along with the increase of temperature, and finally some grains grow rapidly at the temperature, and the phenomenon of more serious hard agglomeration is also caused by overhigh sintering temperature. In addition, it can be seen from FIGS. 4-7 that sanding significantly reduces the grain size of the grains, while making the distribution of the grains more uniform.

The results of examples 1-12 are plotted as sand milling time versus grain size for BT1 powder, as shown in fig. 8. It can be seen from FIG. 8 that the grain size of the grains rapidly decreased with the increase of the sanding time during 2h to 3h, but the problem of the increase of the grain size also occurred when the sanding was carried out for 4 h. The problem of increased particle size due to prolonged sanding can be explained by agglomeration. With the increase of the sanding time, the grain size of the grains is gradually reduced, so that the specific surface area of the powder is gradually increased, meanwhile, the defects of the grains are increased, the tendency of mutual adhesion is increased, and finally, the agglomeration phenomenon of finer grains is caused to form larger grains. This also explains that example 20 corresponds to a graph in which both larger particles are present and a large number of smaller grain sizes are present. Meanwhile, the initial particle size of the BT1 powder is much smaller than that of the BT3 powder, so that the grain size is smaller due to the prolonged sanding time, the aggregation phenomenon is greatly generated, and the increase of the particle size is more obvious. Under the condition that other parameters are not changed, the particle size of the powder is gradually reduced along with the prolonging of the sanding time. When the particle size is too small, the specific surface area increases, and agglomeration occurs, resulting in larger particles, which in turn leads to an increase in the average particle size.

SEM images and particle size distribution diagrams of the nanocrystalline barium titanate ceramics obtained in examples 13 to 20 are shown in FIGS. 9 to 10. Based on the results of examples 13 to 20, FIG. 11 was obtained using the sanding time as the abscissa and the average particle diameter as the ordinate. As can be seen from FIGS. 9 to 11, at 1000 ℃ the grain size gradually decreases with increasing sanding time; when the sanding time is 2h-3h, the particle size distribution is more uniform, but the average particle size of the sand after 3h is basically unchanged compared with that of the sand after 2 h. When the sanding time was extended to 4 hours, the average particle size again decreased, but the particle size distribution graph showed that the particle size of the crystal grains began to be bipolar, and a large number of crystal grains with smaller particle size began to be generated at the same time. SEM image shows that the particle size distribution of the sintered barium titanate after 4h sanding is not uniform. When the temperature was increased to 1100 c, the grain size of the first 3h grains decreased with the extension of the sanding time, but when sanding was performed for 4h, the grain size of the grains did not continue to decrease but rather increased. When the SEM image of the sand-milled image of 4h was observed, it was found that large crystal grains were formed in the center of the image and that crystal grains having a much smaller particle diameter than normal were distributed around the periphery.

SEM images and particle size distribution diagrams of the nanocrystalline barium titanate ceramics obtained in examples 21 to 35 are shown in FIGS. 12 to 14. Based on the results of examples 21 to 35, FIG. 15 was obtained using the sanding time as the abscissa and the average particle diameter as the ordinate. It can be seen from fig. 12-15 that the particle size distribution of the powder was very uneven when not subjected to sanding, and the particle size of the powder was larger due to more severe agglomeration of the powder. After sanding for 1h, the agglomeration of the powder is broken, the particle size of the powder is rapidly reduced, but as the sanding time is prolonged, from sanding for 2h, the particle size of the crystal particles tends to be stable due to the agglomeration phenomenon of small particles.

In order to investigate the influence of the sintering temperature on the tetragonality, the powder after BT1 sintering was subjected to XRD characterization, and XRD images were analyzed, and the results of the influence of the sintering temperature on the tetragonality of BT1 powder were plotted, as shown in fig. 16-17. 16-17, the crystal grains tend to have an increasing tetragonality with increasing temperature, consistent with expectations; when the sintering temperature is increased to 1200 ℃, the tetragonality of the crystal grains can be increased to about 1.009, but according to the influence of the sintering temperature on the grain size, the crystal grains are extremely seriously agglomerated when the temperature is increased to 1200 ℃, and the grain size of the formed crystal grains is far more than 200 nm. The tetragonality of the crystal grains is obviously changed in the process of increasing the sintering temperature to 1100 ℃, but the change in the grain size is not obvious, and the obvious change is only generated when the temperature is increased to 1200 ℃. It is presumed that the optimum temperature for sintering is between 1000 ℃ and 1100 ℃.

Since the BT3 powder particle size was the largest of the three powders and also the largest variation with increasing sanding time, examples 13-20 were selected to test the effect of sanding time on tetragonality, and the results are shown in fig. 18-19. It can be seen that as the sanding time is prolonged, the particle size of the powder becomes smaller, defects are generated to cause the decrease of the tetragonality; the elongation of the sanding time significantly reduces the tetragonality of the grains, and the process does not tend to be smooth, but the grain size of the grains tends to be smooth as the sanding time is prolonged. When the sanding time exceeded 2 hours, the efficiency of sanding in reducing particle size decreased significantly, but the effect on tetragonality was still a rapid decline, suggesting that the optimum balance point for sanding time was between 1 and 2 hours.

The particle diameters of the three powders were compared with the tetragonality, and the results are shown in FIGS. 20 to 21. When the sanding time was progressed to 2 hours, the grain size of the crystal grains began to stabilize, but the tetragonality was still decreased as the sanding time was prolonged. The BT1 powder has poor tetragonality due to its small particle size. Comparing the BT2 with BT3, the difference of the grain sizes of the BT2 and the BT3 is not big when sanding is carried out for 2 hours, but the tetragonality of the BT2 powder is obviously better than that of BT 3. BT2 has poor tetragonality when the sanding time is 0, because of the unsanded powderThe uniformity of the powder is poor, and partial powder is not completely reacted due to overlarge particles, so that miscellaneous items exist in the powder. The tetragonality is improved by the fact that a part of small particles are agglomerated when the sand is ground for 3 hours, and the tetragonality is improved. Another problem reflected in the figure is that the milled BT2 powder having a smaller primary particle size is slightly larger than the BT3 powder, and the tetragonality is greatly improved, which is slightly contradictory to the view that pure tetragonality is proportional to the particle size. The supposition that the tetragonality of the powder is not only related to the particle size of the raw material, but also depends on the TiO content of the raw material powder₂The influence of the crystallinity is measured that the crystallinity of the BT2 powder is much higher than that of BT3 than that of BT 1.

To further derive the optimum sanding time, the effect of sanding time on tetragonality is plotted according to examples 36-42, as shown in FIG. 22. When the sanding time is increased from 1.5h to 2h, the tetragonality is greatly reduced. When the powder is sanded for 1.5h, the phenomena of large agglomeration and unevenness are basically eliminated, so that the sanding for 1.5h is considered to be the best balance point of the particle size and the tetragonality of the BT2 powder. In this case, the average particle diameter of the powder was 213.73nm, and c/a was 1.0084.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A preparation method of nanocrystalline barium titanate ceramic is characterized by comprising the following steps:

sanding the slurry A to obtain slurry B;

2. The method for preparing a nano-crystalline barium titanate ceramic according to claim 1, wherein the particle size of the titanium dioxide is 60nm to 200 nm.

3. The method for preparing a nano-crystalline barium titanate ceramic according to claim 1, wherein the sanding time is 1-4 hours; and/or

The rotational speed of the sand grinding is 2000rpm-3500 rpm.

4. The method of preparing a nano-crystalline barium titanate ceramic according to claim 1, wherein the calcining comprises debinding and sintering.

5. The method for preparing nano-crystalline barium titanate ceramic according to claim 4, wherein the temperature of the binder removal is 500-1000 ℃; and/or

The heating rate of the rubber discharge is 1-5 ℃/min; and/or

The glue discharging time is 1h-10 h; and/or

The sintering temperature is 900-1200 ℃; and/or

The temperature rise rate of the sintering is 2-10 ℃/min; and/or

The sintering time is 1-10 h.

6. The method for preparing a nano-crystalline barium titanate ceramic according to any one of claims 1 to 5, wherein in the step of mixing and ball-milling barium carbonate and titanium dioxide, the molar ratio of barium carbonate to titanium dioxide is (0.5-1.6): 1.

7. The method for preparing nano-crystalline barium titanate ceramic according to any one of claims 1 to 5, wherein in the step of mixing and ball-milling barium carbonate and titanium dioxide, the mixing and ball-milling time is 1h to 10 h.

8. The method for preparing nano-crystalline barium titanate ceramic according to any one of claims 1 to 5, wherein in the step of mixing and ball-milling barium carbonate and titanium dioxide, a grinding medium and water are further added to the mixing and ball-milling; and/or

The mixed ball mill is also added with a dispersant; and/or

In the step of sanding the slurry A, grinding media and water are added into the sanding; and/or

The sand mill is also added with a dispersant.

9. The method for preparing a nano-crystalline barium titanate ceramic according to any one of claims 1 to 5, wherein the drying temperature is 50 ℃ to 150 ℃; and/or

The mesh number of the sieved screen is 60-400 meshes.

10. The nanocrystalline barium titanate ceramic prepared by the method for preparing nanocrystalline barium titanate ceramic according to any one of claims 1 to 9.