RU2224729C2 - Dispersible metal oxide-coated barium titanate-based materials - Google Patents

Abstract

FIELD: composite materials. SUBSTANCE: invention provides suspension, dispersion, and ceramic slurry of barium titanate-based particles in nonaqueous. Particles have coatings including metal oxide, metal hydroxide, and organic acid salt with metal other than barium or titanium. At least 90% particles of coated particles dispersed with high shear thrust have size below 0.9 mcm. EFFECT: enabled preparation of material suitable for manufacturing condensers with finer dielectric ceramic layers, good electric properties including constant current loss and disruption voltage, not requiring longtime grinding on ball mill. 62 cl, 8 dwg, 1 tbl, 7 ex

Description

BACKGROUND OF THE INVENTION

The high dielectric constant of barium titanate-based materials makes them suitable materials for multilayer ceramic capacitors, commonly referred to as “MSCCs”. MSCCs contain alternating layers of dielectric and conductive materials. Examples of MSCCs are described in US Pat. Nos. 3,612,963 and 3,435,738. Common electrical conductive materials used in MSCCs are palladium, silver, palladium and silver alloys, and nickel. MCCC dielectric layers are usually obtained from a concentrated dispersion of solid particles, known in the art as “slip”. Such slips typically contain powdered barium titanate-based material and a polymer binder in an aqueous and non-aqueous solution. Binder-stabilized powder films obtained by injection molding or slip coating are dried to form a “green” ceramic dielectric layer. The green layers are covered with conductive materials, forming a certain pattern, and then stacked to obtain a layered material consisting of alternating layers of a green ceramic dielectric and a conductor. The feet are cut into cubes of MSCC size, which are heated to burn out such organic materials as a binder and dispersant, and then fired to sinter particles of material based on barium titanate with the formation of a capacitor structure with laminated, dense layers of ceramic dielectric and conductor. Sintering temperatures, as a rule, are in the range of 1000-1500 ° C. During sintering, an increased density of the ceramic dielectric is achieved as a result of melting and agglomeration of particles with the formation of grains. Even when using grain growth inhibitors, the size of ceramic grains of an MSCC insulator is usually larger, for example, by 3-5 times than the size of the initial initial particles. In addition, during sintering, not all porosity is eliminated. As a rule, the residual porosity in the MSCC insulator layers is 2-10%. These pores or hole defects in the dielectric layer tend to increase in ceramics having a larger grain size. Some critical properties of capacitors, such as breakdown voltage and DC leakage, depend on the thickness of the dielectric, grain size and pore type defects. For example, it is believed that effective dielectric layers should have a thickness of several, for example at least 3-5 grains. Since a defect in any of the MSCC layers can be fatal for its performance, MSCCs are made with a sufficient dielectric layer thickness to effectively reduce the effects of ceramic defects that can be caused by random large grains or pores and adversely affect the properties of MSCCs.

Since the market requires microminiaturization of the design of electronic devices, there is a need in the MSCC industry for ceramic materials that provide thinner dielectric layers that are not subject to the catastrophic effect of large grain sizes and pores due to the thickness of the dielectric.

Barium titanate powders obtained using known processes, such as calcination or hydrothermal processes, have large particles and / or highly agglomerated fine particles, the size of which is much larger than 1 μm, as a result of which such particles and agglomerates are not easily used in the manufacture of MSCCs with fine-grained, ultrafine, for example less than 4-5 microns, with dielectric layers. Thus, it can be considered that a step forward in the art will be the production of barium titanate-based material that would be suitable for the manufacture of MSCCs with thinner, for example less than 4-5 microns, ceramic dielectric layers having acceptable or exceptional electrical properties, including DC leakage and breakdown voltage, without the need for long grinding.

Summary of the invention

This invention provides particles based on barium titanate having a coating containing metal oxide, metal oxide hydrate, metal hydroxide or a salt of an organic metal acid other than barium or titanium, with at least 90% of these particles having a particle size of less than 0.9 micrometer, when the coated particles are dispersed by mixing with high shear. In this sense, as used herein, the term “based on barium titanate” refers to barium titanate having a coating of a different metal oxide and other barium and titanate based oxides having a general ABO ₃ structure, wherein A is one or more divalent metals such as barium, calcium, lead, strontium, magnesium and zinc, and B represents one or more tetravalent metals such as titanium, tin, zirconium and hafnium. This invention also provides compositions containing such barium titanate-based particles of the invention, for example in a variety of forms, such as a suspension, wet cake, powder, dispersion, and slip.

Such particles are easily dispersed without the need for grinding into submicron dispersions, which are preferable in the production of MSCCs with thin dielectric layers having a submicron grain size and high breakdown voltage. High shear mixing is effective in reducing the size of the particle agglomerates of the invention and causes the agglomerates to be deagglomerated or split into smaller coated particles without grinding, i.e. without affecting the particles with solid grinding means, such as rods, balls or zirconium particles, etc. Since grinding can contribute to the splitting of particles to obtain a size smaller than the size of the original particles, and lead to unequal particles with exposure, i.e. uncoated surface, in a preferred particular embodiment, the particles corresponding to this invention do not grind, for example - differ in that they have a major part of the surface coated with a coating. In another aspect of the invention, non-ground particles are characterized in that they are equiaxed or spherical.

Another aspect of this invention provides a method for producing submicron particles based on barium titanate coated with a metal oxide, which consists in the fact that

(a) receive submicron particles based on barium titanate in a liquid medium,

(b) add one or more soluble metal salts to the liquid medium to obtain coated submicron particles containing an oxide, oxide hydrate, hydroxide or organic acid salt of the metal.

And yet another aspect of this invention provides a method for preparing a dispersion of barium titanate-based submicron particles in a liquid medium, comprising the step of deagglomerating a barium titanate-based particle dispersion in a liquid medium until the particle size distribution is less than 0.9 μm . Such deagglomeration is preferably carried out by mixing with high shear.

Brief Description of the Drawings

1A and 1B are photographs illustrating a specific embodiment of barium titanate-based particles of this invention; the depicted particles are coated with a metal oxide and the size of the initial particles in the range of 0.1-0.2 microns.

Figure 2 is a titration curve depicting the effect of a dispersant on viscosity for a particular dispersion embodiment in accordance with this invention.

3A and 3B are bar graphs showing a particle size distribution for a particular embodiment of barium titanate particles in accordance with this invention, where FIG. 3A shows a particle size distribution for a dispersion prepared from a wet cake and FIG. 3B shows a particle size distribution of the same dispersion after mixing with high shear.

Figure 4 is a bar graph showing the particle size distribution of barium titanate according to the prior art and containing highly agglomerated particles.

5A and 5B are bar graphs showing the particle size distribution of barium titanate according to this invention, where FIG. 5A shows the particle size distribution of a dispersion prepared from a wet cake, and FIG. 5B shows a particle size distribution of the same dispersion after mixing with great effort shear.

Detailed Description of Preferred Specific Embodiments

This invention provides particles based on barium titanate having a coating containing metal oxide, metal oxide hydrate or metal hydroxide, or mixtures thereof, wherein said coated particles have a particle size of less than 0.9 micrometers.

Such particles are easily dispersed without the need for grinding into submicron dispersions, which are preferable in the production of MSCCs with thin dielectric layers having a submicron grain size and high breakdown voltage. High shear mixing is effective in reducing the size of the particle agglomerates of the invention and causes the agglomerates to be deagglomerated or split into smaller coated particles without grinding, i.e. exposure of particles to solid grinding media, such as rods, balls or zirconium particles, etc. Since grinding can contribute to the splitting of particles to obtain a size smaller than the size of the original particles, and lead to unequal particles with exposure, i.e. uncoated surface, in a preferred particular embodiment, the particles corresponding to this invention do not grind, for example - differ in that they have a major part of the surface coated with a coating. In another aspect of the invention, non-ground particles are characterized in that they are equiaxed or spherical.

Such particles are used in the preparation of monolithic capacitors containing a ceramic body having a grain size of less than 0.3 micrometers. Preferred capacitors have a temperature coefficient of capacitance corresponding to the X7R type, and have a dielectric thickness of less than 4 μm and an dielectric strength of at least 100 volts per μm.

The size of the initial particles corresponding to this invention, it is convenient to determine the micrographs obtained using a scanning electron microscope (MPREM), for example such as those shown in figure 1. Although it is clear that the particles of this invention may contain initial particles of different sizes, in preferred aspects of the invention, barium titanate-based particles coated with a metal oxide have an initial particle size of, for example, an average initial particle size of less than 0.6 microns. In other preferred aspects of the invention, the particles have an initial particle size of less than 0.5 micrometers or less, and preferably less than 0.4 micrometers. In even more preferred aspects of this invention, the particles have an initial particle size of less than 0.3 micrometers or less, and in some cases even more preferably less than 0.2 micrometers.

Particles corresponding to this invention may exist in a different form than the original particles, for example, in the form of aggregates of initial particles and / or aggregates of agglomerates of initial particles. MPPEM are ineffective in searching for differences in the size distribution among the initial particles, aggregates of the initial particles and agglomerates of the aggregates of the initial particles. Thus, analysis of particle size distribution, for example by light scattering methods, is the preferred method for characterizing the size of barium titanium particles according to this invention, provided that the preparation for analysis does not include processing that could change the distribution of aggregated or agglomerated particles , an example of which is deagglomeration due to ultrasonic treatment, mixing with a large shear or grinding force. Thus, in the sense in which it is used here, the term "particle size" is used to indicate the size of the initial particles, aggregates of the original particles and agglomerates of the aggregates. When implementing a convenient automated light scattering method, a Horiba LA-900 particle size analyzer (Horiba LA-900) or a similar device is used with a laser scattering light. Such an analysis, as a rule, gives an idea of the volume fraction, normalized in frequency, of discrete particle sizes, including initial particles, aggregates, and agglomerates in ten groups, i.e. deciles, as shown in the histograms in figure 3-5. In more preferred aspects of this invention, at least 90% of the metal oxide coated barium titanate-based particles have a particle size of less than 0.8 micrometers, and preferably less than 0.7 micrometers and even more preferably less than 0.6 micrometers. In even more preferred aspects of this invention, at least 90% of the particles have a particle size of less than 0.5 micrometers, and preferably less than 0.4 micrometers and, in some cases, even more preferably less than 0.3 micrometers.

Particle size distribution characteristics include the D ₉₀ value, which is the size of the smallest particles in the decile of the largest particles, the D ₅₀ value, which represents the average diameter, and the D ₁₀ value, which is the size of the largest particles in the decile of the smallest particles. The ratio D ₉₀ / D ₁₀ is a convenient characteristic for identifying the width of the particle size distribution curve. In various aspects of this invention, the particle size distribution is narrow, preferably having a D ₉₀ / D ₁₀ ratio of less than 4, more preferably less than 3, and, in some cases, even more preferably less than 2.5.

In this sense, as used here, the term "dispersion" is used to indicate two-phase systems of solid particles suspended (suspended) in a liquid medium. In a preferred particular embodiment, the dispersion stability, i.e. its resistance to subsidence can be improved by using a dispersant. A useful dispersant for aqueous systems is a feedable water-soluble polymer, for example polyacrylic acid.

Except where it is apparent in the context that it is only a metal oxide, the term “metal oxide”, as used herein, is used to describe coatings of metal oxides, metal hydroxides, hydrates of metal oxides and organic salts acids of metals. Such an organic acid salt can be converted to an oxide or hydroxide, for example by thermal decomposition that takes place during heating, to burn the binder ceramic and / or sinter the ceramic.

As used herein, the term “high shear mixing” means mixing in a liquid medium that provides significant energy to separate agglomerates of coated particles of the invention into smaller particles without the action of a solid agent such as rods, cylinders , or solid spherical media such as spheres made of zirconium. Solids are used in certain mixing equipment with high shear, in which solids are used to create shear without impact. Although, as described below, mixing with high shear can be carried out using various equipment, it is difficult to accurately determine the force exerted to separate agglomerates when mixed with high shear.

In the sense in which it is used here, the term “based on barium titanate” refers to barium titanate, barium titanate having a coating of another metal oxide, and other barium and titanate based oxides having the general structure ABO ₃ , where A represents one or more divalent metals such as barium, calcium, lead, strontium, magnesium and zinc, and B represents one or more tetravalent metals such as titanium, tin, zirconium and hafnium. A preferred barium titanate-based material has the structure Ba _(1-x) A _x O · Ti _(1-y) B _y O ₂ , where x and y can have values in the range 0-1, wherein A represents one or more divalent metals other than barium, such as lead, calcium or strontium, and B represents one or more tetravalent metals other than titanium, such as tin, zirconium and hafnium. When other metals are present as impurities, the value of x and y may be small, for example, less than 0.1. In other cases, another metal or metals may be added to provide an important identifiable compound, such as barium-calcium titanate, barium-strontium titanate, barium zirconate titanate, and the like. In additional other cases where x or y is 1, barium or titanium can be replaced with another metal of suitable valency to obtain a compound such as lead titanate or barium zirconate. In additional other cases, the compound may have multiple partial substitutions of barium or titanium. An example of such a composition with multiple partial substitutions is represented by the structural formula

Ba _{(1-x · x'-x``)</sub> Pb <sub>x</sub> Ca <sub>x '</sub> Sr <sub>x''</sub> O · Ti <sub>(1-y · y'-y``)} Sn _y Zr _y' Hf _{y ''} O ₂ ,

where each value from x, x ’, x’ ’, y, y’ and y’’≥0 and (x + x ’+ x’ ’) <1 and (y + y’ + y ’’) <1. In many cases, barium titanate-based material will be placed with the perovskite crystal structure. In many cases, it is preferred that the barium titanate material has a perovskite structure.

It has been found that when barium titanate particles obtained by the hydrothermal process are usually dried to produce powders, these particles are converted into relatively highly agglomerated particles that are inefficiently deagglomerated by simple mixing with high shear. Thus, dispersions prepared from such dry agglomerated powders based on barium titanate, which have a submicron size of the initial particles, require a very long duration of impact grinding to obtain particles in the micron range and further intensive grinding to obtain submicron particles. In contrast, agglomerated barium titanate-based particles coated with a metal oxide layer in compositions of this invention having a submicron size of the original particles in a wet form, for example in the form of a suspension, wet cake, dispersion or slip or, even more surprisingly, in the form of a dry powder, it can be deagglomerated with the transition to a range of submicron sizes of coated particles due to the moderate effect of mixing dispersions containing such particles with a large shear.

Particles based on barium titanate, embodied in various aspects of this invention, can be obtained from particles based on barium titanate, which in turn are obtained by a hydrothermal process, which are not dried, but kept in a humid environment, at least until these particles will not be coated with metal oxide. Preferably, the barium titanate-based particles made by the hydrothermal process are held in an aqueous suspension until they are coated with a metal oxide. A suspension of submicron particles based on barium titanate can be prepared by a hydrothermal process, such as described in US Pat. titanium oxide and heated, usually to a temperature in the range of 100-200 ° C, to create submicron particles with a crystalline structure of perovskite. Particle size and particle size distribution can be manipulated by controlling process variables such as the temperature of the suspension and solutions, the rate of addition, and the rate of heating to and cooling from the perovskite formation temperature. Specialists in the art can easily make the selection of process variables to obtain the desired product in the form of particles, following the general principles of crystallization. For example, larger particles can be obtained by relatively slowly adding barium hydroxide to the suspension at a relatively low temperature, for example about 35 ° C, while smaller particles can be obtained by relatively quickly adding barium hydroxide to the suspension at a relatively high temperature, for example about 95 ° C . To obtain uniform particles, good mixing is important.

After the perovskite is crystallized to the barium titanate particles by heat treatment of the suspension, the particles are preferably washed to remove unreacted metal species, such as barium ions. Rinsing with deionized water can be carried out at pH 10 to prevent the dissolution of barium from the particles. Wash water can be removed by filtration or decantation from the settled particles. The number of washing cycles will be determined by the required purity in the aqueous phase, for example, it must be sufficient to obtain a suspension in a weak ionic solution having a conductivity of less than 5 milliseconds, preferably less than 1 millisecond. It was found that four to five washing cycles are sufficient to reduce the ion content of the aqueous phase to a low level characterized by a specific conductivity not exceeding about 100 milliseconds.

The barium titanate-based particles of this invention have a coating comprising an oxide, oxide hydrate, hydroxide or organic acid salt of at least one metal other than barium and titanium. Suitable organic acids, due to the low solubility of many of their metal salts, include oxalic acid, citric acid, tartaric acid and palmitic acid. It is believed that the salt of the organic acid will be converted to metal oxide during the burning of the binder. The choice of metal is preferably carried out on the basis of improvements made to the processing or properties of MSCC. The metal in the coatings is usually selected among bismuth, lithium, magnesium, calcium, strontium, scandium, zirconium, hafnium, vanadium, niobium, tantalum, manganese, cobalt, nickel, zinc, boron, silicon, antimony, tin, yttrium, lanthanum, lead and elements of the lanthanide group. In preferred aspects of this invention, the barium titanate particles have a barium and titanium free metal oxide coating. When ceramic capacitors with X7R dielectric properties are needed, it is useful to produce barium titanate particles with dopants such as niobium oxide, tantalum oxide or neodymium oxide in combination with nickel oxide or cobalt oxide. When it is necessary to obtain ceramic capacitors that are sintered at relatively low temperatures, for example in the range of 1000-1200 ° C, compared with 1300-1600 ° C, it is useful to obtain barium titanate particles with an alloying impurity, which contributes to low-temperature sintering. Such low temperature sintering additives include bismuth oxide, zinc oxide, zinc borate, zinc vanadate, lithium borate, and combinations thereof. Modifying the dielectric and lowering the sintering temperature, metal oxides can be effectively added to barium titanate-based particles after washing these particles and before forming a dispersible wet cake. Coatings of metal oxides can be obtained by adding to the miscible suspension of particles based on barium titanate an aqueous solution (aqueous solutions) of salts, for example nitrates, oxalates, and the like. metals corresponding to the desired coating. The deposition of metal oxide on the coating is stimulated by a suitable pH, for example, using ammonium hydrochloride. Salt solutions can be added either as a single salt mixture to form a single homogeneous coating, or individually and sequentially to form layers of individual metal oxides. In the case of metals with relatively greater solubility, such as cobalt and nickel, there is a tendency to more difficult deposition and maintenance of oxide coatings without re-dissolution; thus, it is often preferable to apply the oxide coatings of these more soluble metals as a topcoat over the relatively easier deposited metal oxide layers. The alkaline environment also minimizes the dissolution of barium and allows easy coating of barium and titanium-free metal oxide on the particles. Coatings of metal oxides for particles intended for use in ceramic capacitors typically have a thickness of less than 10 percent of the particle diameter, often a thickness of less than 20 nanometers, and preferably a thickness of not more than 5-10 nanometers.

Suspensions of barium titanate-based particles coated with a metal oxide are conveniently prepared at a relatively low concentration of solid particles, for example, less than 30 wt.% Based on barium titanate. Higher levels of particulate concentration, such as over 30% by weight of barium titanate-based particles, are generally preferred for the production of MSCCs. Thus, in the case where the suspension corresponding to this invention is used directly in the manufacture of MSCCs, it is useful to concentrate the suspension, for example, to remove water, say by filtration, to obtain a concentration of at least 40 wt.% Solid particles or at least 50 wt. %, more preferably at least 55 wt.%, and in some cases, even more preferably in the range of at least about 60 wt.% or 75 wt.% of the particles of this invention. In some cases, it may be necessary to replace the aqueous phase with an organic liquid phase, for example alcohol, by replacing the solvent. A dispersant and a binder can be added to the concentrated suspension to obtain a slip or stable dispersion of particles based on barium titanate.

After coating the metal oxide on the barium titanate-based particles obtained by the hydrothermal process, the suspension can be washed and the water content of the suspension can be reduced to obtain a concentrated suspension, wet cake or powder, for example wet or dry powder. In addition, the suspension, wet cake or powder can be treated with a binder and other additives to obtain a slip. Water is preferably removed in a manner that prevents or at least minimizes the formation of highly agglomerated particles, for example by calcination. Due to the fact that they were not calcined or dried, some metal oxides may tend to maintain the shape of the hydrated metal oxide, which can dissolve if it is not maintained at a pH close to the minimum solubility point for this metal oxide. For example, nickel oxide or cobalt oxides tend to dissolve somewhat if they are not maintained at a pH close to 10. Thus, in order to keep the coated particle in good condition, the pH of the aqueous component of the compositions of this invention is preferably maintained in the range of 9 -eleven.

The suspension can also be concentrated, for example by filtration, to obtain a solid wet cake, i.e. non-flowing solid material containing barium titanate-based particles coated with a metal oxide and a liquid. The aqueous wet cake may be in a solid state and contain only about 60% by weight of solid particles mixed with an aqueous solution, for example, be a solid cake of particles in a continuous liquid phase. More preferably, the wet cake will contain at least 65 wt.% Particles, even more preferably at least 70 wt.%. The wet cake may contain up to about 80 wt.% Solid particles or, in some cases, only 75 wt.% Particles. In an aqueous wet cake, the aqueous solution must have a pH of more than 8 in order to inhibit the dissolution of the metal. The preferred pH range is 8-12, the more preferred 9-11. Such a wet cake made from barium titanate particles is a precursor to colloidal dispersion. That is, the wet cake can be dispersed, for example, by mixing with a dispersant. To convert a wet cake from a solid state to a liquid dispersion, a little extra liquid medium is needed, if at all.

At least in the case of a water-containing wet cake, the particles in the cake will remain weakly agglomerated for a relatively long time, since the cake maintains a water content of at least 15 wt.%, More preferably at least 20 wt.% Or more, even more preferably - at least 25 wt.%.

A preferred specific embodiment of this invention provides a wet cake that can be stored and transported. Such a wet cake with an extended shelf life is placed in a moisture-proof casing to prevent loss of water content, which may contribute to the formation of highly agglomerated particles that are not easily deagglomerated. Such a moisture-proof casing, for example polyethylene bags or polyethylene-coated cardboard drums, can provide an extended shelf life, for example at least one day or more, for example at least 3 days, more preferably longer, for example at least 30 days or even more preferably at least 90 days.

The solid wet cake of this invention is readily converted to a dispersion in a fluid by introducing a dispersant into the cake without significant addition of aqueous fluid. Although the fluid can be added to the cake, the amount of dispersant needed to convert the solid cake to dispersion in the fluid is noticeably small, for example, typically less than 2 wt.% Based on the weight of the barium titanate-based material. In some cases, an additional fluid other than the volume of the dispersant fluid is not needed to convert the wet cake into a suspension in the fluid. Estimated dispersants are polyelectrolytes, which include organic polymers with anionic or cationic functional groups. Anionically functionalized polymers include carboxylic acid polymers such as polystyrenesulfonic acid and polyacrylic acid; canonically functionalized polymers include polyimides such as polyetherimide and polyethyleneimine. Polyacrylic acids are preferred for many applications. Although groups of polymeric acids can be protonated, it is preferable that such groups have a countable cation, which will prevent the pH of the dispersion from being reduced to a level that will help dissolve barium or other types of metals that may be present, for example, in dopant coatings. For use in capacitors, the preferred cation is ammonium ion. In some cases, it is possible to use alloying metals as a counting cation for a polymer acid based dispersant. Regardless of the dispersant selected, those skilled in the art will be able to easily determine the appropriate amount of dispersant through the titration process to construct the curve depicted in FIG. 2, which shows the dependence of the dispersion viscosity on the amount of dispersant used. When the amount of dispersant selected is such that it provides the lowest viscosity for the dispersion, the concentration of dispersant when using the dispersion may decrease, for example, due to dilution or interaction with additives, causing the viscosity to increase to an undesirably high level. Thus, for many applications, it is desirable to use a “viscosity-minimizing amount” of dispersant to provide a viscosity of the ultimate dispersion in the minimum viscosity range, and this viscosity is almost at branch A of the titration curve depicted in FIG. 2.

It has been found that the preferred dispersant for use in colloidal dispersions for use in capacitors and for such testing is ammoniated polyacrylic acid having a quantitative average molecular weight of about 8000. For example, it was found that 0.75 wt.% Of such ammoniated polyacrylic acid (in in the form of an aqueous solution of a concentration of 40 wt.%) it is useful to use for converting a wet cake into a liquid dispersion. The introduction of the dispersant can be carried out by convenient means, for example, by mechanically mixing the dispersant into a wet cake. When high shear mixing is used, the excess dispersant is consumed by the new particle surface area exposed by deagglomeration. Thus, it may be convenient to increase the dispersion during mixing with high shear.

Wet cake differs from suspensions, dispersions, slips and dry powders in that the wet cake is a non-flowing solid material, while suspensions, dispersions and slips are flowing liquids and dry powders are flowing solid particles. Wet powders have or do not flow, depending on the amount of liquid present. The more liquid is removed, the drier the moisture-containing powder becomes. It is understood, however, that the dry powder is not necessarily completely dehydrated. Spray drying, freeze drying, and low temperature drying are preferred methods for preparing dry powders of barium titanate-based particles coated with metal oxide, which are still dispersed simply by mixing with an aqueous solution containing a dispersant, for example by mixing with high shear . Thus, barium titanate-based particles coated with metal oxide according to this invention have the property of surprising dispersibility to produce dispersions of submicron particles without the need for prolonged impact grinding, for example, grinding by impact rods or vibration grinding. Unlike known materials, grinding with high energy costs for several hours is not required in order to reduce the particle size to the moment when the dispersion or slip of the oxide coated metal particles of barium titanate based on this invention can be used for the manufacture of capacitors with fine-grained, thin dielectric layers and high breakdown voltage.

Another aspect of this invention provides a method for preparing a dispersion of submicron metal oxide-coated barium titanate-based particles coated with metal oxide in an aqueous solution by deagglomerating a dispersion of large (larger than 1 μm), slightly agglomerated, metal oxide-coated barium titanate particles to those then, until essentially all of these particles become less than 1 μm or less. In a preferred method according to this invention, dispersions of high concentration solid particles, for example containing from about 30 to 75% by weight of the particles, are de-agglomerated by high shear mixing with a dispersing agent. The optimal mixing time with high shear is easy to determine by conventional experiments. Mixing with high shear can be carried out in a centrifugal pumping deagglomerating mill, supplied by Silverson Machine Inc. (Silverson Machine Inc.) from East Longmidow, Massachusetts. Other plants for producing de-agglomerated dispersions of this invention include equipment known as supermills, colloidal mills and cavitation mills. The supermills supplied by Premier Mill from Reading, PA have a media-filled grinding chamber with high-speed rotating discs on the central shaft. Colloidal mills supplied by Premier Mill in Reading, PA have a clearance for grinding between the extended surfaces of a high speed rotor and a fixed stator. In cavitation mills supplied by Arde Barinko Inc. (Arde Barinco Inc.) of Norwood, New Jersey, the fluid is pumped through a series of rapidly opening and closing chambers that rapidly compress and decompress the fluid, introducing a high-frequency shear effect that can deagglomerate the particles. It is expected that a concentrated suspension, dispersion, wet cake, wet powder or dry powder will exhibit equally good performance in the production of slips for the manufacture of high-quality capacitors in accordance with this invention, with preference being given to dispersions, wet pellets or powders depending on specific technological installations or methods for manufacturing capacitors.

The determinative test for weakly agglomerated, metal oxide coated barium titanate-based particles of this invention involves the use of a high shear laboratory strainer of the Silverson Model L4R equipped with a square mesh screen providing a high shear for mixing with high force shear of a dispersion sample in an amount of 500 g containing 70 wt.% of coated particles in an alkaline aqueous solution at a temperature in the range of 25-30 ° C and pH, at which the coating does not b children dissolve and containing an effective amount of a dispersing agent for an effective time to deagglomeration coated particles. An effective amount of dispersant is sufficient to maintain the separated agglomerates and aggregates in the range of smaller particle sizes without repeated agglomeration. The effective amount of dispersant particles will vary depending on factors such as particle size, nature of the coating, and dispersant powder. Those skilled in the art can easily determine the effective amount of dispersant and the effective time using a few common experiments, observing the effect of these variables, i.e. the concentration of the dispersing substance and the mixing time with a large shear, to reduce the amplitude of the distribution of particle sizes. An effective amount of these variables will allow an analysis of particle sizes, which reflects the actual effect of mixing with a large shear on deagglomeration. In many cases, it was found that an effective amount of a dispersant based on ammoniated polyacrylic acid (a molecular weight of about 8000) is 1 wt.% Dispersant, calculated on the total weight of the particles and dispersant, and an effective mixing time with a large shear is 1 minute

In some aspects of this invention, barium titanate-based metal oxide coated particles manufactured by hydrothermal processes and illustrated in FIG. 1 are substantially spherical, i.e. equiaxed in appearance, in contrast to particles having an irregular shape and / or surface with corners, usually subjected to grinding and / or calcination. Such particles remain substantially spherical even after downsizing by mixing with high shear. Sometimes, essentially spherical particles can be paired, i.e. connected particles that are fused together. It is desirable that the appearance of such paired particles is rare. The use of such spherical particles, in comparison with ground powders of non-spherical particles, makes it possible to obtain powders with an exceptionally large surface area, for example, Brunauer, Emett and Teller surface area (BET surface area) of at least 4 square meters per gram (m ² / g ) or more, for example at least 8 m ² / g or even more, about 12 m ² / g.

The submicron barium titanate-based particles coated with metal oxide of the invention can form a suspension with a wide range of binders, dispersants and release agents using aqueous or non-aqueous solvents to form ceramic slip slips. When used in the manufacture of ceramic capacitors, barium titanate-based particles corresponding to this invention are easily dispersed, for example, with a dispersant based on ammoniated polyacrylic acid, at a concentration of solid particles of 50-80 wt.%, In an aqueous solution of 5-20 wt. % dissolved or suspended film-forming polymer binder, to obtain a slip. Film-forming polymer binders widely used in the field of ceramics are polyvinyl acetate, polyvinyl chloride, poly (vinyl acetate / vinyl chloride), polyvinyl butyral, polystyrene, polymethyl acrylates. In some aqueous systems, it is preferable to use an emulsion of a latex binder, for example poly (acrylate), polystyrene acrylate, polyacrylonitrile acrylate, polyvinyl chloride, polystyrene, poly (butadiene styrene) and carboxylated poly (butadiene styrene), for example, as described in U.S. Patent No. 4,968,460 referred to herein. For aqueous systems, emulsions of water-insoluble polymers or water-soluble polymers, for example polyvinyl alcohol, are preferred.

When non-aqueous slips are preferred, barium titanate-based particles are dispersed in an organic solvent containing a dissolved polymer binder and, optionally, other dissolved materials, such as plasticizers, release agents, dispersants, bleaches and humectants. The organic solvents used have low boiling points and include benzene, methyl ethyl ketone, acetone, xylene, methyl alcohol, ethyl alcohol, propyl alcohol, 1,1,1-trichloroethane, tetrachlorethylene, amyl acetate, 2,2,4-triethylpentadiol-1,3- monoisobutyrate, toluene, turpentine and mixtures with water, such as mixtures of methyl alcohol and water. Polymeric materials used in non-aqueous slips include poly (vinyl butyral), poly (vinyl acetate), poly (vinyl alcohol), cellulose polymers such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, methoxyethyl cellulose, polypropylene, polyethylene, organosilicon polymers such as poly (methylsiloxane) and poly (methylphenylsiloxane), polystyrene, butadiene-styrene copolymer, poly (vinylpyrrolidone), polyamides, polyethers, poly (ethylene oxide-propylene oxide), polyacrylamides and acrylic polymers such as polyacrylate atria, poly (methyl acrylate), poly (methyl methacrylate) and copolymers such as copolymers of ethyl methacrylate and methyl acrylate. A preferred acrylate polymer is Acryloid B-7 (Acryloid B-7), supplied by the Rum & Haas Company (Rohm & Haas Company). Dispersing agents used for suspensions and slurries based on organic solvents include Alosa menhaden family fish oil, corn oil, polyethyleneimine and ammoniated polyacrylic acid.

The polymer binder is used in a concentration range of 5-20 wt.%. Often, the organic material will also contain a small amount of plasticizer to lower the glass transition temperature (Tg) of the binder polymer. The choice of plasticizers is determined primarily by the polymer, which must be modifiable and may include phthalic acid esters such as diethyl phthalate, dibutyl phthalate, dioctyl phthalate, butyl benzyl phthalate, alkyl phosphates, polyethylene glycol, glycerin, poly (ethylene oxides, polyethylenediethyl) isobutylene).

When preparing dispersions in an organic solvent, it is preferable to remove water from a water-containing wet cake of barium titanate-based particles, for example, in a vacuum oven at 200 ° C, followed by sieving of large particles, for example, at 100 mesh (mesh size (mesh) of a sieve corresponding to 0.149 mm). Used suspensions can be obtained by mixing with high shear particles based on barium titanate in a mixture of an organic solvent and a dispersing substance. A polymer binder or plasticizer can be added before or after mixing with high shear. In one specific embodiment, the organic solvent-based slip according to the invention contains 100 wt. parts of particles based on barium titanate:

25-40 parts of an organic solvent,

2-5 parts of a dispersant,

5-20 parts of a polymer binder, and

0-15 parts of plasticizer.

Both in aqueous slurries and in organic solvent-based slips, by means known to those skilled in the art, green streaks can be introduced into the surface of the carrier. See, for example, an article by J.K. Williams (JC Williams) on pp. 173-197 of the collection "Ceramic Fabrication Processes", vol. 9 "Course of research and technology of materials" (Treatise on Materials Science and Technology), "Academic Press" (1976), and US Pat. Nos. 3,717,487 and 4,640,905, incorporated herein by reference.

In addition, there are many methods for converting slurries into thin films, green layers, and fired ceramics. It is believed that the dispersions according to this invention will find application with minimal modification, for example, by choosing the preferred medium and binder suspension, diluting to the desired viscosity of the fluid, etc., in various methods for producing ceramics to obtain dielectric layers for MCCS . Films can be formed from slips by spraying, layering on a moving sheet, carried out from a water cascade or die (for example, using a doctor blade), and other methods used in the MSCC industry. When enough water has been removed from the film, a cohesive, solid “green” film is obtained that can be coated by forming a recorded pattern on one or both sides with a conductive material or a precursor to a conductive material, such as an ink paste containing small particles of palladium, silver, nickel or alloys palladium and silver. Such conductive ink pastes may contain fine particles of metal and ceramics. Sheets of a green film are usually stacked, for example, up to 250 layers or more, and cubes with MSCS sizes are cut out of them, then they are burned to burn out the polymer binder and dispersant and sintered to form a dense multilayer capacitor structure with fine-grained dielectric layers. The conductive material deposited on the ends can connect alternating conductive intermediate layers forming the MSCC.

It is expected that the special particle size-related properties of barium titanate-based particles of this invention will make it possible to produce new MSCCs, for example having ultra-thin layers of dielectric ceramics with submicron grains. Such dielectric materials should facilitate a significant increase in volumetric capacity. Moreover, it is expected that the MSCCs will have an unexpectedly high breakdown voltage. The absence of large particles, for example larger than 1 μm, should ensure industrial production with high yields, for example, over 98%, of suitable MSCCs containing numerous, for example, more than 40, dielectric layers. It is expected that the particles corresponding to this invention will preferably be used for the manufacture of MSCCs having a ceramic dielectric layer with a maximum grain size of 0.9 μm or less, for example 0.8 μm or even less, say 0.7 μm. Another aspect of this invention provides for producing X7R type capacitors containing more than 20 dielectric layers of barium titanate-based material sintered into a ceramic structure, the thickness of these layers being less than 5 μm, for example, in the thickness range of 2-4 μm. Depending on the design of the MSCC, a larger number of dielectric layers, for example 250 or 500, may be preferred. Thin dielectric layers allow the use of MSCCs with an increased number of dielectric layers in standard MSCCs, or MCCCs with a fixed number of layers for installation in smaller enclosures. As a result, the capacity of a standard size MSCC housing can be increased by 5-10 times or more.

To obtain monolithic MSCCs of type X7R, the particles used in the preparation of the dielectric are preferably coated with oxides of niobium, cobalt, nickel and manganese. With a low ability to anneal, for example, in the case of sintering at temperatures below 1200 ° C, the preferred metal oxide coating may also contain bismuth oxide. To obtain ultrathin dielectric layers with a thickness of less than 4 micrometers, the particles preferably have an initial particle size of less than 0.3 micrometers, for example in the range of 0.1-0.2 micrometers. The same size of small grains, for example less than 0.3 micrometers, in superthin dielectric layers provides excellent dielectric strength exceeding 100 volts per micrometer and a small loss tangent. These properties provide increased reliability for high-voltage ceramic capacitors. The ability to obtain thin dielectric layers ensured the manufacture of capacitors having a capacitance 5-10 times greater than the capacitance in the case of a standard case size. Such MSCCs preferably comprise a monolithic ceramic case, for example, of barium titanate doped with metal oxide, two groups of electrodes made in the form of a counter-comb structure enclosed in said case and extending respectively to opposite sides of said case, and two conductive ends in contact with said two groups respectively at the indicated opposite ends. MSCCs with characteristics corresponding to type X7R have a temperature coefficient of capacitance in the temperature range from -55 ° C to 125 ° C, which provides a deviation of no more than ± 15% from the value of capacitance at 25 ° C. In a preferred aspect of this invention, ceramic in an X7R type MSCC has a grain size of less than 0.3 micrometers and contains 93-98 wt. percent of ceramics based on barium titanate and 2-7 wt. percent of other metal oxides.

The following examples illustrate the implementation of certain specific embodiments of various aspects of this invention, but should not be construed as limiting the scope of the claims of this invention.

Example 1

This example illustrates one hydrothermal treatment method for preparing a suspension of barium titanate-based particles that are used to prepare coated barium titanate-based particles of this invention. An aqueous solution with a concentration of titanium oxychloride (TiOCl ₂ ) of 37 wt.% Was diluted by mixing with about 9 parts of water in the reactor; ammonium hydroxide was titrated in this solution to pH 4 to obtain a thick white gel. Soluble ammonium chloride was removed by filtration, followed by washing with hot deionized water and re-preparing the suspension to obtain a suspension of aqueous titanium hydroxide at 85 ° C and a concentration of titanium dioxide of about 4.2 wt.%. A solution with a concentration of barium hydroxide of about 25 wt.% Was obtained by dissolving barium hydroxide octahydrate in water at a temperature of 95 ° C. An excess barium hydroxide solution (120 molar percent) was added to the titanium oxide slurry for about 9 minutes, and then heated to a temperature of about 200 ° C to form submicron barium titanate particles having a perovskite structure with a narrow size distribution and equiaxial morphology. The suspension was cooled to a temperature below 100 ° C and washed with approximately 400 liters of ammoniated deionized water (pH 10). Wash water was decanted, and then another 4 washes were performed until the specific conductivity of the wash water fell below 100 microseeks. The resulting low conductivity suspension contained particles of barium titanate mainly in the form of agglomerates of essentially spherical initial particles, where the typical particle size of the agglomerates, determined from microphotographs obtained using a scanning electron microscope (MPREM), was in the range of about 10 micrometers, and the size of the initial particles, determined by MPREM, was approximately 0.15 micrometers. Such suspensions are materials used in the coating of metal oxides to obtain coated with metal oxide particles based on barium titanate, corresponding to this invention.

Example 2

To illustrate the effect of high shear mixing on barium titanate particles without a metal oxide coating, the suspension obtained by the method described in Example 1 was concentrated in a filter press at a pressure drop of 1000 kPa (159 psi) to obtain wet cake containing about 72 wt.% solid particles. The pellet was dispersed in a binder with polyacrylic acid (quantitative average molecular weight 8000) as a dispersant in an amount sufficient to obtain 75 g of polyacrylic acid per 100 g of barium titanate. The resulting dispersion had a particle size distribution with a D _{90 of} 1.8 μm. After processing a 500 g sample of the initially obtained dispersion for 1 minute using a Silverson model L4R laboratory mixer providing high shear, equipped with a square hole sieve, providing high shear, and operating at a speed of approximately 8000 rpm, the value D ₉₀ was 2.1 μm.

Example 3

This example illustrates the preparation of one particular embodiment of barium titanate-based metal oxide coated particles of the invention. The suspension was obtained essentially the same as in Example 1, and it contained approximately 22 kg of particles of barium titanate and 200 liters of ammoniated deionized water at pH 10. A solution of 1 gram molecule per kilogram of (unipolar) bismuth nitrate in bimolar nitric acid was added into the suspension in an amount necessary to obtain 3 g of bismuth per 100 g of barium titanate, simultaneously with a solution of ammonium hydroxide at a concentration of 29 wt.% in an amount sufficient to maintain the suspension at pH 10. On the particles of barium titanate easily formed ytie bismuth oxide. After adding a solution of bismuth, a solution of niobium bioxalate (containing about 5 wt.% Niobium with an excess of oxalic acid) was added to a suspension of bismuth-coated particles in an amount sufficient to obtain 1.5 g of niobium per 100 g of barium titanate, simultaneously with a solution of ammonium hydroxide in concentration of 29 wt.% in an amount sufficient to maintain the suspension at pH 10. On the particles of barium titanate, a coating of niobium oxide was easily formed. After the addition of niobium oxide, the suspension was washed with ammonized water and a suspension was again obtained in 200 liters of ammoniated water at pH 10. A solution of co-nitrate monopolar nitrate in water was added in an amount sufficient to obtain about 0.18 g of cobalt per 100 g of barium titanate. A cobalt oxide coating was formed on the particles. The suspension was washed several times with ammonized water and filtered to obtain a wet cake containing about 72 wt.% Coated with metal oxide particles based on barium titanate in the constant phase of an aqueous solution at pH 9-10. The wet cake was dispersed using ammoniated polyacrylic acid, essentially the same as in Example 2, to obtain a dispersion of barium titanate-based particles coated with metal oxide, more than 95 wt.% Of which passed through a sieve with a nylon mesh having a mesh size of 10 micrometers. The size distribution of such particles is illustrated by the histogram shown in figa. Particle size analysis showed that the average diameter of D ₅₀ was 0.64 micrometers, the value of D ₁₀ was 0.37 micrometers, and the value of D ₉₀ was 1.2 micrometers. A narrow particle size distribution is shown by a ratio of D ₉₀ / D _{10 of} about 3. A dispersion sample was processed by mixing with high shear, essentially the same as in Example 2, to reduce the size of the agglomerated particles. The particle size distribution of the dispersion obtained by mixing with high shear is illustrated by the histogram shown in figv. Particle size analysis showed that the average diameter decreased to 0.28 micrometers at D _{10 of} 0.20 micrometers and D _{90 of} 0.46 micrometers. A narrow particle size distribution is shown by a ratio of D ₉₀ / D _{10 of} about 2. About 1.2 g of a concentrated dispersion of solid particles (70 wt.% Solid particles) was placed in a plastic tube with a diameter of 12.5 mm (mm), placed in a porous form from a model gypsum, and allowed to dry in a high humidity chamber for 24 hours. The dried disk (12.5 mm in diameter and 2 mm thick) was separated from the mold and sintered at 1125 ° C for 2 hours to 94% of the theoretical density (5.64 g / cm ³ ). A sintered ceramic disk based on barium titanate had a dielectric constant of 2105 at 25 ° C. Characteristics corresponding to type X7R were indicated as the temperature coefficient of capacitance (TKE), which, when the temperature changed from -55 ° C to 125 ° C, was within the tolerance of ± 15%; TKE was 6.28 at -55 ° C and 3.45 at 125 ° C.

Example 4

This example is a comparative illustration of the presence of highly agglomerated particles in dispersions prepared from dried, hydrothermally prepared barium titanate particles available in the prior art. A suspension of submicron particles of barium titanate was obtained essentially the same as in Example 1, except that the suspension was filtered and dried to obtain a dry powder. Then, from about 22 kg of powder, a suspension was again obtained in 200 liters of deionized water, ammoniated to pH 10, and then a metal oxide coating was applied in accordance with the method described in Example 3. The suspension was pressed to form a wet cake with a solids content of 72 wt. % and dried. The metal oxide coated powder was then dispersed in an aqueous solution using a dispersant based on polyacrylic acid to obtain a dispersion of large (larger than 10 μm) agglomerates of highly agglomerated particles. Essentially, all barium titanate particles were agglomerated to a size at which they should remain on a sieve with a nylon mesh having a mesh size of 10 micrometers. After mixing with high shear, essentially all the particles of barium titanate remained on a sieve with a nylon mesh having a mesh size of 5 micrometers, which indicates the presence of highly agglomerated particles, for example, as a result of the fact that the drying of the powders favors the agglomeration of particles with a relatively large bond strength between particles that are not deagglomerated by mixing with high shear. Particle size analysis showed a three-mode distribution with peaks at about 0.3, 1.2, and 12 micrometers, with D ₁₀ about 0.5 micrometers, D ₅₀ about 6.4 micrometers, and D ₉₀ about 35 micrometers, as illustrated by the histogram shown figure 4. A wide particle size distribution is also characterized by a ratio of D ₉₀ / D ₁₀ equal to 70.

Example 5

This example also illustrates the preparation of a dispersion of barium titanate-based metal oxide-coated particles in accordance with this invention. The dispersion of barium titanate-based particles coated with a metal oxide was obtained from a wet cake essentially the same as in Example 3, and it was determined that it has a particle size distribution illustrated by the histogram shown in FIG. 5A, where the D ₁₀ value was 0.525 micrometer, the D ₅₀ value was 1.7 micrometers and the D ₉₀ value was 4.1 micrometers. The dispersion volume of 3.8 liters (1 gallon) was processed by mixing with high shear for 45 minutes in the Premier Mill supermarket mill model AshEm-1.5 (NM-1.5) with recirculation at a flow rate of 30 gallons (114 liters) per minute; the mill was filled with grinding media doped with yttrium containing particles with a diameter of 0.65 mm. The particle size of the agglomerates decreased with the transition to the particle distribution illustrated in the histogram shown in FIG. 5B, where the D ₁₀ value was 0.13 micrometers, the D ₅₀ value was 0.19 micrometers and the D ₉₀ value was 0.36 micrometers. The ceramic structure of the dielectric made of such dispersions had a grain size in the range of 0.2-0.3 microns.

Example 6

This example also illustrates the preparation of another specific embodiment of barium titanate-based metal oxide coated particles in accordance with the invention. The wet cake, prepared essentially the same as in Example 3, was dried for 24 hours in a vacuum oven at 200 ° C under vacuum - 100 kilopascals to obtain a dispersible powder, which is a barium titanane-based powder coated with a metal oxide. The powder was dispersed by mixing with an aqueous solution containing 72 wt.% Solid particles and 0.75 wt.% Dispersing substance based on ammoniated polyacrylic acid. The dispersion had a particle size distribution with a D _{90 of} 1.9 μm. The size of the agglomerated particles in the dispersion was reduced by mixing with high shear for 1 minute in a Silverson model L4R laboratory mixer providing high shear to obtain a colloidal dispersion with D _{90 of} 0.6 μm.

Example 7

This example is a comparative illustration of the impossibility of deagglomeration of a known metal oxide-coated barium titanate powder by high shear mixing. Barium titanate-coated metal oxide supplied by Degussa Corporation in the form of an AD302L dielectric powder (defined as having a particle size distribution such that 90% of the particles is less than 1.2 μm) for X7R MSC was dispersed in an aqueous solution containing the dispersant is essentially the same as in Example 6. The dispersed particles had a D ₉₀ value of 1.8 micrometers and a D ₅₀ value of 1.1 micrometers. After mixing with high shear in a laboratory providing high shear mix le models for 1 minute "Silverson" firm L4R values D ₉₀ and D ₅₀ were unchanged. After grinding with high energy during 2 hours in a vibratory mill D ₅₀ value decreased to 1.2 microns and the D ₅₀ value is reduced to 0, 7 microns.

Example 8

This example illustrates MSCCs made from barium titanate particles according to this invention. The dispersion of barium titanate particles coated with metal oxide obtained essentially in the same manner as in Example 3 was mixed with a polymeric binder and thin films with several different thicknesses were formed from it and these films were dried to obtain green ribbons. Green tapes were coated with an electrically conductive ink paste to form a suitable pattern, cut into layers and stacked, cut and fired at 1125 ° C with the formation of MSCCs having 40 ceramic dielectric layers with a thickness of about 3.5, 4.2 and 7.2 microns . The properties of the forty-layer MSCCs are given in the table below, where TCE is the temperature coefficient of the capacitance.

Given the fact that the above examples serve to illustrate a limited number of specific embodiments, the entire scope of the claims of the invention is defined by the following claims.

Claims (62)

1. Particles based on barium titanate having a coating containing metal oxide, metal oxide hydrate, metal hydroxide or a salt of an organic metal acid other than barium or titanium, wherein at least 90% of said coated particles have a particle size of less than 0.9 μm . 2. Particles based on barium titanate according to claim 1, having an initial particle size of less than 0.6 microns. 3. Particles based on barium titanate according to claim 1, having an initial particle size of less than 0.5 microns. 4. Particles based on barium titanate according to claim 1, having an initial particle size of less than 0.4 microns. 5. Particles based on barium titanate according to claim 1, having an initial particle size of less than 0.3 microns. 6. Particles based on barium titanate according to claim 1, having an initial particle size of less than 0.2 microns. 7. Particles based on barium titanate according to claim 1, wherein said coated particles have a decile ratio D ₉₀ / D _{10 of} a particle size distribution of less than 4. 8. Particles based on barium titanate according to claim 1, wherein said coated particles have a decile ratio D ₉₀ / D _{10 of} a particle size distribution of less than 3. 9. Particles based on barium titanate according to claim 1, wherein said coated particles have a decile ratio D ₉₀ / D _{10 of} a particle size distribution of less than 2.5. 10. Particles based on barium titanate according to claim 1, wherein at least 90% of said coated particles have a particle size of less than 0.8 microns when said particles are dispersed by mixing with high shear. 11. Particles based on barium titanate according to claim 1, wherein at least 90% of said coated particles have a particle size of less than 0.7 μm when said particles are dispersed by mixing with high shear. 12. Particles based on barium titanate according to claim 1, wherein at least 90% of said coated particles have a particle size of less than 0.6 microns when said particles are dispersed by mixing with high shear. 13. Particles based on barium titanate according to claim 1, wherein at least 90% of said coated particles have a particle size of less than 0.5 microns when said particles are dispersed by mixing with high shear. 14. Particles based on barium titanate according to claim 1, wherein at least 90% of said coated particles have a particle size of less than 0.4 μm when said particles are dispersed by mixing with high shear. 15. Particles based on barium titanate according to claim 1, wherein at least 90% of said coated particles have a particle size of less than 0.3 μm when said particles are dispersed by mixing with high shear. 16. Particles based on barium titanate according to claim 1, moreover, essentially all of these particles are equiaxed or spherical. 17. A suspension, dispersion or slip containing (containing) at least 50 wt.% Coated particles in accordance with claim 1. 18. The slip according to 17, additionally containing 3-20 wt.% The composition of the binder containing dissolved or suspended film-forming polymer. 19. A wet cake containing coated particles in accordance with claim 1 and 15-35 wt.% Aqueous liquid. 20. The wet cake according to claim 19, further comprising a moisture-proof shell that provides such a shelf life that after 30 days it is possible to disperse said wet cake using a dispersing substance mixed by a high shear mixture into an aqueous dispersion of coated particles, 90 % of which have a particle size of less than 1 μm. 21. Particles based on barium titanate having an initial particle size of less than 0.6 μm and a coating containing an oxide, oxide hydrate, hydroxide of at least one metal selected from the group consisting of lithium, magnesium, calcium, strontium, scandium, zirconium , hafnium, vanadium, niobium, tantalum, manganese, cobalt, nickel, zinc, boron, silicon, antimony, tin, yttrium, lanthanum, lead, bismuth and an element of the lanthanide group, with at least 90% of the coated particles having a particle size of less than 0 , 9 microns. 22. Particles based on barium titanate according to item 21, having an initial particle size of less than 0.5 microns. 23. Particles based on barium titanate according to item 21, having an initial particle size of less than 0.4 microns. 24. Particles based on barium titanate according to item 21, having an initial particle size of less than 0.3 microns. 25. Particles based on barium titanate according to item 21, having an initial particle size of less than 0.2 microns. 26. Particles based on barium titanate according to item 21, wherein said coated particles have a decile ratio D ₉₀ / D _{10 of} a particle size distribution of less than 4. 27. Particles based on barium titanate according to item 21, wherein said coated particles have a decile ratio D ₉₀ / D _{10 of} a particle size distribution of less than 3. 28. Particles based on barium titanate according to item 21, wherein said coated particles have a decile ratio D ₉₀ / D _{10 of} a particle size distribution of less than 2.5. 29. Particles based on barium titanate according to item 21, and at least 90% of these coated particles have a particle size of less than 0.8 microns, when these particles are dispersed by mixing with high shear. 30. Particles based on barium titanate according to item 21, and at least 90% of these coated particles have a particle size of less than 0.7 microns, when these particles are dispersed by mixing with high shear. 31. Particles based on barium titanate according to item 21, and at least 90% of these coated particles have a particle size of less than 0.6 microns, when these particles are dispersed by mixing with high shear. 32. Particles based on barium titanate according to item 21, and at least 90% of these coated particles have a particle size of less than 0.5 microns, when these particles are dispersed by mixing with high shear. 33. Particles based on barium titanate according to item 21, and at least 90% of these coated particles have a particle size of less than 0.4 microns, when these particles are dispersed by mixing with high shear. 34. Particles based on barium titanate according to item 21, and at least 90% of these coated particles have a particle size of less than 0.3 microns, when these particles are dispersed by mixing with high shear. 35. Particles based on barium titanate according to item 21, and, essentially, all of these particles are equiaxed or spherical. 36. A suspension, dispersion or slip containing (containing) at least 50 wt.% Of the specified coated particles in accordance with paragraph 21. 37. The slip according to clause 36, further containing 3-20 wt.% The composition of the binder containing a dissolved or suspended film-forming polymer. 38. A wet cake containing coated particles in accordance with paragraph 21 and 15-35 wt.% Aqueous liquid. 39. The wet cake according to claim 38, further comprising a moisture-proof shell that provides such a shelf life that after 30 days it remains possible to disperse the said wet cake when a dispersant is added by mixing with high shear into an aqueous dispersion of coated particles, 90 % of which have a particle size of less than 1 μm. 40. Non-milled barium titanate-based particles having a coating containing metal oxide, metal oxide hydrate, metal hydroxide or a salt of an organic metal acid other than barium or titanium, wherein at least 90% of said coated non-milled particles have a particle size of less than 0 , 9 μm, when said coated non-ground barium titanate-based particles are dispersed by mixing with high shear. 41. Non-milled particles based on barium titanate according to claim 40, having an initial particle size of less than 0.6 microns. 42. Non-milled particles based on barium titanate according to claim 40, having an initial particle size of less than 0.5 microns. 43. Non-milled particles based on barium titanate according to claim 40, having an initial particle size of less than 0.4 microns. 44. Non-milled particles based on barium titanate according to claim 40, having an initial particle size of less than 0.3 microns. 45. Non-milled particles based on barium titanate according to claim 40, having an initial particle size of less than 0.2 microns. 46. Non-milled particles based on barium titanate according to claim 40, wherein said coated non-milled particles have a decile ratio D ₉₀ / D _{10 of} a particle size distribution of less than 4. 47. Non-milled particles based on barium titanate according to claim 40, wherein said coated non-milled particles have a decile ratio D ₉₀ / D _{10 of} a particle size distribution of less than 3. 48. Non-milled particles based on barium titanate according to claim 40, wherein said coated non-milled particles have a decile ratio D ₉₀ / D _{10 of} a particle size distribution of less than 2.5. 49. Non-milled particles based on barium titanate according to claim 40, wherein at least 90% of said coated non-milled particles have a particle size of less than 0.8 μm when said particles are dispersed by mixing with high shear. 50. Non-milled particles based on barium titanate according to claim 40, wherein at least 90% of said coated non-milled particles have a particle size of less than 0.7 μm when said particles are dispersed by mixing with high shear. 51. Non-milled particles based on barium titanate according to claim 40, wherein at least 90% of said coated non-milled particles have a particle size of less than 0.6 μm when said particles are dispersed by mixing with high shear. 52. Non-milled particles based on barium titanate according to claim 40, wherein at least 90% of said coated non-milled particles have a particle size of less than 0.5 μm when said particles are dispersed by mixing with high shear. 53. Non-milled particles based on barium titanate according to claim 40, wherein at least 90% of said coated non-milled particles have a particle size of less than 0.4 μm when said particles are dispersed by mixing with high shear. 54. Non-milled particles based on barium titanate according to claim 40, wherein at least 90% of said coated non-milled particles have a particle size of less than 0.3 μm when said particles are dispersed by mixing with high shear. 55. Non-milled particles based on barium titanate according to claim 40, wherein substantially all of said non-milled particles are equiaxed or spherical. 56. A suspension, dispersion or slip containing (containing) at least 50 wt.% Of the specified coated non-ground particles in accordance with paragraph 40. 57. The slip according to claim 56, further comprising 3-20 wt.% A binder composition containing a dissolved or suspended film-forming polymer. 58. A wet cake containing coated non-ground particles based on barium titanate in accordance with paragraph 40 and 15-35 wt.% Aqueous liquid. 59. The wet cake of claim 58, further comprising a moisture-proof shell that provides such a shelf life that after 30 days it is possible to disperse said wet cake by adding a dispersant carried out by mixing with high shear into an aqueous dispersion of coated particles, 90 % of which have a particle size of less than 1 μm. 60. The dispersion of particles based on barium titanate having a coating containing a metal oxide, a metal oxide hydrate, a metal hydroxide or a salt of an organic metal acid other than barium or titanium, the dispersion comprising more than 30 wt.% Of these coated particles, and at least 90% of said dispersed coated particles have a particle size of less than 0.9 microns. 61. The dispersion of particles based on barium titanate having an initial particle size of less than 0.6 μm and a coating containing an oxide, oxide hydrate, hydroxide or salt of an organic acid of at least one metal selected from the group consisting of lithium, magnesium, calcium, strontium, scandium, zirconium, hafnium, vanadium, niobium, tantalum, manganese, cobalt, nickel, zinc, boron, silicon, antimony, tin, yttrium, lanthanum, lead, bismuth and elements of the lanthanide group, and the dispersion includes more than 30 wt .% of the specified coated particles and at least 90% of said dispersed coated particles have a particle size less than 0.9 microns. 62. A dispersion of non-ground barium titanate-based particles having a coating comprising metal oxide, metal oxide hydrate, metal hydroxide or a salt of an organic metal acid other than barium or titanium, the dispersion comprising more than 30 wt.% Of said coated particles, and at least 90% of said dispersed coated non-ground particles have a particle size of less than 0.9 microns when said non-ground coated barium titanate-based particles are dispersed by high shear mixing.

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