PT99450A - METHOD FOR PREPARING POSTS OF METAL METAL OXIDES PRESENTING DIELECTRIC PROPERTIES AND PROCESS FOR THE PRODUCTION OF DIELECTRICS OBTAINED FROM PARTS REFERRED TO - Google Patents

Description

Description of the patent application of SOLVAY (Société Anonyme), Belgian, industrial and commercial, headquartered at 33, rue du Prince Albert, B-1050 Bruxelles, Belgium, for: " PROCESS FOR THE PREPARATION OF OXIDES POS METALLICS PRESENTING DIELECTRIC PROPERTIES AND PROCESS FOR THE PRODUCTION OF DIELECTRICS OBTAINED FROM THESE POS " The invention relates to powders of mixed metal oxides having dielectric as well as dielectric properties produced from said powders, and to the respective production processes, barium titanate is known to be a compound having ferroelectric properties. This compound, however, is rarely suitable for the manufacture of dielectrics because of the very high value of its Curie point. This is in fact about 120 ° C, and the dielectric constant of barium titanate decreases very rapidly on both sides of the Curie point.

In order to produce dielectrics having a high dielectric constant in the vicinity of the ambient temperature, it was sought to associate with the barium titanate other compounds having the effect, on the one hand, to shift the Curie temperature of the barium titanate to lower temperatures and, on the other hand 1 side, reduce the slope of the dielectric constant curve as a function of temperature, on both sides of the Curie point. Thus, US-A-3410705 (TDK Electronics Co., Ltd.) discloses dielectric compositions obtained by sintering a mixture of barium titanate, lead titanate and bismuth stannate. These known dielectric compositions, however, have a relatively weak dielectric constant, which does not exceed 2500 to 25 ° C. On the other hand, they present the drawbacks of containing lead, which runs the risk of being used in the course of sintering. US-A-4335216 discloses dielectric compositions obtained by sintering a mixture of barium titanate, strontium titanate, barium zirconate, titanium dioxide, manganese dioxide and a flux consisting of zinc, silicon dioxide, boron oxide, lead oxide, bismuth trioxide and cadmium oxide. The dielectric constant of these compositions at room temperature is relatively high, in the range of 4800 to 5800. These known compositions have, in turn, several drawbacks: the presence of lead which is in danger of volatilizing during sintering, of the constituents of the blend, the need to obtain the blend in the state of a coarse-grained powder, which impairs the mechanical strength of the dielectric obtained by siixation. The invention aims to provide powders of mixed metal oxides for the manufacture of dielectric materials, which avoid the drawbacks mentioned above of the known ceramic compositions. The invention therefore relates to powders of mixed metal oxides having dielectric properties of the general molar formula.

BaaCabM9cZrdsieT10x 2

in which a, b, c, d, e and x denote integers or fractions such that one has: 0.05 < b &lt; 0.12 0.00 &lt; c &lt; 0.015 0.10 &lt; d &lt; 0.23 0.000 < and &lt; 0.010 0.95 &lt; a + b + c &lt; 1.05 d + e + 1 x = a + b + c + 2d + 2e + 2

In powders according to the invention the mixed metal oxides are by definition solid solutions, i.e., homogeneous mixtures at the molecular or ionic level.

The powders according to the invention are intended for the production of ceramic materials by a sintering operation. They are specially adapted to the manufacture of ceramic materials having dielectric properties.

In powders according to the invention calcium has the effect of reducing the slope of the dielectric constant curve as a function of temperature on both sides of the Curie point. Magnesium and zirconium have the function of displacing the Curie point of the composition for temperatures around room temperature; the zirconium also has the effect of increasing the value of the dielectric constant at the Curie point, whereas the magnesium decreases the dielectric losses. Tue:

In powders according to the invention it is preferable c &lt; 0.010.

In a particular embodiment of the powders according to the invention the composition thereof is such that,

formula described above: · 0.005 < c &lt; 0.010 0.12 &lt; d &lt; 0.16 0.99 &lt; a + b + c &lt; 1.01 d + e + 1

In an interesting variant the silicon content is such that it has 0.005 < and &lt; 0.010

In a further variant, which is preferred, the composition of the powders is such that a + b + c = 1 d + e + 1

In a particular embodiment of the powders according to the invention, they are characterized by obtaining, after sintering at 1325Â ° C for 2 h, a ceramic having the dielectric properties defined below: KT &quot; K25 -0.82 &lt; _ &lt; 0.22 K25 for T-values comprised between -30 ° C and + 125 ° C, where 7 denotes the temperature expressed in degrees centigrade, K25 designates the dielectric constant at 25 ° C and Ky designates the dielectric constant at temperature T. s

The powders according to the invention thus allow the production of dielectric ceramics in accordance with the standards Z5U, Z5V, Y5U, Y5V, Y6V and Y7V, which are defined by the following relationships (American National Standard ANSI / EIA-198-C-1983 , EIA 4 wr

Standard, Ceramic dielectric capacitors classes I, II9 and IV, Engineering Department Electronic Industries Association, page 12): KT &quot; K25 to &lt; _ &lt; b K25 for the values of T comprised between and T2, where: T represents the temperature expressed in degrees centigrade, K25 represents the dielectric constant at 25 ° C,

Ky represents the dielectric constant at temperature T, a, b, T, | and T2 are defined in Table 1 below.

Standard ab T1 (eC) T2 (SC) Z5U - 0.56 + 0.22 + 10 + 85 Z5V - 0.82 + 0.22 + 10 + 85 Y5U - 0.56 + 0.22 - 30 + 85 Y5V - 0.82 + 0.22 - 30 + 85 Y6V - 0.82 + 0.22 - 30 + 105 Y7V - 0.82 + 0.22 - 30 + 125

Accordingly, powders according to an advantageous embodiment of the invention are those which are characterized by obtaining, after sintering at 1325 ° C for 2 hours, a ceramic in accordance with at least one of the standards set out in the above table.

In a preferred variant of this embodiment of the powders according to the invention they are characterized by the parameter 25-25, preferably 8000, K25 &lt; 11,000.

The powders according to the invention are generally in the form of fine particles of irregular or regular shape, for example spherical. The average particle diameter is preferably less than 5 microns, for example between 0.05 and 2 microns.

The powders according to the invention may be obtained by means of a process in which the barium hydroxide, a titanium alcoholate, a zirconium alcoholate, optionally a silicon alcoholate and water are mixed in a common organic solvent containing a calcium salt and a magnesium salt derived from carboxylic acids containing less than 10 carbon atoms.

In this process the metal alcoholate refers to any compound in which a metal is attached via an oxygen atom to a hydrocarbon group, such as an aromatic group or a linear or cyclic, saturated or unsaturated, unsubstituted or substituted aliphatic group wholly or partially . Metal alcoholates with aliphatic groups are particularly recommended; those having saturated or substituted aliphatic groups are preferred, such as, for example, the methyl, ethyl, n-propyl, isopropyl, n-butyl and isobutyl groups.

On contact with water the metal alcoholates (titanium, zirconium and, as appropriate, silicon) undergo hydrolysis. The hydrolysis must be regulated in a manner known per se to precipitate mixed oxides of barium, calcium, magnesium 6

sodium, zirconium, silicon and titanium in the form of a powder without bulk gelation of the reaction medium resulting from the hydrolysis. For this purpose it is recommended that the mixture of titanium, zirconium and silicon alcohols, barium hydroxide, water and calcium and magnesium salts in the common organic solvent is homogenised as soon as possible before nucleation. Various operating modes are available for mixing. According to a first operating method barium hydroxide, the titanium, zirconium and silicon alcohols, the organic calcium and magnesium salts and the water are dissolved separately in organic solvents, and the organic solutions thus obtained are introduced simultaneously but in separated in a reaction chamber. According to a second operating method two different premixes are carried out first, one of which contains the barium hydroxide and the water, while the other contains the alcoholates and the organic salts, then the pre- mixtures in the reaction chamber. In these operative methods of the process according to the invention it is advisable to avoid the presence of solid particles in the organic solutions prior to mixing. The same or different organic solvents may be used for barium hydroxide, alcoholates, organic salts and water, but the organic solvent in which the alcoholates are dissolved must be free of water. In the case of different organic solvents it is necessary that they are miscible to form the common organic solvent together. The alcohols and their derivatives are quite convenient, namely methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol. Optimal dilution rates :; barium hydroxide, alcoholates, organic salts and water in their respective solvents depend on a number of factors, in particular the alcohol from which the alcoholates are derived: the carboxylic acid from which the organic calcium and magnesium salts are derived, the temperature of quality of the powder; should be determined in each particular case by routine laboratory work. For example, alcoholic solutions may be advantageously used whose respective contents in barium hydroxide in alcoholates in organic salts prior to mixing do not exceed 5 moles per liter and are preferably between 0, 02 and 0.5 moles per liter. The mixture may be carried out in the ambient air. However, in order to avoid carbonation of the barium hydroxide it is advisable to use a CO2-free atmosphere. On the other hand, to avoid the risk of uncontrolled decomposition of alcoholates, it is preferred to work in an atmosphere free of moisture. Dry, dehydrated and decarbonated air, nitrogen and argon are examples of atmospheres usable for carrying out the process. To ensure mixing it is possible to work advantageously in the manner set forth in GB-A-2168334.

In the process just described it is advantageous to use a hydrated barium hydroxide the hydration water of which then constitutes at least a part (but preferably all) of the water necessary for the hydrolysis of the alcoholates. It is convenient on the other hand to dissolve in the common organic solvent an organic organic compound containing more than 6 carbon atoms in its molecule, which is by definition an organic acid or an organic acid derivative. In the case of a derivative of an organic acid this derivative may have an acid character or be devoid of acid character, for example a neutral substance. Saturated or unsaturated carboxylic acids and their derivatives are particularly recommended. It is convenient to choose acids or acid derivatives containing more than 6 carbon atoms in the molecule. Particularly advantageous carboxylic acids are those which contain at least 8 carbon atoms in their molecule, such as octanoic, lauric, palmitic, isopalmytic, oleic and stearic acids. Carboxylic acids comprising more than 10 carbon atoms in their molecule are preferred. Examples of acid derivatives 8

organic compounds useful in the process of the invention include the anhydrides, esters and salts thereof. It will be appreciated that the organic acid compound acts on the morphology of the powder inhibiting in this the agglomeration of the grains and giving them a spherical prefilter. The organic acid compound is preferably used in an amount of 20 to 200 g per mole of the compound.

BaaCabM3cZrdsleTi0x ·

After the hydrolysis reaction which follows the mixture, a fine particulate powder consisting of a complex combination of more or less hydrated amorphous metal oxides and organic residues is collected. The powder is essentially formed by generally spherical particles having a diameter not exceeding 5 microns, and usually comprised between 0.05 and 2 microns. The powder may optionally undergo drying followed by a heat treatment at a suitable temperature to eliminate excess water, the organic solvent and, as the case may be, the organic acid compound. The heat treatment may be regulated to control the porosity or to eliminate it completely. It may on the other hand be regulated to cause crystallization of the metal oxides. The powders according to the invention find an application in the manufacture of dielectrics usable in electrical apparatus. They are particularly suitable for the manufacture of dielectrics in accordance with the standards Z5U, Z5V, Y5U, Y5V, Y6V and Y7V as defined above, by means of a metallurgical sintering operation at a temperature not exceeding 1500Â ° C, generally ranging from 1250 and 14002C. The invention also relates, therefore, to the 9

dielectrics obtained by sintering powders according to the invention.

The following examples serve to illustrate the invention. These examples are given with reference to figures 1 to 8 attached.

Figures 1 to 4 are photographic reproductions of powders of mixed metal oxides according to the invention, observed under the electron transmission microscope at a magnification of 20,000 x.

Figures 5 to 8 are diagrams which provide, as a function of temperature, the dielectric constant of dielectric ceramics produced by sintering of the powders shown in Figures 1 to 5. 1 to 4.

In the embodiment of the examples the following description was worked out as follows.

A solution comprising, per liter, 0.08 moles of barium hydroxide monohydrate in an organic solvent formed by mixing in equal volumes of methanol and iso-propanol, - a solution comprising, per liter, 0.08 moles of titanium isopropoxide and 0.05 moles of oleic acid in an organic solvent formed by mixing in equal volumes of methanol and isopropanol, a solution comprising, per liter, 0.08 moles of n- zirconium oxide in isopropanol, - a solution comprising, per liter, 0.02 mol of calcium acetate hydrate in methanol, - a solution comprising, per liter, 0.01 mol of acetate 10

And 4¾ of hydrated magnesium in an organic solvent formed by mixing in equal volumes of methanol and isopropanol, a solution comprising, per liter, 0.02 mole of tetraethyl ortho-silicate in isopropanol.

Solutions of titanium isopropoxide, calcium acetate and, as the case may be, magnesium acetate and tetraethyl orthosilicate were first introduced into a reaction chamber under anhydrous nitrogen atmosphere. The zirconium n-propoxide solution and the hydrated barium hydroxide solution were then separately and simultaneously introduced. The mixture of the solutions was subjected to intense stirring to effect a homogeneous reaction mixture before nucleation began. The reaction medium was then subjected to a two hour maturation at 60Â ° C with moderate agitation. Upon maturation, the reaction medium was subjected to evaporation and a powder of mixed metal oxides was collected. The dried powder was then subjected to a calcination treatment which comprised a treatment under a humid nitrogen atmosphere at 500Â ° C, followed by a treatment in dry air for 2 hours at 860Â ° C. After the calcination treatment the powder was collected and a measurement of its granule-metric distribution was carried out by means of a &quot; MasterSizer &quot; (Mal-Vern Instruments Limited) using a measuring method which is based on the diffusion of a laser beam. The cumulative granulometric distribution curve determines the following characteristics: - the diameter D (0,5), corresponding to 50¾ of the quantity (expressed in volume) of particles; - the diameter D (0,9), corresponding to 90% of the quantity (expressed in volume) of particles; - the diameter D (0,1), corresponding to 10¾ of the quantity (expressed in volume) of particles; 11

- the dispersion of the mean E, defined by the ratio D (0,9) - D (0,1) E = _ D (0,5)

To evaluate its dielectric characteristics the powder was compressed under a pressure of 500 kg / cm2 to form a 10 mm diameter pellet and sintered at a temperature of 1350 ° C for 2 hours. The pellet was inserted between the two faces of a flat condenser, the capacity of the condenser thus obtained was measured by means of an AC current bridge (1600 Hz) and the dielectric constant of the pellet was calculated from the capacitance measured at different temperatures. The values obtained are shown in the diagrams of Figures 5 to 8, in which the abscissa axis reproduces the extreme temperature at - ° C and the ordinate axis reproduces the dielectric constant. In the examples: K-30 designates the dielectric constant at -30 ° C, K10 designates the dielectric constant at 109 ° C, K25 designates the dielectric constant at 25 ° C, K85 designates the dielectric constant at 85 ° C, K105 designates the dielectric constant at 105 ° C, K125 designates the dielectric constant at 125 ° C, 1 / max designates the maximum value of the dielectric constant

Example 1

The solutions of barium hydroxide, titanium isopropoxide, zirconium propoxide and calcium acetate were mixed in regulated proportions to obtain the product of molar formula 12

Fig. 1 shows the powder obtained after the calcination treatment. The following granulometric characteristics were determined: D (0.5) = 0.79 æm D (0.9) = 2.03 æm D (Ås) = 0.34 æm E = 2.2 The diagram of Figure 5 provides the dielectric constant of the dielectric tablet obtained from the powder. The following characteristic values were determined: K25 = 9500 &gt;

Kmax = 10735 (at 39 ° C) K-30 &quot; K25 -0.81 K25 K10 "K25 K25 Lf) 00 &quot; K25 K25 1 / max; "K25 - 0.40 - 0.44 + 0.13 K25

These characteristic values are in accordance with the Z5U, Z5V, and Y5V standards defined above. 13

Example 2

The solutions of barium hydroxide, titanium isopropoxide, zirconium propoxide and calcium acetate were mixed in regular proportions to obtain the product of molar formula

Fig. 2 shows the powder obtained following the calcination treatment. The following grammometric characteristics were determined: D (0.5) = 0.86 D (0.9) = 2.47 μm D (0.1) = 0.37 μm E = 2.4 0 diagram of fig. 6 provides the dielectric constant of the dielectric tablet obtained from the powder. The following characteristic values have been determined in accordance with the previously defined Z5U, Z5V, Y5V and Y6V standards: 14

Jil-i '· * V *' '

I K25 &quot; 11425, 1 / max = 12854 (at 33 1 o PO K25 = -0.81 K25 K10 = -0.47 K25 K85 = - 0.53 K25 K105 - K25 = -0.68 K25 1 / max K25 = 0.13 Κ25

Example 3 s

The solutions of barium hydroxide, titanium isopropoxide, zirconium propoxide, magnesium acetate and calcium acetate were mixed in proportions to give the product of formula

Ba1, 077Ca0.075Mg0.008Zr ') TiOg 4Q Fig. 3 shows the powder obtained after the calcination treatment. The following granulometric characteristics were determined:

D (0.5) = 0.58 yum D (0.9) = 1.49 jum D (0.1) = 0.26 yum E = 2.1 The diagram in Figure 7 provides the dielectric constant of the dielectric tablet obtained from the powder The following characteristic values were determined therein, which are in accordance with the standards Z5U, Z5V, Y5V and Y7V defined above: K25 = 9500, [/ max = 9900 K-30 &quot; K25 K25 K 10 "K25 K25 I LO 00 K25 K25 K125" K25 K25 K max K25 - 0.77 0.32 0.55 -0.78 0.04

K 25

Example 4

The solutions of barium hydroxide, isopropoxide 16

titanium, zirconium propoxide, ethyl orthosilicate, calcium acetate and magnesium acetate were mixed in proportions to give the product of molar formula:

Ba1.06Ca0.14M90.005Zr0.185 TIS0.005 ° 3.565 Fig. 4 shows the powder obtained after the calcination treatment. The following granulometric characteristics were determined: D (0.5) = 0.82 æm D (0.9) = 3.79 æm D (0.1) = 0.30 æm E = diagram of Fig. 8 provides the dielectric constant of the dielectric tablet obtained from the powder. The following characteristic values were determined in accordance with the Z5U, Z5V, Y5V and Y7V standards defined above: 17

'

K25 = 7580,

Kmav = 8524 (at 38 ° C) max "K-30" K25

K25 K10 &quot; K25 K25 K85 &quot; K25 K25 K125 &quot; K25 K25 K max K25 -0.7 0.15 K25 - 0.78 0.40 0.36 18

Claims (1)

A process for the production of a powder of mixed metal oxides in which a metal hydroxide, a metal alcoholate and water are mixed in a common organic solvent in which an organic salt has previously been dissolved, characterized in that to obtain powders of mixed metal oxides having dielectric properties and correspond to the general formula BaaCabMgcZl &quot; dsieTi0x in which a, b, c, d, e and x are integers or fractions such that: b &lt; 0.12 0.000 £ c £ 0.015 0.10 &lt; d &lt; 0.23 0.000 £ e < A process according to claim 1, characterized in that the compound of formula (I): wherein R 1, R 2, R 2, R 2 and R 2 are as defined above. to obtain powders of mixed metal oxides in which 0.005 &lt; c &lt; 0.010 0.12 &lt; d &lt; 0.16 0.005 &lt; and &lt; 0.010 0.99 &lt; a + b + c &lt; 1.01 d + e + 1 - 3 - Process according to claims 1 or 2, characterized in that powders of mixed metal oxides in which a + b + c = 1 d + e + 1 - 4 are obtained. Process according to any of claims 1 to 3, characterized in that the fact that powders of mixed metal oxides are obtained in which the following ratio is observed after sintering at 1325 ° C for 2 hours: KT &quot; K25 -0.82 &lt; _ &lt; 0.22 K25 for T-values comprised between -30 and 85, where T represents the temperature expressed in degrees centigrade, K25 represents the dielectric constant at 25 ° C Kj represents the dielectric constant at the temperature T. according to claim 4, characterized in that powders of mixed metal oxides 20 having the following ratio after sintering at 1325 ° C for 2 hours: KT-K25 at &lt; _ &lt; b K25 for the values of T comprised between T and T, such that parameters a, b, and T2 pertain to at least one of the standards Z5U, Z5V, Y5U, Y5V, Y6V and Y7V defined in the following table l: Standard ab 0.6 + 0.22 + 10 + 85 Z5V - 0.82 + 0.22 + 10 + 85 Y5U - 0.56 + 0.22 - 30 + 85 Y5V - 0 , 82 + 0, 22-30 + 85 Y6V - 0,82 + 0, 22-30 + 105 Y7V - 0,82 + 0, 22-30 + 125 - 6 - A process according to claim 4 or 5 characterized in that powders of mixed metal oxides are obtained in which the parameter K obeys the relation K25 &gt; 5000. Process according to claim 6, characterized in that powders of mixed metal oxides are obtained in which the parameter K obtates the relation 8000 < K25 &lt; 11000. A process according to any one of claims 1 to 7, characterized in that powders of mixed metal oxides which are in the form of particles having an average diameter of between 0.05 and 2 microns are obtained. 9. A process according to any one of claims 1 to 8, characterized in that powders of mixed metal oxides are formed which are composed of spherical particles. 10. A process for the production of dielectrics characterized in that they are obtained by sintering powders of mixed metal oxides obtained by a process according to the preceding claims. They were inventors Henri Wautier, Belgian, doctor in chemical sciences, resident at Rue Louis Catala, 19, B-7090 Braine-le-Comte, Belgium; Franz Legrand, Belgian, industrial engineer, residing at Rue des Vaches, 71, B-7390 Quaregnon, Belgium; and Joel Bourjot, French engineer, ceramist, residing at Avenue des Croix de Guerre, 353, B-1120 Bruxelles, Belgium. The applicant states that the first application of this 23