DD291741A5 - METHOD FOR THE PRODUCTION OF TITANATES AND STANNATES - Google Patents

Abstract

For electrical and electronic applications, such as piezoelectric ceramics, dielectric ceramics, ceramic resistors or semiconductor ceramics, the use of high-quality titanates and stannates of Ba, Sr, Ca, Mg, Al, Zn, Ni and Cu in pure form or in the form of complex compounds necessary. The solution of these claims is achieved by producing the titanates or stannates via the stage of complex precipitates, aqueous solutions containing earth-alkali metal ions containing the 2-ethoxyethoxides of Ti (IV) and / or Sn (IV) and other metal-2 -Ethoxyethoxide of Mg, Al, Zn, Ni (II) and Cu (II) are reacted. Due to the complete miscibility of said 2-ethoxyethoxides in suitable solvents and the almost simultaneous hydrolysis in the reaction with aqueous Ba, Sr and Ca-containing solutions at a certain p H-value successful Ausfaellung succeeds and Mischfaellung several, im Extreme case of all interesting metal ions. By subsequent thermal decomposition of the dried precipitates at relatively low temperatures, the desired titanate or stannate compositions are obtained in highly pure and highly dispersed form with high reproducibility of the crucial quality parameters. {Titanates and stannates of Ba, Sr, Ca, Mg, Al, Zn, Ni , Cu; complex rainfall; 2-ethoxyethoxides of * * Mg, Al, Zn, * * hydrolysis; Mischfaellung; piezoelectric ceramics; dielectric ceramics; ceramic resistors; Semiconductor ceramics}

Description

Field of application of the invention

The invention relates to a process for the preparation of titanates and stannates simple and complex composition on a wet-chemical way, which is suitable for electroceramic applications, eg. As piezoelectric ceramics, dielectric ceramics, ceramic resistors and semiconductor ceramics are suitable.

As used herein, the term "complex titanates and stannates" includes barium, strontium, calcium, magnesium, aluminum, zinc, nickel and copper titanate or stannate in the respective pure form and mixtures containing at least two of the named titanates or stannates may contain auc.i from all listed titanates or stannates or mixed titanates / stannates.

Characteristic of the known state of the art

Titanates and stannates ri js Ba, Sr, Ca, Mg, Al, Zn, Ni, and Cu have heretofore been prepared almost exclusively by solid state chemical reaction. Titanium dioxide, tin dioxide and the corresponding metal carbonates or oxides are preferably used as starting materials. A disadvantage proves that very high synthesis temperatures are necessary and that the reaction products often have insufficient purity, relatively large grain diameter (usually greater than 1 pm) and inhomogeneous particle size distributions.

Titanates or stannates can also be obtained by reaction in the liquid medium. In this case, products are precipitated, which can be converted by subsequent thermal treatment in the titanates or stannates. The precipitates already contain the desired atomic ratios MetalliTitan or metal: tin which are to be achieved in the titanate or stannate. Due to the relatively low temperatures of about 600 to 900 ° C, which are necessary for conversion into the titanates or stannates, no strong grain growth occurs, d. h "very small particle sizes are achieved. The powders also consist of particles with a relatively narrow particle size distribution and contain only small amounts of impurities. A disadvantage of the known wet-chemical synthesis methods is that the representation of complex titanate or Stannatzusammensetzungen usually limited possible Ux. Known is the representation of complex titanates of Ba. Sr, Ca, Mg, La, Fe, and Mn via the precipitation of titanyloxalates. In contrast, only special, simple compositions can be precipitated quantitatively in conventional alkoxide-hydroxide processes. Starting from the known metal alkoxides, in which a common solubility in one and the same solvent is partially excluded, no homogeneous distributions of the components in the starting solution and hence also in the later-forming solid can be guaranteed in connection with the inorganic metal hydroxides used in addition , It is therefore desirable to process all of the above-mentioned metals as complex precipitates and then transform them under relatively mild thermal conditions into highly pure and finely divided titanate or stannate powders, which also have a narrow particle size distribution.

Object of the invention

The invention aims to provide a process for the preparation of highly dispersed, high purity single or mixed titanates or stannates which can be used for improved titanate or stannate based ceramics, such as piezoelectric ceramics, dielectric ceramics, ceramic resistors and semiconductor ceramics ,

Explanation of the essence of the invention

The object of the invention is to produce titanates, stannates or titanates of the Ba, Sr, Cp, Mg, Al, Zn, Ni and Cu individually or as complex compounds via a precipitation reaction and subsequent thermal decomposition of the precipitation products.

According to the invention the object is achieved in that aqueous erdalkalimetallionenenthaltende solutions with the 2-ethoxyethoxides of Ti (IV) and / or Sn (JV) and other metal 2-ethoxyethoxides to form highly dispersed complex precipitates reacted and the precipitated products then by E Heat to temperatures above 600 ° C into the corresponding metal titanates, stannates or titanate astonates. The alkaline earth metal ions used may be those of Ba, Sr, Ca and of metal 2-ethoxyethoxides of Mg, Al, Zn, Ni (II) and Cu (I). In contrast to previously known technical solutions, the precipitated precursors of the titanates or stannates of all the metals mentioned and their mixtures are synthesized by a uniform method and used in the following for the titanate or stannate representation. The ability to precipitate the components in the desired composition at the same time results from the complete miscibility of the 2-ethoxyethoxides of Ti (IV), Sn (IV), Mg, Al, Zn, Ni (II) and Cu (I) in suitable Solvents and from the nearly simultaneous hydrolysis in the reaction with aqueous solutions of Ba, Sr and Cahaltigen at a pH of 8. The precipitation conditions are so low that the metals mentioned are all eliminated quantitatively. The thus to be obtained highly dispersed precipitates are subsequently converted by thermal decomposition above 600 ⁰ C to give the corresponding titanates, stannates and mixed titanate / stannates. Due to their physical and chemical properties, the fumed and highly pure powders of the desired stoichiometry obtained in this way can be used for piezoelectric ceramics, dielectric ceramics, ceramic resistors and semiconductor ceramics with highest quality requirements and permit the replacement of other titanates or stannates hitherto used for this purpose ,

In the context of the process according to the invention, first of all an aqueous hydroxide solution of Ba and / or Sr, Ca is prepared which is neutralized by aciduria up to pH 8. A solution is added to this solution at 90.degree Mixture of the 2-ethoxyethoxides of the metals detected according to the invention (Ti [IV], Sn (IV), Mg, Al, Zn, Ni (II), Cu [I)] in ethyl glycol was dripped in. The preparation of the corresponding J ethoxyethoxides was already described WP DDR 3147340, 3221858 or 3221866 described.

The starting concentrations of the solutions used are usually 0.05-1.0 mol / l in the hydroxides Ba, Sr and Ca. the 2-ethoxyethoxides are mixed in the required ratio and combined with about twice the volume of dried ethyl glycol. The volume ratio aqueous solution 2-ethoxyethoxides / ethyl glycol is in the size of 1:10 to 1:20.

When the 2-ethoxyethoxide / ethyl glycol mixture is dropped into the aqueous phase, the corresponding complex precipitates precipitate virtually quantitatively in highly disperse form. For the exact reproducibility of a precipitation, the exact observance of the stoichiometric ratio of the components as well as of the temperature and of the pH value is unavoidable. The pH drops slightly in the course of the reaction and is kept constantly at 8 by the dropwise addition of sodium hydroxide solution. After completion of the dropwise addition of the 2-ethoxyethoxide / ethyl glycol mixture, the suspension is stirred for a further 0.5 h at 90.degree.

The precipitate is washed with a mixture of one part of ethanol and one part of water and then dried and pulverized. A thermal treatment is carried out at temperatures of 600X and above, the decomposition to the titanates, stannates or mixed titanate / stannates takes place. It is expedient to work at relatively low decomposition temperatures in order to obtain relatively large specific surface areas and small particle sizes. This realizes a high sintering activity of the powders. The yield is in all cases 95 to 100%.

example 1

To prepare a disperse BaTiO ₃ sintering powder, 15.33 g (0.1 mol) of BaO are dissolved in 750 ml of distilled water in a reaction vessel with stirrer, reflux condenser, pH measuring point and dropping funnel. Subsequently, 50% acetic acid is added until a pH of 8 is reached. The solution is heated to 90 ⁰ C. Now, a mixture consisting of 40.39g (0.1 mol) of titanium (IV) -2-ethoxyethoxide and 75ml of dried ethyl glycol is added dropwise with stirring. Deviations from pH 8 are constantly compensated by the addition of 30% sodium hydroxide solution. The reaction leads to a precipitation, wherein Ba and Ti are quantitatively contained in the precipitate. The suspension is kept for 0.5 h at 9O ⁰ C and stirred after completion of the addition.

The precipitate is washed ethanol and one part water with a mixture of a portion to be then dried at 100 ⁰ C. After pulverization, the substance is calcined at 900 ⁰ C for 1 h. The yield of BaTiO ₃ is approximately 100%. The electron microscopically determined particle sizes of the BaTiO ₃ powder produced in this way are between 0.05 and 0.15 μm. The BET surface area is 14.5m ² / g.

Example 2

For the preparation of a disperse sintered powder of composition Ba ₀ 7Sr ₀₁ JCa ₀ ^ TiO ₃ , 10.73 g (0.07 mol) of BaO, 2.07 g (0.02 mol.) Are used in a reaction vessel equipped with stirrer, reflux condenser, pH measuring point and dropping funnel ) SrO and 0.56 g (0.01 mol) of CaO dissolved in 750 ml of distilled water. Subsequently, 50% acetic acid is added until a pH of 8 is reached. The solution is heated to 90 ° C. Now, a mixture consisting of 47.47 g (0.1 mol) of tin (IV) -2-ethoxyethoxide and 75 ml of dried ethyl glycol is added dropwise with stirring. Deviations from pH 8 are constantly compensated by the addition of 30% sodium hydroxide solution. The reaction leads to a precipitation, wherein Ba, Sr, Ca and Ti are quantitatively contained in the precipitate. The suspension is kept for 0.5 h at 90 ° C and stirred after completion of the addition. The further work-up of the precipitate is carried out analogously to Example 1. The yield after decomposition is approximately 100%.

The particle sizes of the product calcined at 900 ° C. after 1 h are between 0.5 and 0.15 μm. The BET surface area is

16, OmVg.

Example 3

For the preparation of a disperse sintered powder of composition Bao, 4Mgo, iZno, iAlo, 2Tio, 6Sn ₀ , ₆ 0 ₃ are in a reaction vessel with stirrer, reflux condenser, pH measuring point and dropping funnel 6.37 g (0.04 mol) of BaO in 750 ml distilled Water dissolved. Subsequently, 50% acetic acid is added until a pH of 8 is reached. The solution is heated to 9O ⁰ C. Now, a mixture consisting of 20.20 g (0.05 mol) of titanium (IV) -2-ethoxyethoxide, 23.73 g (0.05 mol) tin (IV) -2-

Ethoxy ethoxide, 2.02 g (0.01 mol) of magnesium 2-ethoxyethoxide, 2.43 g (0.01 mol) of zinc 2-ethoxyethoxide, 2.37 g (0.01 mol) of nickel (II) x 2-ethoxyethoxide and 2.94 g (0.02 mol) of aluminum 2-ethoxyethoxide and 75 ml of dried ethyl glycol were added dropwise with stirring.

Deviations from pH 8 are constantly compensated by the addition of 30% sodium hydroxide solution. The reaction leads to a precipitation, wherein Ba, Mg, Zn, Ni, Al, Ti and Sn are contained quantitatively in the precipitate. The suspension is kept for 0.5 h after the addition at 90 ° C and stirred.

The further work-up of the precipitate is carried out analogously to Example 1. The yield after decomposition for 1 h at 900 ⁰ C is approximately 100%.

The particle sizes of the powder thus obtained are 0.05 to 0.15 μm. The BET surface area is 15, OmVg.

Claims (3)

1. A process for the preparation of titanates and stannates simple and complex composition wet-chemical way, characterized in that aqueous earth alkali metal ions containing solutions with the 2-E'choxyethoxiden of Ti (IV) and / or Sn (IV) and other metal-2 Ethoxyethoxide reacted to form highly dispersed complex precipitates and the precipitated products are then converted by heating to temperatures above 600 ⁰ C in the corresponding metal titanates, stannates or titanate / stannates. 2. The method according to claim 1, characterized in that as the alkaline earth metal ions of the Ba, Sr and Ca and as metal 2-ethoxyethoxides of the Mg, Al, Zn, Ni (II) and Cu (I) are used. 3. The method according to claim 1 and 2, characterized in that any ratios of titanium (IV) - and tin (IV) -2-ethoxyethoxide and the 2-ethoxyethoxides of Mg, Al, Zn, Ni (II) and Cu (I. ) as well as the alkaline earth metal ions can be realized.