JPH0329007B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a perovskite compound containing lead, such as lead titanate, lead zirconate, or lead zirconate titanate, which has a perovskite crystal structure. Lead titanate, lead zirconate, or lead zirconate titanate having a perovskite crystal structure are widely used in fields such as dielectric ceramics, resistor ceramics, and semiconductor ceramics. The most common manufacturing method for synthesizing such a lead-containing composite oxide is to mix oxide powders of perovskite-type constituent raw materials and conduct a solid phase reaction at high temperature. However, the products obtained by such solid-phase reactions have the disadvantage of being extremely homogeneous in composition. For this reason, the composite oxide obtained by solid phase reaction is crushed and fired again.
Complex and expensive operations must be repeated. Furthermore, the composite oxide obtained by this solid phase reaction is
Since it is subjected to thermal history at high temperatures, it has the drawbacks of coarse particle size and poor reactivity and sinterability. In order to improve the above-mentioned drawbacks in solid-phase reactions, it is already known to produce by a solution method. For example, titanium oxynitrate is reacted with a water-soluble lead salt such as lead nitrate in an aqueous solution containing oxalic acid to form a precipitate of oxalate, and this precipitate is thermally decomposed at a temperature of 700°C or higher. , the method is to obtain oxides. However, in this coprecipitation method, it is difficult to coprecipitate at a desired component ratio because the oxalate of each component has a different solubility in water. Also,
A method is also known in which the alkoxides of the component elements are hydrolyzed and co-precipitated.This method yields highly pure and highly homogeneous products, but it requires that the various components be synthesized once as alkoxides. , manufacturing becomes complicated and the price becomes expensive. The reason why such a wet method using expensive alkoxides and titanium oxynitrate was considered is that when cheap titanium tetrachloride is used as a raw material, the chlorine in titanium tetrachloride reacts with lead and forms a white precipitate. occurs, making it impossible to perform a wet coprecipitation method. Therefore, as a method of using inexpensive chlorides together with lead compounds, first the lead compounds are precipitated as hydroxides with an alkaline precipitant, and chlorides such as titanium tetrachloride and other chlorides are added to the precipitate-containing solution. It is also possible to add a compound and then add a precipitant to precipitate a hydroxide such as titanium, but when using this method, the precipitated lead hydroxide is first converted into chloride ions as a hydroxide. It is estimated that lead chlorides such as basic lead chloride and lead oxychloride are produced by reacting with lead chloride. It is extremely difficult to remove the chlorine in this lead chloride by washing with water, and as a result it remains in the perovskite compound and has an extremely negative effect on the physical properties after drying and sintering, so chlorine is removed as much as possible by precipitation. It is necessary to do so. Based on such a technical background, the present inventors have repeatedly studied a method for producing a perovskite compound having an extremely low chlorine content using a wet method, and as a result, have arrived at the present invention as detailed below. That is, an object of the present invention is to solve the problems that occur when using inexpensive chloride as a raw material and lead as a constituent of a perovskite compound. Therefore, the present invention provides a method for producing a perovskite compound containing lead using a water-soluble chloride as at least one raw material.
Water-soluble lead compound and carbonic acid or alkali carbonate
After reacting at CO ₃ /Pb (molar ratio) of 1.1 or more to generate a precipitate, other compounds other than lead compounds containing chlorine are precipitated as hydroxides, or at least one compound contains chlorine. After precipitating compounds other than lead compounds as hydroxides, in a solution containing this precipitate, the lead compound and carbonic acid or alkali carbonate were mixed with CO ₃ /Pb (molar ratio) 1.1.
The present invention relates to a method for producing a perovskite compound containing lead, which comprises causing the above reaction to produce a precipitate. The perovskite compound of the present invention is represented by the general formula (Pb, A) BO ₃ , and the A component is an alkaline earth metal such as Ba, Sr, Ca, etc., or a rare earth metal such as La, and the B component is an alkaline earth metal such as Ba, Sr, Ca, etc. as,
Examples include Ti, Zr, Mg, W, Nb, Mn, Sn, Ni, etc., and one or more of these may be used depending on the purpose. In the present invention, the chloride of either component A or component B can be used, but the effects of the present invention are best exhibited when titanium chloride is used in place of the expensive titanium nitrate. Describing the method of the present invention in detail, a water-soluble lead compound, such as lead nitrate or lead acetate, is reacted with carbonic acid or an alkali carbonate in an aqueous solution to precipitate a lead carbonate. The reaction ratio between the two is CO ₃ /Pb (molar ratio) of 1.1 or more. Below this range, chlorine coexists in the precipitate and the effects of the present invention cannot be obtained. Naturally, other alkaline precipitants can also be used in the production of carbon lead. It goes without saying that when precipitating lead carbonate, water-soluble compounds other than the chlorides of component A and component B can be made to coexist and co-precipitated as hydroxides. The metal salt concentration in this precipitation reaction is generally desirably in the range of 1 to 10% by weight of the metal oxide. Next, in the precipitate-containing solution thus obtained, at least one of component A and component B is used as a chloride, and this is precipitated as a hydroxide. During the precipitation reaction, it is desirable to stir sufficiently to make the ingredients uniform. As the precipitant in this case, in addition to alkali carbonate, alkaline substances such as ammonium hydroxide and alkali hydroxide can be used. Also, along with chloride, A
There is no problem in using other salts of component B, such as nitrates and acetates. The perovskite-type compound thus obtained is separated from an aqueous solution, washed with water, and then dried, but compared to conventional perovskite-type compounds using chloride, the chlorine in the dried product is in a form that can be sufficiently removed by washing with water. There are only traces of chlorine. Regarding other production methods that hardly retain chlorine radicals, first, at least one type of chloride other than the lead compounds of components A and B is precipitated as a hydroxide, and then in this hydroxide-containing solution. , a water-soluble lead compound and carbonic acid or an alkali carbonate are reacted at a CO ₃ /Pb (molar ratio) of 1.1 or more to form a precipitate. During the formation of this precipitate, other A components other than lead,
Naturally, the compound of component B can coexist, but it must be avoided to use it as a chloride. Moreover, as a precipitant, it is of course possible to use other precipitants in addition to the alkali carbonate. Although the precipitation reaction of the present invention is all carried out at room temperature, heating and pressurization may be applied as necessary. As is clear from the above description, the present invention utilizes at least a two-step precipitation reaction, and when a water-soluble lead compound is precipitated as a carbonate, it is preferable to use another compound as a chloride. It is possible to avoid this, produce a precipitate with a uniform composition, and produce a perovskite compound with a small amount of chlorine radicals and good physical properties. Hereinafter, the present invention will be explained in detail according to examples. Example 1 Lead nitrate 30.140g, lanthanum nitrate hexahydrate 6.897g
Prepare 500 c.c. of an aqueous solution containing g.
The precipitate containing basic lead carbonate was added dropwise to 300 c.c. of precipitant containing 11.502 g of ammonium bicarbonate and 25.6 g of concentrated ammonium water so that the CO ₃ /Pb molar ratio was 1.6. It was adjusted. While stirring this suspended aqueous solution, 500 c.c. of an aqueous solution containing 13.6479 g of a titanium tetrachloride aqueous solution (TiO ₂ 20 wt%) and 16.9897 g of zirconium oxynitrate dihydrate was added dropwise, and lead, A precipitate containing lanthanum, zirconium, and titanium was obtained. A part of this precipitate was dissolved in nitric acid to form AgNO ₃
The sample was washed with distilled water until no chlorine was detected. The amount of washing water in this case was about 1500 c.c. After washing with water, drying and calcining at 700℃ for 1 hour.
PPLZT raw material powder was obtained. Comparative Example 1 The same amount of lead and lanthanum solution as in Example 1 was mixed with CO ₃ /
Ammonium bicarbonate so that the Pb molar ratio is 0.9.
6.470 g of concentrated ammonium water was added dropwise to 300 c.c. of the precipitant containing 29.5 g of concentrated ammonium water, and the same amount of titanium and zirconium solution as in Example 1 was added dropwise to the precipitant.
After washing with 1500 c.c. of washing water, it was dried and calcined at 700°C for 1 hour to obtain a PLZT raw powder. These calcined powders were molded to a diameter of 12 mm under a pressure of 1.5 t/cm ² and sintered at 1100° C. for 40 hours at normal pressure in a mixed atmosphere of oxygen gas and lead vapor.

[Table] Example 2 Prepare 300 c.c. of an aqueous solution containing 19.12 g of lead nitrate, and add 10.489 g of ammonium bicarbonate and 8.46 g of concentrated aqueous ammonia so that the CO ₃ /Pb molar ratio is 2.3.
was added dropwise to 200 c.c. of a precipitant containing acetate while stirring to form a precipitate. While stirring this suspended aqueous solution, zirconium oxychloride dihydrate was added to it.
30 c.c. of an aqueous solution containing 18.594 g was added dropwise to obtain a precipitate containing lead and zirconium. After filtering, distilled water
It was washed with water at 1000 c.c., and the chlorine concentration in the precipitate was measured. Comparative Example 2 The same amount of lead solution as in Example 2 was added to concentrated ammonia water.
The precipitate obtained by dropping it into 200 c.c. of precipitant containing 16.52 g was washed with 1000 c.c. of distilled water, and the chlorine concentration in the precipitate was measured. Example 3 300 c.c. of an aqueous solution containing 23.06 g of titanium tetrachloride aqueous solution (TiO ₂ 20 wt%) was prepared, and concentrated aqueous ammonia was added.
10 g of ammonium bicarbonate, and 200 c.c. of precipitant containing 10.261 g of ammonium bicarbonate was added dropwise with stirring to form a precipitate. While stirring this suspended aqueous solution, 300 c.c. of an aqueous solution containing 19.12 g of lead nitrate was added dropwise to obtain a precipitate containing lead and titanium. After filtering, the precipitate was washed with 1000 c.c. of distilled water, and the chlorine concentration in the precipitate was measured. Comparative Example 3 The same amount of titanium tetrachloride aqueous solution as in Example 3 was dropped into 200 c.c. of precipitant containing 20 g of concentrated ammonia water,
The same amount of lead nitrate aqueous solution as in Example 3 was added dropwise to this,
The obtained precipitate was washed with 1000 c.c. of distilled water, and the chlorine concentration in the precipitate was measured. Example 4 300 c.c. of an aqueous solution containing 11.53 g of titanium tetrachloride aqueous solution (TiO ₂ 20 wt%) and 7.714 g of zirconium oxynitrate dihydrate was prepared, and added to 150 c.c. of a precipitant containing 10 g of concentrated aqueous ammonia. It was added dropwise with stirring to form a precipitate. While stirring this suspended aqueous solution, 50 c.c. of an aqueous solution containing 10.489 g of ammonium bicarbonate was added, and then 300 c.c. of an aqueous solution containing 19.12 g of lead nitrate was added dropwise. zirconium,
A precipitate containing titanium was obtained. Distilled water after filtration 1000c.c.
The precipitate was washed with water and the chlorine concentration in the precipitate was measured. Comparative Example 4 The same amount of titanium tetrachloride and zirconium oxynitrate aqueous solution as in Example 4 was dropped into 200 c.c. of precipitant containing 20 g of concentrated ammonia water, and the same amount of lead nitrate aqueous solution as in Example 4 was added dropwise thereto. and soak the resulting precipitate in distilled water.
It was washed with water at 1000 c.c., and the chlorine concentration in the precipitate was measured. Example 5 Titanium tetrachloride aqueous solution (TiO ₂ 20wt%) 8.807g,
Aqueous solution containing 1.54 g of barium chloride dihydrate
300 c.c. was prepared and added dropwise to 200 c.c. of a precipitant containing 11.97 g of ammonium bicarbonate and 15 g of concentrated aqueous ammonia while stirring to form a precipitate. While stirring this suspended aqueous solution, 16.90 g of lead nitrate was added to it.
300 c.c. of an aqueous solution containing 2.46 g of lanthanum nitrate hexahydrate and 10.94 g of zirconium oxynitrate dihydrate was dropped to obtain a precipitate containing lead, lanthanum, barium, zirconium, and titanium. After filtering, distilled water
It was washed with water at 1000 c.c., and the chlorine concentration in the precipitate was measured. Comparative Example 5 The same amount of titanium tetrachloride and barium chloride aqueous solution as in Example 5 was added to a precipitant containing 30 g of concentrated ammonia water.
200 c.c., and the same amount of lead nitrate as in Example 5 was added to this.
Lanthanum nitrate and zirconium oxynitrate aqueous solution were added dropwise, and the resulting precipitate was washed with 1000 c.c. of distilled water.
The chlorine concentration in the precipitate was measured.

[Table] As shown in Example 1 and Comparative Example 1, CO ₃ /
If the Pb molar ratio is less than 1.1, chlorine in the precipitate tends to remain, and removal requires a large amount of washing water and time, which is obviously not economical, and also causes poor sintering and transparency. Only sintered bodies with low optical properties can be obtained.

Claims (1)

[Claims] 1 In a method for producing a perovskite compound containing lead using a water-soluble chloride as at least one raw material, a water-soluble lead compound and carbonic acid or an alkali carbonate are reacted at a CO ₃ /Pb (molar ratio) of 1.1 or more. or precipitate other compounds containing chlorine as hydroxides, or precipitate other compounds other than lead compounds, at least one of which contains chlorine, after forming a precipitate. After that, in a solution containing this precipitate, a lead compound is reacted with carbonic acid or an alkali carbonate at a CO ₃ /Pb (molar ratio) of 1.1 or more to produce a precipitate, thereby producing a perovskite-type compound containing lead. Method.