JPH02172805A - Production of ceramic powder - Google Patents

Abstract

PURPOSE:To obtain the fine ceramic powder only by drying by neutralizing a soln. contg. the coprecipitates of plural metal oxalates, removing only the supernatant by decantation, repeating the agitation and washing of the precipi tate, and uniformly washing the fine grains of the precipitate. CONSTITUTION:A soln. of oxalic acid in water, methanol, etc., equivalent to the formation of the precipitate of metals is added to an acidic soln. of nitric acid, etc., contg. the metals such as Ca, Sr, Ti, and Zr. The obtained mixed soln. is violently agitated, and neutralized by an amine or NH3 to coprecipitate the oxalates of the metals. The supernatant of the reaction product is removed by decantation, and a precursor slurry as the precipitates is washed with water or alcohol to remove the amine nitrate or ammonium nitrtate from the slurry. The washing and the removal of supernatant are repeated, and then the slurry is dried. By this method, the dried fine-powder precursor is obtained practically without the powder being aggregated. The precursor is then calcined, for exam ple, at 500-1100 deg.C to obtain the desired ceramic powder.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a powdered ceramic precursor, which is characterized in that the ceramic precursor in a solution is recovered as a dry powder that does not require crushing. It is. More specifically, the present invention relates to the production of a precursor for producing fine powder perovskite oxides which are excellent as piezoelectric materials, dielectric materials, and pyroelectric materials, for example, by themselves or by mixing with rubber, plastic, etc. It is about the method.

[Conventional technology and issues]

In resin composite applications, for example, fine powder oxide ceramics with high crystallinity and a narrow particle size distribution are required as materials for composite film capacitors. An oxalate method has been proposed as a method for producing these.

That is, in ABO, perovskite type oxide ceramics, oxalic acid is soluble in ethanol, and oxalate of element A (Pb, Ca, Ba or Sr, etc.) and oxalate of element B (Ti, Zr, etc.) Utilizing the property that both acid salts are poorly soluble in ethanol, element A ions and Ti ions are reacted with oxalic acid in ethanol, and these elemental ions are co-precipitated as oxalate ( JP-A-5939722, etc.) are known.

After filtration, drying, and pulverization, these are
The desired perovskite-type oxide can be obtained by firing at 000°C until thermal decomposition is completely completed and no weight change is observed; however, according to the disclosure, the fired product produced is The powder is ground and mixed again, and this powder is then molded and sintered at 1000 to 1400°C.

In other words, in this prior improved technology, the finely powdered perovskite-type oxide obtained by firing the co-precipitate required a re-grinding process because the particles were fused together. .

This re-grinding step, which is necessary in the prior improved invention, not only increases the process cost and reduces the reliability of the final product due to the contamination of impurities, but is also problematic in terms of the characteristics of the perovskite oxide powder. That is, these perovskite-type oxide powders are mixed with polyvinylidene fluoride resin,
Development of technology to manufacture highly flexible piezoelectric films and dielectric films by combining polyoxymethylene resin, nitrile butadiene rubber, etc. is progressing, but in this case, the particle size distribution is uniform and crystalline. This is because a strain-free, easily dispersible fine powder is required, and fine powder obtained by re-pulverization causes crystal strain, making it impossible to obtain the expected performance.

In addition, for dielectric films, it is necessary to uniformly disperse fine ceramic particles in a thin film of, for example, 10 μl or less, preferably 1 to 5 μl. There is a problem that it is not possible to secure the

In order to solve these problems, the applicant previously filed an earlier application (for example, Japanese Patent Application Laid-open No. 72523/1983).

It has been disclosed that easily dispersible fine particles with controlled composition can be obtained by applying a new stoichiometric ratio of oxalic acid, which is a precipitant, to T1 ions and Zr ions. In other words, the precipitate formation stoichiometric ratio of T + O(N O-) 2 and oxalic acid, which is a precipitant, is not the conventionally accepted oxalic acid/T i = 1/1 (1 mole), but 1/1 mole. Tsutsumi proposed that it would be possible to achieve this quantitatively and stably over time by using Pb as the A element and Ti and Zr as the B elements by applying this new stoichiometric ratio. It has been disclosed that ABO3 type oxide fine particles can be stably synthesized in an oxalic acid/ethanol system by combining at least one selected element.

In these methods, the generated ceramic precursor precipitate and the reaction solution are separated by filtration, and the precursor is recovered as a filter cake, and in subsequent cleaning, the cake is broken up by sufficient stirring to improve the cleaning effect. was. In addition, the filter cake after washing is dried and crushed until it becomes powder.
Methods have been consistently used to ensure adequate supply of oxygen into the powder during subsequent firing.

When attempting to separate the produced precipitate from the reaction solution or washing solution by filtration, the produced precipitate is in the form of fine particles, which tends to clog the p-filtration equipment, and the precipitate is bulky and the filter cake has a high water content. , it was difficult to move to the next process. Furthermore, the filter cake that has been consolidated by filtration cannot be completely crushed in the washing stage 11,
Some of the precipitates remained in the form of lumps, so-called "r-dumps", which made it difficult to uniformly wash the precipitates.

In addition, ceramic precursors are often fine particles containing toxic substances such as lead or barium, so when handling the filter cake or crushing the dry cake, you may come into contact with the precursor or inhale the scattered fine particles. It is necessary to completely avoid the risk of

[Means to solve the problem]

That is, the present invention, as a means to solve the above-mentioned problems, brings an acidic 78 liquid containing multiple types of metals into contact with a solution containing oxalic acid in an amount equivalent to forming a precipitate of the metals,
In a method for producing a powdered ceramic precursor by generating an oxalate coprecipitate, neutralizing it with ammonia or amine, washing and drying the precipitate, the washing between the coprecipitates is first carried out in a solution. After settling the coprecipitate suspended in water, remove the supernatant of the reaction liquid by decantation, mix the washing liquid with it and perform stirring washing, drain the washing liquid again by decantation, and repeat this process thereafter. The present invention provides a method for packaging a powdered ceramic precursor, characterized in that the method is carried out by:

[Detailed description of the invention]

The ceramic precursor targeted by the present invention is a precursor of a perovskite-type oxide. Specifically, A B O3
The basic structure is a mold, and A is lead, calcium,
It represents strontium, lanthanum, etc., and B represents titanium, zirconium, etc.

Furthermore, it is also possible to add and co-precipitate various trace components such as manganese and nickel.

To produce these precursors, an acidic metal solution is brought into contact with an oxalic acid solution as a precipitant, and then nitric acid or an organic acid produced in the oxalate precipitate formation reaction and nitric acid coexisting in the acidic solution in advance are added. is neutralized with amine or ammonia.

Thereafter, a powdered ceramic precursor can be obtained by washing, neutralizing, and drying. Ceramic perovskite is obtained by firing this precursor.

Below, the explanation will be further divided into sections.

11 to 1IL As raw materials for the acidic solution of metals, examples of group A metals for ABO type perovskite include button, calcium, strontium, lanthanum, etc., and group 8 metals include titanium,
Examples include nitrates and organic acid salts of various elements such as zirconium. A plurality of these metal salts are mixed in a proportion that forms the desired ceramic composition, and water? 'fJ? rf or an aqueous solution to which alcohol is added to an extent that no precipitate is formed.

The concentration of metal element ions in the acidic solution can be made high as long as the metal element ions of the target composition can be completely dissolved under the given conditions, but the concentration of group A element ions is 0.05. ~1 mol/1, preferably 0.1-0
．． A concentration of 5 mol/1 can be chosen.

The concentration of each element is such that the B element ion concentration is 0.05 to 1 gram atom/1, preferably 0.1 to 0.5 gram atom/1.
A range of l is appropriate.

The acidity of the metal solution can be varied greatly by adding an acid, generally nitric acid.

By setting the nitric acid/titanium or zirconium (mol) ratio in the range of 0 to 5, preferably 0.01 to 4, the particle size and particle size distribution of the oxide ceramics obtained as the final product can be narrowed. It becomes possible to control.

As a general rule, the amount of oxalic acid added as a precipitant is in the range of ±3% of the precipitation equivalent of each metal ion, preferably ±2%.
, more preferably within a range of ±1%. Specifically, for example, metal ions include Pb2', Sr2°, Ca''
etc., 0.9 oxalic acid per 1 gram atom
7 to 1,03 mol, preferably 0,98 to 1,02 mol, more preferably 0.99 to 1.01 mol, La'°
etc., 1.4 oxalic acid per 1 gram atom
55-1.545 mol, preferably 1.47-1.53
mol, more preferably 1.485 to 1.515 mol. T; 4°, Zr'', 0485 to 0.515 mol, preferably 0849 to 0.51 mol, more preferably 0.49 oxalic acid per gram atom thereof
5 to 0.515 mol. Oxalate precipitation of titanium or zirconium was previously considered. Oxalic acid / titanium (or zirconium) = 1 / 1 (
Since the coexistence of excess oxalic acid causes re-dissolution of the oxalate precipitate of titanium or zirconium, it is obtained at a stoichiometric ratio of 1/2 instead of a stoichiometric ratio of 1/2 (molar ratio). In the process of leaving the produced precipitate in the reaction solution for a relatively long time, as in the present invention, it is necessary to minimize the deviation from the stoichiometric ratio.

A predetermined amount of oxalic acid is dissolved in at least one solvent selected from water, methanol, ethanol, and propatool' for metal ions suited to the composition of the intended ceramic.

The reaction temperature can be selected from a wide range, preferably from around 0°C to 50°C, more preferably 0°C.
You can choose from 30°C to 30°C.

Low temperatures that cause the solution to freeze must be avoided. Furthermore, considering the thermal stability of ions in the solution, it is necessary to avoid reactions at high temperatures that may cause decomposition during the precipitation synthesis reaction.

The oxide constituent elements can be precipitated as oxalates by dropping an acidic aqueous solution of the metal into a vigorously stirred oxalic acid solution, and vice versa. The oxalate production rate can be appropriately selected within a range that does not cause the reaction system temperature to rise rapidly.

Rainbow = 1 After adding oxalic acid, the mixed solution is neutralized with amine or ammonia while stirring occasionally. The amines used for neutralization include, for example, hydrazine, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, alkylamines such as triethylamine, alkylenediamines such as ethylenediamine, 1,3-propanediamine, ethanolamine, 1
- Alkanolamines such as amino-2-oxypropane, 2-amino-1-hydroxypropane, hydroxylamine, and mixtures thereof; and ammonia include ammonia gas or concentrated ammonia water; It is preferable to use In this case, crushed ammonia water is added to the precursor precipitation solution to control pt (6 to 8, preferably 62 or 67.8).

The p l-1 of the slurry-containing solution after ammonia neutralization is
PL (can be measured using test paper) with a limited measurement range. The optimum pH varies depending on the combination of each element, but the final PL after neutralization is, for example, 6 to 8, preferably 6.2 to 7. By setting it within the range of 8, the abundance ratio of the target constituent elements can be precisely controlled.

After addition of oxalic acid and addition of amines such as ammonia,
In order to complete each reaction, it is preferable to continue stirring for an appropriate time to carry out the reaction.

After allowing the obtained precursor precipitate to stand and settle, the supernatant of the reaction solution is removed by decantation.

In forming oxalate precipitates from metal-containing acidic solutions,
Focusing on the feature of the present inventors' prior invention that the precipitate does not re-dissolve unless an excess precipitant (unhydric acid) is added, after the reaction is complete, the precipitate is left to settle slowly, and then the supernatant liquid is drained. It was removed using the decantation method. Brooding of the washing solution was also carried out by the same decantation method.

It is preferable to sufficiently precipitate the precursor and remove as much supernatant as possible in order to increase the efficiency of washing. In other words, in this synthesis method, there is a risk that the obtained precursor precipitate may change over time. Therefore, it is preferable to allow sufficient time for natural sedimentation so that a large amount of clear supernatant can be removed without compacting the sediment.

Furthermore, a method in which a nonionic flocculant is added to block the precursor precipitate and precipitate it (for example, Japanese Patent Application No. 63-1
No. 21810) is also applicable.

Sedimentation methods that involve applying a large external force to compact the precipitate, such as centrifugation, do not meet the purpose of this patent.

After removing the supernatant, it is desirable to wash the precursor slurry with water or alcohol in order to remove the amine nitrate or ammonium nitrate produced by neutralization.

Separation of the washing liquid and the precursor slurry is also carried out in the manner described above, and the washing is repeated, preferably by decantation, without compacting the precursor precipitate. In this way, the concentration of amine nitrate or ammonium nitrate in the slurry; 8 liquid is adjusted to 3% or less, preferably 2% or less.
More preferably, it is 1% or less.

The slurry concentration at this stage is usually 05 to 50%, preferably 2 to 15%.

LJL The precursor in the precursor slurry solution is dried and collected without being agglomerated to obtain a finely powdered dry precursor. As a specific example of this method, the precursor slurry solution is supplied into a heated long tube whose powder collector side is kept under reduced pressure, and only the precursor is removed from the mixture of slurry solvent vapor and precursor powder using a bag filter. There is a method of drying it by collecting it.

Another method is to spray a precursor slurry solution into hot air to obtain a dry powder.

The absorbent precursor dry powder is heated to a suitable temperature, e.g. 500-1100.
■ Bake at ℃. Although it is desirable that the firing temperature be low, it is necessary to carry out the firing until no weight change is observed.

[1((Pb, , 6゜Cao, -o)Tio
, Synthesis of fine particles] Titanium oxynitrate 9720m&' with a titanium concentration of 0.1001y/mff1 and commercially available special grade lead nitrate (purity 99.5%
) 4058.60g, commercially available special grade calcium nitrate tetrahydrate (purity 98.5% N948.75g, ion exchange water 8
7.341 and P b/Ca/ T i =
0.6010.40/1.00 (molar ratio), HNO)
/Ti=3/1 (molar ratio), 0.2 plow o1- Ti
/1 aqueous solution was obtained and kept at room temperature. Commercially available special grade oxalic acid dihydrate (purity 9, 5%>3862.11 g was dissolved in 304.81 g of anhydrous undenatured ethanol, (Co
OH)2/<Pb+Ca+Ti)=0.75 (molar ratio)
A solution of ethanol/the aqueous solution-3/1 (volume ratio) was prepared and maintained in a cooled reactor by circulating cooling water at about 15° C. through a jacket.

About 560 ml of the acidic solution was added to the vigorously stirred ethanolic oxalic acid solution at a rate of 1 minute to obtain a white slurry. After the addition was completed, stirring was continued for 10 minutes, and approximately 233 ml of special grade ammonia water 12.81 was added! /min to the stirred slurry solution and continued stirring for 10 minutes thereafter. pH
The p)l of the slurry solution was measured using test paper (bromthymol blue) and was found to be 7.4.

It was left standing overnight to allow the precursor precipitate to settle naturally.

Close the top lid of the device except for the supernatant liquid discharge pipe and nitrogen pressurizing line, and gently pressurize with nitrogen to draw out the supernatant liquid (siphon method).While looking inside the device, remove the supernatant liquid to the lowest possible position without sucking up the slurry. I pulled it out. The amount of supernatant liquid extracted at this time was 3091. Add ethanol 1441 to the thick slurry solution remaining in the reactor.
was added and the solution was cleaned for 30 minutes, and then left to stand for 24 hours.

1502 was extracted using the same siphon method, and 144
! of ethanol was poured into the solution for 30 minutes, and -
The solution was left to stand day and night, and the supernatant liquid was removed. Based on the material balance, the obtained slurry solution contained 9.5 wL% of ceramic precursor, 0.4 wL% of ammonium nitrate, and 86% of ethanol. OwL
%, water 4.1 wL%.

The slurry stock solution was supplied into a heated long tube whose collector side was kept under reduced pressure and dried. Specifically, the drying was carried out using "rcRUX-8B instant drying system" manufactured by Orient Chemical Industry Co., Ltd. Sura and Lee were supplied to a heating tube maintained at 140 to 150°C for approximately 333IIllZ minutes, dried, and heated to a temperature of 8°C.
The powder was collected in a powder collector maintained at 0 to 120°C and a vacuum level of 4.0 to 70 Torr.

The precursor powder obtained was a fine powder that did not require any resolving.

The precursor powder was heated at 800°C in a Matsufuru furnace with air flowing through it.
I baked it for 8 hours.

The particle size distribution measured with a Microtrac particle size meter is shown in FIG. The X-ray diffraction diagram is shown in FIG.

As can be seen from FIG. 1, the ceramic powder obtained here had a volume average diameter of 0.68 μm.

In addition, the second [21] X-ray diffraction diagram is
Compared to b T i O3, the peak has shifted slightly and the difference in the interplanar spacing can be confirmed.
o, s Ca 0.40 ) T i O3. All of these were equivalent to ceramic powders synthesized on a small scale.

and IM-YC (P bo, , Cao, zs) T io
)) mfn synthetic titanium concentration 0.0971y/d titanium xyl nitrate 17
00Tn1 and special grade nitrate (99.5% purity) 860.7
0y, special grade calcium nitrate tetrahydrate (purity 98.5%
>206.64y, special grade nitric acid 772peng! , mixed 14770m of ion-exchanged water, Pb/Ca/Ti=0.7
510.25/1.00 (molar ratio), [INO/T
i = 3/1 (molar ratio) An aqueous solution with a titanium concentration of 02 mol/l was obtained and left in a chamber. Special grade oxalic acid trihydrate (99.5% purity) 655.24g in anhydrous undenatured ethanol 51710ml+! (COOl(), /(Pb+Ca+Ti)=0.
75 (molar ratio), ethanol/the acidic aqueous solution -3/1 (
A solution with the following volume ratio was prepared.

A dihydric acidic aqueous solution was added to the vigorously stirred oxalic acid ethanol solution at a rate of about 210 ml and 17 minutes to obtain a white slurry. After the addition was complete, stirring was continued for approximately 5 minutes. Furthermore, 2173ml of special grade ammonia water! was applied to the stirring slurry liquid at 167 mN/min, and stirring was continued for t&5 minutes. pH
The t+)I of the slurry liquid was measured using M test paper (bromthymol blue) and 7.4 was obtained.

The precursor precipitate was left to settle overnight.

The supernatant liquid was drawn out using a pump. The supernatant extracted at this time was 42.91. Ethanol 27I to the thick slurry 'lfJ liquid in the reactor! The sample was oiled, crushed and cleaned for 30 minutes, and left to stand for half a day.

Similarly, the supernatant was removed using a pump. The volume of the supernatant at this time was 2171. Washing was performed again with ethanol 271, and the supernatant of apparatus 113481 was extracted overnight to obtain a slurry for drying. Drying was carried out in the same manner as in Example 1, and dried at 1000°C for 5 minutes in a Matsufuru furnace with air circulation.
Time ■ Baked.

Figure 3 shows the particle size distribution measured with the Microtrunk particle size meter.
Shown below. As can be seen from this figure, the obtained perovskite was fine particles with a particle size of about 5 μm or less.

〔Effect of the invention〕

In the present invention, since the precipitate is settled and the precipitate is separated from the liquid by decantation, the precipitate is not strongly compacted, and even a weak stirring force can be used to sufficiently solve the problem during washing, and it remains in the form of fine particles. Uniform cleaning is now possible.

Since the precipitated particles are not compacted, a uniform slurry containing no "clumps" etc. is obtained, so a method can be used to obtain dry powder from the slurry solution all at once. In addition, since the process does not cause clogging of drying pipes or distributors, it can now be used as an industrial process.

In addition, since the synthesis of the precipitate and the washing can be carried out in a single reaction tank in a sealed state, there is no risk of contact with harmful precipitates, and a large amount of solvent is always coexisting until the precipitate is dried, making it possible to perform There is no need to worry about the scattering of fine particles of the precipitate, which could not be avoided using the method, and handling safety has been greatly improved. Additionally, the resulting dry powder does not require a pulverization process, which has the highest probability of powder scattering, resulting in a further significant improvement in safety and health.

Furthermore, it is possible to dry the surface precursor by obtaining a dry powder from a precipitate-containing solution all at once, without requiring filtration, separation, or mechanical concentration. etc. can be omitted, and fixed costs, variable costs, etc. can also be reduced.

[Brief explanation of the drawing]

FIG. 1 shows the particle size distribution of the perovskite powder obtained in Example 1, as measured by a Microtrac particle size meter. In the figure, the horizontal axis shows the particle size (IZ), and the vertical axis shows %. FIG. 2 is an X-ray diffraction diagram of the Velozysky l-powder obtained in Example 1. FIG. 3 is a diagram showing the particle size distribution of the Velodisky powder obtained in Example 2, as determined by a Mike 1 Cotrac ablation meter. Figure 2 J Scream

Claims (1)

[Claims] An acidic solution containing multiple metals is brought into contact with a solution containing oxalic acid in an amount equivalent to the precipitation of the metal to form an oxalate co-precipitate, and after neutralization with ammonia or amine, the precipitate is In a method for producing a powdered ceramic precursor by washing and drying, washing the coprecipitate,
First, the coprecipitate suspended in the solution is precipitated, the supernatant of the reaction solution is removed by decantation, the washing liquid is mixed with this, stirring washing is performed, the washing liquid is discharged again by decantation, and this is used thereafter. A method for producing a powdered ceramic precursor, characterized in that the method is carried out by repeating the process.