JPH02289429A - Production of iron-based multiple oxide - Google Patents

Abstract

PURPOSE:To enable conversion into garnet by calcining at a low temp. and to produce an iron-based multiple oxide at a low cost by coprecipitating hydroxides from an aq. soln. contg. Fe<2+> ions and ions of other metal, synthesizing a coprecipitate while oxidizing iron to trivalent iron and separating the coprecipitate, which is then calcined, molded and sintered. CONSTITUTION:A mixed aq. soln. contg. Fe<2+> ions and ions of other metal such as Y or a rare earth metal in the form of metallic salts is prepd. and mixed with a base such as ammonia. After hydroxides are coprecipitated from the soln., oxygen-contg. gas is blown into the soln. to synthesize a coprecipitate as well as to perfectly oxidize Fe<2+> ions to Fe<3+> ions. The coprecipitate is separated, washed, dried and calcined at about 600-1,300 deg.C. The resulting calcined body is crushed, mixed, molded and sintered at about 1,000 deg.C to produce the subject oxide.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing iron-based composite oxides, particularly garnet-type ferrite useful for magneto-optical elements such as optical isolators, particularly by solid phase reaction method. The present invention relates to a method for producing an iron-based composite oxide suitable for producing a garnet-type ferrite single crystal or for obtaining a translucent garnet-type ferrite polycrystal.

(Prior Art) Powder mixing methods, wet coprecipitation methods, and the like have been known as methods for obtaining raw material powder for producing garnet-type ferrite (hereinafter referred to as garnet-type ferrite powder).

The powder mixing method is a method in which a garnet-type ferrite powder is obtained by mixing raw material powders such as oxides or carbonates with a desired composition, and calcining and pulverizing this mixture. This is a method in which a base is added to an aqueous raw material salt solution to produce a hydroxide, and then the hydroxide is washed, filtered, dried, calcined, and ground to obtain a garnet-type ferrite powder.

(Problem to be Solved by the Invention) By the way, according to the conventional powder mixing method, garnet is produced by a solid phase reaction between raw material particles, and the production temperature is 1200''C when YTG (yttrium iron garnet) is used. Due to the high temperature, grain growth occurs and the particle size after pulverization becomes large, resulting in insufficient formability and sintered density.

Furthermore, when attempting to obtain bismuth-substituted iron garnet powder, there is a problem in that the bismuth component volatilizes at the temperature at which the reaction between raw material particles occurs, making it impossible to obtain garnet having the desired composition.

In this regard, in the conventional wet coprecipitation method, hydroxide is obtained directly from a mixture of metal ions, so for example, in YIG,
Mixing on the molecular order is possible, and fine garnet powder can be obtained by calcining at 900°C or higher; however, when coprecipitation is performed using a trivalent iron aqueous solution as a starting material, the coprecipitate produced The powder is extremely fine, and the particle size distribution of the powder after calcination is wide, and the formability and sintering density are insufficient, making it impossible to obtain a satisfactory garnet-type ferrite using such powder as a raw material. There wasn't.

In addition, when attempting to obtain bismuth-substituted iron garnet powder by a wet coprecipitation method, these hydroxides are obtained by coprecipitation reaction from an aqueous solution containing sulfate ions and chloride ions of iron, etc. as raw materials. Due to the adsorption of ions, it becomes difficult to turn into garnet at low temperatures, so it was necessary to set the calcination temperature to 900°C or higher.

For this reason, if a large amount of bismuth is substituted, 900°C
If the temperature is lower than that, the sulfuric acid radicals and hydrochloric acid radicals will not be completely decomposed, making it impossible to obtain a calcined powder with good moldability.

In order to solve the above-mentioned conventional problems, we have created a raw material powder with a narrow particle size distribution according to the desired garnet composition by particularly making improvements to the coprecipitation method, and this has enabled us to create a garnet type with good properties. It is an object of the present invention to provide a new method by which ferrite can be obtained relatively easily.

(Means for Solving the Problems) This invention coprecipitates hydroxide from a mixed aqueous solution containing divalent iron ions and other metal ions with a base, oxidizes iron to trivalent iron, and converts the coprecipitate. Synthesis, then separation, drying,
A method for producing an iron-based composite oxide (first invention) characterized by further mixing, molding, and sintering the powder obtained by calcining, and this invention also provides a method for producing an iron-based composite oxide, which is characterized in that the powder obtained by calcining is further mixed, molded, and sintered. Using a mixed aqueous solution containing nitrates as a raw material, the hydroxide is coprecipitated by dropping this metal salt mixed aqueous solution into an aqueous base solution, and then the powder obtained by separating, drying, and calcining is further mixed. This is a method for producing an iron-based composite oxide (second invention), characterized by molding and sintering.

(Function) In the first invention, especially when producing garnet type ferrite powder, trivalent hydroxide is produced by blowing oxygen-containing gas into the aqueous solution after co-precipitating the hydroxide. Gradual growth of iron results in uniform grain size,
After that, further heating and aging are performed, so that there are no particularly fine particles due to melting and precipitation reactions.

Further, in the second invention, the starting material for the coprecipitation reaction is
A nitrate that can be decomposed at a temperature of about 0"C is dropped into a base such as ammonia to generate a hydroxide.
Since the coprecipitation reaction is carried out in such a way that segregation does not occur during mixing of metal components with a large + value, sufficient garnetization can be achieved even during calcination at a low temperature of about 600°C.

In addition, when nitrate is mainly used as a starting material as in the second invention, there is an advantage that bismuth-substituted garnet type ferrite can be produced at a low temperature.

The method for producing garnet type ferrite according to the present invention will be explained in detail below, with particular reference to the case of obtaining raw material powder, distinguishing between the first invention and the second invention.

First, regarding the first invention, a mixed aqueous solution containing at least divalent iron ions and yttrium or rare earth metal ions is prepared.

Here, carbonate ions may be present in the mixed aqueous solution in order to prevent coprecipitation of sulfate groups.

Next, the metal salt mixed aqueous solution and a base such as ammonia are mixed to obtain a hydroxide. At this time, p which produces hydroxide
When using metals with approximately the same H, a base is added to the mixed aqueous solution, but when using metals with significantly different pl, hydroxides are simultaneously generated, so water with a constant p)I is used. It is preferable to gradually drop the above mixed aqueous solution into 'jJ f&. In addition, the bases used during coprecipitation include ammonia, tetramethylammonium hydroxide,
It is preferable to use a base that does not contain metal ions, such as tetraethylammonium hydroxide and triethylphenylammonium hydroxide.

The reason for this is that if the base contains metal ions, they will remain as impurities and have adverse effects such as the formation of a liquid phase during sintering.

Next, a gas containing oxygen is blown into the aqueous solution after coprecipitation. Here, the oxidation rate varies depending on the concentration of oxygen blown in and the size of the bubbles.It is fastest to use 100% oxygen gas and generate a large number of small bubbles, and the liquid temperature during the oxidation reaction depends on the reaction rate and reaction time. Considering this, a temperature of 40°C or higher is appropriate.This operation is usually completed in 1 to 2 hours.

After the oxidation reaction is completed, the aqueous solution is heated and oxygen is blown continuously for 30 minutes or more to completely convert unreacted divalent iron ions into trivalent co-precipitates, and to reduce the particle size by dissolution precipitation reaction of ultrafine particles. make it uniform.

Regarding the second invention, first, an aqueous solution of trivalent iron nitrate and an aqueous metal solution containing a nitrate of yttrium or a rare earth metal are weighed to have a desired molar ratio to create a mixed aqueous solution.

Next, a metal salt mixed aqueous solution and a base such as ammonium are mixed to obtain a hydroxide. At this time, in this invention, the pH of the trivalent iron ion and the yttrium or rare earth metal ion in the metal salt mixed aqueous solution is significantly different,
At the same time, in order to generate hydroxide, it is necessary to gradually drop the metal salt mixed aqueous solution into the aqueous base solution. for example,
The pH of hydroxide generation is: Bi: pH 1 or higher, Fe”
: pH is 2 or more, Y: 9117 or more. Furthermore, the base used during coprecipitation is preferably a base that does not contain metal ions, such as ammonia or tetramethylammonium hydroxide. This is because if the base contains metal ions, they will remain as impurities and have adverse effects such as the formation of a liquid phase during sintering.

Next, the coprecipitate obtained according to the above procedure is separated and washed, but in both the first invention and the second invention, anions of starting materials such as sulfuric acid, nitric acid, ammonium, etc. are hardly detected in the washing solution. Repeat the separation and washing operation until

Next, the separated coprecipitated hydroxide is dried.

The dry fine powder obtained according to the first invention has a temperature of 600°C to 1300°C.
Calcinate in the temperature range of °C. The optimum calcination temperature varies greatly depending on the composition of the garnet. In particular, bismuth-based garnet with a low melting point requires a low temperature. The reason why the calcination temperature is preferably 600 to 1300°C is that 600°C
This is because if the temperature is less than 1,300°C, the garnetization reaction hardly occurs, whereas if it exceeds 1,300°C, the powder will sinter, making it impossible to obtain a powder with good moldability.

Taking YIG as an example, the powder in the first invention is 900″
Garnetization begins at about C, and at 1000'C, more than 90% of the garnetization occurs, making it possible to lower the temperature by 200 to 300°C compared to when the powder mixing method is applied.

600 for the dry fine powder obtained according to the second invention.
Preliminary firing is performed at a temperature range of 1100°C to 1100°C. The optimum calcination temperature varies greatly depending on the composition of garnet, especially the amount of bismuth substitution. In this invention, the calcination temperature is 600°C.
The reason why the temperature is preferably 1100°C is that below 600°C, almost no garnetization reaction occurs;
This is because if the temperature exceeds 0°C, the powder tends to sinter, making it impossible to obtain a powder with good moldability.

The powder in this second invention is Bit, oYz, oF
Taking esO+z as an example, garnetization starts at about 700"C, and almost 100% becomes garnetization at 800"C, which is 400~500% lower than when applying the powder mixing method.
'C can be lowered.

The obtained calcined body is then pulverized, and the particle size after pulverization is 0.5 to 2.5 μm in both the first invention and the second invention.
This results in a powder with a narrow particle size distribution.

In addition, in this invention, itria and rare earth elements (La,
ce, Pr, Nb, Pm, Sml Eu, G
d, Tb, oy, Ho, Er, Tm+ Yb
, Lu, ), the magneto-optical properties can be improved as shown in the table below.

Table-1 (Example) First, an embodiment of the first invention will be described.

Prepare an aqueous solution of about 101 with a composition of YJ'L'sO+z of about 600 g by mixing an aqueous solution of ferrous sulfate and an aqueous solution of yttrium nitrate, and adjust this aqueous solution to pHB with aqueous ammonia. It was added dropwise to an approximately 2ON aqueous solution with stirring at a temperature of 75°C over approximately 30 minutes. During this time, aqueous ammonia was added dropwise to maintain the pH at 8. Next, oxygen gas was blown into the green slurry at a rate of 101/min in the form of fine bubbles. The reaction was completed in about 2 hours, resulting in a brownish slurry, but in the present invention, heating and oxygen injection were continued for about 3 hours in order to make the powder particles uniform. In this process, along with the oxidation reaction, the pH
Since the pH would drop, ammonia water was added dropwise to maintain the pH at 8.0.

The generated slurry is separated and washed until the cleaning solution contains almost no sulfate ions and nitrate ions.
Dry.

After drying, the fine powder was calcined at 1100°C for 4 hours, then crushed using an attritor pulverizer, and then press-formed and sintered at 1400°C for 14 hours to a thickness of 7.
A sintered body having a width of 20 mm and a length of 30 mm was obtained.

Next, after processing this into a thickness of 5M, a width of 10mm, and a length of 10mm, Y3Fe50. □As a result of joining a seed single crystal made from a single crystal and heating it to 1520°C, the seed crystal became 5M.
It was confirmed that it is possible to grow single crystals using the solid phase reaction method.

Mix ferrous sulfate aqueous solution, yttrium nitrate aqueous solution, and terbium chloride aqueous solution to obtain Tbo, hYz, a
About 1O1 with a concentration of about 600g based on the composition of FesOrz
An aqueous solution of Tbo, 6Y1. When the seed single crystal made from the aFesO+□ single crystal was bonded and heated to 1500°C, it was confirmed that the seed single crystal grew in size of 5 or more.

Old ferrous sulfate aqueous solution, yttrium nitrate aqueous solution and bismuth nitrate aqueous solution are mixed. , SY! , Prepare an aqueous solution of about 102 with a composition of 5Fe50□ and a concentration of about 600 g, and add 200
g of ammonium carbonate was added, dissolved, and adjusted to pH 8 with aqueous ammonia.The solution was then added dropwise to the aqueous solution 2042 at a temperature of 75°C in about 30 minutes.Then, only the calcination temperature and firing temperature were adjusted to 900°C and 11100°C, respectively. A garnet-type ferrite powder was produced by changing the method, and Bi was added to the sintered body of the obtained powder.
b. As a result of joining a seed single crystal made from a SY2.5FesO□ single crystal and heat-treating it at 1200°C, it was confirmed that the seed single crystal grew 5- or more as in Examples 1 and 2.

324.6g of ferric oxide powder and 2 yttrium oxide powder
Add 75.4g to 600g of water and mix in a ball mill for 2
Wet mixed for an hour. After drying the obtained mixed slurry, it was calcined at 1200°C for 4 hours, crushed using an Atreita crusher, and then baked at 1400''C for 14 hours in a press molding cloth to form a product with a thickness of 7 mm, a width of 20 m++++, and a length of 30+ nm.
A fired body was produced.

Next, this is made to have a thickness of 5III11, a width of 10+nm, and a length of 3
After processing into a zero cylinder, the same test as in Example 1 was conducted, but the growth distance of the seed single crystal was about 0.5 to 2M, and it was found that many pores remained in the grown single crystal. understood.

, Comparison "R ferric sulfate aqueous solution and yttrium nitrate aqueous solution are mixed to give a concentration of about 600 g with a composition of Y3Fe, O, □.
An aqueous solution of OX is prepared, and the same conditions as in Example 1 are subsequently used, in which case no oxidation reaction is involved. ), and a similar test was conducted on the sintered body. As a result, the growth distance of the seed crystal is 0.5 to 2 mm.
It was confirmed that many pores remained within the single crystal.

Table 2 shows the results of the average particle diameter and sintered density of the powders in Examples 1 to 3 and Comparative Examples 1 to 2, and FIG. 1 shows the results of the particle size distribution.

Table-2 Next, an embodiment of the second invention will be described.

Example 1: Mixing bismuth yate, iron nitrate, and yttrium nitrate, an aqueous solution having a concentration of about 600 g with the composition of YJiPe50H□ was mixed with 5 Q f4t (+iii).
The prepared mixed solution was added dropwise to 10 f of ammonia aqueous solution kept at 0° C. over about 1 hour. During this time, the aqueous solution was stirred to ensure that the reaction occurred uniformly. After the dropwise addition was completed, heating and stirring were continued for about 2 hours to ripen the produced coprecipitate.

Next, the generated slurry was separated and washed, dried, and
When calcined at °C, a bismuth-substituted yttrium iron garnet powder with a garnet conversion rate of nearly 100% was obtained. When this powder was molded and fired at 950''C for 10 hours, a single-phase garnet sintered body with a density of 99.9% was obtained.

Next, the obtained sintered body was processed into a cylinder with a thickness of 5 mm, a width of 10 mm, and a length of 10 mm, and then a seed crystal of the same composition was joined and heated to 1000'C. As a result, the seed crystal grew over 5 mm. However, it was confirmed that it is possible to grow a single crystal by the solid phase reaction method.

Fruit■I Tripod Bismuth nitrate, iron nitrate, yttrium nitrate, and gadolinium nitrate are mixed to produce B11Y+, :+Gdo, Pe5O
51 aqueous solutions having a concentration of approximately 600 g at +z were prepared.

Next, add ammonia water kept at 70°C to 10°C at night.
The prepared mixed solution was added dropwise to f over a period of about 1 hour. During this time, the aqueous solution was stirred 1↑ to ensure that the reaction occurred uniformly.

After the dropwise addition was completed, heating and stirring were continued for about 2 hours to ripen the produced coprecipitate.

Next, the generated slurry was separated and washed, dried, and
When calcined at °C, a bismuth-substituted yttrium gadolinium iron garnet with a garnetization rate of nearly 100% was obtained. When this powder was molded and fired at 950''C for 10 hours, a single-phase garnet sintered body with a density of 99.9% was obtained.

Next, the obtained sintered body was processed to have a thickness of 5 mm, a width of 10 plates, and a length of 10 mm, and then a seed crystal of the same composition was joined and heated to 1000°C. As a result, the seed crystal became larger than 5 mm. We were able to confirm that it is possible to grow Matsu crystals using the solid phase reaction method.

Mix bismuth nitrate, iron nitrate, yttrium nitrate, and gallium nitrate to make B11YzFeiGa10+z approximately 600
Fifty-one aqueous solutions having a concentration of 1.5 g were prepared. Next, 70'C
The prepared mixed solution was added dropwise to the ammonia aqueous solution 101 kept warm over about 1 hour. During this time, stir the aqueous solution,
This ensured that the reaction occurred uniformly. After the dropwise addition was completed, heating and stirring were continued for about 2 hours to ripen the produced coprecipitate.

Next, the generated slurry was separated and washed, dried, and
When calcined at °C, bismuth-substituted yttrium gallium iron garnet with a garnetization rate of approximately 100% was obtained. When this powder was molded and fired at 960'C for 10 hours, a single-phase garnet sintered body with a density of 99.9% was obtained.

Next, the obtained sintered body was processed to have a thickness of 5 mm, a width of 10 mm, and a length of 10 mm, and then a seed crystal of the same composition was joined and heated to 1000°C. As a result, the seed crystal grew over 5 mm. It was confirmed that it is possible to grow single crystals using the solid phase reaction method.

This 1 Tsu 1 Mix bismuth chloride, iron nitrate, and indolium nitrate to make Y
About 600 g of an aqueous solution was mixed with JiFesO+ 2 for 5i.
! .

Prepared. Thereafter, the slurry was dried and calcined using the same steps as in Example 1.

In this calcination, almost no garnet formation occurred when calcination was performed at 800°C, and 95% garnet formation occurred during calcination at 950°C. When this powder was molded and fired at 1050°C, the density was 99.5%, and it was a sintered body containing a second phase (hematite phase) other than the garnet phase. When the composition of this sintered body was analyzed, it was clear that the old content was lower than that of the blended composition. Furthermore, it has been impossible to grow single crystals using solid phase reaction methods.

Mix bismuth oxide powder, ferric oxide powder, and yttrium oxide powder to make Y2BiFesO+2.
00g was weighed. 600 g of water was added to this and wet mixed in a ball mill for 2 hours. The obtained mixed slurry was dried and then calcined.

In this calcination, almost no garnetization occurred at 800"C, and 80% garnetization occurred at 1000"C.This powder was molded and heated at 1050C.
When fired, the density was 99.0%, and the sintered body contained a second phase (hematite phase) other than the garnet phase.

When the composition of this sintered body was analyzed, it was clear that the old content was lower than that of the blended composition. Furthermore, it has been impossible to grow single crystals using solid phase reaction methods.

The above results are summarized in Table 3 along with the range of the average particle diameter of the powders used.

Table 3 (Effects of the invention) As is clear from the above explanation, according to the methods for producing iron-based composite oxides of the first and second inventions, the coprecipitation method is selected depending on the desired garnet composition. Therefore, it is possible to form garnet by low-temperature calcination, and it is possible to obtain garnet-type ferrite powder with good moldability and sinterability.

Translucent iron garnet polycrystals prepared from the obtained garnet I-type ferrite powder or iron garnet single crystals grown by the solid phase reaction method are suitable as materials for optical isolators used in optical communications, etc. It can be used for.

Further, in both the first invention and the second invention, a homogeneous garnet type ferrite single crystal containing a seed element can be produced at low cost.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the particle size distribution of garnet type ferrite powder. h+diameter 011N)

Claims (1)

[Claims] Hydroxide is coprecipitated with a base from a mixed aqueous solution containing monovalent and divalent iron ions and other metal ions, a coprecipitate is synthesized while iron is oxidized to trivalent, and then a coprecipitate is synthesized, and then a coprecipitate is synthesized while iron is oxidized to trivalent. Separation and drying of sediment
A method for producing an iron-based composite oxide, characterized by further mixing, molding, and sintering the powder obtained by calcination. Using a mixed aqueous solution containing di- and trivalent iron nitrate and nitrates of other metals as a raw material, the metal salt mixed aqueous solution is dropped into an aqueous base solution to coprecipitate the hydroxide, and then the coprecipitate is A method for producing an iron-based composite oxide, characterized by further mixing, molding, and sintering the powder obtained by separation, drying, and calcination.