阅读说明：本技术 尖晶石粉末 (Spinel powder ) 是由 大崎善久 于 2020-03-06 设计创作，主要内容包括：该尖晶石粉末的纯度为99.95wt%以上。该尖晶石粉末以氧化物换算所表示的Mg以及Al的含量为MgO：9wt%以上78wt%以下、Al-(2)O-(3)：22wt%以上91wt%以下。该尖晶石粉末的制备方法包括：将纯度为99.95wt%以上的镁源和纯度为99.95wt%以上的铝源混合和从而得到混合粉末的混合工序；将该混合粉末粉碎从而得到前驱体的粉碎工序；和将该前驱体在1500℃以下的温度下烧成的烧成工序。(The spinel powder has a purity of 99.95wt% or more. The spinel powder has a content of Mg and Al expressed in terms of oxides as MgO: 9 to 78wt% of Al 2 O 3 : 22wt% or more and 91wt% or less. The preparation method of the spinel powder comprises the following steps: a mixing step of mixing a magnesium source having a purity of 99.95wt% or more and an aluminum source having a purity of 99.95wt% or more to obtain a mixed powder; a pulverization step of pulverizing the mixed powder to obtain a precursor; and a firing step of firing the precursor at a temperature of 1500 ℃ or lower.)

1. A spinel powder characterized in that,

the purity thereof is 99.95wt% or more, and the contents of Mg and Al expressed in terms of oxides are MgO: 9 to 78wt% of Al₂O₃: 22wt% or more and 91wt% or less.

2. The spinel powder of claim 1,

the purity of the product is more than 99.99 wt%.

3. Spinel powder according to claim 1 or 2,

the content of Ca is less than 30ppm and the content of Si is less than 30 ppm.

4. The spinel powder of any one of claims 1 to 3,

the total content of elements other than Mg, Al and O is less than 500 ppm.

5. The spinel powder of any one of claims 1 to 4,

the magnesium alloy is obtained by subjecting a magnesium source having a purity of 99.95wt% or more and an aluminum source having a purity of 99.95wt% or more to a solid-phase reaction at a reaction temperature of 1500 ℃ or lower.

6. A method of preparing spinel powder, comprising:

a mixing step of mixing a magnesium source having a purity of 99.95wt% or more and an aluminum source having a purity of 99.95wt% or more to obtain a mixed powder;

a pulverization step of pulverizing the mixed powder to obtain a precursor; and

and a firing step of firing the precursor at a temperature of 1500 ℃ or lower.

7. The production method according to claim 6,

the magnesium source and the aluminum source are powders composed of a plurality of particles, and the ratio D50 (1)/D50 (2) of a particle diameter D50 (1) in which the cumulative volume-based distribution of the magnesium source is 50% and a particle diameter D50 (2) in which the cumulative volume-based distribution of the aluminum source is 50% is 0.2 to 5.0.

8. The production method according to claim 6 or 7,

the pulverization step is performed by wet pulverization.

Technical Field

The present invention relates to a spinel powder. In particular, the present invention relates to a magnesium aluminate spinel powder.

Background

Chemical composition is expressed as MgAl₂O₄Magnesium aluminate spinel (MgO-Al)₂O₃Spinel, hereinafter referred to as "spinel") is used in various fields as a ceramic sintered body excellent in thermal stability and chemical stability. The ceramic sintered body using the spinel is used for applications such as an optical material, a heat-resistant container, an insulating material, a catalyst carrier, an adsorbent, a support, a coating material, and the like.

Generally, a ceramic sintered body using spinel is obtained by sintering spinel powder. It is known that trace elements contained in spinel powder affect the characteristics of a ceramic sintered body used for various applications.

Japanese patent publication (Kokai) No. 2018-501178 (patent document 1) discloses a composition comprising MgO, at least 0.1wt% of a dopant and Al₂O₃And a sintered ceramic constituting element having a total impurity content of less than 0.7 wt%. WO2015/140459 (patent document 2) proposes a magnesium aluminum oxide MgAl constructed from spinel₂O₄And/or MgO-MgAl₂O₄A matrix of eutectic mixture (matrix). More than 95.0% by weight of the fused particles represents Al₂O₃And chemical composition of MgO, CaO and ZrO₂The cumulative content of (B) is less than 4000 mass ppm.

WO2014/119177 (patent document 3) discloses a gas nozzle including a main body made of a spinel sintered body. The main component of the spinel sintered body comprises more than 90wt% and less than 99.9wt% of magnesium aluminate, and the sintering aid comprises more than 0.1wt% and less than 10wt% of Ca, Mg or Zr. WO2013/038916 (patent document 4) proposes that the contents of Zn and K are converted into ZnO and K, respectively₂The total content of the magnesium aluminate sintered body after O is more than 30ppm and less than 500 ppm. Patent document 4 describes that the contents of Si, Ca, and P are converted to SiO respectively₂CaO and P₂O₅The total amount of the latter is controlled to be 500ppm to 2500 ppm.

As disclosed in patent documents 1 to 4, when a desired characteristic is imparted or enhanced by a trace element, it is important not to contain other unnecessary elements as impurities. In addition, the impurities affect the thermal expansion rate of the ceramic sintered body. When the impurity content is large and the purity is low, the thermal expansion coefficient of the ceramic sintered body varies. Further, in the use of optical materials, there is a problem that absorption or dispersion of light due to impurities occurs to impair transparency. Therefore, spinel having a high purity is required for various applications.

Japanese patent laid-open publication No. 62-72556 (patent document 5) discloses a method for passing throughPre-sintering the coprecipitate obtained by alkoxide coprecipitation method to obtain high-purity MgAl with the purity of more than 99.9 percent₂O₄The technology of raw materials. In japanese patent application publication No. 2018-507156 (patent document 6), a technique for preparing magnesium aluminate spinel by adding an alumina dispersant with PH adjusted to an aqueous dispersant of a magnesium compound to obtain a slurry (slurry) and drying and calcining the slurry is proposed. Jp 2018 a-52747 (patent document 7) discloses a method for producing spinel powder containing magnesium oxide, which comprises a step of mixing magnesium source particles and aluminum source particles having a predetermined particle diameter, and then calcining the mixture at 900 to 1400 ℃.

Prior art documents:

patent documents:

patent document 1: japanese Kohyo publication 2018-501178

Patent document 2: WO2015/140459

Patent document 3: WO2014/119177

Patent document 4: WO2013/038916

Patent document 5: japanese laid-open patent publication No. 62-72556

Patent document 6: japanese Kokai publication No. 2018-507156

Patent document 7: japanese patent laid-open publication No. 2018-52747.

Disclosure of Invention

The problems to be solved by the invention are as follows:

the methods disclosed in patent documents 5 and 6 have problems that the operation is complicated and the particle size is difficult to control. In addition, the method of patent document 5 has a problem in terms of cost because an expensive alkoxide is used.

In the case of the solid phase method as in patent document 7, it is considered that the spinel obtained is highly purified by using high-purity magnesium source particles and high-purity aluminum source particles as raw materials. However, it is known that a trace element as an impurity in the solid phase method promotes MgAl caused by firing₂O₄And (4) generating. For example, when a raw material having a purity of 99.95wt% or more is used, the accelerating effect cannot be obtained, and thus it is difficult to sufficiently perform spinel at a firing temperature of about 900 to 1400 ℃. By passing at 1600 deg.CThe long-time firing at the above high temperature may progress to spinel, but not only the possibility of mixing impurities during firing is increased, but also the high-temperature firing may cause a problem of lowering of activity such as sinterability. Further, since the spinel after high-temperature firing is strongly sintered, it is necessary to strongly crush and pulverize the spinel to obtain a predetermined particle size, and there is a high possibility that impurities are mixed in the spinel. Further, the method is very disadvantageous in industrial aspects such as productivity, equipment, and energy cost, and has a problem in practical use.

According to the findings of the present inventors, the purity of the spinel powder for industrial use is almost 99.9%. In various applications, in order to make a ceramic sintered body using spinel more functional and have higher added value, it is necessary to further highly purify spinel powder as a raw material thereof.

The purpose of the present invention is to provide a spinel powder having high purity and free from deterioration in activity due to high-temperature firing, and a method for producing the same.

Means for solving the problems:

the present inventors have made extensive studies and found that the particle diameter of a magnesium source and an aluminum source can be controlled in a solid-phase reaction, and that the resulting product can be fired at a relatively low temperature even at a high purity, thereby completing the present invention.

That is, the spinel powder of the present invention has a purity of 99.95wt% or more. The spinel powder has a content of Mg and Al expressed in terms of oxides as MgO: 9 to 78wt% of Al₂O₃: 22wt% or more and 91wt% or less.

Preferably, the spinel powder has a purity of 99.99wt% or more.

Preferably, the spinel powder has a Ca content of less than 30ppm and a Si content of less than 30 ppm. Preferably, the spinel powder has a total content of elements other than Mg, Al and O of less than 500 ppm.

Preferably, the spinel powder is formed by subjecting a magnesium source having a purity of 99.95wt% or more and an aluminum source having a purity of 99.95wt% or more to a solid-phase reaction at a reaction temperature of 1500 ℃ or less.

Furthermore, the invention relates to a method for the preparation of the spinel powder. The preparation method comprises the following steps:

(1) a mixing step of mixing a magnesium source having a purity of 99.95wt% or more and an aluminum source having a purity of 99.95wt% or more to obtain a mixed powder;

(2) a pulverization step of pulverizing the mixed powder to obtain a precursor; and

(3) a firing step of firing the precursor at a temperature of 1500 ℃ or lower.

Preferably, the magnesium source and the aluminum source are each a powder composed of a plurality of particles. The ratio D50 (1)/D50 (2) of a particle diameter D50 (1) in which the volume-based cumulative distribution of the magnesium source is 50% to a particle diameter D50 (2) in which the volume-based cumulative distribution of the aluminum source is 50% is 0.2 to 5.0.

Preferably, the pulverization step is carried out by wet pulverization.

The invention has the following effects:

the spinel powder of the present invention has a purity of 99.95wt% or more. The spinel powder is obtained by a method in which a magnesium source and an aluminum source are mixed and then fired at a temperature of 1500 ℃ or lower. The spinel powder is free from a reduction in activity due to high-temperature firing and has a sufficiently small content of impurity elements, and therefore, is suitable for various applications requiring high purity.

Further, as described in the background art, spinel powder of about 99.9wt% has been conventionally used. However, in the art to which the present invention pertains, not only are the numerical differences between the purity 99.9wt% (3N) and the purity 99.95wt% (3N 5), but also the technical levels thereof are greatly different. The invention overcomes the technical difficulty.

Detailed Description

The present invention will be described in detail below based on preferred embodiments, but the present invention is not limited to the embodiments below, and various modifications can be made within the scope shown in the claims. In the present specification, "X to Y" indicating a range means "X to Y. Unless otherwise noted, "%" and "ppm" mean "wt%", respectively.

In the present specification, "spinel" means having MgAl₂O₄The magnesium aluminate spinel of chemical composition is MgO-Al₂O₃A two-component compound of (a). The spinel powder of the present invention is not a mixture in which a magnesium oxide matrix and an aluminum oxide matrix are separated, such as a simple mixture of magnesium oxide and aluminum oxide, but is formed wholly or partially as an oxide in which magnesium and aluminum are combined, and has a composition with higher uniformity.

The spinel powder of the present invention has a purity of 99.95wt% or more, preferably 99.99wt% or more. Here, the purity means a value obtained by subtracting the impurity content contained in the spinel powder from 100%.

The spinel powder having a purity of 99.95wt% or more has a sufficiently smaller content of elements other than Mg, Al, and O, i.e., impurities, than conventional spinel powders. The spinel powder reduces variations in the coefficient of thermal expansion of the ceramic sintered body obtained. Further, by using the spinel powder, a ceramic sintered body having high transparency can be obtained. The spinel powder is suitable for various applications requiring a high purity of 99.95wt% or more.

The spinel powder of the present invention has a content of Mg and Al expressed in terms of oxides of MgO: 9 to 78wt%, Al₂O₃: 22wt% or more and 91wt% or less. The ceramic sintered body obtained by using the spinel powder within this range can be provided with various characteristics required for various applications. From this viewpoint, the content of Mg and Al is preferably MgO: 12wt% or more and 70wt% or less, Al₂O₃: 30wt% or more and 88wt% or less, more preferably, MgO: 14 to 61wt% of Al₂O₃: 39wt% or more and 86wt% or less. Preferably, the spinel powder has a stoichiometric ratio of Mg to Al of 9: 1-2: 8, in the above range. For example, when the spinel powder is used as a ceramic material, an increase in the proportion of Mg tends to increase the thermal expansion coefficient and decrease the spalling resistance. If the Mg ratio is decreased, the corrosion resistance may be decreased. Further, since the hardness of the spinel powder increases with an increase in the proportion of Al, the possibility of impurities being mixed during pulverization increases. The method for measuring the contents of Mg and Al will be described in the following examples.

The spinel powder may contain elements other than Mg, Al, and O within a range not to impair the effects of the present invention. Examples of the element other than Mg, Al, and O contained in the spinel powder include Ca, Si, Fe, Mn, Ni, Cu, Zn, and Na. P, S, B, Ti, Zr, Ba, etc. may be contained.

Preferably, the spinel powder has a Ca content of less than 30ppm and a Si content of less than 30 ppm. By reducing Si and Ca to an extremely small amount, the change in characteristics due to impurities becomes extremely small, and therefore, the characteristics of the spinel powder can be controlled more precisely. Thus, high functionality and high added value are achieved. From this viewpoint, the content of Ca is more preferably 25ppm or less, and still more preferably 20ppm or less. From the same viewpoint, the content of Si is more preferably 25ppm or less, and still more preferably 20ppm or less.

Preferably, the spinel powder has a total content of elements other than Mg, Al and O of less than 500 ppm. By making the total content of elements other than Mg, Al, and O within this range, a high purity of 99.95wt% or more is achieved. From this viewpoint, the total content of elements other than Mg, Al and O is more preferably 100ppm or less, and more preferably 70ppm or less. The total content is determined as the sum of the contents of the elements other than Mg, Al, and O. The kind of the "other elements" is not particularly limited, and elements other than Mg, Al, and O detected by the measurement method described in the following examples are used as the "other elements" for calculating the total content. Specific examples of the "other elements" include Ca, Si, Fe, Mn, Ni, Cu, Zn, Na, P, S, B, Ti, Zr, and Ba.

Preferably, the spinel powder is a product obtained by mixing a magnesium source having a purity of 99.95wt% or more and an aluminum source having a purity of 99.95wt% or more as raw materials and then performing a solid-phase reaction at a temperature of 1500 ℃ or less. The solid phase reaction at 1500 ℃ or lower suppresses the strong sintering of the spinel powder obtained. The spinel powder prevents impurities from being mixed due to strong crushing and pulverization after firing. Further, since the spinel powder is not subjected to an excessive high-temperature treatment, it can maintain the activity such as sinterability.

The method for producing the spinel powder of the present invention will be described in detail below.

The preparation method comprises a mixing process, a crushing process and a sintering process. The mixing step is a step of mixing a magnesium source having a purity of 99.95wt% or more and an aluminum source having a purity of 99.95wt% or more to obtain a mixed powder. The pulverization step is a step of pulverizing the mixed powder to obtain a precursor. The firing step is a step of firing the precursor at a temperature of 1500 ℃ or lower. The preparation method can also comprise a particle size adjusting procedure after the sintering procedure. The production method may further include other steps as long as the object of the present invention is achieved.

In the production method, the purity of the magnesium source used as the raw material is 99.95wt% or more. By using a magnesium source of this purity, a high degree of purification of the resulting spinel powder is achieved. From this viewpoint, the purity of the magnesium source is preferably 99.99wt% or more.

The kind of the magnesium source is not particularly limited as long as the effect of the present invention is not impaired. Specific examples of the magnesium source include magnesium hydroxide, magnesium oxide, magnesium carbonate, basic magnesium carbonate, magnesium nitrate, magnesium acetate, and magnesium sulfate. Magnesium hydroxide and magnesium oxide are preferred, and magnesium hydroxide is more preferred. The magnesium hydroxide becomes magnesium oxide with a high specific surface area during firing. By the presence of the high specific surface area magnesium oxide around the aluminum source, MgAl is promoted₂O₄The formation reaction of (2) realizes sufficient spinel formation in a relatively low firing temperature range.

The method for producing the magnesium source having a purity of 99.95wt% or more is not particularly limited. For example, as an example of a method for producing magnesium hydroxide having a purity of 99.95wt% or more, there is a method in which an alkaline aqueous solution such as ammonia, calcium hydroxide, or sodium hydroxide is added to an aqueous solution containing magnesium chloride to carry out a reaction, and then dried to obtain a magnesium hydroxide powder. The magnesium oxide powder obtained by calcining the magnesium hydroxide powder thus obtained and then pulverizing the calcined magnesium hydroxide powder to a desired particle size can be used as a magnesium source. For example, there is a method of obtaining a magnesium oxide powder by a gas phase method of burning and oxidizing magnesium metal.

The magnesium source is preferably a powder composed of a plurality of fine particles. The particle size of the magnesium source is preferably 0.1 μm or more and 1.0 μm or less in a particle size D50 (1) having a volume-based cumulative distribution of 50%. When the particle size of the magnesium source is within this range, the spinel powder obtained is free from matrix residues of magnesium oxide, and a spinel phase obtained by compounding magnesium oxide and aluminum oxide is sufficiently formed. From this viewpoint, the particle diameter D50 (1) at which the volume-based cumulative distribution of the magnesium source is 50% is more preferably 0.2 μm or more and 0.9 μm or less, and still more preferably 0.2 μm or more and 0.8 μm or less. The method for measuring the particle diameter D50 (1) in which the volume-based cumulative distribution of the magnesium source is 50% will be described in the following examples.

In the production method, the purity of the aluminum source used as a raw material is 99.95wt% or more. By using an aluminum source of this purity, a high degree of purification to obtain a spinel powder is achieved. From this viewpoint, the purity of the aluminum source is preferably 99.99wt% or more.

The kind of the aluminum source is not particularly limited as long as the effect of the present invention is not hindered. Specific examples of the aluminum source include aluminum hydroxide, aluminum oxide, aluminum carbonate, aluminum nitrate, aluminum acetate, and aluminum sulfate. A preferred aluminum source is alumina.

The method for producing the aluminum source having a purity of 99.95wt% or more is not particularly limited. For example, as an example of a method for producing aluminum hydroxide having a purity of 99.95wt% or more, there is a method in which bauxite is reacted with an aqueous sodium hydroxide solution under pressure and heat, the resulting aqueous solution is filtered to extract a sodium aluminate solution, and the sodium aluminate solution is cooled to obtain aluminum hydroxide. Further, alumina obtained by calcining the aluminum hydroxide thus obtained and then pulverizing the calcined aluminum hydroxide to a desired particle size can be used as an aluminum source.

The aluminum source is preferably a powder composed of a plurality of fine particles. The particle size of the aluminum source is preferably 0.1 μm or more and 1.0 μm or less in the particle size D50 (2) having a volume-based cumulative distribution of 50%. When the particle size of the magnesium source is within this range, the spinel powder obtained is sufficiently formed into a spinel phase in which magnesium oxide and aluminum oxide are combined, without leaving a matrix of aluminum oxide in the spinel powder. From this viewpoint, the particle diameter D50 (2) having a volume-based cumulative distribution of the aluminum source of 50% is more preferably 0.2 μm or more and 0.9 μm or less, and still more preferably 0.2 μm or more and 0.8 μm or less. The method of measuring the particle diameter D50 (2) having a cumulative volume-based distribution of aluminum sources of 50% will be described in the following examples.

Preferably, the ratio D50 (1)/D50 (2) of the particle diameter D50 (1) of the magnesium source and the particle diameter D50 (2) of the aluminum source is 0.2 to 5.0. By mixing the magnesium source and the aluminum source in the mixing step in which the ratio D50 (1)/D50 (2) is within this range, a mixed powder having a relatively uniform particle size distribution can be obtained. The particle size distribution of the precursor (pre-firing mixture) obtained by pulverizing the mixed powder was also uniform. In the precursor having a uniform particle size distribution, the reaction between the magnesium source and the aluminum source proceeds at a relatively low firing temperature, and the formation of the spinel phase is promoted. From this viewpoint, the ratio D50 (1)/D50 (2) is preferably 0.4 to 4.0, and particularly preferably 0.3 to 3.0.

The mixing ratio of the magnesium source and the aluminum source to be mixed in the mixing step may be adjusted so that the content (also referred to as a composition ratio) of Mg and Al in the spinel powder to be obtained falls within the above range. In this production method, the method for mixing the magnesium source and the aluminum source is not particularly limited, and a known mixing device can be appropriately selected and used. Specific examples thereof include a container rotary mixer such as a V-type mixer, a ribbon mixer, a Henschel mixer, a plow mixer (ploughhare mixer), a high-speed mixer, and a dry ball mill. Preferably as homogeneously as possible.

The mixed powder obtained in the mixing step is pulverized to a predetermined particle size in a pulverization step before firing. The formation of the spinel phase in a relatively low firing temperature range is further promoted by this pulverization step.

In this production method, the method for pulverizing the mixed powder is not particularly limited, and wet pulverization or dry pulverization may be employed. From the viewpoint of easily obtaining a more uniform particle size distribution, wet pulverization is preferred. In the case of wet pulverization, the mixed powder is pulverized in a state of being dispersed in a solvent. Examples of the solvent used include water and ethanol. Water and ethanol may also be mixed for use.

Examples of the pulverizing device used in the pulverizing step include a jaw crusher, a cone crusher, an impact crusher, a roller crusher, a chopper, a masher, a ring mill, a jet mill, a hammer mill, a pin mill, a ball mill, a vibration mill, a bead mill, a cyclone mill, and the like. The pulverization conditions are not particularly limited. The desired particle size distribution can be achieved by appropriately adjusting the pulverization time, the rotation speed, and the like according to the particle size of the mixed powder, the type of the pulverization device used, and the like.

In this production method, the pulverized mixed powder is supplied to a firing step as a precursor (pre-firing mixture). The particle size of the precursor to be used in the firing step is not particularly limited as long as the object of the present invention is achieved. From the viewpoint of promoting the recombination of magnesia and alumina at a relatively low firing temperature, the particle size of the precursor (D50) having a volume-based cumulative distribution of 50% is preferably 0.1 μm or more and 1.0 μm or less, more preferably 0.2 μm or more and 0.9 μm or less, and still more preferably 0.2 μm or more and 0.8 μm or less. The particle size of the precursor can be measured by the same method as that for the magnesium source and the aluminum source.

When the pulverization in the pulverization step is wet pulverization, a pulverized product slurry including the pulverized mixed powder and the solvent is obtained. The dried powder obtained by drying the slurry of the pulverized material and removing the solvent is supplied to the firing step as a precursor. The drying method of the pulverized slurry is not particularly limited, and a known dryer such as a vacuum dryer, a spray dryer, or a freeze dryer can be appropriately selected and used. The drying method is not particularly limited, and may be adjusted in accordance with the drying apparatus used, the characteristics of the pulverized slurry, and the like.

In this production method, the temperature at which the precursor is fired in the firing step is 1500 ℃ or lower. The spinel raw material obtained by compounding magnesia with alumina can be obtained by firing the precursor at a temperature of 1500 ℃ or lower. In addition, when the firing temperature is 1500 ℃ or lower, since strong sintering does not occur after firing, the possibility of inclusion of foreign matter accompanying the grinding operation is reduced. The firing temperature is preferably 1500 ℃ or less, more preferably 1470 ℃ or less, and still more preferably 1450 ℃ or less, from the viewpoint of achieving the desired high purity without causing deterioration in activity due to high-temperature firing. The firing temperature is preferably 1400 ℃ or higher from the viewpoint of the reaction efficiency for forming the spinel phase.

The firing time can be appropriately adjusted according to the firing temperature. For example, in the case where the temperature is 1450 ℃ to 1500 ℃, the firing time is preferably 1 hour to 12 hours, and in the case where the temperature is 1400 ℃ to 1450 ℃, the firing time is preferably 3 hours to 18 hours. By making the firing time in this range, the spinel phase is sufficiently formed, and strong sintering is avoided.

The firing of the precursor is usually carried out using a firing vessel. The type of firing vessel is not particularly limited, and a general alumina sagger, a magnesium oxide sagger, or the like can be used. Preferably, in the firing step, the top surface of the firing container into which the precursor is charged is covered with a cover. Thus, impurities can be prevented from being mixed from the outside during the firing process. The material of the firing vessel and the lid is preferably high-purity magnesium oxide having a purity of 99.99wt% or more. By making the material of the firing vessel and the lid high purity magnesium oxide, the transfer and mixing of impurities from the firing vessel and the lid are avoided, and higher purification of the obtained spinel powder is achieved.

The apparatus used for firing is not particularly limited as long as it can perform firing at 1500 ℃ or lower. Known firing furnaces such as a box furnace, a crucible furnace, a tube furnace, a tunnel furnace, a vacuum furnace, a hearth furnace, a resistance heating furnace, an induction heating furnace, and a direct electric furnace can be used.

The spinel powder can also be obtained by crushing or pulverizing the spinel raw material obtained in the firing step and adjusting the particle size and particle size distribution. As the crushing or pulverizing, for example, a jaw crusher, a gyratory crusher, a cone crusher, an impact crusher, a roll crusher, a chopper mill, a masher, a ring mill, a roll mill, a jet mill, a hammer mill, a roll mill, a vibration mill, a planetary mill, a ball mill, a cyclone mill or the like can be used.

The conditions for crushing or pulverizing are not particularly limited, and may be appropriately adjusted depending on the kind of the apparatus used, the composition and particle size of the precursor, the firing conditions, and the like. For example, the purity of the spinel powder is maintained by adjusting the number of revolutions, the processing time, and the like during crushing and pulverization to avoid the inclusion of impurities. Thereby, a high-purity spinel powder having a desired particle diameter and particle size distribution is obtained. For example, when the pulverization is carried out using a dry ball mill, the preferable pulverization time is 24 hours, and the preferable rotation speed is 80 rpm.

Example (b):

hereinafter, the effects of the present invention are illustrated by examples, but the present invention should not be construed restrictively based on the description of the examples. In the examples and comparative examples described below, the properties of various substances were measured by the following methods.

[ diameter of particle ]

The spinel powder was measured for a particle diameter (D10) having a volume-based cumulative distribution of 10%, a particle diameter (D50) having a volume-based cumulative distribution of 50%, and a particle diameter (D90) having a volume-based cumulative distribution of 90%, using a laser diffraction/scattering particle size distribution measuring instrument (product of japan electronics corporation, trade name "MT 3300"). The assay samples were prepared by the following method: each spinel powder was added to methanol, and then dispersed at 120W for 3 minutes by an ultrasonic homogenizer (manufactured by Nippon Seiko Co., Ltd., trade name "US-300T").

[ composition ratio of spinel powder ]

The composition of the spinel powder was analyzed by a micro glass bead milling method using a multi-element simultaneous X-ray fluorescence analyzer (product of Rigaku corporation, under the trade name "Simultix 12"). The contents of Al and Mg were calculated in terms of oxides, and MgO and Al were determined₂O ₃The composition ratio of (1).

[ purity of spinel powder and content of various elements ]

A solution in which the spinel powder was completely dissolved and diluted with ultrapure water was prepared as a measurement sample. The contents of the respective elements in the measurement sample were measured by an ICP emission spectrometer (manufactured by Hitachi High-Tech Science Corporation, Ltd., under the trade name "PS 3520 VDD"). The elements other than Mg and Al detected were Ca, Si, Fe, Mn, Ni, Cu, Zn, Na, P, S, B, Ti, Zr and Ba. The total content of these elements was determined as the total content (ppm). In addition, when the content is less than 1ppm (< 1), the total content is not taken into account because the content is below the detection limit. The purity (wt%) of the spinel powder was calculated by converting the total content to% and subtracting it from 100%.

[ purity of magnesium oxide and aluminum oxide ]

Magnesium oxide and aluminum oxide were measured using a multi-element simultaneous X-ray fluorescence analyzer (product of Rigaku corporation, under the trade name "Simultix 12"). The purity of magnesium oxide and aluminum oxide was determined by converting the total content (ppm) of the elements other than Mg, Al and O detected to% and subtracting it from 100%. The main elements other than Mg and Al detected were Ca, Si, Fe, Mn, Ni, Cu, and Zn.

[ example 1 ]

An aqueous magnesium chloride solution having a Mg ion concentration of 2.0mol/L and an aqueous sodium hydroxide solution having a Mg ion concentration of 2.7mol/L were transferred to a reaction tank by a metering pump, respectively, to carry out a continuous chemical combination reaction. The reaction rate of sodium hydroxide to magnesium chloride was controlled to 90 mol%. The resulting reaction slurry was recovered by overflowing from the reaction tank with a retention time of 30 minutes. This reaction slurry (magnesium hydroxide slurry) was filtered, washed, and dried to obtain a magnesium hydroxide dry powder. The purity of the obtained magnesium hydroxide dry powder was 99.99% or more, and the particle diameter (D50) at 50% volume-based cumulative distribution was 0.58. mu.m.

MgO in terms of the ratio of Mg to Al as an oxide: al (Al)₂O₃Is 1: the form 1 is a form in which a magnesium hydroxide powder having a purity of 99.99% or more and a particle diameter (D50) of 0.20 μm with a volume-based cumulative distribution of 50% is mixed with the magnesium hydroxide dry powder obtained by the above method, and then the mixture is thoroughly and uniformly mixed by a dry method, thereby obtaining a mixed powder of magnesium hydroxide and aluminum hydroxide.

Mixing the obtained mixed powder with a solvent (industrial ethanol) in a mass ratio of 1: 1 was charged into a pot mill (filling rate: 35%) and wet-pulverized by a ball mill (rotation speed: 80rpm/24 hours). Thereafter, the slurry of the content was recovered and sufficiently dried by an explosion-proof dryer, thereby obtaining a pre-firing mixture (precursor).

The pre-firing mixture was filled in a square alumina sagger, heated at 1400 ℃ for 3 hours, and then cooled to obtain a spinel raw material. Mixing the spinel raw material with a solvent (industrial ethanol) in a mass ratio of 1: mode 1 the mixture was charged into a pot mill (filling rate: 35%) and wet-milled by a ball mill (rotation speed: 80rpm/24 hours). Thereafter, the spinel powder of example 1 was obtained by recovering a slurry of the content and passing through a 500-mesh sieve, followed by drying with an explosion-proof drier. The composition ratio, particle size, and purity of the spinel powder of example 1 are shown in table 1 below. The contents and total contents of the respective elements in the spinel powder are shown in table 2 below.

[ COMPARATIVE EXAMPLE 1 ]

A spinel powder of comparative example 1 was obtained in the same manner as in example 1 except that an aluminum hydroxide powder having a purity of 99.99% or more and a volume-based cumulative distribution of 50% and a particle diameter (D50) of 8.3 μm was used. The composition ratio, particle size, and purity of the spinel powder of comparative example 1 are shown in table 1 below. The contents and total contents of the respective elements in the spinel powder are shown in table 2 below.

[ TABLE 1 ]

(Table 1)

。

[ TABLE 2 ]

(Table 2)

。

As shown in tables 1 and 2, in example 1, spinel powder having a purity of 99.95wt% or more and a very small impurity content was obtained. The contents of Ca and Si in the spinel powder are both less than 30 mm. On the other hand, in comparative example 1, the purity was less than 99.95wt%, and the contents of Ca and Si were each 30ppm or more. From the evaluation results, the superiority of the present invention is clear.

Industrial applicability:

the spinel powder described above is suitable for use in various fields requiring a high purity ceramic sintered body.