CN1743269A - Method for preparing alpha-aluminium oxide powder - Google Patents

Abstract

The invention provides a method for preparing α-alumina powder. The method for preparing α-alumina powder comprises the following steps: (1) in the presence of a pulverizing agent, pulverize a metal compound having a main peak half-width (Ho) in an XRD pattern to obtain a metal compound having a main peak half-width (H ) in an XRD pattern ), (2) mixing the resulting seed crystals with an aluminum salt, (3) calcining said mixture, and wherein the ratio of H/Ho is 1.06 or more.

Description

Method for preparing α-alumina powder

technical field

The present invention relates to a method for preparing α-alumina powder having a high α-ratio and a large BET specific surface area.

Background technique

α-alumina is an oxide of aluminum represented by the formula Al ₂ O ₃ and has a corundum structure, and is widely used as a raw material for preparing a sintered body such as a translucent tube.

In view of improving the strength of the sintered body, α-alumina used as a raw material is required to have a high α-ratio and a large BET specific surface area.

Contents of the invention

Summary of the invention

The present inventors have studied a method for producing α-alumina powder, resulting in the completion of the present invention.

That is, the present invention provides a method for preparing α-alumina powder, the method comprising the following steps:

(1) In the presence of a pulverizing agent, pulverize a metal compound having a half-width (hereinafter referred to as "FWHM") (Ho) of the main peak in an X-ray diffraction (hereinafter referred to as "XRD") figure, to obtain a metal compound in the XRD figure There is the seed crystal of the FWHM(H) of the main peak in (2) the seed crystal obtained is mixed with aluminum salt,

(3) calcining said mixture, and

Wherein the ratio of H/Ho is 1.06 or more.

Description of drawings

Figure 1 shows the method for calculating the FWHM Ho of the metal compound and the FWHM H of the seed crystal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The method for preparing α-alumina powder of the present invention comprises: crushing a metal compound of FWHM (Ho) having a main peak in an XRD pattern to obtain a seed crystal of FWHM (H) having a main peak in an XRD pattern (1).

The metal compound can advantageously promote the phase transformation of the aluminum compound into α-alumina in calcination described later. Examples of metal compounds include metal oxides such as α-alumina (Al ₂ O ₃ ), α-iron oxide (Fe ₂ O ₃ ), and α-chromium oxide (Cr ₂ O ₃ ); metal hydroxides such as diaspore (AlOOH), preferably a metal oxide, more preferably α-alumina.

Pulverization is carried out in the presence of a pulverizing agent.

Pulverizing agents can effectively facilitate pulverization. Examples of pulverizing agents include alcohols such as ethanol, propanol; glycols such as ethylene glycol (molecular weight [mw]: 62, boiling point [bp]: 197.2°C), polyethylene glycol, propylene glycol ( mw: 76, bp: 187.4°C), polypropylene glycol (in the case of dipropylene glycol, mw: 134, bp: 231.8°C), 1,3-butanediol (mw: 90, bp: 207.5°C) and 1,4-butanediol (mw: 90, bp: 235°C); amines such as triethanolamine; fatty acids such as palmitic acid, stearic acid and oleic acid; metal alkoxides such as aluminum alkoxides; carbon materials such as carbon black and graphite. Preference is given to diols, more preferably diols having a MW of 50 to 300 and a boiling point of 150° C. to 300° C., further preferably polypropylene glycol. The pulverizing agents may be used alone or in combination of two or more of them. Based on 100 parts by weight of the metal compound, the amount of the pulverizer is usually about 0.01 parts by weight or more, preferably about 0.5 parts by weight or more, more preferably about 0.75 parts by weight or more, and usually about 10 parts by weight or less, It is preferably about 5 parts by weight or less, more preferably about 2 parts by weight or less.

When carried out in the presence of water, pulverization can also be carried out in the presence of a dispersant or a surfactant. Examples of dispersants include acids such as nitric acid, hydrochloric acid, sulfuric acid, acetic acid and oxalic acid; alcohols such as methanol, ethanol, isopropanol; aluminum salts such as aluminum nitrate, aluminum chloride, aluminum oxalate and aluminum acetate. Examples of surfactants include anionic surfactants, cationic surfactants, nonionic surfactants and amphoteric surfactants.

Comminution can be performed by batch or continuous methods. Pulverization can be advantageously carried out, for example, by using pulverizers such as ball mills, vibration mills, planetary mills, pin mills, intermediate agitation mills and jet mills. In pulverization, it is preferable to reduce pollution, and for this reason, it is recommended to use alumina, preferably alumina with a purity of 99% by weight or more, as a raw material for components that come into contact with aluminum compounds, such as pulverization media, containers, nozzles and liners.

In addition, the seed crystals obtained by pulverization may be classified. By classification, 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more of coarse particles (eg, particles with a particle diameter of about 1 μm or more) can be removed from the seed crystals.

The average primary particle diameter of the seed crystals obtained in the above method is usually about 0.01 μm or more, preferably about 0.05 μm or more, and usually about 0.5 μm or less. The seed crystal has a BET specific surface area of usually about 12 m ² /g or more, preferably 15 m ² /g or more, and usually about 150 m ² /g or less.

The pulverization is carried out under conditions where the metal compound having FWHM of Ho is changed to a metal compound having FWHM of H, wherein the ratio of H to Ho is about 1.06 or more, preferably about 1.08 or more, and usually about 5 or less, preferably is about 4 or less, more preferably about 3 or less. The ratio of H/Ho indicates the degree of pulverization, which is calculated from the main peak between 45 degrees and 70 degrees in the XRD pattern measured before pulverization and the FWHM(H) of the main peak in the XRD pattern measured after pulverization, as shown in Figure 1 shown.

When the metal compound is α-alumina and the X-ray source is a CuKα beam, the ratio expressed by H/Ho can be obtained from the alumina (116) Calculated from the FWHM(Ho) of the diffraction peak and the FWHM(H) of the alumina (116) diffraction peak in the pulverized XRD pattern.

As for α-iron oxide (Fe ₂ O ₃ ), α-chromium oxide (Cr ₂ O ₃ ) or diaspore (AlOOH), its main peak between 45° and 70°, usually the (116) peak, is Observed in the vicinity of the (116) peak of α-alumina in an XRD pattern measured using a CuKα beam as an X-ray source.

The method of the present invention also includes the step (2) of mixing the obtained seed crystals with an aluminum salt.

The aluminum salt may be a compound converted into α-alumina by calcination described later, and examples thereof include inorganic aluminum salts such as aluminum nitrate, aluminum sulfate, aluminum ammonium sulfate, and ammonium aluminum carbonate hydroxide (ammonium aluminum carbonate hydroxide ); or organic aluminum salts, such as aluminum oxalate, aluminum acetate, aluminum stearate, aluminum lactate and aluminum laurate, preferably inorganic salts of aluminum, more preferably aluminum nitrate.

The mixing in step (2) is performed by using a ball mill, a container with a stirrer, or the like.

The mixing can be advantageously performed, for example, by a method in which an aluminum salt is added to a solvent to obtain a solution or slurry, seed crystals are added thereto, and the solvent is then removed. Through the above mixing, an aluminum salt is obtained in which the seed crystals are uniformly dispersed.

In mixing, seeds may be dispersed in a solvent before addition to the above-mentioned solution or slurry, and then, the solvent may be removed.

In addition, mixing can also be carried out by a method in which seed crystals are added to the aluminum salt and the mixture is stirred. Agitation can be advantageously performed by using equipment such as vertical mills and Henschel mixers. In this mixing, it is possible to disperse a seed crystal in a solvent before adding to the above-mentioned aluminum salt, and then, remove the solvent.

Based on 100 parts by weight of the total amount of the seed crystal and the aluminum salt, the amount of the seed crystal is usually about 1 part by weight or more, preferably about 2 parts by weight or more, more preferably about 4 parts by weight or more, and usually about 50 parts by weight or less, preferably 40 parts by weight or less, more preferably 30 parts by weight or less.

The resulting mixture can also be dried. Drying can be performed by using a freeze dryer, a vacuum dryer, etc. at a temperature of usually about 100°C or below.

The method of the present invention also comprises the step (3) of calcining the mixture obtained above.

Calcination can advantageously be carried out using equipment such as electric tube furnaces, electric chamber furnaces, tunnel furnaces, far-infrared furnaces, microwave ovens, shaft furnaces, reverberatory furnaces, rotary furnaces and roller hearth furnaces. Calcination can be performed batchwise or continuously. It can be done statically or fluidly.

The calcination temperature is not lower than the temperature at which the aluminum compound is converted to α-alumina, usually 600°C or above, preferably about 700°C or above, and usually about 1000°C or below, preferably about 950°C or below. The calcination time is usually 10 minutes or longer, preferably about 30 minutes or longer, and usually about 24 hours or shorter, preferably 10 hours or shorter.

Calcination is usually performed under air or inert gases such as _N2 and Ar. Calcination can also be carried out in air with a controlled water vapor partial pressure, for example, air with a water vapor partial pressure of 600 Pa or below.

The obtained α-alumina powder may be pulverized. Pulverization can be performed by using, for example, an intermediate pulverizer such as a vibration mill and a ball mill, or an air mill such as a jet mill. In addition, α-alumina powder can be classified.

The average particle diameter of the α-alumina powder obtained by the method of the present invention is usually about 0.01 μm or more, preferably about 0.05 μm or more, and usually about 1 μm or less, preferably about 0.1 μm or less, and the α-ratio is about 90% or more, preferably about 95% or more, and the BET specific surface area is about 8 m ² /g or more, preferably 13 m ² /g or more, more preferably about 15 m ² /g or more, and about 100 m ² /g or less, preferably about 50 m ² /g or less, more preferably about 30 m ² /g or less.

α-alumina has a high α-ratio and a large BET specific surface area as described above, and therefore, this powder can be used as a raw material for producing an α-alumina sintered body having high strength. The obtained α-alumina sintered body is suitable as members requiring high strength, such as cutting tools, bioceramics, low-resistance routing pattern ceramics (for example, alumina ceramics having copper patterns thereon) and bulletproof panels. The α-alumina sintered body is used to produce components of semiconductor devices such as wafer handlers; electronic components such as oxygen sensors; translucent tubes such as sodium lamps and metal halide lamps; or ceramics due to chemical stability such as excellent corrosion resistance filter. Ceramic filters are used to remove solid components contained in exhaust gases, to filter aluminum melts, to filter beverages such as beer, or to selectively permeate gases from petroleum processing or CO, CO ₂ , N ₂ , O ₂ , H ₂ gases . The α-alumina powder can be used as a sintering agent for ceramics such as thermally conductive ceramics (for example, AlN), YAG, and phosphors.

In addition, α-alumina powder can be used as an additive of toner or resin filler to improve magnetic head cleaning performance and friction resistance by adding it to the coating layer of application-type magnetic media. In addition, α-alumina powder can also be used as an additive for cosmetics or brake pads.

In addition, α-alumina powder can be used as a polishing material. For example, a slurry obtained by dispersing α-alumina powder in a medium such as water can be suitably used for polishing of semiconductor CMP and polishing of hard disk substrates. The polishing tape obtained by coating α-alumina particles on the surface of the tape is suitable for precise polishing of hard disks and magnetic heads.

Detailed ways

Example

The present invention is described in more detail by the following examples, which should not be construed as limiting the scope of the present invention.

The properties of α-alumina and seeds were evaluated as follows.

(1) α-ratio

It is calculated according to the following formula (i) by using the peak intensity I _25.6 at 2θ=25.6° and the peak intensity I ₄₆ at 2θ=46°, said peak intensity I _25.6 corresponding to that of α-alumina (012) Peak intensity, and the peak intensity I ₄₆ corresponds to the peak intensity of alumina except α-alumina, and the peak intensity comes from the diffraction spectrum measured under the following conditions by using a powder X-ray diffractometer: Radiation source: CuKα beam, 40kV×20mA, monochromator: graphite,

α-ratio=I _25.6 /(I _25.6 +I ₄₆ )×100(%) (i)

(2) BET specific surface area

It is measured by a nitrogen adsorption method by using a specific surface area analyzer (trade name "FLOWSORB II 2300", manufactured by SHTMADZU CORPORATION).

(3) Average diameter of primary particles

From the transmission electron micrograph of the α-alumina powder, the maximum diameter along the constant direction of each primary particle of any 20 or more particles was measured, and the average value of the measured values was calculated.

(4) Grinding degree

The XRD spectra of the seed crystals (α-alumina) before and after pulverization were measured by an X-ray diffractometer. The half-widths of phase (116), i.e. HO(116) (front) and H(116) (back), were obtained from the XRD spectrum, and then calculated by equation (ii):

Grinding degree = H(116)/HO(116) (ii)

Example 1

[Preparation of metal compound (α-alumina)]

Aluminum hydroxide is obtained by hydrolysis of aluminum isopropoxide, followed by pre-calcination to obtain transition alumina, in which the main crystal phase is theta phase and contains 3% by weight of alpha phase; the transition alumina is pulverized by jet mill to obtain bulk density It is a powder of 0.21g/cm ³ .

The obtained powder was calcined by a furnace filled with air (partial pressure of water vapor: 165Pa) with a dew point of -15°C under the following conditions:

Mode: continuous feeding and unloading,

Average retention time: 3 hours,

Maximum temperature: 1170°C,

Then, α-alumina having a half width of HO ₍₁₁₆₎ and a BET specific surface area of 14 m ³ /g was obtained.

[Grinding of α-alumina]

100 parts by weight of α-alumina and 1 part by weight of propylene glycol as a crushing agent are packed into a vibratory mill, and the α-alumina powder is pulverized under the following conditions:

Media: Aluminum oxide beads with a diameter of 15mm

Retention time: 12 hours,

Thus, a seed crystal having a half width of H _{(116 )} , a BET specific surface area of 16.6 m ³ /g, and an average particle diameter of 0.1 μm was obtained. In this example, the degree of pulverization of H ₍₁₁₆₎ /HO ₍₁₁₆₎ was 1.1.

[Preparation of seed slurry]

In 80 parts by weight of a 0.0001 mol/L aluminum nitrate aqueous solution, 20 parts by weight of seed crystals were dispersed to obtain a slurry. The slurry and alumina beads with a diameter of 2 mm were loaded into a ball mill and stirred. The contents of the ball mill were taken out, and the alumina beads were removed by filtration, thus obtaining a seed crystal slurry.

[mixture of seed and aluminum salt]

375.13 g (1 mole) of aluminum nitrate nonahydrate (Al(NO ₃ ) ₃ 9H ₂ O) (manufactured by Kansai Catalyst Co., Ltd., reagent grade, appearance: powder) was dissolved in water to obtain 1000 ^cm of aluminum nitrate solution. 2.83 g of the above seed crystals (0.566 g as Al ₂ O ₃ ) were added to 100 cm ³ of aluminum nitrate solution to obtain a mixture. Then, water was evaporated from the mixture by using a reduced-pressure drier at 75°C to obtain a powder. For every 100 parts by weight of powder, the amount of seed crystals was 10 parts by weight in terms of Al ₂ O ₃ .

[calcination]

2.8 g of powder was charged into an alumina crucible, and the alumina crucible was placed in a box-type electric furnace at 25°C. In air, the powder was heated to 850° C. at a heating rate of 300° C./hour, and then calcined at 950° C. for 3 hours to obtain α-alumina powder. The α-ratio of the α-alumina powder was 95%, the specific surface area was 15.9 m ² /g and the average primary particle diameter was 96 nm.

Claims (11)

1. method for preparing alpha-alumina powder, this method may further comprise the steps:

(1) in the presence of disintegrator, pulverize metallic compound with main peak half-width (Ho) in XRD figure, obtaining having the crystal seed of main peak half-width (H) in XRD figure,

(2) crystal seed that obtains is mixed with aluminium salt,

(3) calcine described mixture and

Wherein the ratio of H/Ho be 1.06 or more than.

2. according to the process of claim 1 wherein that described metallic compound is to be selected from least a in metal oxide and the metal hydroxides.

3. according to the method for claim 2, wherein said metallic compound is to be selected from α-Al ₂O ₃, α-Fe ₂O ₃And α-Cr ₂O ₃At least a with in the diaspore.

According to the process of claim 1 wherein the ratio of H/Ho be 5 or below.

5. according to the process of claim 1 wherein that described disintegrator is to be selected from least a in alcohol, dibasic alcohol, amine, lipid acid, metal alkoxide and the carbon material.

6. according to the process of claim 1 wherein that described disintegrator is to be selected from 1,2 ethylene glycol, polyoxyethylene glycol, propylene glycol, polypropylene glycol, 1,3 butylene glycol and 1, at least a in the 4-butyleneglycol.

7. according to the process of claim 1 wherein that described aluminium salt is inorganic aluminate.

8. according to the method for claim 7, wherein said inorganic aluminate is an aluminum nitrate.

9. according to the process of claim 1 wherein that the BEF specific surface area that obtains crystal seed is 12m ²/ g or more than.

10. according to the total amount that the process of claim 1 wherein based on the crystal seed and the aluminium salt of 100 weight parts, the amount that obtains crystal seed is 1 to 50 weight part.

11. according to the process of claim 1 wherein that calcining is 600 ℃ or above carrying out.

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