KR20070010777A - PREPARING METHOD FOR PLATEY alpha;- ALUMINA - Google Patents

Abstract

A process of fabricating alpha alumina platelet with desired aspect ratio of 50 to 500 is provided to the alumina platelet with neither twinning nor flocculation but with narrow particle distribution and favorable dispersion, thereby becoming raw material of various pigments, resin filler and/or polishing pad, etc. by furnace cooling hot mixture of alumina powder and other additives. The process includes the steps of: heating a mixture of alumina powder and other additives at elevational temperature rate of 180-1800deg.C/hr up to 800-950deg.C; leaving in-situ the heated material at the purposed temperature for 0.1 to 5 hours; re-heating the mixture at 300-600deg.C/hr up to 1000-1400deg.C; leaving in-situ the heated material at the purposed temperature for 1 to 10 hours; then furnace cooling the hot mixture, so that the alpha alumina platelet is obtained with average particle diameter of 10-50 micrometers, particle thickness of 0.1-0.8 micrometers and aspect ratio of 50-500. The process further includes a step of removing solvent with water at -110deg.C to room temperature after the furnace cooling step.

Description

       Preparation method of plate-shaped alpha alumina {Preparing Method for Platey α-Alumina}

       1A and 1B are scanning electron micrographs of the plate-shaped alpha alumina particles prepared in Example 1;

       2 is an X-ray diffraction peak diagram of the plate-shaped alpha alumina particles prepared in Example 1. FIG.

The present invention relates to a method for producing a plate-shaped alpha alumina suitable as a raw material for pearl pigments, cosmetic pigments, white pigments, resin fillers, polishing pads, etc. More specifically, there are no twins or agglomerates, no fine particles or fragments, and a narrow particle size. It is related with the method of manufacturing plate-like alpha-alumina which has distribution and is excellent in dispersibility efficiently.

In general, the plate-shaped alumina is characterized by a particle shape similar to a hexagonal tile, and the aspect ratio of the particle defined as the particle size divided by the particle thickness is about 10: 1 or more. This particle size is measured by standard measurement methods such as using a coulter multisizer counter.

       Typically, plate alumina is marketed by controlling and calcining alumina hydrates (e.g., P-25 alumina from Alcoa, or MNY alumina from Lonza). These plate aluminas, commonly known as "calcined alumina," are strongly fused together with small platelets. Since it contains a considerable amount of aggregates and is inferior in dispersibility, there is a high possibility of causing problems in spreadability, coating properties, or filling properties when used as a pigment or resin filler such as cosmetics or paints, and undesired scratching may occur during wrapping. There is great concern.

       As a conventional method for solving the problems of the conventional plate-shaped alumina, Japanese Patent Publication No. 35-6977 proposes a method of adding a mineralizer such as aluminum fluoride as a heat treatment step for the raw material, and also a Japanese patent Bulletin 37-7750 proposes a hydrothermal synthesis method. However, according to these production methods, not only the particle size of the plate-shaped alumina particles produced is difficult to control, but there is a problem in that the thickness reduction of the plate-shaped particles is particularly difficult.

       Accordingly, an object of the present invention is to provide an effective method for producing a plate-shaped alpha alumina, which is free from twins, agglomerates, fine particles or fragments, has a narrow particle size distribution and is excellent in dispersibility.

       According to one preferred aspect of the present invention for smoothly achieving the above object of the present invention, in the method for producing a plate-shaped alumina by the fluxing method, the temperature is 700 to 950 ° C at a temperature increase rate of 180 to 1800 ° C / hr. It is heated to up to 0.1 ~ 5 hours, then reheated up to 1000 ~ 1400 ℃ at a heating rate of 30 ~ 600 ℃ / hr, and then maintained for 1 ~ 10 hours, and then cooled to room temperature. A method for producing a plate-shaped alpha alumina having an average particle diameter of 10 to 50 µm, a particle thickness of 0.1 to 0.8 µm, and an aspect ratio of 50 to 500 is provided.

       According to another preferred aspect of the present invention for smoothly achieving the above object of the present invention, in the first to second aspects described above, following the furnace cooling described above, the flux is removed with water at room temperature to 110 ° C. Provided is a method for producing a plate-like alpha alumina.

       According to another preferred aspect of the present invention for smoothly achieving the above object of the present invention, in the first to second aspects described above, a post treatment consisting of a classification treatment and an acid treatment is performed following the removal of the flux. There is provided a method for producing a plate-like alpha alumina to be performed further.

Referring to the manufacturing method according to the present invention, first, after pulverizing an aluminum salt such as aluminum hydroxide or aluminum sulfate, or a transition alumina obtained by heat treatment, fluorine compounds such as NaF or AlF ₃ and NaPF ₆ Phosphorus compounds such as Na ₂ SiF ₆ Or as MgSiF ₆ and 6H ₂ silicon compound such as O, or K ₂ TiF ₆ or Na ₂ TiF _6, such as titanium fluoride and K ₂ ZrF ₆ or the transition metal fluoride, or MgF _2, such as zirconium fluoride, such as Na ₂ ZrF ₆ Such as magnesium fluoride, or calcium fluoride of CaF ₂ or CaSO ₄ 1 / 2H ₂ O, and a mixture of Na ₂ SO ₄ (forget) or Na ₂ SO ₄ (forget) and K ₂ SO ₄ as flux and dry or wet After pulverizing to adjust the particle size, the pulverized mixture is placed in an alumina crucible and sealed, heated to a temperature of 700 to 950 ° C. at a heating rate of 180 to 1800 ° C./hr, and then maintained for 0.1 to 5 hours. After reheating to 1000 ~ 1400 ° C. at a temperature raising rate of / hr, and holding for 1 to 10 hours, after cooling to room temperature, dissolving the flux or the like with water, and then subjecting the obtained powder to acid treatment and drying. Grading, classifying and pulverizing, twinning and agglomeration, fine particle and no particle fragments 10-50㎛, particle thickness 0. Make plate-shaped alumina with 1-0.8 μm and aspect ratio 50-500.

       The production of plate-shaped alpha alumina by the flux method is performed by the nucleation of alpha alumina when the transition alumina or aluminum salt is dissolved and precipitated in the flux around 800 to 900 ° C., and the nucleus is grown.

       At this time, various additives are added to dissolve the transition alumina or aluminum salt in the flux, and representative ones of these are fluorine compounds.

       On the other hand, depending on the type of additives, the characteristics of anisotropic growth change when the nucleus grows, and the materials that promote such anisotropic growth include phosphorus (P), silicon (Si), transition metal (Ti), and the like. Magnesium (Mg), calcium (Ca), etc. are mentioned as a substance to inhibit. Therefore, the addition of a compound consisting of P, Si, or transition metal and a compound composed of Mg or Ca ions facilitates the production of plate-shaped alpha-alumina with controlled shape.

       In the production of plate-shaped alpha alumina by the fluxing method according to the present invention, nuclei of alpha alumina are generated when the transition alumina is dissolved in the flux around 800 to 900 ° C. and precipitated, and the growth of the nucleus is performed. At this time, by controlling the rate of melting the transition alumina, the rate of nucleation and the rate of nuclear growth, it is possible to produce a plate-like alpha-alumina particles having better dispersibility.

       However, since the vapor pressure of the fluoride as an additive is very high, the evaporation of fluoride is minimized until around 700 ~ 950 ° C., which is the temperature at which transition alumina or aluminum salt is transferred to alpha alumina, while nucleation occurs with a uniform distribution in this temperature range. If the nuclear growth is continued, the plate-shaped alumina with less twins or aggregates and fewer fine particles or fragments can be effectively produced.

       Therefore, it is necessary to minimize the evaporation of fluoride by raising the temperature as fast as possible to 700 ~ 950 ℃, the transition temperature of the transition alumina or aluminum salt to alpha alumina, so the temperature increase rate is 180 ~ 1800 ℃ / hr, generally 180 ~ 1200 ℃ / hr, preferably 300 ~ 1200 ℃ / hr, more preferably 300 ~ 900 ℃ / hr, most preferably 600 ~ 900 ℃ / hr heated to 800 ~ 950 ℃ then 0.1 ~ 5 Time, preferably 0.1 to 3 hours, more preferably 0.5 to 2 hours, most preferably 0.5 to 1 hour to homogeneously distribute the nucleation, and then again the temperature increase rate 30 ~ 600 ℃ / hr, preferably 60 to 400 ° C./hr, more preferably 90 to 300 ° C./hr, most preferably 90 to 200 ° C./hr, reheat to 1000 to 1400 ° C., and then reach this temperature for 1 to 10 hours, Preferably after 1 to 8 hours, more preferably 1 to 5 hours, most preferably 1 to 3 hours, And furnace cooling to come.

       In the production method of the present invention, the amount of NaF added is 0.0001 to 2 mol, preferably 0.0001 to 1 mol, more preferably 0.0001 to 0.7 mol, most preferably 0.0001 to 0.5 with respect to 1 mol (mol) of aluminum salt or transition alumina. is added in an amount of mol.

       On the other hand, the addition amount of the anhydrous aluminum sulfate is 0.0001 to 0.1 mol, preferably 0.0001 to 0.05 mol, more preferably 0.0001 to 0.01 mol, most preferably 0.01 to 0.001 mol with respect to 1 mol (mol) of aluminum salt or transition alumina Is added in the amount of.

AlF ₃ is added in an amount of 0.0001 to 1 mol, preferably 0.0001 to 0.5 mol, more preferably 0.0001 to 0.3 mol, and most preferably 0.01 to 0.1 mol relative to 1 mol of aluminum salt or transition alumina. do.

In addition, the addition amount of the fluoride and the phosphorus ion represented by KPF ₆ or NaPF ₆ is 0.0001 to 0.3 mol, preferably 0.0001 to 0.1 mol, more preferably 0.0001 to 0.05 with respect to 1 mol (mol) of aluminum salt or transition alumina. mol, most preferably in an amount of 0.0001 to 0.01 mol.

When adding silicon fluorides and silicon ions represented by Na ₂ SiF ₆ or MgSiF ₆ .6H ₂ O as optional additives, the addition amount is 0.0001 to 0.1 mol, preferably 1 mol (mol) of aluminum salt or transition alumina. Is 0.0001 to 0.03 mol, more preferably 0.0001 to 0.01 mol, and most preferably 0.0001 to 0.005 mol.

When titanium fluoride and titanium ions represented by K ₂ TiF ₆ or Na ₂ TiF ₆ as optional additives are added, the amount is 0.0001 to 0.3 mol, preferably 0.0001 to 1 mol of aluminum salt or transition alumina. 0.1 mol, more preferably 0.000 to 0.05 mol, most preferably 0.0001 to 0.03 mol.

When magnesium ions represented by MgF ₂ as optional additives are added, the added amount is 0.0001 to 0.2 mol, preferably 0.0001 to 0.1 mol, more preferably 0.0001 to 1 mol (mol) of aluminum salt or transition alumina. 0.05 mol, most preferably 0.0001 to 0.02 mol.

When CaF ₂ and CaSO ₄ 1 / 2H ₂ O representative calcium ions are added as optional additives, the added amount is 0.0001 to 1.0 mol, preferably 0.0001 to 0.7 with respect to 1 mol (mol) of aluminum salt or transition alumina. mol, more preferably 0.0001 to 0.5 mol, most preferably 0.0001 to 0.2 mol.

When optional zirconium fluorides and zirconium ions represented by K ₂ ZrF ₆ or Na ₂ ZrF ₆ as optional additives are added, the amount is 0.0001 to 0.5 mol, preferably 0.0001 to 1 mol (mol) of aluminum salt or transition alumina. 0.2 mol, more preferably 0.0001 to 0.1 mol, most preferably 0.0001 to 0.05 mol.

In order to remove the heat-treated sample to effectively remove the flux (Na ₂ SO ₄ ) through the washing process, room temperature ~ 110 ℃, preferably 30 ~ 80 ℃, more preferably 30 ~ 60 ℃, most preferably per 100 g of the sample Put 1L of water at 35 ~ 50 ℃ to remove the flux while stirring the water with a stirrer.

       After drying the filtered sample, the plate-shaped alumina was removed by using an air flow classifier to remove the aggregated particles, and then pulverized with a plate mill or the like and classified again using an air flow classifier, followed by acid treatment and washing with water. Thus, the plate-shaped alumina according to the present invention without twins and agglomeration, fine particles or fragments can be produced.

       Hereinafter, the present invention will be described in more detail with reference to Examples, which are intended to illustrate the present invention but are not intended to limit the present invention.

Example 1

       First, aluminum hydroxide was heat-treated at 700 ° C. for 2 hours to convert to transition alumina.

700 millimeters of 5mm alumina balls, 50g converted transition alumina, 500g sodium sulfate, 0.89g KPF ₆ , Na00 9.00g, AlF ₃ 1.94g, MgSiF ₆ 0.73 g of 6H ₂ O and 0.67 g of MgF ₂ were added and dry pulverized for 48 hours. After grinding, the ball was removed, the mixture was placed in an alumina crucible, and the lid was covered. Then, the mixture was heat-treated at 1200 ° C. for 2 hours, and then cooled. The heat-treated sample was removed from sodium sulfate with 50 ° C. water, and then dried at 90 ° C. for 1 hour with 1 mol hydrochloric acid solution. After treatment, the product was washed with water several times and filtered and dried.

       When the resulting plate alumina particles were examined by X-ray diffraction, only the detected diffraction peaks were alpha alumina. In the observation by SEM, the particles were plate-shaped bodies, and the particle size was 10 to 50 µm and 0.1 to 0.7 µm in thickness (see FIGS. 1A and 1B and 2).

       Beautiful streamline was observed when the obtained plate-shaped alpha alumina was suspended and stirred in water.

Example 2

       First, aluminum hydroxide was heat-treated at 700 ° C. for 2 hours to convert to transition alumina.

In a 1 liter ball mill, 700 mm diameter alumina balls 700 g, converted transition alumina 50 g, sodium sulfate 500 g, KPF ₆ 0.89 g, NaF 9.00 g, AlF ₃ 1.94 g, Na ₂ SiF ₆ 0.51 g, CaF ₂ 0.85 g, CaSO ₄ 4.88 g of 1 / 2H ₂ O was added and dry pulverized for 48 hours. After grinding, the ball was removed, the mixture was placed in an alumina crucible, and the lid was covered. Then, the mixture was heat-treated at 1200 ° C. for 2 hours, and then cooled. The heat-treated sample was washed with water to remove sodium sulfate and the like. 5 hours, washed several times, and dried by filtration. When the resulting alumina particles were examined by X-ray diffraction, only the detected diffraction peaks were alpha alumina. In the observation by SEM, the particles were plate-shaped bodies, and the particle size was 10 to 50 µm and 0.1 to 0.7 µm in thickness.

       Streamline was observed when the obtained plate-shaped alpha-alumina was suspended and stirred in water.

Example 3

       First, aluminum hydroxide was heat-treated at 700 ° C. for 2 hours to convert to transition alumina.

1mm ball mill, 700mm diameter alumina ball 700g, aluminum hydroxide 75g, sodium sulfate 500g, KPF ₆ 0.89g, NaF 9.00g, AlF ₃ 1.94g, MgSiF ₆ 6H ₂ O 0.73 g and 0.67 g of MgF ₂ were added and dry pulverized for 48 hours. After grinding, the ball is removed, the mixture is placed in an alumina crucible, and the lid is covered. Then, the mixture is heat-treated at 1200 ° C. for 2 hours, and then cooled. The heat-treated sample is washed with water to remove sodium sulfate and the like. After 5 hours treatment with water washed several times and dried by filtration.

       When the resulting alumina particles were examined by X-ray diffraction, only the detected diffraction peaks were alpha alumina. In the observation by SEM, the particles were plate-shaped bodies, and the particle size was 10 to 40 µm and 0.1 to 0.7 µm in thickness.

       Mammary gland was observed when this platelet alpha alumina was suspended and stirred in water.

Example 4

       First, aluminum hydroxide was heat-treated at 700 ° C. for 2 hours to convert to transition alumina.

700 liters of 5mm alumina balls, 50g converted transition alumina, 500g sodium sulfate, 0.45g KF ₆ , NaF 5.94g, AlF ₃ 1.94g, K ₂ TiF ₆ 2.08g, MgF ₂ 0.25g, MgSiF ₆ 6H ₂ O 0.24 g was added and pulverized dry for 48 hours. After grinding, the ball is removed, the mixture is placed in an alumina crucible, and the lid is covered. After the heat treatment at 1200 ° C. for 2 hours, the furnace is cooled and then cooled. The heat-treated sample is washed with water to remove sodium sulfate and the like. After treatment for 5 hours, the product was washed several times and filtered and dried.

       When the resulting alumina particles were examined by X-ray diffraction, only the detected diffraction peaks were alpha alumina. In the observation by SEM, the particle was a plate-like body, and the particle size was 10 to 50 µm and 0.1 to 0.7 µm in thickness.

       Streamline was observed when the obtained plate-shaped alpha alumina was suspended and stirred in water.

Example 5

       First, aluminum hydroxide was heat-treated at 700 ° C. for 2 hours to convert to transition alumina.

700 g of 5mm alumina balls, 50 g of converted transition alumina, sodium sulfate 500 g, KPF ₆ 0.89 g, NaF 9.00 g, AlF ₃ 1.94 g, K ₂ ZrF ₆ 1.35 g, CaF ₂ 0.85 g, CaSO ₄ 4.88 g of 1 / 2H ₂ O was added and dry pulverized for 48 hours. After grinding, the ball was removed, the mixture was placed in an alumina crucible, covered with a lid, and then heat-treated at 1200 ° C. for 2 hours. The furnace was then cooled, and the heat-treated sample was added to 5 L of water, stirred to remove sodium sulfate, and the like. The solution was treated with hydrochloric acid for 5 hours, washed several times, and filtered and dried.

       When the resulting alumina particles were examined by X-ray diffraction, only the detected diffraction peaks were alpha alumina. In the observation by SEM, the particles were plate-shaped bodies, and the particle sizes were 20 to 40 µm and 0.2 to 0.7 µm in thickness.

       Streamline was observed when the obtained plate-shaped alpha alumina was suspended and stirred in water.

Example 6

       First, aluminum hydroxide was heat-treated at 700 ° C. for 2 hours to convert to transition alumina.

700g 5mm alumina ball, converted transition alumina 50g, 0.5g anhydrous aluminum sulfate, sodium sulfate 500g, KPF ₆ 0.89g, NaF 7.00g, AlF ₃ 1.94g, Na ₂ SiF ₆ 0.67g, CaF ₂ 0.85 g and 4.88 g of CaSO ₄ 1 / 2H ₂ O were added thereto, followed by dry grinding for 48 hours. After grinding, the ball is removed, the mixture is placed in an alumina crucible, and the lid is covered, and then heat-treated at 1200 ° C. for 2 hours, and then cooled. The heat-treated sample is placed in 5 L of water and stirred to remove sodium sulfate, and then at 1 ° C. at 90 ° C. The mixture was treated with molar hydrochloric acid solution for 5 hours, washed several times, and filtered and dried.

       When the resulting alumina particles were examined by X-ray diffraction, only the detected diffraction peaks were alpha alumina. In the observation by SEM, the particle was a plate-shaped body, the particle size was 20 ~ 35㎛, thickness 0.2 ~ 0.7㎛.

       Streamline was observed when the obtained plate-shaped alpha-alumina was suspended and stirred in water.

Example 7

       1kg of plate-shaped alpha alumina prepared in Example 1 was classified using an air flow classifier ([Wonjin TECH WJTS ~ 015], 2500 ~ 5000 cycles / minute rotation speed, blower pressure 0.3 ~ 0.7 atmosphere, channel air) Pressure 1.5 ~ 2.5 atmosphere, nozzle pressure 1.5 ~ 2.5 atmosphere), pulverize using wheel mill and reclassify the pulverized product with air classifier (2500 ~ 5000 cycles / minute rotation speed, blower pressure 0.3 ~ 0.7 atm, channel air pressure 1.5-2.5 atm, nozzle pressure 1.5-2.5 atm), and then retreated with aqua regia to remove contaminants. When the obtained plate-shaped alumina particles were examined by X-ray diffraction, only the detected diffraction peaks were alpha alumina. Moreover, as a result of observation by SEM, it turned out that it was plate-shaped particle | grains without twins or aggregation. The resulting particle size was 10 to 30 µm and the thickness was 0.1 to 0.7 µm.

       Mammary gland was observed when the resulting plate-shaped alumina was suspended in water and stirred.

       As described above, the plate-shaped alumina prepared according to the production method of the present invention is pure plate-shaped alumina, which is free from twins, aggregates, fine particles or fragments, has a narrow particle size distribution, and the resulting plate-shaped particles have a particle size of 10 to 50 μm, Its thickness ranges from 0.1 to 0.8 µm and its aspect ratio is 50 to 500, which results in a beautiful streamline when suspended and agitated in water. Therefore, it is suitable as a raw material for pearl pigments, cosmetic pigments, white pigments, resin fillers and polishing pads due to its excellent dispersibility. Can be used.

Claims (12)

        In the manufacturing method of the plate-shaped alumina by the fluxing method,         After heating to 800 ~ 950 ℃ at a heating rate of 180 ~ 1800 ℃ / hr, and maintained for 0.1 ~ 5 hours, and reheated to 1000 ~ 1400 at a temperature rising rate of 30 ~ 600 ℃ / hr, and then maintained for 1 to 10 hours, Next, consisting of furnace cooling to room temperature,         A method for producing a plate-shaped alpha alumina having an average particle diameter of 10 to 50 µm, a particle thickness of 0.1 to 0.8 µm, and an aspect ratio of 50 to 500.         The method for producing a plate-shaped alpha alumina according to claim 1, wherein the flux is removed with water at room temperature to 110 ° C following the furnace cooling.         The method for producing a plate-shaped alpha alumina according to claim 2, further comprising a post treatment consisting of a classification treatment and an acid treatment subsequent to the removal of the flux.        The method for producing a plate-shaped alpha alumina according to any one of claims 1 to 3, wherein the amount of anhydrous aluminum sulfate added is added in an amount of 0.0001 to 0.1 mole with respect to 1 mole of aluminum hydroxide or transition alumina.        The method for producing a plate-shaped alpha alumina according to any one of claims 1 to 3, wherein NaF is added in an amount of 0.0001 to 2 moles with respect to 1 mole of aluminum salt or transition alumina. The method for producing a plate-shaped alpha alumina according to any one of claims 1 to ₃ , wherein AlF ₃ is added in an amount of 0.0001 to 1 mole with respect to 1 mole of aluminum salt or transition alumina. The method for producing a plate-shaped alpha alumina according to any one of claims 1 to 3, wherein the fluoride or phosphorus ion of KPF ₆ or NaPF ₆ is added in an amount of 0.0001 to 0.3 moles with respect to 1 mole of aluminum salt or transition alumina. . The method of claim 1, wherein Na ₂ SiF ₆ or MgSiF _6. ㆍ A method for producing a plate-shaped alpha alumina in which silicon fluoride or silicon ions of 6H ₂ O are added in an amount of 0.0001 to 0.1 mole with respect to 1 mole of aluminum salt or transition alumina. The titanium fluoride or titanium ion represented by any one of claims 1 to 3, which is represented by K ₂ TiF ₆ or Na ₂ TiF ₆ , is added in an amount of 0.0001 to 0.3 mol based on 1 mol of aluminum salt or transition alumina. Method for producing plate-shaped alpha alumina. The method for producing a plate-shaped alpha alumina according to any one of claims 1 to 3, wherein magnesium ions of MgF ₂ are added in an amount of 0.0001 to 0.2 mol relative to 1 mol of an aluminum salt or transition alumina. The plate-shaped alpha-alumina according to any one of claims 1 to 3, wherein calcium ions of CaF ₂ or CaSO ₄ 1 / 2H ₂ O are added in an amount of 0.0001 to 1.0 mole with respect to 1 mole of aluminum salt or transition alumina. Manufacturing method. The plate-like alpha according to any one of claims 1 to 3, wherein zirconium fluoride and zirconium ions of K ₂ ZrF ₆ or Na ₂ ZrF ₆ are added in an amount of 0.0001 to 0.5 moles with respect to 1 mole of aluminum salt or transition alumina. Method for producing alumina.

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