JP4601497B2 - Spherical alumina powder, production method and use thereof - Google Patents

Description

  The present invention relates to spherical alumina powder, a method for producing the same, and use thereof.

One application of inorganic powders such as alumina powder is a thermal spray material. For thinning the coating, it is preferable that the thermal spray material has a small particle size. However, the smaller the particle size, the more pulsation occurs when the thermal spray material is carried in and out of the thermal spraying device and the like. Since it becomes difficult, there is a problem that the variation in the thickness of the film becomes large. In order to solve this, there is a proposal to treat the thermal spray material with a fatty acid compound such as stearic acid (Patent Document 1), but there is a problem that the purity remains due to remaining in the coating film.
JP 2002-332559 A

  An object of the present invention is to provide a spherical alumina powder finer than before and an easy production method thereof. Another object is to provide a fine and highly fluid inorganic powder containing spherical alumina powder, which is particularly suitable as a thermal spray material.

The present invention provides an alumina powder having an average particle size of 3 to 40 μm and an average particle size of 0.02 to 0.5 μm and an average particle size (μm) adhered to the surface at an adhesion rate of 30% or more (including 100%). ) × specific surface area (m ² / g) is an alumina powder made of spherical alumina powder having a value of 1.2 to 3.0.

Moreover, this invention is a thermal spray material which consists of an alumina powder as described above .

Further, the present invention supplies a slurry containing metal aluminum powder to a flame using a spray gas containing 0.5 to 2.5 times the amount of oxygen of the theoretical combustion oxygen amount of the metal aluminum powder, Produced by supplying oxygen outside the flame supplied from the outer peripheral part of the metal at a ratio larger than the amount of oxygen contained in the atomized gas and not more than 9 times the theoretical combustion oxygen amount of the metal aluminum powder. A spherical alumina powder having an average particle size of 0.02 to 0.5 μm and an average particle size (μm) × specific surface area (m ² / g) of 1.2 to 3.0 is obtained. This is a method for producing alumina powder mixed and adhered to 40 μm alumina powder.

In this case, the average particle size is 0.02 to 0.5 μm and the average particle size (μm) × specific surface area (m ² / G) is a method for producing a spherical alumina powder having a value of 1.2 to 3.0, the sum of the amount of oxygen contained in the spray gas and the amount of oxygen outside the flame is based on the theoretical combustion oxygen amount of the metal aluminum powder. It is preferably 2 to 8 times.

  According to the present invention, an unprecedented fine spherical alumina powder having an average particle size of 0.02 to 0.5 μm and an easy production method thereof are provided. Further, according to the present invention, there are provided a fine and highly fluid inorganic powder containing the spherical alumina powder of the present invention, and a thermal spray material comprising the inorganic powder.

  The spherical alumina powder of the present invention (hereinafter referred to as “spherical alumina ultrafine powder”) has an average particle size of 0.02 to 0.5 μm. When the average particle size is larger than 0.5 μm, it is not easy to adhere to the surface of the ceramic powder when mixed with a ceramic powder other than the spherical alumina ultrafine powder (hereinafter simply referred to as “ceramic powder”). Moreover, even if it adheres, the improvement effect of fluidity | liquidity will become scarce. On the other hand, if the average particle size is smaller than 0.02 μm, the powders are agglomerated so that uniform mixing with the ceramic powder becomes difficult.

In the spherical fine alumina powder, the average particle size (μm) × specific surface area (m ² / g) value (hereinafter, this value is referred to as “existence index of ultrafine particles”) is 1.2 to 3. In the case of 0.0, the effect of improving the fluidity is further enhanced. The existence index of the ultrafine particles can be controlled by adjusting the amount of oxygen used when producing the spherical alumina ultrafine powder.

The term “spherical” as used in the present invention means that the average sphericity measured below is 0.80 or more. The average sphericity is preferably 0.9 or more, particularly preferably 0.92 or more. That is, when a projected area (A) and a perimeter (PM) from an SEM photograph of powder are measured and the area of a perfect circle with respect to the perimeter (PM) is (B), a perfect circle having the same circumference is assumed. Then, since PM = 2πr and B = πr ² , B = π × (PM / 2π) ² , and the sphericity of the particle is calculated as sphericity = A / B = A × 4π / (PM) ^2. Is done. The sphericity is measured for 100 particles, and the average value is taken as the average sphericity of the powder.

  The average particle diameter can be measured by a laser diffraction light scattering method (an example of a measuring apparatus: “Model LS-230” (manufactured by Beckman Coulter)). The sample was prepared by using water as a dispersion medium and dispersing the sample for 1 minute with a homogenizer (output: 200 W). Measurement conditions are PIDS (Polarization Intensity Differential Scattering) concentration of 45 to 55%, refractive index of water 1.33, and sample value of literature (1.73 for alumina).

  Further, the specific surface area value is a one-point bed method, and can be measured by, for example, a product name “Macsorb HM Model 1208” manufactured by Mountec.

  The method for producing the spherical alumina ultrafine powder is a method in which a slurry containing metal aluminum powder is supplied to a flame by a spray gas to oxidize the metal aluminum powder. .5 to 2.5 times the amount of oxygen-containing gas, and the amount of oxygen outside the flame supplied from the outer periphery of the flame is larger than the amount of oxygen contained in the atomized gas, and the theoretical combustion oxygen of the metal aluminum powder It is characterized in that it is supplied at a ratio of 9 times the amount or less. In particular, the total amount of oxygen contained in the spray gas and the amount of oxygen outside the flame is preferably 2 to 8 times the theoretical combustion oxygen amount of the metal aluminum powder.

  As an apparatus, what consists of a furnace and the collection apparatus connected to this furnace is preferable, and the example is shown in Unexamined-Japanese-Patent No. 2001-335313. More specifically, the furnace may be either a vertical furnace or a horizontal furnace, but is preferably a vertical furnace. The furnace is composed of a melting zone for converting metal aluminum into an oxide and spheroidizing the oxide into a molten or semi-molten state, and a cooling zone for cooling and solidifying the spheroidized particles.

  Although the melting zone is formed by a flame, the oxidation energy of the metal aluminum powder is further used in the present invention. In the cooling zone, the spheroidized particles are cooled to a temperature at which the operation in the collecting device is easy. Cooling is performed by natural cooling or forced cooling. In the case of natural cooling, the cooling zone is designed to be long enough for the spheroidized particles to stay during the time to reach that temperature. The forced cooling is performed by supplying a cooling gas such as air between the cooling zone and the collector. In the collection device, for example, at least one collector such as a heavy sedimentation chamber, a cyclone, or a bag filter is installed.

  The slurry supply port is attached to one of the furnaces. In the case of a vertical furnace, it is usually attached to the upper surface of the furnace. It is preferable that a fuel burner for forming a melting zone (flame) is provided on the upper surface of the furnace, and a slurry supply port is provided at the center of the burner.

  The concentration of the slurry is preferably 75% by mass or less from the viewpoint of dispersibility of the metal aluminum powder in the furnace. The lower limit is not limited, but the production volume decreases in proportion to the decrease in the concentration. Therefore, the slurry is preferably a high concentration slurry, and a dispersant such as a polycarboxylic acid type polymer anion can be used therefor. As the dispersion medium, water, alcohol such as methanol, petroleum, and the like can be used.

  The average particle size of the metal aluminum powder is preferably 1 to 50 μm. When it is larger than 50 μm, there is a possibility that inconveniences such as sedimentation in the slurry and inability to burn remain. On the other hand, if it is smaller than 1 μm, it is difficult to adjust the high-concentration slurry. For mixing the metal aluminum powder and the dispersion medium, it is preferable to use a stirrer having a high-speed rotation (for example, trade name “DESPA” manufactured by Asada Tekko Co., Ltd.) so that the metal aluminum powder does not settle.

  The slurry is supplied by a spray gas containing oxygen in an amount of 0.5 to 2.5 times the theoretical combustion oxygen amount of the metal aluminum powder. For this purpose, a method is generally used in which slurry is supplied to an injection nozzle by a mechanical means such as a piston and sprayed into the furnace from the injection nozzle using an atomizing gas. As the spray nozzle, a two-fluid nozzle is preferable because it is dispersed by fine droplets. If the oxygen amount of the atomizing gas is less than 0.5 times the amount of combustion oxygen of the metal aluminum powder, the metal aluminum powder may not be able to react sufficiently, and if it is more than 2.5 times, the metal aluminum powder In any case, it is difficult to obtain an average particle size of the spherical alumina ultrafine powder.

  The number of slurry supply ports can be one or more, but it is preferable to divide the supply ports into two to five supply ports rather than one wide supply port. . In the case of division, it is preferable to collect them as a single supply port rather than separating the supply ports of each slurry.

The “theoretical combustion oxygen amount” in the present invention is a theoretical oxygen amount necessary for the metal aluminum powder supplied into the furnace to become alumina, and an oxygen amount of 0.622 Nm ³ per 1 kg of metal aluminum. That is.

  The flame can be formed by a combination of a flammable gas such as propane gas, butane gas, or hydrogen and oxygen, air, or the like for auxiliary combustion. What is important in the present invention is that oxygen outside the flame supplied from the outer periphery of the flame is supplied in a larger amount than the amount of oxygen contained in the spray gas. Preferably, 2.6 to 9 times as much oxygen as the theoretical combustion oxygen amount is supplied, and in particular, the total of the oxygen amount contained in the spray gas and the oxygen amount outside the flame is the theoretical combustion of the metal aluminum powder. It is 9 times or less, especially 2 to 8 times the amount of oxygen. Thereby, the grain growth of the produced alumina powder can be suppressed, so that the existence index of the ultrafine particles can be within the target range.

  The inorganic powder of the present invention is a fine and highly fluid powder composed of spherical alumina ultrafine powder and ceramic powder. Examples of the ceramic powder include oxide ceramics such as alumina, amorphous silica, and crystalline silica, nitride ceramics such as aluminum nitride, silicon nitride, and boron nitride, and carbide ceramics such as silicon carbide and titanium carbide. Among these, alumina powder other than the spherical alumina ultrafine powder, particularly spherical alumina powder is preferable. The average particle size of the ceramic powder is preferably 3 to 40 μm, and is preferably spherical.

  The ratio between the spherical alumina ultrafine powder and the ceramic powder is preferably determined by the average particle size and specific surface area of the ceramic powder. For example, when the ceramic powder is a spherical alumina powder having an average particle diameter of 3 to 20 μm and the average particle diameter of the spherical alumina ultrafine powder is 0.1 to 0.3 μm, the ceramic powder is spherical with respect to 100 parts by mass of the ceramic powder. Alumina ultrafine powder is 1 to 30 parts by mass. According to such an inorganic powder of the present invention, the fluidity is remarkably improved.

  Further, the ceramic powder is preferably in a state in which the spherical alumina ultrafine powder adheres to the particle surface. It is preferable that the adhesion rate of the particles including the spherical alumina ultrafine powder adhered to the surface of the ceramic powder is 30% or more (including 100%). The content of ceramic particles to which such spherical alumina ultrafine powder is adhered is preferably 80% or more (including 100%). By these, the fluidity | liquidity of the inorganic powder of this invention improves further significantly.

  The adhesion rate is determined by observing the particle image with an SEM, and measuring the area (A) of the adhered particles and the area (B) of the non-adhered portion of the ceramic particles for one ceramic particle. ) = 100 × A / (A + B). This is measured for 50 particles, and the average value is taken as the adhesion rate. Moreover, the content rate of the ceramic particles to which the spherical alumina ultrafine powder adhered was determined by measuring the number of ceramic particles to which the spherical alumina ultrafine powder adhered for 50 particles, and calculating the ratio in the 50 particles. Can be sought.

  The reason for the improvement in fluidity of the inorganic powder of the present invention is that the spherical alumina ultrafine powder that has entered the gap between the ceramic powder promotes the rolling of the inorganic powder, and the spherical alumina ultrafine powder is present on the ceramic particle surface. It is believed that the adhesion is related to a decrease in adhesion energy to the outside (Van der Waals force, liquid crosslinking force, etc.).

  The quality of the fluidity of the inorganic powder can be determined by measuring the angle of repose. High fluidity as used in the field of this invention is an angle of repose of 55 degrees or less. A preferred angle of repose is 50 degrees or less. The angle of repose can be measured, for example, with a powder tester “PT-E type” manufactured by Hosokawa Micron.

  The inorganic powder of the present invention can be produced by mixing the spherical alumina ultrafine powder of the present invention and a ceramic powder. As the mixing device, for example, a known mixing device such as a stirrer or an air blender is sufficient. The amount of adhesion can be adjusted by the operating time of the mixing device.

  Since the inorganic powder of the present invention has high fluidity, it is suitable as a thermal spray material. This is particularly suitable when an alumina thin film is formed on a small part such as an electronic part by plasma spraying. Until now, in order to inject a certain amount without spraying a pulsation, the material having an average particle size of 40 μm or more was the limit, so that sufficient thinning could not be achieved. On the other hand, since the thermal spray material of the present invention does not cause pulsation even when the maximum particle size is 55 μm or less and the average particle size is 5 μm or less, finer powder can be sprayed than before, and the film thickness can be further reduced.

A burner including a nozzle installation pipe, a combustible gas supply unit, and an auxiliary combustion gas (oxygen) supply unit was installed on the upper surface of a vertical furnace (diameter 700 mm × height 5000 mm). The burner has a cylindrical shape with a diameter of 150 mm, and is provided with a nozzle installation pipe into which the nozzle can be inserted at the center of the nozzle. Product name “BNH-160S”) was inserted. Further, a spray gas supply line for slurry dispersion is connected to the two-fluid nozzle. A flammable gas and auxiliary combustion gas (oxygen) supply unit is provided on the outer periphery of the nozzle installation pipe, supplying 5 Nm ³ of LPG gas per hour as a flammable gas and 25 Nm ³ of oxygen per hour as a auxiliary gas, A flame was formed. Furthermore, a slit of 20 mm was provided in a circumferential portion 250 mm away from the center on the upper surface of the vertical furnace to serve as a supply port for oxygen outside the flame. The produced spherical alumina ultrafine powder was sucked and transported from the lower part of the vertical furnace to the collection system by a blower and collected by a bag filter.

Examples 1-6 Comparative Examples 1-4
Production of Spherical Alumina Ultra Fine Powder A slurry composed of 60 parts by mass of metal aluminum (average particle size 15 μm) and 40 parts by mass of ion-exchanged water was supplied into a flame from a two-fluid nozzle. Using a commercially available liquid feed pump, the liquid was fed to the two-fluid nozzle and sprayed into the furnace using oxygen as a spray gas. The production conditions are shown in Table 1, and the characteristics of the collected spherical alumina ultrafine powder are shown in Table 2. In addition, powder G of Table 2 is a commercially available non-spherical alumina powder (trade name “AL-45-1”, average particle diameter of 2 μm, manufactured by Showa Denko KK).

Preparation of inorganic powders Two types of commercially available spherical alumina powders (trade name “DAW-05” manufactured by Denki Kagaku Kogyo Co., Ltd., average particle diameter of 5 μm) 45 μm) were passed through a mesh of 55 μm openings to obtain ceramic powder (H) (average particle size 5 μm) and ceramic powder (I) (average particle size 20 μm), respectively. Were mixed at a ratio shown in Table 3 and mixed for 20 minutes with a mixer (trade name “Double Cone Blender” manufactured by Deoksugaku Kosakusho) to prepare an inorganic powder.

Example 7
An inorganic powder was produced in the same manner as in Example 1 except that the mixing time was 40 minutes.

  In the obtained inorganic powder, the adhesion rate of particles containing the spherical alumina ultrafine powder and the content rate of the adhered ceramic particles were measured according to the above, and the angle of repose was measured in order to evaluate the fluidity. The results are shown in Table 3. As a result, the inorganic powder to which the spherical alumina ultrafine powder was added had a repose angle lower than that of the comparative example, and was extremely fluid. As a result, it was shown that the inorganic powder of the present invention is suitable as a thermal spray material.

  The spherical alumina powder of the present invention can be used as a thermal spray material or a material for adjusting various resin / rubber fillers. In addition, the inorganic powder of the present invention has features such as good fluidity in the transport pipe and hardly bridging in the tank, so it can be used as a thermal spray material and a filler for various resins and rubbers. it can.

Claims (4)

Alumina powder having an average particle size of 3 to 40 μm and an average particle size of 0.02 to 0.5 μm and an average particle size (μm) × specific surface area attached to the surface with an adhesion rate of 30% or more (including 100%) (M ² / G) alumina powder composed of spherical alumina powder having a value of 1.2 to 3.0. A thermal spray material comprising the alumina powder according to claim 1 . A slurry containing metal aluminum powder is supplied to the flame using a spray gas containing 0.5 to 2.5 times the amount of oxygen of the theoretical combustion oxygen amount of the metal aluminum powder, and supplied from the outer periphery of the flame. flame out oxygen, the average particle diameter of the spray large amounts also than the oxygen content in the gas, moreover, prepared by and supplying in the ratio of 9 times or less relative to the theoretical combustion oxygen content of metallic aluminum powder Is a spherical alumina powder having a mean particle size (μm) × specific surface area (m ² / g) of 1.2 to 3.0, and an alumina powder having an average particle size of 3 to 40 μm. The method for producing an alumina powder according to claim 1, wherein the alumina powder is mixed and adhered. A method for producing spherical alumina powder having an average particle size of 0.02 to 0.5 μm and an average particle size (μm) × specific surface area (m ² / g) of 1.2 to 3.0 is included in the spray gas. The method for producing an alumina powder according to claim 3 , wherein the total amount of oxygen and oxygen outside the flame is 2 to 8 times the theoretical combustion oxygen amount of the metal aluminum powder .