JPS604131B2 - Method for producing ultrafine aluminum oxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing ultrafine powdered aluminum oxide, and more particularly to a method for producing such powdered aluminum oxide starting from metallic aluminum.

Fine and uniformly sized (high purity) aluminum oxide powder has a wide range of uses, including as an abrasive, a constituent raw material for heat-resistant materials manufactured by powder metallurgy, a filler for various resins, and an addition to printing inks. Therefore, it is desired to easily obtain finer powder.

In particular, if the powder is amorphous, when it is used as a raw material for heat-resistant materials manufactured by powder metallurgy, chemical reactions occur at the powder interface with other components, resulting in better compatibility, resulting in higher filling rates and other applications. It is expected that the range will be extremely wide. Conventionally, high-purity aluminum oxide powder is produced by alkali neutralization of an aqueous solution of aluminum salts such as chlorides and nitrates, or precipitation from a supersaturated aqueous solution of sodium aluminate, or neutralization with an acid. Y-alumina powder obtained by heat treatment of Common.

However, these methods do not yield fine powders having a particle size of 0.5 mm or less. On the other hand, it is also known that fine 6- to y-alumina is produced when aluminum chloride vapor is brought into contact with oxygen or water vapor at a concentration of 1000 q0 or more.

Among these, the aluminum oxide powder obtained by contacting aluminum chloride vapor with oxygen has a particle size of 0.1 peak or more and has distinct crystal types of 6- and y-alumina. In addition, in the method of obtaining aluminum oxide powder by contacting with water vapor at high temperatures, hydrolysis occurs immediately when water vapor and aluminum chloride vapor come into contact, so pipes are likely to become clogged, making continuous production on an industrial scale impossible. In addition to being difficult, since water vapor and aluminum chloride vapor are not sufficiently mixed (until they come into contact with each other at high temperatures), high-temperature hydrolysis does not proceed uniformly, resulting in aluminum oxide powder with a particle size of 0.1 French or less. Although it also exists, it shows a wide particle distribution and is a mixture of amorphous and y-alumina. The present invention
The purpose is to obtain amorphous fine aluminum oxide powder with a uniform particle size and a particle size of 0.1 μm or less.

The present inventors noticed that the method of hydrolyzing aluminum chloride vapor at high temperature was the easiest to obtain the finest powder among conventional methods, and attempted to improve this method.

Aluminum chloride is extremely hygroscopic at room temperature;
Since it exists as a highly sticky powder or granular solid, it is difficult to supply it in a fixed amount to a vaporizer to obtain aluminum chloride vapor, and even after obtaining the vapor, it is difficult to supply it in a fixed amount to the vaporizer that is used to obtain aluminum chloride vapor. could not be mixed uniformly.

The present inventors improved this point and generated aluminum trichloride by blowing a gas containing hydrogen chloride onto a metallic aluminum melt or solid. The supply amount can be controlled freely, and the by-product hydrogen and aluminum trichloride are evenly mixed, so the hydrogen in this mixed gas is combusted,
It has been found that high temperature hydrolysis of aluminum trichloride can be achieved simply by forming an oxyhydrogen flame.

According to the present invention, a mixed gas of aluminum trichloride vapor and hydrogen obtained by blowing a gas containing hydrogen chloride onto aluminum (molten or solid) heated to a temperature range of 200 to 1200oC is mixed with an oxygen-containing gas. Then, burn the hydrogen and heat the resulting fine powder to 90°C.
There is provided a method for producing ultrafine aluminum oxide, which is characterized in that it is separated from combustion exhaust gas at the above temperature. In the present invention, aluminum and hydrogen chloride are reacted according to the reaction formula of AI 10 dregs CI→AIC13 13/is L, and the generated MCI3 is reacted with AIC13 13/Spot 2011/2AI
Following the reaction of 2033HCI, aluminum oxide is produced.

As described above, the supply of aluminum dichloride can be controlled by controlling the amount of hydrogen chloride supplied. The minimum amount of water vapor required for hydrolysis is 3'2 days 23'402 → 3/2 in an oxyhydrogen flame where aluminum is chlorinated.
It is produced by a reaction of 20 days, and does not require any special means for mixing aluminum trichloride, which has a high specific gravity, and water vapor, which has a low specific gravity.

This point is extremely advantageous compared to conventional high-temperature hydrolysis using steam. When aluminum trichloride is obtained by chlorinating aluminum with a gas containing hydrogen chloride, the product aluminum trichloride and hydrogen are mixed completely and uniformly, and when this mixed gas is introduced into an oxyhydrogen flame, it is Hydrolysis of aluminum chloride occurs uniformly and instantaneously in the flame, and aluminum oxide powder with a particle size of 0.1 A or less and a uniform particle size is obtained.

If the temperature of the aluminum melt or solid to which the hydrogen chloride-containing gas is blown is below 20,000, the rate of aluminum trichloride production will be slow and the produced aluminum trichloride will condense on the piping, which is unsuitable.

Moreover, if it is over 1200 pm, it is unsuitable because there is no suitable equipment material to hold the aluminum melt in a hydrogen chloride atmosphere. The generated aluminum oxide fine powder coexists with the oxyhydrogen flame exhaust gas and is guided to the solid-gas separator while being cooled. , a temperature higher than the melting point of hydrogen chloride coexisting in the exhaust gas is required, and this temperature is usually 90 qo or higher, and when cooled to 90°C or lower, hydrogen chloride condenses in the form of hydrochloric acid in the gas-solid separator. It is not suitable as it corrodes the equipment. Hydrogen chloride in a gas containing hydrogen chloride to be sprayed onto an aluminum body or solid is usually
The supply rate and concentration of hydrogen chloride cannot be specified here, as it reacts with aluminum sufficiently quickly to produce aluminum trichloride compared to the engineeringly possible ventilation temperature, and the coexisting gas It may also be inert gas such as helium, argon, nitrogen, etc., hydrogen that helps combustion in an oxyhydrogen flame, or chlorine that helps chlorinate aluminum. In the method of the present invention, a mixed gas of aluminum trichloride vapor and hydrogen obtained by blowing hydrogen chloride-containing gas onto heated aluminum (molten or solid) is mixed with an oxygen-containing gas and the hydrogen is combusted. ,
Better results can be obtained by adding more hydrogen and burning in a hydrogen-excess state. In this case, it is usually convenient to mix the added hydrogen with hydrogen chloride from the beginning as described above. The metal aluminum used in the method of the present invention may be either a new product or a recycled product, as long as it is normally commercially available as an isogot.

The hydrogen chloride used in the process of the invention may be any conventional commercially available hydrogen chloride.

Example 1 500 kg of aluminum was placed in a closed-type rubbo heated to 1000 q0, and a mixed gas containing 50% hydrogen chloride and 50% argon was passed through it at a flow rate of 200 q/min, and the resulting gas was kept at a temperature of 200 qC or higher. ) 25 so' of oxygen
After the exhaust gas was cooled down to 250 qo by introducing it into an oxyhydrogen flame burner supplied at a flow rate of 10 min, the generated powder was separated and recovered from the exhaust gas in a dust chamber. In 10 minutes, 680 qo of aluminum oxide powder with an average grain size of about 8 mm was produced. Obtained.

This powder shows no particular pattern in X-ray diffraction and is considered amorphous. Example 2 1,000 mm of aluminum was placed in a closed-type lupus heated to 700 mm, and a mixed gas containing 70% hydrogen chloride and 30% nitrogen was passed through at a flow rate of 143 mm, and the resulting gas was heated to 200°C or higher. (while keeping warm) Air 125 t/mi
After the exhaust gas was cooled down to 170°C by introducing it into an oxyhydrogen flame burner supplied at a flow rate of n, the generated powder was separated and collected from the exhaust gas using a bag filter. 1440 kg of aluminum powder was obtained.

Example 3 1,500 kg of aluminum was placed in a closed crucible heated to 400 qO, and a mixed gas containing 90% hydrogen chloride and 10% hydrogen was passed through at a flow rate of 110 〆'min, and the resulting gas was kept at a temperature of 200 qO or more. M) Air 155〆/
After the exhaust gas was cooled down to 120°C by passing through an oxyhydrogen flame burner supplied at a flow rate of 2210 kg of powder was obtained.

Claims (1)

[Claims] 1. A mixed gas of aluminum trichloride vapor and hydrogen, which is obtained by blowing a gas containing hydrogen chloride onto aluminum (molten or solid) heated to a temperature range of 200 to 1200°C, is A method for producing ultrafine aluminum oxide, which comprises mixing hydrogen with a contained gas, burning the hydrogen, and separating the resulting fine powder from the combustion exhaust gas at a temperature of 90° C. or higher. 2. The method according to claim 1, in which a mixed gas of aluminum trichloride and hydrogen obtained by spraying hydrogen chloride onto heated aluminum is mixed with an oxygen-containing gas to combust the hydrogen. A method characterized by adding hydrogen to hydrogen chloride.