JPS5929526B2 - Alumina manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing pure alumina, consisting primarily of alpha-alumina.

Today's high engineering demands require the highest quality basic materials for industrial processing of alumina for the production of oxide-based ceramic products.

The quality of alumina is generally judged by its purity, grain size, and its crystal form or modification.

Purity 99.9 as alumina starting material in processing industry
9% or better quality is required.

In addition to this purity, it is generally required that the particle size be less than 1μ and that only the α-crystalline form be present, as these factors are critical to the quality of the final product as well as the economics of the dynamometer. This is because it has a significant impact.

A difficulty in the production of α-alumina is that its stable α-form can only be obtained by heat treatment at high temperatures, ie, temperatures above 1500°C.

Although the desired stable α-form can be obtained at such temperatures, however, the crystals solidify into large nodules and shrink.

In this form, alumina is largely unsuitable for producing oxide-based ceramic products.

It therefore has to be pulverized, for example, and even classified.

However, during its pulverization, most of the alumina crystals are damaged, split, and fractured, thereby losing some of their strength.

The strength and quality of oxide-based ceramic products made from damaged crystals are inferior to those made from undamaged crystals.

Additionally, during such grinding, the high-purity α-alumina is contaminated with impurities, which has an adverse effect on its quality.

Aluminas of higher purity than industrial chemical grade aluminas are produced from bauxite, but these are generally manufactured to meet predetermined purposes and requirements; 99
．． The requirements for the highest purity materials, such as those analyzed for 10 to 15 components with a 99% purity requirement, are not met.

Higher purity can be obtained by methods using water-soluble aluminum salts or thermally decomposable aluminum compounds as starting materials.

A weakness of these methods is that they generally require very large amounts and/or volumes of starting material to obtain a unit amount of alumina.

Good examples are aluminum sulfate and aluminum ammonium sulfate, which have as many as 18 molecules of water of crystallization, and are often used as starting materials to obtain alumina by pyrolysis.

Taking into account the amounts and proportions of starting material and final product, the most preferred method is undoubtedly one using aluminum as starting material.

In this case, 1025P alumina can be obtained from 540g of metal material.

This is clearly why a large number of methods are known for producing alumina from aluminum.

That is, it is known that aluminum is pulverized and burned until it reaches a constant weight, and aluminum is also subjected to spark processing (5.
It is also known to produce alumina by heating water-containing aluminum made in water by park machining.

Furthermore, a number of methods are known for producing hydric alumina in pressurized or actuators in the presence of mercury or mercury salts.

Also, methods such as those in which aluminum is reacted at normal pressure in the presence of steam, water, mercury, or mercury salts, resulting in hydrated alumina in the form of elongated loose flakes or in an agglomerated state. is also publicly known.

Utilization of torrefaction capacity is extremely poor when torrefying these loose flakes, and heat transfer between individual flakes is uneven, thus requiring undesirably high temperatures. Moreover, the quality of alumina is also uneven.

Another method is the so-called thermal grinding method.
nding) is used to crush the agglomerated alumina mentioned above.

In this method, two batches are stored in a furnace with an appropriate heat capacity.
A sufficient amount of moist hydrated alumina is charged so that it can be heated to a temperature of 1100° C. or higher within minutes.

Under the influence of the steam generated, this raw material is ground, that is to say thermally ground.

The object of the present invention is to provide a method for economically producing high-purity α-alumina, preferably α-alumina with a particle size of 1 micron or less, which is simpler than the previously known methods. be.

The present invention therefore relates to a method for producing alumina consisting primarily of pure α-alumina, which comprises at least 99% pure α-alumina.
．． The oxide film of metallic aluminum having a purity of 5% or more is removed, the thus activated state is reacted in an aqueous medium, and the resulting reaction product is heat-treated.

A feature of the invention is that its activation (removal of the oxidation layer) takes place exclusively in an aqueous solution with an acidic pH value, and the subsequent washing takes place in an aqueous solution with a neutral pH value, and the reaction (water oxidation (product production) in an aqueous solution with an alkaline, neutral or acidic pH value.

Depending on whether the pH value of the reaction solution is alkaline, neutral, or acidic, the aqueous alumina reaction product will be in the form of fine powder, plate crystals, or gel.

This product is heat-treated by a known method to form fine powder, particles,
A final product in the form of plates or chips is produced.

According to the present invention, the starting material is small (both 8 crA/
Metallic aluminum having a specific surface area of 1 or more is desirable.

In one of the preferred methods according to the invention, the alumina has a purity of 99.5% or more and a specific surface area of 8 cvi/? Made from the above metal aluminum (plate, foil, cuttings or powder).

The protective oxide coating can be removed from the metal in a known manner, i.e. by chemically exposing the aluminum metal to an acidic pH.
Activate in aqueous solution of value.

Subsequent washing takes place in water at a neutral pH value.

The activated and washed metal is then placed in the presence of water for 1 hour.
Conversion to hydrated alumina at normal pressure at 0-100°C.

Alumina is then obtained after heat treatment.

A very great advantage of the present invention is that alumina of superior properties and, if desired, of fine grain size can be produced in a very simple manner by changing a single engineering parameter and using equipment that can be easily automated. This means that alumina with a plate-like crystal structure can be produced.

The method according to the invention will be explained in more detail below by Morio, but the invention is not limited to these examples.

Example 1 In order to remove the oxidation layer and activate the surface of an aluminum foil with a purity of 99.99% or more and a thickness of 0.05 mm, 0.1% HgCl2 was added in twice-distilled water and pH adjusted with hydrochloric acid. The above foil was passed through a water bath adjusted to 5 to 6.
The dive was made at a speed of m/min.

From this water bath the foil is then passed at the same speed of 10 m/min through a second neutral (pH 7) bath of double-distilled water, where the salts remaining on the metal surface after the activation are removed. and the acid was removed.

The aluminum foil thus activated was further processed as described below.

The aluminum foil was passed at the same speed as above through a bath in which twice-distilled water was adjusted to an alkaline pH value of 8 to 9 with 25% aqueous ammonia.

The temperature of this reaction bath liquid is 80° to 90°C, and maintaining this temperature at a constant value requires the reaction heat and the cold replenishment reaction to replenish the amount extracted and sent to the exchange bed to renew the reaction liquid. This was done by balancing the addition of liquid.

The violent exothermic reaction between the metallic aluminum and the bath liquid produced a suspension of fine water-containing alumina in a form that easily settled.

The resulting water alumina crystals did not agglomerate into large clumps and maintained their submicron particle size throughout subsequent processing.

Irrigated alumina particles with electrically the same polarity or charge repel each other, and this property ensures prevention of agglomeration and good r-permeability properties.

The hydrated alumina crystals were continuously separated from the aqueous solution by filtration and then dried to produce a powder.

The hydrated alumina powder had a particle size of 0.005 to 0.9 microns.

By heating this hydrated alumina to 800° to 1000°C, it was possible to obtain γ-type alumina with a specific surface area of 25 to 30 m/f.

By heating this alumina to 1000°C to 1200°C, the specific surface area of γ-type and α-type is 15 to 2.
It is possible to obtain a mixture with a specific surface area of 1.
It was possible to obtain α-alumina of 0 to 15 m/S'.

Example 2 99.99% purity aluminum foil was used as the starting material and was activated and washed as described in Example 1 above, except that instead of the alkaline aqueous reaction solution, a neutral
Double-distilled water with an H value was used.

The chemical reaction that occurred resulted in a hydrated alumina suspension of plate-like crystals.

From this, the following product could be obtained.

At 800° to 1000°C: specific surface area 9 to 15r
rt/? γ-alumina powder with plate-like crystals.

At 1000° to 1200°C: Specific surface area 5 to 9
rrl/? Mixed powder of γ- and α-alumina with plate-like crystals.

At 1250° to 1800°C: Specific surface area 1 to 5 m
/f plate-like crystalline α-alumina powder Example 3 Using 99.5% pure aluminum foil as the starting material, the foil was activated and washed as described in Example 1 above, and acidified with hydrochloric acid. The reaction was carried out in an acidic aqueous solution having a pH of 5 to 6.

The reaction product was an alumina gel.

This material could not be washed and dried in situ, resulting in a mass with a cracked structure.

By heating this material to 800° to 1000°C, lump-like γ-alumina with a specific surface area of IO to 15 m/f can be obtained, and by heating this material to 1000° to 1200°C, a specific surface area of 8 to 12 m/f can be obtained. ? lumpy γ of
- and α-alumina mixtures were obtained, while 1400
By heating from ° to 1800 °C, solid specific gravity (
A lattice-like α-alumina with a submicron particle size is obtained, which has a solid 5 specific gravity of 3.87 S'/nu, a hardness of 92 to 94 HRa or more, and a bending strength of 50 to 70 kg/-. It was in the shape of a fragment of a solid.

Example 4 Purity 9999% or more and specific surface area 8 crii/f1
The above aluminum foil was passed through a solution of twice-distilled water adjusted to an acidic pH value of 5 to 6, and further passed through a layer of mercury present at the bottom of this solution.

This was then carried out as described in Examples 1.2 and 3 above with the same results given on each side.

Example 5 Granular aluminum with a purity of 99.5% and a specific surface area of 8 crA/y', prepared by scattering molten metal through a protective atmosphere into the aqueous activating solution described in Example 1, was used as starting material.

Using the solutions described in Examples 1.2 and 3, washing and reaction were carried out in three serially connected continuous transfer tubes in continuous operation.

The reaction and heat treatment yielded the same material as previously described.

In the examples above, the alumina produced had a purity equal to or greater than that of the starting aluminum.

Claims (1)

[Claims] 1 Aluminum having a purity of at least 99.5% and preferably a specific surface area of at least 8 crA/1 is added to the
Activated by removing the oxide layer in an aqueous medium of H, washed in an aqueous medium of neutral pH, and at a neutral pH of 15 to 6 or other acidic range of pH 1 or 8.
Reacting in an aqueous medium at a pH of 1 to 9 or other alkaline to form an alumina hydrate, which is then preferably
A product alumina is obtained by roasting at a temperature of 50° C. or higher, which is sufficient to provide pure α-alumina.
Alumina manufacturing method.