Process for preparing fine-particulate metal hydroxide comprising aluminum hydroxide and metal oxide comprising aluminum oxide

The present invention discloses a process for preparing a fine-particulate metal hydroxide comprising aluminum hydroxide as a major component which comprises continuously supplying water and a mixture of an aluminum alkoxide and at least one alkoxide of a metal selected from Mg, Ca, La, Fe, Si, Ti and Zr, to a high shear rate stirring area and a process for preparing a fine-particulate metal oxide comprising aluminum oxide as a major component which comprises drying and then calcining said metal hydroxide at 500.degree.-1500.degree. C.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for preparing fine-particulate 
metal hydroxide comprising aluminum hydroxide as a major component and 
fine-particulate metal oxide comprising aluminum oxide as a major 
component. More precisely, it relates to a process for preparing 
fine-particulate metal hydroxide comprising aluminum hydroxide as a major 
component and fine-particulate metal oxide comprising aluminum oxide as a 
major component, having high industrial productivity and no tendency of 
producing coarse particles. 
2. Description of the Related Art 
Hydrolysis reaction of metal alkoxides has been the subject of growing 
interest as a method for preparing a sol, a gel and fine particles for 
precursors of ceramics in view the following advantages: 
(1) the metal alkoxides are easily hydrolyzed at room temperature to 
produce metal hydroxides, and 
(2) there is no possibility that the product is contaminated with anions as 
impurities, and a number of reports on said reaction have been published 
[see, for example, Amer., Ceram. Soc. Bull., 54, 286 (1975) and Nippon 
Ceramics Kyokai Gakujutsu Ronbunshi, 99 (10), 1036-1046 (1991)). 
When a silicon alkoxide or a titanium alkoxide is used as the starting 
material, monodispersed spherical particles of uniform particle size 
containing no coarse particles can easily be obtained by hydrolysis (see, 
for example, J. Colloid Interface Sci., 26, 62 (1968) and J. Am. Ceram. 
Soc., 65, C199 (1982)). However, when an aluminum alkoxide is used as the 
starting material, colloidal gel or gel-form precipitate tends to be 
formed due to its higher hydrolysis reaction rate. Therefore, it has been 
considered that the production of monodispersed particles of uniform 
particle size without containing coarse particles is difficult. 
Metal oxide comprising aluminum oxide as a major component, produced by 
calcining powdered metal hydroxide comprising aluminum hydroxide as a 
major component, is a material which has been widely used as a raw 
material for sintering and as various kinds of fillers. It is desirable to 
produce a metal oxide comprising aluminum oxide as a major component, 
which has a narrow particle size distribution and can be easily dispersed, 
in order to obtain excellent properties. 
In the synthesis of aluminum hydroxide by hydrolysis of an aluminum 
alkoxide, several inventions and researches have been made to prepare 
monodispersed fine particles under certain specific conditions (JP-A-Sho 
62-158116 and J. Am. Ceram. Soc., 74, 2263 (1991)). 
Those approaches use the hydrolysis reaction at a low concentration of the 
raw material in a reaction medium to which a solvent other than the 
alcohol constituting the aluminum alkoxide is added. While the 
monodispersed particles containing no coarse particle may be produced by 
those processes, productivity is low in industrial production.. Further, 
the alcohol used as the solvent must be purified before it is recycled to 
the synthesis of aluminum alkoxide. 
In addition, as aluminum oxide having a narrow particle size distribution, 
aluminum oxide produced by vapor phase hydrolysis in which anhydrous 
aluminum chloride is evaporated and combustively hydrolyzed in an 
oxyhydrogen flame, has been known. 
The aluminum oxide produced by this method suffers from a drawback that, 
when used as various kinds of fillers, it is corrosive due to the presence 
of an inevitable chlorine component as an impurity. 
Further, particulate aluminum oxide produced by pulverization, milling, 
grinding or the like of aluminum oxide containing coarse particles also 
suffers from a drawback that it has a broad particle size distribution and 
is susceptible to reagglomeration. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a process for preparing 
fine-particulate metal hydroxide comprising aluminum hydroxide as a major 
component, having high industrial productivity and no tendency of 
producing coarse particles. 
Another object of the present invention is to provide a process for 
preparing fine-particulate metal oxide comprising aluminum oxide as a 
major component, having high industrial productivity and no tendency of 
producing coarse particles. 
After an extensive study on the processes for preparing fine-particulate 
metal hydroxide comprising aluminum hydroxide as a major component and 
metal oxide comprising aluminum oxide as a major component, the present 
inventors discovered the facts that the above object can be achieved by 
conducting hydrolysis of an aluminum alkoxide in the presence of a 
specific metal alkoxide under specific stirring conditions, and that the 
object can more effectively be accomplished by drying the produced metal 
hydroxide under specific conditions, which facts lead them to the present 
invention. 
Accordingly, the present invention relates to a process for preparing 
fine-particulate metal hydroxide comprising aluminum hydroxide as a major 
component which comprises continuously supplying water and a mixture of an 
aluminum alkoxide and at least one alkoxide of a metal selected from Mg, 
Ca, La, Fe, Si, Ti and Zr, to a high shear rate stirring area; and a 
process for preparing fine-particulate metal oxide comprising aluminum 
oxide as a major component which comprises drying and then calcining said 
metal hydroxide at 500.degree.-1500.degree. C.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is explained in more detail in the following 
description. 
Metal hydroxide in fine-particulate form comprising aluminum hydroxide as a 
major component can be obtained by continuously hydrolyzing by separately 
supplying water and a mixture of aluminum alkoxide and at least one 
alkoxide of a metal selected from Mg, Ca, La, Fe, Si, Ti and Zr into a 
high shear rate stirring area. 
In the present invention, the fine-particulate metal hydroxide comprising 
aluminum hydroxide as a major component (in this specification, it is 
referred to as "said hydroxide") contains 0.1 to 15% by mole, preferably 1 
to 10% by mole in total of a metal component selected from Mg, Ca, La, Fe, 
Si, Ti and Zr as compared to aluminum component [(total molar weight of 
Mg, Ca, La, Fe, Si, Ti and Zr)/(molar weight oral)]. It may also contain a 
compound having an alkoxy group or a chemically modified group derived 
from chemical modifiers described later in place of a part of hydroxy 
groups in aluminum hydroxide or in hydroxide of other metal, as long as it 
is formed in the precipitate of said hydroxide when the mixture of an 
aluminum alkoxide and at least one alkoxide of a metal selected from Mg, 
Ca, La, Fe, Si, Ti and Zr is hydrolyzed by mixing with water according to 
the present invention. 
The aluminum alkoxides used in the present invention may be represented by 
the general formula: 
EQU Al(OR').sub.3 
wherein R' is normal chain or branched alkyl group. 
Examples of R' include an ethyl group, n-propyl group, isopropyl group, 
n-butyl group, sec-butyl group, t-butyl group and the like. 
Examples of such alkoxides include those having usually 1 to 8 and 
preferably 2 to 4 carbon atoms, such as aluminum ethoxide, aluminum 
n-propoxide, aluminum isopropoxide, aluminum n-butoxide, aluminum 
sec-butoxide, aluminum t-butoxide and the like. 
The alkoxide of a metal selected from Mg, Ca, La, Fe, Si, Ti and Zr (in 
this specification, it is referred to as "said other metal alkoxide") to 
be used in the present invention includes metal alkoxides represented by 
the general formulae: 
EQU Mg(OR).sub.2, Ca(OR).sub.2, La(OR).sub.3, Fe(OR).sub.2, Si(OR).sub.4, 
Ti(OR).sub.4, Zr(OR).sub.4 
wherein R is alkyl, and/or derivatives of the metal alkoxides, so called 
chemically modified metal alkoxides, formed by substituting a part of the 
alkoxy group of the metal alkoxides with at least one chemical modifier 
(in this specification, it is referred to as "said chemical modifier") 
such as diketone, ketoester, diester, carboxylic acid, diol, ketoalcohol, 
aidehyde, amino acid, polyhydric alcohol acetate, amine, polyether and the 
like. 
The molar amount of the metal alkoxide as compared to said chemical 
modifier in the preparation of said chemically modified metal alkoxide is 
more than 0.25 and preferably 1 to 30. 
R includes normal chain or branched alkyl groups containing usually 1 to 8, 
preferably 2 to 4 carbon atoms, such as ethyl group, n-propyl group, 
isopropyl group, n-butyl group, sec-butyl group, t-butyl group and the 
like. 
Specific examples of the chemical modifiers are diketones such as diacetyl, 
acetylbenzoyl, benzil, acetylacetone, benzoylacetone, dibenzoylmethane, 
trifluoroacetylacetone, hexafluoroacetylacetone, dipivaloylmethane, 
pivaloyltrifluoroacetone, and so on; ketoesters such as methyl 
acetoacetate, ethyl acetoacetate, and so on; diesters such as dimethyl 
malonate, diethyl malonate, dimethyl phthalate, diethyl phthalate, dibutyl 
phthalate, dioctyl phthalate, dioctyl adipate, diisodecyl adipate, 
dimethyl oxalate, diethyl oxalate, and so on; diols such as ethylene 
glycol, propylene glycol, trimethylene glycol, 1,3-butanediol, 
1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, hexylene glycol, 
heptanediol, octanediol, nonanediol, decanediol, pinacol, diethylene 
glycol, and so on; ketoalcohols such as acetol, acetoin, 
acetoethylalcohol, diacetonealcohol, phenacylalcohol, benzoin, and so on; 
aldehydes such as salicylaldehyde, and so on; carboxylic acids such as 
formic acid, acetic acid, butyric acid, valetic acid, caproic acid, 
enanthic acid, caprylic acid, pelargonic acid, captic acid, undecylic 
acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, 
palmitic acid, heptadecylic acid, stearic acid, oxalic acid, citric acid, 
fumaric acid, iminodibutyric acid, octylic acid, oleic acid, and so on; 
amino acids such as glycine; polyhydric alcohol acetates such as 
diethylene glycol monoethylether acetate, diethylene glycol monobutylether 
acetate, and so on; amines such as ethylenediamine, diethylenetriamine, 
triethylenetetramine, diethanolamine, triethanolamine, ethylenediamine 
tetraacetate, and so on; and polyethers such as diethylene glycol 
monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol 
monoethyl ether, diethylene glycol diethyl ether, diethylene glycol 
dibutyl ether, triethylene glycol dimethylether, tetraethylene glycol 
dimethyl ether, ethylcellosolve, dodecanediol dimethyl ether, decanediol 
dimethyl ether, hexanediol dimethyl ether, hexanediol diethyl ether, 
diethylene glycol monobutyl ether, dipropylene glycol dimethyl ether, 
diethylene glycol butylmethyl ether, and so on. 
Said other metal alkoxides may be used singly or as a mixture of at least 
two kinds. 
Specific examples of said other metal alkoxides are magnesium diethoxide, 
magnesium diisopropoxide, calcium diethoxide, calcium diisopropoxide, 
tetraethoxy silane, tetraisopropoxy silane, tetra-n-butoxy silane, 
titanium tetramethoxide, titanium tetra-n-propoxide, titanium 
tetraethoxide, titanium tetraisopropoxide, titanium tetra-n-butoxide, 
zirconium tetraethoxide, zirconium tetra-n-propoxide, zirconium 
tetraisopropoxide, zirconium tetra-n-butoxide, triethoxy iron, 
triisopropoxy iron, triethoxy lanthanum, triisopropoxy lanthanum, 
magnesium dimethoxide, magnesium di-n-propoxide, 
tetrakis(2-ethylhethyloxy)titanium, tetrastearyloxy titanium, diisopropoxy 
bis (acetylacetonato) titanium, di-n-butoxy bis (triethanolaminato) 
titanium, dihydroxy bis(lactato)titanium, propanedioxy titanium (ethyl 
acetoacetate), propanedioxy titanium (acetylacetonate), titanium 
isopropoxyoctylene glycolate, titanium lactate, butyl titanate dimer, 
propanedioxy titanium (ethyl acetoacetate), calcium dipivalomethanate and 
so on. 
The aluminum alkoxides and said other metal alkoxides are generally solid 
or viscous liquids at room temperature and it is preferred to use a 
mixture comprising an aluminum alkoxide and said other metal alkoxide (in 
this specification, it is referred to as "said mixture") in the form of a 
solution in a solvent for convenience in handling. The solvent is usually 
an alcohol. Specific examples of the alcohol include ethanol, n-propanol, 
isopropanol, n-butanol, sec-butanol, t-butanol and the like. It is 
preferred from the practical point of view to use the same alcohol as that 
produced by hydrolysis of alkoxy group of aluminum alkoxide or said other 
metal alkoxide, for example, isopropanol when aluminum isopropoxide and 
titanium isopropoxide are used, because fractional distillation or other 
purification may be eliminated or greatly reduced when recycling and reuse 
of the solvent are intended. 
In order to form a derivative of said other metal alkoxide using said 
chemical modifier, any method can be applied as long as said other metal 
alkoxide can be chemically modified. It is preferred to mix a solution of 
said other metal alkoxide in the alcohol and said chemical modifier or a 
solution of said chemical modifier in the alcohol at a temperature between 
room temperature and the boiling temperature of the solvent and then the 
mixture is stirred for about an hour. 
As aluminum alkoxide, a derivative of the aluminum alkoxide wherein a part 
of the alkoxy group of the aluminum alkoxide is substituted by at least 
one of said chemical modifiers, so called chemically modified aluminum 
alkoxide, may be used. The method of preparing such derivative may be 
conducted in the same manner as that of said other metal alkoxide. 
The process for forming the mixture comprising the aluminum alkoxide and 
said other metal alkoxide is not particularly limited and may usually be 
carried out by combining a solution of aluminum alkoxide in an alcohol and 
said other metal alkoxide or a solution of said other metal alkoxide in an 
alcohol at a temperature between room temperature and the boiling 
temperature of the solvent. Alternatively, when an alkoxide of Mg is used 
as said other metal alkoxide, said mixture may be obtained by adding 
magnesium to a solution of aluminum alkoxide in an alcohol and refluxing 
to dissolve the magnesium. 
The molar content of said other metal alkoxide to the aluminum 
alkoxide[(total molar weight of said other metal alkoxides)/(molar weight 
of aluminum alkoxide)] is usually 0.1 to 15%, preferably 1 to 10%. If the 
amount of said other metal alkoxide is too small, the micronizing effect 
for said hydroxide to be obtained is not sufficient. 
The concentration of the aluminum alkoxide in the solution of said mixture 
is not particularly limited and it may depend on the solubility of 
respective compounds in the solvent. Usually, the concentration calculated 
in terms of aluminum alkoxide is about 30 to about 90% by weight. In this 
specification, the concentration calculated in terms of aluminum alkoxide 
means the concentration obtained by converting chemically modified 
aluminum alkoxide to unmodified aluminum alkoxide, in the case where the 
chemically modified aluminum alkoxide is used. When the concentration is 
too low, the concentration of said hydroxide in the resulting slurry is 
also low so that an excessive amount of alcohol must be distilled off in 
order to obtain said hydroxide from the slurry. When, on the contrary, the 
concentration is too high, some aluminum alkoxides having low solubility 
tend to precipitate, or reagglomeration may occur due to the too high 
concentration of said hydroxide in the resulting slurry during and/or 
after hydrolysis. 
In the present invention, high shear rate stirring means stirring by 
mechanical energy such as shearing stress, pressure change, cavitation, 
collision force, potential core and the like, which are generated between 
a turbine or rotor rotating usually at a high peripheral speed of about 1 
m/sec. to about 40 m/sec. and a stator for the turbine or screen for the 
rotor of a special mixer generically known as a homomixer or homogenizer, 
which comprises a specially designed turbine or rotor rotating at a high 
speed and a stator or screen provided around the turbine or rotor with a 
clearance of usually 2 mm or less. The high shear rate stirring area (in 
this specification, it is referred to as "said stirring area") means the 
area in which the high shear rate stirring state is generated. 
Examples of such mixer for high shear rate stirring (in this specification, 
it is referred to as "the high shear rate mixer") are T.K. Homomixer 
(manufactured by Tokushu Kika Kogyo Kabushikikaisha), Cleamix 
(manufactured by M Technique Kabushikikaisha) Polytron homogenizer and 
Megatron homogenizer (both manufactured by KINEMATICA), Supraton 
(manufactured by Tsukishima Kikai Kabushikikaisha) and the like. 
The conditions for high shear rate stirring can be expressed by a shear 
rate represented by the formula: 
EQU x/y.times.10.sup.3 sec..sup.-1 
wherein x is a peripheral speed (m/sec.) of the turbine (rotor) which 
rotates at a high speed and y is a clearance (mm) between the turbine 
(rotor) and the stator (screen). 
In the process of the present invention, the high shear rate stirring 
condition should generate a shear rate of usually at least 3000 
sec..sup.-1, preferably at least 5000 sec..sup.-1 and more preferably at 
least 8000 sec..sup.-1. When the shear rate is less than 3000 sec..sup.-1, 
mixing of said mixture solution and water and mechanical dispersion of 
said hydroxide particles produced are insufficient, so that the coarse 
particles tend to be formed. 
In the hydrolysis reaction of said mixture by water and subsequent 
precipitation of said hydroxide, aluminum hydroxide gel is instantaneously 
precipitated because the higher reaction rate of aluminum alkoxide. 
Therefore, low or moderate rate rotating type stirrers represented by the 
usual paddle type or screw type, as well as motionless mixer such as a 
static mixer, are not appropriately used in the present invention due to 
the fact that generation of coarse particles of some tens .mu.m cannot be 
avoided. 
In the process of the present invention, a residence time, the period from 
the time of supplying of said mixture and water to said stirring area, to 
the time of discharge of said hydroxide from said stirring area, is 
usually from about 5 seconds to about 15 minutes, preferably from about 30 
seconds to about 8 minutes. When the residence time in the stirring area 
is too short, the reaction is not completed in the stirring area so that 
the particles discharged from the stirring area are polymerized or 
agglomerated, whereby the particles are reagglomerated or insufficiently 
dispersed. When the residence time in the stirring area is too long, 
productivity may be decreased. 
As the continuous reactor for the purpose of the present invention, any 
type of continuous reactor such as a tank continuous-type reactor or a 
pipeline continuous-type reactor may be used. 
The reaction in the tank continuous-type reactor is carried out by 
continuously supplying said mixture and water to a tank equipped with the 
high shear rate mixer and continuously discharging the reaction mixture in 
the same amount as that of the supplied liquid to produce said hydroxide 
particles. 
The reaction in the pipeline continuous-type reactor is carried out by 
supplying said mixture and water to the high shear rate mixer installed in 
a pipeline. 
Since the continuous reaction can achieve a higher productivity and make 
the particle precipitation conditions more uniform than a batchwise 
reaction, said hydroxide having the uniform particle size distribution and 
containing no coarse particles can be produced. 
For the purpose of the present invention, it is preferred to conduct the 
reaction at a constant molar ratio of said mixture and water to be 
supplied in order to unify the degree of completion of the hydrolysis and 
the properties such as crystal form and the like of said hydroxide. The 
molar ratio (water/Al) is preferably about 1.5 to about 6.0. 
In addition, water may be supplied in any desired form, for example, as it 
is or as a solution with the alcohol, as long as the molar ratio 
(water/Al) is in the range described above. 
The reaction temperature is not limited. Usually, the reaction is carried 
out in a temperature range from room temperature to the boiling 
temperature of the solvent. 
The reaction pressure is preferably 0.1 kgG/cm.sup.2 or higher. When the 
reaction pressure is lower than 0.1 kgG/cm.sup.2, bubbles tend to be 
trapped in said stirring area, which may increase the mechanical energy 
loss. 
To improve the dispersion of precipitated particles to a and prevent form 
agglomeration of the particles in said hydroxide slurry, a surface charge 
regulator such as an acid or a base, or a surfactant such as a dispersant 
or an emulsifier may be added in the hydrolysis reaction. 
Examples of the acid are hydrochloric acid, nitric acid, acetic acid, and 
the like, and examples of the base are ammonia, triethylamine, and the 
like. Examples of the surfactant are nonionic surfactants such as sorbitan 
monooleate, sorbitan trioleate, sorbitan monolaurate, triolein, 
polyoxyethylene phenyl ether, and so on; anionic surfactants such as 
sodium alkyldiphenyldisulfonate, sodium salt of dialkylsulfosuccinate, and 
so on; cationic surfactants such as N-alkyltrimethylenediamine oleate, and 
so on. 
Said hydroxide slurry prepared by the process of the present invention can 
be separated into solid and liquid by the treatment such as evaporation, 
drying and filtration. 
As the solid-liquid separation, the method using a pneumatic conveying 
dryer (in this specification it is referred to as "said pneumatic 
conveying drying method") and the method comprising heating said hydroxide 
slurry to or above the boiling temperature of the liquid at atmospheric 
pressure and spraying said heated hydroxide slurry with pressure from a 
nozzle using flash dryer (in this specification, it is referred to as 
"said flash drying method") are preferred as a particularly suitable 
embodiment, since said hydroxide can be effectively isolated without 
agglomeration. 
Dryers are generally classified into 8 kinds, as shown below, based on 
their mechanism: 
1. material standing-type dryer, 
2. material transferring-type dryer, 
3. material stirring-type dryer, 
4. hot-air transferring-type dryer, 
5. cylindrical dryer, 
6. infrared rays dryer, 
7. freeze dryer, and 
8. high-frequency dryer, 
(reference: "Kagaku Kogaku Binran" Fifth Edition, p.683, Published by 
Maruzen). 
The pneumatic conveying dryer is included in the hot-air transferring-type 
dryer and the flash dryer does not fall under the conventional 
classification and utilizes flash evaporation. 
The pneumatic conveying dryer acts by instantly dispersing and drying wet 
powders such as slurry in an air flow at high temperature and high speed. 
The dryer may be manufactured and set in a plant in which the dryer is used 
or alternatively is commercially available from Kurimoto Ltd., or 
Kabushiki Kaisha Seishin Kigyo (Tradename: Flash Jet Dryer). 
Conditions of said pneumatic conveying drying method are not particularly 
limited and said fine-particulate hydroxide with good powder dispersion is 
obtained by, for example, adjusting pressure, air flow, temperatures at 
inlet and outlet of the dryer and amount of feeding slurry. 
The flash dryer produces solid particles upon evaporation of the liquid 
from the slurry by spraying, with pressure, the slurry heated to or above 
the boiling temperature of the liquid at the atmospheric pressure from a 
nozzle. 
Conditions of said flash drying method are not particularly limited and 
said fine-particulate hydroxide with good powder dispersion is obtained 
by, for example, adjusting drying temperature, drying period, residence 
period, spraying pressure and so on. 
The temperature for drying is not particularly limited and it may be within 
a range from the boiling point of the liquid up to just below the lowest 
decomposition point of one of the components in the liquid. 
In the case where said pneumatic conveying drying method or said flash 
drying method is applied, said hydroxide slurry is sprayed out with 
pressure or the particles are dried in jet flow at high temperature and 
high pressure. Consequently, the liquid between particles is evaporated 
instantaneously, and said fine-particulate hydroxide can be obtained 
because the particles can pass through the granulation zone very shortly. 
Said hydroxides obtained in the above manner are fine particles having 
average particle size of about 5 .mu.m below and usually about 3 .mu.m or 
below, and are substantially free of coarse particles of 10 .mu.m or 
above. They can be used in the same way as the fine-particulate aluminum 
hydroxide as fillers for various resins, papers and textiles. 
By calcining said hydroxide at about 500.degree. C. to abut 1500.degree. 
C., fine-particulate metal oxide comprising .gamma., .delta., .THETA. 
and/or .alpha.-aluminum oxide as a major component (in this specification, 
it is referred to as "said fine-particulate oxide") is obtained which is 
suitably used like fine-particulate .gamma., .delta., .THETA. and/or 
.alpha.-alumina as a filler for various resins such as PET films or epoxy 
resins, a coating filler for paper and textile for ink jet printing, a 
carrier for catalyst, a raw material for single crystal, an abrasive or a 
raw material for sintering. 
Said fine-particulate oxide usually contains 0.1 to 15% by mole, preferably 
1 to 10% by mole in total of other metal component(s) of metal oxide(s) 
derived from at least one said other metal alkoxide as compared to the 
aluminum component [(total molar weight of Mg, Ca, La, Fe, Si, Ti and 
Zr)/(molar weight of Al)]. 
The period for calcination depends on the method of calcination and, in 
practical production, is selected on the basis of experiment such that a 
desired crystal form is obtained. Usually, the period is within a range 
from several seconds to 100 hours. 
The method for calcination is not particularly limited and my be a 
conventional process using a rotary kiln, flash calcining furnace, 
packing-type calcining furnace, fluidized calcining furnace, tunnel 
furnace, vacuum furnace, shuttle furnace and the like. Usually, a method 
using a rotary kiln, tunnel furnace, shuttle furnace and the like is 
suitable from the view point of productivity and heat resistance of 
material. 
In the case where said hydroxide, obtained by hydrolyzing said mixture 
comprising Ti alkoxide and aluminum alkoxide and then drying the product, 
is calcined, the calcination is promoted as compared with the case of 
aluminum alkoxide alone. In other words, when said fine-particulate oxide 
having certain specific surface is intended, said fine-particulate oxide 
containing Ti is suitable from the industrial point of view because it can 
be prepared by calcination at a lower temperature than that of aluminum 
oxide alone. 
Said fine-particulate oxide comprising aluminum oxide as a major component 
obtained above has an average particle size of about 5 .mu.m less and 
usually about 3 .mu.m less, and is substantially free from coarse 
particles of 10 .mu.m or more. 
As described in detail, according to the present invention, 
fine-particulate metal hydroxide comprising aluminum hydroxide as a major 
component and free from coarse or agglomerated particles may be obtained 
effectively and with good industrial productivity by continuous hydrolysis 
of a mixture comprising an alkoxide of specific metal and aluminum 
alkoxide with water under specific stirring conditions, and further, by 
combining specific drying process, said hydroxide may be obtained more 
effectively. In addition, by calcining said hydroxide, fine-particulate 
metal oxide comprising aluminum oxide as a major component and free from 
coarse or agglomerated particles may be obtained. 
The present invention will be illustrated in more detail by the following 
Examples. However, the present invention should not be construed to be 
limited by such Examples. 
In the following Examples, the crystal form and particle sizes D50 
(particle size at 50% cummulation) and D90 (particle size at 90% 
cummulation) were measured as follows: 
Crystal form: The crystal form was measured using a powder X-ray 
diffraction apparatus (Geiger Flex RAD Series manufactured by Rigaku Denki 
Kogyo Kabushikikaisha): 
Particle size: The particle size is measured by the MICROTRACK MK II 
particle size analyzer (SPA Model 7997-20 manufactured by Nikkiso 
Kabushikikaisha). 
The BET specific surface and pore volume were measured as follows: 
Apparatus: Gas absorption/desorption analyzer "Omunisorb 360" (manufactured 
by COULTER LTD.,) 
Method of analysis: A sample was degassed as its original shape, overnight 
at 130.degree. C., less than 2.times.10.sup.-5 torr, and assayed for 
absorption and desorption by continuous volume method using nitrogen gas. 
EXAMPLE 1 
In a 1600 cc pressure vessel which was resistant to 10.5 kg/cm.sup.2 
(working pressure: 0.5 kg/cm.sup.2), there was equipped a high shear rate 
mixer Cleamix CLM-L 3.7S (manufactured by M Technique Kabushikikaisha), 
having a rotor of 57 mm in maximum diameter and 25 mm in minimum diameter 
leaving a clearance of 0.3 mm. At a rate gradient of 43,700 to 100,000 
sec..sup.-1, a mixture of 75% by weight of aluminum isopropoxide and 
isopropanol and a mixture of titanium tetraisopropoxide and isopropanol 
were mixed. The mixture of titanium tetraisopropoxide, aluminum 
isopropoxide and isopropanol wherein molar content of titanium as compared 
to aluminum is 3%, the concentration of aluminum isopropoxide is 60% by 
weight, and aqueous isopropanol, wherein the concentration of water is 30% 
by weight, were continuously and separately supplied in the mixer for a 
residence time of 8 minutes at a constant molar ratio of water/aluminum 
isopropoxide at 2.7, and hydrolyzed at a temperature of 40.degree. to 
70.degree. C. to obtain metal hydroxide comprising aluminum hydroxide as a 
major component, which was amorphous and had D50 of 1.3 .mu.m and D90 of 
2.7 .mu.m. 
Comparative Example 1 
In a 2 liter separable flask, there was equipped a stirrer having stirring 
blades of maximum diameter of 145 mm and the minimum diameter of 10 mm, 
which were designed so that a clearance between the inner flask wall and 
the blade tips was about 5 mm. Then, a mixture of 75% by weight of 
aluminum isopropoxide and isopropanol and a mixture of water and 
isopropanol containing 30% by weight of water were continuously and 
separately supplied in the flask, at a molar ratio of water/aluminum 
isopropoxide of 2.0, and hydrolyzed at a temperature of 40.degree. to 
70.degree. C. for 60 minutes while rotating the stirring blades at 100 
rpm, corresponding to the shear rate of from about 10 sec..sup.-1 to about 
150 sec..sup.-1 to obtain aluminum hydroxide, which was amorphous and had 
particle sizes D50 of 9.9 .mu.m and D90 of 21.6 .mu.m. 
EXAMPLE 2 
Preparation was performed in the same manner as in Example 1, except that 
the molar content of titanium as compared to aluminum was changed to 6%, 
and said mixture was hydrolyzed to obtain said fine-particulate hydroxide, 
which was amorphous and had particle Sizes D50 of 1.5 .mu.m and D90 of 3.1 
.mu.m. 
EXAMPLE 3 
Preparation was performed in the same manner as in Example 1, except that 
titanium tetraisopropoxide was replaced by ethyl silicate and the molar 
content of silicon as compared to aluminum was changed to 2%, and said 
mixture was hydrolyzed to obtain said fine-particulate hydroxide, which 
was amorphous and had particle sizes D50 of 1.2 .mu.m and D90 of 2.7 
.mu.m. 
EXAMPLE 4 
Preparation was performed in the same manner as in Example 1, except that 
titanium tetraisopropoxide was replaced by ethyl silicate and the molar 
content of silicon as compared to aluminum was changed to 1%, and said 
mixture was hydrolyzed to obtain said fine-particulate hydroxide, which 
was amorphous and had particle sizes D50 of 1.6 .mu.m and D90 of 5.1 
.mu.m. 
EXAMPLE 5 
The obtained slurry in Example 1 is dried in a pneumatic conveying dryer 
(Tradename: Flash Jet Dryer FJD-4, manufactured by K.K. Seishin Kigyo) at 
a drying temperature (inlet temperature of about 270.degree. C. and outlet 
temperature of about 130.degree. C.) for a residence time of about 0.7 
second under a pressure of about 0.3 kg/cm.sup.2 G with a air flow of 14 
m.sup.3 /minute and a supplying rate of slurry of 114 kg/hour to obtain 
said dryed fine-particulate hydroxide, which has no coarse particle. 
Said dryed fine-particulate hydroxide is calcined at 950.degree. C. for 3 
hours to obtain fine-particulate metal oxide, which has no coarse 
particle. 
The invention being thus described, it will be obvious that the same my be 
varied in many ways. Such variations are no to be regarded as a departure 
from the spirit and scope of the invention, and all such modifications as 
would be obvious to one skilled in the art are intended to be included 
within the scope of the following claims.