Note: Descriptions are shown in the official language in which they were submitted.
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ALUMINUM HYDROXIDE-BASED BUILDING MATERIALS AND METHOD FOR MANU-
FACTUXING SAME
BACKGROUND OF THE INVENTION
The present invention relates to a building material such
as ceiling and wall boards or, more particularly, to a building
material formed of aluminum hydroxide as the main component as
reinforced with a fibrous material as well as to a method for
manufacturing such a building material.
Needless to say, there are currently on use in the building
industry a great variety of building materials depending on the
requirements for the particular building and locality. The
requirements for the building materiais are so diversified that
a material suitable in a building is not always useful in another.
Several characteristics are, however, almost always important in
any types of building materials-among which, for example, mechanical
strengths, non-inflammability or flame retardancy and heat and
sound insulation as well as inexpensiveness are mentioned.
In relation to the inexpensiveness of the building materials,
there may be obtained two-way advantages simultaneously if an
industrial waste can be processed or fabricated into building
materials having satisfactory characteristics in the dissolution
of the problem caused by the burdensome waste material such as
the environmental pollution and the commercial benefit obtained
with the building materials produced therefrom with outstanding
inexpensiveness.
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Accordingly there have been made varicus attempts to utilize
useless industrial waste materials for the production of building
materials. Unfortunately there are known very few examples of
success in which excellent building materials suitable for
practical use are manufactured from an otherwise useless or
rather harmful industrial waste as the main starting material.
Turning now to give an overview of the industries involving
a serious problem of waste disposal to avoid environmental pollution,
the works of aluminum fabrication are typically notorious due to
the difficulties in the waste disposal. As is well known, aluminum
articles in recent years are used rarely as shaped by extrusion,
casting or other shaping means with the metallic aluminum surface
exposed but almost always used after surface finishing.
The method of surface finishing most widely undertaken in
the aluminum industry is, of course, the surface anodization in
which the surface of the aluminum article is e~ectrolytically
oxidized in an acidic electrolyte bath to be covered with a thin
but dense layer of aluminum oxide and imparted with increased
chemlcal and physical stability as well as beautifulness. A
problem in the anodizatlon treatment of aluminum articles is
that a considerable amount of aluminum metal unavoidably is
dissolved in the electrolyte bath and the thus dissolved aluminum
finally precipitates in the form of amorphous aluminum hydroxide
when the electrolyte solution is neutralized for sewage disposal.
The aluminum hydroxide thus precipitated usually forms a
gel-like sludge containing considerable amounts of impurities
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coming from several steps of the aluminum fabrication such as
sulfates, e.g. aluminum sulfate, aluminum hydroxysulfate, sodium
sulfate and the like and sodium aluminate. The gel-like sludge
usually contains large volumes, e.g. 70 to 90 ~ by weight, of
water but is hardly filtrable so that drying up of such an
aluminum hydroxide sludge is practically impossible. Therefore,
the only way in the prior art for the disposal of the aluminum
hydroxide sludge is to discard it in a reclaimed land or in the
ocean in the gel-like form as such.
Such a method of waste disposal is, of course, not quite
acceptable even by setting aside the problem of the iarge cost
for the transportation of such a waterish waste material to the
reclaimed land or off to the ocean. For example, a reclaimed
land filled with such a gel-like sludge is naturally weak in
the yield strength of the ground resulting in a decreased
utilizability of the land. Discarding of the sludge in the
ocean is also not free from regulations to prevent pollution
of water. Thus the waste disposal of the gel-like aluminum
hydroxide sludge has been the most troublesome problem in the
industry of aluminum fabrication.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide
a novel building material composed mainly of an amorphous
aluminum hydroxide converted at least partly to ettringite by
the reaction with a calciferous material and shaped into a
desired form by the aid of a fibrous reinforcing material. The
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mechanical properties of the shaped body may be further improved
by the combined use of a hydraulic material such as a Portland
cement.
Another object of the present invention is to provide a
novel and improved method for the manufacture of the above
mentioned building material starting with the above mentioned
gel-like aluminum hydroxide sludge produced in the process of
surface anodization of aluminum articles.
In the method of the invention, the gel-like sludge of
amorphous aluminum hydroxide is first admixed with a calciferous
material such as lime or gypsum whereby to be reacted at least
partly with the calciferous material to form ettringite 6CaO-
A1203 3SO3 31H20 and the aluminum hydroxide sludge containing
ettringite is then blended with a fibrous reinforcing material
and, optionally, a hydraulic material such as a Portland cement
and shaped into a desired form followed by drying.
The inventive building material described above is very
advantageous in the building industry, in addition to the out-
standing inexpensiveness, with high mechanical strengths by
virtue of the entrammeling structure of the fibrous reinforcing
material and the aluminum hydroxide andtor ettringite and the
excellent flame retardancy or non-inflammability due to the
large amount of the water of crystallization contained in the
ettringite as given above.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As is described above, the principal starting material used
in the invention is a gel-like sludge of amorphous aluminum hydro-
xide produced in large quantities as a waste material hardly
disposable in the anodization treatment of aluminum articles.
The sludge usually contains from 70 to 90 % by weight of water
or, in other words, only 10 to 30 % by weight of solid and has
fluidity. The sludge contains several kinds of impurities origi-
nating in various steps of the anodization treatment including
pre-treatment and post-treatment. For example, the alkaline
waste solution containing sodium aluminate formed in the pre-
treatment of degreasing with sodium hydroxide and following
washing with water is combined with the acidic waste solutions
formed in the anodization in an acidic electrolyte bath and
subsequent washing with water of the aluminum articles contain-
ing sulfuric acid, aluminum sulfate, aluminum hydroxysulfate and
the like according to the conditions of neutralization.
The aluminum hydroxide sludge above described is admixed
with a suitable amount of a calciferous material which can be
reacted with the aluminum hydroxide to form ettringite coopera-
tively with the sulfate constituents contained in the sludge.
Various kinds of calciferous materials are suitable for the
purpose including quick or slated lime, i.e. calcium oxide or
calcium hydroxide, calcium carbonate, gypsum, i.e~ calcium
sulfate, and the like. Limes are preferred due to the relatively
high reactivity with the aluminum hydroxide. For example, the
calcium hydroxide residue produced by the reaction of calcium
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carbide with water to evolve acetylene gas is suitably used.
Calcium oxide is sometimes preferred, however, because calcium
oxide is effective in controlling the water content of the
resultant sludge by the reaction with water content of the sludge
to form calcium hydroxide as well as in elevating the temperature
of the mixture with the heat of reaction with water to acceler-
ate the reaction of ettringite formation. It is of course
optional that the sludge is further diluted with an additional
amount of water but no additional water is usually required because
of the large water content in the starting aluminum hydroxide
sludge. Calcium sulfate, i.e. gypsum, is also an inexpensive
calciferous material obtained, for example, in the desulfurization
of exhaust gas from petroleum combustion. Dihydrated gypsum is
preferred although anhydrous and calcined gypsums may be used.
It is sometimes advantageous to use two kinds or more of the
calciferous materials in combination. In particular, combined
use of calcium oxide and dihydrated gypsum is recommended when
the balance among the aluminum, calcium and sulfate ions should
be taken into consideration to facilitate formation of the
ettringite.
The amount of the calciferous material to be added to the
aluminum hydroxide sludge naturally depends on the composition
of the sludge as well as the kind of the calciferous material
though not particularly limitative. It should be noted that
the use of an excessively large amount of calcium oxide or
hydroxide is undesirable because the free lime remaining in the
resultant product as unreacted with the aluminum hydroxide is
detrimental to the stability of the inventive building material.
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A preferred formulation in this respect is that 100 kg of the
aluminum hydroxide sludge is first admixed with 15 to 20 kg of
calcium oxide and the mixture is further admixed with dihydrated
gypsum in an amount of 1.0 to 1.2 times or, more preferably,
from 1.15 to 1.20 times by weight per dry amount of the mixture
of calcium oxide and the sludge.
The aluminum hydroxide sludge thus uniformly blended with
the calciferous material still retains fluidity with increased
temperature when calcium oxide is used as the calciferous
material by the heat of reaction with water. The mixture is
then kept standing at room temperature or above for 24 to 48
hours so that the reaction takes place between the amorphous
aluminum hydroxide and the calciferous material to form ettringite
of the formula 6CaO Al2O3 3SO3 3lH2O. It is optional that the
reaction is further accelerated by heating the mixture when a
suitable heating means is available. The formation of the
ettringite is readily detectable by the X-ray diffractometric
analysis and the reaction is continued until substantial
stability of the reaction mixture has been attained. As is
indicated by the X-ray analysis, the reaction mixture a~ter
completion of the reaction almost always contains several other
crystalline compounds such as calcite, gibbsite, woodfordite
and the like in addition to the ettringite depending on the
composition of the starting sludge as well as the kind of the
calciferous material.
The next step is blending of a fibrous reinforcing material
with the above obtained slurry-like aluminum hydroxide sludge
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at least partly converted to ettringite. When a fibrous material
is admixed and well blended with the sludge, coagulation takes
place in the mixture as the fibers are entrammeled by the gel-
like mass of the aluminum hydroxide and/or ettringite in the
sludge.
The fibrous material may be either organic or inorganic
according to need. The organic fibrous materials suitable for
use include wood pulp, unentangled cellulosic fibers obtained by
beating scrapped papers and various kinds of fibrous flues
originating in fiber-processing factories such as spinning and
weaving plants. These organic fibrous materials are preferred
when lightweight building materials with good heat insulation
are desired. On the other hand, inorganic fibrous materials
suitable for use include asbestos, rock wool, glass fibers and
the like and are preferred when high non-inflammability or flame
retardancy is desired of the inventive building material.
The amount of the fibrous material is naturally determined
with consideration of various factors. It should be noted that
no satisfaCtrY mechanical strengths or, in particular, bending
strength, can be imparted to the finished building material of
the invention when the amount of the fibrous reinforcing material
is too small.
The thus obtained blend of the ettringite-containing
reaction mixture and the fibrous reinforcing material may be
shaped into a desired form of a ceiling or wall board and the
like by a suitable shaping method in accordance with the
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consistency of the blend. It is noteworthy that the blend is
further admixed with ahydraulic material, i.e. a material curable
bY the reaction with water, such as a Portland cement or gypsum.
Various kinds of hydraulic cements are also suitable in place
of a Portland cement such as alumina cement, blastfurnace cement,
silica cement and the like. When an industrially advantageous
shaping process is desired, it is recommended that a high early
strength cement is used as combined with gypsum.
Although the additional admixture of the hydraulic material
is optional, the preferred proportions by weight of the ettringite-
containing reaction mixture, fibrous reinforcing material and
hydraulic material are as follows in a typical formulation: from
20 to 80 % or, preferably, from 40 to 60 % of the ettringite-
containing reaction mixture; from 15 to 55 % or, preferably, from
30 to 50 ~ of the hydraulic material; and from 10 to 55 % or,
preferably, from 15 to 25 % of the fibrous reinforcing material.
The addition of the hydraulic material is effective in improving
the moldability of the blend as well as in improving the mechanical
strengths and the dimensional stability of the finished building
material.
The blend of the ettringite-containing reaction mixture and
the fibrous reinforcing material with or without admixture of the
hydraulic material is then shaped into a desired form such as a
ceiling or wall board in a suitable shaping method, for example,
just in the same manner as in the manufacture of asbestos cement
boards. The inventive building material manufactured in the above
described manner has usually at least 80 kg/cm2 of the bending
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strength or up to 150 kg/cm or more of the bending strength in
some cases with an apparent density of about 0.9 to 1.3 g/cm3
after complete curing and drying. Accordingly, the inventive
building materials are very useful with these advantageous
characteristics not only for the buildings of factories and
warehouses but also living houses in general when beautiful or
decorative surface finishing is provided.
It is noteworthy that, when lime, i.e. calcium oxide or
hydroxide, is used as the calciferous material, the presence of
the free lime in the finished building material is undesirable
due to the decreased mechanical strengths and stability of the
material in the lapse of time so that the free lime should
desirably be converted into a stable form such as gypsum. In
this respect, it is sometimes advantageous to admix a sulfate such
as aluminum sulfate into the mixture before shaping so that the
free lime is converted to gypsum, i.e. calcium sulfate, by the
double decomposition reaction.
It is further noteworthy that some improvement in the
mechanical strengths, e.g. bending strength, is obtained by
partly replacing the aluminum hydroxide constituent of the
gel-like aluminum hydroxide sludge with a commercial grade
aluminum hydroxide, which is more or less crystalline. In
some most favorable cases, the bending strength of the resultant
building material may be increased by 20 to 35 % over the value
obtained without the replacement of the aluminum hydroxide
sludge with the crystalline aluminum hydroxide. The amount of
this replacement, however, should not exceed 20 % of the overall
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amount of the aluminum hydroxide constituent in the mixture
since the mechanical strengths of the building material rather
decrease by an excessive amount of the crystalline aluminum
hydroxide in addition to the economical disadvantage caused by
the use of such a relatively expensive material. Therefore, the
amount of the replacement is preferably 15 % or below or, more
preferably, in the range from 3 to 10 %.
Following are the examples to illustrate the present invention
in further detail but not to limit the scope of the invention in
any way.
Example 1.
A gel-like aluminum hydroxide sludge obtained from a plant
for the anodizat~on treatment of aluminum articles was admixed
with calcium oxide and dihydrated gypsum, which wasa by-product
obtained in the desulfurization of exhaust gas of petroleum
combustion. The lime and the gypsum were added in amounts of 5 kg
and 35 kg, respectively, per 40 kg of the dry material in the
sludge. By blending the calcium oxide, the temperature of the
mixture was markedly increased and, after thorough mixing, the
mixture still having fluidity was kept standing fro 48 hours.
The X-ray diffractometric analysis of the mixture after 48 hours
of standing indicated that the calcium constituent had almost
completely reacted and was converted to ettringite.
The thus obtained ettringite-containing slurry was then
admixed with 8 kg of wood pulp and 12 kg of asbestos. As these
fibrous materials were blended well with the slurry, the
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ettringite-containing solid matter in the slurry entrammeled the
fibers of the pulp and asbestos and coagulated. The thus obtained
mixture was relatively dry and in a condition disintegrable into
lumps substantially without free water.
The mixture was shaped into a form of a board of 6.8 mm
thickness by the techniques similar to the manufacture of
asbestos cement boards by use of a sheeting roller under a
linear pressure of 35 kg/cm and the thus shaped board was cured
for 7 days as wrapped followed by complete drying into a finished
board material. The board had an apparent density of 0.94 g/cm3
and a bending strength of 82.9 kg/cm2 as the averaged values for
100 boards prepared in the same way and was useful as a building
material.
Example 2.
The experimental procedure was substantially the same as
in Example 1 except that 10 kg of a Portland cement were added
to the ettringite-containing slurry together with the fibrous
materials of which the cellulosic fibrous material was not the
wood pulp but a reclaimed pulp obtained from scrapped papers.
The resultant board material had an apparent density of
1.15 g/cm3 and a bending strength of 128.5 kg/cm2 as the averaged
values for 100 boards prepared in the same way.
Example 3.
The experimental procedure was substantially the same as in
Example 2 except that 3 kg of a commercial grade aluminum hydro-
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xide were admixed with the reaction mixture of the gel-like
aluminum hydroxide sludge, calcium oxide and gypsum.
The resultant board material had an apparent density of
1.17 g/cm3 and a bending strength of 176.5 kg/cm2 as the averaged
values for 100 boards prepared in the same way.
