U.S. patent number RE42,352 [Application Number 12/285,248] was granted by the patent office on 2011-05-10 for method for producing aluminum magnesium titanate sintered product.
This patent grant is currently assigned to Ohcera Co., Ltd.. Invention is credited to Masaaki Fukuda, Masahiro Fukuda, Tsutomu Fukuda, Masahide Takahashi, Toshinobu Yoko.
United States Patent |
RE42,352 |
Fukuda , et al. |
May 10, 2011 |
Method for producing aluminum magnesium titanate sintered
product
Abstract
The present invention provides a process for preparing a
sintered body comprising as a basic component aluminum magnesium
titanate represented by the composition formula:
Mg.sub.xAl.sub.2(1-x)Ti.sub.(1+x)O.sub.5 wherein the value of x is
0.1.ltoreq.x<1. The process comprises a step of sintering a
formed product from a raw material mixture comprising 100 parts by
weight, calculated on an oxide basis, of a mixture comprising a
Mg-containing compound, an Al-containing compound and a
Ti-containing compound at the same metal component ratio as the
metal component ratio of Mg, Al and Ti in the above composition
formula, and 1 10 parts by weight of an alkali feldspar represented
by the composition formula: (Na.sub.yK.sub.1-y)AlSi.sub.3O.sub.8
wherein the value of y is 0.ltoreq.y.ltoreq.1. According to the
process of the present invention, a sintered body of aluminum
magnesium titanate having stability in continuous use at high
temperatures and excellent mechanical strength, while maintaining
inherently low thermal expansibility of a sintered body of aluminum
magnesium titanate, can be obtained.
Inventors: |
Fukuda; Tsutomu (Kakogawa,
JP), Fukuda; Masahiro (Uji, JP), Fukuda;
Masaaki (Kakogawa, JP), Yoko; Toshinobu (Uji,
JP), Takahashi; Masahide (Uji, JP) |
Assignee: |
Ohcera Co., Ltd. (Osaka,
JP)
|
Family
ID: |
32211826 |
Appl.
No.: |
12/285,248 |
Filed: |
October 9, 2003 |
PCT
Filed: |
October 09, 2003 |
PCT No.: |
PCT/JP03/12933 |
371(c)(1),(2),(4) Date: |
April 06, 2005 |
PCT
Pub. No.: |
WO2004/039747 |
PCT
Pub. Date: |
May 13, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
10530476 |
Apr 6, 2005 |
7166552 |
Jan 23, 2007 |
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Foreign Application Priority Data
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Nov 1, 2002 [JP] |
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2002-319934 |
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Current U.S.
Class: |
501/136; 264/674;
501/134; 501/118; 264/681 |
Current CPC
Class: |
C04B
35/465 (20130101); C04B 35/478 (20130101); C04B
35/638 (20130101); C04B 2235/3222 (20130101); C04B
2235/3472 (20130101); C04B 2235/3206 (20130101); C04B
2235/3231 (20130101); C04B 2235/6562 (20130101); C04B
2235/9607 (20130101); C04B 2235/80 (20130101); C04B
2235/3217 (20130101); C04B 2235/3232 (20130101); C04B
2235/96 (20130101) |
Current International
Class: |
C04B
35/478 (20060101) |
Field of
Search: |
;501/134,136,118
;264/674,681 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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506475 |
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Sep 1992 |
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EP |
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1338581 |
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May 2003 |
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EP |
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1652830 |
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May 2006 |
|
EP |
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4-280863 |
|
Oct 1992 |
|
JP |
|
07025662 |
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Jan 1995 |
|
JP |
|
2002-145659 |
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May 2002 |
|
JP |
|
0238519 |
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May 2002 |
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WO |
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Other References
Buscaglia et al; Decomposition of AI2TiO5 and AIMgTiO5 Ceranics, J.
Am. Ceram. Soc. 81 (10)(1998)pp. 2645-2653. cited by examiner .
International Search report dated Jan. 27, 2004. cited by examiner
.
"Property and Application of Aluminum Titanate Ceramics", Foshan
Ceramics (2003), vol. 10, No. 3, Serial 41;pp. 4-6 with English
Abtract. cited by examiner .
"Aluminum Titanate Ceramics and Application", Shandong
Ceramics,(2000) vol. 23, No. 2; with English Abstract. cited by
examiner .
"New Development in Research of Aluminum Tianate Ceramics",
Bulletin of the Chinese Ceramic Society (1999); No. 4, pp. 53-59
with English Abstract. cited by examiner .
"The Effect of Additives to the Property of Aluminum Tianate",
Refractories (2001), col. 35, No. 2, pp. 87-88, with English
Abstract. cited by examiner .
"Research of the Efeect of Different ASdditives to Coefficient of
Thermal Expansion of Aluminum Titanate", J. of In. Mat. (2000),
vol. 15, No. 3 pp. 438-440, with English Abstract. cited by
examiner .
Cinese Office Action dated Jun. 30, 2006 with English Translation.
cited by examiner .
Huang et al.: "Thermal and mechanical properties of aluminum
titanate-mullite composites." J. Mater. Res., vol. 15, No. 2, Feb.
2000, pp. 357-363. cited by other .
Supplementary European Search Report dated Apr. 10, 2007. cited by
other.
|
Primary Examiner: Group; Karl E
Attorney, Agent or Firm: Kratz, Quintos & Hanson,
LLP
Claims
The invention claimed is:
1. A process for producing a sintered body comprising as a basic
component aluminum magnesium titanate represented by the
composition formula: Mg.sub.xAl.sub.2(1-x)Ti.sub.(1+x)O.sub.5
wherein the value of x is 0.1.ltoreq.x<1, the process comprising
a step of sintering a formed product from a raw material mixture
comprising the ingredients (i) and (ii) below: (i) 100 parts by
weight, calculated on an oxide basis, of a mixture comprising a
Mg-containing compound, an Al-containing compound and a
Ti-containing compound at the same metal component ratio as the
metal component ratio of Mg, Al and Ti in the composition formula,
(ii) 1 10 parts by weight of an alkali feldspar represented by the
composition formula: (Na.sub.yK.sub.1-y)AlSi.sub.3O.sub.8 wherein
the value of y is 0.ltoreq.y.ltoreq.1.
2. A process of producing a sintered body of aluminum magnesium
titanate according to claim 1, wherein the value of x in the
composition formula: Mg.sub.xAl.sub.2(1-x)Ti.sub.(1+x)O.sub.5 is
0.25.ltoreq.x.ltoreq.0.75.
3. A process of producing a sintered body of aluminum magnesium
titanate according to claim 1, wherein the value of y in the
composition formula: (Na.sub.yK.sub.1-y)AlSi.sub.3O.sub.8 is
0.15.ltoreq.y.ltoreq.0.85.
4. A process of producing a sintered body of aluminum magnesium
titanate according to claim 1, wherein a sintering temperature is
1000 1700.degree. C.
5. A sintered body of aluminum magnesium titanate which is
obtainable by the process of claim 1.
.Iadd.6. A sintered body of aluminum magnesium titanate comprising,
calculated on an oxide basis, the following amounts of components
(i) to (v): (i) 100 parts by weight of aluminum magnesium titanate
represented by the composition formula:
Mg.sub.xAl.sub.2(1-x)Ti.sub.(1+x)O.sub.5 wherein the value of x is
0.1.ltoreq.x<1, (ii) 0.18 to 1.95 parts by weight of
Al.sub.2O.sub.3; (iii) 0.65 to 6.87 parts by weight of SiO.sub.2;
(iv) 0 to 1.18 parts by weight of Na.sub.2O; and (v) 0 to 1.69
parts by weight of K.sub.2O, and the amounts of Si, Na and K
contained in the sintered body, calculated as SiO.sub.2, Na.sub.2O
and K.sub.2O respectively, satisfy the following relation:
(Na.sub.2O+K.sub.2O)/SiO.sub.2=0.172 to 0.261. .Iaddend.
.Iadd.7. The sintered body of aluminum magnesium titanate according
to claim 6 wherein Si dissolves into the crystal system of aluminum
titanate and occupies mainly Al site. .Iaddend.
.Iadd.8. The sintered body of aluminum magnesium titanate according
to claim 6 wherein a pair of Si and Mg replaces neighboring two Al
atoms. .Iaddend.
Description
TECHNICAL FIELD
The present invention relates to a process of producing a sintered
body of aluminum magnesium titanate.
BACKGROUND ART
Aluminum magnesium titanate is a solid solution which has a
complete solubility in the solid state throughout the entire
composition region of aluminum titanate-magnesium titanate. A
sintered body of the same has as low a coefficient of thermal
expansion and as high a corrosion resistance as aluminum titanate
sintered bodies. The melting point of aluminum magnesium titanate
is, for example, about 1640.degree. C. in a sintered body in which
aluminum titanate and magnesium titanate are dissolved into each
other at an approximately equivalent molar ratio. This temperature
is lower than the melting point of aluminum titanate, about
1870.degree. C., but is higher than the melting point of magnesium
titanate, about 1600.degree. C. Therefore, in general, the
heat-resistant high temperature limit of aluminum magnesium
titanate is lower than that of aluminum titanate, but is higher
than that of magnesium titanate.
Aluminum titanate sintered bodies and magnesium titanate sintered
bodies are constructed from the crystal grains having the
pseudobrookite type crystal structure, and their coefficients of
thermal expansion are anisotropic. For this reason, displacement at
the crystal grain boundary tends to be caused when heated or cooled
and micro cracks and apertures may be formed, leading to
disadvantageously lowered mechanical strength. Since aluminum
magnesium titanate has similar disadvantages, the strength of its
sintered body is also insufficient. Particularly when used for an
application in which high temperatures and heavy loads are applied,
it cannot exhibit sufficient durability.
The lower limit of the temperature for synthesizing aluminum
titanate is 1280.degree. C., while the lower limit of the
temperature for synthesizing magnesium titanate is 900.degree. C.
Both are unstable in the temperature region lower than their
synthesizing temperatures. A solid solution of these compounds,
aluminum magnesium titanate is unstable at a temperature lower than
the synthesizing temperature region as well as aluminum titanate
and magnesium titanate, and thus is tend to thermally decompose
into TiO.sub.2 (rutile) and MgAl.sub.2O.sub.4 (spinel) when
continuously used in the decomposition temperature range for a long
time. Herein, the decomposition temperature range of aluminum
magnesium titanate differs depending on the dissolving ratio of
aluminum titanate and magnesium titanate, but is normally within
the temperature range of about 800 1280.degree. C. For example, a
sintered body of aluminum magnesium titanate in which aluminum
titanate and magnesium titanate are dissolved at an approximately
equivalent molar ratio, when continuously used for a long period in
a temperature range of about 1100.degree. C., thermally decomposes
into TiO.sub.2 (rutile) and MgAl.sub.2O.sub.4 (spinel) (Vincenzo
Buscaglia et al. "Decomposition of Al.sub.2TiO.sub.5 and
Al.sub.2(1-x)Mg.sub.xTi.sub.(1+x)O.sub.5 Ceramics", Journal of
American Ceramic Society, 1998, 81 [10], pp. 2645 2653). For this
reason, a sintered body of aluminum magnesium titanate cannot be
continuously used in such a decomposition temperature range.
DISCLOSURE OF THE INVENTION
A primary object of the present invention is to provide a sintered
body of aluminum magnesium titanate having excellent mechanical
strength and stability in continuous use at high temperatures, as
well as inherently low thermal expansibility of sintered body of
aluminum magnesium titanate.
The inventors of the present invention carried out extentsive
research to overcome the foregoing problems of known art. They
consequently found that a sintered body of aluminum magnesium
titanate having high mechanical strength, a low coefficient of
thermal expansion, excellent decomposition resistance and fire
resistance can be obtained by using a raw material mixture prepared
by adding a specific alkali feldspar to a mixture comprising a
Mg-containing compound, an Al-containing compound and a
Ti-containing compound. The present invention was accomplished on
the basis of this finding.
Specifically, the present invention provides the following
processes for producing a sintered body of aluminum magnesium
titanate:
1. A process for producing a sintered body comprising as a basic
component aluminum magnesium titanate represented by the
composition formula: Mg.sub.xAl.sub.2(1-x)Ti.sub.(1+x)O.sub.5
wherein the value of x is 0.1.ltoreq.x<1,
the process comprising a step of sintering a formed product from a
raw material mixture comprising the ingredients (i) and (ii)
below:
(i) 100 parts by weight, calculated on an oxide basis, of a mixture
comprising a Mg-containing compound, an Al-containing compound and
a Ti-containing compound at the same metal component ratio as the
metal component ratio of Mg, Al and Ti in the composition
formula,
(ii) 1 10 parts by weight of an alkali feldspar represented by the
composition formula: (Na.sub.yK.sub.1-y)AlSi.sub.3O.sub.8 wherein
the value of y is 0.ltoreq.y.ltoreq.1.
2. A process of producing a sintered body of aluminum magnesium
titanate according to item 1, wherein the value of x in the
composition formula: Mg.sub.xAl.sub.2(1-x)Ti.sub.(1+x)O.sub.5 is
0.25.ltoreq.x.ltoreq.0.75.
3. A process of producing a sintered body of aluminum magnesium
titanate according to item 1 or 2, wherein the value of y in the
composition formula: (Na.sub.yK.sub.1-y)AlSi.sub.3O.sub.8 is
0.15.ltoreq.y.ltoreq.0.85.
4. A process of producing a sintered body of aluminum magnesium
titanate according to any one of items 1 3, wherein a sintering
temperature is 1000 1700.degree. C.
5. An sintered body of aluminum magnesium titanate which is
obtainable by the process of any one of claims 1 4.
The process of the present invention is a process for preparing a
sintered body comprising as a basic component aluminum magnesium
titanate represented by the composition formula:
Mg.sub.xAl.sub.2(1-x)Ti.sub.(1+x)O.sub.5 (wherein the value of x is
0.1.ltoreq.x<1),
and comprises a step of sintering a formed product from a raw
material mixture comprising the ingredients (i) and (ii) below:
(i) 100 parts by weight, calculated on an oxide basis, of a mixture
comprising a Mg-containing compound, an Al-containing compound and
a Ti-containing compound at the same metal component ratio as the
metal component ratio of Mg, Al and Ti in the composition
formula,
(ii) 1 10 parts by weight of an alkali feldspar represented by the
composition formula: (Na.sub.yK.sub.1-y)AlSi.sub.3O.sub.8 wherein
the value of y is 0.ltoreq.y.ltoreq.1.
In the above composition formula:
Mg.sub.xAl.sub.2(1-x)Ti.sub.(1+x)O.sub.5, the value of x is
0.1.ltoreq.x<1, preferably 0.25.ltoreq.x.ltoreq.0.75.
Any Mg-containing compound, Al-containing compound and
Ti-containing compound can be used as a raw material without
limitation insofar as it is a substance which can synthesize
aluminum magnesium titanate by sintering. As a Mg-containing
compound, an Al-containing compound and a Ti-containing compound, a
different compound may be used for each, or a compound comprising
two or more of the metal components may be used. These compounds
used can be normally suitably selected from those used as a raw
material for forming ceramics such as alumina ceramics, titania
ceramics, magnesia ceramics, aluminum titanate ceramics, magnesium
titanate ceramics, spinel ceramics, aluminum magnesium titanate
ceramics and the like. For example, Al.sub.2O.sub.3, TiO.sub.2,
MgO, and like oxides; MgAl.sub.2O.sub.4, Al.sub.2TiO.sub.5, various
oxide having spinel-structures comprising Mg and Ti, and like
complex oxides comprising two or more types of metal components;
compounds (carbonates, nitrates, sulfates, etc.) comprising one or
more types of metal components selected from the group consisting
of Al, Ti and Mg; among others, can be used.
Mg-, Al- and Ti-containing compounds can be mixed at such a ratio
that the ratio of the metal components contained in these compounds
is the same ratio as that of the metal components Mg, Al and Ti in
the above aluminum magnesium titanate represented by the
composition formula: Mg.sub.xAl.sub.2(1-x)Ti.sub.(1+x)O.sub.5
(wherein x is the same as described above). By using the above
compounds in such a proportion, it is possible to obtain a sintered
body comprising as a basic component an aluminum magnesium titanate
which has the ratio of the metal components equal to the ratio of
the metal components in a mixture used as a raw material.
In the present invention, it is necessary to further add an alkali
feldspar as an additive to the above mixture comprising a
Mg-containing compound, an Al-containing compound and a
Ti-containing compound.
Alkali feldspar used herein is represented by the composition
formula: (Na.sub.yK.sub.1-y)AlSi.sub.3O.sub.8. Such an alkali
feldspar is a sintering aid for aluminum magnesium titanate, and
also serves to add a Si component to aluminum magnesium titanate.
In the above composition formula, the value of y is
0.ltoreq.y.ltoreq.1, preferably 0.1.ltoreq.y.ltoreq.1, more
preferably 0.15.ltoreq.y.ltoreq.0.85. The alkali feldspar with the
value of y in this range has a low melting point, and is
particularly effective in prompting sintering of aluminum magnesium
titanate.
The amount of an alkali feldspar used may be about 1 10 parts by
weight, preferably about 3 5 parts by weight, relative to 100 parts
by weight, calculated on an oxide basis, of the total amount of the
Mg-, Al- and Ti-containing compounds used as raw materials. The
amounts of the raw material compounds in this case are those
calculated the Mg-, Al- and Ti-containing compounds as MgO,
Al.sub.2O.sub.3 and Ti.sub.2O, respectively.
According to the present invention, the above specific alkali
feldspar is added to a mixture comprising a Mg-containing compound,
an Al-containing compound and a Ti-containing compound as an
additive and this mixture is formed into a predetermined shape to
be sintered, whereby an sintered body of aluminum magnesium
titanate with high mechanical strength and resistance to thermal
decomposition can be obtained.
The reason why the sintered body with high mechanical strength and
resistance to thermal decomposition can be obtained by the process
of the present invention is undetermined, but is presumably as
follows:
Thus, the alkali feldspar used in the process of the present
invention becomes in the liquid state around a temperature at which
aluminum magnesium titanate is synthesized. By adding such an
alkali feldspar to the raw material mixture and sintering the same,
a reaction which synthesizes aluminum magnesium titanate is caused
in the liquid phase, forming a compact sintered body. Because this
additive has been dissolved into aluminum magnesium titanate in the
first sintering step, the additive does not become liquid when
heating again the formed sintered body. The strength of the
sintered body is therefore not lowered. In addition, when a Si
component contained in an alkali feldspar dissolves into the
aluminum magnesium titanate crystal lattice in sintering step for
synthesizing aluminum magnesium titanate, it dissolves
preferentially into the crystal system of aluminum titanate rather
than into the crystal system of magnesium titanate. This is because
aluminum titanate has greater distortion in the octahedron
structure constituting the crystal than magnesium titanate among
pseudobrookite type crystal structures, and hence the
crystallographic anisotropy is significantly high and crystal
structure is unstable. Therefore, Si dissolving into aluminum
magnesium titanate crystal lattice dissolves into the crystal
system of aluminum titanate, and occupies mainly the Al sites. At
this time, tetravalent Si, instead of solely replacing the Al sites
which originally keep their electrical charge balance by being
trivalent, make pairs with divalent Mg present in the system to be
sexivalent with both Si and Mg in total and replace the neighboring
two Al atoms (sexivalent in total) more easily. This can be also
explained from the correlation of the ion radius of each cation.
That is, since the ion radii of Si.sup.4+ and Mg.sup.2+ are 0.54
.ANG. and 0.86 .ANG., respectively, and the mean ion radius of them
is thus 0.70 .ANG., which is approximate to the ion radius of
Al.sup.3+, 0.68 .ANG.. Accordingly, the occupation of the Al sites
by the pair of Si and Mg can be thought to be a dissolving state
more reasonable in energy than replacing solely by Si. Thus, it is
considered that aluminum magnesium titanate can inhibit the ion
diffusion between the cations even at high temperatures by the use
of Si and Mg in combination, thus having a stable crystal
structure.
From the reasons mentioned above, the obtained sintered body of
aluminum magnesium titanate is thought to show improved mechanical
strength and very high resistance to thermal decomposition due to
stabilization of the crystal structure.
A raw material mixture prepared by adding alkali feldspar to a
mixture comprising a Mg-containing compound, an Al-containing
compound and a Ti-containing compound may be sufficiently mixed and
pulverized to an appropriate grain size, and then formed into a
predetermined shape.
The mixing and pulverizing process of the raw material mixture is
not particularly restricted and may be conducted according to a
known method. For example, mixing and pulverizing can be conducted
by using a ball mill, stirred media mill, etc.
The degree of pulverization of the raw material mixture is not
particularly limited. It is normally pulverized to the grain size
of about 1 .mu.m or less, preferably to as small grain size as
possible, as long as secondary particles are not formed.
A forming aid, if necessary, may be further added to the raw
material mixture. As a forming aid, a known substance which has
been used may be used depending on the forming process.
As such a forming aid, for example, polyvinyl alcohol, microwax
emulsion, carboxymethyl cellulose and like binders, stearic acid
emulsion and like mold releasing agents, n-octyl alcohol,
octylphenoxy ethanol and like antifoaming agents, diethylamine,
triethylamine and like deflocculants can be used.
The amount of a forming aid used is not particularly limited
either, and may be suitably selected from the range of amounts for
a known one depending on the forming process. For example, when
forming is conducted by slip casting, it is possible to use about
0.2 0.6 parts by weight of a binder, about 0.5 1.5 parts by weight
of a deflocculant, about 0.2 0.7 parts by weight of a mold
releasing agent (solid basis), and about 0.5 1.5 parts by weight of
an antifoaming agent, relative to 100 parts by weight, calculated
on an oxide basis, of the total amount of the Mg- , Al- and
Ti-containing compounds used as raw materials.
The forming process of the raw material mixture is not particularly
limited, and, for example, press molding, sheet casting, slip
casting, extrusion, injection molding, CIP molding and like known
forming processes may be suitably employed.
The sintering temperature may be any temperature which is necessary
for aluminum magnesium titanate to be synthesized. Normally, it may
be about 1000 1700.degree. C., preferably about 1250 1450.degree.
C.
The atmosphere for sintering is not particularly limited, and may
be any of an oxygen-containing atmosphere such as air, a reducing
atmosphere and an inert atmosphere, which are heretofore
employed.
The sintering time is not particularly limited, and may be such
that the formed product is sufficiently sintered, depending on the
shape of the formed product, etc. Normally, the product may be
maintained in the above temperature range for about 1 10 hours.
The heating rate and cooling rate in sintering are not particularly
limited, and may be suitably selected so that no cracks are formed
in the sintered body. For example, to sufficiently remove water,
organic binder and the like contained in the raw material, it is
preferable to raise the temperature not abruptly but gradually. In
addition, prior to heating to the above sintering temperature,
calcination can be conducted, if necessary, by slowly heating in a
temperature range of about 700 1000.degree. C. for about 10 30
hours. By this calcination, when aluminum magnesium titanate is
synthesized, the stress in the sintered body, which causes cracks,
can be mitigated to inhibit the formation of cracks, providing a
compact and uniform sintered body.
The sintered body of aluminum magnesium titanate obtained by the
process of the present invention is a sintered body which comprises
the aluminum magnesium titanate represented by the above
composition formula: Mg.sub.xAl.sub.2(1-x)Ti.sub.(1+x)O.sub.5
(wherein the value of x is 0.1.ltoreq.x<1) as a basic component
and in which the Si component contained in the alkali feldspar as
an additive is dissolved into the crystal lattice of aluminum
magnesium titanate. Such a sintered body has excellent resistance
to thermal decomposition because it has both high mechanical
strength and low coefficient of thermal expansion and its crystal
structure is stabilized. As a result, the thermal decomposition
reaction of aluminum magnesium titanate is inhibited and therefore
the sintered body can be stably used at a temperature ranging from
room temperature to as high as about 1600.degree. C. The mechanical
strength is very high compared to a conventional sintered body of
aluminum magnesium titanate as it can have mechanical strength up
to about 70 MPa.
Furthermore, according to the process of the present invention,
sintering can be conducted without forming cracks, providing a
compact sintered body. Accordingly, the obtained sintered body is
given good resistance to thermal shock and corrosion
resistance.
Using the above excellent characteristics, the sintered body of
aluminum magnesium titanate obtained by the process of the present
invention can be used as, for example, an automobile exhaust
filter, an automobile exhaust filter for DPF (diesel particulate
filter) apparatus, etc. Further, using its low thermal
expansibility, it can also be effectively used as a surface plate
for printing process in the LSI manufacturing process, etc. It can
also be applied for the furnace walls of high-temperature furnaces
and the furnace walls of refuse incinerators etc.
As stated above, the sintered body of aluminum magnesium titanate
obtained by the preparation processes of the present invention has
high mechanical strength and resistance to thermal decomposition,
while maintaining the inherently low coefficient of thermal
expansion of aluminum magnesium titanate, and can be stably used in
the temperature range of 800.degree. C. 1280.degree. C. in which a
known sintered body of aluminum titanate cannot be used for a long
period continuously. In addition, the sintered body of aluminum
magnesium titanate also has good refractoriness, and can be used in
a high temperature range of 1500.degree. C. or higher in which
magnesium titanate cannot be used.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing the change of residual aluminum magnesium
titanate percentage .alpha. (%) over time in the sintered bodies
obtained in Example 2 and Comparative Example 2 placed in the
atmosphere at 1100.degree. C.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is described below in more details with
reference to Examples.
EXAMPLE 1
To 100 parts by weight of a mixture comprising 26.7% by weight (20
mol %) of sinterable .alpha.-alumina, 62.8% by weight (60 mol %) of
titanium oxide in anatase form and 10.5% by weight (20 mol %) of a
natural mineral, magnesium oxide in periclase form, were added 4
parts by weight of an alkali feldspar represented by the chemical
formula: (Na.sub.0.6K.sub.0.4)AlSi.sub.3O.sub.8, 0.25 parts by
weight of polyvinyl alcohol as a binder, 1 part by weight of
diethylamine as a deflocculant, and 0.5 parts by weight of
polypropylene glycol as an antifoaming agent. The mixture was mixed
using a ball mill for 3 hours, and then dried using a dryer at
120.degree. C. for at least 12 hours, giving a raw material
powder.
The resulting raw material powder was pulverized to about 150 mesh
and pressed under a pressure of 60 MPa, giving a molded product
measuring 100 mm.times.100 mm.times.10 mm.
This molded product was sintered according to the heating pattern 1
below in the atmosphere and thereafter left to cool, giving a
sintered body of aluminum magnesium titanate.
(Heating Pattern 1)
from room temperature to 140.degree. C. for 21 hours maintained at
140.degree. C. for 14 hours (water evaporation) from 140 to
216.degree. C. for 21 hours (gradual evaporation of water inside
the sample) from 216 to 295.degree. C. for 16 hours (organic binder
combustion) from 295 to 379.degree. C. for 46 hours (magnesium
hydroxide removal) from 379 to 458.degree. C. for 20 hours (organic
binder combustion) from 458 to 700.degree. C. for 28 hours
(residual carbon combustion) maintained at 700.degree. C. for 3
hours from 700 to 1000.degree. C. for 26 hours (calcination) from
1000 to 1250.degree. C. for 2 hours maintained at 1250.degree. C.
for 2 hours (sintering)
A 3 mm.times.4 mm.times.40 mm sample was cut from the sintered body
of aluminum magnesium titanate obtained by the above process. The
surface of the sample was polished and the arris of the sample was
ground (removal of sharp edges), and then its three-point bending
strength was determined. As a result, the three-point bending
strength was 69.3.+-.3.1 MPa.
As Comparative Example 1, a sintered body of aluminum magnesium
titanate was obtained in the same manner as the above process
except that no alkali feldspar was added. The three-point bending
strength of this sintered body was determined in the same process.
The result was 21.1.+-.2.1 MPa.
It can be seen from these results that the sintered body of
aluminum magnesium titanate obtained by the process of the present
invention has very high mechanical strength compared to a known
sintered body of aluminum magnesium titanate.
EXAMPLE 2
To 100 parts by weight of a mixture comprising 37.3% by weight (25
mol %) of an oxide having a spinel structure and represented by the
chemical formula: MgAl.sub.2O.sub.4 and 62.7% by weight (75 mol %)
of titanium oxide in anatase form were added 4 parts by weight of
an alkali feldspar represented by the chemical formula:
(Na.sub.0.6K.sub.0.4)AlSi.sub.3O.sub.8, 0.25 parts by weight of
polyvinyl alcohol as a binder, 1 part by weight of diethylamine as
a deflocculant and 0.5 parts by weight of polypropylene glycol as
an antifoaming agent. The mixture was mixed using a ball mill for 3
hours, and then dried using a dryer at 120.degree. C. for at least
12 hours, giving a raw material powder.
The resulting raw material powder was pulverized to about 150 mesh
and pressed under a pressure of 60 MPa, giving a molded product
measuring 100 mm.times.100 mm.times.10 mm.
This molded product was sintered in the atmosphere according to the
heating pattern 2 below and then left to cool, giving a sintered
body of aluminum magnesium titanate.
(Heating Pattern 2)
from room temperature to 140.degree. C. for 21 hours maintained at
140.degree. C. for 14 hours (water evaporation) from 140 to
216.degree. C. for 21 hours (gradual evaporation of water inside
the sample) from 216 to 295.degree. C. for 16 hours (organic binder
combustion) from 295 to 379.degree. C. for 46 hours (magnesium
hydroxide removal) from 379 to 458.degree. C. for 20 hours (organic
binder combustion) from 458 to 700.degree. C. for 28 hours
(residual carbon combustion) maintained at 700.degree. C. for 3
hours from 700 to 1000.degree. C. for 26 hours (calcination) from
1000 to 1400.degree. C. for 3 hours maintained at 1400.degree. C.
for 4 hours (sintering)
The three-point bending strength of the resulting sintered body of
aluminum magnesium titanate was determined in the same manner as
Example 1. The result was 28.2.+-.1.7 MPa.
In contrast, As Comparative Example 2, a sintered body of aluminum
magnesium titanate was obtained in the same manner as the above
process except that no alkali feldspar was added. The three-point
bending strength of this sintered body was determined by the same
process. The result was 9.6.+-.0.6 MPa.
It can be seen from these results that the sintered body of
aluminum magnesium titanate obtained by the process of the present
invention has very high mechanical strength compared to a known
sintered body of aluminum magnesium titanate.
Meanwhile, a 5 mm.times.5 mm.times.20 mm sample was cut from each
of the sintered body of aluminum magnesium titanate of Example 2
and the sintered body of Comparative Example 2. After the surfaces
of the samples were polished, the coefficients of thermal expansion
of the samples were determined at the heating rate of 20.degree.
C./min. The results are shown in Table 1 below.
TABLE-US-00001 TABLE 1 Percentage of Coefficient of thermal
expansion thermal Temperature (.DELTA.L/L) expansion .degree. C. %
.times.10.sup.-06 (1/K) Example 2 Aluminum magnesium titanate with
additive (x = 0.5) 50 0.002 0.57 150 0.007 0.52 250 0.017 0.76 350
0.033 0.99 450 0.051 1.18 550 0.073 1.38 650 0.100 1.59 750 0.138
1.90 850 0.191 2.30 Comparative Example 2 Aluminum magnesium
titanate with no additive (x = 0.5) 50 -0.001 -0.44 150 -0.003
-0.20 250 0.001 0.04 350 0.005 0.16 450 0.015 0.36 550 0.029 0.55
650 0.045 0.72 750 0.070 0.97 850 0.109 1.32
As can be seen from the results shown above, the sintered body of
aluminum magnesium titanate obtained in Example 2 has a very low
coefficient of thermal expansion as the sintered body of aluminum
magnesium titanate obtained in Comparative Example 2. This
demonstrates that the sintered body in Example 2 maintains
inherently low thermal expansibility of aluminum magnesium
titanate.
Next, a 10 mm.times.10 mm.times.10 mm samples was cut from each of
the sintered body of aluminum magnesium titanate of Example 2 and
the sintered body of aluminum magnesium titanate of Comparative
Example 2. The samples were placed in the atmosphere at
1100.degree. C. and their changes of residual aluminum magnesium
titanate percentage .alpha.(%) over time were determined.
The residual aluminum magnesium titanate percentage was determined
by X-ray diffraction measurement (XRD) by the following manner.
First, since TiO.sub.2 (rutile) and MgAl.sub.2O.sub.4 (spinel) are
formed when aluminum magnesium titanate thermally decomposes, the
ratio R of the diffraction intensity of aluminum magnesium titanate
to that of rutile was determined by the formula below using the
integrated intensity (I.sub.T102(110)) of the diffraction peak of
the (110) face of rutile and the integrated intensity
(I.sub.MAT(023)) of the diffraction peak of the (023) face of
aluminum magnesium titanate:
R=I.sub.MAT(023)/{I.sub.MAT(023)+I.sub.TiO2(110)}
Further, the ratio R.sub.0 of the diffraction intensity of aluminum
magnesium titanate to that of rutile for the sintered body prior to
conducting heat treatment at 1100.degree. C. was also determined by
the same manner.
Second, using R and R.sub.o, determined by the above manner, the
residual aluminum magnesium titanate percentage .alpha.(%) was
determined by the following formula:
.alpha.=(R/R.sub.0).times.100
The changes of the residual aluminum magnesium titanate percentage
.alpha.(%) of the sintered bodies of Example 2 and Comparative
Example 2 over time are shown in a graph of FIG. 1.
As can be seen from FIG. 1, the sintered body of aluminum magnesium
titanate of Example 2 can maintain a high value of the residual
aluminum magnesium titanate percentage for a long period, compared
with the sintered body of aluminum titanate of Comparative Example
2 obtained without adding an alkali feldspar, when left under a
high temperature condition of 1100.degree. C. It can be known from
this result that the sintered body of Example 2 has excellent
resistance to thermal decomposition.
EXAMPLES 3 8
Sinterable .alpha.-alumina, titanium oxide in anatase form and
magnesium oxide in periclase form were mixed in the proportion
shown in Table 2 below, giving a raw material mixture.
TABLE-US-00002 TABLE 2 Percentage of raw materials in mol %
Al.sub.2O.sub.3 TiO.sub.2 MgO Example 3 43 52 5 Example 4 33 56 11
Example 5 25 58 17 Example 6 15 62 23 Example 7 9 64 27 Example 8 2
66 32
To 100 parts by weight of the obtained mixture were added 4 parts
by weight of an alkali feldspar represented by the chemical
formula: (Na.sub.0.6K.sub.0.4)AlSi.sub.3O.sub.8, 0.25 parts by
weight of polyvinyl alcohol as a binder, 1 part by weight of
diethylamine as a deflocculant and 0.5 parts by weight of
polypropylene glycol as an antifoaming agent. The mixture was mixed
using a ball mill for 3 hours, and then dried using a dryer at
120.degree. C. for at least 12 hours, giving a raw material
powder.
The resulting raw material powder was pulverized to about 150 mesh
and pressed under a pressure of 60 MPa, giving a molded product
measuring 100 mm.times.100 mm.times.10 mm.
This molded product was sintered in the atmosphere under the same
conditions as the heating conditions (heating pattern 2) in Example
2 and then left to cool, giving a sintered body of aluminum
magnesium titanate.
A 3 mm.times.4 mm.times.40 mm sample was cut from each of the
obtained sintered bodies of aluminum magnesium titanate. After the
surfaces of the samples were polished and their arrises were ground
(removal of sharp edges), their three-point bending strength were
determined.
Meanwhile, a 5 mm.times.5 mm.times.20 mm sample was cut from each
of the sintered bodies. After the surfaces of the samples were
polished, their coefficients of thermal expansion were determined
based on the expansion in the longitudinal direction when they were
heated from 50.degree. C. to 800.degree. C. at the heating rate of
20.degree. C./min.
The results are shown in Table 3 below. The measurement results of
the sintered bodies of Examples 1, 2 and Comparative Examples 1, 2
are also described in Table 3.
Furthermore, the value of X in the composition formula:
Mg.sub.xAl.sub.2(1-x)Ti.sub.(1+x)O.sub.5 is also described in Table
3.
TABLE-US-00003 TABLE 3 Three-point bending strength Coefficient
(.+-.standard of thermal Value deviation) expansion of X Mpa
.times.10.sup.-06 (l/K) Heating pattern 1 Example 1 0.5
69.3(.+-.3.1) 2.6 Comparative 0.5 21.1(.+-.2.1) 2.4 Example 1
Heating pattern 2 Example 2 0.5 28.2(.+-.1.7) 1.9 Example 3 0.1
45.6(.+-.1.5) 0.3 Example 4 0.25 38.6(.+-.1.1) 1.0 Example 5 0.4
42.8(.+-.2.2) 1.7 Example 6 0.6 47.4(.+-.1.6) 1.6 Example 7 0.75
43.4(.+-.1.9) 2.2 Example 8 0.95 51.0(.+-.1.6) 2.4 Comparative 0.5
9.6(.+-.0.6) 1.7 Example 2
As can be seen from the results shown above, the sintered bodies of
Examples 1 8 have excellent mechanical strength, while maintaining
inherently low coefficient of thermal expansion of aluminum
magnesium titanate.
Further, the changes of the residual aluminum magnesium titanate
percentage .alpha.(%) over time in the sintered bodies when placed
in the atmosphere at 1100.degree. C. were determined by the same
manner as Example 2. The residual aluminum magnesium titanate
percentage .alpha.(%) of the sintered bodies after 300 hours have
passed and 400 hours have passed is shown in Table 4 below. In
Table 4, the measurement results of the sintered bodies of Example
2 and Comparative Example 2 are also described.
TABLE-US-00004 TABLE 4 Residual aluminum magnesium titanate
percentage .alpha.(%) After 300 hours After 400 hours have passed
have passed Example 2 95.9 78.6 Example 3 93.1 85.6 Example 4 98.6
97.4 Example 5 99.8 95.3 Example 6 97.8 94.1 Example 7 100 98.4
Example 8 100 100 Comparative 34.8 0 Example 2
As can be seen from the results shown above, the sintered bodies of
the above Examples have excellent resistance to thermal
decomposition.
* * * * *