CA1215838A - Process for manufacturing ceramic fibers consisting mainly of alumina and silica - Google Patents
Process for manufacturing ceramic fibers consisting mainly of alumina and silicaInfo
- Publication number
- CA1215838A CA1215838A CA000462260A CA462260A CA1215838A CA 1215838 A CA1215838 A CA 1215838A CA 000462260 A CA000462260 A CA 000462260A CA 462260 A CA462260 A CA 462260A CA 1215838 A CA1215838 A CA 1215838A
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- Canada
- Prior art keywords
- fibers
- weight
- temperature
- heated
- set forth
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Organic Insulating Materials (AREA)
- Inorganic Fibers (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A mixture containing 35 to 65% by weight of Al2O3, 30 to 60% by weight of SiO2, 1.5 to 4% by weight of Cr2O3, and 0.01 to 0.1% by weight of carbon, the balance being unavoidable impurities, is melted, and amorphous fibers are formed from said molten material by blowing or spinning. The fibers are heated rapidly to a temperature of 950°C to 1,150°C, held at that temperature for several to about a dozen minutes, and cooled rapidly to ordinary room temperature.
A mixture containing 35 to 65% by weight of Al2O3, 30 to 60% by weight of SiO2, 1.5 to 4% by weight of Cr2O3, and 0.01 to 0.1% by weight of carbon, the balance being unavoidable impurities, is melted, and amorphous fibers are formed from said molten material by blowing or spinning. The fibers are heated rapidly to a temperature of 950°C to 1,150°C, held at that temperature for several to about a dozen minutes, and cooled rapidly to ordinary room temperature.
Description
PROCESS FOR MANUFACTURING CERAMIC FIBERS
CCeNSlSTlNG MAINLY OIL ALUMINA AVID SILICA
BACKGROUND OF TITHE INVENTION
1. Field ox the Invention This invention relates to a process for manufacturing ceramic fibers consisting mainly of alumina and silica.
CCeNSlSTlNG MAINLY OIL ALUMINA AVID SILICA
BACKGROUND OF TITHE INVENTION
1. Field ox the Invention This invention relates to a process for manufacturing ceramic fibers consisting mainly of alumina and silica.
2. Descrip~iorl of the Prior Art:
It is known that amorphous ceramic fibers consisting mainly of alumina (Aye) and silica (Sue) can be produced by melting a material containing 40 to 70~b by weight of alumina, 3û to 60% by weight of silica and minor quints of impurities, and blowing or spinning the molten material It is also known that the thermal shrinkability of these ceramic fibers can be lowered if they are heated at a temperature not lower than their devitrification temperature so that the crystallization of Malta (AYE 25iO~) may take place in the vitreous material .
Amorphous ceramic fibers, however, lose their heat resistance and strength if they are exposed to a temperature of at least about l,000C for a long time, since a coarse crystal structure is formed by the growth of Malta crystals in gloss, and makes the fibers brittle. Ceramic fibers containing Malta crystals have an improved resistance to thermal shrinkage, but it lasts only for a short time. As the growth of Malta crystals further proceeds, the formation of a coarse crystal structure brings about a reduction in fiber strength.
US. Patent No. 3,449,137 teaches the manufacture of ceramic fibers containing about I to about 6% by weight of chromium oxide (Cry) in addition to alumina and silica. The process taught by this patent has been tested, but the ceramic fibers thereby obtained have not shown any appreciable improvement in physical properties. The addition of chromium oxide is not sufficient for preventing the formation of coarse crystals by recrystallization,which results in higher degrees of thermal shrinkage and embrittlement of --I--`
I I
ceramic fibers, when they are exposed to a high temperature for a long time.
Sledgehammer OF THE INVENTION
It is an object of this invention to provide a process which enables the manufacture of ceramic fibers which have a high degree of thermal stability even it a high temperature. This invention is particularly featured by employing a small quantity of carbon.
The object is attained by a process which essentially comprises melting a material containing 35 to 65% by weight of alumina, 30 to 60,6 by weight of silica, 1.5 to 4% by weight of chromium oxide and 0.01 to 0.1% by weight of carbon, forming amorphous fibers from the molten material, heating the fibers rapidly to a temperature of 950C to 1,150C, holding the heated fibers at trot temperature for severGI to about a dozen minutes, and cooling the heated fibers rapidly to ordinary room temperature.
The high thermal stability of the fibers is due to the separation of phases which takes place in the vitreous structure as a result of the heat treatment atq relatively low temperature. The fibers have a linear shrinkage not exceeding 2% even if they are exposed to a temperature of 1 ~300C or above. They do not undergo any appreciable embrittiement.
BRIEF DESCRIPTIOI\I OF THE DRAWINGS
FIGURE I shows by X-ray diffraction patterns the relationship between the quantity of chromium oxide in ceramic fibers and the formation of Malta crystals therein;
FIGURE 2 shows by X-ray diffraction patterns the relationship between the temperature for the heat treatment of ceramic fibers and the formation of I Malta crystals therein; and FIGURE 3 is an electron microphotograph of 10,û00 magnifications showing the ceramic fibers treated in accordance with this invention, and etched.
33~
CASE 45 i 2 SHUTTLED DESCRIPTION OF THE INVENTION
The process of this invention includes melting a material containing I to 65,6 by weight of alumina (Aye), 30 to 60h by weight of silica (Sue), 1.5 to 4% by weight of chromium oxide (Cry and 0.01 to 0.1% by weight of carbon, the balance being unavoidable impurities. This melting can be carried out by an electric furnace. Amorphous fibers are formed from the molten material by a customary method, such as blowing or spinning.
It is necessary to employ at least 1.5% by weight of Cry end at least kiwi% by weight of carbon. If less Cry and carbon are used, the formation of Malta crystals proceeds markedly, and em brittles the fibers, even if they are heat treated in accordance with this invention, as is obvious from the X-ray diffraction patterns in FIGURE 1. The use of more than 4% by weight of Cry undo more than Owe% by weight of carbon does not produce any appreciably better results. The use of carbon in addition to Cry is important for avoiding the formation of coarse crystals in ceramic fibers, which results in an increasein their thermal shrinkage, and a reduction in their resiliency due to embrittlement, when they are exposed to a high temperature for a long time.
The fibers are heated to a temperature s3f 950C to 1,150C, and held at that temperature for a period of several to a dozen or so minutes. These conditions have been experimentally found necessary and sufficient for causing the separation of phases in the amorphous structure of the ceramic fibers. If the fibers are held at a temperature below 95ûC for a shorter time than the range hereinabove defined, no satisfactory improvement in their resistance to thermal shrinkage can be expected, us will be obvious from the following description. If the fibers are held Gut a temperature above 1,150C for a longertime than the range hereinabove specified the forrnatiGn of Malta crystals proceeds, and em brittles the fibers, as is obvious from the fang description and FIGURE 2 showing the X-ray diffraction patterns of the fibers containing 3.8% by weight of Cry.
The fibers are heated rapidly to a temperature of 950C to 1,150C, since sly only rapid heating enables the separation of phases in the ceramic structure. Ifthe fibers are heated slowly, they have a linear shrinkage exceeding 2% when they are exposed to a temperature of 1,300C or above for a long time, and moreover) the embrittlement of the fibers takes place. According to the experimental results, it is preferable to heat the fibers at a rate of 100C to 1,000C per minute.
The invention will now be described by way of example.
EXAMPLE
A material containing 4ûh by weight of Aye, 56h by weight of Sue, OWE by weight of Cry and 0.1% by weight of carbon, the balance being unavoidable impurities, was melted in an electric furnace. The molten material was formed by blowing into amorphous fibers having an average diameter of 2.5 microns and a maximum length of 150 mm. A blanket having a thickness of 25 mm and a bulk specific density of 0.14 was formed from the fibers, and heat treated under the conditions shown in TABLES I and 2. TABLE I shows the linear shrinkage of the blankets heated at a ternperatue of l,100C to 1,4û0C
for 24 hours. TABLE 2 shows the resiliency of the fibers in terms of the restorability of blanket thickness after compression under heat. The blanket was heated under the conditions shown in TABLE 2, and compressed to a half in thickness.
IL Z a _ to, ._ ._ E I a I' I '` I
._ ,.
'` EYE _ I
o Jo O O c --I us I
I o Jo o I o 3 ,- c c I
I
..
'E c m I., o .
, . -c E
c a c o c C' c lo O O
_ ., . o I c c I
.
Lo 3~3 _ -- O
-TV
c ,~, c C
a o CO
c go Us Jo I I I
I m Y
._ C
c o Jo owe cay Jo o -- 00 o . _ YE --o Jo ISLE
As is obvious from TABLES I and 2, the process of this invention produces a blanket of ceramic fibers having a linear shrinkage less than 2% when heated at 1,300C for 24 hours, and which it satisfactorily resilient.
The thermal stability and resiliency of a blanket of ceramic fibers produced by the process of this invention are apparently due Jo the separation of phases. The chromium oxide (Cry) replaces a punt of Aye in the Aye-Sue glass structure, and causes a stress in its lattice to inhibit crystallization.
In the presence of a smell quantity of atomic curbon9 it is scattered in the lattices of the glass structure, and restricts their rearrangement. The rapid heating shortens the distance of diffusion of the constituents in the glass structure and inhibits their crystalli~ation9 whereby there are formed a lot of finely divided separate phases consisting mainly of Cry and having different proportions of constituents.
The ceramic fibers of this invention having separate phases hardly undergo recrystallization even if they are exposed to a high temperature. Even if they may undergo recrystallization by exposure to a higher temperature for a long time, the crystals are very small, since the separate phases forming the crystal grains, in which Cry forming the nucleus of the crystal coexists with carbon, are scattered numerously. The adjoining crystal grains mutually restrict their growth, and yield fibers composed of numerous fine crystals.
These fibers provide a thermally stable and resilient blanket. FIGURE 3 is an electron microphotograph of lû,000 magnifications showing the gibers which were treated in accordance with this invention, and etched. As is obvious therefrom, the fibers as a whole comprise finely divided separate phases. On the other hand, fibers not containing such separate phases and crystals are totally melted by similar etching treatment.
It is known that amorphous ceramic fibers consisting mainly of alumina (Aye) and silica (Sue) can be produced by melting a material containing 40 to 70~b by weight of alumina, 3û to 60% by weight of silica and minor quints of impurities, and blowing or spinning the molten material It is also known that the thermal shrinkability of these ceramic fibers can be lowered if they are heated at a temperature not lower than their devitrification temperature so that the crystallization of Malta (AYE 25iO~) may take place in the vitreous material .
Amorphous ceramic fibers, however, lose their heat resistance and strength if they are exposed to a temperature of at least about l,000C for a long time, since a coarse crystal structure is formed by the growth of Malta crystals in gloss, and makes the fibers brittle. Ceramic fibers containing Malta crystals have an improved resistance to thermal shrinkage, but it lasts only for a short time. As the growth of Malta crystals further proceeds, the formation of a coarse crystal structure brings about a reduction in fiber strength.
US. Patent No. 3,449,137 teaches the manufacture of ceramic fibers containing about I to about 6% by weight of chromium oxide (Cry) in addition to alumina and silica. The process taught by this patent has been tested, but the ceramic fibers thereby obtained have not shown any appreciable improvement in physical properties. The addition of chromium oxide is not sufficient for preventing the formation of coarse crystals by recrystallization,which results in higher degrees of thermal shrinkage and embrittlement of --I--`
I I
ceramic fibers, when they are exposed to a high temperature for a long time.
Sledgehammer OF THE INVENTION
It is an object of this invention to provide a process which enables the manufacture of ceramic fibers which have a high degree of thermal stability even it a high temperature. This invention is particularly featured by employing a small quantity of carbon.
The object is attained by a process which essentially comprises melting a material containing 35 to 65% by weight of alumina, 30 to 60,6 by weight of silica, 1.5 to 4% by weight of chromium oxide and 0.01 to 0.1% by weight of carbon, forming amorphous fibers from the molten material, heating the fibers rapidly to a temperature of 950C to 1,150C, holding the heated fibers at trot temperature for severGI to about a dozen minutes, and cooling the heated fibers rapidly to ordinary room temperature.
The high thermal stability of the fibers is due to the separation of phases which takes place in the vitreous structure as a result of the heat treatment atq relatively low temperature. The fibers have a linear shrinkage not exceeding 2% even if they are exposed to a temperature of 1 ~300C or above. They do not undergo any appreciable embrittiement.
BRIEF DESCRIPTIOI\I OF THE DRAWINGS
FIGURE I shows by X-ray diffraction patterns the relationship between the quantity of chromium oxide in ceramic fibers and the formation of Malta crystals therein;
FIGURE 2 shows by X-ray diffraction patterns the relationship between the temperature for the heat treatment of ceramic fibers and the formation of I Malta crystals therein; and FIGURE 3 is an electron microphotograph of 10,û00 magnifications showing the ceramic fibers treated in accordance with this invention, and etched.
33~
CASE 45 i 2 SHUTTLED DESCRIPTION OF THE INVENTION
The process of this invention includes melting a material containing I to 65,6 by weight of alumina (Aye), 30 to 60h by weight of silica (Sue), 1.5 to 4% by weight of chromium oxide (Cry and 0.01 to 0.1% by weight of carbon, the balance being unavoidable impurities. This melting can be carried out by an electric furnace. Amorphous fibers are formed from the molten material by a customary method, such as blowing or spinning.
It is necessary to employ at least 1.5% by weight of Cry end at least kiwi% by weight of carbon. If less Cry and carbon are used, the formation of Malta crystals proceeds markedly, and em brittles the fibers, even if they are heat treated in accordance with this invention, as is obvious from the X-ray diffraction patterns in FIGURE 1. The use of more than 4% by weight of Cry undo more than Owe% by weight of carbon does not produce any appreciably better results. The use of carbon in addition to Cry is important for avoiding the formation of coarse crystals in ceramic fibers, which results in an increasein their thermal shrinkage, and a reduction in their resiliency due to embrittlement, when they are exposed to a high temperature for a long time.
The fibers are heated to a temperature s3f 950C to 1,150C, and held at that temperature for a period of several to a dozen or so minutes. These conditions have been experimentally found necessary and sufficient for causing the separation of phases in the amorphous structure of the ceramic fibers. If the fibers are held at a temperature below 95ûC for a shorter time than the range hereinabove defined, no satisfactory improvement in their resistance to thermal shrinkage can be expected, us will be obvious from the following description. If the fibers are held Gut a temperature above 1,150C for a longertime than the range hereinabove specified the forrnatiGn of Malta crystals proceeds, and em brittles the fibers, as is obvious from the fang description and FIGURE 2 showing the X-ray diffraction patterns of the fibers containing 3.8% by weight of Cry.
The fibers are heated rapidly to a temperature of 950C to 1,150C, since sly only rapid heating enables the separation of phases in the ceramic structure. Ifthe fibers are heated slowly, they have a linear shrinkage exceeding 2% when they are exposed to a temperature of 1,300C or above for a long time, and moreover) the embrittlement of the fibers takes place. According to the experimental results, it is preferable to heat the fibers at a rate of 100C to 1,000C per minute.
The invention will now be described by way of example.
EXAMPLE
A material containing 4ûh by weight of Aye, 56h by weight of Sue, OWE by weight of Cry and 0.1% by weight of carbon, the balance being unavoidable impurities, was melted in an electric furnace. The molten material was formed by blowing into amorphous fibers having an average diameter of 2.5 microns and a maximum length of 150 mm. A blanket having a thickness of 25 mm and a bulk specific density of 0.14 was formed from the fibers, and heat treated under the conditions shown in TABLES I and 2. TABLE I shows the linear shrinkage of the blankets heated at a ternperatue of l,100C to 1,4û0C
for 24 hours. TABLE 2 shows the resiliency of the fibers in terms of the restorability of blanket thickness after compression under heat. The blanket was heated under the conditions shown in TABLE 2, and compressed to a half in thickness.
IL Z a _ to, ._ ._ E I a I' I '` I
._ ,.
'` EYE _ I
o Jo O O c --I us I
I o Jo o I o 3 ,- c c I
I
..
'E c m I., o .
, . -c E
c a c o c C' c lo O O
_ ., . o I c c I
.
Lo 3~3 _ -- O
-TV
c ,~, c C
a o CO
c go Us Jo I I I
I m Y
._ C
c o Jo owe cay Jo o -- 00 o . _ YE --o Jo ISLE
As is obvious from TABLES I and 2, the process of this invention produces a blanket of ceramic fibers having a linear shrinkage less than 2% when heated at 1,300C for 24 hours, and which it satisfactorily resilient.
The thermal stability and resiliency of a blanket of ceramic fibers produced by the process of this invention are apparently due Jo the separation of phases. The chromium oxide (Cry) replaces a punt of Aye in the Aye-Sue glass structure, and causes a stress in its lattice to inhibit crystallization.
In the presence of a smell quantity of atomic curbon9 it is scattered in the lattices of the glass structure, and restricts their rearrangement. The rapid heating shortens the distance of diffusion of the constituents in the glass structure and inhibits their crystalli~ation9 whereby there are formed a lot of finely divided separate phases consisting mainly of Cry and having different proportions of constituents.
The ceramic fibers of this invention having separate phases hardly undergo recrystallization even if they are exposed to a high temperature. Even if they may undergo recrystallization by exposure to a higher temperature for a long time, the crystals are very small, since the separate phases forming the crystal grains, in which Cry forming the nucleus of the crystal coexists with carbon, are scattered numerously. The adjoining crystal grains mutually restrict their growth, and yield fibers composed of numerous fine crystals.
These fibers provide a thermally stable and resilient blanket. FIGURE 3 is an electron microphotograph of lû,000 magnifications showing the gibers which were treated in accordance with this invention, and etched. As is obvious therefrom, the fibers as a whole comprise finely divided separate phases. On the other hand, fibers not containing such separate phases and crystals are totally melted by similar etching treatment.
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for manufacturing ceramic fibers consisting mainly of alumina and silica, which comprises:
melting a material containing 35 to 65% by weight of Al2O3, 30 to 60% by weight of SiO2, 1.5 to 4% by weight of Cr2O3, and 0.01 to 0.1% by weight of carbon, the balance being unavoidable impurities;
forming amorphous fibers from said molten material;
heating said amorphous fibers rapidly to a temperature of 950°C to 1,150°C;
holding the heated fibers at said temperature for several to about a dozen minutes; and cooling the heated fibers rapidly to ordinary room temperature.
melting a material containing 35 to 65% by weight of Al2O3, 30 to 60% by weight of SiO2, 1.5 to 4% by weight of Cr2O3, and 0.01 to 0.1% by weight of carbon, the balance being unavoidable impurities;
forming amorphous fibers from said molten material;
heating said amorphous fibers rapidly to a temperature of 950°C to 1,150°C;
holding the heated fibers at said temperature for several to about a dozen minutes; and cooling the heated fibers rapidly to ordinary room temperature.
2. A process as set forth in claim 1, wherein said amorphous fibers are heated to said temperature at a rate of 100°C to 1,000°C per minute.
3. A process as set forth in claim 2, wherein said amorphous fibers are formed by a method selected from blowing and spinning.
4. A process as set forth in claim 3, wherein said material is melted by an electric furnace.
5. A ceramic fiber product consisting mainly of alumina and silica, which is produced by a method comprising:
melting a material containing 35 to 65% by weight of Al2O3, 30 to 60% by weight of SiO2, 1.5 to 4% by weight of Cr2O3 and 0.01 to 0.1% by weight of carbon;
forming amorphous fibers from said molten material;
heating said amorphous fibers rapidly to a temperature of 950°C to 1,150°C;
holding the heated fibers at said temperature for several to about a dozen minutes; and cooling the heated fibers rapidly to ordinary room temperature.
melting a material containing 35 to 65% by weight of Al2O3, 30 to 60% by weight of SiO2, 1.5 to 4% by weight of Cr2O3 and 0.01 to 0.1% by weight of carbon;
forming amorphous fibers from said molten material;
heating said amorphous fibers rapidly to a temperature of 950°C to 1,150°C;
holding the heated fibers at said temperature for several to about a dozen minutes; and cooling the heated fibers rapidly to ordinary room temperature.
6. A ceramic fiber product as set forth in claim 5, wherein said amorphous fibers are heated to said temperature at a rate of 100°C to 1,000°C per minute.
7. A ceramic fiber product as set forth in claim 6, wherein said amorphous fibers are formed by a method selected from blowing and spinning.
8. A ceramic fiber product as set forth in claim 7, wherein said material is melted by an electric furnace.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP18657483A JPS6077308A (en) | 1983-10-04 | 1983-10-04 | Method of producing insulated electric device |
| JP58-186574 | 1983-10-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1215838A true CA1215838A (en) | 1986-12-30 |
Family
ID=16190916
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000462260A Expired CA1215838A (en) | 1983-10-04 | 1984-08-31 | Process for manufacturing ceramic fibers consisting mainly of alumina and silica |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS6077308A (en) |
| CA (1) | CA1215838A (en) |
-
1983
- 1983-10-04 JP JP18657483A patent/JPS6077308A/en active Granted
-
1984
- 1984-08-31 CA CA000462260A patent/CA1215838A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0320001B2 (en) | 1991-03-18 |
| JPS6077308A (en) | 1985-05-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |