CA1214475A - Process for producing an alumina-silica-chromia ternary fiber - Google Patents
Process for producing an alumina-silica-chromia ternary fiberInfo
- Publication number
- CA1214475A CA1214475A CA000447474A CA447474A CA1214475A CA 1214475 A CA1214475 A CA 1214475A CA 000447474 A CA000447474 A CA 000447474A CA 447474 A CA447474 A CA 447474A CA 1214475 A CA1214475 A CA 1214475A
- Authority
- CA
- Canada
- Prior art keywords
- alumina
- chromia
- silica
- powder
- weight
- 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.)
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- Inorganic Fibers (AREA)
Abstract
ABSTRACT
A process for producing an alumina-silica-chromia fiber comprises the steps of blending an alumina powder, a silica powder and a powder of a solid solution comprising 10 - 60% by weight of chromia in alumina, melting the blend to form thin molten streams of the blend and fabricating molten material into fiber form. The invention also provides improved alumina-silica-chromia fibers having uniform thickness and length made by blending an alumina powder, a silica powder and a solid solution of 10 to 60%
by weight of chromia in alumina into a mix, melting the mix, and fabricating the fibers therefrom.
A process for producing an alumina-silica-chromia fiber comprises the steps of blending an alumina powder, a silica powder and a powder of a solid solution comprising 10 - 60% by weight of chromia in alumina, melting the blend to form thin molten streams of the blend and fabricating molten material into fiber form. The invention also provides improved alumina-silica-chromia fibers having uniform thickness and length made by blending an alumina powder, a silica powder and a solid solution of 10 to 60%
by weight of chromia in alumina into a mix, melting the mix, and fabricating the fibers therefrom.
Description
7~
CASE 4~13 PROCESS FO~ P~ODVCING AN Al UMINA-SILICA-CHROMIA
TERNARY FlaE~
BACKGROUND OF TH~ INVENTION
The present invention relates to a process for producing an alumina-silica-chromia ternary fiber.
There is known an alumina-silica-chromia based refractory fiber which is produced by rrelting a powder blend comprising 35 - 65% by weight of A1203, 30 - 60~6 by weight of SiO2, 1.5 - 6% by weight of Cr203 and small amounts of other additives or impurities in an electric furnace and thereafter fabrication of fibers by either the blowing method or the spinning method. This fiber, when compared with alumina-silica based fibers containing no chromia, is said to have less deterioration at high temperatures because of the decrease in the amount of growth of the mullite crystals above 950C. The known method of preparation of an alumina-silica-chromia fiber is to blend high-grade silica sand, alumina powder and chromia powder. However, when blended in this manner, the chromia evaporates upon melting and thus it is difficult to obtain a productof the desired composition. At the same time air pollution is caused by the chromia evaporation~ The fluctuation in desired output composition becomes greater when removing the molten product as thin streams during the fiber fabrication step.
It is believed that the fluctuation in output composition is created during electrical meltingO The viscosity and the electric resistance are lowered with the increase of the chromia content, hence the viscosity and the electric resistance greatly Eluctuate depending on the local chromia content within the crucible. Since the melting points of the respective powder starting materials are different, i.e. 2050C for alumina, 1723C for silica and 2300C for chromia, there is a time lag in melting and, 2S a result, a less viscous poftion of the melt which has a higher chromia content is locally generated before the composition becomes uniform. Thus this portion flows out of the crucible in a considerably large amount prior to the flow of the other components. At a somewha~ later time, the more highly viscous portion of ~he melt, having a 7~
lower content of chromia, starts to flow gradually~ Since the flow output fluctuates greatly within a short time, it ls very difficult to control the fur~ace temperatures in order to suppress such a fluctuation, and therefore the quality and composition obtained vary from product to product.
One approach to solve the above described problems has been to mix and mold all of the respective starting materials, then calcine to homogenize the melt and finally grind the cooled homogenized composition for use as the starting material.
However, this process is not economically advantageous because of the heat energy required for calcining all the s-tarting materials beforehand and the process costs for mixing, kneadiny, molding, drying etc. Alternatively, it is also contemplated to previously mix and calcine chromia and silica and use the mixtures as the starting material, but experimental results reveal that as in the case of merely blending the silica sand, alumina and chromia powders~ the composition of output of the molten product greatly fluctuated.
It has been discovered in the present invention that by employing a solid solution comprising 10 - 60% by weight of chromia in alumina as a starting material, the fluctuation in flow output can be greatly reduced as compared with the above-described processes.
Accordingly, the object of the present invention is to provide a process for producing an alumina-silica-chromia ternary fiber of uniform composition.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a process for producing an alumina-silica-chromia fiber comprising the steps of blending an alumina powder, a silica powder and a powder of a solid solution comprising 10-60~ by weight of chromia in alumina, melting the blend to form thin molten streams of the blend and fabricating molten material into fiber form.
According to a further aspect of the present invention . . ~
4~
there are provided alumina-silica-chromia fibers produeed by a process according to said one aspect of the invention.
According to a still further aspect of the invention there is provided an alumina-silica-chromia melt having an improved uniform viscosity made by the process comprising:
(a) mixing alumina powder, silica powder and a solid solution of ehromia in alumina and (b) thereafter heating the mix to a temperature above 2300C to form a melt.
CASE 4~13 PROCESS FO~ P~ODVCING AN Al UMINA-SILICA-CHROMIA
TERNARY FlaE~
BACKGROUND OF TH~ INVENTION
The present invention relates to a process for producing an alumina-silica-chromia ternary fiber.
There is known an alumina-silica-chromia based refractory fiber which is produced by rrelting a powder blend comprising 35 - 65% by weight of A1203, 30 - 60~6 by weight of SiO2, 1.5 - 6% by weight of Cr203 and small amounts of other additives or impurities in an electric furnace and thereafter fabrication of fibers by either the blowing method or the spinning method. This fiber, when compared with alumina-silica based fibers containing no chromia, is said to have less deterioration at high temperatures because of the decrease in the amount of growth of the mullite crystals above 950C. The known method of preparation of an alumina-silica-chromia fiber is to blend high-grade silica sand, alumina powder and chromia powder. However, when blended in this manner, the chromia evaporates upon melting and thus it is difficult to obtain a productof the desired composition. At the same time air pollution is caused by the chromia evaporation~ The fluctuation in desired output composition becomes greater when removing the molten product as thin streams during the fiber fabrication step.
It is believed that the fluctuation in output composition is created during electrical meltingO The viscosity and the electric resistance are lowered with the increase of the chromia content, hence the viscosity and the electric resistance greatly Eluctuate depending on the local chromia content within the crucible. Since the melting points of the respective powder starting materials are different, i.e. 2050C for alumina, 1723C for silica and 2300C for chromia, there is a time lag in melting and, 2S a result, a less viscous poftion of the melt which has a higher chromia content is locally generated before the composition becomes uniform. Thus this portion flows out of the crucible in a considerably large amount prior to the flow of the other components. At a somewha~ later time, the more highly viscous portion of ~he melt, having a 7~
lower content of chromia, starts to flow gradually~ Since the flow output fluctuates greatly within a short time, it ls very difficult to control the fur~ace temperatures in order to suppress such a fluctuation, and therefore the quality and composition obtained vary from product to product.
One approach to solve the above described problems has been to mix and mold all of the respective starting materials, then calcine to homogenize the melt and finally grind the cooled homogenized composition for use as the starting material.
However, this process is not economically advantageous because of the heat energy required for calcining all the s-tarting materials beforehand and the process costs for mixing, kneadiny, molding, drying etc. Alternatively, it is also contemplated to previously mix and calcine chromia and silica and use the mixtures as the starting material, but experimental results reveal that as in the case of merely blending the silica sand, alumina and chromia powders~ the composition of output of the molten product greatly fluctuated.
It has been discovered in the present invention that by employing a solid solution comprising 10 - 60% by weight of chromia in alumina as a starting material, the fluctuation in flow output can be greatly reduced as compared with the above-described processes.
Accordingly, the object of the present invention is to provide a process for producing an alumina-silica-chromia ternary fiber of uniform composition.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a process for producing an alumina-silica-chromia fiber comprising the steps of blending an alumina powder, a silica powder and a powder of a solid solution comprising 10-60~ by weight of chromia in alumina, melting the blend to form thin molten streams of the blend and fabricating molten material into fiber form.
According to a further aspect of the present invention . . ~
4~
there are provided alumina-silica-chromia fibers produeed by a process according to said one aspect of the invention.
According to a still further aspect of the invention there is provided an alumina-silica-chromia melt having an improved uniform viscosity made by the process comprising:
(a) mixing alumina powder, silica powder and a solid solution of ehromia in alumina and (b) thereafter heating the mix to a temperature above 2300C to form a melt.
- 2~
?".,.'~
,i . ~q~.t.
s DETAILED DESC~IPTION OF THE ~R~ERREI~ EMBODIMENTS
OF T~IE INVE~llON
In acsordance with the present invention an improved process produces an alumina-silica-chromia fiber which exhibits a significant improvement in high temperature shrinkage and corrosion resistance.
A ternary Eiber comprised of alumina-silica-chromia is produced by forming a melt from alumina powder, silica sand and an alumina-chromia solid solution powder. This melt is charged in an electric furnace at a temperature in excess of the melting temperature of chromia i.e. 2300C. The melt is allowed to flow through a tapping nozzle and the thin stream oE melt is subjected to a jet stream of air which fiberizes the melt.
The solid solution of alumina and chromia may be obtained by adequately mixing a chromia powder in alumina and caicining the mixture at 1700 -1800C.
In the present invention, the content of chromia in the alumina-chromia solid solution must be at least 10~6 by weight, otherwise the amount of the solid solution needed in order to obtain a fiber having the desired chromia content isincreased and therefore economically disadvantageous. If the chromia content is greater than 60% by weight~ the upper limit, the dilution effect due to the alumina cannot be obtained. The chromia content in the alumina-chrornia solid solution is preferably 30 - 50% by weight. Although the particle size of the alumina-chromia solid solution starting material is not particularly res~ricted9 it rnay preferably be of such particle size as to prevent physical separa-tion fromthe other starting materials.
The following Examples are given to illustrate the present invention.
Example 1 is illustrative of the method according to the present invention and Examples 11 and 111 are indicative of prior art methods of making alumina-silica-chromia fibers.
FXAMPLE I
In accordance with the present invention 38 parts by weight of an alumina powder comprising 99.8% by weight of A1203, 56 parts by weight oE silica sand comprising 99.8% by weight of Si02 and 6 parts by weight of an alumina-CP~SE 4513 chromia solid solution powder comprising 50% by weight of A1203 and 50% by weight of Cr203 were blended and mixed. This starting material mixture was then charged into an electric furnace used in producing ceramic fibers. The melt flowed through a tapping nozzle as then streams and was thereafter fabricated into fiber form by blowing method.
COMP~RATIVE~ EXAMPLE 11 41 parts by weight of the alumina, 56 parts by weight of the silica sand, both being ~he same as those used in Example 1, and 3 parts by weight of a chromia powder comprising 99.3% by weight of Cr203 were mixed, and ternary 1 0 fibers were fabricated as in Example 1.
COMPAI~AllVE EXAMPLI~ 111 41 parts by weight of the alumina, 53 parts by weight of the silica sand, both being the same as thGse used in Example I, and 6 parts by weight of a silica-chromia calcined product comprisin~ 50% by weight of Si02 and 50% by weight of Cr203 were mixed, and ternary fibers were fabricated as in Example I.
T~ST METHC~D A~D RESULTS
The flow output from the tapping nozzle in each above case was measured 13 times at 30 minute intervals. At each of the 13 measurement periods, three measurements, ~i.e. the first for 18 seconds, the second for 18 seconds one minute later and the third for 18 seconds one minute later~ were made. The results are given below. The numerical values are those relative to the average taken as 100.
~XA~lPLE I
CO~iSPARATIVE EXAMPLE 11 45 39 95 36 87 104 84 90 36 63 18 8l~ 39 90 7~ 78 15 152 128 125 60 128 107 116 98 167 6386 15 113 131 158 214 110 77 113 63 4~ 12 ~598 95 36 185 77 83 146 68 21 125 18 57 The standard deviation is 16.4 in Example 1, 54.5 in Example 11 and 61.9 in Example 111. It is evident that by the present invention, the flow output may beaveraged much better than in comparative Examples 11 or 111, and thus the thickness, length etc. of the fiber may be more uniform, leading to the enhancement of the quality of the fibers.
For reference the results of the chemical analysis of the fiber compositions are as follows, and it is shown that a fiber of the desired composition may be obtained easily.
Fiber Component (96 by weight) A1203 sio2 ~r23 Example 1 40.8 55.9 3.0 Comparative Example II 41.0 56.1 2.5 Comparative Example 111 41.4 55.5 2.7
?".,.'~
,i . ~q~.t.
s DETAILED DESC~IPTION OF THE ~R~ERREI~ EMBODIMENTS
OF T~IE INVE~llON
In acsordance with the present invention an improved process produces an alumina-silica-chromia fiber which exhibits a significant improvement in high temperature shrinkage and corrosion resistance.
A ternary Eiber comprised of alumina-silica-chromia is produced by forming a melt from alumina powder, silica sand and an alumina-chromia solid solution powder. This melt is charged in an electric furnace at a temperature in excess of the melting temperature of chromia i.e. 2300C. The melt is allowed to flow through a tapping nozzle and the thin stream oE melt is subjected to a jet stream of air which fiberizes the melt.
The solid solution of alumina and chromia may be obtained by adequately mixing a chromia powder in alumina and caicining the mixture at 1700 -1800C.
In the present invention, the content of chromia in the alumina-chromia solid solution must be at least 10~6 by weight, otherwise the amount of the solid solution needed in order to obtain a fiber having the desired chromia content isincreased and therefore economically disadvantageous. If the chromia content is greater than 60% by weight~ the upper limit, the dilution effect due to the alumina cannot be obtained. The chromia content in the alumina-chrornia solid solution is preferably 30 - 50% by weight. Although the particle size of the alumina-chromia solid solution starting material is not particularly res~ricted9 it rnay preferably be of such particle size as to prevent physical separa-tion fromthe other starting materials.
The following Examples are given to illustrate the present invention.
Example 1 is illustrative of the method according to the present invention and Examples 11 and 111 are indicative of prior art methods of making alumina-silica-chromia fibers.
FXAMPLE I
In accordance with the present invention 38 parts by weight of an alumina powder comprising 99.8% by weight of A1203, 56 parts by weight oE silica sand comprising 99.8% by weight of Si02 and 6 parts by weight of an alumina-CP~SE 4513 chromia solid solution powder comprising 50% by weight of A1203 and 50% by weight of Cr203 were blended and mixed. This starting material mixture was then charged into an electric furnace used in producing ceramic fibers. The melt flowed through a tapping nozzle as then streams and was thereafter fabricated into fiber form by blowing method.
COMP~RATIVE~ EXAMPLE 11 41 parts by weight of the alumina, 56 parts by weight of the silica sand, both being ~he same as those used in Example 1, and 3 parts by weight of a chromia powder comprising 99.3% by weight of Cr203 were mixed, and ternary 1 0 fibers were fabricated as in Example 1.
COMPAI~AllVE EXAMPLI~ 111 41 parts by weight of the alumina, 53 parts by weight of the silica sand, both being the same as thGse used in Example I, and 6 parts by weight of a silica-chromia calcined product comprisin~ 50% by weight of Si02 and 50% by weight of Cr203 were mixed, and ternary fibers were fabricated as in Example I.
T~ST METHC~D A~D RESULTS
The flow output from the tapping nozzle in each above case was measured 13 times at 30 minute intervals. At each of the 13 measurement periods, three measurements, ~i.e. the first for 18 seconds, the second for 18 seconds one minute later and the third for 18 seconds one minute later~ were made. The results are given below. The numerical values are those relative to the average taken as 100.
~XA~lPLE I
CO~iSPARATIVE EXAMPLE 11 45 39 95 36 87 104 84 90 36 63 18 8l~ 39 90 7~ 78 15 152 128 125 60 128 107 116 98 167 6386 15 113 131 158 214 110 77 113 63 4~ 12 ~598 95 36 185 77 83 146 68 21 125 18 57 The standard deviation is 16.4 in Example 1, 54.5 in Example 11 and 61.9 in Example 111. It is evident that by the present invention, the flow output may beaveraged much better than in comparative Examples 11 or 111, and thus the thickness, length etc. of the fiber may be more uniform, leading to the enhancement of the quality of the fibers.
For reference the results of the chemical analysis of the fiber compositions are as follows, and it is shown that a fiber of the desired composition may be obtained easily.
Fiber Component (96 by weight) A1203 sio2 ~r23 Example 1 40.8 55.9 3.0 Comparative Example II 41.0 56.1 2.5 Comparative Example 111 41.4 55.5 2.7
Claims (5)
1. A process for producing an alumina-silica-chromia fiber which comprises blending an alumina powder, a silica powder, and a powder of a solid solution of 10 to 6096 by weight of chromia in alumina, into a mix, melting the mix, and fabricating the fibers therefrom.
2. The process according to claim 1 wherein the mix comprises blending by weight 38 parts of high purity alumina, 56 parts of high purity silica and 6 parts of a solid solution of 50% alumina and 50% of chromia.
3. An improved alumina-silica-chromia fibers having uniform thickness and length made by blending an alumina powder, a silica powder and a solid solution of 10 to 60% by weight of chromia in alumina into a mix, melting the mix, and fabricating the fibers therefrom.
4. An alumina-silica-chromia melt having an improved uniform viscosity made by the process comprising:
(a) mixing alumina powder, silica powder and a solid solution of chromia in alumina and (b) thereafter heating the mix to a temperature above 2300°C to form a melt.
(a) mixing alumina powder, silica powder and a solid solution of chromia in alumina and (b) thereafter heating the mix to a temperature above 2300°C to form a melt.
5. The melt according to claim 4 wherein the value of the viscosity has a standard deviation of less than 17.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000447474A CA1214475A (en) | 1984-02-15 | 1984-02-15 | Process for producing an alumina-silica-chromia ternary fiber |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000447474A CA1214475A (en) | 1984-02-15 | 1984-02-15 | Process for producing an alumina-silica-chromia ternary fiber |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1214475A true CA1214475A (en) | 1986-11-25 |
Family
ID=4127197
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000447474A Expired CA1214475A (en) | 1984-02-15 | 1984-02-15 | Process for producing an alumina-silica-chromia ternary fiber |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1214475A (en) |
-
1984
- 1984-02-15 CA CA000447474A patent/CA1214475A/en not_active Expired
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