CA1197267A - Method of making magnesiachrom refractories - Google Patents
Method of making magnesiachrom refractoriesInfo
- Publication number
- CA1197267A CA1197267A CA000424891A CA424891A CA1197267A CA 1197267 A CA1197267 A CA 1197267A CA 000424891 A CA000424891 A CA 000424891A CA 424891 A CA424891 A CA 424891A CA 1197267 A CA1197267 A CA 1197267A
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- Prior art keywords
- magnesia
- chromium
- weight
- weight content
- sio2
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
- C04B35/03—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on magnesium oxide, calcium oxide or oxide mixtures derived from dolomite
- C04B35/04—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on magnesium oxide, calcium oxide or oxide mixtures derived from dolomite based on magnesium oxide
- C04B35/043—Refractories from grain sized mixtures
- C04B35/047—Refractories from grain sized mixtures containing chromium oxide or chrome ore
- C04B35/0476—Refractories from grain sized mixtures containing chromium oxide or chrome ore obtained from prereacted sintered grains ("simultaneous sinter")
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Organic Chemistry (AREA)
- Compositions Of Oxide Ceramics (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A refractory magnesia-chromium product is manufactured by a mixture of caustically burned magnesia having a grain size of less than 0.2 mm and of chromium ore having a grain size not exceeding 1.5 mm, the magnesia having a weight content of more than 97% MgO, no more than 0.2% SiO2 and no more than 0.7% Fe2O3+Al2O3, and the chromium ore having a weight content of 20% to 28% FeO and no more than 1-5% SiO2, the caustically burned magnesia and the chromium ore being mixed in a ratio producing in the mixture a weight content of 10% to 30% Cr2O3 and a Cr2O3/Al2O3 weight ratio of more than 2.5, and the mixture having a weight content of no more than 1.1% CaO and no more than 0.7% SiO2, the sum of the weight content of CaO+SiO2 not exceeding 1.3%.
A refractory magnesia-chromium product is manufactured by a mixture of caustically burned magnesia having a grain size of less than 0.2 mm and of chromium ore having a grain size not exceeding 1.5 mm, the magnesia having a weight content of more than 97% MgO, no more than 0.2% SiO2 and no more than 0.7% Fe2O3+Al2O3, and the chromium ore having a weight content of 20% to 28% FeO and no more than 1-5% SiO2, the caustically burned magnesia and the chromium ore being mixed in a ratio producing in the mixture a weight content of 10% to 30% Cr2O3 and a Cr2O3/Al2O3 weight ratio of more than 2.5, and the mixture having a weight content of no more than 1.1% CaO and no more than 0.7% SiO2, the sum of the weight content of CaO+SiO2 not exceeding 1.3%.
Description
~'7;2G~
METHOD OF MANUFACTURING REFRACTORY MAGNESIA-CHROMIUM PRODUCT.
The present invention relates to a method of manufacturing a refractory magnesia-chromium product by preparing a mixture of caustically burned magnesia having a grain size of less than 0.2 mm, preferably no more than 0.12 mm, and of finely granulated chromium ore having a weight content of 20~ to ~8~ FeO, the caustically burned magnesia ; and the chromium ore being mixed in a ratio producing in the , mixture a weight content of 10% to 30%, preferably 15-25~, ;
Cr2o3, and a Cr2O3/A12O3 weight ration of more I than 2.5, preferably more than 3, shaping the mixiure into shaped bodies, such as briquettes, and sintering the same without melting at a minimum temperature of 2000C, preferably at least 2100C, and further treating the resultant sintered magnesia-chromium shaped bodies at temperatures of at least about 1800C to obtain the refractory product, including burned bricks and unburned ! br icks .
Several methods have been proposed for manufacturing pre-20 , reacted magnesia-chromium sintered materials and of l refrac~ories made therefrom by simultaneously sintering a ¦ material producing magnesia and chromium ore at a high temperature, the chromium ore being dissolved during the sintering process in the periclase matrix by a reaction proceeding essentially in the solid state and being contained therein after cooling in the form of newly formed spinel precipitate so that any residue of the original chromium ore grains are present at a maximum volume of no Imore than lQ~, preferably no more than 5~.
In the method described in Austrian patent No. 301,43~, 'I
li coarse granules of chromium ore having a minor component (at !
most 20%, by weight) of a grain size of less than 0.1 mm ancl I a major component (at least 40%, by weight) of a grain size ! exceeding 1 mm, and magnesite ore of a grain size of less than 0.1 mm as the material producing the magnesia are used, I
the maximum acceptable limits of the SiO2 and CaO contents being set forth. It is necessary in this method to use coarse granules of chromium ore to obtain a dense sintered I material, When finely granulated chromium ore and magnesite 1 ore are used, the resultant sintered grains show unfavorable il porosity values. However, it is not easy to obtain coarse '! granules of chromium ores of the required purity. It is easier to obtain so-called chromium ore concentrates, i.e.
chromium ores whose SiO2 and CaO contents have been reduced by suitable treatments which, however, produce I concentrates in finely granulated form~
According to the method of Austrian patent No. 290,374, a sinter material containing, by weight, no more than 2.5%
SiO2 and no more than 4% CaO, with a molar ratio CaO/SiO2 of 0.6 to 2.5, is produced Erom such a chromium ore concentrate 20-80~, by weight, of which has a grain size below 0.12 mm and a finely granulated magnesia matrix having a MgO-content, based on the burned state, of less than 95%, by weight, oP MgO, as well as, optionally, magnesite flue dust, at temperatures of at least 1750C, for example 2000C or more. However, the bricks made from this sinter material can be fired only at relatively low temperatures of, ~or example, 1560C to 1580C, which limits their ~ use to correspondly low operating temperatures and does not ,produce refrac~ory properties satisfying the highest ilrequirements.
,1 6~
The iron content is also a quality characteristic of the chromium ore, this value being determined by the fact that the entire iron content is present in the form of FeO in the I chromium ore. Chromium ore types poor in FeO-content, for ! example less than 15~, by weight, are considered as higher-quality ores but the iron-rich concentrates with an FeO-content of, for example, 18-27~, by weight, are obtainable at lower costs.
In accordance with Austrian patent No. 336,478, a sinter i materiall having a weight content of 11-20% Fe2o3 is ' obtained from such an iron-rich chromium ore concentrate of !'~ an average grain size of 0.1-1.5 mm and a caustic magnesia, which may be a magnesite flue dust. The bricks shaped from this sinter material are fired at a temperature of about 1800C, just below the softening temperature of the sinter material, and they show a high pyro-plasticity and good resistance to heat, which makes them suitable for operating temperatures above 1600C but below 1800C because they are subject to continuous wear in this temperature cange.
These bricks are not suitable for higher operating ,temperatures or for uses where they are subjected to continuous heat in this range~
It is the object of this invention to produce a magnesia-chromium sinter material from a finely granulated, iron-rich I
chromium ore to obtain refractory products which satisEy very high refractory requirements.
We have found that this object can be accomplished with caustically burned magnesia of high MgO-content and a low content of impurities if the SiO2-content of the chromium I
,l ore and the CaO- and SiO~-contents of the sinter material are subject to certain limiting conclitions.
Therefore, according to the invention, the mixture in the first hereinabove described manufacturing method is Iprepared from caustically burned magnesia having a weight I content of more than 97% MgO, no more than 0.2% SiO2 and I no more than 0.7%, preferably no more than 0.3%, ; Fe203~A1203, and the chromium ore having a grain I size ~ot exceeding 1. 5 mm and a weight content of no more 10 ! than 1.5%, preferably no more than 1~, SiO~, the mixture having a weight content of no more than 1.1% CaO and no more than 0.7~ SiO2, the sum of the weight content of CaO~SiO2 not exceeding 1.3~.
The use of a magnesia matrix in the form of the de~ined composition containing only minor SiO2, Fe203 and Al2o3 impurities produces a substantial increase in the refractory quality of the sinter material and the products ~made therefrom. The high FeO-content of the chromium ore lcomponent of the mixture has no deleterious effect on the 20 Iheat resistance if its SiO2 content does not exceed 1.5%, preferably 1%, by weight, and the mixture of caustically burned magnesia and chromium ore and the resultant sinter material has the indicated low CaO- and Sio2-content ~alues and Cr23~A123 weig~t ratio. In addition and preferably, the magnesia-chromium mixture has a Cr203/Fe203 weight ratio of 1.6 to 3.
The present invention makes it possible to ~se chromium ores having a high weight content of 20-28% FeO. The Ichromium ore is comminuted to a grain size of no more than 30 1.5 mm to prepare it for ~reatment, primarily to reduce its ., S12-content. It is of advantage in the method of the present invention if the grain size of at least 60~, by i weight, of the chromium ore is less than 0.7 mm.
The caustically burned magnesia used in the method of ' this invention may be prepared synthetically, for example by i the thermal decomposition of a purified slurry of magnesium chloride. However, it may also be obtained from lake water. While the synthetically produced magnesia will have l¦ a B2O3-~ontent of only a few tho~sandths of 1%, by , weight, the magnesia obtained from lake water contains higher amounts of B~2O3, ~hich may unfavorably influence the refractocy qualities of the product. Good types of lake water magnesia have a weight content of about 0.03-0.05 B~o3 and may be used for the method of the invention.
Magnesia containing more than 0.06%, by weight, B2O3 is generally not desirable for this use.
It is preferred to use a caustic magnesia having a weight content of no more than 2~ CaO and a chromium ore ,having a weight content of no more than 0.2~ CaO to obtain ~ the required low CaO- and Cao+sio2~contents of the mixture and resultant sinter material.
A conventional binder, for example a magnesium sulfate solution which may be prepared from kieserite or Epsom salt, is preferably added when the caustically burned magnesia and chromium ore mixture is prepared~ The mixture is then shaped in a press, for example a roller press, to form briquettes, the applied pressures being preferably as high as can be achieved with such presses, for example ~ressures ' of the order of magnitude of 14 to 20 N/mm2. ~owever, any ; type of compacting the mixture may be used. The shaped _5_ ;
.
;I bodies or brique~tes are dried and subsequently fired for sintering at a temperature of at least 2000C, preferably at least 2100C, which is obtained by the use of gaseous ,l oxygen. The sinter`ing furnace is preferably a shaft i furnace, preferably one with at least two superposed firing zones, the gaseous oxygen being delivered to the lower zone. However, it is also possible to use a rotary kiln as . long as the required high temperatures can be produced therein.
1 In the sinter, the chromium ore is dissolved in the periclase matrix in~a process proceeding practically in the solid state since a melting of the mate~ial is neither ; required nor desired, except for a minor amount of a molten phase derived from any impurities in the type of chromium ore used. When the sinter material is cooled, the chromium ore c~mponents are practically completely precipitated in I the magnesia matrix as newly formed spinels. The structure of the sinter material approaches that of a molten granular I material without, however, requiring an expensive melting 20 process for its manufacture. Residues of the original chromium ore granules, if present at all, should be limited to a maximum volume of 10~, preferably no more than 5%.
The sinter material, which is an intermediate product of the method of the present invention, has a low open grain porosity o~ an average of about 7~, by volume, measured in a grain size of 3 to 4 mm, the grain volume including all pores being determined by the mercury reception in a vacuum pycnometer with an input pressure of about 265 m~ar l,according to DIN (German Industry Norm) 51 065, Part 2, and the solid grain volume including the cLosed pores being determined by an air comparison pycnometer. This measuring method is also used for the values of the open sin~er grain porosity in the examples and comparison tests.
The bricks produced by the method of this invention may be fired without damaging them at temperatures up to 2000C and higher, and they exhibit a very high resistance I to heat. The values of the resistance to pressure under ' heat, measured at 1600C, lie in the range of 15 N/mm2 I and higher.
I The inven~ion will be elucidated further in the following operating~examples and comparison tests.
Example 1 Fifty-seven weight percent of caustic magnesia A having a grain size up to 0.1 mm and 43~, by weight, chro~ium ore concen~rate (chromium ore A) having a grain size up to 1.5 a Imm of which 90%, by weight, had a grain size of less than 0.7 mm were mixed, with the addition of a magnesium sulfate solution. ~he mixture was then pressed to form briquettes, the briquettes were dried and then fired in a shaft furnace at a temperature of 2100C to produce magnesia-chromium sinter material A. The composition of the raw materials and ! the resultant sinter material was as follows, all percentages being by weight:
Caustic ChromiumSinter Magnesia A Ore AMaterial A
SiO2 0.01~ 0.91~ 0.45%
FeO - 25.93 Fe23 ~ ~ 12.20 l A123 0.02 14.90 6.50 Cr23 ~ 47 03 20.10 CaO 1.35 0.07 0.77 MgO 98.60 10.90 59O90 --7~
Sinter material A ha~ the following properties, ll ; percentages beinq by weight:
: CaO+SiO2 1.22%
CaO/SiO~ 1.71 Cr2O3/Fe2O3 1.65 Coarse grain density 3.60 g/cm3 Sinter grain porosity~ open 6.1%/volume A brick mixture was prepared from th.is sinter material A
accor~ing to the following recipee, all percentages being by weight 3.0 ~ 5.0 mm ~ 20%
~i 1.0 - 3.0 mm 45%
0.1 - 1.0 mm 10 up to 0.]. mm 25~
This mixture was mixed with 3.7%, by weight, of imagne~ium sulfate solution, pressed to bricks under a pressure of 110 N/mm2, the bricks were dried and then fired for four hours (not counting the heating up and cooling period) at 18Q0C. Resultant bricks A had the 20 following properties:
j Coarse brick density 3.20 g/cm3 ! Brick porosity, open 17.~%, by volume Resistance to pressure at room temp. 55.4 N/mm2 Re~istance to pressure at 1600C 23.9 N/mm2 For purposes o comparison, a sinter material B was prepared in the identical manner but with the use of a chromium ore concentrate ~chromium ore B) poorer in iron and of a grain size up to 1.5 mm, B0%, by weight, being smaller than 0~7 mm~ Caustic magnesia A was again used as the 30 magnesia component. Chromium ore B and the resultant , I
~7~
,, magnesia-chromium sinter material B had the following composition, all percentages being by weight:
Chromium ore B Sinter material B
SiO2 0.36% 0.30%
FeO 15.00~ -Fe23 - 5.75%
A123 11.70~ 4.17 Cr~o3 57.70~ 20.47%
~I CaO 0.15% 0.83%
, MgO 14.90% 68.40~
Fired bricks B~were prepared from this sinter material B
under the identical conditions as hereinabove described, producing the following properties:
Coarse ~rain density 3.61 g/cm3 Sinter grain porosity, open 6.1%, by vol.
Coarse brick density 3.20 g/cm3 ; Brick porosity, open 17.5%, by vol.
Resistance to pressure at room temp.45.S N/mm2 Resistance to pressure at 160~C 23.3 N/mm2 The comparison shows that bricks A prepared in accordance with the invention have properties generally equivalent ~o those of comparison bricks B prepared from the more expensive chromoum ore B, even slightly surpassing them with respect to their resistance to pressure.
Example 2 Sinter materials and bricks fired from such materials ,were prepared in the same manner as in Example 1 from caustic magnesia A and chromium ores with different SiO~
,icontents. Sinter material C and resultant bricks C were made from chromium ore C which satisfies the conditions of _g _ 7~
the present invention. Sinter material D and comparison ~ bricks D wexe prepared Erom chromium ore D having a larger ! SiO2 content. The chromium ores and resultant sinter materials had the following compositions, all percentages being by weight:
Chromium Sinter Chromium Sinter ore C material C ore Dmaterial D
SiO2 0.41~ 0.30~ 1.52% 0.66%
FeO 25.51% - 23.63%
;I Fe23 ~ 12.07% - 11.90%
: Al 203 15.77~ 6.33~ 14.22~ 6.63%
Cr23 46-8g% 19.60% 46.99~ 19.95%
CaO 0.11% 0.73% 0.06~ 0.74%
MgO 10.21% 60.90% 14.40~ 60.10~
Sinter materials and bricks C and D had the following properties, all percentages being by weighto Sinter CSinter D
CaO~SiO2 1.03~ 1.40 Cao/SiO2 2.43 1.12 Cr2O3/Fe2O3 1.62 1.68 Coarse qrain density 3.62 g/cm33.66 g/cm3 ISin~er grain porosity, open (by vol.~ 7.6% 7.1%
BricksBricks D
Coarse brick density 3.18 g/cm33.19 g/cm3 Brick porosity, open (by vol.) 18.4~ 18.1%
Resistance to pressure (room temp.)59.0 N/mm260.8 N/mm2 Resistance to prepssure ll600C) 20.9 N/mm214~4 N/mm2 It was shown that the comparative quality D with a ~ CaO~sio2-content above 1.3%, by weight, indicated a 30%
lower resistance to heat of the fired bricks than that of quality C obtained according to the invention.
Example 3 Sinter material and resultant bricks C produced in accordance with the present invention in the manner of ; Example 2 were compared to sir.~er material and resultant bricks E produced with caustic magnesia E containing an amoun~ o Fe2o3 in excess of that required by this invention. Chromium ore ~ had a grain size up to l.5 mm, o~
which 80~, by weight, had a grain size smaller than 0~7 mm, to satisfy the conditions of the invention. Caustic , magnesia E and chromium ore E were mixed in a weight ratio of 62 : 38, with the addition of magnesium sulfate solution as a binder. The mixture was shaped into briquettes, dried and fired in a shaft furnace in the presence of gaseo~s oxy~en at a temperature of about 2100C to obtain sinter material E, the indicated substances having the following Icompositions, all percentages being by weight:
Caustic Chromi~mSinter Magnesia E Ore EMaterial E
SiO;2 0 ~ 19% 1 . 32~ 0 . 68%
FeO - 2 3 . 7 9 F~203 3 . 22 _ 13 . 09 A123 o 43 14 . 23 6 . 36 Cr2~3 - 47 .15 2û . 27 CaO 1.05 0.14 0.66 MgO 95 .11 13 . 37 58 . 94 CaO+SiO2 1. 34 Cr203/~e203 1. 54 Bricks C and E, respectively, were produced in the manner described in Example l from sinter material C of the invention ~Example 2) and comparison sinter material E but portions of these bricks were fired at different - 1 1 `
METHOD OF MANUFACTURING REFRACTORY MAGNESIA-CHROMIUM PRODUCT.
The present invention relates to a method of manufacturing a refractory magnesia-chromium product by preparing a mixture of caustically burned magnesia having a grain size of less than 0.2 mm, preferably no more than 0.12 mm, and of finely granulated chromium ore having a weight content of 20~ to ~8~ FeO, the caustically burned magnesia ; and the chromium ore being mixed in a ratio producing in the , mixture a weight content of 10% to 30%, preferably 15-25~, ;
Cr2o3, and a Cr2O3/A12O3 weight ration of more I than 2.5, preferably more than 3, shaping the mixiure into shaped bodies, such as briquettes, and sintering the same without melting at a minimum temperature of 2000C, preferably at least 2100C, and further treating the resultant sintered magnesia-chromium shaped bodies at temperatures of at least about 1800C to obtain the refractory product, including burned bricks and unburned ! br icks .
Several methods have been proposed for manufacturing pre-20 , reacted magnesia-chromium sintered materials and of l refrac~ories made therefrom by simultaneously sintering a ¦ material producing magnesia and chromium ore at a high temperature, the chromium ore being dissolved during the sintering process in the periclase matrix by a reaction proceeding essentially in the solid state and being contained therein after cooling in the form of newly formed spinel precipitate so that any residue of the original chromium ore grains are present at a maximum volume of no Imore than lQ~, preferably no more than 5~.
In the method described in Austrian patent No. 301,43~, 'I
li coarse granules of chromium ore having a minor component (at !
most 20%, by weight) of a grain size of less than 0.1 mm ancl I a major component (at least 40%, by weight) of a grain size ! exceeding 1 mm, and magnesite ore of a grain size of less than 0.1 mm as the material producing the magnesia are used, I
the maximum acceptable limits of the SiO2 and CaO contents being set forth. It is necessary in this method to use coarse granules of chromium ore to obtain a dense sintered I material, When finely granulated chromium ore and magnesite 1 ore are used, the resultant sintered grains show unfavorable il porosity values. However, it is not easy to obtain coarse '! granules of chromium ores of the required purity. It is easier to obtain so-called chromium ore concentrates, i.e.
chromium ores whose SiO2 and CaO contents have been reduced by suitable treatments which, however, produce I concentrates in finely granulated form~
According to the method of Austrian patent No. 290,374, a sinter material containing, by weight, no more than 2.5%
SiO2 and no more than 4% CaO, with a molar ratio CaO/SiO2 of 0.6 to 2.5, is produced Erom such a chromium ore concentrate 20-80~, by weight, of which has a grain size below 0.12 mm and a finely granulated magnesia matrix having a MgO-content, based on the burned state, of less than 95%, by weight, oP MgO, as well as, optionally, magnesite flue dust, at temperatures of at least 1750C, for example 2000C or more. However, the bricks made from this sinter material can be fired only at relatively low temperatures of, ~or example, 1560C to 1580C, which limits their ~ use to correspondly low operating temperatures and does not ,produce refrac~ory properties satisfying the highest ilrequirements.
,1 6~
The iron content is also a quality characteristic of the chromium ore, this value being determined by the fact that the entire iron content is present in the form of FeO in the I chromium ore. Chromium ore types poor in FeO-content, for ! example less than 15~, by weight, are considered as higher-quality ores but the iron-rich concentrates with an FeO-content of, for example, 18-27~, by weight, are obtainable at lower costs.
In accordance with Austrian patent No. 336,478, a sinter i materiall having a weight content of 11-20% Fe2o3 is ' obtained from such an iron-rich chromium ore concentrate of !'~ an average grain size of 0.1-1.5 mm and a caustic magnesia, which may be a magnesite flue dust. The bricks shaped from this sinter material are fired at a temperature of about 1800C, just below the softening temperature of the sinter material, and they show a high pyro-plasticity and good resistance to heat, which makes them suitable for operating temperatures above 1600C but below 1800C because they are subject to continuous wear in this temperature cange.
These bricks are not suitable for higher operating ,temperatures or for uses where they are subjected to continuous heat in this range~
It is the object of this invention to produce a magnesia-chromium sinter material from a finely granulated, iron-rich I
chromium ore to obtain refractory products which satisEy very high refractory requirements.
We have found that this object can be accomplished with caustically burned magnesia of high MgO-content and a low content of impurities if the SiO2-content of the chromium I
,l ore and the CaO- and SiO~-contents of the sinter material are subject to certain limiting conclitions.
Therefore, according to the invention, the mixture in the first hereinabove described manufacturing method is Iprepared from caustically burned magnesia having a weight I content of more than 97% MgO, no more than 0.2% SiO2 and I no more than 0.7%, preferably no more than 0.3%, ; Fe203~A1203, and the chromium ore having a grain I size ~ot exceeding 1. 5 mm and a weight content of no more 10 ! than 1.5%, preferably no more than 1~, SiO~, the mixture having a weight content of no more than 1.1% CaO and no more than 0.7~ SiO2, the sum of the weight content of CaO~SiO2 not exceeding 1.3~.
The use of a magnesia matrix in the form of the de~ined composition containing only minor SiO2, Fe203 and Al2o3 impurities produces a substantial increase in the refractory quality of the sinter material and the products ~made therefrom. The high FeO-content of the chromium ore lcomponent of the mixture has no deleterious effect on the 20 Iheat resistance if its SiO2 content does not exceed 1.5%, preferably 1%, by weight, and the mixture of caustically burned magnesia and chromium ore and the resultant sinter material has the indicated low CaO- and Sio2-content ~alues and Cr23~A123 weig~t ratio. In addition and preferably, the magnesia-chromium mixture has a Cr203/Fe203 weight ratio of 1.6 to 3.
The present invention makes it possible to ~se chromium ores having a high weight content of 20-28% FeO. The Ichromium ore is comminuted to a grain size of no more than 30 1.5 mm to prepare it for ~reatment, primarily to reduce its ., S12-content. It is of advantage in the method of the present invention if the grain size of at least 60~, by i weight, of the chromium ore is less than 0.7 mm.
The caustically burned magnesia used in the method of ' this invention may be prepared synthetically, for example by i the thermal decomposition of a purified slurry of magnesium chloride. However, it may also be obtained from lake water. While the synthetically produced magnesia will have l¦ a B2O3-~ontent of only a few tho~sandths of 1%, by , weight, the magnesia obtained from lake water contains higher amounts of B~2O3, ~hich may unfavorably influence the refractocy qualities of the product. Good types of lake water magnesia have a weight content of about 0.03-0.05 B~o3 and may be used for the method of the invention.
Magnesia containing more than 0.06%, by weight, B2O3 is generally not desirable for this use.
It is preferred to use a caustic magnesia having a weight content of no more than 2~ CaO and a chromium ore ,having a weight content of no more than 0.2~ CaO to obtain ~ the required low CaO- and Cao+sio2~contents of the mixture and resultant sinter material.
A conventional binder, for example a magnesium sulfate solution which may be prepared from kieserite or Epsom salt, is preferably added when the caustically burned magnesia and chromium ore mixture is prepared~ The mixture is then shaped in a press, for example a roller press, to form briquettes, the applied pressures being preferably as high as can be achieved with such presses, for example ~ressures ' of the order of magnitude of 14 to 20 N/mm2. ~owever, any ; type of compacting the mixture may be used. The shaped _5_ ;
.
;I bodies or brique~tes are dried and subsequently fired for sintering at a temperature of at least 2000C, preferably at least 2100C, which is obtained by the use of gaseous ,l oxygen. The sinter`ing furnace is preferably a shaft i furnace, preferably one with at least two superposed firing zones, the gaseous oxygen being delivered to the lower zone. However, it is also possible to use a rotary kiln as . long as the required high temperatures can be produced therein.
1 In the sinter, the chromium ore is dissolved in the periclase matrix in~a process proceeding practically in the solid state since a melting of the mate~ial is neither ; required nor desired, except for a minor amount of a molten phase derived from any impurities in the type of chromium ore used. When the sinter material is cooled, the chromium ore c~mponents are practically completely precipitated in I the magnesia matrix as newly formed spinels. The structure of the sinter material approaches that of a molten granular I material without, however, requiring an expensive melting 20 process for its manufacture. Residues of the original chromium ore granules, if present at all, should be limited to a maximum volume of 10~, preferably no more than 5%.
The sinter material, which is an intermediate product of the method of the present invention, has a low open grain porosity o~ an average of about 7~, by volume, measured in a grain size of 3 to 4 mm, the grain volume including all pores being determined by the mercury reception in a vacuum pycnometer with an input pressure of about 265 m~ar l,according to DIN (German Industry Norm) 51 065, Part 2, and the solid grain volume including the cLosed pores being determined by an air comparison pycnometer. This measuring method is also used for the values of the open sin~er grain porosity in the examples and comparison tests.
The bricks produced by the method of this invention may be fired without damaging them at temperatures up to 2000C and higher, and they exhibit a very high resistance I to heat. The values of the resistance to pressure under ' heat, measured at 1600C, lie in the range of 15 N/mm2 I and higher.
I The inven~ion will be elucidated further in the following operating~examples and comparison tests.
Example 1 Fifty-seven weight percent of caustic magnesia A having a grain size up to 0.1 mm and 43~, by weight, chro~ium ore concen~rate (chromium ore A) having a grain size up to 1.5 a Imm of which 90%, by weight, had a grain size of less than 0.7 mm were mixed, with the addition of a magnesium sulfate solution. ~he mixture was then pressed to form briquettes, the briquettes were dried and then fired in a shaft furnace at a temperature of 2100C to produce magnesia-chromium sinter material A. The composition of the raw materials and ! the resultant sinter material was as follows, all percentages being by weight:
Caustic ChromiumSinter Magnesia A Ore AMaterial A
SiO2 0.01~ 0.91~ 0.45%
FeO - 25.93 Fe23 ~ ~ 12.20 l A123 0.02 14.90 6.50 Cr23 ~ 47 03 20.10 CaO 1.35 0.07 0.77 MgO 98.60 10.90 59O90 --7~
Sinter material A ha~ the following properties, ll ; percentages beinq by weight:
: CaO+SiO2 1.22%
CaO/SiO~ 1.71 Cr2O3/Fe2O3 1.65 Coarse grain density 3.60 g/cm3 Sinter grain porosity~ open 6.1%/volume A brick mixture was prepared from th.is sinter material A
accor~ing to the following recipee, all percentages being by weight 3.0 ~ 5.0 mm ~ 20%
~i 1.0 - 3.0 mm 45%
0.1 - 1.0 mm 10 up to 0.]. mm 25~
This mixture was mixed with 3.7%, by weight, of imagne~ium sulfate solution, pressed to bricks under a pressure of 110 N/mm2, the bricks were dried and then fired for four hours (not counting the heating up and cooling period) at 18Q0C. Resultant bricks A had the 20 following properties:
j Coarse brick density 3.20 g/cm3 ! Brick porosity, open 17.~%, by volume Resistance to pressure at room temp. 55.4 N/mm2 Re~istance to pressure at 1600C 23.9 N/mm2 For purposes o comparison, a sinter material B was prepared in the identical manner but with the use of a chromium ore concentrate ~chromium ore B) poorer in iron and of a grain size up to 1.5 mm, B0%, by weight, being smaller than 0~7 mm~ Caustic magnesia A was again used as the 30 magnesia component. Chromium ore B and the resultant , I
~7~
,, magnesia-chromium sinter material B had the following composition, all percentages being by weight:
Chromium ore B Sinter material B
SiO2 0.36% 0.30%
FeO 15.00~ -Fe23 - 5.75%
A123 11.70~ 4.17 Cr~o3 57.70~ 20.47%
~I CaO 0.15% 0.83%
, MgO 14.90% 68.40~
Fired bricks B~were prepared from this sinter material B
under the identical conditions as hereinabove described, producing the following properties:
Coarse ~rain density 3.61 g/cm3 Sinter grain porosity, open 6.1%, by vol.
Coarse brick density 3.20 g/cm3 ; Brick porosity, open 17.5%, by vol.
Resistance to pressure at room temp.45.S N/mm2 Resistance to pressure at 160~C 23.3 N/mm2 The comparison shows that bricks A prepared in accordance with the invention have properties generally equivalent ~o those of comparison bricks B prepared from the more expensive chromoum ore B, even slightly surpassing them with respect to their resistance to pressure.
Example 2 Sinter materials and bricks fired from such materials ,were prepared in the same manner as in Example 1 from caustic magnesia A and chromium ores with different SiO~
,icontents. Sinter material C and resultant bricks C were made from chromium ore C which satisfies the conditions of _g _ 7~
the present invention. Sinter material D and comparison ~ bricks D wexe prepared Erom chromium ore D having a larger ! SiO2 content. The chromium ores and resultant sinter materials had the following compositions, all percentages being by weight:
Chromium Sinter Chromium Sinter ore C material C ore Dmaterial D
SiO2 0.41~ 0.30~ 1.52% 0.66%
FeO 25.51% - 23.63%
;I Fe23 ~ 12.07% - 11.90%
: Al 203 15.77~ 6.33~ 14.22~ 6.63%
Cr23 46-8g% 19.60% 46.99~ 19.95%
CaO 0.11% 0.73% 0.06~ 0.74%
MgO 10.21% 60.90% 14.40~ 60.10~
Sinter materials and bricks C and D had the following properties, all percentages being by weighto Sinter CSinter D
CaO~SiO2 1.03~ 1.40 Cao/SiO2 2.43 1.12 Cr2O3/Fe2O3 1.62 1.68 Coarse qrain density 3.62 g/cm33.66 g/cm3 ISin~er grain porosity, open (by vol.~ 7.6% 7.1%
BricksBricks D
Coarse brick density 3.18 g/cm33.19 g/cm3 Brick porosity, open (by vol.) 18.4~ 18.1%
Resistance to pressure (room temp.)59.0 N/mm260.8 N/mm2 Resistance to prepssure ll600C) 20.9 N/mm214~4 N/mm2 It was shown that the comparative quality D with a ~ CaO~sio2-content above 1.3%, by weight, indicated a 30%
lower resistance to heat of the fired bricks than that of quality C obtained according to the invention.
Example 3 Sinter material and resultant bricks C produced in accordance with the present invention in the manner of ; Example 2 were compared to sir.~er material and resultant bricks E produced with caustic magnesia E containing an amoun~ o Fe2o3 in excess of that required by this invention. Chromium ore ~ had a grain size up to l.5 mm, o~
which 80~, by weight, had a grain size smaller than 0~7 mm, to satisfy the conditions of the invention. Caustic , magnesia E and chromium ore E were mixed in a weight ratio of 62 : 38, with the addition of magnesium sulfate solution as a binder. The mixture was shaped into briquettes, dried and fired in a shaft furnace in the presence of gaseo~s oxy~en at a temperature of about 2100C to obtain sinter material E, the indicated substances having the following Icompositions, all percentages being by weight:
Caustic Chromi~mSinter Magnesia E Ore EMaterial E
SiO;2 0 ~ 19% 1 . 32~ 0 . 68%
FeO - 2 3 . 7 9 F~203 3 . 22 _ 13 . 09 A123 o 43 14 . 23 6 . 36 Cr2~3 - 47 .15 2û . 27 CaO 1.05 0.14 0.66 MgO 95 .11 13 . 37 58 . 94 CaO+SiO2 1. 34 Cr203/~e203 1. 54 Bricks C and E, respectively, were produced in the manner described in Example l from sinter material C of the invention ~Example 2) and comparison sinter material E but portions of these bricks were fired at different - 1 1 `
2~
temperatures. The resistance to pressure (DF) of these bricks at 1600C was measured in the following manner in N/mm2:
~! Brick firing temperature 1700C 1~00 C
2000~C
Bricks C DF 10.4 20.~ 26.4 33.8 Bricks E DF 4.8 10.5 * *
*could not be measured because i~ was not possible to produce the bricks Icompletely deformed and fissured) It can be seen that bricks may be readily fired from sinter material C ~repared according to the invention even at very high temperat-lres, i.e. 2000C. However, with sinter material E outside the scope of this invention, the highest firing temperature is about 1800C. ~urthermore, these bricks show a considerably lower resistance to heat than correspondingly prepared bricks C.
., ;
!
temperatures. The resistance to pressure (DF) of these bricks at 1600C was measured in the following manner in N/mm2:
~! Brick firing temperature 1700C 1~00 C
2000~C
Bricks C DF 10.4 20.~ 26.4 33.8 Bricks E DF 4.8 10.5 * *
*could not be measured because i~ was not possible to produce the bricks Icompletely deformed and fissured) It can be seen that bricks may be readily fired from sinter material C ~repared according to the invention even at very high temperat-lres, i.e. 2000C. However, with sinter material E outside the scope of this invention, the highest firing temperature is about 1800C. ~urthermore, these bricks show a considerably lower resistance to heat than correspondingly prepared bricks C.
., ;
!
Claims (11)
1. A method of manufacturing a refractory magnesia-chromium product, which comprises the steps of (a) preparing a mixture of caustically burned magnesia having a grain size of less than 0.2 mm and of chromium ore having a grain size not exceeding 1.5 mm, (1) the magnesia having a weight content of more than 97% MgO, no more than 0.2% SiO2 and no more than 0.7% Fe2O3+Al2O3, and (2) the chromium ore having a weight content of 20% to 28% FeO and no more than 1.5% SiO2, (3) the caustically burned magnesia and the chromium ore being mixed in a ratio producing in the mixture a weight content of 10% to 30% Cr2O3 and a Cr2O3/Al2O3 weight ratio of more than 2.5, and (4) the mixture having a weight content of no more than 1.1% CaO and no more than 0.7% SiO2, the sum of the weight content of CaO+SiO2 not exceeding 1.3%, (b) shaping the mixture into shaped bodies and sintering the same without melting at a minimum temperature of 2000°C, and (c) further treating the resultant sintered magnesia-chromium shaped bodies at temperatures of at least about 1800°C to obtain the refractory product.
2. The manufacturing method of claim 1, wherein the caustically burned magnesia has a grain size of no more than 0.12 mm.
3. The manufacturing method of claim 1, wherein the weight content of Fe2O3+Al2O3 is no more than 0.3.%.
4. The manufacturing method of claim 1, wherein the Cr2O3 weight content is between 15% and 25%.
5. The manufacturing method of claim 1, wherein the Cr2O3/A12O3 weight ratio is more than 3.
6. The manufacturing method of claim 1, wherein the SiO2 weight content in the chromium ore is no more than 1%.
7. The manufacturing method of claim 1, wherein the minimum sintering temperature is 2100°C.
8. The manufacturing method of claim 1, wherein the grain size of at least 60%, by weight, of the chromium ore is less than 0.7 mm.
9. The manufacturing method of claim 1, wherein the magnesia-chromium shaped bodies have a Cr2O3/Fe2O3 weight ratio of 1.6 to 3.
10. The manufacturing method of claim 1, wherein the caustically burned magnesia has a weight content of no more than 0.06% B2O3.
11. The manufacturing method of claim 1, wherein the caustically burned magnesia has a weight content of no more than 2% CaO and the chromium ore has a weight content of no more than 0.2% CaO.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AT0141082A AT373229B (en) | 1982-04-08 | 1982-04-08 | METHOD FOR PRODUCING A FIREPROOF MAGNESIACHROME SINTER MATERIAL |
| ATA1410/82 | 1982-04-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1197267A true CA1197267A (en) | 1985-11-26 |
Family
ID=3513283
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000424891A Expired CA1197267A (en) | 1982-04-08 | 1983-03-30 | Method of making magnesiachrom refractories |
Country Status (14)
| Country | Link |
|---|---|
| EP (1) | EP0091704B1 (en) |
| JP (1) | JPS58185476A (en) |
| AT (1) | AT373229B (en) |
| BR (1) | BR8301745A (en) |
| CA (1) | CA1197267A (en) |
| DD (1) | DD209614A5 (en) |
| DE (1) | DE3364146D1 (en) |
| ES (1) | ES8405749A1 (en) |
| GR (1) | GR78156B (en) |
| IE (1) | IE54202B1 (en) |
| IL (1) | IL68226A (en) |
| MX (1) | MX156507A (en) |
| TR (1) | TR21803A (en) |
| YU (1) | YU42620B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3527789C3 (en) * | 1985-08-02 | 1994-02-24 | Refratechnik Gmbh | Coarse ceramic molded body and its use |
| JPS63110929U (en) * | 1987-01-06 | 1988-07-16 |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1571638B2 (en) * | 1966-12-24 | 1972-01-05 | International Minerals and Chemical Corp., Skokie, 111. (V.StA.) | METHOD OF MANUFACTURING A FIRE-RESISTANT BODY FROM A GRANULATED MIXTURE OF CHROME SPINEL AND PERICLAS |
| AT290374B (en) * | 1969-04-03 | 1971-05-25 | Oesterr Amerikan Magnesit | Process for the production of refractory chromium and chromium magnesite bricks |
| DE2015566C3 (en) * | 1969-05-15 | 1975-07-24 | General Refractories Co., Philadelphia, Pa. (V.St.A.) | Process for the production of directly bonded, refractory moldings |
| AT336478B (en) * | 1972-09-29 | 1977-05-10 | Veitscher Magnesitwerke Ag | METHOD OF MANUFACTURING FIRED REFRACTORY BRICKS |
| AT353154B (en) * | 1973-10-03 | 1979-10-25 | Pickford Holland & Company Lim | MATERIAL FOR THE MANUFACTURE OF REFRACTORY STONES AND THE LIKE |
| HU176631B (en) * | 1977-06-10 | 1981-03-28 | Veszpremi Vegyipari Egyetem | Process for preparing compact simultaneous sinters of direct bond |
-
1982
- 1982-04-08 AT AT0141082A patent/AT373229B/en not_active IP Right Cessation
-
1983
- 1983-03-24 IL IL68226A patent/IL68226A/en unknown
- 1983-03-25 EP EP83200420A patent/EP0091704B1/en not_active Expired
- 1983-03-25 DE DE8383200420T patent/DE3364146D1/en not_active Expired
- 1983-03-28 IE IE678/83A patent/IE54202B1/en unknown
- 1983-03-30 CA CA000424891A patent/CA1197267A/en not_active Expired
- 1983-04-04 GR GR70982A patent/GR78156B/el unknown
- 1983-04-06 TR TR21803A patent/TR21803A/en unknown
- 1983-04-06 YU YU808/83A patent/YU42620B/en unknown
- 1983-04-06 DD DD83249611A patent/DD209614A5/en not_active IP Right Cessation
- 1983-04-06 BR BR8301745A patent/BR8301745A/en not_active IP Right Cessation
- 1983-04-07 JP JP58061512A patent/JPS58185476A/en active Granted
- 1983-04-07 ES ES521297A patent/ES8405749A1/en not_active Expired
- 1983-04-08 MX MX196873A patent/MX156507A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| ES521297A0 (en) | 1984-06-16 |
| IL68226A (en) | 1986-03-31 |
| EP0091704A1 (en) | 1983-10-19 |
| JPS58185476A (en) | 1983-10-29 |
| IE830678L (en) | 1983-10-08 |
| IE54202B1 (en) | 1989-07-19 |
| DD209614A5 (en) | 1984-05-16 |
| AT373229B (en) | 1983-12-27 |
| JPS6331428B2 (en) | 1988-06-23 |
| MX156507A (en) | 1988-09-05 |
| YU80883A (en) | 1986-02-28 |
| ES8405749A1 (en) | 1984-06-16 |
| GR78156B (en) | 1984-09-26 |
| YU42620B (en) | 1988-10-31 |
| DE3364146D1 (en) | 1986-07-24 |
| BR8301745A (en) | 1983-12-13 |
| ATA141082A (en) | 1983-05-15 |
| EP0091704B1 (en) | 1986-06-18 |
| TR21803A (en) | 1985-07-18 |
| IL68226A0 (en) | 1983-06-15 |
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