CA2007460A1 - Method and apparatus for producing boron carbide crystals - Google Patents
Method and apparatus for producing boron carbide crystalsInfo
- Publication number
- CA2007460A1 CA2007460A1 CA002007460A CA2007460A CA2007460A1 CA 2007460 A1 CA2007460 A1 CA 2007460A1 CA 002007460 A CA002007460 A CA 002007460A CA 2007460 A CA2007460 A CA 2007460A CA 2007460 A1 CA2007460 A1 CA 2007460A1
- Authority
- CA
- Canada
- Prior art keywords
- hot zone
- boron carbide
- furnace
- nitrogen
- mixture
- 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.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
- C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
- C01B3/34—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
- C01B3/36—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents using oxygen or mixtures containing oxygen as gasifying agents
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/90—Carbides
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/90—Carbides
- C01B32/914—Carbides of single elements
- C01B32/991—Boron carbide
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Health & Medical Sciences (AREA)
- General Health & Medical Sciences (AREA)
- Engineering & Computer Science (AREA)
- Combustion & Propulsion (AREA)
- Carbon And Carbon Compounds (AREA)
- Crystals, And After-Treatments Of Crystals (AREA)
- Ceramic Products (AREA)
Abstract
ABSTRACT
The invention is a method and apparatus for producing boron carbide crystals in which a major portion of the crystals are of sub-micrometer size, and the crystals have a low combined nitrogen content. A
nitro-gen-free, particulate mixture of a boric oxide compound and a carbon compound are dropped into the hot zone of a high temperature furnace through a liquid--cooled feed tube. The particles fall from the feed tube into boat members that move out of the hot zone to a collection point. As the particulate mixture falls through the hot zone, it is rapidly heated above the initiation reaction temperature of boron carbide. The result is a product in which most of the boron carbide crystals are less than on (1) micrometer in size.
The invention is a method and apparatus for producing boron carbide crystals in which a major portion of the crystals are of sub-micrometer size, and the crystals have a low combined nitrogen content. A
nitro-gen-free, particulate mixture of a boric oxide compound and a carbon compound are dropped into the hot zone of a high temperature furnace through a liquid--cooled feed tube. The particles fall from the feed tube into boat members that move out of the hot zone to a collection point. As the particulate mixture falls through the hot zone, it is rapidly heated above the initiation reaction temperature of boron carbide. The result is a product in which most of the boron carbide crystals are less than on (1) micrometer in size.
Description
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METH0D AND APPARATUS FOR PRODUCING ~ --BORON CARBIDE C~YSTALS
. . :
Thls invention relates to a method and ~ -apparatus for producing boron carbide crystals. More qpecifically, the invention is directed to the production of boron carbide crystals of a submicron siz~.
Boron carbide (B4C) is a ceramic material having a high degree of hardness, good structural ~ `;
integrity at high temperatures, and chemical inertne3s.
These properties make boron carbide a useful material for fabricating devices such as armor plating, sand blasting nozzles, bearings, dies, control rods ~or nuclear reactors, and rePractory liner~. In many of these applications it i9 de3irable to use a high purity, 5 monodispersedl boron carbide powder in which the ;
crystals are less than one (1) micrometer in size. The narrow particle size di~tribution gives the product certain advantages. One advantage is optimum reactivity. Another is that the material can be hot-pressed to yield a uniform, fine-grained material that is free of pores, excess carbon, and low mélting metallic carbide impurities.
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METH0D AND APPARATUS FOR PRODUCING ~ --BORON CARBIDE C~YSTALS
. . :
Thls invention relates to a method and ~ -apparatus for producing boron carbide crystals. More qpecifically, the invention is directed to the production of boron carbide crystals of a submicron siz~.
Boron carbide (B4C) is a ceramic material having a high degree of hardness, good structural ~ `;
integrity at high temperatures, and chemical inertne3s.
These properties make boron carbide a useful material for fabricating devices such as armor plating, sand blasting nozzles, bearings, dies, control rods ~or nuclear reactors, and rePractory liner~. In many of these applications it i9 de3irable to use a high purity, 5 monodispersedl boron carbide powder in which the ;
crystals are less than one (1) micrometer in size. The narrow particle size di~tribution gives the product certain advantages. One advantage is optimum reactivity. Another is that the material can be hot-pressed to yield a uniform, fine-grained material that is free of pores, excess carbon, and low mélting metallic carbide impurities.
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The usual method ~or producing boron carbide crystals i~ to place a particulate mixture of a boric oxide compound and a carbon compound in a crucible and pass the crucible through ~he hot zone of a high temperature furnace. A major problem with this method is that the mixture iq heated to it~ reaction temperature at a rate which produce~ only a very broad range of crystals in the micron size range, and essentially no crystals that are smaller than one (1) micrometer in size.
The invention is directed to an apparatus and method for producing a quantity o~ boron carbide crystal3 in which a major portion of the crystals are o~
sub-micrometer size.
The apparatu~ used in the practice o~ thi~
invention i~ a modified verqion of a graphite reqistance push-type Yurnace that operates at extremely high temperatures. The furnace unit includes a floor member and a roof member, with the space between these two members defining a hot zone. Heat ii delivered to the hot zone by heater means located inside the furnace unit adjacent to the roof member.
Another component of the furnace unit is a vertical feed tube, which iq poqitioned above the furnace hot zone. The feed tube is designed for feeding a nitrogen-free particulate mixture of a boric oxide compound and a carbon compound into the hot zone. A
coollng fluid is ciroulated around the feed tube, which cools the tube enough to maintain the boric oxide ~eed compound below it~ melting point. The furnace unit also includeq a group of boat members de~igned to move along 34,924-F -2-2~074~i0 ... . .
the floor of the furnace hot zone in a path that passes direotly below the feed tube.
In a typical operation of the furnace unit, as the particulate mixture falls from the feed tube through the furnace hot zone, the temperature of the hot zone is maintained above 1570C. At this temperature the boric oxide compound will react with the carbon compound to form boron carbide crystal~. As each boat member moves underneath the the feed tube, the boat is filled with a load of the boron carbide crystals, which are carrisd in the boat to a collection point outside of the furnace hot zone. ;
Figure 1 is a front elevation view, mostly in ~chematic, of a high temperature furnace u~ed in making boron carbide according to this invention.
Figure 2 is a detail view, partly in schematic, of component~ of the furnace ~hown in Fig. 1 which are used to feed a starting material for boron carbide into the furnace.
In the drawing7 referring particularly to Figure 1, the high temperature furnace of thi~ invention i9 generally designated by the letter F. The outside of the furnace is defined by a metal qhell 10. The inside part of the furnace i~ defined generally by a roo~
~ection and a floor member. The roof section consist~
of three deck~, namely, an upper deck 11, intermediate deck 12, and lower deck 13, with the floor member 14 being located below deck 13. The roof section decks and trle floor member are constructed of graphite. The space between the shell and the rooP section, and the shell and the floor member provides an insulation section 15.
34,924-F -3--. . . . , ................... . . . ....... ; ., . ~
, . .. ! ' ', . . . ..
2~)~746 In the furnace illustrated herein the insula-tion section 15 is filled with lampblack 16~ The space between the deck 12 and floor member 14 defines the hot zone 17 of the ~urnace. Heater boards 18, which are fabricated of graphite, are positioned directly above the hot zone 17 in a space 19 between the upper deck 11 and the intermediate deck 12. A DC current is passed through each board as the heating medium.
Above the hot zone 17 of the furnace is a vertical chute ~tructure that consi3ts of three pieces.
The lower part of the chute is de~ined by a sleeve 207 that fastens into the deck 12 and extends up through deck 11. The upper part of the chute is defined by a leeve 21, of qmaller diameter than sleeve 20. The lower end of aleeve 21 i~ coupled to the upper end o~
sleeve 20 by a transition piece 22. The top end of sleeve 21 is fitted with a packing gland 23 and gland nut 23a, which provide a seal aqqembly.
As shown particularly in Fig. 2, a cooling jacket i~ mounted lengthwise inqide the sleeve 21 of the chute. The jacket is defined by an inside tube 24, which is enclosed within an outside tube 25. A vertical feed tube 26 is mounted lengthwise inqide tube 24, and an annulu~ between these tubes defines a passage 27 for circulating a cooling fluid along the outside of the feed tube. The cooling fluid enter~q passage 27 through an inlet fitting 28. Another annulus between the out-3 side of tube 24 and the in_ide of tube 25 defineq apa~sage 29 for the cooling fluid to leave the jacket through an outlet fitting 30.
In the practice of this invention, the starting material for producing boron carbide is a particulate -~, "
. ..
34,924-F _4_ .
.
2~ 6~ -:'`.`: -;
mixture of a boric oxide compound and a carbon compound.
A device for ~eeding the particulate mixture into the feed tube 26 i3 located above the upper end of the ~eed tube. As shown in Figure 2, one type of feeder device that may be used is a screw feeder 31. An outlet spout -~
31a on the screw feeder iq connected to the top end of a glass sight tube 32 with a flexible coupling 33. At its - -bottom end the sight tube is connected to the top end of ``
feed tube 26 by another flexible coupling 34.
O~eration A typical example will now be given to illustrate the production of boron carbide crystals according to the practice of this invention. The particulate mixture consisted of a physical blend of technical grade boric acid (U.S. Borax), size -200 mesh tles9 than 74 micrometers) and 50 percent compressed acetylene carbon black (Gul~ Oil Co.). The mixture was blended for 30 minutes in a modified mortar mixer coated with an epoxy film. The mixture was prepared to give an excess of boron over carbon of approximately 20 percent, based on the reaction stoichiometry:
2B203 + 7C ~ B4C + 6CO
The invention is directed to an apparatus and method for producing a quantity o~ boron carbide crystal3 in which a major portion of the crystals are o~
sub-micrometer size.
The apparatu~ used in the practice o~ thi~
invention i~ a modified verqion of a graphite reqistance push-type Yurnace that operates at extremely high temperatures. The furnace unit includes a floor member and a roof member, with the space between these two members defining a hot zone. Heat ii delivered to the hot zone by heater means located inside the furnace unit adjacent to the roof member.
Another component of the furnace unit is a vertical feed tube, which iq poqitioned above the furnace hot zone. The feed tube is designed for feeding a nitrogen-free particulate mixture of a boric oxide compound and a carbon compound into the hot zone. A
coollng fluid is ciroulated around the feed tube, which cools the tube enough to maintain the boric oxide ~eed compound below it~ melting point. The furnace unit also includeq a group of boat members de~igned to move along 34,924-F -2-2~074~i0 ... . .
the floor of the furnace hot zone in a path that passes direotly below the feed tube.
In a typical operation of the furnace unit, as the particulate mixture falls from the feed tube through the furnace hot zone, the temperature of the hot zone is maintained above 1570C. At this temperature the boric oxide compound will react with the carbon compound to form boron carbide crystal~. As each boat member moves underneath the the feed tube, the boat is filled with a load of the boron carbide crystals, which are carrisd in the boat to a collection point outside of the furnace hot zone. ;
Figure 1 is a front elevation view, mostly in ~chematic, of a high temperature furnace u~ed in making boron carbide according to this invention.
Figure 2 is a detail view, partly in schematic, of component~ of the furnace ~hown in Fig. 1 which are used to feed a starting material for boron carbide into the furnace.
In the drawing7 referring particularly to Figure 1, the high temperature furnace of thi~ invention i9 generally designated by the letter F. The outside of the furnace is defined by a metal qhell 10. The inside part of the furnace i~ defined generally by a roo~
~ection and a floor member. The roof section consist~
of three deck~, namely, an upper deck 11, intermediate deck 12, and lower deck 13, with the floor member 14 being located below deck 13. The roof section decks and trle floor member are constructed of graphite. The space between the shell and the rooP section, and the shell and the floor member provides an insulation section 15.
34,924-F -3--. . . . , ................... . . . ....... ; ., . ~
, . .. ! ' ', . . . ..
2~)~746 In the furnace illustrated herein the insula-tion section 15 is filled with lampblack 16~ The space between the deck 12 and floor member 14 defines the hot zone 17 of the ~urnace. Heater boards 18, which are fabricated of graphite, are positioned directly above the hot zone 17 in a space 19 between the upper deck 11 and the intermediate deck 12. A DC current is passed through each board as the heating medium.
Above the hot zone 17 of the furnace is a vertical chute ~tructure that consi3ts of three pieces.
The lower part of the chute is de~ined by a sleeve 207 that fastens into the deck 12 and extends up through deck 11. The upper part of the chute is defined by a leeve 21, of qmaller diameter than sleeve 20. The lower end of aleeve 21 i~ coupled to the upper end o~
sleeve 20 by a transition piece 22. The top end of sleeve 21 is fitted with a packing gland 23 and gland nut 23a, which provide a seal aqqembly.
As shown particularly in Fig. 2, a cooling jacket i~ mounted lengthwise inqide the sleeve 21 of the chute. The jacket is defined by an inside tube 24, which is enclosed within an outside tube 25. A vertical feed tube 26 is mounted lengthwise inqide tube 24, and an annulu~ between these tubes defines a passage 27 for circulating a cooling fluid along the outside of the feed tube. The cooling fluid enter~q passage 27 through an inlet fitting 28. Another annulus between the out-3 side of tube 24 and the in_ide of tube 25 defineq apa~sage 29 for the cooling fluid to leave the jacket through an outlet fitting 30.
In the practice of this invention, the starting material for producing boron carbide is a particulate -~, "
. ..
34,924-F _4_ .
.
2~ 6~ -:'`.`: -;
mixture of a boric oxide compound and a carbon compound.
A device for ~eeding the particulate mixture into the feed tube 26 i3 located above the upper end of the ~eed tube. As shown in Figure 2, one type of feeder device that may be used is a screw feeder 31. An outlet spout -~
31a on the screw feeder iq connected to the top end of a glass sight tube 32 with a flexible coupling 33. At its - -bottom end the sight tube is connected to the top end of ``
feed tube 26 by another flexible coupling 34.
O~eration A typical example will now be given to illustrate the production of boron carbide crystals according to the practice of this invention. The particulate mixture consisted of a physical blend of technical grade boric acid (U.S. Borax), size -200 mesh tles9 than 74 micrometers) and 50 percent compressed acetylene carbon black (Gul~ Oil Co.). The mixture was blended for 30 minutes in a modified mortar mixer coated with an epoxy film. The mixture was prepared to give an excess of boron over carbon of approximately 20 percent, based on the reaction stoichiometry:
2B203 + 7C ~ B4C + 6CO
4 mol~ B: 7 mols C = 100%
4 x 1.2 mol~ B: 7 molq C = 20% exceqs B
The mixture was heated in ti~anium pan~q for 3.5 hourq at 350C to dehydrate it to B203 + C. The pan~ measured 2 in. high x 24 in. wide x 72 in.
(5 cm x 61 cm x 183 cm) long and they were closed with titanium covers having 1/2 in. (1.3 cm) dia. holes -therein to allow water vapor to escape from the mixture during heating. A~ter cooling the dried mixture is ' ' " '`
:
34,924-F -5-2~q6~
loosely agglomerated, but it can be easily broken up into <10 me~h (1.68 mm) aggregates.
At this point in the preparation, the mixture has a bulk density of about 15 lbs/cu. ft.
(240.3 kg/m3), since it contains a ~ubstantial amount oP
entrapped air. The entrapped air includes about 80 percent N2, which is undesire-able because it can react to form boron nitride. To correct t~he problem, a vacuum i~ pulled on the mixture to deaerate it, and argon i~ used to fill the evacuated feed mixture. The deaerating ~tep thus reduces the N2 concentration in the boron carbide product to about 0.3 to 0.4 percent. In situationi where the feed mixture i3 not deaerated, the nitrogen content of the submicrometer boron carbide crystals can be as high as 1 to 3 percent.
Following the deaerating step9 the particulate mlxture 35 is loaded into a hopper 36, which is mounted on the screw conveyor 31 at the end opposite from the outlet spout 31a. During the production operation, argon, as a purge gas, is directed into the hopper through a purge line 37, and into the screw conveyor through a purge line 38. The screw qhaft 31b in the conveyor is driven by a motor 39, which has a variable speed drive. The argon purge gas provides an inert environment for the reaction of the boric oxide and carbon compounds in the mixture 35.
As the mixture 35 moves from the conveyor 31 Lnto the feed tube 26, it passes through the glass sight tube 32. The sight tube thu~ provides a "window" for the furnace operator to periodically view the flow of the reactive mixture into the furnace, and take corrective action if it become~ necessary. From the 34,924-F -6-~o~
_ . ..
. .
screw conveyor, the mixture ii3 delivered into the feed ~-tube at a rate of not more than 0.3 lbs/min.
(0.7 kg/min), and preferably 0.1 to 0.2 lbi~3imin.
(0.2-0.4 kg/min). A~ the mixture falls through the feed tube, water (or some other isuitable cooling fluid) is 5 continuou~ly circulated through the passagei~ 27 and 29 ~-of the cooling jacket.
Cooling the feed tube ais described herein keeps the temperature inside the tube below 300C, which ii~ the i~oftening point o~ boric anhydride. If the particulate mixture is not cooled as it moves through the feed tube, it will rapidly convert to a semi-liquid pha~e and plug off the tube. From the feed tube 26, the 1~ particulate mixture 35 Pallis downwardly through the hot zone 17 oY furnace F and into a product boat 40, which iq bein3 puished along the floor 14 of the furnace. As shown in Figure 1, there is a continuous string oP the product boati3, and they are moved by a suitable conveyor i~yistem (not shown).
The boats are pu~hed through the hot zone 17 at a rate of about 2 in. to 3 in. per minute (5 to 18 cm/min.). Ais the par-ticles 35 enter the hot zone 17 at the discharge end 26a of the feed tube 26, the temperature ii~ about 1500C. The temperature increases to about 2000C at the point where the particles fall into the produ¢t boats. When each product boat 40 passes directly below the discharge end of the feed 3 tube, it is filled with a load of boron carbide cryistals, and the product is carried to a collection point (not shown) outside of the hot zone.
During the production operation, the hot ~ ~
zone 17 is filled with carbon monoxide and argon gas, to -34,924-F -7~
~0~7460 provide a desireable inert environment for the reaction of the i~tarting material to boron carbide~ Ai~ ishown in Figure 1, the argon i~ introduced into the hot zone at two point~; one point is through the feed inlet pipe 26 and the other point i~ at the le~t end of the zone, a~
indicated by arrow 42. The argon !Ytream entering the hot zone from the left end also serves another purpose.
Thi_ streiam move~ in a direction countercurrent to the path followed by the product boats 40 a~ they leave the hot zone. The ga_ _tream thus acts ai~ a barrier to prevent the particlei~ in the mixture 35 from being swept out of the hot zone before the boron carbide reaction i completed.
A key to obtaining boron carbide cry~tal~ in a _ub-micrometer size iq to be able to heat the starting material above it~ initiation reaction temperature very rapldly. In the practice of thii~ invention, therefore, it i9 critical that the temperature of the hot zone be maintained above 1570C. Another critical factor i3 the time it take~ to heat the particles above the reaction temperature. In the operation de~cribed herein the temperature of the hot zone will be 1600C to 2100C and the rate at which the particleq are heated a~ they move ~
through the hot zone is at lea~t 200C per isecond. The ~ ;
amount of boron carbide cryiqtal~ produced was about one (1) pound per hour (0.46 hg/hr), of which about 90 percent by weight of the cry3tals were of 3ub-micrometer ~ize. The actual size wai~ 0.1 to 0.3 miorometer~. ~
~'":' ,"
' ' : . .: -;'' " ' ' 34,924-F -8-:
: ' "
4 x 1.2 mol~ B: 7 molq C = 20% exceqs B
The mixture was heated in ti~anium pan~q for 3.5 hourq at 350C to dehydrate it to B203 + C. The pan~ measured 2 in. high x 24 in. wide x 72 in.
(5 cm x 61 cm x 183 cm) long and they were closed with titanium covers having 1/2 in. (1.3 cm) dia. holes -therein to allow water vapor to escape from the mixture during heating. A~ter cooling the dried mixture is ' ' " '`
:
34,924-F -5-2~q6~
loosely agglomerated, but it can be easily broken up into <10 me~h (1.68 mm) aggregates.
At this point in the preparation, the mixture has a bulk density of about 15 lbs/cu. ft.
(240.3 kg/m3), since it contains a ~ubstantial amount oP
entrapped air. The entrapped air includes about 80 percent N2, which is undesire-able because it can react to form boron nitride. To correct t~he problem, a vacuum i~ pulled on the mixture to deaerate it, and argon i~ used to fill the evacuated feed mixture. The deaerating ~tep thus reduces the N2 concentration in the boron carbide product to about 0.3 to 0.4 percent. In situationi where the feed mixture i3 not deaerated, the nitrogen content of the submicrometer boron carbide crystals can be as high as 1 to 3 percent.
Following the deaerating step9 the particulate mlxture 35 is loaded into a hopper 36, which is mounted on the screw conveyor 31 at the end opposite from the outlet spout 31a. During the production operation, argon, as a purge gas, is directed into the hopper through a purge line 37, and into the screw conveyor through a purge line 38. The screw qhaft 31b in the conveyor is driven by a motor 39, which has a variable speed drive. The argon purge gas provides an inert environment for the reaction of the boric oxide and carbon compounds in the mixture 35.
As the mixture 35 moves from the conveyor 31 Lnto the feed tube 26, it passes through the glass sight tube 32. The sight tube thu~ provides a "window" for the furnace operator to periodically view the flow of the reactive mixture into the furnace, and take corrective action if it become~ necessary. From the 34,924-F -6-~o~
_ . ..
. .
screw conveyor, the mixture ii3 delivered into the feed ~-tube at a rate of not more than 0.3 lbs/min.
(0.7 kg/min), and preferably 0.1 to 0.2 lbi~3imin.
(0.2-0.4 kg/min). A~ the mixture falls through the feed tube, water (or some other isuitable cooling fluid) is 5 continuou~ly circulated through the passagei~ 27 and 29 ~-of the cooling jacket.
Cooling the feed tube ais described herein keeps the temperature inside the tube below 300C, which ii~ the i~oftening point o~ boric anhydride. If the particulate mixture is not cooled as it moves through the feed tube, it will rapidly convert to a semi-liquid pha~e and plug off the tube. From the feed tube 26, the 1~ particulate mixture 35 Pallis downwardly through the hot zone 17 oY furnace F and into a product boat 40, which iq bein3 puished along the floor 14 of the furnace. As shown in Figure 1, there is a continuous string oP the product boati3, and they are moved by a suitable conveyor i~yistem (not shown).
The boats are pu~hed through the hot zone 17 at a rate of about 2 in. to 3 in. per minute (5 to 18 cm/min.). Ais the par-ticles 35 enter the hot zone 17 at the discharge end 26a of the feed tube 26, the temperature ii~ about 1500C. The temperature increases to about 2000C at the point where the particles fall into the produ¢t boats. When each product boat 40 passes directly below the discharge end of the feed 3 tube, it is filled with a load of boron carbide cryistals, and the product is carried to a collection point (not shown) outside of the hot zone.
During the production operation, the hot ~ ~
zone 17 is filled with carbon monoxide and argon gas, to -34,924-F -7~
~0~7460 provide a desireable inert environment for the reaction of the i~tarting material to boron carbide~ Ai~ ishown in Figure 1, the argon i~ introduced into the hot zone at two point~; one point is through the feed inlet pipe 26 and the other point i~ at the le~t end of the zone, a~
indicated by arrow 42. The argon !Ytream entering the hot zone from the left end also serves another purpose.
Thi_ streiam move~ in a direction countercurrent to the path followed by the product boats 40 a~ they leave the hot zone. The ga_ _tream thus acts ai~ a barrier to prevent the particlei~ in the mixture 35 from being swept out of the hot zone before the boron carbide reaction i completed.
A key to obtaining boron carbide cry~tal~ in a _ub-micrometer size iq to be able to heat the starting material above it~ initiation reaction temperature very rapldly. In the practice of thii~ invention, therefore, it i9 critical that the temperature of the hot zone be maintained above 1570C. Another critical factor i3 the time it take~ to heat the particles above the reaction temperature. In the operation de~cribed herein the temperature of the hot zone will be 1600C to 2100C and the rate at which the particleq are heated a~ they move ~
through the hot zone is at lea~t 200C per isecond. The ~ ;
amount of boron carbide cryiqtal~ produced was about one (1) pound per hour (0.46 hg/hr), of which about 90 percent by weight of the cry3tals were of 3ub-micrometer ~ize. The actual size wai~ 0.1 to 0.3 miorometer~. ~
~'":' ,"
' ' : . .: -;'' " ' ' 34,924-F -8-:
: ' "
Claims (10)
1. A method for producing boron carbide crystals in which a major portion of the crystals are less than one micrometer in size and have a low combined nitrogen content, comprising:
mixing a boric oxide compound and a carbon compound to form a particulate feed mixture, said mixture containing a substantial amount of nitrogen;
deaerating the particulate feed mixture to remove the nitrogen contained therein such that said nitrogen is removed and replaced with an inert gas;
dropping the nitrogen-free particulate feed mixture through a vertical feed tube having a discharge end that extends into a hot zone of a high temperature furnace; and allowing the nitrogen-free particulate feed mixture to fall from the discharge end of the vertical tube through the furnace hot zone, while maintaining the temperature of the hot zone above 1570°C such that the boric oxide compound reacts with the carbon compound to form boron carbide crystals as the nitrogen-free particulate feed mixture falls through the hot zone of the furnace.
mixing a boric oxide compound and a carbon compound to form a particulate feed mixture, said mixture containing a substantial amount of nitrogen;
deaerating the particulate feed mixture to remove the nitrogen contained therein such that said nitrogen is removed and replaced with an inert gas;
dropping the nitrogen-free particulate feed mixture through a vertical feed tube having a discharge end that extends into a hot zone of a high temperature furnace; and allowing the nitrogen-free particulate feed mixture to fall from the discharge end of the vertical tube through the furnace hot zone, while maintaining the temperature of the hot zone above 1570°C such that the boric oxide compound reacts with the carbon compound to form boron carbide crystals as the nitrogen-free particulate feed mixture falls through the hot zone of the furnace.
2. The method of Claim 1, further comprising:
moving a group of boat members through the furnace hot zone along a path that passes directly below the discharge end of the vertical feed tube;
filling each boat member with a load of boron carbide crystals as the boat passes under the discharge end of the feed tube; and carrying the load of boron carbide crystals in each boat member to a collection point outside of the furnace hot zone.
moving a group of boat members through the furnace hot zone along a path that passes directly below the discharge end of the vertical feed tube;
filling each boat member with a load of boron carbide crystals as the boat passes under the discharge end of the feed tube; and carrying the load of boron carbide crystals in each boat member to a collection point outside of the furnace hot zone.
3. The method of Claim 1 in which the furnace hot zone is maintained at a temperature of 1600°C to 2100°C.
4. The method of Claim 1 in which the nitrogen-free particulate feed mixture is dropped into the vertical feed tube at a rate of 0.1 to 0.3 lbs. per minute (0.05-0.13 kg/min).
5. The method of Claim 1 in which the boat members move through the hot zone of the furnace at a rate of 1 to 3 inches per minute (2.5-7.6 cm/min).
6. The method of Claim 1 in which the boric oxide compound is boric anhydride and the carbon compound is acetylene carbon black.
7. The method of Claim 1 in which at least 50 percent by weight of the boron carbide crystals are of less than one micrometer in size.
8. The method of Claim 7 in which the boron carbide crystal contain not more than 0.5 percent by weight nitrogen.
9. The method of Claim 1 in which the size of the boron carbide crystals is 0.1 micrometers to 0.3 micrometers.
10. A high temperature furnace unit for producing boron carbide crystals, in which a major portion of the crystals are less than one micrometer in size and have a low combined nitrogen content, the furnace unit comprising:
a floor member (14) and a roof member (11) spaced from the floor member, the space between the floor and roof members defining a hot zone (17);
heaters (18) for delivering heat to the furnace hot zone (17), the heaters being located inside the furnace adjacent to the roof member (11);
a vertical feed tube (26) positioned above the furnace hot zone (17), the feed tube being designed for feeding a nitrogen-free particulate mixture (35) of a boric oxide compound and a carbon compound into said hot zone, and the feed tube being cooled by a cooling fluid to maintain the boric oxide feed compound below its melting point;
the furnace hot zone (17) being at a temperature which causes the particulate mixture to form boron carbide crystals as said mixture moves through said hot zone; and a group of boats (40), each boat being adapted to move along the floor ( 14) of the furnace hot zone (17) in a path that passes directly below the vertical feed tube (26), and each boat (40) being adapted to carry a load of the boron carbide crystals to a collection point outside of said hot zone.
a floor member (14) and a roof member (11) spaced from the floor member, the space between the floor and roof members defining a hot zone (17);
heaters (18) for delivering heat to the furnace hot zone (17), the heaters being located inside the furnace adjacent to the roof member (11);
a vertical feed tube (26) positioned above the furnace hot zone (17), the feed tube being designed for feeding a nitrogen-free particulate mixture (35) of a boric oxide compound and a carbon compound into said hot zone, and the feed tube being cooled by a cooling fluid to maintain the boric oxide feed compound below its melting point;
the furnace hot zone (17) being at a temperature which causes the particulate mixture to form boron carbide crystals as said mixture moves through said hot zone; and a group of boats (40), each boat being adapted to move along the floor ( 14) of the furnace hot zone (17) in a path that passes directly below the vertical feed tube (26), and each boat (40) being adapted to carry a load of the boron carbide crystals to a collection point outside of said hot zone.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US29568289A | 1989-01-11 | 1989-01-11 | |
| US295,682 | 1989-01-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2007460A1 true CA2007460A1 (en) | 1990-07-11 |
Family
ID=23138787
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002007460A Abandoned CA2007460A1 (en) | 1989-01-11 | 1990-01-10 | Method and apparatus for producing boron carbide crystals |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0429557A4 (en) |
| JP (1) | JPH03503158A (en) |
| KR (1) | KR910700196A (en) |
| AU (1) | AU621989B2 (en) |
| CA (1) | CA2007460A1 (en) |
| FI (1) | FI904446A0 (en) |
| IL (1) | IL93018A0 (en) |
| WO (1) | WO1990008102A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110357106A (en) * | 2019-08-26 | 2019-10-22 | 燕山大学 | A method of preparing nano twin crystal boron carbide powder |
| CN114506846A (en) * | 2022-02-15 | 2022-05-17 | 厦门金鹭特种合金有限公司 | Production method and production device of superfine carbide |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NO20010929D0 (en) * | 2001-02-23 | 2001-02-23 | Norsk Hydro As | A method for conducting thermal reactions between reactants and an oven for the same |
| CN106810261A (en) * | 2017-04-12 | 2017-06-09 | 郑州嵩山硼业科技有限公司 | A kind of method that use intermediate frequency furnace smelts boron carbide |
| CN113880093A (en) * | 2021-11-24 | 2022-01-04 | 郑州嵩山硼业科技有限公司 | Boron carbide production process |
Family Cites Families (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1897214A (en) * | 1930-05-14 | 1933-02-14 | Norton Co | Boron carbide and method of making the same |
| US2155682A (en) * | 1935-11-21 | 1939-04-25 | Norton Co | Method of making abrasive metal carbides |
| US3377141A (en) * | 1964-08-26 | 1968-04-09 | Cabot Corp | Process for producing metal carbides utilizing a solution treatment prior to reaction |
| US3379647A (en) * | 1966-05-04 | 1968-04-23 | Carborundum Co | Metal carbide and boride production |
| US3535080A (en) * | 1969-02-18 | 1970-10-20 | Norton Co | Apparatus and method for the continuous furnacing of borides,carbides and silicides |
| US4017587A (en) * | 1969-10-03 | 1977-04-12 | The United States Of America As Represented By The Secretary Of The Navy | Boron carbide |
| US4137295A (en) * | 1977-04-20 | 1979-01-30 | Tamers Murry A | Carbide production using molten metals as heat source |
| JPS55113609A (en) * | 1979-02-21 | 1980-09-02 | Ibiden Co Ltd | Manufacturing apparatus for beta crystallbase silicon carbide |
| JPS5825044B2 (en) * | 1979-05-23 | 1983-05-25 | 安藤 義則 | Method and device for producing ultrafine carbide powder |
| US4529575A (en) * | 1982-08-27 | 1985-07-16 | Ibiden Kabushiki Kaisha | Process for producing ultrafine silicon carbide powder |
| US4804525A (en) * | 1986-04-14 | 1989-02-14 | The Dow Chemical Company | Producing boron carbide |
| JPS63166709A (en) * | 1986-12-26 | 1988-07-09 | Ibiden Co Ltd | Production of carbide |
-
1989
- 1989-12-27 JP JP90503055A patent/JPH03503158A/en active Pending
- 1989-12-27 EP EP19900902739 patent/EP0429557A4/en not_active Withdrawn
- 1989-12-27 KR KR1019900701997A patent/KR910700196A/en not_active Application Discontinuation
- 1989-12-27 AU AU50364/90A patent/AU621989B2/en not_active Ceased
- 1989-12-27 WO PCT/US1989/005871 patent/WO1990008102A1/en not_active Application Discontinuation
-
1990
- 1990-01-09 IL IL93018A patent/IL93018A0/en unknown
- 1990-01-10 CA CA002007460A patent/CA2007460A1/en not_active Abandoned
- 1990-09-10 FI FI904446A patent/FI904446A0/en not_active IP Right Cessation
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110357106A (en) * | 2019-08-26 | 2019-10-22 | 燕山大学 | A method of preparing nano twin crystal boron carbide powder |
| CN110357106B (en) * | 2019-08-26 | 2022-07-29 | 燕山大学 | Method for preparing nano twin crystal boron carbide powder |
| CN114506846A (en) * | 2022-02-15 | 2022-05-17 | 厦门金鹭特种合金有限公司 | Production method and production device of superfine carbide |
| CN114506846B (en) * | 2022-02-15 | 2023-06-06 | 厦门金鹭特种合金有限公司 | Production method and production device of superfine carbide |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH03503158A (en) | 1991-07-18 |
| AU621989B2 (en) | 1992-03-26 |
| WO1990008102A1 (en) | 1990-07-26 |
| FI904446A0 (en) | 1990-09-10 |
| KR910700196A (en) | 1991-03-14 |
| IL93018A0 (en) | 1990-11-05 |
| AU5036490A (en) | 1990-08-13 |
| EP0429557A4 (en) | 1992-04-22 |
| EP0429557A1 (en) | 1991-06-05 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |