JPH0553723B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL FIELD OF THE INVENTION The present invention relates to a process for producing boron nitride using particulate boron oxide as the reactant material, and more particularly to a continuous process for producing boron oxide. BACKGROUND OF THE INVENTION Boron nitride is a thermally stable, highly refractory material of increasing commercial importance. Boron nitride is typically made by a process that uses boric acid as the boron source in the reaction composition. The proposed process for producing boron nitride from boric acid is described in U.S. Pat.
3261667, as well as British patents 874166 and 874165.
No. 1241206. The process of producing boron nitride from boron oxide as opposed to boric acid is such that boron oxide contains more boron per unit weight of reactant material than boric acid, and the additional boron theoretically provides a higher concentration of boron than boron nitride. It is of particular interest because it allows for product yields. However, processes in which boron oxide is a reactant are typically complex and cumbersome procedures. For example: U.S. Pat. No. 3,208,824 discloses a process for producing boron nitride using compounds such as B ₂ O ₃ , H ₃ BO ₃ , alkali metal and alkaline earth metal borates as boron sources. . The process involves mixing a selected boron-containing compound and an inert solid diluent with water to form a paste mass, extruding the paste mass into small particles, and drying the particles at a temperature high enough to vaporize the water. , including nitriding the dried particles with ammonia. No. 3,232,706 discloses a process for producing boron nitride by introducing boron oxide into the high temperature reaction zone of an arc furnace, vaporizing it, and reacting with a reactive nitrogen-containing gas such as ammonia. The process requires the use of a specialized high temperature furnace in which a high temperature reaction zone is created by using one or more non-consumable electrodes to generate a high temperature arc. U.S. Pat. No. 3,429,722 discloses that boron oxide fibers having a maximum diameter of approximately 30 microns are placed in a stream of ammonia.
A process is disclosed for producing boron nitride fibers by heating at a temperature increase of 25° to 5000° C. per hour to a final temperature of 300° to 1500° C. The patent states that the particle size
discloses that B ₂ O ₃ is critical for obtaining substantially complete conversion to boron nitride (column 2, 72
line ~ 3 column 11 line). U.S. Pat. No. 3,427,722 further teaches that heating the oxide in ammonia provides the boron oxide fibers with a protective shield of nitrogen- and hydrogen-containing compounds to preserve the fibrous morphology of _{the B2O3} reactants and Discloses preventing melting. U.S. Pat. No. 4,130,631 forms a shaped article from a blend of boron oxide fibers and boric acid and melts some of the boric acid in an anhydrous gas to a temperature above the melting temperature of boric acid to form boron oxide fibers. Discloses a process for forming a shaped article of molten boron nitride comprising heating for a period of time and then heating the article in an ammonia atmosphere for a period of time or thereafter to convert the boron oxide and boric acid to boron nitride. ing. The '631 patent requires heating the shaped article in such a way that the boron oxide fibers are not destroyed by melting or decomposition. Additionally, the boron oxide and ammonia are heated to a temperature of about 900 ml in the presence of a tricalcium phosphate carrier.
It is known that boron nitride can be produced by reaction at .degree. (Gmelin's Handbuch as cited in U.S. Pat. No. 4,107,276)
deranorganischen Chemie, 8th edition supplement, volume 13,
Part 1, pages 1-6 (Springer Verlag, 1974)
In this process, the tricalcium phosphate carrier distributes the boron oxide into a thin sheet, giving it more surface area for the oxide reaction with the ammonia, so that the boron oxide forms large unreacted clumps or agglomerates. Decreasing tendency. However, such reactions require the use of extremely pure reactants and involve various heating, drying,
Homogenization and passing steps are adopted. The process described above is a time-consuming, multi-step procedure that produces commercially unattractive yields of boron nitride, requires the use of fibrous boron oxide, or requires the use of highly specialized equipment. It's normal. Moreover, the process typically requires the use of an ammonia nitriding atmosphere, which is often undesirable for environmental and toxicity reasons. Accordingly, one aspect of the present invention is to provide a simple, high-yield method for producing boron nitride directly from particulate boron oxide. A further aspect of the invention is to produce boron nitride by a process that can use nitrogen instead of ammonia as the nitriding agent. SUMMARY OF THE INVENTION The present invention provides a method for applying a nitrogen-containing nitride promoter to a mixture of boron oxide and boric acid in an amount sufficient to enhance the formation of boron nitride in a non-oxidizing atmosphere, preferably ammonia or the like. The boron nitride is preferably provided in contact with a nitrogen-containing atmosphere of nitrogen and maintained at a sufficiently high temperature, preferably from about 700° to about 1200°C, most preferably from about 900° to about 1050°C. The present invention is directed to a method of producing boron nitride, including producing boron nitride. DETAILED DESCRIPTION OF THE INVENTION The process of the present invention provides a method for producing high purity boron nitride from particulate boron oxide in relatively high yields. Additionally, the present invention eliminates the need for time-consuming reactant drying steps and is compatible with continuous production of boron nitride. For purposes of the present invention, a mixture of boron oxide and boric acid comprises at least one compound capable of reacting with and expanding the boron oxide when heated.
It can be produced by heating the seeds in the presence of a puffing agent, thereby producing a porous material containing a homogeneous mixture of boron oxide and metaboric acid. In the practice of this invention, a nitrogen-containing nitride promoter can be combined with boron oxide and at least one thickener into a reactive composition, which can then be heated as described above to produce boron nitride. . Thickening agents include compounds such as metaboric acid, orthoboric acid, pyroboric acid, ammonium pentaborate tetrahydrate, and mixtures thereof. Preferred thickeners are compounds such as metaboric acid, orthoboric acid, pyroboric acid, ammonium pentaborate tetrahydrate, etc., which add additional boron to the reaction composition beyond that provided by the boron oxide reactant. to increase the overall efficiency of the process. For purposes of the present invention, orthoboric acid and ammonium pentaborate tetrahydrate are particularly preferred thickening agents. Boron oxide particles having a wide range of sizes are suitable for use in the present invention. In order to sufficiently increase the surface area of the oxide available for reaction,
It is usually desirable to use particles with a diameter of less than about 30 microns, preferably an effective diameter of less than about 10 microns. Nitrogen-containing nitride promoters contemplated for use in the present invention include organic primary, secondary, and tertiary amines, including compounds such as diphenylamine, ethyleneamine, hexamethyleneamine, and melamine, and organic amides such as dicyandiamide. Preferred amines are those compounds that undergo polymerization under the reaction conditions to form linear bonds, thus optimizing nitrogen sites available for reaction. Note that under the conditions described herein, melamine typically forms volatile polymerization byproducts that tend to collect on the furnace walls, requiring periodic cleaning of the system. Should. Dicyandiamide does not form such by-products and is therefore particularly preferred as a promoter. The reactive compositions of this invention are subject to wide variation. Typically, compositions suitable for use in the present invention include:
from about 30% to about 55% by weight promoter, based on the total weight of reactant materials, and from about 45% to about 70% by weight, based on the total weight of reactant materials, a combination of boron oxide and a thickening agent. The weight ratio of boron oxide to thickener in the combination ranges from about 4:1 to about 1:3. Approximately 55% based on the total weight of reactant materials
At concentrations greater than % by weight, nitride promoters can produce undesirably high amounts of carbon, resulting in a product of less than desired purity. Nitride production can be significantly reduced if the promoter concentration is less than about 40% by weight based on the total weight of reactant materials. Similarly, if a thickener is present in the composition in an amount greater than that indicated by the weight percentages and oxide to thickener weight ratios listed above, it may reduce nitride yield. Conversely, if the thickener is present in the composition in an amount less than indicated by the weight percentages and weight ratio ranges listed above, the result is the formation of a glassy boron oxide/boron nitride composite. An incomplete reaction may occur as a result. The preferred composition range depends on the reactant components selected. Particularly effective product yields are obtained when the components are melamine, boron oxide, and boric acid. from about 50% to about 55% by weight, based on the total weight, of a combination of boron oxide and orthoboric acid, wherein the weight ratio of boron oxide to orthoboric acid is from about 3:1 to about 4:1, preferably about
3.2:1.0 to about 3.6 to 1.0. In contrast, particularly good product yields are obtained when dicyandiamide, boron oxide, and orthoboric acid are the components, from about 35 to about 40% by weight of dicyandiamide, based on the total weight of the reaction composition. , from about 60 to about 65% by weight, based on the total weight of the reaction composition, of a combination of boron oxide and orthoboric acid, wherein the weight ratio of boron oxide to orthoboric acid is from about 2:1 to about 1:1; Preferably about
from a reaction composition ranging from 1.4:1.0 to about 1.0:1.0. Particularly high yields are obtained when melamine, boric acid oxide, and ammonium pentaborate tetrahydrate are the reaction components, with a yield of about 30% based on the total weight of the reaction composition.
~40% by weight melamine and a combination of boron oxide and ammonium pentaborate tetrahydrate from about 60 to about 70% by weight, based on the total weight of the reaction composition; The weight ratio of ammonium acid tetrahydrate is about 1:1 to about 1:2, preferably about
It is contemplated that reaction compositions ranging from 1.0:1.2 to about 1.0:1.4 may be obtained. Additionally, when dicyandiamide, boron oxide, and ammonium pentaborate tetrahydrate form the reaction composition, good nitride yields are from about 40 to about 50% based on the total weight of the reaction composition. % by weight of dichyadiamide and about 50 to about 60% by weight, based on the total weight of the reaction composition, of a combination of boron oxide and ammonium pentaborate tetrahydrate. It is contemplated that this may be achieved using a reaction composition in which the weight ratio of hydrates ranges from about 2:1 to about 3:1, preferably from about 2.3:1.0 to about 2.5:1.0. Note that while the specific composition ranges listed above usually result in relatively high product yields, acceptable nitride yields can also be obtained from compositions that fall outside these preferred ranges. (see Example 9 for an example). It is hypothesized that proportional changes in reaction composition affect the amount and rate of intermediate by-product production (eg, ammonia, water, metaboric acid, etc.), which in turn affects the mechanism by which the reaction proceeds. However, the relationship between the proportional change in reaction composition and nitride yield compared to the formation of intermediate byproducts is not completely understood. A preferred method of the invention may more particularly be described as comprising the following steps: (a) boron oxide and a thickening agent, preferably metaboric acid, orthoboric acid, pyroporic acid, ammonium pentaborate 4 A thickener selected from the group consisting of hydrates and mixtures thereof, most preferably acid or ammonium pentaborate tetrahydrate, in admixture with a nitrogen-containing nitride promoter, preferably melamine or diandiamide. forming a reaction composition, and (b) maintaining the reaction composition at a temperature in the range of about 700° to about 1200°C in a reaction zone under a non-oxidizing atmosphere, preferably under a nitrogen-containing atmosphere, most preferably a nitrogen atmosphere. (c) reacting the reaction composition in the reaction zone to produce amorphous boron nitride; and (d) removing the produced amorphous boron nitride from the reaction zone. The reaction zone is about -2 psi to about 10 psi (-0.1 to 0.7 Kg/cm ² )
It is best to maintain the pressure at a pressure of about -1 to about
Maintain pressure at 5psi (-0.07~0.4Kg/ ^cm2 ). The time required to convert the boron-containing reactant to amorphous boron nitride can vary widely depending, in part, on the temperature of the reaction zone. There is usually an inverse function between reaction time and temperature, with reaction operations at higher temperatures requiring shorter reaction times than reaction operations at lower temperatures. Typically, reaction times will vary between about 15 minutes and about 1 hour. Although the temperature within the reaction zone may be subject to variation, the reaction is run at a temperature of at least 850°C to ensure that all reaction gases and residual carbon impurities are removed from the reaction product.
It is especially desirable to keep it for a period of 15 minutes. After nitride formation, the formed product is cooled to a temperature below about 50°C, ground to a particle size of about 25 mm, preferably less than about 10 mm, and placed in a non-oxidizing atmosphere, preferably a nitrogen-containing atmosphere. (e.g., ammonia or nitrogen), most preferably in a nitrogen atmosphere, to a second higher temperature of about 1300° to about 2000°C to crystallize the amorphous boron nitride produced by the first heating. can be done.
The resulting product can then be washed, preferably with a solvent such as methanol or a 1% aqueous solution of nitric acid to produce a fine, white, high purity crystalline boron nitride powder. The method of the invention can be carried out in batch mode or in continuous mode. In the continuous manufacturing method, the produced amorphous boron nitride is directly heated to a temperature of about 1300°C after being heated to a first high temperature, preferably from about 700°C to about 1200°C.
to about 2000° C., and within said second higher temperature region an essentially complete reaction mixture is introduced under a non-oxidizing atmosphere, preferably a nitrogen-containing atmosphere, most preferably a nitrogen atmosphere. It is held for a period of time to ensure nitridation, typically from about 45 minutes to about 2 hours, and then ground and washed as described above to yield a highly pure crystalline product. Preferably, the method of the invention provides at least 40%
Preferably a conversion efficiency of at least 50% is achieved, most preferably at least 55%. For the purposes of this invention, conversion efficiency is defined as follows: 100 x (grams of washed and dried BN produced after nitriding at 1400°C)/(B ₂ O ₃ added as reactant)
(grams of diffusing agent added as reactant) The following example is given for the purpose of illustrating the process of the present invention. The examples should not be considered as limiting the invention in any way. Examples 1-13 illustrate the changes in product yield and conversion efficiency that result from using different reaction compositions. Examples 12 and 13 provide estimated product yields for reaction compositions containing ammonium pentaborate tetrahydrate. Example 1 A 12 inch x 12 inch x 2 inch (30.48 cm
It was applied to a graphite pan measuring 30.48 cm x 5.08 cm). The pan was placed on a continuous belt and introduced into the oven, where it was heated in the first reaction zone at 1000° C. for a period of 20 minutes. Heating was continued under nitrogen gas at a pressure of 1 atmosphere (1.01 bar). After this first heating, the resulting product, an amorphous boron nitride cake, was cooled to about 50° C. and weighed. The weight of the cake was recorded as 400 grams. The cake was then ground to a particle size of approximately 13 mm and heat treated in a nitrogen atmosphere at a second higher temperature of 1400 DEG C. and a pressure of 1 atmosphere (1.01 bar) for a period of 60 minutes. After a second higher temperature heat treatment, the particles were washed with methanol and dried to yield 3.9% by weight of N.
212 grams of finely divided boron nitride with an analytical composition of 42.4% B, 75% O, and 0.11% C were produced. Examples 2-5 The procedure according to Example 1 was repeated using the reaction compositions specified in the table. Product yields of the finely divided boron nitride powders produced varied between 186 and 274 grams based on 1000 grams of starting material. Example 6 482 grams of melamine, 400 grams of boron oxide and 118 grams of orthoboric acid were blended together and coated with oxidation-resistant ceramic paint.
inch x 12 inch x 2 inch (30.48cm x 30.48cm
× 5.08 cm) graphite pan. The bread is placed on a continuous belt and introduced into the oven, where it is
After heating in the first reaction zone at 1000°C for a period of 30 minutes
Complete nitridation was achieved by heating at a second higher temperature of 1400° C. for a period of 3 hours. Heating was carried out at a pressure of 1 atmosphere (1.01 bar) under nitriding gas. After the second heating, the resulting product, an amorphous boron nitride cake, was ground to a particle size of 13 mm, washed with methanol, and dried to produce 240 grams of finely divided boron nitride powder. Examples 7-11 The procedure according to Example 6 was repeated using the reaction compositions specified in the table. The product yield of the finely divided boron nitride powder produced varied between 215 and 283 grams based on 1000 grams of starting material. Example 12 344 grams of melamine, 285 grams of boron oxide, and 371 grams of ammonium pentaborate tetrahydrate were blended together and coated with oxidation-resistant ceramic paint. Apply to graphite pan (cm x 30.48cm x 5.08cm). The bread is placed on a continuous belt and introduced into a furnace where it is heated for 30 minutes in a first reaction zone at 1000°C.
After heating for a period of 1 minute, complete nitridation is achieved by heating at a second higher temperature of 1400° C. for a period of 3 hours. Heating under nitriding gas pressure 1 atm (1.01 bar)
Do it with After the second heating, the resulting product is ground to a particle size of 13 mm, washed with methanol and dried. The estimated yield of boron nitride based on these reactants is 372 grams. Example 13 534 grams of dicyandiamide and 330 grams of boron oxide
gram and 136 grams of ammonium pentaborate tetrahydrate were blended together and coated with oxidation-resistant ceramic paint.
Apply to 2 inches (30.48 cm x 30.48 cm x 5.08 cm) of graphite. The bread is placed on a continuous belt and introduced into an oven where it is heated within a temperature range of 1000°C for a period of 30 minutes followed by a second higher temperature of 1400°C for a period of 3 hours to achieve complete nitridation. do.
Heating is carried out under nitriding gas at a pressure of 1 atmosphere (1.01 bar). After the second heating, the product formed is ground to a particle size of 13 mm, washed with methanol and dried. The estimated yield of boron nitride based on these reactants is 341 grams. Comparative Example 1 541 grams of orthoboric acid was blended with 459 grams of melamine and charged into a stainless steel pan.
It was dried at 300° C. for a period of 2 hours to form a dry cake. The cake was ground to a particle size of approximately 10 mm and reacted in an ammonia atmosphere at a temperature of 1000° C. for a period of 10 minutes. Next, the reacted substances were placed under nitrogen gas.
heated at 1400°C and 1 atmosphere (1.01 bar) for a period of 1 hour, acid washed with a 1% aqueous solution of nitric acid at 70°C,
Crushed and dried N55.0% by weight, B43.2% by weight,
154 grams of finely divided boron nitride powder was produced with an analytical composition of less than 3.1% O, 0.1% C by weight. A comparison of the conversion efficiencies of Examples 1-6 and 9-11 with that of Comparative Example 1 shows that superior conversion efficiencies and product yields are obtained by the process of the invention in which boron oxide is the reactant material. Show that. Comparative Example 2 500 grams of boron oxide and 500 grams of melamine were blended together and applied to a 12 inch x 12 inch x 2 inch pan coated with oxidation resistant ceramic paint. did.
The pan was placed on a continuous belt and introduced into an oven where it was heated in a first reaction zone at 1000° C. for a period of 30 minutes. Heating under nitrogen gas at a pressure of 1 atmosphere (1.01 bar)
I went there. The resulting product was a yellowish-black material covered with a hard, thick layer of glassy boron oxide. The product was unsuitable for further processing. Comparative Example 2 shows that it is not viable to produce boron nitride from boron oxide and melamine reactants in the absence of thickeners. The invention has been described in terms of certain specific embodiments for purposes of illustration. Those skilled in the art will recognize that modifications to these embodiments are possible without departing from the scope and spirit of the invention. Such modifications, although not illustrated, are intended to be included in the present invention.

【table】

[Claims]

1 Hexagonal boron nitride with a specific surface area of 5 m ² /g or more was dispersed in water or hot water, and after washing and removing water-soluble boron compounds, the drying time was set to a [hour] and the drying temperature was set to b [°C]. When the boron nitride obtained by drying under conditions satisfying a/2+b≦100 is boiled and leached with pure water, the amount of boron in the extracted water is 100 μg/g-BN or less. Characteristic manufacturing method of hexagonal boron nitride.

Claims (1)

45-50 based on the weight of the reaction composition by mixing
Forming a reaction composition comprising 50-55% by weight of a combination of boron oxide and orthoboric acid based on the weight of the reaction composition, wherein the weight ratio of boron oxide to orthoboric acid in the combination is 3: 1
5. A method according to any one of claims 1 to 4, wherein the ratio is ˜4:1. 7. Mixing boron oxide, orthoboric acid, and didiandiamide to produce 35 to 40% by weight of dicyandiamide based on the weight of the reaction composition and 60 to 65% by weight of oxidation based on the weight of the reaction composition. Claims 1 to 3 form a reactive composition comprising a combination of boron and orthoboric acid, wherein the weight ratio of boron oxide to boric acid in the combination is from 2:1 to 1:1.
The method described in any one of Section 4. 8. Boron oxide, ammonium pentaborate tetrahydrate, and melamine are mixed to produce 30 to 40% by weight of melamine based on the weight of the reaction composition and 60 to 70% by weight based on the weight of the reaction composition. % by weight of a combination of boron oxide and ammonium pentaborate tetrahydrate, wherein the weight ratio of boron oxide to ammonium pentaborate tetrahydrate in the combination is from 1:1 to 1:2. The method according to any one of claims 1 to 4. 9. Boron oxide, ammonium pentaborate tetrahydrate, and dicyandiamide combined to form 40-50% by weight of dicyandiamide, based on the weight of the reaction composition, and 50-60% by weight, based on the weight of the reaction composition. % of boron oxide and ammonium pentaborate tetrahydrate, wherein the weight ratio of boron oxide to ammonium pentaborate tetrahydrate in the combination is from 2:1 to 3:1. 5. A method according to any one of claims 1-4. 10. The method according to any one of claims 1 to 9, wherein the reaction composition is heated to a temperature of 700° to 1200°C. 11 Claims 1-1 wherein the reaction composition is maintained at a temperature of at least 850°C for a period of at least 15 minutes.
The method described in any one of item 0. 12. The method according to any one of claims 1 to 11, wherein the boron nitride thus formed is extracted as amorphous boron nitride. 13. After heating to a temperature of 700° to 1200°C, the resulting product is heated to a second higher temperature of 1300° to 2000°C under a non-oxidizing atmosphere. The method described in 1. 14 In addition: (a) the amorphous boron nitride formed in the reaction zone is cooled to a temperature below 50°C, and (b) the cooled amorphous boron oxide is ground to 25 mm.
(c) The crushed particles are heated at 1300° to 1300° under a nitrogen atmosphere.
13. A method as claimed in any one of claims 1 to 12, including the step of nitriding at a second higher temperature of 2000<0>C to produce a crystalline product. 15. The method according to any one of claims 1 to 12, wherein the non-acidic atmosphere is an ammonia or nitrogen atmosphere.