CA1051634A - Manufacture of hexagonal boron nitride - Google Patents
Manufacture of hexagonal boron nitrideInfo
- Publication number
- CA1051634A CA1051634A CA242,712A CA242712A CA1051634A CA 1051634 A CA1051634 A CA 1051634A CA 242712 A CA242712 A CA 242712A CA 1051634 A CA1051634 A CA 1051634A
- Authority
- CA
- Canada
- Prior art keywords
- nitrogen
- boride
- starting material
- boron nitride
- boron
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B21/00—Nitrogen; Compounds thereof
- C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
- C01B21/064—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with boron
-
- 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
- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
Abstract
ABSTRACT OF THE DISCLOSURE
Process for the manufacture of hexagonal boron nitride which comprises causing a starting material contain-ing an alkali metal boride or an alkaline earth metal boride, preferably a hexa-or dodecaboride, to react with nitrogen at temperatures of at least 900°C and if desired up to 2500°C.
The process is promoted by impurities or additives of other boron compounds or compounds of the alkaline or alkaline earth metals being present in the starting materials. Boron nitride has many uses in various fields, among them electronics and crucible melting for most non metallic melts.
Process for the manufacture of hexagonal boron nitride which comprises causing a starting material contain-ing an alkali metal boride or an alkaline earth metal boride, preferably a hexa-or dodecaboride, to react with nitrogen at temperatures of at least 900°C and if desired up to 2500°C.
The process is promoted by impurities or additives of other boron compounds or compounds of the alkaline or alkaline earth metals being present in the starting materials. Boron nitride has many uses in various fields, among them electronics and crucible melting for most non metallic melts.
Description
63~ ~
This invention relates to a process for the manu-facture of hexagonal boron nltride.
Hexagonal boron nitride, also known as "~hite i`
graphite", has a number of valuable properties. It has a low density, a low dielectric constant, a good resistance to ternperature changes, and a good corrosion resistance. In a - hot~-pressed form, it can be worked in a way similar to grap-hite. It is also a good conductor of heat and an excellent ; electrical insulator. These properties make it a very useful material for a number of purposes. It is useful in electronics, ~ecause of its outstanding dielectric properties. It is used up to a temperature of about 2500C as a crucible material for many fused non~Ametallic substances; which do not wet it. It is chemically very inert, and in particular is more resistant than ` graphite to oxidation,, and it can therefore be considered as one of the most valuable refractory nitrides.
Many processes for the manufacture of hexagonal boron - nitride have been described, and a review of these is given in Gmelin's Handbuch der anorganischen Chemie, supplement to 8th edltion, vol. 13, part 1, pages 1~6 (Springer Verlag, 1974).
One commonly used industrial proces~ mentioned by Gmelin is to cause horic acid or boron trioxide to react with ~ania at ahout 900C in the presence of tertiary calcium phosphate. The calcium phosphate serves as a carrier to pre-vent the boron oxide, which is liquid at the reaction tempera-ture of - 700C, from fusing together whereby an approximate~
ly complete reaction with -NH3 becomes feasable. The steam formed during the reaction according to the equation B203 + 2NH3--~ 2 BN + 3 H20 is permitted to escape unimpeded.
In a British compilation in "Special Ceramicsl' by Popper, London Heywood & Company, Ltd., 1960, p. 146~the re-1- ' ~ .
~5~3fl~ ~
action is described as follows: "The reaction occurs at 800 ~
1200C. A solid filler is used to prevent f~sion of the Thus, without a carrier the B203, which is liquid at that temperature, would form large agglomerations or lumps - so that only at the surlace could some minor reaction take place, but not in the interior. However, when a solid carrier is present, the liquid ~23 is distributed in a thin sheet and provides a larger surface for NH3 to react; moveover, hetter permeability for gas is obtained in this manner, that facili tates the removal of steam together with excess of gaseous ammonia, such removal being necessary to prevent reversal of the reaction illustrated by the above equation. This process, however, has a nu~ber of disadvantages.-Pirst, care has to be taken regarding the purity,and especially the moisture content, of the ammonia. Because of the large volume of the reactants, the space~time yield is poor. When operating in a continuous manner, it is necessary to perform the reaction with a~monia in at least two separate 20- heating steps in order to achieve as quantitative as possible a conversion of the B203 compound. The boron nitride obtained after washing out the calcium carrier with dilute mineral acid, generally has a purity of only 80 to 90%, thus necessitating a further purification step. This may be carried out either in a stream of ammonia at about 1200C or above, or in a stream -of nitrogen or ar~on at about 1800C. Any boron oxide still re--maining r then has to be washed out or removed in a further re-action with ammonia. Furthermore, various comminution, homog-enization, filtration, granulation, and drying steps are neces-sary between the several reaction steps, and the chemical com-position and particle size of the products has to be monitored.
` ' `
:-3~ .
These steps are, of course, both time consuming and expensive.
Finally, t~e use of gaseous ammonia necessitates specia]. atten-tion being paid to safety regulations and environmental pol-lution. In general, the processes listed in Gmelin are un-satisfactory ~or large scale industrial use : in many cases, the yields are poor, whereas in other cases, the products have to be purified by a number oE time consuming and expensive stepsj as set forth.
It is an object of the present invention to provide a process for preparing hexagonal boron nitride, which over-comes the disadvantages of the known processes and permits hexagonal boron nitride of high purity and good yield to be obtained by simple operations without the use o~ additional .
carrier materials and the inconvenience of incurring environ--mental pollution.
The present invention provides a process for the manu facture of hexagonal boron nitride, which comprises causing a - starting ~aterial containing an alkali metal boride or an alka-line earth metal boride to react with nitrogen at a temperature 2V of at least about 900C, in the presence of impurities or addi-tives in addition to the boride.
- ~ It is particuiarly surprising that boron nitride can be obtained in good yields and good purity by the nitridation of an alkali metal boride or alkaline earth metal boride, since it had previously been thought that alkaline earth metal borides were inert to nitrogen even at high temperatures, calcium hexa-boride bein~ thought to be inert to nitrogen even at tempera-tures of up to 2000C (cf. N.N. Greenwood, _omprehensive In-o ganic Chemistry, Pergamon Press 1973, vol. 1, p. 729). Liter-30) ally, Greenwood states "The alkaline earth hexaborides are un-,. affecteA by nitrogen or ammonia at high temperatures and CaB6 . is stable to at least 2000C." ~ctually, Greenwood went back ,._ , . ~ 1 ~5~63~
to an original publication by M.I,. Andrieux in Rev. Met 32, pgs. 487 - 493 (1935) according to which the investigated CaB6 had been obtained by electrolysis and had almost theore-tical composition : 61.84% B; 38.16~ Ca. It was, therefore, very pure. Pa~e 490 states "It did not react with ~l2 even when heated to 2000C. At that temperature, a heavy atta~k of the yraphite vessel took place, in which it was heated." Thus, this literature did not disclose the fact that CaB6 reacts with nitrogen at temperatures above 2000C with ~ormation o~
~N. Moreover, by analogy with silicon, it would have been ex-pected that any reaction of an alkali metal boride or alkaline earth metal boride with nitrogen would produce a stable ter~
nary metal-boron-nitrogen phase, and that there would be con-tamination with carbon or oxygen thus preventing the manufac-ture of pure boron nitride.
Surprisingly, these expected difficulties do not occur, and the present process enables boron nitride to be pro-- duced in a relatively simple manner, without the use of a carrier material, causiny additional costs without the need
This invention relates to a process for the manu-facture of hexagonal boron nltride.
Hexagonal boron nitride, also known as "~hite i`
graphite", has a number of valuable properties. It has a low density, a low dielectric constant, a good resistance to ternperature changes, and a good corrosion resistance. In a - hot~-pressed form, it can be worked in a way similar to grap-hite. It is also a good conductor of heat and an excellent ; electrical insulator. These properties make it a very useful material for a number of purposes. It is useful in electronics, ~ecause of its outstanding dielectric properties. It is used up to a temperature of about 2500C as a crucible material for many fused non~Ametallic substances; which do not wet it. It is chemically very inert, and in particular is more resistant than ` graphite to oxidation,, and it can therefore be considered as one of the most valuable refractory nitrides.
Many processes for the manufacture of hexagonal boron - nitride have been described, and a review of these is given in Gmelin's Handbuch der anorganischen Chemie, supplement to 8th edltion, vol. 13, part 1, pages 1~6 (Springer Verlag, 1974).
One commonly used industrial proces~ mentioned by Gmelin is to cause horic acid or boron trioxide to react with ~ania at ahout 900C in the presence of tertiary calcium phosphate. The calcium phosphate serves as a carrier to pre-vent the boron oxide, which is liquid at the reaction tempera-ture of - 700C, from fusing together whereby an approximate~
ly complete reaction with -NH3 becomes feasable. The steam formed during the reaction according to the equation B203 + 2NH3--~ 2 BN + 3 H20 is permitted to escape unimpeded.
In a British compilation in "Special Ceramicsl' by Popper, London Heywood & Company, Ltd., 1960, p. 146~the re-1- ' ~ .
~5~3fl~ ~
action is described as follows: "The reaction occurs at 800 ~
1200C. A solid filler is used to prevent f~sion of the Thus, without a carrier the B203, which is liquid at that temperature, would form large agglomerations or lumps - so that only at the surlace could some minor reaction take place, but not in the interior. However, when a solid carrier is present, the liquid ~23 is distributed in a thin sheet and provides a larger surface for NH3 to react; moveover, hetter permeability for gas is obtained in this manner, that facili tates the removal of steam together with excess of gaseous ammonia, such removal being necessary to prevent reversal of the reaction illustrated by the above equation. This process, however, has a nu~ber of disadvantages.-Pirst, care has to be taken regarding the purity,and especially the moisture content, of the ammonia. Because of the large volume of the reactants, the space~time yield is poor. When operating in a continuous manner, it is necessary to perform the reaction with a~monia in at least two separate 20- heating steps in order to achieve as quantitative as possible a conversion of the B203 compound. The boron nitride obtained after washing out the calcium carrier with dilute mineral acid, generally has a purity of only 80 to 90%, thus necessitating a further purification step. This may be carried out either in a stream of ammonia at about 1200C or above, or in a stream -of nitrogen or ar~on at about 1800C. Any boron oxide still re--maining r then has to be washed out or removed in a further re-action with ammonia. Furthermore, various comminution, homog-enization, filtration, granulation, and drying steps are neces-sary between the several reaction steps, and the chemical com-position and particle size of the products has to be monitored.
` ' `
:-3~ .
These steps are, of course, both time consuming and expensive.
Finally, t~e use of gaseous ammonia necessitates specia]. atten-tion being paid to safety regulations and environmental pol-lution. In general, the processes listed in Gmelin are un-satisfactory ~or large scale industrial use : in many cases, the yields are poor, whereas in other cases, the products have to be purified by a number oE time consuming and expensive stepsj as set forth.
It is an object of the present invention to provide a process for preparing hexagonal boron nitride, which over-comes the disadvantages of the known processes and permits hexagonal boron nitride of high purity and good yield to be obtained by simple operations without the use o~ additional .
carrier materials and the inconvenience of incurring environ--mental pollution.
The present invention provides a process for the manu facture of hexagonal boron nitride, which comprises causing a - starting ~aterial containing an alkali metal boride or an alka-line earth metal boride to react with nitrogen at a temperature 2V of at least about 900C, in the presence of impurities or addi-tives in addition to the boride.
- ~ It is particuiarly surprising that boron nitride can be obtained in good yields and good purity by the nitridation of an alkali metal boride or alkaline earth metal boride, since it had previously been thought that alkaline earth metal borides were inert to nitrogen even at high temperatures, calcium hexa-boride bein~ thought to be inert to nitrogen even at tempera-tures of up to 2000C (cf. N.N. Greenwood, _omprehensive In-o ganic Chemistry, Pergamon Press 1973, vol. 1, p. 729). Liter-30) ally, Greenwood states "The alkaline earth hexaborides are un-,. affecteA by nitrogen or ammonia at high temperatures and CaB6 . is stable to at least 2000C." ~ctually, Greenwood went back ,._ , . ~ 1 ~5~63~
to an original publication by M.I,. Andrieux in Rev. Met 32, pgs. 487 - 493 (1935) according to which the investigated CaB6 had been obtained by electrolysis and had almost theore-tical composition : 61.84% B; 38.16~ Ca. It was, therefore, very pure. Pa~e 490 states "It did not react with ~l2 even when heated to 2000C. At that temperature, a heavy atta~k of the yraphite vessel took place, in which it was heated." Thus, this literature did not disclose the fact that CaB6 reacts with nitrogen at temperatures above 2000C with ~ormation o~
~N. Moreover, by analogy with silicon, it would have been ex-pected that any reaction of an alkali metal boride or alkaline earth metal boride with nitrogen would produce a stable ter~
nary metal-boron-nitrogen phase, and that there would be con-tamination with carbon or oxygen thus preventing the manufac-ture of pure boron nitride.
Surprisingly, these expected difficulties do not occur, and the present process enables boron nitride to be pro-- duced in a relatively simple manner, without the use of a carrier material, causiny additional costs without the need
2~ for a large number o~ purification steps, and with a good - yield and purity. A better space-time yield i5 obtained with -the present process than with the previously described process, since the boron-containing reactant is less voluminous and richer in boron. The use of nitrogen has the advantage that it does not entail pollution problems as does the use of ammonia~ At temperatures akove 1400C~BN is obtained, which is very stable against moisture and acids and no heating to 1800C ~or stabilizatinn is required as recommended in low temperature processes.
Of the various alkali metal borides and alkaline earth metal burides, it is pre~erred to use hexaborides and '~, 105~3~ .
dodecaborides. Calcium hexaboride is a particularly suit-able starting material, especially technical grade calcium hexaboride. Calcium hexaboride can be manufactured on a large industrial scale from various cheap boron ores, such as colemanite. Processes for the manufacture of this and other borides are described in German Auslegeschriften Nos.
1,22~,236 and 1,229,505. Mixtures of borides or mixed crystals of borides can be used as starting materials.
It is characteristic for the invention that the borides used in the present process contain impurities or additives. In fact, such impurities or additives will aid ~ in achieving an improved yield, a lowering of the nitridation - temperature, or a purer final product. ~ome of the impuri-ties may be present in the Ca~6 used. They may, moreover, deliberately be added to the borides to the same end. Par-ticularly suitable additlves and/or impurities are carbon, boron carbide, boric acid, boron trio~ide, carbonates, borates, hydroxides and oxides of alkali or alkaline earth metals, as well as iron and iron oxide combinations of im-purities and/or additlves can result in the formation of ad-ditional boron nitride from boron or boride formed in sltl~, by carbothermal reduction as described in greater detail below.
The presence of these impurities and/or additives can, of course, result in the formation of products in addition to boron nitride, but these can, in general be removed either in the gas phase during the reaction or by wet chemistry with dilute mineral acids, e.g., hydrochloric acid.
The starting material advantageously has a boride content of at least 10~ by weight, and preferahly of from 40 to 98% by weight.
.
_r~_ jl
Of the various alkali metal borides and alkaline earth metal burides, it is pre~erred to use hexaborides and '~, 105~3~ .
dodecaborides. Calcium hexaboride is a particularly suit-able starting material, especially technical grade calcium hexaboride. Calcium hexaboride can be manufactured on a large industrial scale from various cheap boron ores, such as colemanite. Processes for the manufacture of this and other borides are described in German Auslegeschriften Nos.
1,22~,236 and 1,229,505. Mixtures of borides or mixed crystals of borides can be used as starting materials.
It is characteristic for the invention that the borides used in the present process contain impurities or additives. In fact, such impurities or additives will aid ~ in achieving an improved yield, a lowering of the nitridation - temperature, or a purer final product. ~ome of the impuri-ties may be present in the Ca~6 used. They may, moreover, deliberately be added to the borides to the same end. Par-ticularly suitable additlves and/or impurities are carbon, boron carbide, boric acid, boron trio~ide, carbonates, borates, hydroxides and oxides of alkali or alkaline earth metals, as well as iron and iron oxide combinations of im-purities and/or additlves can result in the formation of ad-ditional boron nitride from boron or boride formed in sltl~, by carbothermal reduction as described in greater detail below.
The presence of these impurities and/or additives can, of course, result in the formation of products in addition to boron nitride, but these can, in general be removed either in the gas phase during the reaction or by wet chemistry with dilute mineral acids, e.g., hydrochloric acid.
The starting material advantageously has a boride content of at least 10~ by weight, and preferahly of from 40 to 98% by weight.
.
_r~_ jl
3~
Moreover, the starting material is advantageously .
, in the form of particles having an average particle siæe of less than 10 ~ and a specific surface area measured by the BET method of greater than 1 m2/g~ Preferabiy, the average ~: particle size is less than 3 ~n and the specific surface area is greater than 5 m2/g., especially greater than 20 m2/g.
Various known methods of intensive co~inution and gxinding may be used to obtain a starting material of the desired par-ticle size; jet mills or agitator ball mills may, for example, ~- 10 be used.
In order to facilitate the circulation of the nitro-gen through the boride powder, it is advantageous for the powder to be made up into porous granules. Such granules may suitably be in the form of cylindrical moldings having a .
diameter of from 3 to 15 mm and a length of from 10 to 50 m~.
The granules should (when dry) advantageously have a ratio of bulk density of the granules to the density of the powder of not more than 70%, preferably not more than 60%. A suitable - r,lethod of preparing the granules is to work the boride powder in~o a stif~ paste, uslng a binder (for example, 1% Polyviol solution, (trademark for polyvinyl alcohol owned by Wacker Chemie GmbH)or 3~ boric acid solution) if necessary, processing the paste on an extruder to form cylindrical moldings, and drying these at a temperature oE up to 400C, preferably about 250C. In some cases,for example, if the boride powder con-not .
tains adhering boron oxide, the use of a binder may/be neces-- sary~
The process is carried out at a temperature of at least 900C. Advantageously, it is carried out ~n a stream of nitrogen, in which case it is preferable to use a temperature of at least 1400C, especially of from 1600 to 1~00C. It is .
105~3~ ~
also preferable for the nitrogen and the boride to be flowing in counter--current to one another. The process may, alter-natively, be carried out in a stationary manner, in which .
case the nitrogen may be used at an elevated pressure and in - which case it is advantageous to use a temperature of from 900 to 1400C.
The gas used for the reaction with the boride should contain at least 90~ by volume of nitrogen.. Nitrogen gas of technical pur~ty may be used in the present process, since the impurities present in conventional nitrogen gas do not inter-fere with the reaction. In the case of nitrogen-containing gases, the nitrogen may be admi~ed with, for exaniple, carbon monoxide, air or oxygen. Industrial nitrogen-containing gas mixtures, for example, generator gas ~nitrogen-carbon monoxide mixture~ and cracked ammonia (nitrogen--hydrogen mixture), may be used. The rate at which the nitridation reaction proceeds increases with increasing temperature. An upper limit is im-posed on the reaction temperature by the fact that boron ni-tride begins to dissociate at about 3000C.
The manufacture and pur.ification of the boron ni-tride can be carried out in various ways. For example, it is ` possible to carry out the manufacture and purification in one process stage, that is to say without a separate purification stage using wet chemistry subsequent to the nitridation. In this case, the process is generally carried out at a tempera-ture above the boiling point of the alkali metal or - of the alkaline earth metal~boride. In this method, it is advan-*ageous, especially when using an alkaline earth metal boride, .. either to use reactants (boride and nitrogen) that are free of oxygen or to remove any oxygen present by doping with the calculated a~ount ol carbon or a suitable carbon-containing .~ ~
- -7` . ~1 7A ' . I i ' ~35~34 compound; thus forming carbon monoxide. This prevents the formation of stable metal oxides or metal borates, in the final product. In some cases, carbon or a carbon-containing compound may be added to aid in the removal of the metal vla the gas phase. When using calcium boride, for example, the addition of carbon or boron carbide results in the formation of calcium cyanamide, which can be sublimated without decom--position in a nitrogen stream at a temperature of at least - 1~00C.
This method of carrying out the process is advan-tageously performed in a discontinuous, or batchwise, pro duction. This is because long reaction times are generally required for complete removal of by products vla the gas phase, and because volatilised by-products may condense in the cooler parts of ~e reactor, which, in a continuous method, could cause blockages.
If, by a suitable choice of starting material, nitrogen-containing gas, and/or reaction conditions the by products will not, or not wholly, be removed _ia the gas . ~.20 phase, they can be removed by wet chemistry. The solid by-- products may suitably be removed by treating the product .
.~ ~ ~ith a dilute mineral acid, for example dilute hydrochloric acid, thus dissolving the by-products and leaving the insoluble boron nitride. This method of nitridation, lends itself to a simple and economical production in a continuous manner.
One advantage of this method of operation is that it enables the reducing action of the metal formed inter-- mediately from the metal boride to be utilized in reducing any oxygen-containing boron compounds, for example, boron-trioxide, or alkali metal or alkaline earth metal borates, that are present in the reaction mixture. This enables addi-~.
.. 1,;
Si 16 ~3~ 4 ional boron nitride to be obtained from the boron in the boron-oxygen compounds. A similar effect can be achieved by the presence of carbon or boron carbide in the reaction mix-,;
ture.
When using calcium hexaboriae as the boride withadhering boron oxide, an optimum starting composition (assum~
ing the calcium hexaboride to be stoichiometric and carbon-free) is 82~ by weight calcium hexaboride and 18% by weigh'c boron trioxide, in accordance with the equation - --l 10 3 CaB6 ~ B203 ~ 10 N2 20 BN + 3 CaO.
If the boron trioxide content is higher than the optimum ~ amount, it lS advantageous to ~ix sufficient carbon with the - boride to ensure that all the boron oxide is converted to -~ boron nitride.
- It is, moreover, ~ossible to use a high proportion of boron oxide and to allow the latter reaction to proceed predominantly, alongside the nitridation of the boride. In this case, in contrast to a process solely using boron trioxide and carbon with no boride, carbon-free boron nitride is obtain-ed in high yield.
The starting material may also comprise a combina--tion of substances which, on heating , under an inert gas or in vacuo, will give a boride. Such a com-bination is, for example, calcium oxide, boron trioxide and carbon in a molar ratio of 1 : 3 : 10 respectively. In batches which are rich in boron trioxide, the boride or the boron nit-ride produced therefrom, acts as a carrier or diluent for the - boron trioxide thus preventing it from stic~ing and avoiding the associated processing and engineering difficulties.
I~ was further found that calcium hexaboride con~
~ .
taminated with up to 10~ by weight of iron can be used quite .
~9_ , .
63~
successfully in the present process, since the iron can read-ily be removed after nitridation from the boron nitride by treatment with a dilute mineral acid, e.g. hydrochloric acid.
A suitable reactor for carrying out the present process ln continuous manner at a temperature of up to 2000C
consists of a vertical graphite tube heated by the direct passage of a current, through which granules of the boride starting material may be passed downward under their own weight while nitrogen may be passed upward. Such tubes are known by the name Tamman furnace. If the nitridation is in~
complete after one passage of the material through such a - furnace, for example because of too short a residence time in the zone of maximum temperature, nitridation may be completed by a second passage through the furnace, or by passage through a second furnace. In this case, it is advantageous for the product from the first passage to be homogenized by a short grinding step and again formed into granules, pribr to the second passage. The COmpQsitiOn of the mixture may also be altered at this intennediate stage, if desired.
If it is desired to use temperatures exceeding - 2000C in order to achieve higher reaction rates, the process - may, for example, be carried out in a plasma jet furnace.
- The following examples illustrate the process of the invention. Percentages are by weight unless stated otherwise.
Example 1 10 g of lithium dode~aboride powder, having an analytical composition of 87.~5% B (total), 5.20% Li, 0.90%
C and 4.59-O B203, and a specific `(BET) surface area of 7.6 m2/g, was mixed with a little water to form a paste and then pressed in an extruder to give cylindrical moldings of a di-ameter of about 8 mm and a length of 15 to 30 mm. The moist moldings were dried in a circulating-air over at 250C. The ," 1~.
11~516~4 dried granules were then introduced into the heatin~ zone (zone of maximum constant temperature~ of a carbon tu~e-short `~ circuit Tammann furnace; the inside of the heating tube o~
which had been lined with a thin protective layer of boron nitride, in order to prevent as far as possible a reaction of the granules with the carbon of the heating tube. After suf-ficient flushing (300 litres/h) of the installation with technical grade nitrogen (main impurity about 0.1% of oxygen) from a cylinder, the furnace was heated up under a stationary , 10 nitrogen atmosphere, to 2000 + 100C, and this temperature was maintained constant for 60 minutes. The furnace was then switched off and cooled to room temperature under a nitrogen atmosphere. After con~inution of the product in a fixed-~ hammer mill, 19 g of boron nitride ppwder having a nitrogen content of 55.65% were obtained. An X-ray diffractometer diagra~ of the material obtained showed only lines of the hexagonal modification ~ boron nitride. The yield of BN was 94%.
Example 2 The procedure followed was as in Example 1, ~ut with the difference that magnesium dodecaboride powder, having an analytical composition of 80.01% B (total), 14.Z4% Mg, 0.40%
C and 1.71% B203, and a specific surface area ~ 14.0 m2/g, was employed as the starting material and a stream of nitrogen was used. 17 g of B~, which according to X-ray examination - was a single phase and contained 54.30% of nitrogen, were ob- tained. Yield of BN 93%.
Example 3 74 g of a pulverulent mixture, consisting of 96~ of -30 CaB6, having an analytical composition of 58.31% B (total~,i 35.47~ Ca, 4.17% C and 3-03% ~23' and a specific (BET) sur-face area of 15.1 m2/g, and 4~ af carbon in the form of car~on ~ o5~G3~ , , black, were formecl into granules using.a 1% solution of Polyviol. After nitriding the granules in a stream of ni-trogen at 1800 + 50C for 3 hours, 85 g of boron nitride ~- with a nitrogen content of 55.15% were obtained. Yield of BN:
92%.
., , ~ .
57 g of calcium bori~e powder, having an analytical composition of 62.14% B (total), 36.15% Ca, 0.75% C and 1.29 B203, and a specific (BET) surface area of 13.8 m2/g, were granulated using a 1% sol.ution of Polyviol. After nitriding the clried granules in a stream of nitrogen at 1800 + 50C for one hour, 86 g of a light grey reaction product were obtained, having an analytical composition of 46.45% N, 37.17% B ~total), 8.84% Ca, 0.18% C and 1.28% B203. An X-ray examination showed the presence of BN as well as small amounts of calcium hydrox-ide. After treating the powdered nitridation product with .
dilute hydrochloric acid, 75 g of white BN, having an analyti -~ cal composition of 55.51% Nj 44.31% B, C0.1% Ca and 0.1% C, were obtained. Yield of BN: 93%.
Example 5 50 g of a pulverulent mixture, consisting of 85% of ; CaB6 of the same composition as in Example 4 and 15% of car-bon in the form of carbon black, were formed into granules using a 1% solution of Polyviol~ The drie~ granules were then heated at 1600 + 50C in an atmosphere of flowing nitrogen for 60 minutes. Obtained were 80 g oF a light grey product, having an analytical composition of 45.50% N, 30,73% B (total), 15.85% Ca, 2.73% C and 1.95% B203V After treating the nitri-dation product with dilute hydrochloric acid, 54 g of BN, having an anal.ytical composition of 54.40% N, 43.44% B, 0.37%
Ca and 0.50~ C, were obtained. Yield of BN: 88~.
1~51634 ~ le 6 The procedure followed was as in Example 5, with the difference that 50 g of a pulverulent mixture, of 65~ of CaB6, of the composition as in Example 4, and 35% of ~13B03, were employed 63 g of a white nitridation product, having an analytical composition of 40.20~ N, 33.75% B (total), 14.0%
Ca, 2.58% B203 and 0.1% C, were obtained. 47 g of BN, having an analytical composition of 55.70% N, 43.87% B, ~ 0.1% Ca and C0.1% C, resulted from treatment with dilute hydrochloric acid. Yield of BN: 90%.
Example 7 The procedure followed was as in Example 5, with the dlfference that 63 g of a pulverulent mixture of 65% of CaB6 and 35~ of colemanite were e~ployed. Af-ter treatment with - dilute hydrochloric acid, 58 g of BN, having an analytical composition of 55.65% N, 43.77% B, C 0.1% Ca and ~0.1% C, were obtained. Yield of BN: 88%.
- Example 8 - - The procedure followed was as in Example 5, with the - 20 difference that 50 g of a pulverulent mixture of 75% of CaB6 - and 25% of B4C (grade 1500) were employed. The nitridation-was carried out at 1800 ~ 50C. After treatment with dilute - hydrochloric acid, 68 g of BN, having an analytical composition of 55.95~ N, 44.39% B, ~0.1% Ca and ~0.1~ C, were obtained.
Yield of BN: 87%.
; Example 9 -The procedure followed was as in Examr)le 4, with the difference that 60 g of a technically pure calcium boride powder, having an analy-tical composition of 58.31% B (total), - 30 35.47~ Ca, 4.17% C and 3.03~ B203, and a specific (BET) sur-face area of 15.1 m2/g, were employed. 85 g of a white nitri-dation product with 44.85~ N and, after treatment with dilu-te ~l~
~!
!
~L~3S~i34 .
hydrochloric acid. 71 g of BN wi-th 55.90% N, were obtained.
Yield of BN: 88~.
Example 10 The procedure followed was as in Example 4, with the difference that 80 g of a calcium boride powder, contami-- nated with iron and having an analytical comvosition of 47.27 B (total) 28.38% Ca, 3.57% C, 5.82% B203 and 13.40~ Fe and a specific (BET) surface area of 7.0 m2/g, were employed. After treating the nitridation product with dilute hydrochloric acid, 81 g of BN, having an analytical composition of 55.41% N, 44.10%
B, C0.1% Ca, ~0.1% C and C0.01% Fe, were obtained. Yield of BN: 94%.
Example 11 ` 50 g of a mixture, consisting of 50% of CaB6 powder, having an analytical composition of 58.24% B (total), 34.68%
Ca, 4.13% C and 4.00% B203, and a specific (BET) surface area of 7.0 m2/g, 40% of H3B03 powder and 10% of C in the form of carbon black, were formed into granules using a 1% solution of Polyviol. After drying the granules at 300C, and nitriding them at 1700 ~ 50C in a nitrogen stream for t~o hours, and treatment of *he nitridation product with dilute hydrochloric - acid, 36 g of B~ with a nitrogen content of 55.35% were obtain~
ed. Yield of B~l: 87%.
Example 12 - 70 g of calclum hexaboride, having an analytical com-position of 55.97% B (total), 33.22% Ca, 3.86% C and 7.15%
; B203 and a specific (BET) surface area of 21.2 m2/g, were form-- ed into granules without using an additional binder. The gran ules I obtained were dried and then heated at 1600 ~ 50C in a stream of nitrogen for 30 minutes. This gave 108 g of a light grey nitridation product I, which was pulverized in a .
j !;
~o~634 fixed-~har~er mill. The resulting fine powder was formed into ; yranules using a 3% solution of boric acid, to give, after drying, 105 g of granules II. These were heated in a second nitriding stage, at 1600 ~ 50C in a stream of nitrogen for 30 minutes, analogously to the first nitriding step. This gave lOS g of nitridation product II
and, after treatment with dilute hydrochloric acid, 77 g of pure BN. Yield of BN: 86%.
Example l3 -10 g of calcium boride powder, which passed through a sieve with an open mesh width of 0.041 ~m ~-325 mesh) and had an analytical composition of 59.90% B (total), 27.50% Ca, 6.03% C and 2.75% B203, and a specific (BET) surface area of 2.7 m2/g, were nitrided in loose form~ that is to say without ; granulacion, at 1400C under a nitrogen pressure of 100 atmos-pheres gauge for 30 minutes. After treating the nitridation product with dilute hydrochloric acid, 12 g of pure BN were obtained. Yield of BN: 87%.
Example_l~
The procedure followed was as in Example 13, with the difference that 15 g of calcium boride powder, having an ana-lytical composition of 55.97% B (total), 33.22% Ca, 3~86% C
and 7.15% B203, and a specific (BET) surface area of 21.2 m /g, were employed. 17 g of BN were obtained. Yield of BN:
88%.
Example 15 .. .. _ -The procedure followed was as in Example 13, with the difference that lO g of lithium dodecaboride powder, having an analytical composition of 87.85~ B (total), S.20%
Li, 0.90% C and 4.5g% B203, and a specific (BET) surface area' of 7.6 ~ /g, were employed. This gave 18 g of hexagonal BN.
Yield of BN- 8~.
1S~
r j.
j.
::
~1~5~3 :. ~rom the foregoing description, one skilled in the art can easily ascertain the essential charac-teristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Con-sequently, such changes and modifications are properly, equitably, and intended to be, within the full range of eguivalen-e of the following claims.
: . ' .
... . ' .
:'` ' ' '' '' . ' , . . .
. ~16-
Moreover, the starting material is advantageously .
, in the form of particles having an average particle siæe of less than 10 ~ and a specific surface area measured by the BET method of greater than 1 m2/g~ Preferabiy, the average ~: particle size is less than 3 ~n and the specific surface area is greater than 5 m2/g., especially greater than 20 m2/g.
Various known methods of intensive co~inution and gxinding may be used to obtain a starting material of the desired par-ticle size; jet mills or agitator ball mills may, for example, ~- 10 be used.
In order to facilitate the circulation of the nitro-gen through the boride powder, it is advantageous for the powder to be made up into porous granules. Such granules may suitably be in the form of cylindrical moldings having a .
diameter of from 3 to 15 mm and a length of from 10 to 50 m~.
The granules should (when dry) advantageously have a ratio of bulk density of the granules to the density of the powder of not more than 70%, preferably not more than 60%. A suitable - r,lethod of preparing the granules is to work the boride powder in~o a stif~ paste, uslng a binder (for example, 1% Polyviol solution, (trademark for polyvinyl alcohol owned by Wacker Chemie GmbH)or 3~ boric acid solution) if necessary, processing the paste on an extruder to form cylindrical moldings, and drying these at a temperature oE up to 400C, preferably about 250C. In some cases,for example, if the boride powder con-not .
tains adhering boron oxide, the use of a binder may/be neces-- sary~
The process is carried out at a temperature of at least 900C. Advantageously, it is carried out ~n a stream of nitrogen, in which case it is preferable to use a temperature of at least 1400C, especially of from 1600 to 1~00C. It is .
105~3~ ~
also preferable for the nitrogen and the boride to be flowing in counter--current to one another. The process may, alter-natively, be carried out in a stationary manner, in which .
case the nitrogen may be used at an elevated pressure and in - which case it is advantageous to use a temperature of from 900 to 1400C.
The gas used for the reaction with the boride should contain at least 90~ by volume of nitrogen.. Nitrogen gas of technical pur~ty may be used in the present process, since the impurities present in conventional nitrogen gas do not inter-fere with the reaction. In the case of nitrogen-containing gases, the nitrogen may be admi~ed with, for exaniple, carbon monoxide, air or oxygen. Industrial nitrogen-containing gas mixtures, for example, generator gas ~nitrogen-carbon monoxide mixture~ and cracked ammonia (nitrogen--hydrogen mixture), may be used. The rate at which the nitridation reaction proceeds increases with increasing temperature. An upper limit is im-posed on the reaction temperature by the fact that boron ni-tride begins to dissociate at about 3000C.
The manufacture and pur.ification of the boron ni-tride can be carried out in various ways. For example, it is ` possible to carry out the manufacture and purification in one process stage, that is to say without a separate purification stage using wet chemistry subsequent to the nitridation. In this case, the process is generally carried out at a tempera-ture above the boiling point of the alkali metal or - of the alkaline earth metal~boride. In this method, it is advan-*ageous, especially when using an alkaline earth metal boride, .. either to use reactants (boride and nitrogen) that are free of oxygen or to remove any oxygen present by doping with the calculated a~ount ol carbon or a suitable carbon-containing .~ ~
- -7` . ~1 7A ' . I i ' ~35~34 compound; thus forming carbon monoxide. This prevents the formation of stable metal oxides or metal borates, in the final product. In some cases, carbon or a carbon-containing compound may be added to aid in the removal of the metal vla the gas phase. When using calcium boride, for example, the addition of carbon or boron carbide results in the formation of calcium cyanamide, which can be sublimated without decom--position in a nitrogen stream at a temperature of at least - 1~00C.
This method of carrying out the process is advan-tageously performed in a discontinuous, or batchwise, pro duction. This is because long reaction times are generally required for complete removal of by products vla the gas phase, and because volatilised by-products may condense in the cooler parts of ~e reactor, which, in a continuous method, could cause blockages.
If, by a suitable choice of starting material, nitrogen-containing gas, and/or reaction conditions the by products will not, or not wholly, be removed _ia the gas . ~.20 phase, they can be removed by wet chemistry. The solid by-- products may suitably be removed by treating the product .
.~ ~ ~ith a dilute mineral acid, for example dilute hydrochloric acid, thus dissolving the by-products and leaving the insoluble boron nitride. This method of nitridation, lends itself to a simple and economical production in a continuous manner.
One advantage of this method of operation is that it enables the reducing action of the metal formed inter-- mediately from the metal boride to be utilized in reducing any oxygen-containing boron compounds, for example, boron-trioxide, or alkali metal or alkaline earth metal borates, that are present in the reaction mixture. This enables addi-~.
.. 1,;
Si 16 ~3~ 4 ional boron nitride to be obtained from the boron in the boron-oxygen compounds. A similar effect can be achieved by the presence of carbon or boron carbide in the reaction mix-,;
ture.
When using calcium hexaboriae as the boride withadhering boron oxide, an optimum starting composition (assum~
ing the calcium hexaboride to be stoichiometric and carbon-free) is 82~ by weight calcium hexaboride and 18% by weigh'c boron trioxide, in accordance with the equation - --l 10 3 CaB6 ~ B203 ~ 10 N2 20 BN + 3 CaO.
If the boron trioxide content is higher than the optimum ~ amount, it lS advantageous to ~ix sufficient carbon with the - boride to ensure that all the boron oxide is converted to -~ boron nitride.
- It is, moreover, ~ossible to use a high proportion of boron oxide and to allow the latter reaction to proceed predominantly, alongside the nitridation of the boride. In this case, in contrast to a process solely using boron trioxide and carbon with no boride, carbon-free boron nitride is obtain-ed in high yield.
The starting material may also comprise a combina--tion of substances which, on heating , under an inert gas or in vacuo, will give a boride. Such a com-bination is, for example, calcium oxide, boron trioxide and carbon in a molar ratio of 1 : 3 : 10 respectively. In batches which are rich in boron trioxide, the boride or the boron nit-ride produced therefrom, acts as a carrier or diluent for the - boron trioxide thus preventing it from stic~ing and avoiding the associated processing and engineering difficulties.
I~ was further found that calcium hexaboride con~
~ .
taminated with up to 10~ by weight of iron can be used quite .
~9_ , .
63~
successfully in the present process, since the iron can read-ily be removed after nitridation from the boron nitride by treatment with a dilute mineral acid, e.g. hydrochloric acid.
A suitable reactor for carrying out the present process ln continuous manner at a temperature of up to 2000C
consists of a vertical graphite tube heated by the direct passage of a current, through which granules of the boride starting material may be passed downward under their own weight while nitrogen may be passed upward. Such tubes are known by the name Tamman furnace. If the nitridation is in~
complete after one passage of the material through such a - furnace, for example because of too short a residence time in the zone of maximum temperature, nitridation may be completed by a second passage through the furnace, or by passage through a second furnace. In this case, it is advantageous for the product from the first passage to be homogenized by a short grinding step and again formed into granules, pribr to the second passage. The COmpQsitiOn of the mixture may also be altered at this intennediate stage, if desired.
If it is desired to use temperatures exceeding - 2000C in order to achieve higher reaction rates, the process - may, for example, be carried out in a plasma jet furnace.
- The following examples illustrate the process of the invention. Percentages are by weight unless stated otherwise.
Example 1 10 g of lithium dode~aboride powder, having an analytical composition of 87.~5% B (total), 5.20% Li, 0.90%
C and 4.59-O B203, and a specific `(BET) surface area of 7.6 m2/g, was mixed with a little water to form a paste and then pressed in an extruder to give cylindrical moldings of a di-ameter of about 8 mm and a length of 15 to 30 mm. The moist moldings were dried in a circulating-air over at 250C. The ," 1~.
11~516~4 dried granules were then introduced into the heatin~ zone (zone of maximum constant temperature~ of a carbon tu~e-short `~ circuit Tammann furnace; the inside of the heating tube o~
which had been lined with a thin protective layer of boron nitride, in order to prevent as far as possible a reaction of the granules with the carbon of the heating tube. After suf-ficient flushing (300 litres/h) of the installation with technical grade nitrogen (main impurity about 0.1% of oxygen) from a cylinder, the furnace was heated up under a stationary , 10 nitrogen atmosphere, to 2000 + 100C, and this temperature was maintained constant for 60 minutes. The furnace was then switched off and cooled to room temperature under a nitrogen atmosphere. After con~inution of the product in a fixed-~ hammer mill, 19 g of boron nitride ppwder having a nitrogen content of 55.65% were obtained. An X-ray diffractometer diagra~ of the material obtained showed only lines of the hexagonal modification ~ boron nitride. The yield of BN was 94%.
Example 2 The procedure followed was as in Example 1, ~ut with the difference that magnesium dodecaboride powder, having an analytical composition of 80.01% B (total), 14.Z4% Mg, 0.40%
C and 1.71% B203, and a specific surface area ~ 14.0 m2/g, was employed as the starting material and a stream of nitrogen was used. 17 g of B~, which according to X-ray examination - was a single phase and contained 54.30% of nitrogen, were ob- tained. Yield of BN 93%.
Example 3 74 g of a pulverulent mixture, consisting of 96~ of -30 CaB6, having an analytical composition of 58.31% B (total~,i 35.47~ Ca, 4.17% C and 3-03% ~23' and a specific (BET) sur-face area of 15.1 m2/g, and 4~ af carbon in the form of car~on ~ o5~G3~ , , black, were formecl into granules using.a 1% solution of Polyviol. After nitriding the granules in a stream of ni-trogen at 1800 + 50C for 3 hours, 85 g of boron nitride ~- with a nitrogen content of 55.15% were obtained. Yield of BN:
92%.
., , ~ .
57 g of calcium bori~e powder, having an analytical composition of 62.14% B (total), 36.15% Ca, 0.75% C and 1.29 B203, and a specific (BET) surface area of 13.8 m2/g, were granulated using a 1% sol.ution of Polyviol. After nitriding the clried granules in a stream of nitrogen at 1800 + 50C for one hour, 86 g of a light grey reaction product were obtained, having an analytical composition of 46.45% N, 37.17% B ~total), 8.84% Ca, 0.18% C and 1.28% B203. An X-ray examination showed the presence of BN as well as small amounts of calcium hydrox-ide. After treating the powdered nitridation product with .
dilute hydrochloric acid, 75 g of white BN, having an analyti -~ cal composition of 55.51% Nj 44.31% B, C0.1% Ca and 0.1% C, were obtained. Yield of BN: 93%.
Example 5 50 g of a pulverulent mixture, consisting of 85% of ; CaB6 of the same composition as in Example 4 and 15% of car-bon in the form of carbon black, were formed into granules using a 1% solution of Polyviol~ The drie~ granules were then heated at 1600 + 50C in an atmosphere of flowing nitrogen for 60 minutes. Obtained were 80 g oF a light grey product, having an analytical composition of 45.50% N, 30,73% B (total), 15.85% Ca, 2.73% C and 1.95% B203V After treating the nitri-dation product with dilute hydrochloric acid, 54 g of BN, having an anal.ytical composition of 54.40% N, 43.44% B, 0.37%
Ca and 0.50~ C, were obtained. Yield of BN: 88~.
1~51634 ~ le 6 The procedure followed was as in Example 5, with the difference that 50 g of a pulverulent mixture, of 65~ of CaB6, of the composition as in Example 4, and 35% of ~13B03, were employed 63 g of a white nitridation product, having an analytical composition of 40.20~ N, 33.75% B (total), 14.0%
Ca, 2.58% B203 and 0.1% C, were obtained. 47 g of BN, having an analytical composition of 55.70% N, 43.87% B, ~ 0.1% Ca and C0.1% C, resulted from treatment with dilute hydrochloric acid. Yield of BN: 90%.
Example 7 The procedure followed was as in Example 5, with the dlfference that 63 g of a pulverulent mixture of 65% of CaB6 and 35~ of colemanite were e~ployed. Af-ter treatment with - dilute hydrochloric acid, 58 g of BN, having an analytical composition of 55.65% N, 43.77% B, C 0.1% Ca and ~0.1% C, were obtained. Yield of BN: 88%.
- Example 8 - - The procedure followed was as in Example 5, with the - 20 difference that 50 g of a pulverulent mixture of 75% of CaB6 - and 25% of B4C (grade 1500) were employed. The nitridation-was carried out at 1800 ~ 50C. After treatment with dilute - hydrochloric acid, 68 g of BN, having an analytical composition of 55.95~ N, 44.39% B, ~0.1% Ca and ~0.1~ C, were obtained.
Yield of BN: 87%.
; Example 9 -The procedure followed was as in Examr)le 4, with the difference that 60 g of a technically pure calcium boride powder, having an analy-tical composition of 58.31% B (total), - 30 35.47~ Ca, 4.17% C and 3.03~ B203, and a specific (BET) sur-face area of 15.1 m2/g, were employed. 85 g of a white nitri-dation product with 44.85~ N and, after treatment with dilu-te ~l~
~!
!
~L~3S~i34 .
hydrochloric acid. 71 g of BN wi-th 55.90% N, were obtained.
Yield of BN: 88~.
Example 10 The procedure followed was as in Example 4, with the difference that 80 g of a calcium boride powder, contami-- nated with iron and having an analytical comvosition of 47.27 B (total) 28.38% Ca, 3.57% C, 5.82% B203 and 13.40~ Fe and a specific (BET) surface area of 7.0 m2/g, were employed. After treating the nitridation product with dilute hydrochloric acid, 81 g of BN, having an analytical composition of 55.41% N, 44.10%
B, C0.1% Ca, ~0.1% C and C0.01% Fe, were obtained. Yield of BN: 94%.
Example 11 ` 50 g of a mixture, consisting of 50% of CaB6 powder, having an analytical composition of 58.24% B (total), 34.68%
Ca, 4.13% C and 4.00% B203, and a specific (BET) surface area of 7.0 m2/g, 40% of H3B03 powder and 10% of C in the form of carbon black, were formed into granules using a 1% solution of Polyviol. After drying the granules at 300C, and nitriding them at 1700 ~ 50C in a nitrogen stream for t~o hours, and treatment of *he nitridation product with dilute hydrochloric - acid, 36 g of B~ with a nitrogen content of 55.35% were obtain~
ed. Yield of B~l: 87%.
Example 12 - 70 g of calclum hexaboride, having an analytical com-position of 55.97% B (total), 33.22% Ca, 3.86% C and 7.15%
; B203 and a specific (BET) surface area of 21.2 m2/g, were form-- ed into granules without using an additional binder. The gran ules I obtained were dried and then heated at 1600 ~ 50C in a stream of nitrogen for 30 minutes. This gave 108 g of a light grey nitridation product I, which was pulverized in a .
j !;
~o~634 fixed-~har~er mill. The resulting fine powder was formed into ; yranules using a 3% solution of boric acid, to give, after drying, 105 g of granules II. These were heated in a second nitriding stage, at 1600 ~ 50C in a stream of nitrogen for 30 minutes, analogously to the first nitriding step. This gave lOS g of nitridation product II
and, after treatment with dilute hydrochloric acid, 77 g of pure BN. Yield of BN: 86%.
Example l3 -10 g of calcium boride powder, which passed through a sieve with an open mesh width of 0.041 ~m ~-325 mesh) and had an analytical composition of 59.90% B (total), 27.50% Ca, 6.03% C and 2.75% B203, and a specific (BET) surface area of 2.7 m2/g, were nitrided in loose form~ that is to say without ; granulacion, at 1400C under a nitrogen pressure of 100 atmos-pheres gauge for 30 minutes. After treating the nitridation product with dilute hydrochloric acid, 12 g of pure BN were obtained. Yield of BN: 87%.
Example_l~
The procedure followed was as in Example 13, with the difference that 15 g of calcium boride powder, having an ana-lytical composition of 55.97% B (total), 33.22% Ca, 3~86% C
and 7.15% B203, and a specific (BET) surface area of 21.2 m /g, were employed. 17 g of BN were obtained. Yield of BN:
88%.
Example 15 .. .. _ -The procedure followed was as in Example 13, with the difference that lO g of lithium dodecaboride powder, having an analytical composition of 87.85~ B (total), S.20%
Li, 0.90% C and 4.5g% B203, and a specific (BET) surface area' of 7.6 ~ /g, were employed. This gave 18 g of hexagonal BN.
Yield of BN- 8~.
1S~
r j.
j.
::
~1~5~3 :. ~rom the foregoing description, one skilled in the art can easily ascertain the essential charac-teristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Con-sequently, such changes and modifications are properly, equitably, and intended to be, within the full range of eguivalen-e of the following claims.
: . ' .
... . ' .
:'` ' ' '' '' . ' , . . .
. ~16-
Claims (16)
1. A process for the manufacture of hexagonal boron nitride, which comprises causing a starting material compris-ing an alkali metal boride or an alkaline earth metal boride to react with nitrogen at a temperature of at least about 900°C in the presence of at least one substance selected from the group consisting of carbon, boron carbide, boric acid, boron trioxide, carbonates, borates, hydroxides and oxides of alkali or alkaline earth metals, iron and iron oxide in addi-tion to the boride.
2. A process as claimed in claim 1 wherein the boride is a hexaboride or a dodecaboride.
3. A process as claimed in claim 2 wherein the boride is calcium hexaboride.
4. The process as claimed in claim 1 wherein the starting material comprises at least 10% by weight of the boride.
5. The process as claimed in claim 4 wherein the starting material comprises from 40 to 98% by weight of boride.
6. The process as claimed in claim 1 wherein the nitridation is carried out above about 900°C under nitrogen pressure.
7. The process as claimed in claim 6 wherein the reaction is carried out at a temperature of at least about 1400°C in a nitrogen current.
8. The process as claimed in claim 6 wherein the re-action is carried out at a temperature of from 1600 to 1800°C.
9. The process as claimed in claim 1 wherein a gas mixture comprising nitrogen is used as the source of the nitrogen, the amount of nitrogen being at least 90%.
10. The process as claimed in claim 1 wherein tech-nical grade nitrogen is used as the source of the nitrogen.
11. The process as claimed in claim 1 wherein the starting material has an average particle size of less than 10 um and a specific surface area greater than 1 m2/g.
12. The process as claimed in claim 11 wherein the starting material has an average particle size of less than 3 um and a specific surface area greater than 5 m2/g.
13. The process as claimed in claim 12 wherein the starting material has a specific surface area greater than 20 m2/g.
14. The process as claimed in claim 11 wherein the starting material of powdery particle size is made into porous granules before nitridation.
15. The process as claimed in claim 1 wherein reaction products other than the boron nitride are removed during the heating operation via the gas phase.
16. The process as claimed in claim 15 wherein only a part of the reaction products other than the boron nitride are removed from the boron nitride via the gas phase and the remainder by dissolution in a dilute mineral acid.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2461821A DE2461821C3 (en) | 1974-12-30 | 1974-12-30 | Process for the production of hexagonal boron nitride |
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| Publication Number | Publication Date |
|---|---|
| CA1051634A true CA1051634A (en) | 1979-04-03 |
Family
ID=5934749
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|---|---|---|---|
| CA242,712A Expired CA1051634A (en) | 1974-12-30 | 1975-12-29 | Manufacture of hexagonal boron nitride |
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| JP (1) | JPS5347320B2 (en) |
| AT (1) | AT360491B (en) |
| BE (1) | BE837184A (en) |
| CA (1) | CA1051634A (en) |
| CH (1) | CH601103A5 (en) |
| DE (1) | DE2461821C3 (en) |
| FR (1) | FR2296590A1 (en) |
| GB (1) | GB1516689A (en) |
| IT (1) | IT1052623B (en) |
| NL (1) | NL7514877A (en) |
| SE (1) | SE405244B (en) |
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| JPS5939362B2 (en) * | 1981-11-12 | 1984-09-22 | 昭和電工株式会社 | Boron nitride compound and its manufacturing method |
| CA1260671A (en) * | 1984-06-07 | 1989-09-26 | Takahisa Koshida | High-purity powder of hexagonal boron nitride and a method for the preparation thereof |
| FR2817855B1 (en) * | 2000-12-11 | 2003-09-05 | Saint Gobain Ct Recherches | BORON NITRIDE POWDER AND PROCESS FOR ITS PREPARATION |
| DE102011009834B4 (en) * | 2011-01-31 | 2015-06-03 | Georg Vogt | Process for the preparation of cubic boron nitride |
| CN114524418B (en) * | 2022-02-16 | 2023-06-16 | 中国人民解放***箭军工程大学 | Preparation method of hammer-shaped short boron nitride nanotube |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US2834650A (en) * | 1955-10-04 | 1958-05-13 | Union Carbide Corp | Production of boron nitride |
| DE1229505B (en) * | 1964-01-23 | 1966-12-01 | Kempten Elektroschmelz Gmbh | Process for the preparation of alkaline earth metal borides and carbides |
| DE1228236B (en) * | 1964-04-30 | 1966-11-10 | Kempten Elektroschmelz Gmbh | Process for the production of a hard material consisting of calcium, boron and optionally carbon |
| DE1567452B2 (en) * | 1966-02-19 | 1974-12-19 | Deutsche Gold- Und Silber-Scheideanstalt Vormals Roessler, 6000 Frankfurt | Process for the production of boron nitride |
-
1974
- 1974-12-30 DE DE2461821A patent/DE2461821C3/en not_active Expired
-
1975
- 1975-12-09 GB GB50418/75A patent/GB1516689A/en not_active Expired
- 1975-12-19 NL NL7514877A patent/NL7514877A/en not_active Application Discontinuation
- 1975-12-23 IT IT7552845A patent/IT1052623B/en active
- 1975-12-25 JP JP15572675A patent/JPS5347320B2/ja not_active Expired
- 1975-12-29 SE SE7514729A patent/SE405244B/en unknown
- 1975-12-29 FR FR7539949A patent/FR2296590A1/en active Granted
- 1975-12-29 AT AT987475A patent/AT360491B/en not_active IP Right Cessation
- 1975-12-29 CA CA242,712A patent/CA1051634A/en not_active Expired
- 1975-12-30 BE BE163200A patent/BE837184A/en unknown
- 1975-12-30 CH CH1689675A patent/CH601103A5/xx not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| GB1516689A (en) | 1978-07-05 |
| JPS5191000A (en) | 1976-08-10 |
| ATA987475A (en) | 1980-06-15 |
| DE2461821B2 (en) | 1978-06-08 |
| DE2461821C3 (en) | 1984-10-18 |
| IT1052623B (en) | 1981-07-20 |
| FR2296590A1 (en) | 1976-07-30 |
| AT360491B (en) | 1981-01-12 |
| FR2296590B1 (en) | 1978-05-19 |
| JPS5347320B2 (en) | 1978-12-20 |
| DE2461821A1 (en) | 1976-07-08 |
| SE405244B (en) | 1978-11-27 |
| BE837184A (en) | 1976-06-30 |
| SE7514729L (en) | 1976-07-31 |
| NL7514877A (en) | 1976-07-02 |
| CH601103A5 (en) | 1978-06-30 |
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