Fine metallic nitride powders having a high purity are prepared, without causing any plugging or other problems in the reaction apparatus and with easy heat control of the reaction, by reacting a metallic halide with liquid ammonia in the presence of an organic solvent which has a specific gravity higher than that of liquid ammonia, and also is not miscible or is only slightly miscible with liquid ammonia at a reaction temperature. The process according to the present invention is effected by introducing the metallic halide into the lower organic solvent layer of the reaction system.
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1. In a process for producing metallic nitride powder wherein a metallic halide is reacted with liquid ammonia to form a metallic amide or metallic imide, the resulting metallic amide or metallic imide is separated from the reaction mixture and the separated product is thermally decomposed in an atmosphere of nitrogen or ammonia to produce metallic nitride powder, the improvement which comprises carrying out the reaction in the presence of an organic solvent having a specific gravity higher than that of the liquid ammonia, said organic solvent and the liquid ammonia being not soluble or only slightly soluble with each other at the reaction temperature employed, by first charging liquid ammonia and the organic solvent into a reaction vesel vessel with the organic solvent and liquid ammonia separating into two layers; an upper liquid ammonia layer and a lower organic solvent layer, and then introducing the metallic halide into the lower organic solvent layer; the so introduced metallic halide diffusing through the organic solvent layer and reacting with the liquid ammonia at the interface of the two layers to deposit metallic amide or metallic imide at said interface and form ammonium chloride which is absorbed into the liquid ammonia layer.
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The present invention relates to a process for producing metallic nitride powder suitable for use in the manufacture of sintered metallic nitride which is useful as a super hard heat resisting material.
Sintered nitrides of metals such as silicon, boron, titanium and the like, have generated remarkable interest recently as super hard heat resisting materials. However, in order to improve the properties of the sintered products an increase in the purity of the starting metal nitride and a reduction in the powder particle size of the metal nitride, from those of the metal nitride conventionally used, are required in the art.
The following four typical prior processes for producing metallic nitrides are known in the art.
(1) Direct nitridation methods, wherein the metal is heated at a high temperature in the presence of nitrogen or ammonia.
(2) Methods wherein the reduction and nitridation are simultaneously carried out by heating the mixture of the metallic oxide and carbon at a high temperature in the presence of nitrogen.
(3) Vapor phase reaction methods, wherein mixtures of the gaseous metallic halide and gaseous ammonia diluted with nitrogen are reacted at a high temperature.
(4) Thermal decomposition methods of the amides or imides, wherein the metallic halide and liquid ammonia are reacted with each other at an ambient or lower temperature and, then, the resulting metallic amides or imides are heated at a high temperature in an atmosphere of nitrogen or ammonia after they are separated from the reaction mixture (See: Powder Metallurgy International 6, No. 3, p144 (1974)).
However, the above mentioned prior art processes have several disadvantages from the standpoint of obtaining the desired metallic nitride fine powders having a high purity. Although the above-mentioned method (1) is industrially used at the present time, the purity and the particle size of the product directly depend upon those of the starting metal, so that the manufacture of fine metallic powder having high purity is first required. In the above-mentioned method (2) use of the fine metallic oxide powder having a high purity is also required, as in the method (1), and further, free carbon and metallic carbide are likely to contaminate the product. According to the above-mentioned method (3), although a metallic halide having high purity can be prepared, because the metallic halide is easily and highly purified by means of distillation and sublimation techniques, there are problems in that, since a very diluted gas-phase reaction is used, the productivity is low, and the yield of powders is low due to the deposition of the resultant nitride on, for example, the wall surface of the reaction tube. For this reason, this method is suitable for use in the surface coating of a metal, rather than the production of the nitride powder.
According to the above-mentioned method (4), the starting metallic halide can be easily purified, the productivity is high due to the liquid-phase reaction and a product having a powder particle size of the order of a micron or less can be obtained. Thus, this method seems to be suitable for use in the mass-production of fine metallic nitride powder having a high purity. However, since the reaction of the metallic halide with the liquid ammonia is a very vigorous exothermic reaction and a large amount of ammonium halide in the form of fumes is formed as a by-product, reaction control is very difficult, and plugging and other various problems are caused by the deposition of the ammonium halide by-product on the inner surface of the reactor, the supply nozzles of the starting materials and the tube wall of the gas outlet. For these reasons, this method has not been considered practical for use in industry.
An object of the present invention is to obviate the above-mentioned problems of the prior method (4) and to provide a process for producing a fine metallic nitride powder having high purity, without causing any plugging and other various problems in the reaction apparatus, and which process facilitates the heat control of the reaction.
Other objects and advantages of the present invention will be apparent from the following description.
In
The liquid-phase reaction was carried out in the reaction vessel 1 in a similar manner to that described in Example 1, except that a solution of 12.0 g of vanadium tetrachloride in 40 ml of n-heptane was used as the starting material, a 1:2 mixture (by weight ratio) of n-heptane and toluene was used as the organic solvent, and the temperature of the reaction vessel 1 was -60°C The reaction products were transported into the calcination tube 9 and, after washing and drying, were heated at a temperature of 1000°C for 3 hours under a gaseous ammonia stream. The product thus obtained was further baked at a temperature of 1500°C for 1 hour.
3.82 g of brown powder, which was determined to be cubic vanadium nitride (VN) by X-ray diffraction analysis, were obtained. The yield of the product based on the starting vanadium tetrachloride was 94%. The nitrogen content was 19.2% (the theoretical value in terms of VN was 21.6%). Fine particulates having a diameter of 0.01 through 0.1 micron were observed by an electron microscope.
The liquid-phase reaction was carried out in the reaction vessel 1 in a similar manner to that described in Example 1, except that a solution of 12.8 g of silicon tetrabromide in 10 ml of toluene was used as the starting material, toluene was used as the organic solvent and the temperature of the reaction vessel 1 was -35°C The products thus obtained were transported into the calcination tube 9 and, after washing and drying, heated at a temperature of 1000°C, for 3 hours, in a gaseous ammonia stream. The product was further baked at a temperature of 1550°C, for 5 hours, in an electric furnace, while nitrogen gas was purged.
1.68 g of off-white powder, which was determined to be α-silicon nitride containing 10% or less of β-silicon nitride therein by X-ray diffraction analysis, were obtained. The yield of the product based on the starting silicon tetrabromide was 98%. The nitrogen content was 38.9% (the theoretical value in terms of Si3 N4 was 39.9%). Results similar to those of Example 1 were observed through an electron microscope.
The liquid-phase reaction was carried out in the reaction vessel 1 in a similar manner to that described in Example 1, except that a solution of 13.6 g of trichlorosilane in 10 ml of toluene was used as the starting material, toluene was used as the organic solvent and the temperature of the reaction vessel 1 was -40°C The products thus obtained were transported into the calcination tube 9 and, after washing and drying, were heated at a temperature of 1000°C for 3 hours in a gaseous ammonia stream. The product was further baked at a temperature of 1550°C, for 5 hours, in an electric furnace, while nitrogen gas was purged.
3.35 g of off-white powder, which was determined to be α-silicon nitride containing 10% or less of β-silicon nitride therein by X-ray diffraction analysis, were obtained. The yield of the product based on the starting trichlorosilane was 72%. The nitrogen content was 39.3% (the theoretical value in terms of Si3 N4 was 39.9%). Results similar to those of Example 1 were observed through an electron microscope.
Into a 5 liter reaction vessel provided with a cooling jacket made of pressure resistant glass (usual operating pressure: 10 kg/cm2), 1 liter of liquid ammonia (as the upper layer) and 1 liter of a 4:1 mixed solvent (by weight ratio) of cyclohexane and benzene (as the lower layer) were charged and cooled to a temperature of 5°C After the atmosphere in the reaction vessel was replaced by nitrogen, a mixed solution of 200 g of silicon tetrachloride and 1 liter of the above mentioned mixed solvent, which was separately prepared, were introduced into the mixed solvent of the lower portion of the reaction vessel by a supply pump. As a result, the reaction occurred in the liquid phase. A white powder which was formed was filtered off and washed with liquid ammonia. The powder so obtained was heated at a temperature of 1000°C, for 3 hours, under a gaseous ammonia stream and, further, was baked at a temperature of 1550°C, for 5 hours, in a nitrogen gas stream. As a result, about 52 g of greyish white powders were obtained (yield: 95%). The nitrogen analytical value of the product was 39.0% (the theoretical value in terms of Si3 N4 was 39.9%). It was found that the product contained α-silicon nitride, including 10% or less of β-silicon nitride therein, as a result of X-ray diffraction analysis.
Into the reaction vessel 1 cooled to a temperature of -40°C, only about 100 ml of liquid ammonia was charged, and then a starting solution of 9.8 g of silicon tetrachloride in 40 ml of a 4:1 mixed solvent (by weight ratio) of cyclohexane and benzene was fed, through the pipe 2, int into the bottom portion of the reaction vessel 1. As soon as the starting material began to be added dropwise through the pipe 2, white solids formed simultaneously, with fumes being generated. As a result, the inside of the supply pipe 2 for the starting material was plugged, so that further addition was not possible.
As described above, according to the present invention, since fine metallic nitride powders having high purity which are especially useful for the manufacture of super hard heat resisting materials can be produced with high yield, the present invention has provided a significant advance in the technology relating to super high temperature apparatus such as rockets, missiles, plasma jets and the like; nuclear industries; chemical industries involving the handling of high temperature gases, and; the like .
Yamada, Tetsuo, Kawahito, Takashi, Iwai, Tadashi
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| Dec 20 1982 | Ube Industries, Inc. | (assignment on the face of the patent) | / |
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