JP4756259B2 - Method for producing single crystal having M-Al-B composition and single crystal having M-Al-B composition produced by the production method - Google Patents

Description

  The present invention relates to a method for producing a single crystal composed of Al (aluminum), M (M represents an alkali metal or alkaline earth metal) and B (boron), and more particularly, an M-Al-B composition. And a single crystal having an M-Al-B composition produced by the production method.

  Boron-rich highly boronated compounds having a skeleton of icosahedral boron are high-hardness materials for cutting tools, thermoelectric conversion elements, light-sensitive elements for photosensitive devices, neutron-absorbing materials, and heat resistance and hardness. The material is expected to be applied to a neutron detector and the like, and the present inventors have made various studies on its physical properties (Non-Patent Documents 1 to 3). As described in Non-Patent Documents 1 to 3, various physical properties have been studied for single crystals of highly borated compounds. However, the M-Al-B single crystal manufacturing method manufactured by the method described in Non-Patent Documents 1 to 3 is capable of manufacturing a single crystal having a large maximum size. From the viewpoint of overall production, the yield of single crystal production is not sufficient, and it is not sufficient to efficiently produce a single crystal of a predetermined size or more, which is sufficient for industrial use. Therefore, the examination of the application has been limited.

  For this reason, in the above non-patent literature, the hardness and the size of the largest single crystal produced are disclosed, and some basic physical properties are disclosed, but the M-Al-B composition is further disclosed. In order to study the industrial application of a single crystal having a high molecular weight, a new method for producing a relatively large M-Al-B single crystal with a higher yield than the above-described conventional production method has been required.

  Furthermore, in order to further examine industrial applications, M-Al-B single crystals produced by the above-described new production method have been required.

East et al., J. Crystal Growth, 128 (1993) 1113 Kudo et al., Jpn. J. Appl. Phys. Vol. 41, (2002) pp.L928-930 Okada et al., "Growth of new high boride single crystals from Na-Al-B flux", 48th Annual Meeting of Artificial Crystals, November 4, 2003, p.45-p.46

  The present invention solves the above-described problems in the production of a single crystal having a conventional M-Al-B composition (hereinafter simply referred to as a single crystal in the present invention), and provides this for the study of industrial applications. It is an object to provide a method for producing a single crystal having an M-Al-B composition having a sufficient amount and a crystal size, and a single crystal produced by the production method.

  As a result of diligent investigations, the present inventors have used, as an Al supply source to be used, flaky Al on which no oxide is formed on the surface, and actively heated in a reaction vessel in which the raw material is melted. It has been found that by forming a temperature gradient so as to cause convection, it is possible to produce a single crystal with high efficiency while promoting the generation of a single crystal having a crystal size of a certain size or more, and the present invention has been achieved. It is.

  That is, the present inventors suppress the production of bi-products by using Al having a fresh metal surface obtained by cutting an aluminum ingot as an Al supply source, instead of powdered aluminum. Furthermore, it has been found that the crystal growth of the single crystal of the present invention can be made efficient.

At the same time, in order to further improve the production efficiency of the single crystal, the reaction vessel is heated so as to generate a temperature gradient to increase the production efficiency of the single crystal, and between the boron supply source and the M supply source. The inventors have found that selective MAlB ₁₄ single crystals can be produced by setting the ratio (B / M) within a predetermined range, and the present invention has been achieved.

That is, according to the present invention, there is provided a method for producing a single crystal having a composition of M-Al-B, wherein the production method is cut out from an ingot and stored in a non-oxidizing environment or ingot in a non-oxidizing environment. The flaky Al from which the Al metal obtained by cutting is exposed, the M component supply source and the boron supply source, and the mixture of the flaky Al, the M component supply source and the boron supply source alternately. A single crystal having an M-Al-B composition is packed in a reaction vessel in a layered manner, melted by causing a temperature gradient between the central portion and the upper and lower ends of the reaction vessel, and then gradually cooled. A production method (wherein M represents an alkali metal or an alkaline earth element) is provided. The M of the present invention can be selected from one or more elements selected from the group comprising Li, Na, K, Rb, Cs, Be, Mg. The single crystal of the present invention is MALB _14. The mixing ratio of the boron component (B) and M components in the boron source and the M component supply source in the present invention (B / M), it is preferable to 1-4 at a mass ratio.

  According to the present invention, a single crystal having an M-Al-B composition can be selectively produced with high efficiency. As a result, a single crystal having an M-Al-B composition can be produced in a high yield. It can be produced as a relatively large crystal size. For this reason, it becomes possible not only to measure the crystal system and basic physical properties as described above, but also to provide an M-Al-B single crystal for examination of industrial applications.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited to the embodiments described below.

  FIG. 1 shows a manufacturing apparatus used in the present invention. The manufacturing apparatus shown in FIG. 1 generally controls an electric furnace 10, a gas supply system 12 for introducing a rare gas such as He, Ne, and Ar into the electric furnace 10, and the temperature of the electric furnace 10. Programmable controller 14. A reaction vessel 16 is disposed in the electric furnace 10, and single crystals are produced under a temperature and environment controlled by the electric furnace 10. The electric furnace 10 includes a heating means 18 and a heat insulating material 20 in order to generate a temperature gradient described later in the present invention. The reaction vessel 16 may be a reaction vessel formed of alumina, BN, fused quartz, or the like. In consideration of the influence of nitrogen and Si elements, in a specific embodiment, the reaction vessel 16 is made of alumina. It is preferable to use a Tamman tube (SSA type, manufactured by Nippon Special Ceramics Co., Ltd.). The manufactured single crystal is taken out from the electric furnace 10 after a programmed slow cooling operation to room temperature, washed with hydrochloric acid or the like, and then taken out as a single crystal.

  In the present invention, the single crystal is produced by mixing, melting, and cooling an Al supply source, an element supply source represented by M, and a boron supply source.

As a result of intensive studies, the present inventors have found that the surface oxide of aluminum greatly affects the formation of a single crystal. Aluminum is very susceptible to oxidation, and usually an Al ₂ O ₃ film is formed on the surface. That is, in the present invention, as the Al supply source to be used, flaky Al in which a fresh aluminum metal is exposed is used instead of Al that has been previously formed into a powder or a foil ribbon and an oxide is formed on the surface. Has been found necessary for the efficient formation of single crystals. Such flaky Al can be obtained by cutting from an Al ingot immediately before production and immediately storing it in a non-oxidizing environment. In the present invention, the cutting of the Al ingot can be automated, and the Al ingot can be cut in a non-oxidizing environment such as in an inert gas such as Ar.

  In addition, as the M component that can be used in the present invention, alkali metals and alkaline earth metals can be used, and alkali metal sources include metal sodium, metal lithium, potassium, rubidium, cesium, and these Preferably, it is selected from the group consisting of fluoride, chloride, carbonate, or tetraborate. The alkaline earth element is preferably selected from the group consisting of beryllium, magnesium, their fluorides, chlorides, carbonates, and tetraborate.

  Furthermore, in the present invention, high purity crystalline or amorphous boron can be used as the boron source, and is not particularly limited.

  FIG. 1 also shows the arrangement of the heating means 18 in the electric furnace 10. In the present invention, in order to give a temperature gradient to the reaction vessel 16, the heating means 18 is arranged at the highest density in the center of the reaction vessel and is formed so that the temperature becomes lower in the vertical direction. As the heating means 18, a resistance heating member known so far can also be used. The heating means 18 is formed so that the winding density is reduced from the center of the reaction vessel 16 to the upper and lower ends. In the present invention, the temperature in the reaction vessel 16 can be measured using a platinum-rhodium thermocouple, and other than this, several temperature measuring means known so far can also be used. In this case, the reaction temperature is measured by bringing a thermocouple into contact with the outer wall of the reaction vessel 16, and the temperature gradient is measured by the temperatures of the upper and lower end outer walls of the reaction vessel. In the present invention, the configuration of the heating means 18 is not particularly limited as long as the above-described effects can be given.

  As described above, the temperature gradient in the present invention is set so as to be highest at the central portion of the reaction vessel 16 and lower toward the upper end portion and the lower end portion. Although the temperature gradient varies depending on the size of the reaction vessel 16 to be used, it is preferable to set the temperature gradient so that a temperature difference of about 7 K to 10 K is given from the center to the upper end. Moreover, it is preferable to give a temperature gradient as a temperature difference of about 7K-10K also about the temperature difference from a center part to a lower end part. In certain embodiments of the invention, the above temperature difference provides a temperature gradient of approximately 2-5 K / cm. By providing the temperature gradient as described above, a convection heading upward from the central portion is formed, and at the same time, a stirring effect associated with mass transfer caused by the convection heading upward is given on the lower side. For this reason, the area | region in which the single crystal of this invention is formed in the inside of the reaction container 16 can be increased.

  In the present invention, examination is made to further increase the reaction efficiency, and the flaky Al and the M supply source such as powdered Na and Li and the boron supply source are not mixed uniformly but alternately. It has been found that the reaction efficiency can be further increased by laminating the layers. Among the components described above, when a material other than an alkali metal is used, the lowest melting point is about 660 ° C. of aluminum. Therefore, by laminating aluminum in layers rather than mixing aluminum and other components evenly, the molten aluminum component reacts more efficiently with other components, and M as a fresh Al metal. It is believed that the reaction with the source and the B source promotes the formation of the single crystal of the present invention.

In the present invention, the composition ratio of the raw material mixture can be set such that the compounding ratio of the boron component (B) and the M component is in a mass ratio of 0.2 ≦ B / M ≦ 8, more preferably, The range can be 1 ≦ B / M ≦ 4. It has been found that the (B / M) ratio has an important influence on the production of the single crystal of the present invention, and promotes the selective production of the crystal of the present invention particularly in the range of 1.0 to 4.0. Even if the (B / M) ratio is lower than 1, the single crystal of the present invention can be produced, but the yield tends to decrease as the B supply source decreases. Further, the blending ratio (B + M): Al of the (B + M) component and the Al flakes can be within a range of 1:15 to 1:20 by mass ratio. In the present invention, α-AlB ₁₂ , β-AlB ₁₂ and AlB ₂ crystals are also produced as a biproduct. In particular, according to the method of the present invention, it is possible to form a single crystal that is more efficient and relatively larger than the amount of biproduct produced such as α-AlB ₁₂ , β-AlB _12, and AlB ₂ .

  Hereinafter, the production method of the present invention will be described in detail. The heating sequence in the present invention is shown in FIG. In the present invention, the temperature is raised from room temperature to a temperature at which each component is sufficiently melted at about 300 K / hr, then maintained at a temperature of about 1500 K to 2000 K for several hours, preferably about 1 hour, and then about 50 K / hr. Slowly cool at a rate of hr. If the temperature is lower than 1500 K, the efficiency of melting and mass transfer is low, and the yield of single crystals is lowered. If the temperature is higher than 2000 K, sublimation of components occurs, and the yield of single crystals is similarly lowered. Further, it was found that when the slow cooling rate is further reduced, the formation of the single crystal itself is promoted although the crystal shape becomes irregular. Further, when the cooling rate is further increased, the shape of the crystal changes from a plate-like crystal to a needle-like crystal, and although the number increases, it is difficult to obtain a crystal having a certain size (crystal size). Obtained.

  For this reason, in the present invention, the slow cooling rate can be set in the range of several K / hr to about 200 K / hr. From the viewpoint of obtaining crystals having cooling efficiency and a certain size or more, It is preferable to set it as the range of K-50K / hr. Moreover, in this invention, after each phase becomes below thermodynamically stable temperature (about 1000K-800K), it is preferable from a viewpoint of improving manufacturing efficiency to cool with a still higher cooling rate.

  After slow cooling, the reaction mass is acid washed to separate the single crystal of the present invention. Although various acids such as hydrochloric acid, sulfuric acid, and nitric acid can be used for this acid cleaning, it is preferable to use dilute hydrochloric acid from the viewpoint of the persistence and removability of the components after the cleaning.

  The single crystal described above can be separated using a mesh or the like to separate crystals having a size larger than a predetermined size. In the present invention, the crystal having a predetermined size means a single crystal having a size of approximately 200 μm or more. Further, when the shape of the crystal is three-dimensional, it means the maximum length of the crystal plane. In addition, a mesh having an opening of about 80 μm can be used as the mesh having an opening of about 200 μm.

FIG. 3 shows a scanning electron micrograph (JEOL, T-20) of the NaAlB ₁₄ single crystal obtained in the present invention. As shown in FIG. 3, it is shown that the obtained crystal is produced as a columnar crystal. The crystal size is about 500 μm along the maximum side of the single crystal, and has a size of about 200 μm × 300 μm on the (100) plane orthogonal to the maximum side. It is shown to have. FIG. 4 shows a powder X-ray diffraction pattern obtained using a powder X-ray diffractometer (RIGAKU, RU-200). The peak indicated by ◯ is a peak due to NaAlB ₁₄ obtained by the present invention, and Δ is the peak of Al ₂ O ₃ due to contamination due to the reaction vessel. Furthermore, the present inventors performed a crystal structure simulation using the obtained powder X swirl folding pattern data. In the simulation, simulators SIR92 and SHELXL-97 were used. The result of the crystal structure simulation is shown in FIG. As shown in FIG. 5, the obtained single crystal was shown to be an orthorhombic system having a space group Imma of a conventionally reported MAlB ₁₄ single crystal.

Hereinafter, the present invention will be described with specific embodiments, but the present invention is not limited to the examples described below.
Example 1
Al flakes cut from an aluminum ingot (purity 99.99%: Sumitomo Chemical Co., Ltd.), Na ₂ B ₄ O ₇ (purity 99%: Aldrich Chemical Co., Ltd.) as the sodium source, and crystalline boron as the boron source (Purity 99%: Mitsuwa Chemicals Co., Ltd.), the B / Na ratio is set to 2.0, and the ratio of (B + Na): Al flakes is set to 1:15 by weight, and Al ₂ An O ₃ reaction vessel (SSA type, Nippon Special Ceramics Co., Ltd.) was filled. At the time of filling, the Al flakes are stacked at the bottom, and the powder of the Na source and the B supply source are added thereon, and then Al flakes are further deposited, and this is repeated several layers. Source powder was placed.

Thereafter, the reaction vessel is covered with an Al ₂ O ₃ lid, and the reaction vessel is immediately set in an electric furnace replaced with Ar, heated at a heating rate of 300 K / hr, held at about 1600 K for 1 hour, and then gradually The solution was gradually cooled to about 1073 K at a cooling rate of 30 K / hr. Then, it cooled at about 400 K / hr. At this time, the center of the reaction vessel became the highest temperature, and a temperature gradient of about 4 K / cm was given at the upper and lower ends of the reaction vessel. The temperature increase rate, the holding temperature, and the slow cooling rate are the temperatures at the center of the reaction vessel. Then, after cooling a reaction container to room temperature, the rod-shaped thing in reaction container was wash | cleaned with the diluted hydrochloric acid-ethanol mixed solution, and the produced | generated single crystal was isolate | separated. The separated single crystals were classified with a mesh having an opening of about 200 μm, and single crystals having a size of 200 μm or more were separated.

Table 1 shows the X-ray diffraction data of NaAlB ₁₄ obtained. Table 2 shows the results of elemental analysis of single crystals obtained using EPMA (JEOL Co., JXA-8600MX) with NaAlSi ₃ O ₈ and B _4.5 C as standard samples.

As shown in Table 1, the X-ray diffraction data of the obtained single crystal was in good agreement with the data of NaAlB ₁₄ obtained in the past, and as shown in Table 2, the elemental analysis values were obtained. In the manufacturing method of the present invention consistent with the present invention within the error range, it was shown that the single crystal was manufactured. Furthermore, a considerable amount of single crystals remained on the mesh, and crystals having a crystal size of 200 μm or more were generated in a considerable proportion.

(Examples 2 to 5)
NaAlB ₁₄ was produced in the same manner as in Example 1 except that the B / Na ratio was changed to 1.0, 4.0, 6.0, and 8.0. went. The obtained results are shown in Table 3 together with the results of Example 1.

(Example 6)
Using lithium tetraborate (Li ₂ B ₄ O ₇ : purity 99%, Aldrich Chemical Co., Ltd.) as the M supply source, the temperature was raised at a temperature rising rate of 300 K / hr, held at about 1573 K for 1 hr, and then gradually A single crystal (LiAlB ₁₄ ) was produced and evaluated in the same manner as in Example 1 except that it was cooled to room temperature at a cooling rate of 50 K / hr.

(Example 7)
A single crystal (MgAlB ₁₄ ) was produced in the same manner as in Example 1 except that basic magnesium carbonate (MgCO ₃ , heavy: Wako Standard Practical grade, Wako Pure Chemical Industries, Ltd.) was used as the M supply source. And evaluated. The obtained results are shown in Table 3.

(Examples 8 to 17)
A single crystal was produced and evaluated in the same manner as in Example 1 except that a source corresponding to Na, K, Rb, Cs, Be, and Mg was selected from M as fluoride and carbonate. Examples 8-14). The results are shown in Table 3. Moreover, the B / M ratio was further changed to produce a single crystal in the same manner as in Example 1, and the upper limit of the B / M ratio was examined (Examples 15 to 17). The results are shown in Table 3.

(Comparative Examples 1-6)
Example 1 except that aluminum powder was used and uniformly mixed as an aluminum source, and the resulting mixture was charged into a reaction vessel and reacted in a commercial electric furnace without causing a temperature gradient. A single crystal was produced in the same manner as in Example 6. The obtained results are shown in Table 3. As shown in Table 3, in Examples 1 to 6, a sufficient amount of single crystal was obtained, but in Comparative Examples 1 to 6, crystals having a size of 200 μm or more were hardly obtained. Recognize. For this reason, the single crystals produced in Comparative Examples 1 to 6 had to be subjected to various evaluations by selecting the crystals using a stereomicroscope.

(Comparative Examples 7 and 8)
As Comparative Example 7 and Comparative Example 8, single crystals were produced in the same manner as in Example 1 except that they were changed to 16, 20, and the selective production of the single crystals of the present invention with respect to other compounds was measured. In the measurement, the sample was pulverized, powder X-ray diffraction measurement was performed, and measurement was performed using the peak ratios of AlB _2, α-AlB _12, and β-AlB ₁₂ crystals.

Figure 6 shows the rate of production of single crystals of Examples 1 to 5, Example 15~17 NaAlB ₁₄ which were obtained in Comparative Examples 7 and 8. The production rate was determined by grinding the product and using the peak intensity ratio in powder X-ray diffraction. With single crystals of NaAlB ₁₄ the ratio of B / Na is increased, easily crystals AlB ₂ and _{alpha-AlB 12} and _{beta-AlB 12} is formed, that the yield of NaAlB ₁₄ single crystal is lowered shows Has been. On the other hand, when B / Na = 1.0 or less, the generation of biproduct is not remarkable, but the amount of the single crystal of the present invention is small, and it is not sufficient to obtain a single crystal efficiently.

  Further, Table 4 shows the hardness of each crystal plane obtained by the micro Vickers hardness tester (JISZ2244) for the single crystals obtained in Example 1, Example 6, and Example 7. As shown in Table 4, the Vickers hardness of the single crystal obtained in the present invention shows the same value as that obtained by the conventional method, and has a high hardness comparable to about SiC (about 28 GPa). It was shown that it was maintained.

  As described above, according to the present invention, it is possible to efficiently produce a single crystal having an M-Al-B composition, and the M-Al-B-based material is a high-hardness material for a cutting tool, thermoelectric conversion. It is possible to study as a material expected to be applied to an element, a light detection element of a photosensitive device, a neutron absorbing material, and a neutron detection apparatus.

The figure which showed schematic structure of the electric furnace used in this invention. The figure which showed the temperature control profile in this invention. It shows a scanning electron microscope photograph showing the crystal structure of NaAlB ₁₄ obtained in the present invention. It shows the powder X-ray diffraction pattern of NaAlB ₁₄ obtained in the present invention. Figure crystal structure of the obtained NaAlB ₁₄ single crystal in the present invention was simulated. The figure which showed the relationship of B / Na ratio in this invention, and biproduct production | generation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electric furnace: 12 ... Gas supply system: 14 ... Programmable controller: 16 ... Reaction container: 18 ... Heating means: 20 ... Heat insulation material

Claims (4)

A method for producing a single crystal having a composition of M-Al-B, which is obtained by cutting from an ingot and storing it in a non-oxidizing environment or cutting an ingot in a non-oxidizing environment. The reaction vessel is filled with the flaky Al from which the metal is exposed, the M component source and the boron source, and the mixture of the flaky Al and the M component source and the boron source alternately in layers, A method for producing a single crystal having an M-Al-B composition, in which a temperature gradient is generated between a central portion of the reaction vessel and an upper end portion and a lower end portion, and the mixture is melted and gradually cooled (wherein M is Indicates an alkali metal or alkaline earth element).   The manufacturing method according to claim 1, wherein M is selected from one or more elements selected from the group including Li, Na, K, Rb, Cs, Be, and Mg. The manufacturing method according to claim 1, wherein the single crystal is MAlB ₁₄ . Said boron component (B) and M component compounding ratio of the M component supply source and the boron source the (B / M), and 1-4 at a mass ratio, according to any one of claims 1 to 3 Manufacturing method.