JPH0336800B2 - - Google Patents

Description

[Detailed description of the invention]

≪Industrial Application Fields≫ The present invention applies to beryl single crystals (emeralds doped with Cr ions), which are currently widely used as decorative synthetic gemstones and are expected to become important crystals in the field of laser optics in the future. It concerns methods for improving quality. ≪Summary of the Invention≫ The present invention uses beryl single crystal, which has many defects and impurities and cannot be used as an optical grade, as a raw material, and in an autoclave, NaNO 3 , NaNO ₃ ,
By recrystallizing the raw material by applying a predetermined temperature and pressure with an aqueous alkali metal nitrate solution such as KNO ₃ or LiNO ₃ , it is possible to reduce defects and impurities and provide optical grade and uniform beryl single crystals. It is possible. <<Prior Art>> Previous attempts to synthesize beryl single crystals by human hands have been made using various methods, mainly in the field of emeralds doped with Cr ions, which also aim to be used as synthetic gemstones. The main methods are flux method and hydrothermal synthesis method. In the flux method, a mixture of Li ₂ O, MoO ₃ , etc. is used as a flux, and
Beryl single crystals are produced by melting Al ₂ O ₃ , BeO, and SiO ₂ into a flux molten at a high temperature of around 1000°C, and then creating a temperature difference or slowly cooling it.
Be ₃ Al ₂ (SiO ₃ ) ₆ is synthesized. On the other hand, in the hydrothermal synthesis method, HCl, HF,
Acidic aqueous solutions such as NH ₄ F are mainly used, and the raw materials are Al(OH) ₃ , Be(OH) ₂ , and SiO ₂ at 500°C.
Dissolve it in an aqueous solution in an atmosphere of around 1000Kg/ ^cm2 ,
Beryl single crystal is produced by applying a temperature difference.
Be ₃ Al ₂ (SiO ₃ ) ₆ is synthesized. This prior art is described in detail in the following documents. Kurt Natsou James Made By
Man (1980 Chilton Book Company)
Radnor Pennsylvania) 125−158 (Kurt
Nassau, Ph.D.GEMS MADE BY MAN
(1980 Chilton Book Company Radnor,
Pennsylvania) 125-158 <<Problems to be Solved by the Invention>> The prior art as described above has the following problems. (1) There are many defects inside the single crystal. This is especially noticeable in the flux method;
Single crystals are synthesized from molten flux at a high temperature of around 1000°C, so flux is poured into it.
It becomes an internal flaw as an inclusion. In addition, in the flux method, internal strain caused by high temperatures around 1000°C also causes large defects. In any case, crystals synthesized by the flux method may cause optical damage or scattering due to internal defects, and cannot be used as optical grade materials that use lasers. On the other hand, in the hydrothermal synthesis method, the solvent is an aqueous solution with a lower viscosity than in the flatus method, and the synthesis temperature is also low at around 500°C, so the degree of occurrence of inclusions or internal distortion due to heat is low, and there are fewer defects. This is a method that can synthesize small single crystals. However, even in this hydrothermal synthesis method, in the case of beryl single crystals, it is common to use extremely corrosive solutions such as hydrochloric acid, and impurities from the autoclave (usually sealed with a noble metal liner) are used. It is impossible to completely eliminate the introduction of impurities)
becomes a problem. Furthermore, the presence of microracks is a problematic defect in both the flux method and the hydrothermal synthesis method. This is beryl crystal
This becomes clearer when doping with Cr ions, Nd ions, etc., but in the case of natural emeralds, it is said that there is no rough stone without cracks, and beryl single crystals are prone to cracks, and these micro-cracks and their causes are Removal of distortions, inclusions, impurities, and dislocations is a major challenge for laser optical materials. (2) The physical properties of the single crystal are non-uniform depending on the location. Another problem with materials for laser optics is the problem of material non-uniformity. This is the same in both the current flux method and hydrothermal synthesis method, and the problem is that physical properties such as specific gravity and refractive index differ depending on the portion of the single crystal. (In the case of synthesized emerald, the specific gravity is between 2.65 and 2.69, and the refractive index is between 1.560 and 1.576.) This is the oxidation of a ternary system of Al, Be, and Si, such as beryl single crystal. In the case of beryl, the stability range as a beryl single crystal is narrow because each oxide has a different solubility in flux or aqueous solution. If you try to synthesize beryl single crystals in this narrow area, mainly for the purpose of obtaining large crystals rather than the presence of defects, such as for use as synthetic gemstones,
It is more efficient to separate each oxide raw material and mix them individually to prepare a raw material, and it is possible to obtain a large single crystal. However, in this case, Al ₂ O ₃ , BeO, SiO ₂ is produced in the flux method, and Al in the hydrothermal synthesis method.
The ratio of the concentrations of each component of the raw material (OH) ₃ , Be(OH) ₂ , and SiO ₂ changes as the crystal synthesis progresses and grows into a large crystal, and the ratio of the concentrations of the synthesized single crystal changes accordingly. It also causes non-uniformity in physical properties. This problem becomes even more serious when attempting to dope with transition metal element ions such as Cr ions, rare earth metal element ions such as Nd ions, etc. In order to eliminate this problem, a method is required that does not change the balance of the concentration of raw materials as the crystals are synthesized. ≪Means for solving the problems≫ In order to solve the two problems associated with the synthesis of beryl single crystals: (1) defects and (2) non-uniformity, the conventional technology of hydrothermal synthesis was further developed. I got the means to do it. The summary is as follows. (1) Among crystal synthesis methods, hydrothermal synthesis has a greater possibility of minimizing internal defects. (2) In order to eliminate non-uniformity inside the single crystal, a raw material with the composition of beryl single crystal Be ₃ Al ₂ (SiO ₃ ) ₆ is used. (3) An aqueous alkali metal nitrate solution is used as a solvent for stable recrystallization of beryl single crystals. <<Operation>> In order to remove internal defects, which is one of the problems, it is effective to employ the hydrothermal synthesis method as described above.
However, in conventional hydrothermal synthesis methods, the oxides or hydroxides of Al, Be, and Si are separated and used individually as raw materials in the form of a mixture. Therefore, as the synthesis progresses, the ratio of the concentrations of each component changes compared to the initial stage. Changes in the concentration ratio of each component in this aqueous solution cause non-uniformity of the synthesized crystal. In order to remove this, it is sufficient to use a raw material in which the ratio of the concentrations of each component is constant from the beginning to the end of the reaction.In other words, it is ideal to use a beryl single crystal similar to the target beryl single crystal as a raw material. be. Although it is possible to form a ceramic by mixing and firing each component to have the composition of a beryl single crystal, it is more effective to use a single crystal as a raw material. Next, we needed a solvent that could dissolve and recrystallize the beryl single crystal in the form of a ternary oxide without decomposing it, and we discovered an aqueous alkali metal nitrate solution as one of the ideal solvents. Hereinafter, a detailed explanation will be given based on examples. <<Example>> Raw material preparation First, beryl single crystal is prepared as a raw material. This is a commercially available high-purity reagent Li ₂ O using the Fratus method.
MoO ₃ was used as a flux, and commercially available high-purity reagents Al ₂ O ₃ , BeO, and SiO ₂ were heated at 1100°C as raw materials.
A beryl single crystal can be easily obtained by a known method such as dissolving it in a flux in a platinum crucible and slowly cooling it. 30 hours after 2 hours of dissolution
By slow cooling to 900°C and then rapid cooling to room temperature, countless hexagonal columnar beryl single crystals with a length of about 0.5 mm can be synthesized. Also, unlike green emerald, colorless beryl rough is easily available, so it can also be used as a raw material. In any case, it is used by crushing it into powder with a milk pestle. Apparatus and process The structure of the experimental autoclave and test tube used is shown in Figure 1. Autoclave body 1
is pressure-sealed by a plunger 2 through a cover 3. The plunger 2 is provided with a pressure measurement hole 4, and is connected to a pressure gauge through the pressure measurement hole 4, making it possible to measure the pressure inside the autoclave.At the same time, it is also connected to an external pump to measure the pressure inside the autoclave using distilled water as a medium. It is possible to adjust the pressure. On the other hand, a gold capsule 5 is installed inside the autoclave, and inside the gold capsule 5, the raw material 6 prepared as described above and an aqueous alkali metal nitrate solution 7 serving as a solvent are sealed at an appropriate filling rate. There is. Encapsulation is done by electric welding to ensure complete sealing. A test tube with the above structure is installed in an electric furnace. When this test tube is heated, the gold capsule 5 is also heated, and a quantity of distilled water is generated inside the gold capsule depending on the filling rate of the aqueous alkali metal nitrate solution and the heated temperature. Balance is achieved by injecting and generating pressure,
Prevents the gold capsule from bursting or collapsing. Hydrothermal treatment results Table 1 shows the results of hydrothermal treatment. First, a 3-molar solution of LiNO ₃ , a 3-molar solution of KNO ₃ , and a 3-molar solution of NaNO ₃ are used individually as aqueous solutions of alkali metal nitrates. A detailed explanation will be given below according to Examples and processing numbers. Processing No. A uses as a raw material a beryl single crystal synthesized by the above-mentioned flux method using a LiNO ₃ solution (hereinafter referred to as flux rigid crystal), which is heated to 800 kg/cm ² at 380°C in a gold capsule. Te7
After being treated for several days, the entire autoclave was placed in water and rapidly cooled. When the gold capsule was opened after treatment, hexagonal columnar microcrystals were observed at the top of the gold capsule. This microcrystal had a shape clearly different from that of the raw material powder, and when fixed by X-ray diffraction, it was confirmed that it was a beryl single crystal. In other words, the gold melts into the solution due to the temperature difference inside the gold capsule.
Be ₃ Al ₂ (SiO ₃ ) ₆ became supersaturated and recrystallized on the upper inner wall of the gold capsule at a lower temperature. The recrystallized beryl single crystal was large enough to evaluate its optical properties, and its optical properties were evaluated using an optical microscope. Although some cracks were observed, the beryl crystal obtained by the cracks method was used as the raw material. In comparison, there are no obvious defects such as internal inclusions, and the properties are greatly improved by recrystallization. The following are similar processing and evaluation methods. Treatment No. B was similarly treated at 390° C. and 750 kg/cm ² for 7 days using a KNO ₃ solution and flux synthetic crystals as the raw material. In this case as well, the beryl single crystal could be recrystallized. Its optical properties include processing
There are even fewer cracks than No. A, and it can be said to be at a sufficiently optical level. Treatment No. C was treated at 380° C. and 700 Kg/cm ² using flux synthetic crystal as a raw material with NaNO ₃ solution, but no recrystallized beryl single crystal could be observed. NaNO ₃ uses KNO ₃ , LiNO ₃ as a solvent
It is more inert, so the recrystallization temperature has to be increased and at 380°C the solubility of the raw material is still insufficient. The following examples are all based on NaNO ₃ solutions. Treatment No. D was treated at 390℃ and 800Kg/cm ² using flux synthetic crystals as raw materials.
Recrystallized beryl single crystals were observed. Similar to Matsutaku, treatment No.E is 400℃, 750Kg/cm ² , treatment No.F
is 410℃, 700Kg/cm ² , Processing No. G is 420℃, 800Kg/cm 2
A beryl single crystal that had been treated and recrystallized at cm ² was observed. Treatment No. H was treated at 430° C. and 750 kg/cm ² , but recrystallization of the beryl single crystal was not observed, but other crystals were observed. Although it was fixed by X-ray diffraction, it is assumed that it is not a beryl single crystal but a composite oxide or hydroxide of Al, Si, etc. That is, it seems that the beryl single crystal Be ₃ Al ₂ (SiO ₃ ) ₆ did not recrystallize but decomposed into oxides or hydroxides such as Al and Si. To summarize the results of the NaNO ₃ solution made from flux synthetic crystals, the processing temperature range in which recrystallization is possible is 380°C.
℃ to 430℃, and when the temperature exceeds 400℃, it becomes easier to obtain larger beryl single crystals.As for its optical properties, there are few cracks and all of them are at the optical level, but especially between 390℃ and 410℃. Cracks are minimized. In other words, overall
The highest processing temperature is around 410°C, and beryl single crystals with excellent optical properties can be obtained. (Empirically, the major factor in this case is temperature, and pressure is 700
It is thought that the change from Kg/cm ² to 800 Kg/cm ² has almost no effect) Finally, in Process No. I, the raw material was changed from flux synthetic crystal to natural beryl single crystal powder, and the same was true. A recrystallized beryl single crystal can be obtained. Although its properties are lower than those of flux synthetic crystals, it can be used industrially. FIG. 2 shows a diagram showing the relationship between temperature and solubility of a beryl single crystal in a 3-molar NaNO ₃ solution. 380℃
There is almost no melting in the vicinity, but when the temperature exceeds 390℃, melting starts and progresses to around 430℃.
When the temperature exceeds 430°C, the beryl single crystal begins to decompose, and its solubility appears to increase rapidly.

【table】

【table】

[Table] ○…Beryl single crystal is grown.
×... Beryl single crystal is not grown.
≪Effects of the Invention≫ As detailed above, in the present invention, it is possible to recrystallize a beryl single crystal in an extremely stable state by hydrothermal treatment in an aqueous solution of alkali metal nitrate, and as a result, internal defects can be eliminated. and non-uniformity can be removed, and the effect is extremely large. In particular, by using an aqueous alkali metal nitrate solution, which has not been used until now,
Since sufficient solubility can be obtained at temperatures as low as around 100°C, beryl single crystals with excellent optical quality can be obtained at lower temperatures. Among alkali metal nitrate aqueous solutions, particularly good results are obtained with NaNO ₃ aqueous solutions. Although no additive elements were added in the examples of the present invention, the present invention can also be applied to beryl single crystals doped with transition metal ions such as Cr ions, or doped with rare earth metal ions such as Nd ions. Of course. The present invention provides a basic manufacturing method for the industrialization of optical grade beryl single crystals in the future.Based on the present invention, a temperature difference is created using seed crystals that are currently being mass-produced as artificial quartz crystals. It is extremely easy to develop a method for obtaining large single crystals through long-term growth, and its effects are extremely large.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing the structure of the test tube.
FIG. 2 is a characteristic diagram showing the solubility of beryl single crystal in a 3 molar NaNO ₃ solution. 1... Autoclave body, 2... Plunger, 3... Cover, 4... Pressure measurement hole, 5... Gold capsule, 6... Raw material, 7... Nitrate aqueous solution.

Claims (1)

[Claims] 1. Beryl, characterized in that a raw material is placed in an autoclave filled with an aqueous solution containing an alkali metal nitrate as a main component, and a predetermined temperature and pressure are applied to recrystallize a beryl single crystal. Method for recrystallizing single crystals. 2. The recrystallization method according to claim 1, wherein the nitrate is NaNO ₃ . 3. The recrystallization method according to claim 1, wherein the nitrate is _KNO3 . 4. The recrystallization method according to claim 1, wherein the nitrate is LiNO ₃ . 5. The recrystallization method according to claim 1, wherein the raw material is natural beryl single crystal. 6. The recrystallization method according to claim 1, wherein the raw material is a beryl single crystal synthesized by a flux method.