JP2610638B2 - Single crystal manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a single crystal having a large grain size and a uniform phase.

[Conventional technology and its problems]

2. Description of the Related Art In recent years, in the field of optical information and optical communication using laser oscillation, opportunities to utilize the functions of compounds in the form of single crystals are increasing. In particular, the role of the organic single crystal is increasing from the viewpoints of environmental resistance, durability against a light source, ease of imparting a function by molecular design, and the like. When an organic single crystal is used industrially in an actual application field, it is necessary to process it to a certain size with high precision. Therefore, it is desirable to cut out a single crystal as large as possible. Furthermore, in order to exhibit a sufficient function, it is necessary to minimize the non-uniformity of crystals caused by lattice defects and transformation phenomena.

As a method for forming a single crystal with an organic compound, since the organic compound itself generally has a low melting point and is easily decomposed even below the melting point, a single crystal is grown by a solution method as compared with other single crystal generation methods. Is most preferred. The solution method includes a solution temperature constant cooling rate method and a solution temperature constant method. Originally, the organic compound itself has low symmetry, and in a crystalline state, a weak intermolecular bond called van der Waals bond allows a crystalline state to be formed. In addition, a constant solution temperature cooling rate method involving a temperature change of the solution is not preferable in that a uniform phase crystal is grown, for example, because a transformation phenomenon occurs due to a subtle change in temperature conditions.

Also, in the solution temperature constant method, that is, in the crystal precipitation method in which the degree of supersaturation of the solution is constant, when the grown single crystal is small, that is, when the single crystal surface area is small, the surface area is large compared to the single crystal surface area. To increase. On the other hand, a single crystal grows,
When the single crystal surface area is increased, the increase in the surface area is smaller than when the grown single crystal is small, and thus the crystal line growth rate is reduced. In other words, when trying to grow a single crystal while maintaining a constant solution temperature and a constant solution supersaturation degree, the crystal line growth rate after the start of growth is large, but as the single crystal grows, the crystal line growth rate decreases, It becomes difficult to obtain a large single crystal.

[Means for solving the problem]

In view of the above, the present inventor has worked diligently to develop a huge and uniform single crystal that can be practically used industrially by a solution method, with a simple method, and completed the present invention. Things.

That is, the present invention, when obtaining a single crystal from the solution,
By detecting the size of the single crystal, the concentration of the solution in the single crystal growing tank is adjusted so that the degree of supersaturation is gradually increased within the range of 1.1 or less, and the crystal line growth rate of the single crystal is controlled. And a method for producing a single crystal.

The present invention seeks to control the crystal line growth rate by manipulating the solution concentration, thereby adjusting the degree of supersaturation.

In the present invention, the solution concentration is manipulated by means as exemplified below, but other means may be used as long as the solution concentration can be manipulated as well as these means. .

 There are the following methods for operating the solution concentration.

(A) Separating the crystallized solute dissolution tank and the crystal growth tank maintained at a constant temperature, connecting both tanks so that the solution circulates, and adjusting the flow rate in the part flowing from the dissolution tank to the growth tank, Adjust the concentration.

(A) Separating the crystallization solute dissolving tank and the crystal growing tank, connecting both tanks so that the solution circulates, and changing the temperature of the dissolving tank to adjust the concentration of the crystal growing tank.

(C) The concentration in the tank is adjusted by controlling the evaporation rate of the solvent by flowing gas into the evaporation area of the solvent in the crystal growth tank.

(D) The evaporation rate of the solvent is controlled by applying a pressure reducing operation to the evaporation area of the solvent in the crystal growing tank, and the concentration in the tank is adjusted.

In the above method, automatic control may be performed in a sequence or manual operation may be performed. Further, these methods may be variously combined.

The timing for adjusting the crystal line growth rate is such that the crystal line growth rate is at least 1 mm / day, preferably 2 mm / day or more.

The method of adjusting the crystal line growth rate is achieved by increasing the solution concentration in the crystal growing tank from before the adjustment, that is, by increasing the degree of supersaturation. Even after the concentration of the solution is adjusted, the growth rate of the crystal line gradually decreases as the growth of the single crystal continues. In that case, adjust the solution concentration again,
A higher concentration, and thus a higher supersaturation, than before adjustment. That is,
In order to control the crystal line growth rate together with the growth of the single crystal, the concentration of the solution is kept at a low supersaturation level at the start of crystal growth, and is maintained at a high supersaturation level as the single crystal grows. The solution supersaturation at the start of crystal growth and the change in supersaturation due to adjustment are preferably controlled to a supersaturation of 1.1 or less and a supersaturation change of 0.001 or less, at which secondary nucleation due to differences in the target substance and operating conditions is suppressed. Preferably at the start of crystal growth supersaturation 1.00001 ~ 1.01, more preferably 1.0
0001 ~ 1.0001, supersaturation 1.
00003 to 1.08, more preferably 1.00005 to 1.01, and particularly preferably, the degree of supersaturation is 1.00001 to 1.0 at the start of crystal growth.
[0003] With the growth of the single crystal, the degree of supersaturation is 1.00025-1.0005.
It is.

The optimal operating temperature for growing a single crystal is preferably a temperature not higher than the thermal decomposition temperature of the single crystal substance and not higher than the boiling point of the solvent substance.

The single crystal compound to be obtained may be inorganic or organic, but the method of the present invention is more difficult to obtain organic,
In particular, in the case of a molecular crystal (thiourea, octane, nitrobenzene, stearic acid, oxalic acid, pentaerythritol) in which intermolecular bonds are formed only in Van der Waals bonds, the effect is further exhibited.

The method of the present invention is particularly suitable for various applications (elements for optoelectronics, optical elements, elements for quantum electronics, etc.). Ideal for growing crystals.

The crystal line growth rate is determined by monitoring the crystal length in the growth tank using a video camera or the like and determining the change in the size per unit time. The solution concentration is measured using a refractometer or the like. From the crystal line growth rate and the solution concentration measured as described above, the solution concentration was increased so that the crystal line growth rate could be kept constant,
Try to increase the degree of supersaturation.

The apparatus used is preferably made of a transparent material (glass, acrylic resin, polycarbonate resin, polystyrene resin, etc.) in order to observe the crystal length, but is not limited to these, and by using an optical fiber or the like, It may be opaque as long as the crystal length in the crystal growth tank can be observed. When detecting the concentration of the solution, the container may be transparent or opaque, but a circulating system for guiding the solution to the refractometer or other concentration detecting means (sensor) is required.

In practicing the present invention, it is also possible to use a combination of other methods for obtaining a commonly used single crystal, a solution temperature constant cooling rate method, and furthermore, the crystal growth tank is cooled to a predetermined supercooling temperature at the start. Keeping is also an effective method. Preferably, the use of a seed crystal is also an effective method. The seed crystal to be used may have the same composition as the compound to be crystallized, or may be another compound capable of epitaxial growth in some cases.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 A two-chamber circulation type apparatus as shown in FIG. 1 was assembled in a constant temperature and humidity room at a temperature of 25 ° C. and a humidity of 60% to grow a single crystal of urea.

The crystal growing tank 1 and the crystallized solute dissolving tank 2 are both 1-volume glass containers with a jacket. The crystal growing tank 1 is circulated from the thermostat 3 and the crystallized solute dissolving tank 2 is circulated from the thermostat 4. A controlled temperature of ± 0.1 ° C. was obtained with water.

Urea was used as a crystallizing substance, and water was used as a solvent. A commercial urea (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) was recrystallized twice,
Further, a substance purified by sublimation at 10 ⁻³ Torr and 90 ° C. to an impurity concentration of 1 ppm or less was used, and water obtained by ion-exchanging tap water and then distilling three times was used.

A seed crystal 6 having a (110) / (110) face-to-face distance of 2 mm was attached to the tip of a platinum wire, hung in a crystal growing tank 1, and a video camera 8
To monitor the state of crystal growth, and adjust the flow rate from the crystallization solute dissolving tank 2 to the crystal growing tank 1 by the quantitative pump 5 connecting the two tanks so that the crystal line growth rate can be controlled.
Urea single crystal was grown.

For single crystal growth, both the crystal growing tank 1 and the crystallized solute dissolving tank 2 are set to 45 ° C., and the crystal growing tank 1 is saturated at 45 ° C. Thereafter, the crystal growing tank 1 was cooled to 44 ° C., and a seed crystal was suspended. At this time, the crystallization solute dissolution tank 2 was maintained at 45 ° C., and the solution was circulated from the crystallization solute dissolution tank 2 to the crystal growth tank 1 at a flow rate of 0.2 ml / min immediately after the seed crystal was added. The degree of supersaturation immediately after seed crystal addition, that is, immediately after the start of single crystal growth, was 1.000013, and the crystal growth rate was 100.8 mm / day. After 60 minutes, the degree of supersaturation did not change, but the growth rate of the crystal line decreased to 30.6 mm / day, and at this time, the distance between (110) / (110) planes (hereinafter referred to as “crystal length”) was 4.2 mm. . After 24 hours, the crystal growth rate was reduced to 3.9 mm / day. The crystal length at this time is 10.7m
m. At this point, in order to increase the crystal growth rate, the inflow rate from the crystallized solute dissolution tank 2 into the crystal growth tank 1 was increased to 0.3 ml / min in order to increase the degree of supersaturation. The degree of supersaturation immediately after this adjustment operation was 1.000027, and the crystal growth rate was 4.4 mm / day. After 48 hours, the crystal growth rate was reduced to 2.9 mm / day, at which point the flow rate was increased to 0.4 ml / min. Immediately after this operation, the degree of supersaturation is 1.00003, and the crystal growth rate is 3.9 mm / day. After 72 hours, the crystal line growth rate is 2.6mm / day, and the crystal length is 29.8mm
Met. After 72 hours, the inflow rate is 0.5 ml / day
Was raised. Immediately after this operation, the degree of supersaturation was 1.000038, and the crystal line growth rate was 3.3 mm / day. Thereafter, the growth of the single crystal was continued until 100 hours. The crystal length after 100 hours was 26.2 mm, and the average crystal growth rate was 6.24 mm / day.

Example 2 Using the same system and apparatus as in Example 1, and after performing the same pretreatment, a seed crystal was added. The operation during single crystal growth is as follows: the circulating flow rate from the crystallized solute dissolving tank 2 to the crystal growing tank 1 is fixed at 0.2 ml / min, and the temperature of the crystallized solute dissolving tank 2 is 45 hours from the start of the growth until 24 hours later. The temperature was kept at 45.5 ° C. from 24 hours to 48 hours, 46 ° C. from 48 hours to 72 hours, and 46.5 ° C. until the end of single crystal growth. The crystal length of the urea single crystal at the end of crystal growth (100 hours after the start of crystal growth) is 2
The average crystal growth rate was maintained at 6.55 mm / day.

Comparative Example 1 After the same pretreatment was performed using the same system and apparatus as in Examples 1 and 2, a seed crystal was added. The operation at the time of growing a single crystal is as follows. The circulation flow rate from the crystallization solute dissolving tank 2 to the crystal growing tank 1 is 0.2 ml / mi.
The temperature of the crystallization solute dissolving tank 2 was kept constant at 45 ° C. and the temperature of the crystal growing tank 1 was kept constant at 44 ° C., and a single crystal was grown up to 100 hours. In the early stage of single crystal growth, a relatively fast crystal line growth rate was shown as in Examples 1 and 2, but it decreased with time. The crystal length after 100 hours was 15.2 mm, and the average crystal growth rate was 3.60 mm / day.

Example 3 A solvent evaporation removal type apparatus as shown in FIG. 2 was assembled in a constant temperature and humidity room at 25 ° C. and 60% humidity, and a single crystal of urea was grown in a methanol solution. Water was removed by adding sodium to methanol (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.), and further purified by distillation to 99.9% or more. Pretreatment of urea is the same as in the first embodiment. A seed crystal having a crystal length of 2 mm is attached to the tip of a platinum wire, suspended in the crystal growing tank 1, and air is flowed at a predetermined flow rate from the gas inlet 13 using the metering pump 5 to replace methanol vapor in the tank. As a result, stable evaporation of the solvent methanol was promoted, and a single crystal of urea was grown.

At the start of single crystal growth, the solution in crystal growth tank 1 contains 45
The temperature was kept at 44 ° C with respect to the saturated state at 0 ° C, and air was introduced immediately after the seed crystal was added. The flow rate of air is 200 ml / hr from the start of single crystal growth until 24 hours, 250 ml / hr from 24 hours to 48 hours, 300 ml / hr from 48 hours to 72 hours,
3 until the end of single crystal growth (100 hours after crystal growth starts)
It was kept at 50 ml / hr. At the end of the crystal growth, the crystal length of the urea single crystal was 29.6 mm, and the average crystal growth rate could be maintained at 7.05 mm / day.

Example 4 Using the same system and apparatus as in Example 3, a single crystal of urea was grown from a methanol solution. However, at this time, the gas inlet 13 is sealed.

Purification of urea / methanol is the same as in Example 3.

A seed crystal having a crystal length of 2 mm was attached to the tip of a platinum wire, hung in a crystal growing tank 1 and depressurized using a metering pump 5, to promote the discharge of methanol vapor as a solvent to grow a single crystal of urea. Methanol is trapped after passing through the metering pump 5,
The amount of suction was determined from the amount of methanol trap. At the start of the crystal growth, the solution in the crystal growth tank 1 was kept at 44 ° C. with respect to the 45 ° C. saturated state, and the pump was operated immediately after the addition of the seed crystal to perform suction and pressure reduction. A methanol trap volume of 1 ml / hr from immediately after seed crystal addition to 24 hours later, 1.5 ml / hr from 24 hours to 48 hours later, 2.0 ml / h from 48 hours to 72 hours later
r, and then, the pressure was reduced at 2.5 ml / hr until crystal growth was completed (100 hours after the start of growth). At the end of the crystal growth, the crystal length of the urea single crystal was 18.6 mm, and the average crystal growth rate was 4.41 mm / day.

Comparative Example 2 A single crystal of urea was grown in the same manner as in Example 3, except that the system was opened without forcibly flowing air.

In the initial stage of crystal growth, the crystal growth rate was the same as that in Example 3 or Example 4. However, as the time elapses, the crystal growth rate decreases as the size of the single crystal increases. 100 hours after the start of the growth, the crystal length was 8.46 mm, and the average crystal growth rate was 2.0 mm / day.

 Table 1 summarizes the above results.

[Effects of the Invention] The method of the present invention enables single crystallization of an organic compound, which was conventionally considered difficult, and can grow a large crystal with a uniform crystal phase and a large grain size. The huge crystal obtained by the present invention is processed according to the purpose of use, and as optical elements, optical information,
It can be used in fields such as optical communication.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing an example of an apparatus used in the method of the present invention, and FIG. 2 is a schematic view showing another example of an apparatus. 1 ... crystal growing tank, 2 ... crystallized solute dissolving tank, 3,4 ... constant temperature bath, 5 ... constant volume pump, 6 ... seed crystal, 7 ... stirring blade, 8 ... camera, 9 ... Thermocouple, 10… Temperature recorder, 11… Solute, 12… Pump, 13… Gas inlet

Claims (6)

(57) [Claims] 1. When a single crystal is obtained from a solution, the concentration of the solution in the single crystal growing tank is adjusted so as to gradually increase the supersaturation within a range of 1.1 or less by detecting the size of the single crystal, A method for producing a single crystal, comprising controlling a growth rate of a single crystal crystal line. 2. The method according to claim 1, wherein the concentration of the solution in the single crystal growing tank is maintained at a supersaturation of 1.00001 to 1.01 at the start of crystal growth, and is adjusted to 1.00003 to 1.08 as the single crystal grows. 3. The method according to claim 2, wherein the concentration of the solution in the single crystal growing tank is maintained at a supersaturation of 1.00001 to 1.00001 at the start of crystal growth, and is adjusted to 1.00005 to 1.01 as the single crystal grows. 4. The supersaturation degree at the start of crystal growth is 1.00001 to 1.0.
0003, and the degree of supersaturation during growth of the single crystal is 1.00025 to 1.00025.
The production method according to claim 3, wherein the production method is 005. 5. The substance to be single-crystallized is an organic substance.
The production method according to 1, 2, 3 or 4. 6. The method according to claim 5, wherein the organic substance to be single-crystallized is a molecular compound.