JPS5938192B2 - Manufacturing method of corundum single crystal that emits starry colors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a starry corundum single crystal.

Traditionally, corundum single crystals have been manufactured using the Bernoulli method, in which raw material powder is dropped little by little into a high-temperature area where oxygen and hydrogen are burned, forming a round rod-shaped crystal downward, or the raw material is melted in a crucible, and seed crystals are placed in this. This method uses a pulling method in which a round rod-shaped single crystal is created by inserting a crystal and pulling it up while rotating it slowly.

In the Bernoulli method, it is difficult to uniformly mix titanium dioxide (TiO2) mixed into the crystal to generate star shadows, and it is also difficult to mix it into the center of the produced crystal.

In addition, although the pulling method has the advantage of being able to mix titanium dioxide uniformly to the center of the crystal, since the crystal growth follows the simple solidification method, the concentration is not uniform in the length direction of the obtained crystal. The disadvantage is that the cost is high because an expensive crucible is used.

Corundum single crystals that emit star shadows, such as star rubies and star sapphires, are produced by TiO2 contained as an impurity in corundum as a mother crystal precipitating in a specific direction due to dissolution, which causes a light diffraction effect and star shadows. It is something that emits.

Therefore, in order to produce a corundum single crystal that emits starry shadows, it is first necessary to produce a corundum single crystal in which the TiO2 component is homogeneously dissolved.

However, since the conventional floating zone method uses air as the atmosphere, the amount of solid solution of the TiO component in corundum is at most 0.5 mol% or less, and the amount of solid solution of TiO2 component in corundum is not enough to produce a star shadow effect. 0.0% in the raw material rod.
Even if more than 5 mol% of TiO2 component is added, the maximum amount of solid solution is 0.5 mol% or less, and the excess TiO
The two components had the disadvantage of being dispersed in the crystal and becoming opaque.

The present invention provides a method for producing corundum single crystals that emit starry shadows by increasing the amount of TiO2 component in solid solution and making it homogeneous in solid solution using the floating zone method.

As a result of research to achieve the above object, the present inventors found that the amount of TiO2 solid solution contained in corundum changes depending on the oxygen partial pressure of the single crystal growth atmosphere, and when the oxygen partial pressure becomes low, TiO2
A new finding was obtained that the amount of solid solution of O2 component increases.

In other words, the amount of solid solution in an air atmosphere is 0.5 mol%.
However, when the partial pressure of oxygen in the atmosphere becomes 10 −1 atm, the amount of solid solution increases, and the maximum amount of solid solution can be increased to 3 mol %.

In addition, when the TiO2 component is dissolved in corundum, T
It was found that the solid solution was formed not as iO2 but as Ti2O3.

Therefore, it has been found that when the growth atmosphere is a reducing atmosphere, particularly a reducing atmosphere of 10@-1 atmosphere or less, the TiO2 component can be easily dissolved in solid solution.

However, as a coloring agent, for example, chromium ditrioxide (c
When trying to color using r203sae, if the atmosphere is reducing, chromium oxide will be reduced before TiO2, and this reduced chromium oxide component will easily evaporate, making it difficult to introduce it into the solid phase. becomes.

Therefore, it is sufficient to reduce the TiO2 component to the state of Ti2O3 in advance and make it a solid solution in a neutral atmosphere.Also, even when coloring with other colorants that are difficult to reduce, Ti
e. If a Ti2q component is used in advance, the TiO2 component can be effectively introduced into the solid phase under a reducing atmosphere.

In this way, to grow a single crystal in which the TiO□ component and colorant are uniformly dissolved in solid solution, without changing the precipitation temperature of the solid phase,
It is necessary to continue the growth, and for this purpose, the traveling zone method is suitable, and when the obtained single crystal is annealed in an acidic atmosphere, the TiO2 component is precipitated by dissolution, resulting in corundum that gives off a starry shadow. It was found that a single crystal could be obtained.

The present invention was completed based on the findings.

The present invention uses aluminum oxide (A1203 ) and Ti2q as the titanium oxide component, and an oxygen partial pressure of 10-
Grow a single crystal by keeping it under a reducing atmosphere of 1 atm or less,
This method is for producing a star-like corundum single crystal in which the obtained single crystal is annealed in an oxidizing atmosphere to precipitate the TiO2 component.

The floating zone method used in the present invention is, for example,
The raw material rod is set at the top and the seed crystal is set at the bottom, and a molten zone of solvent is formed between the two, which is held by surface tension.

Next, when the bath melting zone is slowly moved upward, melting of the raw material rod occurs above the melting zone, and crystal precipitation occurs below the melting zone.

At this time, the raw material rod and the seed crystal are rotated in opposite directions at appropriate speeds to give a stirring effect to the molten zone.

In this way, the molten zone is used as an intermediary to connect the materials, and the molten zone is slowly moved with no support other than the raw material rod and the seed crystal to grow a single crystal.

As for the raw material rod, it is preferable that the molar ratio of aluminum oxide (A4o3) and titanium ditrioxide (Ti203) is approximately 1:0.0005 to 1:0.05.

If the proportion of titanium dioxide is less than the above-mentioned proportion, the star shadow will become faint, and if it is greater than the above-mentioned proportion, the whole will become cloudy and not beautiful.

The solvent has a molar ratio of atubenium oxide (A4(), ) and titanium ditrioxide (Ti203) of approximately 1.
:O,OO1 to 1:0.1, and the melting point is lower than the melting point of the raw material rod.

As the Ti2O3 component increases, its melting point decreases, so
The amount of Ti2O3 in the solvent may be adjusted depending on the composition of the raw material rod.

Although it is possible to precipitate a single crystal without using a solvent, if it is not used, the composition of the initially formed crystal will deviate from the intended one, resulting in poor walking performance.

Moreover, if there is no seed crystal, polycrystals will initially be produced, which has the disadvantage of being wasted.

Aluminum oxide and titanium ditrioxide, which are the raw materials for the raw material rod and the solvent, can be used as they are at ordinary reagent grade, but in order for the mutual chemical reaction to proceed quickly, the particle size must be adjusted. The smaller the value, the better;
The thickness is preferably 10 μm or less, particularly 10 μm or less.

It is necessary to mix these raw materials as uniformly as possible.

For this purpose, it may be sufficiently mixed with an organic reagent such as an alcohol or acetone in a mortar, or by using a ball mill or the like.

In this case, if necessary, Fe, Mg, Ca, B
a.

Colorability, processability, etc. can be changed by blending trace components of V, Cr, Mn, Co, Ni, Cu, Zn, Ge, or rare earth elements.

These mixed raw material powders are press-molded.

For pressure molding, a molding method using one-way or two-way compression using a mold may be used, but in order to prevent bending during heating, a rubber press method in which pressure is applied isotropically is used. It is preferable to do so.

The rubber press method is a method in which raw material powder is placed in a rubber tube, both ends of which are sealed, and the tube is pressurized with high hydraulic pressure in a closed hydraulic pressure vessel.

The liquid pressure can be any pressure as long as it is 500 kg/ff1 or higher, but 1 to 2 t0rL/c is cheap and easy to obtain.
ytF is preferred.

The pressurization time is 5 seconds or more, preferably 1 minute.

Molded products that are not sufficiently pressurized are likely to break.

The shape of the pressure-molded product may be long and thin, but a cylindrical shape is preferred.

Its size is, for example, 1 to 10 cTL in diameter and 1 to 1 in length.
Preferably, the diameter is 37/lr/L to 3c1rL1 and the length is 5mm to 30crn.

The press-molded product is calcined.

This calcining can be done by heating it in a crucible in a horizontal furnace, but to prevent contamination of impurities and bending during calcining,
It is preferable to heat the product in a suspended state in a vertical furnace.

The press-formed product is heated under a non-oxidizing atmosphere, such as an inert gas such as nitrogen or argon, or a mixed gas with a molar ratio of nitrogen and hydrogen of 10=1.
~1850°C, preferably 1300~1700°C in the case of a solvent.

The longer the heating time, the better. Particularly in the case of a raw material rod, it is preferable to heat it for a sufficiently long time so that the bulk density after sintering becomes 80% or more of the true density.

The solvent is preferably fused under the raw material rod or on top of the seed crystal.

The amount of solvent is most preferably a hemisphere having the same diameter as the raw material rod.

The seed crystal may be any solid material that can withstand high temperatures and does not cause a chemical reaction with the solvent, but it is preferable to use the same material as the raw material rod, especially corundum single crystal.

To melt the solvent by the floating zone method, for example, a condensing heating method in which light from a high-temperature light source is condensed using a mirror or lens is used to heat the solvent over a range of 3 to 30 degrees above and below to a temperature above the melting temperature.

The crystal growth rate is equal to the downward feeding rate of the raw material rod and the seed crystal, and the feeding rate is preferably maintained at at least 0.1 per hour.

A particularly preferred speed is 1 to 10 mm per hour.

The atmosphere for this crystal growth should be an inert gas atmosphere such as nitrogen or argon if it contains easily reducible substances such as chromium trioxide.

Further, when an easily reducible colorant is not included, it is preferable to carry out under a reducing atmosphere.

As a reducing atmosphere, for example, CO2 and hydrogen are mixed in a ratio of 1:5.
．． A mixed gas containing nitrogen and hydrogen at a ratio of 10:1 is exemplified.

When the obtained single crystal is annealed in an oxidizing atmosphere having an oxygen partial pressure of 0.1 atm or more, the TiO2 component precipitates by dissolution and starts to emit star shadows.

In addition, as a raw material rod, the above-mentioned sintered raw material rod,
Once a monocrystalline product is used, the dissolution of the raw material into the solvent becomes uniform, and therefore the crystallization on the seed crystal becomes stable, and a high-quality product can be obtained.

As described above, according to the method of the present invention, the titanium oxide component is converted to corundum by using Ti20jl as the titanium oxide raw material and by making the single crystal growth atmosphere a reducing atmosphere with an oxygen partial pressure of 10-1 atm or less. By using the floating zone method, high purity and large-sized crystals can be easily obtained, and by annealing the obtained single crystal in an oxidizing atmosphere. , it has an excellent effect of producing corundum single crystals that emit beautiful star shadows.

Example 1 Aluminum oxide (A72Q,) with a purity of 99.9% or more
Powder and tri-titanium oxide (Ti) with a purity of 99.9% or more
203) Powder and 100 for corundum raw material:
0.15, solvent raw materials were weighed at a ratio of 100:0.3, and for each raw material, commercially available special grade reagents cobalt oxide (CoO) and chromium trioxide (Cr203) were weighed at a molar ratio of 2% and 0.2, respectively. %, ethyl alcohol was added in a mortar and thoroughly mixed to obtain a mixture of two types of fine powder with an average particle size of 1 μm.

Approximately 12 g of the two mixtures were each put into a thin-walled rubber tube with an inner diameter of 11 mm, and both ends were sealed and the inner diameter was 11.5 mm.
1 t in a hydraulic hydrostatic pressure generator.
It was pressed and molded at a pressure of tyn,/(2711) for about 1 minute.

The outer diameter obtained by the above operation is about 9 mm, and the length is about 80 m.
A round rod-shaped sample was inserted into a vertical electric furnace maintained at 1600°C in the case of the colloidal raw material, and 1500°C in the case of the solvent raw material, and calcined.

Inserting the sample into the furnace and removing it from the furnace took 1 hour each to prevent destruction of the sample due to rapid heating and cooling.

The atmosphere was a mixed gas of titanium and hydrogen at a molar ratio of 10:1.

The outer diameter obtained by the above operation is about 7.5 mm, and the length is about 7.
A 0-long corundum raw material rod was fixed to the upper rotating shaft of a floating zone method single crystal manufacturing device that adopted an infrared concentrated heating method, and a solvent raw material rod with an outer diameter of about 8 volts obtained in the same manner was used with a length of about 20 mm. The seed crystal was cut into pieces, fixed to the lower seed crystal rotating shaft of the above device, and a mixed gas of nitrogen and hydrogen mixed at a molar ratio of 10:1 was introduced as an atmosphere into the crystal growth chamber, which was isolated from the outside air with a fused quartz tube. , started heating.

The atmosphere is at a linear velocity of 0.0 per second near the floating zone.
Supplied in 6 mins.

Adjust the tip of the solvent raw material rod so that it goes around the part where the temperature is highest in the above single crystal production equipment, and at the same time as this tip melts by heating, keep the heating constant to fix the temperature, and insert the corundum raw material rod from above. It was moved downward and connected to the solvent raw material rod using the melting section as an intermediary, and both raw material rods were rotated in opposite directions at a speed of 50 revolutions per minute.

The rotation continued until the end of crystal growth.

After finely adjusting the temperature and the distance between the two raw material rods to obtain a state in which the molten zone is neither too large nor too small, both raw material rods are moved downward at the same speed at a speed of 2.0 mm/hour. to precipitate hecorundum crystals on the solvent raw material rod.

The precipitated crystals were polycrystalline at first, but after 10 to 30 crystals had grown, they had a single crystal cross section.

When the corundum raw material rod was almost completely consumed, the grown single crystal was separated from the raw material rod, and the cooling diameter was 6.5 my.
A corundum single crystal in the shape of a round rod with a length of 45 mttt was obtained.

This single crystal was inserted into a vertical electric furnace maintained at 1350° C. and annealed in an oxygen atmosphere of 1 atm for 48 hours.

Insertion into the furnace and withdrawal from the furnace took one hour each to prevent deterioration of crystal quality and destruction of the sample due to rapid heating and cooling.

After cutting the single crystal subjected to the above operation, it was polished to obtain a cabochon type quarried stone.

The quarry showed clear star shadow under single light.

The amount of TiO2 solid solution in the produced crystals was <1.5 mol%, which was the same as the amount of Ti2O3 component in the raw material.

When T 120 a is increased, the amount of solid solution of T t 02 component in corundum can be made up to 3 mol %.

Comparative Example 1 When the atmosphere gas in Example 1 was used as air, and other conditions were the same, 'ri2Q, the raw material was not homogeneously dissolved in the crystals, and only cloudy crystals were obtained. .

Excess Ti2O3 component was present in the cloudy part as it was converted to TiO2.

The maximum solid solution amount of TiO2 was 0.5 mol% or less.

Comparative Example 2 Air was used as the atmospheric gas, and Ti was used as the titanium oxide.
When crystals were grown using O2 in the same manner as described above, the amount of TiO2 component dissolved in corundum as a solid solution was 0.5 mol% or less.

Example 2 Using the single crystal obtained by the crystal growth method of Example 1 as a raw material, it was recrystallized by the same operation as the crystal growth method of Example 1 to obtain a crystal with a diameter of 6.5 mm and a length of 45 mm. High quality corundum single crystals were obtained.

This single crystal was annealed in the same manner as in Example 1, then cut, and the cut pieces were polished to obtain a cabochon type quarry.

The quarry showed clear star shadow under single light.

Further, the cut surface was treated with potassium hydrogen sulfate (KHSO3) at 670°C for 1 minute, and the presence of foreign phases and phagocytic bacteria was observed using a microscope.

As a result, the presence of different phases was not observed in this single crystal, and
It was confirmed that the density of phagocytic bacteria, which is thought to be caused by rearrangement, was less than 1000 per 1 d.

Claims (1)

[Claims] 1. In a single crystal growth method using a floating zone method in which one end of a raw material rod is melted and the formed melt zone is moved to continue melting of the raw material rod and precipitation of a solid phase, , a composition consisting of aluminum oxide (A1203) and titanium ditrioxide (T1203) is used, and the single crystal growth atmosphere is maintained in a reducing atmosphere with an oxygen partial pressure of 10-1 atm or less to grow the single crystal. A method for producing a corundum single crystal that gives off a starry shadow, which is characterized by growing and annealing the obtained single crystal in an oxidizing atmosphere to exsolute and precipitate the TiO2 component. 2 The floating zone method places the solvent under the raw material rod,
The method according to claim 1, wherein a seed crystal is further provided under the solvent, and the solvent portion is heated and the melting zone is moved. 3. The raw material rod has a molar ratio of aluminum oxide and titanium dioxide from 1:0.0005 to 1:0.
．． 2. The method according to claim 1, wherein the method comprises a proportion of 1. 4 In a single crystal growth method using a floating zone method in which one end of the raw material rod is melted and the formed melt zone is moved to continue melting of the raw material rod and precipitation of the solid phase, aluminum oxide (A403) and Using a raw material rod consisting of titanium ditrioxide (Ti20s), a single crystal is grown by maintaining the single crystal growth atmosphere in a reducing atmosphere with an oxygen partial pressure of 10-1 atm or less, and the resulting single crystal is A method for producing a corundum single crystal that gives off a starry shadow, characterized by repeatedly growing a similar single crystal as a raw material rod, annealing the obtained single crystal in an oxidizing atmosphere, and precipitating the TiO2 component.