JPH05319994A - Method for recovering oxide single crystal material - Google Patents

Abstract

PURPOSE:To improve the recovery ratio by heating mixed powder of an oxide single crystal with impurities produced in working the oxide single crystal, passing the mixed powder through an electric field and applying the oxide single crystal powder to positive and negative electrodes. CONSTITUTION:Mixed powder 1 of an oxide single crystal such as LiTa2O3 or LiNb2O3 with impurities is fed to a powder feeding part 2 and dropped from the lower part at a constant velocity while being heated with a heater 3. Only the oxide single crystal powder (1a) in the mixed powder 1 is electrified by piezoelectric effects to attract the oxide single crystal powder (1a) to electrodes 4 in a high electric field at 100-500 V/cm with positive and negative electrodes 4 heated at 80-90 deg.C. The impurity powder (1b) is directly dropped and separated. The positive and negative electrodes 4 are moved in the direction of arrows with thin beltlike rollers 5 made of a metal to apply a high voltage to the respective earths. The attracted high-purity oxide single crystal powder (1a) is separated from the electrodes 4 with separators 6 and collected in containers 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering an oxide single crystal material, and in particular, the processing waste generated during the machining of a lithium tantalate or lithium niobate single crystal is reused as a raw material for growing a single crystal. Therefore, it relates to a method of separating and purifying from contaminants such as abrasives and oil.

[0002]

2. Description of the Related Art Metal tantalate is also called a strategic metal and is used in the fields of capacitors, nuclear power generation, gas turbines for aircraft, etc., but its production is unevenly distributed in Brazil, Southeast Asia, Africa, Canada, etc. However, price rises and supply instability are likely to occur, and recovery of tantalum resources is desired. At present, recovery is performed from by-products from tin refined slag, tantalum capacitors, cemented carbide cutting chips, lithium tantalate (hereinafter abbreviated as LT) single crystals, and the like.

In the case of LT single crystals, the current objects to be recovered are residues in crucibles for pulling up, boules with cracks, debris, etc., and LT processed waste discharged exceeding the product weight is not recovered. I haven't been. Regarding the discharge amount of the LT processing waste, for example, in the case of producing 141 wafers of diameter 4 ″ × 0.5 mm in thickness from an LT boule for diameter 4 ″ (effective length 12 cm), 100 parts of the product wafer are weighed. Loss 82 due to cylindrical grinding, loss 40 due to cutting with a wire saw
Part, the loss due to lapping and polishing is 30 parts,
The total amount of lost LT processing waste is 152 parts, which is actually 1.5 times the weight of the product wafer. If the thickness of the product wafer becomes smaller (for example, the one having a thickness of 0.05 mm is also used), the relative loss of LT is further increased.

[0004]

In view of the above points, the present invention is LT or lithium onibate (hereinafter abbreviated as LN).
It is intended to provide a method for efficiently separating and purifying a single crystal contained in a material processing waste generated at the time of machining an oxide single crystal material such as, for example, and reusing it.

[0005]

The present invention is to solve the above problems, that is, by heating a mixed powder of an oxide single crystal and impurities produced during processing of the oxide single crystal in an electric field. The oxide single crystal powder is allowed to adhere to the positive and negative electrodes by passing the oxide single crystal material.

When a part of the crystals of the heteropolar image group is heated, an electric charge appears on the surface. This phenomenon is called the pyroelectric effect.
The crystals of the heteropolar image group are naturally polarized (spontaneous polarization), and the surface polarization charge is neutralized by the attached ions, etc., and the magnitude of polarization changes when the temperature is changed, Changes are observed. Since both LT and LN belong to the heteropolar image crystal group, they have pyroelectricity and have spontaneous polarization in the Z-axis direction of the crystal. Generation of large polarized charges is observed in the Z-axis direction 9 (FIG. 2A shows a state before heating, and FIG. 2B shows a state after heating). This charged powder is, for example, 100-50
When dropped in a high electric field of 0 V / cm, the charged body (pyroelectric body) powder adheres to the electrode due to the effect of polarization charge, and the non-charged body falls as it is, and the pyroelectric body and the non-pyroelectric body are separated. Will be separated.

FIG. 1 exemplifies a separation apparatus used in the present invention, which is a mixed powder 1 of the above-mentioned oxide single crystal and impurities.
Is supplied to the powder supply unit 2 and dropped from the lower part at a constant speed. At this time, the mixed powder 1 is heated by the heater 3, and only the oxide single crystal powder therein is charged by the pyroelectric effect. Further, the charged powder falls into the electric field of the positive and negative electrodes 4, and the charged oxide single crystal powder 1a is adsorbed by the positive and negative electrodes 4 by the pyroelectric effect and separated from the contaminant powder 1b. The positive and negative electrodes 4 are made of thin belt-shaped metal and are moved in the direction of the arrow by rollers 5, and a high voltage is applied to each ground. The adsorbed oxide single crystal powder is separated from the electrodes by the separator 6 and collected in the container 7. Here, the electrode 4 is preferably heated to 80 to 90 ° C.

For the machining of the single crystal material, a machine such as a cylindrical polishing machine, a wire saw, a multi-blade wafer ring machine, an inner peripheral blade cutting machine, an outer peripheral blade cutting machine, a lapping machine, a polishing machine and a beveling machine is used. Done.

[0009]

EXAMPLES The present invention will be described below with reference to examples. All composition% in the examples are based on weight.

Example 1 An LT single crystal diameter 4 ″ wafer was lapped on both sides with SiC free abrasive grains. The initial composition of the lapping solution was 8 liters of water, free abrasive grains (manufactured by Fujimi Abrasive Industry Co., Ltd.). , FO # 1
200) 4 kg, rust preventive (shrek # 101, manufactured by Daichi Chemical Industry Co., Ltd.) 700 cc. The slurry after polishing contains LT single crystal particles, SiC particles, rust preventive agent, iron (from platen), resin, glass fiber (from FRP spacer) and the like. The slurry is subjected to centrifugal separation, washing with a surfactant, centrifugal separation and drying, and the solid content obtained is loosened with a ball mill to give a powder. In this case, consideration was given to making the temperature rise as small as possible. Here, the LT single crystal powder is contained in about 15%. This mixed powder was supplied to the powder supply unit 2 of the apparatus shown in FIG. 1 and dropped from the lower part at a speed of 2 l / hr. At this time, it is heated to about 90 ° C by the infrared heater 3 and LT
Only the single crystal powder is charged by the pyroelectric effect (see Fig. 2),
The charged LT single crystal powder falls along with other contaminants in the electric field (1000 V / 10 cm) by the electrode 4 and is adsorbed by the electrode 4 (height 1 m), and the contaminant powder falls straight as it is. The adsorbed LT single crystal powder is separated by a separator 6
Were separated by and collected in a container 7. By this method, LT single crystals with a purity of 99.5% were obtained in a yield of 90%.

Example 2 A grown LN single crystal boule having a diameter of 4 "was cut by an inner peripheral blade cutting machine. When the inner peripheral blade cutting machine was used for cutting, LN single crystal powder, solid abrasive grains, carbon and glass were cut. , A mixed slurry of adhesive, iron powder, rust preventive, etc. This slurry is subjected to centrifugal separation, surfactant washing, centrifugal separation drying, and the resulting solid content is pulverized with a ball mill. When the LN single crystal powder was separated in the same manner as in Example 1, 80% of the LN single crystal in the dry mixed powder was converted to LN of 99.7% purity.
Single crystals were obtained with a yield of 85%.

[0012]

EFFECTS OF THE INVENTION According to the present invention, the oxide single crystal material is efficiently recovered from the mixed powder of the oxide single crystal and the impurities produced during the machining of the oxide single crystal by utilizing the pyroelectric effect. In particular, it is industrially useful because the resource-saving effect can be achieved by the recycle use of the lithium tantalate and lithium niobate single crystal materials.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an apparatus used in the method of the present invention.

FIG. 2 is an explanatory view showing a charged state of a single crystal used in the method of the present invention. (A) shows the state before heating and (B) shows the state after heating.

[Explanation of symbols]

 1 Mixed powder 1a Oxide single crystal powder 1b Contaminant powder 2 Powder supply part 3 Heater 4 Electrode 5 Roller 6 Separator 7 Container 8 Single crystal 9 Z axis

Claims (2)

[Claims] 1. The oxide single crystal powder is adhered to the positive and negative electrodes by heating a mixed powder of the oxide single crystal and impurities generated during processing of the oxide single crystal and allowing the mixed powder to pass through an electric field. Method for recovering oxide single crystal material. 2. The recovery method according to claim 1, wherein the oxide single crystal is a lithium tantalate or lithium niobate single crystal.