Plasma smelting furnace and method for preparing high-density MgO target

Abstract

The application discloses a plasma smelting furnace and a preparation method of high-density MgO target material. The smelting furnace has a furnace body, a magnesium oxide crucible and an inductive plasma gun. The magnesium oxide crucible is embedded in the furnace body, and the inductive plasma gun is vertically arranged above the magnesium oxide crucible with its muzzle inserted into the magnesium oxide crucible. The inductive plasma gun comprises a magnesium oxide outer tube, a graphite initiation rod and an induction coil. The graphite initiation rod is inserted into the magnesium oxide outer tube, and the induction coil is sleeved on the outer wall of the magnesium oxide outer tube. The upper part of the inductive plasma gun is connected to an argon source, and the lower muzzle of the inductive plasma gun is an outlet of the plasma flame. The high-density MgO target material is prepared by using the plasma smelting process, and the steps are less and the cycle is short. The method can reduce the mixing of other impurities, ensure the high purity of the target material, and make the density of the MgO target material reach more than 99.99%.

Description

Technical Field

[0001] This invention relates to the field of target manufacturing technology, specifically to a plasma melting furnace and a method for preparing high-density MgO targets. Background Technology

[0002] MgO thin films possess advantages such as high-temperature stability, high dielectric constant, low dielectric loss, and good lattice matching with various substrate materials, making them suitable for layered electronic devices, such as the magnetic recording layer in magnetic recording media. Typically, electronic MgO thin films are formed by magnetron sputtering. In magnetron sputtering, MgO molecules are ejected from the MgO target by high-energy ions and deposited on the underlying layer to form the MgO thin film. Therefore, the quality of the MgO target is crucial for film formation; higher target density leads to higher sputtering efficiency and better film quality. Currently, MgO target preparation is primarily achieved through powder metallurgy methods, such as the technique described in Reference 1.

[0003] Reference 1: Chinese patent document with patent publication number CN114736013A.

[0004] Reference 1 discloses a zinc oxide magnesium target and its preparation method, belonging to the fields of semiconductor optoelectronic materials, magnetron sputtering coating, and powder metallurgy sintering technology. The method includes the following steps: taking ZnO and MgO powder raw materials according to the design group; processing the powder raw materials using processes such as segmented ball milling, wet blanking, segmented degreasing, segmented sintering, machining, and grinding; according to the method proposed in this invention, a finished zinc oxide magnesium target with high density, guaranteed purity, no defects, uniform and fine grains, and resistance to cracking can be obtained.

[0005] Existing powder metallurgy preparation steps are complex, and impurity elements are easily mixed in at each stage of the preparation process. Once impurities are mixed in, they cannot be removed. In addition, the density of MgO targets prepared by powder metallurgy methods is difficult to reach 99.99%. Summary of the Invention

[0006] The purpose of this invention is to solve the problem of insufficient density of MgO targets prepared in the prior art, and to provide a plasma melting furnace and a method for preparing high-density MgO targets.

[0007] To address the shortcomings of the aforementioned technical problems, the present invention adopts the following technical solution: a plasma melting furnace, which has the following characteristics:

[0008] Furnace body; and

[0009] Magnesium oxide crucibles, embedded inside the furnace body; and

[0010] The inductive plasma gun is vertically positioned above the magnesium oxide crucible, with its nozzle inserted into the magnesium oxide crucible.

[0011] The inductive plasma gun consists of a magnesium oxide outer tube, a graphite initiating rod, and an induction coil. The graphite initiating rod is inserted inside the magnesium oxide outer tube, and the induction coil is sleeved on the outer wall of the magnesium oxide outer tube. The upper part of the inductive plasma gun is connected to an argon gas source, and the lower nozzle of the inductive plasma gun is the plasma flame outlet.

[0012] As a further optimization of the plasma melting furnace of the present invention: the bottom of the magnesium oxide crucible is a hemispherical structure.

[0013] As a further optimization of the plasma melting furnace of the present invention: the side wall of the magnesium oxide crucible is also provided with an annular storage cavity, which is connected to the interior of the magnesium oxide crucible through an inclined overflow channel. The overflow channel is located at a horizontal position of the opening on the inner wall of the magnesium oxide crucible that is higher than the horizontal position of the opening on the annular storage cavity.

[0014] As a further optimization of the plasma melting furnace of the present invention, a pressure gauge is also provided on the furnace body for detecting the gas pressure inside the furnace body.

[0015] A method for preparing a high-density MgO target material involves first sieving MgO powder, then placing the sieved MgO in a plasma melting furnace for melting in a vacuum environment, cooling and removing the MgO ingot after melting, cutting the MgO ingot into round pieces, and then welding the round MgO pieces to a backing plate for further processing into a MgO target material.

[0016] As a further optimization of the preparation method of the high-density MgO target material of the present invention: MgO powder with a purity of more than 99% is selected and sieved through a 100-300 mesh sieve.

[0017] As a further optimization of the preparation method of a high-density MgO target material of the present invention: MgO powder is passed through 100 mesh, 200 mesh and 300 mesh sieves in sequence. After screening, 20-30% of 100 mesh powder, 50-70% of 200 mesh powder and 10-20% of 300 mesh powder are selected and mixed to obtain mixed MgO powder. Then the mixed MgO powder is placed in a plasma furnace for melting.

[0018] As a further optimization of the preparation method of the high-density MgO target of the present invention: firstly, a layer of high-purity MgO powder with a purity greater than 99.99% is laid at the bottom of the magnesium oxide crucible, and then mixed MgO powder is laid on the high-purity MgO powder.

[0019] As a further optimization of the preparation method of a high-density MgO target material of the present invention: MgO powder is passed through 100 mesh, 200 mesh and 300 mesh sieves in sequence. After screening, 20% of 100 mesh powder, 65% of 200 mesh powder and 15% of 300 mesh powder are selected and mixed to obtain mixed MgO powder. Then the mixed MgO powder is placed in a plasma furnace for melting.

[0020] As a further optimization of the preparation method of a high-density MgO target material of the present invention: MgO powder is passed through 100 mesh, 200 mesh and 300 mesh sieves in sequence. After screening, 30% of 100 mesh powder, 60% of 200 mesh powder and 10% of 300 mesh powder are selected and mixed to obtain mixed MgO powder. Then the mixed MgO powder is placed in a plasma furnace for melting.

[0021] The present invention has the following beneficial effects: The present invention utilizes plasma melting process to prepare high-density MgO target material, which has fewer steps and shorter cycle, can reduce the mixing of other impurities, can ensure high purity of target material, and the density of MgO target material can reach more than 99.99%. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the plasma melting furnace of the present invention;

[0023] The markings in the diagram are: 1. Furnace body, 2. Magnesium oxide crucible, 3. Induction plasma gun, 301. Magnesium oxide outer tube, 302. Graphite initiator rod, 303. Induction coil, 201. Annular storage cavity, 202. Overflow channel. Detailed Implementation

[0024] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0025] Plasma Melting Furnace

[0026] like Figure 1 As shown, a plasma melting furnace includes: a furnace body 1, a magnesium oxide crucible 2, and an induction plasma gun 3.

[0027] A magnesium oxide crucible 2 is embedded inside the furnace body 1. An induction plasma gun 3 is vertically positioned above the magnesium oxide crucible 2, with its nozzle inserted into the crucible 2. A pressure gauge is also installed on the furnace body 1 to detect the gas pressure inside the furnace body 1.

[0028] The inductive plasma gun 3 consists of a magnesium oxide outer tube 301, a graphite initiator 302, and an induction coil 303. The graphite initiator 302 is inserted inside the magnesium oxide outer tube 301, and the induction coil 303 is sleeved on the outer wall of the magnesium oxide outer tube 301. The upper part of the inductive plasma gun 3 is connected to an argon gas source, and the lower nozzle of the inductive plasma gun 3 is the plasma flame outlet.

[0029] Plasma is an independent form of matter, composed of free electrons, cations, and neutral particles, exhibiting an overall electrically neutral state. Plasma is a powerful, high-temperature heat source, and plasma arcs can be used to melt, refine, or remelt metallic or non-metallic materials. The main methods for generating plasma are the electric arc method and the high-frequency induction method. The high-frequency induction method, with its advantages of high temperature and no electrode material contamination, is a promising melting method for the future.

[0030] Brief working principle: After the furnace is evacuated, argon gas is introduced into the argon gas port of the induction plasma gun; the induction coil is connected to the high-frequency induction power supply, the graphite initiator heats up and ionizes the argon gas to form ions. Under the action of the electric field, the argon ions continue to collide with other argon gases to generate plasma. The plasma rushes out of the outlet under the argon gas flow rate, releasing a large amount of energy to form a plasma flame. The high heat of the plasma flame melts MgO powder.

[0031] Argon-generated plasma possesses high energy and density, exceeding that of nitrogen, oxygen, or air, enabling the efficient melting of magnesium oxide powder. Gas mixtures can also be used as plasma gases or supplementary gases. A recirculation system for the hot gases extracted from the furnace can be included, allowing these gases to be reused as plasma gases in the cycle. Closed-loop operation reduces the amount of plasma gas that needs to be added, thereby lowering costs, particularly the cost of argon.

[0032] As a special structural design, the bottom of the magnesium oxide crucible 2 is hemispherical. The sidewall of the magnesium oxide crucible 2 also features an annular storage cavity 201, which is connected to the interior of the crucible 2 via an inclined overflow channel 202. The overflow channel 202 is positioned at a higher level than the opening of the annular storage cavity 201 on the inner wall of the magnesium oxide crucible 2. During the smelting process, impurities can form short-range diffusion pathways and gradually diffuse to the solid-liquid boundary. The overflow channel 202 allows the liquid phase containing impurities to enter the annular storage cavity 201, thereby improving the purity of the MgO ingot and facilitating subsequent processing (after complete crystallization, the edges of the MgO ingot are trimmed).

[0033] Plasma generates a large amount of heat, enabling the melting of various metallic and non-metallic materials. High-frequency induction plasma, with its high temperature and lack of electrode material contamination, represents a promising future melting method. By designing appropriate plasma gun structures and parameters such as working gas flow rate, velocity, induction coil size, and induction power frequency, MgO raw materials can be effectively melted while protecting other structures from melting. Compared to powder metallurgy methods, plasma melting for MgO target preparation involves fewer process steps, avoids unnecessary impurities, and can produce MgO targets with theoretical density.

[0034]

[0035] A method for preparing a high-density MgO target material involves first sieving MgO powder, then placing the sieved MgO in a plasma furnace for melting in a vacuum environment, cooling and removing the MgO ingot after melting, cutting the MgO ingot into round pieces, and then welding the round MgO pieces to a backing plate for further processing into a MgO target material.

[0036] Because MgO has a high melting point, graphite, which also has an even higher melting point, is used as the plasma initiator. After evacuating the plasma furnace, argon gas is introduced at a certain flow rate and velocity. When the induction coil is connected to a high-frequency induction power supply, the graphite initiator heats up, ionizing the argon gas to form ions. Under the influence of the electric field, these argon ions continue to collide with other argon gases to generate plasma. The plasma, propelled by the argon gas flow rate, rushes out of the outlet, releasing a large amount of energy to form a plasma flame. The high heat of this plasma flame is sufficient to melt MgO powder. During the melting process, the temperature gradient can also be utilized to gradually migrate or precipitate low-melting-point impurities towards the edge of the molten pool, thus purifying the central MgO. Example 1

[0037] MgO powder with a purity of 99.99% or higher was selected and sieved through 100-mesh, 200-mesh, and 300-mesh screens to obtain particle sizes of 20%, 65%, and 15% respectively. After mixing the powders of different particle sizes, the mixture was placed in a magnesium oxide crucible. After evacuating the plasma furnace, argon gas was introduced at a certain flow rate and velocity. The appropriate parameters such as the argon gas flow rate and velocity, and the frequency of the induction coil power supply were adjusted to melt the MgO powder. After melting and complete crystallization, the edges of the MgO ingot were trimmed, and the resulting discs were processed into round pieces. After welding with a backing plate, the discs were further processed into high-density MgO targets. Example 2

[0038] MgO powder with a purity of 99.99% or higher was selected and sieved through 100-mesh, 200-mesh, and 300-mesh screens to obtain particle sizes of 30%, 60%, and 10% respectively. After mixing the powders of different particle sizes, the mixture was placed in a magnesium oxide crucible. After evacuating the plasma furnace, argon gas was introduced at a certain flow rate and velocity. The appropriate parameters such as the argon gas flow rate and velocity, and the frequency of the induction coil power supply were adjusted to melt the MgO powder. After melting and complete crystallization, the edge of the MgO ingot was cut off, and the ingot was processed into a disc. After welding with a backing plate, it was further processed into a high-density MgO target material.

[0039] After powders of different particle sizes are mixed together, the smaller particles fill the gaps between the larger particles, which helps in the smelting of MgO.

[0040] The purity and density of the MgO targets in Examples 1 and 2 were tested. The purity of Example 1 was over 99.994%, and the density was 99.992%. The purity of Example 2 was 99.993%, and the density was 99.996%.

[0041] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A plasma melting furnace, characterized in that, It has the following characteristics: Furnace body (1); and A magnesium oxide crucible (2) is embedded inside the furnace body (1); as well as The inductive plasma gun (3) is vertically positioned above the magnesium oxide crucible (2), with its nozzle inserted into the magnesium oxide crucible (2). The inductive plasma gun (3) includes a magnesium oxide outer tube (301), a graphite initiator (302), and an induction coil (303). The graphite initiator (302) is inserted inside the magnesium oxide outer tube (301), and the induction coil (303) is sleeved on the outer wall of the magnesium oxide outer tube (301). The upper part of the inductive plasma gun (3) is connected to an argon gas source, and the lower nozzle of the inductive plasma gun (3) is the plasma flame outlet. The side wall of the magnesium oxide crucible (2) is also provided with an annular storage cavity (201). The annular storage cavity (201) is connected to the interior of the magnesium oxide crucible (2) through an inclined overflow channel (202). The overflow channel (202) is located at a horizontal position higher than the horizontal position of the opening of the annular storage cavity (201) on the inner wall of the magnesium oxide crucible (2).

2. The plasma melting furnace as described in claim 1, characterized in that: The bottom of the magnesium oxide crucible (2) has a hemispherical structure.

3. The plasma melting furnace as described in claim 1, characterized in that: A pressure gauge is also installed on the furnace body (1) to detect the gas pressure inside the furnace body (1).

4. A method for preparing a high-density MgO target, characterized in that: First, MgO powder is sieved. Then, the sieved MgO is placed in the plasma melting furnace described in claim 1 or 3 and melted in a vacuum environment. After melting, the MgO ingot is cooled and removed. The MgO ingot is cut into round pieces. Then, the round MgO pieces are welded to the back plate and further processed into MgO target material. MgO powder with a purity of 99% or higher is selected and sieved through a 100-300 mesh screen. MgO powder is passed through 100-mesh, 200-mesh and 300-mesh sieves in sequence. After screening, 20-30% of the 100-mesh powder, 50-70% of the 200-mesh powder and 10-20% of the 300-mesh powder are selected and mixed to obtain mixed MgO powder. Then the mixed MgO powder is placed in a plasma furnace for melting.

5. The method for preparing a high-density MgO target as described in claim 4, characterized in that: First, lay a layer of high-purity MgO powder at the bottom of the magnesium oxide crucible. The purity of the high-purity MgO powder is greater than 99.99%. Then, lay mixed MgO powder on top of the high-purity MgO powder.

6. The method for preparing a high-density MgO target as described in claim 4, characterized in that: MgO powder is passed through 100-mesh, 200-mesh and 300-mesh sieves in sequence. After screening, 20% of the 100-mesh powder, 65% of the 200-mesh powder and 15% of the 300-mesh powder are selected and mixed to obtain mixed MgO powder. Then the mixed MgO powder is placed in a plasma furnace for melting.

7. The method for preparing a high-density MgO target as described in claim 4, characterized in that: MgO powder is passed through 100-mesh, 200-mesh and 300-mesh sieves in sequence. After screening, 30% of the 100-mesh powder, 60% of the 200-mesh powder and 10% of the 300-mesh powder are selected and mixed to obtain mixed MgO powder. Then the mixed MgO powder is placed in a plasma furnace for melting.

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