Liquid metal filtration device for vacuum distillation of magnesium metal

Abstract

The present invention provides a liquid metal filtering device for vacuum distillation of magnesium metal. The filtering device is installed in a vacuum distillation furnace and comprises a crucible, a filter screen and a liquid metal filter, wherein a metal melt is placed in the liquid metal filter. The filtering device provided by the present invention first filters coarse particles with a filter screen, and then filters fine particles and adsorbed gas impurities through the metal melt in the liquid metal filter. The filtering structure design significantly reduces the impurity content in magnesium vapor while avoiding the substantial inhibition of the evaporation process of magnesium metal by conventional filtering structures. The cost of using parts is low, and the quality of high-purity magnesium products is improved without significantly increasing production costs.

Description

Technical Field

[0001] The invention belongs to the technical field of magnesium metal purification, and in particular relates to a liquid metal filtering device for magnesium metal vacuum distillation. Background Art

[0002] As the lightest metal structural material, magnesium and magnesium alloys are often used in transportation, 3C electronics, biomedicine and other fields due to their low density, high specific strength and specific stiffness. However, magnesium and magnesium alloys still have problems of poor corrosion resistance and insufficient mechanical properties, which is largely related to the presence of oxides and other metal impurities. One way to solve the above problems is to reduce the impurity content in the raw materials to improve the quality of subsequent products.

[0003] Vacuum distillation is an important method for purifying magnesium metal. It is generally believed that the preparation of high-purity magnesium by vacuum distillation only involves the solid-gas or liquid-gas transformation of magnesium metal, that is, directly obtaining clean magnesium vapor by gasifying magnesium metal. Studies have shown that when high-purity magnesium is prepared by vacuum distillation, a large number of oxides and refractory metal impurity particles will exist on the evaporation surface. These particles can be carried into the product by magnesium vapor, thus affecting the product quality. And because the size distribution of these impurity particles is wide, a simple filter system cannot capture all impurity particles. In addition, while blocking impurity particles, the filter will also inhibit the evaporation of magnesium metal, and the smaller the pores of the filter, the stronger the inhibitory effect on evaporation. Therefore, it is necessary to develop a filtration system with high impurity particle capture efficiency and low inhibitory effect on magnesium metal evaporation. Summary of the invention

[0004] The purpose of the present invention is to provide a liquid metal filtration device for magnesium vacuum distillation. Based on the analysis of impurity particle size and impurity type in magnesium vacuum distillation, starting from the strategy of graded filtration, a double-layer filtration structure of pore filtration of coarse particles and liquid phase adhesion filtration of fine particles and absorption of gas impurities is adopted to achieve filtration efficiency that cannot be achieved by a single filtration structure such as a filter screen, and at the same time, it can also avoid the inhibition of the magnesium evaporation process by the too small pores of the filter screen, significantly improve the production efficiency, and achieve high purification of magnesium vapor.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The liquid metal filtering device for vacuum distillation of magnesium metal provided by the present invention is installed in a vacuum distillation furnace, and comprises a crucible, a filter screen and a liquid metal filter, wherein the liquid metal filter comprises a filter base and a filter upper cover;

[0007] The bottom of the crucible is provided with a magnesium raw material reaction zone for generating magnesium vapor, and the inner wall surface of the crucible above the magnesium raw material reaction zone is provided with a first annular groove, a second annular groove, and a third annular groove from bottom to top, respectively used to embed a filter screen, a filter base, and a filter upper cover; the filter screen is composed of a metal mesh surrounded by a fixed ring, and the size of the fixed ring matches the first annular groove; the filter base is composed of a hollow cylindrical barrel with openings at both ends, and a bottom plate located outside the hollow cylindrical barrel and surrounding the lower edge of the hollow cylindrical barrel , the outer edge of the bottom plate matches the second annular groove; the filter cover is a hollow cylindrical structure with an open lower end, the filter cover is coaxially arranged outside the hollow cylindrical barrel and is spaced a certain distance from the filter base, so that magnesium vapor can flow along the S-shaped curve from the inner channel inside the hollow cylindrical barrel, the middle channel between the filter base and the filter cover to the outer channel surrounded by the filter cover, the bottom plate and the side wall of the crucible, the outer channel contains filtering metal, and the top of the filter cover is embedded in the third annular groove through the fixing part;

[0008] The liquid metal filter includes a three-channel structure design including an inner channel, a middle channel, and an outer channel: on the one hand, a liquid storage area is provided for the metal melt formed by melting at the working temperature of the filtering metal disposed above the magnesium vapor, so that the magnesium vapor passes through the metal melt while the metal melt does not fall; on the other hand, based on the density difference between the magnesium vapor and the impurity particles, the magnesium vapor must be centrifuged twice to throw the impurity particles in the magnesium vapor outward with the movement of the magnesium vapor, thereby providing an opportunity for the impurity particles to better contact the metal melt. Due to the lower surface tension of the metal melt, the melt covers the impurity particles when contacting them, thereby separating the impurities from the vapor.

[0009] The working temperature of the filtering metal is above 700°C, and at the working temperature, P 滤 <P Mg ×10 -8 , P 滤 is the saturated vapor pressure of the metal used for filtration, P Mg The filtration metal melts at the working temperature to form a metal melt and has a certain viscosity. Preferably, the filtration metal is tin or aluminum, and the impurity limit of the tin or aluminum satisfies the following conditions: the saturated vapor pressure at the working temperature is greater than P Mg ×10 -6 The impurity element content is less than 10ppm, and the sum of other impurity elements is less than 1000ppm.

[0010] After magnesium metal evaporates, magnesium vapor needs to rely on its own saturated vapor pressure to squeeze the metal melt out of the middle channel before it can escape from the outer channel. 滤 gh=P Mg -P环 When (h is the maximum height of the metal melt filling the outer channel, ρ 滤 is the density of the melt, g is the acceleration due to gravity, P Mg is the saturated vapor pressure of magnesium metal at the evaporation temperature, P 环 =((P) / (h)) = ( ... Mg -P 环 ) / (ρ 滤 ×ɡ)]×80%, among which,.

[0011] The cross-sectional area ratio of the outer channel, the middle channel and the inner channel is any ratio. Since the steam flow capacity is relatively strong, while the gas-liquid two-phase flow capacity is relatively poor, increasing the cross-sectional area of ​​the outer channel can reduce the steam resistance. Therefore, preferably, among the outer channel, the middle channel and the inner channel, the cross-sectional area of ​​the outer channel is the largest. Further preferably, the cross-sectional area ratio of the outer channel, the middle channel and the inner channel is 2:1:1.

[0012] The liquid metal filter is made of any material that does not significantly react with the filtering metal and magnesium vapor, preferably high-purity graphite.

[0013] The mesh size of the filter cannot significantly inhibit the evaporation of metal magnesium, preferably 10-100 mesh. The material of the filter can be any material that has certain mechanical properties at high temperature (450-950°C), can maintain the filter structure, and does not react with metal magnesium vapor, preferably titanium.

[0014] The crucible should not react with metal magnesium under high temperature conditions and will not pollute metal magnesium vapor. The preferred material is high-purity graphite.

[0015] The working principle of the present invention is as follows: impurity particles in magnesium vapor produced by vacuum distillation are classified, large-sized particles are intercepted by a filter screen with large pores, and when small-sized particles pass through a metal melt using magnesium vapor, the metal melt has a stronger adhesion effect on the small-sized particles than the magnesium vapor, so that the small-sized particles can remain in the metal melt, thereby achieving the purpose of removing impurity particles in the magnesium vapor to the maximum extent.

[0016] In addition, taking aluminum melt as an example, because the partial pressure of gas impurities in magnesium vapor is higher than the partial pressure of impurities in aluminum melt (i.e., P i >c i ×γ i ×P i * , where P iis the partial pressure of impurity i in magnesium vapor, c i is the content of impurity i in the aluminum melt, γ i is the activity coefficient of impurity i under the current melt composition, P i * = is the saturated vapor pressure of impurity i in magnesium vapor at the current temperature), so the gas impurities can be dissolved into the aluminum melt spontaneously from a thermodynamic point of view, and some impurities can also form intermetallic compounds with aluminum, thus being wrapped and precipitated by the aluminum melt. For example, gas molecules such as Ca, Fe, and Si can interact with the aluminum melt and dissolve into the aluminum melt.

[0017] Compared with the prior art, the filtering device provided by the present invention adopts a graded filtering structural design, that is, coarse particles are first filtered with a filter mesh, and then fine particles and gas impurities are filtered through the metal melt in the liquid metal filter. The filtering structure design significantly reduces the impurity content in the magnesium vapor while avoiding the substantial inhibition of the evaporation process of the metal magnesium by the conventional filtering structure. The cost of using parts is low, and the quality of high-purity magnesium products is improved without significantly increasing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 It is a schematic structural diagram of a liquid metal filtration device for vacuum distillation of magnesium metal according to the present invention;

[0020] Among them: 1-crucible; 2-filter screen; 3-hollow cylindrical barrel; 4-bottom plate; 5-filter cover; 6-fixing part; 7-external channel; 8-inner channel; 9-middle channel. DETAILED DESCRIPTION

[0021] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0022] In the description of the present invention, it is necessary to understand that the orientations or positional relationships indicated by the terms "upper", "lower", "middle", "inside", "outside", etc. are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0023] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0024] Example 1

[0025] like Figure 1 As shown, this embodiment provides a liquid metal filtration device for vacuum distillation of magnesium metal, which is installed in a vacuum distillation furnace and includes a crucible 1, a filter screen 2 and a liquid metal filter, and the liquid metal filter includes a filter base and a filter upper cover 5;

[0026] The crucible 1 is made of high-purity graphite, and a magnesium raw material reaction zone is provided at the bottom to generate magnesium vapor. Above the magnesium raw material reaction zone, the inner wall surface of the crucible 1 is provided with a first annular groove, a second annular groove, and a third annular groove from bottom to top, which are used to embed the filter screen 2, the filter base, and the filter cover 5, respectively;

[0027] The filter screen 2 is composed of a metal mesh embedded in a fixing ring, the size of the fixing ring matches the first annular groove, the mesh number of the filter screen 2 is 10 meshes, and the material is titanium metal;

[0028] The material of the liquid metal filter is high-purity graphite, wherein the filter base is composed of a hollow cylindrical barrel 3 with openings at both ends, and a bottom plate 4 located outside the hollow cylindrical barrel 3 and surrounding the lower edge of the hollow cylindrical barrel 3, and the outer edge of the bottom plate 4 matches the second annular groove; the filter cover 5 is a hollow cylindrical structure with an opening at the lower end, and the filter cover 5 is coaxially arranged outside the hollow cylindrical barrel 3 and is spaced a certain distance from the filter base, so that magnesium vapor can flow along an S-shaped curve from an inner channel 8 located inside the hollow cylindrical barrel 3, an intermediate channel 9 between the filter base and the filter cover 5 to an outer channel 7 surrounded by the filter cover 5, the bottom plate 4 and the side wall of the crucible, and the cross-sectional area ratio of the outer channel 7, the intermediate channel 9 and the inner channel 8 is 1:1:1, and the outer channel 7 contains metal tin for filtering, and the liquid level height H when it is completely located in the outer channel under the action of magnesium vapor in a molten state is less than [(P Mg -P 环 ) / (ρ 滤 × ɡ)] × 80%, where P Mg is the saturated vapor pressure of magnesium metal at the evaporation temperature, P 环 is the ambient vapor pressure in the vacuum distillation furnace, ρ 滤is the density of the filtering metal, ɡ is the gravitational acceleration; the top of the filtering upper cover 5 is embedded in the third annular groove through the fixing part 6.

[0029] Example 2

[0030] The difference between Example 2 and Example 1 is that the cross-sectional area ratio of the outer channel 7, the middle channel 9, and the inner channel 8 of the liquid metal filtration device for vacuum distillation of magnesium metal provided in this example is 2:1:1.

[0031] Example 3

[0032] The difference between Example 3 and Example 1 is that the mesh size of the filter screen 2 of the liquid metal filtration device for vacuum distillation of magnesium metal provided in this example is 100 meshes.

[0033] During operation, when the vacuum degree of the vacuum distillation furnace is below 10Pa, the filter device and the crucible are heated to 800℃ successively, the filter metal is first melted into a metal melt, and magnesium vapor is generated after the magnesium raw material reaction zone. When the magnesium vapor rises through the filter, the filter intercepts large-sized impurity particles and obtains a primary filtration. After the primary filtration, the magnesium vapor carries small-sized impurity particles and continues to rise, and successively passes through the inner channel and the middle channel of the liquid metal filter to reach the outer channel, and contacts with the metal melt in the outer channel. The metal melt allows the small-sized impurity particles to remain in the metal melt through the following two mechanisms, thereby realizing the secondary filtration of the magnesium vapor: 1) Thermodynamically, the surface energy of small-sized impurity particles is large, while the surface energy of the metal melt is small. In order to reduce the energy of the system, the metal melt spontaneously wraps the impurity particles when contacting the small-sized impurity particles; 2) The viscosity of the metal melt is higher than that of the magnesium vapor. Compared with the magnesium vapor, the impurity particles are more easily adhered to the metal melt and remain in the metal melt. The filtered magnesium vapor is directly condensed to obtain high-purity crystalline magnesium.

[0034] Using crude magnesium produced by the silicon thermal method with the highest impurity content among pure magnesium on the market as raw material, the GDMS test results of the direct distillation product (removing the filter screen and liquid metal filter in Example 2) and the product after distillation and filtration using Example 2 of the present invention are compared, as shown in Table 1.

[0035] Table 1 Comparison of test results

[0036]

[0037] The filtering device provided by the present invention significantly reduces the impurity content of magnesium vapor, can increase the purity of magnesium to more than 99.9998%, and further improves the product quality of high-purity magnesium prepared by vacuum distillation. Moreover, compared with other traditional filtering methods, the filtering device of the present invention has low requirements on raw materials and a wider range of raw material selection.

[0038] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A liquid metal filtration device for vacuum distillation of magnesium metal, the filtration device being installed in a vacuum distillation furnace, characterized in that: It comprises a crucible (1), a filter screen (2) and a liquid metal filter, wherein the liquid metal filter comprises a filter base and a filter upper cover (5); The bottom of the crucible (1) is provided with a magnesium raw material reaction zone for generating magnesium vapor, and the inner wall surface of the crucible (1) above the magnesium raw material reaction zone is provided with a first annular groove, a second annular groove, and a third annular groove from bottom to top, respectively used to embed a filter screen (2), a filter base, and a filter upper cover (5); the filter screen (2) is composed of a metal mesh with a periphery embedded in a fixing ring, and the size of the fixing ring matches the first annular groove; the filter base is composed of a hollow cylindrical barrel (3) with openings at both ends, and a bottom plate (4) located outside the hollow cylindrical barrel (3) and surrounding the lower edge of the hollow cylindrical barrel (3), and the bottom plate (4) The outer edge of the filter cover (5) matches the second annular groove; the filter cover (5) is a hollow cylindrical structure with an open lower end; the filter cover (5) is coaxially arranged outside the hollow cylindrical barrel (3) and is spaced a certain distance from the filter base, so that magnesium vapor can flow along an S-shaped curve from an inner channel (8) located inside the hollow cylindrical barrel (3) and an intermediate channel (9) between the filter base and the filter cover (5) to an outer channel (7) surrounded by the filter cover (5), the bottom plate (4) and the side wall of the crucible; the outer channel (7) contains a filter metal; and the top end of the filter cover (5) is embedded in the third annular groove through a fixing portion (6); The working temperature of the filtering metal is above 700°C, and at the working temperature, P 滤 <P Mg ×10 -8 , P 滤 is the saturated vapor pressure of the metal used for filtration, P Mg is the saturated vapor pressure of magnesium.

2. The liquid metal filtration device for vacuum distillation of magnesium metal according to claim 1, characterized in that: The filtering metal is tin or aluminum, and the impurity limit of the tin or aluminum meets the following conditions: the saturated vapor pressure at the working temperature is greater than 10 -6 ×P Mg The impurity element content is less than 10ppm, and the sum of other impurity elements is less than 1000ppm; Mg is the saturated vapor pressure of magnesium.

3. The liquid metal filtration device for vacuum distillation of magnesium metal according to claim 1, characterized in that: The liquid level height H of the filtering metal when it is in a molten state and completely located in the outer channel is <[(P Mg -P 环 ) / (ρ 滤 ×ɡ)]×80%, where P Mg is the saturated vapor pressure of magnesium metal at the evaporation temperature, P 环 is the ambient vapor pressure in the vacuum distillation furnace, ρ 滤 is the density of the filtering metal and ɡ is the acceleration due to gravity.

4. The liquid metal filtration device for vacuum distillation of magnesium metal according to claim 1, characterized in that: The cross-sectional area ratio of the outer channel (7), the middle channel (9) and the inner channel (8) is any ratio.

5. The liquid metal filtration device for vacuum distillation of magnesium metal according to claim 4, characterized in that: The cross-sectional area of ​​the outer channel (7) is larger than the cross-sectional area of ​​the middle channel (9), and the cross-sectional area of ​​the outer channel (7) is larger than the cross-sectional area of ​​the inner channel (8).

6. The liquid metal filtration device for vacuum distillation of magnesium metal according to claim 1, characterized in that: The liquid metal filter is made of any material that does not significantly react with the filtering metal and magnesium vapor.

7. The liquid metal filtration device for vacuum distillation of magnesium metal according to claim 6, characterized in that: The material of the liquid metal filter is high-purity graphite.

8. The liquid metal filtration device for vacuum distillation of magnesium metal according to claim 1, characterized in that: The mesh number of the filter screen (2) is 10-100 meshes, and the material is any material that can withstand high temperatures of 450-950° C. and does not react with magnesium vapor.

9. The liquid metal filtration device for vacuum distillation of magnesium metal according to claim 1, characterized in that: The material of the crucible (1) is high-purity graphite.

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