阅读说明：本技术 一种实现稀土熔盐电极钨、钼阴极延寿的熔盐非电解渗局部处理方法 (Fused salt non-electrolytic infiltration local treatment method for prolonging service life of tungsten and molybdenum cathodes of rare earth fused salt electrode ) 是由 唐长斌 俞永奇 刘子龙 崔段段 陈红霞 许妮君 薛娟琴 于 2021-07-07 设计创作，主要内容包括：本发明一种实现稀土熔盐电极钨、钼阴极延寿的熔盐非电解渗局部处理方法,通过钛制防渗夹具保护非渗区域,而后在中性熔盐中对稀土金属电解用的钨、钼阴极材料进行高温扩散渗原位反应制备一层金属硅化物渗层,利用该渗层具有抗熔盐热腐蚀和抵御高温氧化的特性,实现有效抑制钨、钼阴极处于熔盐液面上部快速热腐蚀损伤,延长阴极使用寿命,这一熔盐渗硅防护技术具有操作简便、过程可控、成本低廉的优势。(The invention relates to a fused salt nonelectrolysis infiltration local treatment method for realizing the service life extension of a rare earth fused salt electrode tungsten and molybdenum cathode.)

1. A fused salt non-electrolysis infiltration local treatment method for realizing the service life extension of a tungsten and molybdenum cathode of a rare earth fused salt electrode is characterized by comprising the following steps:

step (1), protecting a non-seepage area by using a titanium anti-seepage clamp;

step (2), pretreating the surface of a part to be infiltrated of a tungsten cathode or a molybdenum cathode;

immersing the pretreated tungsten cathode or molybdenum cathode in mixed molten salt for non-electrolysis neutral molten salt siliconizing, and preparing a metal silicide infiltrated layer on the tungsten cathode or molybdenum cathode through in-situ reaction, wherein the mixed molten salt consists of neutral salt, siliconizing agent and Si powder;

and (4) after the silicide infiltrated layer is prepared, taking out the tungsten cathode or the molybdenum cathode, placing the tungsten cathode or the molybdenum cathode in the air for natural cooling, and cleaning and drying.

2. The fused salt nonelectrolytic infiltration local treatment method for realizing the service life of the rare earth fused salt electrode tungsten and molybdenum cathode according to claim 1, characterized in that in the step (1), a pure titanium protection clamp is designed and processed according to the size of the tungsten cathode or the molybdenum cathode to protect a non-infiltration area so as to ensure that the non-infiltration area is not contacted by high-temperature fused salt and avoid a siliconizing process.

3. The method for realizing the local treatment of the molten salt non-electrolytic infiltration of the rare earth molten salt electrode tungsten and molybdenum cathode for prolonging the service life of the rare earth molten salt electrode according to claim 1, wherein in the step (2), the pretreatment is mechanical leveling and oil removal, so as to ensure that the surface has no oil stain, no pollutant adhesion and no obvious oxide layer.

4. The method for local treatment of molten salt nonelectrolysis of tungsten and molybdenum cathodes serving as rare earth molten salt electrodes for prolonging the service life of the rare earth electrodes as claimed in claim 1, wherein in the step (3), the mixed molten salt is placed in an alumina crucible.

5. The method for realizing the local treatment of the molten salt nonelectrolytic infiltration of the cathode service life of the rare earth molten salt electrode tungsten and molybdenum according to claim 1, wherein in the step (3), the neutral salts are NaCl, KCl and NaF, and the siliconizing agent is Na₂SiF₆。

6. The molten salt nonelectrolysis infiltration local treatment method for prolonging the service life of the rare earth molten salt electrode tungsten and molybdenum cathode according to claim 5, characterized in that the mixed molten salt comprises 30-35% of NaCl, 30-35% of KCl, 10-15% of NaF and 0-5% of Na in terms of mole fraction₂SiF₆15 to 20% Si and Na₂SiF₆The amount is different from 0.

7. The molten salt nonelectrolytic infiltration local treatment method for realizing the rare earth molten salt electrode tungsten and molybdenum cathode life prolonging according to claim 1, 5 or 6, characterized in that in the step (3), before the mixed molten salt is prepared, neutral salt is dried at 100-110 ℃ for 2-6 h, then is uniformly mixed with a siliconizing agent and then is ground into fine powder, finally Si powder is added, and a quartz rod is placed in the prepared mixed molten salt to stabilize the concentration of an Si source in the infiltration plating process.

8. The molten salt nonelectrolytic infiltration local treatment method for realizing the service life prolongation of the rare earth molten salt electrode tungsten and molybdenum cathode according to claim 7, characterized in that in the step (3), the preparation temperature of the silicide infiltration layer is 830-900 ℃, and the heat preservation time is 2-6 h.

9. The molten salt nonelectrolytic infiltration local treatment method for realizing the service life prolongation of the rare earth molten salt electrode tungsten and molybdenum cathode according to claim 1, characterized in that in the step (4), residual salt on the surface of the sample is removed by repeatedly cleaning with clear water, and the sample is dried after being sequentially subjected to ultrasonic cleaning with acetone and absolute ethyl alcohol.

Technical Field

The invention belongs to the technical field of preparation of tungsten and molybdenum cathode materials in rare earth metal production, and particularly relates to a fused salt non-electrolytic infiltration local treatment method for prolonging the service life of a rare earth fused salt electrode tungsten and molybdenum cathode.

Background

The molten salt electrolysis method is the most extensive method for preparing a large amount of mixed rare earth metals, single light rare earth metals (except samarium) and rare earth alloys at present. The method is a process of heating and melting rare earth compounds such as rare earth oxide, rare earth chloride, rare earth fluoride and the like to be used as electrolysis raw materials, taking a tungsten rod or a molybdenum rod and the like as a cathode, taking graphite as an anode, and electrifying direct current to carry out electrolysis so as to separate out rare earth metals on the cathode. The electrode material is the core of electrochemical reaction and is also an important factor related to production cost, product quality and production management. The metal molybdenum and tungsten are more stable to rare earth metal and halide thereof below 1400 ℃, particularly, the tungsten has the advantages of high melting point, good electric and thermal conductivity, low sputtering corrosion rate, small thermal expansion coefficient, low vapor pressure, excellent high-temperature strength at high temperature and the like, so the molybdenum and tungsten alloy is the preferred rare earth metal molten salt electrolysis cathode material.

Although the electrode tungsten metal has higher melting point (3407 +/-20 ℃) and thermal stability, the electrode tungsten metal is gradually eroded and consumed by the evaporated and attached molten salt at a slow speed in the electrolytic production process.

A tungsten cathode on a molten salt liquid surface is rapidly corroded and researched in J thermal processing technology 2015,044(002) 88-92, and the problem of too rapid thermal corrosion damage caused by the combined action of high-temperature oxidation and deposited salt exists at a position 70-80 mm away from the liquid surface of an electrolyte and close to a top power joint in the production of a rare earth company is discovered. Therefore, in practical production, some enterprises often adopt a method of using the cathode tungsten rod for a period of time and then turning the cathode tungsten rod upside down to prolong the service life of the cathode tungsten rod.

In the second prior art, CN2011200849157 discloses a tungsten cathode for molten salt electrolysis, and proposes a water cooling protection method for solving the problem that a part of a tungsten rod close to the molten salt liquid level is strongly oxidized under the action of furnace mouth airflow at a high temperature of 800 ℃.

However, in practical application, the protection methods such as water cooling and iron wire winding are difficult to be conveniently implemented, and even if the protection methods are used upside down, the total service life of the tungsten cathode cannot exceed 1 year due to the fact that the local rapid size of the tungsten cathode is reduced, so that the inert cathode material is rapidly consumed, and the cost is increased.

Disclosure of Invention

In order to solve the problems of tungsten and molybdenum cathodes in the process of preparing rare earth metals by molten salt electrolysis in the prior art, the invention aims to provide a molten salt non-electrolysis infiltration local treatment method for prolonging the service life of the tungsten and molybdenum cathodes of the rare earth molten salt electrode. The method has the advantages of simple process, easy operation, low synthesis temperature, short heat preservation time and the like, and the infiltrated layer and the matrix metal are metallurgically bonded, so the bonding is very firm and is not easy to fall off.

In order to achieve the purpose, the invention adopts the technical scheme that:

a fused salt non-electrolysis infiltration local treatment method for realizing the service life extension of a tungsten cathode and a molybdenum cathode of a rare earth fused salt electrode is used for carrying out fused salt infiltration silicon preparation on the tungsten cathode and the molybdenum cathode to improve the hot corrosion resistance, and comprises the following steps:

and (1) protecting a non-seepage area by using a titanium anti-seepage clamp.

Specifically, by utilizing the characteristic that the metal titanium and the molten salt do not generate the siliconizing reaction and the titanium material is easy to process, the pure titanium protection clamp is designed and processed according to the size of the tungsten cathode or the molybdenum cathode to protect a non-infiltration area so as to ensure that the non-infiltration area, namely a protection area, is not contacted by the high-temperature molten salt and stop the siliconizing process.

And (2) pretreating the surface of the part to be infiltrated of the tungsten cathode or the molybdenum cathode.

Specifically, the pretreatment is mechanical leveling and oil removal, and the surface is ensured to have no oil stain, no pollutant adhesion and no obvious oxide layer. Wherein, the surface mechanical leveling can be selected from manual polishing, mechanical polishing and the like. The degreasing step can be ultrasonic cleaning with acetone for 15min, dehydrating with anhydrous ethanol, and drying at 60 deg.C for 6 h.

And (3) immersing the pretreated tungsten cathode or molybdenum cathode in the mixed molten salt for non-electrolysis neutral molten salt siliconizing, and preparing a metal silicide infiltrated layer on the tungsten cathode or molybdenum cathode through in-situ reaction, wherein the mixed molten salt consists of neutral salt, siliconizing agent and Si powder.

Specifically, the mixed molten salt may be contained in an alumina crucible. The neutral salt adopted by the invention can be a mixture of NaCl, KCl and NaF, and the siliconizing agent adopts Na₂SiF₆. The mixed molten salt comprises 30-35% of NaCl, 30-35% of KCl, 10-15% of NaF and 0-5% of Na in terms of mole fraction₂SiF₆15 to 20% Si and Na₂SiF₆The dosage is not 0; preferably 33% NaCl, 33% KCl, 14% NaF, 5% Na₂SiF₆15% Si. Before the mixed molten salt is prepared, drying neutral salt at 100-110 ℃ for 2-6 h, then uniformly mixing the neutral salt with a siliconizing agent, grinding the mixture into fine powder, finally adding Si powder, and putting a quartz rod into the prepared mixed molten salt to stabilize the concentration of an Si source in the diffusion plating process.

The preparation temperature of the silicide infiltration layer in the step is generally 830-900 ℃, and the heat preservation time is about 2-6 hours.

And (4) after the silicide infiltrated layer is prepared, quickly taking out the tungsten cathode or the molybdenum cathode, placing the tungsten cathode or the molybdenum cathode in air for natural cooling, and cleaning and drying.

Specifically, the residual salt on the surface of the sample can be removed by repeatedly cleaning with clear water, and the sample is dried after being sequentially subjected to ultrasonic cleaning with acetone and absolute ethyl alcohol.

Compared with the prior art, the method adopts the fused salt non-electrolysis infiltration technology to generate the WSi on the pretreated tungsten/molybdenum base material through the surface thermal diffusion reaction₂/MoSi₂The infiltration layer forms metallurgical bonding with the matrix, the connection is firm and not easy to fall off, and the WSi can be fully exerted₂/MoSi₂The characteristics of refractory property, molten salt corrosion resistance and high-temperature oxidation resistance of the intermetallic compound coating material make the intermetallic compound coating material utilized as a protective coating material. More importantly, the preparation process can regulate and control the thickness of the infiltrated layer by controlling the temperature and the heat preservation timeThe method has the advantages of good controllability, simple and convenient operation, low cost, good compactness of the obtained infiltrated layer, capability of batch production, obvious prolongation of the service life of the tungsten/molybdenum cathode, reduction of the production cost of enterprises and good application prospect.

Drawings

Fig. 1 is a microstructure diagram of a carburized layer cross section of a tungsten/molybdenum base material subjected to molten salt nonelectrolytic carburization, where (a) is a metallographic photograph of a carburized layer cross section of a tungsten sample coated with a metal silicide carburized layer prepared in example 1, (b) is an SEM photograph of a carburized layer cross section of a tungsten sample coated with a metal silicide carburized layer prepared in example 1, (c) is a metallographic photograph of a carburized layer cross section of a molybdenum sample coated with a metal silicide carburized layer prepared in example 2, and (d) is an SEM photograph of a carburized layer cross section of a molybdenum sample coated with a metal silicide carburized layer prepared in example 2.

FIG. 2 is an XRD spectrum of the surface of the infiltrated layer after molten salt non-electrolytic infiltration treatment of the tungsten-based and molybdenum-based materials. Wherein (a) is the diffusion layer surface XRD pattern of the tungsten sample coated with the metal silicide diffusion layer prepared in example 1, and (b) is the diffusion layer surface XRD pattern diffusion layer section of the molybdenum sample coated with the metal silicide diffusion layer prepared in example 2.

FIG. 3 is a graph showing the hardness distribution of a tungsten-based or molybdenum-based material after molten salt non-electrolytic cementation treatment. Wherein (a) is a hardness profile of a cross section of the tungsten sample coated with the metal silicide infiltrated layer prepared in example 1, and (b) is a hardness profile of a cross section of the molybdenum sample coated with the metal silicide infiltrated layer prepared in example 2.

FIG. 4 is the mass change rate of the carburized layer of the tungsten substrate of example 1 and the molybdenum substrate of example 2 after molten salt nonelectrolytic carburization after being thermally corroded for 120 hours in a mixed molten salt of cerium fluoride and lithium fluoride at 700 + -10 ℃.

Detailed Description

The titanium anti-seepage fixture is used for protecting a non-seepage area, then the high-temperature diffusion seepage in-situ reaction is carried out on the tungsten and molybdenum cathode materials for electrolyzing the rare earth metal in neutral molten salt to prepare a metal silicide seepage layer, and the seepage layer has the characteristics of molten salt hot corrosion resistance and high-temperature oxidation resistance, so that the rapid hot corrosion damage of the tungsten and molybdenum cathodes on the upper part of the molten salt liquid level is effectively inhibited, the service life of the cathode is prolonged, and the molten salt siliconizing protection technology has the advantages of simplicity and convenience in operation, controllable process and low cost.

The embodiments of the present invention will be described in detail below with reference to the drawings and examples.

Example 1

(1) Cutting the sintered tungsten rod into 2X 0.5 (cm) by spark cutting³) The surface of the sample is sequentially polished on two sides by using 240#, 400#, 600#, 800# and 1000# metallographic water sand paper, then is ultrasonically cleaned for 15min by using acetone, is dehydrated by using absolute ethyl alcohol and is dried at the temperature of 60 ℃, and the drying time is 6h, so that the surface of the sample is smooth and flat, has metallic luster, does not have oil stain and rust attachment, and does not have an obvious oxide layer.

(2) The massage fraction is 33 percent of NaCl, 33 percent of KCl, 14 percent of NaF and 5 percent of Na₂SiF₆And 15% of Si are respectively weighed and put into an oven, dried for 2 hours at 105 ℃, ground into molten salt fine powder and uniformly mixed. And (2) pouring the molten salt into a 50mL alumina crucible, then immersing the tungsten sample treated in the step (1) into the mixed molten salt contained in the crucible to ensure that the surface of the sample is fully contacted with the molten salt, and vertically placing a quartz rod in the molten salt to stabilize the Si source infiltration agent.

(3) Then the crucible is put into a box type resistance furnace, and heat preservation is carried out for 4 hours after the temperature reaches 850 +/-10 ℃.

(4) And after the preparation of the permeable layer is finished, quickly taking out the quartz rod and the sample, placing the quartz rod and the sample in the air for natural cooling, repeatedly cleaning the quartz rod and the sample by using clear water to remove residual salt on the surface of the sample, sequentially and respectively ultrasonically cleaning the quartz rod and the sample by using acetone and absolute ethyl alcohol for 15min, and drying the quartz rod and the sample in an oven at 60 ℃ for 6 h.

As shown in fig. 1 (a) and (b), the tungsten sample coated with the metal silicide infiltrated layer prepared by the present example had an infiltrated layer (actually, a compound layer) with a thickness of 5 μm, and the infiltrated layer bonded to the tungsten substrate was metallurgically bonded and was not easily detached, and was clearly confirmed by a scanning electron microscope.

As shown in FIG. 2(a), infiltration of the tungsten sample coated with the metal silicide infiltration layer prepared by the present exampleThe XRD pattern of the surface of the layer shows that the positions of diffraction peaks all correspond to WSi₂Phase, a small amount of SiO was found₂The existence of molten salt impurities and no W element is found, which indicates that WSi detected on the surface of the substrate under the reaction condition₂The phases are the product of silicide percolation. Therefore, after the tungsten substrate is embedded for 4 hours at 850 ℃, a layer of dense and uniform WSi is formed on the surface₂And (5) infiltrating the layer.

As shown in fig. 3(a), the hardness profile of the cross section of the tungsten sample coated with the metal silicide infiltrated layer prepared by this example shows that there is an infiltrated layer about 15 μm thick, where the compound layer is about 5 μm (i.e., fig. 1) and the diffusion layer is about 10 μm thick. The hardness of the infiltration layer is far higher than that of the base material, so that the base material can be well protected.

As shown in FIG. 4, the tungsten sample coated with the metal silicide infiltrated layer prepared by this example had a mass change of +0.009g/cm after being thermally corroded in a molten salt of cerium fluoride and lithium fluoride at 700. + -. 10 ℃ for 120 hours²Compared with an untreated tungsten sample (-0.1256 g/cm)²) The protective layer plays a good role in protecting and can greatly reduce the hot corrosion rate of the tungsten cathode.

Example 2

(1) By means of spark-cutting atThe sintered molybdenum rod is cut into a wafer sample with the thickness of 5mm, the surface of the wafer sample is subjected to double-side polishing by using metallographic waterproof abrasive paper of No. 240, No. 400, No. 600, No. 800 and No. 1000 in sequence, then the wafer sample is ultrasonically cleaned for 15min by using acetone, dehydrated by using absolute ethyl alcohol and dried at the temperature of 60 ℃, and the drying time is 6h, so that the surface of the sample is smooth and flat, has metallic luster, does not have oil stain and rust attachment, and does not have an obvious oxide layer.

(2) The massage fraction is 33 percent of NaCl, 33 percent of KCl, 14 percent of NaF and 5 percent of Na₂SiF₆And 15% of Si are respectively weighed and put into an oven, dried for 2 hours at 105 ℃, ground into molten salt fine powder and uniformly mixed. Pouring the molten salt into a 50mL alumina crucible, and then immersing the molybdenum sample treated in the step (1) into the mixed molten salt contained in the crucible to ensure that the surface of the sample is fully connected with the molten saltAnd (3) contacting and vertically placing a quartz rod in the molten salt to stabilize the Si source permeating agent.

(3) Then the crucible is put into a box type resistance furnace, and heat preservation is carried out for 4 hours after the temperature reaches 850 +/-10 ℃.

(4) And after the preparation of the permeable layer is finished, quickly taking out the quartz rod and the sample, placing the quartz rod and the sample in the air for natural cooling, repeatedly cleaning the quartz rod and the sample by using clear water to remove residual salt on the surface of the sample, sequentially and respectively ultrasonically cleaning the quartz rod and the sample by using acetone and absolute ethyl alcohol for 15min, and drying the quartz rod and the sample in an oven at 60 ℃ for 6 h.

As shown in fig. 1 (c) and (d), the molybdenum sample coated with the metal silicide infiltrated layer prepared by the example had an infiltrated layer (actually, a compound layer) with a thickness of 17 μm, and the infiltrated layer bonded to the molybdenum substrate was metallurgically bonded and not easily detached, and could be clearly observed by a scanning electron microscope.

As shown in FIG. 2 (b), the XRD pattern of the surface of the diffusion layer of the molybdenum sample coated with the diffusion layer of metal silicide prepared in this example shows that the diffraction peaks are all corresponding to MoSi₂Phase, and found partial Si and SiO₂Residual salt exists, which indicates that MoSi is detected on the surface of the substrate under the reaction condition₂The phases are the product of silicide percolation. Therefore, after the molybdenum substrate is embedded for 4 hours at 850 ℃, a layer of dense and uniform MoSi is formed on the surface₂And (5) infiltrating the layer.

As shown in fig. 3 (b), the hardness profile of the cross section of the molybdenum sample coated with the metal silicide infiltrated layer prepared by this example shows that the compound layer is present only on the surface of the substrate and a part of the diffused layer is deep into the substrate, but the structure of the substrate itself is not changed. The substrate had a percolated layer of about 40 μm thickness, with a compound layer of about 17 μm (i.e., (c), (d) in FIG. 1) and a diffusion layer of about 23 μm thickness. And the hardness of the infiltration layer is far greater than that of the base material, so that the base material can be well protected.

As shown in FIG. 4, the molybdenum sample coated with the metal silicide infiltrated layer prepared by the example had a mass change rate of +0.0165g/cm after being thermally corroded in a molten salt of cerium fluoride and lithium fluoride at 700 + -10 ℃ for 120 hours²Compared with an untreated molybdenum sample (-0.4738 g/cm)²) The weight loss is greatly slowed down, which shows that the hot corrosion resistance rate of the molybdenum cathode can be greatly improved.

The molten salt siliconizing treatment method for remarkably reducing the hot corrosion rate of the rare earth molten salt electrolysis tungsten/molybdenum cathode by preparing the metal silicide infiltrated layer with the surface comprehensive properties of high melting property, molten salt corrosion resistance and high temperature oxidation resistance can effectively prolong the service life of the molten salt electrolysis tungsten/molybdenum cathode. The principles and embodiments of the present invention are explained in detail by taking W or Mo as an example, and the above description of the embodiments is only for the purpose of helping understanding the method and the core idea of the present invention, and a person skilled in the art can modify and adjust the method and the core idea of the present invention accordingly, so the content of the description should not be construed as limiting the present invention.