De-alumination method and application of periodic lamella structure coating

Abstract

The application belongs to the field of new materials and new material preparation technology, and particularly relates to a method for removing Al from a periodic lamellar structure coating and application, the method comprising soaking a test piece containing a periodic lamellar structure coating in MoCl5 molten salt for immersion corrosion, specifically, Fe-Cr-B cast steel is subjected to hot-dip pure Al-diffusion heat treatment, and then a periodic lamellar structure composed of Cr-Al-B MAB phase and FeAl3 arranged alternately is generated in situ. Then the coating of the periodic lamellar structure is immersed in MoCl5 molten salt at 200-250 DEG C for a certain time (0.5-2 h) and taken out, and the periodic lamellar structure coating with Al removed can be obtained, and the Al removal mode is to generate AlCl3 and volatilize. The periodic lamellar structure coating with Al removed can be obtained at a lower temperature and in a shorter time through a simple process, and the corrosion of MoCl5 molten salt can be blocked.

Description

Technical Field

[0001] This invention relates to the field of novel materials, and in particular to a method and application for removing Al from a periodic layered coating. Background Technology

[0002] Studies on hot-dip aluminizing have revealed that when Fe-Cr-B cast steel with specific compositions is hot-dip aluminized, a periodic lamellar structure (PLS) coating is formed in situ at the interface between (Cr, Fe)₂B and the molten aluminum. This PLS consists of alternating FeAl₃ and Cr-Al-B MAB phases. Elements such as Zn and Si in the molten aluminum significantly affect the composition of the Cr-Al-B MAB phase, forming Cr-(Al, Zn)-B or Cr-(Al, Si)-B MAB solid solutions, respectively. The MAB phase is a special type of compound with atomically layered arrangements, where M is a transition metal, A is a group 13-16 element, and B is boron. The MAB phase is similar to the widely studied MAX phase (where X represents C and N).

[0003] Huang Qing et al. from the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, studied the reaction between powdered Ti2AlC and other MAX phase precursors and Lewis acid molten salts such as ZnCl2. They found that when the ratio of MAX phase powder to molten salts such as ZnCl2 is small, the MAX phase undergoes a topological transformation to form a new Ti2ZnC MAX phase. However, when the ratio of molten salt is large, the MAX phase undergoes complete de-Al removal to form MXene. Similarly, other researchers have studied the reaction of MoAlB MAB phases with molten salts such as ZnCl2, finding that the MoAlB MAB phase undergoes de-Al removal to form a new Mo2AlB2MAB phase, indicating that the de-Al removal of MoAlB MAB under the influence of molten salt is incomplete. Furthermore, the above reactions occurred at relatively high temperatures, all above 500℃, and for relatively long times (generally exceeding 5 hours). Clearly, the chemical reactions occurring when the MAX phase and MAB phase react with molten salt are not entirely the same. On the other hand, MXene / MBene has great application prospects in lithium batteries, hydrogen production, and other fields due to its unique layered structure and large specific surface area. However, the de-Al removal mechanism of the Cr-Al-B MAB phase is still unknown. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method and application for removing Al from a periodic layered structure coating, for preparing a periodic layered structure coating with Al removed.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for removing Al from a periodic lamellar structure coating, wherein the sample containing the periodic lamellar structure coating is immersed in MoCl5 molten salt for etching at a temperature of 200~250℃ for 0.5~2 hours, and then taken out to obtain a sample containing a periodic lamellar structure coating with Al removed.

[0006] In a preferred embodiment, the preparation method of the specimen containing the periodic lamellar structure coating is as follows: Fe-Cr-B cast steel is immersed in pure Al melt for hot-dip coating with pure Al. The Fe-Cr-B cast steel has a Cr content of 15~30 wt.% and a B content of 4~7 wt.%. After the hot-dip coating reaction has been carried out for a certain period of time, the specimen is quickly removed from the aluminum melt, air-cooled, and then subjected to diffusion heat treatment. A periodic lamellar structure coating composed of alternating Cr-Al-B MAB phase and FeAl3 is generated on the interface of the boride (Cr, Fe)2B / Al melt in the Fe-Cr-B cast steel.

[0007] In a preferred embodiment, the temperature of the MoCl5 molten salt is 200°C.

[0008] In a preferred embodiment, the atmosphere for the MoCl5 molten salt corrosion of the specimen containing the periodic lamellar structure coating is any one of atmosphere, argon, or vacuum.

[0009] In the preferred embodiment, when the specimen containing the periodic lamellar structure coating is subjected to the MoCl5 molten salt corrosion, the Al removal is achieved by generating AlCl3 and volatilizing it at high temperature.

[0010] In a preferred embodiment, the Al removal process of the Cr-Al-B MAB phase in the periodic lamellar structure coating undergoes the following intermediate reaction: 8Cr3AlB4(s) + 9Cl - (l)→2 Cr2B(s)+ 5 Cr4AlB6(s) + 3 AlCl3(g).

[0011] In a preferred embodiment, the final Al removal products of the Cr-Al-B MAB phase in the periodic layered coating are Cr2B and Cr2B3, which block the erosion of MoCl5 molten salt.

[0012] In a preferred embodiment, the Al removal reaction of the FeAl3 phase in the periodic lamellar structure coating undergoes the following intermediate reaction: FeAl3(s) + 9Cl - (l)→Fe (s)+ 3 AlCl3(g).

[0013] In a preferred embodiment, the final product of the FeAl3 phase in the periodic lamellar structure coating after being corroded by MoCl5 molten salt is FeCl3, which volatilizes to form pores.

[0014] This invention also provides an application of a method for removing Al from periodic layered coatings, specifically for removing Al from hot-dip aluminized coatings on Fe-Cr-B cast steel.

[0015] The present invention provides a method and application for removing Al from a periodic layered coating, which has the following beneficial effects: 1. By hot-dip galvanizing Fe-Cr-B cast steel with pure Al and then performing diffusion heat treatment, a PLS coating consisting of alternating FeAl3 and Cr-Al-BMAB phases can be obtained. Then, by performing MoCl5 molten salt corrosion, Al-free PLS can be prepared.

[0016] 2. When the Cr-Al-B MAB phase in PLS reacts with MoCl5, a complete Al removal reaction occurs, generating Cr2B and Cr2B3. This is completely different from the partial Al removal that occurs when the MoAlB MAB phase reacts with ZnCl2 molten salt, generating Mo2AlB2.

[0017] 3. During the above Al removal reaction, the temperature of the MoCl5 molten salt is relatively low (200-250℃) and the reaction time is also short (0.5-2h), which greatly improves the efficiency of Al removal.

[0018] 4. The Cr2B and Cr2B3 mixture generated after Al removal by PLS is distributed in the original Cr-Al-B MAB phase, which acts as a barrier to prevent the erosion of MoCl5 molten salt. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 The image shows the cross-sectional microstructure of the Fe-Cr-B cast steel prepared in Example 1 after hot-dip aluminized and diffusion heat-treated treatment and MoCl5 molten salt corrosion. Figure 2 The Cr element distribution diagram of the cross section of the hot-dip aluminized and diffusion-heat-treated Fe-Cr-B cast steel prepared in Example 1 after MoCl5 molten salt corrosion; Figure 3 Al element distribution diagram of the cross section of the hot-dip aluminized and diffusion-heat-treated Fe-Cr-B cast steel prepared in Example 1 after MoCl5 molten salt corrosion; Figure 4 The Fe element distribution diagram of the cross section of the hot-dip aluminized and diffusion-heat-treated Fe-Cr-B cast steel prepared in Example 1 after MoCl5 molten salt corrosion; Figure 5This is a cross-sectional microstructure of the PLS coating in Example 2 after being etched with MoCl5 molten salt; Figure 6 This is a cross-sectional microstructure of the PLS coating in Example 3 after being etched with MoCl5 molten salt. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0021] The embodiments described herein are clearly and completely provided; however, they are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0022] The periodic lamellar (PLS) coatings in the following embodiments are prepared by the following methods: Step 1: Prepare Fe Cr Cast steel B was cut into 70mm pieces. 10mm A 4mm sample, suspended by a steel wire, was immersed in pure Al melt for hot-dip aluminizing. The Fe-Cr-B cast steel contained 15-30 wt.% Cr and 4-7 wt.% B. The pure Al melt temperature was 750℃, and the hot-dip coating time was 30 minutes. After the time was up, the sample was removed and cooled to room temperature in air. The sample was cut in half using wire cutting, and after grinding and polishing, a metallographic specimen was prepared. The microstructure was observed using a scanning electron microscope in backscattered electron mode, revealing that PLS was generated at the (Cr,Fe)2B / Al melt interface after hot-dip aluminizing.

[0023] Step 2: Place the hot-dip aluminized sample into a muffle furnace for diffusion heat treatment at 750℃ for 60 minutes, followed by furnace cooling. Cut the sample from the center using wire cutting, and after grinding and polishing, observe the cross-sectional microstructure. An increase in the number and thickness of PLS ​​can be observed.

[0024] The above two steps can be used to prepare a specimen with a PLS coating.

[0025] Fe Cr B-cast steel is prepared by the following method: 1. Batching: Calculate the required amount of micro-carbon ferrochrome Fe based on the designed alloy composition. 58wt.%Cr 0.06wt.%C, Fe The total weight of 18 wt.%B master alloy and pig iron is 10 kg.

[0026] 2. Melting: The weighed raw materials from step ① are placed into a vacuum melting furnace. After complete melting, the furnace is superheated to 1600℃ and held for 15 minutes. The melted material is then poured into a metal mold and cooled to obtain Fe. Cr B cast steel.

[0027] The microstructure of the prepared Fe-Cr-B cast steel mainly consists of a grayish-black (Cr,Fe)₂B phase and grayish-white α-Fe. The microstructures in the examples were captured using a scanning electron microscope in backscattered electron mode; the whiter the area, the higher the average atomic number.

[0028] Example 1: The prepared Fe-Cr-B cast steel containing a PLS coating was immersed in a MoCl5 molten salt at 250℃ for 1.5 h, and then removed to obtain an Al-free PLS coating. After polishing, the cross-sectional microstructure was observed, as shown... Figure 1 As shown, the PLS coating after Al removal, especially the original FeAl3 phase in the PLS, appears noticeably "white." The surface distributions of Cr, Al, and Fe are as follows: Figure 2 , 3 As shown in Figure 4, Cr represents the location of the original Cr-Al-B MAB phase in PLS, while Fe represents the location of the original FeAl3 phase. It can be seen that the PLS coating corroded by MoCl5 molten salt is noticeably "whiter," especially at the FeAl3 phase sites, where the whitening is more severe. The Al content in the corroded area is very low, which is significantly different from the Al distribution in the uncorroded PLS area, indicating that Al removal occurred in the PLS coating after MoCl5 molten salt corrosion. The Cr-Al-B MAB phase forms a large number of layered phases after being corroded by MoCl5 molten salt, which can be identified as Cr2B and Cr2B3. These layered phases can block the erosion of MoCl5 molten salt.

[0029] Example 2: Unlike Example 1, the prepared Fe-Cr-B cast steel containing PLS coating was immersed in MoCl5 molten salt at a temperature of 200°C for 0.5 h, and then removed to obtain the Al-free PLS coating.

[0030] After grinding and polishing, the cross-sectional microstructure was observed, such as... Figure 5 As shown, compared to the uncorroded inner PLS coating area, the outer side of the PLS coating in contact with the MoCl5 molten salt appears "white," indicating Al desorption. Furthermore, the PLS coating shows no obvious corrosion pits, demonstrating strong resistance to MoCl5 molten salt corrosion.

[0031] Example 3: Unlike Example 1, the prepared Fe-Cr-B cast steel containing a PLS coating was immersed in MoCl5 molten salt at 250°C for 2 hours, yielding an Al-degraded PLS coating. After polishing, the cross-sectional microstructure revealed that the original FeAl3 phase in the PLS coating had turned white, indicating Al removal. Numerous corrosion pits were also observed at the locations of the whitened FeAl3 phase, suggesting that the final corrosion products had volatilized under the high-temperature molten salt. However, the Al-degraded Cr-Al-B MAB phase still effectively resisted molten salt corrosion, demonstrating strong resistance to MoCl5 molten salt corrosion.

[0032] The above embodiments are merely preferred technical solutions of the invention and should not be considered as limitations on the invention. The scope of protection of the invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the invention.

Claims

1. A method for removing Al from a periodic layered plating structure, characterized in that, The specimen containing the periodic lamellar structure coating was immersed in MoCl5 molten salt for etching at a temperature of 200~250℃ for 0.5~2h, and then removed to obtain the specimen containing the periodic lamellar structure coating with Al removal. The preparation method of the specimen containing the periodic lamellar structure coating is as follows: Fe-Cr-B cast steel is immersed in pure Al melt for hot-dip aluminum plating. The Cr content of the Fe-Cr-B cast steel is 15~30 wt.% and the B content is 4~7 wt.%. After the hot-dip aluminum plating reaction has been carried out for a certain period of time, the specimen is quickly taken out of the aluminum melt, air-cooled, and then subjected to diffusion heat treatment. As a result, a periodic lamellar structure coating composed of alternating Cr-Al-B MAB phase and FeAl3 is generated on the interface of the boride (Cr, Fe)2B / Al melt in the Fe-Cr-B cast steel.

2. The method for removing Al from a periodic layered plating structure according to claim 1, characterized in that: The temperature of the MoCl5 molten salt is 200℃.

3. The method for removing Al from a periodic layered plating structure according to claim 1, characterized in that, The atmosphere for the MoCl5 molten salt corrosion of the specimen containing the periodic lamellar structure coating is any one of atmosphere, argon, or vacuum.

4. The method for removing Al from a periodic layered plating structure according to claim 1, characterized in that, When specimens with periodic lamellar coatings undergo MoCl5 molten salt corrosion, Al removal is achieved by generating AlCl3 and then volatilizing it at high temperature.

5. The method for removing Al from a periodic layered plating structure according to claim 1, characterized in that, The Al removal process of the Cr-Al-B MAB phase in the periodic lamellar coating undergoes the following intermediate reaction: 8Cr3AlB4(s) + 9Cl - (l)→2 Cr2B(s)+ 5 Cr4AlB6(s) + 3 AlCl3(g).

6. The method for removing Al from a periodic layered plating structure according to claim 1, characterized in that, The final Al removal products of the Cr-Al-B MAB phase in the periodic layered coating are Cr2B and Cr2B3, which can block the erosion of MoCl5 molten salt.

7. The method for removing Al from a periodic layered plating structure according to claim 1, characterized in that, The de-Al reaction of the FeAl3 phase in the periodic lamellar coating undergoes the following intermediate reaction: FeAl3(s) + 9Cl - (l)→Fe(s)+ 3 AlCl3(g).

8. The method for removing Al from a periodic layered plating structure according to claim 1, characterized in that, The FeAl3 phase in the periodic lamellar structure coating is corroded by MoCl5 molten salt, and the final product is FeCl3, which volatilizes to form pores.

9. The application of the Al removal method for a periodic layered plating structure according to any one of claims 1 to 8, characterized in that, Al removal applied to hot-dip aluminized coatings on Fe-Cr-B cast steel.

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