A method for regenerating a titanium-based electrode with a magneli phase as a transition layer

Abstract

The application discloses a kind of Magneli phase as transition layer's titanium-based electrode regeneration method, comprising the following operating steps: S1, waste electrode pretreatment: sequentially to the failure titanium-based electrode containing Magneli phase sub-titanium oxide transition layer is cleaned, dried, and surface attachments are removed;S2, electrolytic reduction: with failure titanium-based electrode as cathode, inert electrode is anode, is placed in electrolytic system and carries out electrolytic reduction;S3, transition layer stripping: by physical action makes reduction layer from the titanium-based body surface separation;S4, titanium-based body regeneration: to the titanium-based body after stripping is chemically cleaned, removes surface residual oxide, obtains clean regenerated titanium-based body.The application is by controlling the phase evolution law of transition layer itself, from micro interface, the binding force of transition layer and matrix is broken down, on the premise of guaranteeing titanium-based body zero damage, realizes the efficient peeling of transition layer and the collaborative recovery of resources.

Description

Technical Field

[0001] This invention relates to the field of electrode material recycling technology, and in particular to a method for regenerating titanium-based electrodes with a Magneille phase as the transition layer. Background Technology

[0002] In the chlor-alkali industry, hydrometallurgy, electroplating, water treatment, and cathodic protection, titanium-based coated electrodes (commonly known as DSA electrodes) have become indispensable core components. To further improve the service life, current efficiency, and adhesion between the coating and the substrate under extreme electrochemical environments, a dense intermediate layer is introduced between the titanium substrate and the active oxide layer. Magnelix phase titanium suboxide (general formula TinO2n-1, where n is an integer from 4 to 10) has become the preferred material for preparing high-performance electrode transition layers due to its metalloid conductivity, chemical stability, and excellent thermal expansion matching with the titanium substrate. Currently, the industrial sector commonly uses high-energy beam surface treatment technologies such as atmospheric plasma spraying (APS) or vacuum plasma spraying (VPS) to melt and deposit Magnelix phase powder onto the surface of a roughened titanium substrate, thereby constructing a physical barrier with a thickness typically of 50–500 μm, an interfacial bonding strength of over 50 MPa, and a hardness of 1000–1500 HV.

[0003] While the Magneli phase transition layer significantly enhances electrode durability, the subsequent recycling and regeneration of failed electrodes remains a long-standing pain point in the industry. Due to the strong physical intercalation and partial metallurgical bonding between the Magneli phase transition layer formed by plasma spraying and the titanium substrate, coupled with the extremely high chemical inertness and hardness of the Magneli phase material itself, it is extremely difficult to completely peel the failed transition layer off the substrate. Traditional mechanical peeling methods, such as high-pressure sandblasting or diamond grinding, while able to remove surface residues to some extent, easily cause irreversible physical damage to the titanium substrate during operation. Frequent mechanical impacts and grinding not only cause significant thinning and geometric deformation of the titanium substrate but also result in severe work hardening and deep scratches on its surface. This leads to uncontrolled flatness and roughness Ra value of the regenerated substrate. This damage directly weakens the structural integrity of the substrate, making the recycled titanium plates often unable to meet the assembly requirements of high-precision electrolytic cells, and even rendering them completely unusable after multiple reuses.

[0004] Besides the limitations of mechanical methods, existing chemical stripping technologies also face severe environmental and quality control challenges. Traditional chemical methods typically employ strong acids (such as concentrated sulfuric acid and hydrofluoric acid) or high-temperature molten alkalis for aggressive corrosion stripping. While strong acid etching can dissolve some oxides, it is extremely aggressive towards the titanium substrate itself, easily causing over-corrosion and hydrogen embrittlement, severely affecting the quality of subsequent coatings. High-temperature alkali fusion methods are not only energy-intensive but also operate in extremely harsh environments, producing waste alkali solutions and heavy metal-containing chemical sludge, which are typical hazardous wastes with high treatment costs and inconsistent with green manufacturing policies. More importantly, due to the unique crystal structure and chemical stability of Magneille phase materials, conventional acid and alkali media often fail to achieve directional and gentle stripping of the transition layer without damaging the substrate. This forces a large number of waste titanium electrodes to be treated as low-value waste titanium, resulting in a significant waste of metal resources.

[0005] It is evident that current recycling processes generally lack in-depth utilization of the physicochemical properties of Magneille phase materials. In actual production loops, if a full lifecycle cycle of "low-loss stripping - precise regeneration - in-situ recoating" of the titanium substrate cannot be achieved, the overall operating cost of the electrodes will remain high. Therefore, a new technology that can break through the limitations of traditional mechanical and chemical stripping is urgently needed. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for regenerating titanium-based electrodes using a Magneli phase as a transition layer. By regulating the phase evolution of the Magneli phase itself, the bonding force between the transition layer and the substrate is broken down at the microscopic interface. This achieves efficient shedding of the transition layer and synergistic resource recovery while ensuring zero damage to the titanium substrate.

[0007] The technical solution provided by this invention is as follows: A method for regenerating a titanium-based electrode with a Magneille phase as the transition layer includes the following steps: S1. Pretreatment of waste electrodes: The failed titanium-based electrodes containing the Magneli phase titanium suboxide transition layer are cleaned and dried in sequence to remove surface deposits. S2. Electrolytic reduction: Using the failed titanium-based electrode as the cathode and the inert electrode as the anode, electrolytic reduction is carried out in an electrolytic system to cause the Magneli phase suboxide titanium to undergo a phase transition and generate a reduced layer with weakened bonding force with the titanium matrix. S3. Transition layer peeling: The reduced layer is detached from the surface of the titanium substrate by physical action; S4. Titanium substrate regeneration: The stripped titanium substrate is chemically cleaned to remove residual oxides on the surface and obtain a clean regenerated titanium substrate.

[0008] The working principle of the titanium-based electrode regeneration method with Magneille phase as transition layer of the present invention is as follows: By utilizing the cathodic reduction phase transition effect of Magneli-phase titanium suboxide under specific electrochemical conditions, non-destructive exfoliation between the Magneli-phase titanium suboxide transition layer and the titanium substrate can be achieved. Magneli-phase materials possess high chemical stability and mechanical hardness, and a strong physical intercalation and micro-metallurgical bond is formed between the Magneli-phase material and the titanium substrate through plasma spraying. In the electrolytic reduction step, the failed electrode, acting as the cathode, is immersed in an alkaline or neutral electrolyte system and driven by an external constant current or voltage. Electrons are transferred through the titanium substrate to the interface between the substrate and the transition layer. Since the Magneli phase is an integral compound, its crystal structure undergoes an irreversible reduction reaction during the process of gaining electrons and accompanied by the migration equilibrium of cations in the electrolyte. This electrochemical reduction transforms Ti4O7 or Ti5O9, which has a high bonding strength crystal structure, into low-valence phases such as TiO, Ti2O, or even metallic titanium in situ. The phase transformation process induces the evolution of the microstructure inside the transition layer and at the interface. The phase transformation reaction causes changes in the cell volume and generates significant lattice distortion and non-uniform internal stress inside the originally dense transition layer. As the reduction reaction penetrates from the interface to the coating surface, the bonding force between the transition layer and the titanium substrate rapidly decreases from the initial 50 MPa or more to a weak van der Waals force level. At this time, the coating exhibits macroscopic looseness and physical embrittlement characteristics. In the subsequent physical stripping stage, the phase-change-transformed reduced layer completely detaches from the titanium substrate surface due to the loss of mechanical support caused by the cavitation effect generated by ultrasound or the kinetic energy impact of compressed air. The post-stripping regeneration process is primarily based on chemical complexation and surface purification. Utilizing the specific reactivity between oxalic acid solution and titanium oxides, the substrate surface is briefly immersed at high temperature. This step precisely dissolves the trace amounts of low-valence titanium oxides remaining in the micropores of the substrate after stripping. Simultaneously, the mild reaction conditions prevent over-corrosion or hydrogen embrittlement damage to the metallic titanium substrate. This process effectively removes impurities at the interface, restoring the substrate to its initial metallic cleanliness. Since the entire regeneration process in this invention does not involve mechanical grinding or strong corrosive corrosion, the titanium substrate retains the microscopic anchoring morphology and surface energy formed by the initial sandblasting treatment. This synergistic restoration of physical structure and chemical purity ensures that the regenerated substrate can re-form a high-strength bond with the newly sprayed Magneille phase powder during subsequent plasma recoating.

[0009] Preferably, the titanium-based electrode regeneration method with Magneille phase as transition layer further includes step S5, resource utilization of stripping product: collecting the powder generated by stripping in step S3, washing and drying the powder, and then oxidizing and calcining it at 400-600°C. The product obtained after calcination is reused as a spraying material to prepare Magneille phase transition layer.

[0010] Preferably, the general molecular formula of the Magneille phase suboxide in step S1 is Ti. n O 2n-1 , where n is an integer from 4 to 10.

[0011] Preferably, the phase composition of the reduction layer in step S2 includes low-valence titanium oxide, metallic titanium, or a mixture thereof; The low-valent titanium oxides include TiO and / or Ti2O.

[0012] Preferably, the electrolyte used in the electrolysis system in step S2 is at least one of NaOH solution, KOH solution, NaCl solution or Na2SO4 solution; The concentration of the electrolyte is 0.5–5 mol / L.

[0013] Preferably, the process parameters for electrolytic reduction in step S2 are: voltage 1.5–5V, current density 10–100 mA / cm². 2 Temperature 20–60℃, polarization time 10–120 min.

[0014] Preferably, the physical action in step S3 is selected from at least one of ultrasonic treatment, compressed air purging, or scraping.

[0015] Preferably, when the physical action in step S3 includes ultrasonic treatment, the parameters of the ultrasonic treatment are: power 100-500W, frequency 20-40kHz, and treatment time 5-20min.

[0016] Preferably, in step S4, the chemical cleaning process uses oxalic acid solution as the cleaning agent for soaking and cleaning. The oxalic acid solution has a mass percentage concentration of 1-20 wt%. The soaking temperature is 60-100℃, and the soaking time is 10-60 minutes.

[0017] Preferably, the surface roughness Ra of the regenerated titanium substrate obtained in step S4 is 1.6 to 6.3 μm, and the regenerated titanium substrate meets the requirement of being directly used to re-prepare titanium-based electrodes containing a Magneille phase transition layer.

[0018] The present invention has the following advantages over the prior art: 1. The titanium-based electrode regeneration method of the present invention, which uses the Magneille phase as a transition layer, utilizes the cathodic reduction phase transition principle to achieve active peeling of the Magneille phase transition layer. The titanium substrate is not thinned, deformed, or scratched, and the titanium substrate recycling rate is ≥95%. 2. In the titanium-based electrode regeneration method of the present invention with Magneli phase as transition layer, the stripped product can be regenerated in situ through simple oxidation calcination. The resulting regenerated substrate retains the original micro-anchoring structure. After recoating, the interfacial bonding strength is ≥50MPa, restoring it to the level of a newly made electrode. This method can be used as a principle for the preparation of new titanium-based electrodes, forming a complete industrial chain cycle of "recycling-regeneration-recoating". This not only realizes the recycling of resources and avoids waste pollution and resource waste, but also effectively reduces the production cost of the entire industry, which is conducive to sustainable development. 3. The titanium-based electrode regeneration method of the present invention with Magneille phase as transition layer adopts mild electrolyte and low concentration of oxalic acid throughout the process, replacing strong acid and strong alkali and high temperature alkali melting process, which significantly reduces hazardous waste discharge and environmental pollution; at the same time, the process conditions are mild (room temperature or low heat) and the processing time is short, which greatly reduces energy costs compared with traditional physical grinding or chemical peeling. 4. The titanium-based electrode regeneration method of the present invention with Magneli phase as transition layer has excellent compatibility with titanium-based electrodes of different specifications (TA2, TC4) and different sizes (especially large-area industrial electrodes), and is suitable for large-scale promotion and application. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a process flow diagram of the titanium-based electrode regeneration method using the Magneille phase as a transition layer in an embodiment of the present invention. Figure 2 These are SEM images comparing the surface morphology of the titanium substrate before and after peeling in Example 1 of the present invention. Figure 2 (a) is a SEM image of the surface of the titanium substrate before peeling in Example 1 of the present invention. Figure 2 (b) SEM image of the surface of the titanium substrate after peeling in Example 1 of the present invention; Figure 3 This is a microstructure diagram of the TC4 regenerated substrate after recoating in Example 2 of the present invention. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0022] like Figure 1 As shown, this embodiment of the invention provides a method for regenerating a titanium-based electrode with a Magneille phase as the transition layer, comprising the following steps: S1. Pretreatment of waste electrodes: The failed titanium-based electrodes containing the Magneli phase titanium suboxide transition layer are cleaned and dried in sequence to remove surface deposits. S2. Electrolytic reduction: Using a failed titanium-based electrode as the cathode and an inert electrode as the anode, electrolytic reduction is carried out in an electrolytic system to cause a phase transition in the Magneli phase of titanium suboxide, generating a reduced layer with weakened bonding to the titanium matrix. S3, Transition layer peeling: The reduced layer is detached from the surface of the titanium substrate through physical action; S4. Titanium substrate regeneration: The stripped titanium substrate is chemically cleaned to remove residual oxides on the surface and obtain a clean regenerated titanium substrate.

[0023] The following specific embodiments and comparative examples illustrate the titanium-based electrode regeneration method with Magneille phase as the transition layer in this invention.

[0024] Example 1: In this embodiment, a failed TA2 industrial pure titanium-based electrode was selected, and its surface was loaded with a Ti4O7 transition layer through a plasma spraying process. The measured average thickness of the transition layer was 200 μm.

[0025] First, the waste electrodes are placed in deionized water and deep cleaned for 20 minutes using ultrasonic cavitation effect to thoroughly remove residual electrolytes and impurities in the micropores; then they are placed in a forced-air drying oven and dried with hot air circulation at 70°C for 40 minutes to ensure that the electrode surface and pores are completely dry.

[0026] A 3 mol / L NaOH solution was used as the electrolyte, a waste electrode was used as the cathode, and a chemically stable titanium mesh was used as the anode. It operated in constant current mode, with a set voltage of 3V and a current density maintained at 30 mA / cm². 2 The cell temperature was maintained at 40℃. After the reaction began, the cathode surface color was observed to gradually change from a typical bluish-black to a dark gray, which is a macroscopic characterization of the phase transition reduction of Ti4O7. After 35 minutes of electrolysis, the internal lattice structure of the transition layer was distorted, and the original high-strength bonds were destroyed.

[0027] The reacted electrode was transferred to an ultrasonic cleaner and treated for 12 minutes at 300W and 30kHz. Due to interfacial stress mismatch caused by the phase transition, the transition layer flaked off in a flat, fragmented manner. Subsequently, the exposed substrate was immersed in a 10wt% oxalic acid solution and chemically regenerated at 90°C for 20 minutes to remove trace amounts of residual oxides from the surface.

[0028] The powder collected from the stripping process was washed, dried, and then calcined at 500°C. The resulting product was reused as a coating material for preparing the Magneli phase transition layer.

[0029] The surface of the regenerated titanium substrate was found to be smooth and free of microscopic corrosion pits or physical scratches after profiling using the stylus profilometry method. The measured surface roughness Ra was 3.2 μm. Since the original sandblasting morphology was not damaged, the titanium substrate can be used to re-prepare titanium-based electrodes containing a Magneille phase transition layer (plasma recoating) without secondary treatment.

[0030] Example 2: The difference between this embodiment and Embodiment 1 is that a failed high-strength TC4 titanium alloy base electrode is selected, with its transition layer consisting of a mixed phase of Ti4O7 and Ti5O9. After pretreatment, cathodic polarization is performed in a 1 mol / L NaCl neutral solution, with a voltage of 2.5 V and a current density of 50 mA / cm². 2 The reaction was carried out at 25°C for 60 minutes; the loosened reduction layer was initially purged with compressed air at 0.5 MPa to peel off over a large area, followed by short-term ultrasonic cleaning, and finally the matrix was regenerated by soaking in 15 wt% oxalic acid at 85°C for 25 minutes.

[0031] Surface testing of the regenerated titanium substrate (using existing coating peeling test methods) showed that the transition layer peeling rate was as high as 99.2%, and the titanium substrate recycling rate reached 96%. Electron microscopy observation of samples after recoating the regenerated substrate with a Magneille phase transition layer revealed that the interface bonding of the samples was extremely dense, with a measured bonding strength as high as 62 MPa, demonstrating the excellent applicability of the process to the alloy substrate.

[0032] like Figure 3 As shown, this interface state diagram corresponds to the microstructure of the TC4 regenerated substrate after recoating in Example 2. Figure 3 The newly sprayed Magneli phase showed a dense bond with the substrate interface, without cracks or pores, which is in complete agreement with the high bonding strength of 62 MPa measured in Example 2, proving the high activity and reliability of the regenerated substrate.

[0033] Example 3: The difference between this embodiment and Embodiment 1 is that a failed orthographic projection area of ​​1.0m² is selected. 2 A large plate-type titanium electrode (1000mm × 1000mm) with a transition layer thickness of 300μm was used. A high-concentration electrolyte of 5mol / L NaOH was employed to ensure high conductivity over a large area. The set voltage was 4V and the current density was 40mA / cm. 2 The reaction was carried out at 50℃ for 90 minutes. The peeling process employed a moving spray ultrasonic peeling technique to ensure uniform peeling of large workpieces. Finally, deep regeneration was achieved by immersion in 20wt% oxalic acid at 95℃ for 30 minutes. This process successfully solved the bottleneck problems of easy deformation and incomplete peeling of large workpieces in traditional recycling. The regenerated substrate fully meets the process standards for high-precision spraying.

[0034] Comparative Example 1: Waste titanium-based electrodes of the same type (TA2 / Ti4O7) were treated using traditional mechanical grinding methods, and the results were compared with those of Example 1. When using the traditional grinding process, due to the extremely high hardness of the Magneille phase, a large grinding force was required to completely remove the coating, resulting in a significant reduction in the thickness of the titanium substrate by 0.12 mm and severe mechanical scratches on the surface. The surface roughness Ra soared to over 12 μm, exceeding the range of the spraying process. Mechanical stress caused a geometric deformation of 0.8 mm in the titanium plate. After recoating the damaged substrate, the interfacial bonding strength was only 28 MPa, which could not meet the electrode service requirements. In contrast, after treatment using the cathodic reduction method of Example 1 of this invention, the titanium substrate achieved near-zero loss peeling. The titanium substrate was neither thinned nor scratched, completely retaining its original geometric dimensions and mechanical properties. The bonding strength of the regenerated substrate after recoating reached over 60 MPa, significantly better than the traditional process.

[0035] like Figure 2 As shown, the reduction and stripping effects of Example 1 and Comparative Example 1 were compared using SEM. Figure 2 (a) shows the dense Magneli phase coating before stripping; Figure 2 (b) shows the regenerated substrate after treatment in Example 1, with a clean surface that retains the original micro-anchoring points and without the severe scratches or excessive corrosion pits seen in Comparative Example 1. It is evident that the present invention achieves effective non-destructive peeling compared to existing conventional mechanical peeling methods.

[0036] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for regenerating a titanium-based electrode with a Magneille phase as the transition layer, characterized in that, The following steps are included: S1. Pretreatment of waste electrodes: The failed titanium-based electrodes containing the Magneli phase titanium suboxide transition layer are cleaned and dried in sequence to remove surface deposits. S2. Electrolytic Reduction: Using the failed titanium-based electrode as the cathode and the inert electrode as the anode, electrolytic reduction is performed in an electrolytic system to cause a phase transition in the Magneille phase of titanium suboxide, generating a reduced layer with weakened adhesion to the titanium matrix. The electrolyte used in the electrolytic system is at least one of NaOH solution, KOH solution, NaCl solution, or Na2SO4 solution, with a concentration of 0.5–5 mol / L. The process parameters for electrolytic reduction are: voltage 1.5–5 V, current density 10–100 mA / cm². 2 Temperature 20–60℃, polarization time 10–120 min; S3. Transition layer peeling: The reduced layer is detached from the surface of the titanium substrate by physical action; S4. Titanium substrate regeneration: The stripped titanium substrate is chemically cleaned to remove residual oxides on the surface and obtain a clean regenerated titanium substrate. S5. Resource utilization of stripping products: Collect the powder generated from the stripping in step S3, wash and dry the powder, and then oxidize and calcine it at 400-600℃. The product obtained after calcination is reused as a raw material for preparing the Magneli phase transition layer.

2. The method for regenerating a titanium-based electrode with a Magneille phase as the transition layer according to claim 1, characterized in that, The general molecular formula of the Magneille phase titanium suboxide in step S1 is Ti. n O 2n-1 , where n is an integer from 4 to 10.

3. The method for regenerating a titanium-based electrode with a Magneille phase as the transition layer according to claim 1, characterized in that, The phase composition of the reduction layer in step S2 includes low-valence titanium oxide, metallic titanium, or a mixture thereof; The low-valent titanium oxides include TiO and / or Ti2O.

4. The method for regenerating a titanium-based electrode with a Magneille phase as a transition layer according to any one of claims 1-3, characterized in that, The physical action in step S3 is selected from at least one of ultrasonic treatment, compressed air purging, or scraping.

5. The method for regenerating a titanium-based electrode with a Magneille phase as the transition layer according to claim 4, characterized in that, When the physical action in step S3 includes ultrasonic treatment, the parameters of ultrasonic treatment are: power 100-500W, frequency 20-40kHz, and treatment time 5-20min.

6. The method for regenerating a titanium-based electrode with a Magneille phase as a transition layer according to any one of claims 1-3, characterized in that, In step S4, the chemical cleaning process uses oxalic acid solution as a cleaning agent for soaking and cleaning. The oxalic acid solution has a mass percentage concentration of 1-20 wt%. The soaking temperature is 60-100℃, and the soaking time is 10-60 minutes.

7. The method for regenerating a titanium-based electrode with a Magneille phase as a transition layer according to any one of claims 1-3, characterized in that, The surface roughness Ra of the regenerated titanium substrate obtained in step S4 is 1.6 to 6.3 μm, and the regenerated titanium substrate meets the requirements for direct use in the re-preparation of titanium-based electrodes containing a Magneille phase transition layer.

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