Method for preparing TiB2 cathode coating through oxide electrodeposition

Abstract

The invention discloses a method for preparing a TiB2 cathode coating by using oxide electrodeposition, which comprises the following steps: preparing LiF, NaF, KF, AlF3 and KCl according to a certain molar ratio as a supporting electrolyte, adding B2O3 and TiO2 according to different boron-titanium molar ratios as electrolysis raw materials to prepare a LiF-NaF-KF-AlF3-KCl-B2O3-TiO2 mixed molten salt system, melting at a high temperature of 700-900 DEG C, immersing into a double graphite electrode for electrolysis for 0.5-6 hours, controlling the current density to be 0.3-1A / cm < 2 >, and carrying out electrodeposition to obtain a TiB2 cathode coating. The distance between electrodes is 2-8cm, and a uniform and flat TiB2 coating can be formed on a cathode carbon block. According to the method, the uniform and flat TiB2 cathode coating can be prepared, meanwhile, the method has the advantages that equipment is simple, cost is low, reaction conditions are easy to control, and the method is relatively friendly to the environment and has practicability and economical efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of cathode coating preparation, and in particular to a method for preparing a TiB2 cathode coating by molten salt electrodeposition. Background Art

[0002] Aluminum electrolysis production is an energy-intensive industrial process, accounting for about 2% of global electricity consumption. Traditional graphite cathodes consume and produce a large amount of carbon dioxide during use, causing environmental pollution. In addition, graphite cathodes have a limited lifespan and need to be replaced regularly, increasing production costs.

[0003] TiB2 has a high melting point and hardness, can withstand high temperatures and highly corrosive electrolytes, and prolongs the life of the cathode; it also has good electrical conductivity, which can effectively transfer current to the electrolyte and improve electrolysis efficiency. In addition, TiB2 also has good oxidation resistance and low permeability, which can prevent the cathode from oxidizing at high temperatures and prevent the electrolyte from penetrating into the cathode, thereby slowing down cathode oxidation corrosion and increasing its service life. TiB2 cathode coating technology has been widely used in aluminum electrolysis production, which can significantly improve production efficiency and reduce production costs.

[0004] At present, the preparation methods of titanium boride cathode coating mainly include chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma spraying and electrodeposition. Chemical vapor deposition is a method in which the reactants react chemically in the gas phase with the help of thermal radiation under the conditions of controlled temperature and pressure and deposit a coating on the surface of the substrate. Its limitations are high requirements for reactants, complex and expensive equipment, and the generation of toxic and corrosive gases during the reaction. Physical vapor deposition is a method in which the surface of the material source is vaporized into gaseous atoms, molecules or partially ionized into ions under vacuum conditions by physical methods, and a coating is deposited on the surface of the substrate through low-pressure gas or plasma. Its limitations are uneven deposition, high equipment investment costs, difficult maintenance, and low production efficiency. Plasma spraying is spraying in a plasma state. Through the action of plasma energy, the spraying material is melted and sprayed onto the surface of the material. Its limitations are complex mechanical structure, low material utilization, poor stability, etc. The titanium boride cathode coating prepared by electrodeposition has high purity and good density, and can fit tightly with the graphite cathode. In addition, this method has simple process and low production cost, and has attracted much attention in recent years.

[0005] The molten salt system for preparing titanium boride cathode coating by electrodeposition generally has two types: halides and oxides. The halide system is generally composed of a low-melting mixture of alkali metal fluoroborate (KBF4) as an active electrolyte, alkali metal fluorotitanate, and alkali metal halides as a carrier electrolyte. The oxide system is generally composed of titanium and boron oxides, mainly including Me2B4O7, MeBO2, B2O3, TiO2, etc., where Me refers to alkali metals. Among them, the halide system has a low melting point and a low electrolysis temperature, and the obtained coating is coherent and uniform with good quality. However, it is relatively expensive, and toxic or corrosive gases will be generated during use. In contrast, the oxide system is cheap, simple and stable, does not produce harmful gases, is very environmentally friendly, and has more development prospects.

[0006] In view of the above problems existing in the preparation and use of TiB2 cathode coating, the present invention proposes to use oxide electrodeposition to prepare TiB2 cathode coating in LiF-NaF-KF-AlF3-KCl molten salt system, and proves its feasibility through practice. Summary of the invention

[0007] In view of the above-mentioned shortcomings and deficiencies of the prior art, the object of the present invention is to provide a method for electrodepositing a titanium boride cathode coating using oxides as electrolytic raw materials at a relatively low electrolysis temperature while minimizing pollution and corrosion. The cathode coating prepared by this method is dense, flat and uniform, which provides reference and guidance for actual industrial preparation.

[0008] A method for preparing a TiB2 cathode coating by oxide electrodeposition comprises the following steps:

[0009] S1: LiF-NaF-KF-AlF3-KCl is configured as a supporting electrolyte in a certain molar ratio, and B2O3 and TiO2 are added as electrolytic raw materials in different molar ratios of boron and titanium to prepare a LiF-NaF-KF-AlF3-KCl-B2O3-TiO2 mixed molten salt system.

[0010] S2: Put the molten salt system described in step S1 into a crucible and heat it to the electrolysis temperature in the furnace to melt it, immerse it in double graphite electrodes, connect a DC power supply for electrolysis, and electrolytically deposit a TiB2 coating on the cathode carbon block.

[0011] Further features, in step S1, the LiF content is 0-10 mol%, the NaF content is 0-10 mol%, the KF content is 40-50 mol%, the AlF3 content is 0-10 mol%, and the KCl content is 30-40% mol.

[0012] Further features, in step S1, the B2O3 content is 15-18 mol%, the TiO2 content is 2-5 mol%; the boron-titanium molar ratio is 3-9:1.

[0013] Further characterized in that the electrolysis temperature in step S2 is 700°C to 900°C.

[0014] Further features, the electrolysis described in step S2 is constant current electrolysis, wherein the current is 1.44 to 4.8 A and the current density is 0.3 to 1 A / cm 2 , the inter-electrode distance is 2 to 8 cm, and the electrolysis time is 0.5 to 6 h.

[0015] Further features: In step S2, the depth of the graphite electrode immersed in the molten salt is about 1 cm, and the effective current area at such a depth is about 4.8 cm 2 .

[0016] The crucible may be a corundum crucible, which can effectively prevent potassium salt corrosion.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention can prepare TiB2 cathode coating at a lower electrolysis temperature, reduce energy consumption and reduce the cost of coating preparation, and is relatively environmentally friendly;

[0019] (2) The coating prepared by the present invention is dense, uniform and flat, of high quality, and closely adheres to the cathode carbon block and is not easy to fall off;

[0020] (3) The raw material cost of the present invention is low and stable, the process is simple, the required equipment and labor costs are low, the properties of the deposited coating can be accurately controlled by process parameters, and a uniform and coherent coating can be easily covered on irregularly shaped samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is an XRD analysis image of the TiB2 coating on the graphite cathode carbon block prepared by molten salt electrolysis of the present invention;

[0022] Figure 2 It is a surface microscopic morphology of the TiB2 coating on the graphite cathode carbon block prepared by molten salt electrolysis of the present invention;

[0023] Figure 3 This is a surface microscopic morphology image (high magnification) of the TiB2 coating on the graphite cathode carbon block prepared by molten salt electrolysis of the present invention;

[0024] Figure 4 It is a cross-sectional microscopic morphology of the TiB2 coating on the graphite cathode carbon block prepared by molten salt electrolysis of the present invention;

[0025] Figure 5 This is a cross-sectional microscopic morphology image (high magnification) of the TiB2 coating on the graphite cathode carbon block prepared by molten salt electrolysis of the present invention;

[0026] Figure 6It is a three-dimensional surface morphology of the TiB2 coating on the graphite cathode carbon block prepared by molten salt electrolysis of the present invention. DETAILED DESCRIPTION

[0027] The specific embodiments of the present invention are described in detail below in combination with the technical solutions and the accompanying drawings.

[0028] Example 1

[0029] KF:KCl was configured as a supporting electrolyte at a molar ratio of 9:7, and B2O3 and TiO2 were added as electrolytic raw materials at a boron-titanium molar ratio of B / Ti=6:1 to prepare a KF-KCl-B2O3-TiO2 mixed molten salt system. After grinding and mixing in a mortar, it was placed in a corundum crucible and dried in an oven. After being taken out, it was placed in a resistance furnace and heated to 750°C at a heating rate of 7.5°C / min to melt. Furthermore, the fixed double graphite electrodes were immersed in the molten salt to a depth of 1 cm below the liquid surface, argon gas was introduced, and a current of 2.4A was output for constant current electrolysis. The electrode spacing was 3 cm, the immersion depth was 1 cm, and the effective current area was 4.8 cm 2 After 120 min of electrolysis, a dense TiB2 coating with a thickness of about 80 μm was formed on the graphitized cathode carbon block.

[0030] Figure 1 XRD analysis image of the TiB2 coating on the graphite cathode carbon block prepared for molten salt electrolysis, which shows that the TiB2 coating was successfully prepared by this method. Figure 2 and Figure 3 The surface micromorphology of the TiB2 coating on the graphite cathode carbon block prepared for molten salt electrolysis shows that the coating grows in a lamellar structure, and a large number of flaky TiB2 are tightly stacked, making the coating dense and uniform. Figure 4 and Figure 5 The cross-sectional microscopic morphology of the TiB2 coating on the graphite cathode carbon block prepared for molten salt electrolysis shows an obvious layered structure. The upper dense part is the TiB2 coating, and the lower loose and porous part is the graphite substrate. Figure 6 The three-dimensional surface morphology of the TiB2 coating on the graphite cathode carbon block prepared for molten salt electrolysis shows that the coating surface is flat and smooth.

[0031] Example 2

[0032] KF:KCl was configured as a supporting electrolyte in a molar ratio of 9:7, and B2O3 and TiO2 were added as electrolytic raw materials in a boron-titanium molar ratio of B / Ti=9:1 to prepare a KF-KCl-B2O3-TiO2 mixed molten salt system. After grinding and mixing in a mortar, it was placed in a corundum crucible and dried in an oven. After being taken out, it was placed in a resistance furnace and heated to 750°C at a heating rate of 7.5°C / min to melt. Furthermore, the fixed double graphite electrodes were immersed in the molten salt to a depth of 1cm below the liquid surface, and a constant current electrolysis was performed with an output current of 2.4A, wherein the electrode spacing was 3cm, the immersion depth was 1cm, and the effective current area was 4.8cm 2 After 90 min of electrolysis, a dense and smooth TiB2 coating was formed on the graphitized cathode carbon block.

[0033] Example 3

[0034] KF:KCl was configured as a supporting electrolyte at a molar ratio of 9:7, and B2O3 and TiO2 were added as electrolytic raw materials at a boron-titanium molar ratio of B / Ti=5:1 to prepare a KF-KCl-B2O3-TiO2 mixed molten salt system. After grinding and mixing in a mortar, it was placed in a corundum crucible and dried in an oven. After being taken out, it was placed in a resistance furnace and heated to 750°C at a heating rate of 7.5°C / min to melt. Furthermore, the fixed double graphite electrodes were immersed in the molten salt to a depth of 1cm below the liquid surface, and the output current was 2.88A for constant current electrolysis. The electrode spacing was 3cm, the immersion depth was 1cm, and the effective current area was 4.8cm 2 After 150 min of electrolysis, a dense TiB2 coating was formed on the graphitized cathode carbon block.

[0035] Example 4

[0036] LiF:KF:KCl was configured as a supporting electrolyte in a molar ratio of 1:8:7, and B2O3 and TiO2 were added as electrolytic raw materials in a boron-titanium molar ratio of B / Ti=7:1 to prepare a LiF-KF-KCl-B2O3-TiO2 mixed molten salt system. After grinding and mixing in a mortar, it was placed in a corundum crucible and dried in an oven. After being taken out, it was placed in a resistance furnace and heated at a heating rate of 7.5℃ / min until the molten salt melted. Furthermore, the fixed double graphite electrode was immersed in the molten salt to a depth of 1cm below the liquid surface, and a constant current electrolysis was performed with an output current of 2.88A, wherein the electrode spacing was 3cm, the immersion depth was 1cm, and the effective current area was 4.8cm 2 After 150 min of electrolysis, a dense and smooth TiB2 coating was formed on the graphitized cathode carbon block.

[0037] Example 5

[0038] NaF:KF:KCl was configured as supporting electrolyte in a molar ratio of 2:7:7, and B2O3 and TiO2 were added as electrolytic raw materials in a boron-titanium molar ratio of B / Ti=6:1 to prepare a NaF-KF-KCl-B2O3-TiO2 mixed molten salt system. After grinding and mixing in a mortar, it was placed in a corundum crucible and dried in an oven. After being taken out, it was placed in a resistance furnace and heated at a heating rate of 7.5℃ / min until the molten salt melted. Furthermore, the fixed double graphite electrode was immersed in the molten salt to a depth of 1cm below the liquid surface, and a constant current electrolysis was performed with an output current of 2.88A, wherein the electrode spacing was 3cm, the immersion depth was 1cm, and the effective current area was 4.8cm 2 After 120 min of electrolysis, a dense and smooth TiB2 coating was formed on the graphitized cathode carbon block.

[0039] Example 6

[0040] KF:AlF3:KCl was configured as a supporting electrolyte in a molar ratio of 8:1:7, and B2O3 and TiO2 were added as electrolytic raw materials in a boron-titanium molar ratio of B / Ti=5:1 to prepare a KF-AlF3-KCl-B2O3-TiO2 mixed molten salt system. After grinding and mixing in a mortar, it was placed in a corundum crucible and dried in an oven. After being taken out, it was placed in a resistance furnace and heated at a heating rate of 7.5℃ / min until the molten salt melted. Furthermore, the fixed double graphite electrodes were immersed in the molten salt to a depth of 1cm below the liquid surface, and the output current was 3.36A for constant current electrolysis, wherein the electrode spacing was 3cm, the immersion depth was 1cm, and the effective current area was 4.8cm 2 After 180 min of electrolysis, a dense and smooth TiB2 coating was formed on the graphitized cathode carbon block.

[0041] Example 7

[0042] LiF:NaF:KF:AlF3:KCl was configured as a supporting electrolyte in a molar ratio of 1:1:7:6:1, and B2O3 and TiO2 were added as electrolytic raw materials in a boron-titanium molar ratio of B / Ti=6:1 to prepare a LiF-NaF-KF-AlF3-KCl-B2O3-TiO2 mixed molten salt system. After grinding and mixing in a mortar, it was placed in a corundum crucible and dried in an oven. After being taken out, it was placed in a resistance furnace and heated at a heating rate of 7.5℃ / min until the molten salt melted. Furthermore, the fixed double graphite electrode was immersed in the molten salt to a depth of 1cm below the liquid surface, and a constant current electrolysis was performed with an output current of 2.88A, wherein the electrode spacing was 3cm, the immersion depth was 1cm, and the effective current area was 4.8cm 2After 180 min of electrolysis, a dense and smooth TiB2 coating was formed on the graphitized cathode carbon block.

Claims

1. A method for preparing a TiB2 cathode coating using oxide electrodeposition, characterized in that: The steps include: S1. LiF-NaF-KF-AlF3-KCl is configured as a supporting electrolyte in a certain molar ratio, and B2O3 and TiO2 are added as electrolytic raw materials according to different molar ratios of boron and titanium to prepare a LiF-NaF-KF-AlF3-KCl-B2O3-TiO2 mixed molten salt system; S2. Place the molten salt system described in step S1 into a crucible and heat it to the electrolysis temperature in a furnace to melt it. Immerse the double graphite electrodes and connect a DC power supply for electrolysis to electrolytically deposit a TiB2 coating on the cathode carbon block.

2. A method for preparing a TiB2 cathode coating by oxide electrodeposition according to claim 1, characterized in that: In step S1, the LiF content is 0-10 mol%, the NaF content is 0-10 mol%, the KF content is 40-50 mol%, the AlF3 content is 0-10 mol%, and the KCl content is 30-40% mol.

3. A method for preparing a TiB2 cathode coating by oxide electrodeposition according to claim 1, characterized in that: In step S1, the content of B2O3 is 15-18 mol%, the content of TiO2 is 2-5 mol%, and the molar ratio of boron to titanium is 3-9:

1.

4. A method for preparing a TiB2 cathode coating by oxide electrodeposition according to claim 1, characterized in that: In step S2, the electrolysis temperature is 700°C to 900°C.

5. The method for preparing a TiB2 cathode coating by oxide electrodeposition according to claim 1, characterized in that: The electrolysis in step S2 is constant current electrolysis, wherein the current is 1.44-4.8A and the current density is 0.3-1A / cm 2 , the inter-electrode distance is 2 to 8 cm, and the electrolysis time is 0.5 to 6 h.

6. A method for preparing a TiB2 cathode coating by oxide electrodeposition according to claim 1, characterized in that: Step S2: The depth of the graphite electrode immersed in the molten salt is about 1 cm, and the effective current area is about 4.8 cm 2 .

Images