A high-conductivity, high-heat-conductivity, high-temperature-molten-salt-corrosion-resistant metal ceramic inert anode and its preparation method

Abstract

The present invention discloses a high-conductivity, heat-conductivity, high-temperature molten salt corrosion-resistant metal ceramic inert anode and a preparation method thereof; the method introduces a ceramic component ZrB2 (conductivity 1×10 4 S / cm~1.2×10 5 S / cm) and SiC (thermal conductivity of 320 W / m·K-348 W / m·K), a ceramic component with good thermal conductivity, thereby reducing the (Cu)Ni metal content in the NiFe2O4-NiO-based cermet, improving the electrical and thermal conductivity of the cermet inert anode and simultaneously enhancing the anode's resistance to molten salt corrosion. The annual corrosion rate is below 0.64 cm / y, and the cathode raw aluminum also has a high purity of over 99.7%. This method is simple to operate and efficient, making it conducive to widespread application.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum electrolysis, and in particular to a NiFe2O4-NiO-SiC-ZrB2-based high-conductivity thermal-electrical-high-temperature-molten-salt-corrosion-resistant metal ceramic inert anode and a preparation method thereof. Background Art

[0002] In the aluminum electrolysis process, the performance of the anode material has a crucial impact on the electrolysis efficiency, cost and product quality. Traditional anode materials have many shortcomings. For example, in order to achieve a balance between density, mechanical properties, electrical and thermal conductivity, and high-temperature molten salt corrosion resistance, the Cu (Ni) metal content in the NiFe2O4-NiO-based cermet inert anode is often increased. This will cause the Cu (Ni) metal to corrode preferentially during the electrolysis process, resulting in a large number of micropores on the surface of the cermet inert anode, providing a penetration channel for the high-temperature molten salt electrolyte, and the corrosion of the cermet inert anode will be very serious. Although it is possible to add a certain amount of zirconium boride powder to the ceramic phase to replace the spinel oxide to slow down the oxide ceramic peeling phenomenon caused by the preferential corrosion of the metal phase in high-temperature molten salt (202110489130.6); or to use a multi-layer prefabricated sintering method to control the metal phase content in the metal ceramic layer in contact with the electrolyte melt and the metal phase content in the metal material in the connection area with the metal guide rod to improve the corrosion resistance of the anode (202410555733.5), it has little effect on large-scale aluminum electrolysis.

[0003] SiC, a material with high hardness, high thermal conductivity, good chemical stability, and moderate electrical conductivity, has potential application value in the field of inert anode materials. The addition of SiC to the ceramic phase facilitates heat dissipation, maintaining the temperature stability of the anode during the electrolysis process. Compared with some metal phases, it has stronger corrosion resistance, can effectively resist erosion by molten salts, and extend the service life of the anode.

[0004] The electrical conductivity of ZrB2 ceramics is 1×10 4 ~1.2×10 5 The conductivity of ZrB2 ceramics is 10-100 S / cm, which is three orders of magnitude higher than the 10-100 S / cm of NiFe2O4-NiO. The addition of ZrB2 ceramics can reduce the Cu (Ni) metal content in NiFe2O4-NiO-based cermets, thus preventing the formation of numerous holes on the anode surface due to preferential corrosion of Cu (Ni), which can lead to premature failure of the anode.

[0005] The incorporation of ZrB2 and SiC ceramics can effectively improve the electrical and thermal conductivity and high-temperature molten salt corrosion resistance of metal-ceramic inert anodes. This method is simple to operate and highly efficient, making it suitable for industrial application. Therefore, an innovative preparation method is needed to fully utilize the advantages of SiC and ZrB2 to obtain high-performance metal-ceramic inert anodes. Summary of the Invention

[0006] In view of the problems in the prior art of aluminum electrolysis inert anodes, such as rapid erosion of oxide ceramic grain boundaries by infiltrated electrolyte due to preferential corrosion of the metal phase, and local overheating of the electrode due to poor thermal conductivity, the purpose of the present invention is to provide a NiFe2O4-NiO-SiC-ZrB2-based high-conductivity and thermal conductivity metal ceramic inert anode resistant to high-temperature molten salt corrosion and a preparation method thereof. By rationally introducing SiC and ZrB2 and optimizing the proportion of each component, the problems of the difficulty in balancing the conductivity and molten salt corrosion resistance of existing anode materials and the limitations of SiC when used alone are solved, the comprehensive performance of the anode is improved, the annual corrosion rate is reduced, and the high purity of the cathode raw aluminum is ensured.

[0007] In order to achieve the above technical objectives, the technical solution provided by the present invention is:

[0008] The present invention provides a high-electrical and thermal-conductive metal ceramic inert anode for aluminum electrolysis that is resistant to high-temperature molten salt corrosion. The metal ceramic inert anode material consists of a metal phase and a ceramic phase, wherein the metal phase is composed of non-spinel oxide NiO, and the ceramic phase contains ZrB2 ceramic, SiC ceramic, and NiFe2O4-based ceramic; the metal ceramic inert anode contains the following components in mass percentage: spinel oxide NiFe2O4 40% to 90%, non-spinel oxide NiO 1% to 40%, SiC 1% to 20%, and ZrB2 1% to 10%.

[0009] The present invention adds ZrB2, a ceramic component with excellent electrical conductivity, and SiC, a ceramic component with excellent thermal conductivity, to a NiFe2O4-NiO metal ceramic inert anode, thereby reducing the Cu (Ni) metal content in the NiFe2O4-NiO-based metal ceramic, improving the electrical and thermal conductivity of the metal ceramic inert anode, and simultaneously improving the molten salt corrosion resistance of the inert anode.

[0010] In a preferred embodiment, the mass fraction of the spinel oxide NiFe2O4 in the metal ceramic inert anode material is 50-80 wt%.

[0011] In a preferred embodiment, the mass fraction of the SiC ceramic phase in the metal ceramic inert anode material is 1-10 wt%.

[0012] In a preferred embodiment, the mass fraction of the ZrB2 ceramic in the metal ceramic inert anode material is 5-10 wt%.

[0013] In a preferred embodiment, the non-spinel oxide is NiO, and its mass fraction in the metal ceramic inert anode material is preferably 10-30 wt%.

[0014] The method for preparing the high-electrical and thermal-conductive high-temperature molten salt corrosion-resistant metal ceramic inert anode comprises the following steps:

[0015] The raw materials NiFe2O4, NiO, SiC and ZrB2 powders are mixed and evenly milled in a ball mill according to proportion; the mixed powders are cold-pressed into an anode green body, and then the anode green body is sintered in an inert atmosphere.

[0016] The above method is preferably as follows: the raw materials NiFe2O4, NiO, SiC and ZrB2 powders are mixed uniformly in a ball mill in proportion, with a ball-to-material ratio of 5:1~8:1, a rotation speed of 300~400r / min, and a ball milling time of 4~5h; the mixed powder is cold-pressed into an anode green body under a pressure of 150~200MPa, and then the anode green body is sintered in an inert atmosphere at 1200~1300℃ for 5~6h.

[0017] Preferably, the raw materials NiFe2O4, NiO, SiC and ZrB2 powders are mixed uniformly in a ball mill in proportion, with a ball-to-material ratio of 5:1, a rotation speed of 300 r / min, and a ball milling time of 4 h; the mixed powder is cold-pressed into an anode green body under a pressure of 200 MPa, and then the anode green body is sintered in an inert atmosphere at 1300°C for 5 h.

[0018] The electrolyte used in the electrolysis experiments consisted of Na3AlF6 and / or K3AlF6, AlF3, CaF2, and Al2O3. Preferably, the electrolyte contained the following components by weight: Na3AlF6 and / or K3AlF6 60-80%, AlF3 5-30%, CaF2 ≤10%, and Al2O3 3-5%.

[0019] The technical principles of this invention and the beneficial technical effects compared with the existing technology are as follows:

[0020] Principle: A large number of studies have shown that under the temperature and current density of the present invention, ZrB2 ceramics with good electrical conductivity and SiC ceramics with good thermal conductivity are jointly introduced into a metal ceramic inert anode, and then placed in an appropriate electrolyte for electrolytic corrosion. Since there are fewer metal components in the metal ceramic inert anode, and ZrB2 ceramics have good electrical conductivity and SiC ceramics have good thermal conductivity, then in the aluminum electrolysis process, the NiFe2O4-NiO-SiC-ZrB2-based metal ceramic inert anode will be compared with the NiFe2O4-NiO metal ceramic inert anode. The electrical conductivity, thermal conductivity and molten salt corrosion resistance are improved, and the anode corrosion rate can be effectively slowed down. At the same time, there are fewer anode components dissolved in the electrolyte, and the amount of impurity metal generated by cathode discharge is also small, thereby maintaining the higher purity of the cathode original aluminum.

[0021] Beneficial effects: (1) The technical solution of the present invention can improve the electrical conductivity, thermal conductivity and corrosion resistance of the metal ceramic inert anode for aluminum electrolysis, while also improving the purity of the original aluminum. It solves the problems of the current NiFe2O4-NiO metal ceramic inert anode in the aluminum electrolysis process, such as preferential corrosion of Cu (Ni) metal, which leads to a decrease in electrical conductivity and the need to improve the anode's resistance to molten salt corrosion. (2) The technical solution of the present invention is simple and convenient, and can be easily promoted and applied. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to the embodiments, but is not intended to limit the scope of protection of the claims of the present invention.

[0023] Example 1

[0024] The raw material powders used in this example had the following mass fraction composition: 70% NiFe2O4, 15% NiO, 5% SiC, and 10% ZrB2. These raw material powders were uniformly mixed in a ball mill with a ball-to-material ratio of 5:1, a rotation speed of 300 r / min, and a milling time of 4 hours. The mixed powders were cold-pressed under a pressure of 200 MPa to form a green anode. The green anode was then sintered at 1300°C in an inert atmosphere for 5 hours to obtain a 5(SiC) / 85(NiFe2O4-15NiO)-10ZrB2 cermet inert anode.

[0025] The electrolyte used in the electrolysis experiment is a mixture of 78.07% Na3AlF6-9.5% AlF3-5.0% CaF2-7.43% Al2O3 (primary crystallization temperature 947℃, superheat 13℃), the electrolysis temperature is 960℃, and the electrolysis time is 120h. According to the formula (W loss =W b ×C b +W a ×Ca )×106×365×24 / (S 阳极 ×ρ 阳极 ×t) (1)

[0026] In formula (1), W loss Defined as the annual anode corrosion rate (cm / year), W b is the total amount of electrolyte (g), C b is the impurity concentration entering the electrolyte (ppm), W a is the total amount of cathode aluminum (g), C a is the impurity concentration in the aluminum liquid entering the cathode (ppm), S anode is the surface area of ​​the anode immersed during electrolysis (cm 2 ), ρanode is the volume density of the anode (g / cm 3 ), t is the electrolysis time (h).

[0027] 5(SiC) / 85(NiFe2O4-15NiO)-10ZrB2 metal ceramic inert anode, its conductivity at 960℃ is 183.7S / cm; in the electrolyte 78.07% Na3AlF6-9.5%AlF3-5.0%CaF2-7.43%Al2O3 (primary crystallization temperature 947℃, superheat 13℃, current density 1.0 A / cm 2 After 120 hours of electrolysis (electrolysis temperature 960°C), the corrosion rate of the 5(SiC) / 85(NiFe2O4-15NiO)-10ZrB2 anode was found to be 0.64 cm / year. The original aluminum purity was 99.7%, indicating that the introduction of SiC and ZrB2 improves the high-temperature conductivity and high-temperature molten salt corrosion resistance of the cermet inert anode.

[0028] Example 2

[0029] The conductivity of the 10(SiC) / 85(NiFe2O4-15NiO)-5ZrB2 metal ceramic inert anode at 960℃ is 168.2 S / cm; in the low-temperature electrolyte 78.07% Na3AlF6-9.5%AlF3-5.0%CaF2-7.43%Al2O3 (primary crystallization temperature 947℃, superheat 13℃, current density 1.0 A / cm 2 ) After 120h of electrolysis (electrolysis temperature 960℃), it was found that the corrosion rate of 10(SiC) / 85(NiFe2O4-15NiO)-5ZrB2 anode was 0.71 cm / year and the purity of the original aluminum was 99.6%.

[0030] Example 3

[0031] The conductivity of the 5(SiC) / 95(NiFe2O4-15NiO) metal ceramic inert anode at 960℃ is 52.5 S / cm; in the low-temperature electrolyte 78.07% Na3AlF6-9.5%AlF3-5.0%CaF2-7.43%Al2O3 (primary crystallization temperature 947℃, superheat 13℃, current density 1.0 A / cm 2 ) After 120h of electrolysis (electrolysis temperature 960 ℃), it was found that the corrosion rate of 5(SiC) / 95(NiFe2O4-15NiO) anode was 1.92cm / y and the purity of the original aluminum was 99.1%.

[0032] Example 4

[0033] The conductivity of the 10(SiC) / 90(NiFe2O4-15NiO) metal ceramic inert anode at 960℃ is 45.8 S / cm; in the low-temperature electrolyte 78.07% Na3AlF6-9.5%AlF3-5.0%CaF2-7.43%Al2O3 (primary crystallization temperature 947℃, superheat 13℃, current density 1.0 A / cm 2 ) After 120h of electrolysis (electrolysis temperature 960 ℃), it was found that the corrosion rate of 10(SiC) / 90(NiFe2O4-15NiO) anode was 2.32cm / y and the purity of the original aluminum was 98.5%.

[0034] Example 5

[0035] The conductivity of the 5(20Ni-Cu) / 85(NiFe2O4-15NiO)-10ZrB2 metal ceramic inert anode at 960℃ is 145.2 S / cm; in the electrolyte 78.07% Na3AlF6-9.5%AlF3-5.0%CaF2-7.43%Al2O3 (primary crystallization temperature 947℃, superheat 13℃, current density 1.0A / cm 2 After 120 hours of electrolysis (electrolysis temperature 960°C), the corrosion rate of the 5(20Ni-Cu) / 85(NiFe2O4-15NiO)-10ZrB2 anode was found to be 2.23 cm / year. The original aluminum purity was 98.7%.

[0036] Example 6

[0037] The conductivity of the 10(20Ni-Cu) / 85(NiFe2O4-15NiO)-5ZrB2 metal ceramic inert anode at 960℃ is 113.1 S / cm; in the electrolyte 78.07% Na3AlF6-9.5%AlF3-5.0%CaF2-7.43%Al2O3 (primary crystallization temperature 947℃, superheat 13℃, current density 1.0A / cm 2After 120 hours of electrolysis (electrolysis temperature 960°C), the corrosion rate of the 10(20Ni-Cu) / 85(NiFe2O4-15NiO)-10ZrB2 anode was found to be 2.89 cm / year. The original aluminum purity was 98.3%.

[0038] Example 7

[0039] The conductivity of the 15(20Ni-Cu) / 85(NiFe2O4-15NiO) metal ceramic inert anode at 960℃ is 43.1 S / cm; in the electrolyte 78.07% Na3AlF6-9.5%AlF3-5.0%CaF2-7.43%Al2O3 (crystallization temperature 947℃, superheat 13℃, current density 1.0A / cm 2 After 120 hours of electrolysis (electrolysis temperature 960°C), the corrosion rate of the 15(20Ni-Cu) / 85(NiFe2O4-15NiO) anode was found to be 3.35 cm / year. The purity of the original aluminum was 97.4%.

Claims

1. A highly conductive and thermally conductive metal ceramic inert anode that is resistant to high-temperature molten salt corrosion, comprising NiFe2O4, NiO, SiC, and ZrB2; the mass proportions of each component are: NiFe2O4 40% to 90%, NiO 1% to 40%, SiC 1% to 20%, and ZrB2 1% to 10%.

2. The high electrical and thermal conductivity high temperature molten salt corrosion resistant metal ceramic inert anode according to claim 1 is characterized in that: The mass ratio of each component is: NiFe2O4 50-80%, NiO 10-30%, SiC 1-10%, ZrB2 5-10%.

3. The method for preparing the high-electrical-thermal-conductivity and high-temperature-molten-salt-corrosion-resistant metal ceramic inert anode according to claim 1 or 2, characterized in that: The following steps are involved: The raw materials NiFe2O4, NiO, SiC and ZrB2 powders are mixed and evenly milled in a ball mill according to proportion; the mixed powders are cold-pressed into an anode green body, and then the anode green body is sintered in an inert atmosphere.

4. The preparation method according to claim 3, characterized in that The raw materials NiFe2O4, NiO, SiC and ZrB2 powders are mixed uniformly in a ball mill in proportion, with a ball-to-material ratio of 5:1~10:1, a rotation speed of 200~500r / min, and a ball milling time of 3~6h; the mixed powder is cold-pressed into an anode green body under a pressure of 100~300MPa, and then the anode green body is sintered in an inert atmosphere at 1100~1400℃ for 4~6h.

5. The preparation method according to claim 4, characterized in that The raw materials NiFe2O4, NiO, SiC and ZrB2 powders are mixed evenly in a ball mill in proportion, with a ball-to-material ratio of 5:1, a rotation speed of 300r / min, and a ball milling time of 4h; the mixed powder is cold-pressed into an anode green body under a pressure of 200MPa, and then the anode green body is sintered in an inert atmosphere at 1300℃ for 5h.