High-density corrosion-resistant metal ceramic inert anode and preparation method thereof

Abstract

The invention provides a high-density corrosion-resistant metal ceramic inert anode and a preparation method thereof. During preparation, rare earth metal holmium, zinc oxide, nickel oxide, chromic oxide and copper powder are selected as raw materials, the zinc oxide, the nickel oxide, the chromic oxide and the copper powder are subjected to ball milling for 12 h and screened, the copper powder is heated and subjected to heat preservation for 2 h at the temperature of 450 DEG C in the hydrogen atmosphere, and then all the raw materials are put into a three-dimensional mixer to be mixed for 10 h; and carrying out vacuum drying, pressing a green body under the pressure of 50-60MPa, putting the green body into thermal shock sintering equipment, carrying out thermal shock sintering at 1100 DEG C for 5-10s, and cooling and curing at the speed of 20 + / -5 DEG C / min to obtain the metal ceramic inert anode. According to the preparation method, the metal copper and the metal oxide powder serve as main raw materials, the production cost is low, the prepared metal ceramic anode has high conductivity and corrosion resistance, emission of greenhouse gas can be effectively reduced, and green and sustainable development of aluminum electrolysis is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials, and specifically to a highly dense and corrosion-resistant cermet inert anode and a preparation method thereof. Background Art

[0002] Aluminum metal has outstanding characteristics in terms of light weight, strong ductility, easy processing, good corrosion resistance, and renewable recycling. The basic principle of aluminum production is to dissolve Al2O3 in a Na3AlF6 melt at a high temperature of 960 °C, use carbon materials as the cathode and anode of the electrolytic cell respectively and conduct direct current. Through an electrochemical reaction, molten aluminum is deposited on the cathode, complex ions discharge and oxidize the carbon anode, mainly producing CO2 gas. Producing 1 t of primary aluminum generates approximately 1.5 - 1.8 t of CO2. In the traditional carbon anode aluminum electrolysis process, there are disadvantages such as continuous consumption of the carbon anode, emission of greenhouse gases CO2 and harmful gases such as fluorocarbons, and unstable production. Improving the anode quality and energy conservation and emission reduction have become the main development and research directions of the current aluminum electrolysis industry.

[0003] Using an inert anode to replace the consumable carbon anode during the molten salt electrolysis process can not only avoid the generation of greenhouse gases and harmful gases, but also reduce energy consumption. It is an effective way to achieve clean production of aluminum electrolysis and also a major demand for the future development of the industry. However, during the molten salt electrolysis process, the working environment of the inert anode is very unfriendly. It not only faces the corrosion of high-temperature molten salt, but also suffers from the oxidation of high-temperature oxygen, greatly reducing its working life and polluting the obtained metal products. Therefore, finding a suitable inert anode material, extending its working life, and reducing the pollution to the product have become the key to the successful application of the inert anode.

[0004] Cermet inert anodes combine the advantages of metal materials and ceramic materials. Their corrosion resistance and oxidation resistance are stronger than those of metal anodes, and their electrical conductivity and thermal shock resistance are stronger than those of oxide ceramic anodes. However, there are still the following problems: low electrical conductivity, corrosion products are likely to pollute aluminum products, and poor thermal shock resistance. Summary of the Invention

[0005] In order to solve the deficiencies in the prior art, the present invention provides a highly dense and corrosion-resistant cermet inert anode and a preparation method thereof. The preparation method uses metallic copper and metal oxides (zinc oxide powder, nickel oxide powder, and chromium oxide powder) as the main raw materials, with low production costs, and the obtained cermet inert anode has high electrical conductivity and corrosion resistance, can effectively reduce greenhouse gas emissions, and achieve green and sustainable development of aluminum electrolysis.

[0006] To achieve the above object, the specific solution adopted by the present invention is as follows: A preparation method of a highly dense and corrosion-resistant cermet inert anode mainly includes the following steps: Step 1: Take rare earth metal holmium, metal oxide powder and copper powder as raw materials respectively for standby; among them, the metal oxide powder includes zinc oxide powder, nickel oxide powder and chromium oxide powder; Step 2: Ball-mill the metal oxide powder and copper powder taken in Step 1 in an absolute ethanol medium for 12 hours respectively. The metal oxide powder is sieved through a 1350-mesh sieve, and the copper powder is sieved through a 200-mesh sieve; Step 3: Heat the copper powder taken in Step 2 to 450 °C in a hydrogen atmosphere and keep it at 450 °C for 2 hours; Step 4: Put the rare earth metal holmium taken in Step 1, the metal oxide powder after ball-milling in Step 2 and the copper powder heated in Step 3 into a three-dimensional mixer and mix for 10 h to obtain a mixed material for standby; Step 5: First put the mixed material into a vacuum furnace and dry it at 80 °C for 2 hours; Step 6: Weigh the mixed material dried in Step 5 and put it into a stainless steel mold for cold isostatic pressing to obtain a green body; Step 7: Put the green body prepared in Step 6 into a thermal shock sintering device, and carry out thermal shock sintering at 1100 °C under the protection of high-purity argon. The sintering time is 5 - 10 s; then cool and solidify at a cooling rate of 20 ± 5 °C / min to obtain a cermet inert anode.

[0007] Furthermore, in Step 1, according to weight percentage, the dosages of each raw material are as follows: holmium 0.05 - 0.1%, zinc oxide powder 7 - 12%, nickel oxide powder 7 - 12%, chromium oxide powder 15 - 20%, copper powder 65 - 75%.

[0008] Furthermore, in Step 6, press under a pressure of 50 - 60 MPa to obtain a green body with a diameter of 30 mm and a height of 50 mm.

[0009] On the other hand, the present invention discloses a highly dense and corrosion-resistant cermet inert anode prepared by the above method.

[0010] Furthermore, the room temperature conductivity reaches 35.6 S / cm, the primary thermal shock strength ratio reaches 95%, and the corrosion rate is lower than 1.06 cm·year⁻¹.

[0011] The principle of the present invention: The following reactions will occur to the raw materials during the rapid thermal shock sintering process: xZnO+(1-x)NiO+Cr2O3=Zn x Ni 1-x Cr2O4 The relatively stable Zn x Ni 1-xCr2O4 covers the surface of metallic copper, hindering the further corrosion and oxidation of the anode during aluminum electrolysis, as well as enhancing the toughness and overall thermal shock resistance of the cermet inert anode.

[0012] Beneficial effects (1)ZnxNi1₋xCr2O4 formed by the reaction of zinc oxide, nickel oxide, and chromium oxide during rapid thermal shock sintering covers the copper surface, forming a dense protective layer that effectively hinders the further corrosion and oxidation of the anode during aluminum electrolysis. Meanwhile, the role of Zn²⁺ in inhibiting ion diffusion, in coordination with this protective layer, greatly reduces the corrosion rate of the anode. The rare earth metal holmium refines the grains, reducing the voids between the corrosion area and the anode matrix, further enhancing the corrosion resistance of the anode, enabling the raw materials to cooperate with each other in terms of corrosion resistance and improving the overall corrosion resistance of the anode.

[0013] (2)The ultrafast heating rate, ultra-high temperature, and extremely fast cooling rate of the rapid thermal shock sintering method promote the densification process of the cermet inert anode. During this process, the generated ZnxNi1₋xCr2O4 not only enhances the corrosion resistance of the anode but also improves its toughness and overall thermal shock resistance. The role of the rare earth metal holmium in refining the grains further improves the thermal shock resistance of the anode. The raw materials cooperate with each other under this sintering process, enabling the anode to withstand drastic temperature changes and reducing structural damage caused by thermal shock.

[0014] (3)The good electrical conductivity of copper provides a conductive basis for the anode, and its continuous distribution in the anode matrix ensures the smooth conduction of current. The stable structure formed by other raw materials does not have a negative impact on the electrical conductivity of copper. On the contrary, by improving the densification and stability of the anode, it creates a better environment for the conduction of copper, enabling the anode to maintain a high electrical conductivity while having good corrosion resistance and thermal shock resistance.

[0015] (4)The L+Ho2Cu3 formed by the rare earth metal holmium and copper powder promotes the sintering reaction, making the sintered product more uniform. This uniformity is not only reflected in the composition distribution but also in the microstructure, which helps the raw materials to combine better, form a stable cermet structure, and further improve the comprehensive performance of the anode.

[0016] (5) In the present invention, each raw material plays an important role in enhancing the corrosion resistance, thermal shock resistance, electrical conductivity of the cermet inert anode and promoting the sintering uniformity, etc., making the obtained cermet inert anode have good properties. The room temperature electrical conductivity reaches 35.6 S / cm, the primary thermal shock strength ratio reaches 95%, the corrosion rate is lower than 1.06 cm·year⁻¹, the purity of the primary aluminum reaches 98.5%, effectively meeting the performance requirements of the aluminum electrolysis industry for the inert anode, and being able to effectively reduce the emission of greenhouse gases and achieve the green and sustainable development of aluminum electrolysis. Specific Embodiments

[0017] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0018] Example 1 A preparation method of a highly dense and corrosion-resistant cermet inert anode includes the following steps: Step 1: Respectively take 0.06% rare earth metal holmium, 7% zinc oxide powder, 7% nickel oxide powder, 15% chromium oxide powder, and 70.94% copper powder as raw materials by mass percentage and set aside; Step 2: Ball-mill the zinc oxide powder, nickel oxide powder, chromium oxide powder, and copper powder taken in Step 1 in an absolute alcohol medium for 12 hours. The metal oxides (zinc oxide powder, nickel oxide powder, and chromium oxide powder) are sieved through a 1350-mesh sieve, and the copper powder is sieved through a 200-mesh sieve; Step 3: Heat the copper powder taken in Step 2 to 450°C in a hydrogen atmosphere and keep it at 450°C for 2 hours; Step 4: Put the rare earth metal holmium taken in Step 1, the metal oxides (zinc oxide powder, nickel oxide powder, and chromium oxide powder) after ball-milling in Step 2, and the copper powder heated in Step 3 into a three-dimensional mixer and mix for 10 h to obtain a mixed material and set aside; Step 5: First put the mixed material after mixing into a vacuum furnace and dry it at 80°C for 2 hours; Step 6: Weigh the mixed material after drying in Step 5 and put it into a stainless steel mold, and press a green body with a diameter of 30 mm and a height of 50 mm under a pressure of 50 MPa; Step 7: Put the green body prepared in Step 6 into a thermal shock sintering device, fill and discharge high-purity argon three times to ensure that the sample is in an inert atmosphere, conduct thermal shock sintering at 1100 °C for 5 s; then cool and solidify at a cooling rate of 20 ± 5 °C / min to obtain a cermet inert anode.

[0019] Example 2 The differences between Example 2 and Example 1 are as follows: (1) In Step 1, take 0.08% rare earth metal holmium, 8% zinc oxide powder, 7% nickel oxide powder, 16% chromium oxide powder, and 68.92% copper powder by mass percentage as raw materials for standby; (2) In Step 6, press at a pressure of 60 MPa.

[0020] Example 3 The differences between Example 2 and Example 1 are as follows: (1) In Step 1, take 0.09% rare earth metal holmium, 9% zinc oxide powder, 7% nickel oxide powder, 18% chromium oxide powder, and 65.91% copper powder by mass percentage as raw materials for standby.

[0021] Comparative Example 1 (without rare earth metal holmium) The differences between Comparative Example 1 and Example 1 are as follows: (1) In Step 1, take 7% zinc oxide powder, 7% nickel oxide powder, 15% chromium oxide powder, and 71% copper powder by mass percentage as raw materials for standby.

[0022] Comparative Example 2 (without zinc oxide powder and chromium oxide powder) The differences between Comparative Example 2 and Example 1 are as follows: (1) In Step 1, take 0.08% rare earth metal holmium, 7% nickel oxide powder, and 92.92% copper powder by mass percentage as raw materials for standby.

[0023] Comparative Example 3 (ordinary sintering) The differences between Comparative Example 3 and Example 1 are as follows: (1) In Step 7, conduct ordinary sintering, the sintering temperature is 1100 °C, and the holding time is 2 hours.

[0024] Test the conductivity, primary thermal shock strength ratio, corrosion rate, and the purity of the obtained primary aluminum of the products obtained in Examples 1-3 and Comparative Examples 1-3.

[0025] The method for measuring conductivity is as follows: Fix the regular-shaped inert anode sample to be measured between two parallel plates, continuously pass direct current, measure the voltage at both ends of the anode, and calculate the conductivity according to the following formula: (S / cm): σ = (IL) / (US); In the formula, S: the cross-sectional area of the anode sample (cm 2); L: length of the anode sample (cm); I: current intensity (A); U: voltage across the two ends of the anode sample (V).

[0026] Thermal shock resistance: The anode material is placed in a high-temperature furnace at room temperature and heated to 750 °C, held for 10 min and then taken out, cooled to room temperature in air, and one thermal shock is completed. Then, the anode material after one thermal shock is subjected to a flexural strength test (the flexural strength test refers to GB / T 232-2010). The ratio of the flexural strength after thermal shock to that before thermal shock is the strength retention rate (i.e., thermal shock resistance). The greater the strength retention rate, the better the thermal shock resistance of the material.

[0027] Annual corrosion rate of the inert anode: The inert anode is electrolyzed in a molten salt system for a certain period of time; it is calculated according to parameters such as the concentration of metal elements in the anode entering the electrolyte and the surface area of the anode immersed during electrolysis. The formula is as follows: W loss =(W b ×C b +W a ×C a )×10-6×365×24 / (S 阳极 ×ρ 阳极 ×t) In the formula, W loss is the annual corrosion rate of the anode (cm·year -1 ), 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 entering the aluminum liquid (ppm), S 阳极 is the surface area of the anode immersed during electrolysis (cm 2 ), ρ 阳极 is the bulk density of the anode (g / cm 3 ), and t is the electrolysis time (h).

[0028] Specifically, in the present invention, the low-temperature electrolyte is 45KF-50AlF3-5Al2O3 (electrolysis temperature 750 °C); the anode is immersed 2 cm in the electrolyte; the height of the aluminum liquid is 2.5 cm; the pole pitch is 3 cm; the height of the electrolyte liquid surface is 5 cm; the inert anode corrosion rate is tested after electrolysis for 120 h.

[0029] The test results are shown in Table 1.

[0030] Table 1 Test results of the products obtained in Examples 1-3 and Comparative Examples 1-3 As can be seen from Table 1, compared with the comparative example, the cermet inert anode prepared by the method of the present invention has high conductivity, high primary thermal shock strength ratio, low corrosion rate, and high purity of primary aluminum. Therefore, it can be seen that the cermet inert anode prepared by the method of the present invention has high conductivity and corrosion resistance.

[0031] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any equivalent transformation or modification made according to the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of a highly dense and corrosion-resistant cermet inert anode, characterized in that, It mainly includes the following steps: Step 1: Take rare earth metal holmium, metal oxide powder and copper powder as raw materials respectively and set aside. Among them, the metal oxide powder includes zinc oxide powder, nickel oxide powder and chromium oxide powder; Step 2: Ball-mill the metal oxide powder and copper powder taken in Step 1 in an absolute alcohol medium for 12 hours respectively. The metal oxide powder is sieved through a 1350-mesh sieve, and the copper powder is sieved through a 200-mesh sieve; Step 3: Heat the copper powder taken in Step 2 to 450 °C in a hydrogen atmosphere and keep it at 450 °C for 2 hours; Step 4: Put the rare earth metal holmium taken in Step 1, the metal oxide powder after ball-milling in Step 2 and the copper powder heated in Step 3 into a three-dimensional mixer and mix for 10 h to obtain a mixed material and set it aside; Step 5: First, put the mixed material into a vacuum furnace and dry it at 80 °C for 2 hours; Step 6: Weigh the mixed material dried in Step 5 and put it into a stainless-steel mold for cold isostatic pressing to obtain a green compact; Step 7: Put the green compact prepared in Step 6 into a thermal shock sintering device, and carry out thermal shock sintering at 1100 °C under the protection of high-purity argon. The sintering time is 5 - 10 s; then cool and solidify at a cooling rate of 20 ± 5 °C / min to obtain a cermet inert anode.

2. The preparation method of a highly dense and corrosion-resistant cermet inert anode according to claim 1, wherein In Step 1, according to the weight percentage, the dosages of the respective raw materials are: holmium 0.05 - 0.1%, zinc oxide powder 7 - 12%, nickel oxide powder 7 - 12%, chromium oxide powder 15 - 20%, copper powder 65 - 75%.

3. The preparation method of a highly dense and corrosion-resistant cermet inert anode according to claim 1, characterized in that, In Step 6, press at a pressure of 50 - 60 MPa to obtain a green compact with a diameter of 30 mm and a height of 50 mm.

4. A highly dense and corrosion-resistant cermet inert anode, characterized in that, It is prepared by the method described in any one of Claims 1 - 3.

5. A highly dense and corrosion-resistant cermet inert anode according to claim 1, characterized in that, The room-temperature conductivity reaches 35.6 S / cm, the primary thermal shock strength ratio reaches 95%, and the corrosion rate is lower than 1.06 cm·year⁻¹.

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