Corrosion resistance testing method of inert anode for aluminum chloride electrolysis

Abstract

The invention provides a corrosion resistance testing method of an inert anode for aluminum chloride electrolysis, and belongs to the field of corrosion resistance evaluation of inert anodes. The method comprises the following steps: processing an inert anode sample into a to-be-tested sample with a preset shape; immersing the to-be-tested sample part into the chloride electrolyte melt, and carrying out high-temperature soaking treatment with set temperature and set heat preservation time; detecting the content of metal elements dissolved out after the to-be-detected sample is subjected to high-temperature soaking treatment; removing residual chloride electrolyte on the surface of the to-be-tested sample so as to analyze and compare the shape and size change of the to-be-tested sample before and after the high-temperature soaking treatment; and evaluating the corrosion resistance of the inert anode sample according to the content of metal elements dissolved out after the to-be-tested sample is subjected to high-temperature soaking treatment and the shape and size change of the to-be-tested sample before and after the high-temperature soaking treatment. Therefore, the corrosion resistance of the inert anode in a chloride electrolyte system can be rapidly and accurately tested and screened without passing an aluminum chloride electrolysis test.

Description

Technical Field

[0001] This application relates to the technical field of evaluating the corrosion resistance of inert anodes, and particularly to a method for testing the corrosion resistance of an inert anode for aluminum chloride electrolysis. Background Art

[0002] Conventional aluminum chloride electrolysis uses carbon anodes and a vertical multi-chamber electrolytic cell structure. Since the decomposition voltage of oxides (such as alumina) is less than that of aluminum chloride under carbon anodes, when the electrolyte or aluminum chloride raw material contains oxygen or oxide impurities, the oxides will decompose preferentially, and the carbon anode will become a consumable anode. Moreover, a crust will form on the cathode surface, resulting in the abnormal progress of aluminum chloride electrolysis. Therefore, high-purity anhydrous aluminum chloride (oxygen impurity less than 0.03%) must be used in conventional aluminum chloride electrolysis. However, the preparation, storage, and transportation of high-purity anhydrous aluminum chloride are difficult and costly, which has become a key bottleneck problem in the industrialization of aluminum chloride electrolysis. Inert anode aluminum electrolysis usually refers to alumina electrolysis carried out in a fluoride electrolyte system. Since the anode does not participate in the decomposition reaction of alumina and only has a trace amount of consumption, it is called an inert anode. Under the condition of an inert anode, the decomposition voltage of alumina rises to about 2.3V, which is higher than the decomposition voltage of aluminum chloride, 1.85V. After the oxygen (water or other oxide impurities) in the aluminum chloride raw material enters the electrolyte melt, it will not affect the normal decomposition reaction of aluminum chloride, so the purity requirement for anhydrous aluminum chloride can be reduced.

[0003] However, there is little research on the corrosion resistance of inert anodes for alumina electrolysis in a chloride electrolyte system. In addition to the difference between the molten salt system and the fluoride salt system in the chloride electrolyte system, the chloride system has a large evaporation rate, and chlorine gas, HCl, etc. will be generated during the electrolysis process. Therefore, to investigate the corrosion resistance of an inert anode in a chloride system, it is necessary to test not only its corrosion resistance to the electrolyte melt but also its corrosion resistance to the electrolyte atmosphere. Directly using the method of aluminum chloride electrolysis can achieve the testing and screening of the corrosion resistance of an inert anode, but it is costly, difficult, and time-consuming. Currently, there is still no ready-made method for quickly testing and screening the corrosion resistance of an inert anode in a chloride electrolyte system without passing the aluminum chloride electrolysis test. Summary of the Invention

[0004] This application provides a method for testing the corrosion resistance of an inert anode for aluminum chloride electrolysis, so as to provide a new, efficient method for testing the corrosion resistance of an inert anode without passing the aluminum chloride electrolysis test.

[0005] An embodiment of this application provides a method for testing the corrosion resistance of an inert anode for aluminum chloride electrolysis, and the method includes:

[0006] Processing an inert anode sample into a test sample with a preset shape;

[0007] Immerse the sample to be tested partially in a chloride electrolyte melt, and conduct a high-temperature soaking treatment with a set temperature and a set soaking time;

[0008] Detect the content of metal elements dissolved from the sample to be tested after the high-temperature soaking treatment;

[0009] Remove the residual chloride electrolyte on the surface of the sample to be tested to analyze and compare the morphological and dimensional changes of the sample to be tested before and after the high-temperature soaking treatment; and

[0010] Evaluate the corrosion resistance of the inert anode sample according to the content of metal elements dissolved from the sample to be tested after the high-temperature soaking treatment, and the morphological and dimensional changes of the sample to be tested before and after the high-temperature soaking treatment.

[0011] Optionally, the preset shape is a cuboid, a cylinder, a cube or a sphere.

[0012] Optionally, the chloride electrolyte raw material of the chloride electrolyte melt is an AlCl3-NaCl-LiCl system electrolyte.

[0013] Optionally, by mass fraction, in the AlCl3-NaCl-LiCl system electrolyte, the content of AlCl3 is 3% - 7%, the content of LiCl is 40% - 45%, and the content of NaCl is 45% - 60%.

[0014] Optionally, the set temperature is 740°C - 760°C, and the set soaking time is 22h - 26h.

[0015] Optionally, the detection of the content of metal elements dissolved from the sample to be tested after the high-temperature soaking treatment includes:

[0016] After the high-temperature soaking treatment is completed, use a graphite rod to stir the chloride electrolyte melt, and then use a sampling rod to dip into the chloride electrolyte melt to obtain the electrolyte to be tested;

[0017] Use an inductively coupled plasma emission spectrometer to detect the contents of nickel, iron, and copper elements in the electrolyte to be tested, and obtain the content of metal elements dissolved from the sample to be tested after the high-temperature soaking treatment.

[0018] Optionally, the sampling rod is a graphite rod or a 310S stainless steel rod.

[0019] Optionally, the removal of the residual chloride electrolyte on the surface of the sample to be tested is carried out by boiling in water or ultrasonic water washing.

[0020] Optionally, evaluating the corrosion resistance of the inert anode sample based on the content of metal elements dissolved from the sample to be tested after high-temperature immersion treatment and the morphological and dimensional changes of the sample to be tested before and after high-temperature immersion treatment includes:

[0021] Observing whether the sample to be tested expands, cracks, or breaks after high-temperature immersion treatment;

[0022] If expansion, cracking, or breakage occurs, it is determined that the corrosion resistance of the inert anode sample is unqualified;

[0023] If no expansion, cracking, or breakage occurs, it is judged whether the dimensional change of the sample to be tested before and after high-temperature immersion treatment is within the range of +0.1 mm to -0.2 mm;

[0024] If it is not within the range of +0.1 mm to -0.2 mm, it is determined that the corrosion resistance of the inert anode sample is unqualified;

[0025] If it is within the range of +0.1 mm to -0.2 mm, it is judged whether the content of metal elements dissolved from the sample to be tested after high-temperature immersion treatment meets the requirement of not exceeding the standard value of dissolved metal elements;

[0026] If it does not meet the requirement, it is determined that the corrosion resistance of the inert anode sample is unqualified;

[0027] If it meets the requirement, it is determined that the corrosion resistance of the inert anode sample is qualified.

[0028] Optionally, the standard value of dissolved metal elements is 0.7%.

[0029] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0030] The embodiments of the present application provide a method for testing the corrosion resistance of an inert anode for aluminum chloride electrolysis. By comparing the morphological dimensions of the inert anode sample before and after the high-temperature immersion test, and comparing the analysis results of the contents of metal elements such as nickel and iron in the electrolyte contained in the inert anode with the standard value, it is possible to quickly and accurately test and screen the corrosion resistance of the inert anode in the chloride electrolyte system without passing through the aluminum chloride electrolysis test. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0032] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 It is a schematic flow chart of a corrosion resistance test method for an inert anode used in aluminum chloride electrolysis provided by an embodiment of the present application;

[0034] Figure 2 It is a schematic diagram of a sample of the inert anode to be tested in the present application under high-temperature immersion treatment;

[0035] Reference numerals:

[0036] 1 - Pit furnace; 2 - Corundum crucible; 3 - Corundum crucible lid; 4 - Furnace tube; 5 - Furnace tube lid; 6 - Inert anode sample; 7 - Electrolyte melt; 8 - Spacer block. Detailed implementation manners

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0038] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0039] In addition, in the description of the specification of this application, terms such as "include" and "comprise" mean "including but not limited to". In this text, relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this text, "and / or" describes the associated relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural. In this text, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one item (piece) below" or similar expressions refer to any combination of these items, including any combination of single item (piece) or plural items (pieces). For example, "at least one item (piece) among a, b, or c", or, "at least one item (piece) among a, b, and c" can both mean: a, b, c, a-b (that is, a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple respectively. The "parts representation method" such as weight parts and mass parts represents the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0040] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in this application can be obtained through market purchase or can be prepared by existing methods.

[0041] Figure 1 It is a schematic flow chart of a corrosion resistance test method for an inert anode used in aluminum chloride electrolysis provided by an embodiment of this application.

[0042] As Figure 1 shown, this application provides a corrosion resistance test method for an inert anode used in aluminum chloride electrolysis, and the method includes:

[0043] S1. Process the inert anode specimen into a test specimen with a preset shape;

[0044] In some embodiments, the preset shape is a cuboid, a cylinder, a cube, or a sphere.

[0045] Regular shapes (such as cuboids and cylinders) ensure that the immersion area and the exposed ratio of the specimen in the melt are consistent, reducing the deviation of corrosion evaluation caused by shape differences.

[0046] S2. Immerse the sample to be tested partially in the chloride electrolyte melt, and perform a high-temperature soaking treatment with a set temperature and a set soaking time.

[0047] It should be noted that processing the inert anode sample into a sample with a regular shape and using an electrolyte with a fixed mass and chemical composition are to ensure that for each high-temperature soaking test, the surface area of the sample immersed in the electrolyte and the exposed surface area are the same, making them comparable. In addition, during the high-temperature soaking process, part of the sample is exposed to the electrolyte melt, enabling the simultaneous testing of the sample's resistance to corrosion by the electrolyte melt and the electrolyte atmosphere.

[0048] In some embodiments, the chloride electrolyte raw material of the chloride electrolyte melt is an AlCl3-NaCl-LiCl system electrolyte.

[0049] In some embodiments, by mass fraction, in the AlCl3-NaCl-LiCl system electrolyte, the content of AlCl3 is 3% - 7%, the content of LiCl is 40% - 45%, and the content of NaCl is 45% - 60%.

[0050] AlCl3 is the active component of the electrolyte. If the concentration is too low (<3%), it will lead to insufficient melt conductivity; if it is too high (>7%), it will exacerbate the corrosion of the anode. LiCl can lower the melting point of the melt and improve fluidity; NaCl can be used as an inert component to stabilize the molten salt structure and prevent high-temperature volatilization. Exemplarily, the content of AlCl3 can be 3%, 4%, 5%, 6%, 7%, etc., the content of LiCl can be 40%, 41%, 43%, 43%, 44%, 45%, etc., and the content of NaCl can be 45%, 47%, 49%, 50%, 52%, 56%, 58%, 60%, etc.

[0051] In some embodiments, the set temperature is 740°C - 760°C, and the set soaking time is 22h - 26h.

[0052] Defining the temperature of the high-temperature soaking treatment as 740°C - 760°C, which is higher than the melting point of the AlCl3-NaCl-LiCl system, ensures that the melt is completely liquefied and the corrosion reaction proceeds fully. At the same time, it inhibits excessive volatilization of the molten salt (such as LiCl is prone to sublimation at high temperatures) and avoids structural damage of the sample due to thermal expansion. Defining the soaking time as 22h - 26h can simulate the continuous operation cycle of an industrial electrolytic cell and balance the requirements for short-term corrosion rate and long-term stability assessment. Exemplarily, the temperature of the high-temperature soaking treatment can be 740°C, 745°C, 750°C, 755°C, 760°C, etc., and the soaking time can be 22h, 23h, 24h, 25h, 26h, etc.

[0053] In some embodiments, the container for the high-temperature soaking treatment is a covered corundum crucible, and the heating device for the high-temperature soaking treatment is a heating furnace.

[0054] S3. Detect the content of metal elements dissolved in the test sample after the high-temperature soaking treatment;

[0055] In some embodiments, detecting the content of metal elements dissolved in the test sample after the high-temperature soaking treatment includes:

[0056] After the high-temperature soaking treatment is completed, use a graphite rod to stir the chloride electrolyte melt, and then use a sampling rod to dip into the chloride electrolyte melt to obtain the electrolyte to be tested;

[0057] Use an inductively coupled plasma emission spectrometer to detect the contents of nickel, iron, and copper elements in the electrolyte to be tested, and obtain the content of metal elements dissolved in the test sample after the high-temperature soaking treatment.

[0058] In some embodiments, the sampling rod is a graphite rod or a 310S stainless steel rod.

[0059] It should be noted that using a graphite rod to stir the electrolyte melt can avoid the introduction of foreign impurities. However, a 310S stainless steel rod can be used during the dipping process because the dipping process is relatively fast and the 310S stainless steel rod will not introduce impurities.

[0060] When analyzing the electrolyte, using an inductively coupled plasma emission spectrometer (ICP-OES) to measure the contents of nickel, iron, and copper metal elements in the electrolyte can ensure the accuracy of the element content measurement. Moreover, nickel, iron, and copper are representative elements in the inert anode and are not originally contained in the electrolyte. Therefore, by analyzing the contents of these elements in the electrolyte, it can represent the corrosion resistance of the inert anode to the electrolyte.

[0061] S4. Remove the residual chloride electrolyte on the surface of the test sample to analyze and compare the morphological and dimensional changes of the test sample before and after the high-temperature soaking treatment; and

[0062] In some embodiments, the residual chloride electrolyte on the surface of the test sample is removed by boiling in water or ultrasonic water washing.

[0063] It should be noted that using boiling in water or ultrasonic water washing to clean the electrolyte on the surface of the inert anode sample is for two reasons. On the one hand, the chloride electrolyte can dissolve in water. On the other hand, it is to avoid damage to the sample caused by the cleaning process to ensure more accurate observation of the inert anode sample.

[0064] S5. Evaluate the corrosion resistance of the inert anode sample based on the content of metal elements dissolved from the sample to be tested after high-temperature immersion treatment, and the morphological and dimensional changes of the sample to be tested before and after high-temperature immersion treatment.

[0065] In some embodiments, the evaluating the corrosion resistance of the inert anode sample based on the content of metal elements dissolved from the sample to be tested after high-temperature immersion treatment, and the morphological and dimensional changes of the sample to be tested before and after high-temperature immersion treatment includes:

[0066] S501. Observe whether the sample to be tested expands, cracks or breaks after high-temperature immersion treatment;

[0067] S502. If expansion, cracking or breaking occurs, determine that the corrosion resistance of the inert anode sample is unqualified;

[0068] S503. If no expansion, cracking or breaking occurs, judge whether the dimensional change of the sample to be tested before and after high-temperature immersion treatment is within the range of +0.1 mm to -0.2 mm;

[0069] S504. If it is not within the range of +0.1 mm to -0.2 mm, determine that the corrosion resistance of the inert anode sample is unqualified;

[0070] S505. If it is within the range of +0.1 mm to -0.2 mm, judge whether the content of metal elements dissolved from the sample to be tested after high-temperature immersion treatment meets the requirement of not being greater than the standard value of dissolved metal elements;

[0071] S506. If it does not meet the requirement, determine that the corrosion resistance of the inert anode sample is unqualified;

[0072] S507. If it meets the requirement, determine that the corrosion resistance of the inert anode sample is qualified.

[0073] It should be noted that the embodiments of the present application can use a step-by-step determination or a comprehensive determination method to evaluate the corrosion resistance of the inert anode, specifically including checking whether the sample expands, cracks or breaks, measuring whether the dimensional change is within ±0.1 to -0.2 mm, and detecting whether the dissolved amount of metal elements does not exceed the standard value.

[0074] Within the range of +0.1 mm to -0.2 mm, +0.1 mm means that the size of the sample to be tested expands by less than 0.1 mm before and after high-temperature immersion treatment, and -0.2 mm means that the size of the sample to be tested shrinks by less than 0.2 mm before and after high-temperature immersion treatment.

[0075] In some embodiments, the standard value of dissolved metal elements is 0.7%.

[0076] It should be noted that the standard values of the dissolved metal elements are obtained from the actual analytical values obtained by subjecting the inert anode specimens that have passed the aluminum chloride electrolysis test to high-temperature immersion tests under the same conditions.

[0077] The same conditions refer to using inert anode specimens with the same external dimensions, chloride electrolytes with the same composition and weight, the same corundum crucible, the same high-temperature immersion test temperature and time, the same sampling and analysis method, and the same surface area of the inert anode specimen immersed in the electrolyte during the high-temperature immersion process.

[0078] The standard values for comparison are determined based on the actual analytical values of the inert anode specimens that have passed the aluminum chloride electrolysis test after high-temperature immersion tests under the same conditions, which ensures the reliability of the standard values. Because the aluminum chloride electrolysis test, although costly, difficult, slow, and not easy to implement, is the most direct and accurate test method. In addition, industry personnel using this method can also set the standard values according to their actual needs for the aluminum chloride electrolysis results of the inert anode, which also ensures the flexibility of the patented method.

[0079] In summary, the present invention can quickly and accurately test and screen the corrosion resistance of inert anodes in a chloride electrolyte system without passing through an aluminum chloride electrolysis test.

[0080] The corrosion resistance test method for the inert anode used in aluminum chloride electrolysis proposed in the embodiments of the present application has the following significant advantages:

[0081] (1) Standardization and comparability: By specifying the preset shapes (such as cuboids, cylinders, etc.) of the inert anode specimens and using electrolytes with fixed masses and chemical compositions, the conditions for each test are ensured to be consistent, improving the comparability and accuracy of the test results.

[0082] (2) Comprehensive evaluation: The test method not only considers the immersed part of the specimen in the electrolyte melt but also the resistance of the exposed part to the electrolyte atmosphere, enabling a comprehensive evaluation of the corrosion resistance of the inert anode.

[0083] (3) Optimized test conditions: By carefully setting the temperature range (740°C - 760°C) and holding time (22h - 26h), it not only ensures that the corrosion reaction proceeds fully but also avoids excessive volatilization of the molten salt and damage to the specimen structure, making the test results more reliable.

[0084] (4) Precise detection means: Using an inductively coupled plasma optical emission spectrometer (ICP-OES) to detect the content of metal elements in the electrolyte ensures the accuracy of the element content measurement, thereby accurately reflecting the corrosion resistance of the inert anode.

[0085] (5) System evaluation process: By observing the morphology and size changes of the test samples and detecting the content of dissolved metal elements, a systematic evaluation process has been formed, which can comprehensively and accurately evaluate the corrosion resistance of the inert anode.

[0086] (6) Flexibility and reliability: The determination of the standard value of the dissolved metal elements adopts the actual analysis value of the inert anode sample that has passed the high-temperature immersion test under the same conditions after the aluminum chloride electrolysis test, ensuring the reliability of the standard value. At the same time, industry personnel can also set the standard value according to their actual needs, ensuring the flexibility of this method.

[0087] (7) High efficiency and economy: Compared with the aluminum chloride electrolysis test, this method has lower cost, faster speed, and simpler implementation. It can quickly and accurately test and screen the corrosion resistance of the inert anode in the chloride electrolyte system, which is beneficial to industrial application and promotion.

[0088] The following further elaborates on this application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate this application and not to limit the scope of this application. The experimental methods without specific conditions noted in the following embodiments are usually determined according to industry standards. If there is no corresponding industry standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0089] Example 1

[0090] Test and screen the corrosion resistance of a certain cermet inert anode. Adopt the Figure 1 steps shown. The schematic diagram of the high-temperature immersion test is as shown in Figure 2 .

[0091] (1) Processing of the inert anode sample and preparation of the chloride system electrolyte. The inert anode to be tested is processed into a regular cuboid sample 6 with a length, width, and height of 40.12 mm, 15.64 mm, and 60.46 mm respectively; the AlCl3-NaCl-LiCl system electrolyte is prepared in a vacuum glove box using reagents, where 5 wt.% AlCl3, 42 wt.% LiCl, and 53 wt.% NaCl. After mixing, it is placed in a drying oven for later use.

[0092] (2) High-temperature immersion test and sampling analysis. Take 100 g of the chloride electrolyte prepared in step S1, together with the inert anode specimen 6 prepared in step S1, and place them in a covered corundum crucible 2. Keep them at 750 °C in the heating furnace 1 for 24 h. During the high-temperature immersion process, part of the inert anode specimen 6 is exposed to the electrolyte melt 7. After 24 h, first stir the electrolyte melt 7 with a graphite rod, and then use other graphite rods as sampling rods to dip into the electrolyte melt for sampling. For the electrolyte solidified on the sampling rod, use an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the contents of nickel, iron, and copper metal elements in the electrolyte for composition analysis. After sampling, cover the crucible lid 3 and the furnace tube lid 5, turn off the heating 1, and cool with the furnace.

[0093] (3) Observe the morphology and dimensions of the inert anode specimen. After cooling, separate the crucible, the electrolyte, and the inert anode specimen. Clean the electrolyte on the surface of the inert anode specimen by boiling in water, and there are no phenomena such as swelling, cracking, etc. on the inert anode specimen. Use a vernier caliper to measure the external dimensions of the anode specimen, and the length, width, and height are 40.14 mm, 15.62 mm, and 60.48 mm respectively, within ±0.1 mm compared with before the test;

[0094] (4) Screening and evaluation. According to the observed morphology, there is no significant swelling, cracking, and corrosion. According to the electrolyte analysis results, the contents of nickel, iron, and copper are 0.305 wt.%, 0.243 wt.%, and 0.035 wt.% respectively, and the total is 0.583 wt.%, which is less than the standard value of 0.7 wt.%. It shows that the corrosion resistance of this inert anode specimen is good and can meet the needs of aluminum chloride electrolysis.

[0095] Among them, the source of the standard value is the actual analysis value obtained by performing the same-condition high-temperature immersion test on the inert anode specimen that has passed the 20 A aluminum chloride electrolysis test. The same conditions mean using inert anode specimens with the same external dimensions, chloride electrolytes with the same components and weights, the same corundum crucibles, the same high-temperature immersion test temperature and time, the same sampling analysis method, and the same surface area of the inert anode specimen immersed in the electrolyte during the high-temperature immersion process.

[0096] Example 2

[0097] Test and screen the corrosion resistance of a certain cermet inert anode. Adopt the Figure 1 shown steps, and the schematic diagram of the high-temperature immersion test is as shown in Figure 2 shown.

[0098] (1) Processing of inert anode samples and preparation of chloride-based electrolyte. The inert anode to be tested was processed into regular cuboid samples 6 with length, width, and height of 40.84 mm, 15.88 mm, and 60.96 mm respectively. An AlCl3-NaCl-LiCl system electrolyte was prepared using reagents in a vacuum glove box, containing 5 wt.% AlCl3, 42 wt.% LiCl, and 53 wt.% NaCl. After mixing, it was placed in a drying oven for later use.

[0099] (2) High-temperature immersion test and sampling analysis. Take 100 g of the chloride electrolyte prepared in step S1, together with the inert anode sample 6 prepared in step S1, and place them in a covered corundum crucible 2, and keep them at 750 °C in a heating furnace 1 for 24 h. During the high-temperature immersion process, part of the inert anode sample 6 was exposed to the electrolyte melt 7. After 24 h, first stir the electrolyte melt with a graphite rod, and then use a 310S stainless steel rod as a sampling rod to dip into the electrolyte melt for sampling. For the electrolyte solidified on the sampling rod, an inductively coupled plasma optical emission spectrometer (ICP-OES) was used to measure the contents of nickel, iron, and copper metal elements in the electrolyte for composition analysis. After sampling, cover the crucible lid 3 and the furnace tube lid 5, turn off the heating 1, and cool with the furnace.

[0100] (3) Observing the morphology and dimensions of the inert anode sample. After cooling, separate the crucible, electrolyte, and inert anode sample. Clean the electrolyte on the surface of the inert anode sample by ultrasonic water washing, and there is a slight swelling phenomenon of the inert anode sample. Use a vernier caliper to measure the external dimensions of the anode sample, with length, width, and height of 41.26 mm, 16.24 mm, and 61.12 mm respectively, exceeding +0.1 mm compared with before the test;

[0101] (4) Screening and evaluation. According to the observed morphology, there is a swelling phenomenon. According to the electrolyte analysis results, the contents of nickel, iron, and copper are 0.532 wt.%, 0.451 wt.%, and 0.218 wt.% respectively, and the total is 1.201 wt.%, which is greater than the standard value of 0.7 wt.%. It shows that the corrosion resistance of this inert anode sample is not good and cannot meet the needs of aluminum chloride electrolysis.

[0102] Among them, the source of the standard value is the actual analysis value obtained by performing the same-condition high-temperature immersion test on the inert anode sample that has passed the 20A aluminum chloride electrolysis test. The same conditions refer to using inert anode samples with the same external dimensions, chloride electrolytes with the same components and weights, the same corundum crucible, the same high-temperature immersion test temperature and time, the same sampling analysis method, and the same surface area of the inert anode sample immersed in the electrolyte during the high-temperature immersion process.

[0103] Example 3

[0104] The corrosion resistance of a certain cermet inert anode was tested and screened. The steps shown in Figure 1 were adopted. The schematic diagram of the high-temperature immersion test is shown in Figure 2 .

[0105] (1) Processing of the inert anode sample and preparation of the chloride-based electrolyte. The inert anode to be tested was processed into a regular cuboid sample 6 with a length, width, and height of 40.26 mm, 15.38 mm, and 60.46 mm respectively; the AlCl3-NaCl-LiCl system electrolyte was prepared using reagents in a vacuum glove box, with 5 wt.% AlCl3, 42 wt.% LiCl, and 53 wt.% NaCl. After mixing, it was placed in a drying oven for later use.

[0106] (2) High-temperature immersion test and sampling analysis. Take 100 g of the chloride electrolyte prepared in step S1, together with the inert anode sample 6 prepared in step S1, and place them in a covered corundum crucible 2, and keep it at 750 °C in a heating furnace 1 for 24 h. During the high-temperature immersion process, part of the inert anode sample 6 was exposed to the electrolyte melt 7. After 24 h, first stir the electrolyte melt with a graphite rod, and then use a 310S stainless steel rod as a sampling rod to dip into the electrolyte melt for sampling. For the electrolyte solidified on the sampling rod, an inductively coupled plasma optical emission spectrometer (ICP-OES) was used to measure the contents of nickel, iron, and copper metal elements in the electrolyte for composition analysis. After sampling, cover the crucible lid 3 and the furnace tube lid 5, turn off the heating 1, and cool it with the furnace.

[0107] (3) Observing the morphology and dimensions of the inert anode sample. After cooling, separate the crucible, electrolyte, and inert anode sample. Clean the electrolyte on the surface of the inert anode sample by boiling in water, and there is no swelling or cracking phenomenon on the inert anode sample. Use a vernier caliper to measure the external dimensions of the anode sample, with a length, width, and height of 40.04 mm, 15.12 mm, and 60.20 mm respectively, which is more than -0.2 mm compared with before the test;

[0108] (4) Screening and evaluation. According to the observed morphology, there is no swelling phenomenon, but the corrosion rate is relatively fast. According to the electrolyte analysis results, the contents of nickel, iron, and copper are 0.343 wt.%, 0.524 wt.%, and 0.121 wt.% respectively, and the total is 0.988 wt.%, which is greater than the standard value of 0.7 wt.%. It shows that the corrosion resistance of this inert anode sample is not good and cannot meet the needs of aluminum chloride electrolysis.

[0109] Among them, the source of the standard value is the actual analysis value obtained by performing high-temperature immersion tests under the same conditions on inert anode specimens that have been tested through 20A aluminum chloride electrolysis tests. The same conditions refer to using inert anode specimens with the same external dimensions, chloride electrolytes with the same components and weights, the same corundum crucibles, the same high-temperature immersion test temperature and time, the same sampling and analysis methods, and the same surface area of the inert anode specimens immersed in the electrolyte during the high-temperature immersion process.

[0110] In addition, one or more technical solutions in the embodiments of the present application at least further have the following technical effects or advantages:

[0111] In the embodiments of the present application, in view of the problems such as high test cost, great difficulty, and long cycle in testing the inert anode under chloride electrolysis conditions, a method is developed that can quickly test and screen the corrosion resistance of the inert anode in a chloride electrolyte system without passing through an aluminum chloride electrolysis test.

[0112] In the embodiments of the present application, the provided method for testing the corrosion resistance of the inert anode is simple, convenient, and easy to implement, and can quickly screen out inert anodes with qualified corrosion resistance for aluminum chloride electrolysis of the inert anode.

[0113] The above are only specific implementation manners of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather will conform to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A corrosion resistance test method for an inert anode used in aluminum chloride electrolysis, the method comprising: Processing an inert anode specimen into a test specimen with a preset shape; Partially immersing the test specimen in a chloride electrolyte melt and performing a high-temperature soaking treatment with a set temperature and a set soaking time; Detecting the content of metal elements dissolved from the test specimen after the high-temperature soaking treatment; Removing the residual chloride electrolyte on the surface of the test specimen to analyze and compare the morphology and size changes of the test specimen before and after the high-temperature soaking treatment; and Evaluating the corrosion resistance of the inert anode specimen according to the content of metal elements dissolved from the test specimen after the high-temperature soaking treatment, and the morphology and size changes of the test specimen before and after the high-temperature soaking treatment.

2. The method according to claim 1, characterized in that, The preset shape is a cuboid, a cylinder, a cube or a sphere.

3. The method according to claim 1, wherein The chloride electrolyte raw material of the chloride electrolyte melt is an AlCl3-NaCl-LiCl system electrolyte.

4. The method according to claim 3, wherein By mass fraction, in the AlCl3-NaCl-LiCl system electrolyte, the content of AlCl3 is 3% - 7%, the content of LiCl is 40% - 45%, and the content of NaCl is 45% - 60%.

5. The method according to claim 1, wherein The set temperature is 740°C - 760°C, and the set soaking time is 22h - 26h.

6. The method according to claim 1, characterized in that, The detecting the content of metal elements dissolved from the test specimen after the high-temperature soaking treatment includes: After the high-temperature soaking treatment ends, using a graphite rod to stir the chloride electrolyte melt, and then using a sampling rod to dip into the chloride electrolyte melt to obtain a test electrolyte; Using an inductively coupled plasma emission spectrometer to detect the contents of nickel, iron, and copper elements in the test electrolyte to obtain the content of metal elements dissolved from the test specimen after the high-temperature soaking treatment.

7. The method according to claim 6, wherein The sampling rod is a graphite rod or a 310S stainless steel rod.

8. The method according to claim 1, wherein The removing the residual chloride electrolyte on the surface of the test specimen is carried out by boiling in water or ultrasonic water washing.

9. The method according to claim 1, wherein The evaluating the corrosion resistance of the inert anode specimen according to the content of metal elements dissolved from the test specimen after the high-temperature soaking treatment, and the morphology and size changes of the test specimen before and after the high-temperature soaking treatment includes: Observing whether the test specimen expands, cracks or breaks after the high-temperature soaking treatment; If expansion, cracking or breaking occurs, it is determined that the corrosion resistance of the inert anode specimen is unqualified; If no expansion, cracking or breaking occurs, it is judged whether the size change of the test specimen before and after the high-temperature soaking treatment is within the range of +0.1mm to -0.2mm; If it is not within the range of +0.1mm to -0.2mm, it is determined that the corrosion resistance of the inert anode specimen is unqualified; If it is within the range of +0.1mm to -0.2mm, it is judged whether the content of metal elements dissolved from the test specimen after the high-temperature soaking treatment meets the requirement of not being greater than the standard value of dissolved metal elements; If it does not meet the requirement, it is determined that the corrosion resistance of the inert anode specimen is unqualified; If it meets the requirement, it is determined that the corrosion resistance of the inert anode specimen is qualified.

10. The method according to claim 9, characterized in that, The standard value of dissolved metal elements is 0.7%.

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