Method for evaluating corrosion resistance of saggar

Abstract

The invention provides a sagger corrosion resistance evaluation method which comprises the following steps: burying sagger fragments to be tested into a material to be sintered, and sintering to obtain sintered sagger fragments; and evaluating the corrosion resistance of the saggar according to the weight loss of the saggar fragments before and after sintering. The evaluation method is simple and convenient, the corrosion resistance of the saggar can be effectively evaluated, the saggar does not need to be tried and verified in the whole life cycle on a production line, and the evaluation method has very important reference value for selection of the saggar.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of testing, and relates to a method for evaluating the corrosion resistance of a sagger. BACKGROUND

[0002] The sodium ion positive electrode material is seriously corroded in the sintering process, and the main reason is that the sodium ion positive electrode material needs to use sodium salt (mainly sodium carbonate). The sodium salt will decompose to produce strong corrosive sodium-containing compounds such as molten sodium carbonate and sodium oxide in the high-temperature calcination process. Corrosive substances such as sodium hydroxide are also generated in the sintering and cooling process.

[0003] The sagger currently used in the industrial sintering is made of mullite, and the main component of mullite is aluminosilicate (SiO2-Al2O3). In the process of calcining the sodium ion positive electrode material precursor and sodium salt, the mullite sagger will be seriously corroded by the material, resulting in a short service life of the sagger. In addition, there is a risk of pollution by elements such as Si and Al in the positive electrode material prepared by calcination. Although the sagger made of corundum has excellent corrosion resistance, it has a very high cost and is prone to uneven heating and cracking during the heating process. Considering the practicality and economy, the mullite sagger still cannot be replaced in the actual industrial production of positive electrode materials. In order to improve the service life and corrosion resistance of the mullite sagger, various rare earth element doping measures are often used in the preparation process of the mullite sagger to improve the corrosion resistance.

[0004] However, there is currently a lack of corrosion resistance evaluation standards, which cannot well judge the corrosion resistance of the sagger. Only the actual use in the whole life cycle can be used for comprehensive judgment, which leads to the inability to select a suitable sagger supplier before actual use.

[0005] Therefore, there is an urgent need for a simple and convenient evaluation method to accurately evaluate the corrosion resistance of the sagger, which is of great significance for guiding the industrial production of sodium ion positive electrode materials. SUMMARY

[0006] In view of the deficiencies in the prior art, the purpose of the present application is to provide a method for evaluating the corrosion resistance of a sagger. The evaluation method of the present application is simple and convenient, and can effectively evaluate the corrosion resistance of the sagger. It is not necessary to test and verify the sagger in the whole life cycle on the production line. By burying sagger fragments of different manufacturers and different models in the material to be sintered, the corrosion resistance of each sagger can be effectively evaluated in a short time, which is time-saving, cost-effective, and has a very important reference value for the selection of sagger quality and sagger manufacturers.

[0007] To achieve this purpose, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a method for evaluating the corrosion resistance of a sagger, the method comprising:

[0009] The sagger fragments to be tested are buried in the sintering material to be sintered, and sintering is performed to obtain sintered sagger fragments; and the corrosion resistance of the sagger is evaluated according to the weight loss of the sagger fragments before and after sintering.

[0010] The present application provides a method for evaluating the corrosion resistance of a sagger, the method comprising: burying sagger fragments to be tested in sintering material to be sintered, and sintering is performed to obtain sintered sagger fragments; and the corrosion resistance of the sagger is evaluated according to the weight loss of the sagger fragments before and after sintering. The smaller the weight loss of the sagger fragments before and after sintering, the stronger the corrosion resistance of the sagger. The evaluation method of the present application is simple and convenient, and can effectively evaluate the corrosion resistance of the sagger. It is not necessary to test and verify the sagger in the whole life cycle on the production line. By burying sagger fragments of different models from different manufacturers in the sintering material to be sintered, the corrosion resistance of each sagger can be effectively evaluated in a short time, which is time-saving and cost-effective, and has a very important reference value for the selection of sagger quality and sagger manufacturers.

[0011] In the present application, when evaluating saggars of different models from different manufacturers, the weight range of the sagger fragments corresponding to each sagger is ≤5g to reduce variables.

[0012] Preferably, the material of the sagger fragments comprises mullite.

[0013] Preferably, the sintering material to be sintered comprises a sodium salt and / or a sodium ion oxide-based positive electrode material precursor.

[0014] In the present application, the sintering material to be sintered is preferably a sodium salt and a sodium ion oxide-based positive electrode material precursor. After sintering of the sintering material to be sintered, a sodium ion oxide-based positive electrode material NaMO2 is obtained, wherein M is a transition metal. The sodium ion oxide-based positive electrode material is in O3 phase or P2 phase.

[0015] Optionally, the mass of the sintering material to be sintered is 3-6kg, for example, it can be 3.2kg, 3.5kg, 4kg, 5kg or 6kg, but is not limited to the listed values, and other values not listed in this range are also applicable.

[0016] Preferably, the shape of the sagger fragments is square or approximately square.

[0017] Preferably, the length and width of the sagger fragments are independently 5-10cm, for example, they can be 5cm, 5.5cm, 6cm, 6.5cm, 7cm, 7.5cm, 8cm, 8.5cm, 9cm, 9.5cm or 10cm, but are not limited to the listed values, and other values not listed in this range are also applicable.

[0018] Preferably, the thickness of the fragments of the sintering pot is 1-2 cm, for example, it can be 1 cm, 1.2 cm, 1.5 cm, 1.8 cm or 2 cm, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0019] Preferably, the sintering material to be placed in the sintering pot, and there is a distance between the fragments of the sintering pot and the inner cavity side wall of the sintering pot.

[0020] Preferably, when the fragments of the sintering pot are buried in the sintering material, the fragments of the sintering pot are completely buried and do not contact the inner cavity bottom surface of the sintering pot.

[0021] In the present application, when the fragments of the sintering pot are directly placed on the sintering material without being buried, only the contact part below the fragments of the sintering pot is corroded, that is, the corrosion is insufficient, and the corrosion resistance of the sintering pot cannot be effectively evaluated; when the fragments of the sintering pot are not completely buried but partially buried, only the buried part is corroded, and the corrosion is also insufficient, and the corrosion resistance of the sintering pot cannot be effectively evaluated.

[0022] When the fragments of the sintering pot directly contact the inner cavity bottom surface of the sintering pot, interference between them will occur, and the sintering of the material will be affected. Because under normal circumstances, during sintering, air can penetrate the surface layer of the material and enter the interior to fully contact the sintering material, and the waste gas generated during the sintering process of the material can also be discharged through the loose material. When the fragments of the sintering pot contact or are close to the inner cavity bottom surface of the sintering pot, the air permeability of the material will be affected, further affecting whether the sintering can be fully carried out, and the corrosion under the condition of insufficient sintering cannot represent the corrosion ability of the material under normal circumstances, that is, the final result is not representative.

[0023] It should be noted that in the present application, when the fragments of the sintering pot to be tested are buried in the sintering material, they can be placed horizontally or obliquely. Horizontally placed means that the plane where the fragments of the sintering pot are located is parallel to the bottom surface of the sintering pot, and obliquely placed means that the plane where the fragments of the sintering pot are located intersects the bottom surface of the sintering pot.

[0024] Preferably, the distance between the fragments of the sintering pot and the inner cavity side wall of the sintering pot is ≥1 cm, for example, it can be 1 cm, 1.2 cm, 1.5 cm, 2 cm, 2.5 cm, 3 cm, 4 cm, 5 cm, 8 cm, 10 cm or 15 cm, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0025] In the present application, when the distance between the sagger fragments and the inner cavity side wall of the sintering sagger is <1 cm, the sagger fragments are too close to the inner cavity side wall of the sintering sagger, which will cause mutual interference, and the sintering of the material will be affected, affecting the air permeability of the material, further affecting whether the sintering can be fully carried out, and the corrosion under the condition of insufficient sintering cannot represent the corrosion ability of the material under normal conditions, that is, the final result is not representative.

[0026] Preferably, the upper and lower of the sagger fragments form a layer of material to be sintered, the thickness of the upper layer of material to be sintered is ≥1 cm, for example, it can be 1 cm, 1.2 cm, 1.5 cm, 2 cm, 2.5 cm, 3 cm, 4 cm, 5 cm, 8 cm, 10 cm or 15 cm, etc.; the thickness of the lower layer of material to be sintered is ≥1 cm, for example, it can be 1 cm, 1.2 cm, 1.5 cm, 2 cm, 2.5 cm, 3 cm, 4 cm, 5 cm, 8 cm, 10 cm or 15 cm, etc., but not limited to the listed values, other values not listed within this range are also applicable.

[0027] In the present application, when the thickness of the upper layer of material to be sintered on the sagger fragments is <1 cm, the corrosion will be insufficient, and the sagger corrosion resistance cannot be effectively evaluated. When the thickness of the lower layer of material to be sintered on the sagger fragments is <1 cm, the corrosion is also insufficient, and the sagger corrosion resistance cannot be effectively evaluated.

[0028] Preferably, the number of sagger fragments is at least 2, for example, it can be 2, 3, 5, 6, 8, 10 or 15, etc., the distance between adjacent sagger fragments is ≥1 cm, for example, it can be 1 cm, 1.2 cm, 1.5 cm, 2 cm, 2.5 cm, 3 cm, 4 cm, 5 cm, 8 cm, 10 cm or 15 cm, etc., but not limited to the listed values, other values not listed within this range are also applicable.

[0029] In the present application, when the distance between adjacent sagger fragments is <1 cm, the adjacent sagger fragments are too close, which will interfere with each other, and there is less material to be sintered between adjacent sagger fragments, making it difficult for the material to be sintered to fully corrode the sagger fragments, and the sagger corrosion resistance cannot be effectively evaluated.

[0030] In the present application, when the number of sagger fragments is at least 2, they can be sagger fragments of different models to explore the corrosion resistance of sagger of different models.

[0031] Preferably, the number of sintering is n times, n ≥ 1 and n is an integer, for example, n can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 15 or 20, etc., but not limited to the listed values, other values not listed within this range are also applicable.

[0032] Preferably, the weight of the to-be-tested saggar fragment is denoted as M0, the weight of the saggar fragment after sintering is denoted as M n , the weight loss of the saggar fragment before and after sintering is denoted as Φ, and the calculation formula of the Φ is: φ=(1-M n / M0) / n.

[0033] It should be noted that the weight M n of the saggar fragment after sintering is the weight of the saggar fragment after sintering obtained after the last sintering. When n≥2, the calculated φ can be referred to as the average weight loss of the saggar fragment before and after single sintering.

[0034] In the present application, the smaller the value of the φ is, the stronger the corrosion resistance of the saggar is.

[0035] Preferably, the n satisfies the following condition: n≥5.

[0036] In the present application, considering the actual evaluation effect, single sintering or a small number of sintering cannot accurately judge the corrosion resistance of the to-be-tested saggar. The reason is that the new saggar has relatively strong corrosion resistance, and the corrosion does not occur obviously or the corrosion resistance does not differ greatly in the first few times of sintering. After multiple sintering, the corrosion resistance decreases, that is, the corrosion degree gradually increases. Through actual evaluation verification, sintering for 5 times or more can effectively evaluate the corrosion resistance of the saggar.

[0037] Preferably, the n satisfies the following condition: 5≤n≤10.

[0038] In the present application, considering the actual evaluation effect, the optimal number of sintering is 5-10 times, which can effectively evaluate the corrosion resistance of the saggar, and can also shorten the evaluation time, save resources, and reduce costs.

[0039] Preferably, the sintering temperature is 900-1000℃, for example, it can be 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, 980℃ or 990℃, but it is not limited to the listed values. Other values not listed in this value range are also applicable.

[0040] Preferably, the sintering time is 10-20h, for example, it can be 10h, 12h, 15h, 18h or 20h, but it is not limited to the listed values. Other values not listed in this value range are also applicable.

[0041] In the present application, the temperature range of single sintering is 900-1000℃, and the time range of single sintering is 10-20h. This temperature range and time range are suitable for sintering the mixture of sodium salt and sodium ion oxide positive electrode material precursor.

[0042] As a preferred technical solution of the present application, the evaluation method specifically comprises:

[0043] (1) crushing the to-be-tested saggar to obtain to-be-tested saggar fragments, wherein the material of the saggar comprises mullite, the shape of the saggar fragments is square or approximately square, and the weight of the saggar fragments is denoted as M0;

[0044] (2) placing a to-be-sintered material into a sintering saggar, wherein the to-be-sintered material comprises a sodium salt and a sodium ion oxide-based positive electrode material precursor; burying the to-be-tested saggar fragments in the to-be-sintered material, so that the distance between the saggar fragments and the inner cavity side wall of the sintering saggar is greater than or equal to 1 cm, and the upper and lower parts of the saggar fragments are both formed with a to-be-sintered material layer, the thickness of the to-be-sintered material layer on the upper part is greater than or equal to 1 cm, and the thickness of the to-be-sintered material layer on the lower part is greater than or equal to 1 cm; then performing n times of sintering in an air atmosphere to obtain sintered saggar fragments, and then cleaning the sintered saggar fragments with a sodium citrate solution and water in sequence, and then drying, wherein the weight of the dried saggar fragments is denoted as M n ; and calculating the weight loss Φ of the saggar fragments before and after sintering according to φ=(1-M n / M0) / n, wherein the smaller the value of φ is, the stronger the corrosion resistance of the to-be-tested saggar is; wherein 5≤n≤10 and n is an integer.

[0045] The numerical range of the present application includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed, and the present application does not exhaustively list the specific point values included in the range for the sake of brevity and simplicity.

[0046] Compared with the prior art, the present application has the following beneficial effects:

[0047] The present application provides an evaluation method for the corrosion resistance of a saggar, which buries to-be-tested saggar fragments in to-be-sintered material for sintering, and evaluates the corrosion resistance of the saggar according to the weight loss of the saggar fragments before and after sintering, wherein the smaller the weight loss of the saggar fragments before and after sintering is, the stronger the corrosion resistance of the saggar is. The evaluation method of the present application is simple and convenient, and can effectively evaluate the corrosion resistance of the saggar without the need for trial verification of the saggar in the whole life cycle on the production line. By burying saggar fragments of different models from different manufacturers in to-be-sintered material for sintering, the corrosion resistance of each saggar can be effectively evaluated in a short time, which is time-saving and cost-effective, and has a very important reference value for the selection of saggar quality and saggar manufacturers. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The present application provides an evaluation method for the corrosion resistance of a saggar, which buries to-be-tested saggar fragments in to-be-sintered material for sintering, and evaluates the corrosion resistance of the saggar according to the weight loss of the saggar fragments before and after sintering, wherein the smaller the weight loss of the saggar fragments before and after sintering is, the stronger the corrosion resistance of the saggar is. The evaluation method of the present application is simple and convenient, and can effectively evaluate the corrosion resistance of the saggar without the need for trial verification of the saggar in the whole life cycle on the production line. By burying saggar fragments of different models from different manufacturers in to-be-sintered material for sintering, the corrosion resistance of each saggar can be effectively evaluated in a short time, which is time-saving and cost-effective, and has a very important reference value for the selection of saggar quality and saggar manufacturers. DETAILED DESCRIPTION

[0049] The technical solutions of the present application are further illustrated below through specific embodiments.

[0050] In one embodiment, the present application provides a method for evaluating the corrosion resistance of a sagger, the method comprising:

[0051] (1) crushing at least 3 saggars to be tested to obtain at least 3 sagger fragments to be tested, wherein the materials of the saggars to be tested are all mullite;

[0052] (2) placing a sintering material into a sintering sagger, the sintering material comprising a sodium salt and a sodium ion oxide-based positive electrode material precursor; embedding the at least 3 sagger fragments to be tested into the sintering material, as shown in Figure 1 so that the distance between the sagger fragments and the inner cavity side wall of the sintering sagger is >1 cm, and the upper and lower parts of the sagger fragments are both formed into a sintering material layer, the thickness of the upper sintering material layer is >1 cm, the thickness of the lower sintering material layer is >1 cm, and the distance between adjacent sagger fragments is >1 cm; then sintering under an air atmosphere to obtain sintered sagger fragments; and evaluating the corrosion resistance of the corresponding sagger according to the weight loss of each sagger fragment before and after sintering.

[0053] Example 1

[0054] The present embodiment provides a method for evaluating the corrosion resistance of a sagger, the method comprising:

[0055] (1) taking 4 saggars of mullite material to be evaluated, crushing them into small fragments respectively, taking 1 sagger piece with appropriate size from each, and naming them as sample 1, sample 2, sample 3 and sample 4 respectively, the shapes of sample 1-4 are all approximately square, the length x width x thickness of sample 1 is 9 cm x 9 cm x 9 cm, the length x width x thickness of sample 2 is 10 cm x 10 cm x 1.2 cm, the length x width x thickness of sample 3 is 9 cm x 9 cm x 1.2 cm, and the length x width x thickness of sample 4 is 9 cm x 9 cm x 1.2 cm, cleaning the dust on the 4 samples with a brush, and weighing and recording M0 respectively, the weight difference of the sagger samples is controlled to be ≤5 g, see Table 1;

[0056] (2) placing a sintering material into a sintering sagger, the sintering material being Na2CO3 and Ni 1 / 3 Fe 1 / 3 Mn 1 / 3(OH)2, total mass 5 kg; the sintering pot is a mullite pot with length x width x height of 33 cm*33 cm*11 cm; then sample 1, sample 2, sample 3 and sample 4 are buried in the sintering material, and the nearest distance between each sample and the inner cavity side wall of the sintering pot is 2 cm, wherein the distance between the adjacent two pieces of pot fragments is 3-5 cm; the upper and lower parts of the pot fragment samples 1-4 are formed with a sintering material layer, the thickness of the sintering material layer above each sample is 2 cm, and the thickness of the sintering material layer below each sample is 3-5 cm, i.e. the distance between each sample and the bottom surface of the inner cavity of the sintering pot is 3-5 cm;

[0057] (3) After sintering at 950℃ for 15h in air atmosphere, the sample 1, sample 2, sample 3 and sample 4 are taken out of the sintering material, washed with 1 mol / L sodium citrate solution for 3 times, then washed with pure water, dried in an oven at 120℃, weighed and recorded as M1, and the weight loss of the pot fragment before and after sintering is calculated as φ (1) , φ (1) =1-M1 / M0, see Table 1; the sodium ion positive electrode material obtained after sintering is O3 phase NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0058] (4) Steps (2) and (3) are repeated for 4 times, the final weight M5 is recorded, and the average weight loss of the pot fragment before and after sintering after 5 times of sintering is calculated as Φ (5) , Φ (5) =(1-M5 / M0) / 5, see Table 1.

[0059] Table 1

[0060]

[0061] Data analysis:

[0062] From the single sintering results, it can be found that the corrosion resistance performance is as follows: sample 4 is the best, with a corrosion amount of 0.451%, sample 2 is the second, also relatively good, with a corrosion amount of 0.455%, sample 1 is relatively poor, with a corrosion amount of 1.813%, and sample 3 is the worst, with a corrosion amount of 2.892%; the single sintering can judge the pros and cons, but in the case of sample 2 and sample 4 being relatively good, it is difficult to distinguish the corrosion resistance performance in the long-term practical situation.

[0063] From the results of 5 sintering, it can be found that the corrosion resistance is optimal for sample 4, the average single corrosion amount is only 0.477%, which is slightly increased compared to single sintering, sample 2 has a trend of deterioration after 5 sintering, the average corrosion amount changes from 0.455% to 0.702%, which indicates that the corrosion resistance is obviously deteriorated with the increase of sintering times, but the overall corrosion resistance is still better; the corrosion amount of sample 1 is 2.927%, which is the second worse, and the corrosion amount of sample 3 is 3.265%, which is the worst; the corrosion resistance of sample 1 and sample 3 is deteriorated with the increase of use times.

[0064] From the above data, it is not difficult to find that the evaluation method of the application can evaluate the corrosion resistance of the sagger to a certain extent through single sintering, but the change of the corrosion resistance after multiple uses is difficult to judge through single sintering, therefore, the more optimal evaluation method is multiple sintering evaluation (≥5 times).

[0065] Example 2

[0066] The difference between the present embodiment and example 1 is that sample 1, sample 2 and sample 3 are omitted, and only sample 4 is tested, the closest distance between sample 4 and the inner cavity side wall of the sintering sagger is 3cm, the thickness of the sintering material layer above sample 4 is 3-5cm, and the thickness of the sintering material layer below sample 4 is 3cm.

[0067] The remaining parameters remain the same as those in example 1.

[0068] Example 3

[0069] The difference between the present embodiment and example 1 is that sample 1, sample 2 and sample 3 are omitted, and only sample 4 is tested, the closest distance between sample 4 and the inner cavity side wall of the sintering sagger is 2cm, the thickness of the sintering material layer above sample 4 is 3-5cm, and the thickness of the sintering material layer below sample 4 is 2cm.

[0070] The remaining parameters remain the same as those in example 1.

[0071] Example 4

[0072] The difference between the present embodiment and example 1 is that sample 1, sample 2 and sample 3 are omitted, and only sample 4 is tested, the closest distance between sample 4 and the inner cavity side wall of the sintering sagger is 1cm, the thickness of the sintering material layer above sample 4 is 3-5cm, and the thickness of the sintering material layer below sample 4 is 1cm.

[0073] The remaining parameters remain the same as those in example 1.

[0074] Example 5

[0075] The difference between this example and Example 4 is that the thickness of the layer of sinterable material below sample 4 is 0.5 cm.

[0076] The remaining parameters are consistent with Example 4.

[0077] Example 6

[0078] The difference between this example and Example 4 is that the closest distance between sample 4 and the inner cavity side wall of the sintering pot is 0.5 cm.

[0079] The remaining parameters are consistent with Example 4.

[0080] Example 7

[0081] The difference between this example and Example 4 is that the distance between sample 4 and the inner cavity side wall of the sintering pot is 3-5 cm, the thickness of the layer of sinterable material above sample 4 is 0.5 cm, and the thickness of the layer of sinterable material below sample 4 is 3-5 cm.

[0082] The remaining parameters are consistent with Example 4.

[0083] Example 8

[0084] The difference between this example and Example 4 is that sample 4 directly contacts the inner cavity bottom surface of the pot, i.e., there is no layer of sinterable material below sample 4.

[0085] The remaining parameters are consistent with Example 4.

[0086] Comparative Example 1

[0087] The difference between this comparative example and Example 7 is that sample 4 is placed on the sinterable material without being buried, i.e., there is no layer of sinterable material above sample 4.

[0088] The remaining parameters are consistent with Example 7.

[0089] Weight loss Φ of single sintering before and after of Examples 2-8 and Comparative Example 1 (1) and the average weight loss φ of the pot fragments after sintering 5 times (5) The results are shown in Table 2.

[0090] Table 2

[0091]

[0092] Data analysis:

[0093] From Examples 2-4, it can be seen that when the distance between sample 4 and the inner cavity side wall of the pot and the thickness of the layers of sinterable material above and below satisfy ≥1 cm, the weight loss data before and after sintering are relatively close and maintain good consistency.

[0094] From Examples 4-8 and Comparative Example 1, when the distance between sample 4 and the inner cavity side wall of the sagger, the thickness of the layer of sinterable material above, or the thickness of the layer of sinterable material below is <1, the degree of corrosion of sample 4 is obviously affected by the distance. When sample 4 directly contacts the bottom of the sagger or is placed directly on the top of the material, the evaluation results deviate seriously and have certain uncontrollability. Therefore, the distance between sample 4 and the inner cavity side wall of the sagger, the thickness of the layer of sinterable material above, and the thickness of the layer of sinterable material below need to meet the defined condition of ≥1 cm.

[0095] The above merely provides a specific implementation of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily conceived by those skilled in the art, and all such changes and replacements fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for evaluating the corrosion resistance of a sagger, characterized in that, The evaluation methods include: The sagger fragments to be tested are buried in the material to be sintered and sintered to obtain sintered sagger fragments; the corrosion resistance of the sagger is evaluated based on the weight loss of the sagger fragments before and after sintering.

2. The method for evaluating the corrosion resistance of a sagger according to claim 1, characterized in that, The material of the saggar fragments includes mullite; Preferably, the material to be sintered includes sodium salt and / or sodium ion oxide-based cathode material precursors.

3. The method for evaluating the corrosion resistance of a sagger according to claim 1 or 2, characterized in that, The shape of the sagger fragments is square or approximately square; Preferably, the length and width of the sagger fragments are independently 5-10 cm; Preferably, the thickness of the sagger fragments is 1-2 cm.

4. The method for evaluating the corrosion resistance of a sagger according to any one of claims 1-3, characterized in that, The material to be sintered is placed in a sintering sagger, and there is a distance between the sagger fragments and the inner wall of the sintering sagger. Preferably, when the sagger fragments are buried in the material to be sintered, the sagger fragments are completely buried and do not contact the bottom surface of the inner cavity of the sintering sagger.

5. The method for evaluating the corrosion resistance of a sagger according to claim 4, characterized in that, The distance between the sagger fragment and the inner wall of the sintering sagger is ≥1cm; Preferably, a layer of material to be sintered is formed above and below the sagger fragments, with the thickness of the upper layer of material to be sintered being ≥1cm and the thickness of the lower layer of material to be sintered being ≥1cm. Preferably, the number of sagger fragments is at least 2, and the distance between adjacent sagger fragments is ≥1cm.

6. The method for evaluating the corrosion resistance of a sagger according to any one of claims 1-5, characterized in that, The sintering is performed n times, where n ≥ 1 and n is an integer; Preferably, the weight of the sagger fragment to be tested is denoted as M0, and the weight of the sintered sagger fragment is denoted as M. n The weight loss of the sagger fragments before and after sintering is denoted as Φ, and the formula for calculating Φ is: Φ=(1-M n / M0) / n.

7. The method for evaluating the corrosion resistance of a sagger according to claim 6, characterized in that, The n satisfies the following condition: n≥5.

8. The method for evaluating the corrosion resistance of a sagger according to claim 6 or 7, characterized in that, The n satisfies the following condition: 5≤n≤10.

9. The method for evaluating the corrosion resistance of a sagger according to any one of claims 1-8, characterized in that, The sintering temperature is 900-1000℃; Preferably, the sintering time is 10-20 hours.

10. The method for evaluating the corrosion resistance of a sagger according to any one of claims 1-9, characterized in that, The evaluation method specifically includes: (1) The sagger to be tested is broken to obtain sagger fragments to be tested, wherein the material of the sagger includes mullite, the shape of the sagger fragments is square or approximately square, and the weight of the sagger fragments is denoted as M0. (2) Place the material to be sintered into a sintering sagger, the material to be sintered including sodium salt and sodium ion oxide cathode material precursor; bury the sagger fragment to be tested into the material to be sintered, such that the distance between the sagger fragment and the inner wall of the sintering sagger is ≥1cm, and form material layers above and below the sagger fragment, with the thickness of the upper material layer being ≥1cm and the thickness of the lower material layer being ≥1cm; then perform n sintering cycles in an air atmosphere to obtain sintered sagger fragments, then wash the sintered sagger fragments with sodium citrate solution and water respectively, and then dry them. The weight of the dried sagger fragments is recorded as M. n According to Φ=(1-M) n The weight loss Φ of the sagger fragment before and after sintering is calculated by / M0) / n. The smaller the value of Φ, the stronger the corrosion resistance of the sagger to be tested. Wherein, 5≤n≤10 and n is an integer.

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