A kind of tricobalt tetroxide and its preparation method and application

Abstract

The application provides a kind of tricobalt tetraoxide and its preparation method and application, the preparation method of the tricobalt tetraoxide includes, bivalent cobalt solution and precipitant solution are passed into the microchannel reactor with bottom water and carry out precipitation reaction;Collecting cobalt carbonate precursor, post-processing is carried out, obtains tricobalt tetraoxide;Wherein, the pH of the bottom water is 7.0-7.3, the flow rate of the bivalent cobalt solution is 5.0-20.0g / min.The application uses microchannel reactor to prepare cobalt carbonate precursor, and tricobalt tetraoxide is prepared by post-processing, and the hold-up is small, and the intrinsic safety is high;Operation is flexible, can be modularized and parallel amplification;At the same time, the application optimizes the composition of reaction system, and by controlling the flow rate of bivalent cobalt solution, the specific surface area of cobalt carbonate precursor is optimized, so that the specific surface area of tricobalt tetraoxide obtained by post-processing is greater than 50m 2 / g.

Description

Technical Field

[0001] This invention relates to the field of cobalt oxide technology, specifically to a cobalt tetroxide, its preparation method, and its applications. Background Technology

[0002] Cobalt tetroxide, as an important functional material, is in high demand in fields such as lithium-ion batteries, catalysis, sensors, and magnetic materials, and research on its preparation methods is becoming increasingly in-depth. In recent years, with the rapid development of nanoscience and technology, increasingly higher requirements have been placed on the microstructure of cobalt tetroxide materials (including particle size, morphology, crystal form, specific surface area, etc.), based on the fact that the microstructure of the material has a significant impact on its physical and electrochemical properties.

[0003] Currently, cobalt tetroxide is typically derived from nano-cobalt carbonate precursors through low-temperature calcination. Therefore, the morphology, particle size, and uniformity of nano-cobalt carbonate directly determine the final performance of cobalt tetroxide. Existing methods for preparing cobalt carbonate mainly include hydrothermal methods, solvothermal methods, and traditional batch co-precipitation methods. However, these traditional processes generally have many inherent drawbacks: First, the mass and heat transfer efficiency of traditional batch reactors is limited, especially in the initial feeding stage, where local supersaturation is difficult to control precisely, leading to uneven particle nucleation and growth, resulting in a wide particle size distribution and irregular morphology, which fails to meet the stringent requirements for additive particle size uniformity in high-end cathode materials. Second, the co-precipitation reaction of cobalt carbonate is highly sensitive to temperature, pH, and mixing intensity. Local concentration fluctuations in batch reactions can easily trigger secondary nucleation or particle agglomeration, affecting product performance and increasing the difficulty of subsequent washing and calcination. Finally, the scale-up effect of traditional batch processes is significant. From pilot-scale to pilot-scale to mass production, a large amount of time and resources are required for parameter optimization, severely restricting the rapid market response of new products.

[0004] Against this backdrop, microreactor technology, as a novel process intensification approach, has demonstrated significant advantages in the controllable preparation of nanomaterials due to its superior mass and heat transfer performance and precise process control capabilities. It has already achieved controllable synthesis in multiple fields, including metal nanoparticles, quantum dots, metal-organic frameworks, and biomedical nanomaterials. However, there are currently very few reports on the use of microchannel reactors for the preparation of cobalt carbonate / cobalt tetroxide. Summary of the Invention

[0005] To overcome the problems existing in the prior art, the present invention provides a method for preparing cobalt tetroxide, comprising, A divalent cobalt solution and a precipitant solution are passed into a microchannel reactor containing bottom water to carry out a precipitation reaction. The cobalt carbonate precursor was collected and post-processed to obtain cobalt tetroxide; The bottom water has a pH of 7.0-7.3, and the flow rate of the divalent cobalt solution is 5.0-20.0 g / min.

[0006] Furthermore, the concentration of cobalt in the divalent cobalt solution is 120-140 g / L.

[0007] Furthermore, the concentration of the precipitant in the precipitant solution is 240-260 g / L, and the precipitant includes at least one of ammonium bicarbonate, potassium bicarbonate, sodium bicarbonate, ammonium carbonate, potassium carbonate, and sodium carbonate.

[0008] Furthermore, the flow rate of the precipitant solution is 4.0-4.8 times that of the divalent cobalt solution.

[0009] Furthermore, the cobalt carbonate precursor includes real-time monitoring of the particle size of the material at the discharge port, and collection begins when the D50 of the material is ≤0.5μm; The precipitation reaction was carried out at a temperature of 20-30℃.

[0010] Furthermore, the post-processing includes demagnetization, washing, and heat treatment; The washing process reduces the concentration of impurity ions to below 20 ppm.

[0011] Furthermore, the heat treatment includes drying and calcination, wherein the calcination is carried out at a temperature of 350-400°C for 3-8 hours.

[0012] Furthermore, the volume of the bottom water is the same as the volume of the microchannel reactor, and the volume of the bottom water is 1-2L.

[0013] The present invention also provides cobalt tetroxide, which is obtained by the above preparation method.

[0014] The present invention also provides the application of the above-mentioned cobalt tetroxide in lithium-ion batteries, catalysts, sensors, magnetic materials, pigments, and ceramics.

[0015] Compared with the prior art, the beneficial effects of the present invention include: The method for preparing cobalt tetroxide provided by this invention uses a microchannel reactor to prepare a cobalt carbonate precursor and then prepares cobalt tetroxide through post-processing. It has low liquid holdup, high intrinsic safety, flexible operation, and can be modularized and scaled up in parallel.

[0016] This invention optimizes the composition of the reaction system and, by controlling the flow rate of the divalent cobalt solution, optimizes the specific surface area of ​​the cobalt carbonate precursor, thereby obtaining a specific surface area greater than 50 m² after post-processing. 2 / g of cobalt tetroxide.

[0017] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0019] Figures 1-4 The following are scanning electron microscope images of cobalt carbonate prepared in Example 1 at different magnifications; Figures 5-8 The following are scanning electron microscope images of cobalt carbonate prepared in Example 2 at different magnifications; Figures 9-12 The following are scanning electron microscope images of cobalt carbonate prepared in Example 3 at different magnifications; Figures 13-16 The following are scanning electron microscope images of cobalt carbonate prepared in Example 4 at different magnifications; Figures 17-20 The following are scanning electron microscope images of cobalt tetroxide prepared in Example 4 at different magnifications; Figure 21 A scanning electron microscope image of cobalt carbonate prepared in Comparative Example 1 is shown; Figure 22 A scanning electron microscope image of cobalt carbonate prepared in Comparative Example 2 is shown; Figure 23 A scanning electron microscope image of cobalt carbonate prepared in Comparative Example 3 is shown; Figure 24 A scanning electron microscope image of cobalt carbonate prepared in Comparative Example 4 is shown. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] Microchannel reactors were used to prepare materials with a surface area greater than 50 m². 2 The core challenge in producing cobalt tetroxide ( / g) lies in balancing the high-efficiency mixing advantages of microreactors with the stringent requirements of the material's high specific surface area for a fine microstructure. In the millisecond-level instantaneous mixing within microchannels, local supersaturation is prone to runaway, leading to instantaneous nucleation bursts and the generation of highly agglomerated fine particles. The inherent magnetism of the material makes nascent nanoparticles easily aggregate and grow due to magnetic attraction. The gas-liquid-solid multiphase flow behavior within the microchannels is extremely complex, making precise control highly difficult. To overcome these challenges, the key lies in leveraging the advantages of microreactors and optimizing process control.

[0024] Therefore, the design concept of this invention lies in optimizing the composition of the reaction system by introducing a divalent cobalt solution and a precipitant solution into a microchannel reactor containing low-alkalinity bottom water for precipitation; and by controlling the flow rate of the divalent cobalt solution, optimizing the specific surface area of ​​the cobalt carbonate precursor, thereby obtaining a specific surface area greater than 50 m² after post-processing. 2 / g of cobalt tetroxide.

[0025] Accordingly, the present invention provides a method for preparing cobalt tetroxide, comprising, A divalent cobalt solution and a precipitant solution are passed into a microchannel reactor containing bottom water to carry out a precipitation reaction. The cobalt carbonate precursor was collected and post-processed to obtain cobalt tetroxide; The bottom water has a pH of 7.0-7.3, and the flow rate of the divalent cobalt solution is 5.0-20.0 g / min.

[0026] In some preferred embodiments, the concentration of cobalt in the divalent cobalt solution is 120-140 g / L.

[0027] In some preferred embodiments, the concentration of the precipitant in the precipitant solution is 240-260 g / L, and the precipitant includes at least one selected from ammonium bicarbonate, potassium bicarbonate, sodium bicarbonate, ammonium carbonate, potassium carbonate, and sodium carbonate.

[0028] It should be noted that the cobalt source in the divalent cobalt solution is not strictly limited, and can be, for example, at least one of cobalt chloride hexahydrate, cobalt sulfate heptahydrate, cobalt acetate dihydrate, and cobalt acetate tetrahydrate. The solvents for the divalent cobalt solution and the precipitant solution are not strictly limited, and can be, for example, at least one of water, ethanol, isopropanol, and acetone, preferably water.

[0029] In some preferred embodiments, the flow rate of the precipitant solution is 4.0-4.8 times that of the divalent cobalt solution.

[0030] In some preferred embodiments, the cobalt carbonate precursor includes real-time monitoring of the particle size of the material at the discharge port, and collection begins when the D50 of the material is ≤0.5μm; The precipitation reaction was carried out at a temperature of 20-30℃.

[0031] In some preferred embodiments, the post-processing includes demagnetization, washing, and heat treatment; The washing process reduces the concentration of impurity ions to below 20 ppm.

[0032] In some preferred embodiments, the heat treatment includes drying and calcination, wherein the calcination is carried out at a temperature of 350-400°C for 3-8 hours.

[0033] In some preferred embodiments, the volume of the bottom water is the same as the volume of the microchannel reactor, and the volume of the bottom water is 1-2L.

[0034] The present invention will be further described in detail below through specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0035] Example 1 A method for preparing cobalt tetroxide includes the following steps: S1. Dissolve cobalt chloride hexahydrate in water to prepare a divalent cobalt solution with a cobalt concentration of 130 g / L; dissolve ammonium bicarbonate in water to prepare a precipitant solution with a concentration of 250 g / L.

[0036] S2. A microchannel reactor with 1.5L solvent is filled with water and precipitant solution as bottom water, the pH of which is 7.2. Stirring is started at 400 rpm. Then, divalent cobalt solution and ammonium bicarbonate solution are simultaneously introduced into the microchannel reactor, with flow rates of 5.0 g / min and 22.5 g / min, respectively. Precipitation reaction is carried out at 20℃. The particle size of the material at the outlet is monitored in real time. When the particle size stabilizes at D50≤0.5μm, collection begins. S3. The collected cobalt carbonate precursor is demagnetized in a cycle until it is qualified, then washed until the chloride ion concentration in the washing solution is less than 20 ppm, and finally transferred to a vacuum oven for drying to obtain cobalt carbonate with a water content of less than 0.5%; the cobalt carbonate is transferred to a muffle furnace and calcined at 375℃ for 6 hours to obtain cobalt tetroxide.

[0037] Example 2 A method for preparing cobalt tetroxide includes the following steps: S1. Dissolve cobalt chloride hexahydrate in water to prepare a divalent cobalt solution with a cobalt concentration of 130 g / L; dissolve ammonium bicarbonate in water to prepare a precipitant solution with a concentration of 250 g / L.

[0038] S2. Fill a 1.5L microchannel reactor with water and precipitant solution as bottom water. The pH of the bottom water is 7.2. Start stirring at 400 rpm. Then, simultaneously introduce divalent cobalt solution and ammonium bicarbonate solution into the microchannel reactor. The flow rates of divalent cobalt solution and ammonium bicarbonate solution are 10.0 g / min and 45 g / min, respectively. Carry out the precipitation reaction at 20℃. Monitor the particle size of the material at the outlet in real time. When the particle size stabilizes at D50≤0.5μm, start collecting. S3. The collected cobalt carbonate precursor is demagnetized in a cycle until it is qualified, then washed until the chloride ion concentration in the washing solution is less than 20 ppm, and finally transferred to a vacuum oven for drying to obtain cobalt carbonate with a water content of less than 0.5%; the cobalt carbonate is transferred to a muffle furnace and calcined at 375℃ for 6 hours to obtain cobalt tetroxide.

[0039] Example 3 A method for preparing cobalt tetroxide includes the following steps: S1. Dissolve cobalt chloride hexahydrate in water to prepare a divalent cobalt solution with a cobalt concentration of 130 g / L; dissolve ammonium bicarbonate in water to prepare a precipitant solution with a concentration of 250 g / L.

[0040] S2. A microchannel reactor with a solvent of 1.5L is filled with water and a precipitant solution as bottom water. The pH of the bottom water is 7.2. Stirring is started at 400 rpm. Then, a divalent cobalt solution and an ammonium bicarbonate solution are simultaneously introduced into the microchannel reactor. The flow rates of the divalent cobalt solution and the ammonium bicarbonate solution are 15.0 g / min and 67.5 g / min, respectively. The precipitation reaction is carried out at 20℃. The particle size of the material at the outlet is monitored in real time. When the particle size stabilizes at D50≤0.5μm, collection begins. S3. The collected cobalt carbonate precursor is demagnetized in a cycle until it is qualified, then washed until the chloride ion concentration in the washing solution is less than 20 ppm, and finally transferred to a vacuum oven for drying to obtain cobalt carbonate with a water content of less than 0.5%; the cobalt carbonate is transferred to a muffle furnace and calcined at 375℃ for 6 hours to obtain cobalt tetroxide.

[0041] Example 4 A method for preparing cobalt tetroxide includes the following steps: S1. Dissolve cobalt chloride hexahydrate in water to prepare a divalent cobalt solution with a cobalt concentration of 130 g / L; dissolve ammonium bicarbonate in water to prepare a precipitant solution with a concentration of 250 g / L.

[0042] S2. A microchannel reactor with a solvent of 1.5L is filled with water and a precipitant solution as bottom water. The pH of the bottom water is 7.2. Stirring is started at 400 rpm. Then, a divalent cobalt solution and an ammonium bicarbonate solution are simultaneously introduced into the microchannel reactor. The flow rates of the divalent cobalt solution and the ammonium bicarbonate solution are 20.0 g / min and 90.0 g / min, respectively. The precipitation reaction is carried out at 20℃. The particle size of the material at the outlet is monitored in real time. When the particle size stabilizes at D50≤0.5μm, collection begins. S3. The collected cobalt carbonate precursor is demagnetized in a cycle until it is qualified, then washed until the chloride ion concentration in the washing solution is less than 20 ppm, and finally transferred to a vacuum oven for drying to obtain cobalt carbonate with a water content of less than 0.5%; the cobalt carbonate is transferred to a muffle furnace and calcined at 375℃ for 6 hours to obtain cobalt tetroxide.

[0043] Example 5 A method for preparing cobalt tetroxide includes the following steps: S1. Dissolve cobalt sulfate heptahydrate in water to prepare a divalent cobalt solution with a cobalt concentration of 130 g / L; dissolve sodium bicarbonate in water to prepare a precipitant solution with a concentration of 250 g / L.

[0044] S2. Fill a 1.5L microchannel reactor with water and precipitant solution as bottom water. The pH of the bottom water is 7.2. Start stirring at 400 rpm. Then, simultaneously introduce divalent cobalt solution and sodium bicarbonate solution into the microchannel reactor. The flow rates of divalent cobalt solution and sodium bicarbonate solution are 20.0 g / min and 90.0 g / min, respectively. The precipitation reaction is carried out at 20℃. The particle size of the material at the outlet is monitored in real time. When the particle size stabilizes at D50≤0.5μm, collection begins. S3. The collected cobalt carbonate precursor is demagnetized in a cycle until it meets the requirements, and then washed in a washing solution. The sulfate concentration is less than 20 ppm. Finally, it is transferred to a vacuum oven for drying to obtain cobalt carbonate with a water content of less than 0.5%. The cobalt carbonate is transferred to a muffle furnace and calcined at 375℃ for 6 hours to obtain cobalt tetroxide.

[0045] Example 6 A method for preparing cobalt tetroxide includes the following steps: S1. Dissolve cobalt acetate dihydrate in water to prepare a divalent cobalt solution with a cobalt concentration of 140 g / L; dissolve sodium bicarbonate in water to prepare a precipitant solution with a concentration of 260 g / L.

[0046] S2. Fill a 1.5L microchannel reactor with water and precipitant solution as bottom water. The pH of the bottom water is 7.2. Start stirring at 400 rpm. Then, simultaneously introduce divalent cobalt solution and sodium bicarbonate solution into the microchannel reactor. The flow rates of divalent cobalt solution and sodium bicarbonate solution are 20.0 g / min and 90.0 g / min, respectively. The precipitation reaction is carried out at 20℃. The particle size of the material at the outlet is monitored in real time. When the particle size stabilizes at D50≤0.5μm, collection begins. S3. The collected cobalt carbonate precursor is demagnetized in a cycle until it meets the requirements, and then washed in a washing solution. The sulfate concentration is less than 20 ppm. Finally, it is transferred to a vacuum oven for drying to obtain cobalt carbonate with a water content of less than 0.5%. The cobalt carbonate is transferred to a muffle furnace and calcined at 375℃ for 6 hours to obtain cobalt tetroxide.

[0047] Comparative Example 1 The difference from Example 4 is that the precipitation reaction is carried out at 45°C in step S2.

[0048] Comparative Example 2 The difference from Example 4 is that the pH of the bottom water in step S2 is 8.0.

[0049] Comparative Example 3 Compared with Example 4, the difference is that the flow rates of the divalent cobalt solution and the ammonium bicarbonate solution in step S2 are 20.0 g / min and 60.0 g / min, respectively.

[0050] Comparative Example 4 Compared with Example 4, the difference is that the flow rates of the divalent cobalt solution and the ammonium bicarbonate solution in step S2 are 20.0 g / min and 110.0 g / min, respectively.

[0051] Test case The microstructure of cobalt carbonate prepared in Examples 1-4, and cobalt tetroxide obtained in Example 4, was observed using scanning electron microscopy. Figures 1-4 , Figures 5-8 , Figures 9-12 , Figures 13-16 As can be seen, cobalt carbonate is a three-dimensional interconnected structure composed of stacked nanoparticles of different sizes. With increasing flow rates of both the divalent cobalt solution and the precipitant solution, the size of the nanoparticles increases, and aggregation is suppressed. (Comparison) Figures 13-16 and Figures 17-20 It can be seen that some structures were destroyed after calcination, and there was a certain collapse structure. This was caused by the decomposition of cobalt carbonate, but overall, it maintained a low-agglomeration, three-dimensional interconnected structure composed of stacked different nanoparticles.

[0052] The microstructure of cobalt carbonate prepared in Comparative Examples 1-4 was tested. Figure 21 As can be seen, when the temperature is raised to 45℃ for precipitation, the resulting cobalt carbonate particles are large and exhibit severe agglomeration. From... Figure 22 It can be seen that when the bottom water pH is high, partial aggregation will occur. From... Figure 23 and Figure 24 It can be seen that the flow rate (alkali-cobalt ratio) of the precipitant solution and the divalent cobalt solution also has a certain impact on the size of cobalt carbonate particles. When the alkali-cobalt ratio is 4.0-4.8:1, cobalt carbonate with uniform particle size, small size and less agglomeration can be obtained.

[0053] The nitrogen adsorption-desorption curves of cobalt carbonate and cobalt tetroxide obtained in Examples 1-4 were tested using a fully automated specific surface area and pore size analyzer, and the BET specific surface area was calculated. The results are shown in Table 1.

[0054] Table 1. Specific surface area test results of cobalt tetroxide

[0055] As can be seen from the test results in Table 1, this invention successfully prepared a material with a specific surface area greater than 130 m². 2 / g of cobalt carbonate yielded a specific surface area greater than 60m². 2 / g of cobalt tetroxide. This demonstrates that under the reaction conditions of fixed bottom water with low alkalinity and continuous introduction of divalent cobalt solution and precipitant solution, the specific surface area of ​​cobalt carbonate can be effectively adjusted by controlling the inflow rate of divalent cobalt solution and precipitant solution, thereby preparing cobalt tetroxide with high specific surface area.

[0056] In summary, this invention utilizes a microchannel reactor to prepare cobalt carbonate precursors and then proceeds to obtain cobalt tetroxide through post-processing. It features low liquid holdup, high intrinsic safety, flexible operation, and modular parallel scale-up. This invention optimizes the reaction system composition and, by controlling the flow rate of the divalent cobalt solution, optimizes the specific surface area of ​​the cobalt carbonate precursor, resulting in a post-processing yield with a specific surface area greater than 50 m². 2 / g of cobalt tetroxide.

[0057] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing cobalt tetroxide, characterized in that, include, A divalent cobalt solution and a precipitant solution are passed into a microchannel reactor containing bottom water to carry out a precipitation reaction. The cobalt carbonate precursor was collected and post-processed to obtain cobalt tetroxide; The bottom water has a pH of 7.0-7.3, and the flow rate of the divalent cobalt solution is 5.0-20.0 g / min.

2. The method for preparing cobalt tetroxide according to claim 1, characterized in that, The concentration of cobalt in the divalent cobalt solution is 120-140 g / L.

3. The method for preparing cobalt tetroxide according to claim 1, characterized in that, The concentration of the precipitant in the precipitant solution is 240-260 g / L, and the precipitant includes at least one of ammonium bicarbonate, potassium bicarbonate, sodium bicarbonate, ammonium carbonate, potassium carbonate, and sodium carbonate.

4. The method for preparing cobalt tetroxide according to claim 1, characterized in that, The flow rate of the precipitant solution is 4.0-4.8 times that of the divalent cobalt solution.

5. The method for preparing cobalt tetroxide according to claim 1, characterized in that, The cobalt carbonate precursor includes real-time monitoring of the particle size of the material at the discharge port, and collection begins when the D50 of the material is ≤0.5μm; The precipitation reaction was carried out at a temperature of 20-30℃.

6. The method for preparing cobalt tetroxide according to claim 1, characterized in that, The post-processing includes demagnetization, washing, and heat treatment; The washing process reduces the concentration of impurity ions to below 20 ppm.

7. The method for preparing cobalt tetroxide according to claim 6, characterized in that, The heat treatment includes drying and calcination, wherein the calcination is carried out at a temperature of 350-400℃ for 3-8 hours.

8. The method for preparing cobalt tetroxide according to claim 1, characterized in that, The volume of the bottom water is the same as the volume of the microchannel reactor, and the volume of the bottom water is 1-2L.

9. A cobalt tetroxide, characterized in that, It is obtained by the preparation method according to any one of claims 1-8.

10. The application of cobalt tetroxide as described in claim 9 in lithium-ion batteries, catalysts, sensors, magnetic materials, pigments, and ceramics.

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