Preparation method and application of high tap density permanent magnet ferrite pre-fired material

Abstract

The application relates to the technical field of permanent magnet ferrite pre-sintering material, and discloses a preparation method and application of high-tapping-density permanent magnet ferrite pre-sintering material. The preparation method of the pre-sintering material comprises the following steps: mixing raw materials of pre-sintering material including strontium carbonate and iron red, ball-milling the pre-sintering material with water to obtain a ball-milling slurry, and then drying and removing water; ball-milling and vibrating the material after drying and removing water at a holding temperature of 80-200 DEG C for 30 min-2 h to crush and obtain a powder; and pre-sintering the obtained powder to obtain a pre-sintering material. Compared with the prior art that the pre-sintering material is processed into material balls and then pre-sintered, the preparation method of the application further carries out vibration milling treatment on the ball-milling slurry after drying under certain holding conditions, realizes preliminary ferritization, and then pre-sintering. The obtained pre-sintering material has high tapping density, the ferritization reaction is sufficient, and the remanence and maximum magnetic energy product of the prepared permanent magnet ferrite can be improved.

Description

Technical Field

[0001] This invention relates to the field of permanent magnet ferrite pre-sintering technology, specifically to a method for preparing and applying a high tap density permanent magnet ferrite pre-sintering material. Background Technology

[0002] The traditional preparation method of permanent magnet ferrite pre-sintered material is as follows: put uniformly mixed iron oxide, strontium carbonate (or barium carbonate) and rare earth raw materials into the kiln body and sinter at high temperature (1100~1300℃) to obtain permanent magnet ferrite pre-sintered material. After decades of production practice, it is now widely used.

[0003] In the traditional preparation process of permanent magnet ferrite pre-sintered materials, the mixture needs to be pelletized before high-temperature sintering to ensure sufficient contact between various elements, so as to promote their reaction and formation of permanent magnet ferrite during high-temperature pre-sintering. For example, Chinese patent application 2017109923877 discloses a processing method for permanent magnet ferrite pre-sintered materials, which includes ball milling strontium carbonate, iron oxide red, etc. with water in a ball mill until uniform, processing them into pellets using a briquetting machine, pre-sintering, and then vibrating and grinding to obtain the pre-sintered material. However, in actual production, due to poor pelletizing consistency, the pellet diameter and density are inconsistent, resulting in incomplete ferrite formation in the pre-sintered material, affecting its quality. Extending the reaction time of the pellets in the high-temperature zone can easily cause high-temperature bright crystallization. Therefore, it is necessary to develop a new pre-sintered material preparation method to avoid the adverse effects of pellet forming on the quality of the pre-sintered material. Summary of the Invention

[0004] To address the problem that incomplete iron oxidation of the pre-sintered material is easily caused by processing it into pellets during the traditional preparation process of permanent magnet ferrite pre-sintered material, the present invention aims to provide a method for preparing permanent magnet ferrite pre-sintered material with high tap density. In the preparation process of permanent magnet ferrite pre-sintered material, it is not necessary to process it into pellets, thereby improving the ferrite degree of the pre-sintered material and the prepared pre-sintered material has a high tap density.

[0005] This invention provides the following technical solution: a method for preparing a high tap density permanent magnet ferrite pre-sintered material, comprising the following steps:

[0006] 1) Mix the raw materials, including strontium carbonate and iron oxide red, and ball mill them with water to obtain ball mill slurry. The preferred raw material to water mass ratio is 1:1 to 2. Then dry the slurry to remove water.

[0007] 2) The dried material is ball-milled and vibrated at a temperature of 80-200℃ for 30 minutes to 2 hours to obtain powder;

[0008] 3) The obtained powder is pre-fired to obtain pre-fired material.

[0009] The method of this invention involves mixing the raw materials of the pre-fired material, wet ball milling to obtain a ball mill slurry, drying it, and then ball milling and vibrating it again at a holding temperature of not less than 80°C to obtain powder. During this holding ball milling process, various elements in the powder are fully contacted and form preliminary ferrite. After pre-firing and sintering, a full ferrite reaction is achieved. The pre-fired powder has a high tap density, indicating that the degree of ferrite formation of the pre-fired material is significantly improved compared with the traditional ball mill sintering. Moreover, when using this pre-fired material to prepare permanent magnet ferrite, the remanence and maximum energy product of the permanent magnet ferrite are further improved while maintaining the coercivity performance of the permanent magnet ferrite basically unchanged.

[0010] As a preferred embodiment of the method of the present invention,

[0011] In step 2), the holding temperature during ball milling vibration is 80–200°C. Too low a holding temperature will make it difficult for the ferrite formation reaction to proceed, while too high a temperature may cause excessive ferrite formation and is also not conducive to the control of the pre-calcination process.

[0012] As a preferred embodiment of the method of the present invention,

[0013] In step 2), the insulation temperature during ball mill vibration is 85–95℃. This insulation temperature condition is mild and can be achieved using hot water.

[0014] As a preferred embodiment of the method of the present invention,

[0015] In step 2), the holding temperature is gradually increased at a rate of 0.5–1 °C / min during ball milling vibration. Research has shown that this gradual and slow heating process allows the initial ferrite formation to occur at varying temperatures, which is more effective than a fixed temperature approach in enhancing the degree of initial ferrite formation. The inventors believe this is because ferrite formation itself is a gradual process, and therefore the heat supply is adapted to the ferrite formation process by gradually increasing the heat, thus improving the efficiency of the initial ferrite formation.

[0016] As a preferred embodiment of the method of the present invention,

[0017] In step 1), the molar ratio of iron oxide red to strontium carbonate is 5.5–6.5:1;

[0018] And / or, step 1) also includes the addition of a grain inhibitor, wherein the amount of grain inhibitor added is 0.1 wt% to 0.3 wt% of the total mass of iron oxide red and strontium carbonate.

[0019] As a preferred embodiment of the method of the present invention,

[0020] The grain inhibitor is one or both of silicon dioxide and calcium carbonate.

[0021] As a preferred embodiment of the method of the present invention,

[0022] The preheating temperature in step 3) is 1200–1300℃;

[0023] The preferred pre-firing temperature is 1230–1260℃.

[0024] This invention also provides a method for preparing permanent magnet ferrite with improved remanence, comprising the following steps:

[0025] 1) The prepared permanent magnet ferrite pre-calcined material is pulverized, and after adding additives, it is ball-milled a second time. The additives contain one or more of La, Co, Si, Ca or Al.

[0026] 2) The ball-milled material is wet-pressed into shape by magnetic field and then sintered to obtain permanent magnet ferrite.

[0027] The pre-sintered material prepared by the method of this invention is used to prepare permanent magnet ferrite. The resulting permanent magnet ferrite has higher remanence and maximum energy product while maintaining the coercivity basically unchanged, thus improving the quality of the permanent magnet ferrite.

[0028] As a preferred embodiment of the method of the present invention,

[0029] The additive is one or more of silicon dioxide, calcium carbonate, aluminum oxide, lanthanum oxide, or cobalt oxide;

[0030] And / or, the additives are 1wt% to 2wt% of the pre-burned material;

[0031] And / or, the sintering temperature in step 2) is 1230–1250 °C. Preferably, the additive is a mixture of silica and calcium carbonate, with the amount of silica added being 0.1 wt%–0.4 wt% and the amount of calcium carbonate added being 1 wt%–1.5 wt%.

[0032] The beneficial effects of this invention are as follows:

[0033] Compared to the traditional method of preparing ferrite pre-sintered materials by processing milled slurry into balls and then pre-firing them, the preparation method of this invention involves drying the milled slurry and further vibrating it under certain heat preservation conditions to achieve preliminary ferrite formation, followed by pre-firing. The resulting pre-sintered material has a high tap density and a complete ferrite formation reaction, which can improve the remanence and maximum energy product of the prepared permanent magnet ferrite. Detailed Implementation

[0034] The specific embodiments of the present invention will be further described below.

[0035] Unless otherwise specified, all raw materials used in this invention are commercially available or commonly used in the field. Unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0036] Example 1

[0037] A method for preparing a high tap density permanent magnet ferrite pre-sintered material, comprising the following steps:

[0038] 1) Mix iron oxide red (Xinkai) and strontium carbonate (Hongdie) in a molar ratio of 6.0:1, add 0.2wt% of silica, add water (material-to-water mass ratio of 1:1), and ball mill for 5 hours to obtain ball mill slurry. Then dry and dehydrate in an oven to obtain mixed powder.

[0039] 2) Place 30 kg of mixed powder into a vibratory ball mill and vibrate and mill for 30 min at 20 kW. At the same time, fill the space between the wall of the vibratory ball mill and the inner liner with hot water at 80 ℃.

[0040] 3) Place the powder processed in step 2) into a pre-firing furnace and pre-firing at 1230℃. After pre-firing, crush it to obtain pre-fired material.

[0041] Example 2

[0042] A method for preparing a high tap density permanent magnet ferrite pre-sintered material, comprising the following steps:

[0043] 1) Mix iron oxide red (Xinkai) and strontium carbonate (Hongdie) in a molar ratio of 5.5:1, add 0.3wt% of silica, add water (material-to-water mass ratio of 1:2), and ball mill for 5 hours to obtain ball mill slurry. Then dry and dehydrate in an oven to obtain mixed powder.

[0044] 2) Place 30 kg of mixed powder into a vibratory ball mill and vibrate and mill for 60 min at 20 kW. At the same time, fill the space between the wall of the vibratory ball mill and the inner liner with hot water at 85 ℃.

[0045] 3) Place the powder processed in step 2) into a pre-firing furnace and pre-firing at 1260℃. After pre-firing, crush it to obtain pre-fired material.

[0046] Example 3

[0047] A method for preparing a high tap density permanent magnet ferrite pre-sintered material, comprising the following steps:

[0048] 1) Mix iron oxide red (Xinkai) and strontium carbonate (Hongdie) in a molar ratio of 6.5:1, add 0.1wt% of silica, add water (material-to-water mass ratio of 1:1.5), and ball mill for 5 hours to obtain ball mill slurry. Then dry and dehydrate in an oven to obtain mixed powder.

[0049] 2) Place 30 kg of mixed powder into a vibratory ball mill and vibrate and mill for 120 min at 20 kW. At the same time, fill the space between the wall of the vibratory ball mill and the inner liner with 95°C hot water for circulation.

[0050] 3) Place the powder processed in step 2) into a pre-firing furnace and pre-firing at 1250℃. After pre-firing, crush it to obtain pre-fired material.

[0051] Example 4

[0052] A method for preparing a high tap density permanent magnet ferrite pre-sintered material, comprising the following steps:

[0053] 1) Mix iron oxide red (Xinkai) and strontium carbonate (Hongdie) in a molar ratio of 6.0:1, add 0.25wt% of silica, add water (material-to-water mass ratio of 1:1), and ball mill for 5 hours to obtain ball mill slurry. Then dry and dehydrate in an oven to obtain mixed powder.

[0054] 2) Place 30 kg of mixed powder into a vibratory ball mill and vibrate and mill for 50 min at 20 kW. At the same time, fill the space between the wall of the vibratory ball mill and the inner liner with hot water at 100 ℃.

[0055] 3) Place the powder processed in step 2) into a pre-firing furnace and pre-fire it at 1300℃. After pre-firing, crush it to obtain pre-fired material.

[0056] Example 5

[0057] A method for preparing a high tap density permanent magnet ferrite pre-sintered material, comprising the following steps:

[0058] 1) Mix iron oxide red (Xinkai) and strontium carbonate (Hongdie) in a molar ratio of 6.5:1, add 0.25wt% of silica, add water (material-to-water ratio of 1:1), and ball mill for 5 hours to obtain ball mill slurry. Then dry and dehydrate in an oven to obtain mixed powder.

[0059] 2) Place 30 kg of mixed powder into a vibratory ball mill and vibrate and mill for 90 min at 20 kW. At the same time, fill the space between the wall of the vibratory ball mill and the inner liner with 200°C high-temperature superheated steam.

[0060] 3) Place the powder processed in step 2) into a pre-firing furnace and pre-firing at 1200℃. After pre-firing, crush it to obtain pre-fired material.

[0061] Example 6

[0062] The difference from Example 1 is that the holding temperature of the vibratory ball mill in step 2 is 110°C.

[0063] Example 7

[0064] The difference from Example 1 is that in step 2), electric heating is used to raise the holding temperature from 80°C to 110°C at a rate of 1°C / min, and then the vibratory grinding is stopped.

[0065] Comparative Example 1

[0066] The difference from Example 1 is that the dried material obtained in step 1) is directly pre-burned and pulverized according to the operation in step 3).

[0067] Comparative Example 2

[0068] The difference from Example 1 is that the ball mill slurry obtained in step 1) is processed into balls with a diameter of 5 mm, and then pre-fired and crushed according to the operation in step 3).

[0069] Comparative Example 3

[0070] The difference from Example 1 is that there is no 80°C hot water circulation between the wall of the vibratory ball mill and the inner liner in step 2).

[0071] Comparative Example 4

[0072] The difference from Example 1 is that in step 2), the dried mixed powder is first vibrated and ball-milled in a vibrating ball mill. After the ball milling is completed, 80°C hot water is circulated and kept warm between the wall of the vibrating ball mill and the inner liner for the same amount of time.

[0073] Comparative Example 5

[0074] The difference from Example 1 is that the temperature of the circulating hot water between the wall of the vibratory ball mill and the inner liner in step 2) is 70°C.

[0075] Comparative Example 6

[0076] The difference from Example 5 is that the temperature of the superheated steam between the wall of the vibratory ball mill and the inner liner is 230°C in step 2).

[0077] Comparative Example 7

[0078] The difference from Example 1 is that, during the preparation of the pre-calcined material,

[0079] In step 1), while ball milling, 80°C hot water is circulated and kept warm between the ball mill cylinder wall and the inner liner.

[0080] During the vibratory ball milling of the mixed powder in step 2), there is no 80°C hot water circulation between the ball mill cylinder wall and the inner liner.

[0081] Comparative Example 8

[0082] The difference from Example 1 is that the vibration ball milling time in step (2) is 10 min.

[0083] Comparative Example 9

[0084] The difference from Example 1 is that the vibration ball milling time in step (2) is 150 min.

[0085] 0.3 wt% silica and 1.0 wt% calcium carbonate were added to the pre-calcined materials obtained in the above examples and comparative examples, respectively, and the mixture was ball-milled for 16 hours. After discharge, the materials were wet-pressed in a magnetic field and then pre-calcined at 1230℃ and 1250℃ for 1 hour, respectively, to obtain permanent magnet ferrite. The properties of the obtained permanent magnet ferrite are shown in Table 1 below.

[0086] The tap density of each pre-burned material and the properties of the prepared permanent magnet ferrite are shown in Table 1 below.

[0087]

[0088] Analysis of the test results in the table above shows that the ferrite pre-sintered material prepared by the method of this invention has a higher tap density of pre-sintered powder, with a tap density ≥ 2.35 g / cm³. 3 The permanent magnet ferrite prepared using this ferrite pre-sintered material exhibits higher remanence and energy product while maintaining coercivity. Specifically:

[0089] As can be seen from the comparison of Example 1 with Comparative Examples 1 and 2, when the milled slurry is dried and then subjected to secondary vibratory milling under heat preservation, the resulting pre-calcined material has a higher tap density compared to Comparative Example 1, which directly calcined the slurry after drying, or Comparative Example 2, which processed the slurry into pellets before pre-calcination. The resulting permanent magnet oxide Br and (BH)max are also higher. Furthermore, as can be seen from the comparison of Example 7 with Examples 1 and 8, the use of a slow-heating variable-temperature mode during the heat preservation vibratory milling process is more beneficial for improving the performance of the pre-calcined material.

[0090] However, as shown in Comparative Example 3, secondary vibratory milling alone cannot achieve the desired effect because the initial oxidation of ferrite is difficult to proceed without heating. This can also be demonstrated by the unsatisfactory results of secondary vibratory milling followed by heat treatment in Comparative Example 4. Furthermore, as shown in Comparative Example 7, advancing the heat treatment process to the first wet ball milling process also fails to achieve preliminary ferrite oxidation. This is because wet ball milling contains a large amount of water, and its main purpose is to ensure uniform mixing and similar particle size; this process cannot achieve a pre-oxidation effect.

[0091] However, as shown in Comparative Examples 5, 6, and 8, the achievement of initial ferrite formation in ball-milled slurries through secondary vibratory milling and heat preservation is clearly correlated with the milling time and temperature. In reality, the slurry particle size already reaches approximately 0.7 μm after the first wet ball milling. Secondary vibratory milling will not further refine the material, but sufficient milling time and heat are required to achieve initial ferrite formation. Extending the milling time beyond this point is not very meaningful, as shown in Comparative Example 9.

Claims

1. A method for preparing a high tap density permanent magnet ferrite pre-sintered material, characterized in that, Includes the following steps: 1) Mix the raw materials, including strontium carbonate and iron oxide red, and ball mill them with water to obtain a ball mill slurry, then dry it to remove water; 2) The dried material is ball-milled and vibrated at a temperature of 80-200℃ for 30 minutes to 2 hours to obtain powder; 3) The obtained powder is pre-fired to obtain pre-fired material.

2. The preparation method according to claim 1, characterized in that, The heat preservation temperature during ball mill vibration in step 2) is 85-95℃.

3. The preparation method according to claim 1 or 2, characterized in that, In step 2), the holding temperature is gradually increased at a rate of 0.5–1 °C / min during ball mill vibration.

4. The preparation method according to claim 1, characterized in that, In step 1), the molar ratio of iron oxide red to strontium carbonate is 5.5–6.5:1; And / or, step 1) also includes the addition of a grain inhibitor, wherein the amount of grain inhibitor added is 0.1 wt% to 0.3 wt% of the total mass of iron oxide red and strontium carbonate.

5. The preparation method according to claim 4, characterized in that, The grain inhibitor is one or both of silicon dioxide and calcium carbonate.

6. The preparation method according to claim 1, characterized in that, In step 3), the preheating temperature is 1200-1300℃.

7. The preparation method according to claim 6, characterized in that, In step 3), the preheating temperature is 1230–1260°C.

8. A method for preparing ferrite with improved remanence in permanent magnets, characterized in that, Includes the following steps: 1) The pre-calcined permanent magnet ferrite material prepared by any one of the preparation methods of claims 1 to 7 is pulverized, and after adding additives, it is ball-milled. The additives contain one or more of La, Co, Si, Ca or Al. 2) The ball-milled material is wet-pressed into shape by magnetic field and then sintered to obtain permanent magnet ferrite.

9. The preparation method according to claim 8, characterized in that, The additive is one or more of silicon dioxide, calcium carbonate, aluminum oxide, lanthanum oxide, or cobalt oxide; And / or, the additives are 1wt% to 2wt% of the pre-burned material; And / or, the sintering temperature of step 2) is 1230 to 1250°C.

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