Production method and production device of inert modified electrical grade magnesium oxide

Abstract

The invention provides a production method and a production device of inert modified electrical grade magnesium oxide. The production device comprises a material treatment system and a gas circulation system. The material treatment system comprises a coating machine, a vibrating screen, at least one preheating furnace, a high-temperature calcining furnace and a cooling furnace which are connected in sequence; the gas circulation system comprises a nitrogen generator, an induced draft fan and a gas circulation loop; the nitrogen generator can provide stable nitrogen, under the action of the induced draft fan, part of the nitrogen sequentially passes through the induced draft fan, the high-temperature calcining furnace and the multi-stage preheating furnace through the gas circulation loop and then returns to the induced draft fan, and circulation of the nitrogen is achieved. By adopting the production device, the surface of the magnesium oxide powder can be uniformly coated with a nitride film by combining the multi-section nitrogen atmosphere heat treatment mechanism after coating pretreatment, and spherical composite powder with good sphericity is obtained, so that the problems of high nitride consumption, non-uniform coating, low product quality and the like in the existing nitride coating method are solved. And the problem of spheroidizing shaping cannot be solved.

Description

Technical Field

[0001] The invention relates to the technical field of magnesium oxide manufacturing, and in particular to a production method and a production device for inert modified electrical grade magnesium oxide. Background Art

[0002] Electrical grade magnesium oxide is widely used as a filler for electric heating appliances because of its high resistance, high voltage resistance, low leakage current and high thermal conductivity. However, electrical grade magnesium oxide is hygroscopic, and hygroscopic water will react with magnesium oxide to form magnesium hydroxide. The density of magnesium hydroxide is lower than that of magnesium oxide, which can easily lead to volume expansion of the filler, thereby damaging the heating tube, causing leakage or even explosion of the heating tube, posing a major safety hazard. Although non-oxide filler materials such as boron nitride and silicon nitride, which are alternative materials, have good chemical inertness and thermal conductivity, their high prices restrict their large-scale preparation and large-scale application.

[0003] However, uniformly coating a thin layer of nitride on the surface of magnesium oxide powder particles can organically combine the characteristics of the two materials and solve the problem of high cost of directly applying nitride. However, the existing method of coating nitride on the surface of magnesium oxide powder is: mixing nitride or nitride precursor powder with magnesium oxide powder, and then calcining to obtain a composite powder material of nitride and magnesium oxide.

[0004] However, due to factors such as the temperature gradient and uneven atmosphere during the calcination process, the diffusion and reaction rates of the nitride on the surface of the magnesium oxide powder are inconsistent, so that the nitride powder cannot be evenly coated on the surface of the magnesium oxide powder, and most of them present a continuous bridging overlap. Therefore, the required amount of nitride powder is large, and the chemical inertness of the base powder cannot be well improved. Further hydrophobic treatment is usually required, which leads to complicated processes and increased preparation costs. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method and a production device for spheroidizing electrical grade magnesium oxide. Through coating pretreatment combined with a multi-stage nitrogen atmosphere heat treatment mechanism, the surface of the magnesium oxide powder can be uniformly coated with a nitride film, and a spherical composite powder with good sphericity can be obtained, thereby solving the problems of large nitride dosage, uneven coating, and inability to solve spheroidization shaping in the existing nitride coating method.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a production device for spheroidizing electrical grade magnesium oxide, including a material processing system and a gas circulation system;

[0007] The material processing system comprises a coating machine, a vibrating screen, at least one preheating furnace, a high temperature calcining furnace and a cooling furnace connected in sequence;

[0008] The gas circulation system includes a nitrogen generator, an induced draft fan and a gas circulation loop; the nitrogen generator can provide stable nitrogen, and under the action of the induced draft fan, part of the nitrogen passes through the gas circulation loop and sequentially passes through the induced draft fan, the high-temperature calcining furnace, and the multi-stage preheating furnace and returns to the induced draft fan, thereby realizing the circulation of nitrogen.

[0009] Furthermore, the material processing system also includes an auxiliary heating device, which can heat the gas introduced into the high-temperature calcining furnace to a certain temperature.

[0010] Furthermore, there are two preheating furnaces, namely a primary preheating furnace and a secondary preheating furnace. The nitrogen generator can provide stable nitrogen. Under the action of the induced draft fan, part of the nitrogen passes through the induced draft fan, the high-temperature calcining furnace, and the secondary preheating furnace in sequence through the gas circulation loop; part of the nitrogen passes through the cooling furnace and the primary preheating furnace in sequence and then merges with the nitrogen discharged from the secondary preheating furnace. The merged nitrogen returns to the induced draft fan to realize the circulation of nitrogen.

[0011] Furthermore, during the process of transferring the material from the high-temperature calcining furnace to the cooling furnace, a small amount of nitrogen will enter the cooling furnace along with the material, and then enter the primary preheating furnace through the cooling furnace; and / or

[0012] The nitrogen generator is arranged between the induced draft fan and the high-temperature calcining furnace to replenish the lost nitrogen.

[0013] Furthermore, it also includes a bag dust collector, which is arranged at the air inlet end of the induced draft fan, so that the combined nitrogen enters the induced draft fan through the bag dust collector.

[0014] Furthermore, it also includes a product collecting device, which is arranged at the discharge port end of the cooling furnace.

[0015] Furthermore, the primary preheating furnace is arranged at an inclination, and the inlet end of the primary preheating furnace is higher than the outlet end; and / or

[0016] The secondary preheating furnace is arranged in an inclined manner, and the inlet end of the secondary preheating furnace is higher than the outlet end; and / or

[0017] The high temperature calcining furnace is arranged in an inclined manner, and the inlet end of the high temperature calcining furnace is higher than the outlet end; and / or

[0018] The cooling furnace is arranged in an inclined manner, and the inlet end of the cooling furnace is higher than the outlet end.

[0019] Furthermore, the inclination angle of the primary preheating furnace is 5° to 15°; and / or

[0020] The inclination angle of the secondary preheating furnace is 5° to 15°; and / or

[0021] The high temperature calcining furnace has an inclination angle of 5° to 15°; and / or

[0022] The inclination angle of the cooling furnace is 5° to 15°.

[0023] Furthermore, the ratio of the inner diameter to the length of the primary preheating furnace is 0.15:1 to 0.3:1; and / or

[0024] The ratio of the inner diameter to the length of the secondary preheating furnace is 0.1:1 to 0.25:1; and / or

[0025] The ratio of the inner diameter to the length of the high temperature calcining furnace is 0.05:1 to 0.15:1; and / or

[0026] The ratio of the inner diameter to the length of the cooling furnace is 0.075:1 to 0.2:1.

[0027] Furthermore, the auxiliary heating device uses a plasma torch as a heat source.

[0028] Furthermore, the preheating furnace, high temperature calcining furnace and cooling furnace are all rotary kilns.

[0029] Furthermore, the powder feed and discharge ports adopt a screw conveying device.

[0030] Furthermore, the gas circulation loop includes a gas inlet connecting the high-temperature calcining furnace and the outlet of the induced draft fan, a gas outlet connecting the high-temperature calcining furnace and the gas inlet of the secondary preheating furnace, a gas outlet connecting the secondary preheating furnace and the inlet of the bag filter, a gas outlet connecting the first preheating furnace and the inlet of the bag filter, and several gas delivery pipelines connecting the gas outlet of the bag filter and the inlet of the induced draft fan.

[0031] Another object of the present invention is to provide a method for producing inert modified electrical grade magnesium oxide using the production device, comprising the following steps:

[0032] (1) Raw material preparation

[0033] The fused magnesia powder is obtained by crushing, screening and magnetic separation of fused magnesia blocks with a magnesium content of 95-99.9%wt;

[0034] The micro powder and the binder are stirred and mixed and then filtered to obtain a coating slurry;

[0035] (2) Coating treatment

[0036] The fused magnesium oxide powder and the coating slurry prepared in step (1) are added into a coating machine, and the coating slurry is coated on the surface of the fused magnesium oxide powder which is continuously stirred; after drying, the coated material is transferred to a vibrating screen to screen out fine dust, thereby obtaining coated fused magnesium oxide powder;

[0037] (3) Multi-stage preheating and nitriding treatment

[0038] Turn on the nitrogen generator and the induced draft fan to fill the gas pipeline with nitrogen; when the preheating furnace and the high-temperature calcining furnace both reach the set temperature, the coated fused magnesia powder is sequentially transferred to the preheating furnace for multi-stage preheating treatment under a nitrogen atmosphere, and then transferred to the high-temperature calcining furnace for nitriding treatment, so that the micro powder on the surface of the coated fused magnesia powder is nitrided to form molten nitride;

[0039] (4) Finalization

[0040] The nitrided material is transferred to a cooling furnace for cooling and shaping to obtain a spherical composite powder with a nitride coating evenly covered on the surface.

[0041] Furthermore, the coating slurry includes micropowder and a binder.

[0042] Furthermore, the micro powder is silicon powder and / or boron powder;

[0043] The binder is one or more of silica sol, polyvinyl alcohol, dextrin and carboxymethyl cellulose.

[0044] Furthermore, the mass ratio of the micro powder to the fused magnesium oxide powder is 0.1-0.3:1;

[0045] The mass ratio of the binder to the fused magnesium oxide powder is 0.05-0.4:1.

[0046] Furthermore, the particle size of the fused magnesium oxide powder can be selected to be 50-1000 mesh; and / or

[0047] The coated material is sieved through a vibrating screen to remove ultrafine powder with a particle size less than 1000 mesh to obtain coated fused magnesium oxide powder.

[0048] Furthermore, the multi-stage preheating method is: first react at 150-200°C for 15-20 minutes, and then react at 400-600°C for 15-20 minutes.

[0049] Furthermore, the set temperature of the first-stage preheating furnace is 150-200°C; the set temperature of the second-stage preheating furnace is 400-600°C.

[0050] Furthermore, during the nitriding process, the ratio of the powder dosage to the nitrogen flow rate entering the high-temperature calcining furnace is 1kg / h: 0.15-0.3L / min, and the set temperature of the high-temperature calcining furnace is 1500-2000°C.

[0051] Furthermore, the nitriding treatment time is 15 to 20 minutes.

[0052] Furthermore, the thickness of the nitride coating is 0.5-100 nm.

[0053] Furthermore, the sphericity of the spherical composite powder is 0.98-1.00.

[0054] Furthermore, during the coating process, the inlet air temperature can be selected to be 65-70°C, and the outlet air temperature can be selected to be 40-50°C.

[0055] Furthermore, the drying temperature can be selected to be 100-120°C.

[0056] Due to the adoption of the above technical solution, the present invention has the following positive effects compared with the prior art:

[0057] First, the present invention adopts a specific material processing system, so that the material is subjected to coating treatment, multi-stage preheating treatment and nitriding treatment in sequence, so as to obtain a composite powder having a spherical core-shell structure, with the inner core being magnesium oxide and the outer shell being a nitride coating. This not only enables the electrical grade magnesium oxide powder to withstand high temperature and be moisture-proof, but more importantly, ensures the thermal conductivity of magnesium oxide and improves the fluidity and filling efficiency of the powder. At the same time, the multi-stage preheating treatment enables the nitride precursor to be firmly coated on the surface of the magnesium oxide powder to prevent cracking of the coating layer caused by drastic temperature rise.

[0058] Second, the present invention circulates the nitrogen provided by the nitrogen generator in each reaction furnace (high-temperature calcining furnace, preheating furnace, cooling furnace) through an induced draft fan, realizing the recycling of nitrogen and heat source, which helps to reduce energy consumption and waste generation. In addition, the inexpensive nitride precursor is used as the coating material to achieve in-situ nitride uniform coating of magnesium oxide powder in a high-temperature nitrogen atmosphere without the need for subsequent modification and grinding treatment.

[0059] Third, the present invention can continuously produce nitride-coated magnesium oxide spherical powder through the above-mentioned device. By accurately controlling parameters such as flow rate, temperature and time, the high quality and stability of the product can be ensured, and it is suitable for large-scale production of high-quality thermal conductive fillers. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0061] Figure 1 The present invention is a flow chart of the production method of inert modified electrical grade magnesium oxide;

[0062] Figure 2The present invention is a schematic diagram of the structure of the production device for spheroidizing electrical grade magnesium oxide.

[0063] In the figure: 1. Coating machine; 2. Vibrating screen; 2A. Feed inlet; 2B. Coarse particle outlet; 3. Primary preheating; 3A. Powder feed inlet; 3C. Powder outlet; 3D. Gas outlet; 4. Secondary preheating furnace; 4A. Powder feed inlet; 4B. Powder outlet; 4C. Gas inlet; 4D. Gas outlet; 5. High-temperature calcining furnace; 5A. Powder feed inlet; 5B. Powder outlet; 5C. Gas inlet; 5D. Gas outlet; 6. Cooling furnace; 6A. Feed inlet; 6B. Outlet; 7. Product collector; 8. Bag filter; 8A. Inlet; 8B. Outlet; 9. Draft fan; 9A. Inlet; 9B. Outlet; 10. Plasma torch generator; 11. Nitrogen generator. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0065] Example 1

[0066] The production device for spheroidizing electrical grade magnesium oxide involved in the present application includes a material handling system and a gas circulation system;

[0067] The material handling system includes a coating machine 1, a vibrating screen 2, a primary preheating furnace 3, a secondary preheating furnace 4, a high-temperature calcining furnace 5, a cooling furnace 6, a product collecting device 7, and multiple screw conveying devices and auxiliary heating devices connected in sequence;

[0068] After the coating treatment is completed inside the coating machine 1, the material is discharged from the discharge port of the coating machine 1, and the discharged material enters the vibrating screen 2 from the feed port 2A of the vibrating screen 2 through the screw conveyor. The material is sieved inside the vibrating screen 2 to remove the ultrafine powder with a particle size less than 1000 mesh to obtain the coated material; the coated material enters the first-level preheating furnace 3 from the coarse particle discharge port 2B of the vibrating screen 2 through the screw conveyor and from the powder feed port 3A of the first-level preheating furnace 3 to undergo the first-level preheating treatment; the material after the first-level treatment is discharged from the powder discharge port 3C of the first-level preheating furnace 3 and is discharged from the second level through the screw conveyor The powder feed port 4A of the preheating furnace 4 enters the interior of the secondary preheating furnace 4, and undergoes secondary preheating treatment in the secondary preheating furnace 4; the material after the secondary preheating treatment passes through the powder discharge port 4B of the secondary preheating furnace 4 and enters the interior of the high-temperature calcining furnace 5 from the powder feed port 5A of the high-temperature calcining furnace 5 through a screw conveying device, and undergoes nitriding treatment in the high-temperature calcining furnace 5; the material after the nitriding treatment passes through the powder discharge port 5B of the high-temperature calcining furnace 5 and enters the cooling furnace 6 from the feed port 6A of the cooling furnace 6 through a screw conveying device, and is cooled to room temperature, and then is transported to the product collector 7 from the discharge port 6B of the cooling furnace 6.

[0069] In some embodiments, the auxiliary heating device is preferably a plasma torch generator 10, which is connected to the gas inlet 5C of the high-temperature calcining furnace 5 through a pipeline, and can use nitrogen as an atmosphere to introduce the high temperature of the plasma torch into the high-temperature calcining furnace 5, so that a nitriding reaction occurs on the surface of the powder. In the plasma torch generator 10, the arc is the key to generating high-temperature plasma. Ventilation can provide a stable airflow to maintain the stability and continuity of the arc. If there is a lack of sufficient gas flow, the arc may become unstable or even extinguished.

[0070] In some embodiments, the gas circulation system includes a nitrogen generator 11, an induced draft fan 9, a gas circulation loop and a bag filter 8;

[0071] The outlet 9B of the induced draft fan 9 is connected to the gas inlet 5C of the high temperature calcining furnace 5 through a gas delivery pipeline, the gas outlet 5D of the high temperature calcining furnace 5 is connected to the gas inlet 4C of the secondary preheating furnace 4 through a gas delivery pipeline, the gas outlet 4D of the secondary preheating furnace 4 and the gas outlet 3D of the primary preheating furnace 3 are respectively connected to the inlet 8A of the bag filter 8 through a gas delivery pipeline, and the outlet 8B of the bag filter 8 is connected to the inlet 9A of the induced draft fan 9 through a gas delivery pipeline to form a gas circulation loop. The nitrogen generator 11 is connected in series on the gas delivery pipeline from the induced draft fan 9 to the high temperature calcining furnace 5.

[0072] Start the nitrogen generator 11, which can provide stable nitrogen, and introduce the nitrogen into the high-temperature calcining furnace 5. Then start the induced draft fan 9. Under the action of the induced draft fan 9, the nitrogen enters the gas inlet 4C of the secondary preheating furnace 4 through the gas outlet 5D of the high-temperature calcining furnace 5, so that the nitrogen atmosphere fills the gas circulation loop, the primary preheating furnace 3, the secondary preheating furnace 4, the high-temperature calcining furnace 5 and the cooling furnace 6.

[0073] Part of the nitrogen passes through the induced draft fan 9, the high-temperature calcining furnace 5, and the secondary preheating furnace 4 in sequence through the gas circulation loop; part of the nitrogen passes through the cooling furnace 6 and the primary preheating furnace 3 in sequence and then merges with the nitrogen discharged from the secondary preheating furnace 4. The merged nitrogen returns to the induced draft fan 9 to realize the circulation of nitrogen.

[0074] In addition, when the powder is discharged from the powder discharge port 5B of the high-temperature calcining furnace 5 to the cooling furnace 6, a part of the nitrogen will enter the cooling furnace 6 along with the powder, and this part of the nitrogen will finally return to the primary preheating furnace 3. Since the inlet 9A of the induced draft fan 9 is connected to the gas discharge port 5D of the high-temperature calcining furnace 5, the outlet of the nitrogen generator 11 is connected to this section of the loop, which can replenish the lost nitrogen.

[0075] In some embodiments, the primary preheating furnace 3, the secondary preheating furnace 4, the high temperature calcining furnace 5 and the cooling furnace 6 are all rotary kilns.

[0076] In some embodiments, the primary preheating furnace 3, the secondary preheating furnace 4, the high-temperature calcining furnace 5 and the cooling furnace 6 are all arranged at an angle so that the material inlet end (i.e., the powder feed inlet side) is higher than the material outlet end (i.e., the powder discharge port side). Since the furnace body has an inclination angle and is rotating, the powder in the furnace will slide toward the discharge port, making it easier to transport the powder to the next stage.

[0077] In some embodiments, the inclination angle of the primary preheating furnace 3 is 5° to 15°; for example, the inclination angle of the primary preheating furnace can be any one of 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15° or a range between any two of them.

[0078] It is understandable that the inclination angle of the primary preheating furnace 3 needs to be within the above range. This is because if the inclination angle is too small, the residence time of the powder is too long and the processing efficiency is low. If the inclination angle is too large, the residence time of the powder is too short and the processing effect is not good.

[0079] In some embodiments, the ratio of the inner diameter to the length of the primary preheating furnace 3 is 0.15: 1 to 0.3: 1. For example, the ratio of the inner diameter to the length of the primary preheating furnace can be any one of 0.15: 1, 0.2: 1, 0.25: 1, 0.3: 1, or any range between two thereof.

[0080] It can be understood that the ratio of the inner diameter to the length of the primary preheating furnace 3 needs to be within the above range. This is because if the ratio of the inner diameter to the length is too small, the residence time of the powder is too short and the treatment effect is not good. If the ratio of the inner diameter to the length is too large, the residence time of the powder is too long and the treatment efficiency is low.

[0081] In some embodiments, the inclination angle of the secondary preheating furnace 4 is 5° to 15°; for example, the inclination angle of the secondary preheating furnace can be any one of 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15° or a range between any two of them.

[0082] It is understandable that the inclination angle of the secondary preheating furnace 4 needs to be within the above range. This is because if the inclination angle is too small, the residence time of the powder is too long and the processing efficiency is low. If the inclination angle is too large, the residence time of the powder is too short and the processing effect is not good.

[0083] In some embodiments, the ratio of the inner diameter to the length of the secondary preheating furnace 4 is 0.1:1 to 0.25:1. For example, the ratio of the inner diameter to the length of the primary preheating furnace can be any one of 0.1:1, 0.15:1, 0.2:1, 0.25:1 or any range between two thereof.

[0084] It can be understood that the ratio of the inner diameter to the length of the secondary preheating furnace 4 needs to be within the above range. This is because if the ratio of the inner diameter to the length is too small, the residence time of the powder is too short and the treatment effect is not good. If the ratio of the inner diameter to the length is too large, the residence time of the powder is too long and the treatment efficiency is low.

[0085] In some embodiments, the inclination angle of the high temperature calcining furnace 5 is 5° to 15°; for example, the inclination angle of the high temperature calcining furnace can be any one of 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15° or a range between any two of them.

[0086] It is understandable that the inclination angle of the high-temperature calcining furnace 5 needs to be within the above range. This is because if the inclination angle is too small, the residence time of the powder is too long and the processing efficiency is low. If the inclination angle is too large, the residence time of the powder is too short and the processing effect is not good.

[0087] In some embodiments, the ratio of the inner diameter to the length of the high temperature calcining furnace 5 is 0.05: 1 to 0.15: 1. For example, the ratio of the inner diameter to the length of the primary preheating furnace can be any one of 0.05: 1, 0.1: 1, 0.15: 1, or any range between two thereof.

[0088] It can be understood that the ratio of the inner diameter to the length of the high-temperature calcining furnace 5 needs to be within the above range. This is because if the ratio of the inner diameter to the length is too small, the residence time of the powder is too short and the treatment effect is not good. If the ratio of the inner diameter to the length is too large, the residence time of the powder is too long and the treatment efficiency is low.

[0089] In some embodiments, the inclination angle of the cooling furnace 6 is 5° to 15°; for example, the inclination angle of the cooling furnace can be any one of 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15° or a range between any two of them.

[0090] It is understandable that the inclination angle of the cooling furnace 6 needs to be within the above range. This is because if the inclination angle is too small, the residence time of the powder is too long and the processing efficiency is low. If the inclination angle is too large, the residence time of the powder is too short and the processing effect is not good.

[0091] In some embodiments, the ratio of the inner diameter to the length of the cooling furnace 6 is 0.075: 1 to 0.2: 1. For example, the ratio of the inner diameter to the length of the primary preheating furnace can be any one of 0.075: 1, 0.08: 1, 0.085: 1, 0.09: 1, 0.095: 1, 0.01: 1, 0.15: 1, 0.2: 1 or any range between two thereof.

[0092] It can be understood that the ratio of the inner diameter to the length of the cooling furnace 6 needs to be within the above range. This is because if the ratio of the inner diameter to the length is too small, the residence time of the powder is too short and the treatment effect is not good. If the ratio of the inner diameter to the length is too large, the residence time of the powder is too long and the treatment efficiency is low.

[0093] Example 2

[0094] The present application relates to a method for producing electrical grade magnesium oxide by inertization modification using the above-mentioned device, and its preparation process is as follows: Figure 1 As shown, in order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below.

[0095] A method for producing inert modified electrical grade magnesium oxide comprises the following steps:

[0096] (1) Raw material preparation

[0097] Taking fused magnesia blocks with a magnesium content of 95-99.9%wt, crushing, screening and magnetic separation to obtain fused magnesia powder with a particle size of 50-800 mesh;

[0098] The silicon powder and the silicon sol are stirred and mixed and then filtered to obtain a coating slurry; the mass ratio of magnesium oxide to silicon powder and the silicon sol is 1:1.

[0099] (2) Coating treatment

[0100] The fused magnesium oxide powder and the coating slurry prepared in step (1) are added to a coating machine, and the coating machine is turned on to uniformly coat the coating slurry on the surface of the continuously stirred fused magnesium oxide powder in the form of a spray to obtain a coated material; after drying in a drying system inside the coating machine, the coated material is transferred to a vibrating screen through a screw conveyor, and the fine dust is sieved out through the vibrating screen, and the ultrafine powder with a particle size of less than 1000 mesh is removed to obtain the coated fused magnesium oxide powder;

[0101] The mass ratio of fused magnesium oxide powder to coating slurry is 1:0.2.

[0102] (3) Multi-stage preheating and nitriding treatment

[0103] Turn on the nitrogen generator and introduce nitrogen into the high-temperature calcining furnace, then turn on the induced draft fan to replace the air in each furnace with nitrogen to complete the gas purge. After the gas purge, turn on the plasma torch generator, which can heat the nitrogen to increase the temperature in the first-stage preheating furnace, the second-stage preheating furnace and the high-temperature calcining furnace. When the temperature of the first-stage preheating furnace reaches 150°C, the temperature of the second-stage preheating furnace reaches 400°C and the temperature of the high-temperature calcining furnace reaches 1500°C, start adding the coated fused magnesium oxide powder obtained in step (2) to the first-stage preheating furnace;

[0104] The powder dosage is controlled to be 100kg / h, the nitrogen flow rate is 30L / min, and in a nitrogen atmosphere, the coated fused magnesia powder is preheated in the primary preheating furnace and then transferred to the secondary preheating furnace for secondary preheating. After two preheating treatments, the nitride precursor is basically firmly coated on the surface of the magnesia powder, and then transferred to a high-temperature calcining furnace for nitriding treatment. After nitriding treatment for 15 minutes, the micro powder on the surface of the coated fused magnesia powder is nitrided to form molten nitride;

[0105] (4) Finalization

[0106] After nitriding treatment for 15 minutes, the nitrided material is separated from the high-temperature flame zone and transferred to a cooling furnace for cooling and shaping, and finally collected by a product collecting device to obtain a spherical composite powder with a nitride coating evenly covered on the surface.

[0107] Example 3

[0108] A method for producing inert modified electrical grade magnesium oxide comprises the following steps:

[0109] (1) Raw material preparation

[0110] Taking fused magnesia blocks with a magnesium content of 95-99.9%wt, crushing, screening and magnetic separation to obtain fused magnesia powder with a particle size of 50-325 mesh;

[0111] The silicon powder and the silica sol are stirred and mixed and then filtered to obtain a coating slurry; the mass ratio of magnesium oxide to silicon powder and silica sol is 0.2:0.3.

[0112] (2) Coating treatment

[0113] The fused magnesium oxide powder and the coating slurry prepared in step (1) are added to a coating machine, and the coating machine is turned on to uniformly coat the coating slurry on the surface of the continuously stirred fused magnesium oxide powder in the form of a spray to obtain a coated material; after drying in a drying system inside the coating machine, the coated material is transferred to a vibrating screen through a screw conveyor, and the fine dust is sieved out through the vibrating screen, and the ultrafine powder with a particle size of less than 1000 mesh is removed to obtain the coated fused magnesium oxide powder;

[0114] The mass ratio of fused magnesium oxide powder to coating slurry is 1:0.5.

[0115] (3) Multi-stage preheating and nitriding treatment

[0116] Turn on the nitrogen generator and introduce nitrogen into the high-temperature calcining furnace, then turn on the induced draft fan to replace the air in each furnace with nitrogen to complete the gas purge. After the gas purge, turn on the plasma torch generator, which can heat the nitrogen to increase the temperature in the first-stage preheating furnace, the second-stage preheating furnace and the high-temperature calcining furnace. When the temperature of the first-stage preheating furnace reaches 180°C, the temperature of the second-stage preheating furnace reaches 500°C and the temperature of the high-temperature calcining furnace reaches 1800°C, start adding the coated fused magnesium oxide powder obtained in step (2) to the first-stage preheating furnace;

[0117] The powder dosage is controlled to be 100kg / h, the nitrogen flow rate is 30L / min, and in a nitrogen atmosphere, the coated fused magnesia powder is preheated in the primary preheating furnace and then transferred to the secondary preheating furnace for secondary preheating. After two preheating treatments, the nitride precursor is basically firmly coated on the surface of the magnesia powder, and then transferred to a high-temperature calcining furnace for nitriding treatment. After nitriding treatment for 15 minutes, the micro powder on the surface of the coated fused magnesia powder is nitrided to form molten nitride;

[0118] (4) Finalization

[0119] After nitriding treatment for 15 minutes, the nitrided material is separated from the high-temperature flame zone and transferred to a cooling furnace for cooling and shaping, and finally collected by a product collecting device to obtain a spherical composite powder with a nitride coating evenly covered on the surface.

[0120] Example 4

[0121] A method for producing inert modified electrical grade magnesium oxide comprises the following steps:

[0122] (1) Raw material preparation

[0123] Taking fused magnesia blocks with a magnesium content of 95-99.9%wt, crushing, screening and magnetic separation to obtain fused magnesia powder with a particle size of 50-1000 mesh;

[0124] The silicon powder and polyvinyl alcohol are stirred and mixed and then filtered to obtain a coating slurry; the mass ratio of magnesium oxide to silicon powder and silica sol is 1:1.

[0125] (2) Coating treatment

[0126] The fused magnesium oxide powder and the coating slurry prepared in step (1) are added to a coating machine, and the coating machine is turned on to uniformly coat the coating slurry on the surface of the continuously stirred fused magnesium oxide powder in the form of a spray to obtain a coated material; after drying in a drying system inside the coating machine, the coated material is transferred to a vibrating screen through a screw conveyor, and the fine dust is sieved out through the vibrating screen, and the ultrafine powder with a particle size of less than 1000 mesh is removed to obtain the coated fused magnesium oxide powder;

[0127] The mass ratio of fused magnesium oxide powder to coating slurry is 1:0.2.

[0128] (3) Multi-stage preheating and nitriding treatment

[0129] Turn on the nitrogen generator and introduce nitrogen into the high-temperature calcining furnace, then turn on the induced draft fan to replace the air in each furnace with nitrogen to complete the gas purge. After the gas purge, turn on the plasma torch generator, which can heat the nitrogen to increase the temperature in the first-stage preheating furnace, the second-stage preheating furnace and the high-temperature calcining furnace. When the temperature of the first-stage preheating furnace reaches 180°C, the temperature of the second-stage preheating furnace reaches 500°C and the temperature of the high-temperature calcining furnace reaches 1800°C, start adding the coated fused magnesium oxide powder obtained in step (2) to the first-stage preheating furnace;

[0130] The powder dosage is controlled to be 100kg / h, the nitrogen flow rate is 30L / min, and in a nitrogen atmosphere, the coated fused magnesia powder is preheated in the primary preheating furnace and then transferred to the secondary preheating furnace for secondary preheating. After two preheating treatments, the nitride precursor is basically firmly coated on the surface of the magnesia powder, and then transferred to a high-temperature calcining furnace for nitriding treatment. After nitriding treatment for 15 minutes, the micro powder on the surface of the coated fused magnesia powder is nitrided to form molten nitride;

[0131] (4) Finalization

[0132] After nitriding treatment for 15 minutes, the nitrided material is separated from the high-temperature flame zone and transferred to a cooling furnace for cooling and shaping, and finally collected by a product collecting device to obtain a spherical composite powder with a nitride coating evenly covered on the surface.

[0133] Example 5

[0134] A method for producing inert modified electrical grade magnesium oxide comprises the following steps:

[0135] (1) Raw material preparation

[0136] Taking fused magnesia blocks with a magnesium content of 95-99.9%wt, crushing, screening and magnetic separation to obtain fused magnesia powder with a particle size of 50-325 mesh;

[0137] The silicon powder and dextrin are stirred and mixed and then filtered to obtain a coating slurry; the mass ratio of magnesium oxide to silicon powder and silica sol is 0.2:0.3.

[0138] (2) Coating treatment

[0139] The fused magnesium oxide powder and the coating slurry prepared in step (1) are added to a coating machine, and the coating machine is turned on to uniformly coat the coating slurry on the surface of the continuously stirred fused magnesium oxide powder in the form of a spray to obtain a coated material; after drying in a drying system inside the coating machine, the coated material is transferred to a vibrating screen through a screw conveyor, and the fine dust is sieved out through the vibrating screen, and the ultrafine powder with a particle size of less than 1000 mesh is removed to obtain the coated fused magnesium oxide powder;

[0140] The mass ratio of fused magnesium oxide powder to coating slurry is 1:0.5.

[0141] (3) Multi-stage preheating and nitriding treatment

[0142] Turn on the nitrogen generator and introduce nitrogen into the high-temperature calcining furnace, then turn on the induced draft fan to replace the air in each furnace with nitrogen to complete the gas purge. After the gas purge, turn on the plasma torch generator, which can heat the nitrogen to increase the temperature in the first-stage preheating furnace, the second-stage preheating furnace and the high-temperature calcining furnace. When the temperature of the first-stage preheating furnace reaches 180°C, the temperature of the second-stage preheating furnace reaches 500°C and the temperature of the high-temperature calcining furnace reaches 1800°C, start adding the coated fused magnesium oxide powder obtained in step (2) to the first-stage preheating furnace;

[0143] The powder dosage is controlled to be 600kg / h, the nitrogen flow rate is 100L / min, and in a nitrogen atmosphere, the coated fused magnesia powder is preheated in the primary preheating furnace and then transferred to the secondary preheating furnace for secondary preheating. After two preheating treatments, the nitride precursor is basically firmly coated on the surface of the magnesia powder, and then transferred to a high-temperature calcining furnace for nitriding treatment. After nitriding treatment for 20 minutes, the micro powder on the surface of the coated fused magnesia powder is nitrided to form molten nitride;

[0144] (4) Finalization

[0145] After nitriding for 20 minutes, the nitrided material is separated from the high-temperature flame zone and transferred to a cooling furnace for cooling and shaping, and finally collected by a product collecting device to obtain a spherical composite powder with a nitride coating evenly covered on the surface.

[0146] In some embodiments, during the nitriding process of step (3), the ratio of the powder dosage entering the high-temperature calcining furnace to the nitrogen flow rate is 1kg / h: 0.15 to 0.3L / min, for example, it can be any one of 1kg / h: 0.15L / min, 1kg / h: 0.2L / min, 1kg / h: 0.25L / min, 1kg / h: 0.3L / min, or a range between any two values.

[0147] It can be understood that the ratio of powder addition amount to nitrogen flow rate needs to be within the above range. This is because when the gas flow rate is high, the time in the plasma torch flame zone is short, the melting time is insufficient, and the thickness of the nitrided layer is thin; when the gas flow rate is low, the time in the plasma torch flame zone is long, the nitridation is sufficient, but the production efficiency is low and the cost is high.

[0148] In some embodiments, the set temperature of the high temperature calcining furnace is 1500-2000° C. For example, it can be any value among 1500, 1600, 1700, 1800, 1900, 2000, or a range between any two values.

[0149] It is understandable that the nitriding treatment temperature of the high temperature calcining furnace needs to be within the above range, because silicon nitride begins to melt above 1500°C, wraps the sphere, forms a shell and tends to spherical. If the temperature is too high, silicon nitride will decompose.

[0150] Comparative Example

[0151] Comparative Example 1

[0152] The difference from Example 2 is that only the primary preheating is performed, and the secondary preheating is not performed, and the silicon-coated fused magnesium oxide powder after the primary preheating is directly nitrided.

[0153] Performance Testing

[0154] The performance comparison of the spherical composite powders prepared in Examples 2-5, the ordinary high temperature electrical grade magnesium oxide powder of the control example, and the magnesium oxide prepared in the comparative example is recorded in Table 1. The control example is ordinary high temperature electrical grade magnesium oxide powder produced by Liaoning Rongbang Technology Co., Ltd. with a magnesium content of 95%wt.

[0155] The spherical composite powders prepared in Examples 2-5, Comparative Example 1 and ordinary high-temperature electrical grade magnesium oxide powder were respectively made into standard electric heating elements (Note: sample tube SUS304 steel tube length: 500mm110V / 500W), and the water absorption, thermal conductivity and flow rate were determined with reference to GB / T8508-1996; the sphericity was determined with reference to GB / T37406-2019, and the test results are shown in Table 1.

[0156] Table 1

[0157]

[0158] As can be seen from Table 1, the control example uses ordinary high-temperature electrical grade magnesium oxide powder. Since the surface is not passivated and spheroidized, it has high activity, is easy to absorb moisture, has too many surface pores, affects thermal conductivity, and has poor flow performance due to low sphericity; since comparative example 1 has not undergone secondary preheating treatment, a large temperature gradient is formed on the surface of the particles during high-temperature nitriding, resulting in uneven coating of the nitriding layer, affecting water absorption performance and thermal conductivity. The production method of the present invention is used to achieve uniform coating of the nitride film on the surface of the magnesium oxide powder by accurately controlling parameters such as flow rate, temperature and time, and the thermal conductivity and sphericity of the prepared inert modified electrical grade magnesium oxide are greatly improved, and the water absorption rate and flow rate are greatly reduced.

[0159] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A production device for spheroidizing electrical grade magnesium oxide, characterized in that: Including material handling system and gas circulation system; The material processing system comprises a coating machine (1), a vibrating screen (2), at least one preheating furnace, a high-temperature calcining furnace (5) and a cooling furnace (6) which are connected in sequence; The gas circulation system comprises a nitrogen generator (11), an induced draft fan (9) and a gas circulation loop; the nitrogen generator (11) can provide stable nitrogen, and under the action of the induced draft fan (9), part of the nitrogen passes through the induced draft fan (9), the high-temperature calcining furnace (5), the multi-stage preheating furnace and returns to the induced draft fan (9) through the gas circulation loop in sequence, thereby realizing the circulation of nitrogen.

2. The production device according to claim 1, characterized in that: The material processing system further comprises an auxiliary heating device, which is capable of heating the gas introduced into the high-temperature calcining furnace (5) to a certain temperature.

3. The production device according to claim 1, characterized in that: The gas circulation system further comprises a bag dust collector (8), wherein the bag dust collector (8) is arranged at the inlet (9A) end of the induced draft fan (9).

4. The production device according to claim 1, characterized in that: The preheating furnace is arranged in an inclined manner, and the inlet end of the preheating furnace is higher than the outlet end; and / or The high temperature calcining furnace (5) is arranged in an inclined manner, and the inlet end of the high temperature calcining furnace (5) is higher than the outlet end; and / or The cooling furnace (6) is arranged in an inclined manner, and the inlet end of the cooling furnace is higher than the outlet end.

5. The production device according to claim 4, characterized in that: The inclination angle of the preheating furnace is 5° to 15°; and / or The high temperature calcining furnace (5) has an inclination angle of 5° to 15°; and / or The inclination angle of the cooling furnace (6) is 5° to 15°.

6. The production device according to claim 1, characterized in that: The ratio of the inner diameter to the length of the high temperature calcining furnace (5) is 0.05:1 to 0.15:1; and / or The ratio of the inner diameter to the length of the cooling furnace (6) is 0.075:1 to 0.2:

1.

7. A method for producing inert modified electrical grade magnesium oxide using the production device according to any one of claims 1 to 6, characterized in that: The steps include: (1) Raw material preparation The fused magnesia powder is obtained by crushing, screening and magnetic separation of fused magnesia blocks with a magnesium content of 95-99.9%wt; (2) Coating treatment The fused magnesium oxide powder and the coating slurry prepared in step (1) are added to a coating machine (1), and the coating slurry is coated on the surface of the fused magnesium oxide powder which is continuously stirred; after drying, the coated material is transferred to a vibrating screen (2), and fine dust is screened out to obtain coated fused magnesium oxide powder; (3) Multi-stage preheating and nitriding treatment The nitrogen generator (11) and the induced draft fan (9) are turned on to fill the gas pipeline with nitrogen. When the preheating furnace and the high-temperature calcining furnace (5) both reach the set temperature, the coated fused magnesia powder is sequentially transferred to the preheating furnace for multi-stage preheating treatment under a nitrogen atmosphere, and then transferred to the high-temperature calcining furnace (5) for nitriding treatment, so that the micro powder on the surface of the coated fused magnesia powder is nitrided to form molten nitride. (4) Finalization The nitrided material is transferred to a cooling furnace (6) for cooling and shaping, thereby obtaining a spherical composite powder with a nitride coating evenly covering the surface.

8. The method according to claim 7, characterized in that The coating slurry comprises micro powder and a binder.

9. The method according to claim 8, characterized in that The micro powder is silicon powder and / or boron powder; The binder is one or more of silica sol, polyvinyl alcohol, dextrin and carboxymethyl cellulose.

10. The method according to claim 7, characterized in that In step (3), the multi-stage preheating method is: first react at 150-200°C for 15-20 minutes, and then react at 400-600°C for 15-20 minutes.

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