A passivated magnesium powder and its preparation method

Abstract

This invention belongs to the technical field of iron and steel metallurgical industry, specifically relating to a passivated magnesium powder and its preparation method. The passivated magnesium powder preparation method provided by this invention uses a combination of chemical and physical passivation to form a uniformly distributed passivation film on the surface of the magnesium powder. This reduces magnesium powder loss and imparts excellent antioxidant properties, enabling it to exhibit good reactivity when applied to molten iron desulfurization. In this invention, a chemical passivating agent composed of a salt solution, oxidant, surfactant, and complexing agent is used to chemically passivate the magnesium powder. The thickness of the passivation film on the surface of the magnesium powder is controlled by adjusting the concentration of the passivating agent, the particle size of the inorganic mineral powder, and the amounts of inorganic mineral powder and nano-silica. This effectively avoids phenomena such as magnesium powder combustion due to an excessively thin passivation film or reduced magnesium powder activity due to an excessively thick passivation film.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgical industry technology, specifically relating to a passivated magnesium powder and its preparation method. Background Technology

[0002] Sulfur, as one of the harmful elements in steel, causes various problems such as hot brittleness. This is especially true for steel companies using continuous casting technology, where sulfide segregation is a significant cause of cracks in continuously cast billets and a key factor affecting billet yield. In recent decades, the development of offshore oil extraction, the automotive industry, and large-scale construction projects have placed increasingly stringent demands on steel quality, requiring high strength, low-temperature toughness, good cold forming properties, and weldability. To meet these market requirements, steel industries worldwide are striving to improve steel quality by reducing impurities, particularly sulfur content.

[0003] Magnesium-based composite powder injection desulfurization technology is the mainstream process for molten iron desulfurization, and magnesium powder is the key factor determining the desulfurization effect. Metallic magnesium is highly reactive, therefore it must undergo passivation treatment before safe transportation, storage, and use. There are many methods for passivating the surface of metallic magnesium, such as organic film protection, electroplating, and chromate passivation film methods. However, these are generally suitable for the surface treatment of magnesium ingots, not for the surface passivation of magnesium particles used as desulfurizing agents. Currently, there are two methods for the surface treatment of magnesium particles: one is the chemical reaction method, where the magnesium on the surface of the magnesium particles reacts with a passivating agent to form a relatively dense reaction product film layer; the other is the surface coating method, which involves covering the surface of the magnesium particles with another substance that does not react with metallic magnesium. Magnesium particles treated using method one have a uniform passivation layer and good passivation effect, but some metallic magnesium is lost; using method two does not result in the loss of metallic magnesium, but there are problems such as uneven passivation and poor passivation effect. In addition, existing dry processes for producing magnesium powder and aluminum-magnesium alloy powder require inert gas protection during production, which places high demands on the airtightness of the equipment; otherwise, dust leakage or even safety accidents may occur.

[0004] Chinese patent application CN107088655A discloses a passivated magnesium powder, passivated aluminum-magnesium alloy powder, and their wet production process. Specifically, magnesium particles, aluminum-magnesium alloy particles, and an antioxidant aqueous solution are added to a wet pulverizing device for wet pulverization. The solid-liquid mixture is then separated by wet sieving or hydraulic classification. After drying, passivated magnesium powder or passivated aluminum-magnesium alloy powder is obtained. The antioxidant used in this method is one or more of phytic acid, boric acid, and potassium dichromate. However, the antioxidant can only form a thin oxide film on the surface of the magnesium powder, which is insufficient for steelmaking requirements. The magnesium powder rapidly oxidizes and burns before being added to the molten steel, significantly reducing its desulfurization efficiency. Therefore, this method is not optimal in terms of safety and desulfurization efficiency. Summary of the Invention

[0005] In order to solve the technical problems existing in related technologies, such as uneven passivation film, poor passivation effect, and magnesium powder combustion, this invention provides a passivated magnesium powder and its preparation method.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for preparing passivated magnesium powder includes the following steps:

[0008] S1: Under inert gas protection, magnesium particles are mixed evenly with magnesium oxide powder and erbium oxide powder, a passivating agent is added, the temperature is raised to 85-90℃, stirred and ground, cooled and filtered to obtain powder I;

[0009] S2: Mix the powder I obtained in step S1 with inorganic mineral powder evenly to obtain powder II;

[0010] S3: Add the powder II obtained in step S2 to the polyvinylpyrrolidone aqueous solution, stir, filter, dry, and grind to obtain powder III;

[0011] S4: Mix the powder III obtained in step S3 with nano-silica and grind at high speed to obtain passivated magnesium powder.

[0012] The passivating agent in step S1 includes a salt solution and an oxidizing agent; the salt solution is a carbonate solution and / or a phosphate solution; the oxidizing agent is hydrogen peroxide.

[0013] In the above technical solution, the mixing of magnesium oxide powder and magnesium powder can form an antioxidant layer on the surface of the magnesium powder. After reacting with the passivating agent, a more uniform and robust passivation layer can be generated, effectively preventing further oxidation of the magnesium powder and improving the thermal stability of the passivation layer. Erbium oxide has a high melting point and good thermal stability. During stirring and grinding, it can form a solid solution and a dense and stable oxide film on the surface of the magnesium powder. This film can effectively block oxygen and moisture from contacting the magnesium powder, thereby preventing oxidation. Adding the pre-oxidized magnesium powder to a mixed solution of salt solution and oxidant can further form a composite salt film with anti-corrosion properties on the surface of the magnesium powder, effectively increasing the ignition point of the magnesium powder, reducing the gasification rate, and thus improving desulfurization efficiency.

[0014] In this invention, adding inorganic mineral powder to magnesium powder disrupts the continuity of the magnesium powder, thereby slowing down the gasification rate of magnesium under the desulfurization temperature of molten iron, reducing the vapor pressure of magnesium, and improving the desulfurization efficiency of magnesium. Simultaneously, it prevents nozzle clogging during the injection process, ensuring that the magnesium powder ultimately enters the slag and does not participate in the desulfurization reaction. The magnesium powder mixed with inorganic mineral powder is added to a polyvinylpyrrolidone aqueous solution, stirred, and dried. A polyvinylpyrrolidone film is then coated onto the surface of the magnesium powder and inorganic mineral powder mixture, further improving the oxidation and water resistance of the magnesium powder. Finally, it is mixed with nano-silica and ground at high speed. The nano-silica coats the surface of powder III. At the high temperature of molten iron, the nano-silica forms a thin ceramic film, effectively preventing the gasification of magnesium powder and improving the desulfurization efficiency.

[0015] Furthermore, the mixing mass ratio of magnesium particles, magnesium oxide powder, and erbium oxide powder in step S1 is 17-20:5-9:2-4.

[0016] In the above technical solution, the amount of magnesium oxide powder and erbium oxide powder will affect the flame retardant performance of passivated magnesium powder. Excessive use of magnesium oxide powder and erbium oxide powder will not only fail to increase the flame retardant time of magnesium powder, but will also reduce the reactivity of passivated magnesium powder. This is because excessive use of magnesium oxide powder and erbium oxide powder will lead to poor uniformity of the passivation film layer.

[0017] Furthermore, the carbonate solution in the passivating agent is an ammonium bicarbonate solution and / or a sodium bicarbonate solution, and the concentration of carbonate in the passivating agent is 1.5-2.2 mol / L; the phosphate solution is one of sodium dihydrogen phosphate solution, disodium hydrogen phosphate solution, and diammonium hydrogen phosphate, and the concentration of phosphate in the passivating agent is 1.7-2.4 mol / L; the mass concentration of hydrogen peroxide in the passivating agent is 20%-30%.

[0018] Furthermore, the carbonate solution is an ammonium bicarbonate solution with a concentration of 1.8 mol / L; the phosphate solution is a diammonium hydrogen phosphate solution with a concentration of 2.1 mol / L.

[0019] In the above technical solution, the carbonate solution can react with magnesium powder to form basic magnesium carbonate, and the phosphate solution can react with magnesium powder to form magnesium phosphate. The basic magnesium carbonate and magnesium phosphate can effectively isolate the magnesium powder from the external environment, prevent oxygen in the external atmosphere from penetrating into the magnesium liquid, prevent the magnesium liquid from volatilizing, and increase the ignition point of the magnesium powder.

[0020] Furthermore, the passivating agent in step S1 further includes a surfactant and a complexing agent; the surfactant is one or more of stearic acid, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium fatty alcohol polyoxyethylene ether sulfate, and sodium diisooctyl succinate sulfonate; the complexing agent is one or more of tartaric acid, ethylenediaminetetraacetic acid, citric acid, and pyridine dicarboxylic acid; the mass concentration of the surfactant in the passivating agent is 4%-9%, and the mass concentration of the complexing agent is 11%-15%.

[0021] The surfactant in the passivation solution reduces the surface tension of the passivation solution, making it easier for the passivation solution to spread on the magnesium powder and form a uniform passivation film. This is beneficial for forming a uniform passivation film on the metal surface and also ensures that the metal powder is evenly distributed in the passivation solution, preventing metal powder agglomeration that could lead to an uneven passivation film. Furthermore, magnesium ions can form stable complexes with the complexing agent, thereby controlling the concentration of free magnesium ions in the passivation solution and preventing uneven precipitation or over-deposition of the passivation film due to uneven magnesium ion distribution, which would negatively impact the passivation film performance.

[0022] Furthermore, the inorganic mineral powder in step S2 has a particle size of 3-7 μm, and the inorganic mineral powder is calcite powder and magnesite powder, with a mass ratio of calcite powder to magnesite powder of 3-5:7-11.

[0023] Studies have found that the type, particle size, and distribution uniformity of inorganic mineral powders all affect their antioxidant effect. Fine inorganic mineral powders can be evenly dispersed on the surface of magnesium powder. Calcite powder decomposes at high temperatures to generate calcium oxide, which adheres to the surface of magnesium powder. Magnesite powder decomposes at high temperatures to generate magnesium oxide, forming a mixed oxide film with CaO and MgO on the upper layer and MgO and Er2O3 on the lower layer. This oxide film can effectively prevent oxygen in the external atmosphere from penetrating into the magnesium liquid, while also preventing the volatilization of the magnesium liquid and reducing the gasification rate of magnesium, thereby improving the ignition point and desulfurization efficiency of magnesium powder.

[0024] Furthermore, in step S2, the amount of inorganic mineral powder added is 5%-9% of the mass of powder I.

[0025] Adding an appropriate amount of inorganic mineral powder can effectively improve the oxidation resistance and corrosion resistance of magnesium powder. However, excessive addition of inorganic mineral powder may lead to uneven coating, reduced activity of magnesium powder, and more pores in the coating, thus reducing the effectiveness of inorganic mineral powder.

[0026] Furthermore, the mass fraction of the polyvinylpyrrolidone aqueous solution in step S3 is 25%-30%.

[0027] Furthermore, in step S4, the mixing mass ratio of powder III and nano-silica is 16-20:7-9.

[0028] The present invention also provides passivated magnesium powder prepared by the above-described method for preparing passivated magnesium powder.

[0029] Compared with the prior art, the passivated magnesium powder and its preparation method provided by the present invention have the following technical advantages:

[0030] (1) The passivated magnesium powder preparation method provided by the present invention uses chemical passivation + physical passivation to form a uniformly distributed passivation film on the surface of magnesium powder, which reduces magnesium powder loss and gives magnesium powder good antioxidant properties, making it have good reactivity when applied to desulfurization of molten iron.

[0031] (2) In this invention, the thickness of the passivation film on the surface of the magnesium powder is controlled by controlling the concentration of the passivating agent, the particle size of the inorganic mineral powder, the amount of inorganic mineral powder and nano silica, etc., which effectively avoids the phenomenon of magnesium powder burning due to the passivation film layer being too thin or magnesium powder activity being reduced due to the passivation film layer being too thick.

[0032] (3) The passivated magnesium powder provided in this invention has a high active magnesium content. When performing desulfurization treatment of molten iron, the use of passivated magnesium will not affect the quality of molten iron or cause the composition of molten iron to deviate. Moreover, the passivation liquid provided in this invention has low environmental pollution and low treatment cost, and has good market prospects. Attached Figure Description

[0033] Figure 1 The oxidation kinetics curve of the passivated magnesium powder prepared in Example 1;

[0034] Figure 2 The oxidation kinetics curve of the passivated magnesium powder prepared in Example 2;

[0035] Figure 3 The oxidation kinetics curve of the passivated magnesium powder prepared in Example 3;

[0036] Figure 4 The oxidation kinetics curve of the passivated magnesium powder prepared in Example 4;

[0037] Figure 5 The oxidation kinetics curve of the passivated magnesium powder prepared in Example 5;

[0038] Figure 6 The oxidation kinetics curve of the passivated magnesium powder prepared in Example 6;

[0039] Figure 7 The oxidation kinetics curve of the passivated magnesium powder prepared in Comparative Example 1 is shown.

[0040] Figure 8 The oxidation kinetics curve of the passivated magnesium powder prepared in Comparative Example 2 is shown.

[0041] Figure 9The oxidation kinetics curve of the passivated magnesium powder prepared in Comparative Example 3 is shown.

[0042] Figure 10 The oxidation kinetics curve of the passivated magnesium powder prepared in Comparative Example 4 is shown.

[0043] Figure 11 The oxidation kinetics curve of the passivated magnesium powder prepared in Comparative Example 5 is shown.

[0044] Figure 12 Here is a SEM image of the passivated magnesium powder prepared in Example 4;

[0045] Figure 13 Here is a SEM image of the passivated magnesium powder prepared in Example 5;

[0046] Figure 14 This is a SEM image of the passivated magnesium powder prepared in Example 6. Detailed Implementation

[0047] The following description, in conjunction with specific embodiments, provides further details, but the present invention is not limited to these embodiments. Those skilled in the art can make various modifications based on the fundamental principles of the present invention, but all modifications that do not depart from the fundamental principles of the present invention are within its scope.

[0048] Example 1

[0049] A method for preparing passivated magnesium powder includes the following steps:

[0050] S1: Under nitrogen gas flow protection, 17g of magnesium granules, 5g of magnesium oxide powder, and 2g of erbium oxide powder are thoroughly mixed evenly, 30g of passivating agent is added, the temperature is raised to 85℃, and the mixture is stirred and ground until the average particle size of magnesium powder is 80μm. After cooling, the mixture is filtered, the filter cake is dried at 70℃, and the powder is ground to obtain powder I.

[0051] The passivating agent is a mixture of ammonium bicarbonate solution, sodium dihydrogen phosphate solution, hydrogen peroxide, sodium dodecylbenzenesulfonate and tartaric acid, wherein the concentration of ammonium bicarbonate is 1.5 mol / L, the concentration of sodium dihydrogen phosphate is 2.4 mol / L, the mass concentration of hydrogen peroxide is 20%, the mass concentration of sodium dodecylbenzenesulfonate is 4%, and the mass concentration of tartaric acid is 11%.

[0052] S2: Mix the powder I obtained in step S1 with inorganic mineral powder with a particle size of 3μm evenly. The amount of inorganic mineral powder added is 5% of the mass of powder I to obtain powder II.

[0053] The inorganic mineral powder consists of calcite powder and magnesite powder, with a mass ratio of calcite powder to magnesite powder of 3:7.

[0054] S3: Add the powder II obtained in step S2 to 50g of a 25% polyvinylpyrrolidone aqueous solution, stir for 1.2h, filter, dry the filter cake at 60℃, grind, and obtain powder III.

[0055] S4: Mix the powder III obtained in step S3 with nano-silica at a mass ratio of 16:7 and grind at 1200 rpm to obtain passivated magnesium powder.

[0056] Example 2

[0057] A method for preparing passivated magnesium powder includes the following steps:

[0058] S1: Under nitrogen gas flow protection, 20g of magnesium granules, 9g of magnesium oxide powder, and 4g of erbium oxide powder are thoroughly mixed evenly, 30g of passivating agent is added, the temperature is raised to 90℃, and the mixture is stirred and ground until the average particle size of magnesium powder is 120μm. After cooling, the mixture is filtered, the filter cake is dried at 80℃, and the powder is ground to obtain powder I.

[0059] The passivating agent is a mixture of sodium bicarbonate solution, disodium hydrogen phosphate solution, hydrogen peroxide, stearic acid and ethylenediaminetetraacetic acid, wherein the concentration of sodium bicarbonate is 2.2 mol / L, the concentration of disodium hydrogen phosphate is 1.7 mol / L, the mass concentration of hydrogen peroxide is 30%, the mass concentration of stearic acid is 9%, and the mass concentration of ethylenediaminetetraacetic acid is 15%.

[0060] S2: Mix the powder I obtained in step S1 with inorganic mineral powder with a particle size of 7μm evenly. The amount of inorganic mineral powder added is 9% of the mass of powder I to obtain powder II.

[0061] The inorganic mineral powder consists of calcite powder and magnesite powder, with a mass ratio of calcite powder to magnesite powder of 5:11.

[0062] S3: Add the powder II obtained in step S2 to 50g of a 30% polyvinylpyrrolidone aqueous solution, stir for 1.5h, filter, dry the filter cake at 70℃, grind, and obtain powder III.

[0063] S4: Mix the powder III obtained in step S3 with nano-silica at a mass ratio of 20:9 and grind at 1400 rpm to obtain passivated magnesium powder.

[0064] Example 3

[0065] A method for preparing passivated magnesium powder includes the following steps:

[0066] S1: Under nitrogen gas flow protection, 18g of magnesium granules, 8g of magnesium oxide powder, and 3g of erbium oxide powder are thoroughly mixed evenly. 30g of passivating agent is added, and the temperature is raised to 90℃. While stirring, the mixture is ground until the average particle size of the magnesium powder is 100μm. After cooling, the mixture is filtered, and the filter cake is dried at 75℃. The powder is then ground to obtain powder I.

[0067] The passivating agent is a mixture of ammonium bicarbonate solution, diammonium hydrogen phosphate solution, hydrogen peroxide, sodium dodecyl sulfate and citric acid, wherein the concentration of ammonium bicarbonate is 2.1 mol / L, the concentration of diammonium hydrogen phosphate is 2.0 mol / L, the mass concentration of hydrogen peroxide is 25%, the mass concentration of sodium dodecyl sulfate is 6%, and the mass concentration of citric acid is 13%.

[0068] S2: Mix the powder I obtained in step S1 with inorganic mineral powder with a particle size of 5μm evenly. The amount of inorganic mineral powder added is 7% of the mass of powder I to obtain powder II.

[0069] The inorganic mineral powder consists of calcite powder and magnesite powder, with a mass ratio of calcite powder to magnesite powder of 4:9.

[0070] S3: Add the powder II obtained in step S2 to 50g of a 28% polyvinylpyrrolidone aqueous solution, stir for 1.4h, filter, dry the filter cake at 65℃, grind, and obtain powder III.

[0071] S4: Mix powder III obtained in step S3 with nano-silica at a mass ratio of 17:8 and grind at 1300 rpm to obtain passivated magnesium powder.

[0072] Example 4

[0073] A method for preparing passivated magnesium powder includes the following steps:

[0074] S1: Under nitrogen gas flow protection, 19g of magnesium granules, 7g of magnesium oxide powder, and 3g of erbium oxide powder are thoroughly mixed evenly, 30g of passivating agent is added, the temperature is raised to 90℃, and the mixture is stirred and ground until the average particle size of magnesium powder is 100μm. After cooling, the mixture is filtered, the filter cake is dried at 75℃, and the powder is ground to obtain powder I.

[0075] The passivating agent is a mixture of ammonium bicarbonate solution, diammonium hydrogen phosphate solution, hydrogen peroxide, sodium fatty alcohol polyoxyethylene ether sulfate, and pyridine dicarboxylic acid. The concentration of ammonium bicarbonate is 1.8 mol / L, the concentration of diammonium hydrogen phosphate is 2.1 mol / L, the mass concentration of hydrogen peroxide is 26%, the mass concentration of sodium fatty alcohol polyoxyethylene ether sulfate is 8%, and the mass concentration of pyridine dicarboxylic acid is 14%.

[0076] S2: Mix the powder I obtained in step S1 with inorganic mineral powder with a particle size of 5μm evenly. The amount of inorganic mineral powder added is 7% of the mass of powder I to obtain powder II.

[0077] The inorganic mineral powder consists of calcite powder and magnesite powder, with a mass ratio of calcite powder to magnesite powder of 4:9.

[0078] S3: Add the powder II obtained in step S2 to 50g of a 28% polyvinylpyrrolidone aqueous solution, stir for 1.4h, filter, dry the filter cake at 65℃, grind, and obtain powder III.

[0079] S4: Mix powder III obtained in step S3 with nano-silica at a mass ratio of 17:8 and grind at 1300 rpm to obtain passivated magnesium powder.

[0080] Example 5

[0081] The preparation method of passivated magnesium powder in this embodiment is similar to that in Example 4. The difference between this embodiment and Example 4 is as follows: Step S1 in this embodiment is as follows:

[0082] Under nitrogen gas flow protection, 19g of magnesium granules, 6g of magnesium oxide powder, and 4g of erbium oxide powder were thoroughly mixed evenly, 30g of passivating agent was added, the temperature was raised to 90℃, and the mixture was stirred and ground until the average particle size of magnesium powder was 100μm. After cooling, the mixture was filtered, the filter cake was dried at 75℃, and the powder was ground to obtain powder I.

[0083] The passivating agent is a mixture of ammonium bicarbonate solution, sodium dihydrogen phosphate solution, hydrogen peroxide, sodium fatty alcohol polyoxyethylene ether sulfate and pyridine dicarboxylic acid. The concentration of ammonium bicarbonate is 1.7 mol / L, the concentration of sodium dihydrogen phosphate is 1.9 mol / L, the mass concentration of hydrogen peroxide is 25%, the mass concentration of sodium fatty alcohol polyoxyethylene ether sulfate is 7%, and the mass concentration of pyridine dicarboxylic acid is 13%.

[0084] Example 6

[0085] The preparation method of passivated magnesium powder in this embodiment is similar to that in Example 4. The difference between this embodiment and Example 4 is as follows: Step S1 in this embodiment is as follows:

[0086] S1: Under nitrogen gas flow protection, 19g of magnesium granules, 7g of magnesium oxide powder, and 3g of erbium oxide powder are thoroughly mixed evenly, 30g of passivating agent is added, the temperature is raised to 90℃, and the mixture is stirred and ground until the average particle size of magnesium powder is 100μm. After cooling, the mixture is filtered, the filter cake is dried at 75℃, and the powder is ground to obtain powder I.

[0087] The passivating agent is a mixture of ammonium bicarbonate solution, sodium dihydrogen phosphate solution, hydrogen peroxide, sodium diisooctyl succinate sulfonate and citric acid, wherein the concentration of ammonium bicarbonate is 1.9 mol / L, the concentration of sodium dihydrogen phosphate is 2.2 mol / L, the mass concentration of hydrogen peroxide is 27%, the mass concentration of sodium diisooctyl succinate sulfonate is 6%, and the mass concentration of citric acid is 15%.

[0088] Comparative Example 1

[0089] The preparation method of the passivated magnesium powder described in this comparative example is similar to that in Example 4. The difference between this comparative example and Example 4 is that the amounts of magnesium particles, magnesium oxide powder, and erbium oxide used in step S1 of this comparative example are 19g, 15g, and 8g, respectively.

[0090] Comparative Example 2

[0091] The preparation method of the passivated magnesium powder described in this comparative example is similar to that in Example 5. The difference between this comparative example and Example 5 is that the concentration of ammonium bicarbonate in the passivating agent used in step S1 of this comparative example is 3.0 mol / L, the concentration of sodium dihydrogen phosphate is 1.0 mol / L, and the mass concentration of hydrogen peroxide is 40%.

[0092] Comparative Example 3

[0093] The preparation method of the passivated magnesium powder in this comparative example is similar to that in Example 5. The difference between this comparative example and Example 5 is that the inorganic mineral powder in step S2 of this comparative example is magnesite powder.

[0094] Comparative Example 4

[0095] The preparation method of the passivated magnesium powder described in this comparative example is similar to that in Example 5. The difference between this comparative example and Example 5 is that the amount of inorganic mineral powder added in step S2 of this comparative example is 15% of the mass of powder I.

[0096] Comparative Example 5

[0097] The preparation method of the passivated magnesium powder in this comparative example is similar to that in Example 6. The difference between this comparative example and Example 6 is that the mass ratio of powder III to nano-silica in step S4 of this comparative example is 8:17.

[0098] Experimental Example 1: Thermal Performance Test

[0099] Test samples: Passivated magnesium powder prepared in Examples 1-6 and Comparative Examples 1-5;

[0100] Flame retardant time test: Place a 0.4g sample on a thin quartz plate, raise the furnace temperature to 1273K, and then push the quartz plate to the constant temperature zone inside the furnace. Timing is taken from the time the sample is placed in until it begins to burn. Measure each sample multiple times and take the average value. The test results are shown in Table 1.

[0101] Ignition point test: The ignition point of the sample was tested using a TGA2050 thermogravimetric analyzer from TA Instruments (USA), heated from room temperature to 900℃ at a rate of 20℃ / min under air conditions. The test results are shown below. Figures 1-11 .

[0102] Table 1 Flame retardant time test results

[0103]

[0104] From Table 1, Figures 1-11 It can be seen that the passivated magnesium powder provided by the present invention has a flame retardant time of more than 17s, reaching a maximum of 20.3s, and an ignition point of more than 620℃, reaching a maximum of 660℃, which has a good flame retardant effect. This indicates that the passivated magnesium powder provided by the present invention has a uniform passivation film, which can effectively reduce the gasification and combustion of magnesium powder.

[0105] Compared to Example 4, Comparative Example 1 changed the amounts of magnesium powder, magnesium oxide powder, and erbium oxide powder, but the flame retardant time and ignition point both decreased, indicating that the amounts of magnesium oxide powder and erbium oxide powder affect the flame retardant time of passivated magnesium powder. Compared to Example 5, Comparative Example 2 changed the concentrations of salt solution and hydrogen peroxide in the passivating agent, but the flame retardant time and ignition point both decreased, indicating that the concentrations of salt solution and hydrogen peroxide in the passivating agent are key factors affecting the thickness and uniformity of the passivation film. Comparative Example 3 changed the type of inorganic mineral powder, and Comparative Example 4 changed the amount of inorganic mineral powder added, but the flame retardant time and ignition point decreased slightly, indicating that the type and amount of inorganic mineral powder affect the thickness and uniformity of the passivation film. Compared to Example 6, Comparative Example 5 changed the mixing mass ratio of powder III and nano-silica, but the flame retardant time and ignition point decreased. This is because excessive nano-silica caused it to agglomerate on the surface of magnesium powder, reducing the uniformity of the passivation film.

[0106] Experimental Example 2: Characterization of Passivation Film

[0107] In this experiment, the passivated magnesium powders prepared in Examples 4-6 were subjected to scanning electron microscopy (SEM) testing. The test results are shown in [Figure 1]. Figures 12-14 .

[0108] Depend on Figures 12-14 It can be seen that the passivated magnesium powder provided by the present invention has a uniform surface coating without obvious protrusions, holes or cracks, and has good density. This indicates that the passivation layer can effectively block the contact between oxygen and the internal magnesium metal and prevent the magnesium liquid from vaporizing and volatilizing.

[0109] The above embodiments are merely illustrative of the present invention and are not intended to limit the invention. Those skilled in the art should not modify the above embodiments without departing from the spirit and scope of the present invention. All equivalent modifications or alterations made by those skilled in the art without departing from the technical concept of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing passivated magnesium powder, characterized in that, Includes the following steps: S1: Under inert gas protection, magnesium particles are mixed evenly with magnesium oxide powder and erbium oxide powder, a passivating agent is added, the temperature is raised to 85-90℃, stirred and ground, cooled and filtered to obtain powder I; the mixing mass ratio of magnesium particles, magnesium oxide powder and erbium oxide powder is 17-20:5-9:2-4. S2: Mix the powder I obtained in step S1 with inorganic mineral powder evenly to obtain powder II; the particle size of the inorganic mineral powder is 3-7 μm, and the inorganic mineral powder is calcite powder and magnesite powder, the mass ratio of calcite powder to magnesite powder is 3-5:7-11; the amount of inorganic mineral powder added is 5%-9% of the mass of powder I; S3: Add powder II obtained in step S2 to a polyvinylpyrrolidone aqueous solution, stir, filter, dry, and grind to obtain powder III; the mass fraction of the polyvinylpyrrolidone aqueous solution is 25%-30%; S4: Mix the powder III obtained in step S3 with nano-silica and grind at high speed to obtain passivated magnesium powder; the mass ratio of powder III to nano-silica is 16-20:7-9. The passivating agent in step S1 comprises a salt solution and an oxidizing agent; the salt solution is a carbonate solution and / or a phosphate solution; the oxidizing agent is hydrogen peroxide; the carbonate solution in the passivating agent is an ammonium bicarbonate solution and / or a sodium bicarbonate solution, and the concentration of carbonate in the passivating agent is 1.5-2.2 mol / L; the phosphate solution is one of sodium dihydrogen phosphate solution, disodium hydrogen phosphate solution, and diammonium hydrogen phosphate, and the concentration of phosphate in the passivating agent is 1.7-2.4 mol / L; the mass concentration of hydrogen peroxide in the passivating agent is 20%-30%.

2. The method for preparing passivated magnesium powder according to claim 1, characterized in that, The carbonate solution is an ammonium bicarbonate solution with a concentration of 1.8 mol / L; the phosphate solution is a diammonium hydrogen phosphate solution with a concentration of 2.1 mol / L.

3. The method for preparing passivated magnesium powder according to claim 1, characterized in that, The passivating agent in step S1 further includes a surfactant and a complexing agent; the surfactant is one or more of stearic acid, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium fatty alcohol polyoxyethylene ether sulfate, and sodium diisooctyl succinate sulfonate; the complexing agent is one or more of tartaric acid, ethylenediaminetetraacetic acid, citric acid, and pyridine dicarboxylic acid; the mass concentration of the surfactant in the passivating agent is 4%-9%, and the mass concentration of the complexing agent is 11%-15%.

4. Passivated magnesium powder prepared by the method of any one of claims 1-3.

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