Preparation method of magnesium-calcium refractory aggregate with core-shell structure

Abstract

The invention discloses a preparation method of magnesium-calcium refractory aggregate with a core-shell structure, which comprises the following steps: granulating dolomite powder to form core particles, and uniformly adhering magnesium source powder to the core particles to form precursor particles with a double-layer structure; the adding amount of the magnesium source powder is controlled according to the mass ratio of the content of MgO in the magnesium source powder to the content of MgCa (CO3) 2 in the dolomite powder being (5-30): 100; and finally, heating and sintering the dried product of the precursor particles at the heating rate of 5 DEG C / min, and preserving heat to obtain the magnesium-calcium refractory aggregate with the core-shell structure. The method has the advantages of easily available raw materials and low production cost; the process is simple and suitable for large-scale production; the product is high in hydration resistance, high in refractoriness, excellent in slag corrosion resistance and wide in market prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of refractories, and particularly relates to a preparation method of magnesium-calcium refractory aggregate with a core-shell structure. Background Art

[0002] Magnesium-calcium refractory materials have magnesium oxide (MgO) and calcium oxide (CaO) as core components, and have the advantages of high refractoriness, resistance to alkaline slag erosion, thermal shock resistance and molten steel purification function; its core advantage lies in the strong binding ability of CaO with impurities such as sulfur and phosphorus in molten steel, which can form stable compounds to improve the purity of molten steel. Therefore, it plays an important role in the smelting of clean steel, the firing zone of cement kilns and vacuum refining equipment. With the improvement of the quality requirements of steel in fields such as automobiles and aerospace, the market demand for magnesium-calcium materials continues to grow, and it is mainly used in the production of special steels (bearing steel, electrical steel, etc.) and the cement industry.

[0003] The anti-hydration performance is the core bottleneck of magnesia-calcium materials. Free CaO in magnesia-calcium refractory materials is extremely prone to reacting with water to form Ca(OH)2, not only releasing a large amount of heat but also accompanied by a huge volume expansion, which leads to the pulverization of magnesia-calcium refractory materials, causing great difficulties in production, storage, and use, and severely restricting the development and application of magnesia-calcium refractory materials. Existing technologies have carried out multi-dimensional research on anti-hydration performance through raw material modification, surface treatment, and binder optimization. Currently, the main methods for waterproofing magnesia-calcium refractory materials at home and abroad mainly include: high-temperature calcination to improve crystal density, surface coating with a covering layer to isolate water vapor, and adding compounds to improve the microstructure of the material; among them, the calcination method has high energy consumption, the secondary calcination preparation process is complex, and the production cost is relatively high; in the surface treatment method, the reaction to form an inorganic covering layer is not easy to control, uneven coverage will affect the high-temperature performance of the material, and the organic covering layer is prone to generating toxic substances at high temperatures, endangering the operator and polluting the environment; the cost of rare earth additives is too high, the types and optimal ratios of composite additives need further research, in addition, the addition of additives will increase the impurity content in magnesia-calcium materials, affecting the excellent performance of the materials. For example: Document I (WU Zhandé, YANG Yang. Research on the preparation and properties of high-quality magnesia-calcium sand by ultra-high temperature calcination [J]. Refractories & Lime, 2018, 43(6): 1-8) used natural dolomite and magnesite as raw materials, pressed them into shape at 140 MPa, and calcined them at 1700-2000 °C to prepare magnesia-calcium refractory materials, and then detected their anti-hydration performance by the boiling method; the results showed that: with the increase of the calcination temperature, the growth of periclase grains was very rapid, and the pulverization rate of the prepared materials could be reduced to below 2 wt%, improving the anti-hydration performance of the products, but this method has high energy consumption, the calcination temperature needs to reach above 1800 °C in industrial production, has high requirements for sintering equipment conditions, and high production costs. Document II (GHASEMI-KAHRIZSANGI S, DEHSHEIKH HG. BOROU-JERDNIAM. MgO-CaO-Cr2O3 composition as a novel refractory brick: use of Cr2O3 nanoparticles [J]. Boletín de La de Cerámica y Vidrio, 2017, 56(2): 83-89) used magnesia and dolomite as raw materials, added 0-3% of nano-Cr2O3, pressed them into shape at 50 MPa, and kept them at 1650 °C for 5 h to prepare magnesia-calcium refractory materials, and then detected their anti-hydration performance under constant temperature and humidity conditions. The results showed that: when adding 1.5% (w) of Cr2O3 nanoparticles by mass, the anti-hydration effect of the material was the best, and the hydration mass increase rate was 1.5%; this was mainly because the formation of CaCr2O4 and MgCr2O4 aggregates improved the density of the material, thereby enhancing the anti-hydration performance of the material; but due to Cr 6+The pollution to the environment has been reduced in use at present. Therefore, it is worthy of in-depth research how to improve the anti-hydration performance of magnesia-calcia refractory materials in an energy-saving and environmental-friendly way without affecting the high-temperature performance of the materials. Summary of the Invention

[0004] To overcome the above-mentioned defects existing in the prior art, the present invention uses dolomite powder and magnesium source powder as the inner core and the outer shell respectively. The dolomite powder is granulated in a granulator to form uniform inner core particles with a certain strength; then the magnesium source powder is uniformly adhered to form a precursor with a double-layer structure, and after high-temperature sintering in an electric resistance furnace, magnesia-calcia refractory aggregates with good performance are obtained; the raw materials of this technical solution are easy to obtain, the process is economical and simple, the product has strong anti-hydration property, and has great market competitiveness.

[0005] To achieve the above-mentioned invention purpose, the present invention provides a preparation method of magnesia-calcia refractory aggregates with a core-shell structure, and the method comprises the following steps:

[0006] ① Placing the dolomite powder in a granulator for granulation, and spraying during the granulation process to form inner core particles;

[0007] ② Then adding the magnesium source powder into the granulator, so that the magnesium source powder is uniformly adhered to the inner core particles to form precursor particles with a double-layer structure;

[0008] ③ Placing the precursor particles obtained in step ② in a drying oven for drying;

[0009] ④ Placing the dried product obtained in step ③ in an electric resistance furnace for sintering to obtain magnesia-calcia refractory aggregates with a core-shell structure.

[0010] In the above technical solution, further, the mass content of the main component MgCa(CO3)2 in the dolomite powder in step ① is 80% - 99%.

[0011] Further, the rotation speed of the granulator in step ① is 10 - 100 rpm.

[0012] Further, the liquid selected for spraying in step ① is one of water and zirconium sol, the spraying flow rate is 10 - 100 ml / min, the mass of the spraying liquid is 5% - 15% of the mass of the inner core particles, and the solid content of the zirconium sol is 10% - 14%; when the inner core powder rolls in the granulator, atomized water or zirconium sol is sprayed onto its surface to form spheres.

[0013] Further, the diameter of the inner core particles obtained in step ① is 1 - 5 mm.

[0014] Further, the magnesium source powder in step ② is one of magnesium oxide, magnesium hydroxide, and magnesium carbonate.

[0015] Furthermore, the particle size of the magnesium source powder described in step ② is 0.1 - 100 μm.

[0016] Furthermore, the addition amount of the magnesium source powder described in step ② is controlled according to the mass ratio of the MgO content in the magnesium source powder to the MgCa(CO3)2 content in the dolomite powder, which is 5 - 30:100.

[0017] Furthermore, the drying temperature in step ③ is 110°C - 130°C, and the time is 11 - 13 h.

[0018] Furthermore, the sintering in step ④ is carried out by heating at a heating rate of 5°C / min to 1500°C - 1800°C and holding for 1.5 - 2.5 h.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] ① In the present invention, dolomite powder and magnesium source powder are used as the inner core and outer shell respectively. The dolomite powder is granulated in a granulator to form uniform core particles with a certain strength; then the magnesium source powder is uniformly adhered to form a precursor with a double-layer structure; and finally, a magnesium-calcium refractory aggregate with good performance is obtained after high-temperature sintering in an electric resistance furnace. Dolomite, magnesite (magnesium carbonate), brucite (magnesium hydroxide), etc. in this technical solution are all common raw materials in industrial production, with wide sources and easy availability, and there is no need to add expensive additives or special materials, thus significantly reducing the production cost and further improving the economy and feasibility of the process.

[0021] ② The present invention makes full use of natural mineral resources such as dolomite and magnesite, without the need to add additional chemical reagents or high-energy-consuming treatments, which conforms to the concept of energy conservation, emission reduction and green manufacturing. The core-shell structured magnesium-calcium refractory aggregate is prepared through three main steps: granulation, adhesion and high-temperature sintering, avoiding the high-purity magnesium oxide powder and complex forming processes required in the preparation of traditional magnesia-calcia materials, and realizing in-situ optimization of material properties through the core-shell structure design; its process flow is simple, easy to operate, does not require complex equipment or special conditions, has a short process, is easy to scale up production, and has high industrial promotion value.

[0022] ③The present invention solves the technical problem that the current magnesia-calcia refractory has poor anti-hydration performance and is prone to react with water in the air, resulting in powdering of the material. Through the design of the core-shell structure, the dolomite powder in the core forms dense core particles after granulation, with reduced pores and accelerated crystal growth rate; the magnesium source powder layer on the shell shrinks in volume at high temperature to form sintered magnesia. Its high density and high melting point endow it with excellent anti-hydration performance, high-temperature performance and slag erosion resistance. As a protective layer for magnesia-calcia refractories, it effectively isolates water in the air and the erosion of external substances, improves the anti-hydration performance of refractories, can significantly enhance the high-temperature strength of aggregates, enhance the durability of aggregates, and can be widely used in high-temperature industrial fields such as steel, cement, and glass, improving the service life and performance of refractories, and having high market competitiveness. Detailed implementation mode

[0023] The following further illustrates the present invention with specific embodiments, but does not limit the present invention in any way. To avoid repetition, in the following embodiments, raw materials are commercially available products without special instructions, and methods used are conventional methods without special instructions.

[0024] A preparation method of magnesia-calcia refractory aggregate with a core-shell structure, the method comprising the following steps:

[0025] ①Place the dolomite powder in a granulator for granulation, and spray during the granulation process to form core particles;

[0026] ②Then add the magnesium source powder to the granulator so that the magnesium source powder adheres uniformly to the core particles to form precursor particles with a double-layer structure;

[0027] ③Place the precursor particles obtained in step ② in a drying oven for drying;

[0028] ④Place the dried product obtained in step ③ in a resistance furnace for sintering to obtain magnesia-calcia refractory aggregate with a core-shell structure.

[0029] For matters not described in the following embodiments, they are the same as the description content of the above specific implementation mode.

[0030] Example 1

[0031] A preparation method of magnesia-calcia refractory aggregate with a core-shell structure, the method comprising the following steps:

[0032] ①Place the dolomite powder in a granulator for granulation, and spray during the granulation process to form core particles;

[0033] The mass content of the main component MgCa(CO3)2 in the dolomite powder is 80%, and the rotation speed of the granulator is 10 rpm. In step ①, the liquid selected for spraying is water, with a flow rate of 10 ml / min and a usage amount of 5% of the mass of the core powder. The diameter of the core particles obtained in step ① is 1 - 5 mm.

[0034] ② Then, add the magnesium source powder to the granulator so that the magnesium source powder adheres uniformly to the core particles to form precursor particles with a double-layer structure;

[0035] The magnesium source powder is magnesium oxide with a particle size of 0.1 μm; the addition amount of the magnesium source powder is controlled according to the mass ratio of MgO content in the magnesium source powder to MgCa(CO3)2 content in the dolomite powder of 5:100.

[0036] ③ Place the precursor particles obtained in step ② in an oven at 120 °C and dry for 12 h.

[0037] ④ Place the dried product obtained in step ③ in a resistance furnace for sintering, heat it to 1500 °C at a heating rate of 5 °C / min, and hold for 2.5 h to obtain magnesium-calcium refractory aggregate with a core-shell structure.

[0038] The magnesium-calcium refractory aggregate sample with a core-shell structure prepared in Example 1 was placed in a constant temperature and humidity chamber at a temperature of 25 °C and a humidity of 80% for 24 h, and the weight gain rate of the aggregate was measured to be less than 1%, indicating that the magnesium-calcium refractory material has excellent anti-hydration performance.

[0039] Example 2

[0040] A preparation method of magnesium-calcium refractory aggregate with a core-shell structure, the method comprising the following steps:

[0041] ① Place the dolomite powder in a granulator for granulation, and spray during the granulation process to form core particles;

[0042] The mass content of the main component MgCa(CO3)2 in the dolomite powder is 99%, and the rotation speed of the granulator is 100 rpm. In step ①, the liquid selected for spraying is zirconia sol with a solid content of 10%, the flow rate is 100 ml / min, and the mass is 15% of the mass of the core powder. The diameter of the core particles obtained in step ① is 1 - 5 mm.

[0043] ② Then, add the magnesium source powder to the granulator so that the magnesium source powder adheres uniformly to the core particles to form precursor particles with a double-layer structure;

[0044] The magnesium source powder is magnesium hydroxide (brucite powder), and the particle size of the magnesium source powder is 0.1 μm; the addition amount of the magnesium source powder is controlled according to the mass ratio of MgO content in the magnesium source powder to MgCa(CO3)2 content in the dolomite powder of 30:100.

[0045] ③ Place the precursor particles obtained in step ② in a drying oven at 110 °C and dry for 13 h.

[0046] ④ Place the dried product obtained in step ③ in a resistance furnace for sintering, heat it up to 1800 °C at a heating rate of 5 °C / min, and hold for 1.5 h to obtain magnesium-calcium refractory aggregate with a core-shell structure.

[0047] The magnesium-calcium refractory aggregate sample with a core-shell structure prepared in Example 2 was placed in a thermostatic and humidistatic chamber at a temperature of 25 °C and a humidity of 80% for 24 h. The measured weight gain rate of the aggregate was less than 1%, indicating that the magnesium-calcium refractory material has excellent anti-hydration performance.

[0048] Example 3

[0049] A preparation method of magnesium-calcium refractory aggregate with a core-shell structure, the method comprising the following steps:

[0050] ① Place the dolomite powder in a granulator for granulation, spray during the granulation process to form core particles;

[0051] The mass content of the main component MgCa(CO3)2 in the dolomite powder is 90%, and the rotation speed of the granulator is 60 rpm. The liquid selected for spraying in step ① is zirconium sol with a solid content of 14%, the spraying flow rate is 100 ml / min, and the mass is 15% of the mass of the core powder. The diameter of the core particles obtained in step ① is 1 - 5 mm.

[0052] ② Then add the magnesium source powder to the granulator so that the magnesium source powder adheres uniformly to the core particles to form a precursor with a double-layer structure;

[0053] The magnesium source powder is magnesium carbonate (magnesite powder), and the particle size of the magnesium source powder is 50 μm; the addition amount of the magnesium source powder is controlled according to the mass ratio of the MgO content in the magnesium source powder to the MgCa(CO3)2 content in the dolomite powder of 20:100.

[0054] ③ Place the precursor particles obtained in step ② in a drying oven at 130 °C and dry for 11 h.

[0055] ④ Place the dried product obtained in step ③ in a resistance furnace for sintering, heat it up to 1650 °C at a heating rate of 5 °C / min, and hold for 2.0 h to obtain magnesium-calcium refractory aggregate with a core-shell structure.

[0056] The magnesium-calcium refractory aggregate sample with a core-shell structure prepared in Example 3 was placed in a thermostatic and humidistatic chamber at a temperature of 25 °C and a humidity of 80% for 24 h. The measured weight gain rate of the aggregate was less than 1%, indicating that the magnesium-calcium refractory material has excellent anti-hydration performance.

[0057] For any person skilled in the art, without departing from the scope of the technical solution of the present invention, many possible changes and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or it can be modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A preparation method of a magnesium-calcium refractory aggregate with a core-shell structure, characterized in that, The method includes the following steps: ① Place the dolomite powder in a granulator for granulation, and spray during the granulation process to form core particles; ② Then add the magnesium source powder to the granulator so that the magnesium source powder uniformly adheres to the core particles to form precursor particles with a double-layer structure; ③ Dry the precursor particles obtained in step ②; ④ Sinter the dried product obtained in step ③ to obtain magnesium-calcium refractory aggregates with a core-shell structure.

2. The preparation method according to claim 1, wherein The mass content of the main component MgCa(CO3)2 in the dolomite powder described in step ① is 80% to 99%.

3. The preparation method according to claim 1, characterized in that, The rotation speed of the granulator described in step ① is 10 to 100 rpm.

4. The preparation method according to claim 1, characterized in that, The liquid selected for spraying in step ① is one of water and zirconium sol. The spraying flow rate is 10 to 100 ml / min, the mass of the spraying liquid is 5% to 15% of the mass of the core particles, and the solid content of the zirconium sol is 10% to 14%.

5. The preparation method according to claim 1, characterized in that, The diameter of the core particles obtained in step ① is 1 to 5 mm.

6. The preparation method according to claim 1, wherein The magnesium source powder described in step ② is one of magnesium oxide, magnesium hydroxide, and magnesium carbonate.

7. The preparation method according to claim 1, wherein The particle size of the magnesium source powder described in step ② is 0.1 to 100 μm.

8. The preparation method according to claim 1, characterized in that, The addition amount of the magnesium source powder described in step ② is controlled according to the mass ratio of the MgO content in the magnesium source powder to the MgCa(CO3)2 content in the dolomite powder of 5 to 30:

100.

9. The preparation method according to claim 1, characterized in that, The drying temperature in step ③ is 110°C to 130°C, and the drying time is 11 to 13 h.

10. The preparation method according to claim 1, characterized in that, In step ④, the sintering is carried out by heating at a heating rate of 5°C / min to 1500°C to 1800°C and holding for 1.5 to 2.5 h.