A composite crystal sand powder and a preparation method thereof

Abstract

This application relates to the technical field of casting shell-making materials, and specifically discloses a composite crystal sand powder and a preparation method thereof. A preparation method of a composite crystal sand powder includes the following steps: 1) Separating and purifying bauxite to obtain refined bauxite; 2) Mixing carrageenan and tetrabutylphosphonium hydroxide evenly, drying, performing a first calcination treatment, and then grinding to obtain a first calcined material; mixing and grinding aluminum powder, silicon powder, and the first calcined material, and then performing a second calcination treatment under vacuum and grinding to obtain a second calcined material; 3) Mixing the refined bauxite, the second calcined material, and a multi-metal doping material evenly, and then adding a modifier and grinding to obtain the product; the multi-metal doping material is composed of at least two of nano titanium oxide, nano ferrite, nano zirconium oxide, and nano zinc oxide. The composite crystal sand powder prepared in this application has the advantages of a low linear expansion coefficient, a high true porosity after sintering, high slag erosion resistance, and high thermal shock resistance.

Description

Technical Field

[0001] This application relates to the technical field of casting shell-making materials, and more specifically, to a composite crystal sand powder and a preparation method thereof. Background Art

[0002] Composite crystal sand powder is a material widely used in the field of precision casting. It uses bauxite as the base material, undergoes chemical purification, and is then synthesized with other materials. It has good high-temperature stability, is not likely to react with alloy solutions during the casting process, and will not affect the metal composition and morphology of the casting surface. Currently, in some high-end precision casting fields, composite crystal sand powder has gradually replaced other shell-making materials such as zircon sand.

[0003] For example, the Chinese patent application document with the publication number CN108356210A discloses a new composite crystal sand powder shell-making material and its production process, including the following components: Al2O3≥80%, SiO2≤18%, Fe2O3≤0.06%, formulation agent≤0.1%. It is applicable to all metal castings and their alloy castings with a pouring temperature below 1750°C, such as high manganese steel, low-carbon stainless steel, high-temperature alloy steel, and titanium alloy. It can effectively increase the pouring temperature, ensure the easy handling and placement of materials used in the factory, and can increase the relative mechanical strength of the poured castings and significantly reduce production costs.

[0004] Another example is the Chinese patent application document with the publication number CN103030409A, which discloses a spherical α-aluminum oxide for investment casting shell-making materials and its preparation method. The spherical α-aluminum oxide has the following characteristics: the particle shape is round and the sphericity≥0.9; the content of α-Al2O3≥99%; the refractoriness is high, ≥1960°C. Using non-spherical industrial alumina with a loose structure and subjecting it to high-temperature flame melting and spheroidization to obtain dense spherical α-aluminum oxide. The performance characteristics of spherical α-aluminum oxide are: round particle shape, small thermal expansion, high thermal stability and thermal shock stability, good high-temperature chemical stability, and high refractoriness. Using spherical α-aluminum oxide as an investment casting shell-making material brings the following beneficial effects to the casting: improved shell mold collapsibility and smooth casting surface. Although the effect of spherical α-aluminum oxide is very good, its air permeability is poor, and it will lead to a relatively high production cost of the shell-making material.

[0005] In addition to high-temperature stability, the shell-making materials for precision casting also require good air permeability, creep resistance, and low linear expansion coefficient. The comprehensive performance of traditional composite crystal sand powder has certain advantages compared with zircon sand or zircon powder. However, in the face of the continuously developing precision casting industry, its deficiencies are gradually emerging. How to further improve the performance of composite crystal sand powder is an urgent problem to be solved in the future. Summary of the Invention

[0006] In order to further improve the comprehensive application performance of polycrystalline sand powder in precision casting, the present application provides a polycrystalline sand powder and a preparation method thereof.

[0007] In the first aspect, the present application provides a preparation method of polycrystalline sand powder, adopting the following technical scheme:

[0008] A preparation method of polycrystalline sand powder, comprising the following steps:

[0009] 1) Separate and purify bauxite to obtain refined bauxite;

[0010] 2) Take carrageenan and tetrabutylphosphonium hydroxide, mix them evenly, dry them, then perform a first calcination treatment, and then grind to obtain a first calcined material; mix and grind aluminum powder, silicon powder, and the first calcined material, and then perform a second calcination treatment under vacuum, and grind to obtain a second calcined material;

[0011] 3) Take refined bauxite, the second calcined material, and a multi-metal doping material, mix them evenly, and then add a modifier and grind to obtain it; the multi-metal doping material is composed of at least two of nano-titanium oxide, nano-ferrite, nano-zirconium oxide, and nano-zinc oxide.

[0012] Preferably, in the step 1), it further includes at least one of the following technical features:

[0013] 11) The separation and purification include acid leaching and crystallization;

[0014] 12) In the composition of the refined bauxite, Al2O3≥82%, SiO2≤15%.

[0015] Preferably, in the step 2), it further includes at least one of the following technical features:

[0016] 21) The mass ratio of carrageenan to tetrabutylphosphonium hydroxide is 1:(0.15 - 0.2);

[0017] 22) The first calcination treatment is to first calcine at a temperature of 1000 - 1100°C for 15 - 30 min, and then calcine at a temperature of 700 - 850°C for 2 - 3.5 h;

[0018] 23) The mass ratio of aluminum powder, silicon powder, and the first calcined material is 1:(0.2 - 0.25):(0.8 - 1).

[0019] Preferably, in the step 3), the mass ratio of refined bauxite, the second calcined material, and the multi-metal doping material is 1:(0.1 - 0.15):(0.01 - 0.02).

[0020] Preferably, in the step 3), the modifier is prepared by the method of the following steps:

[0021] S1: Add triethanolamine to absolute ethanol. After mixing evenly, add calcium chloride and barium chloride, and homogenize to obtain a reaction solution.

[0022] S2: Pass excessive carbon dioxide into the reaction solution, then dry and grind to obtain the product.

[0023] Preferably, in step S1, the mass ratio of calcium chloride to barium chloride is 1:(0.35 - 0.5).

[0024] Preferably, the multi-metal doping material consists of nano-titanium oxide, nano-ferrite, and nano-zirconium oxide with a mass ratio of 1:0.3:0.75.

[0025] In a second aspect, the present application provides a composite crystal sand powder prepared by the above preparation method.

[0026] Preferably, the linear expansion coefficient of the composite crystal sand powder is ≤ 4.8×10 -6 / °C.

[0027] Preferably, the refractoriness of the composite crystal sand powder is > 1800°C.

[0028] In summary, the present application has the following beneficial effects:

[0029] 1. The present application selects bauxite as the initial raw material. After separation and purification, the composite crystal sand powder prepared by adding a second calcined material and a multi-metal doping material is a high-end precision casting shell-making material, which has a stable and consistent crystal structure, a large elastic modulus, a high decomposition temperature, good high-temperature thermochemical stability, and a small high-temperature creep. Moreover, the composite crystal sand powder of the present application also has a low linear expansion coefficient, a high true porosity after sintering, a high slag erosion resistance, and a high thermal shock resistance.

[0030] 2. In the present application, carrageenan and tetrabutylphosphonium hydroxide are mixed and then calcined to obtain a carbon precursor with sulfur defects and phosphorus defects. Then, it is mixed with aluminum powder and silicon powder and vacuum calcined. Aluminum atoms and silicon atoms form a carbon-silicon-aluminum composite material in the carbon precursor. And during the calcination process, the sulfur defects and phosphorus defects in the carbon precursor play a certain catalytic role, regulating and promoting the formation of the carbon-silicon-aluminum composite material. When the second calcined material is used in combination with bauxite, it can improve the heat dissipation and air permeability of the mold shell after sintering, and at the same time block the oxidation effect, making it difficult for the surface of the casting to produce pitting, black spots and other defects.

[0031] 3. Based on refined bauxite and the second calcined material, this application also adds a multi-metal doping material and a modifier. The multi-metal doping material can cause the migration of metal atoms during the mold shell sintering and casting processes, form infiltration doping on the surface of the composite crystal sand powder, cause lattice distortion, form a more stable crystal structure, have a stronger ability to block the oxidation of the casting surface, improve the thermal shock resistance and slag erosion resistance, and at the same time have better air permeability, and it is not easy to have pores on the casting surface. The modifier of this application uses calcium chloride and barium chloride as template agents, and forms an inorganic cross-linking body of calcium carbonate and barium carbonate under the action of first capping and then decapping with triethylamine. During the casting process, it can form crystal epitaxial growth on the surface of the composite crystal sand powder, improve the stability of the crystal structure during the casting process, and the true porosity of the refractory layer formed during the sintering process is high, improving the air permeability of the mold shell, which is beneficial to the disintegration and sand cleaning of the mold shell after pouring. Description of the Drawings

[0032] Figure 1 It is the XRD pattern of the composite crystal sand powder of Examples 1-3 of this application.

[0033] Figure 2 It is the XRD pattern of the composite crystal sand powder of Comparative Examples 1-3 of this application.

[0034] Figure 3 It is a schematic diagram of the true porosity of the refractory layer of the composite crystal sand powder mold shell of Examples 1-3 and Comparative Examples 1-3 of this application.

[0035] Figure 4 It is a schematic diagram of the linear expansion coefficient of the refractory layer of the composite crystal sand powder mold shell of Examples 1-3 and Comparative Examples 1-3 of this application.

[0036] Figure 5 It is the SEM image of the surface of the casting of Example 3.

[0037] Figure 6 It is the microscopic image of the cross-section of the casting of Example 3. Detailed Description of the Embodiments

[0038] The following further describes this application in detail with reference to the embodiments.

[0039] The raw materials of the examples and comparative examples of this application are all ordinary commercially available except as otherwise specified.

[0040] This application provides a composite crystal sand powder and its preparation method. The composite crystal sand powder prepared by this application can be used for all metal castings and their alloy castings with a pouring temperature below 1750 °C, such as high manganese steel, low-carbon stainless steel, high-temperature alloy steel, titanium alloy, etc.

[0041] The preparation method of the composite crystal sand powder of this application includes the following steps:

[0042] 1) Separate and purify bauxite to obtain refined bauxite;

[0043] 2) Mix carrageenan and tetrabutylphosphonium hydroxide evenly, dry them, and then conduct a first calcination treatment, and then grind to obtain the first calcined material; mix and grind aluminum powder, silicon powder, and the first calcined material, and then conduct a second calcination treatment under vacuum, and grind to obtain the second calcined material;

[0044] 3) Take refined bauxite, the second calcined material, and the multi-metal doping material and mix them evenly, and then add a modifier and grind to obtain it; the multi-metal doping material is composed of at least two of nano titanium oxide, nano ferrite, nano zirconium oxide, and nano zinc oxide.

[0045] In step 2) of the preparation method of the composite crystal sand powder of the present application, the mass ratio of carrageenan to tetrabutylphosphonium hydroxide is 1:1:(0.15 - 0.2). In some specific embodiments, the mass ratio of carrageenan to tetrabutylphosphonium hydroxide is 1:0.15, 1:0.155, 1:0.16, 1:0.165, 1:0.17, 1:0.175, 1:0.18, 1:0.185, 1:0.19, 1:0.195, 1:0.2.

[0046] In step 2) of the preparation method of the composite crystal sand powder of the present application, the first calcination treatment is to first calcine at a temperature of 1000 - 1100 °C for 15 - 30 min, and then calcine at a temperature of 700 - 850 °C for 2 - 5 h. In some specific embodiments, the first calcination treatment is to first calcine at a temperature of 1000 °C, 1030 °C, 1050 °C, 1100 °C for 15 min, 20 min, 25 min, 30 min, and then calcine at a temperature of 700 °C, 750 °C, 800 °C, 850 °C for 2 h, 2.5 h, 3 h, 3.5 h.

[0047] In step 2) of the preparation method of the composite crystal sand powder of the present application, the mass ratio of aluminum powder, silicon powder, and the first calcined material is 1:(0.2 - 0.25):(0.8 - 1). In some specific embodiments, the mass ratio of aluminum powder, silicon powder, and the first calcined material is 1:0.2:0.8, 1:0.22:0.8, 1:0.24:0.8, 1:0.2:0.85, 1:0.2:0.9, 1:0.2:0.95, 1:0.2:0.85, 1:0.22:0.85, 1:0.24:0.85, 1:0.22:0.9, 1:0.24:0.9, 1:0.22:0.95, 1:0.24:0.95, 1:0.25:1.

[0048] In step 2) of the preparation method of the polycrystalline sand powder of the present application, the average particle size of the first calcined material is 50 - 200 μm, and the average particle size of the second calcined material is 200 - 500 μm. Optionally, the average particle size of the first calcined material is 50 - 100 μm, 100 - 150 μm, or 150 - 200 μm, etc. Optionally, the average particle size of the second calcined material is 200 - 300 μm, 300 - 400 μm, or 400 - 500 μm, etc. In some specific embodiments, the average particle size of the first calcined material can be 50 μm, 100 μm, 150 μm, 200 μm, and the average particle size of the second calcined material can be 200 μm, 300 μm, 400 μm, 500 μm.

[0049] In step 3) of the preparation method of the polycrystalline sand powder of the present application, the mass ratio of the refined bauxite, the second calcined material, and the multi-metal doping material is 1:(0.1 - 0.15):(0.01 - 0.02). In some specific embodiments, the mass ratio of the refined bauxite, the second calcined material, and the multi-metal doping material is 1:0.12:0.01, 1:0.135:0.01, 1:0.15:0.01, 1:0.15:0.01, 1:0.15:0.015, 1:0.15:0.02, 1:0.13:0.01, 1:0.13:0.015, 1:0.13:0.02.

[0050] In step 3) of the preparation method of the polycrystalline sand powder of the present application, the addition amount of the modifier is 0.2 - 0.5% of the mass of the refined bauxite. In some specific embodiments, the addition amount of the modifier is 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5% of the mass of the refined bauxite.

[0051] In step S1 of the present application, the mass ratio of calcium chloride to barium chloride is 1:(0.35 - 0.5). In some specific embodiments, the mass ratio of calcium chloride to barium chloride can be 1:0.35, 1:0.4, 1:0.45, 1:0.5.

[0052] Example 1

[0053] The preparation method of the polycrystalline sand powder of this example includes the following steps:

[0054] 1) Add bauxite into a centrifuge, then add dilute sulfuric acid and hydroxyproline, stir and impregnate, then perform centrifugal solid-liquid separation to obtain a centrifugate, then neutralize, concentrate and crystallize the centrifugate, wash the crystallized product, and dry it to obtain refined bauxite;

[0055] 2) Add carrageenan and tetrabutylphosphonium hydroxide into the stirring kettle, mix them evenly, dry and then conduct a first-stage calcination treatment at a temperature of 1000 °C for 1 h; then grind in a ball mill to obtain a first calcined material with an average particle size of 200 μm; mix and grind aluminum powder, silicon powder and the first calcined material according to a mass ratio of 1:0.22:0.85, and then conduct a second-stage calcination treatment in a vacuum calcination furnace at a calcination temperature of 1550 °C for 2 h, and grind to obtain a second calcined material with an average particle size of 500 μm;

[0056] 3) Add refined bauxite, the second calcined material and the multi-metal doping material into the ball mill, mix them evenly and then add a modifier and grind to obtain the product.

[0057] Among them, the addition amount of hydroxyproline is 0.5% of the mass of bauxite. The mass ratio of carrageenan to tetrabutylphosphonium hydroxide is 1:0.175. In the composition of refined bauxite, Al2O3 ≥ 82% and SiO2 ≤ 15%. The mass ratio of refined bauxite, the second calcined material and the multi-metal doping material is 1:0.1:0.02. The multi-metal doping material is composed of nano-titanium oxide and nano-ferrite according to a mass ratio of 1:2. The modifier is nano-calcium carbonate, and the addition amount of the modifier is 0.5% of the mass of refined bauxite.

[0058] The composite crystal sand powder of this example is prepared by the above preparation method. The linear expansion coefficient of the composite crystal sand powder ≤ 4.8×10 -6 / °C, and the refractoriness of the composite crystal sand powder > 1800 °C.

[0059] Example 2

[0060] The preparation method of the composite crystal sand powder of this example includes the following steps:

[0061] 1) Add bauxite into a centrifuge, then add dilute sulfuric acid and hydroxyproline, stir and impregnate, then conduct centrifugal solid-liquid separation to obtain a centrifugate, then neutralize, concentrate and crystallize the centrifugate, wash the crystallized product, and dry to obtain refined bauxite;

[0062] 2) Add carrageenan and tetrabutylphosphonium hydroxide into the stirring kettle, mix them evenly, dry and first conduct calcination at a temperature of 1100 °C for 15 min, and then conduct calcination at a temperature of 850 °C for 2 h; then grind in a ball mill to obtain a first calcined material with an average particle size of 50 μm; mix and grind aluminum powder, silicon powder and the first calcined material according to a mass ratio of 1:0.22:0.85, and then conduct a second-stage calcination treatment in a vacuum calcination furnace at a calcination temperature of 1550 °C for 2 h, and grind to obtain a second calcined material with an average particle size of 200 μm;

[0063] 3) Add refined bauxite, the second calcined material and the multi-metal doping material into the ball mill, mix them evenly and then add a modifier and grind to obtain the product.

[0064] The modifier of this embodiment is prepared by the following method:

[0065] S1: Add absolute ethanol into a beaker, add triethanolamine while stirring continuously. The volume ratio of absolute ethanol to triethanolamine is 3:1. After mixing evenly, add calcium chloride until it is saturated and dissolved, and then add barium chloride. After homogenization, a reaction solution is prepared;

[0066] S2: Pass excessive carbon dioxide into the reaction solution, then dry to remove and recover waste ethanol and triethanolamine, and obtain the product after grinding.

[0067] Among them, the addition amount of hydroxyproline is 0.5% of the mass of bauxite. The mass ratio of carrageenan to tetrabutylphosphonium hydroxide is 1:0.175. In the composition of refined bauxite, Al2O3≥82%, SiO2≤15%. The mass ratio of refined bauxite, the second calcined material, and the multi-metal doping material is 1:0.1:0.02. The multi-metal doping material is composed of nano-titanium oxide, nano-ferrite, and nano-zirconia with a mass ratio of 1:0.3:0.75. The mass ratio of calcium chloride to barium chloride is 1:0.5. The addition amount of the modifier is 0.2% of the mass of refined bauxite.

[0068] The polycrystalline sand powder of this embodiment is prepared by the above preparation method. The linear expansion coefficient of the polycrystalline sand powder ≤4.8*10 -6 / °C, and the refractoriness of the polycrystalline sand powder >1800°C.

[0069] Example 3

[0070] The preparation method of the polycrystalline sand powder of this embodiment includes the following steps:

[0071] 1) Add bauxite into a centrifuge, then add dilute sulfuric acid and hydroxyproline. After stirring and impregnating, perform centrifugal solid-liquid separation to obtain a centrifugate. Then neutralize, concentrate and crystallize the centrifugate, wash the crystallized product, and obtain refined bauxite after drying;

[0072] 2) Add carrageenan and tetrabutylphosphonium hydroxide into a stirring kettle and mix evenly. After drying, first calcine at a temperature of 1000°C for 30 min, and then calcine at a temperature of 700°C for 3.5 h; then grind in a ball mill to obtain a first calcined material with an average particle size of 100 μm; Mix and grind aluminum powder, silicon powder, and the first calcined material according to a mass ratio of 1:0.22:0.85, and then perform two-stage calcination treatment in a vacuum calcination furnace at a calcination temperature of 1550°C and a calcination time of 2 h, and grind to obtain a second calcined material with an average particle size of 300 μm;

[0073] 3) Add refined bauxite, the second calcined material, and the multi-metal doping material into a ball mill, mix evenly, add the modifier, and grind to obtain the product.

[0074] The modifier of this embodiment is prepared by the following method:

[0075] S1: Add absolute ethanol into a beaker, add triethanolamine while stirring continuously. The volume ratio of absolute ethanol to triethanolamine is 3:1. After mixing evenly, add calcium chloride until it is saturated and dissolved, and then add barium chloride. After homogenization, a reaction solution is prepared.

[0076] S2: Pass excessive carbon dioxide into the reaction solution, then dry to remove and recover waste ethanol and triethanolamine, and obtain the product after grinding.

[0077] Among them, the addition amount of hydroxyproline is 0.5% of the mass of bauxite. The mass ratio of carrageenan to tetrabutylphosphonium hydroxide is 1:0.175. In the composition of refined bauxite, Al2O3 ≥ 82%, SiO2 ≤ 15%. The mass ratio of refined bauxite, the second calcined material, and the multi-metal doping material is 1:0.15:0.0l. The multi-metal doping material is composed of nano-titanium oxide, nano-ferrite, and nano-zirconium oxide with a mass ratio of 1:0.3:0.75. The mass ratio of calcium chloride to barium chloride is 1:0.35. The addition amount of the modifier is 0.5% of the mass of refined bauxite.

[0078] The polycrystalline sand powder of this embodiment is prepared by the above preparation method. The linear expansion coefficient of the polycrystalline sand powder ≤ 4.8×10 -6 / °C, and the refractoriness of the polycrystalline sand powder > 1800°C.

[0079] Comparative Example 1

[0080] The preparation method of the polycrystalline sand powder of this comparative example includes the following steps: Add refined bauxite and iron oxide into a ball mill, mix and grind, then melt at high temperature, and then cool, crush, and grind to obtain the product.

[0081] Among them, in the composition of refined bauxite, Al2O3 ≥ 82%, SiO2 ≤ 15%. The mass ratio of refined bauxite to iron oxide is 1:0.02.

[0082] The preparation method of the polycrystalline sand powder of this comparative example is obtained by the above preparation method.

[0083] Comparative Example 2

[0084] The preparation method of the polycrystalline sand powder of this comparative example includes the following steps:

[0085] 1) Add bauxite into a centrifuge, then add dilute sulfuric acid and hydroxyproline, stir and impregnate, then perform centrifugal solid-liquid separation to obtain a centrifugate, and then neutralize, concentrate and crystallize the centrifugate, wash the crystallized product, and dry to obtain refined bauxite.

[0086] 2) Mix and grind aluminum powder, silicon powder, and carbon powder according to a mass ratio of 1:0.22:0.85, and then conduct calcination treatment in a vacuum calcination furnace at a calcination temperature of 1550 °C for 2 h to obtain a calcined material with an average particle size of 300 μm after grinding;

[0087] 3) Add refined bauxite, the calcined material, and the multi-metal doping material into a ball mill. After mixing evenly, add a modifier and grind to obtain the product.

[0088] The modifier in this comparative example is prepared by the following method:

[0089] S1: Add absolute ethanol into a beaker, add triethanolamine while stirring continuously. The volume ratio of absolute ethanol to triethanolamine is 3:1. After mixing evenly, add calcium chloride until it is saturated and dissolved, and then add barium chloride. After homogenization, a reaction solution is prepared;

[0090] S2: Pass excessive carbon dioxide into the reaction solution, then dry to remove and recover waste ethanol and triethanolamine, and grind to obtain the product.

[0091] Among them, the addition amount of hydroxyproline is 0.5% of the mass of bauxite. The mass ratio of carrageenan to tetrabutylphosphonium hydroxide is 1:0.175. In the composition of refined bauxite, Al2O3 ≥ 82%, SiO2 ≤ 15%. The mass ratio of refined bauxite, the second calcined material, and the multi-metal doping material is 1:0.15:0.01. The multi-metal doping material is composed of nano-titanium oxide, nano-ferrite, and nano-zirconia with a mass ratio of 1:0.3:0.75. The mass ratio of calcium chloride to barium chloride is 1:0.35. The addition amount of the modifier is 0.5% of the mass of refined bauxite.

[0092] The composite crystal sand powder in this comparative example is prepared by the above preparation method.

[0093] Comparative Example 3

[0094] The preparation method of the composite crystal sand powder in this comparative example includes the following steps:

[0095] 1) Add bauxite into a centrifuge, then add dilute sulfuric acid and hydroxyproline, stir and impregnate, then centrifuge to separate the solid and liquid to obtain a centrifugate. Then neutralize, concentrate and crystallize the centrifugate, wash the crystals, and dry to obtain refined bauxite;

[0096] 2) Add carrageenan and tetrabutylphosphonium hydroxide into a stirring kettle and mix evenly. After drying, first calcine at a temperature of 1000 °C for 30 min, and then calcine at a temperature of 700 °C for 3.5 h; then grind in a ball mill to obtain a first calcined material with an average particle size of 100 μm;

[0097] 3) Add refined bauxite and the first calcined material into a ball mill. After mixing evenly, grind to obtain the product.

[0098] Among them, the addition amount of hydroxyproline is 0.5% of the mass of bauxite. The mass ratio of carrageenan to tetrabutylphosphonium hydroxide is 1:0.175. In the composition of refined bauxite, Al2O3 ≥ 82% and SiO2 ≤ 15%. The mass ratio of refined bauxite to the first calcined material is 1:0.15.

[0099] The composite crystal sand powder of this comparative example is prepared by the above preparation method.

[0100] Performance detection test

[0101] Take the composite crystal sand powder of Examples 1-3 and Comparative Examples 1-3 for XRD detection, and the test results are as Figure 1 and Figure 2 shown.

[0102] Take the composite crystal sand powder of Examples 1-3 and Comparative Examples 1-3 for casting tests. Among them, the surface layer material is the composite crystal sand powder, the powder-liquid ratio is 2.6:1, the viscosity is 38 ± 2 (s), the surface layer drying temperature is 23 ± 2 °C, and the drying time is 3 h. The shell baking temperature is 1150 ± 30 °C, the molten steel pouring temperature is 1100 °C, without covering the box, and the molten steel material is 430# stainless steel. According to GB / T2997-2015, detect the true porosity and linear expansion coefficient of the refractory layer of the mold shell during the casting process, and the test data are as Figure 3 and Figure 4 shown. The SEM image of the surface of the casting in Example 3 is as Figure 5 shown. The micrograph of the cross-section of the casting in Example 3 is as Figure 6 shown.

[0103] Analyze Examples 1-3 and Comparative Examples 1-3 and combine with Figures 1-5 It can be seen that the composite crystal sand powder of the present application has very good high-temperature thermochemical stability in precision casting applications, good heat dissipation and air permeability, and can effectively block oxidation under the condition of not covering the box. And under the same conditions, the dosage is small, the slag erosion resistance and thermal shock resistance are strong, the surface of the casting is smooth and beautiful, it is not easy to appear pits, pockmarks and black spots, and the product appearance and overall quality of the casting are very good.

[0104] This specific embodiment is only an explanation of the present application, and it is not a limitation of the present application. Those skilled in the art can make modifications without creative contributions to this embodiment according to needs after reading this specification, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A preparation method of composite crystal sand powder, characterized in that It includes the following steps: 1) Separate and purify bauxite to obtain refined bauxite; 2) Take carrageenan and tetrabutylphosphonium hydroxide, mix them evenly, dry them, and then perform a first calcination treatment, and then grind to obtain a first calcined material; mix and grind aluminum powder, silicon powder, and the first calcined material, and then perform a second calcination treatment under vacuum, and grind to obtain a second calcined material; the mass ratio of carrageenan to tetrabutylphosphonium hydroxide is 1:(0.15 - 0.2); the first calcination treatment is to first calcine at a temperature of 1000 - 1100 °C for 15 - 30 min, and then calcine at a temperature of 700 - 850 °C for 2 - 3.5 h; the mass ratio of aluminum powder, silicon powder, and the first calcined material is 1:(0.2 - 0.25):(0.8 - 1); 3) Take refined bauxite, the second calcined material, and a multi-metal doping material, mix them evenly, and then add a modifier and grind to obtain; the multi-metal doping material is composed of at least two of nano-titanium oxide, nano-ferrite, nano-zirconium oxide, and nano-zinc oxide; the mass ratio of refined bauxite, the second calcined material, and the multi-metal doping material is 1:(0.1 - 0.15):(0.01 - 0.02); the modifier is prepared by the following steps: S1: Add triethanolamine to absolute ethanol, mix evenly, then add calcium chloride and barium chloride, and homogenize to obtain a reaction solution; S2: Pass excessive carbon dioxide into the reaction solution, and then dry and grind to obtain.

2. The preparation method of the polycrystalline sand powder according to claim 1, characterized in that, In the step 1), it also includes at least one of the following technical features: 11) The separation and purification include acid leaching and crystallization; 12) In the composition of the refined bauxite, Al2O3 ≥ 82%, SiO2 ≤ 15%.

3. The preparation method of a polycrystalline abrasive powder according to claim 1, wherein, In the step S1, the mass ratio of calcium chloride to barium chloride is 1:(0.35 - 0.5).

4. A method for preparing polycrystalline sand powder according to claim 1, characterized in that, The multi-metal doping material is composed of nano-titanium oxide, nano-ferrite, and nano-zirconium oxide with a mass ratio of 1:0.3:0.

75.

5. A composite crystal sand powder, characterized in that, Prepared by the preparation method according to any one of claims 1 - 4.

6. A composite crystal sand powder according to claim 5, characterized in that, The linear expansion coefficient of the composite crystal sand powder ≤ 4.8×10 -6 / °C.

7. A composite crystal sand powder according to claim 5, characterized in that, The refractoriness of the composite crystal sand powder > 1800 °C.

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