An alumina-based ceramic shell back layer paste added with graphene oxide and a preparation method thereof

Abstract

The application relates to the field of nickel-based single-crystal high-temperature alloy blade investment casting, in particular to an alumina-based ceramic shell back layer slurry added with graphene oxide and a preparation method thereof. The slurry comprises the following components in percentage by weight: 50-70% of 260-360-mesh white corundum powder, 20-45% of silica sol binder and 5-10% of graphene oxide aqueous solution. The method comprises the following steps: adding the binder into a batching bucket, continuously stirring, then adding the white corundum powder into the binder, continuously stirring until uniform; on the other hand, the graphene oxide aqueous solution is poured into another small batching bucket, after uniform stirring, the graphene oxide aqueous solution is added into the batching bucket of the back layer slurry, continuous stirring is carried out, deionized water is added to adjust the viscosity to a proper range, and the uniformly stirred slurry is used for shell back layer coating. The application can enhance the strength of the ceramic shell and improve the air permeability of the ceramic shell, and has the characteristics of slurry stability, easy operation and strong applicability.

Description

TECHNICAL FIELD

[0001] The application relates to the field of nickel-based single crystal superalloy blade investment casting, in particular to an alumina-based ceramic shell back layer slurry added with graphene oxide and a preparation method thereof. BACKGROUND

[0002] The investment casting process is widely applied to the casting field of high-temperature-resistant castings such as turbine blades of airplane engines and gas turbines. The preparation of a ceramic shell is a key link of the investment casting, and the strength, air permeability and other performances of the shell have an important influence on the yield of the castings. In the actual production process, the shell needs to have a high enough wet strength and bending strength of the sintered shell to ensure that the shell will not crack during the processes of handling, dewaxing, sintering and alloy pouring, thereby improving the yield of the shell and avoiding the influence of the cracking of the shell on the quality of the high-temperature alloy castings; in addition, the shell also needs a certain air permeability to prevent the formation of defects such as underfilling on the surface of the castings due to the difficulty of gas dissipation during the alloy pouring process.

[0003] At present, the addition of organic solvents is one of the main methods for improving the strength of the shell at home and abroad, but the volatilization and combustion of the organic solvents are easy to pollute the air and further harm the health of workers; in addition, the use of various types of organic fibers as additives can simultaneously play the roles of enhancing the strength of the shell and improving the air permeability of the shell, but the dispersion of the organic fibers in the shell slurry still needs to be improved. Therefore, it is of great significance for the investment casting technology to find suitable additives and prepare the shell slurry for the manufacture of ceramic shells with high strength and high air permeability. SUMMARY

[0004] In view of the above problems, the purpose of the present application is to provide an alumina-based ceramic shell back layer slurry added with graphene oxide and a preparation method thereof, so as to solve the problems of limited strength and air permeability of the ceramic shell at present, and to enhance the strength and improve the air permeability of the ceramic shell.

[0005] The present application is realized by the following technical solutions:

[0006] An alumina-based ceramic shell back layer slurry added with graphene oxide, according to mass percentage, the slurry comprises: 50-70wt% of 260-360 mesh white corundum powder, 20-45wt% of silica sol binder and 1-10wt% of graphene oxide aqueous solution.

[0007] The alumina-based ceramic shell back layer slurry added with graphene oxide, the white corundum powder is used as the back layer refractory material of the ceramic shell, and the alpha-alumina content of the electrically fused corundum powder is above 99.5wt%.

[0008] The graphene oxide added alumina-based ceramic shell back layer slurry, the aqueous graphene oxide solution is a multilayer aqueous graphene oxide solution, the content of graphene oxide is 2-10wt%, and the parameters of graphene oxide are: specific surface area 50-150m 2 / g, sheet diameter 5-50um, and thickness 1-10nm.

[0009] The graphene oxide added alumina-based ceramic shell back layer slurry, the silica sol binder is an aqueous silica sol, and the parameters of the aqueous silica sol are: silica content 26-31wt%, sodium oxide content not more than 0.5wt%, density 1.15-1.20g / cm 3 , room temperature viscosity not higher than 8Pa·s, and silica sol particle size 8-15nm.

[0010] The preparation method of the graphene oxide added alumina-based ceramic shell back layer slurry comprises the following preparation process:

[0011] Step one: the silica sol binder is added to a batching barrel, stirring is carried out at a speed of 280-320rpm, white corundum powder is gradually added to the silica sol binder, and stirring is continuously carried out at a speed of 180-220rpm for 24h, so that the white corundum powder is uniformly dispersed in the silica sol binder;

[0012] Step two: the aqueous graphene oxide solution is added to another batching barrel, stirring is continuously carried out at a speed of 380-420rpm for 1h, then the aqueous graphene oxide solution is gradually added to the batching barrel in which the white corundum powder and the silica sol binder are mixed, uniform stirring is carried out at a speed of 380-420rpm, then uniform stirring is continuously carried out at a speed of 180-220rpm for 24h, deionized water is added to adjust the slurry viscosity to 6-12Pa·s, and an alumina-based ceramic shell back layer slurry is formed, which is used for shell coating of the shell back layer.

[0013] The design idea of the present application is:

[0014] The ceramic shell needs sufficient bending strength and air permeability to meet the requirements of shell manufacturing and application. The addition of organic fiber filler can improve the wet strength of the shell before sintering, and at the same time, the organic fiber can be fully burned and residual holes can be left during the sintering process, thereby improving the air permeability of the shell. However, the organic fiber is difficult to uniformly disperse in the shell slurry, and even can be wound on the stirring rod of the slurry barrel, thereby hindering the operation of the stirring rod and causing serious hidden dangers to the production. Therefore, the present application adopts the method of adding aqueous graphene oxide dispersion to prepare the ceramic shell back layer slurry, which avoids the agglomeration of graphene oxide in the back layer slurry during long-term stirring, thereby ensuring the uniformity of the prepared shell composition, so as to prepare a ceramic shell with high strength and high air permeability.

[0015] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0016] 1) Oxidized graphene can be dispersed stably for a long time. Oxidized graphene is prepared from graphite powder by oxidation and exfoliation, and a large number of hydroxyl groups and carboxyl groups are left on the surface of the graphene due to the oxidation process, which can form hydrogen bonds with water, so that the graphene oxide can be dispersed in water. Therefore, by adding the aqueous dispersion of graphene oxide to the silica sol with water as the solvent, the long-term stable dispersion of graphene oxide can be achieved.

[0017] 2) The prepared ceramic shell has high bending strength. Oxidized graphene has the advantages of high Young's modulus and fracture toughness, which can inhibit the growth of microcracks in the wet shell, so the present application uses graphene oxide as a pore-forming additive for the back layer slurry of the alumina-based ceramic shell. When the shell is heated during the dewaxing process, the wax mold coated by the shell will expand, causing the shell to bear external pressure. At this time, the graphene oxide can disperse and bear part of the external pressure, thereby avoiding the cracking of the shell. In addition, during the sintering process of the ceramic shell, the graphene oxide will burn to form micropores, which can inhibit the continuous growth of cracks when the micropores are not parallel to the growth direction of the cracks, thereby improving the bending strength of the shell.

[0018] 3) Improve the air permeability of the ceramic shell. During the sintering process of the shell, the graphene oxide will be fully burned, and the remaining pores can enhance the air permeability of the shell. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figures 1-2 The bending strength test sample of the ceramic shell prepared by the ceramic shell back layer slurry. Among them, Figure 1 is the ceramic shell back layer slurry using the existing ceramic shell back layer slurry, Figure 2 is the ceramic shell back layer slurry using the ceramic shell back layer slurry of the present application.

[0020] Figures 3-4 The bending strength test results of the ceramic shell prepared by the ceramic shell back layer slurry. Among them, Figure 3 is the ceramic shell back layer slurry using the existing ceramic shell back layer slurry, Figure 4 is the ceramic shell back layer slurry using the ceramic shell back layer slurry of the present application. DETAILED DESCRIPTION

[0021] In the specific implementation process, the application provides an alumina-based ceramic shell back layer slurry added with graphene oxide and a preparation method thereof. The slurry comprises 50-70 wt% of 260-360 mesh white corundum powder, 20-45 wt% of silica sol binder and 5-10 wt% of graphene oxide aqueous solution. The method comprises the following steps: adding the binder into a batching bucket, continuously stirring, then adding the white corundum powder into the binder, continuously stirring until uniform; on the other hand, pouring the graphene oxide aqueous solution into another small batching bucket, continuously stirring until uniform, then adding the graphene oxide aqueous solution into the batching bucket of the back layer slurry, continuously stirring, adding appropriate deionized water to adjust the viscosity to a suitable range, and using the uniformly stirred slurry for shell back layer coating.

[0022] In the following, the application is further described in detail in combination with the drawings and specific embodiments.

[0023] Embodiment 1

[0024] In this embodiment, the preparation method of the ceramic shell back layer slurry added with graphene oxide comprises the following steps:

[0025] (1) adding 34 wt% of the total mass of silica sol binder into a batching bucket according to the mass percentage, continuously stirring at a speed of 300 rpm, gradually adding 65 wt% of the total mass of 320 mesh white corundum powder (the content of α-alumina is more than 99.5 wt%) into the silica sol binder, then continuously stirring at a speed of 200 rpm for 24 h until the white corundum powder is uniformly dispersed. The silica sol binder is aqueous silica sol, and the parameters are as follows: the content of silicon oxide is 26-31 wt%, the content of sodium oxide is not more than 0.5 wt%, the density is 1.18-1.20 g / cm 3 , the viscosity at room temperature is not higher than 8 Pa·s, and the particle size of the silica sol is 8-15 nm.

[0026] (2) preparing 8 wt% of the concentration of graphene oxide aqueous solution, pouring into another small batching bucket, continuously stirring at a speed of 400 rpm until uniform; the parameters of the graphene oxide are as follows: the specific surface area is 50-150 m 2 / g, and the thickness is 1-4 nm.

[0027] (3) then, taking 1 wt% of the total mass of graphene oxide aqueous solution, gradually adding into the batching bucket of the mixed white corundum and silica sol binder, initially stirring uniformly at a speed of 400 rpm, then reducing the speed to 200 rpm and continuously stirring for 24 h, measuring the viscosity of the slurry and adding deionized water to adjust the viscosity to 8 Pa·s, forming the alumina-based ceramic shell back layer slurry, and using the uniformly stirred slurry for shell back layer coating.

[0028] Embodiment 2

[0029] A ceramic shell back layer slurry with graphene oxide added was prepared according to the method described in Example 1, and an alumina-based ceramic shell without graphene oxide added was prepared as a control sample. The ceramic shell back layer slurry without graphene oxide added included, by mass percentage: white corundum powder 65wt%, silica sol 35wt%, and other conditions were the same as in Example 1. Ceramic shell samples were prepared using the two slurries described above for flexural strength testing. Figures 1-2 ).

[0030] As shown in Table 1, the test results show that, without graphene oxide added, the wet green strength and sintered strength of the ceramic shell were 3.03 MPa and 11.58 MPa, respectively, while the wet green strength and sintered strength of the ceramic shell with graphene oxide added were increased to 5.12 MPa and 13.51 MPa, respectively. Figures 3-4 Example 3

[0031] In this example, a method for preparing a ceramic shell back layer slurry with graphene oxide added was as follows:

[0032] (1) A total mass of 42wt% silica sol binder was added to a mixing bucket, and the total mass of 55wt% 320 mesh white corundum powder (alpha-alumina content of 99.5wt% or more) was gradually added to the silica sol binder under continuous stirring at a speed of 300 rpm; then, the white corundum powder was uniformly dispersed under continuous stirring at a speed of 200 rpm for 24h.

[0033] (2) A 4wt% graphene oxide aqueous solution was prepared and poured into another small mixing bucket, and was stirred uniformly at a speed of 400 rpm.

[0034] (3) Then, a total mass of 3wt% graphene oxide aqueous solution was gradually added to the mixing bucket of the white corundum and silica sol binder mixture, and was initially stirred uniformly at a speed of 400 rpm, and then was continuously stirred at a speed of 200 rpm for 24h. The viscosity of the slurry was measured and deionized water was added to adjust the viscosity to 6Pa·s, forming an alumina-based ceramic shell back layer slurry. The uniformly stirred slurry was used for coating the back layer of the shell.

[0035] In this example, the wet green strength and sintered strength of the ceramic shell with graphene oxide added were increased to 5.98 MPa and 12.19 MPa, respectively.

[0036] Example 4

[0037] In this example, a method for preparing a ceramic shell back layer slurry with graphene oxide added was as follows:

[0038]

[0039] ​(1) Add 27wt% of silica sol binder in total mass to a batching barrel, continuously stir at a rotation speed of 300rpm, and gradually add 69wt% of 320 mesh white corundum powder (α-alumina content is above 99.5wt%) in total mass to the silica sol binder; then continuously stir at a rotation speed of 200rpm for 24h until the white corundum powder is uniformly dispersed.

[0040] (2) Pour the 10wt% graphene oxide aqueous solution into another small batching barrel, and continuously stir at a rotation speed of 400rpm until uniform.

[0041] (3) Then, gradually add 4wt% of the graphene oxide aqueous solution in total mass to the white corundum and silica sol binder mixed batching barrel, initially stir at a rotation speed of 400rpm until uniform, then reduce the rotation speed to 200rpm and continuously stir for 24h, measure the viscosity of the slurry and add deionized water to adjust the viscosity to 10Pa·s, form the alumina-based ceramic shell back layer slurry, and use the uniformly stirred slurry for the coating of the shell back layer.

[0042] In this embodiment, the wet green strength and sintering strength of the ceramic shell with added graphene oxide are increased to 3.72MPa and 13.38MPa, respectively.

[0043] The results of the embodiment show that the addition of graphene oxide in the ceramic shell back layer slurry can improve the strength of the shell, thereby avoiding the problem of shell swelling or cracking during handling, dewaxing, pouring, etc., which leads to the shell being scrapped, and the slurry is stable, easy to operate, and has strong applicability.

[0044] Those skilled in the art will readily understand that the above description is only an embodiment of the present application and is not intended to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A slurry for an alumina-based ceramic shell backing layer with added graphene oxide, characterized in that, By weight percentage, the slurry comprises: 50-70 wt% 260-360 mesh white corundum powder, 20-45 wt% silica sol binder, and 1-10 wt% aqueous solution of graphene oxide, for investment casting of nickel-based single crystal superalloy blades. The graphene oxide aqueous solution is an aqueous solution of multilayer graphene oxide. Graphene oxide is prepared by oxidation and exfoliation of graphite powder. The surface of the graphene oxide contains residual hydroxyl and carboxyl groups from the oxidation process, which can form hydrogen bonds with water, allowing the graphene oxide to disperse in water. Adding the graphene oxide aqueous dispersion to a silica sol using water as a solvent achieves long-term stable dispersion of the graphene oxide. The graphene oxide content is 2–10 wt%, and the parameters of the graphene oxide are: specific surface area 50–150 m² / g. 2 / g, sheet diameter 5~50μm, thickness 1~10nm; White corundum powder, used as a ceramic-type shell backing refractory material, employs fused corundum powder with an α-alumina content of over 99.5 wt%. The preparation method of the alumina-based ceramic shell backing slurry with added graphene oxide includes the following preparation process: Step 1: Add the silica sol binder to the mixing tank and stir at a speed of 280-320 rpm. Gradually add the white fused alumina powder to the silica sol binder and continue stirring at a speed of 180-220 rpm for 24 hours to ensure that the white fused alumina powder is evenly dispersed in the silica sol binder. Step 2: Add the graphene oxide aqueous solution to another mixing tank and stir continuously at 380-420 rpm for 1 hour. Then, gradually add the graphene oxide aqueous solution to the mixing tank containing white corundum powder and silica sol binder. Stir evenly at 380-420 rpm and continue stirring at 180-220 rpm for 24 hours. Add deionized water to adjust the slurry viscosity to 6-12 Pa·s to form an alumina-based ceramic shell backing slurry, which is used for coating the shell backing layer.

2. The alumina-based ceramic shell backing slurry with added graphene oxide according to claim 1, characterized in that, The silica sol binder is an aqueous silica sol with the following parameters: silica content 26–31 wt%, sodium oxide content not exceeding 0.5 wt%, and density 1.15–1.20 g / cm³. 3 The viscosity at room temperature is not higher than 8 Pa·s, and the particle size of the silica sol is 8–15 nm.

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