Alumina-based ceramic shell back layer slurry added with graphene oxide and preparation method of alumina-based ceramic shell back layer slurry

Abstract

The invention relates to the field of investment casting of nickel-based single-crystal high-temperature alloy blades, in particular to alumina-based ceramic shell back layer slurry added with graphene oxide and a preparation method of the alumina-based ceramic shell back layer slurry. The slurry comprises 50 to 70 wt% of 260 to 360-mesh white corundum powder, 20 to 45 wt% of a silica sol binder and 5 to 10 wt% of a graphene oxide aqueous solution. The method comprises the following steps: adding a binder into a batching barrel, continuously stirring, then adding white corundum powder into the binder, and continuously stirring until the mixture is uniform; and on the other hand, the graphene oxide aqueous solution is poured into another small batching barrel and is continuously and uniformly stirred, then the graphene oxide aqueous solution is added into the batching barrel of the back layer slurry, stirring is continued, deionized water is added to adjust the viscosity to a proper range, and the uniformly stirred slurry is used for coating the back layer of the shell. The method can enhance the strength of the ceramic shell and improve the air permeability of the ceramic shell, and has the characteristics of stable slurry, easiness in operation and high applicability.

Description

Technical Field

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

[0002] The investment casting process is widely used in the casting field of high-temperature castings such as turbine blades for aircraft engines and gas turbines. The preparation of ceramic shells is a key link in investment casting. The strength, air permeability and other properties of the shells have an important impact on the yield of castings. In the actual production process, the shells need to have a sufficiently high flexural strength of the wet blank and the shells after sintering to ensure that the shells will not crack during transportation, dewaxing, sintering and alloy pouring, thereby improving the yield of the shells and avoiding the cracking of the shells that affects the quality of high-temperature alloy castings; in addition, the shells also need a certain degree of air permeability to prevent defects such as undercasting on the surface of the castings due to the difficulty of gas escape during the alloy pouring process.

[0003] At present, adding organic solvents is one of the main methods to improve the strength of mold shells at home and abroad. However, the volatilization and combustion of organic solvents can easily cause air pollution, which in turn endangers the health of workers. In addition, the use of various organic fibers as additives can simultaneously enhance the strength of the mold shell and improve the air permeability of the mold shell, but the dispersion of organic fibers in the mold shell slurry still needs to be improved. Therefore, finding suitable additives and preparing mold shell slurry for the manufacture of ceramic mold shells with both high strength and high air permeability is of great significance to investment casting technology. Summary of the invention

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

[0005] The present invention is achieved through the following technical solutions:

[0006] A graphene oxide-added alumina-based ceramic shell back layer slurry comprises, by mass percentage, 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 with added graphene oxide uses white corundum powder as the ceramic shell back layer refractory material, adopts fused corundum powder, and has an alpha-alumina content of more than 99.5wt%.

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

[0009] The alumina-based ceramic shell back layer slurry with added graphene oxide, the silica sol binder is aqueous silica sol, and its parameters are: silicon oxide content 26-31wt%, sodium oxide content not exceeding 0.5wt%, density 1.15-1.20g / cm 3 , the room temperature viscosity is no higher than 8Pa·s, and the silica sol particle size is 8 to 15nm.

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

[0011] Step 1: Add the silica sol binder into the batching barrel, stir at a speed of 280-320 rpm, gradually add the white corundum powder into the silica sol binder, and continue stirring at a speed of 180-220 rpm for 24 hours to evenly disperse the white corundum powder in the silica sol binder;

[0012] Step 2: Add the graphene oxide aqueous solution to another mixing barrel, stir it continuously at a speed of 380-420 rpm for 1 hour, then gradually add the graphene oxide aqueous solution to the mixing barrel mixed with white corundum powder and silica sol binder, stir it evenly at a speed of 380-420 rpm, continue stirring at a speed of 180-220 rpm for 24 hours, add deionized water to adjust the slurry viscosity to 6-12 Pa·s, and form an alumina-based ceramic shell back layer slurry for shell coating of the shell back layer.

[0013] The design concept of the present invention is:

[0014] Ceramic shells require sufficient flexural strength and air permeability to meet the needs of shell manufacturing and application. Adding organic fiber fillers can improve the wet blank strength of the shell before sintering, and can fully burn and leave residual holes during the sintering process, thereby improving the air permeability of the shell. However, organic fibers are difficult to achieve uniform dispersion in the shell slurry, and may even entangle on the stirring rod of the slurry barrel, thereby hindering the operation of the stirring rod, posing serious hidden dangers to production. For this reason, the present invention adopts a method of adding graphene oxide aqueous dispersion to prepare the back layer slurry of the ceramic shell, so as to avoid the agglomeration of graphene oxide in the back layer slurry during long-term stirring, thereby ensuring the uniformity of the prepared shell components, so as to prepare a ceramic shell with both high strength and high air permeability.

[0015] Compared with the prior art, the advantages and beneficial effects of the present invention are:

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

[0017] 2) The prepared ceramic shell has high flexural strength. Graphene oxide has advantages in mechanical properties such as high Young's modulus and fracture toughness, and can inhibit the growth of microcracks in the wet blank of the ceramic shell. Therefore, the present invention uses graphene oxide as a pore-forming additive for the back layer slurry of the alumina-based ceramic shell. When the wet blank of the shell is heated during the dewaxing process, the wax mold coated with the shell will expand, causing the shell to be subjected to external pressure. At this time, the graphene oxide can disperse and withstand part of the external pressure, thereby avoiding cracking of the shell. In addition, during the sintering process of the ceramic shell, the combustion of graphene oxide will form micropores. When the micropores are not parallel to the crack growth direction, they can inhibit the continued growth of the cracks, thereby improving the flexural 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 holes can enhance the air permeability of the shell. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1-Figure 2 The ceramic shell flexural strength test specimen is prepared from the ceramic shell back layer slurry. Figure 1 In order to use the existing ceramic shell back layer slurry, Figure 2 The ceramic shell back layer slurry of the present invention is adopted.

[0020] Figure 3-Figure 4 The flexural strength test results of the ceramic shell prepared by the ceramic shell backing slurry. Figure 3 Using the existing ceramic shell back layer slurry, Figure 4 The ceramic shell back layer slurry of the present invention is adopted. DETAILED DESCRIPTION

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

[0022] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Example 1

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

[0025] (1) Add 34wt% of the total mass of silica sol binder into the batching barrel according to the mass percentage, continue stirring at a speed of 300rpm, and gradually add 65wt% of the total mass of 320 mesh white corundum powder (α-alumina content is above 99.5wt%) into the silica sol binder; then continue stirring at a speed of 200rpm for 24h until the white corundum powder is evenly dispersed. The silica sol binder is an aqueous silica sol with the following parameters: silicon oxide content 26-31wt%, sodium oxide content not exceeding 0.5wt%, density 1.18-1.20g / cm 3 , the room temperature viscosity is no higher than 8Pa·s, and the silica sol particle size is 8 to 15nm.

[0026] (2) Pour a graphene oxide aqueous solution with a concentration of 8 wt% into another small mixing barrel and stir it evenly at a speed of 400 rpm; wherein the parameters of the graphene oxide are: specific surface area 50-150 m 2 / g, thickness 1~4nm.

[0027] (3) Then, 1 wt% of the total mass of graphene oxide aqueous solution was gradually added to the mixing barrel of white corundum and silica sol binder, and initially stirred evenly at a speed of 400 rpm. Then, the speed was reduced to 200 rpm and stirring was continued for 24 h. The viscosity of the slurry was measured and deionized water was added to adjust the viscosity to 8 Pa·s to form an alumina-based ceramic shell back layer slurry. The evenly stirred slurry was used for coating the shell back layer.

[0028] Example 2

[0029] In this embodiment, a ceramic shell back layer slurry with added graphene oxide was prepared as described in Example 1, and an alumina-based ceramic shell without added graphene oxide was prepared as a control sample. In terms of mass percentage, the ceramic shell back layer slurry without added graphene oxide includes: 65wt% white corundum powder, 35wt% silica sol, and other conditions are the same as in Example 1. The above two slurries are used to prepare ceramic shell samples for flexural strength test ( Figure 1-Figure 2 ).

[0030] like Figure 3-Figure 4 As shown, the test results show that when no graphene oxide is added, the wet strength and sintered shell strength of the ceramic shell are 3.03MPa and 11.58MPa respectively, while the wet strength and sintered strength of the ceramic shell with the addition of graphene oxide are increased to 5.12MPa and 13.51MPa respectively.

[0031] Example 3

[0032] In this embodiment, a method for preparing a ceramic shell back layer slurry with added graphene oxide comprises the following steps:

[0033] (1) Add 42 wt% of the total mass of silica sol binder into the mixing barrel according to the mass percentage, continue stirring at a speed of 300 rpm, and gradually add 55 wt% of the total mass of 320 mesh white corundum powder (α-alumina content is above 99.5 wt%) into the silica sol binder; then, continue stirring at a speed of 200 rpm for 24 hours until the white corundum powder is evenly dispersed.

[0034] (2) A graphene oxide aqueous solution with a concentration of 4 wt% was prepared and poured into another small mixing barrel, and stirred continuously at a rotation speed of 400 rpm.

[0035] (3) Then, 3 wt% of the total mass of graphene oxide aqueous solution was gradually added to the mixing barrel of white corundum and silica sol binder, and initially stirred evenly at a speed of 400 rpm. Then, the speed was reduced to 200 rpm and stirring was continued for 24 h. The viscosity of the slurry was measured and deionized water was added to adjust the viscosity to 6 Pa·s to form an alumina-based ceramic shell back layer slurry. The evenly stirred slurry was used for coating the shell back layer.

[0036] In this embodiment, the wet strength and sintered strength of the ceramic shell with graphene oxide added are increased to 5.98 MPa and 12.19 MPa, respectively.

[0037] Example 4

[0038] In this embodiment, a method for preparing a ceramic shell back layer slurry with added graphene oxide comprises the following steps:

[0039] (1) Add 27 wt% of the total mass of silica sol binder into a mixing barrel according to the mass percentage, and continue stirring at a speed of 300 rpm. Gradually add 69 wt% of the total mass of 320 mesh white corundum powder (α-alumina content is above 99.5 wt%) into the silica sol binder; then, continue stirring at a speed of 200 rpm for 24 hours until the white corundum powder is evenly dispersed.

[0040] (2) A graphene oxide aqueous solution with a concentration of 10 wt% was prepared and poured into another small mixing barrel, and stirred continuously at a rotation speed of 400 rpm.

[0041] (3) Then, a 4 wt% aqueous solution of graphene oxide was gradually added to a mixing barrel containing white corundum and silica sol binder, and initially stirred at 400 rpm. The speed was then reduced to 200 rpm and stirring was continued for 24 h. The viscosity of the slurry was measured and deionized water was added to adjust the viscosity to 10 Pa·s to form an alumina-based ceramic shell back layer slurry. The evenly stirred slurry was used for coating the shell back layer.

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

[0043] The results of the embodiments show that the addition of graphene oxide to the back layer slurry of the ceramic shell of the present invention can improve the strength of the shell, thereby helping to avoid the problem of the shell being scrapped due to shell expansion or cracking during transportation, dewaxing, pouring, etc. The slurry is stable, easy to operate, and has strong applicability.

[0044] Those skilled in the art will easily understand that the above description is only an embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An alumina-based ceramic shell back layer slurry with added graphene oxide, characterized in that: Calculated by 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.

2. The alumina-based ceramic shell back layer slurry with added graphene oxide according to claim 1, characterized in that: White corundum powder is used as the refractory material of the ceramic shell back layer, and fused corundum powder is used, and the α-alumina content is above 99.5wt%.

3. The alumina-based ceramic shell back layer slurry with added graphene oxide according to claim 1, characterized in that: The graphene oxide aqueous solution is an aqueous solution of multilayer graphene oxide, the content of graphene oxide is 2-10wt%, and the parameters of graphene oxide are: specific surface area 50-150m 2 / g, flake diameter 5 to 50 μm, thickness 1 to 10 nm.

4. The alumina-based ceramic shell back layer slurry with added graphene oxide according to claim 1, characterized in that: The silica sol binder is an aqueous silica sol, and its parameters are: silicon oxide content 26-31wt%, sodium oxide content not exceeding 0.5wt%, density 1.15-1.20g / cm 3 , the room temperature viscosity is no higher than 8Pa·s, and the silica sol particle size is 8 to 15nm.

5. A method for preparing the alumina-based ceramic shell back layer slurry with added graphene oxide according to any one of claims 1 to 4, characterized in that: The preparation process includes the following: Step 1: Add the silica sol binder into the batching barrel, stir at a speed of 280-320 rpm, gradually add the white corundum powder into the silica sol binder, and continue stirring at a speed of 180-220 rpm for 24 hours to evenly disperse the white corundum powder in the silica sol binder; Step 2: Add the graphene oxide aqueous solution to another mixing barrel, stir it continuously at a speed of 380-420 rpm for 1 hour, then gradually add the graphene oxide aqueous solution to the mixing barrel mixed with white corundum powder and silica sol binder, stir it evenly at a speed of 380-420 rpm, continue stirring at a speed of 180-220 rpm for 24 hours, add deionized water to adjust the slurry viscosity to 6-12 Pa·s, and form an alumina-based ceramic shell back layer slurry for shell coating of the shell back layer.

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