Modified silica sol as well as preparation method and application thereof

Abstract

The invention provides modified silica sol as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing silica sol with aluminum-based metal salt to obtain a mixed solution; and (2) mixing the mixed solution obtained in the step (1) with an alkyl coupling agent to obtain the modified silica sol. The modified silica sol provided by the invention can improve the stability of the casting back layer slurry, a shell prepared from the casting back layer slurry containing the modified silica sol is high in wet strength, low in residual strength and short in quick drying time, the production efficiency is improved, and the cost is saved.

Description

Technical Field

[0001] The invention belongs to the technical field of investment casting, and in particular relates to a modified silica sol and a preparation method and application thereof. Background Art

[0002] Silica sol is a colloidal solution of silicon dioxide in water. It is widely used in the investment casting industry as a high-temperature binder and is the main raw material for investment casting. For a long time, silica sol binders have been continuously improved and developed, but their rapid development has been restricted by their shortcomings such as slow drying speed, poor stability, low shell making efficiency, poor wettability to wax molds and poor stability.

[0003] CN103962506A discloses a method for preparing a fiber-reinforced composite silica sol mold shell for investment casting, which comprises the following steps in sequence: (1) preparing a surface coating; (2) preparing a surface mold shell; (3) preparing a transition layer coating and a mold shell; (4) preparing a back layer coating; adding mullite powder to silica sol at a mass ratio of 2.2 to 3.0:1 of refractory powder mullite powder in the back layer coating to obtain a paste coating, adding polypropylene fiber at a mass ratio of 0.4% to 2.0% of the mass of the refractory powder mullite powder in the back layer coating to the stirring paste coating to make it evenly dispersed, and then adding silica sol; (5) preparing a back molding shell; (6) sealing slurry; (7) roasting. The fiber-reinforced composite silica sol shell for investment casting produced by this technical solution has high wet strength and low residual strength of the shell. However, the polypropylene fiber subsequently introduced in the slurry preparation process will inevitably have a great impact on the overall stability. In addition, the operation process requires strict control of the amount, order, rate and stirring time of addition. The process is complicated and the production efficiency cannot be guaranteed.

[0004] CN103192024A discloses a mixed binder of water glass and silica sol and a preparation method thereof. The preparation method comprises the following steps: firstly selecting the following raw materials in parts by weight: 88 to 92 parts of water glass, 8 to 12 parts of silica sol solution, 125 to 135 parts of refractory powder, 0.4 to 0.6 parts of penetrant, and 0.04 to 0.06 parts of defoamer; then, at a temperature of 15 to 30° C., putting the water glass, silica sol solution, refractory powder and penetrant into a stirring barrel together, stirring evenly to obtain a mixed solution; then, at a temperature of 15 to 30° C., adding the defoamer into the mixed solution and stirring evenly; finally, at a temperature of 15 to 30° C., placing the mixed solution with the defoamer for more than 8 hours to obtain a mixed binder of water glass and silica sol. The binder prepared by the above method has a high powder-liquid ratio of the back layer coating, and the surface of the shell is relatively smooth, which improves the surface finish of the casting, but it has a long drying time and poor stability, and the process control stability is poor, and the production efficiency cannot be guaranteed.

[0005] Therefore, it is necessary to develop a modified silica sol with good bonding properties, which can improve the wet strength of the casting backing slurry, reduce the residual strength of the shell, and enhance the quick-drying effect. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention aims to provide a modified silica sol and a preparation method and application thereof. The modified silica sol can improve the stability of the casting backing slurry, and the mold shell made of the casting backing slurry including the modified silica sol has high wet strength, low residual strength, short quick drying time, improved production efficiency and saved costs.

[0007] In a first aspect, the present invention provides a method for preparing a modified silica sol, the preparation method comprising the following steps:

[0008] (1) mixing silica sol and aluminum-based metal salt to obtain a mixed solution;

[0009] (2) Mixing the mixed solution obtained in step (1) with an alkyl coupling agent to obtain the modified silica sol.

[0010] In the present invention, the preparation method of the modified silica sol is first modified by adding aluminum-based metal salts, and then modified by using alkyl coupling agents. The double modification can improve the stability of the silica sol and shorten the quick-drying time of the mold shell; by adding aluminum-based metal salts, the silanol groups on the outer layer of the silica sol are combined with the hydroxyl groups of the aluminum-based metal salts, thereby improving the adhesion of the silica sol, and at the same time, the aluminum ions increase the surface charge of the sol particles, improve the electrostatic repulsion, and thus enhance the stability of the modified silica sol; and the use of the alkyl coupling agent not only improves the compatibility of the silica sol with organic matter, but also enhances its hydrophobicity, which helps to improve the stability of the casting back layer slurry, so that the mold shell made of the casting back layer slurry including the modified silica sol has high wet strength and crack resistance, effectively improves the apparent quality of the casting, and reduces the repair cost of the casting. In addition, the modification of the aluminum-based metal salt and the alkyl coupling agent reduces the surface tension of the silica sol, can promote the evaporation of water, accelerate the drying speed, and shorten the quick-drying time of the mold shell. The modification of aluminum-based metal salt and alkyl coupling agent has a synergistic effect, which not only improves the performance of silica sol, but also greatly improves the production efficiency of investment casting back layer, shortens the quick drying time, and significantly saves costs. In addition, since the combination of silica sol and alkyl coupling agent is more difficult than the combination with aluminum-based metal salt, if the order of addition of the two is reversed, the obtained modified silica sol will have extremely poor use effect and cannot be used. The preparation method of the modified silica sol has mild process conditions, simple operation process, is environmentally friendly, easy to mass produce, and has broad application prospects.

[0011] Preferably, the solid content of the silica sol is 15% to 55%, for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or 34%.

[0012] Preferably, the pH of the silica sol is 9.0 to 11.0 (eg, 9.2, 9.4, 9.6, 9.8, 10.0, 10.2, 10.4, 10.6 or 10.8, etc.), and more preferably 9.5 to 10.5.

[0013] In the present invention, if the pH of the silica sol is less than 9.5, the stability of the modified silica sol becomes poor and the use effect is poor; if the pH is greater than 10.5, the alkalinity is too strong, which will cause the aluminum-based metal salt to decompose, thereby failing to obtain a modified silica sol with better performance and achieving the desired use effect.

[0014] Preferably, the aluminum-based metal salt includes any one of sodium metaaluminate, N-nitroso-N-phenylhydroxylamine aluminum salt, aluminum acetylacetonate, aluminum phosphate, aluminum isopropoxide, aluminum tripolyphosphate or sodium hexafluoroaluminate, or a combination of at least two thereof.

[0015] Preferably, the alkyl coupling agent includes any one of 3-glycidyloxypropyltrimethoxysilane, (3-mercaptopropyl)trimethoxysilane, tert-butyldimethylchlorosilane or 3-isocyanatepropyltrimethoxysilane, or a combination of at least two thereof.

[0016] Preferably, the step (1) further includes the step of stirring the silica sol before mixing the silica sol with the aluminum-based metal salt, and the stirring time is 20 to 40 min (for example, 22 min, 24 min, 26 min, 28 min, 30 min, 32 min, 34 min, 36 min or 38 min, etc.), and the stirring speed is 100 to 200 rpm (for example, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm, 160 rpm, 170 rpm, 180 rpm or 190 rpm, etc.).

[0017] Preferably, the mixing temperature in step (1) is 60-65°C (e.g., 60.5°C, 61°C, 61.5°C, 62°C, 62.5°C, 63°C, 63.5°C, 64°C or 64.5°C, etc.).

[0018] Preferably, the mixing speed in step (1) is 200-350 rpm (e.g., 220 rpm, 240 rpm, 260 rpm, 280 rpm, 300 rpm, 320 rpm or 340 rpm, etc.).

[0019] Preferably, the mixing time in step (1) is 1 to 2 h (e.g., 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h or 1.9 h, etc.).

[0020] Preferably, the mixing of the silica sol and the aluminum-based metal salt specifically includes mixing a portion of the aluminum-based metal salt for a first time, and then mixing the remaining aluminum-based metal salt for a second time.

[0021] Preferably, based on the total mass of the aluminum-based metal salt as 100%, the mass percentage of the aluminum-based metal salt in the portion is 40% to 50% (for example, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48% or 49%, etc.).

[0022] Preferably, the mixing temperature in step (2) is 70-80°C, for example, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C or 79°C.

[0023] Preferably, the mixing speed in step (2) is 300-400 rpm, for example, 310 rpm, 320 rpm, 330 rpm, 340 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm or 390 rpm.

[0024] Preferably, the mixing time in step (2) is 1 to 3 h, for example, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2.0 h, 2.2 h, 2.4 h, 2.6 h or 2.8 h.

[0025] Preferably, the weight proportion of the silica sol in step (1) is 95 to 100 parts (for example, 95.5 parts, 96 parts, 96.5 parts, 97 parts, 97.5 parts, 98 parts, 98.5 parts, 99 parts or 99.5 parts, etc.), and the weight proportion of the aluminum-based metal salt is 0.1 to 2 parts (for example, 0.3 parts, 0.5 parts, 0.7 parts, 0.9 parts, 1.1 parts, 1.3 parts, 1.5 parts, 1.7 parts or 1.9 parts, etc.).

[0026] Preferably, the alkyl coupling agent in step (2) is 0.1 to 2 parts (e.g., 0.3 parts, 0.5 parts, 0.7 parts, 0.9 parts, 1.1 parts, 1.3 parts, 1.5 parts, 1.7 parts or 1.9 parts, etc.).

[0027] In the present invention, the weight proportion of the aluminum-based metal salt is preferably 0.1 to 2 parts, and the weight proportion of the alkyl coupling agent is preferably 0.1 to 2 parts. The silica sol is modified by using the aluminum-based metal salt and the alkyl coupling agent in a specific ratio, so that the modified silica sol has good stability, the quick-drying time is shortened to 1 to 2 hours, and the surface quality of the obtained casting is good, and there are no cracks or fewer cracks on the surface of the casting. If the weight proportion of the aluminum-based metal salt or the alkyl coupling agent is too high, the stability of the modified silica sol will be reduced, and the service life of the modified silica sol will be greatly reduced. The shell made of the casting back layer slurry including the modified silica sol has poor performance and a long quick-drying time.

[0028] Preferably, the mass ratio of the aluminum-based metal salt to the alkyl coupling agent is (0.5-2):1, for example, 0.7:1, 0.9:1, 1.1:1, 1.3:1, 1.5:1, 1.7:1 or 1.9:1.

[0029] In the present invention, if the mass ratio of the aluminum-based metal salt and the alkyl coupling agent is less than 0.5:1, the proportion of the aluminum-based metal salt is small, the stability of the modified silica sol is poor, and the service life is short, resulting in an increase in the residual strength of the mold shell made of the casting back layer slurry including the modified silica sol and a high mortar residual rate; if the mass ratio of the aluminum-based metal salt and the alkyl coupling agent is greater than 2:1, the proportion of the alkyl coupling agent combined in the modified silica sol is small, the performance of the modified silica sol is poor, resulting in low wet strength, high residual strength, and high mortar residual rate made of the casting back layer slurry including the modified silica sol.

[0030] Preferably, after the mixing in step (1), a dispersant is added and then mixed.

[0031] Preferably, the remixing temperature in step (1) is 60-65°C, for example, 60.5°C, 61°C, 61.5°C, 62°C, 62.5°C, 63°C, 63.5°C, 64°C or 64.5°C, etc.

[0032] Preferably, the remixing rotation speed in step (1) is 250-350 rpm, for example, 260 rpm, 270 rpm, 280 rpm, 290 rpm, 300 rpm, 310 rpm, 320 rpm, 330 rpm or 340 rpm.

[0033] Preferably, the remixing time in step (1) is 1 to 2 h, for example, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h or 1.9 h.

[0034] Preferably, the adding of dispersant and mixing in step (1) specifically includes adding part of the dispersant for a third mixing, and adding the remaining dispersant for a fourth mixing.

[0035] In the present invention, the purpose of adding the dispersant in batches for mixing is to allow it to be uniformly mixed with the mixed solution of the aluminum-based metal salt and the silica sol, and to activate and further disperse the mixed solution of the aluminum-based metal salt and the silica sol.

[0036] Preferably, the dispersant includes any one or a combination of at least two of sodium lauryl sulfate, methylpentyl alcohol, a cellulose derivative, guar gum or polyethylene glycol ester of fatty acids.

[0037] In the present invention, the dispersant contains ammonium ions, which can increase the dispersibility among the aluminum-based metal salt, the alkyl coupling agent and the silica sol.

[0038] Preferably, the weight portion of the dispersant is 0.1 to 1 part, for example, 0.2 part, 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part or 0.9 part, etc.

[0039] Preferably, after the mixing in step (2), the step of adding an aqueous co-solvent and mixing again is also included.

[0040] Preferably, the remixing temperature in step (2) is 70-80°C, for example, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C or 79°C.

[0041] Preferably, the remixing rotation speed in step (2) is 300-400 rpm, for example, 310 rpm, 320 rpm, 330 rpm, 340 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm or 390 rpm.

[0042] Preferably, the remixing time in step (2) is 1 to 3 h, for example, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2.0 h, 2.2 h, 2.4 h, 2.6 h or 2.8 h.

[0043] Preferably, the aqueous cosolvent includes any one of sodium benzoate, sodium salicylate, citric acid, isooctyl alcohol or Tween, or a combination of at least two thereof.

[0044] Preferably, the weight portion of the aqueous co-solvent is 0.1 to 1 part, for example, 0.2 part, 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part or 0.9 part, etc.

[0045] Preferably, the preparation method specifically comprises the following steps:

[0046] (1) The silica sol is mixed with a part of the aluminum-based metal salt for a first time, and then the remaining aluminum-based metal salt is added for a second mixing, and then a part of the dispersant is added for a third mixing, and the remaining dispersant is added for a fourth mixing to obtain a mixed solution.

[0047] (2) The mixed solution obtained in step (1) is mixed with an alkyl coupling agent, and then an aqueous co-solvent is added and mixed again to obtain the modified silica sol.

[0048] Preferably, the temperatures of the first mixing, the second mixing, the third mixing and the fourth mixing are each independently 60-65°C, for example, 60.5°C, 61°C, 61.5°C, 62°C, 62.5°C, 63°C, 63.5°C, 64°C or 64.5°C, etc.

[0049] Preferably, the rotation speeds of the first mixing, the second mixing, the third mixing and the fourth mixing are each independently 250-350 rpm, for example, 260 rpm, 270 rpm, 280 rpm, 290 rpm, 300 rpm, 310 rpm, 320 rpm, 330 rpm or 340 rpm.

[0050] Preferably, the time for the first mixing and the third mixing is independently 20 to 40 min, for example, 22 min, 24 min, 26 min, 28 min, 30 min, 32 min, 34 min, 36 min or 38 min.

[0051] Preferably, the time for the second mixing and the fourth mixing is independently 30 to 100 min, for example, 40 min, 50 min, 60 min, 70 min, 80 min or 90 min.

[0052] In a second aspect, the present invention provides a modified silica sol, wherein the modified silica sol is prepared by the preparation method described in the first aspect.

[0053] In a third aspect, the present invention provides a casting backing slurry, wherein the casting backing slurry comprises the modified silica sol as described in the second aspect.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] In the present invention, the preparation method of the modified silica sol is first modified by aluminum-based metal salt and then modified by alkyl coupling agent, and the stability of the silica sol can be improved by double modification. The modified silica sol can improve the stability of the casting back layer slurry, and the mold shell made of the casting back layer slurry including the modified silica sol has high wet strength, low residual strength, short quick drying time, improved production efficiency, and saved costs. DETAILED DESCRIPTION

[0056] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0057] Example 1

[0058] This embodiment provides a modified silica sol and a preparation method thereof, wherein the preparation method of the modified silica sol comprises the following steps:

[0059] (1) 95 parts by weight of silica sol (solid content 30%, pH 9.5, particle size 15 nm, sourced from Guangdong Huierte Nanotechnology Co., Ltd.) were placed in a 1000 mL flask, a stirring bar was added, and the mixture was stirred at a speed of 250 rpm for 30 min. Under stirring conditions, 1 part by weight of aluminum-based metal salt (sodium aluminate) was slowly added thereto, the speed was adjusted to 300 rpm, and the mixture was stirred at 60° C. for 30 min for the first mixing. The speed and temperature were maintained, and 1 part by weight of aluminum-based metal salt (sodium aluminate) was added and stirred for 60 min for the second mixing. Then, 0.25 parts by weight of dispersant (sodium dodecyl sulfate) was added while maintaining the speed and temperature, and the mixture was stirred for 30 min for the third mixing. Finally, the temperature was raised to 65° C., the stirring speed was adjusted to 350 rpm, and 0.25 parts by weight of dispersant (sodium dodecyl sulfate) was added and stirred for 120 min for the fourth mixing to obtain a mixed solution.

[0060] (2) Slowly add 2 parts by weight of an alkyl coupling agent (3-glycidyloxypropyltrimethoxysilane) to the mixed solution obtained in step (1), and stir continuously for 2 hours at 70° C. and a rotation speed of 350 rpm to mix, then add 0.5 parts by weight of an aqueous cosolvent (sodium benzoate) while maintaining the temperature and rotation speed unchanged, stir for 2 hours, and then mix again to obtain the modified silica sol.

[0061] Example 2

[0062] This embodiment provides a modified silica sol and a preparation method thereof, wherein the preparation method of the modified silica sol comprises the following steps:

[0063] (1) 100 parts by weight of silica sol (solid content of 30%, pH of 9.4, particle size of 12 nm) were placed in a 1000 mL flask, a stirring bar was added, and the mixture was stirred at a speed of 200 rpm for 30 min. Under stirring conditions, 1 part by weight of aluminum-based metal salt (aluminum acetylacetonate) was slowly added thereto, the speed was adjusted to 250 rpm, and the mixture was stirred at 62° C. for 20 min for the first mixing. The speed and temperature were maintained, and 1 part by weight of aluminum-based metal salt (aluminum acetylacetonate) was added and stirred for 40 min for the second mixing. Then, 0.05 part by weight of dispersant (methyl amyl alcohol) was added while maintaining the speed and temperature, and the mixture was stirred for 20 min for the third mixing. Finally, the temperature was maintained at 62° C., the stirring speed was adjusted to 350 rpm, and 0.05 part by weight of dispersant (methyl amyl alcohol) was added and stirred for 60 min for the fourth mixing to obtain a mixed solution.

[0064] (2) Slowly add 2 parts by weight of an alkyl coupling agent (tert-butyldimethylsilyl chloride) to the mixed solution obtained in step (1), and stir continuously for 1 hour at 75° C. and a rotation speed of 300 rpm to mix, then add 1 part by weight of an aqueous cosolvent (sodium salicylate) while keeping the temperature and rotation speed unchanged, stir for 3 hours, and then mix again to obtain the modified silica sol.

[0065] Example 3

[0066] This embodiment provides a modified silica sol and a preparation method thereof, wherein the preparation method of the modified silica sol comprises the following steps:

[0067] (1) 98 parts by weight of silica sol (solid content of 30%, pH of 9.5, particle size of 14 nm) were placed in a 1000 mL flask, a stirring bar was added, and the mixture was stirred at a speed of 250 rpm for 30 min. Under stirring conditions, 1 part by weight of aluminum-based metal salt (sodium hexafluoroaluminate) was slowly added thereto, the speed was adjusted to 350 rpm, and the mixture was stirred at 65° C. for 40 min for the first mixing. The speed and temperature were maintained, and 1 part by weight of aluminum-based metal salt (sodium hexafluoroaluminate) was added and stirred for 30 min for the second mixing. Then, 0.5 part by weight of dispersant (sodium dodecyl sulfate) was added while maintaining the speed and temperature, and the mixture was stirred for 40 min for the third mixing. Finally, the temperature was maintained at 65° C., the stirring speed was adjusted to 350 rpm, and 0.5 part by weight of dispersant (sodium dodecyl sulfate) was added and stirred for 30 min for the fourth mixing to obtain a mixed solution.

[0068] (2) Slowly add 2 parts by weight of an alkyl coupling agent (3-isocyanatepropyltrimethoxysilane) to the mixed solution obtained in step (1), and stir continuously for 3 hours at 80° C. and a rotation speed of 400 rpm to mix, then add 1 part by weight of an aqueous cosolvent (isooctanol) while maintaining the temperature and rotation speed unchanged, stir for 1 hour, and then mix again to obtain the modified silica sol.

[0069] Example 4

[0070] The present embodiment provides a modified silica sol and a preparation method thereof, which differs from the embodiment 1 only in that the weight fractions of the dispersant (sodium dodecyl sulfate) added in the third mixing and the fourth mixing in step (1) are both adjusted to 0.5 parts, the weight fractions of the alkyl coupling agent (3-glycidyloxypropyltrimethoxysilane) in step (2) are adjusted to 1 part, and the weight fraction of the aqueous cosolvent (sodium benzoate) is adjusted to 1 part, and the other conditions are the same as those in embodiment 1.

[0071] Example 5

[0072] The present embodiment provides a modified silica sol and a preparation method thereof, which differs from the embodiment 1 only in that the weight fractions of the aluminum-based metal salt (sodium aluminate) added in the first mixing and the second mixing in step (1) are both adjusted to 0.5 parts, the weight fractions of the dispersant (sodium dodecyl sulfate) added in the third mixing and the fourth mixing are both adjusted to 0.5 parts, the weight fraction of the aqueous co-solvent (sodium benzoate) in step (2) is adjusted to 1 part, and the other conditions are the same as those in embodiment 1.

[0073] Example 6

[0074] This embodiment provides a modified silica sol and a preparation method thereof, which differs from Embodiment 1 only in that the weight fractions of the dispersant (sodium dodecyl sulfate) added in the third and fourth mixing in step (1) are adjusted to 0.5 parts, and the weight fractions of the alkyl coupling agent (3-glycidyloxypropyltrimethoxysilane) in step (2) are adjusted to 1.5 parts, and the other conditions are the same as in Embodiment 1.

[0075] Example 7

[0076] The present embodiment provides a modified silica sol and a preparation method thereof, which differs from the embodiment 1 only in that the weight fractions of the aluminum-based metal salt (sodium aluminate) added in the first mixing and the second mixing in step (1) are both adjusted to 0.75 parts, and the weight fractions of the dispersant (sodium dodecyl sulfate) added in the third mixing and the fourth mixing are both adjusted to 0.5 parts, and the other conditions are the same as those in the embodiment 1.

[0077] Example 8

[0078] This embodiment provides a modified silica sol and a preparation method thereof, which differs from Embodiment 1 only in that the weight portion of the alkyl coupling agent (3-glycidyloxypropyltrimethoxysilane) in step (2) is adjusted to 0.5 parts, and other conditions are the same as those in Embodiment 1.

[0079] Example 9

[0080] This embodiment provides a modified silica sol and a preparation method thereof, which differs from Embodiment 1 only in that the weight fractions of the aluminum-based metal salt (sodium aluminate) added in the first mixing and the second mixing in step (1) are both adjusted to 0.25 parts, and the other conditions are the same as in Embodiment 1.

[0081] Example 10

[0082] This embodiment provides a modified silica sol and a preparation method thereof, which differs from Embodiment 1 only in that the weight proportions of the aluminum-based metal salt (sodium aluminate) added in the first mixing and the second mixing in step (1) are both adjusted to 2 parts, and other conditions are the same as in Embodiment 1.

[0083] Embodiment 11

[0084] This embodiment provides a modified silica sol and a preparation method thereof. The difference between this embodiment and embodiment 1 is that the weight proportion of the alkyl coupling agent (sodium dodecyl sulfate) in step (2) is adjusted to 4 parts, and other conditions are the same as those in embodiment 1.

[0085] Comparative Example 1

[0086] This comparative example provides a modified silica sol and a preparation method thereof, which differs from Example 1 only in that no aluminum-based metal salt is added in step (1), and other conditions are the same as those in Example 1.

[0087] Comparative Example 2

[0088] This comparative example provides a modified silica sol and a preparation method thereof, which differs from Example 1 only in that no alkyl coupling agent is added in step (2), and other conditions are the same as those in Example 1.

[0089] Comparative Example 3

[0090] This comparative example provides a silica sol, which has a solid content of 30%, a pH of 9.5, and a particle size of 15 nm, and is sourced from Guangdong Huierte Nanotechnology Co., Ltd.

[0091] Performance Testing

[0092] (1) Viscosity: The viscosity of the modified silica sols provided in Examples 1 to 11 and Comparative Examples 1 to 2 and the silica sol provided in Comparative Example 3 was measured using a Brookfield viscometer.

[0093] (2) The modified silica sols provided in Examples 1 to 11 and Comparative Examples 1 to 2 and the silica sol provided in Comparative Example 3 were respectively used as binders to prepare casting backing slurries (the other components and contents in the casting backing slurries except the binder were exactly the same), and the casting backing slurries were used to prepare mold shells, and the following performance tests were performed:

[0094] Quick drying time between mold shells: The quick drying time is measured by the moisture content, which specifically includes recording the drying time of each shell layer formed by the back slurry of the casting during the preparation of the mold shell. The drying is considered to be completed when the moisture content on the surface of the mold shell is ≤10% or the mold shell no longer loses water (the moisture exists in the form of crystal water). The average value is recorded as the quick drying time between the layers of the mold shell.

[0095] Wet strength of the shell: tested using the JB / T 13038-2017 method, a wet strength of 5MPa or above is considered good;

[0096] Residual strength of the shell: tested using the JB / T 13038-2017 method, a residual strength below 5MPa is considered good;

[0097] In addition, the wet strength of the mold shell is much greater than the residual strength of the mold shell, and the best sand cleaning is when it is ≥2 times;

[0098] Mortar residual rate: Shell the cast test blocks with shells and roughly calculate the proportion of the parts that have not been completely shelled by visual inspection.

[0099] The test results are shown in Table 1 below:

[0100] Table 1

[0101]

[0102]

[0103] From the content of Table 1, it can be seen that the interlayer quick drying time of the mold shell made of the casting back layer slurry containing the modified silica sol is 1 to 6 hours, the wet strength of the mold shell is 4.68 to 8.24 MPa, the residual strength of the mold shell is 3.22 to 7.32 MPa, and the mortar residual rate is 0 to 40%.

[0104] Compared with Example 1, if the mass ratio of the aluminum-based metal salt and the alkyl coupling agent is too small (Example 8), the stability of the prepared modified silica sol is poor, the interlayer quick-drying time of the mold shell made of the casting back layer slurry containing the modified silica sol is increased, the wet strength is reduced, the residual strength is improved, and the mortar residual rate is high; if the mass ratio of the aluminum-based metal salt and the alkyl coupling agent is too large (Example 9), the stability of the prepared modified silica sol is poor, the interlayer quick-drying time of the mold shell made of the casting back layer slurry containing the modified silica sol is increased, the wet strength is reduced, the residual strength is improved, and the mortar residual rate is high. It can be seen from this that in the present invention, by controlling the mass ratio of the aluminum-based metal salt and the alkyl coupling agent within a specific range, the modified silica sol prepared has better performance.

[0105] Compared with Example 1, if the weight fraction of the aluminum-based metal salt is too high (Example 10), the stability of the modified silica sol is reduced, the quick-drying time is prolonged, and the wet strength of the mold shell is greatly reduced; if the weight fraction of the alkyl coupling agent is too high (Example 11), the stability of the modified silica sol is reduced, the quick-drying time is prolonged, the residual strength of the mold shell is greatly improved, and the performance of the mold shell made of the casting back layer slurry containing the modified silica sol is deteriorated.

[0106] Compared with Example 1, if no aluminum-based metal salt (Comparative Example 1) or alkyl coupling agent (Comparative Example 2) is added, the stability of the modified silica sol is reduced, the quick-drying time is prolonged, and the performance of the mold shell made of the casting backing slurry containing the modified silica sol is deteriorated.

[0107] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate a modified silica sol and its preparation method and application, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a modified silica sol, characterized in that: The preparation method comprises the following steps: (1) mixing silica sol and aluminum-based metal salt to obtain a mixed solution; (2) Mixing the mixed solution obtained in step (1) with an alkyl coupling agent to obtain the modified silica sol.

2. The preparation method according to claim 1, characterized in that: The solid content of the silica sol is 15% to 55%; Preferably, the pH of the silica sol is 9.0 to 11.0; Preferably, the aluminum-based metal salt includes any one or a combination of at least two of sodium metaaluminate, N-nitroso-N-phenylhydroxylamine aluminum salt, aluminum acetylacetonate, aluminum phosphate, aluminum isopropoxide, aluminum tripolyphosphate or sodium hexafluoroaluminate; Preferably, the alkyl coupling agent includes any one of 3-glycidyloxypropyltrimethoxysilane, (3-mercaptopropyl)trimethoxysilane, tert-butyldimethylchlorosilane or 3-isocyanatepropyltrimethoxysilane, or a combination of at least two thereof.

3. The preparation method according to claim 1 or 2, characterized in that: The step (1) further comprises the step of stirring the silica sol before mixing the silica sol with the aluminum-based metal salt, wherein the stirring time is 20 to 40 minutes and the stirring speed is 100 to 200 rpm; Preferably, the mixing temperature in step (1) is 60-65°C; Preferably, the mixing speed in step (1) is 200 to 350 rpm; Preferably, the mixing time in step (1) is 1 to 2 hours; Preferably, the mixing of the silica sol and the aluminum-based metal salt specifically includes mixing a portion of the aluminum-based metal salt for a first time, and then mixing the remaining aluminum-based metal salt for a second time; Preferably, based on the total mass of the aluminum-based metal salt being 100%, the mass percentage of the aluminum-based metal salt in the portion is 40% to 50%.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The mixing temperature in step (2) is 70-80° C. Preferably, the mixing speed in step (2) is 300-400 rpm; Preferably, the mixing time in step (2) is 1 to 3 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The weight proportion of the silica sol in step (1) is 95 to 100 parts, and the weight proportion of the aluminum-based metal salt is 0.1 to 2 parts; Preferably, the alkyl coupling agent in step (2) is 0.1 to 2 parts.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The mass ratio of the aluminum-based metal salt to the alkyl coupling agent is (0.5-2):

1.

7. The preparation method according to any one of claims 1 to 6, characterized in that: After the mixing in step (1), a dispersant is added and then mixed; Preferably, the temperature of the remixing in step (1) is 60-65°C; Preferably, the remixing speed in step (1) is 250-350 rpm; Preferably, the remixing time in step (1) is 1 to 2 hours; Preferably, the adding of dispersant and mixing in step (1) specifically includes adding part of the dispersant for a third mixing, and adding the remaining dispersant for a fourth mixing; Preferably, the dispersant comprises any one or a combination of at least two of sodium lauryl sulfate, methylpentyl alcohol, a cellulose derivative, guar gum or polyethylene glycol ester of fatty acids; Preferably, the weight portion of the dispersant is 0.1 to 1 part; Preferably, after the mixing in step (2), the step further comprises adding an aqueous co-solvent and mixing again; Preferably, the temperature of the remixing in step (2) is 70-80°C; Preferably, the remixing speed in step (2) is 300-400 rpm; Preferably, the remixing time in step (2) is 1 to 3 hours; Preferably, the aqueous cosolvent comprises any one or a combination of at least two of sodium benzoate, sodium salicylate, citric acid, isooctyl alcohol or Tween; Preferably, the weight portion of the aqueous co-solvent is 0.1 to 1 part.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The preparation method specifically comprises the following steps: (1) mixing the silica sol with a portion of the aluminum-based metal salt for a first time, adding the remaining aluminum-based metal salt for a second time, then adding a portion of the dispersant for a third time, and adding the remaining dispersant for a fourth time to obtain a mixed solution; (2) mixing the mixed solution obtained in step (1) with an alkyl coupling agent, then adding an aqueous cosolvent and mixing again to obtain the modified silica sol; The temperatures of the first mixing, the second mixing, the third mixing and the fourth mixing are each independently 60 to 65° C.; The rotation speeds of the first mixing, the second mixing, the third mixing and the fourth mixing are each independently 250-350 rpm; The time of the first mixing and the third mixing is independently 20 to 40 minutes; The time for the second mixing and the fourth mixing is independently 30 to 100 minutes.

9. A modified silica sol, characterized in that: The modified silica sol is prepared by the preparation method according to any one of claims 1 to 8.

10. A casting backing slurry, characterized in that: The casting backing layer slurry comprises the modified silica sol as claimed in claim 9.

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