A method for preparing a high-purity single-phase gamma-c-s-h gel

Abstract

The application provides a preparation method of high-purity single-phase gamma-C-S-H gel and belongs to the technical field of cement-based materials. The method comprises the following steps: mixing, stirring and reacting sodium metasilicate solution, sodium hydroxide solution and calcium nitrate tetrahydrate solution, adding polyoxyethylene alkylamine and mixing and stirring, and finally filtering, washing and drying in sequence to obtain high-purity single-phase gamma-C-S-H gel. The method of the application can inhibit the growth of calcium hydroxide, reduce carbonization and adjust the pH value of the solution, so that the prepared gel has high purity and high crystallinity.

Description

Technical Field

[0001] This invention relates to the field of cement-based materials technology, and in particular to a method for preparing high-purity single-phase γ-CSH gel. Background Technology

[0002] Calcium silicate hydrate (CaO-SiO2-H2O or CSH) is known as the "gene" of cement-based materials. It is formed by the hydration of dicalcium silicate and tricalcium silicate in cement clinker, and occupies about 50% of the solid phase volume of hardened cement paste. It determines the strength, shrinkage performance and structural durability of cement-based materials.

[0003] For a long time, because cement hydration produces not only CSH but also other hydration products such as calcium hydroxide and ettringite, directly extracting hardened cement paste to study the structure and basic properties of CSH has been insufficient to reflect its true state, and the characterization results are often affected by other hydration products. Therefore, the method of synthesizing pure, single-phase CSH in the laboratory has been recognized and widely used by scientists.

[0004] The calcium-to-silicon ratio is one of the most important stoichiometric coefficients of CSH. Based on the different molar ratios of calcium and silicon in its structure, it can be divided into α-CSH (Ca / Si < 1.0), β-CSH (1.0 < Ca / Si < 1.5), and γ-CSH (Ca / Si > 1.5). Existing methods for synthesizing CSH include the pozzolanic reaction method, the double decomposition method, and the sol-gel method. These methods can only prepare α-CSH and β-CSH, that is, CSH with a calcium-to-silicon ratio below 1.5. It is difficult to synthesize a single-phase pure CSH phase with a higher calcium-to-silicon ratio.

[0005] The γ-CSH gel prepared by existing methods consists of two parts: one component is a layered silicate chain structure similar to natural hydrated calcium silicate (tobermorite), i.e., the CSH phase structure; the other component is nano-Ca(OH)2, which is generally believed to be distributed in the pores of the CSH phase or interwoven as a layered structure within the CSH phase. However, thermodynamic modeling and crystal chemistry theory have shown that the properties of this binary structure are significantly different from those of single-phase CSH. Therefore, this has affected the understanding of the properties and structure of high calcium-to-silicon ratio CSH to some extent, and has limited the refined design of characterization experiments for single-phase CSH.

[0006] Therefore, it is very important to provide a method for synthesizing high-purity single-phase γ-CSH gel. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing high-purity single-phase γ-CSH gel, so as to solve the technical problems of low purity and complex phase of γ-CSH gel in the prior art.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] This invention provides a method for preparing high-purity single-phase γ-CSH gel, comprising the following steps:

[0010] (1) Sodium metasilicate solution and sodium hydroxide solution were stirred and mixed under a protective gas to obtain mixed solution A;

[0011] (2) Mix the mixed solution A and calcium nitrate tetrahydrate solution by stirring and reacting to obtain mixed solution B;

[0012] (3) Add polyoxyethylene alkylamine to mixed solution B and stir to obtain a suspension;

[0013] (4) The suspension was sequentially filtered, washed and dried to obtain high-purity single-phase γ-CSH gel.

[0014] Furthermore, the volume ratio of the sodium metasilicate solution, sodium hydroxide solution, and calcium nitrate tetrahydrate solution is 150–250: 65–75: 150–250;

[0015] The concentration of the sodium metasilicate solution is 0.05–0.2 mol / L;

[0016] The concentration of the sodium hydroxide solution is 0.5–2 mol / L;

[0017] The concentration of the calcium nitrate tetrahydrate solution is 0.1–0.3 mol / L;

[0018] The volume of the polyoxyethylene alkylamine is 0.5 to 1.5% of the sum of the volumes of the sodium metasilicate solution, sodium hydroxide solution, and calcium nitrate tetrahydrate solution.

[0019] Furthermore, in step (1), the protective gas is nitrogen or argon.

[0020] Furthermore, in step (1), the rate at which the protective gas is introduced is 1 to 2 L / min.

[0021] Furthermore, in step (1), the stirring speed is 600-800 rpm and the stirring temperature is ≤15℃.

[0022] Furthermore, in step (2), the stirring speed is 1000-1200 rpm;

[0023] The temperature of the reaction is ≤15℃.

[0024] Furthermore, in step (3), the stirring speed is 600-800 rpm and the stirring temperature is ≤15℃.

[0025] Furthermore, in step (4), the filtration uses a nylon filter membrane with a pore size of 0.3 to 1 μm.

[0026] Furthermore, the washing process involves first washing with a mixed solution of water and anhydrous ethanol, and then washing with anhydrous ethanol.

[0027] The volume ratio of water to anhydrous ethanol is 1-3:1-3.

[0028] Furthermore, in step (4), the drying temperature is 15-30°C and the time is 5-8 hours.

[0029] The beneficial effects of this invention are:

[0030] This invention improves the purity of γ-CSH gel by adding polyoxyethylene alkylamine, which can absorb CO2 and further reduce gel carbonization caused during the reaction. The γ-CSH gel prepared by the method of this invention has a structure in which short-range ordered crystalline state and long-range disordered amorphous state coexist, with a high degree of crystallinity. Attached Figure Description

[0031] Figure 1 This is a SEM image of the high-purity single-phase γ-CSH gel from Example 1.

[0032] Figure 2 The image shows the XRD pattern of the high-purity single-phase γ-CSH gel from Example 1. Detailed Implementation

[0033] This invention provides a method for preparing high-purity single-phase γ-CSH gel, comprising the following steps:

[0034] (1) Sodium metasilicate solution and sodium hydroxide solution were stirred and mixed under a protective gas to obtain mixed solution A;

[0035] (2) Mix the mixed solution A and calcium nitrate tetrahydrate solution by stirring and reacting to obtain mixed solution B;

[0036] (3) Add polyoxyethylene alkylamine to mixed solution B and stir to obtain a suspension;

[0037] (4) The suspension was sequentially filtered, washed and dried to obtain high-purity single-phase γ-CSH gel.

[0038] In this invention, the volume ratio of the sodium metasilicate solution, sodium hydroxide solution, and calcium nitrate tetrahydrate solution is 150-250:65-75:150-250, preferably 160-240:67-73:160-240, and more preferably 170-230:68-71:170-230;

[0039] The concentration of the sodium metasilicate solution is 0.05–0.2 mol / L, preferably 0.08–0.18 mol / L, and more preferably 0.1–0.15 mol / L;

[0040] The concentration of the sodium hydroxide solution is 0.5–2 mol / L, preferably 0.6–1.8 mol / L, and more preferably 0.7–1.6 mol / L;

[0041] The concentration of the calcium nitrate tetrahydrate solution is 0.1–0.3 mol / L, preferably 0.12–0.28 mol / L, and more preferably 0.15–0.25 mol / L;

[0042] The volume of the polyoxyethylene alkylamine is 0.5 to 1.5% of the sum of the volumes of the sodium metasilicate solution, sodium hydroxide solution, and calcium nitrate tetrahydrate solution, preferably 0.6 to 1.4%, and more preferably 0.7 to 1.3%.

[0043] In this invention, in step (1), the protective gas is nitrogen or argon, preferably nitrogen.

[0044] In this invention, the purpose of introducing nitrogen or argon gas is to prevent interference from substances such as carbon dioxide in the air.

[0045] In this invention, in step (1), the rate of introduction of the protective gas is 1 to 2 L / min, preferably 1.2 to 1.8 L / min, and more preferably 1.4 to 1.6 L / min.

[0046] In this invention, in step (1), the stirring speed is 600-800 rpm, preferably 620-780 rpm, and more preferably 650-750 rpm;

[0047] The reaction temperature is ≤15℃, preferably ≤14℃, and more preferably ≤13℃.

[0048] In this invention, in step (2), the stirring speed is 1000-1200 rpm, preferably 1050-1150 rpm, and more preferably 1100 rpm; the stirring temperature is ≤15℃, preferably ≤14℃, and more preferably ≤13℃.

[0049] In this invention, the stirring and mixing temperature is ≤15℃ in order to reduce the precipitation of calcium hydroxide during the synthesis of γ-CSH gel. By lowering the reaction temperature, the solubility of calcium hydroxide is increased.

[0050] In this invention, in step (3), the stirring speed is 600-800 rpm, preferably 620-780 rpm, and more preferably 650-750 rpm; the stirring temperature is ≤15℃, preferably ≤14℃, and more preferably ≤13℃.

[0051] In this invention, in step (4), the filtration uses a nylon filter membrane with a pore size of 0.3 to 1 μm, preferably 0.4 to 0.9 μm, and more preferably 0.45 to 0.8 μm.

[0052] In this invention, the washing process involves first washing with a mixed solution of water and anhydrous ethanol, and then washing with anhydrous ethanol.

[0053] The volume ratio of water to anhydrous ethanol is 1-3:1-3, preferably 1.2-2.5:1.2-2.5, and more preferably 1.5-2:1.5-2.

[0054] In this invention, the water in the mixed solution is preferably ultrapure water. The ultrapure water is boiled and then cooled in an ice bath for 1 hour to prepare sodium silicate and calcium nitrate solutions, which can avoid the formation of carbonates in subsequent steps.

[0055] In this invention, the purpose of adding NaOH solution is to simulate the alkaline growth environment in concrete pores.

[0056] In this invention, polyoxyethylene alkylamine can absorb CO2, further reducing sample carbonization caused during the preparation process.

[0057] In this invention, in step (4), the drying temperature is 15-30°C, preferably 18-28°C, and more preferably 20-25°C; the time is 5-8 hours, preferably 5.5-7.5 hours, and more preferably 6-7 hours.

[0058] In this invention, drying is carried out in a nitrogen atmosphere.

[0059] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0060] The batch reactor used in this embodiment of the invention is manufactured by Iwasei Instruments (Guangzhou) Co., Ltd., model number Micro-reactor; the polyoxyethylene alkylamine is manufactured by Kao Corporation of Japan, model number AMIET 105.

[0061] Example 1

[0062] 200 mL of 0.1 mol / L sodium metasilicate solution was added to a closed batch reactor, and nitrogen gas was introduced at a rate of 1.5 L / min. 69.5 mL of 1 mol / L sodium hydroxide solution was added and stirred at 700 rpm. Then, 200 mL of 0.224 mol / L calcium nitrate tetrahydrate solution was added and stirred at 1100 rpm. The reaction was carried out at 15 °C. Next, 1% of polyoxyethylene alkylamine (based on the total volume of sodium metasilicate, sodium hydroxide, and calcium nitrate tetrahydrate solutions) was added and stirred at 15 °C at 700 rpm to obtain a suspension. The suspension was filtered through a 0.45 μm nylon filter membrane, washed with a 1:1 volume ratio of ultrapure water and anhydrous ethanol, and then washed with anhydrous ethanol. Finally, nitrogen gas was introduced at a rate of 1.5 L / min, and the mixture was dried at 25 °C for 6 h to obtain high-purity single-phase γ-CSH gel.

[0063] The γ-CSH gel prepared in Example 1 was tested. The microstructure of the γ-CSH gel in Example 1 was examined using a Sigma 500 field emission scanning electron microscope (Zeiss GmbH, Germany). Figure 1 The image shown is a SEM image of the high-purity single-phase γ-CSH gel from Example 1. Qualitative analysis of the gel was performed using a Bruker D8 Advance X-ray diffractometer (Germany). The test conditions were: Cu target, voltage 45 kV, current 40 mA, scan range 5–80°2θ, step size 0.13°2θ, and scan speed 0.15 s / step. The test results are shown below. Figure 2 As shown, Figure 2 The image shows the XRD pattern of the high-purity single-phase γ-CSH gel from Example 1. Figure 1 and Figure 2 It can be seen that the γ-CSH gel prepared by the method of the present invention has a structure in which short-range ordered crystalline state and long-range disordered amorphous state coexist. Figure 2 The absence of diffraction peaks for calcium carbonate and calcium hydroxide crystals indicates that the γ-CSH gel prepared using the method of this invention has high purity and is free of impurities. Furthermore... Figure 2 The characteristic peaks at the (110), (200) and (020) crystal planes have high peak intensities and sharp shapes, indicating that the γ-CSH gel has a high degree of crystallinity.

[0064] Example 2

[0065] 180 mL of 0.1 mol / L sodium metasilicate solution was added to a closed batch reactor, and nitrogen gas was introduced at a rate of 1.5 L / min. 65 mL of 1 mol / L sodium hydroxide solution was added and stirred at 800 rpm. Then, 180 mL of 0.224 mol / L calcium nitrate tetrahydrate solution was added and stirred at 1000 rpm. The reaction was carried out at 15 °C. Next, 1% of polyoxyethylene alkylamine (based on the total volume of sodium metasilicate, sodium hydroxide, and calcium nitrate tetrahydrate solutions) was added and stirred at 15 °C at 600 rpm to obtain a suspension. The suspension was filtered through a 0.45 μm nylon membrane, washed with a 1:1 volume ratio of ultrapure water and anhydrous ethanol, and then washed with anhydrous ethanol. Finally, nitrogen gas was introduced at a rate of 1.5 L / min, and the mixture was dried at 15 °C for 8 h to obtain high-purity single-phase γ-CSH gel.

[0066] Example 3

[0067] 240 mL of 0.1 mol / L sodium metasilicate solution was added to a closed batch reactor, and nitrogen gas was introduced at a rate of 1.5 L / min. 75 mL of 1 mol / L sodium hydroxide solution was added and stirred at 800 rpm. Then, 240 mL of 0.224 mol / L calcium nitrate tetrahydrate solution was added and stirred at 1200 rpm. The reaction was carried out at 14 °C. Next, 1% of polyoxyethylene alkylamine (based on the total volume of sodium metasilicate, sodium hydroxide, and calcium nitrate tetrahydrate solutions) was added and stirred at 14 °C at 800 rpm to obtain a suspension. The suspension was filtered through a 0.45 μm nylon membrane, washed with a 1:1 volume ratio of ultrapure water and anhydrous ethanol, and then washed with anhydrous ethanol. Finally, nitrogen gas was introduced at a rate of 1.5 L / min, and the mixture was dried at 30 °C for 5 h to obtain high-purity single-phase γ-CSH gel.

[0068] As shown in the above embodiments, this invention provides a method for preparing high-purity single-phase γ-CSH gel. The method involves mixing and stirring sodium metasilicate solution, sodium hydroxide solution, and calcium nitrate tetrahydrate solution, then adding polyoxyethylene alkylamine for reaction, and finally sequentially filtering, washing, and drying to obtain high-purity single-phase γ-CSH gel. This invention prepares a gel with high purity and high crystallinity by inhibiting calcium hydroxide growth, reducing carbonization, and adjusting the solution pH.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity single-phase γ-CSH gel, characterized in that, Includes the following steps: (1) Sodium metasilicate solution and sodium hydroxide solution are stirred and mixed under a protective gas to obtain mixed solution A; (2) Mix the mixed solution A and the calcium nitrate tetrahydrate solution and then react them to obtain mixed solution B; In step (2), the stirring speed is 1000~1200 rpm; The temperature of the reaction is ≤15℃; (3) Add polyoxyethylene alkylamine to mixed solution B and stir to obtain a suspension; In step (3), the stirring speed is 600~800 rpm and the stirring temperature is ≤15℃; (4) The suspension was sequentially filtered, washed and dried to obtain high-purity single-phase γ-CSH gel; The volume ratio of the sodium metasilicate solution, sodium hydroxide solution, and calcium nitrate tetrahydrate solution is 150~250:65~75:150~250; The concentration of the sodium metasilicate solution is 0.05~0.2 mol / L; The concentration of the sodium hydroxide solution is 0.5~2 mol / L; The concentration of the calcium nitrate tetrahydrate solution is 0.1~0.3 mol / L; The volume of the polyoxyethylene alkylamine is 0.5 to 1.5% of the sum of the volumes of the sodium metasilicate solution, sodium hydroxide solution, and calcium nitrate tetrahydrate solution.

2. The preparation method according to claim 1, characterized in that, In step (1), the protective gas is nitrogen or argon.

3. The preparation method according to claim 2, characterized in that, In step (1), the rate at which the protective gas is introduced is 1~2 L / min.

4. The preparation method according to claim 3, characterized in that, In step (1), the stirring speed is 600~800 rpm and the stirring temperature is ≤15℃.

5. The preparation method according to claim 4, characterized in that, In step (4), the filtration uses a nylon filter membrane with a pore size of 0.3~1μm.

6. The preparation method according to claim 5, characterized in that, The washing process involves first washing with a mixed solution of water and anhydrous ethanol, followed by washing with anhydrous ethanol. The volume ratio of water to anhydrous ethanol is 1~3:1~3.

7. The preparation method according to claim 6, characterized in that, In step (4), the drying temperature is 15~30℃ and the time is 5~8h.

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