Nano calcium hydroxide as well as preparation method and application thereof

Abstract

The invention discloses nano calcium hydroxide as well as a preparation method and application thereof.The specific preparation method comprises the following steps: adding clay mineral into a soluble calcium salt solution, and enabling the clay mineral to be in a suspended and dispersed state to obtain a soluble calcium salt-clay mineral-water system; dropwise adding a hydroxide solution into the soluble calcium salt-clay mineral-water system, uniformly stirring, and standing for reaction; and after the reaction is completed, adding a flocculant and stirring to obtain a reaction liquid, and filtering to obtain the nano calcium hydroxide dispersion liquid. A clay mineral-water system is utilized, the system is in a suspended and dispersed state, the dispersed clay mineral has thixotropy, clay particles are mutually lapped in water to form a micron-level micro space, and the synthesis range of calcium hydroxide is limited in the micro space, so that the size of a reaction product can be effectively limited; and thus, the nano calcium hydroxide with the particle size of 50-200 nm is synthesized.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, specifically to a nano-calcium hydroxide, its preparation method, and its application. Background Technology

[0002] Murals, as precious cultural heritage, carry historical, artistic, and scientific value. However, due to the erosion of the natural environment and time, they face threats such as pigment peeling, efflorescence, flaking, and hollowing. Calcium hydroxide bonding and repair materials are widely used in the reinforcement and restoration of murals. Essentially a calcium-based inorganic material, its chemical composition is compatible with the mural ground layer (containing calcium carbonate and clay minerals). It can fuse with the matrix through a carbonation reaction (reacting with CO2 in the air to form calcium carbonate), forming a stable structure. It can neutralize acidic pollutants in the mural ground layer (such as microbial metabolic acids and atmospheric acid deposition), adjust the microenvironment pH to a slightly alkaline level (matching the original formation environment of the mural), inhibit efflorescence and microbial erosion, delay mural deterioration, and extend its preservation life. Moreover, the repair layer is reversible; if necessary, it can be gently removed with a weakly acidic solution (such as ammonium formate solution), conforming to the principle of "minimal intervention and reprocessability" in cultural relic restoration. Currently used calcium hydroxide has a large particle size (micrometers and above), making it difficult to penetrate the fine pores and cracks in the ground layer of murals, and thus unable to accurately fill and reinforce them. It also has weak bonding with the mural substrate (which often contains calcium carbonate, clay minerals, etc.), and the repair layer is prone to falling off. For example, when repairing Tang Dynasty murals, conventional calcium hydroxide is difficult to effectively integrate with the alkali-affected ground layer, resulting in short-lived repair effects.

[0003] Using nano-calcium hydroxide for mural restoration offers numerous advantages and can meet the needs of mural restoration. Due to its fine particle size, it can quickly penetrate the micropores and cracks in the mural's base layer, filling the pores formed by alkali degradation, reconstructing the dense structure of the base layer, strengthening the bond between the pigment layer and the base layer, and solving problems such as flaking and hollowing. For example, in the restoration of a Song Dynasty tomb mural in Gansu, nanoparticles could penetrate 0.2~0.5mm into the alkali-depleted layer, achieving microscopic reinforcement. Currently, commonly used methods for synthesizing nano-calcium hydroxide include aqueous solution methods, pure solution methods, co-precipitation methods, and sol-gel methods. However, these methods are complex and have poor dispersibility. Furthermore, the calcium hydroxide synthesized for cultural relic preservation currently has the problem of large particle size. For example, the ideal size and morphology of nano-calcium hydroxide used in mural preservation is 50~250nm, with an average particle size of approximately 150nm, requiring further synthesis optimization. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a nano-calcium hydroxide, its preparation method, and its application. It utilizes a clay mineral-water system, placing the system in a suspended and dispersed state. The dispersed clay minerals exhibit thixotropic properties, and the overlapping of clay particles in the water forms micron-sized microspaces. This limits the synthesis range of calcium hydroxide within these microspaces, effectively restricting the size of the reaction products, thereby synthesizing nano-calcium hydroxide with a particle size of 50 nm to 200 nm.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for synthesizing nano-calcium hydroxide using clay minerals, the specific preparation method of which is as follows: Clay minerals are added to a soluble calcium salt solution to suspend and disperse the clay minerals, thus obtaining a soluble calcium salt-clay mineral-water system. Add the hydroxide solution dropwise to the above soluble calcium salt-clay mineral-water system, stir well, and let it stand to react; After the reaction is complete, add flocculant and stir to obtain a reaction solution. Filter to obtain a nano calcium hydroxide dispersion.

[0006] Furthermore, the soluble calcium salt is calcium chloride, calcium nitrate, or calcium acetate; the concentration of the soluble calcium salt solution is 5wt%~15wt%.

[0007] Furthermore, the clay minerals include one or two of the montmorillonite, kaolinite, illite, chlorite, and sepiolite groups; when two clay minerals are used, the ratio of the two clay minerals is 1:1 to 3.

[0008] Furthermore, in the soluble calcium salt-clay mineral-water system, the amount of clay mineral added is 5wt%~36wt%.

[0009] Furthermore, the hydroxide is one of LiOH, NaOH, KOH, and RbOH, and the amount of hydroxide used is 3.5wt% to 16.5wt%.

[0010] Furthermore, the static reaction time is 20 min to 180 min.

[0011] Furthermore, the flocculant is one of polyaluminum chloride, polyferric sulfate, and ferric chloride, and the dosage is 40 mg / L to 200 mg / L.

[0012] Furthermore, the filter paper used for filtration has a pore size of 1μm to 10μm.

[0013] The present invention also provides a nano-calcium hydroxide, which is prepared by the above method, and the particle size of the prepared nano-calcium hydroxide is 50 nm to 200 nm.

[0014] The present invention also provides a method for mural restoration, which involves dissolving the above-mentioned nano-calcium hydroxide in a solvent to form a nano-calcium hydroxide suspension, and then spraying the nano-calcium hydroxide suspension to cover the part of the mural to be restored.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: This invention provides a method for synthesizing nano-calcium hydroxide using clay minerals. The method utilizes a clay mineral-water system, placing the system in a suspended, dispersed state. The dispersed clay minerals exhibit thixotropic properties, and the overlapping of clay particles in the water forms a micron-sized microreactor, confining the synthesis of calcium hydroxide within this tiny space. This effectively limits the size of the reaction products, resulting in the synthesis of nano-calcium hydroxide with a particle size of 50-200 nm. This provides an ideal size and morphology for nano-calcium hydroxide used in mural preservation, allowing it to efficiently penetrate the micropores and cracks in the mural's base layer and fill the pores formed by alkali degradation. Attached Figure Description

[0016] Figure 1 This is a scan diagram of clay particles, showing that bentonite particles have a nanosheet-like structure.

[0017] Figure 2 This is a schematic diagram of the process by which clay particles disperse in water and then overlap to form a thixotropic pseudo-coagulation state.

[0018] Figure 3 A schematic diagram of a micro-scale microreactor formed by clay particles and a reaction solution.

[0019] Figure 4 The image shown is an electron microscope image of the nano-calcium hydroxide prepared in Example 1. It can be seen that the synthesized nano-calcium hydroxide has a certain degree of dispersibility and the synthesized size is nano-sized.

[0020] Figure 5 The particle size distribution of the nano-calcium hydroxide prepared in Example 1 is shown in the calculation diagram. It can be seen that the size of 50nm accounts for a large proportion.

[0021] Figure 6 This is a sample of a Tang Dynasty mural prepared using nano-calcium hydroxide through penetration curing in Example 1. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0023] It should be noted that the terms "first," "second," etc., in the specification and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0024] This invention discloses a method for synthesizing nano-sized calcium hydroxide using clay minerals. The method employs a clay mineral-water system as the reaction vessel. The overlapping of clay particles in the water forms micron-sized microspaces, confining the synthesis of calcium hydroxide within these microspaces. This effectively limits the size of the reaction products, resulting in nano-sized calcium hydroxide with a specific particle size. The specific steps are as follows: S1: Dissolve soluble calcium salts in water to prepare a soluble calcium salt solution; S2: Add an appropriate amount of clay minerals to a soluble calcium salt solution to keep the clay minerals in a suspended and dispersed state; S3: Quickly add the hydroxide solution dropwise to the above soluble calcium salt-clay mineral-water system, stir quickly and evenly, and let it stand to allow the clay mineral to exhibit a thixotropic pseudo-coagulation state. At this time, the calcium salt and hydroxide react in the tiny space formed by the clay mineral. S4: After the reaction is complete, add flocculant and stir to precipitate and separate the clay minerals. After centrifugation, take out the upper reaction liquid and filter out the residual clay particles with ordinary filter paper to obtain a nano calcium hydroxide dispersion with a particle size of 50-200 nm.

[0025] Preferably, in S1, the soluble calcium salt is one of calcium chloride (CaCl2), calcium nitrate (Ca(NO3)2), or calcium acetate (Ca(CH3COO)2), with a concentration of 5wt% to 15wt%.

[0026] Preferably, in S2, the clay minerals include one or two of the montmorillonite, kaolinite, illite, chlorite, and sepiolite groups. When two clay minerals are used, the ratio of the two clays can be 1:1, 1:2, or 1:3. In the final suspension dispersion of the clay mineral-water system, the proportion of clay minerals is 5wt% to 36wt%.

[0027] Preferably, in S3, the hydroxide used is one of LiOH, NaOH, KOH, and RbOH, and the amount of hydroxide used is 3.5wt%~16.5wt%. After the clay suspension undergoes false coagulation, the subsequent reaction time is 20min~180min.

[0028] Preferably, the flocculant in S4 is one of polyaluminum chloride (PAC), polyferric sulfate (PFS), and ferric chloride (FeCl3), and the dosage is 40 mg / L to 200 mg / L.

[0029] Preferably, quantitative filter paper with a pore size of 1μm to 10μm is used.

[0030] Example 1 This invention provides a method for synthesizing nano-calcium hydroxide using clay minerals, which specifically follows these steps: (1) Preparation of soluble calcium salt solution: Dissolve 10wt% calcium chloride in water to prepare soluble calcium salt solution.

[0031] (2) Preparation of suspension dispersion: 24% of montmorillonite group bentonite (e.g.) Figure 1 (As shown) is added to a soluble calcium salt solution to keep the clay minerals in a suspended and dispersed state.

[0032] (3) Quickly add 9 wt% sodium hydroxide solution dropwise to the above calcium chloride-clay mineral-water system, stir quickly and evenly, and let stand to allow the clay minerals to exhibit a thixotropic pseudo-coagulation state (e.g. Figure 2 As shown), at this time, calcium chloride and sodium hydroxide form a microreactor in the clay mineral (such as...). Figure 3 The reaction is shown in the figure, and the reaction time is 100 min.

[0033] (4) After the reaction is complete, add 120 mg / L of PAC flocculant and stir to precipitate and separate the bentonite. After centrifugation, take out the upper reaction liquid. The centrifugation speed is 8000 r / min. Filter out the residual clay particles with ordinary filter paper with a pore size of 1 μm to obtain a nano-calcium hydroxide dispersion (e.g. Figure 4 As shown), the median particle size of the nano-calcium hydroxide is 50 nm (as shown). Figure 5 (As shown).

[0034] (5) The obtained nano-calcium hydroxide was used for the reinforcement and repair of mural samples (e.g. Figure 6(As shown). Soil mural samples were prepared. To more closely resemble the state of a real mural, all samples were placed in a UV aging chamber for aging treatment. The prepared nano-calcium hydroxide material was dissolved in isopropanol, ultrasonically dispersed for 5 minutes, and then placed into the nozzle of a spray gun. The nozzle was 15 cm away from the mural surface, and the suspension was sprayed onto the mural surface. Spraying was stopped after the adhesive material was evenly adhered to the surface. The mural was placed in a constant temperature and humidity test chamber for 12 days to allow the nano-calcium hydroxide to fully solidify, resulting in a reinforced mural sample. The reinforced mural sample exhibited high mechanical properties, with a flexural strength of 0.5378 MPa and a peel strength of 0.03149 mg / cm². 2 Meanwhile, no obvious particulate matter was observed on the newly reinforced simulated mural surface, indicating that the material has good permeability in the mural's pigment layer, minimizing its impact on the pigment layer. The material does not clog the pores of the unreinforced mural, preventing moisture condensation and thus avoiding damage. This characteristic is particularly important for the long-term preservation of murals, as it ensures the stability of the mural's microenvironment and prevents additional damage caused by improper material application. The development and application of this material provides a new solution for mural conservation, contributing to the sustainable preservation of cultural heritage.

[0035] Example 2 This invention provides a method for synthesizing nano-calcium hydroxide using clay minerals, which specifically follows these steps: (1) Nano-sized calcium hydroxide was prepared by the method described in Example 1, wherein the amount of calcium chloride was 15 wt%, the amount of bentonite was 30%, the amount of sodium hydroxide was 16.5 wt%, the calcium chloride and sodium hydroxide were reacted in a microreactor formed by clay minerals, the reaction time was 140 min, after the reaction was completed, 120 mg / L of PAC flocculant was used, the speed of the high-speed centrifuge was 2000 r / min, and the filter paper pore size was 5 μm.

[0036] (2) The particle size of the nano-calcium hydroxide was measured to be 180 nm.

[0037] (3) Following the method in Example 1, the obtained nano-calcium hydroxide was used to reinforce the mural sample. The reinforced mural sample had a flexural strength of 0.4876 MPa and a peel strength of 0.03829 mg / cm. 2 No obvious particulate matter was observed on the surface.

[0038] Example 3 This invention provides a method for synthesizing nano-calcium hydroxide using clay minerals, which specifically follows these steps: (1) Nano-sized calcium hydroxide was prepared by the method described in Example 1, wherein the amount of calcium chloride was 5 wt%, the amount of bentonite was 10%, the amount of sodium hydroxide was 3.5 wt%, the calcium chloride and sodium hydroxide were reacted in a microreactor formed by clay minerals, the reaction time was 40 min, after the reaction was completed, 60 mg / L of PAC flocculant was used, the speed of the high-speed centrifuge was 1600 r / min, and the filter paper pore size was 2 μm.

[0039] (2) The particle size of the nano-calcium hydroxide was measured to be 150 nm.

[0040] (3) Following the method in Example 1, the obtained nano-calcium hydroxide was used to reinforce the mural sample. The reinforced mural sample had a flexural strength of 0.5163 MPa and a peel strength of 0.03442 mg / cm. 2 No obvious particulate matter was observed on the surface.

[0041] Example 4 This invention provides a method for synthesizing nano-calcium hydroxide using clay minerals, which specifically follows these steps: (1) Nano-calcium hydroxide was prepared by the method described in Example 1, wherein 10 wt% calcium chloride was used, the amount of bentonite and clay was 24% and the ratio was 1:1, the amount of sodium hydroxide was 9 wt%, calcium chloride and sodium hydroxide were reacted in a microreactor formed by clay minerals, the reaction time was 100 min, after the reaction was completed, 100 mg / L PAC flocculant was used, the speed of the high-speed centrifuge was 2000 r / min, and the filter paper pore size was 2 μm.

[0042] (2) The particle size of the nano-calcium hydroxide was measured to be 110 nm.

[0043] (3) Following the method in Example 1, the obtained nano-calcium hydroxide was used to reinforce the mural sample. The reinforced mural sample had a flexural strength of 0.5409 MPa and a peel strength of 0.03189 mg / cm. 2 No obvious particulate matter was observed on the surface.

[0044] Example 5 This invention provides a method for synthesizing nano-calcium hydroxide using clay minerals, which specifically follows these steps: (1) Nano-calcium hydroxide was prepared by the method described in Example 1, wherein 10 wt% calcium chloride was used, the amount of bentonite and clay was 24% and the ratio was 1:2, the amount of sodium hydroxide was 9 wt%, calcium chloride and sodium hydroxide were reacted in a microreactor formed by clay minerals, the reaction time was 100 min, after the reaction was completed, 100 mg / L PAC flocculant was used, the speed of the high-speed centrifuge was 2000 r / min, and the filter paper pore size was 2 μm.

[0045] (2) The particle size of the nano-calcium hydroxide was measured to be 120 nm.

[0046] (3) Following the method in Example 1, the obtained nano-calcium hydroxide was used to reinforce the mural sample. The reinforced mural sample had a flexural strength of 0.5417 MPa and a peel strength of 0.03201 mg / cm². 2 No obvious particulate matter was observed on the surface.

[0047] Example 6 This invention provides a method for synthesizing nano-calcium hydroxide using clay minerals, which specifically follows these steps: (1) Nano calcium hydroxide was prepared by the method described in Example 1, wherein the amount of calcium nitrate was 10 wt%, the amount of bentonite was 24%, the amount of sodium hydroxide was 9 wt%, the calcium nitrate and sodium hydroxide were reacted in a microreactor formed by clay minerals, the reaction time was 20 min, after the reaction was completed, 100 mg / L of PFS flocculant was used, the speed of the high-speed centrifuge was 2000 r / min, and the filter paper pore size was 2 μm.

[0048] (2) The particle size of the nano-calcium hydroxide was measured to be 200 nm.

[0049] (3) Following the method in Example 1, the obtained nano-calcium hydroxide was used to reinforce the mural sample. The reinforced mural sample had a flexural strength of 0.4706 MPa and a peel strength of 0.04009 mg / cm. 2 No obvious particulate matter was observed on the surface.

[0050] Example 7 This invention provides a method for synthesizing nano-calcium hydroxide using clay minerals, which specifically follows these steps: (1) Nano-calcium hydroxide was prepared by the method described in Example 1, wherein 15 wt% calcium chloride, 5% bentonite, and 9 wt% potassium hydroxide were used. Calcium chloride and sodium hydroxide were reacted in a microreactor formed by clay minerals for 180 min. After the reaction was completed, 100 mg / L FeCl3 flocculant was used. The speed of the high-speed centrifuge was 2000 r / min and the filter paper pore size was 2 μm.

[0051] (2) The particle size of the nano-calcium hydroxide was measured to be 170 nm.

[0052] (3) Following the method in Example 1, the obtained nano-calcium hydroxide was used to reinforce the mural sample. The reinforced mural sample had a flexural strength of 0.4912 MPa and a peel strength of 0.03912 mg / cm. 2 No obvious particulate matter was observed on the surface.

[0053] Example 8 This invention provides a method for synthesizing nano-calcium hydroxide using clay minerals, which specifically follows these steps: (1) Nano-sized calcium hydroxide was prepared by the method described in Example 1, wherein 10 wt% calcium chloride was used, 24% kaolin was used as the clay mineral, and 9 wt% sodium hydroxide was used. Calcium chloride and sodium hydroxide were reacted in a microreactor formed by clay minerals for 150 min. After the reaction was completed, 40 mg / L FeCl3 flocculant was used. The speed of the high-speed centrifuge was 2000 r / min and the filter paper pore size was 2 μm.

[0054] (2) The particle size of the nano-calcium hydroxide was measured to be 150 nm.

[0055] (3) Following the method in Example 1, the obtained nano-calcium hydroxide was used to reinforce the mural sample. The reinforced mural sample had a flexural strength of 0.5133 MPa and a peel strength of 0.03382 mg / cm. 2 No obvious particulate matter was observed on the surface.

[0056] Example 9 This invention provides a method for synthesizing nano-calcium hydroxide using clay minerals, which specifically follows these steps: (1) Nano-sized calcium hydroxide was prepared by the method described in Example 1, wherein the amount of calcium acetate was 10 wt%, the amount of bentonite and kaolin was 36% and the ratio was 1:3, the amount of sodium hydroxide was 9 wt%, the calcium acetate and sodium hydroxide were reacted in a microreactor formed by clay minerals, the reaction time was 120 min, after the reaction was completed, 200 mg / L of PAC flocculant was used, the speed of the high-speed centrifuge was 2000 r / min, and the filter paper pore size was 10 μm.

[0057] (2) The particle size of the nano-calcium hydroxide was measured to be 140 nm.

[0058] (3) Following the method in Example 1, the obtained nano-calcium hydroxide was used to reinforce the mural sample. The reinforced mural sample had a flexural strength of 0.5236 MPa and a peel strength of 0.03199 mg / cm². 2No obvious particulate matter was observed on the surface.

[0059] In summary, this invention discloses a method, approach, and application for synthesizing nano-sized calcium hydroxide using clay minerals, belonging to the field of nanomaterial preparation technology. A method for synthesizing nano-sized calcium hydroxide using clay minerals. This method utilizes a clay mineral-water system as the reaction vessel. The overlapping of clay particles in the water forms micron-sized microspaces, confining the synthesis of calcium hydroxide within these microspaces. This effectively limits the size of the reaction product, resulting in nano-sized calcium hydroxide with a specific particle size. The above description is merely illustrative of the technical concept of this invention and should not be construed as limiting the scope of protection of this invention. Any modifications made to the technical solution based on the technical concept proposed in this invention fall within the scope of protection of the claims of this invention.

Claims

1. A method for synthesizing nano-calcium hydroxide using clay minerals, characterized in that, The specific preparation method is as follows: Clay minerals are added to a soluble calcium salt solution to suspend and disperse the clay minerals, thus obtaining a soluble calcium salt-clay mineral-water system. Add the hydroxide solution dropwise to the above soluble calcium salt-clay mineral-water system, stir well, and let it stand to react; After the reaction is complete, add flocculant and stir to obtain a reaction solution. Filter to obtain a nano calcium hydroxide dispersion.

2. The method for synthesizing nano-calcium hydroxide using clay minerals according to claim 1, characterized in that, The soluble calcium salt is calcium chloride, calcium nitrate, or calcium acetate; the concentration of the soluble calcium salt solution is 5wt%~15wt%.

3. The method for synthesizing nano-calcium hydroxide using clay minerals according to claim 1, characterized in that, Clay minerals include one or two of the montmorillonite, kaolinite, illite, chlorite, and sepiolite groups; when two clay minerals are used, the ratio of the two clay minerals is 1:1 to 3.

4. The method for synthesizing nano-calcium hydroxide using clay minerals according to claim 1, characterized in that, In the soluble calcium salt-clay mineral-water system, the amount of clay mineral added is 5wt%~36wt%.

5. The method for synthesizing nano-calcium hydroxide using clay minerals according to claim 1, characterized in that, The hydroxide is one of LiOH, NaOH, KOH, and RbOH, and the amount of hydroxide used is 3.5wt%~16.5wt%.

6. The method for synthesizing nano-calcium hydroxide using clay minerals according to claim 1, characterized in that, The static reaction time is 20 min to 180 min.

7. The method for synthesizing nano-calcium hydroxide using clay minerals according to claim 1, characterized in that, The flocculant is one of polyaluminum chloride, polyferric sulfate, and ferric chloride, and the dosage is 40 mg / ~200 mg / L.

8. The method for synthesizing nano-calcium hydroxide using clay minerals according to claim 1, characterized in that, The filter paper used for filtration has a pore size of 1μm to 10μm.

9. A nano-calcium hydroxide, characterized in that, The nano-calcium hydroxide was prepared by the method according to any one of claims 1 to 8, and the particle size of the prepared nano-calcium hydroxide was 50 nm to 200 nm.

10. A method for restoring murals, characterized in that, The nano-calcium hydroxide described in claim 9 is dissolved in a solvent to form a nano-calcium hydroxide suspension, and the nano-calcium hydroxide suspension is sprayed to cover the part of the mural to be repaired.

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