A calcium-alcohol complex and its preparation method and application

Abstract

The present invention relates to a calcium-alcohol complex and its preparation method and application, the method comprising the following steps: dissolving a calcium source into an alcohol ligand, mixing, and filtering; adding a poor solvent to the filtered solution, heating, and centrifuging to obtain a calcium-alcohol complex gel; and allowing the calcium-alcohol complex gel to stand to obtain a calcium-alcohol complex solution. Compared with the prior art, the present invention adopts a solution-gel-solution conversion path, wherein alcohol ligands such as ethylene glycol are complexed with a calcium source to form a complex, the complex precipitates a gel when heated, and the gel is allowed to stand for an appropriate time and then transformed back into a solution, ultimately achieving the synthesis of the calcium-alcohol complex solution, with low cost and simple operation. The obtained calcium-alcohol complex can enter tiny pores that are difficult for nanoparticles to enter, and the protective effect is relatively thorough, and has the advantages of high solid content and good permeability, and has good application potential in the field of calcium carbonate cultural relics protection.

Description

Technical Field

[0001] The invention belongs to the technical field of cultural relics protection materials and relates to a calcium-alcohol complex and a preparation method and application thereof. Background Art

[0002] Calcium carbonate artifacts are a series of material remains composed primarily of calcium carbonate, imbued with cultural value and historical heritage. These primarily include grottoes, inscriptions, and sculptures. They bear witness to the development and evolution of world civilizations and embody the essence of human civilization. However, these invaluable calcium carbonate artifacts have weathered the test of time and, for the most part, have been exposed to the elements for extended periods. Due to the long-term interaction of multiple environmental factors, such as temperature and humidity fluctuations, air pollution, and the crystallization of soluble salts, these artifacts suffer from numerous conditions, including weathering, erosion, cracking, pulverization, scaling, and herpes, causing significant damage to these precious artifacts. Therefore, scientifically protecting these artifacts to prevent and slow their deterioration is currently a pressing task.

[0003] Calcium carbonate artifacts generally develop a loose, porous structure due to the loss of calcium carbonate and the formation of microcracks during the deterioration process. One of the most important ways to prevent further deterioration is to develop suitable conservation materials that fill and bond the pores of calcium carbonate artifacts to reinforce them. Consequently, significant research and development efforts have been devoted to these materials over the past few decades, resulting in the development of a wide range of conservation materials, including organic polymers, silicon-based materials, and calcium-based materials. Organic polymers, primarily including polyacrylic resins, epoxy resins, organic fluororesins, and polyurethanes, have attracted widespread attention and application due to their excellent permeability and film-forming properties. However, organic polymer-based conservation materials often suffer from poor durability and irreversibility. Silicon-based conservation materials are oligomers prepared by the hydrolysis and polymerization of a series of different siloxane monomers. They offer advantages such as good permeability and aging resistance. However, these materials pose challenges such as potential glare and susceptibility to cracking. In addition, organic polymer protective materials and silicon-based protective materials may block pores due to their polymer properties; and these materials are different from the components and basic physical and chemical properties of calcium carbonate cultural relics, which may cause protective damage and other problems.

[0004] Compared to organic polymer and silicon-based protective materials, calcium-based protective materials are durable and compatible with calcium carbonate artifacts, making them ideal for the conservation of these materials. Calcium hydroxide is the most widely studied calcium-based protective material, primarily consisting of limewater and stabilized nano-calcium hydroxide dispersions. Limewater, an aqueous solution of calcium hydroxide, can penetrate the larger pores of porous artifacts and react with carbon dioxide within the pores to form calcium carbonate, thereby filling and bonding the porous calcium carbonate artifacts. However, calcium hydroxide's poor solubility in water results in a low solids content in limewater, limiting the effectiveness of a single application. Repeated use also introduces significant amounts of water into the artifacts, leading to water and salt damage. Compared to limewater, stabilized nano-calcium hydroxide dispersions have a higher solids content and are therefore widely studied and used in the field of cultural relic conservation. However, nano-sized particles cannot penetrate the tiny pores within the artifact's internal structure, which are accessible only to solutions. Furthermore, the solids content of nano-calcium hydroxide is still limited compared to organic polymer and silicon-based protective materials, necessitating repeated reinforcement. Furthermore, degraded calcium carbonate artifacts often have complex, uneven porous structures. Calcium hydroxide nanoparticles can easily clog small pores on the walls of larger pores, preventing the internal reinforcement of the larger pores. Therefore, developing new calcium carbonate artifact conservation materials to address this issue is both an urgent need and a significant challenge.

[0005] Patent CN114133208A discloses a material for reinforcing and protecting stone cultural relics, its preparation method, and its application. The material comprises an alcohol solvent and amorphous nano-calcium carbonate dispersed in the alcohol solvent. The material reinforces and protects the cultural relic substrate through the spontaneous conversion of the amorphous nano-calcium carbonate to crystalline calcium carbonate. The material can be prepared in solution or powder form through dispersion, reaction, separation, or drying. While this patent effectively protects rocks using amorphous nano-calcium carbonate dissolved in an alcohol solution, the nano-calcium carbonate is actually dispersed in the alcohol solvent in the form of nanoparticles. Due to the limited size of the nanoparticles, the nano-calcium carbonate cannot effectively protect tiny pores and cracks within the porous structure of the rock, which are inaccessible to the nanoparticles. Furthermore, the alcohol solvent used in this patent has a low boiling point, which can easily cause the amorphous calcium carbonate to seep back onto the surface upon evaporation, forming a calcium carbonate layer, adversely affecting the appearance of the protected object. Finally, the amorphous nano-calcium carbonate dispersion in this patent has a low content of calcium, an effective substance. Summary of the Invention

[0006] The purpose of the present invention is to provide a calcium-alcohol complex and its preparation method and application in order to overcome at least one defect of the above-mentioned prior art. The present invention can enter tiny pores that are difficult for nanoparticles to enter, has a relatively thorough protective effect, and has advantages such as high solid content and good permeability. It has good application potential in the field of calcium carbonate cultural relics protection.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] One of the technical solutions of the present invention is to provide a method for preparing a calcium-alcohol complex, which comprises the following steps:

[0009] (1) dissolving the calcium source in the alcohol ligand, and filtering after the calcium source is completely dissolved and mixed;

[0010] (2) adding a poor solvent to the filtered solution to form a mixed solution, and after the mixed solution is affected by the poor solvent to precipitate a gel during heating, centrifugation is performed to obtain a calcium-alcohol complex gel;

[0011] (3) The calcium-alcohol complex gel is allowed to stand until it turns into a colorless transparent solution to obtain a calcium-alcohol complex solution.

[0012] Furthermore, in step (1), the alcohol ligand is ethylene glycol, and the calcium source is selected from one or more of calcium, calcium oxide, and calcium hydroxide.

[0013] Furthermore, in step (1), the mass / volume ratio of the calcium source to the alcohol ligand is (0.2-1 g):(5-20 mL).

[0014] Furthermore, in step (1), the mixing temperature is room temperature and the mixing time is 3-5 hours.

[0015] Furthermore, in step (2), the poor solvent is ethanol.

[0016] Furthermore, in step (2), the volume / mass ratio of the poor solvent to the calcium source is (5-40 mL):(0.2-1 g).

[0017] Furthermore, in step (2), the heating temperature is 90-120° C. and the heating time is 10-30 min.

[0018] As a preferred technical solution, the centrifugal speed in step (2) is 8000-10000 rpm and the time is 1-3 min.

[0019] Furthermore, in step (3), the standing temperature is 0-40° C. and the standing time is 1-3 h.

[0020] One of the technical solutions of the present invention is to provide a calcium-alcohol complex prepared by the method described above, wherein the complex is in a solution state.

[0021] One of the technical solutions of the present invention is to provide an application of the calcium-alcohol complex, wherein the complex is used as a reinforcing and protective agent for the protection of calcium carbonate cultural relics.

[0022] The working principle of the present invention includes the following aspects:

[0023] (1) The alcohol ligand ethylene glycol molecules complex with the calcium source at high temperature to form a complex, which then gels under the induction of the poor solvent ethanol;

[0024] (2) The complex gel obtained by centrifugation can be transformed back into a solution form when allowed to stand for an appropriate time under suitable temperature conditions. The calcium-alcohol complex solution can enter the tiny pores that are difficult for nanoparticles to enter, and the protective effect is relatively thorough.

[0025] (3) Calcium-alcohol complexes can react with carbon dioxide in the air at the pores to be repaired to generate a three-dimensional continuous calcium carbonate network in situ. They have the advantages of high solid content and good permeability, and have good application potential in the field of calcium carbonate cultural relics protection.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention uses a solution-gel-solution conversion path, wherein the alcohol ligand ethylene glycol is complexed with the calcium source to form a complex, the complex precipitates a gel when heated, and the gel is allowed to stand for an appropriate time under suitable temperature conditions and then converted back into a solution, thereby finally achieving the synthesis of a calcium-alcohol complex solution. The method has low cost and simple operation. The obtained calcium-alcohol complex can enter tiny pores that are difficult for nanoparticles to enter, and the protective effect is relatively thorough. In addition, the method has advantages such as high solid content and good permeability, and has good application potential in the field of calcium carbonate cultural relics protection.

[0028] (2) The calcium-alcohol complex of the present invention exists stably in the form of a true solution over a wide temperature range and has better penetration ability. This calcium-diol complex solution has a high effective substance (calcium solid content of up to greater than 7%) and can penetrate into the tiny pores in cultural relics that are difficult for nanoparticles to enter;

[0029] (3) The calcium-alcohol complex of the present invention reacts with carbon dioxide in the air in situ at the pores to be repaired to form a three-dimensional continuous calcium carbonate network that fills and binds the pores, thereby reinforcing the damaged calcium carbonate cultural relics and improving their mechanical properties and weathering resistance.

[0030] (4) The solvent of the calcium-alcohol complex solution of the present invention is a high-boiling-point alcohol, which will not reversely permeate back to the surface to form a calcium carbonate layer, and has no adverse effect on the appearance of the protected object. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a photograph of the calcium-alcohol complex gel in Example 1 of the present invention;

[0032] Figure 2 This is a photograph of the calcium-alcohol complex solution in Example 1 of the present invention;

[0033] Figure 3 This is a graph showing the thermogravimetric test results of the calcium-alcohol complex solution in Example 1 of the present invention;

[0034] Figure 4 This is a scanning electron microscope image of the simulated cultural relic sample in Comparative Example 2 of the present invention;

[0035] Figure 5 This is a transmission electron micrograph of the simulated cultural relic sample after being reinforced with a calcium-alcohol complex in Example 1 of the present invention;

[0036] Figure 6 Graph showing the color difference test results of simulated cultural relic samples in Example 1 and Comparative Example 2 of the present invention;

[0037] Figure 7 Graph showing the compressive strength test results of simulated cultural relic samples in Example 1 of the present invention and the comparative example;

[0038] Figure 8 Graph showing the Leeb hardness test results of the simulated cultural relic samples in Example 1 of the present invention and the comparative example. DETAILED DESCRIPTION

[0039] The present invention is described in detail below with reference to specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0040] Unless otherwise specified, the equipment used in the following examples are all conventional equipment in the art; the reagents used are all commercially available products or prepared by conventional methods in the art unless otherwise specified. Anything not described in detail in the following examples can be achieved by conventional experimental means in the art.

[0041] The present invention provides a method for preparing a calcium-alcohol complex, which comprises the following steps:

[0042] (1) dissolving a calcium source in an alcohol ligand, wherein the alcohol ligand is ethylene glycol, and the calcium source is selected from one or more of calcium, calcium oxide, and calcium hydroxide, and the mass / volume ratio of the calcium source to the alcohol ligand is (0.2-1 g): (5-20 mL), and after the calcium source is completely dissolved and mixed at room temperature for 3-5 hours, filtering;

[0043] (2) adding a poor solvent to the filtered solution to form a mixed solution, wherein the poor solvent is ethanol, and the volume / mass ratio of the poor solvent to the calcium source is (5-40 mL): (0.2-1 g), heating at 90-120° C. for 10-30 min, after the mixed solution is affected by the poor solvent to precipitate a gel, centrifuging at 8000-10000 rpm for 1-3 min to obtain a calcium-alcohol complex gel;

[0044] (3) The calcium-alcohol complex gel is allowed to stand at 0-40° C. for 1-3 hours until it turns into a colorless transparent solution to obtain a calcium-alcohol complex solution.

[0045] The calcium-alcohol complex prepared by the above method is in solution state.

[0046] The calcium-alcohol complex is used as a reinforcing and protective agent in the protection of calcium carbonate cultural relics.

[0047] Example 1:

[0048] A method for preparing a calcium-alcohol complex comprises the following steps:

[0049] (1) Prepare a 30 mg / mL calcium hydroxide solution using 600 mg of calcium hydroxide as a solute and 20 mL of ethylene glycol as a solvent. Dissolve the calcium hydroxide at room temperature for 4 hours until complete, and then filter.

[0050] (2) The 20 mL calcium hydroxide solution obtained by filtration was stirred evenly, and then anhydrous ethanol twice the volume of the calcium hydroxide solution was added and mixed thoroughly. The solution was heated at 110° C. for 15 minutes. After the solution was affected by anhydrous ethanol and a gel was precipitated, it was centrifuged at 7000 rpm for 3 minutes. The supernatant was poured out to obtain a calcium-alcohol complex gel, such as Figure 1 As shown;

[0051] (3) The calcium-alcohol complex gel obtained as a result of centrifugation was allowed to stand at 25°C for 65 minutes and completely transformed into a colorless transparent solution, thereby obtaining a calcium-alcohol complex solution, such as Figure 2 shown.

[0052] The calcium-alcohol complex prepared by the above method is in solution state. After thermogravimetric testing, the remaining substance is calcium oxide with a solid content greater than 10%, and the solid content after conversion to calcium element is greater than 7%. Figure 3 shown.

[0053] The simulated cultural relic samples used for protection are natural stones from Leshan cut into 2cm cubes with no cracks on the surface. The stones have no defects as a whole and no holes visible to the naked eye on the surface.

[0054] In order to simulate the effect of cultural relics being eroded in nature, the acid erosion method is used to simulate the damage caused by the coupling of multiple factors in the natural environment. The acid erosion simulation method process is as follows:

[0055] Place the stone in 0.1mol / L hydrochloric acid at a pressure of -0.1MPa for 2 hours to allow the hydrochloric acid to penetrate into the stone and corrode it evenly. Then soak the stone in hydrochloric acid of the same concentration at room temperature for 24 hours. After soaking, wash and dry it with deionized water.

[0056] The above calcium-alcohol complex is used to penetrate and reinforce the simulated cultural relics. The specific steps are as follows:

[0057] The acid-etched stone was immersed in a calcium-alcohol complex solution at a pressure of -0.1 MPa for 2±0.5 h, until no more bubbles were generated on the surface of the stone, so that the calcium-alcohol complex solution could fully penetrate into the porous structure inside the stone. The stone surface was then cleaned and dried with deionized water and then protected at a temperature of 25°C, a humidity of 60%, and a time of 120 h.

[0058] Comparative Example 1:

[0059] Untreated stones.

[0060] Comparative Example 2:

[0061] Stones not protected by calcium-alcohol complexes after acid attack.

[0062] like Figure 4 As shown, the unprotected stone sample in Comparative Example 2 has an irregular flaky surface structure.

[0063] like Figure 5 As shown, the pores and cracks inside the stone sample are filled with the calcium-alcohol complex solution of this embodiment. The calcium-alcohol complex reacts with carbon dioxide in the air to form a three-dimensional continuous calcium carbonate network that performs filling and bonding functions.

[0064] Color difference tests were conducted on untreated, acid-etched, and reinforced stones. The color difference was measured using a CR-400 colorimeter. Delta L, Delta a, and Delta b represent the differences in lightness (L) and chromaticity indices (a and b) before and after reinforcement. Delta E represents the overall color difference. The color difference test was performed at nine measurement points on the flat surface of the stone, and the average of the color difference results was calculated.

[0065] like Figure 6 As shown, the surface color change of the stone sample reinforced with the calcium-alcohol complex of this embodiment is within an acceptable range.

[0066] The mechanical properties and weathering resistance of the untreated, acid-etched, and reinforced stones were tested. Tested properties included Leeb hardness and compressive strength. Leeb hardness was measured using an HT-2000A pen-type Leeb hardness tester. The Leeb hardness test was performed at three points on the flat surface of the stone, and the results were averaged. All stones were placed on the same substrate for the Leeb hardness test. Compressive strength was measured using an E44 electronic universal testing machine. Three compressive strength measurements were taken for each type of stone (untreated, acid-etched, and reinforced), and the average was taken.

[0067] like Figure 7 As shown, the peak load of the stone sample reinforced with the calcium-alcohol complex of this embodiment reaches 25.4 MPa, which is higher than the average peak load of 11.8 MPa of the acid-etched sample in Comparative Example 2 and close to the average peak load of 27.8 MPa of the untreated sample in Comparative Example 1.

[0068] like Figure 8 As shown, the Leeb hardness of the stone sample reinforced with the calcium-alcohol complex of this embodiment reaches 132HL, which is also higher than the average Leeb hardness of 108HL of the acid-etched sample in Comparative Example 2, and close to the average Leeb hardness of 156HL of the untreated sample in Comparative Example 1.

[0069] Example 2:

[0070] A calcium-alcohol complex and its preparation method and application are basically the same as Example 1, except that in step (1), a calcium oxide solution with a concentration of 35 mg / mL is prepared using 700 mg of calcium oxide as a solute and 20 mL of ethylene glycol as a solvent, and in step (2), the heating time is 20 min.

[0071] The peak load of the stone sample reinforced with the calcium-alcohol complex of this example reached 23.4 MPa, which was higher than the average peak load of 11.8 MPa of the acid-etched sample in Comparative Example 2 and close to the average peak load of 27.8 MPa of the untreated sample in Comparative Example 1.

[0072] The Leeb hardness of the stone sample reinforced with the calcium-alcohol complex of this embodiment reaches 134HL, which is also higher than the average Leeb hardness of 108HL of the acid-etched sample in Comparative Example 2, and close to the average Leeb hardness of 156HL of the untreated sample in Comparative Example 1.

[0073] Example 3:

[0074] A calcium-alcohol complex and its preparation method and application are basically the same as Example 1, except that in step (1), a calcium oxide solution with a concentration of 20 mg / mL is prepared using 200 mg of calcium oxide as a solute and 10 mL of ethylene glycol as a solvent, and in step (2), the heating time is 20 minutes.

[0075] The peak load of the stone sample reinforced with the calcium-alcohol complex of this example reached 24.8 MPa, which was higher than the average peak load of 11.8 MPa of the acid-etched sample in Comparative Example 2 and close to the average peak load of 27.8 MPa of the untreated sample in Comparative Example 1.

[0076] The Leeb hardness of the stone sample reinforced with the calcium-alcohol complex of this embodiment reaches 150HL, which is also higher than the average Leeb hardness of 108HL of the acid-etched sample in Comparative Example 2, and close to the average Leeb hardness of 156HL of the untreated sample in Comparative Example 1.

[0077] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing a calcium-alcohol complex, characterized in that: The method comprises the following steps: (1) Dissolve the calcium source in the alcohol ligand, mix, and filter; (2) Adding a poor solvent to the filtered solution, heating, and centrifuging to obtain a calcium-alcohol complex gel; (3) allowing the calcium-alcohol complex gel to stand to obtain a calcium-alcohol complex solution; In step (1), the alcohol ligand is ethylene glycol, and the calcium source is selected from one or more of calcium, calcium oxide, and calcium hydroxide; The poor solvent in step (2) is ethanol.

2. The method for preparing a calcium-alcohol complex according to claim 1, wherein The mass / volume ratio of the calcium source to the alcohol ligand in step (1) is (0.2-1 g):(5-20 mL).

3. The method for preparing a calcium-alcohol complex according to claim 1, wherein The mixing temperature in step (1) is room temperature and the mixing time is 3-5 h.

4. The method for preparing a calcium-alcohol complex according to claim 1, wherein The volume / mass ratio of the poor solvent to the calcium source in step (2) is (5-40 mL):(0.2-1 g).

5. The method for preparing a calcium-alcohol complex according to claim 1, wherein In step (2), the heating temperature is 90-120°C and the heating time is 10-30 min.

6. The method for preparing a calcium-alcohol complex according to claim 1, wherein In step (3), the standing temperature is 0-40°C and the standing time is 1-3 h.

7. A calcium-alcohol complex prepared by the method according to any one of claims 1 to 6, characterized in that: The complex is in solution.

8. Use of the calcium-alcohol complex according to claim 7, characterized in that: The complex is used as a reinforcing and protecting agent for the protection of calcium carbonate cultural relics.

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