New crystal containing ions such as Mg, Al and Ca and water and preparation method thereof

Abstract

The invention discloses a novel crystal containing ions such as Mg, Al and Ca and water and a preparation method of the novel crystal. The XRD diffraction peak of the crystal is unconventional, and the XRD diffraction pattern of the crystal has diffraction peaks at (1), (2), (3) and (4); the preparation method of the crystal comprises the following steps: adding deionized water into a material obtained by mixing tricalcium aluminate and magnesium oxide for hydration, putting a hydrated sample into a plastic bottle, filling nitrogen for sealing, then putting into a curing box for constant-temperature curing, and hydrating for 3 days, so that an obvious diffraction peak can appear, the MgO doping amount is 40% of the mass of tricalcium aluminate, the water-solid ratio is 10: 1, and the optimal curing temperature is 50 DEG C. The preparation method has universality, the preparation process is simple, and operation is easy.

Description

Technical Field

[0001] The present invention belongs to the technical field of anionic compound materials, relates to a new composition of hydrotalcite materials, and particularly relates to a new crystal containing Mg, Al, Ca and other ions and water and a preparation method thereof. Background Art

[0002] Hydrotalcite is a layered double hydroxide, and its crystal structure has broad application prospects, such as catalysis, adsorbent, drug carrier, etc. Its structural general formula is [Me 1-x 2+ Me x 3+ (OH) 2 ) x+ [A m- ) x / m ·xH 2 O. The structural formula of hydrotalcite in the cement paste containing dolomite is: Mg (1-x) Al x (OH) 2 (CO 3 ) x / 2 ·nH 2 O (Science, 2018, 105: 1 - 17). Due to its unique physical and chemical properties, it has received a large amount of research and attention.

[0003] The preparation of existing hydrotalcite materials includes coprecipitation method, hydrothermal synthesis method, etc. The formation conditions are harsh, such as solution pH value, solution concentration, pressure, temperature, etc., and the preparation cost is relatively high, and it is mostly applied to fields such as chemical industry and medicine.

[0004] Therefore, although the preparation process of hydrotalcite is becoming more and more perfect, the research on the magnesium - aluminum hydrotalcite formed by the hydration of clinker in the cement industry is still a huge challenge, especially the hydration reaction of aluminate phase is rapid and the products are complex and diverse. Summary of the Invention

[0005] In order to overcome the above - mentioned disadvantages of the prior art, the purpose of the present invention is to provide a new crystal containing Mg, Al, Ca and other ions and water and a preparation method thereof. The new crystal of the present invention is similar to magnesium - aluminum hydrotalcite, and the preparation process is simple and easy to operate. It can provide a new solution for the expansion effect of magnesium oxide in cement hydration, thereby improving the soundness of concrete.

[0006] To achieve the above - mentioned purpose, the technical solution adopted by the present invention is as follows:

[0007] A new crystal containing Mg, Al, Ca ions and water, the crystal is layered, and its X-ray diffraction pattern shows characteristic diffraction peaks not found in the existing crystal structure database. Specifically, obvious diffraction peaks appear at 2θ = 6.7°, 13.38°, 20.14°, and 26.96° in the XRD diffraction pattern.

[0008] The present invention also provides a preparation method of the new crystal containing Mg, Al, Ca ions and water. Add tricalcium magnesium aluminate material to deionized water for hydration, seal the hydrated sample in a nitrogen environment, cure it in a constant temperature water bath, and then dry it to obtain the product.

[0009] In one embodiment, the tricalcium magnesium aluminate material is a mixed material with the mass of magnesium oxide being 20 - 60% of the mass of tricalcium aluminate, further preferably 30 - 50%, and more preferably 40%. This material can be prepared by the following method:

[0010] Mix calcium carbonate and alumina with a Ca / Al molar ratio of 1.5, and then incorporate a certain amount of magnesium oxide and calcine to obtain tricalcium magnesium aluminate. Incorporate magnesium oxide into the mixture of calcium carbonate and alumina according to the ratio of 30 - 50 parts by weight of magnesium oxide per 100 parts by weight of tricalcium aluminate; the calcination scheme is to heat up to 1000°C in a high-temperature furnace at a heating rate of 10°C / min, then heat up to 1400°C - 1500°C at a rate of 5°C / min, hold for 0.5 h - 3 h and then take out, and use a blower to quickly cool it to room temperature.

[0011] In one embodiment, the magnesium oxide is obtained by calcining basic magnesium carbonate at 900°C for 30 min, and the calcium carbonate, alumina, and basic magnesium carbonate are respectively screened using a 75μm square-hole sieve.

[0012] In one embodiment, the water-solid ratio of the hydration is 10:1.

[0013] In one embodiment, the temperature of the constant temperature water bath curing is 20 - 50°C, further preferably 20°C, 50°C or 80°C, and more preferably 50°C. The age is more than 3 days. The crystal begins to form after 2 days of curing, and as the hydration age increases, the crystal gradually increases. The formation of the crystal is basically completed at 56 days.

[0014] In one embodiment, after the constant temperature water bath curing, soak it in isopropanol to terminate the hydration.

[0015] In one embodiment, the drying is carried out at 35 - 45°C under vacuum conditions for 22 - 26 h. More preferably, it is at 40°C and dried for 24 h. The vacuum condition can be a negative pressure range of -0.06 - -0.10 MPa, and more preferably -0.08 MPa.

[0016] Based on the principle of the preparation method of the present invention, the present invention also provides a method for inhibiting chemical corrosion of high-magnesium cement. The high-magnesium cement is calcined and ground, and then hydrated with water. After curing, a hydrated product containing the crystals is obtained. The hydrated product containing the crystals can absorb erosive ions such as Cl - , SO 4 2- etc., thereby improving the durability of cement concrete in the above corrosive environment.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] 1. Magnesium oxide in the cement clinker exists in two forms. One is dissolved in the clinker minerals to form a stable solid solution, and the other exists in the form of free periclase. The dissolved magnesium oxide has no expansibility, while free periclase will hydrate and expand, affecting the soundness of the cement in the later stage of hydration. The new crystal and its preparation method of the present invention provide a new idea for solving the expansion problem of free periclase in high-magnesium cement, that is, during the hydration process of the clinker, the aluminum phase can combine with the periclase crystal, converting this part of the periclase into a stable compound, such as the new crystal containing Mg, Al, Ca and other ions and water, reducing the harm caused by periclase.

[0019] 2. The preparation method of the present invention has universality, the preparation process is simple, easy to operate, and realizes the preparation of the new crystal under low-temperature curing conditions, with good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a flow schematic diagram of the preparation method of the present invention.

[0021] Figure 2 In Example 1 of the present invention, after mixing basic magnesium carbonate, calcium carbonate, and alumina, tablet pressing and high-temperature calcination were carried out. Among them, (a) is before calcination and (b) is after calcination.

[0022] Figure 3 It is an XRD detection chart of tricalcium magnesium aluminate hydrated for 56 days at a curing temperature of 50°C in Example 1 of the present invention.

[0023] Figure 4 It is an XRD detection chart of different hydration ages in Example 1 of the present invention.

[0024] Figure 5 It is an SEM diagram of the crystal in Experimental Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. The experimental methods not specified in the following examples are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0026] The present invention provides a new crystal containing Mg, Al, Ca ions and water and a preparation method thereof. The crystal has a hydrotalcite-like structure and has wide applications.

[0027] The main peak positions of the XRD diffraction peaks of the crystal of the present invention are at 6.7°, 13.38°, 20.14°, and 26.96°. The peaks at these positions have extremely high intensities and there is no corresponding crystal, which is a new crystal similar to magnesium-aluminum hydrotalcite. The preparation method of the present invention has universality, the preparation process is simple and easy to operate, realizing that magnesium ions mainly form the crystal rather than magnesium hydroxide during the hydration process of tricalcium aluminomagnesate, providing a new idea for solving the problem of delayed expansion of periclase in high-magnesium cement. At the same time, the crystal shows a hydrotalcite-like structure and has good application prospects.

[0028] Reference Figure 1 As shown, the preparation method of the crystal of the present invention includes the following steps:

[0029] Add tricalcium aluminomagnesate to deionized water for hydration. The hydrated sample is filled into a plastic bottle, sealed with nitrogen, placed in a constant temperature water bath for curing for a certain age, terminate the hydration, filter and sample, and the taken sample is placed in a vacuum drying oven for drying; wherein, the water-solid ratio of hydration is 10:1, the curing temperature is 20°C to 80°C, and more preferably 50°C.

[0030] In the present invention, the tricalcium aluminomagnesate is a mixed material with 20 - 60 g of magnesium oxide doped in every 100 g of tricalcium aluminate, and preferably 40 g.

[0031] In the present invention, the tricalcium aluminomagnesate can be prepared by high-temperature calcination. Specifically, basic magnesium carbonate, calcium carbonate, and alumina are respectively screened using a 75μm square-hole sieve. The basic magnesium carbonate is calcined at 900°C for 30 min to obtain magnesium oxide. Therefore, the present invention can also use basic magnesium carbonate as a raw material, control the calcination process to first convert it into magnesium oxide, or directly use magnesium oxide as a raw material. The present invention weighs calcium carbonate and alumina according to the Ca / Al molar ratio of 1.5 for the screened materials. In order to simulate the actual situation of cement clinker, magnesium oxide and aluminum are co-calcined. As Figure 2 shown in (a), before calcination, the mixture is pressed into tablets with a diameter of 40 mm and a thickness of 5 mm. The prepared tablets are placed in an alumina ark for calcination. As Figure 2 shown in (b), after calcination, both the diameter and thickness of the tablets become smaller. The calcined material is ground to obtain a tricalcium aluminomagnesate sample.

[0032] The calcination process of the present invention is as follows: heating up to 1000 °C in a high-temperature furnace at a heating rate of 10 °C / min, then heating up to the required temperature at a rate of 5 °C / min, taking it out after holding for a certain period of time, and rapidly cooling it to room temperature using a blower. The calcination temperature is 1400 °C to 1500 °C, preferably 1450 °C, and the holding time is 0.5 h to 3 h, preferably 3 h. During the calcination process, at around 900 °C, CaCO 3 decomposes into CaO and CO 2 , and CaO and Al 2 O 3 gradually react through diffusion at high temperature to form a transition phase. As the temperature rises to 1400 °C to 1500 °C, these intermediate phases further react to finally form stable tricalcium aluminate (Ca 3 Al 2 O 6 ) crystals. During the holding stage, the grains further grow, and the crystal phase tends to be purified and homogenized. The rapid cooling treatment helps to inhibit abnormal grain growth, optimize the microstructure of the material, and improve its sintering activity and performance.

[0033] The termination of hydration in the present invention can be achieved by soaking the hydrated sample in isopropyl alcohol. As an organic solvent, isopropyl alcohol effectively terminates the hydration process by displacing water, inhibiting ion diffusion, and reducing the hydration reaction rate, and can replace water and inhibit the continuation of the hydration reaction.

[0034] The drying temperature of the vacuum drying oven in the present invention is 35 - 45 °C, preferably 40 °C, the drying time is 22 - 26 h, preferably 24 h, and the negative pressure for vacuum pumping is -0.06 to -0.10 MPa, preferably -0.08 MPa.

[0035] The preparation method of the present invention has universality, the preparation process is simple, easy to operate, and has good application prospects. The following are specific examples of the present invention.

[0036] Example 1

[0037] Preparation of the crystal by hydration of tricalcium aluminate containing magnesium:

[0038] Take 20 g of tricalcium aluminate containing magnesium clinker, add 200 mL of deionized water for hydration, fill with nitrogen to isolate air, place it in a constant temperature water bath at 50 °C for curing for a certain age, preferably 56 d, terminate hydration, and sample to obtain the crystal.

[0039] (1) Test results of XRD (X-ray diffraction)

[0040] Figure 3XRD detection pattern of tricalcium aluminate containing magnesium hydrated for 56 days at a curing temperature of 50°C in Example 1. It can be seen that the main peaks of the XRD diffraction pattern of the crystal are at 2θ = 6.7° (1), 13.38° (2), 20.14° (3), and 26.96° (4), and there are no characteristic diffraction peaks in the existing crystal structure database.

[0041] Figure 4 XRD detection patterns of the hydrated samples at different ages under the curing condition of 50°C in Example 1. It can be seen that weak diffraction peaks of the crystal appear when the tricalcium aluminate containing magnesium sample is hydrated for 2 days, and the diffraction peaks gradually become stronger as the hydration age increases.

[0042] (2) Scanning electron microscope test results

[0043] Figure 5 SEM image of the sample hydrated for 56 days at a curing temperature of 50°C in Example 1. The microscopic morphology of the crystal can be seen, forming a layered structure with a size of about 0.5 μm.

[0044] (3) Analysis of test results

[0045] The XRD test results show that at a curing temperature of 50°C, XRD crystal diffraction peaks appear when hydrated for 2 days. As the age increases, the diffraction peaks become more significant, and a significant crystal structure has been formed at 56 days. The SEM image shows that the crystal structure is layered.

[0046] Example 2

[0047] The hydrated sample is placed in a constant temperature water bath at 20°C for curing for a certain age, the hydration is terminated, and samples are taken.

[0048] Example 3

[0049] The hydrated sample is placed in a constant temperature water bath at 80°C for curing for a certain age, the hydration is terminated, and samples are taken.

[0050] It is found experimentally that at a curing temperature of 20°C, the crystal will also be formed after 28 days of hydration. Compared with the curing temperature of 50°C, the reaction is slower and fewer new crystals are formed. Under the curing condition of 80°C, it is difficult to form the crystal, probably because at a higher temperature, the crystal cannot exist stably.

[0051] For the cement industry, using high-magnesium limestone as a calcareous raw material promotes the utilization of low-grade limestone resources. The high-magnesium cement is calcined at 1450°C for 3 hours, then ground, sampled for hydration curing, the water-solid ratio of 10:1 is selected, the curing temperature is 50°C, and it is cured for a certain age, the hydration is terminated, and dried to obtain a hydrated product containing the crystal. Subsequently, the hydrated product is added to the cement concrete to exert its effect on Cl - , SO 42- The absorption function of corrosive ions is used to improve the application of cement concrete in resisting the erosion of corrosive environments. Here, high-magnesium cement generally refers to cement with a magnesium content of about 5%.

[0052] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that this is only an example, and the protection scope of the present invention is defined by the appended claims. Without departing from the principles and essence of the present invention, those skilled in the art can make various changes or modifications to these embodiments, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A new crystal containing Mg, Al, Ca ions and water, characterized in that: The crystal is layered, and its XRD diffraction spectrum shows diffraction peaks at 2θ=6.7°, 13.38°, 20.14° and 26.96°.

2. The method for preparing the new crystal containing Mg, Al, Ca ions and water as claimed in claim 1, characterized in that: The tricalcium magnesium aluminate material is added to deionized water for hydration, the hydrated sample is sealed in a nitrogen environment, maintained in a constant temperature water bath, and then dried.

3. The method for preparing the new crystal containing Mg, Al, Ca ions and water according to claim 2, characterized in that: The magnesium-containing tricalcium aluminate material is a mixed material in which the magnesium oxide content accounts for 20 to 60% of the mass of the tricalcium aluminate.

4. The method for preparing the new crystal containing Mg, Al, Ca ions and water according to claim 2, characterized in that: The magnesium-containing tricalcium aluminate material is prepared by the following method: Calcium carbonate and alumina with a Ca / Al molar ratio of 1.5 are mixed, and then a certain amount of magnesium oxide is added and calcined to obtain magnesium-containing tricalcium aluminate. Magnesium oxide is added to the calcium carbonate and alumina mixture at a ratio of 20-60 parts by weight of magnesium oxide per 100 parts by weight of tricalcium aluminate. The calcination scheme is to heat the mixture to 1000°C at a heating rate of 10°C / min in a high-temperature furnace, and then heat the mixture to 1400°C-1500°C at a heating rate of 5°C / min, keep the mixture warm for 0.5h-3h, then take it out and cool it to room temperature using a blower.

5. The method for preparing the new crystal containing Mg, Al, Ca ions and water according to claim 4, characterized in that: The magnesium oxide is obtained by calcining basic magnesium carbonate at 900° C. for 30 minutes.

6. The method for preparing the new crystal containing Mg, Al, Ca ions and water according to claim 5, characterized in that: The calcium carbonate, aluminum oxide and basic magnesium carbonate were sieved respectively using a 75 μm square hole sieve, and the water-to-solid ratio of the hydration was 10:

1.

7. The method for preparing the new crystal containing Mg, Al, Ca ions and water according to claim 2, characterized in that: The temperature of the constant temperature water bath curing is 20-50°C, the curing period is more than 3 days, the crystals begin to form after 2 days of curing, and as the hydration period increases, the number of crystals gradually increases, and the formation of the crystals is basically completed after 56 days.

8. The method for preparing the new crystal containing Mg, Al, Ca ions and water according to claim 2, characterized in that: After the constant temperature water bath curing, the hydration is terminated by soaking in isopropanol, and the drying is carried out at 35-45° C. under vacuum conditions for 22-26 hours.

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