CO2 foamed magnesium phosphate cement and preparation method thereof

Abstract

The invention relates to the technical field of novel building materials, in particular to CO2 foamed magnesium phosphate cement and a preparation method thereof. The CO2 foamed magnesium phosphate cement is prepared from the following components: magnesium oxide, phosphate, a retarder, a hydrotalcite compound, nano particles and water. The foamed magnesium phosphate cement prepared by the method is small in average pore size, high in closed porosity, small in apparent density and relatively high in strength. Compared with a traditional magnesium phosphate cement material, the CO2 foaming magnesium phosphate cement has better heat preservation and heat insulation performance and a higher light-weight effect. Meanwhile, due to the introduction of CO2 gas, the flame retardance and acoustic performance of the material can be improved, and the material has a wider application prospect in the fields of fire prevention, sound insulation and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of new building materials, in particular to a CO 2 Foamed magnesium phosphate cement and its preparation method. Background Art

[0002] Magnesium phosphate cement (MPC) is a cementitious material made by the acid-base neutralization reaction of dead-burned magnesium oxide and acid phosphate. Due to the special hydration process, MPC exhibits low shrinkage, high early strength and bonding strength, and low pH value. Therefore, MPC is widely used in rapid repair, repair reinforcement, and curing. With the deepening of research and the expansion of applications, lightweight and high-strength MPC is required for application scenarios such as exterior wall insulation and fire-retardant coatings. Traditional magnesium phosphate cement materials often have a large density and are difficult to meet the above requirements. Improving the foaming efficiency of the material is one of the current conventional improvement practices. In order to solve this problem, many scholars have studied the foaming method of MPC based on the characteristics of MPC.

[0003] Zinc powder and aluminum powder are commonly used foaming materials for preparing lightweight cement-based materials. Zinc powder or aluminum powder is added to the acidic MPC slurry to form H 2 , to prepare foamed MPC. The average pore size of zinc powder foamed MPC exceeds 0.45 mm. However, H 2 is extremely flammable and has the risk of explosion in a closed environment. In addition, the Zn generated by this reaction 2+ It is not conducive to the strength development of MPC. 2 O 2 As a foaming agent, MnO 2 Foamed MPC was prepared in the presence of 2 As a combustion agent, MnO2 is not conducive to the development of MPC strength. 2 Thermal conductivity (0.024W / (m·K)) and H 2 Compared with the thermal conductivity of CO (0.176W / (m·K)), 2 The thermal conductivity at 1 standard atmosphere and 20°C is only 0.0143 W / (m·K). In addition, carbon dioxide also acts as a flame retardant. 2 It is more suitable as the foaming gas for foaming MPC in steel structure fire retardant coatings.

[0004] Currently, NaHCO is added to MPC 3 , prepared a low bulk density (550kg / m 3 ) and thermal conductivity (0.072W / (m·K)) of CO 2 Foaming MPC. However, the foaming rate of this foamed cement is too high, and the reaction controllability is low. 2 CO 3Instead of NaHCO 3 Prepare CO 2 Foam MPC. However, NaHCO 3 and Na 2 CO 3 dispersion is likely to cause swelling of the foam MPC paste. In addition, there are also some technical problems in the preparation process of CO 2 foamed magnesium phosphate cement, such as how to control the size and distribution of voids without reducing the performance of the cement such as thermal conductivity.

[0005] Therefore, selecting components with appropriate activity is the key to preparing lightweight, high-performance, and environmentally friendly CO 2 foamed MPC. Summary of the Invention

[0006] In order to overcome the deficiencies of the prior art, one of the objectives of the present invention is to provide a CO 2 foamed magnesium phosphate cement, which has good heat insulation performance, and the foamed magnesium phosphate cement has a small average pore diameter, a high closed porosity, a small apparent density, and relatively high strength.

[0007] Another objective of the present invention is to provide a method for preparing CO 2 foamed magnesium phosphate cement, which has low production costs, a simple process, and an easy-to-understand operation method.

[0008] One of the objectives of the present invention is achieved by adopting the following technical solutions:

[0009] A CO 2 foamed magnesium phosphate cement, comprising the following components: magnesium oxide, phosphate, retarder, hydrotalcite-like compound, nanoparticles, and water.

[0010] Further, the hydrotalcite-like compound is at least one of magnesium aluminum hydrotalcite, calcium aluminum hydrotalcite, zinc aluminum hydrotalcite, nickel aluminum hydrotalcite, and copper aluminum hydrotalcite.

[0011] Further, the magnesium oxide is dead-burned magnesium oxide or light-burned magnesium oxide, and the particle size of the magnesium oxide is less than 75 μm.

[0012] Further, the phosphate is at least one of ammonium dihydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, aluminum dihydrogen phosphate, and zinc dihydrogen phosphate.

[0013] Further, the retarder is at least one of borax, boric acid, and sodium tripolyphosphate.

[0014] Further, the nanoparticles are nano-CaCO 3 , nano-SiO 2 , nano-Al 2 O 3, at least one of nano-TiO 2 , graphene and carbon nanotubes.

[0015] Furthermore, the mass ratio of the magnesium oxide to the phosphate is (0.5 - 4):1, the mass ratio of the retarder to the magnesium oxide is 0.10:1, and the mass ratio of the hydrotalcite-like compound to the magnesium oxide is (0.03 - 2):1.

[0016] Even further, the mass ratio of the magnesium oxide to the phosphate is (0.5 - 3):1, the mass ratio of the retarder to the magnesium oxide is 0.10:1, and the mass ratio of the hydrotalcite-like compound to the magnesium oxide is (0.03 - 0.15):1.

[0017] Furthermore, the mass of the nanoparticles is 0.1% - 0.5% of the sum of the masses of the magnesium oxide, the phosphate, the retarder and the hydrotalcite-like compound.

[0018] Furthermore, the mass of the water is 0.1 - 0.2 times the sum of the masses of the magnesium oxide, the phosphate, the retarder and the hydrotalcite-like compound.

[0019] The second object of the present invention is achieved by the following technical solution:

[0020] The above-mentioned CO 2 The preparation method of the foamed magnesium phosphate cement comprises the following steps:

[0021] Mix the magnesium oxide, the retarder, the hydrotalcite-like compound, the phosphate, and the nanoparticles evenly, add water and stir evenly to obtain the slurry of the foamed magnesium phosphate cement, pour the slurry into a mold and foam for 10 - 15 minutes, and demold to obtain the product.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. The present invention provides a CO 2 foamed magnesium phosphate cement (MPC). The core of the present invention is to introduce a hydrotalcite-like compound as a gas-generating component for the first time. Aiming at the defects of high thermal conductivity and unsatisfactory pore structure of traditional foaming materials, the decomposition characteristics of the magnesium phosphate cement paste in an acidic medium before setting and hardening are innovatively utilized. Carbon dioxide gas is generated by adding hydrotalcite, so as to achieve the foaming effect. The generated CO with low thermal conductivity 2The gas can significantly reduce the thermal conductivity of the foamed MPC, thereby enhancing its thermal insulation performance. Due to its suitable activity, hydrotalcite can react with the acidic magnesium phosphate cement paste at an ideal rate to generate gas, ensuring that all the generated gas can be effectively used in the foaming process, thus achieving a high foaming efficiency. In addition, due to its large specific surface area, hydrotalcite also plays the function of a partial foam stabilizer, which helps to form foamed magnesium phosphate cement products with a small average pore size, a high closed porosity, a low apparent density and excellent strength.

[0024] 2. Compared with traditional magnesium phosphate cement materials, the CO 2 foamed magnesium phosphate cement of the present invention exhibits a lower density, better thermal insulation performance and more significant light-weighting effect. At the same time, the introduction of CO 2 gas also enhances the flame retardancy and acoustic properties of the material, making it have broader application potential in the fields of fire prevention, sound insulation, etc.

[0025] 3. The present invention provides a method for preparing CO 2 foamed magnesium phosphate cement, which is simple and easy to implement and convenient for industrial production. Brief Description of the Drawings

[0026] Figure 1 It is a diagram of the void statistics results of the foamed magnesium phosphate cement specimen of the present invention. Detailed Description of the Embodiments

[0027] Next, in combination with the drawings and specific embodiments, the present invention will be further described. It should be noted that, on the premise of no conflict, the following-described embodiments or technical features can be arbitrarily combined to form new embodiments.

[0028] The particle size of the magnesium oxide described in the present invention is less than 75 μm.

[0029] Example 1

[0030] This Example 1 provides a CO 2 foamed magnesium phosphate cement, which includes the following components: dead-burned magnesia, ammonium dihydrogen phosphate, borax, magnesium-aluminum hydrotalcite, nano-Al 2 O 3 , water. Among them, the mass ratio of dead-burned magnesia to ammonium dihydrogen phosphate is 2 (M / P is 2), the mass ratio of borax to dead-burned magnesia is 0.1 (B / M is 0.1), the mass ratio of magnesium-aluminum hydrotalcite to dead-burned magnesia is 3%, the mass of nano-Al 2 O 3 is 0.3% of the sum of the masses of the above solid raw materials, and the mass of water is 0.2 times the sum of the masses of the above solid raw materials.

[0031] This example also provides a CO 2Preparation method of foamed magnesium phosphate cement, comprising the following steps:

[0032] According to the above mass relationship, calcined magnesia, ammonium dihydrogen phosphate, borax, magnesium aluminum hydrotalcite, nano-Al 2 O 3 are stirred and mixed evenly, water is added and stirred evenly to obtain the slurry of foamed magnesium phosphate cement, and the slurry is poured into a mold for foaming for 10 minutes, and then demolded to obtain the product.

[0033] Example 2

[0034] This Example 2 provides a CO 2 foamed magnesium phosphate cement, comprising the following components: calcined magnesia, ammonium dihydrogen phosphate, borax, magnesium aluminum hydrotalcite, nano-Al 2 O 3 , and water. Among them, the mass ratio of calcined magnesia to ammonium dihydrogen phosphate is 2 (M / P is 2), the mass ratio of borax to calcined magnesia is 0.1 (B / M is 0.1), the mass ratio of magnesium aluminum hydrotalcite to calcined magnesia is 6%, and the mass of nano-Al 2 O 3 is 0.3% of the sum of the masses of the above solid raw materials, and the mass of water is 0.2 times the sum of the masses of the above solid raw materials.

[0035] This example also provides a method for preparing a CO 2 foamed magnesium phosphate cement, and the specific steps are the same as those in Example 1.

[0036] Example 3

[0037] This Example 3 provides a CO 2 foamed magnesium phosphate cement, comprising the following components: calcined magnesia, ammonium dihydrogen phosphate, borax, magnesium aluminum hydrotalcite, nano-Al 2 O 3 , and water. Among them, the mass ratio of calcined magnesia to ammonium dihydrogen phosphate is 2 (M / P is 2), the mass ratio of borax to calcined magnesia is 0.1 (B / M is 0.1), the mass ratio of magnesium aluminum hydrotalcite to calcined magnesia is 9%, and the mass of nano-Al 2 O 3 is 0.3% of the sum of the masses of the above solid raw materials, and the mass of water is 0.2 times the sum of the masses of the above solid raw materials.

[0038] This example also provides a method for preparing a CO 2 foamed magnesium phosphate cement, and the specific steps are the same as those in Example 1.

[0039] Example 4

[0040] This Example 4 provides a CO 2Foamed magnesium phosphate cement, comprising the following components: dead-burned magnesia, ammonium dihydrogen phosphate, borax, magnesium aluminum hydrotalcite, nano-Al 2 O 3 , and water. Among them, the mass ratio of dead-burned magnesia to ammonium dihydrogen phosphate is 2 (M / P is 2), the mass ratio of borax to dead-burned magnesia is 0.1 (B / M is 0.1), the mass ratio of magnesium aluminum hydrotalcite to dead-burned magnesia is 12%, and the mass of nano-Al 2 O 3 is 0.3% of the sum of the masses of the above solid raw materials, and the mass of water is 0.2 times the sum of the masses of the above solid raw materials.

[0041] This example also provides a method for preparing CO 2 foamed magnesium phosphate cement, and the specific steps are the same as those in Example 1.

[0042] Example 5

[0043] This Example 5 provides a CO 2 foamed magnesium phosphate cement, comprising the following components: dead-burned magnesia, ammonium dihydrogen phosphate, borax, magnesium aluminum hydrotalcite, nano-Al 2 O 3 , and water. Among them, the mass ratio of dead-burned magnesia to ammonium dihydrogen phosphate is 2 (M / P is 2), the mass ratio of borax to dead-burned magnesia is 0.1 (B / M is 0.1), the mass ratio of magnesium aluminum hydrotalcite to dead-burned magnesia is 15%, and the mass of nano-Al 2 O 3 is 0.3% of the sum of the masses of the above solid raw materials, and the mass of water is 0.2 times the sum of the masses of the above solid raw materials.

[0044] This example also provides a CO 2 foamed magnesium phosphate cement, and the specific steps are the same as those in Example 1.

[0045] Example 6

[0046] This Example 6 provides a CO 2 foamed magnesium phosphate cement, comprising the following components: dead-burned magnesia, ammonium dihydrogen phosphate, borax, magnesium aluminum hydrotalcite, nano-Al 2 O 3 , and water. Among them, the mass ratio of dead-burned magnesia to ammonium dihydrogen phosphate is 0.5 (M / P is 0.5), the mass ratio of borax to dead-burned magnesia is 0.1 (B / M is 0.1), the mass ratio of magnesium aluminum hydrotalcite to dead-burned magnesia is 12%, and the mass of nano-Al 2 O 3 is 0.3% of the sum of the masses of the above solid raw materials, and the mass of water is 0.2 times the sum of the masses of the above solid raw materials.

[0047] This example also provides a CO2 The preparation method of foamed magnesium phosphate cement is the same as that in Example 1 in specific steps.

[0048] Example 7

[0049] This Example 7 provides a CO 2 foamed magnesium phosphate cement, which comprises the following components: dead-burned magnesia, ammonium dihydrogen phosphate, borax, magnesium aluminum hydrotalcite, nano Al 2 O 3 , and water. Among them, the mass ratio of dead-burned magnesia to ammonium dihydrogen phosphate is 1 (M / P is 1), the mass ratio of borax to dead-burned magnesia is 0.1 (B / M is 0.1), the mass ratio of magnesium aluminum hydrotalcite to dead-burned magnesia is 12%, the mass of nano Al 2 O 3 is 0.3% of the sum of the masses of the above solid raw materials, and the mass of water is 0.2 times the sum of the masses of the above solid raw materials.

[0050] This example also provides a method for preparing a CO 2 foamed magnesium phosphate cement, and the specific steps are the same as those in Example 1.

[0051] Example 8

[0052] This Example 8 provides a CO 2 foamed magnesium phosphate cement, which comprises the following components: dead-burned magnesia, ammonium dihydrogen phosphate, borax, magnesium aluminum hydrotalcite, nano Al 2 O 3 , and water. Among them, the mass ratio of dead-burned magnesia to ammonium dihydrogen phosphate is 3 (M / P is 2), the mass ratio of borax to dead-burned magnesia is 0.1 (B / M is 0.1), the mass ratio of magnesium aluminum hydrotalcite to dead-burned magnesia is 12%, the mass of nano Al 2 O 3 is 0.3% of the sum of the masses of the above solid raw materials, and the mass of water is 0.2 times the sum of the masses of the above solid raw materials.

[0053] This example also provides a method for preparing a CO 2 foamed magnesium phosphate cement, and the specific steps are the same as those in Example 1.

[0054] Example 9

[0055] This Example 9 provides a CO 2 foamed magnesium phosphate cement, which comprises the following components: dead-burned magnesia, potassium dihydrogen phosphate, borax, magnesium aluminum hydrotalcite, nano Al 2 O 3 , and water. Among them, the mass ratio of dead-burned magnesia to ammonium dihydrogen phosphate is 2 (M / P is 2), the mass ratio of borax to dead-burned magnesia is 0.3 (B / M is 0.1), the mass ratio of magnesium aluminum hydrotalcite to dead-burned magnesia is 12%, nano Al2 O 3 The mass of O is 0.5% of the sum of the masses of the above solid raw materials, and the mass of water is 0.1 times the sum of the masses of the above solid raw materials.

[0056] This example also provides a method for preparing CO 2 foamed magnesium phosphate cement, and the specific steps are the same as those in Example 1.

[0057] Example 10

[0058] This Example 10 provides a CO 2 foamed magnesium phosphate cement, which includes the following components: light-burned magnesia, sodium dihydrogen phosphate, boric acid, calcium-aluminum hydrotalcite, nano-Al 2 O 3 , and water. Among them, the mass ratio of light-burned magnesia to sodium dihydrogen phosphate is 2, the mass ratio of borax to light-burned magnesia is 0.2, the mass ratio of magnesium-aluminum hydrotalcite to light-burned magnesia is 12%, and the mass of nano-Al 2 O 3 is 0.1% of the sum of the masses of the above solid raw materials, and the mass of water is 0.15 times the sum of the masses of the above solid raw materials.

[0059] This example also provides a method for preparing CO 2 foamed magnesium phosphate cement, and the specific steps are the same as those in Example 1.

[0060] Comparative Example 1

[0061] This Comparative Example 1 provides a magnesium phosphate cement, which includes the following components: dead-burned magnesia, ammonium dihydrogen phosphate, borax, and water. Among them, the mass ratio of dead-burned magnesia to ammonium dihydrogen phosphate is 2 (M / P is 2), the mass ratio of borax to dead-burned magnesia is 0.1 (B / M is 0.1), and the mass ratio of water to the above solid raw materials is 0.2.

[0062] This comparative example also provides a method for preparing magnesium phosphate cement, and the specific steps are the same as those in Example 1.

[0063] Comparative Example 2

[0064] This Comparative Example 2 provides a CO 2 foamed magnesium phosphate cement, which includes the following components: dead-burned magnesia, ammonium dihydrogen phosphate, borax, limestone powder, nano-Al 2 O 3 and water. Among them, the mass ratio of dead-burned magnesia to ammonium dihydrogen phosphate is 2 (M / P is 2), the mass ratio of borax to dead-burned magnesia is 0.1 (B / M is 0.1), the mass ratio of limestone powder to dead-burned magnesia is 12%, and the mass of nano-Al 2 O 30.3% of the sum of the masses of the above solid raw materials, and the mass ratio of water to the above solid raw materials is 0.2.

[0065] This comparative example also provides a kind of CO 2 Preparation method of foamed magnesium phosphate cement, and the specific steps are the same as those in Example 1.

[0066] Comparative Example 3

[0067] This Comparative Example 3 provides a kind of CO 2 Foamed magnesium phosphate cement, comprising the following components: dead-burned magnesia, ammonium dihydrogen phosphate, borax, basic magnesium carbonate, nano-Al 2 O 3 、 water. Among them, the mass ratio of dead-burned magnesia to ammonium dihydrogen phosphate is 2 (M / P is 2), the mass ratio of borax to dead-burned magnesia is 0.1 (B / M is 0.1), the mass ratio of magnesium aluminum hydrotalcite to dead-burned magnesia is 12%, and nano-Al 2 O 3 is 0.3% of the sum of the masses of the above solid raw materials, and the mass ratio of water to the above solid raw materials is 0.2.

[0068] This comparative example also provides a kind of CO 2 Preparation method of foamed magnesium phosphate cement, and the specific steps are the same as those in Example 1.

[0069] Comparative Example 4

[0070] This Comparative Example 4 provides a kind of CO 2 Foamed magnesium phosphate cement, comprising the following components: magnesium hydroxide, aluminum dihydrogen phosphate, borax, magnesium aluminum hydrotalcite, nano-Al 2 O 3 、 water. Among them, the mass ratio of magnesium hydroxide to aluminum dihydrogen phosphate is 2, the mass ratio of borax to magnesium hydroxide is 0.1, the mass ratio of magnesium aluminum hydrotalcite to magnesium oxide is 12%, and nano-Al 2 O 3 is 0.5% of the sum of the masses of the above solid raw materials, and the mass ratio of water to the above solid raw materials is 0.2.

[0071] This comparative example also provides a kind of CO 2 Preparation method of foamed magnesium phosphate cement, and the specific steps are the same as those in Example 1.

[0072] Test Example

[0073] In order to evaluate the compressive strength, thermal conductivity, apparent density, porosity and pore distribution of the foamed magnesium phosphate cements of Examples 1-10 and Comparative Examples 1-4 of the present invention, the following tests were carried out:

[0074] 1. Compressive strength test

[0075] Under natural conditions, the test blocks were first cured to the specified age, and then the compressive strength of the foamed magnesium phosphate cement of Examples 1-10 and Comparative Examples 1-4 was measured using a universal testing machine at a loading rate of 0.5 kN / s. The average value of three compressive strength measurements was taken as the final compressive strength value. The test ages were 1 d, 7 d, and 28 d. The results are shown in Table 1.

[0076] 2. Thermal Conductivity Measurement

[0077] The cured specimens (10 mm × 10 mm × 1 mm) were first placed in a vacuum drying oven at 40 °C for 1 d, and then the thermal conductivity of the foamed magnesium phosphate cement (MPC) was measured using an LFA467HT instrument produced by Netzsch of Germany in accordance with the American Society for Testing and Materials (ASTM) E1461 standard "Standard Test Method for Thermal Diffusivity by the Flash Method". The results are shown in Table 1.

[0078] 3. Apparent Density and Porosity

[0079] The apparent density and porosity of the foamed magnesium phosphate cement were measured using a vacuum saturation instrument according to the saturated water method described in the Chinese national standard GB / T 24586-2009 "Determination of Apparent Density, True Density and Porosity of Iron Ore". The results are shown in Table 1.

[0080] 4. Pore Distribution

[0081] The cross-section of the foamed magnesium phosphate cement specimen was observed using an optical microscope to record the pore conditions, and at the same time, image analysis software (Image Pro Plus) was used to analyze the pore size distribution of the foamed magnesium phosphate cement. The porosity results are recorded in Table 1.

[0082] Table 1

[0083]

[0084] Analysis of the above test results shows that:

[0085] (1) Compared with Comparative Example 1, Examples 1-5 are the physical and mechanical properties of foamed magnesium phosphate cement doped with different amounts of magnesium aluminum hydrotalcite. With the increase in the amount of magnesium aluminum hydrotalcite, the porosity of the foamed magnesium phosphate cement gradually increases, while the apparent density, thermal conductivity and compressive strength gradually decrease. This indicates that the increase in the amount of magnesium aluminum hydrotalcite increases the gas generation amount in the magnesium phosphate cement, which leads to the increase in the porosity of the foamed magnesium phosphate cement and the decrease in the apparent density, thermal conductivity and compressive strength of the foamed magnesium phosphate cement. Compared with Example 8, Example 10 is a foamed phosphate cement prepared by replacing magnesium oxide with light-burned magnesium oxide and ammonium dihydrogen phosphate with sodium dihydrogen phosphate, and doping with magnesium aluminum hydrotalcite. The porosity decreases, and the apparent density, thermal conductivity and compressive strength increase slightly.

[0086] (2) Examples 4 and Examples 6-8 study the influence of different magnesium-to-phosphorus ratios on the physical and chemical properties of foamed magnesium phosphate cement doped with 12% magnesium aluminum hydrotalcite. As the magnesium-to-phosphorus ratio increases from 0.5 to 3, the porosity of the foamed magnesium phosphate cement gradually decreases, while the apparent density, thermal conductivity and compressive strength gradually increase. This indicates that the increase in the magnesium-to-phosphorus ratio increases the pH of the magnesium phosphate slurry, making it more difficult for the magnesium phosphate slurry to react with magnesium aluminum spinel to generate gas, so the gas generated in the magnesium phosphate cement slurry decreases. This results in a decrease in the porosity of the foamed magnesium phosphate cement and an increase in the apparent density, thermal conductivity and compressive strength.

[0087] (3) Compared with Example 1, Example 9 is a foamed magnesium phosphate cement (magnesium potassium phosphate cement) prepared by replacing ammonium dihydrogen phosphate with potassium dihydrogen phosphate and doping with magnesium aluminum hydrotalcite. Because the pH value of the magnesium potassium phosphate cement slurry is relatively high, the gas generated by the reaction with magnesium aluminum hydrotalcite decreases, reducing the porosity of the foamed magnesium potassium phosphate cement obtained in Example 9 and increasing the apparent density, thermal conductivity and compressive strength of the foamed magnesium phosphate cement.

[0088] Comparative Example 1 is ordinary magnesium phosphate cement, and Comparative Example 2 is magnesium phosphate cement doped with the same amount of limestone powder. Since the limestone powder has low activity and is difficult to react with the magnesium phosphate cement slurry to generate gas, it is similar to the magnesium phosphate cement slurry and has similar physical and mechanical properties to the magnesium phosphate cement after hardening. Comparative Example 3 is a foamed magnesium phosphate cement prepared from basic magnesium carbonate. Compared with Example 1, at the same blowing agent dosage, Comparative Example 3 shows a lower porosity and higher apparent density, thermal conductivity and compressive strength. This is because the basic magnesium carbonate has low activity and is difficult to react with the magnesium phosphate cement slurry to generate gas.

[0089] Comparative Example 4 is a foamed phosphate cement prepared by replacing magnesium oxide with magnesium hydroxide and ammonium dihydrogen phosphate with aluminum dihydrogen phosphate and incorporating zinc-aluminum hydrotalcite. Although the pH of aluminum dihydrogen phosphate is lower than that of ammonium dihydrogen phosphate, which is beneficial to the reaction to generate gas, the activity of magnesium hydroxide is relatively high, and the reaction rate with phosphate is fast. When the hydrotalcite has not fully reacted to generate gas, the paste loses plasticity, resulting in a smaller porosity, an increase in apparent density, thermal conductivity, and compressive strength.

[0090] (4) Considering the pore distribution of the bubbles in the foamed magnesium phosphate cement, software was used to statistically analyze the particle size distribution of the bubbles in Examples 4, 5, and 7 of the foamed magnesium phosphate cement. The results are as Figure 1 shown.

[0091] The average pore diameters of Examples 4, 5, and 7 are 0.192 mm, 0.177 mm, and 0.181 mm, respectively. In previous experiments, the average pore diameter of the foamed MPC exceeded 0.40 mm and even reached 0.89 mm in some cases. However, the pore diameter of the hydrotalcite-foamed MPC used in this study is significantly smaller than 0.20 mm. This result shows that compared with other chemical foaming methods, the reaction rate between the hydrotalcite and the MPC paste used in the present invention may be lower, so the pores generated in the prepared foamed magnesium phosphate cement are smaller and more uniform.

[0092] The above embodiments are only the preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention belong to the scope of protection required by the present invention.

Claims

1. A CO2 foamed magnesium phosphate cement, characterized in that: The invention comprises the following components: magnesium oxide, phosphate, retarder, hydrotalcite compound, nanoparticles and water.

2. A CO2 foamed magnesium phosphate cement according to claim 1, characterized in that: The hydrotalcite compound is at least one of magnesium aluminum hydrotalcite, calcium aluminum hydrotalcite, zinc aluminum hydrotalcite, nickel aluminum hydrotalcite and copper aluminum hydrotalcite.

3. A CO2 foamed magnesium phosphate cement according to claim 1, characterized in that: The magnesium oxide is dead-burned magnesium oxide or light-burned magnesium oxide, and the particle size of the magnesium oxide is less than 75 μm.

4. A CO2 foamed magnesium phosphate cement according to claim 1, characterized in that: The phosphate is at least one of ammonium dihydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, aluminum dihydrogen phosphate, and zinc dihydrogen phosphate.

5. A CO2 foamed magnesium phosphate cement according to claim 1, characterized in that: The retarder is at least one of borax, boric acid or sodium tripolyphosphate.

6. A CO2 foamed magnesium phosphate cement according to claim 1, characterized in that: The nanoparticles are at least one of nano-CaCO3, nano-SiO2, nano-Al2O3, nano-TiO2, graphene and carbon nanotubes.

7. The CO2 foamed magnesium phosphate cement according to claim 1, characterized in that: The mass ratio of the magnesium oxide to the phosphate is (0.5-4):1, the mass ratio of the retarder to the magnesium oxide is 0.10, and the mass ratio of the hydrotalcite compound to the magnesium oxide is (0.03-2):

1.

8. The CO2 foamed magnesium phosphate cement according to claim 1, characterized in that: The mass of the nanoparticles is 0.1%-0.5% of the total mass of magnesium oxide, phosphate, retarder and hydrotalcite compound.

9. A CO2 foamed magnesium phosphate cement according to claim 1, characterized in that: The mass of the water is 0.1-0.2 times the sum of the masses of magnesium oxide, phosphate, retarder and hydrotalcite compound.

10. The method for preparing CO2 foamed magnesium phosphate cement according to any one of claims 1 to 9, characterized in that: The steps include: The magnesium oxide, retarder, hydrotalcite compound, phosphate and nanoparticles are uniformly mixed, water is added and stirred to obtain a slurry of foamed magnesium phosphate cement, the slurry is poured into a mold and foamed for 10-15 minutes, and the mold is demolded to obtain the slurry.

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