A multi-layer coated type gas emitting aluminum paste, a preparation method and application thereof

Abstract

This invention relates to a multi-layer coated gas-generating aluminum paste, its preparation method, and its application. The preparation method includes the following steps: dry ball milling spherical aluminum powder under an inert gas atmosphere, adding a ball milling aid during the dry ball milling process, resulting in pre-coated aluminum powder; the dry ball milling includes ball milling using a single milling medium and / or a mixed milling medium; stirring and kneading the pre-coated aluminum powder, passivating agent, surfactant, and organic solvent under an inert gas atmosphere, and sieving to obtain a kneaded product, which is the multi-layer coated gas-generating aluminum paste. This invention utilizes a segmented combination of single-medium ball milling ("stearic acid-steel balls") and mixed-medium ball milling ("zinc stearate-zirconia beads and glass beads") to construct a gradient coating structure on the surface of the aluminum powder, achieving "slow release in the early stage and high efficiency in the later stage" gas-generating characteristics, which can meet the stringent requirements for gas generation rate in low-density autoclaved aerated concrete.

Description

Technical Field

[0001] This invention belongs to the technical field of aluminum grease for autoclaved aerated concrete, specifically relating to a multi-layer coated aluminum grease, its preparation method, and its application. Background Technology

[0002] As the core gas-generating agent for autoclaved aerated concrete (AAC) and autoclaved lightweight concrete (ALC) products, aluminum grease directly determines the pore structure, density, strength, and thermal insulation performance of the blocks. This type of aluminum grease generates hydrogen gas through a chemical reaction of aluminum powder in an alkaline slurry, forming uniform pores, thus enabling concrete products to achieve lightweight and thermal insulation. It is widely used in the field of building wall materials. Currently, in industry, the preparation of aluminum grease mostly uses a single ball milling media (steel balls) in conjunction with a wet ball milling process. The grinding raw materials are mostly ordinary spherical aluminum powder or aluminum foil. Although wet ball milling can reduce the grinding temperature rise, it requires the introduction of solvents, and subsequent additional drying processes are required, increasing production costs. Moreover, solvent residue may affect the gas generation stability of the aluminum grease.

[0003] In addition, the existing aluminum foaming paste in China is a common water-based foaming paste, which is mostly used in high-density autoclaved aerated concrete products (dry density ≥ 500 kg / m³). 3 Production of low-density autoclaved aerated concrete products (dry density ≤ 300 kg / m³) is difficult to meet. 3 The production of low-density autoclaved aerated concrete (AAC) products requires a very high gas evolution rate for the aluminum paste. Extensive experimental testing has shown that the aluminum paste must have a gas evolution rate of ≤25% in the first two minutes of laboratory testing, begin rapid gas evolution at the third minute, and finish gas evolution in eight minutes. The surface coating of the aluminum paste significantly affects the gas evolution rate. Poorly coated aluminum powder makes it difficult to control the gas evolution rate during the production of low-density AAC, easily leading to defects in the AAC product and failing to meet product requirements. Therefore, this invention focuses on the research and development of surface coating treatment for the aluminum paste required for the production of low-density AAC. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-layer coated aluminum fuming paste, its preparation method, and its application in order to solve the above-mentioned problems.

[0005] The present invention achieves the above objectives through the following technical solutions: This invention provides a method for preparing a multi-layer coated aluminum fuming paste, comprising the following steps: S1. Spherical aluminum powder is dry ball-milled under an inert gas protective atmosphere, and a ball milling aid is added during the dry ball milling process. The resulting ball milling product is pre-coated aluminum powder. The dry ball milling includes ball milling using a single milling media and / or a mixture of milling media; S2. The pre-coated aluminum powder, phosphate ester, sodium dodecylbenzenesulfonate, and diethylene glycol obtained in step S1 are stirred and kneaded under an inert gas protective atmosphere. The kneaded product obtained after sieving is a multi-layer coated gas-generating aluminum paste.

[0006] As a further optimization of the present invention, the raw materials for preparing the multi-layer coated aluminum fuming paste, by weight, include 60-70 parts of spherical aluminum powder, 1-7 parts of ball milling aid, 1-2 parts of phosphate ester, 1-2 parts of sodium dodecylbenzene sulfonate, and 25-30 parts of diethylene glycol. The ball milling aid is at least one of stearic acid and zinc stearate.

[0007] As a further optimization of the present invention, in step S1, the spherical aluminum powder is a low-temperature atomized spherical aluminum powder with a particle size of 1-3 μm, a particle size range of ≤0.8 μm, a purity of ≥99.5%, a sphericity of ≥90%, and a surface oxide layer thickness of ≤5 nm.

[0008] As a further optimization of the present invention, in step S1, the ball milling with a single ball milling medium specifically involves ball milling the spherical aluminum powder or the initially ball-milled aluminum powder and stearic acid obtained by ball milling with mixed ball milling media under a nitrogen protective atmosphere. The ball milling media consists of steel balls with a particle size of 0.8-1 mm, the ball milling time is 1-2 hours, the ball milling speed is 25-35 r / min, and the ball milling temperature is 40-50℃. The mass ratio of the spherical aluminum powder to the ball milling media is 1:10-15.

[0009] As a further optimization of the present invention, in step S1, the ball milling of the mixed ball milling media specifically involves ball milling the spherical aluminum powder or the initially ball-milled aluminum powder obtained by ball milling with a single ball milling media, and zinc stearate, under a nitrogen protective atmosphere. The ball milling media consists of zirconia beads and glass beads with a particle size of 1.5-2.0 mm. The ball milling time is 2-5 hours, the ball milling speed is 28-36 r / min, and the ball milling temperature is 40-55℃. The mass ratio of the spherical aluminum powder to the ball milling media is 1:8-12.

[0010] As a further optimization of the present invention, the mass ratio of zirconium oxide beads to glass beads is 3-5:1; The zirconia beads are yttrium-stabilized zirconia beads with a hardness HV≥1200 and a wear rate <0.01% / h; the glass beads are high-silicon glass beads with a hardness HV≥600 and a wear rate <0.01‰ / h.

[0011] As a further optimization of the present invention, the temperature of the stirring and kneading is 20-25℃ and the time is 0.5-1.5h.

[0012] The present invention also provides a multi-layer coated aluminum fuming paste, which is prepared by the preparation method described above.

[0013] The present invention also provides the application of the multi-layer coated aluminum foaming paste as described above in the preparation of concrete foaming agent, wherein the amount added to the concrete is greater than or equal to 0.06% of the dry weight.

[0014] As a further optimization of the present invention, the concrete includes autoclaved aerated concrete and autoclaved lightweight concrete; The autoclaved aerated concrete has a dry density ≤300 kg / m³. 3 Autoclaved aerated concrete.

[0015] The beneficial effects of this invention are as follows: 1) This invention constructs a gradient coating structure on the surface of aluminum powder by combining a single-media ball milling of "stearic acid-steel balls" with a mixed-media ball milling of "zinc stearate-zirconia beads and glass beads" in stages, thereby achieving the gas generation characteristics of "slow release in the early stage and high efficiency in the later stage", which can meet the stringent requirements of low-density autoclaved aerated concrete for gas generation rate. 2) The autoclaved aerated concrete prepared by the aluminum fumed paste of the present invention has significantly improved compressive strength and significantly reduced collapse rate compared with conventional wet ball milling products. The product has uniform pore structure and complete appearance, and is suitable for the production of high-quality low-density autoclaved aerated concrete blocks and panels. 3) The dry ball milling process of the present invention adopts dry ball milling under inert gas protection throughout the process, without the need for solvent introduction, eliminating the need for subsequent drying process, reducing production costs, and avoiding the impact of solvent residue on gas generation stability. Attached Figure Description

[0016] Figure 1 These are characterization diagrams of the multi-layer coated aluminum paste and the blank aluminum paste of Embodiment 3 of the present invention; Figure 2 This is a comparison diagram of autoclaved aerated concrete block samples with the multi-layer coated gas-generating aluminum paste of Example 3 of the present invention and the blank group of gas-generating aluminum paste. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above application content.

[0018] 1. Spherical aluminum powder: The low-temperature atomized spherical aluminum powder (Inner Mongolia Xuyang New Material Co., Ltd.) used in this invention has a particle size of 1-3 μm, a particle size range of ≤0.8, a purity of ≥99.5%, a sphericity of ≥90%, and a surface oxide layer thickness of ≤5 nm. 2. Ordinary spherical aluminum powder: The ordinary spherical aluminum powder used in this invention (Inner Mongolia Xuyang New Material Co., Ltd.) has a particle size of 1-3 μm, a particle size range of ≤0.8, a purity of ≥99.5%, a sphericity of ≥90%, and a surface oxide layer thickness of 30±2 nm. 3. Single grinding media: steel balls with a particle size of 0.8-1mm, purchased from Shandong Elite Heavy Industry Co., Ltd., with a hardness HV≥800 and roundness ≤0.05mm; 4. Mixed milling media: Zirconia beads and glass beads with a particle size of 1.5-2.0mm. The mass ratio of zirconia beads (preferably yttrium-stabilized zirconia beads from Jiangsu Yuxing Abrasives Co., Ltd., with a hardness HV≥1200, wear rate <0.01% / h, and roundness ≤0.03mm) to glass beads (preferably high-silica glass beads from Jiangsu Yuxing Abrasives Co., Ltd., with a hardness HV≥600, wear rate <0.01‰ / h, and SiO2 content ≥98%) is 3-5:1 (preferably 4:1). 5. Commercially available aluminum fumes paste (obtained by wet ball milling process): purchased from Henan Handing New Materials, purity ≥99.5%, used after passing through a 200-mesh sieve; 6. Stearic acid, zinc stearate, and oleic acid were purchased from Sinopharm Chemical Reagent Co., Ltd., analytical grade, with a content ≥99.0%; phosphate ester and sodium dodecylbenzene sulfonate were purchased from Aladdin Reagent (Shanghai) Co., Ltd., industrial grade, meeting the application standards for concrete admixtures; γ-aminopropyltriethoxysilane (KH-550) and sodium fatty alcohol polyoxyethylene ether sulfate were purchased from Aladdin Reagent (Shanghai) Co., Ltd., industrial grade, with a content ≥98.0%; diethylene glycol was purchased from Sinopharm Chemical Reagent Co., Ltd., industrial grade, with a content ≥99.5%; calcium hydroxide, sodium chloride, and distilled water were purchased from Sinopharm Chemical Reagent Co., Ltd., among which calcium hydroxide was aerated concrete grade, analytical grade; 7. Gas cylinders, gas measuring tubes, test molds, etc., were purchased from Nanjing Feiqi Instrument Co., Ltd. / Jinan Shijin Group and meet the requirements of the standards "JC / T 407-2008" and "GB / T 11969-2020". Note: Unless otherwise specified, the preferred schemes were used in the following verification tests; Unless otherwise specified, all methods used in this invention are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products.

[0019] Example 1

[0020] In this embodiment, the raw materials for preparing the multi-layer coated aluminum fumes paste, by weight, include 67 parts of spherical aluminum powder, 4 parts of stearic acid, 1.5 parts of phosphate ester, 2 parts of sodium dodecylbenzenesulfonate, and 27.5 parts of diethylene glycol; and a method for preparing the multi-layer coated aluminum fumes paste is provided, including the following steps: S1. Spherical aluminum powder and stearic acid were ball-milled under a nitrogen protective atmosphere. The selected ball milling media was a single ball milling media (steel balls). The ball milling time was 1 hour, the ball milling speed was 28 r / min, the ball milling temperature was 45℃, and the mass ratio of spherical aluminum powder to ball milling media was 1:13. Pre-coated aluminum powder was obtained after ball milling. S2. The pre-coated aluminum powder, phosphate ester, sodium dodecylbenzenesulfonate, and diethylene glycol obtained in step S1 are stirred and kneaded under a nitrogen protective atmosphere. The kneaded product obtained after sieving (200 sieves) is a multi-layer coated gas-generating aluminum paste.

[0021] Example 2

[0022] In this embodiment, the raw materials for preparing the multi-layer coated aluminum fumes paste, by weight, include 67 parts of spherical aluminum powder, 4 parts of zinc stearate, 1.5 parts of phosphate ester, 2 parts of sodium dodecylbenzene sulfonate, and 27.5 parts of diethylene glycol; and a method for preparing the multi-layer coated aluminum fumes paste is provided, including the following steps: S1. Spherical aluminum powder and zinc stearate were ball-milled under a nitrogen protective atmosphere. The selected ball milling media was a mixed ball milling media (the mass ratio of zirconia beads and glass beads was 4:1). The ball milling time was 3.5h, the ball milling speed was 30r / min, the ball milling temperature was 45℃, and the mass ratio of spherical aluminum powder to ball milling media was 1:10. After ball milling, pre-coated aluminum powder was obtained. S2. The pre-coated aluminum powder, phosphate ester, sodium dodecylbenzenesulfonate, and diethylene glycol obtained in step S1 are stirred and kneaded under a nitrogen protective atmosphere. The kneaded product obtained after sieving (200 sieves) is a multi-layer coated gas-generating aluminum paste.

[0023] Example 3

[0024] In this embodiment, the raw materials for preparing the multi-layer coated aluminum fumes paste, by weight, include 67 parts of spherical aluminum powder, 2 parts of stearic acid, 2 parts of zinc stearate, 1.5 parts of phosphate ester, 2 parts of sodium dodecylbenzene sulfonate, and 27.5 parts of diethylene glycol; and a method for preparing the multi-layer coated aluminum fumes paste is provided, including the following steps: S1. Spherical aluminum powder and stearic acid were ball-milled under a nitrogen protective atmosphere. The selected ball milling media was a single ball milling media (steel balls). The ball milling time was 1 hour, the ball milling speed was 28 r / min, the ball milling temperature was 45℃, and the mass ratio of spherical aluminum powder to ball milling media was 1:13. After ball milling, the first ball-milled aluminum powder was obtained. S2. The initially ball-milled aluminum powder and zinc stearate obtained in step S1 are ball-milled under a nitrogen protective atmosphere. The selected ball milling media is a mixed ball milling media (the mass ratio of zirconia beads and glass beads is 4:1). The ball milling time is 3.5h, the ball milling speed is 30r / min, the ball milling temperature is 45℃, and the mass ratio of spherical aluminum powder to ball milling media is 1:10. After ball milling, pre-coated aluminum powder is obtained. S3. The pre-coated aluminum powder, phosphate ester, sodium dodecylbenzenesulfonate, and diethylene glycol obtained in step S2 are stirred and kneaded under a nitrogen protective atmosphere. The stirring and kneading temperature is 23°C and the time is 1 hour. The kneaded product obtained after sieving (200 sieves) is a multi-layer coated gas-generating aluminum paste.

[0025] Example 4

[0026] In this embodiment, the raw materials for preparing the multi-layer coated aluminum fumes paste, by weight, include 67 parts of spherical aluminum powder, 2 parts of stearic acid, 2 parts of zinc stearate, 1.5 parts of phosphate ester, 2 parts of sodium dodecylbenzene sulfonate, and 27.5 parts of diethylene glycol; and a method for preparing the multi-layer coated aluminum fumes paste is provided, including the following steps: S1. Spherical aluminum powder and zinc stearate were ball-milled under a nitrogen protective atmosphere. The selected ball milling media was a mixed ball milling media (the mass ratio of zirconia beads and glass beads was 4:1). The ball milling time was 3.5h, the ball milling speed was 30r / min, the ball milling temperature was 45℃, and the mass ratio of spherical aluminum powder to ball milling media was 1:10. After ball milling, the first ball-milled aluminum powder was obtained. S2. The first ball milled aluminum powder and stearic acid obtained in step S1 are ball milled under a nitrogen protective atmosphere. The selected ball milling medium is a single ball milling medium (steel ball). The ball milling time is 1 hour, the ball milling speed is 28 r / min, the ball milling temperature is 45℃, and the mass ratio of spherical aluminum powder to ball milling medium is 1:13. After ball milling, pre-coated aluminum powder is obtained. S3. The pre-coated aluminum powder, phosphate ester, sodium dodecylbenzenesulfonate, and diethylene glycol obtained in step S2 are stirred and kneaded under a nitrogen protective atmosphere. The stirring and kneading temperature is 23°C and the time is 1 hour. The kneaded product obtained after sieving (200 sieves) is a multi-layer coated gas-generating aluminum paste.

[0027] Comparative Example 1 In this comparative example, the difference from Example 3 is that oleic acid of equal mass is used to replace stearic acid, while all other aspects remain the same as in Example 3.

[0028] Comparative Example 2 In this comparative example, the difference from Example 3 is that an equal mass of oleic acid is used to replace zinc stearate, while all other aspects remain the same as in Example 3.

[0029] Comparative Example 3 In this comparative example, the difference from Example 3 is that oleic acid and zinc stearate are replaced with equal masses of oleic acid, while the rest are the same as in Example 3.

[0030] Comparative Example 4 In this comparative example, the difference from Example 3 is that, in this comparative example, when ball milling with a single ball milling medium, zinc stearate is used as a ball milling aid, and when ball milling with mixed ball milling media, stearic acid is used as a ball milling aid. All other aspects are consistent with Example 3.

[0031] Comparative Example 5 In this comparative example, the difference from Example 3 is that an equal mass of γ-aminopropyltriethoxysilane (silane coupling agent KH-550) is used to replace the phosphate ester, while the rest remains the same as in Example 3.

[0032] Comparative Example 6 In this comparative example, the difference from Example 3 is that sodium dodecylbenzenesulfonate is replaced with an equal mass of sodium fatty alcohol polyoxyethylene ether sulfate, while all other aspects remain the same as in Example 3.

[0033] Comparative Example 7 In this comparative example, the difference from Example 3 is that ordinary spherical aluminum powder with a surface oxide layer thickness of 30±2nm of equal mass is used to replace spherical aluminum powder with a surface oxide layer thickness of ≤5nm. All other aspects are the same as in Example 3.

[0034] Blank group In this blank group, commercially available aluminum fumes were used. The fumes were prepared by wet ball milling, purchased from Henan Handing New Materials, with a purity of ≥99.5%, and were used after passing through a 200-mesh sieve.

[0035] III. Experimental Verification (1) Test of the gas-generating performance of multi-layer coated aluminum paste According to the current standard JC / T 407-2008 Aluminum Powder Paste for Autoclaved Aerated Concrete, the 2-minute gas generation rate, gas generation volume, and gas generation end time of the gas-generating aluminum paste in Examples 1-4, Comparative Examples 1-6, and the blank group were tested. The experimental instruments included an autoclaved aerated concrete aluminum powder paste gas generation meter (NF-JC407), a constant temperature water bath (accuracy ±0.1℃), an electronic analytical balance (accuracy 0.0001g), a 100mL gas generation bottle, a 50mL gas volume tube, a three-way stopcock, and a level bottle; the specific methods are as follows: All groups of aluminum paste samples were placed in an environment of 20℃±2℃ and 60%±5% relative humidity for 24 hours to eliminate the influence of ambient temperature and humidity on sample activity. A saturated sodium chloride-hydrogen saturated solution was prepared (sodium chloride was added to distilled water at room temperature until saturated, then high-purity hydrogen was introduced for 30 minutes until the solution was saturated, and the solution was sealed for later use). A calcium hydroxide suspension was prepared (12g of special-grade Ca(OH)₂ and 50mL of distilled water, freshly prepared and used immediately, stirred until homogeneous and free of lumps). The constant temperature water bath and gas flow tube were precisely adjusted to 45℃ and maintained at this temperature. The sealing of the gas-generating bottle and the three-way stopcock was checked. The leakage criterion was: after the liquid level in the leveling bottle had stood for 5 minutes, the fluctuation of the liquid level in the gas flow tube was ≤0.1m. L, otherwise replace the seal; weigh 0.07g of sample into a small plastic dish, place it on the liquid surface of the gas generating bottle and tighten the stopper; immerse the gas generating bottle in a constant temperature water bath until the temperature is balanced, turn the three-way stopcock to allow air to pass through, adjust the level bottle to make the liquid level in the gas measuring tube reach zero; then adjust the stopcock to connect the gas generating bottle and the gas measuring tube, shake the gas generating bottle for 15s to mix the sample with the suspension, and immediately return it to the water bath; accurately read the liquid level reading in the gas measuring tube at 2 minutes, and then read it once every 2 minutes until the difference between two consecutive readings is ≤0.2mL, which is considered the end of gas generation; each group of samples is measured in parallel 3 times, and the arithmetic mean is taken as the experimental result, the relative deviation is ≤2%, otherwise the measurement is repeated; the calculation formula is: X= (V t / V z ) × 100% to calculate the gas generation rate over 2 minutes, where V t V represents the gas production volume (mL) over 2 minutes. z Total gas generation (mL); the total gas generation is converted to mL / g (based on the effective aluminum powder content). Experimental data are shown in Table 1: Table 1. Record of Gas Evaporation Performance Test Data for Aluminum Gas Evaporating Paste ; Experimental Conclusions: The segmented dry ball milling process of this invention, which involves "first ball milling with stearic acid as a single medium and then ball milling with zinc stearate as a mixed medium," results in a gas evolution rate of only 16.8% for the finished gas-evolving aluminum paste at 2 minutes, significantly lower than other groups. This process also meets the technical requirements of low-density autoclaved aerated concrete for "gas evolution rate ≤25% in the first two minutes and gas evolution ending at 8 minutes," effectively controlling the gas evolution rate. The total gas evolution of this embodiment reached 765 mL / g, the highest among all groups, indicating that the process does not sacrifice the total gas evolution while suppressing initial gas evolution. Instead, it improves the effective utilization rate of aluminum powder by optimizing the coating structure. In contrast, the blank group (wet ball milling) had a gas evolution end time of 32 minutes and a total gas evolution of only 559 mL / g. This demonstrates that the multi-layer coating process, which combines dry ball milling with specific reagent combinations, can significantly optimize its gas evolution performance. Furthermore, the ultra-low oxide layer aluminum powder (≤5 nm) prepared by low-temperature atomization is the basis for obtaining excellent gas evolution performance.

[0036] (2) Characterization of multi-layer coated aluminum paste Referring to the standards GB / T 29753-2013 Morphology Analysis Method of Metal Powders for Powder Metallurgy by Scanning Electron Microscopy and GB / T 19077-2016 Performance Test Method of Laser Particle Size Analyzer, the gas-generating aluminum paste of Example 3 and the blank group was characterized using a field emission scanning electron microscope (FE-SEM, SU8010), a laser particle size analyzer (Mastersizer 3000), and an ultrasonic disperser (300W), as detailed below: Take 0.05g of alumina paste sample, add 10mL of anhydrous ethanol, and disperse in an ultrasonic disperser for 5min (300W, intermittent dispersion) to prepare a uniform suspension; take 1 drop of the suspension and drop it onto a clean silicon wafer, and let it air dry in a dust-free environment; place the sample in a scanning electron microscope, set the accelerating voltage to 15kV and the working distance to 8mm, and observe the morphology of the aluminum powder at 5000x and 10000x magnification, respectively, take SEM images, and analyze the regularity of the flakes, silver content, degree of agglomeration, and structural integrity; measure the D50 particle size of the aluminum powder using a laser particle size analyzer, with a test range of 0.1-100μm; take representative morphology and data as experimental results.

[0037] Experimental results are as follows Figure 1 As shown, the results indicate that the finished aluminum fuming paste of Example 3 of the present invention has good regularity in its flakes, high silver content, and no obvious structural damage or agglomeration. Compared with the finished aluminum fuming paste of the control group under the traditional process, it has better flake integrity.

[0038] (3) Test on the application effect of multi-layer coated alumina paste in autoclaved aerated concrete Sample preparation of low-density autoclaved aerated concrete: Refer to GB / T 11968-2020 Autoclaved Aerated Concrete Blocks (dry density ≤300kg / m³) 3 The raw material proportions (by weight) are: 30 parts cement, 50 parts fly ash, 15 parts lime, 5 parts gypsum, and a water-to-material ratio of 0.6; of which, the aluminum fumed paste is 0.06% of the dry concrete material. The sample preparation process is as follows: dry materials are mixed for 2 minutes until uniform, water is added and stirred for 3 minutes until the slurry is free of particles, aluminum efflorescence paste is added and stirred rapidly for 30 seconds, poured into a mold, and left to stand for 4 hours in a static chamber at 45℃±2℃ and 90%±5% relative humidity. Then, the mold is placed in an autoclave and steamed at 0.8MPa for 8 hours. After demolding, the mold is cured in a curing chamber at 20℃±2℃ and 95%±5% relative humidity for 28 days. Ten test blocks are prepared for each group, with 5 blocks used for compressive strength testing and 5 blocks used for mold collapse rate testing and porosity analysis. Experimental instruments: pressure testing machine (YES-2000, accuracy ±1%), 100mm×100mm×100mm steel mold, autoclave (0.8MPa), constant temperature and humidity curing chamber, stereomicroscope (SZ61, 100x), electronic scale (accuracy 0.1g).

[0039] 1. Compressive strength determination Specimen preparation: Cut the specimen from the middle of the cured specimen block, and grind the pressure surface with a grinding wheel to ensure that the pressure surface is completely in contact with the pressure plate of the press. Loading test: Referring to GB / T 11969-2020 Test method for performance of autoclaved aerated concrete, a pressure testing machine was used, the loading rate was controlled at (2.0±0.5) kN / s, and the load was applied perpendicular to the pressure surface until the specimen failed. The maximum failure load P (kN) was recorded. Calculation method: The compressive strength of a single specimen is F=P / A (A is the area under pressure, 0.01m²), in MPa; take the arithmetic mean of 5 specimens, accurate to 0.1MPa, remove outliers (deviation > 15%) and recalculate.

[0040] 2. Determination of collapse rate Slump rate / porosity: Refer to "JGJ / T 70-2009 Standard for Test Methods of Basic Performance of Building Mortar"; Criteria for mold collapse judgment: After demolding, the test block shows surface cracking (crack width ≥ 0.5 mm) or edge / corner peeling (peeling area ≥ 1 cm²). 2 Any deformation of the shape (dimensional deviation > 5mm) is considered a mold collapse. Calculation method: Collapse rate = (Number of collapsed test blocks / Total number of test blocks) × 100%; Measurements were taken immediately after demolding, with each group measured in triplicate and the average value taken. The experimental data are shown in Table 2. Table 2. Test Data Recording Table of Application Effect of Aluminum Gas-Generating Paste ; Experimental Results: When the multi-layer coated aerated aluminum paste of the present invention was applied to autoclaved aerated concrete using the process of Example 3, the compressive strength of the sample reached 5.8 MPa, the highest among all groups, which is 87.1% higher than the blank group (3.1 MPa) and 41.5%-70.6% higher than comparative examples 1-7 (3.4-4.1 MPa). This shows that the aerated aluminum paste can significantly improve the mechanical properties of low-density autoclaved aerated concrete, and the collapse rate is only 0.4%. This indicates that the segmented process of "first ball milling with stearic acid single medium + then ball milling with zinc stearate mixed medium" can obtain the optimal uniformity of aluminum powder surface coating, thereby achieving a stable and controllable gas generation process in the concrete paste and reducing collapse defects.

[0041] like Figure 2 As shown, compared with the addition of the blank group of gas-generating aluminum paste, the addition of the multi-layer coated gas-generating aluminum paste of Example 3 of the present invention significantly improves the uniformity of pores in autoclaved aerated concrete blocks.

[0042] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a multi-layered clad gas-evolving aluminum paste, characterized by: Includes the following steps: S1. Spherical aluminum powder is dry ball-milled under an inert gas protective atmosphere, and a ball milling aid is added during the dry ball milling process. The resulting ball milling product is pre-coated aluminum powder. The dry ball milling includes ball milling using a single ball milling media and a mixture of ball milling media; The ball milling using a single milling medium specifically involves milling spherical aluminum powder and stearic acid under a nitrogen protective atmosphere. The milling medium consists of steel balls with a particle size of 0.8-1 mm. The milling time is 1-2 hours, the milling speed is 25-35 r / min, and the milling temperature is 40-50℃. The mass ratio of the spherical aluminum powder to the milling medium is 1:10-15. The ball milling process using the mixed milling media specifically involves milling the initially milled aluminum powder and zinc stearate obtained from single milling media under a nitrogen protective atmosphere. The milling media consists of zirconia beads and glass beads with a particle size of 1.5-2.0 mm. The milling time is 2-5 hours, the milling speed is 28-36 r / min, and the milling temperature is 40-55℃. The mass ratio of the initially milled aluminum powder to the milling media is 1:8-12. The mass ratio of the zirconium oxide beads to the glass beads is 3-5:1; The zirconia beads are yttrium-stabilized zirconia beads with a hardness HV≥1200 and a wear rate <0.01% / h; the glass beads are high-silica glass beads with a hardness HV≥600 and a wear rate <0.01‰ / h. S2. The pre-coated aluminum powder, phosphate ester, sodium dodecylbenzenesulfonate, and diethylene glycol obtained in step S1 are stirred and kneaded under an inert gas protective atmosphere. The kneaded product obtained after sieving is a multi-layer coated gas-generating aluminum paste.

2. The method for preparing a multi-layer coated aluminum fuming paste according to claim 1, characterized in that: The raw materials for preparing the multi-layer coated aluminum paste, by weight, include 60-70 parts of spherical aluminum powder, 1-7 parts of ball milling aid, 1-2 parts of phosphate ester, 1-2 parts of sodium dodecylbenzene sulfonate, and 25-30 parts of diethylene glycol. The ball milling aid is at least one of stearic acid and zinc stearate.

3. The method for preparing a multi-layer coated aluminum fuming paste according to claim 2, characterized in that: In step S1, the spherical aluminum powder is low-temperature atomized spherical aluminum powder with a particle size of 1-3 μm, a particle size range of ≤0.8 μm, a purity of ≥99.5%, a sphericity of ≥90%, and a surface oxide layer thickness of ≤5 nm.

4. The method for preparing a multi-layer coated aluminum fuming paste according to claim 1, characterized in that: The mixing and kneading process is carried out at a temperature of 20-25℃ for 0.5-1.5 hours.

5. A multi-layer coated aluminum foaming paste, characterized in that: It is prepared by any one of the preparation methods described in claims 1-4.

6. The application of the multi-layer coated aluminum foaming paste as described in claim 5 in the preparation of concrete foaming agents, characterized in that: Its addition amount in concrete is greater than or equal to 0.06% of the dry weight.

7. The application according to claim 6, characterized in that: The concrete includes autoclaved aerated concrete and autoclaved lightweight concrete; The autoclaved aerated concrete is an autoclaved aerated concrete with a dry density of ≤ 300 kg / m 3 .

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