Preparation method of magnesia cementing material with good intermediate frequency sound absorption effect

Abstract

This invention discloses a method for preparing a magnesium cementitious material with good mid-frequency sound absorption effect, comprising the following steps: (1) dissolving magnesium sulfate heptahydrate and an additive in water under heating conditions to obtain a mixed solution; (2) mixing lightly calcined magnesium oxide, a foam stabilizer, a water-reducing agent, and a catalyst, and stirring thoroughly to obtain a mixed material; (3) mixing the mixed solution from step (1) with the mixed material from step (2), and stirring thoroughly to obtain a uniform slurry; (4) adding hydrogen peroxide to the slurry from step (3), stirring thoroughly, and then pouring it into a mold; placing the mold on a frozen copper column, placing a heating plate on the upper surface of the mold, and simultaneously heating and freezing; (5) after the slurry has initially solidified, subjecting it to standard air curing to obtain a magnesium cementitious material. The magnesium cementitious material prepared by the method of this invention has a gradient pore structure inside and has a sound absorption coefficient of up to 0.96 for mid-frequency noise (500–800 Hz).

Description

Technical Field

[0001] This invention relates to a method for preparing a magnesium-based cementitious material with good mid-frequency sound absorption effect. Background Technology

[0002] With the acceleration of urbanization, the problem of building acoustic pollution is becoming increasingly prominent. In particular, low-to-mid-frequency noise (around 250–800Hz) is more likely to create persistent background interference in indoor spaces, significantly impacting the acoustic comfort of buildings. Mid-frequency noise typically has strong penetrating power, slow attenuation, and a tendency to superimpose reverberation, easily leading to decreased speech intelligibility, distraction, and increased auditory fatigue, further reducing the comfort of people working, studying, and living. Mid-frequency noise in the building acoustic environment mainly originates from the low-pitched background noise generated by human activities, the operating noise of air conditioning and ventilation systems, the operating noise of electromechanical equipment, and the vibration noise transmitted through building structures and pipes.

[0003] To reduce noise pollution in this frequency band, existing mid-frequency sound-absorbing materials mainly include polymer foam and inorganic foam. Polymer foam is usually made into sound-absorbing panels in the form of polyurethane foam and melamine foam to reduce indoor reverberation and equipment noise. However, organic foams such as polyurethane pose a risk of combustion, and may release toxic products such as carbon monoxide and hydrogen cyanide during combustion or thermal decomposition, limiting their application in building spaces with high fire protection requirements. At the same time, the absorption of low-mid-frequency noise by polymer foam is significantly limited by its thickness. The sound absorption coefficients of some 1-2 inch polymer foams at 250Hz and 500Hz are only about 0.17-0.29 and 0.36-0.66, respectively. While increasing the thickness can improve sound absorption performance, it increases the thickness of the components and occupies building space. Inorganic foam materials mainly include foam glass, foam ceramics, foam metals, and foam concrete, and are usually processed into sound-absorbing panels, sound barrier filling layers, equipment sound insulation linings, or building envelope components. Taking foamed concrete as an example, this type of material has advantages such as certain mechanical strength, good fire resistance, low release of organic toxic fumes during combustion, and good environmental stability. However, the pore structure formed by conventional foaming is mostly randomly distributed and prone to defects such as closed pores, semi-closed pores, or local large pores. It lacks a pore size and flow resistance control structure that continuously varies along the thickness direction, making it difficult to spontaneously form an effective acoustic impedance matching structure. Therefore, its sound absorption response usually covers a wide frequency range, but the characteristic absorption peak is not prominent, making it difficult to achieve efficient sound absorption for specific low-mid frequency noise bands. In patent CN106927770B, the relevant embodiments have an average sound absorption coefficient of 0.24~0.41 in the range of 50~1600Hz, indicating that the overall sound absorption level of existing uniformly foamed cement-based sound-absorbing materials is still limited, especially in terms of low-mid frequency directional enhancement, there is still room for improvement. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for preparing a magnesium cementitious material with good mid-frequency sound absorption effect. The magnesium cementitious material prepared by this method has a gradient pore structure inside and can achieve a sound absorption coefficient of up to 0.96 for mid-frequency noise (500~800Hz).

[0005] Technical solution: The preparation method of the magnesium cementitious material with good mid-frequency sound absorption effect according to the present invention includes the following steps:

[0006] (1) Dissolve magnesium sulfate heptahydrate and additives in water under heating conditions to obtain a mixed solution;

[0007] (2) Mix lightly calcined magnesium oxide, foam stabilizer, water reducer and catalyst, and stir thoroughly to obtain a mixture;

[0008] (3) Mix the mixed solution from step (1) with the mixed materials from step (2) and stir thoroughly to obtain a uniform slurry;

[0009] (4) Add hydrogen peroxide to the slurry in step (3), stir thoroughly, and pour into a mold; place the mold on a frozen copper pillar (temperature approximately -196°C), place a heating plate on the upper surface of the mold, and heat and freeze simultaneously;

[0010] (5) After the slurry has initially set, it is subjected to standard air curing to obtain magnesium cementitious material.

[0011] In step (1), the additive is citric acid, and the amount of citric acid added is 0.5% of the mass of light-burned magnesium oxide; the mass ratio of magnesium sulfate heptahydrate to water is 8.2:8.4~9; the mass ratio of magnesium sulfate heptahydrate to light-burned magnesium oxide is 8.2~8.5:10.4; and the heating condition is 30~40℃.

[0012] In step (2), the foam stabilizer is hydrophilic silica (CAS: 60676-86-0) or amphiphilic silica modified with organosilane (CAS: 68611-44-9), and its addition amount is 2% of the mass of light-burned magnesium oxide; the water-reducing agent is a naphthalene-based water-reducing agent, and its addition amount is 2% of the mass of light-burned magnesium oxide; the catalyst is MnO2, and its addition amount is 4% of the mass of hydrogen peroxide; the stirring speed is 200~250 rpm, and the stirring time is 2~3 min.

[0013] In step (3), the stirring speed is 500~550 rpm and the stirring time is 3~5 min.

[0014] In step (4), the amount of hydrogen peroxide added is 2-4% of the mass of lightly calcined magnesium oxide; the stirring speed is 200-250 rpm, and the stirring time is 30-45 s. The copper column is used as a cold source and is pre-frozen in liquid nitrogen for 30 min, and the temperature of the heating plate is 40-60℃; the heating and freezing time is 1-2 h.

[0015] In step (5), the material is first cured in standard air for one day, and after demolding, it is cured in standard air for another 28 days.

[0016] This invention utilizes a non-equilibrium gradient temperature field to precisely control the foaming process of magnesium cementitious materials, forming a naturally transitioning gradient pore structure in situ within the magnesium gel. This gradient pore structure, by introducing non-uniform pore size and flow resistance distribution along the thickness direction, helps improve the impedance matching between incident sound waves and the material surface, and enhances the propagation, scattering, and dissipation of sound waves in multi-level channels, thereby enabling the material to exhibit significantly enhanced sound absorption characteristics in the mid-frequency characteristic band.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The method of the present invention prepares a magnesium gradient pore cementitious material with mid-frequency sound absorption effect. The gradient pore structure can improve the impedance matching of sound waves entering the material and prolong the propagation and dissipation path of sound waves in the pores. At the same time, it can induce local resonance response, thereby greatly enhancing the mid-frequency sound absorption effect of the material, with a maximum sound absorption coefficient of 0.96 in the vicinity of 500~800Hz. Attached Figure Description

[0018] Figure 1 This is a cross-sectional view of the magnesium cementitious materials prepared in Example 1 and Comparative Example 1.

[0019] Figure 2 The acoustic impedance curves of the magnesium cementitious materials prepared in Example 1, Comparative Example 8, and Comparative Example 9 are shown. Detailed Implementation

[0020] Example 1

[0021] The present invention discloses a method for preparing a magnesium-based cementitious material with good mid-frequency sound absorption effect, comprising the following steps:

[0022] (1) Dissolve 0.052g (0.5% of the mass of lightly calcined magnesium oxide) of citric acid and 8.2g of magnesium sulfate heptahydrate in 8.4g of water under heating conditions of 30~40℃;

[0023] (2) Weigh 10.4g of lightly calcined magnesium oxide, and add amphiphilic silica (0.208g) and naphthalene-based water-reducing agent (0.208g) at 2% of the mass of lightly calcined magnesium oxide; add MnO2 catalyst (0.008g) at 4% of the mass of 30wt% hydrogen peroxide solution; place the above raw materials in a mixer and dry mix at 200rpm for 3min until the components are evenly dispersed to obtain the precursor dry material;

[0024] (3) Mix the mixed solution from step (1) with the precursor dry material from step (2) and stir at 500 rpm for 3 min in a mixer to obtain a uniform slurry;

[0025] (4) Add 0.208g (2% of the mass of lightly calcined magnesium oxide) of 30wt% hydrogen peroxide solution to the homogeneous slurry in step (3), stir at 200rpm for 30s and then pour into the mold;

[0026] (5) Use the copper column as a cold source. Pre-freeze the copper column in liquid nitrogen for 30 minutes. Place the mold on the frozen copper column. Place a heating plate on the upper surface of the mold. The temperature of the heating plate is 40℃. Simultaneously freeze and heat for 60 minutes.

[0027] (6) After the slurry has initially set, the sample is placed under standard air curing conditions and demolded after 1 day. After demolding, it is continued to be cured in the air for 28 days to obtain magnesium cementitious material.

[0028] Under the bottom-cooling-top-heating conditions of Example 1, the temperature gradient is consistent with the upward direction of the bubbles. The bottom cold zone suppresses excessively rapid foaming and large bubble coalescence in the bottom region, which is conducive to the formation of a fine and stable pore structure. As the bubbles enter the high-temperature region during their upward movement, they gradually expand, thus forming a continuously transitioning gradient pore structure along the thickness direction, such as... Figure 1 As shown in Example 1. After reversing the cold and heat sources in Comparative Example 1, under the condition of upper cooling and lower heating, the lower hot zone causes gas to be rapidly generated and continuously rise, while the upper cold zone, due to increased viscosity, hinders the migration of gas bubbles, causing the gas to accumulate and coalesce inside the material, ultimately leading to the formation of hollow defects inside. Therefore, the material of Comparative Example 1 has a gradient pore structure fault and a large hollow structure inside, such as... Figure 1 As shown in Comparative Example 1.

[0029] Example 2

[0030] The present invention discloses a method for preparing a magnesium-based cementitious material with good mid-frequency sound absorption effect, comprising the following steps:

[0031] (1) Dissolve 0.052g (0.5% of the mass of lightly calcined magnesium oxide) of citric acid and 8.2g of magnesium sulfate heptahydrate in 8.4g of water under heating conditions of 30~40℃;

[0032] (2) Weigh 10.4g of lightly calcined magnesium oxide, and add amphiphilic silica (0.208g) and naphthalene-based water-reducing agent (0.208g) at 2% of the mass of lightly calcined magnesium oxide; add MnO2 catalyst (0.008g) at 4% of the mass of 30wt% hydrogen peroxide solution; place the above raw materials in a mixer and dry mix at 200rpm for 3min until the components are evenly dispersed to obtain the precursor dry material;

[0033] (3) Mix the mixed solution from step (1) with the precursor dry material from step (2) and stir at 500 rpm for 3 min in a mixer to obtain a uniform slurry;

[0034] (4) Add 0.208g (2% of the mass of lightly calcined magnesium oxide) of 30wt% hydrogen peroxide solution to the homogeneous slurry in step (3), stir at 200rpm for 30s and then pour into the mold;

[0035] (5) Use the copper column as a cold source. Pre-freeze the copper column in liquid nitrogen for 30 minutes. Place the mold on the frozen copper column. Place a heating plate on the upper surface of the mold. The temperature of the heating plate is 60℃. Simultaneously freeze and heat for 60 minutes.

[0036] (6) After the slurry has initially set, the sample is placed under standard air curing conditions and demolded after 1 day. After demolding, it is continued to be cured in the air for 28 days to obtain magnesium cementitious material.

[0037] Comparative Example 1

[0038] A method for preparing a magnesium-based cementitious material includes the following steps:

[0039] (1) Dissolve 0.052g (0.5% of the mass of lightly calcined magnesium oxide) of citric acid and 8.2g of magnesium sulfate heptahydrate in 8.4g of water under heating conditions of 30~40℃;

[0040] (2) Weigh 10.4g of lightly calcined magnesium oxide, and add amphiphilic silica (0.208g) and naphthalene-based water-reducing agent (0.208g) at 2% of the mass of lightly calcined magnesium oxide; add MnO2 catalyst (0.008g) at 4% of the mass of 30wt% hydrogen peroxide solution; place the above raw materials in a mixer and dry mix at 200rpm for 3min until the components are evenly dispersed to obtain the precursor dry material;

[0041] (3) Mix the mixed solution from step (1) with the precursor dry material from step (2) and stir at 500 rpm for 3 min in a mixer to obtain a uniform slurry;

[0042] (4) Add 0.208g (2% of the mass of lightly calcined magnesium oxide) of 30wt% hydrogen peroxide solution to the homogeneous slurry in step (3), stir at 200rpm for 30s and then pour into the mold;

[0043] (5) Place the mold on a heating plate at a temperature of 40°C. Place a frozen copper column on top of the mold. Use the copper column as a cold source to freeze the mold in liquid nitrogen for 30 minutes before freezing and heating for 60 minutes.

[0044] (6) After the slurry has initially set, the sample is placed under standard air curing conditions and demolded after 1 day. After demolding, it is continued to be cured in the air for 28 days to obtain magnesium cementitious material.

[0045] The only difference between Comparative Example 1 and Example 1 is the exchange of the hot and cold source positions. Because bubbles in a liquid medium are affected by buoyancy, they tend to move spontaneously upwards. In Comparative Example 1, the heat source is at the bottom of the mold, resulting in a high foaming rate at the bottom and a tendency for the bubbles to rise. However, the temperature at the top is too low, preventing the gas from leaving the mold and causing it to accumulate in the middle of the matrix, resulting in a large internal cavity and structural failure. Figure 1 As shown in Comparative Example 1.

[0046] Comparative Example 2

[0047] A method for preparing a magnesium-based cementitious material includes the following steps:

[0048] (1) Dissolve 0.052g (0.5% of the mass of lightly calcined magnesium oxide) of citric acid and 8.2g of magnesium sulfate heptahydrate in 8.4g of water under heating conditions of 30~40℃;

[0049] (2) Weigh 10.4g of lightly calcined magnesium oxide, and add amphiphilic silica (0.208g) and naphthalene-based water-reducing agent (0.208g) at 2% of the mass of lightly calcined magnesium oxide; add MnO2 catalyst (0.008g) at 4% of the mass of 30wt% hydrogen peroxide solution; place the above raw materials in a mixer and dry mix at 200rpm for 3min until the components are evenly dispersed to obtain the precursor dry material;

[0050] (3) Mix the mixed solution from step (1) with the precursor dry material from step (2) and stir at 500 rpm for 3 min in a mixer to obtain a uniform slurry;

[0051] (4) Add 0.208g (2% of the mass of lightly calcined magnesium oxide) of 30wt% hydrogen peroxide solution to the homogeneous slurry in step (3), stir at 200rpm for 30s and then pour into the mold;

[0052] (5) Use the copper column as a cold source. Pre-freeze the copper column in liquid nitrogen for 30 minutes. Place the mold on the frozen copper column. Place a heating plate on the upper surface of the mold. The temperature of the heating plate is 30°C. Simultaneously freeze and heat for 60 minutes.

[0053] (6) After the slurry has initially set, the sample is placed under standard air curing conditions and demolded after 1 day. After demolding, it is continued to be cured in the air for 28 days to obtain magnesium cementitious material.

[0054] Because the heating plate is at a low temperature, the top does not foam, and the pore structure of the material does not show a significant gradient change.

[0055] Comparative Example 3

[0056] A method for preparing a magnesium-based cementitious material includes the following steps:

[0057] (1) Dissolve 0.052g (0.5% of the mass of lightly calcined magnesium oxide) of citric acid and 8.2g of magnesium sulfate heptahydrate in 8.4g of water under heating conditions of 30~40℃;

[0058] (2) Weigh 10.4g of lightly calcined magnesium oxide, and add amphiphilic silica (0.208g) and naphthalene-based water-reducing agent (0.208g) at 2% of the mass of lightly calcined magnesium oxide; add MnO2 catalyst (0.008g) at 4% of the mass of 30wt% hydrogen peroxide solution; place the above raw materials in a mixer and dry mix at 200rpm for 3min until the components are evenly dispersed to obtain the precursor dry material;

[0059] (3) Mix the mixed solution from step (1) with the precursor dry material from step (2) and stir at 500 rpm for 3 min in a mixer to obtain a uniform slurry;

[0060] (4) Add 0.208g (2% of the mass of lightly calcined magnesium oxide) of 30wt% hydrogen peroxide solution to the homogeneous slurry in step (3), stir at 200rpm for 30s and then pour into the mold;

[0061] (5) Use the copper column as a cold source. Pre-freeze the copper column in liquid nitrogen for 30 minutes. Place the mold on the frozen copper column. Place a heating plate on the upper surface of the mold. The temperature of the heating plate is 80℃. Simultaneously freeze and heat for 60 minutes.

[0062] (6) After the slurry has initially set, the sample is placed under standard air curing conditions and demolded after 1 day. After demolding, it is continued to be cured in the air for 28 days to obtain magnesium cementitious material.

[0063] The excessively high temperature of the heating plate caused the top reaction rate to be too fast, resulting in rapid expansion and rupture of bubbles, and an imbalance in the pore structure, which was not conducive to prolonging the propagation of sound waves in the pore.

[0064] Comparative Example 4

[0065] A method for preparing a magnesium-based cementitious material includes the following steps:

[0066] (1) Dissolve 0.052g (0.5% of the mass of lightly calcined magnesium oxide) of citric acid and 8.2g of magnesium sulfate heptahydrate in 8.4g of water under heating conditions of 30~40℃;

[0067] (2) Weigh 10.4g of lightly calcined magnesium oxide, and add amphiphilic silica (0.208g) and naphthalene-based water-reducing agent (0.208g) at 2% of the mass of lightly calcined magnesium oxide; add MnO2 catalyst (0.008g) at 4% of the mass of 30wt% hydrogen peroxide solution; place the above raw materials in a mixer and dry mix at 200rpm for 3min until the components are evenly dispersed to obtain the precursor dry material;

[0068] (3) Mix the mixed solution from step (1) with the precursor dry material from step (2) and stir at 500 rpm for 3 min in a mixer to obtain a uniform slurry;

[0069] (4) Add 0.208g (2% of the mass of lightly calcined magnesium oxide) of 30wt% hydrogen peroxide solution to the homogeneous slurry in step (3), stir at 200rpm for 30s and then pour into the mold;

[0070] (5) Use the copper column as a cold source. Pre-freeze the copper column in liquid nitrogen for 30 minutes. Place the mold on the frozen copper column. Place a heating plate on the upper surface of the mold. The temperature of the heating plate is 60℃. Simultaneously freeze and heat for 180 minutes.

[0071] (6) After the slurry has initially set, the sample is placed under standard air curing conditions and demolded after 1 day. After demolding, it is continued to be cured in the air for 28 days to obtain magnesium cementitious material.

[0072] Because the heating plate is heated for too long, the temperature gradient inside the slurry continues to act excessively, causing the change in the pore structure along the thickness direction to change from a continuous transition to an abrupt change, forming a cliff-like gradient pore distribution, which is not conducive to prolonging the propagation of sound waves in the pores.

[0073] Comparative Example 5

[0074] A method for preparing a magnesium-based cementitious material includes the following steps:

[0075] (1) Dissolve 0.052g (0.5% of the mass of lightly calcined magnesium oxide) of citric acid and 8.2g of magnesium sulfate heptahydrate in 8.4g of water under heating conditions of 30~40℃;

[0076] (2) Weigh 10.4g of lightly calcined magnesium oxide, and add hydrophilic silica (0.208g) and naphthalene-based water-reducing agent (0.208g) at 2% of the mass of lightly calcined magnesium oxide; add MnO2 catalyst (0.008g) at 4% of the mass of 30wt% hydrogen peroxide solution; place the above raw materials in a mixer and dry mix at 200rpm for 3min until the components are evenly dispersed to obtain the precursor dry material;

[0077] (3) Mix the mixed solution from step (1) with the precursor dry material from step (2) and stir at 500 rpm for 3 min in a mixer to obtain a uniform slurry;

[0078] (4) Add 0.208g (2% of the mass of lightly calcined magnesium oxide) of 30wt% hydrogen peroxide solution to the homogeneous slurry in step (3), stir at 200rpm for 30s and then pour into the mold;

[0079] (5) Use the copper column as a cold source. Pre-freeze the copper column in liquid nitrogen for 30 minutes. Place the mold on the frozen copper column. Place a heating plate on the upper surface of the mold. The temperature of the heating plate is 40℃. Simultaneously freeze and heat for 60 minutes.

[0080] (6) After the slurry has initially set, the sample is placed under standard air curing conditions and demolded after 1 day. After demolding, it is continued to be cured in the air for 28 days to obtain magnesium cementitious material.

[0081] Hydrophilic SiO2 has a poorer bubble stabilization effect compared to amphiphilic SiO2.

[0082] Comparative Example 6

[0083] A method for preparing a magnesium-based cementitious material includes the following steps:

[0084] (1) Dissolve 0.052g (0.5% of the mass of lightly calcined magnesium oxide) of citric acid and 8.2g of magnesium sulfate heptahydrate in 8.4g of water under heating conditions of 30~40℃;

[0085] (2) Weigh 10.4g of lightly calcined magnesium oxide, and add amphiphilic silica (0.208g) and naphthalene-based water-reducing agent (0.208g) at 2% of the mass of lightly calcined magnesium oxide; add MnO2 catalyst (0.016g) at 4% of the mass of 30wt% hydrogen peroxide solution; place the above raw materials in a mixer and dry mix at 200rpm for 3min until the components are evenly dispersed to obtain the precursor dry material;

[0086] (3) Mix the mixed solution from step (1) with the precursor dry material from step (2) and stir at 500 rpm for 3 min in a mixer to obtain a uniform slurry;

[0087] (4) Add 0.416g (4% of the mass of lightly calcined magnesium oxide) of 30wt% hydrogen peroxide solution to the homogeneous slurry in step (3), stir at 200rpm for 30s and then pour into a mold;

[0088] (5) Use the copper column as a cold source. Pre-freeze the copper column in liquid nitrogen for 30 minutes. Place the mold on the frozen copper column. Place a heating plate on the upper surface of the mold. The temperature of the heating plate is 40℃. Simultaneously freeze and heat for 60 minutes.

[0089] (6) After the slurry has initially set, the sample is placed under standard air curing conditions and demolded after 1 day. After demolding, it is continued to be cured in the air for 28 days to obtain magnesium cementitious material.

[0090] The increased amount of hydrogen peroxide leads to a faster foaming rate in the matrix, which is not conducive to the formation of gradient pore structures.

[0091] Comparative Example 7

[0092] A method for preparing a magnesium-based cementitious material includes the following steps:

[0093] (1) Dissolve 0.052g (0.5% of the mass of lightly calcined magnesium oxide) of citric acid and 8.2g of magnesium sulfate heptahydrate in 8.4g of water under heating conditions of 30~40℃;

[0094] (2) Weigh 10.4g of lightly calcined magnesium oxide, and add amphiphilic silica (0.208g) and naphthalene-based water-reducing agent (0.208g) at 2% of the mass of lightly calcined magnesium oxide; add MnO2 catalyst (0.002g) at 4% of the mass of 30wt% hydrogen peroxide solution; place the above raw materials in a mixer and dry mix at 200rpm for 3min until the components are evenly dispersed to obtain the precursor dry material;

[0095] (3) Mix the mixed solution from step (1) with the precursor dry material from step (2) and stir at 500 rpm for 3 min in a mixer to obtain a uniform slurry;

[0096] (4) Add 0.052g (0.5% of the mass of lightly calcined magnesium oxide) of 30wt% hydrogen peroxide solution to the uniform slurry in step (3), stir at 200rpm for 30s and then pour into the mold;

[0097] (5) Use the copper column as a cold source. Pre-freeze the copper column in liquid nitrogen for 30 minutes. Place the mold on the frozen copper column. Place a heating plate on the upper surface of the mold. The temperature of the heating plate is 40℃. Simultaneously freeze and heat for 60 minutes.

[0098] (6) After the slurry has initially set, the sample is placed under standard air curing conditions and demolded after 1 day. After demolding, it is continued to be cured in the air for 28 days to obtain magnesium cementitious material.

[0099] The reduced amount of hydrogen peroxide resulted in less foaming of the matrix and a significant decrease in porosity.

[0100] Comparative Example 8

[0101] A method for preparing a magnesium-based cementitious material includes the following steps:

[0102] (1) Dissolve 0.052g (0.5% of the mass of lightly calcined magnesium oxide) of citric acid and 8.2g of magnesium sulfate heptahydrate in 8.4g of water under heating conditions of 30~40℃;

[0103] (2) Weigh 10.4g of lightly calcined magnesium oxide, and add amphiphilic silica (0.208g) and naphthalene-based water-reducing agent (0.208g) at 2% of the mass of lightly calcined magnesium oxide; add MnO2 catalyst (0.008g) at 4% of the mass of 30wt% hydrogen peroxide solution; place the above raw materials in a mixer and dry mix at 200rpm for 3min until the components are evenly dispersed to obtain the precursor dry material;

[0104] (3) Mix the mixed solution from step (1) with the precursor dry material from step (2) and stir at 500 rpm for 3 min in a mixer to obtain a uniform slurry;

[0105] (4) Add 0.208g (2% of the mass of lightly calcined magnesium oxide) of 30wt% hydrogen peroxide solution to the homogeneous slurry in step (3), stir at 200rpm for 30s and then pour into the mold;

[0106] (5) Place the mold in the air and wait for the slurry to set. Then place the sample under standard air curing conditions and demold after 1 day. After demolding, continue to cure in the air for 28 days to obtain magnesium cementitious material.

[0107] In this comparative example, there is no temperature difference, the matrix pore structure is randomly distributed, and there is no gradient pore structure, which is not conducive to prolonging the propagation of sound waves in the pores.

[0108] Comparative Example 9

[0109] A method for preparing magnesium aerogel includes the following steps:

[0110] (1) Dissolve 0.052g (0.5% of the mass of lightly calcined magnesium oxide) of citric acid and 8.2g of magnesium sulfate heptahydrate in 8.4g of water under heating conditions of 30~40℃;

[0111] (2) Weigh 10.4g of lightly calcined magnesium oxide, and add amphiphilic silica (0.208g) and naphthalene-based water-reducing agent (0.208g) at 2% of the mass of lightly calcined magnesium oxide; add MnO2 catalyst (0.008g) at 4% of the mass of 30wt% hydrogen peroxide solution; place the above raw materials in a mixer and dry mix at 200rpm for 3min until the components are evenly dispersed to obtain the precursor dry material;

[0112] (3) Mix the mixed solution from step (1) with the precursor dry material from step (2) and stir at 500 rpm for 3 min in a mixer to obtain a uniform slurry;

[0113] (4) Pour the uniform slurry from step (3) into a mold and place it on a copper column that has been pre-frozen with liquid nitrogen for 30 minutes and continue to freeze it under liquid nitrogen conditions for 1 hour.

[0114] (5) Demold the sample from step (4) and freeze-dry it in a freeze dryer at -60℃ for 6 hours to obtain magnesium aerogel.

[0115] In this comparative example, magnesium aerogel was prepared as a sound-absorbing material. However, due to the small pore structure formed by the aerogel, the high-efficiency sound absorption frequency range has deviated from the low-mid frequency range.

[0116] Comparative Example 10

[0117] A method for preparing a magnesium-based cementitious material includes the following steps:

[0118] (1) Dissolve 0.052g (0.5% of the mass of lightly calcined magnesium oxide) of citric acid and 8.2g of magnesium sulfate heptahydrate in 8.4g of water under heating conditions of 30~40℃;

[0119] (2) Weigh 10.4g of lightly calcined magnesium oxide, and add hydrophilic silica (0.208g) and naphthalene-based water-reducing agent (0.208g) at 2% of the mass of lightly calcined magnesium oxide; add MnO2 catalyst (0.002g) at 1% of the mass of 30wt% hydrogen peroxide solution; place the above raw materials in a mixer and dry mix at 200rpm for 3min until all components are evenly dispersed to obtain the precursor dry material;

[0120] (3) Mix the mixed solution from step (1) with the precursor dry material from step (2) and stir at 500 rpm for 3 min in a mixer to obtain a uniform slurry;

[0121] (4) Add 0.208g (2% of the mass of lightly calcined magnesium oxide) of 30wt% hydrogen peroxide solution to the homogeneous slurry in step (3), stir at 200rpm for 30s and then pour into the mold;

[0122] (5) Use the copper column as a cold source. Pre-freeze the copper column in liquid nitrogen for 30 minutes. Place the mold on the frozen copper column. Place a heating plate on the upper surface of the mold. The temperature of the heating plate is 40℃. Simultaneously freeze and heat for 60 minutes.

[0123] (6) After the slurry has initially set, the sample is placed under standard air curing conditions and demolded after 1 day. After demolding, it is continued to be cured in the air for 28 days to obtain magnesium cementitious material.

[0124] In this comparative example, the reduced catalyst content in the prepared magnesium cementitious material led to a decrease in foaming efficiency and partial loss of pore structure.

[0125] The sound absorption performance of the magnesium cementitious materials obtained in Examples 1-2 and Comparative Examples 1-10 was tested using an impedance tube acoustic testing experimental device. The results are shown in Table 1.

[0126] Table 1

[0127]

[0128] pass Figure 2 It can be seen that in the mid-to-low frequency range (500-800Hz), the magnesium gel material with gradient pore structure in Example 1 has the highest sound absorption effect, with a sound absorption coefficient of up to 0.96. In contrast, the magnesium gel material with uniform foaming in Comparative Example 8 has poor sound absorption effect, and the aerogel in Comparative Example 9 does not have a sound absorption frequency range in the mid-to-low frequency range.

Claims

1. A method for preparing a magnesium-based cementitious material with good mid-frequency sound absorption effect, characterized in that, Includes the following steps: (1) Dissolve magnesium sulfate heptahydrate and additives in water under heating conditions to obtain a mixed solution; (2) Mix lightly calcined magnesium oxide, foam stabilizer, water reducer and catalyst, and stir thoroughly to obtain a mixture; (3) Mix the mixed solution from step (1) with the mixed materials from step (2) and stir thoroughly to obtain a uniform slurry; (4) Add hydrogen peroxide to the slurry in step (3), stir thoroughly, and pour into a mold; place the mold on a frozen copper pillar, place a heating plate on the upper surface of the mold, and heat and freeze simultaneously; (5) After the slurry has initially set, it is subjected to standard air curing to obtain magnesium cementitious material.

2. The preparation method according to claim 1, characterized in that: In step (1), the additive is citric acid, and the amount of citric acid added is 0.5 to 0.6% of the mass of lightly calcined magnesium oxide.

3. The preparation method according to claim 1, characterized in that: In step (1), the mixing mass ratio of magnesium sulfate heptahydrate to water is 8.2:8.4~9; the mixing mass ratio of magnesium sulfate heptahydrate to lightly calcined magnesium oxide is 8.2~8.5:10.

4.

4. The preparation method according to claim 1, characterized in that: In step (2), the foam stabilizer is hydrophilic silica or amphiphilic silica, and its addition amount is 2 to 2.5% of the mass of lightly calcined magnesium oxide.

5. The preparation method according to claim 1, characterized in that: In step (2), the water-reducing agent is a naphthalene-based water-reducing agent, and its addition amount is 2 to 2.5% of the mass of lightly calcined magnesium oxide.

6. The preparation method according to claim 1, characterized in that: In step (2), the catalyst is MnO2, and the amount added is 4-5% of the mass of hydrogen peroxide.

7. The preparation method according to claim 1, characterized in that: In step (3), the stirring speed is 500~550 rpm and the stirring time is 3~5 min.

8. The preparation method according to claim 1, characterized in that: In step (4), the amount of hydrogen peroxide added is 2-4% of the mass of lightly calcined magnesium oxide; the stirring speed is 200-250 rpm and the stirring time is 30-45 s.

9. The preparation method according to claim 1, characterized in that: In step (4), the frozen copper column refers to a copper column that has been frozen in liquid nitrogen for 20 to 30 minutes, and the temperature of the heating plate is 40 to 60°C; the heating and freezing time is 1 to 2 hours.

10. The preparation method according to claim 1, characterized in that: In step (5), the material is first cured in standard air for one day, and after demolding, it is cured in standard air for another 28 days.

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