Boron enhanced cementitious radiative cooling composite and method of making the same

Abstract

The application discloses a boron-reinforced cement-based radiative cooling composite material and a preparation method thereof, and belongs to the technical field of building materials. In the preparation, silicate cement, ceramic micro powder and other powders are uniformly mixed to obtain mixed powder; mixing water is uniformly mixed with the mixed powder, and after sufficient stirring, a slurry is obtained. The hardened cement slurry with directional pores is obtained by using an ice template method, and the hardened slurry is subjected to high-temperature treatment to obtain the boron-reinforced cement-based radiative cooling composite material. The application combines the ice template method and the high-temperature treatment, obviously improves the radiative cooling capacity, avoids the problem of insufficient material strength caused by the ice template method, and makes the prepared composite material have high radiative cooling capacity and compressive strength.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of building materials, and particularly relates to a boron-enhanced cement-based radiation refrigeration composite material and a preparation method thereof, which can improve the radiation refrigeration capacity of cement-based materials while enhancing the compressive strength and high-temperature resistance of the cement-based materials. BACKGROUND

[0002] Passive radiation cooling technology mainly transmits the heat of an object to the deep cold space through the atmospheric window of 8-13 μm in the form of radiation to achieve the effect of cooling the target object without consuming additional energy. Therefore, the passive radiation cooling performance needs to be achieved by adjusting the characteristics of the material, that is, both the infrared thermal radiation emissivity of the material in the atmospheric window band and the absorption of incident sunlight by the material need to be minimized.

[0003] Cement-based materials are the most widely used building materials in the world, and have the advantages of easy availability and low price. Hardened cement itself has the ability to radiate infrared light. The current literature reports that the main ways to improve the radiation refrigeration capacity of cement-based materials are to add white mineral admixtures and whitening agent particles to improve the reflectivity of sunlight, or to coat the surface of the building with organic and inorganic radiation cooling paint to achieve high sunlight reflectivity. Patent "Cement-based passive refrigeration composite material and preparation method thereof" (CN115466086A) shows that by adding admixtures, white minerals and increasing the water-cement ratio, the solar reflectivity of hardened cement can be improved in the short term, but there are problems such as limited optical performance, decreased mechanical strength, and high cost. Patent "Polymer cement radiation refrigeration paint and coating" (CN113563779B) shows that coating polymer paint on the surface of hardened cement can achieve a reflectivity of greater than or equal to 90% in the full wavelength band of sunlight, but the addition of a large amount of functional fillers (such as rutile titanium dioxide and alumina micropowder) increases the cost of the material, and the coating layer has the risk of weathering and peeling. Patent "Cement-based radiation refrigeration dry powder paint, building coating, and coating preparation method" (CN110105798A) shows that inorganic pigment particles have excellent radiation refrigeration performance, but the interface between the coating layer and the building is only combined by weak van der Waals forces, which is easily damaged by extreme wind and rain, resulting in a significant decrease in optical performance.

[0004] From the above, how to effectively improve the radiation cooling performance of cement-based materials is still a difficult problem to be solved. In existing research reports, most of them focus on using white fillers to improve the reflectivity of hardened cement-based materials in the solar spectrum band, but cannot eliminate the influence of the absorption peaks of hydroxyl near 1.43 μm and 1.95 μm in the near-infrared spectrum on the solar reflectivity spectrum. Almost no report considers designing the pore structure of the material, changing the near-infrared radiation, and improving the infrared radiation efficiency in the atmospheric window area to improve the radiation cooling efficiency. SUMMARY

[0005] To solve the above technical problems, the present application provides a boron-enhanced cement-based radiation cooling composite material and a preparation method thereof. The cement composite material prepared by the present application forms a directional arrangement of microporous structure by ice template method, and further enhances the radiation cooling capacity of the hardened cement test block after high temperature action. More importantly, the preparation method provided by the present application greatly improves the mechanical properties of the cement-based material prepared by the ice template method, effectively making up for the inherent defect of the ice template method that seriously reduces the mechanical properties of the cement-based material.

[0006] To realize the high-temperature enhancement of the radiation cooling performance of cement, the present application uses Portland cement, ceramic micro powder and water to form a cementing system, and adjusts the working performance of the fresh paste by adding a viscosity regulator. The present application uses the ice template method to prepare a hardened cement test block, and the ice crystals in the cement paste grow directionally along the temperature gradient during low-temperature rapid freezing, forming a microporous structure on the surface of the cement, which improves the scattering effect of the hardened test block on sunlight. Then, the high-temperature oxidation activity of the ceramic micro powder is used to treat the cement test block at high temperature, and the generated product has good solar reflectivity, which further improves the radiation cooling capacity and high-temperature resistance of the hardened cement test block. The ceramic micro powder selected by the present application can undergo oxidation reaction at a temperature of 400 ℃ to 1000 ℃, and the corresponding oxidation products are generated. These generated oxidation products are beneficial to enhancing the radiation cooling capacity of the cement. Calcium hydroxide, a hydration product of cement, begins to dehydrate and decompose at about 460 ℃ to generate calcium oxide; with continuous high temperature, the hydration product C-S-H gel decomposes to generate calcium silicate. The high-temperature decomposition products of the hydration product can further react with the high-temperature oxidation products of the ceramic micro powder to form eutectic mixtures with dense structures, such as perovskite, rutile phase, calcium borate, etc. These eutectic mixtures themselves have high strength and high-temperature resistance, which on the one hand increases the compressive strength of the cement test block after high-temperature treatment, and on the other hand, these eutectic mixtures can effectively reflect sunlight, further improving the radiation cooling effect of the cement test block.

[0007] To achieve the above purpose, the present application provides the following technical solutions:

[0008] In one aspect, the present application provides a method for preparing a boron reinforced cement-based radiative cooling composite material, comprising the following steps:

[0009] Step 1, uniformly mixing Portland cement, ceramic micro-powder and admixture to obtain a dry powder mixture;

[0010] Step 2, uniformly mixing the admixture with mixing water and then uniformly stirring the dry powder mixture to obtain a uniform slurry;

[0011] Step 3, pouring the slurry into a mold to prepare a hardened cement-based test piece by using an ice mold method;

[0012] Step 4, drying the hardened cement-based test piece to a constant weight;

[0013] Step 5, high-temperature treating the dried hardened cement-based test piece at a temperature of 400-1000°C, and then cooling to obtain a boron reinforced cement-based radiative cooling composite material.

[0014] As a preferred solution, the ceramic micro-powder is any one or several of zirconium boride, vanadium boride, titanium boride, chromium boride, boron carbide, hafnium boride, and tantalum boride.

[0015] As a preferred solution, the D50 of the particle size distribution of the ceramic micro-powder is less than 50 microns.

[0016] As a preferred solution, 40-80 parts of the ceramic micro-powder are added per 100 parts of the Portland cement by mass fraction.

[0017] As a preferred solution, the water-binder ratio of the obtained slurry is 0.5-1.0.

[0018] As a preferred solution, the admixture is a mixture of one or several of micron-sized silicon dioxide, micron-sized titanium white powder, montmorillonite powder, halloysite nanotube, and micron-sized aluminum oxide.

[0019] As a preferred solution, the admixture is a viscosity regulator, which is a mixture of one or several of hydroxyethyl methyl cellulose, hydroxypropyl cellulose, hydroxymethyl cellulose, and carboxymethyl cellulose.

[0020] As a preferred solution, the viscosity value of the viscosity regulator is about 200,000 mPa·S, and the dosage is less than 2.0% of the mass of the Portland cement, and most preferably 0.6-1% of the mass of the Portland cement.

[0021] As a preferred solution, in Step 2, uniformly mixing the admixture with mixing water and then uniformly stirring the dry powder mixture comprises the following steps:

[0022] Step 2.1, dispersing the admixture in the mixing water and magnetically stirring to obtain an admixture dispersion;

[0023] Step 2.2, the dry powder mixture is added to the admixture dispersion liquid to obtain a slurry by stirring;

[0024] As a preferred solution, in step 2.2, the dry powder mixture is added to the admixture dispersion liquid, first stirred at low speed in a stirring pot for 60-120 seconds, and then stirred at high speed for 180-210 seconds to obtain a uniform slurry.

[0025] As a preferred solution, in step 3, the ice template method for preparing the hardened cement-based test piece includes the following steps:

[0026] Step 3.1, after the slurry is poured into the mold, it is frozen below the freezing point to form a frozen test piece, and the frozen test piece is obtained after demolding;

[0027] Step 3.2, the frozen test piece is placed in a constant temperature oven above the freezing point for constant temperature drying and thawing;

[0028] Step 3.3, the thawed test piece is cured to obtain a hardened cement-based test piece.

[0029] As a preferred solution, in step 3.1, the temperature for the frozen molding is -100 to -50℃, and the frozen molding is unidirectional freezing, so that the ice crystals in the slurry grow along the temperature gradient direction.

[0030] As a preferred solution, in step 3.1, during the freezing process, liquid nitrogen (-196℃) is used as a cold source, a copper plate is used as a cold plate, and the mold is placed on the copper plate; a copper column is used to connect the copper plate with the cold source, the temperature of the copper plate is adjusted as the freezing temperature of the sample by controlling the current of the electric heating sheet on the lower surface of the cold plate, and directional freezing preparation is realized.

[0031] As a preferred solution, in step 3.1, the freezing time is 10-30 minutes.

[0032] As a preferred solution, in step 3.2, the temperature for the constant temperature drying and thawing is 2-10℃, and the thawing time is 48-72 hours.

[0033] As a preferred solution, in step 3.3, the thawed test piece is cured for standard curing, the temperature of the standard curing oven is 20±1℃, and the relative humidity is 95-100%.

[0034] As a preferred solution, in step 3.3, the standard curing is for 7 days, that is, the constant temperature drying and thawing time in step 3.2 plus the curing time in step 3.3 is 7 days.

[0035] As a preferred solution, in step 4, the hardened cement-based test piece is placed in a blast drying oven to dry to a constant weight, and the drying temperature is 40-60℃.

[0036] As a preferred solution, in step 4, the hardened cement-based test piece is dried to a constant weight, that is, the mass difference in the adjacent two weighing processes is less than 2%.

[0037] As a preferred solution, in step 5, the high-temperature treatment device is a muffle furnace, the heating rate is 8-15℃ / min, and the temperature is kept constant for 1-5 hours before natural cooling to room temperature.

[0038] It should be noted that the amount of water is determined after the cementitious material ratio and water-binder ratio are determined.

[0039] It should be noted that the amount of powder of the admixture added to the water is determined by the dispersion degree in the water.

[0040] It should be noted that the types of ceramic micropowder are not limited to the above-mentioned several types, and only need to meet the conditions that the oxidation reaction occurs in the temperature range of 400-1000℃ to form oxides, and the generated oxides can react with the products of the high-temperature decomposition of the cement hydration products to generate new mineral phases, and at the same time, the physical properties of the phases themselves can reflect sunlight.

[0041] Compared with the prior art, the technical method and product provided by the present application have the following beneficial effects:

[0042] The present application realizes the scattering effect of light by using the directional pore-forming technology of the ice mold, but the ice mold technology in the prior art reduces the compressive strength of the cement-based material. To solve this problem, the present application adds ceramic micropowder which generates new crystal phases through oxidation reaction under high temperature, and the decomposition products of the cement hydration products under high temperature also react with the high-temperature oxidation products of the ceramic micropowder under high temperature to form new material structures, thereby improving the compressive strength and reducing the influence of the ice mold forming process on the compressive strength of the cement-based material. At the same time, due to the presence of specific elements such as titanium, boron, zirconium and silicon in the ceramic micropowder, chelation reaction can occur with the hydrate containing hydroxyl groups, reducing the vibration of the hydroxyl groups and almost eliminating the influence of the absorption peaks near 1.43μm and 1.95μm in the near-infrared spectrum. The unexpected effect is that: compared with the case without high-temperature action, these new crystal phases and substances not only improve the compressive strength, but also improve the cement radiation refrigeration capacity.

[0043] The high-temperature reinforced cement radiation refrigeration composite material prepared by the present application can be used for the protection of buildings in extreme high-temperature weather, etc., which reduces the cooling energy consumption demand and also reduces the maintenance cost of the building. BRIEF DESCRIPTION OF DRAWINGS

[0044] In order to make the technical solutions in the present application or prior art clearer, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those of ordinary skill in the art without any creative effort based on these drawings.

[0045] Figure 1 Flow chart for preparing boron-reinforced cement-based radiative cooling composite material of the present application.

[0046] Figure 2 Stereogram of the unidirectional freeze forming device.

[0047] Figure 3 Sectional view of the unidirectional freeze forming device.

[0048] Figure 4 Appearance diagram of the test block prepared in Examples 1-4 and Comparative Examples 1-4.

[0049] Figure 5 UV-Vis-NIR reflectance spectrum of the test block prepared in Examples 1-4 and Comparative Examples 1-4.

[0050] 110- incubator, 120- cold plate, 130- electric heating sheet, 140- heat-conducting column, 150- liquid nitrogen, 160- ice mold mold. DETAILED DESCRIPTION

[0051] The technical solutions in the embodiments of the present application will be described clearly and completely below. The described embodiments are only further detailed descriptions of the present application, and are not limitations of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application belong to the scope of protection of the present application.

[0052] As shown in Figure 1 The present application provides a preparation method of boron-reinforced cement-based radiative cooling composite material, comprising the following steps:

[0053] Step 1, uniformly mixing Portland cement, ceramic micro-powder and admixture to obtain a dry powder mixture;

[0054] Step 2, uniformly mixing the admixture with mixing water, and then uniformly stirring the dry powder mixture to obtain a uniform slurry;

[0055] Step 3, pouring the slurry into a mold, and preparing a hardened cement-based test piece by ice mold method;

[0056] Step 4, drying the hardened cement-based test piece to a constant weight;

[0057] Step 5, after drying, the hardened cement-based test piece is treated at a high temperature of 400 ~ 1000℃, and a boron-reinforced cement-based radiation refrigeration composite material is obtained after cooling.

[0058] As Figure 2 and Figure 3 To achieve one-way freezing of the ice template method, the present application provides a one-way freezing molding device, which comprises an insulation box 110 (having an openable box cover at the top, not shown in the figure), a cold plate 120, an electric heating sheet 130 and a plurality of heat-conducting columns 140. The cold plate 120 can be made of a copper plate, and the heat-conducting columns 140 can be copper columns. Exemplarily, four copper columns are fixed to the bottom of the insulation box 110, the cold plate 120 is fixed to the top of the four copper columns, and the electric heating sheet 130 is located at the bottom of the cold plate 120. In use, the poured ice template mold 160 is placed on the cold plate 120, low-temperature liquid nitrogen 150 (-196 ℃) is injected into the bottom of the insulation box 110 as a cold source, the cold source is transmitted to the copper plate through the copper columns, and the temperature of the copper plate is adjusted to the required freezing temperature, such as -70 ℃, by the electric heating sheet.

[0059] Example 1:

[0060] The specific proportions provided in this example are as follows:

[0061] PW-1 52.5 Portland cement 100 parts

[0062] Ceramic micropowder: titanium boride micropowder 20 parts

[0063] Admixture: hydroxypropyl methylcellulose 0.66 parts

[0064] Admixture: halloysite nanotube 1 part

[0065] Water 65 parts

[0066] The preparation of the boron-reinforced cement-based radiation refrigeration composite material comprises the following steps:

[0067] (1) Mix the Portland cement, titanium boride micropowder and hydroxypropyl methylcellulose uniformly to obtain a dry mixture;

[0068] (2) Add the halloysite nanotube to water, disperse it by a magnetic stirrer at a speed of 540 r / min for 40 minutes to obtain an admixture dispersion liquid;

[0069] (3) Slowly add the admixture dispersion liquid obtained in step (2) into the dry mixture obtained in step (1), stir in a stirring pot at a low speed for 60 ~ 120 seconds, and then stir at a high speed for 180 ~ 210 seconds to obtain a uniform slurry.

[0070] (4) According to the shape of the required test piece, prepare an ice mold mold, pour the slurry into the ice mold mold, and then place it on a copper plate. Freeze form at -60°C for 30 minutes. After demolding, the freeze-formed test piece is obtained;

[0071] (5) Place the freeze-formed test piece in a constant temperature oven at 5°C and dry it for 48 hours.

[0072] (6) After thawing, the test piece is cured for 5 days to obtain a hardened cement-based test piece. The temperature of the standard curing box is 20±1°C, and the relative humidity is 95~100%, to obtain a hardened cement-based test piece.

[0073] (7) After curing, the hardened cement-based test piece is placed in a blast drying oven and dried at 60°C to constant weight.

[0074] (8) The hardened cement-based test piece with constant weight is placed in a muffle furnace for high temperature treatment. The temperature is increased from room temperature to 750°C at a rate of 10°C / min, and then held at 750°C for 2 hours. After natural cooling to room temperature, the test block is obtained.

[0075] Example 2:

[0076] The specific proportions provided in this example are as follows:

[0077] PW-1 52.5 Portland cement 100 parts

[0078] Ceramic micropowder: titanium boride micropowder 20 parts

[0079] Admixture: hydroxypropyl methylcellulose 0.66 parts

[0080] Admixture: halloysite nanotube 1 part

[0081] Water 65 parts

[0082] The preparation of boron-reinforced cement-based radiation refrigeration composite material includes the following steps:

[0083] (1) Mix the Portland cement, titanium boride micropowder and hydroxypropyl methylcellulose uniformly to obtain a dry mixture;

[0084] (2) Add halloysite nanotubes to water and disperse them by a magnetic stirrer at a speed of 540 r / min for 40 min to obtain an admixture dispersion liquid;

[0085] (3) Slowly add the admixture dispersion liquid obtained in step (2) to the dry mixture obtained in step (1), stir in a stirring pot at low speed for 60~120 seconds, and then stir at high speed for 180~210 seconds to obtain a uniform slurry.

[0086] (4) According to the shape of the required test piece, prepare an ice mold mold, pour the slurry into the ice mold mold, and then place it on a copper plate. Freeze form for 30 minutes at -70°C. After demolding, a freeze-formed test piece is obtained;

[0087] (5) Place the freeze-formed test piece in a constant temperature oven and dry at 5°C for 48 hours.

[0088] (6) After thawing, the test piece is cured for 5 days to obtain a hardened cement-based test piece. The temperature of the standard curing box is 20±1°C, and the relative humidity is 95~100%, to obtain a hardened cement-based test piece.

[0089] (7) After curing, place the hardened cement-based test piece in a blast drying oven and dry at 60°C until constant weight.

[0090] (8) Place the dried and constant weight hardened cement-based test piece in a muffle furnace for high temperature treatment. The temperature is increased from room temperature to 750°C at a rate of 10°C / min, and then held at 750°C for 2 hours. After natural cooling to room temperature, a test block is obtained.

[0091] Example 3:

[0092] The specific proportions provided in this example are as follows:

[0093] PW-1 52.5 Portland cement 100 parts

[0094] Ceramic micropowder: titanium boride micropowder 20 parts

[0095] Admixture: hydroxypropyl methylcellulose 0.66 parts

[0096] Admixture: halloysite nanotube 1 part

[0097] Water 65 parts

[0098] The preparation of boron reinforced cement-based radiation refrigeration composite material includes the following steps:

[0099] (1) Mix the Portland cement, titanium boride micropowder and hydroxypropyl methylcellulose uniformly to obtain a dry mixture;

[0100] (2) Add halloysite nanotubes to water and disperse them using a magnetic stirrer at a speed of 540 r / min for 40 min to obtain an admixture dispersion liquid;

[0101] (3) Slowly add the admixture dispersion liquid obtained in step (2) to the dry mixture obtained in step (1) and stir in a pot at low speed for 60~120 seconds, and then stir at high speed for 180~210 seconds to obtain a uniform slurry.

[0102] (4) According to the shape of the required test piece, prepare an ice mold mold, pour the slurry into the ice mold mold, and then place it on a copper plate. Freeze form at -80°C for 30 minutes. After demolding, the freeze-formed test piece is obtained;

[0103] (5) Place the freeze-formed test piece in a constant temperature oven at 5°C and dry it for 48 hours.

[0104] (6) After thawing, the test piece is cured for 5 days to obtain a hardened cement-based test piece. The temperature of the standard curing box is 20±1°C, and the relative humidity is 95-100%, to obtain a hardened cement-based test piece.

[0105] (7) After curing, the hardened cement-based test piece is placed in a blast drying oven and dried at 60°C to a constant weight.

[0106] (8) The hardened cement-based test piece is placed in a muffle furnace for high temperature treatment, from room temperature to 750°C at a rate of 10°C / min, and then naturally cooled to room temperature after 2 hours at 750°C. The test block is obtained.

[0107] Based on Examples 1-3, after the hardened cement-based test piece is dried to a constant weight, no high temperature treatment is performed to form Comparative Examples 1, 2, and 3.

[0108] Comparative Example 4:

[0109] The specific proportions provided in this example are as follows:

[0110] PI 42.5 Portland cement 100 parts

[0111] Ceramic micropowder: zirconium boride micropowder 60 parts

[0112] Admixture: hydroxypropyl methylcellulose 0.4 parts

[0113] Admixture: halloysite nanotube 0.5 parts

[0114] Water 55 parts

[0115] The preparation of the cement-based material includes the following steps:

[0116] (1) Mix the Portland cement, zirconium boride micropowder, and hydroxypropyl methylcellulose uniformly to obtain a dry mixture;

[0117] (2) Add halloysite nanotubes to water and disperse them using a magnetic stirrer at a speed of 540 r / min for 40 minutes to obtain an admixture dispersion;

[0118] (3) Slowly pour the admixture dispersion liquid obtained in step (2) into the dry mixture obtained in step (1), low-speed stirring in the stirring pot for 60 ~ 120s, and high-speed stirring for 180 ~ 210s, to obtain a uniform slurry.

[0119] (4) Prepare a plastic mold according to the shape of the required test piece, pour the slurry into the plastic mold, remove the mold after 1 day, and then place it in a standard curing box for curing to 28 days of age, to obtain a test block.

[0120] Example 4:

[0121] The specific proportions provided in this example are as follows:

[0122] P I 42.5 Portland cement 100 parts

[0123] Ceramic micropowder: zirconium boride micropowder 60 parts

[0124] Admixture: hydroxypropyl methylcellulose 0.4 parts

[0125] Admixture: halloysite nanotube 0.5 parts

[0126] Water 55 parts

[0127] The preparation of the cement-based material includes the following steps:

[0128] (1) Mix the Portland cement, zirconium boride micropowder, and hydroxypropyl methylcellulose uniformly to obtain a dry mixture;

[0129] (2) Add halloysite nanotubes to water and disperse them by a magnetic stirrer at a speed of 540 r / min for 40 minutes to obtain an admixture dispersion liquid;

[0130] (3) Slowly pour the admixture dispersion liquid obtained in step (2) into the dry mixture obtained in step (1), low-speed stirring in the stirring pot for 60 ~ 120s, and high-speed stirring for 180 ~ 210s, to obtain a uniform slurry.

[0131] (4) Prepare a plastic mold according to the shape of the required test piece, pour the slurry into the plastic mold, remove the mold after 1 day, and then place it in a standard curing box for curing to 28 days of age, to obtain a cement test piece.

[0132] (5) After the curing is completed, place the cement test piece in a blast drying oven at 60°C to dry to constant weight.

[0133] (6) Place the hardened cement-based test piece dried to constant weight in a muffle furnace for high-temperature treatment, from room temperature to 900°C at a rate of 10°C / min, and at 900°C for 2 hours, and then naturally cool to room temperature, to obtain a test block.

[0134] Performance test method:

[0135] (1) The reflectivity of the test block in the solar light band 0.2-2.5 μm was measured by using a UV-visible-near infrared spectrophotometer (Lambda 1050+). The size of the test block was 30 mm x 30 mm x 3 mm, and three groups were measured and averaged. The results are shown in Figure 5

[0136] (2) The infrared emissivity of the test block in the range of 5-7 μm and 8-13 μm was measured by using a Fourier infrared spectrometer (Thermo) model NICOLET IS20. The size of the test block was 30 mm x 30 mm x 3 mm, and three groups were measured and averaged.

[0137] (3) The compression test of the test block with a size of 20 mm x 20 mm x 20 mm was carried out by using a UTM5105X universal testing machine, and the determination parameters were referred to the "Building mortar basic performance test method" (JGJ / T 70-2009).

[0138] The related performance test results of the embodiments of the present application are shown in Tables 1 and 2.

[0139] The appearance change of the embodiments of the present application is shown in Figure 4 , which is a reflectivity diagram. Figure 5

[0140] Table 1 Optical performance test results of each group of test blocks

[0141]

[0142] As can be seen from the solar light average reflectivity in Table 1, compared with Comparative Examples 1, 2 and 3, the solar light average reflectivity of Examples 1, 2 and 3 is significantly improved after high temperature treatment, and the average emissivity in the long-wave spectral range of atmospheric window 8-13 μm is not significantly affected; in the mid-wave spectral end atmospheric window 5-7 μm range, the average emissivity in this range is reduced after high temperature treatment, which reduces the influence of part of atmospheric counter-radiation, thereby further improving its radiation cooling capacity. Compared with Comparative Example 4, the solar light average reflectivity of Example 4 is significantly improved after high temperature treatment, and the average emissivity in the two atmospheric window ranges 5-7 μm and 8-13 μm is not significantly affected. This also shows that, compared with the frozen molded sample, the cast molded sample has no obvious effect on the solar light average emissivity in the infrared band, and cannot improve the radiation cooling effect, so the combination of high temperature treatment and frozen molding can achieve the technical effect of the present application.

[0143] Figure 4 is a physical diagram of the test blocks of Examples 1-4 and Comparative Examples 1-4. From Figure 4 ​​It can be seen that the surface color of the test block in the embodiment changes significantly, from dark gray to white or yellow. This is because new mineral phases are generated after high temperature action, which itself changes the appearance of the sample and thus achieves high reflectivity to sunlight.

[0144] Figure 5 For the ultraviolet-visible-near infrared reflectance spectra of each group of test blocks, it can be seen that the spectra of the four implementation groups have no absorption peaks near 1.43 μm and near 1.95 μm in the near infrared spectrum, which indicates that the preparation method of the cement-based composite material proposed in the present application almost eliminates the influence of the absorption peaks near 1.43 μm and near 1.95 μm in the near infrared spectrum of the traditional cement-based material on its solar reflectivity. As can be seen, the preparation method of the boron-enhanced cement-based radiation refrigeration composite material proposed in the present application can improve the radiation refrigeration capacity of the cement-based material. As can be seen from the comparison of Example 1, Example 2, Example 3 and Example 4 in Table 1, changing the temperature during freeze forming can improve the reflectivity of the sample to sunlight. The lower the forming temperature, the higher the average reflectivity to sunlight after firing, and the average emission of the sample in the range of 8 ~ 13 μm is also gradually improved. The average reflectivity of the sample poured and formed at room temperature to sunlight before high temperature action is low, and after high temperature action, its average reflectivity to sunlight is improved, but compared with the solar reflectivity of the sample poured and formed by freezing, there is still a significant gap.

[0145] Therefore, as can be seen from Table 1, when the appropriate freeze forming temperature is selected, the radiation refrigeration capacity of the cement-based material after high temperature action can be further improved.

[0146] Table 2: Compressive strength values of each group of test blocks

[0147]

[0148] As can be seen from the compressive strength test in Table 2, the compressive strength of the test block in each embodiment is improved, which to some extent reduces the influence of the ice mold technology on the compressive strength of the cement-based material. The lower the forming temperature, the smaller the pore channel formed by the ice mold, and the compressive strength is enhanced within a certain range. As can be seen from the comparison of Comparative Example 1 and Comparative Example 2, the lower the forming temperature, the higher the compressive strength; as can be seen from Comparative Example 2 and Comparative Example 3, when the temperature is reduced to a certain extent, it will affect the compressive strength, because the ice crystals grow too fast and may form irregular crystals, therefore, selecting the appropriate forming temperature can further improve the compressive strength.

[0149] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; and although the present application has been described in detail with reference to the foregoing embodiments, it should be appreciated by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a boron-reinforced cement-based radiation cooling composite material, characterized in that, Includes the following steps: Silicate cement, ceramic powder and additives are mixed evenly to obtain a dry powder mixture; After the admixture is mixed evenly with the mixing water, it is stirred evenly with the dry powder mixture to obtain a uniform slurry. The slurry is poured into a mold and then frozen below the freezing point. After demolding, the frozen specimen is obtained. The frozen specimens were placed in a constant temperature chamber and dried and thawed at a constant temperature above the freezing point. The thawed specimens were cured to obtain hardened cement-based specimens; Dry the hardened cement-based specimens to constant weight; The dried hardened cement-based specimens were subjected to high-temperature treatment at 750 ~ 1000℃, and after cooling, boron-reinforced cement-based radiation refrigeration composite material was obtained. The ceramic micro powder is any one or more of the following: zirconium boride, vanadium boride, titanium boride, chromium boride, boron carbide, hafnium boride, and tantalum boride. The freezing temperature is -100~-50 ℃, and the freezing is unidirectional freezing, which causes the ice crystals in the slurry to grow in a directional manner along the temperature gradient direction. The constant temperature drying and thawing temperature is 2~10℃, and the thawing time is 48~72 hours.

2. The preparation method of the boron-reinforced cement-based radiation cooling composite material according to claim 1, characterized in that, For every 100 parts by weight of silicate cement, mix 40 to 80 parts of ceramic powder.

3. The method for preparing the boron-reinforced cement-based radiation cooling composite material according to claim 1, characterized in that, The water-cement ratio of the resulting slurry is 0.5 to 1.

0.

4. The preparation method of the boron-reinforced cement-based radiation cooling composite material according to claim 1, characterized in that, The admixture is one or a mixture of several of the following: micron-sized silica, micron-sized titanium dioxide, montmorillonite powder, halloysite nanotubes, and micron-sized alumina.

5. The method for preparing the boron-reinforced cement-based radiation cooling composite material according to claim 1, characterized in that, The admixture is a viscosity modifier, and its dosage is less than 2.0% of the mass of silicate cement.

6. A boron-reinforced cement-based radiation cooling composite material, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.

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