Modified aluminate cement composite material as well as preparation method and application thereof

Abstract

The invention relates to a modified aluminate cement composite material. The composite material comprises calcium aluminate cement, red sandstone and gypsum whisker / gypsum. The problem that the strength of existing aluminate cement is reduced at high temperature is solved, conversion of a hydrate phase is inhibited, and the high-temperature crack resistance and strength of the aluminate cement are improved; meanwhile, corresponding industrial solid waste phosphogypsum can be subjected to innocent treatment and effective utilization, recycling of the industrial solid waste phosphogypsum is achieved, and the building material is a green, low-carbon and sustainable building material and is suitable for preparation of high-temperature-resistant building materials such as refractory bricks. The invention also provides a preparation method and application of the modified aluminate cement composite material.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and in particular to a modified aluminate cement composite material, a preparation method and an application thereof. Background Art

[0002] As a specialty cement, aluminate cement exhibits excellent properties such as early strength, high-temperature resistance, and corrosion resistance, making it widely used in specialized applications such as high-temperature industrial furnaces, sulfate corrosion resistance projects, and rapid repair projects. However, despite its superior performance under specific conditions, it also suffers from several significant drawbacks, which severely limit its widespread promotion and application in a wider range of fields.

[0003] Aluminate cement undergoes a series of phase transitions during hydration, which are affected by temperature and affect its mechanical properties and microstructure. 10 and C2AH8) are transformed into stable hydration products such as calcium aluminate hydrate (3CaO·Al2O3·6H2O, C3AH6) and AH3 depending on temperature. This transformation is accompanied by an increase in porosity and a decrease in strength. This transformation significantly impacts the durability and mechanical properties of cement, further affecting the performance of aluminate cement. The instability of the hydration products leads to volume shrinkage, increased porosity, and a loose structure, which in turn reduces material strength and affects engineering durability.

[0004] Therefore, addressing the issues of aluminate cement, such as rapid strength loss, pore coarsening, and long-term performance degradation caused by temperature fluctuations, in order to improve its performance stability and application reliability, is a current research focus. For example, Chinese patent application CN117486513A discloses a method for preparing modified aluminate cement, which modifies the setting time and strength of aluminate cement by adding fluorgypsum and KH2PO4 at room temperature. However, this method does not address the temperature-dependent loss of hydration products and the decrease in strength at high temperatures, nor does it address economic and environmental issues. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the present invention provides a modified aluminate cement composite material that solves the problem of existing aluminate cement strength loss at high temperatures, inhibits hydrate phase transformation, and improves the high-temperature crack resistance and strength of aluminate cement. It also enables harmless treatment and effective utilization of corresponding industrial solid waste phosphogypsum, realizing the resource utilization of industrial solid waste phosphogypsum. The present invention also provides a preparation method and application of the modified aluminate cement composite material.

[0006] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a modified aluminate cement composite material, which includes calcium aluminate cement, red sandstone and gypsum whiskers, and the gypsum whiskers account for 0.5-5% of the composite material by mass; wherein, the gypsum whiskers are obtained by treating phosphogypsum by microwave method.

[0007] Furthermore, the composite material includes, by mass percentage, 72-82% of calcium aluminate cement, 17-23% of red sandstone, and 0.5-5% of gypsum whiskers.

[0008] Furthermore, in terms of mass percentage, the gypsum whiskers account for 1 to 5% of the composite material, more preferably 3 to 5%.

[0009] In one embodiment, the calcium aluminate cement (CAC) includes, by mass percentage, main components of Al2O3 45-52% and CaO 36-40%.

[0010] Red sandstone is a sedimentary rock formed by sand-sized quartz, feldspar and other mineral particles cemented together by red clay materials (such as kaolinite, montmorillonite and other clay minerals).

[0011] In one embodiment, the red sandstone comprises main components of SiO2 85-90% and Al2O3 4-7% by mass, and has a particle size of 0.05-2 mm.

[0012] Gypsum whiskers are a type of fibrous single crystal composed of calcium sulfate (CaSO4) that appear as white, fluffy needles.

[0013] In one embodiment, the gypsum whiskers include main components of SO3 52-55% and CaO 45-47% by mass, and the length of the gypsum whiskers is 10-100 μm and the diameter is 0.2-2 μm; preferably, the length is 20-50 μm and the diameter is 0.2-0.8 μm.

[0014] In one embodiment, in the modified aluminate cement composite material, part or all of the gypsum whiskers may be replaced with gypsum.

[0015] Furthermore, the gypsum comprises, by mass percentage, main components of SO3 55-58% and CaO 40-45%.

[0016] A second aspect of the present invention provides a method for preparing the modified aluminate cement composite material, the method comprising the following steps:

[0017] (1) Weighing calcium aluminate cement, red sandstone, gypsum whiskers and / or gypsum according to the raw material ratio;

[0018] (2) Mixing and stirring the above raw materials to obtain a modified aluminate cement composite material, wherein

[0019] The gypsum whiskers are obtained by processing through the following steps:

[0020] S1. washing phosphogypsum and drying it by microwave irradiation, adding it to an ethanol-water solution and mixing it, then adding sulfate and mixing it again;

[0021] S2, placing the mixture obtained in S1 into a sealed container and placing it in a microwave irradiation device, starting the microwave irradiation device under normal pressure, the irradiation temperature is 80-100°C, and the time is 20-35 min, preferably 30 min;

[0022] S3. Filter the irradiated product from S2, and dry the filtrate in a vacuum drying oven at 45-50° C. to obtain gypsum whiskers.

[0023] Furthermore, in S1, the mass concentration of the ethanol aqueous solution is 60% to 90%, preferably 70% to 85%; and the sulfate is Na2SO4 or K2SO4.

[0024] In one embodiment, in S1, phosphogypsum is 10% to 20% by mass of the ethanol aqueous solution; sulfate is 1% to 15% by mass of the phosphogypsum; preferably, phosphogypsum is 13% to 18% by mass of the ethanol aqueous solution; sulfate is 5% to 12% by mass of the phosphogypsum.

[0025] In one embodiment, phosphogypsum is replaced with titanium gypsum or desulfurized gypsum. In the technical solution of the present invention, in addition to obtaining gypsum whiskers by processing solid waste phosphogypsum, titanium gypsum or desulfurized gypsum can also be used to obtain gypsum whiskers.

[0026] Phosphogypsum, titaniferous gypsum, and desulfurization gypsum are all byproducts of industrial production processes. Their primary component is calcium sulfate dihydrate (CaSO4·2H2O), but their sources and impurity content vary. Phosphogypsum is a byproduct produced during the wet-process phosphoric acid production process when phosphate rock reacts with sulfuric acid to produce phosphoric acid. In addition to calcium sulfate dihydrate, it also contains impurities such as soluble phosphorus, fluorine, heavy metals, and organic matter. Titanium gypsum is a byproduct produced during the sulfuric acid process for the production of titanium dioxide. In addition to calcium sulfate dihydrate, it also contains small amounts of impurities such as iron and titanium. Desulfurization gypsum (FGD gypsum) is a byproduct produced during the limestone-gypsum flue gas desulfurization process used to treat sulfur dioxide-containing flue gases generated by burning coal or oil. In addition to calcium sulfate dihydrate, it also contains small amounts of fly ash, calcium carbonate, calcium sulfite, chlorides, and other impurities.

[0027] The third aspect of the present invention provides the use of the modified aluminate cement composite material in the manufacture of refractory bricks.

[0028] Furthermore, the refractory bricks are prepared by the following steps:

[0029] (1) adding water to the modified aluminate cement composite material and stirring to obtain a mixed slurry, wherein the mass ratio of the composite material to water is 2:1;

[0030] (2) pouring the mixed slurry into a mold to form a refractory brick body, and after demoulding, sealing the refractory brick body and placing it in an oven at 50°C for curing for 7 days;

[0031] (3) Place the cured refractory brick body into a muffle furnace, heat it to 200-600°C at a heating rate of 6°C / min, keep it warm for 1 hour, and cool it naturally to room temperature.

[0032] Beneficial effects of the present invention:

[0033] The present invention partially replaces aluminate cement with red sandstone and gypsum whiskers / gypsum. The obtained modified aluminate cement composite material has an inhibitory effect on the conversion of hydration products at high temperatures and can enhance its high-temperature strength.

[0034] In the present invention, gypsum whiskers obtained from solid waste phosphogypsum and the like through a series of microwave treatments have the advantages of high strength, good toughness, and corrosion resistance. They can toughen the product at high temperatures and reduce the occurrence of cracks. At the same time, the resource utilization of solid waste phosphogypsum is also improved, providing a new path for the development of the construction industry. In addition, the addition of red sandstone can slow down the transformation of the metastable phase to the stable phase in aluminate cement, thereby improving the pore structure and reducing strength loss. Red sandstone is also a high-temperature resistant material and can also improve the performance changes of the product at high temperatures.

[0035] By introducing gypsum whiskers and red sandstone into aluminate cement, the present invention significantly inhibits the transition of hydration products from a metastable to a stable state caused by high temperatures, reducing the strength loss caused by increased porosity. Furthermore, the gypsum whiskers and red sandstone synergistically generate new hydration products at high temperatures, further enhancing the material's high-temperature mechanical properties. The bridging effect of the gypsum whiskers at high temperatures also reduces crack formation, contributing to a certain strength improvement.

[0036] Therefore, the modified aluminate cement composite material of the present invention can reduce the loss of hydration products of aluminate cement at different temperatures, improve the strength at high temperatures and reduce the generation of cracks, thereby providing a good basis for the application of refractory cement bricks. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The figure is a SEM image of gypsum whiskers prepared in one embodiment of the present invention.

[0038] Figure 2This is a SEM image of red sandstone used in one embodiment of the present invention.

[0039] Figure 3 These are mesoscopic images of the refractory brick samples in Examples 2-5 and Comparative Examples 1-2 at different temperatures.

[0040] Figure 4 The pore size distribution of the refractory brick samples in Examples 2-5 and Comparative Examples 1-2 at 50°C.

[0041] Figure 5 The pore size distribution of the refractory brick samples in Examples 2-5 and Comparative Examples 1-2 at 200°C.

[0042] Figure 6 The pore size distribution of the refractory brick samples in Examples 2-5 and Comparative Examples 1-2 at 600°C.

[0043] Figure 7 The pore size distribution of the refractory brick samples in Examples 2-5 and Comparative Examples 1-2 at 1000°C. DETAILED DESCRIPTION

[0044] In order to better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings.

[0045] Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0046] Example 1

[0047] Gypsum whiskers were prepared from phosphogypsum by microwave method:

[0048] S1. Washing the phosphogypsum, drying it by microwave irradiation, adding it to an 80% ethanol aqueous solution and mixing it, then adding sodium sulfate and mixing it again; wherein the phosphogypsum is 15% by weight of the ethanol aqueous solution and the sodium sulfate is 10% by weight of the phosphogypsum;

[0049] S2. Place the mixture obtained in S1 into a sealed container and place it in a microwave irradiation device. Start the microwave irradiation device under normal pressure, set the irradiation temperature at 90-95°C, and the time for 30 minutes.

[0050] S3. Filter the irradiated product from S2, and dry the filtrate in a vacuum drying oven at 45-50° C. to obtain gypsum whiskers.

[0051] Figure 1The SEM image of the obtained gypsum whiskers is shown. The obtained gypsum whiskers include 53.74% SO3 and 46.01% CaO as main components.

[0052] Example 2

[0053] Preparation of modified aluminate cement composite material and application of the composite material to prepare refractory bricks:

[0054] (1) Calcium aluminate cement, red sandstone and gypsum whiskers obtained in Example 1 were mixed uniformly according to the proportions to obtain a modified aluminate cement composite material.

[0055] The composite material consists of 79% calcium aluminate cement, 20% red sandstone, and 1% gypsum whiskers. The calcium aluminate cement (CAC) consists mainly of 48.23% Al2O3 and 38.15% CaO; the red sandstone consists mainly of 88.52% SiO2 and 5.56% Al2O3, with a particle size of 0.1 to 1.5 mm. Figure 2 The SEM image of the red sandstone used is shown;

[0056] (2) adding water accounting for 50% of the composite material to the obtained modified aluminate cement composite material, mixing and stirring uniformly to obtain a mixed slurry, wherein the mass ratio of the composite material to water is 2:1;

[0057] (3) Pour the mixed slurry into a mold for molding. After curing for one day, remove the mold to obtain a refractory brick body. Wrap the body with plastic wrap and place it in an oven at 50°C for curing for 7 days.

[0058] (4) The cured refractory brick body was placed in a muffle furnace and heated to 200°C, 600°C and 1000°C at a heating rate of 6°C / min, and kept at the target temperature for 1 hour, and then naturally cooled to room temperature. The compressive strength of the refractory bricks obtained at different temperatures was measured, and the cracks in the refractory bricks were observed.

[0059] Example 3

[0060] A modified aluminate cement composite material was prepared and refractory bricks were prepared using the composite material: the only difference from Example 2 was that the composite material contained 77% calcium aluminate cement, 20% red sandstone, and 3% gypsum whiskers.

[0061] Example 4

[0062] A modified aluminate cement composite material was prepared and refractory bricks were prepared using the composite material: the only difference from Example 2 was that the composite material contained 75% calcium aluminate cement, 20% red sandstone, and 5% gypsum whiskers.

[0063] Example 5

[0064] Preparation of modified aluminate cement composite material and application of the composite material to prepare refractory bricks: The only difference from Example 3 is that ordinary gypsum (CaSO4) is used in the composite material instead of gypsum whiskers.

[0065] Comparative Example 1

[0066] Preparation of modified aluminate cement composite material and application of the composite material to prepare refractory bricks: The only difference from Example 2 is that in the composite material, calcium aluminate cement accounts for 80% and red sandstone accounts for 20% (ie, no gypsum / gypsum whiskers are contained).

[0067] Comparative Example 2

[0068] Preparation of modified aluminate cement composite material and application of the composite material to prepare refractory bricks: The only difference from Example 2 is that the composite material contains 100% calcium aluminate cement (i.e., the cementitious material is only calcium aluminate cement, without red sandstone or gypsum / gypsum whiskers).

[0069] The compressive strength of the refractory bricks obtained in Examples 2-5 and Comparative Examples 1-2 at different temperatures was measured according to GB / T 3995-2014. The results are shown in Table 1.

[0070] Table 1 Compressive strength test results (MPa)

[0071]

[0072] As can be seen from Table 1, after curing at 50°C for 7 days, the strengths of Comparative Examples 1 and 2 were 13.7 MPa and 8 MPa, respectively, while the strength of Example 4 was 14.1 MPa. The strength of Example 4 was similar to that of Comparative Example 1, but higher than that of Comparative Example 2, indicating that the addition of red sandstone and gypsum whiskers can inhibit the transformation of hydration products and compensate for the dilution effect caused by the reduction in cement content. At 200°C, relative to 50°C, the strengths of both the comparative examples and the examples were enhanced, demonstrating that high temperature and high pressure can promote the strength of refractory cement bricks. The strengths of Examples 3 and 4 at 200°C, 600°C, and 1000°C were all greater than those of Comparative Examples 1 and 2, indicating that the addition of gypsum whiskers and red sandstone inhibits the transformation of phases in aluminate cement, thereby reducing its strength loss. This also indicates that adding an appropriate amount of gypsum whiskers can promote strength development. Comparing Example 3 with Example 5, it was found that the strength of Example 3 was greater than that of Example 5 at any temperature, which indicates that gypsum whiskers have better toughness than gypsum at high temperatures, and indirectly proves that gypsum whiskers are more suitable as a refractory material than gypsum.

[0073] from Figure 3It can be observed that as the temperature increases, obvious cracks appear on the samples. Comparison between Example 2 and Comparative Example 2 shows that the cracks at high temperatures are similar, indicating that adding a small amount of gypsum whiskers is not enough to affect the crack width. Comparison between Example 3 and Example 5 shows that the crack width of Example 3 is lower than that of Example 5 at 1000°C, which further indicates that gypsum whiskers have better toughness than gypsum. In addition, it can be seen from Examples 2-4 that as the gypsum whisker content increases, the crack width at 600°C and 1000°C gradually decreases. This shows that the more gypsum whiskers there are at high temperatures, the better the crack resistance of the composite cement, and the smaller the reduction in strength loss.

[0074] from Figures 4 to 7 It can be observed that different temperatures have different effects on the pore size of the samples. At 50°C, when Example 4 is compared with Comparative Example 1 and Comparative Example 2, it can be seen that the addition of gypsum whiskers and red sandstone helps to refine the pore size, so that more hydration products are generated, which helps to develop strength. In addition, as the gypsum whisker content increases, the pores also increase. Compared with Comparative Example 1, Example 4 found that the percentage of pores > 200nm in Example 4 at 200, 600 and 1000°C was lower than that in Comparative Example 1, which further shows that the addition of gypsum whiskers and red sandstone helps to develop strength. As the temperature increases, the addition of gypsum whiskers helps to inhibit pore coarsening. At 1000°C, the addition of 1% gypsum whiskers helps to prevent more pores from converting into pores > 200nm.

[0075] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modified aluminate cement composite material, characterized in that: The composite material comprises calcium aluminate cement, red sandstone and gypsum whiskers, wherein the gypsum whiskers account for 0.5-5% of the composite material by mass; wherein the gypsum whiskers are obtained by treating phosphogypsum by microwave method.

2. The modified aluminate cement composite material according to claim 1, characterized in that Calculated by mass percentage, the composite material comprises 72-82% of calcium aluminate cement, 17-23% of red sandstone and 0.5-5% of gypsum whiskers.

3. The modified aluminate cement composite material according to claim 1 or 2, characterized in that: In terms of mass percentage, the gypsum whiskers account for 1 to 5% of the composite material.

4. The modified aluminate cement composite material according to claim 1 or 2, characterized in that: Calculated by mass percentage, the calcium aluminate cement comprises mainly 45-52% Al2O3 and 6-40% CaO3; the red sandstone comprises mainly 85-90% SiO2 and 4-7% Al2O3, with a particle size of 0.05-2 mm; the gypsum whiskers comprise mainly 52-55% SO3 and 45-47% CaO, with a length of 10-100 μm and a diameter of 0.2-2 μm.

5. The modified aluminate cement composite material according to claim 1 or 2, characterized in that: In the modified aluminate cement composite material, part or all of the gypsum whiskers are replaced by gypsum, and the gypsum includes main components of SO3 55-58% and CaO 40-45% by mass percentage.

6. The method for preparing the modified aluminate cement composite material according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: (1) Weighing calcium aluminate cement, red sandstone, gypsum whiskers and / or gypsum according to the raw material ratio; (2) Mixing and stirring the above raw materials to obtain a modified aluminate cement composite material, wherein The gypsum whiskers are obtained by processing through the following steps: S1. washing phosphogypsum and drying it by microwave irradiation, adding it to an ethanol-water solution and mixing it, then adding sulfate and mixing it again; S2, placing the mixture obtained in S1 into a sealed container and placing it in a microwave irradiation device, starting the microwave irradiation device under normal pressure, the irradiation temperature is 80-100°C, and the time is 20-35 min, preferably 30 min; S3. Filter the irradiated product from S2, and dry the filtrate in a vacuum drying oven at 45-50° C. to obtain gypsum whiskers.

7. The preparation method according to claim 6, characterized in that In S1, the mass concentration of the ethanol aqueous solution is 60% to 90%; and the sulfate is Na2SO4 or K2SO4.

8. The preparation method according to claim 6 or 7, characterized in that In S1, the mass of phosphogypsum is 10% to 20% of the ethanol aqueous solution; the mass of sulfate is 1% to 15% of the phosphogypsum.

9. Use of the modified aluminate cement composite material according to any one of claims 1 to 5 in the manufacture of refractory bricks.

10. The use according to claim 9, characterized in that The refractory bricks are prepared by the following steps: (1) adding water to the modified aluminate cement composite material and stirring to obtain a mixed slurry, wherein the mass ratio of the composite material to water is 2:1; (2) pouring the mixed slurry into a mold to form a refractory brick body, and after demoulding, sealing the refractory brick body and placing it in an oven at 50°C for curing for 7 days; (3) Place the cured refractory brick body into a muffle furnace, heat it to 200-600°C at a heating rate of 6°C / min, keep it warm for 1 hour, and cool it naturally to room temperature.

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