Alpha-type high-strength gypsum and preparation method thereof

Abstract

The invention discloses alpha-type high-strength gypsum and a preparation method thereof, and belongs to the technical field of alpha-type high-strength gypsum preparation, and the preparation method of the alpha-type high-strength gypsum comprises the following steps: carrying out hydrothermal reaction treatment on a gypsum raw material and a crystal modifier to obtain the alpha-type high-strength gypsum, the crystal modifier is prepared from the following raw materials in percentage by mass of a gypsum raw material dry basis: 0.03%-0.40% of maleic acid-acrylic acid copolymer sodium salt, 0.05%-1.2% of a complexing agent, 0.01%-0.5% of a polycarboxylate superplasticizer, 0.01%-0.25% of potassium chloride and 0.02%-0.8% of hydroxyapatite micro powder. The crystal modifier provided by the invention can accurately regulate and control the whole crystal growth process and is adaptive to a low-purity mixed gypsum raw material, so that the product crystal is in a short column shape and has a stable length-diameter ratio, and finally, high-strength alpha gypsum is obtained.

Description

Technical Field

[0001] This invention belongs to the field of α-type high-strength gypsum preparation technology, specifically an α-type high-strength gypsum and its preparation method. Background Technology

[0002] Alpha-type high-strength gypsum is a high-performance cementitious material with α-calcium sulfate hemihydrate (CaSO4·0.5H2O) as its main component. Due to its dense crystal structure and excellent mechanical properties, it is widely used in precision casting, high-end building materials, medical molds, and other fields. Currently, the core technology for the industrial preparation of α-type high-strength gypsum is the hydrothermal method. This method utilizes gypsum raw materials with a high content of calcium sulfate dihydrate, which are converted into α-calcium sulfate hemihydrate crystals under high temperature and high pressure hydrothermal conditions through the induction of a crystal-transforming agent. The finished product is then obtained through subsequent processing such as drying and grinding.

[0003] In existing technologies, crystal-transforming agents mostly use phosphates, sulfates, and polymers as raw materials, which can only achieve single functions such as dissolution, recrystallization, or directional induction, lacking synergistic regulation of the entire crystal growth process. Existing crystal-transforming agents are prone to crystal agglomeration and abnormal growth, forming needle-like or flocculent crystals. After hydration and hardening, the internal porosity is high, and the mechanical properties are limited. Other technologies introduce nucleating agents such as calcium carbonate, but the nucleation efficiency is low, the crystal uniformity is poor, and the batch qualification rate of products is poor, making it difficult to meet the performance stability requirements of high-end applications. Summary of the Invention

[0004] This invention addresses the technical problems of existing crystal transformation systems, such as limited functionality, distorted crystals, and narrow adaptability to raw materials. Therefore, it provides an α-type high-strength gypsum and its preparation method. The crystal transformation agent of this invention can precisely control the entire crystal growth process and is compatible with low-purity mixed gypsum raw materials, resulting in short columnar crystals with a stable aspect ratio, ultimately yielding high-strength α-gypsum.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] This invention discloses a method for preparing α-type high-strength gypsum, comprising the following steps: gypsum raw materials and a crystallizing agent are subjected to hydrothermal reaction treatment to obtain the gypsum.

[0007] The crystallization agent comprises the following raw materials by percentage of the dry weight of the gypsum raw material: 0.03%~0.40% sodium maleic acid-acrylic acid copolymer, 0.05%~1.2% complexing agent, 0.01%~0.5% polycarboxylate superplasticizer, 0.01%~0.25% potassium chloride and 0.02%~0.8% hydroxyapatite micro powder; Preferably, the crystallization agent comprises the following raw materials by percentage of the dry weight of the gypsum raw material: 0.08%~0.30% sodium maleic acid-acrylic acid copolymer, 0.15%~0.7% complexing agent, 0.03%~0.3% polycarboxylate superplasticizer, 0.04%~0.18% potassium chloride and 0.08%~0.4% hydroxyapatite micro powder.

[0008] It is calculated as a percentage of the dry weight of the gypsum raw material, i.e., the dry weight of the gypsum raw material × the corresponding percentage.

[0009] According to some embodiments of the present invention, the gypsum raw material is at least one of desulfurized gypsum, phosphogypsum and natural gypsum.

[0010] According to some embodiments of the present invention, the content of calcium sulfate dihydrate (CaSO4·2H2O) in the gypsum raw material is ≥80wt%.

[0011] According to some embodiments of the present invention, the complexing agent is an organic carboxylic acid or an organic carboxylate salt; the complexing agent can reduce the free Ca in the solution. 2+ Concentration slows down the crystallization rate, resulting in more complete and dense crystal growth.

[0012] According to some embodiments of the present invention, the organic carboxylic acid is at least one of oxalic acid and citric acid; According to some embodiments of the present invention, the organic carboxylate is at least one selected from sodium oxalate, sodium citrate, potassium oxalate, potassium citrate, sodium oxalate, and ammonium citrate.

[0013] According to some embodiments of the present invention, the molecular weight of the sodium maleic acid-acrylic acid copolymer is 2000~10000, preferably 2500~5000; the sodium maleic acid-acrylic acid copolymer, as a main crystal morphology regulator, selectively adsorbs its molecular chains onto the crystal face, and inhibits radial crystal growth and promotes axial growth through steric hindrance and electrostatic repulsion.

[0014] According to some embodiments of the present invention, the modulus of sodium silicate is 2.4 to 2.8.

[0015] According to some embodiments of the present invention, the particle size D50 of the hydroxyapatite micro powder is 40~500nm, preferably 60~300nm; the hydroxyapatite micro powder, as a heterogeneous nucleating agent, provides nucleation sites that match the crystal structure of α-gypsum, refines the grains, and can also serve as a reinforcing phase to improve the mechanical properties of the matrix.

[0016] According to some embodiments of the present invention, the crystallization agent further contains borax, the amount of which is 0.003% to 0.01% of the dry basis mass of the gypsum raw material, preferably 0.006% to 0.009%; trace amounts of borate ions can be adsorbed on the crystal surface, finely adjusting its growth rate and surface state, which may improve early strength.

[0017] According to some embodiments of the present invention, the crystallization agent further comprises sodium silicate, the amount of which is 0.005% to 0.35% of the dry basis mass of the gypsum raw material, preferably 0.02% to 0.25%. Under hydrothermal conditions, some silicate ions can react with the surface of gypsum crystals or form an amorphous calcium silicate layer, thereby enhancing the interfacial bonding force between crystals and improving the overall strength.

[0018] According to some embodiments of the present invention, the preparation method of the α-type high-strength gypsum includes the following steps: S1. Mix the gypsum raw material / water at a mass ratio of 1 / 3.5~6, then add the crystallizing agent to obtain a suspension slurry; S2. Place the suspended slurry in a reactor and react for 0.5 to 6 hours under conditions of pressure 0.1 to 0.5 MPa and temperature 120 to 150 °C. S3. After the hydrothermal reaction is completed, solid-liquid separation is carried out, and the solid material is dried.

[0019] S1 also includes a pretreatment step for gypsum raw materials, which involves crushing and grinding the gypsum raw materials to a fineness of 200-500 mesh.

[0020] In S2, the stirring speed of the hydrothermal reaction is 100~300 rpm.

[0021] In S3, the drying temperature is 80~120℃.

[0022] The present invention also discloses an α-type high-strength gypsum, which is prepared by the aforementioned preparation method.

[0023] According to some embodiments of the present invention, the aspect ratio of the α-ultra-high strength gypsum crystal is 1~2.5:1, preferably 1.2~2.0:1.

[0024] According to some embodiments of the present invention, the 2-hour flexural strength of the α-type high-strength gypsum is 7.0 MPa to 10 MPa, and the 2-hour compressive strength is 68 MPa to 85 MPa.

[0025] According to some embodiments of the present invention, the oven-dry flexural strength of the α-type high-strength gypsum is 12MPa~16MPa, and the oven-dry compressive strength is 110MPa~135MPa.

[0026] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0027] Compared with the prior art, the beneficial effects of the present invention are: 1. The crystallization agent of the present invention has the functions of rate regulation, direction induction, nucleation promotion, and crystal face optimization. The complexing agent complexes Ca... 2+ Precise control of the dissolution and recrystallization rates of calcium sulfate dihydrate, directional adsorption of sodium maleic acid-acrylic acid copolymer onto the crystal face to induce regular growth, hydroxyapatite micropowder as a heterogeneous nucleation center, sodium silicate and potassium chloride both modify the crystal face to reduce defects, and borax enhances the stability of the crystallization agent to achieve coordinated and controllable crystal growth.

[0028] 2. The gypsum raw material contains impurities such as phosphates and sulfates. The complex in the formula can complex with the impurity ions, and sodium silicate forms a protective film to shield the impurities from interfering with crystal growth, thus solving the technical problem of low tolerance to low-purity raw materials in the existing technology.

[0029] 3. The α-type high-strength gypsum crystals prepared by this invention are short columnar, full and dense, and have a smooth, burr-free surface, avoiding the needle-like and flocculent deformed crystals commonly found in existing technologies; thus laying a structural foundation for improved mechanical properties. Due to their excellent mechanical properties and stability, α-type high-strength gypsum products can be widely used in precision casting molds, high-end interior and exterior wall building materials, medical molds, composite material fillers, and other fields. Detailed Implementation

[0030] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0031] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0032] The "range" disclosed in this invention is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is understood that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this invention, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein; "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer greater than or equal to 2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0034] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0035] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0036] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0037] Unless otherwise specified, the term "or" is inclusive in this invention. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0038] The raw material information used in the following examples is as follows: Sodium salt of maleic acid-acrylic acid copolymer has a molecular weight of 3000. The particle size D50 of hydroxyapatite micro powder is 200 nm; The modulus of sodium silicate is 2.5.

[0039] Example 1 The preparation method of type α high-strength gypsum in this embodiment is as follows: S1. 100 kg of natural gypsum was crushed, ground, and passed through a 300-mesh sieve. The ground gypsum powder was collected for later use. The dry basis calcium sulfate dihydrate content was tested to be 92 wt%. Soluble impurities were removed by washing with water to obtain gypsum raw material. S2. Add gypsum raw materials to 450 kg of deionized water. The crystal conversion agent components (gypsum dry basis wt%) are: 0.25% sodium maleic acid-acrylic acid copolymer (molecular weight 3000), 0.4% complexing agent (sodium citrate), 0.15% polycarboxylate superplasticizer, 0.1% potassium chloride, 0.25% hydroxyapatite micro powder, 0.15% sodium silicate, and 0.006% borax. After mixing the crystal conversion agent components according to the above ratio, a suspension slurry is formed. The suspension is added to the reactor, and the stirring speed is 200 r / min. After heating, the pressure in the reactor is increased to 0.3 MPa. The hydrothermal reaction temperature is maintained at 135±2℃ for 3 hours. After the reaction is completed, the reactor is opened after natural cooling. S3. After the above hydrothermal reaction, the material is centrifuged and dehydrated. The solid material after solid-liquid separation is dried at 100°C for 3 hours and then dried to obtain α-type high-strength gypsum.

[0040] Example 2 The difference between this embodiment and Embodiment 1 is as follows: Crystallization agent components (gypsum dry basis wt%): 0.15% sodium maleic acid-acrylic acid copolymer, 0.3% complexing agent (sodium oxalate), 0.2% polycarboxylate superplasticizer, 0.08% potassium chloride, 0.2% hydroxyapatite powder, 0.15% sodium silicate and 0.009% borax; The other raw materials, steps and parameters are the same as in Example 1.

[0041] Example 3 The difference between this embodiment and Embodiment 1 is as follows: The 0.4% complexing agent consists of 0.2% oxalic acid and 0.2% ammonium oxalate; The other raw materials, steps and parameters are the same as in Example 1.

[0042] Example 4 The difference between this embodiment and Embodiment 1 is as follows: The gypsum raw material contains 30% phosphogypsum and 70% desulfurized gypsum, and the calcium sulfate dihydrate content in the gypsum raw material is 89 wt%. The other raw materials, steps and parameters are the same as in Example 1.

[0043] Example 5 The difference between this embodiment and Embodiment 1 is as follows: The gypsum raw material is phosphogypsum, and the calcium sulfate dihydrate content in the gypsum raw material is 82 wt%. The other raw materials, steps and parameters are the same as in Example 1.

[0044] Example 6 The difference between this embodiment and Embodiment 1 is as follows: The crystallization agent in this embodiment does not contain added borax; The other raw materials, steps and parameters are the same as in Example 1.

[0045] Example 7 The difference between this embodiment and Embodiment 1 is as follows: The crystal conversion agent in this embodiment does not contain added sodium silicate; The other raw materials, steps and parameters are the same as in Example 1.

[0046] Example 8 The difference between this embodiment and Embodiment 1 is as follows: The sodium salt of maleic acid-acrylic acid copolymer used in this embodiment has a molecular weight of 20,000 to 30,000; The other raw materials, steps and parameters are the same as in Example 1.

[0047] Example 9 The difference between this embodiment and Embodiment 1 is as follows: The complexing agent used in this embodiment is EDTA; however, EDTA has an excessively strong complexing ability, which slows down the crystallization rate. The other raw materials, steps and parameters are the same as in Example 1.

[0048] Comparative Example 1 The difference between this comparative example and Example 1 is as follows: The crystallization agent in this embodiment does not contain added sodium salt of maleic acid-acrylic acid copolymer; The other raw materials, steps and parameters are the same as in Example 1.

[0049] Comparative Example 2 The difference between this comparative example and Example 1 is as follows: The crystallization agent in this embodiment does not contain any added complexing agent; The other raw materials, steps and parameters are the same as in Example 1.

[0050] Comparative Example 3 The difference between this comparative example and Example 1 is as follows: The crystallization agent in this embodiment does not contain added hydroxyapatite micro powder; The other raw materials, steps and parameters are the same as in Example 1.

[0051] Example of effect The aspect ratio data of the α-type high-strength gypsum obtained in the above embodiments and comparative examples are shown in Table 1.

[0052]

[0053] Test Example—Mechanical Property Test The α-type high-strength gypsum prepared in the above embodiments and comparative examples was subjected to the following tests, and the test results are shown in Table 2. 2-hour flexural strength and 2-hour compressive strength: The test was conducted according to GB / T 17669.3-2020. 150g of α-type high-strength gypsum and 67.5g of deionized water were poured into a cement mortar mixer and mixed. The slurry was then poured into a 40mm×40mm×160mm prism steel mold. After initial setting, the mold was removed 45 minutes later. The mold was then immediately placed in a standard curing chamber with a set temperature of 20℃ and relative humidity ≥90%. After curing for 2 hours, the 2-hour specimens were removed and the surface moisture was wiped off with a dry cloth. The flexural strength was tested using a flexural testing machine. The compressive strength of the specimens that fractured after the flexural test was tested using a compression testing machine. Insulated dry flexural strength and insulated dry compressive strength: Following the aforementioned specimen preparation process, the curing time is as follows: first, cure at 20±1℃ and humidity ≥90% for 24 hours, then dry at 40±2℃. During the drying process, weigh the specimen every 2 hours until the difference between two weighings is ≤0.1%. Test the flexural strength and compressive strength of the insulated dry specimens according to the previous method.

[0054]

[0055] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this invention. It should be understood that the above descriptions are merely specific embodiments of this invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing α-type high-strength gypsum, characterized in that, Includes the following steps: The gypsum raw material and crystallizing agent are obtained through hydrothermal reaction treatment; The crystallization agent comprises the following raw materials by percentage of the dry weight of the gypsum raw material: 0.03%~0.40% sodium maleic acid-acrylic acid copolymer, 0.05%~1.2% complexing agent, 0.01%~0.5% polycarboxylate superplasticizer, 0.01%~0.25% potassium chloride and 0.02%~0.8% hydroxyapatite micro powder; Preferably, the crystallization agent comprises the following raw materials by percentage of the dry weight of the gypsum raw material: 0.08%~0.30% sodium maleic acid-acrylic acid copolymer, 0.15%~0.7% complexing agent, 0.03%~0.3% polycarboxylate superplasticizer, 0.04%~0.18% potassium chloride and 0.08%~0.4% hydroxyapatite micro powder.

2. The method for preparing α-type high-strength gypsum as described in claim 1, characterized in that, The gypsum raw material is at least one of desulfurized gypsum, phosphogypsum and natural gypsum; And / or, the calcium sulfate dihydrate content in the gypsum raw material is ≥80wt%.

3. The method for preparing α-type high-strength gypsum as described in claim 1, characterized in that, The complexing agent is an organic carboxylic acid or an organic carboxylic acid salt; And / or, the organic carboxylic acid is at least one of oxalic acid and citric acid; And / or, the organic carboxylate is at least one of sodium oxalate, sodium citrate, potassium oxalate, potassium citrate, sodium oxalate, and ammonium citrate.

4. The method for preparing α-type high-strength gypsum as described in claim 1, characterized in that, The molecular weight of the sodium salt of maleic acid-acrylic acid copolymer is 2000~10000, preferably 2500~5000; And / or, the modulus of sodium silicate is 2.4~2.8; And / or, the particle size D50 of the hydroxyapatite micro powder is 40~500nm, preferably 60~300nm.

5. The method for preparing α-type high-strength gypsum as described in claim 1, characterized in that, The crystallization agent also contains borax, which is added at a rate of 0.003% to 0.01% of the dry basis weight of the gypsum raw material, preferably 0.006% to 0.009%. The crystallization agent also contains sodium silicate, which is added at a rate of 0.005% to 0.35% of the dry basis weight of the gypsum raw material, preferably 0.02% to 0.25%.

6. The method for preparing α-type high-strength gypsum as described in claim 1, characterized in that, The preparation method of the α-type high-strength gypsum includes the following steps: S1. Mix the gypsum raw material / water at a mass ratio of 1 / 3.5~6, then add the crystallizing agent to obtain a suspension slurry; S2. Place the suspended slurry in a reactor and react for 0.5 to 6 hours under conditions of pressure 0.1 to 0.5 MPa and temperature 120 to 150 °C. S3. After the hydrothermal reaction is completed, solid-liquid separation is carried out, and the solid material is dried.

7. The method for preparing α-type high-strength gypsum as described in claim 6, characterized in that, S1 also includes a pretreatment step for gypsum raw materials, which involves crushing and grinding the gypsum raw materials to a fineness of 200-500 mesh. And / or, in S2, the stirring speed of the hydrothermal reaction is 100~300 rpm; And / or, in S3, the drying temperature is 80~120°C.

8. A type α high-strength gypsum, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. The α-type high-strength gypsum as described in claim 8, characterized in that, The aspect ratio of the α-ultra-high strength gypsum crystal is 1.0~2.5:

1.

10. The α-type high-strength gypsum as described in claim 8, characterized in that, The 2-hour flexural strength of the α-type high-strength gypsum is 7.0 MPa to 10 MPa, and the 2-hour compressive strength is 68 MPa to 85 MPa. The oven-dry flexural strength of the α-type high-strength gypsum is 12MPa~16MPa, and the oven-dry compressive strength is 110MPa~135MPa.

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