A method for preparing hemihydrate calcium sulfate whisker brush in an alcohol-water system

Abstract

A method for preparing a hemihydrate calcium sulfate whisker brush in an alcohol-water system comprises adding a soluble calcium salt and a soluble sulfate salt to an alcohol-water solution, heating each solution, then uniformly mixing the two solutions, insulating the mixture and allowing it to stand. After the reaction is complete, the product is quickly filtered and dried to obtain the hemihydrate calcium sulfate whisker brush. The present invention solves the problems of high equipment requirements, high energy consumption, and complex operation of hydrothermal and atmospheric pressure acidification methods. Hemihydrate calcium sulfate whiskers can be prepared under atmospheric pressure and in a neutral reaction medium. The prepared calcium sulfate whiskers exhibit a "brush" shape, providing new ideas for the application of calcium sulfate whiskers.

Description

Technical Field

[0001] The invention belongs to the technical field of new inorganic materials, and particularly relates to a method for preparing a hemihydrate calcium sulfate whisker brush in an alcohol-water system. Background Art

[0002] Calcium sulfate whiskers are a fibrous, sub-nano single-crystal, needle-like material with a uniform cross-section, large aspect ratio, and specific surface area. Calcium sulfate whiskers are primarily divided into three types based on their water content: anhydrous calcium sulfate whiskers, hemihydrate calcium sulfate whiskers, and dihydrate calcium sulfate whiskers. Calcium sulfate whiskers themselves possess physical and chemical properties such as large specific surface area, high strength, good toughness, wear resistance, high temperature resistance, chemical corrosion resistance, and good compatibility. Compared with other inorganic whisker materials, they offer advantages such as diverse preparation methods, low cost, non-toxicity, and solid waste treatment. They are a new type of inorganic material with broad application prospects and are widely used in composite material modification, asphalt pavement modification, papermaking, friction materials, and wastewater treatment.

[0003] Currently, the most commonly used methods for preparing calcium sulfate whiskers include hydrothermal method, atmospheric pressure acidification method, and microemulsion method. The hydrothermal method involves placing a gypsum suspension in an autoclave for hydrothermal treatment. When heated to a certain temperature and pressure, gypsum whiskers are generated through the action of saturated steam pressure in the autoclave. The hydrothermal method is the most commonly used method for preparing gypsum whiskers. It effectively solves the problem of gypsum's insolubility and produces ideal gypsum whiskers in an autoclave. However, the hydrothermal method needs to be carried out under high temperature and high pressure conditions, so the equipment requirements are relatively strict. The equipment must be resistant to high pressure and highly sealed, and the energy consumption during operation is high.

[0004] The atmospheric pressure acidification method involves placing a gypsum suspension in an acidic environment at a certain temperature. This acidic environment allows calcium sulfate to reach supersaturation more easily. Under the influence of temperature, the calcium sulfate then dissolves and crystallizes, ultimately forming calcium sulfate whiskers. This method is also a common method for producing calcium sulfate whiskers. It does not require strict reaction equipment and is simpler to operate. However, since the reaction is carried out in a strong acid medium, it requires certain acid resistance from the container.

[0005] Microemulsion method refers to take calcium salt and sulfate as raw material, prepares calcium salt and sulfate solution respectively, gently stirs after mixing, and by changing interface property such as surfactant or modifier, makes calcium ion and sulfate ion reaction generate calcium sulfate whisker.The calcium sulfate whisker quality prepared by microemulsion method is more stable, and method is also relatively simple, does not need special equipment, just can be carried out at ambient temperature.Wherein, preparing calcium sulfate whisker in alcohol-water system is commonly used method, by adding alcohol solution in aqueous solution to reduce water activity, thereby realizes preparing calcium sulfate whisker under normal pressure and relatively low temperature condition.Patent CN106745161A discloses a method for preparing nano calcium sulfate and calcium sulfate whisker in a kind of alcohol-water mixed system, utilizes ethanol aqueous solution system to prepare nano calcium sulfate and calcium sulfate whisker, but prepared whisker is short columnar or fibrous.

[0006] At present, the crystal morphology of prepared calcium sulfate whiskers is usually fibrous or rod-shaped, and no one has yet prepared "brush"-shaped calcium sulfate whiskers in an alcohol-water system. Summary of the Invention

[0007] In order to overcome the shortcomings of the above-mentioned prior art, the object of the present invention is to provide a method for preparing calcium sulfate hemihydrate whisker brushes in an alcohol-water system, so as to solve the problems of high reaction equipment requirements, high energy consumption and complicated operation of the hydrothermal method and the atmospheric pressure acidification method. Calcium sulfate hemihydrate whiskers can be prepared under atmospheric pressure conditions and in a neutral reaction medium, and the prepared calcium sulfate whiskers are in a "brush" shape, which provides a new idea for the application of calcium sulfate whiskers.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] The invention discloses a method for preparing a hemihydrate calcium sulfate whisker brush in an alcohol-water system. The method comprises the following steps: adding a soluble calcium salt and a soluble sulfate into an alcohol-water solution, heating the two solutions respectively, mixing the two solutions evenly, keeping the mixture warm and allowing it to stand, and after the reaction is completed, quickly filtering the product and drying it to obtain the hemihydrate calcium sulfate whisker brush.

[0010] In one embodiment, the soluble calcium salt is calcium chloride and / or calcium nitrate, and the soluble sulfate is selected from one or more of anhydrous sodium sulfate, potassium sulfate, and ammonium sulfate.

[0011] In one embodiment, the ratio of the soluble calcium salt to water is 0.2-0.6 mol / L, and the ratio of the soluble sulfate to water is 0.2-0.6 mol / L.

[0012] In one embodiment, the alcohol-water solution uses ethylene glycol and / or glycerol, and the volume ratio of alcohol to water is 2-5:1.

[0013] In one embodiment, the heating is performed at a temperature of 30-70°C; and the drying is performed at a temperature of 40-100°C.

[0014] In one embodiment, the uniform mixing is performed by stirring at a rotation speed of 100-500 r / min for 1-5 minutes, and the rapid filtration is performed by washing with anhydrous ethanol for 1-3 times and vacuum filtration.

[0015] In one embodiment, the heat preservation and standing is performed at a temperature of 30-70° C. and a standing reaction time of 1-3 hours.

[0016] In one embodiment, the calcium sulfate hemihydrate whisker brush is in a bundled shape consisting of multiple brush filaments, which are bound in the middle and diverge at both ends.

[0017] In one embodiment, the calcium sulfate hemihydrate whisker brush has a crystal length of micrometer level, 20-30 μm, and the divergent angles of the whisker brush at both ends are 30°-70°.

[0018] In one embodiment, the method is carried out under normal pressure conditions in a neutral reaction medium.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The prepared calcium sulfate hemihydrate whiskers have a "brush" shape instead of the common rod-like or fiber-like shape, which broadens the research on calcium sulfate whiskers.

[0021] (2) Compared with the commonly used hydrothermal method and atmospheric pressure acidification method, this preparation method is simpler, easier to operate, and has low equipment requirements. Hemihydrate calcium sulfate whiskers can be prepared under atmospheric pressure conditions and in a neutral reaction medium.

[0022] (3) Most methods for preparing calcium sulfate whiskers are to convert gypsum into a physical solution through a "dissolution-crystallization" process. The present invention uses soluble calcium salts and sulfates as raw materials to prepare calcium sulfate whiskers through a chemical method. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a scanning electron microscope image of the calcium sulfate hemihydrate whisker brush described in Example 1.

[0024] Figure 2 This is a scanning electron microscope image of the calcium sulfate hemihydrate whisker brush described in Example 1 (with Figure 1 different angles).

[0025] Figure 3 This is the X-ray diffraction pattern of the calcium sulfate hemihydrate whisker brush described in Example 1. DETAILED DESCRIPTION

[0026] The embodiments of the present invention are described in detail below with reference to the accompanying drawings and examples.

[0027] The present invention provides a method for preparing a calcium sulfate hemihydrate whisker brush in an alcohol-water system, comprising the following steps:

[0028] Step 1: adding soluble calcium salt and soluble sulfate into a certain proportion of alcohol-water solution respectively.

[0029] In the present invention, the soluble calcium salt is selected from one or more of calcium chloride, calcium nitrate, or other soluble calcium salts; the sulfate is selected from one or more of anhydrous sodium sulfate, potassium sulfate, ammonium sulfate, or other soluble sulfates; the alcohol used in the reaction is one or more of ethylene glycol and glycerol; preferably, the alcohol-water volume ratio is 2-5:1. The ratio of the soluble calcium salt to water is 0.2-0.6 mol / L, and the ratio of the soluble sulfate to water is 0.2-0.6 mol / L.

[0030] The purpose of this step is to prepare an alcohol aqueous solution of a soluble calcium salt and an alcohol aqueous solution of a soluble sulfate.

[0031] Step 2: Heat the two solutions obtained above separately.

[0032] The purpose of this step is to dissolve the soluble calcium salt and sulfate into calcium ions and sulfate ions respectively. The dissolution rate can be accelerated by heating the solution. Generally, to achieve this purpose, the heating temperature can be between 30-70°C.

[0033] Step 3: Mix the two heated solutions evenly.

[0034] To promote mixing, in this step, the two can be mixed and then stirred at a speed of 100-500 r / min for 1-5 minutes.

[0035] Step 4: keeping the mixed solution warm and allowing it to stand for reaction.

[0036] The purpose of this step is to provide a stable reaction environment for whisker growth. Insulation and stabilization can ensure constant solution parameters, increase solute supersaturation, and create an ideal environment for whisker growth. Generally, to achieve this goal, the insulation temperature can be set to 30-70°C and the stabilization reaction time can be set to 1-3 hours.

[0037] Step 5: After the reaction is completed, the product is quickly filtered.

[0038] The purpose of this step is to wash the prepared calcium sulfate hemihydrate whiskers and separate them from the alcoholic aqueous solution using rapid filtration. Because calcium sulfate hemihydrate whiskers have low solubility in absolute ethanol and absolute ethanol is volatile, absolute ethanol washing is used. Generally, to achieve this goal, absolute ethanol washing can be used 1-3 times, followed by vacuum filtration.

[0039] Step 6: drying the filtered product to obtain a calcium sulfate hemihydrate whisker brush.

[0040] The purpose of this step is to dry the residual solvent on the surface of the calcium sulfate whisker brush. Generally, to achieve this purpose, the drying temperature can be set to 40-100°C.

[0041] It is worth noting that the above steps of the present invention are all carried out under normal pressure conditions and a neutral solution environment.

[0042] To further illustrate the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments.

[0043] Example 1

[0044] Using calcium chloride and anhydrous sodium sulfate as raw materials and a glycerol aqueous solution as the alcohol-water system, 1.32g of calcium chloride was added to a glycerol aqueous solution (120ml of glycerol, 30ml of water). Separately, 1.704g of anhydrous sodium sulfate was added to a glycerol aqueous solution (120ml of glycerol, 30ml of water). Both solutions were stirred evenly with a glass rod and heated in a water bath to 40°C. The two solutions were then mixed and stirred using a magnetic rotor at 200 rpm for 1 minute. After stirring, the mixture was allowed to stand at 40°C for 2 hours. After the reaction was complete, it was washed with anhydrous ethanol and filtered. The resulting calcium sulfate whiskers were then placed in a 40°C oven for 24 hours to obtain the product. Scanning electron microscopy of the resulting sample revealed a "brush" shape with split ends, unlike the more common fibrous or rod-like shapes. These whiskers have a larger surface area and surface energy, making them suitable for wastewater treatment and the adsorption of harmful heavy metal impurities. The scanning electron microscope image of the sample obtained in this embodiment is as follows Figure 1 and Figure 2 As shown, the generated calcium sulfate whisker brush crystal morphology is a bundled shape composed of multiple brush filaments, which are bound in the middle and diverge in a fan shape at both ends. The whisker brush length is 20-30 μm, and the divergence angle of the fan-shaped brush filaments at both ends is between 30° and 70°.

[0045] The prepared samples were characterized by X-ray diffractometer (XRD). Figure 3 As shown, the prepared sample is CaSO4·0.5H2O.

[0046] Example 2

[0047] Calcium chloride and anhydrous sodium sulfate are used as raw materials, and an aqueous solution of glycerol is used as the alcohol-water system. 1.32g of calcium chloride is weighed and added to the glycerol aqueous solution (120ml of glycerol, 30ml of water). Another 1.704g of anhydrous sodium sulfate is added to the glycerol aqueous solution (120ml of glycerol, 30ml of water). The two solutions are stirred evenly with glass rods and placed in a water bath and heated to 60°C. The two solutions are then mixed evenly, stirred with a magnetic rotor at a speed of 200r / min for 1min. After stirring, the mixture is allowed to stand at 60°C for 2h. After the reaction is completed, it is washed with anhydrous ethanol and filtered. The prepared calcium sulfate whiskers are placed in a 40°C oven for 24h to obtain the product. The obtained sample was observed using a scanning electron microscope, and the generated calcium sulfate whiskers are also "brush" shaped with split ends.

[0048] Example 3

[0049] Calcium chloride and potassium sulfate are used as raw materials, and an aqueous solution of glycerol is used as an alcohol-water system. 1.32g of calcium chloride is weighed and added to a glycerol aqueous solution (120ml of glycerol, 30ml of water). Another 2.088g of potassium sulfate is added to a glycerol aqueous solution (120ml of glycerol, 30ml of water). The two solutions are stirred evenly with a glass rod and placed in a water bath and heated to 40°C. The two solutions are then mixed evenly, stirred with a magnetic rotor at a speed of 200r / min for 1min. After stirring, the mixture is allowed to stand at 40°C for 2h. After the reaction is completed, it is washed with anhydrous ethanol and filtered. The prepared calcium sulfate whiskers are placed in a 40°C oven for 24h to obtain the product.

[0050] Example 4

[0051] Calcium chloride and ammonium sulfate are used as raw materials, and an aqueous solution of glycerol is used as an alcohol-water system. 1.32g of calcium chloride is weighed and added to a glycerol aqueous solution (120ml of glycerol, 30ml of water). Another 1.584g of ammonium sulfate is added to a glycerol aqueous solution (120ml of glycerol, 30ml of water). The two solutions are stirred evenly with a glass rod and placed in a water bath and heated to 40°C. The two solutions are then mixed evenly, stirred with a magnetic rotor at a speed of 200r / min for 1min. After stirring, the mixture is allowed to stand at 40°C for 2h. After the reaction is completed, it is washed with anhydrous ethanol and filtered. The prepared calcium sulfate whiskers are placed in a 40°C oven for 24h to obtain the product.

Claims

1. A method for preparing a hemihydrate calcium sulfate whisker brush in an alcohol-water system, characterized in that: The soluble calcium salt and the soluble sulfate are added to an alcohol-water solution respectively, and the two solutions are heated respectively. The two solutions are then mixed evenly, and the mixture is kept warm and allowed to stand. After the reaction is completed, the product is quickly filtered and dried to obtain a hemihydrate calcium sulfate whisker brush. The method is carried out under normal pressure and in a neutral reaction medium. The soluble calcium salt is calcium chloride and / or calcium nitrate, the soluble sulfate is selected from one or more of anhydrous sodium sulfate, potassium sulfate, and ammonium sulfate, the ratio of the soluble calcium salt to water is 0.2-0.6 mol / L, and the ratio of the soluble sulfate to water is 0.2-0.6 mol / L. The alcohol-water solution uses ethylene glycol and / or glycerol, and the alcohol-water volume ratio is 2-5:

1. The heating is carried out separately at a temperature of 30-70°C, the drying temperature is 40-100°C, the heat preservation and standing temperature is 30-70°C, and the standing reaction time is 1-3h.

2. the method for preparing calcium sulfate hemihydrate whisker brush in the described alcohol water system of claim 1, is characterized in that, The uniform mixing is performed by stirring at a rotation speed of 100-500 r / min for 1-5 minutes, and the rapid filtration is performed by washing with anhydrous ethanol for 1-3 times and vacuum filtering.

3. The method for preparing a calcium sulfate hemihydrate whisker brush in the alcohol-water system according to claim 1, wherein The calcium sulfate hemihydrate whisker brush is in a bundled shape consisting of multiple brush filaments, which are bound in the middle and diverge at both ends.

4. The method for preparing a calcium sulfate hemihydrate whisker brush in the alcohol-water system according to claim 3, wherein The calcium sulfate hemihydrate whisker brush has a crystal length of micrometer level, which is 20-300 μm, and the divergent expansion angles of the two ends of the whisker brush are 30°-70°.

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