阅读说明：本技术 一种结构稳定的半水-无水硫酸钙混合物及其制备方法 (Stable-structure hemihydrate-anhydrous calcium sulfate mixture and preparation method thereof ) 是由 窦焰 胡蒙 崔鹏 李正 马健 沈浩 郑之银 刘荣 彭克荣 朱英俊 陈明 孙诚 于 2021-09-30 设计创作，主要内容包括：一种结构稳定的半水-无水硫酸钙混合物及其制备方法,所述结构稳定的半水-无水硫酸钙混合物,在温度-40℃～40℃、相对湿度小于40%的环境中自然存放,在180天内晶体形貌和晶型均保持稳定；在温度-40℃～40℃、相对湿度40%～60%的环境中自然存放,在15～60天内晶体形貌和晶型均保持稳定；在温度-40℃～40℃、相对湿度60%～100%的环境中自然存放,在5～32天内晶体形貌和晶型均保持稳定；放置在0-40℃的水中,水化时间延长到80min。本发明通过精细地控制加热温度,α-CaSO-(4)·0.5H-(2)O可移除结构中的部分结晶水得到晶型和结构可控的可溶性III型α-CaSO-(4)与α-CaSO-(4)·0.5H-(2)O的混合物,而且仍旧保持原有的晶体形貌。(The hemihydrate-anhydrous calcium sulfate mixture with stable structure is naturally stored in an environment with the temperature of-40 ℃ below zero to 40 ℃ and the relative humidity of less than 40 percent, and the crystal appearance and the crystal form are kept stable within 180 days; naturally storing the crystal in an environment with the temperature of-40 ℃ to 40 ℃ and the relative humidity of 40 percent to 60 percent, and keeping the crystal appearance and the crystal form stable within 15 to 60 days; naturally storing the crystal in an environment with the temperature of-40 ℃ to 40 ℃ and the relative humidity of 60 percent to 100 percent, and keeping the crystal appearance and the crystal form stable within 5 to 32 days; placing in water of 0-40 deg.C, and prolonging hydration time to 80 min. The invention controls the heating temperature by fine control, alpha-CaSO 4 ·0.5H 2 Part of crystal water in the O-removable structure is removed to obtain soluble crystal with controllable crystal form and structurealpha-CaSO of type III 4 With alpha-CaSO 4 ·0.5H 2 O, and still maintains the original crystal morphology.)

1. A structurally stable calcium sulfate hemihydrate mixture characterized by: the hemihydrate-anhydrous calcium sulfate mixture with stable structure is naturally stored in an environment with the temperature of-40 ℃ to 40 ℃ and the relative humidity of less than 40 percent, and the crystal appearance and the crystal form are kept stable within 180 days; naturally storing the crystal in an environment with the temperature of-40 ℃ to 40 ℃ and the relative humidity of 40 percent to 60 percent, and keeping the crystal appearance and the crystal form stable within 15 to 60 days; naturally storing the crystal in an environment with the temperature of-40 ℃ to 40 ℃ and the relative humidity of 60 percent to 100 percent, and keeping the crystal appearance and the crystal form stable within 5 to 32 days; placing in water of 0-40 deg.C, and prolonging hydration time to 80 min.

2. A method for preparing a structure-stable calcium sulfate hemihydrate-anhydrous mixture is characterized by comprising the following steps: comprises the following steps:

step 1: with HNO₃Pickling industrial gypsum raw material, and then using H₂O₂Oxidizing and removing impurities to obtain a pretreated material;

step 2: adjusting the temperature of the treated material to 110-120 ℃, and adding sulfuric acid and water to obtain short column-shaped alpha-CaSO with the diameter of 10-20 mu m and the length-diameter ratio of 3: 1-5: 1₄ˑ0.5H₂O, then ethanol is used for the prepared short column-shaped alpha-CaSO₄ˑ0.5H₂O, cleaning;

and step 3: firstly, the alpha-CaSO obtained in the step 2 is subjected to temperature condition of 50-100 DEG C₄·0.5H₂Drying the O for 0.5-2 hours to remove free water; then the alpha-CaSO is subjected to temperature condition of 150-220 DEG C₄·0.5H₂Baking O for 0.5-3 h to obtain alpha-CaSO with the calcium sulfate component of 31.8-92 wt%₄·0.5H₂O and 8-68.2 wt% soluble III type anhydrous CaSO₄A mixture of (a);

and 4, step 4: calcium sulfate is 31.8-92 wt% of alpha-CaSO₄·0.5H₂O and 8-68.2 wt% soluble III type anhydrous CaSO₄Cooling the mixture to 80-100 ℃, keeping the temperature for 3-12 hours, putting the dried mixture powder into a dryer, and continuously cooling to room temperature to obtain alpha-CaSO with controllable proportion₄·0.5H₂O and soluble anhydrous CaSO of type III₄And (3) mixing the components.

3. The method of preparing a structurally stable calcium sulfate hemihydrate mixture of claim 2 wherein: HNO₃The mass concentration of (A) is 5-25%; h₂O₂The mass concentration of (A) is 5-25%.

4. The method of preparing a structurally stable calcium sulfate hemihydrate mixture of claim 2 wherein: the mass concentration of sulfuric acid is 10%.

Technical Field

The invention relates to a hemihydrate-anhydrous calcium sulfate mixture with a stable structure and a preparation method thereof, belonging to the technical field of calcium sulfate preparation.

Background

The main component of the by-products phosphogypsum and fluorgypsum and the like in the production of desulfurized gypsum and phosphoric acid of a power plant is calcium sulfate dihydrate, namely CaSO₄·2H₂And O, used as industrial solid waste to pollute the environment, generally needs to consume heat to be used as a cement retarder after heating and dehydration treatment, and has lower added value. In order to reduce solid waste discharge and realize high-quality utilization, a great deal of research is currently carried out to convert calcium sulfate dihydrate into calcium sulfate hemihydrate by using an atmospheric pressure salt solution method and a pressurized water solution method. Calcium Sulfate Hemihydrate (HH), CaSO₄·0.5H₂O, gypsum cementing material with HH as main component, is applied in high strength gypsum and building gypsumMuch more. The high-strength gypsum material is mainly formed from short column-shaped alpha-CaSO₄·0.5H₂The cementing material consisting of O (the length-diameter ratio is less than 5:1) is added with water and is converted into CaSO through hydration crystal form when in use₄·2H₂O, the particles are mutually adhered to realize the cementing property, so that the gypsum finished material has high mechanical strength, no toxicity, environmental friendliness and low price. However, the natural storage stability of HH is a difficult problem, and HH belongs to metastable crystals in a calcium sulfate crystal system, and is easy to generate hydration reaction after contacting with water, so that the crystal structure is damaged, the crystals are changed into flaky calcium sulfate dihydrate, the crystal morphology and performance are influenced, and particularly the gelling property is lost, so that the natural storage stability of the calcium sulfate hemihydrate and the hydration activity of the calcium sulfate hemihydrate as a gelling material are necessary conditions for further using the calcium sulfate hemihydrate as a high-strength gypsum gelling material.

The phases which are usually independent in nature are Dihydrate (DH), hemihydrate (HH) and type II calcium sulfate anhydrous RTE (AH), all of which have their own crystal structures and characteristics. The basic skeleton of the crystal structures of the three types of gypsum is [ -Ca-SO ]₄-Ca-SO₄-]And (3) a chain. DH is a monoclinic system and extends along the c-axis direction. In the direction, [ -Ca-SO₄-Ca-SO₄-]The chains alternate with the water-absorbing molecular layers to form a distinct layered structure. Following the conversion of DH to HH, there are two changes: firstly, 3/2 parts of water molecules connected with calcium ions are removed, and 1/2 parts of water molecules are connected with sulfate ions through hydrogen bonds; second is [ -Ca-SO [ ]₄-Ca-SO₄-]The chains are rearranged into hexagonal prisms to form a middle channel with the diameter of about 0.3nm, the special structure is closely related to the metastability of HH, external water molecules easily enter the channel again, and the water molecules in the channel are easily overflowed or replaced by other small molecules. By carefully controlling the heating temperature, HH removes the crystal water from the structure to form soluble form III AH while still maintaining the original crystal structure, i.e., the "semi-hydrated-anhydrous" structure. Insoluble type II AH belongs to an orthorhombic system, no pore channel exists in crystal lattices, and Ca-O, S-O and Ca-Ca atoms in the crystal structure have short spacing and are closely packed to form a solid structure and are difficult to hydrate.

The calcium sulfate hemihydrate exists in alpha and beta crystal forms and is converted from calcium sulfate dihydrate into calcium sulfate hemihydrateAccording to different process methods, calcium sulfate hemihydrate is different in crystal form, alpha-type calcium sulfate hemihydrate is obtained by heating in saturated steam atmosphere or water solution, beta-type calcium sulfate hemihydrate is obtained by heating in dry air, beta 0-hemihydrate is continuously heated to be converted into alpha-III-type anhydrous calcium sulfate, beta-hemihydrate is converted into beta-III-type anhydrous calcium sulfate, and the temperature is continuously increased, so that no matter alpha-III-type anhydrous calcium sulfate or beta-III-type anhydrous calcium sulfate is converted into II-type anhydrous calcium sulfate, the hydration activity is lost. When the alpha-III type anhydrous calcium sulfate is used as a cementing material, the reverse process of the process is carried out, namely the alpha-III type anhydrous calcium sulfate is converted into alpha-calcium sulfate hemihydrate. alpha-CaSO₄·0.5H₂O and beta-CaSO₄·0.5H₂Compared with the prior art, the calcium sulfate hemihydrate is small in specific volume, water-paste ratio and volume change rate, alpha-calcium sulfate hemihydrate is cemented to form a high-strength gypsum product, and the high-strength gypsum product is high in strength after hydration and coagulation and is used for ceramic molds, precision casting, precision industrial molds, oral cavity model materials, high-strength building materials and the like.

At present, the stability research of calcium sulfate hemihydrate mostly focuses on adding a stabilizer, so that the particles are coated by the stabilizer and lose hydration activity, but other impurities are increased to influence the purity of the calcium sulfate. The calcining method utilizes the characteristics that the water content of the three crystal forms of the calcium sulfate is different and the three crystal forms of the calcium sulfate correspond to different crystal forms at different temperatures, and improves the stability of the calcium sulfate hemihydrate through calcining. At present, the research on improving the stability of calcium sulfate hemihydrate by a calcination method mainly focuses on the calcination of whisker-shaped calcium sulfate hemihydrate, the calcination usually adopts a high temperature of more than 600 ℃, and dead-burned anhydrous calcium sulfate is obtained, and although hydration does not occur, the dead-burned anhydrous calcium sulfate does not have the gelling property, so the dead-burned anhydrous calcium sulfate is not suitable for being used as a gelling material. Calcining calcium sulfate hemihydrate synthesized by a hydrothermal method at 200-600 ℃ by Vanhao, wherein the calcium sulfate hemihydrate is effectively stabilized, and products obtained by calcining at 650 ℃ are anhydrous dead-burned calcium sulfate whiskers and are not easy to hydrate, (Vanhao, influence of calcination on stabilization of the calcium sulfate hemihydrate whiskers, university of eastern science and technology (Nature science edition) 2019,45: 388-; calcining the whiskers for 4 hours at 110-700 ℃ in the Hanshenxin, hydrating for 20min, and performing phase analysis on a hydration product to find that the product generates 17% of anhydrous soluble calcium sulfate whiskers and 83% of dead burned calcium sulfate whiskers at 200 ℃ (the Hanshenxin, the influence of calcination on the structure and stability of the calcium sulfate whiskers, chemical minerals and processing, 2008,3: 13-16); calcining the cymbidium at 120-180 ℃ to obtain active calcium sulfate hemihydrate, performing hydrothermal treatment, and calcining at 200-800 ℃ to prepare anhydrous calcium sulfate whiskers (the cymbidium, a controllable preparation method of the ultrafine anhydrous calcium sulfate whisker with high length-diameter ratio, CN 103014869); baking the phosphogypsum at 100-200 ℃ for 2h so that part of the absorbed water and crystal water in the phosphogypsum are removed, the corresponding diffraction peak of gypsum disappears, and the corresponding peak of calcined gypsum is enhanced. (gunn, influence of roasting and quicklime modification on soluble phosphorus content in phosphogypsum, mineral protection and utilization, 2019,39: 9-13.); penglong noble is used for preparing the anhydrous dead-burned calcium sulfate whisker by calcining the calcium sulfate hemihydrate whisker prepared by a hydrothermal method at the high temperature of 700 ℃ for 4 hours (the low-temperature preparation and the structural characterization of the Penglong noble and water-resistant calcium sulfate whisker show in material guidance B:2014, and 28: 74-78).

Disclosure of Invention

The invention aims to provide a structure-stable calcium sulfate hemihydrate-anhydrous mixture and a preparation method thereof.

In order to achieve the above objects and other related objects, the present invention provides the following technical solutions: a structurally stable calcium sulfate hemihydrate mixture characterized by: the hemihydrate-anhydrous calcium sulfate mixture with stable structure is naturally stored in an environment with the temperature of-40 ℃ to 40 ℃ and the relative humidity of less than 40 percent, and the crystal appearance and the crystal form are kept stable within 180 days; naturally storing the crystal in an environment with the temperature of-40 ℃ to 40 ℃ and the relative humidity of 40 percent to 60 percent, and keeping the crystal appearance and the crystal form stable within 15 to 60 days; naturally storing the crystal in an environment with the temperature of-40 ℃ to 40 ℃ and the relative humidity of 60 percent to 100 percent, and keeping the crystal appearance and the crystal form stable within 5 to 32 days; placing in water of 0-40 deg.C, and prolonging hydration time to 80 min.

In order to achieve the above objects and other related objects, the present invention provides the following technical solutions: a method for preparing a structurally stable calcium sulfate hemihydrate mixture comprising the steps of:

step 1: with HNO₃Pickling industrial gypsum raw material, and then using H₂O₂Oxidation impurity removal is carried out to obtain the pretreatedMaterial preparation;

step 2: adjusting the temperature of the treated material to 110-120 ℃, and adding sulfuric acid and water to obtain short column-shaped alpha-CaSO with the diameter of 10-20 mu m and the length-diameter ratio of 3: 1-5: 1₄·0.5H₂O, then ethanol is used for the prepared short column-shaped alpha-CaSO₄·0.5H₂O, cleaning;

and step 3: firstly, the alpha-CaSO obtained in the step 2 is subjected to temperature condition of 50-100 DEG C₄·0.5H₂Drying the O for 0.5-2 hours to remove free water; then the alpha-CaSO is subjected to temperature condition of 150-220 DEG C₄·0.5H₂Baking O for 0.5-3 h to obtain alpha-CaSO with the calcium sulfate component of 31.8-92 wt%₄·0.5H₂O and 8-68.2 wt% soluble III type anhydrous CaSO₄A mixture of (a);

and 4, step 4: calcium sulfate is 31.8-92 wt% of alpha-CaSO₄·0.5H₂O and 8-68.2 wt% soluble III type anhydrous CaSO₄Cooling the mixture to 80-100 ℃, keeping the temperature for 3-12 hours, putting the dried mixture powder into a dryer, and continuously cooling to room temperature to obtain alpha-CaSO with controllable proportion₄·0.5H₂O and soluble anhydrous CaSO of type III₄And (3) mixing the components.

The preferable technical scheme is as follows: HNO₃The mass concentration of (A) is 5-25%; h₂O₂The mass concentration of (A) is 5-25%.

The preferable technical scheme is as follows: the mass concentration of sulfuric acid is 10%.

Due to the application of the technical scheme, compared with the prior art, the invention has the advantages that:

the invention controls the heating temperature by fine control, alpha-CaSO₄·0.5H₂O can remove part of crystal water in the structure to obtain soluble III-type alpha-CaSO with controllable crystal form and structure₄With alpha-CaSO₄·0.5H₂The mixture of O and the crystal still keeps the original crystal morphology, namely a semi-water-anhydrous structure, and the natural storage stability is higher; soluble III type alpha-CaSO when used as cementing material₄First hydrated to alpha-CaSO₄·0.5H₂O, then hydrated to CaSO₄·2H₂And O, simultaneously realizing the cementing property and forming the high-strength gypsum product.

Drawings

FIG. 1 is a diagram of alpha-CaSO₄·0.5H₂O SEM images of the mixed samples before and after calcination.

Figure 2 is a calcium sulfate XRD pattern at different calcination temperatures.

FIG. 3 is a DSC of calcium sulfate hemihydrate.

Detailed Description

The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will be apparent to those skilled in the art from the present disclosure.

Please refer to fig. 1-3. It should be understood that the structures, ratios, sizes, and the like shown in the drawings and described in the specification are for illustrative purposes only and are not intended to limit the scope of the present invention. The following examples are provided for a better understanding of the present invention, and are not intended to limit the invention. The experimental procedures in the following examples are conventional unless otherwise specified. The experimental materials used in the following examples were all purchased from a conventional biochemical reagent store unless otherwise specified.

Example 1: stable-structure hemihydrate-anhydrous calcium sulfate mixture and preparation method thereof

The mixture of semi-hydrated calcium sulfate and anhydrous calcium sulfate with stable structure is prepared with industrial solid waste gypsum as material and through crystal transformation of calcium sulfate dihydrate into short column of semi-hydrated calcium sulfate and anhydrous calcium sulfate, and has high stability and hydration activity.

The hemihydrate-anhydrous calcium sulfate mixture with stable structure is naturally stored in an environment with the temperature of-40 ℃ to 40 ℃ and the humidity of less than 40 percent, and the crystal appearance and the crystal form can be kept stable within 180 days; the crystal is naturally stored in an environment with the temperature of-40 ℃ to 40 ℃ and the humidity of 40 percent to 60 percent, and the crystal appearance and the crystal form can be kept stable within 15 to 60 days; the crystal can be naturally stored in an environment with the temperature of minus 40 ℃ to 40 ℃ and the humidity of 60 percent to 100 percent, and the crystal appearance and the crystal form can be kept stable within 5 to 32 days; placing in water of 0-40 deg.C, and prolonging hydration time to 80 min.

The title method comprises the following steps.

(1) Pretreatment of industrial gypsum raw material

Raw material of industrial gypsum, CaSO₄The content is generally 80 wt%, and the alloy contains other impurities such as Fe, Al, Mg, K, Na, organic matters and the like, and passes through 5-25 wt% of HNO₃Acid washing and 5-25 wt% of H₂O₂Oxidizing to remove impurities to obtain CaSO₄The purity is more than or equal to 95 wt%.

(2) Method for preparing short columnar alpha-CaSO through crystal transformation₄·0.5H₂O

Pretreated material (treated CaSO) by industrial gypsum raw material₄Purity is more than or equal to 95wt percent), the temperature is adjusted to 110-120 ℃ by adopting a normal pressure acid water solution adding method, 10 percent of sulfuric acid and water are added, and short column-shaped alpha-CaSO with the diameter of 10-20 mu m and the length-diameter ratio of 3: 1-5: 1 can be obtained₄·0.5H₂O, then quickly washed with ethanol. (a of FIG. 1).

(3) Step drying

Adopting a step drying process to carry out the reaction of alpha-CaSO₄·0.5H₂Drying the O at the low temperature of 50-100 ℃ for 0.5-2 hours to remove free water; then, baking the alpha-CaSO at 150-220 DEG C₄·0.5H₂O for 0.5 to 3 hours to obtain alpha-CaSO with the calcium sulfate component of 31.8 to 92 weight percent₄·0.5H₂O and 8-68.2 wt% soluble III type anhydrous CaSO₄A mixture of (a). alpha-CaSO₄·0.5H₂O and soluble type III anhydrous CaSO₄The proportion control is shown in table 1, and the discovery shows that two mixtures with different crystal proportions can be obtained by specific different drying temperatures between 150 ℃ and 220 ℃, and the alpha-CaSO at 150 ℃, 180 ℃ and 200 ℃ can be obtained₄·0.5H₂O ratio of 92wt%, 52.1 wt% to 31.8 wt%, and at 220 deg.C, part of the crystals are converted to II-CaSO₄The loss of the hydration activity indicates that the alpha-CaSO can be obtained by controlling through fine and specific different drying temperatures between 150 and 220 DEG C₄·0.5H₂O and soluble type III anhydrous CaSO₄The ratio of (a) to (b). Through the drying process, the crystals are changed from small particles with mutually adhered surfaces and adhered surfaces into smooth surfaces, the dispersibility among the particles is good, and the crystal appearance is regular hexagonal prism (b in figure 1).

(4) Cooling down

Naturally cooling to 80-100 ℃, preserving heat for 3-12 h, then rapidly placing the dried mixture powder in a dryer for continuously cooling to room temperature to prevent crystals from absorbing water so as to fix the crystal form and structure of the mixture, and obtaining the alpha-CaSO with controllable proportion₄·0.5H₂O and soluble anhydrous CaSO of type III₄Mixtures, i.e. "semi-hydrated-anhydrous" structures, and still retaining the original alpha-CaSO₄·0.5H₂Crystal morphology of O.

(5) Storage of

The method provides a basis for maintaining the stability of the crystal form and the structure of the calcium sulfate by downstream process treatment, natural storage (the humidity is controlled to be less than 40 percent) and the like.

Estimation of proportion of different crystal forms in hemihydrate-anhydrous calcium sulfate mixture at different drying temperatures

The proportions of different crystal forms in the hemihydrate calcium sulfate-anhydrous calcium sulfate mixture are calculated by adopting TG (thermogravimetric analyzer), the theoretical molecular weights of the hemihydrate calcium sulfate and the anhydrous calcium sulfate are respectively 6.21 wt% and 0%, and the proportions of the hemihydrate calcium sulfate and the anhydrous calcium sulfate in the mixture can be calculated according to the weight loss of the TG.

TABLE 1 CaSO drying temperatures₄Estimating the ratio of different crystal forms in the mixture

Note: CaSO₄·0.5H₂O is (i), III-CaSO₄Is 2, II-CaSO₄Is (c).

Stability analysis of calcium sulfate hemihydrate-Anhydrous mixtures

At a temperature of-40 ℃ to 40 ℃ and a humidity<alpha-CaSO naturally stored in 40% environment and dried only at 65 DEG C₄·0.5H₂O can be kept stable within 30 days, and the crystal morphology and the crystal form of the semi-hydrated-anhydrous structural mixture can be kept stable within 180 days; naturally storing in an environment with the humidity of 40-60 percent, and drying at 65 ℃ to obtain alpha-CaSO₄·0.5H₂The O can be kept stable within 1-7 days, and the crystal appearance and the crystal form of the semi-hydrated-anhydrous crystal can be kept stable within 15-60 days; naturally storing in an environment with the humidity of 60-100 percent, and drying at 65 ℃ to obtain alpha-CaSO₄·0.5H₂The O can be kept stable within 0.5-24 hours, and the crystal appearance and the crystal form of the semi-hydrated-anhydrous structural crystal can be kept stable within 5-32 days; placing in water, and oven drying at 65 deg.C to obtain alpha-CaSO₄·0.5H₂The hydration time of the O-water-free structure mixture is 20min, and the hydration time of the semi-water-free structure mixture treated by the drying process can be prolonged to 80 min.

The stability identification method can be explained by analyzing the crystal form change through XRD and TG and observing the appearance change through SEM, and if the crystal form and the appearance are not changed, the stability is ensured.

TABLE 2 different crystal forms of CaSO under different temperature and humidity conditions₄Proportional settling time

Note: CaSO₄·0.5H₂O is (i), III-CaSO₄Is 2, II-CaSO₄Is (c).

Thirdly, adopting a normal pressure water solution method and taking industrial gypsum as a raw material (treated CaSO)₄Purity is more than or equal to 95wt percent), and short column-shaped alpha-CaSO with the diameter of 10-20 mu m and the length-diameter ratio of 3: 1-5: 1 can be obtained by a crystal transformation technology₄·0.5H₂O, then quickly washed with ethanol.

The alpha-CaSO is treated by low-temperature drying and baking at 150 DEG C₄·0.5H₂O2 h to obtain alpha-CaSO with the calcium sulfate component of 92wt percent₄·0.5H₂O and 8 wt% soluble type III anhydrous CaSO₄A mixture of (a). The mixture is naturally placed in an environment with the temperature of 30 ℃ and the humidity of 40 percent, the mixture is kept stable within 90 days, the mixture is placed in an environment with the humidity of 60 percent, the semi-water-anhydrous mixture can be kept stable within 10 days, and the crystal appearance and the crystal form are both kept stable; the crystal is placed in an environment with the humidity of 100 percent, and the crystal appearance and the crystal form are kept stable within 1 day; placing in water CaSO₄The hydration time of the mixture can be prolonged to 50 min.

Fourthly

Fourthly, adopting a normal pressure water solution method and taking industrial gypsum as a raw material (treated CaSO)₄Purity is more than or equal to 95wt percent), and short columnar alpha-CaSO with the diameter of 10-20 mu m and the length-diameter ratio of 3: 1-5: 1 can be obtained by crystal transformation₄·0.5H₂O, then quickly washed with ethanol.

The alpha-CaSO is processed by low-temperature drying and baking at 180 DEG C₄·0.5H₂O2 h to obtain alpha-CaSO with the calcium sulfate component of 52.1 weight percent₄·0.5H₂O and 47.9 wt% soluble type III anhydrous CaSO₄A mixture of (a). The semi-hydrated-anhydrous mixture can be kept stable within 180 days when placed in an environment with the temperature of 30 ℃ and the humidity of 40 percent, and the crystal morphology and the crystal form are kept stable within 15 days when placed in an environment with the humidity of 60 percent; the crystal is placed in an environment with the humidity of 100 percent, and the crystal appearance and the crystal form are kept stable within 5 days; placing in water CaSO₄The hydration time of the mixture can be prolonged to 60 min.

Fifthly, adopting a normal pressure water solution method and taking industrial gypsum as a raw material (treated CaSO)₄Purity is more than or equal to 95wt percent), and short columnar alpha-CaSO with the diameter of 10-20 mu m and the length-diameter ratio of 3: 1-5: 1 can be obtained by crystal transformation₄·0.5H₂O, then quickly washed with ethanol.

Baking alpha-CaSO at 200 ℃ by low-temperature drying₄·0.5H₂O2 h to obtain alpha-CaSO with the calcium sulfate component of 30.2wt percent₄·0.5H₂O and 69.8 wt% soluble type III anhydrous CaSO₄A mixture of (a). Ring at 30 ℃ and 40% humidityThe semi-hydrated-anhydrous mixture can be kept stable within 180 days when placed in the environment, and the crystal morphology and the crystal form can be kept stable within 21 days when placed in the environment with the humidity of 60%; the crystal is placed in an environment with the humidity of 100 percent, and the crystal appearance and the crystal form are kept stable within 7 days; placing in water CaSO₄The hydration time of the mixed crystal can be prolonged to 80 min.

Sixthly, adopting an aqueous solution method and taking industrial gypsum as a raw material (treated CaSO)₄Purity is more than or equal to 95wt percent), and short columnar alpha-CaSO with the diameter of 10-20 mu m and the length-diameter ratio of 3: 1-5: 1 can be obtained by crystal transformation₄·0.5H₂O, then quickly washed with ethanol.

Baking alpha-CaSO at 220 ℃ by low-temperature drying₄·0.5H₂O2 h to obtain alpha-CaSO with the calcium sulfate component of 24 weight percent₄·0.5H₂O and 76 wt% III + II anhydrous CaSO₄A mixture of (a). The crystal with the semi-water-anhydrous structure can be placed in an environment with the temperature of 30 ℃ and the humidity of 40%, the crystal appearance and the crystal form are kept stable within 180 days, and the crystal appearance and the crystal form are kept stable within 40 days when the crystal is placed in an environment with the humidity of 60%; the crystal is placed in an environment with the humidity of 100 percent, and the crystal morphology and the crystal form are kept stable within 20 days; placing in water CaSO₄The hydration time of the mixture can be prolonged to 120 min.

Seventhly, drying at low temperature and baking at 200 ℃ to obtain alpha-CaSO₄·0.5H₂O2 h to obtain alpha-CaSO with the calcium sulfate component of 30.2wt percent₄·0.5H₂O and 69.8 wt% soluble type III anhydrous CaSO₄The mixture was used to prepare 2 x 4cm plasterboards, using alpha-CaSO dried at 65 deg.C₄·0.5H₂O preparing gypsum board of 2 x 4cm, testing the strength, and finding that the gypsum board prepared by the mixture after drying treatment has the compression strength of 21.2562MPa, the breaking strength of 9.9503MPa and the alpha-CaSO dried at 65 DEG C₄·0.5H₂The strength of the gypsum board prepared from O is 20.0069MPa, and the breaking strength is 8.9030 MPa.

As shown in FIG. 1, the present invention is directed to a short columnar α -CaSO prepared by a crystal transformation method₄·0.5H₂Carrying out gradient temperature treatment on the O particles, wherein alpha is alpha before treatment-CaSO₄·0.5H₂O is in a short column shape, but the particles are adhered to each other, the dispersibility is poor, after the step temperature treatment, the particles are obviously independent, the dispersibility is improved, but the short column shape is not changed.

As shown in FIG. 2, it can be seen that after the drying process at 50-400 deg.C, alpha-CaSO₄·0.5H₂O appears a little anhydrous calcium sulfate from 150 ℃, the temperature rises to 200 ℃, and alpha-CaSO₄·0.5H₂O and anhydrous CaSO₄Simultaneously, the temperature is increased to 400 ℃, and only anhydrous CaSO is generated₄And (4) crystals. III-CaSO₄And II-CaSO₄Simultaneously anhydrous CaSO₄The difference is mainly III-CaSO₄Hydration reaction in water, II-CaSO₄No hydration reaction occurs.

As shown in FIG. 3, the DSC chart can illustrate the changes of melting, softening, solidifying, phase transition, etc. of the measured substance by the endothermic and exothermic phenomena, the positions of the endothermic and exothermic peaks correspond to the temperatures at which the changes occur, and the appearance of the endothermic peak at 185.9 ℃ in FIG. 3 generally indicates that the obtained crystal is determined to be alpha-CaSO₄·0.5H₂O，β-CaSO₄·0.5H₂O generally has a smooth curve at this temperature and no endothermic reaction.

The foregoing is illustrative of the preferred embodiment of the present invention and is not to be construed as limiting thereof in any way, and any modifications or variations thereof that fall within the spirit of the invention are intended to be included within the scope thereof.