Room-temperature melting salt hydrate and preparation method thereof

Abstract

The invention discloses a salt hydrate capable of melting at room temperature and a preparation method thereof. The salt hydrate is prepared from the following raw materials in parts by weight: 40-80 parts of formate, 20-60 parts of water, 0-5 parts of a crystallization nucleating agent, 0-20 parts of a melting point regulator, 0-10 parts of a thickening agent and 0-20 parts of heat-conducting filler. According to the salt hydrate capable of melting at room temperature and the preparation method of the salt hydrate, the prepared salt hydrate has the advantages of being adjustable in melting point at room temperature and high in melting latent heat, has the advantages of being low in corrosivity, incombustible, high in cost performance and the like, is a novel heat storage material and has obvious application value.

Description

Technical Field

[0001] The invention belongs to the technical field of new materials, and in particular relates to a salt hydrate that melts at room temperature and a preparation method thereof. Background Art

[0002] The melting point of salts is usually as high as 300~1000℃, while the melting point of salt mixtures can drop to 150~300℃, such as potassium nitrate / sodium nitrate molten salt. Salt hydrates containing crystal water have a melting point of room temperature~150℃, such as lithium chlorate trihydrate (melting point 8℃), disodium hydrogen phosphate dodecahydrate (melting point 35℃), sodium acetate trihydrate (melting point 58℃), etc.

[0003] Salts can absorb and release high amounts of heat when they melt and crystallize, so they can be used as heat storage materials. At the same time, because they are non-flammable, they can be used in industry, construction, electronics, etc. However, the currently known hydrate salts have many disadvantages, such as lithium chlorate trihydrate is highly oxidizing and expensive, the melting temperature of disodium hydrogen phosphate dodecahydrate is difficult to adjust, and the melting of sodium acetate trihydrate is inconsistent, resulting in stratification. Summary of the invention

[0004] The purpose of the present invention is to provide a salt hydrate that melts at room temperature and a preparation method thereof, so as to solve the problems that the above-mentioned salt hydrate is expensive, the melting temperature is difficult to adjust and stratification is easy to occur.

[0005] To achieve the above object, the first aspect of the present invention provides a salt hydrate that melts at room temperature, wherein the salt hydrate comprises the following raw materials in parts by weight: Formate 40~80 parts 20~60 parts water Crystallization nucleating agent 0~5 parts Melting point regulator 0~20 parts Thickener 0~10 parts Thermal conductive filler 0~20 parts.

[0006] The salt hydrate in the present invention comprises formate, water, a crystal nucleating agent, a melting point regulator, a thickener and a thermal conductive filler, and each component has a different function.

[0007] The sodium formate and potassium formate in the formate can form low melting point hydrates with water, and the melting point varies with the formate content, so hydrate salts with different melting points can be easily obtained.

[0008] Crystallization nucleating agents can increase the crystallization rate of formate hydrates. Although formate hydrates are easy to crystallize, when their concentration is lower than 55%, the lack of crystal nuclei leads to a high degree of supercooling or a low crystallization rate. Therefore, magnesium salts, calcium salts and barium salts with low solubility can provide a large number of nucleation points, reduce supercooling and increase the crystallization rate. At the same time, magnesium salts, calcium salts and barium salts have the advantages of abundant sources, low cost, easy availability, environmental protection and low toxicity.

[0009] Melting point regulators can adjust the melting point of formate. Although the melting point of formate can be adjusted by its content, when the concentration of formate decreases, the corresponding hydrate content also decreases, resulting in a decrease in the heat of fusion. Since the amount of melting point regulator is large, it is advisable to use inorganic salts with high solubility, abundant sources and low cost, such as cations represented by sodium ions or potassium ions and anions represented by chloride ions, nitrate ions, and thiocyanate ions. At the same time, it is necessary to take into account the common ion effect, and two anions and two cations can be introduced to avoid the influence on the solubility of each component as much as possible, form a synergistic effect, and improve the freeze-thaw cycle stability of the hydrate. Therefore, adding more than one melting point regulator is an effective method to obtain formate materials with high heat of fusion and low melting point.

[0010] Thickeners can increase the viscosity of formate hydrates after melting, reduce the sedimentation of crystal nucleating agents and anhydrous formate, reduce the degree of phase separation, and thus improve the freeze-thaw cycle stability. Soluble polymer thickeners can significantly increase the viscosity of the liquid phase and reduce the degree of phase separation; while insoluble thickeners achieve the effect of physical isolation through physical isolation or hydrogen bond synergy. The soluble polymer thickener is combined with the insoluble thickener to ensure that the formate hydrate achieves long-term freeze-thaw cycle stability.

[0011] Thermally conductive fillers can improve the thermal conductivity of formate hydrates, thereby increasing the storage and release rate of heat. Although metal aluminum and copper have the advantages of high thermal conductivity and low cost, aluminum powder and copper powder are easy to settle, so foamed aluminum, honeycomb aluminum, foamed copper and other forms can avoid sedimentation. Graphite materials are cheap and have high thermal conductivity, and are also widely used as thermally conductive fillers. Therefore, materials such as flake graphite, colloidal graphite, graphene, and expanded graphite can also avoid sedimentation with the assistance of thickeners, ensuring that formate hydrates have high thermal conductivity and long-term stability.

[0012] Preferably, the formate is at least one of sodium formate and potassium formate.

[0013] Preferably, the purity of formate is not less than 95%, more preferably the purity is not less than 98%, further preferably the purity is not less than 99%.

[0014] Preferably, the crystal nucleating agent is at least one of a magnesium salt, a calcium salt and a barium salt having a solubility of less than 5 g / 100 g water.

[0015] Preferably, the crystal nucleating agent is one or more of magnesium carbonate, magnesium hydroxide, magnesium phosphate, calcium carbonate, calcium hydroxide, calcium sulfate, calcium sulfate, calcium silicate, calcium phosphate, barium sulfate, barium carbonate, barium hydroxide, and barium phosphate, and more preferably one of magnesium carbonate, calcium sulfate, and calcium carbonate.

[0016] Preferably, the water of the present invention is municipal water, more preferably softened water, and further preferably deionized water.

[0017] Preferably, the melting point modifier consists of a cation and an anion.

[0018] Preferably, the cation is at least one of a sodium ion or a potassium ion, and the anion is at least one of a chloride ion, a nitrate ion, and a thiocyanate ion.

[0019] Preferably, the melting point regulator is one or more of sodium chloride, potassium chloride, sodium nitrate, potassium nitrate, sodium thiocyanate, and potassium thiocyanate, more preferably one of sodium chloride, sodium nitrate, and sodium thiocyanate, more preferably the purity is not less than 97%, and more preferably the purity is not less than 99%.

[0020] Preferably, the thickener is at least one of polymer resin, white carbon black and attapulgite.

[0021] The thickener of the present invention is preferably a compound of sodium carboxymethyl cellulose and white carbon black, and the purity is not less than 97%, and more preferably not less than 99%.

[0022] Preferably, the polymer resin includes a soluble polymer resin and an insoluble polymer resin.

[0023] Preferably, the soluble polymer resin is at least one of sodium carboxymethyl cellulose, xanthan gum and sodium alginate.

[0024] Preferably, the thermally conductive filler is at least one of flake graphite, colloidal graphite, expanded graphite, graphene, foamed copper, and foamed aluminum.

[0025] The thermally conductive filler of the present invention is preferably expanded graphite, more preferably vermicular graphite, and further preferably expanded graphite having an expansion ratio of 300 to 500 times.

[0026] The second aspect of the present invention provides a method for preparing a salt hydrate that melts at room temperature and a method for preparing the same, comprising the following steps: The thickener is dissolved in water, and a crystal nucleating agent, a melting point regulator, a thermal conductive filler and a formate are added while stirring until the mixture is uniformly stirred to obtain a salt hydrate.

[0027] Therefore, the present invention adopts a room temperature molten salt hydrate and a preparation method thereof of the above structure. The prepared room temperature molten salt hydrate has the advantages of low toxicity, low corrosiveness, non-flammability and high stability, which is conducive to engineering applications.

[0028] The technical solution of the present invention is further described in detail below through embodiments. DETAILED DESCRIPTION

[0029] The present invention will be further described below. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and a specific operation process, but the present invention is not limited to this embodiment.

[0030] The sources and parameters of the experimental materials are shown in Table 1.

[0031] Table 1 Sources and physical properties of experimental materials Element factory parameter Deionized water Commercially available Conductivity <50us / cm Sodium formate Luxi Chemical Purity ≥99% Potassium formate Luxi Chemical Purity ≥99% Precipitated calcium carbonate Commercially available 2000 mesh, purity ≥98% Sodium chloride Commercially available Purity ≥99% Sodium nitrate Commercially available Purity ≥99% CMC Weifang Lite FVH6 Purity ≥99% Meteorological Silica Commercially available <![CDATA[Specific surface area 150~250 m 2 / g]]> Flake Graphite Commercially available 1200 mesh The preparation process of the following examples and comparative examples: Add the thickener into water and stir for 20 to 60 minutes, then add the crystallization nucleating agent, melting point regulator, thermal conductive filler and formate in batches, and stir for 20 to 300 minutes until the material is uniform and there is no stratification, so as to obtain the salt hydrate.

[0032] The salt hydrate compositions of Examples 1-6 are shown in Table 2.

[0033] Performance testing method: The melting point and heat of fusion of the sample were tested using a German NETZSCH Poly-42 DSC, with a heating and cooling rate of 5°C / min. The melting point and heat of fusion were analyzed using the equipment's own software. The test results are shown in Table 2.

[0034] Table 2 Salt hydrate composition and performance test results Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Sodium formate / g 60 40 0 20 30 50 Potassium formate / g 0 0 80 40 35 0 Deionized water / g 40 60 20 40 35 50 CMC / g 10 0 2 0.5 3 4 Fumed silica / g 0 0 1.5 3 0.8 1 Precipitated calcium carbonate / g 0.5 0.5 1.5 2 1.3 1 Sodium chloride / g 0 0 4 12 3 4 Sodium nitrate / g 0 4 4 3 0 0 Potassium thiocyanate / g 0 0 0 4 5 0 Flake graphite / g 20 0 5 10 15 2 total 130.5 100.5 118 135.5 132.3 118 Melting point℃ 26.5 6.2 12 9.6 15.3 21.8 Latent heat of fusion J / g 185.2 153.7 173.2 162.3 178.8 183.5 State after 15 days at room temperature No stratification No stratification No stratification No stratification No stratification No stratification Comparative Example 1 The difference from Example 1 is that the added amount of sodium formate is 100 g.

[0035] Comparative Example 2 The difference from Example 1 is that no thickener CMC is added.

[0036] After the salt hydrates prepared in Comparative Examples 1 and 2 were placed at room temperature for 15 days, stratification occurred. It can be seen from the results that although the formate in the present invention is the main substance that forms a low-melting-point hydrate with water, its content cannot be too high, otherwise it will affect the stable state of the entire salt hydrate that has been formed, and then lead to stratification. In addition, there is a synergistic effect between the thickener and the thermally conductive filler added in the present invention. When the thermally conductive filler flake graphite is added, the thickener must be added, otherwise it is difficult for the thermally conductive filler to obtain a balanced stable state in the salt hydrate, and stratification occurs after being placed for a long time. When the thermally conductive filler and the thickener are added at the same time, the thickener can increase the viscosity of the solution, which is helpful for the construction of a stable system.

[0037] Therefore, the present invention adopts a salt hydrate that melts at room temperature and a preparation method thereof of the above-mentioned structure. The prepared salt hydrate has the advantages of adjustable melting point at room temperature and high latent heat of fusion, and has the advantages of low corrosiveness, non-flammability, high cost performance, etc. It is a new type of heat storage material with obvious application value.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A salt hydrate that melts at room temperature, characterized in that: The salt hydrate comprises the following raw materials in parts by weight: Formate 40~80 parts 20~60 parts water Crystallization nucleating agent 0~5 parts Melting point regulator 0~20 parts Thickener 0~10 parts Thermal conductive filler 0~20 parts.

2. The room temperature molten salt hydrate according to claim 1, characterized in that: The formate is at least one of sodium formate and potassium formate.

3. The room temperature molten salt hydrate according to claim 1, characterized in that: The crystal nucleating agent is at least one of a magnesium salt, a calcium salt and a barium salt having a solubility of less than 5 g / 100 g water.

4. The room temperature molten salt hydrate according to claim 1, characterized in that: Melting point modifiers consist of cations and anions.

5. The room temperature molten salt hydrate according to claim 4, characterized in that: The cation is at least one of a sodium ion or a potassium ion, and the anion is at least one of a chloride ion, a nitrate ion, and a thiocyanate ion.

6. The room temperature molten salt hydrate according to claim 1, characterized in that: The thickener is at least one of polymer resin, white carbon black and attapulgite.

7. The room temperature molten salt hydrate according to claim 6, characterized in that: The polymer resin includes soluble polymer resin and insoluble polymer resin.

8. The room temperature molten salt hydrate according to claim 7, characterized in that: The soluble polymer resin is at least one of sodium carboxymethyl cellulose, xanthan gum and sodium alginate.

9. The room temperature molten salt hydrate according to claim 1, characterized in that: The thermal conductive filler is at least one of flake graphite, colloidal graphite, expanded graphite, graphene, foamed copper, and foamed aluminum.

10. The method for preparing a salt hydrate that melts at room temperature and a method for preparing the same according to any one of claims 1 to 9, characterized in that: The following steps are involved: The thickener is dissolved in water, and a crystal nucleating agent, a melting point regulator, a thermal conductive filler and a formate are added while stirring until the mixture is uniformly stirred to obtain a salt hydrate.