CN108441175B - Lead tungstate shell phase change microcapsule and preparation method thereof - Google Patents
Lead tungstate shell phase change microcapsule and preparation method thereof Download PDFInfo
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- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
- C09K5/02—Materials undergoing a change of physical state when used
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- C09K5/063—Materials absorbing or liberating heat during crystallisation; Heat storage materials
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Abstract
The invention discloses a lead tungstate shell phase change microcapsule and a preparation method thereof, wherein the preparation method comprises the following steps: mixing and emulsifying the phase-change material, citrate, an emulsifier solution and deionized water to obtain a phase-change material emulsion; dripping a lead salt solution into the phase-change material emulsion, stirring, dripping a tungstate solution into the phase-change material emulsion, stirring, and carrying out precipitation reaction on lead salt and tungstate to generate lead tungstate which is deposited on the surface of the phase-change material emulsion drop so as to form a shell for coating the core material; and cooling the reacted system to room temperature, taking out the phase change microcapsule, washing with deionized water, and drying to obtain the lead tungstate shell phase change microcapsule. The lead tungstate shell phase change microcapsule prepared by the invention solves the technical problems of leakage, phase separation and supercooling of a phase change material and low thermal conductivity. Meanwhile, the lead tungstate shell and the paraffin phase-change material have the gamma-ray and neutron shielding capacity, so that the lead tungstate shell phase-change microcapsule has the double functions of phase-change energy storage and radiation protection.
Description
Technical Field
The invention belongs to the technical field of functional materials, relates to a phase change energy storage material and a radiation-proof material, can be widely applied to the aspects of aerospace, textile materials, military and the like, and particularly relates to the technical field of nuclear radiation protection clothes, military buildings and the like which need to shield nuclear radiation and need certain heat storage capacity due to the characteristics of double functions of phase change energy storage and radiation protection.
Background
In recent years, the search for renewable energy has become a concern due to energy shortages and a series of problems caused by the use of fossil fuels. The phase change material is an energy storage material with energy saving and environmental protection, and can absorb or release a large amount of latent heat in the phase change process, thereby attracting people's interest. The organic phase-change material, especially paraffin, can be widely applied to the aspects of spaceflight, buildings, clothes, military affairs and the like due to the advantages of wide phase-change temperature range, strong heat storage capacity and no supercooling. However, since such solid-liquid phase change materials are subject to leakage without treatment and have disadvantages of low thermal conductivity, etc., thereby limiting their commercial applications, it is necessary to coat the phase change materials using a microcapsule technology.
Different types of shells have different application directions, and in recent years, a plurality of reports and technical disclosures on the phase change microcapsule preparation technology of a high molecular organic shell and an inorganic shell are provided. Patent document No. CN106520078A discloses a method for preparing a phase change energy storage microcapsule with inorganic material as wall material, which comprises adding core material stearic acid, emulsifier, calcium chloride and deionized water into a container with inorganic material calcium carbonate as wall material and stearic acid as core material, and stirring to form a stable emulsifying system in the emulsifier; slowly dropwise adding a sodium carbonate solution into an emulsification system to obtain the phase change energy storage microcapsule taking an inorganic material as a wall material. The inorganic wall material phase change microcapsule prepared by the method effectively overcomes the defects of irritation, toxicity and the like of organic wall material reaction monomers, has the characteristics of no toxicity, flame retardance and the like, but has insufficient thermal conductivity and serious leakage problem in the use process.
The reported preparation methods of the phase-change microcapsules do not relate to the phase-change microcapsules which can store energy through phase change and can protect radiation. The organic solid-liquid phase change material is used as a phase change microcapsule core material, has a higher enthalpy value and does not have an supercooling phenomenon. The lead tungstate, as the shell of the phase-change microcapsule, not only protects the core material, increases the thermal conductivity of the material, and solves the problem of low thermal conductivity of the organic phase-change material, but also has the radiation protection effect.
Disclosure of Invention
An object of the present invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
To achieve these objects and other advantages in accordance with the present invention, there is provided a method for preparing lead tungstate shell phase-change microcapsules, comprising the steps of:
step one, mixing 3-6 parts by weight of phase-change material, 1-2 parts by weight of citrate, 25-35 parts by weight of emulsifier solution with the concentration of 1.5-3.5 wt% and 40-50 parts by weight of deionized water, melting into a liquid core material in a constant-temperature water bath at the temperature of 60-80 ℃, and emulsifying to obtain phase-change material emulsion;
step two, according to parts by weight, 60-70 parts of lead salt solution with the mass fraction of 6-7% is dripped into phase-change material emulsion with the temperature of 60-80 ℃, the phase-change material emulsion is stirred for 2-5 hours at the rotating speed of 600-900 r/min, then 55-65 parts of tungstate solution with the mass fraction of 5-6% is dripped into the phase-change material emulsion, the phase-change material emulsion is stirred for 6-9 hours at the rotating speed of 200-400 r/min, lead salt and tungstate are generated through precipitation reaction, lead tungstate is deposited on the surface of phase-change material emulsion droplets, and a shell for coating a core material is formed;
and step three, cooling the system reacted in the step two to room temperature, taking out the phase change microcapsule, washing with deionized water, and drying to obtain the lead tungstate shell phase change microcapsule.
Preferably, the phase change material is an organic solid-liquid phase change material, which comprises one or more of alkane, fatty acid and fatty acid ester.
Preferably, the organic solid-liquid phase change material is paraffin or stearic acid.
Preferably, the emulsifier solution is one or a combination of more of styrene-maleic anhydride copolymer, sodium dodecyl sulfate, sodium dodecyl benzene sulfonate and stearic acid solution; the citrate is any one of sodium citrate, calcium citrate, zinc citrate and potassium citrate.
Preferably, in the first step, the emulsification conditions are as follows: emulsifying by using a high-shear emulsifying machine, wherein the rotating speed of the high-shear emulsifying machine is 5000-20000 r/min, and the time is 1-10 min; in the second step, the speed of dripping the lead salt solution into the phase-change material emulsion is 0.01-0.03 mL/s; the speed of dropping the tungstate solution into the phase-change material emulsion is 0.003-0.008 mL/s.
Preferably, the lead salt solution is any one of a lead acetate solution, a lead nitrate solution and a lead chloride solution.
Preferably, the tungstate solution is any one of a sodium tungstate solution, an ammonium tungstate solution and a calcium tungstate solution.
Preferably, the process in the second step is replaced by: according to the weight parts, 100-120 parts of lead salt solution with the mass fraction of 3.5-4.5% is dripped into phase change material emulsion with the temperature of 60-80 ℃, the phase change material emulsion is stirred for 2-5 hours at the rotating speed of 600-900 r/min, then the phase change material emulsion is placed into a container with a stainless steel spray head in an electrostatic spraying device, voltage is applied to the stainless steel spray head by adopting a high-voltage power supply, the phase change material emulsion is sprayed into a receiving device containing 55-65 parts of tungstate solution with the mass fraction of 5-6%, the phase change material emulsion is stirred for 3-5 hours at the rotating speed of 200-400 r/min, lead tungstate generated by precipitation reaction of the lead tungstate is deposited on the surface of phase change material emulsion droplets, and a shell for coating a core material is formed; the spraying conditions of the electric spraying device are as follows: the environment temperature is 50-60 ℃, the distance between the receiving device and the spray head is 5-10 cm, the flow is 10-20 mL/h, the voltage is 5-10 kV, and the inner diameter of the stainless steel spray head is 0.8-1.6 mm.
Preferably, the method further comprises the steps of introducing nitrogen into the tungstate solution in the receiving device; the aeration rate of the nitrogen is 100-150 mL/min; adding the system obtained after the reaction in the second step into a stainless steel spherical container, simultaneously adding equivalent deionized water, then placing the spherical container on a four-axis grinding instrument, starting the four-axis grinding instrument, driving the stainless steel spherical container to randomly rotate for 30-45 min, then taking out the phase-change microcapsules, washing with deionized water, and drying to obtain lead tungstate shell phase-change microcapsules; the feed inlet of the stainless steel spherical container is sealed by a threaded cover, and the threaded cover is flush with the surface of the stainless steel spherical container after being connected in a sealing way; the rotating shaft rotating speed of the four-shaft grinding instrument is 100-150 rpm, and the random conversion frequency is 30-60 s.
The invention also provides the lead tungstate shell phase change microcapsule prepared by the preparation method, which takes the organic solid-liquid phase change material as a core material and the lead tungstate as a wall material and has the functions of phase change energy storage and radiation protection.
In the second step of the invention, a lead acetate solution with cations is added into the phase-change material emulsion to ensure that free lead ions and phase-change material emulsion drops are combined together under the electrostatic action, and the solution is continuously stirred in the process; and then dropwise adding sodium tungstate solution which can generate precipitation with lead ions, wherein the stirring speed is properly reduced in the process, so that lead tungstate particles generated by reaction can be uniformly deposited on the phase-change material emulsion drops.
The invention takes lead tungstate material as wall material, organic solid-liquid phase change material as core material, anion emulsifier emulsifies and surrounds the core material, and Pb in added lead acetate2+Because the positively charged particles are adsorbed around the emulsifier by the coulomb attraction, sodium tungstate, WO4 2-With Pb2+Reaction to form PbWO4And depositing the lead tungstate on the surface of the core material to prepare the phase change energy storage microcapsule taking the lead tungstate as the wall material.
The citrate of the present invention serves to stabilize the pH so that lead tungstate crystals do not form too quickly.
The invention at least comprises the following beneficial effects: the phase-change microcapsule of the lead tungstate shell prepared by the preparation method of the phase-change microcapsule adopts the inorganic material lead tungstate which is environment-friendly, non-toxic, low in cost and good in heat conductivity as the wall material and the organic solid-liquid phase-change material as the core material, so that the technical problems of leakage, phase separation and supercooling of the phase-change material and low heat conductivity are solved. Meanwhile, the lead tungstate shell and the paraffin phase-change material have the gamma-ray and neutron shielding capacity, so that the lead tungstate shell phase-change microcapsule has the double functions of phase-change energy storage and radiation protection.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Description of the drawings:
FIG. 1 shows the mass attenuation coefficients of phase change microcapsules prepared in embodiments 2 to 4 of the present invention under different gamma radiation energies;
FIG. 2 is a scanning electron micrograph of a phase change microcapsule prepared in example 1 of the present invention;
FIG. 3 is a thermal analysis curve of phase-change microcapsules prepared in example 2 of the present invention;
FIG. 4 is a leakage rate experimental curve of the phase change microcapsules prepared in embodiments 2-4 of the present invention.
The specific implementation mode is as follows:
the present invention is further described in detail below with reference to the attached drawings so that those skilled in the art can implement the invention by referring to the description text.
It will be understood that terms such as "having," "including," and "comprising," as used herein, do not preclude the presence or addition of one or more other elements or groups thereof.
Example 1:
a preparation method of lead tungstate shell phase change microcapsules comprises the following steps:
step one, mixing 5g of stearic acid, 1.6g of sodium citrate, 32mL of 2 wt% anionic surfactant styrene-maleic anhydride copolymer solution and 40mL of deionized water, melting into a liquid core material in a 70 ℃ constant-temperature water bath, and emulsifying by using a high-shear emulsifying machine at the rotating speed of 10000r/min for 3min to obtain a phase-change material emulsion;
step two, respectively adding 60mL of deionized water into 4.17g of lead acetate and 3.62g of sodium tungstate to dissolve the lead acetate and the sodium tungstate into solutions, dripping the lead acetate solution into the phase-change material emulsion at 70 ℃, stirring the solution for 3 hours at the rotating speed of 800r/min, then dripping the sodium tungstate solution into the phase-change material emulsion at the speed of 0.005mL/s, stirring the emulsion for 8 hours at the rotating speed of 300r/min, and generating lead tungstate through precipitation reaction to deposit on the surface of the phase-change material emulsion droplets to form a shell for coating the core material;
step three, cooling the system reacted in the step two to room temperature, taking out the phase change microcapsule, washing with deionized water, and drying at 40 ℃ to obtain the lead tungstate shell phase change microcapsule;
the leakage rate of the phase change microcapsule prepared in the embodiment is 6.12% in 1200min of the experiment; fig. 2 shows a scanning electron micrograph of the phase-change microcapsules prepared in this example.
Example 2:
a preparation method of lead tungstate shell phase change microcapsules comprises the following steps:
mixing 5g of paraffin, 1.6g of sodium citrate, 32mL of 2 wt% anionic surfactant styrene-maleic anhydride copolymer solution and 40mL of deionized water, dissolving the mixture into a liquid core material in a 70 ℃ constant-temperature water bath, and emulsifying the liquid core material by using a high-shear emulsifying machine at the rotating speed of 10000r/min for 3min to obtain a phase-change material emulsion;
step two, respectively adding 60mL of deionized water into 4.17g of lead acetate and 3.62g of sodium tungstate to dissolve the lead acetate and the sodium tungstate into solutions, dripping the lead acetate solution into the phase-change material emulsion at 70 ℃, stirring the solution for 3 hours at the rotating speed of 800r/min, then dripping the sodium tungstate solution into the phase-change material emulsion at the speed of 0.005mL/s, stirring the emulsion for 8 hours at the rotating speed of 300r/min, and generating lead tungstate through precipitation reaction to deposit on the surface of the phase-change material emulsion droplets to form a shell for coating the core material;
step three, cooling the system reacted in the step two to room temperature, taking out the phase change microcapsule, washing with deionized water, and drying at 40 ℃ to obtain the lead tungstate shell phase change microcapsule; the phase change microcapsules prepared in this example were measured by differential scanning calorimetry and, as shown in FIG. 3, had a latent heat value of 80.64J/g and a phase change temperature of 43.13 ℃.
Example 3:
a preparation method of lead tungstate shell phase change microcapsules comprises the following steps:
mixing 5g of paraffin, 1.6g of sodium citrate, 32mL of 2 wt% anionic surfactant styrene-maleic anhydride copolymer solution and 40mL of deionized water, dissolving the mixture into a liquid core material in a 70 ℃ constant-temperature water bath, and emulsifying the liquid core material by using a high-shear emulsifying machine at the rotating speed of 10000r/min for 3min to obtain a phase-change material emulsion;
step two, respectively adding 60mL of deionized water into 2.37g of lead acetate and 1.82g of sodium tungstate to dissolve the lead acetate and the sodium tungstate into solutions, dripping the lead acetate solution into the phase-change material emulsion at 70 ℃, stirring the solution for 3 hours at the rotating speed of 800r/min, then dripping the sodium tungstate solution into the phase-change material emulsion at the speed of 0.005mL/s, stirring the emulsion for 8 hours at the rotating speed of 300r/min, and generating lead tungstate through precipitation reaction to deposit on the surface of the phase-change material emulsion droplets to form a shell for coating the core material;
and step three, cooling the system reacted in the step two to room temperature, taking out the phase change microcapsule, washing with deionized water, and drying at 40 ℃ to obtain the lead tungstate shell phase change microcapsule.
Example 4:
a preparation method of lead tungstate shell phase change microcapsules comprises the following steps:
mixing 5g of paraffin, 1.6g of sodium citrate, 32mL of 2 wt% anionic surfactant styrene-maleic anhydride copolymer solution and 40mL of deionized water, dissolving the mixture into a liquid core material in a 70 ℃ constant-temperature water bath, and emulsifying the liquid core material by using a high-shear emulsifying machine at the rotating speed of 10000r/min for 3min to obtain a phase-change material emulsion;
step two, respectively adding 60mL of deionized water into 7.79g of lead acetate and 7.24g of sodium tungstate to dissolve the lead acetate and the sodium tungstate into solutions, dripping the lead acetate solution into the phase-change material emulsion at 70 ℃, stirring the solution for 3 hours at the rotating speed of 800r/min, then dripping the sodium tungstate solution into the phase-change material emulsion at the speed of 0.005mL/s, stirring the emulsion for 8 hours at the rotating speed of 300r/min, and generating lead tungstate through precipitation reaction to deposit on the surface of the phase-change material emulsion droplets to form a shell for coating the core material;
and step three, cooling the system reacted in the step two to room temperature, taking out the phase change microcapsule, washing with deionized water, and drying at 40 ℃ to obtain the lead tungstate shell phase change microcapsule.
Example 5:
a preparation method of lead tungstate shell phase change microcapsules comprises the following steps:
mixing 5g of paraffin, 1.6g of potassium citrate, 35mL of 2 wt% anionic surfactant sodium dodecyl benzene sulfonate solution and 40mL of deionized water, dissolving the mixture into a liquid core material in a 70 ℃ constant-temperature water bath, and emulsifying the liquid core material by using a high-shear emulsifying machine at the rotating speed of 10000r/min for 3min to obtain a phase-change material emulsion;
step two, respectively adding 60mL of deionized water into 4.17g of lead acetate and 3.62g of sodium tungstate to dissolve the lead acetate and the sodium tungstate into solutions, dripping the lead acetate solution into the phase-change material emulsion at 70 ℃, stirring the solution for 3 hours at the rotating speed of 800r/min, then dripping the sodium tungstate solution into the phase-change material emulsion at the speed of 0.005mL/s, stirring the emulsion for 8 hours at the rotating speed of 300r/min, and generating lead tungstate through precipitation reaction to deposit on the surface of the phase-change material emulsion droplets to form a shell for coating the core material;
and step three, cooling the system reacted in the step two to room temperature, taking out the phase change microcapsule, washing with deionized water, and drying at 40 ℃ to obtain the lead tungstate shell phase change microcapsule.
The phase change microcapsules prepared in this example had a leakage rate of 5.28% at 1200min of the experiment.
Example 6:
a preparation method of lead tungstate shell phase change microcapsules comprises the following steps:
mixing 5g of paraffin, 1.6g of zinc citrate, 30mL of 3 wt% anionic surfactant lauryl sodium sulfate solution and 40mL of deionized water, dissolving the mixture into a liquid core material in a 70 ℃ constant-temperature water bath, and emulsifying the liquid core material by using a high-shear emulsifying machine at the rotating speed of 10000r/min for 3min to obtain a phase-change material emulsion;
step two, respectively adding 60mL of deionized water into 4.17g of lead acetate and 3.62g of sodium tungstate to dissolve the lead acetate and the sodium tungstate into solutions, dripping the lead acetate solution into the phase-change material emulsion at 70 ℃, stirring the solution for 3 hours at the rotating speed of 800r/min, then dripping the sodium tungstate solution into the phase-change material emulsion at the speed of 0.005mL/s, stirring the emulsion for 8 hours at the rotating speed of 300r/min, and generating lead tungstate through precipitation reaction to deposit on the surface of the phase-change material emulsion droplets to form a shell for coating the core material;
and step three, cooling the system reacted in the step two to room temperature, taking out the phase change microcapsule, washing with deionized water, and drying at 40 ℃ to obtain the lead tungstate shell phase change microcapsule.
The phase change microcapsules prepared in this example had a leakage rate of 5.58% at 1200min of the experiment.
Example 7:
the process in the second step is replaced by: adding 7.79g of lead acetate into 100mL of deionized water to be dissolved into a solution, then dripping the lead acetate solution into a phase-change material emulsion at 70 ℃ at the speed of 0.02mL/s, stirring for 3 hours at the rotating speed of 800r/min, then placing the phase-change material emulsion into a container with a stainless steel spray head in an electrostatic spraying device, applying voltage to the stainless steel spray head by adopting a high-voltage power supply, spraying the phase-change material emulsion into a receiving device containing sodium tungstate solution, stirring for 5 hours at the rotating speed of 300r/min, and generating lead tungstate through a precipitation reaction to deposit on the surface of the phase-change material emulsion drop to form a shell for coating a core material; the spraying conditions of the electric spraying device are as follows: the environment temperature is 60 ℃, the distance between the receiving device and the spray head is 10cm, the flow is 15mL/h, the voltage is 8kV, and the inner diameter of the stainless steel spray head is 1.2 mm; the sodium tungstate solution is prepared by adding 7.24g of sodium tungstate into 60mL of deionized water; the electrostatic spraying device is adopted to prepare the phase-change microcapsule, so that the surface acting force of the wall material deposited and loaded on the core material is further enhanced, and the leakage rate of the prepared phase-change microcapsule is reduced.
The remaining process parameters and procedures were exactly the same as in example 4.
The phase change microcapsules prepared in this example had a leakage rate of 3.25% at 1200min of the experiment.
Example 8:
the process in the second step is replaced by: adding 7.79g of lead acetate into 100mL of deionized water to be dissolved into a solution, then dripping the lead acetate solution into a phase-change material emulsion at 70 ℃ at the speed of 0.03mL/s, stirring for 3 hours at the rotating speed of 800r/min, then placing the phase-change material emulsion into a container with a stainless steel spray head in an electrostatic spraying device, applying voltage to the stainless steel spray head by adopting a high-voltage power supply, spraying the phase-change material emulsion into a receiving device containing sodium tungstate solution, stirring for 5 hours at the rotating speed of 300r/min, and generating lead tungstate through a precipitation reaction to deposit on the surface of the phase-change material emulsion drop to form a shell for coating a core material; the spraying conditions of the electric spraying device are as follows: the environment temperature is 50 ℃, the distance between the receiving device and the spray head is 5cm, the flow is 10mL/h, the voltage is 10kV, and the inner diameter of the stainless steel spray head is 1.2 mm; the sodium tungstate solution is prepared by adding 7.24g of sodium tungstate into 60mL of deionized water;
the remaining process parameters and procedures were exactly the same as in example 4.
The phase change microcapsules prepared in this example had a leakage rate of 3.18% at 1200min of the experiment.
Example 9:
introducing nitrogen into the tungstate solution of the receiving device; the aeration rate of the nitrogen is 100 mL/min; the process of the third step is as follows: adding the system obtained after the reaction in the second step into a stainless steel spherical container, simultaneously adding equivalent deionized water, then placing the spherical container on a four-axis grinding instrument, starting the four-axis grinding instrument, driving the stainless steel spherical container to randomly rotate for 45min, then taking out the phase-change microcapsules, washing with deionized water, and drying to obtain lead tungstate shell phase-change microcapsules; the feed inlet of the stainless steel spherical container is sealed by a threaded cover, and the threaded cover is flush with the surface of the stainless steel spherical container after being connected in a sealing way; the rotating speed of the rotating shaft of the four-shaft grinding instrument is 100rpm, and the random conversion frequency is 30 s. The method overcomes the problem of fixed orientation of the traditional flow field, realizes the rotation and solidification without fixed orientation, greatly increases the concentricity power of the phase-change microcapsule, reduces the non-sphericity generated by an external flow field, increases the sphericity degree of the phase-change microcapsule, and further reduces the leakage rate of the prepared phase-change microcapsule.
The remaining process parameters and procedures were exactly the same as in example 7.
The phase change microcapsules prepared in this example had a leakage rate of 2.45% at 1200min of the experiment.
Example 10:
introducing nitrogen into the tungstate solution of the receiving device; the aeration rate of the nitrogen is 120 mL/min; the process of the third step is as follows: adding the system obtained after the reaction in the second step into a stainless steel spherical container, simultaneously adding equivalent deionized water, then placing the spherical container on a four-axis grinding instrument, starting the four-axis grinding instrument, driving the stainless steel spherical container to randomly rotate for 30min, then taking out the phase-change microcapsules, washing with deionized water, and drying to obtain lead tungstate shell phase-change microcapsules; the feed inlet of the stainless steel spherical container is sealed by a threaded cover, and the threaded cover is flush with the surface of the stainless steel spherical container after being connected in a sealing way; the rotating speed of the rotating shaft of the four-shaft grinding instrument is 120rpm, and the random conversion frequency is 60 s.
The rest of the process parameters and procedures were exactly the same as in example 8, and the leakage rate of the phase-change microcapsules prepared in this example was 2.32% at 1200min of the experiment.
The lead tungstate shell phase change microcapsules prepared in embodiments 2-4 are adopted to perform gamma ray shielding tests, and a high-purity germanium gamma spectrometer with two gamma radiation sources is adopted to determine gamma radiation shielding absorption, wherein the gamma radiation sources comprise mixed Eu-155And Na-22(E.about.86 keV, 105keV, 511keV and 1274 keV). The attenuation behavior of high-energy photons can be simply expressed by the following equation: i (t) ═ I0e-μmρtWherein I (t) and I0The intensity of transmitted and incident radiation, respectively, μm is the mass attenuation coefficient dependent on energy and material, and ρ is the bulk density (g/cm) of the composite material3) And t is the thickness (cm) of the composite, table 1 and fig. 1 show the mass attenuation coefficient of each sample at different gamma ray radiation energies;
TABLE 1
| Examples | Example 1 | Example 2 | Example 3 |
| Energy (MeV) | μ | μ | μ |
| 0.086 | 5.966274 | 2.710287 | 1.862252 |
| 0.105 | 10.70214 | 7.127126 | 5.483841 |
| 0.51 | 0.175162 | 0.270322 | 0.208931 |
| 1.274 | 0.018975 | 0.03741 | 0.17386 |
The mass attenuation coefficient is an important parameter for describing the attenuation coefficient of gamma rays. As can be seen from table 1, at low energy, each sample showed a higher mass attenuation coefficient, i.e., the gamma ray shielding performance at low energy was better, and increased as the proportion of lead tungstate shell in the microcapsule increased; this is related to the mass fraction of lead tungstate in the microcapsules; but at high energy gamma rays, the attenuation ratio is poor, i.e. the shielding performance to gamma rays is poor.
And (3) carrying out a leakage rate test experiment on the phase-change microcapsules prepared in the embodiments 2 to 4, wherein the leakage rate test experiment is carried out in a vacuum drying oven, 3 samples are taken from each formula, weighed and used as initial mass, then the samples are placed in the vacuum drying oven for a period of time, taken out, wiped to dry surface paraffin, cooled to room temperature and weighed, and the repeated test is carried out to calculate the leakage rate of the phase-change microcapsules. The test results of the leakage rate are shown in table 2 and fig. 4, and it can be seen that the leakage rate of the phase-change microcapsules prepared in embodiments 2 to 4 of the present invention is gradually stable after 300min, and the leakage rate of the phase-change microcapsules prepared in embodiment 2 is 6.16% at 1200 min; the leakage rate of the phase change microcapsule prepared in example 3 is 7.29%; the phase change microcapsule prepared in example 4 had a leakage rate of 4.74%.
TABLE 2
While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable in various fields of endeavor to which the invention pertains, and further modifications may readily be made by those skilled in the art, it being understood that the invention is not limited to the details shown and described herein without departing from the general concept defined by the appended claims and their equivalents.
Claims (4)
1. A preparation method of lead tungstate shell phase change microcapsules is characterized by comprising the following steps:
mixing 3-6 parts by weight of phase-change material, 1-2 parts by weight of citrate, 25-35 parts by weight of emulsifier solution with the concentration of 1.5-3.5 wt% and 40-50 parts by weight of deionized water, forming a liquid core material in a constant-temperature water bath at the temperature of 60-80 ℃, and emulsifying to obtain a phase-change material emulsion;
step two, according to parts by weight, 60-70 parts of lead salt solution with the mass fraction of 6-7% is dripped into phase-change material emulsion with the temperature of 60-80 ℃, the phase-change material emulsion is stirred for 2-5 hours at the rotating speed of 600-900 r/min, then 55-65 parts of tungstate solution with the mass fraction of 5-6% is dripped into the phase-change material emulsion, the phase-change material emulsion is stirred for 6-9 hours at the rotating speed of 200-400 r/min, lead salt and tungstate are generated through precipitation reaction, lead tungstate is deposited on the surface of phase-change material emulsion droplets, and a shell for coating a core material is formed;
step three, cooling the system reacted in the step two to room temperature, taking out the phase change microcapsule, washing with deionized water, and drying to obtain the lead tungstate shell phase change microcapsule;
the phase change material is an organic solid-liquid phase change material; the organic solid-liquid phase change material is paraffin or stearic acid;
the emulsifier solution is one or a combination of more of styrene-maleic anhydride copolymer, sodium dodecyl sulfate, sodium dodecyl benzene sulfonate and stearic acid solution; the citrate is any one of sodium citrate, calcium citrate, zinc citrate and potassium citrate;
in the first step, the emulsification conditions are as follows: emulsifying by using a high-shear emulsifying machine, wherein the rotating speed of the high-shear emulsifying machine is 5000-20000 r/min, and the time is 1-10 min; in the second step, the speed of dripping the lead salt solution into the phase-change material emulsion is 0.01-0.03 mL/s; the speed of dripping the tungstate solution into the phase-change material emulsion is 0.003-0.008 mL/s;
the lead salt solution is any one of a lead acetate solution, a lead nitrate solution and a lead chloride solution;
the tungstate solution is any one of sodium tungstate solution, ammonium tungstate solution and calcium tungstate solution.
2. The method for preparing lead tungstate shell phase change microcapsules according to claim 1, wherein the process in the second step is replaced by: according to the weight parts, 100-120 parts of lead salt solution with the mass fraction of 3.5-4.5% is dripped into phase change material emulsion with the temperature of 60-80 ℃, the phase change material emulsion is stirred for 2-5 hours at the rotating speed of 600-900 r/min, then the phase change material emulsion is placed into a container with a stainless steel spray head in an electrostatic spraying device, voltage is applied to the stainless steel spray head by adopting a high-voltage power supply, the phase change material emulsion is sprayed into a receiving device containing 55-65 parts of tungstate solution with the mass fraction of 5-6%, the phase change material emulsion is stirred for 3-5 hours at the rotating speed of 200-400 r/min, lead tungstate generated by precipitation reaction of the lead tungstate is deposited on the surface of phase change material emulsion droplets, and a shell for coating a core material is formed; the spraying conditions of the electric spraying device are as follows: the environment temperature is 50-60 ℃, the distance between the receiving device and the spray head is 5-10 cm, the flow is 10-20 mL/h, the voltage is 5-10 kV, and the inner diameter of the stainless steel spray head is 0.8-1.6 mm.
3. The method for preparing lead tungstate shell phase change microcapsules as claimed in claim 2, further comprising introducing nitrogen into the tungstate solution in the receiving device; the aeration rate of the nitrogen is 100-150 mL/min; adding the system obtained after the reaction in the second step into a stainless steel spherical container, simultaneously adding equivalent deionized water, then placing the spherical container on a four-axis grinding instrument, starting the four-axis grinding instrument, driving the stainless steel spherical container to randomly rotate for 30-45 min, then taking out the phase-change microcapsules, washing with deionized water, and drying to obtain lead tungstate shell phase-change microcapsules; the feed inlet of the stainless steel spherical container is sealed by a threaded cover, and the threaded cover is flush with the surface of the stainless steel spherical container after being connected in a sealing way; the rotating shaft rotating speed of the four-shaft grinding instrument is 100-150 rpm, and the random conversion frequency is 30-60 s.
4. The lead tungstate shell phase change microcapsule prepared by the preparation method according to any one of claims 1 to 3, wherein the lead tungstate shell phase change microcapsule takes an organic solid-liquid phase change material as a core material and lead tungstate as a wall material, and has the functions of phase change energy storage and radiation protection.
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| CN112126414B (en) * | 2020-10-12 | 2021-06-25 | 西南科技大学 | Method for preparing phase-change microcapsule by hydrothermal method |
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