CN118289820A - Preparation of magnetic Fe by fused salt electro-deoxidation3O4Is a method of (2) - Google Patents
Preparation of magnetic Fe by fused salt electro-deoxidation3O4Is a method of (2) Download PDFInfo
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Abstract
The invention belongs to the technical field of nano catalysts, and discloses a method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation, which comprises the steps of uniformly mixing Fe 2O3 serving as a raw material with a pore-forming agent and a conductive agent, performing compression sintering to prepare a cathode plate, taking a solid oxide after tablet sintering as a cathode and graphite as an anode. Compared with the prior art, the method is more environment-friendly, simple in process, lower in cost, suitable for large-scale production and higher in purity of produced Fe 3O4.
Description
Technical Field
The invention belongs to the technical field of nano catalysts, and particularly relates to a method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation.
Background
With the continuous development of nano-catalysts, multifunctional composite materials based on nano-ferroferric oxide are receiving a great deal of attention in terms of their efficient catalytic performance, wherein nano-particles represented by ferroferric oxide have been widely used in the catalyst field because of their strong adsorption performance, specific surface area and other characteristics. Over the past decades, many studies have been devoted to the search for efficient synthesis of magnetic ferroferric oxide in an attempt to effectively control its structure and properties. The current methods for preparing the magnetic Fe 3O4 material include coprecipitation method, solvothermal/decomposition method, sol-gel method, microemulsion method and the like. The coprecipitation method is a method of adding a precipitant into a solution containing two or more cations, and completely precipitating all ions at room temperature or high temperature, and has the advantages of low cost, simple operation and short reaction time, but the nucleation and crystallization processes are difficult to separate due to the rapid coprecipitation reaction speed and slow crystal growth process after explosive nucleation, and the dispersibility of the synthetic material is poor; solvothermal/decomposition is synthesized in a sealed pressure vessel with liquid as solvent under high temperature and high pressure anaerobic conditions, and because solvothermal reaction is performed at relatively high temperature and pressure, the cost is relatively high although the solvothermal reaction is studied in a laboratory, and the solvothermal reaction still has difficulty in being applied to large-scale sewage treatment; the ferroferric oxide nano particles prepared by the sol-gel method have small particle size and uniform distribution, but part of raw materials used by the ferroferric oxide nano particles are expensive and are toxic and harmful substances, so that the ferroferric oxide nano particles are easy to cause harm to human bodies, and the ferroferric oxide nano particles are protected during preparation; the microemulsion method has the advantages of short reaction time, uniform particle size of the formed particles, good stability, difficult agglomeration, high yield, suitability for industrial mass production, and imperfect process.
Therefore, it is necessary to develop a method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation to solve the problems of pollution, high cost, difficult mass production and the like of the existing method.
Disclosure of Invention
The invention aims to provide a method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation.
The technical scheme of the invention is as follows:
A method of preparing magnetic Fe 3O4 using molten salt electro-deoxidation, the method comprising:
(1) Fully and uniformly mixing Fe 2O3, a pore-forming agent and a conductive agent to obtain a mixture, and performing compression molding on the mixture to obtain a mixture tablet;
(2) Tabletting the mixture and sintering under a protective atmosphere to obtain a sintered tablet;
(3) Wrapping the sintered sheet and the molybdenum strip by using a stainless steel net, winding by using an iron wire and a stainless steel rod to form a cathode, taking a stone mill rod as an anode, inserting the stone mill rod into an electrolytic tank filled with chloride molten salt for electro-deoxidation, introducing protective gas in the electro-deoxidation process, taking out an electrolysis product after the electro-deoxidation is finished, and removing the molten salt attached to the surface to obtain solid Fe 3O4.
Further, in the step (1), the mass ratio of Fe 2O3, the pore-forming agent and the conductive agent is 1:0.02:0.06.
Further, in the step (1), the pore-forming agent is NH 4HCO3, the conductive agent is metal iron powder, and the purities of NH 4HCO3 and Fe 2O3 are both greater than 99%.
Further, in the step (1), the pressure of the press molding is 10MPa.
Further, in the step (2), the gas of the protective atmosphere is Ar.
Further, in the step (2), the sintering temperature is 800-900 ℃ and the sintering time is 2-7h.
Further, in the step (3), the length of the molybdenum bar is 30mm, the width is 2mm, the thickness is 0.5mm, and the purity of the molybdenum bar is more than or equal to 99.9%.
Further, in the step (3), the stainless steel mesh is 400 mesh, the diameter of the iron wire is 0.1mm, and the diameter of the stainless steel bar is 5mm.
Further, in the step (3), the electrolysis temperature of the electro-deoxidation is 680-722 ℃, the electrolysis voltage is 2.6-3.2V, the electrolysis time is 2-8h, and the protective gas is Ar.
Further, in the step (3), the chloride molten salt is NaCl and CaCl 2, and the molar ratio of NaCl to CaCl 2 is 0.22-0.48:0.52-0.78.
The invention provides a method for preparing magnetic Fe3O4 by using molten salt electro-deoxidation, which has the following advantages:
1. According to the method, fe 2O3 is directly taken as a raw material, uniformly mixed with a pore-forming agent and a conductive agent, pressed and sintered to prepare a cathode, and then electro-deoxidized in molten salt to obtain solid Fe 3O4, so that the complex treatment procedure in the conventional coprecipitation method is omitted, and the process flow of magnetic Fe 3O4 production is greatly simplified;
2. the anode gas generated by the method is O2 instead of Cl2 generated in the conventional chloride electrolysis, so that toxic and harmful substances and the like are not generated, a series of waste pollution problems caused by the toxic and harmful substances are avoided, and the method is a green preparation method;
3. The molten salt adopted by the method has good stability, good conductivity, low solubility to products, high current efficiency in the production process, and higher economic benefit because redundant treatment procedures of the traditional method are omitted;
4. the method can lead the purity of the obtained product magnetic Fe 3O4 to reach more than 98 percent by controlling the cathode performance of Fe 2O3 and the electro-deoxidation process.
Drawings
FIG. 1 is a photograph and XRD spectrum of an electrolytic product of different voltages prepared by a method for preparing magnetic Fe 3O4 by electro-deoxidation of molten salt according to the present invention.
Detailed Description
The invention designs a method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation, which takes Fe 2O3 as a raw material, uniformly mixes the Fe 2O3 with a pore-forming agent and a conductive agent, then carries out pressing and sintering to prepare a cathode plate, takes a solid oxide after tabletting and sintering as a cathode and takes graphite (or an inert material) as an anode. Electrolysis is carried out at a temperature below the melting point of the metal and below the decomposition voltage of the molten salt, the cathodic metal oxide is reduced to a metal or alloy, and O 2- is discharged through the CaCl 2 molten salt to the anode, producing O 2 (inert anode) or CO and CO 2 gases (graphite anode), comprising the steps of:
1. Fe 2O3 is taken as a raw material, and the raw material, a pore-forming agent (NH 4HCO3) and a conductive agent (metal iron powder) are mixed according to the mass ratio of 1:0.02: mixing the materials in a proportion of 0.06, and pressing the mixture into mixture tablets under the condition of 10 MPa.
In this step, the purity of Fe 2O3、NH4HCO3 is 99% or more.
2. Tabletting the mixture, and sintering for 2-7 hours under the condition of 800-900 ℃ in a protective atmosphere Ar to obtain a sintered tablet.
3. Wrapping sintered sheets and molybdenum strips (30 mm long by 2mm wide by 0.5mm thick, purity is more than or equal to 99.9%) with 400 mesh stainless steel mesh, winding iron wires with diameters of 0.1mm and stainless steel rods with diameters of 5mm to form a cathode, taking a stone grinding rod as an anode, inserting the anode into an electrolytic tank containing chloride molten salt (molar ratio of NaCl to CaCl 2 is 0.22-0.48:0.52-0.78), carrying out electro-deoxidation for 2-8h at the temperature of 680-722 ℃ and the voltage of 2.6-3.2V, introducing protective gas Ar in the electrolytic process, taking out electrolytic products and removing the molten salt attached to the surface after the electrolytic process is finished, thus obtaining solid Fe 3O4.
Referring to fig. 1, fig. 1 is a photograph and XRD spectrum of an electrolytic product of different voltages obtained by a method for preparing magnetic Fe 3O4 by electro-deoxidation of molten salt according to the present invention. The microstructure of Fe 2O3 after sintering was analyzed by SEM and the phase composition of the product before and after electrolysis was analyzed by XRD. As shown in fig. 1, at voltages of 3.2-3.0V, only Fe peaks appear in the XRD pattern, indicating that at voltages in this range the electrolysis product is Fe; whereas between 2.6-2.8V the product became Fe 3O4 and FeO, wherein the peak of Fe 3O4 in the spectrum was stronger when the voltage was 2.6V, which also suggests that the purity of the electrolytic product Fe 3O4 at this time was higher. The samples after different voltages are electrolyzed are shown in figure 1, and when the voltages are 3.0V and 3.2V, the surfaces are metallic luster, which further indicates that metallic Fe is generated; when the voltage is 2.8V, the polished surface has slight metallic luster; at a voltage of 2.6V the sample was substantially black, indicating that Fe 3O4 was formed. Therefore, the higher the cell voltage applied during electrolysis, the more the electrolysis product becomes Fe, indicating that as the cell voltage increases, the lower the electrolysis efficiency of the target product, thus optimizing the process conditions for preparing magnetic Fe 3O4 by molten salt electro-deoxidation: the electrolysis time is 8 hours, the sintering temperature is 800-900 ℃, the binder consumption is 1.0-2.5%, and when the electrolysis temperature is 680-722 ℃, 2.6V is selected as the optimal cell voltage.
In order to make the above objects, features and advantages of the present invention more comprehensible, the following embodiments accompanied with examples are further described. The invention is not limited to the embodiments listed but includes any other known modification within the scope of the claims that follow.
Reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic may be included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.
Example 1, this embodiment shows a method for preparing magnetic Fe 3O4 by electro-deoxidation using molten salt as follows:
(1) Taking Fe 2O3 as a raw material, adding 30g of Fe 2O3、0.6g NH4HCO3 and 1.8g of iron powder into a planetary ball mill for ball milling at a rotating speed of 160 r.min -1 for 60min; and screening by using a 200-mesh sieve to obtain uniform mixture powder, weighing 1g of the uniform mixture powder, placing the mixture powder into a stainless steel cylindrical die with phi=15 mm, maintaining the pressure for 5min under the apparent pressure of 10MPa to enable the oxide powder to be rearranged and elastoplastically deformed and the particles to be meshed with each other, enabling the tablet body to obtain larger strength, slowly pressurizing in the pressurizing process, maintaining the pressure and removing air in the tablet body, and finally obtaining the mixture tablet.
(2) In order to remove moisture in the mixture tabletting and fully decompose the pore-forming agent NH 4HCO3, the sintering procedure is firstly to heat up to 300 ℃ and keep the temperature for 1h in 60min, then to heat up to 800 ℃ and keep the temperature for 5h, then cooling to room temperature along with the furnace, the whole sintering atmosphere is carried out in flowing argon atmosphere, and the sintering experiment is carried out after 3 times of vacuum argon furnace washing before roasting, so as to prepare the sintered tablet of Fe 3O4 with the diameter of 14.8mm, the thickness of 1.4mm and the mass of 0.8g, and the apparent porosity of 38% is calculated.
(3) The molten salt electro-deoxidation comprises the following detailed steps:
a. First, 200g of the mixture was contained in a molar ratio of 0.48:0.52 =nacl: the corundum crucible (with the inner diameter of 60mm, the height of 100mm and the purity of 99.95%) of CaCl 2 salt is placed in a vertical resistance furnace sealed with argon protection, the heating rate is set to be 5 ℃ and min -1, the temperature is increased to be 100 ℃ and kept for 2 hours to remove free water, then the temperature is increased to be 300 ℃ and kept for 10 hours to remove deionized water, finally the temperature is increased to be 800 ℃ and kept for 1 hour to enable the salt to be fully melted, then a nickel sheet cathode with a stainless steel wire connected is placed in molten salt and forms a pre-electrolysis loop with a graphite rod anode, electrolysis is carried out for 12 hours at the set voltage of 2.6V, and then some moisture, zn, mn and other elements are removed, so that background current smaller than 200mA is achieved.
B. Wrapping sintered sheets and molybdenum strips (30 mm long by 2mm wide by 0.5mm thick, purity is more than or equal to 99.9%) with 400 mesh stainless steel mesh, winding the stainless steel mesh used for wrapping with iron wires with diameter of 0.1mm and stainless steel iron rods with diameter of 5mm to form a cathode, taking a stone grinding rod as an anode, inserting the anode into an electrolytic tank filled with chloride molten salt for electro-deoxidation, wherein the electrolysis temperature is 700 ℃, the electrolysis voltage is 2.6V, and the electrolysis time is 3h; and (5) introducing protective gas Ar in the electrolysis process.
C. After the electrolysis is finished, the cathode and the anode are lifted, after the salt is cooled to room temperature, the cathode is taken out, ultrasonically cleaned by ethanol and water to remove the salt and other impurities in the sheet, and sanded by sand paper.
By adopting the method of the embodiment, the purity of the magnetic Fe 3O4 is measured to be more than 98% by using a chemical analysis method.
Example 2, this embodiment shows a method for preparing magnetic Fe 3O4 by electro-deoxidation using molten salt as follows:
(1) Taking Fe 2O3 as a raw material, adding 30g of Fe 2O3、0.6g NH4HCO3 and 1.8g of iron powder into a planetary ball mill for ball milling at a rotating speed of 160 r.min -1 for 60min; and screening by using a 200-mesh sieve to obtain uniform mixture powder, weighing 1g of the uniform mixture powder, placing the mixture powder into a stainless steel cylindrical die with phi=15 mm, maintaining the pressure for 5min under the apparent pressure of 10MPa to enable the oxide powder to be rearranged and elastoplastically deformed and the particles to be meshed with each other, enabling the tablet body to obtain larger strength, slowly pressurizing in the pressurizing process, maintaining the pressure and removing air in the tablet body, and finally obtaining the mixture tablet.
(2) In order to remove moisture in the mixture tabletting and fully decompose the pore-forming agent NH 4HCO3, the sintering procedure is firstly to heat up to 300 ℃ and keep the temperature for 1h in 60min, then to heat up to 800 ℃ and keep the temperature for 5h, then cooling to room temperature along with the furnace, the whole sintering atmosphere is carried out in flowing argon atmosphere, and the sintering experiment is carried out after 3 times of vacuum argon furnace washing before roasting, so as to prepare the sintered tablet of Fe 3O4 with the diameter of 14.8mm, the thickness of 1.4mm and the mass of 0.8g, and the apparent porosity of 38% is calculated.
(3) The molten salt electro-deoxidation comprises the following detailed steps:
a. First, 200g of the mixture was contained in a molar ratio of 0.33:0.67 =nacl: the corundum crucible (with the inner diameter of 60mm, the height of 100mm and the purity of 99.95%) of CaCl 2 salt is placed in a vertical resistance furnace sealed with argon protection, the heating rate is set to be 5 ℃ and min -1, the temperature is increased to be 100 ℃ and kept for 2 hours to remove free water, then the temperature is increased to be 300 ℃ and kept for 10 hours to remove deionized water, finally the temperature is increased to be 800 ℃ and kept for 1 hour to enable the salt to be fully melted, then a nickel sheet cathode with a stainless steel wire connected is placed in molten salt and forms a pre-electrolysis loop with a graphite rod anode, electrolysis is carried out for 12 hours at the set voltage of 2.6V, and then some moisture, zn, mn and other elements are removed, so that background current smaller than 200mA is achieved.
B. Wrapping sintered sheets and molybdenum strips (30 mm long by 2mm wide by 0.5mm thick, purity is more than or equal to 99.9%) with 400 mesh stainless steel mesh, winding the stainless steel mesh used for wrapping with iron wires with diameter of 0.1mm and stainless steel iron rods with diameter of 5mm to form a cathode, taking a stone grinding rod as an anode, inserting the anode into an electrolytic tank filled with chloride molten salt for electro-deoxidation, wherein the electrolysis temperature is 700 ℃, the electrolysis voltage is 2.6V, and the electrolysis time is 3h; and (5) introducing protective gas Ar in the electrolysis process.
C. After the electrolysis is finished, the cathode and the anode are lifted, after the salt is cooled to room temperature, the cathode is taken out, ultrasonically cleaned by ethanol and water to remove the salt and other impurities in the sheet, and sanded by sand paper.
By adopting the method of the embodiment, the purity of the magnetic Fe 3O4 is measured to be more than 98% by using a chemical analysis method.
Example 3, this embodiment shows a method for preparing magnetic Fe 3O4 by electro-deoxidation using molten salt as follows:
(1) Taking Fe 2O3 as a raw material, adding 30g of Fe 2O3、0.6g NH4HCO3 and 1.8g of iron powder into a planetary ball mill for ball milling at a rotating speed of 160 r.min -1 for 60min; and screening by using a 200-mesh sieve to obtain uniform mixture powder, weighing 1g of the uniform mixture powder, placing the mixture powder into a stainless steel cylindrical die with phi=15 mm, and maintaining the pressure for 5min under the apparent pressure of 10MPa to enable oxide powder to be rearranged, elastoplastically deformed and meshed among particles so as to enable the sheet body to obtain larger strength. In addition, the mixture is slowly pressurized in the pressurizing process, and air in the tablet is discharged under pressure maintaining, so that the mixture is finally obtained to be tabletted.
(2) In order to remove moisture in the mixture tabletting and fully decompose the pore-forming agent NH 4HCO3, the sintering procedure is firstly to heat up to 300 ℃ and keep the temperature for 1h in 60min, then to heat up to 800 ℃ and keep the temperature for 5h, then cooling to room temperature along with the furnace, the whole sintering atmosphere is carried out in flowing argon atmosphere, and the sintering experiment is carried out after 3 times of vacuum argon furnace washing before roasting, so as to prepare the sintered tablet of Fe 3O4 with the diameter of 14.8mm, the thickness of 1.4mm and the mass of 0.8g, and the apparent porosity of 38% is calculated.
(3) The molten salt electro-deoxidation comprises the following detailed steps:
a. First, 200g of the mixture was contained in a molar ratio of 0.22:0.78 =nacl: the corundum crucible (with the inner diameter of 60mm, the height of 100mm and the purity of 99.95%) of CaCl 2 salt is placed in a vertical resistance furnace sealed with argon protection, the heating rate is set to be 5 ℃ and min -1, the temperature is increased to be 100 ℃ and kept for 2 hours to remove free water, then the temperature is increased to be 300 ℃ and kept for 10 hours to remove deionized water, finally the temperature is increased to be 800 ℃ and kept for 1 hour to enable the salt to be fully melted, then a nickel sheet cathode with a stainless steel wire connected is placed in molten salt and forms a pre-electrolysis loop with a graphite rod anode, electrolysis is carried out for 12 hours at the set voltage of 2.6V, and then some moisture, zn, mn and other elements are removed, so that background current smaller than 200mA is achieved.
B. Wrapping sintered sheets and molybdenum strips (30 mm long by 2mm wide by 0.5mm thick, purity is more than or equal to 99.9%) with 400 mesh stainless steel mesh, winding the stainless steel mesh used for wrapping with iron wires with diameter of 0.1mm and stainless steel iron rods with diameter of 5mm to form a cathode, taking a stone grinding rod as an anode, inserting the anode into an electrolytic tank filled with chloride molten salt for electro-deoxidation, wherein the electrolysis temperature is 700 ℃, the electrolysis voltage is 2.6V, and the electrolysis time is 3h; and (5) introducing protective gas Ar in the electrolysis process.
C. After the electrolysis is finished, lifting the cathode and the anode, taking out the cathode after the salt is cooled to room temperature, ultrasonically cleaning the cathode by ethanol and water to remove the salt and other impurities in the sheet, and polishing the sheet by sand paper.
By adopting the method of the embodiment, the purity of the magnetic Fe 3O4 is measured to be more than 98% by using a chemical analysis method.
Comparative example 1a method for preparing magnetic Fe 3O4 by molten salt electro-deoxidation of this example comprises the steps of:
(1) Taking Fe 2O3 as a raw material, adding 30g of Fe 2O3、0.6g NH4HCO3 and 1.8g of iron powder into a planetary ball mill for ball milling at a rotating speed of 160 r.min -1 for 60min; and screening by using a 200-mesh sieve to obtain uniform mixture powder, weighing 1g of the uniform mixture powder, placing the mixture powder into a stainless steel cylindrical die with phi=15 mm, maintaining the pressure for 5min under the apparent pressure of 10MPa to enable the oxide powder to be rearranged and elastoplastically deformed and the particles to be meshed with each other, enabling the tablet body to obtain larger strength, slowly pressurizing in the pressurizing process, maintaining the pressure and removing air in the tablet body, and finally obtaining the mixture tablet.
(2) In order to remove moisture in the mixture tabletting and fully decompose the pore-forming agent NH 4HCO3, the sintering procedure is firstly to heat up to 300 ℃ and keep the temperature for 1h in 60min, then to heat up to 800 ℃ and keep the temperature for 5h, then cooling to room temperature along with the furnace, the whole sintering atmosphere is carried out in flowing argon atmosphere, and the sintering experiment is carried out after 3 times of vacuum argon furnace washing before roasting, so as to prepare the sintered tablet of Fe 3O4 with the diameter of about 14.8mm, the thickness of about 1.4mm and the mass of 0.8g, and the apparent porosity of about 38 percent is calculated.
(3) The molten salt electro-deoxidation comprises the following detailed steps:
a. firstly, placing a corundum crucible (with the inner diameter of 60mm, the height of 100mm and the purity of 99.95%) containing 200g CaCl 2 salt into a vertical resistance furnace sealed with argon protection, setting the heating rate to be 5 ℃ and -1, heating to 100 ℃ and preserving heat for 2 hours to remove free water, then heating to 300 ℃ and preserving heat for 10 hours to remove deionized water, finally heating to 800 ℃ and preserving heat for 1 hour to enable the salt to be fully melted, then placing a nickel sheet cathode with a stainless steel wire connected into molten salt and a graphite rod anode to form a pre-electrolysis loop, setting the voltage to be 2.6V, and carrying out electrolysis for 12 hours to remove some moisture, zn, mn and other elements so as to achieve background current smaller than 200 mA.
B. Wrapping sintered sheets and molybdenum strips (30 mm long by 2mm wide by 0.5mm thick, purity is more than or equal to 99.9%) with 400 mesh stainless steel mesh, winding the stainless steel mesh used for wrapping with iron wires with diameter of 0.1mm and stainless steel iron rods with diameter of 5mm to form a cathode, taking a stone grinding rod as an anode, inserting the anode into an electrolytic tank filled with chloride molten salt for electro-deoxidation, wherein the electrolysis temperature is 700 ℃, the electrolysis voltage is 2.6V, and the electrolysis time is 3h; and (3) introducing protective gas in the electrolysis process.
C. After the electrolysis is finished, lifting the cathode and the anode, taking out the cathode after the salt is cooled to room temperature, ultrasonically cleaning the cathode by ethanol and water to remove the salt and other impurities in the sheet, and polishing the sheet by sand paper.
The purity of the magnetic Fe 3O4 is measured to be more than 70% by using the chemical analysis method by adopting the method of the comparative example.
Comparative example 2a method for preparing magnetic Fe 3O4 by molten salt electro-deoxidation of this example comprises the steps of:
(1) Taking Fe 2O3 as a raw material, adding 30g of Fe 2O3、0.6g NH4HCO3 and 1.8g of iron powder into a planetary ball mill for ball milling at a rotating speed of 160 r.min -1 for 60min; then, the mixture was sieved with a 200 mesh sieve to obtain a uniform mixture powder. 1g of uniform mixture powder is weighed, placed into a stainless steel cylindrical die with phi=15 mm, and kept for 5 minutes under the apparent pressure of 10MPa, so that oxide powder is rearranged, elastoplastically deformed, particles are meshed with each other, a tablet body obtains larger strength, in addition, the tablet body is slowly pressurized in the pressurizing process, air in the tablet body is discharged under the condition of keeping pressure, and finally, the mixture tabletting is obtained.
(2) In order to remove moisture in mixture tabletting and fully decompose a pore-forming agent NH 4HCO3, a sintering procedure is firstly to heat up to 300 ℃ for 1h in 60min, then to heat up to 800 ℃ for 5h in 90min, then to cool down to room temperature along with a furnace, the whole sintering atmosphere is carried out in flowing argon atmosphere, vacuum argon furnace cleaning is carried out for 3 times before roasting, and then sintering experiment is carried out, thus obtaining a tablet body of Fe 3O4 with the diameter of about 14.8mm, the thickness of about 1.4mm and the mass of 0.8g, and the apparent porosity of about 38% is calculated.
(3) The molten salt electro-deoxidation comprises the following detailed steps:
a. Firstly, placing a corundum crucible (with the inner diameter of 60mm, the height of 100mm and the purity of 99.95%) containing 200g of NaCl salt into a vertical resistance furnace sealed with argon protection, setting the heating rate to be 5 ℃ and -1, heating to 100 ℃ and preserving heat for 2 hours to remove free water, then heating to 300 ℃ and preserving heat for 10 hours to remove deionized water, finally heating to 800 ℃ and preserving heat for 1 hour to enable the salt to be fully melted, then placing a nickel sheet cathode with a stainless steel wire connected into molten salt and forming a pre-electrolysis loop with a graphite rod anode, setting the voltage to be 2.6V for electrolysis for 12 hours, and removing some moisture, zn, mn and other elements so as to achieve background current smaller than 200 mA.
B. Wrapping sintered sheets and molybdenum strips (30 mm long by 2mm wide by 0.5mm thick, purity is more than or equal to 99.9%) with 400 mesh stainless steel mesh, winding the stainless steel mesh used for wrapping with iron wires with diameter of 0.1mm and stainless steel iron rods with diameter of 5mm to form a cathode, taking a stone grinding rod as an anode, inserting the anode into an electrolytic tank filled with chloride molten salt for electro-deoxidation, wherein the electrolysis temperature is 700 ℃, the electrolysis voltage is 2.6V, and the electrolysis time is 3h; and (5) introducing protective gas Ar in the electrolysis process.
C. After the electrolysis is finished, lifting the cathode and the anode, taking out the cathode after the salt is cooled to room temperature, ultrasonically cleaning the cathode by ethanol and water to remove the salt and other impurities in the sheet, and polishing the sheet by sand paper.
The purity of the magnetic Fe 3O4 is measured to be more than 70% by using the chemical analysis method by adopting the method of the comparative example.
Comparative example 3a method for preparing magnetic Fe 3O4 by molten salt electro-deoxidation of this embodiment includes the steps of:
(1) Taking Fe 2O3 as a raw material, adding 30g of Fe 2O3、0.6g NH4HCO3 and 1.8g of iron powder into a planetary ball mill for ball milling at a rotating speed of 160 r.min -1 for 60min; and screening by using a 200-mesh sieve to obtain uniform mixture powder, weighing 1g of the uniform mixture powder, placing the mixture powder into a stainless steel cylindrical die with phi=15 mm, maintaining the pressure for 5min under the apparent pressure of 10MPa to enable the oxide powder to be rearranged and elastoplastically deformed and the particles to be meshed with each other, enabling the tablet body to obtain larger strength, slowly pressurizing in the pressurizing process, maintaining the pressure and removing air in the tablet body, and finally obtaining the mixture tablet.
(2) In order to remove moisture in the mixture tabletting and fully decompose the pore-forming agent NH 4HCO3, the sintering procedure is firstly to heat up to 300 ℃ and keep the temperature for 1h in 60min, then to heat up to 800 ℃ and keep the temperature for 5h, then cooling to room temperature along with the furnace, the whole sintering atmosphere is carried out in flowing argon atmosphere, and the sintering experiment is carried out after 3 times of vacuum argon furnace washing before roasting, so as to prepare the sintered tablet of Fe 3O4 with the diameter of 14.8mm, the thickness of 1.4mm and the mass of 0.8g, and the apparent porosity of 38% is calculated.
(3) The molten salt electro-deoxidation comprises the following detailed steps:
a. Firstly, placing a corundum crucible (with the inner diameter of 60mm, the height of 100mm and the purity of 99.95%) containing 200g of KCl salt into a vertical resistance furnace sealed with argon protection, setting the heating rate to be 5 ℃ and min -1, heating to 100 ℃ and preserving heat for 2 hours to remove free water, then heating to 300 ℃ and preserving heat for 10 hours to remove deionized water, finally heating to 800 ℃ and preserving heat for 1 hour to enable the salt to be fully melted, then placing a nickel sheet cathode with a stainless steel wire connected into molten salt and a graphite rod anode to form a pre-electrolysis loop, setting the voltage to be 2.6V for electrolysis for 12 hours, and removing some moisture, zn, mn and other elements so as to achieve background current smaller than 200 mA.
B. Wrapping sintered sheets and molybdenum strips (30 mm long by 2mm wide by 0.5mm thick, purity is more than or equal to 99.9%) with 400 mesh stainless steel mesh, winding the stainless steel mesh used for wrapping with iron wires with diameter of 0.1mm and stainless steel iron rods with diameter of 5mm to form a cathode, taking a stone grinding rod as an anode, inserting the anode into an electrolytic tank filled with chloride molten salt for electro-deoxidation, wherein the electrolysis temperature is 700 ℃, the electrolysis voltage is 2.6V, and the electrolysis time is 3h; and (5) introducing protective gas Ar in the electrolysis process.
C. After the electrolysis is finished, the cathode and the anode are lifted, after the salt is cooled to room temperature, the cathode is taken out, ultrasonically cleaned by ethanol and water to remove the salt and other impurities in the sheet, and sanded by sand paper.
The purity of the magnetic Fe 3O4 is measured to be more than 50% by using the chemical analysis method by adopting the method of the comparative example.
Comparing comparative examples 1-3 with examples 1-3, it can be seen that changing the different ratio of NaCl to CaCl 2 salt or changing other salts, the purity of the electrolysis product also changes, wherein when the ratio of NaCl to CaCl 2 salt is 0.48: at 0.52, the purity of Fe 3O4 obtained by electrolysis is at most 98%.
Comparative example 4 magnetic Fe 3O4 was prepared by pyrolysis, 1.5g iron acetylacetonate Fe (Acac) 3 was added to 15mL dibenzyl ether and 15mL oleylamine solution, mixed well in a three neck round bottom flask, nitrogen was charged at constant speed during this time, placed on a heat collecting magnetic stirrer, sealed against air, and maintained for 30min. The temperature was heated to 100deg.C for 1h, then 15 ℃ per 10min for 5min, and raised to 295 ℃. Stopping the reaction after the occurrence of the white fog phenomenon for 3 times, cooling to room temperature, washing with absolute ethyl alcohol, repeating for 3 times until the supernatant is free from turbidity, collecting the product, placing in a vacuum drying oven, and adjusting the temperature to 50 ℃ for drying overnight.
Comparative example 5 nano ferroferric oxide (Fe 3O4) was prepared by reverse microemulsion method. Firstly preparing microemulsion, and firstly preparing a mixed solution of a surfactant Triton X-100 (S) and a cosurfactant n-butanol (A) according to different proportions, wherein S: A=2:1, 1:1 and 1:2. Uniformly mixing FeSO 4 and FeCl 3 with a certain concentration according to a certain proportion, and taking the mixed solution as a water phase to prepare W/O type microemulsion A; naOH was used to prepare microemulsion B in the same manner. Introducing N 2 at room temperature, gradually adding the microemulsion A into the quantitative microemulsion B, and reacting for a period of time, wherein the black product is Fe 3O4. The micro emulsion system is destroyed by water bath aging, solid precipitation is carried out, then ethanol, acetone and double distilled water are used for repeatedly washing, magnet separation or centrifugal separation is carried out to obtain solid, nano Fe 3O4 black powder is obtained by low-temperature vacuum drying, the morphology is spherical, and the grain diameter is less than 100nm.
Comparative example 6, N 2 was introduced into distilled water to remove air from the water, and FeCl 3·6H2 O and FeCl 2·4H2 O were dissolved in distilled water according to N (Fe 3+)/n(Fe2+) of 1.25,1.50,1.75,2.00, respectively, to obtain a mixed solution under magnetic stirring. The obtained mixed solution is transferred into a 250mL three-mouth grinding flask, one mouth is filled with N 2, the other mouth is provided with a dropping funnel containing hydrochloric acid or concentrated ammonia water, the remaining mouth is plugged by a grinding mouth, and the temperature is kept at 60 ℃ in a constant temperature magnetic stirring electric heating sleeve. Slowly dropwise adding hydrochloric acid or concentrated ammonia water under magnetic stirring to adjust the pH=3, 5,7, 11 and 13, and then placing the solution in a numerical control ultrasonic oscillator (the temperature is 60 ℃ and the power is 70 kHz) to perform ultrasonic oscillation for 1h to obtain the precursor of Fe 3O4. Then transferring into a polytetrafluoroethylene-lined high-pressure reaction kettle, putting into a DL-101-1 type electric oven, setting the reaction temperature (140, 150, 160, 170 ℃) and the reaction time (3, 4,5,6 hours), and heating the reaction kettle to react. After the reaction is finished, washing the product with distilled water, separating by a centrifuge, pouring out supernatant, repeatedly washing for 4-5 times, and washing until the pH of the supernatant is about 7. Taking out the black powder, drying the black powder for 7 hours at 60 ℃ by a drying oven, and putting the black powder into a mortar for grinding to obtain the black magnetic ferroferric oxide nano powder.
Comparing comparative examples 4 to 6 with a method for preparing magnetic Fe 3O4 by molten salt electro-deoxidation according to the present invention, it can be seen that:
TABLE 1
As shown in table 1, comparing comparative example 4 with examples 1-3, since the reaction of comparative example 4 requires the use of a metal-organic precursor having relatively active chemical properties, it is often necessary to continuously introduce nitrogen gas into the reaction system to remove air, and the reaction conditions are relatively severe; in addition, because some toxic reagents such as organometallic-precursor and the like are needed in the reaction process, the method is poor in environmental friendliness; comparing comparative example 5 with examples 1-3, it is clear that the ferroferric oxide prepared in comparative example 5 has controllable particle size and good dispersion performance, but the purity is worse than that of the examples, and the cost is correspondingly higher; comparing comparative example 6 with examples 1-3, comparative example 6 is simple to operate, low in cost, small in particle size, but poor in dispersity and easy to agglomerate.
In summary, compared with the prior art, the method for preparing the magnetic Fe 3O4 by using the molten salt electro-deoxidation is more environment-friendly, simple in process, lower in cost, suitable for large-scale production and higher in purity of the produced Fe 3O4.
It should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention may be modified or substituted without departing from the spirit and scope of the technical solution of the present invention, which is intended to be covered in the scope of the claims of the present invention.
Claims (10)
1. A method for preparing magnetic Fe 3O4 by electro-deoxidation of molten salt, comprising:
(1) Fully and uniformly mixing Fe 2O3, a pore-forming agent and a conductive agent to obtain a mixture, and performing compression molding on the mixture to obtain a mixture tablet;
(2) Tabletting the mixture and sintering under a protective atmosphere to obtain a sintered tablet;
(3) Wrapping the sintered sheet and the molybdenum strip by using a stainless steel net, winding by using an iron wire and a stainless steel rod to form a cathode, taking a stone mill rod as an anode, inserting the stone mill rod into an electrolytic tank filled with chloride molten salt for electro-deoxidation, introducing protective gas in the electro-deoxidation process, taking out an electrolysis product after the electro-deoxidation is finished, and removing the molten salt attached to the surface to obtain solid Fe 3O4.
2. The method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation as set forth in claim 1, wherein: in the step (1), the mass ratio of the Fe 2O3, the pore-forming agent and the conductive agent is 1:0.02:0.06.
3. The method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation as set forth in claim 1, wherein: in the step (1), the pore-forming agent is NH 4HCO3, the conductive agent is metal iron powder, and the purity of NH 4HCO3 and Fe 2O3 is more than 99%.
4. The method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation as set forth in claim 1, wherein: in the step (1), the pressure of the press molding is 10MPa.
5. The method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation as set forth in claim 1, wherein: in the step (2), the gas of the protective atmosphere is Ar.
6. The method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation as set forth in claim 1, wherein: in the step (2), the sintering temperature is 800-900 ℃ and the sintering time is 2-7h.
7. The method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation as set forth in claim 1, wherein: in the step (3), the length of the molybdenum strip is 30mm, the width is 2mm, the thickness is 0.5mm, and the purity of the molybdenum strip is more than or equal to 99.9%.
8. The method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation as set forth in claim 1, wherein: in the step (3), the stainless steel mesh is 400 meshes, the diameter of the iron wire is 0.1mm, and the diameter of the stainless steel bar is 5mm.
9. The method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation as set forth in claim 1, wherein: in the step (3), the electrolysis temperature of the electro-deoxidation is 680-722 ℃, the electrolysis voltage is 2.6-3.2V, the electrolysis time is 2-8h, and the protective gas is Ar.
10. The method for preparing magnetic Fe 3O4 by using molten salt electro-deoxidation as set forth in claim 1, wherein: in the step (3), the chloride molten salt is NaCl and CaCl 2, and the molar ratio of NaCl to CaCl 2 is 0.22-0.48:0.52-0.78.
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